Document:

<PAGE>

                                                                   Exhibit 10.18

                         AGREEMENT FOR PURCHASE AND SALE

     THIS AGREEMENT FOR PURCHASE AND SALE (the "AGREEMENT") is made and entered
into as of the 6th day of December, 2005 (the "EFFECTIVE DATE") by and between
UNICORN WISCONSIN, LLC, a Delaware limited liability company (the "SELLER") and
Columbia Equity Trust, Inc., a Maryland corporation (the "PURCHASER"), as
follows:

                                   WITNESSETH

     WHEREAS, Seller is the owner of a leasehold interest under that certain
Lease dated December 21, 1959, recorded among the land records of the District
of Columbia (the "LAND RECORDS") on December 28, 1959, as Instrument No. 40566
in Liber 11360 at folio 70, from Mary A.W. Holland and Robert D. Weaver
(predecessors in interest to Thomas W. Holland, Robert M. Holland, Mary
Charlotte Parr and Margaret W. Krull; collectively, the "GROUND LESSOR") to
Norbick Realty Company, as amended and assigned pursuant to: (i) that certain
Amendment to Lease, dated February 8, 1963, recorded February 14, 1963, as
Instrument No. 4952 in Book 11949 at folio 385 of the Land Records; (ii) that
certain Amended Lease dated December 31, 1963, recorded on June 18, 1964, as
Instrument No. 20584 in Liber 12228 at folio 73 of the Land Records; (iii) that
certain Assignment of Leasehold Interest dated August 8, 1966, recorded on
August 15, 1966, as Instrument No. 26678 in Liber 12654 at folio 196 of the Land
Records; (iv) that certain Assignment of Leasehold Interest dated August 1,
1966, recorded on August 15, 1966, as Instrument No. 26679 in Liber 12654 at
folio 199 of the Land Records; (v) that certain Amendment to Lease dated May 23,
1980, recorded May 30, 1980, as Instrument No. 17500 of the Land Records; (vi)
that certain Assignment of Leasehold dated January 10, 1984, recorded January
11, 1984, as Instrument No. 1028 of the Land Records; (vii) that certain
Assignment of Leasehold to 2233 Wisconsin Avenue Associates dated September 28,
1984, recorded December 31, 1984, as Instrument No. 47361 of the Land Records;
(viii) that certain Assignment of Leasehold to The Georgetown Building
Associates Limited Partnership dated March 6, 1986, recorded March 7, 1986, as
Instrument No. 9580 of the Land Records; (ix) that certain unrecorded Amendment
to Lease dated April 10, 1989; (x) that certain Substitute Trustee's Assignment
of Leasehold Interest, dated January 12, 2000, recorded on January 13, 2000, as
Instrument Number 2000004734 of the Land Records; (xi) that certain Assignment
of Leasehold Interest, dated December 14, 2000, by KeyKey Realty, Inc., a
District of Columbia corporation, as Assignor, to Athena Wisconsin LLC, a
Delaware limited liability company ("ATHENA"), as Assignee, recorded on December
18, 2000 as Instrument Number 2000115036 of the Land Records; (xii) that certain
Amendment to Amended Lease dated December 15, 2000, recorded December 18, 2000,
as Instrument No. 2000115037 of the Land Records; (xiii) that certain Second
Amendment to Amended Lease dated April 19, 2003, recorded May 7, 2003, as
Instrument No. 2003055073 of the Land Records; and (xiv) that certain Assignment
and Assumption of Leasehold Estate dated April 30, 2003 by Athena, as Assignor,
to Seller as Assignee, recorded on May 7, 2003 as Instrument No. 2003055069 of
the Land Records, which Ground Lease covers certain real property located at
2233 Wisconsin Avenue N.W., Washington, D.C. as more particularly described on
Exhibit A annexed hereto, (the "LAND"); and

<PAGE>

     WHEREAS, the Land is improved by a five (5) story multi-tenant office and
retail building (together with the underground parking garage and all other
improvements, if any, located on the Land, the "IMPROVEMENTS," which
Improvements, together with the Land, are hereinafter collective the "IMPROVED
REAL ESTATE"); and

     WHEREAS, the Seller has an interest in certain leases and rental agreements
granting a real property interest to other persons for the use or occupancy of
portions of the Improvements (the "TENANT LEASES"); and

     WHEREAS, the Seller owns certain tangible and intangible property used in
connection with its use, enjoyment, ownership and operation of the Land and
Improvements thereon, described on Exhibit B hereto, (collectively, the
"PERSONAL PROPERTY"), which together with all of Seller's right, title and
interest in the Ground Lease and interest in the Land, the Tenant Leases, the
Improvements and the Personal Property (collectively the "Project"); and

     WHEREAS, Seller is a party to that certain Tenant Vacancy Escrow Agreement
dated as of April 30, 2003, by and among Athena, Seller and Chicago Title
Insurance Company ("Chicago Title") pursuant to which a portion of the purchase
price paid to Athena by Seller is held by Chicago Title in escrow pending the
leasing of certain portions of the Improvements (the "VACANCY ESCROW
AGREEMENT"); and

     WHEREAS, the Lender (as hereinafter defined) is holding certain funds of
the Seller as holdbacks or reserves pursuant to the loan documents evidencing
and securing the Existing Financing (as hereinafter defined), which include, but
are not limited to, the following (collectively, "HOLDBACK AGREEMENTS"): Real
Estate Taxes, Insurance, Tenant Improvement and Leasing Commissions Reserve
Agreement, Tenant Improvement and Leasing Commissions Reserve Agreement
(Georgetown University), Holdback Reserve and Security Agreement and Holdback
Reserve and Security Agreement (Ground Lease Rent); and

     WHEREAS, Purchaser desires to purchase the Project from Seller and Seller
desires to sell the Project to Purchaser, all upon the terms and conditions
contained herein.

     NOW, THEREFORE, for and in consideration of the foregoing and of the mutual
covenants and agreements herein contained, the parties agree as follows:

     1. SALE OF THE PROJECT; ASSIGNMENT OF VACANCY ESCROW AGREEMENT AND HOLDBACK
AGREEMENTS. Subject to and in accordance with the terms and provisions contained
in this Agreement, Seller agrees to sell, convey, transfer, assign and deliver
the Improved Real Estate to Purchaser and Purchaser agrees to accept from
Seller, all right, title and interest of Seller in the Project. In addition,
subject to and in accordance with the terms and provisions contained in this
Agreement, Seller agrees to sell, convey, transfer, assign and deliver the
Seller's rights and obligations under the Vacancy Escrow Agreement and Holdback
Agreements to Purchaser and Purchaser agrees to accept from Seller, all right,
title and interest to Seller in the Vacancy Escrow Agreement and Holdback
Agreements.

                                       2

<PAGE>

     2. PURCHASE PRICE. The purchase price for the Project shall be TWENTY-THREE
MILLION FIVE HUNDRED THOUSAND DOLLARS ($23,500,000) (the "PURCHASE PRICE"),
which shall be paid as follows:

          A. Deposit.

               1. Within three (3) business days after the execution of this
Agreement by all parties, time being of the essence, Purchaser shall deposit
with Commonwealth Land Title Insurance Company (the "ESCROW AGENT") the amount
of TWO HUNDRED THOUSAND DOLLARS ($200,000.00) (the "INITIAL DEPOSIT"). Within
three (3) business days following the expiration of the Study Period (provided
that Purchaser does not exercise its right to terminate this Agreement and
receive the return of the Initial Deposit), time being of the essence, Purchaser
shall post an additional deposit in immediately available good funds, by federal
wire transfer (the "ADDITIONAL DEPOSIT", together with the Initial Deposit, the
"DEPOSIT") in an amount equal to TWO HUNDRED THOUSAND DOLLARS ($200,000.00). The
Deposit shall be non-refundable to Purchaser, except as otherwise expressly
provided in this Agreement. The Deposit shall be held by Escrow Agent in escrow
(the "ESCROW DEPOSIT") pursuant to the escrow agreement in the form attached
hereto as Exhibit C, to be entered into among Seller, Purchaser and Escrow Agent
(the "ESCROW AGREEMENT"), and delivered to Escrow Agent concurrently with the
Deposit.

               2. The Deposit shall be invested in accordance with the Escrow
Agreement, and all interest and other amounts earned on the Deposit shall
constitute additional Deposit for all purposes in this Agreement.

               3. At Closing, Escrow Agent shall distribute the Deposit to
Seller, and Purchaser shall receive a credit against the Purchase Price in the
amount of the Deposit distributed to Seller, or if this Agreement is terminated,
the Deposit shall be disbursed by Escrow Agent to Seller or Purchaser in
accordance with the terms of this Agreement.

          B. Assumption of Existing Debt. The Purchaser shall assume at Closing
the indebtedness (the "EXISTING FINANCING") secured by the Project payable to
the order of Wachovia Bank, National Association as Master Servicer on behalf of
Wells Fargo Bank, NA, as Trustee for the benefit of Certificate Holders of
Commercial Mortgage Pass-Through Certificates Series Wachovia Bank 2003-C-5
("LENDER") subject to Purchaser (or Seller, as the case may be) obtaining
Lender's consent to the assumption of the Existing Financing ("LENDER'S
CONSENT") prior to Closing in a form reasonably acceptable to Purchaser. The
loan documents evidencing and securing the Existing Financing are hereinafter
collectively referred to as the "EXISTING LOAN DOCUMENTS." Purchaser
acknowledges that Seller has provided Purchaser with copies of the Existing Loan
Documents and that Purchaser will not request any modifications or additions to
the Existing Loan Documents except for (a) the assumption of the Existing Loan
Documents by Purchaser (or Purchaser's assignee), (b) such modifications or
additions to the Existing Loan Documents as may be identified by Purchaser
during the Study Period, and (c) the release of Saul Eric Uberman and Reuven
Uberman (collectively, "UBERMANS") from all of their guaranties under the
Existing Loan Documents arising after the Closing Date and the substitution of
the Purchaser (or its assignees) or other individuals or entities as the Lender
may require in place of the Ubermans. The Purchaser agrees that in the event
that if, as a condition to obtaining

                                       3

<PAGE>

Lender's Consent, the Lender requires that the Purchaser, or its assignee, shall
be a Delaware, single purpose entity, then the Purchaser (or its assignee, as
applicable) shall comply with such condition. Purchaser further agrees to use
commercially reasonable efforts to comply with any other conditions that the
Lender may place upon Purchaser to grant such Lender's Consent. Within five (5)
business days of the Effective Date, Purchaser shall use commercially reasonable
efforts to furnish to Lender (with a copy to Seller) all information required by
the Lender for the assumption of the Existing Financing, and shall use
commercially reasonable efforts to, within five (5) business days, furnish to
Lender such additional information as may be requested by Lender from time to
time. Purchaser shall use commercially reasonable efforts to obtain Lender's
Consent prior to the expiration of the Study Period. Purchaser acknowledges that
Lender's Consent will not be deemed obtained or granted unless Lender has agreed
to release the Ubermans from their guaranties and liability under the Existing
Loan Documents with respect to events occurring after the date of Closing on
terms and conditions as are satisfactory to the Seller and the Ubermans in their
sole discretion. If Lender's Consent is not obtained on or before the expiration
of the Study Period, then if Purchaser has not otherwise terminated this
Agreement, Seller shall have the right to extend the Closing Date for sixty (60)
days until the Purchaser has obtained Lender's Consent or terminate this
Agreement on or before the expiration of the Study Period. Purchaser shall pay
all costs associated with the assumption of the Existing Financing, including
but not limited to any Lender's attorneys' fees and any assumption fees.
Purchaser shall keep Seller informed as to the status of Purchaser's obtaining
Lender's Consent upon Seller's request. All amounts held in escrow pursuant to
and under the Existing Financing shall be transferred to Purchaser. At Closing,
in addition to paying the Purchase Price, Purchaser shall pay Seller for all
amounts held by Lender pursuant to the Existing Loan Documents, including, but
not limited to, the Holdback Agreements. Notwithstanding anything contained
herein to the contrary, if Lender's Consent (including the release of the
Ubermans) is not obtained on or before the Closing Date (as same may be extended
under this Agreement) then Seller may terminate this Agreement by written notice
to the Purchaser.

          C. Assumption of Vacancy Escrow Agreement. Purchaser acknowledges that
Seller has provided Purchaser with a copy of the Vacancy Escrow Agreement.
Purchaser agrees that at Closing, Purchaser shall assume all of Seller's
obligations and rights under the Vacancy Escrow Agreement. In addition,
Purchaser shall reimburse Seller for certain advances made by Seller pursuant to
the Vacancy Escrow Agreement in the amount of FIVE HUNDRED THOUSAND DOLLARS
($500,000.00) ("SELLER VACANCY REIMBURSEMENT"). Seller will provide Purchaser
with (i) a full accounting for the costs spent or incurred to date pursuant to
the Vacancy Escrow Agreement, (ii) an acknowledgement from Seller and Athena
that the sum of TWENTY TWO AND 22/100 DOLLARS ($22.22) of Permitted Costs (as
defined in the Vacancy Escrow Agreement) per rentable square foot has been paid
or incurred by Seller for the space vacated by Georgetown University and (iii)
an acknowledgement by Seller and Athena as to such other matters as are set
forth in the Vacancy Acknowledgement attached as Exhibit 2(C) hereto dated as of
the Closing Date ("VACANCY ACKNOWLEDGEMENT"). Notwithstanding anything contained
herein to the contrary, the Purchaser is not required to pay the Seller Vacancy
Reimbursement to Seller unless the Purchaser has been provided with the Vacancy
Acknowledgement. The Seller Vacancy Reimbursement shall be released to Seller at
Closing upon Purchaser's receipt of such Vacancy Acknowledgement. Seller shall
not seek or receive any disbursements under the Vacancy Escrow Agreement without
Purchaser's consent except Seller shall be entitled to seek and receive
disbursements under the Vacancy Escrow Agreement

                                       4

<PAGE>

prior to the Closing Date regarding costs and expenses it has incurred in
connection with space formerly occupied by Georgetown University and presently
occupied by Georgetown University, Quatt, Cornerstone and McKinley.
Notwithstanding anything contained herein to the contrary, Seller may extend the
Closing Date for sixty (60) days until Seller has obtained the Vacancy
Acknowledgement that Seller is required to obtain hereunder.

          D. Balance of Purchase Price for Project. The Purchase Price less the
Deposit and the outstanding principal indebtedness of the Existing Financing at
Closing, subject to prorations and adjustments hereinafter set forth shall be
paid to the Escrow Agent at Closing for delivery to Seller by wire transfer of
immediately available funds.

          E. Payment of Holdback Agreements and Seller Vacancy Reimbursement. In
addition to the payments of the Purchase Price at Closing, the Seller Vacancy
Reimbursement (or any part thereof) if it is required to be paid to Seller at
Closing pursuant to Section 2(C) hereinabove and all amounts held by Lender
pursuant to the Existing Loan Documents, including, but not limited to the
Holdback Agreements, shall be paid by Purchaser to the Escrow Agent at Closing
for delivery to Seller by wire transfer of immediately available funds.

     3. TITLE TO THE PROPERTY.

          A. Purchaser shall, within five (5) days after the Effective Date,
order (i) a commitment for title insurance (the "COMMITMENT"), (ii) a photocopy
of all documents ("TITLE DOCUMENTS") describing all title exceptions shown on
the Commitment (the "TITLE EXCEPTIONS"), and (iii) if Purchaser so elects, an
ALTA Land Title Survey of the Land (the "SURVEY"). If Purchaser objects to any
matters disclosed by the Commitment, Title Documents or Survey, Purchaser shall
furnish Seller with a written statement thereof (the "TITLE NOTICE") prior to
expiration of the Study Period (the "TITLE APPROVAL DATE") specifying in detail
all such title and survey objections (collectively, the "TITLE OBJECTIONS").

          B. All matters shown on the Commitment and the Survey and all Title
Exceptions which are not objected to by Purchaser prior to the Title Approval
Date shall be "PERMITTED EXCEPTIONS". Seller shall have no obligation to cure
any such Title Objections noted by Purchaser; provided, however, that Seller
shall obtain a satisfaction and release or bond over any monetary liens existing
as of the Closing Date, including, without limitation, any and all mortgages
(other than the Existing Financing), mechanics' liens (other than monetary liens
which are the result of Purchaser's or Purchaser's agent's or representative's
actions or inactions) and judgment liens (collectively, "MONETARY LIENS").
Seller may elect to have any such Monetary Liens satisfied out of the Purchase
Price at Closing. If Purchaser notifies Seller in writing that Purchaser has
Title Objections, Seller shall have five (5) business days after receipt of the
Title Notice to notify Purchaser in writing (a) that Seller will use reasonable
efforts to remove such Title Objections on or before the Closing or (b) that
Seller elects not to cause such Title Objections to be removed. In the event
Seller fails to give such notice within such five day period, Seller shall be
deemed to have elected clause (b) above. If Seller gives Purchaser notice under
clause (b) above, Purchaser shall have five (5) days (the "TITLE DECISION DATE")
in which to notify Seller that Purchaser will nevertheless proceed with the
purchase and take title to the Project subject to such Title Objections, or that
Purchaser will terminate this Agreement. If this Agreement is terminated
pursuant to the foregoing provisions of this

                                       5

<PAGE>

paragraph, then neither party shall have any further rights or obligations
hereunder (except for any indemnity obligations of Purchaser pursuant to the
other provisions of this Agreement), the Deposit shall be returned to Purchaser
and each party shall bear its own costs incurred hereunder. If Purchaser shall
fail to notify Seller of its election within said five-day period, Purchaser
shall be deemed to have elected to terminate this Agreement. If Seller gives
Purchaser notice under clause (a) above and, if despite its reasonable efforts
to do so, Seller cannot satisfy such objections (other than the Monetary Liens,
which shall be satisfied or bonded over by Seller) on or before Closing, then
Seller shall have the right to extend the Closing Date for an additional sixty
(60) days. If, by such extended Closing Date, Seller can not satisfy such
objections (other than the Monetary Liens, which shall be satisfied or bonded
over by Seller), then Purchaser shall have the option to waive its Title
Objections and proceed to Closing or terminate this Agreement. Notwithstanding
anything contained herein to the contrary, Purchaser shall have the option at
any time to waive its Title Objections and proceed to Closing.

          C. At Closing, the Escrow Agent shall stand ready to issue a standard
ALTA Owner's Policy of Title Insurance (the "TITLE POLICY") covering the Land
and the Improvements, in the full amount of the Purchase Price, subject only to
the Permitted Exceptions. Purchaser shall pay the cost of the Title Policy and
all extended coverage and endorsements requested by Purchaser and shall pay the
cost of the Survey. The Escrow Agent's failure to issue such extended coverage
or additional endorsements shall not affect Purchaser's obligations under this
Agreement.

     4. SELLER'S PRE-CLOSING DELIVERIES.

          A. Purchaser acknowledges that it has received certain information
concerning the Property from Seller, including but not limited to the Existing
Loan Documents, leases, rent rolls, engineer's reports and all other information
relating to the Property which has been made available to Purchaser at
www.peracon.com ("PROPERTY INFORMATION"), and that except as herein provided
Seller makes no representations or warranties of any kind regarding the
accuracy, thoroughness or completeness of or conclusions drawn in the
information contained in any of the Property Information. Except as herein
provided Purchaser hereby waives any and all claims against Seller arising out
of the accuracy, completeness, conclusions or statements expressed in materials
furnished and any and all claims arising out of any duty of Seller to acquire,
seek or obtain such materials.

          B. Purchaser further acknowledges that as part of the Property
Information, Purchaser has received the following:

               1. Copy of the Ground Lease.

     Simultaneously with the execution of this Agreement, Seller shall provide
Purchaser with the following to the extent that such documents were not included
in the Property Information: Copies of the Existing Leases listed on the rent
roll attached hereto as Exhibit D (the "RENT ROLL") and all lease guaranties in
Seller's possession affecting such Existing Leases.

          C. Prior to the execution of this Agreement, Seller has provided
Purchaser with a copy of that certain Phase I Environmental Site Assessment
dated December 17, 2002 and

                                       6

<PAGE>

prepared by IVI International, Inc. ("Environmental Report") and Purchaser
acknowledges receipt of same. Seller shall also provide Purchaser with access to
the Improved Real Estate's Managing Agent, Zalco Realty, Incorporated ("ZALCO")
for the Purchaser to inspect and copy, at Purchaser's cost and expense, any
items regarding the project that are in Zalco's possession. The items set forth
in Section 4 hereof to the extent that same are not a part of the Property
Information are collectively referred to as the "DUE DILIGENCE MATERIALS."

          D. Except as otherwise provided herein, the Due Diligence Materials
and Property Information have been provided to Purchaser without any
representation or warranty of any kind or nature whatsoever and are merely
provided to Purchaser for Purchaser's informational purposes. Except as
expressly stated herein, Seller makes no representation or warranty as to the
truth, accuracy or completeness of any materials, data or information delivered
by Seller, or its brokers or agents (including, but not limited to Zalco) to
Purchaser in connection with the transaction contemplated hereby. Purchaser
acknowledges and agrees that all materials, data and information delivered to
Purchaser by Seller or by Zalco, on Seller's behalf, in connection with the
transaction contemplated hereby are provided to Purchaser as a convenience only
and that any reliance on or use of such materials, data or information by
Purchaser shall be at the sole risk of Purchaser, except as otherwise expressly
stated herein. Except as expressly stated herein, neither Seller, nor any
affiliate of Seller, nor Zalco, nor any person or entity which prepared any
report or reports delivered by Seller or by Zalco, on Seller's behalf, to
Purchaser shall have any liability to Purchaser for any inaccuracy in or
omission from any such reports. Until Closing occurs, Purchaser and Purchaser's
Designees (herein defined) shall maintain all Due Diligence Materials and
Property Information as confidential information.

     5. PURCHASER'S DUE DILIGENCE.

          A. Purchaser shall have until 5:00 p.m. Washington, DC time on thirty
(30) days after the effective date, time being of the essence, to perform a
feasibility study of the Project, at Purchaser's sole cost and expense,
including, but not limited to, review and approval of the physical and
environmental characteristics and condition of the Project and performance of
marketing and feasibility studies, structural and engineering investigations,
auditing of books and records, financial analyses and verification of existing
zoning. Seller agrees to provide Purchaser and its agents and representatives,
reasonable access to the Improved Real Estate during normal business hours,
subject to the rights of tenants, and at Zalco's office to all books, records,
files, financial data, leases and contracts relating to the Project in Seller's
or Zalco's possession (except Seller's corporate or partnership records,
financial projections, budgets, appraisals, accounting and tax records and
similar proprietary, confidential or privileged documents, reports and records
and internally prepared memoranda and reports) and to reasonably cooperate in
such examinations and to cause Zalco to reasonably cooperate in such
examinations following the Effective Date for the purpose of performing, at
Purchaser's sole cost and expense, the above-referenced studies, physical
inspections, investigations and tests on the Project (collectively, the "TESTS")
provided that no such tests shall be conducted without at least two (2) business
days prior written notice to Seller and if any such Tests are invasive Seller's
prior approval of such Tests, which approval shall be in Seller's sole and
absolute discretion. The parties acknowledge that Purchaser may be required to
perform a historical audit of the Project in order to comply with Item 3-14 of
Regulation S-X promulgated under the Securities Act of 1933 and the Securities
Exchange Act of 1934 (the "3-14 REPORT") and Seller shall take

                                       7

<PAGE>

commercially reasonable efforts to allow Purchaser's auditors access to all of
Project's books and records and the certified operating statements and
management balance sheet for the Project in Seller's and Zalco's possession to
enable Purchaser to comply with any such regulations applicable to Purchaser.
Such books and records shall include the detailed general ledger of profits and
loss, accounts receivable records, rent rolls and lease agreements. Purchaser's
access rights shall continue until the earlier to occur of (i) the date
Purchaser gives Seller notice of termination of this Agreement or (ii) the
successful completion of the audit and the filing of the 3-14 Report with the
Securities and Exchange Commission, but in no event any later than ninety (90)
days after Closing. Notwithstanding anything herein to the contrary, Purchaser
shall not need Seller's further consent to conduct Phase I environmental
studies. Purchaser shall be required to conduct such Tests in a manner as to not
disturb or interfere with the current use of the Improved Real Estate or the
rights of the tenants at the Improved Real Estate and upon completion of such
Tests, Purchaser agrees at its sole cost to promptly restore the Improved Real
Estate to the condition it was in immediately prior to such Tests, including,
but not limited to the prompt removal of anything placed on the Improved Real
Estate in connection with such Tests. Seller shall have the right to have a
representative of Seller present at all times while Purchaser is performing any
such Tests, meeting with any tenant and otherwise conducting its feasibility
study. Prior to Purchaser's entering the Improved Real Estate to conduct the
inspections and tests described above, Purchaser shall obtain and maintain, and
shall cause each of its contractors and agents to each obtain and maintain (and
shall deliver to Seller evidence thereof), at Purchaser's sole cost and expense,
general liability insurance, from an insurer reasonably acceptable to Seller, in
the amount of at least One Million and No/100 Dollars ($1,000,000.00) combined
single limit for personal injury and damage per representation, occurrence, such
policies to name Seller as an additional insured party, which insurance shall
provide coverage against any claim for personal liability or damage caused by
Purchaser or its agents, representatives, employees or contractors in connection
with such inspections and tests. Purchaser shall indemnify, defend (with counsel
reasonably satisfactory to Seller), protect, and hold Seller and its agents,
servants, attorneys, officers, partners, shareholders, consultants, contractors,
directors, tenants, members, representatives and employees (collectively, the
"SELLER PARTIES") harmless from and against any and all liability, loss, cost,
expense, claim, damage, or expense (including, without limitation, mechanic's
and materialmen's liens and reasonable attorney's fees and costs) of any kind or
nature whatsoever which any of the Seller Parties may sustain or incur by reason
of or in connection with any Tests made by Purchaser, or any of its employees,
consultants, engineers, agents, representatives or contractors (collectively,
the "PURCHASER'S DESIGNEES") relating to or in connection with the Project, or
entries by any of Purchaser's Designees onto the Project during the conduct of
any of the feasibility studies. Notwithstanding any provision to the contrary in
this Agreement, the indemnity obligations of Purchaser under this Agreement
shall survive any termination of this Agreement or the delivery of the deed and
the transfer of title pursuant to this Agreement. This Section 5(a) shall
survive any termination of this Agreement or Closing hereunder.

          B. If for any reason whatsoever Purchaser determines that the Project
or any aspect thereof is unsuitable for Purchaser's acquisition, Purchaser shall
have the right to terminate this Agreement by giving written notice thereof to
Seller prior to the expiration of the Study Period, time being of the essence,
and if Purchaser gives such notice of termination within the Study Period, this
Agreement shall terminate. If this Agreement is terminated pursuant to the
foregoing provisions of this section, then neither party shall have any further
rights or obligations

                                       8

<PAGE>

hereunder (except for any obligations pursuant to the other provisions of this
Agreement which survive a termination), Purchaser shall return all Due Diligence
Materials and Property Information previously delivered by Seller to Purchaser
and thereafter the Deposit shall be returned to Purchaser and each party shall
bear its own costs incurred hereunder. If Purchaser fails to give Seller a
notice of termination prior to the expiration of the Study Period, Purchaser
shall be deemed to have elected to proceed with the purchase of the Project
pursuant to the terms hereof.

          C. The parties hereto acknowledge that at the time of execution of
this Agreement that Exhibits B (List of Personal Property), D (Rent Roll), E
(Existing Loan Documents), Exhibit F (Ground Leases), Exhibit G (List of Service
Contracts), Exhibit H (Ground Lessor Consent and Waiver Form), Exhibit J
(Assignment and Assumption of Vacancy Escrow Agreement) and Exhibit O (List of
Insurance Policies) were not attached to the Agreement and that the Seller shall
provide such Exhibits to the Purchaser by 5:00 p.m. on Friday, December 9, 2005.
Accordingly, the parties hereto agree that Section 5(A) hereinabove is hereby
modified and amended so that the Study Period will commence on Saturday,
December 10, 2005.

     6. REPRESENTATIONS AND COVENANTS OF SELLER. The Seller hereby makes the
following representations, warranties, and covenants to Purchaser as of the date
hereof, each of which is material to and is relied upon by Purchaser

          A. Seller is a limited liability company duly organized, validly
existing, and in good standing under the laws of the State of Delaware and has
full authority to conduct its business and to own and lease the Project. Seller
is authorized to conduct business in all jurisdictions where the nature of its
business requires such authorization.

          B. Subject to the Ground Lessor Consent and Waiver and the Lender's
Consent, Seller has the right, power and authority to enter into this Agreement
and all documents now or hereafter to be executed and delivered by Seller under
this Agreement, carry out its obligations arising under this Agreement and other
such documents and to transfer and convey the Project in accordance with the
terms and conditions hereof without the consent of any other party, and the
consummation of the transactions contemplated hereby will not violate any laws
or any agreements or obligations by which Seller is bound. This Agreement and
all documents now or hereafter to be executed and delivered by Seller under this
Agreement have been duly authorized, executed and delivered by all necessary
action on the part of the Seller, constitutes the valid and binding agreements
of the Seller and are enforceable against Seller in accordance with their terms.

          C. Except as set forth in the Article XVII of the Ground Lease, there
are no recorded or unrecorded contracts, agreements (written or oral) and/or
options pertaining to or affecting the sale of the Project, or any part thereof.

          D. There is not now pending, or to Seller's knowledge threatened, any
action, suit, or proceeding (including, but not limited to, condemnation or
similar proceedings) before any court or governmental agency or body whatsoever
which would materially and adversely affect the operation or value of the
Project or the operation thereof.

                                       9

<PAGE>

          E. The Rent Roll correctly and completely lists all Tenant Leases and
shows the name of such tenant, the size of the rented space, the commencement
date and expiration date of each such Tenant Lease, the rent payable under each
such Tenant Lease and the date of each such Tenant Lease.

          F. The Rent Roll also contains a list of all current rental
delinquencies under the Leases as of the date set forth therein. Seller agrees
to provide to Purchaser an updated list of rental delinquencies at Closing which
shall be certified by Seller as true, correct and complete in all material
respects.

          G. Except for security deposits placed with the Seller under the
Tenant Leases, a list of which is included on the Rent Roll, to the best of
Seller's knowledge, none of the tenants has paid to the Seller any rent or other
charge of any nature under its Lease or otherwise relating to the Project for a
period of more than thirty (30) days in advance, except for the Embassy of
Burundi.

          H. To the extent Seller is obligated to perform any work or provide
any tenant allowances under any of the Tenant Leases, Seller has performed such
work and provided such tenant allowances which have accrued as of the Effective
Date under the Tenant Leases.

          I. To the best of Seller's knowledge, there are no existing structural
defects in any Improvements at the Project.

          J. Except as discharged, Seller has performed or paid all obligations
(including, without limitation, performance of all work and payment of all work
and other tenant allowances), required to be performed or paid by it under each
of the Tenant Leases and is not in default of any of its obligations under any
of the Tenant Leases, saving and excepting for certain disputes between
Theodore's and Seller regarding the HVAC equipment in Theodore's demised
premises and certain damage to Theodore's demised premise due to such HVAC
equipment.

          K. Attached hereto as Exhibit E are true and correct copies of all
documents evidencing and securing the Existing Debt. Seller has not received a
written notice from the Lender that Seller is in breach of any of its
obligations under such documents and, to the best of Seller's knowledge, no
other party is in breach of its obligations under such documents.

          L. To the best of Seller's knowledge, a true and accurate photocopy of
the Ground Lease is attached hereto and made a part hereof as Exhibit F. The
Ground Lease is in full force and effect and there is no action or proceeding
instituted, or to the best of Seller's knowledge, threatened, against Seller
affecting Seller's interest as lessee under the Ground Lease. Seller, to the
best of Seller's knowledge, is not in breach of its obligations under the Ground
Lease and, to the best of Seller's knowledge, no other party is in breach of its
obligations under the Ground Lease.

          M. Attached hereto as Exhibit G is a complete schedule of all
operating and maintenance agreements and service contracts ("SERVICE CONTRACTS")
for the Improved Real Estate which list includes the names of the contracting
parties, the dates of the Service Contracts and a listing of all amendments to
such Service Contracts, Seller, to the best of Seller's knowledge, is not in
breach of any of its obligations under any of the Service Contracts. To the

                                       10

<PAGE>

best of Seller's knowledge, no other party is in breach of any of its
obligations under any of the Service Contracts. Seller shall assign all Service
Contracts to Purchaser unless Purchaser requests that Seller terminate any or
all Service Contracts. Seller shall terminate any Service Contracts that
Purchaser requests Seller to terminate at Seller's expense on or before the
Closing, provided that such Service Contracts can be terminated and Purchaser
has requested such termination prior to the expiration of the Study Period. In
addition, Seller shall terminate that certain management agreement between
Seller and Zalco Realty Incorporated at Seller's expense on or before the
Closing.

          N. All brokerage commissions due and payable with respect to the
Tenant Leases have been paid by Seller and none are, or will be, due, payable
and owing as of the Closing.

          O. Seller is not a foreign person within the meaning of Section 1445
of the IRC or any regulations promulgated thereunder.

          P. To the best of Seller's knowledge, there is not now pending nor is
there any proposed proceeding for the rezoning of the Improved Real Estate or
any portion thereof. Seller has not received any written notice from any
governmental authority that any zoning, subdivision, environmental, hazardous
waste, building code, health, fire, safety or other law, order, ordinance or
regulation is violated by the continued maintenance, operation or use of the
Improved Real Estate, including, without limitation, any Improvements located
thereon or any parking areas.

          Q. The Seller, to the best of its knowledge, has paid all amounts that
are due and payable, and has performed all of its obligations to the extent
Seller's performance currently is due, under all of the covenants, conditions,
restrictions, rights-of-way and easements constituting the Permitted Exceptions
for the Improved Real Estate.

          R. There are no contracts currently in effect (i) for the sale,
exchange or transfer of the Improved Real Estate or any portion thereof, or (ii)
for the sale, exchange or transfer of any of the membership interests in Seller.

          S. Seller has filed or extended the time period to file all reports
and returns required to be filed with respect to all taxes or other amounts
assessed by any governmental authorities and has paid all such taxes and other
amounts and all penalties or interest thereon.

          T. Except as set forth in the Environmental Report, Seller has no
knowledge: (a) of the presence of any "Hazardous Substances" (as defined below)
on the Project, or any portion thereof, or, (b) of any spills, releases,
discharges, or disposals of Hazardous Substances that have occurred or are
presently occurring on or onto the Project, or any portion thereof, or, (c) of
the presence of any PCB transformers serving, or stored on, the Project, or any
portion thereof, and Seller has no knowledge of any failure to comply with any
applicable local, state and federal environmental laws, regulations, ordinances
and administrative and judicial orders relating to the generation, recycling,
reuse, sale, storage, handling, transport and disposal of any Hazardous
Substances (as used herein, "HAZARDOUS SUBSTANCES" shall mean any substance or
material whose presence, nature, quantity or intensity of existence, use
manufacture, disposal,

                                       11

<PAGE>

transportation, spill, release or effect, either by itself or in combination
with other materials is either: (1) potentially injurious to the public health,
safety or welfare, the environment or the Project, (2) regulated, monitored or
defined as a hazardous or toxic substance or waste by any governmental
authority, or (3) a basis for liability of the owner of the Project to any
governmental authority or third party, and Hazardous Substances shall include,
but not be limited to, hydrocarbons, petroleum, gasoline, crude oil, or any
products, by-products or components thereof, and asbestos). Notwithstanding the
foregoing, the Seller makes no representation or warranty with regard to the
presence, use, storage, manufacture, release or disposal of Hazardous Substances
that are generally recognized to be appropriate to normal and customary office
and/or residential uses or relate to the maintenance of the Project and in
either case are not in excess of any applicable legal limits provided for by the
Environmental Laws and are otherwise used in compliance with applicable
Environmental Laws.

          U. Seller has no employees and no pension plans or employee benefit
plans.

          V. To Seller's knowledge, all copies of documents included in the
Property Information and the Due Diligence Materials are true and accurate
copies of the corresponding documents without any independent investigation or
inquiry having been made or any implied or express duty to investigate, make any
inquiries or review the Property Information and Due Diligence Materials.

          W. References to the "KNOWLEDGE" of Seller shall refer only to the
current actual knowledge of Zalco and Mark Petrusic. Zalco and Mark Petrusic
have been involved personally in the management of the Property and are in the
best position to be aware and have knowledge of the facts and circumstances
pertaining to the representations and warranties made by the Seller herein.
Furthermore, it is understood and agreed that Mark Petrusic shall have no
personal liability in any matter whatsoever hereunder or otherwise related to
the transactions contemplated hereby.

          X. The representations and warranties of Seller set forth in Section 6
hereof shall survive Closing for a period of one (1) year. Any claim which
Purchaser may have against Seller for a breach of any such representation or
warranty, whether such breach is known or unknown, which is not specifically
asserted by written notice to Seller within such one (1) year period, time being
of the essence, shall not be valid or effective and Seller shall have no
liability with respect thereto.

     7. PURCHASER'S WARRANTIES AND REPRESENTATIONS. The Purchaser hereby makes
the following covenants, warranties and representations to Seller, each of which
is material to and relied upon by Seller and each of which shall be deemed made
on the date hereof and again at Closing:

          A. Purchaser is a corporation organized, validly existing, and in good
standing under the laws of the State of Maryland. At the time Seller requests
the Ground Lessor Consent and Waiver (as hereinafter defined), Purchaser (or its
permitted assignee) shall have a net worth exceeding Five Million Dollars
($5,000,000). Purchaser is authorized to conduct business in all jurisdictions
where the nature of its business requires such authorization. The obligations
and undertakings of Purchaser under this Agreement do not and will not violate
or

                                       12

<PAGE>

conflict with any agreement to which Purchaser is a party or by which its assets
are bound. This Agreement has been duly authorized, executed and delivered by
all necessary action on the part of the Purchaser, constitutes the valid and
binding agreement of the Purchaser and is enforceable against Purchaser in
accordance with its terms.

          B. In entering into this Agreement, the Purchaser has not been induced
by and has not relied upon any representations, warranties or statements,
whether express or implied, made by the Seller or any agent, employee or other
representative of the Seller or by any broker or any other person representing
or purporting to represent the Seller, except as expressly set forth in this
Agreement.

          C. As of the Effective Date, Purchaser has no knowledge of the
existence of any facts or circumstances involving Purchaser or its principals
which would entitle the Ground Lessor or Lender to withhold consent to the
assignment of the leasehold interest of Seller to Purchaser or to the
Purchaser's assumption of the Existing Financing, respectively.

          D. The representations and warranties of Purchaser set forth in
Section 7 hereof shall survive Closing for a period of one (1) year.

     8. CONDITIONS.

          A. In addition to all other applicable rights and remedies in the
circumstances, Purchaser's and Seller's respective obligations to consummate the
transactions described herein shall be subject to the representations,
warranties of the other party set forth in this Agreement being true and correct
in all material respects on and as of the Closing in the same manner and with
the same effect as though such representations, warranties and covenants had
been made on and as of the Closing, and the other party shall have performed and
observed, in all material respects, all covenants and agreements to be performed
and observed by such other party under this Agreement.

          B. Purchaser's and Seller's obligations to close under this Agreement
are subject to and conditioned upon receipt of a written statement (the "GROUND
LESSOR CONSENT AND WAIVER") signed by the Ground Lessor, in the form attached
hereto as Exhibit _H, whereby the Ground Lessor (a) consents to the assignment
of Seller's interest in the Ground Lease to Purchaser pursuant to Article XII of
the Ground Lease, if such consent is required, (b) waives the right of Ground
Lessor to purchase the Improved Real Estate under Article XVII of the Ground
Lease, and (c) certifies to the matters set forth therein. Seller shall use
reasonable efforts to obtain the Ground Lessor Consent and Waiver. Purchaser
agrees to cooperate with Seller in the provision of such information as may be
reasonably requested by the Ground Lessor by reason of Seller's request.
Notwithstanding anything contained in this Agreement to the contrary, in the
event that the Seller is not able to obtain the Ground Lessor Consent and Waiver
by the Closing Date (as the same may be extended pursuant to the terms of this
Agreement) then either party may terminate this Agreement by written notice to
the other party.

          C. Seller shall use commercially reasonable efforts (but shall not be
obligated to compensate any tenants in connection therewith) to obtain and
deliver to Buyer no later than three (3) business days prior to the Closing Date
an executed estoppel letter, substantially in the

                                       13

<PAGE>

form attached hereto as Exhibit I (the "TENANT ESTOPPEL"), from all tenants
under Tenant Leases in effect as of the Closing Date (the "TENANTS",
individually, a "TENANT"). As a condition to Purchaser's obligation to
consummate the transactions described herein, Seller is required to deliver
Tenant Estoppels from Tenants whose Leases constitute in the aggregate not less
than eighty percent (80%) of the leased square footage of the Improvements,
including, in all events, a Tenant Estoppel from Georgetown University and
Tenant Estoppels from all other Tenants whose rentable demised premises under
such Tenant Leases equal or exceed Five Thousand (5,000) square feet ("MAJOR
TENANTS"). Notwithstanding the foregoing, if at Closing Seller is unable or
fails to deliver such Tenant Estoppels, Seller may execute and deliver to
Purchaser, at Closing, its own certificate with respect to up to ten percent
(10%) (but not for Major Tenants) of the eighty percent (80%) of Tenants
occupying space, from whom estoppel certificates were not received and whose
Tenant Leases are in full force and effect (substantially in the form of Exhibit
I, appropriately modified to reflect that they are certificates of Seller and
made to Seller's knowledge; hereinafter, the "SELLER'S ESTOPPEL CERTIFICATE")
and the statements of Seller contained therein shall survive the Closing until
the earlier of (a) one year after Closing, and (b) the date Purchaser obtains an
estoppel certificate from a Tenant for whom Seller delivered a Seller's Estoppel
Certificate. Notwithstanding anything contained herein to the contrary, Seller
may extend the Closing Date for sixty (60) days until Seller has obtained the
Tenant Estoppels that Seller is required to obtain hereunder. Notwithstanding
anything contained in this Agreement to the contrary, in the event that the
Seller is not able to obtain the Tenant Estoppels (including, but not limited to
the Tenant Estoppels from the Major Tenants) by the Closing Date (as the same
may be extended pursuant to the terms of this Agreement) and the Purchaser has
not waived the requirement to obtain such Tenant Estoppels then the Seller may
terminate this Agreement by written notice to the Purchaser.

          D. Purchaser's obligation to close under this Agreement is also
subject to and conditioned upon receipt of the Vacancy Acknowledgement and
Lender's Consent and Seller's delivery of the documents set forth in Section 9
below. Seller's obligation to close under this Agreement is also subject to and
conditioned upon receipt of Lender's Consent (including the release of the
Ubermans) and Purchaser's performance of its obligations under this Agreement.
Notwithstanding anything contained herein to the contrary, in the event that the
Seller is not able to obtain the Vacancy Acknowledgement by the Closing Date (as
same may be extended pursuant to the terms of this Agreement) and the Purchaser
has not waived the requirement to obtain such Vacancy Acknowledge then the
Seller may terminate this Agreement by written notice to the Purchaser.

     9. CLOSING, DELIVERIES, PRORATED ITEMS AND CHARGES.

          A. The closing of this Agreement (the "CLOSING") shall be held on
February 15, 2006 or such earlier date as the parties agree (the "CLOSING
DATE"), as such Closing Date may be extended pursuant to the terms and
conditions of this Agreement. TIME BEING OF THE ESSENCE. Closing shall take
place in escrow with the Escrow Agent, at its offices as set forth in Section 18
hereof.

          B. At Closing, Seller shall deliver or cause to be delivered to
Purchaser the following items:

                                       14

<PAGE>

               (i) An assignment to Purchaser, and assumption by Purchaser, of
Tenant Leases in the form attached hereto as Exhibit L.

               (ii) An assignment to Purchaser, and Assumption by Purchaser, in
the form attached hereto as Exhibit M of the Service Contracts and to the extent
assignable, all intangible rights, licenses and/or permits for the Improved Real
Estate.

               (iii) Bill of Sale with warranty of title and no other warranties
or representations, conveying all Personal Property in "as-is" "where-is"
condition in the form attached hereto as Exhibit N.

               (iv) Copies of all records of Seller relating to Leases,
operations, service, repair, and maintenance of the Improved Real Estate.

               (v) Any and all other documents, instruments, certificates,
affidavits, or other items reasonably necessary or appropriate to perform the
obligations hereunder consistent with the terms and provisions of this Agreement
which are reasonably required by Purchaser's attorney or the Title Insurance
Company to evidence the authority of the parties executing documents on behalf
of Seller;

               (vi) A FIRPTA affidavit.

               (vii) A closing statement duly executed by Seller setting forth
in reasonable detail the financial transaction contemplated by this Agreement,
including without limitation the Purchase Price, all prorations, the allocation
of costs specified herein, and the application and disbursement of all funds.

               (viii) Possession of the Project, subject to the Leases, and keys
therefor to the extent such keys are in Seller's and Zalco's possession.

     At Closing, the parties shall also execute an assignment of the Ground
Lease, in the form attached hereto as Exhibit K and an Assignment of the Vacancy
Escrow Agreement, in the form attached hereto as Exhibit J.

          C. At Closing, the Purchaser shall in accordance with the wire
transfer instructions of the Escrow Agent, send the Escrow Agent (i) the portion
of the Purchase Price described in Paragraph 2(C) hereof, (ii) payment for all
amounts held by Lender pursuant to the Existing Loan Documents, including, but
not limited to, the Holdback Agreements, (iii) the Seller Vacancy Reimbursement
(or any part thereof) if the Vacancy Acknowledgement has been delivered to
Purchaser, and (iv) payment for the Supplemental Lease Costs (as hereinafter
defined).

          D. The Seller shall pay its own attorney's fees. The Purchaser shall
pay its own attorney's fees, the cost of any survey update, the cost of title
insurance (including any commitment and title search or examination fees or
costs) and the cost of any deletions, modifications or endorsements to such
title policy desired by Purchaser or its lender. The Purchaser and the Seller
shall each pay one-half of all transfer or recordation taxes imposed by reason
of the conveyance of the Project to Purchaser.

                                       15

<PAGE>

          E. Tenant security deposits held in cash shall be retained by the
Seller, but shall be credited to the Purchaser and, after Closing, the Purchaser
shall be responsible for all cash Tenant security deposits for which Purchaser
receives credit at Closing. At Closing, Seller, at Seller's expense, shall cause
all letters of credit evidencing security deposits to be transferred to
Purchaser and, after Closing, Purchaser shall be responsible for all such
security deposits.

          F. The items in subparagraphs (G) through (J) of this Article 9 shall
be apportioned or prorated between Seller and Purchaser as of 12:01 a.m.,
Washington, D.C. time, on the Closing Date (with all prorations to be made on a
365 day year basis).

          G. All rents actually paid and other income actually received for the
month in which the Closing occurs and expenses (including amounts due under any
Service Contract), ground rent, interest on the Existing Financing and real
estate and personal property taxes and other assessments, utilities (which shall
be placed in Purchaser's name by Purchaser at Closing) (other than recording
taxes) for the year in which the Closing occurs, shall be prorated as of Closing
on a per diem basis based upon the actual number of days in the calendar month
or year (as the case may be) of Closing. If taxes for the year of Closing are
unknown at the time of Closing, prior year's taxes shall be used and when such
taxes become known, the parties shall adjust the proration at that time based
upon such actual taxes. If the Closing shall occur before rents have actually
been paid for the month in which the Closing occurs, the apportionment of such
rents shall be upon the basis of such rents actually received by the Seller.
Subsequent to the Closing, if any such rent or rents for any time prior to
Closing are actually received by the Purchaser, upon its receipt of such rents,
the Purchaser shall promptly pay to the Seller its prorated share thereof, each
such payment to be applied in the following order:

          First, to the month in which Closing shall occur;

          Second, to the most recently accrued obligations until Purchaser is
          current on all rent obligations accruing after Closing.

          Third, to any periods preceding the month of Closing.

     Notwithstanding the foregoing, in the case of rents from the Embassy of
Burundi, which pays its rent quarterly, such rents shall be adjusted when
received as follows:

          First to Seller to the extent of any rentals accruing to the calendar
          quarter in which the Closing shall occur;

          Second, to the most recently accrued obligations until Purchaser is
          current on all rent obligations accruing after Closing.

          Third, to any periods preceding the calendar quarter in which Closing
          occurs.

     If any rents are received by Seller subsequent to the Closing that are
payable to Purchaser by reason of this Agreement, Seller shall promptly pay such
amounts to Purchaser. The Purchaser shall make a good faith effort to collect
delinquent rents for the benefit of the Seller but shall not be required to
initiate any litigation to collect such delinquencies. Seller agrees not to
commence any actions against any tenants subsequent to the Closing, unless such
tenants have

                                       16

<PAGE>

vacated the Project. The Seller shall pay all utilities and other operating
expenses of the Project arising or accruing prior to the Closing. The Purchaser
shall pay all utilities and other operating expenses of the Project arising or
accruing on or after the Closing. The provisions of this subparagraph shall
survive Closing.

          H. To the extent such expenses are the obligation of Seller and not of
tenants under the Tenant Leases, utilities, including water, sewer, electric,
and gas, shall be based upon the last reading of meters prior to the Closing.
Seller shall endeavor to obtain meter readings on the day of the Closing Date,
and if such readings are obtained, there shall be no proration of such items. No
proration shall be made for utility expenses that are separately metered to and
paid directly by tenants and for which Seller has no obligation to pay.
Additionally, Seller shall retain the right to receive reimbursement or refund
from the applicable utility company (or Purchaser) of all security deposits held
by any such utility companies in connection with the provision of services prior
to the Closing Date.

          I. Fees and charges under all Service Contracts as are being assigned
to and assumed by Purchaser at the Closing, on the basis of the periods to which
such Service Contracts relate, to the extent such expenses are the obligation of
Seller and not of tenants under the Tenant Leases. Purchaser shall reimburse
Seller for any prepaid charges under Service Contracts and any deposits being
held by other parties to such Service Contracts.

          J. Where the Tenant Leases contain tenant obligations for taxes,
operating expenses or additional charges of any other nature ("CAM CHARGES"),
and where Seller shall have collected any portion thereof in excess of amounts
incurred by Seller for such items for the period prior to the Closing Date, then
there shall be an adjustment and credit given to Purchaser on the Closing Date
for such excess amounts collected. Purchaser shall apply all such excess amounts
to the charges owed by Purchaser for such items for the period after the Closing
Date and, if required by the Tenant Leases, shall rebate or credit tenants with
any remainder. If it is determined after Closing that the amount collected
during Seller's ownership period is less than the expenses incurred during the
same period, then Purchaser shall promptly pay to Seller the deficiency upon
receipt from tenants of the deficiency. If it is determined at any time after
Closing that the amount collected during Seller's ownership period exceeded
expenses incurred during the same period by more than the amount previously
credited to Purchaser at Closing Seller shall promptly pay to Purchaser the
deficiency. If it is determined after Closing that the amount collected during
Seller's ownership period exceeded expenses incurred during the same period by
less than the amount previously credited to Purchaser at Closing, then Purchaser
shall promptly pay to Seller the deficiency. The foregoing provisions shall
expressly survive the Closing.

          K. Any such adjustments not finally determined or agreed upon as of
such Closing Date shall be paid by Purchaser to Seller, or by Seller to
Purchaser, as the case may be, from time to time in cash as soon as practicable
following the receipt or determination of the information necessary to make the
adjustments after the Closing Date.

          L. Without limiting the generality of subparagraph (K) above, after
year-end (or other applicable period) adjustments with tenants under Tenant
Leases for real estate taxes, assessments, maintenance charges, and operating
expenses, Purchaser shall prepare and present

                                       17

<PAGE>

to Seller a calculation of the re-proration of taxes, assessments, CAM Charges,
and those operating expenses to which the CAM Charges relate, based upon the
actual amount of such items charged to or received by the parties for the year
or other applicable fiscal period. The parties shall make the appropriate
adjusting payment between them within thirty (30) days after presentment to
Seller of Purchaser's calculation.

          M. For a period of twelve (12) months following the Closing Date,
Purchaser and Purchaser's successors and assigns shall make available to Seller
and its successors and assigns, and Seller shall make available to Purchaser and
Purchaser's successors and permitted assigns, and their respective employees,
agents and representatives all books and records maintained with respect to the
Project which relate to any of the items to be prorated or allocated under this
Agreement in connection with such Closing, which books and records shall be made
available for inspection and copying upon reasonable notice during ordinary
business hours. Any such inspection shall be at reasonable intervals and at the
inspecting party's sole cost and expense. The obligations under this Article 9
shall survive the Closing.

     10. RISK OF LOSS; TERMINATION; RIGHTS, REMEDIES.

          A. If, prior to the Closing, action is initiated to take all or a
portion of the Improved Real Estate by eminent domain proceedings or by deed in
lieu thereof, Seller shall notify Purchaser in writing, and the Purchaser may
either (i) terminate this Agreement by delivering written notice to Seller
within five (5) days after receipt of Seller's notice or (ii) consummate the
Closing in which latter event the award of the condemning authority shall be
assigned by the Seller to the Purchaser at the Closing.

          B. In the event of damage by fire, act of God or other casualty to all
or a portion of the Improved Real Estate prior to the Closing which, in the
reasonable estimate of the Seller, would cost ONE MILLION FIVE HUNDRED THOUSAND
DOLLARS ($1,500,000.00) or less to repair, this Agreement shall remain in full
force and effect. In such event, (i) the Seller shall, at Closing, pay to
Purchaser any sums collected under any policies of insurance because of such
casualty, and assign to the Purchaser all rights to collect such sums relating
to such casualty (except for rent loss coverage applicable to periods prior to
Closing) as may then be uncollected, (retaining however, the right to be
reimbursed first therefrom for any sums previously incurred by Seller in
connection with the repair or restoration of the Improved Real Estate) and (ii)
the Purchase Price shall be reduced by the amount of the deductible under
Seller's insurance policy.

          C. If damage referred to Paragraph 10(B) is in excess of ONE MILLION
FIVE HUNDRED THOUSAND DOLLARS ($1,500,000.00), this Agreement may, at the option
of Purchaser, be terminated within five (5) days after Purchaser receives
written notice thereof, and upon return of the Deposit to Purchaser, neither
party shall have any further liability to the other, except as herein
specifically provided. If Purchaser does not elect to terminate, this Agreement
shall remain in full force and effect, and at Closing the Seller shall pay to
the Purchaser any sums collected under any policies of insurance because of such
casualty, and assign to the Purchaser all rights to collect such sums relating
to such casualty as may then be uncollected, (retaining however, the right to be
reimbursed first therefrom for any sums previously incurred by Seller in
connection with the repair or restoration of the Improved Real

                                       18

<PAGE>

Estate and rent loss coverage for periods prior to Closing) and the Purchase
Price shall be reduced by the amount of the deductible under Seller's insurance
policy.

     11. RELEASE OF SELLER. By execution of this Agreement, absent the breach by
Seller of an express representation made by Seller contained in Article 6 above
Purchaser agrees that Seller shall be deemed released from any claim or demand
of any nature concerning the Project including its elements, environmental and
zoning matters, claims related to compliance with any federal or state law, rule
or regulation or any other matter. In furtherance thereof, Seller shall have no
liability with respect to any of the representations and warranties made in this
Agreement or any representations and warranties made in any other document
executed and delivered by Seller to Purchaser, to the extent that, prior to the
Closing, Purchaser obtains actual knowledge (from whatever source, as a result
of its due diligence tests, investigations and inspections of the Project, or
disclosure in writing by Seller or Seller's agents and employees) that
contradicts any such representations and warranties, or renders any such
representations and warranties untrue or incorrect, and Purchaser nevertheless
consummates the transaction contemplated by this Agreement. By Closing,
Purchaser shall be deemed to have waived all such claims and demands described
in the two (2) immediately preceding sentences; and the Purchaser shall not be
entitled to "reserve" any claims or demands at Closing of which it has actual
knowledge. Purchaser acknowledges, represents and warrants that Purchaser is not
in a significantly disparate bargaining position with respect to Seller in
connection with the transaction contemplated by this Agreement; that Purchaser
freely and fairly agreed to this acknowledgment and waiver as part of the
negotiations for the transaction contemplated by this Agreement; that Purchaser
is represented by legal counsel in connection with this transaction and
Purchaser has conferred with such legal counsel concerning this waiver. The
provisions of this Section 11 shall expressly survive the Closing and/or
termination of this Agreement without limitation.

     12. SELLER'S PRE-CLOSING OBLIGATIONS.

          A. Between the Effective Date of this Agreement and the Closing,
Seller shall not, without Purchaser's prior written consent: terminate any
Tenant Lease or tenancy except by reason of a default by the tenant thereunder
or the natural expiration of such tenancy.

          B. Between the Effective Date of this Agreement and the Closing,
Seller shall not enter into any new Tenant Lease or amend, renew (other than by
reason of a renewal arising by reason of an existing renewal option granted
under a Tenant Lease in effect as of the date hereof), or extend any of the
existing Tenant Leases, nor grant any rebate, concession, allowance or free rent
for any period subsequent to Closing without the prior written consent of
Purchaser which consent shall not be unreasonably withheld, conditioned or
delayed and shall be deemed given if Purchaser does not reasonably object
thereto within five (5) days after receipt thereof. Any lease hereafter entered
into by Seller in accordance with the provisions of this Article 12 with the
consent of Purchaser is collectively referred to as a "PERMITTED SUPPLEMENTAL
LEASE." Any tenant improvement concessions, brokerage commissions or any other
costs and expenses attributable to a Permitted Supplemental Lease ("SUPPLEMENTAL
LEASE COSTS") shall be borne solely by Purchaser and shall be paid to Seller at
the Closing to the extent paid or incurred by or on behalf of Seller as of the
Closing Date.

                                       19

<PAGE>

          C. Between the Effective Date of this Agreement and the Closing,
Seller shall maintain or cause to be maintained in full force and effect until
Closing fire and extended coverage insurance providing for replacement cost
insurance. As of the date hereof, the schedule attached hereto as Exhibit O
lists the policies of insurance presently maintained by Seller for the Project.

          D. Between the Effective Date of this Agreement and the Closing,
Seller shall comply with its obligations under the Ground Lease and under each
of the Tenant Leases to the extent required on or before the Closing and operate
the Project in the ordinary course of business. Seller shall continue to
maintain the Project in accordance with its previous practices, subject only to
reasonable use and wear and the terms of Article 9 hereof.

          E. Seller agrees that from the Effective Date to the Closing, it will:
(i) not mortgage or encumber any part of the Project or take or suffer any other
action affecting title to the Project, nor enter into any loan, without the
prior written consent of Purchaser; (ii) not make any commitment or incur any
liability to any labor union, through negotiations or otherwise, with respect to
the Project; and (iii) not become a party to any new licenses, equipment leases,
contracts or agreements of any kind relating to the Project, except such
contracts or agreements as will be terminated at or prior to Closing without
cost or expense to Purchaser or contracts which Purchaser agrees in its sole
discretion to assume at Closing, without having obtained in each case the prior
written consent of Purchaser.

          F. Seller agrees that from the Effective Date to the Closing, it shall
promptly advise Purchaser of any notice of litigation received by Seller that
may affect the ownership or operation of the Project.

          G. Seller agrees that from the Effective Date to the Closing, it shall
not affirmatively encumber the Project, except as required by court order or as
required by law.

          H. Seller agrees that from the Effective Date to the Closing, it shall
not list the Project or any part thereof with any broker or otherwise solicit or
make or accept any offers to sell the Project or any part thereof, engage in any
discussions or negotiations with respect to the sale or disposition of the
Project or any part thereof with any third party, or enter into any contract,
agreement or letter of intent regarding the disposition of the Project or any
part thereof.

     13. TERMINATION; DEFAULT; REMEDIES; LIMITATION ON LIABILITY.

          A. If Purchaser shall default in the performance of its obligation
under this Agreement to purchase the Project, then Seller's sole remedy shall be
to retain the Deposit then held by Escrow Agent as and for liquidated damages
and neither party shall have any further liability to the other. Purchaser and
Seller acknowledge that it would be extremely impracticable and difficult to
ascertain the actual damages that would be suffered by Seller if Purchaser fails
to consummate the purchase of the Project contemplated herein (for any reason
other than Seller's failure, refusal or inability to perform any of Seller's
covenants and agreements hereunder) in accordance with this Agreement. Purchaser
and Seller have considered carefully the loss to Seller as a consequence of the
negotiation and execution of this Agreement; and the personal expenses of Seller
incurred in connection with the preparation of this Agreement and Seller's

                                       20
<PAGE>

performance hereunder; and the other damages, general and special, that
Purchaser and Seller realize and recognize Seller will sustain, but that Seller
cannot at this time calculate with absolute certainty. Based on all those
considerations, Purchaser and Seller have agreed that the damage to Seller would
reasonably be expected to amount to the Deposit.

          B. If prior to Closing, Seller defaults in performing its obligations
hereunder for any reason other than a failure by Purchaser to perform its
obligations hereunder and if Seller has not cured such default after receipt of
written notice specifying such default and twenty (20) days, then Purchaser may
either (i) terminate this Agreement and receive a return of the Deposit, or (ii)
pursue specific performance of Seller's obligation to convey the Project to
Purchaser pursuant to the provisions of this Agreement. Notwithstanding anything
contained herein, in no event will Purchaser be entitled to pursue specific
performance in the event that Closing did not take place due to any matters
outside the control of Seller, including, but not limited to, the failure of the
Seller to obtain any Tenant Estoppels, the Lender Consent or consent of the
Ground Lessor.

          C. Notwithstanding anything to the contrary contained herein, after
the Closing: (a) the maximum aggregate liability of Seller, and the maximum
aggregate amount which may be awarded to and collected by Purchaser (including,
without limitation, for any breach of any representation, warranty and/or
covenant by Seller) under this Agreement or any documents executed pursuant
hereto or in connection herewith, including, without limitation, Assumption of
the Existing Loan, the Assignment of the Ground Lease, the Assignment of the
Vacancy Escrow Agreement (collectively, the "OTHER DOCUMENTS"), shall under no
circumstances whatsoever exceed FIVE HUNDRED THOUSAND AND NO/100 DOLLARS
($500,000.00); and (b) no claim by Purchaser alleging a breach by Seller of any
representation, warranty and/or covenant of Seller contained herein or in any of
the Other Documents may be made, and Seller shall not be liable for any judgment
in any action based upon any such claim, unless and until such claim, either
alone or together with any other claims by Purchaser alleging a breach by Seller
of any such representation, warranty and/or covenant is for an aggregate amount
in excess of TWENTY-FIVE THOUSAND AND NO/100 DOLLARS ($25,000.00) (the "FLOOR
AMOUNT"), in which event Seller's liability respecting any final judgment
concerning such claim or claims shall be for the entire amount thereof, subject
to the limitation set forth in clause (a) above; provided, however, that if any
such final judgment is for an amount that is less than or equal to the Floor
Amount, then Seller shall have no liability with respect thereto. The Ubermans
shall individually guaranty the Seller's liability under this Agreement as
limited by this Section 13(C) for a period of one (1) year after the Closing.

     14. BROKER AND COMMISSION. Pursuant to separate commission agreements, the
Seller has agreed to pay at the Closing, a commission to Summit Commercial Real
Estate (the "SELLER'S BROKER"). Other than the Seller's Broker, Seller and
Purchaser have not engaged the services of, or are they or will they become
liable to, any real estate agent, broker, finder or any other person or entity
for any brokerage or finder's fee, commission or other amount with respect to
the transactions described herein. The Seller and Purchaser shall indemnify,
defend and hold the other harmless against all loss, liability and expense,
including reasonable attorneys' fees and costs, suffered by the other due to a
breach of the foregoing representation, covenant and warranty.

                                       21

<PAGE>

     15. MODIFICATION. This Agreement supersedes all prior discussions and
agreements between the Seller and Purchaser with respect to the purchase/sale of
the Project and other matters contained herein, and this Agreement contains the
sole and entire understanding between the parties hereto with respect to the
transactions contemplated herein. This Agreement is intended by the parties
hereto to be an integration of all prior or contemporaneous promises,
agreements, conditions and undertakings between the parties hereto. This
Agreement shall not be modified or amended except by an instrument in writing
signed by or on behalf of the parties hereto. No waiver of any of the provisions
of this Agreement shall be valid unless in writing and signed by the party
against whom it is sought to be enforced.

     16. APPLICABLE LAW. This Agreement shall be governed by, construed under
and enforced in accordance with the laws of the District of Columbia.

     17. COUNTERPARTS. This Agreement may be executed in several counterparts,
each of which shall be deemed an original, and all of such counterparts together
shall constitute one and the same instrument.

     18. NOTICES. All notices, requests, demands and other communications
hereunder shall be in writing and shall be deemed to have been duly given if
delivered by hand, by overnight courier which maintains evidence of service or
mail, United States certified or registered mail return receipt requested,
postage prepaid (or by facsimile to the following numbers) as follows:

          A.   To Seller:

               c/o 1370 Piccard Drive
               Suite 200
               Rockville, MD 20850
               Attention: Reuven Uberman
               Telephone: (301) 417-0300
               Facsimile: (301) 417-0507

               With Copies to:

               Donald N. Sperling, Esquire
               Beth H. McIntosh, Esquire
               Stein, Sperling, Bennett, De Jong,
               Driscoll & Greenfeig, P.C.
               25 West Middle Lane
               Rockville, MD 20850

                                       22

<PAGE>

          B.   To Purchaser:

               Columbia Equity Trust, Inc.
               1750 H Street, NW, Suite 500
               Washington, DC 20006
               Attention: Oliver T. Carr, III
               Telephone: (202) 303-3060
               Facsimile: (202) 303-3078

               With copies to:

               Hunton & Williams LLP
               1900 K Street, NW, Suite 1200
               Washington, DC 20006
               Attention: John M. Ratino
               Telephone: (202) 778-2221
               Facsimile: (202) 778-2201

          C.   To Escrow Agent:

               Commonwealth Land Title Insurance Company
               1015 15th Street, NW, Suite 300
               Washington, DC 20005
               Attention: Sarah E. Webb
               Telephone: (202) 312-5119
               Facsimile: (202) 737-4108

     All notices given by hand or overnight courier shall be effective upon
delivery and notices by mail shall be effective three (3) business days after
the post-mark from the U.S. Postal Service. All notice given by facsimile shall
be deemed received on the date the same is sent provided there is written
confirmation of receipt. The attorneys are authorized to give any notice
specified on this Agreement on behalf of their respective clients.

     19. LITIGATION. Notwithstanding anything contained herein to the contrary,
in the event of any litigation hereunder, the losing party shall pay all actual
(and not consequential) out of pocket costs of the prevailing party, including
reasonable attorneys' fees.

     20. TIME FOR PERFORMANCE. When the last day prescribed hereunder for
performing any acts falls on a Saturday, Sunday or legal holiday, then such act
shall be performed on the next succeeding day which is not a Saturday, Sunday or
legal holiday.

     21. ASSIGNMENT. The parties agree that Purchaser shall have the right to
assign this Agreement to any entity controlled by Purchaser for the purposes of
acquiring the Project, provided (i) the assignee shall expressly assume the
performance of the obligations of Purchaser hereunder and (ii) the assignee is
structured as Lender and Ground Lessor may require and (iii) the assignee can
satisfy the net worth requirements necessary to obtain the Lender's Consent and
the Consent of the Ground Lessor. However, notwithstanding anything contained
herein to the contrary, no assignment may occur hereunder after the Lender's
Consent has been obtained if

                                       23

<PAGE>

such assignment would invalidate such consent. Any other assignment of this
Agreement by Purchaser shall be subject to the express prior written consent of
Seller, which may be granted, withheld or conditioned by Seller in its sole and
exclusive discretion. Purchaser agrees to deliver to Seller an executed copy of
such assignment prior to Closing.

     22. WAIVER OF TRIAL BY JURY. PURCHASER AND SELLER HEREBY WAIVE, IRREVOCABLY
AND UNCONDITIONALLY, TRIAL BY JURY IN ANY ACTION BROUGHT ON, UNDER OR BY VIRTUE
OF OR RELATING IN ANY WAY TO THIS AGREEMENT OR ANY OF THE DOCUMENTS OR
CERTIFICATES EXECUTED IN CONNECTION HEREWITH, OR ANY CLAIMS, DEFENSES, RIGHTS OF
SETOFF, OR OTHER ACTIONS PERTAINING HERETO, OR TO ANY OF THE FOREGOING. THIS
SECTION SHALL SURVIVE THE CLOSING AND/OR THE TERMINATION OF THIS AGREEMENT.

     23. CONDITION OF PROJECT AND DISCLAIMER. Purchaser has inspected the
Project and shall purchase the Project in its present "AS-IS, WHERE-IS CONDITION
WITH ALL FAULTS", subject to the reasonable and ordinary wear and tear of the
Project and damage by casualty between the Effective Date and the Closing, and
to the other applicable provisions of this Agreement "AS-IS, WHERE-IS CONDITION
WITH ALL FAULTS" shall mean as is, with all faults, including defects seen and
unseen and all conditions natural and artificial without right of set-off or
reduction in the Purchase Price and without representation or warranty of any
kind, expressed or implied, except to the extent of the representations
expressly stated herein. PURCHASER ACKNOWLEDGES AND AGREES THAT SELLER HAS NOT
MADE, DOES NOT MAKE AND SPECIFICALLY NEGATES AND DISCLAIMS ANY REPRESENTATIONS,
WARRANTIES (OTHER THAN THE REPRESENTATIONS EXPRESSLY STATED IN ARTICLE 6 OF THIS
AGREEMENT), PROMISES, COVENANTS, AGREEMENTS OR GUARANTIES OF ANY KIND OR
CHARACTER WHATSOEVER, WHETHER EXPRESS OR IMPLIED, ORAL OR WRITTEN, PAST, PRESENT
OR FUTURE, OF, AS TO, CONCERNING OR WITH RESPECT TO (A) THE VALUE, NATURE,
QUALITY OR CONDITION OF THE PROJECT, INCLUDING, WITHOUT LIMITATION, THE WATER,
SOIL, LEAD PAINT, RADON AND GEOLOGY, (B) THE SUITABILITY OF THE PROJECT FOR ANY
AND ALL ACTIVITIES AND USES WHICH PURCHASER OR ANY TENANT MAY CONDUCT THEREON,
(C) THE COMPLIANCE OF OR BY THE PROJECT OR ITS OPERATION WITH ANY LAWS, RULES,
ORDINANCES OR REGULATIONS OF ANY APPLICABLE GOVERNMENTAL AUTHORITY OR BODY, (D)
THE HABITABILITY, MERCHANTABILITY, PROFITABILITY OR FITNESS FOR A PARTICULAR
PURPOSE OF THE PROJECT, (E) THE COMPLIANCE WITH ANY ENVIRONMENTAL PROTECTION,
POLLUTION OR LAND USE LAWS, RULES, REGULATIONS, ORDERS OR REQUIREMENTS,
INCLUDING THE ENVIRONMENTAL CONDITION OF THE PROJECT AND THE PRESENCE OR ABSENCE
OF OR CONTAMINATION BY HAZARDOUS MATERIALS, OR THE COMPLIANCE OF THE PROJECT
WITH REGULATIONS OR LAWS PERTAINING TO HEALTH OR THE ENVIRONMENT, INCLUDING BUT
NOT LIMITED TO, THE COMPREHENSIVE ENVIRONMENTAL RESPONSE, COMPENSATION AND
LIABILITY ACT, THE RESOURCE CONSERVATION AND RECOVERY ACT, THE CLEAN WATER ACT,
THE CLEAN AIR ACT, AND ANY STATE LAW SIMILAR TO THE FOREGOING, EACH AS MAY BE
AMENDED FROM TIME TO TIME, AND INCLUDING

                                       24

<PAGE>

ANY AND ALL REGULATIONS, RULES OR POLICES PROMULGATED THEREUNDER OR (F) ANY
OTHER MATTER WITH RESPECT TO THE PROJECT AND OR THE CONDITION THEREOF. PURCHASER
FURTHER ACKNOWLEDGES AND AGREES THAT HAVING BEEN GIVEN THE OPPORTUNITY TO
INSPECT THE PROJECT AND EXCEPT FOR THOSE MATTERS EXPRESSLY REPRESENTED BY SELLER
IN THIS AGREEMENT, PURCHASER IS RELYING SOLELY ON ITS OWN INVESTIGATION OF THE
PROJECT AND NOT ON ANY REPRESENTATIONS OR INFORMATION PROVIDED OR TO BE PROVIDED
BY SELLER. PURCHASER FURTHER ACKNOWLEDGES AND AGREES THAT ANY INFORMATION
PROVIDED OR TO BE PROVIDED WITH RESPECT TO THE PROJECT WAS OBTAINED FROM A
VARIETY OF SOURCES AND THAT SELLER HAS NOT MADE ANY INDEPENDENT INVESTIGATION OR
VERIFICATION OF SUCH INFORMATION AND MAKES NO REPRESENTATIONS AS TO THE
ACCURACY, TRUTHFULNESS OR COMPLETENESS OF SUCH INFORMATION. SELLER IS NOT LIABLE
OR BOUND IN ANY MANNER BY ANY VERBAL OR WRITTEN STATEMENT, REPRESENTATION OR
INFORMATION PERTAINING TO THE PROJECT, OR THE OPERATION THEREOF, FURNISHED BY
ANY REAL ESTATE BROKER, CONTRACTOR, ENVIRONMENTAL CONSULTANT, AGENT, EMPLOYEE,
SERVANT OR OTHER PERSON, WITH THE EXPRESS EXCEPTION OF THOSE MATTERS EXPRESSLY
REPRESENTED BY SELLER IN THIS AGREEMENT. THE PROVISIONS HEREOF SHALL SURVIVE THE
CLOSING OR ANY TERMINATION HEREOF AND SHALL BE DEEMED TO SUPERSEDE ANY PROVISION
OF ANY OTHER DOCUMENT OR AGREEMENT NOW OR HEREAFTER ENTERED INTO BY SELLER.

     24. MISCELLANEOUS PROVISIONS.

          A. The indemnities, representations and warranties hereunder shall be
merged into the assignments or other documents executed and delivered at Closing
and shall not be deemed to have survived the Closing, except as expressly set
forth herein.

          B. This Agreement may not be recorded by either party.

          C. Wherever in this Agreement the singular number is used, the same
shall be read to include the plural, and the plural shall be read to include the
singular, and the masculine gender shall be deemed to include the feminine or
neuter genders wherever the context may so require.

          D. Purchaser acknowledges that Purchaser has been advised pursuant to
the provisions of Title 45, Section 308 of the District of Columbia Code
concerning Soil Characteristics, that the soil on the Land in question is noted
in the Soil Survey of the District of Columbia as Urban Land with the following
characteristics: Urban Land Association, not rated, nearly level to moderately
sloping areas, most of which are occupied by structures and works; on all
landscape portions. Purchaser has been further advised that it may obtain
further information with respect thereto by engaging a soil testing laboratory,
the District of Columbia Department of Environmental Services, or the Soil
Conservation Service of the Department of Agriculture.

                                       25

<PAGE>

          E. Time shall be of the essence with respect to each and every
provision of this Agreement.

          F. This Agreement does not constitute an offer to sell and shall not
bind either party unless and until each party has executed and delivered to the
other an executed original counterpart hereof.

          G. If any term or provision of this Agreement or the application
thereof to any person or circumstance shall, to any extent, be invalid or
unenforceable, the remainder of this Agreement, or the application of such term
or provision to persons or circumstances other than those as to which it is held
invalid or unenforceable, shall not be affected thereby, and each term and
provision of this Agreement shall be valid and enforceable to the fullest extent
permitted by law.

          H. The paragraph headings used herein are for reference purposes only,
and do not control or affect the meaning or interpretation of any term or
provision hereof, and shall not be deemed in any manner to modify, explain,
qualify, or restate any of the provisions of this Agreement.

          I. The failure of any party to enforce at any time any provision of
this Agreement shall not be construed as a waiver of such provision, or of the
right of any party, thereafter, to enforce such provision. A waiver of any
breach of this Agreement shall not be held to be a waiver of any other or
subsequent breach.

          J. The representations, warranties, and agreements of the parties
contained herein are intended solely for the benefit of the party to whom such
representations, warranties, or agreements are made, and shall not confer any
right hereunder, whether legal or equitable, in any other party, and no other
party shall be entitled to rely thereon.

          K. A signed copy of this Agreement or any amendment hereto or any
other document related hereto transmitted by telecopier or facsimile machine
shall be deemed an executed original of such document for all purposes, and the
party so providing such signed copy shall deliver promptly, thereafter, by
nationally recognized overnight courier to all other parties an executed
original copy of such signed document.

          L. Seller reserves the right to locate or cause to be located property
of a like-kind suitable to Seller for the purpose of effectuating one or more
exchange transactions solely by the transfer of this Agreement (but not title to
the Project) by Seller to a "QUALIFIED INTERMEDIARY" selected by Seller (the
"ACCOMMODATOR") in connection with a tax-deferred exchange as contemplated by
Section 1031 of the Internal Revenue Code of 1986, as amended. Purchaser agrees
to cooperate with Seller in connection with such tax-deferred exchange,
including the execution of such documents as may be reasonably necessary to
effectuate the same; provided that (i) the Closing Date shall not be delayed as
the result of such exchange; (ii) all additional costs in connection with such
exchange shall be borne by Seller; (iii) such exchange is effectuated through an
Accommodator; (iv) Seller conveys title to the property directly to Purchaser
(or its permitted assignee) by direct deeding and remains liable for all of its
obligations, representations and warranties hereunder; and (v) Seller shall
indemnify Seller and

                                       26

<PAGE>

hold Purchaser harmless from and against any and all claims, demands,
liabilities, costs, expenses, penalties, damages and losses, including, without
limitation, reasonable attorneys' fees relating to Purchaser's participation in
such exchange. This Agreement and Seller's obligations hereunder are not subject
to or conditioned upon Seller's ability to consummate an exchange. Purchaser's
responsibility for reviewing exchange documents shall be limited to determining
whether the terms and conditions of such exchange documents are such that they
are in compliance with the foregoing provisions. Seller shall be responsible for
the payment of all deposits and other costs required to be paid by the
"purchaser" pursuant to the exchange documents and for making all determinations
as to the legal sufficiency or other consideration, including but not limited to
tax considerations, relating to such exchange documents. Purchaser, in so
cooperating in any exchange transaction arranged by Seller, shall in no event be
responsible for, or in any way warrant, the tax consequences of the exchange
transaction.

          M. Seller expressly recognizes that Purchaser, or an entity to be
associated with Purchaser in connection with the acquisition of the Project, may
also desire to structure such acquisition as a tax deferred exchange under
Section 1031 of the Internal Revenue Code of 1986, as amended, and Seller shall
cooperate in the execution and delivery of such documents, including the
assignment of this Agreement to a "qualified intermediary" designated by
Purchaser, as may be reasonably requested by Purchaser in order to obtain such
exchange treatment for federal income tax purposes, provided that (i) the
Closing Date shall not be delayed as the result of such exchange; (ii) all
additional costs in connection with such exchange shall be borne by Purchaser;
(iii) such exchange is effectuated through an Accommodator; (iv) Purchaser
remains liable for all of its obligations, representations and warranties
hereunder; and (v) Purchaser shall indemnify Seller and hold Seller harmless
from and against any and all claims, demands, liabilities, costs, expenses,
penalties, damages and losses, including, without limitation, reasonable
attorneys' fees relating to Seller's participation in such exchange. This
Agreement and Purchaser's obligations hereunder are not subject to or
conditioned upon Purchaser's ability to consummate an exchange. Seller's
responsibility for reviewing exchange documents shall be limited to determining
whether the terms and conditions of such exchange documents are such that they
are in compliance with the foregoing provisions. Purchaser shall be responsible
for the payment of all deposits and other costs required to be paid by the
"seller" pursuant to the exchange documents and for making all determinations as
to the legal sufficiency or other consideration, including but not limited to
tax considerations, relating to such exchange documents. Seller, in so
cooperating in any exchange transaction arranged by Purchaser, shall in no event
be responsible for, or in any way warrant, the tax consequences of the exchange
transaction.

                                       27

<PAGE>

     IN WITNESS WHEREOF, the Seller and Purchaser have signed this Agreement for
Purchase and Sale, as of the day and year first above written.

                                        PURCHASER:

                                        Columbia Equity Trust, Inc., a Maryland
                                        corporation

                                        By: /s/ Oliver T. Carr, III
                                            ------------------------------------
                                            Oliver T. Carr, III,
                                            Chairman and Chief Executive Officer

                                        SELLER:

                                        UNICORN WISCONSIN, LLC, a Delaware
                                        limited liability company

                                        By: Unicorn Management, Inc, a Delaware
                                        corporation, its manager

                                        By: /s/ Reuven Uberman            (Seal)
                                            ------------------------------------
                                            Reuven Uberman, President

     The undersigned hereby confirms its agreement to serve as Escrow Agent
under this Agreement in accordance with the Escrow Agreement attached as Exhibit
C hereto.

                                        ESCROW AGENT:

                                        ----------------------------------------

                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------

                                       28

<PAGE>

                                    EXHIBIT A

                              Property Description

All of that certain lot or parcel of land situated, lying and being in the
District of Columbia, and being more particularly described as follows:

Being parts of Lots 302 and 303 in Phillip Young's subdivision of lots in Square
1299 as per plat recorded in Liber No. 38 at folio 56 in the Office of the
Surveyor for the District of Columbia; and also part of Lots 256 and 257 in
Square 1299 in "Beatty & Hawkins Addition to Georgetown," as shown on Plat of
Survey recorded in Survey Book 170 at Page 287 among said Surveyor's Office
Records; and also part of Lots 298, 299, 300 and 301, inclusive, in Square 1299
in Robert D. Weaver's subdivision as per plat recorded in Liber No. 24 at folio
25, among said Surveyor's Office Records; and being more particularly described
as follows:

BEGINNING for the same at a point on the Easterly line of Wisconsin Avenue, said
point being 130 feet from the South line of Observatory Lane; thence leaving
Wisconsin Avenue,

     1.   North 71 degrees 44 minutes East, 298.41 feet to intersect the
          Westerly line of Observatory Circle; thence running with said Westerly
          line,

     2.   Along the arc of a curve deflecting to the left, having a radius of
          1000.00 feet, an arc distance of 270.005 feet; thence leaving
          Observatory Circle;

     3.   South 74 degrees 19 minutes West, 280.36 feet to intersect the
          aforesaid Easterly line of Wisconsin Avenue; thence running with said
          Easterly line,

     4.   North 33 degrees 41 minutes West, 261.07 feet to the place of
          beginning; containing a calculated area of 1.6667 acres of land, more
          or less.

Note: At the date hereof the above described land is designated on the Records
of the Assessor of the District of Columbia for assessment and taxation purposes
as Lot 1006 in Square 1299.

Subject to right of way as set forth in Deed recorded December 8, 1908 in Liber
No. 3196 at folio 63 among the Land Records of the District of Columbia.

Subject to and together with right of way as set forth in Deed recorded April
28, 1937 in Liber No. 7103 at folio 229 among the Land Records of the District
of Columbia.

                                       29

<PAGE>

                                    EXHIBIT B

                                Personal Property

                                       30

<PAGE>

                                    EXHIBIT C

                                ESCROW AGREEMENT

Case No.: ___________________________

                              EARNEST MONEY DEPOSIT
                                ESCROW AGREEMENT

     THIS AGREEMENT is made as of the ___ day of __________, 2005 by and among
Unicorn Wisconsin, LLC ("Seller"), Columbia Equity Trust, Inc. ("Purchaser"),
and COMMONWEALTH LAND TITLE INSURANCE COMPANY ("Escrow Agent").

WHEREAS, Seller and Purchaser have entered into a certain Agreement for Purchase
and Sale dated __________________, 2005, (the "Contract"), a copy of which is
attached hereto and made a part hereof as "Exhibit A", concerning real property
described in attached "Schedule A" or described as follows:

WHEREAS, in connection with the Contract, the Seller and Purchaser have
requested Escrow Agent to receive the earnest money deposit finds and/or other
property to be held in escrow and applied in accordance with the terms and
conditions of this Escrow Agreement.

NOW THEREFORE, in consideration of the above recitals, the mutual promises set
forth herein and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties agree as follows:

1. COMMONWEALTH LAND TITLE INSURANCE COMPANY hereby agrees to act as Escrow
Agent in accordance with the terms and conditions hereof. Escrow Agent shall not
be deemed to be an agent of Seller or Purchaser. It is understood and agreed
that Escrow Agent is an escrow holder only, and shall not be required to
determine questions of fact or law which may arise hereunder.

2. INITIAL/ADDITIONAL DEPOSIT. Purchaser hereby delivers and Escrow Agent hereby
acknowledges receipt of an initial deposit in the form of a check ______, wired
Funds _____________, promissory note ________, letter of credit ____, or
_________ (specify), in the total amount of _____________________________
Dollars ($ _________). Any additional amount(s) in any such form(s) deposited
with Escrow Agent hereunder shall be added to the initial deposit and together
with the initial deposit shall be referred to herein collectively as the
"Deposit." The Deposit held by Escrow Agent hereunder shall be subject to the
provisions of applicable state statutes governing unclaimed property.

3. DEPOSIT OF FUNDS (Select either 3.1. or 3.2. below).

                3.1. Any and all funds received in this escrow may be deposited
in escrow account(s) of the Escrow Agent from which it may receive direct
benefits of earned interest or indirect benefits such low interest loans. The
Escrow Agent shall have no obligation to account

                                       31

<PAGE>

to the parties to this escrow in any manner for the value of any direct or
indirect benefits received by reason of the deposit of such escrow funds. Any
such benefits shall be deemed additional compensation of the Escrow Agent for
its services in connection with this escrow. All parties depositing funds in
connection with this escrow are hereby notified that the fluids so deposited are
insured only to the limit provided by the Federal Deposit Insurance Corporation.

                3.2. All funds of the Deposit received by Escrow Agent pursuant
to this Agreement shall be processed for collection in the normal course of
business and shall be deposited in an interest-bearing account established by
Escrow Agent pursuant to joint written instructions from Seller and Purchaser.
Said account will be held at the following institution:________________________
_______________________________________________ prior to such deposit, the
taxpayer designated below must execute and deliver to Escrow Agent the
appropriate Internal Revenue Service documentation for the giving of taxpayer
identification information relating to the account. Seller and Purchaser hereby
acknowledge that they are aware that the Federal Deposit Insurance Corporation
coverages apply to a maximum amount of One Hundred Thousand Dollars ($100,000)
per depositor. Further, both Seller and Purchaser understand that Escrow Agent
assumes no responsibility for, nor will Seller or Purchaser hold Escrow Agent
liable for, any loss occurring or arising from a situation or event under the
Federal Deposit Insurance Corporation coverages.

All interest earned on the Deposit funds shall, for income tax purposes, be
reported to the Internal Revenue Service for the account of:

          Name:    _____________________________________________________________

          Address: _____________________________________________________________

                   _____________________________________________________________

          Phone:   _____________________________________________________________

          Tax I.D./Social Security No. _________________________________________

Escrow Agent shall not be responsible for any penalties, or loss of principal or
interest, or in the withdrawal of the Deposit funds which may be imposed by the
depository institution as a result of the making or redeeming of the investment
pursuant to Seller and Purchaser instructions or redeeming of the investment as
otherwise permitted hereunder.

4. DISBURSEMENT/DELIVERY OF DEPOSIT.

          4.1. At the time of settlement under the Contract, the Escrow Agent
shall pay over or otherwise apply the Deposit, together with all interest earned
thereon, if applicable, to the person or entity as provided in the Contract.
Such payment or application of the Deposit and all applicable interest thereon
shall fully release and discharge the Escrow Agent from any and all further
duties and liability under this Agreement, unless the Escrow Agent shall have
received prior thereto a Demand for Payment or a Demand for Refund under Section
4.2. or 4.3. hereof, in

                                       32

<PAGE>

which event the obligation of the Escrow Agent shall be governed accordingly by
Section 4.2. or Section 4.3., as applicable, and by Section 4.4 hereof.

          4.2. If at any time prior to settlement under the Contract while the
Escrow Agent is still holding the Deposit pursuant hereto, the Seller shall be
of the opinion that the Seller is entitled to a forfeiture of the Deposit and
any applicable interest thereon under the terms and conditions of the Contract,
the Seller shall give to the Escrow Agent a written demand for payment or
delivery of the Deposit and the applicable interest thereon (herein a "Demand
for Payment"). The Escrow Agent shall promptly send to the Purchaser a copy of
such Demand for Payment. If the Purchaser is of the opinion that the Seller is
not entitled to such a forfeiture under the terms and provisions of the
Contract, the Purchaser shall cause to be received by the Escrow Agent, within
fifteen (15) calendar days after the date the copy of such Demand is sent to
Purchaser by the Escrow Agent, a written objection to payment or delivery
(hereinafter an "Objection to Payment"), in which event the Escrow Agent shall
continue to hold the Deposit and all applicable interest thereon in escrow until
payment is required pursuant to Section 4.4. hereof. The Escrow Agent shall
promptly send to Seller a copy of such Objection to Payment from Purchaser. If
the Escrow Agent does not receive a written Objection to Payment from the
Purchaser within the time period aforesaid, the Escrow Agent shall promptly pay
over or apply the Deposit and all applicable interest thereon to Seller, and
thereupon the Escrow Agent shall be fully released and discharged of any and all
further liability hereunder with respect to the Deposit and the interest earned
thereon, if any.

          4.3. If at any time prior to settlement under the Contract while the
Escrow Agent is still holding the Deposit pursuant hereto, the Purchaser shall
be of the opinion that the Purchaser is entitled to a refund or return of the
Deposit together with all applicable interest thereon under the terms and
conditions of the Contract, the Purchaser shall give to the Escrow Agent a
written demand for refund or return of the Deposit together with the applicable
interest thereon (herein a "Demand for Refund"). The Escrow Agent shall promptly
send to Seller a copy of such Demand for Refund. If the Seller is of the opinion
that the Purchaser is not entitled to such a refund or return under the terms
and provisions of the Contract, the Seller shall cause to be received by the
Escrow Agent, with fifteen (15) calendar days after the date the copy of such
Demand is sent to Seller by the Escrow Agent, a written objection to refund
(hereinafter an "Objection to Refund"), in which event the Escrow Agent shall
continue to hold the Deposit and all applicable interest thereon in escrow until
payment or application is required pursuant to Section 4.4 hereof. The Escrow
Agent shall promptly send to Purchaser a copy of such Objection to Refund from
Seller. If the Escrow Agent does not receive a written Objection to Refund from
the Seller within the time period aforesaid, the Escrow Agent shall promptly pay
over or return the Deposit and all applicable interest thereon to Purchaser, and
thereupon the Escrow Agent shall be fully released and discharged of any and all
further liability hereunder with respect to the Deposit and the interest earned
thereon, if any.

          4.4(a). If the Escrow Agent shall receive an Objection to Payment
and/or Objection to Refund in the manner and within the time period provided in
Section 4.2. and/or 4.3. hereof, respectively, then in either event or both such
events the Escrow Agent shall continue to hold the Deposit and all applicable
interest thereon, in escrow under the terms and conditions hereof, until the
earlier of: (i) receipt by the Escrow Agent of a statement signed by

                                       33

<PAGE>

both Seller and Purchaser directing how and to whom the Escrow Agent should pay
over or apply the Deposit and all applicable interest thereon, in which event
the Escrow Agent shall pay over or apply the Deposit and applicable interest
thereon in the manner and to the person or persons as so instructed by Seller
and Purchaser, or (ii) receipt by the Escrow Agent of a final judgment, order or
decree from a court of competent jurisdiction instructing the Escrow Agent as to
the manner and to whom the Deposit and applicable interest thereon should be
paid or applied, and the lapse of any time for the taking of art appeal or
petition to a higher court for a writ of certiorari therefrom, in which event
the Escrow Agent shall pay over or apply the Deposit and applicable interest
thereon in the manner and to the person or persons as required by such final
judgment, order or decree. Upon payment or application by the Escrow Agent
pursuant to either clause (i) or (ii) of the preceding sentence, the Escrow
Agent shall be fully discharged of any and all further liability hereunder with
respect to the Deposit and the interest earned thereon, if any.

          4.4(b). If the parties (including Escrow Agent) shall be in
disagreement about the interpretation of this Agreement, or about their
respective rights and obligations, or the propriety of any action contemplated
by Escrow Agent, Escrow Agent may, but shall not be required to, file an action
with an appropriate court it selects to resolve the disagreement. Escrow Agent
shall be indemnified, jointly and severally by Seller and Purchaser, for all
costs and reasonable attorneys' fees in its capacity as Escrow Agent in
connection with any such action and shall be fully protected in suspending all
or part of its activities under this Agreement until a final judgment in the
action is received; provided, however, if Escrow Agent deposits with the court
in connection with such action, the funds and property held by it in escrow
hereunder, then Escrow Agent shall thereupon be fully released and discharged
from all its duties and obligations hereunder. Escrow Agent shall be entitled to
file a claim in such action for its costs, expenses and reasonable counsel fees
not otherwise paid out of the funds of the Deposit

5. ESCROW/DISBURSEMENT FEES.

          5.1. Escrow Agent shall be entitled to receive an Escrow Fee of
$________________________ for its services hereunder. Escrow Agent shall also be
entitled to received a Disbursement Fee of $______________________________ for
each disbursement (by wire or check) it makes hereunder subsequent to its first
disbursement hereunder of less than the entire Deposit funds and applicable
interest thereon. In addition, Escrow Agent shall be entitled to receive an
Additional Escrow Fee of $_____________________ per month or portion thereof it
serves in such capacity hereunder beyond an initial period of ____________ (_)
months from the date of this Agreement.

          5.2. The various fees set forth in Section 5.1. above shall be payable
in full to Escrow Agent at the time of and in connection with its services
hereunder and its disbursement(s) of the Deposit funds and applicable interest
thereon. Payment of such fees shall be shared equally by Seller and Purchaser.
Escrow Agent may (but shall not be obligated to) defer collection of such fees
until the time it conducts the settlement on the aforesaid property. Further,
Escrow Agent may, at its sole option, elect to waive some or all of such fees in
the event a policy of title insurance is purchased from Escrow Agent at the time
of such property settlement. Escrow Agent shall be vested with a lien on the
Deposit funds and other property deposited hereunder to secure payment of such
fees and it shall be entitled to collect and retain the amount of such fees out
of the Deposit and other funds held in escrow hereunder.

                                       34

<PAGE>

6. LIMITATIONS OF LIABILITY. Escrow Agent shall not be liable for any loss or
damage resulting from the following:

          6.1. The effect of the transaction underlying this Agreement including
without limitation, any defect in the title to the real estate, any failure or
delay in the surrender of possession of the property, the rights or obligations
of any party in possession of the property, the financial status or insolvency
of any other party, and/or any misrepresentations of fact made by any other
party.

          6.2. The default, error, act or failure to act by any party to the
escrow.

          6.3. Any loss, loss of value or impairment of funds which have been
deposited in escrow while those funds are in the course of collection or while
those funds are on deposit in a depository institution if such loss or loss of
value or impairment results from the failure, insolvency or suspension of a
depository institution.

          6.4. Any defects or conditions of title to any property that is the
subject of this escrow; provided, however, that this limitation of liability
shall not affect the liability of Commonwealth Land Title Insurance Company
under any title insurance policy which it has issued or may issue. NOTE: No
title insurance liability is created by this Agreement.

          6.5. Escrow Agent's compliance with any legal process including, but
not limited to, subpoenas, writs, orders, judgments and decrees of any court
whether issued with or without jurisdiction and whether or not subsequently
vacated, modified, set aside or reversed.

          6.6. Escrow Agent shall have the right (without incurring any
liability to Seller or Purchaser) to disregard any notices or instructions
received from any party inconsistent with or contrary to the provisions of this
Agreement.

          6.7. It is understood and agreed that the Escrow Agent's only duties
and obligations hereunder are as expressly set forth in this Agreement and no
implied duties or obligations shall be read into this Agreement against Escrow
Agent. The Escrow Agent shall not be liable for any acts or omissions of any
kind nor for any mistakes of fact or errors of judgment hereunder except in the
case of the Escrow Agent's gross negligence or willful misconduct with regard to
its duties under this Agreement. The Escrow Agent shall have the right to
consult with separate counsel of its own choosing (if it deems such consultation
advisable) and shall be fully protected and not be liable for any action taken,
suffered or omitted by it in accordance with the advice of such counsel.

          6.8. The Escrow Agent may rely upon and shall be protected in acting
or refraining from acting upon any writing, instrument or signature furnished to
it hereunder and believed by it to be valid, genuine and to have been signed or
presented by the proper party or parties, without being required to determine
the authenticity or the correctness of any fact stated therein or the propriety
or validity of same and of the service thereof. The Escrow Agent may assume that
any person purporting to give any notice or receipt or advice or make any
statement

                                       35
<PAGE>

or execute any document in connection with the provisions hereof has been duly
authorized to do so.

7. HOLD HARMLESS.

          7.1. Purchaser and Seller shall be jointly and severally obligated to
indemnify and hold harmless the Escrow Agent from all damage, costs, claims, and
expenses arising from performance of its duties as Escrow Agent hereunder,
including reasonable attorneys' fees, except for those damages, costs, claims
and expenses resulting from the gross negligence or willful misconduct of the
Escrow Agent hereunder.

          7.2. In the event of any litigation relating to this escrow, the
parties hereto agree that Escrow Agent shall be held harmless from any and all
attorneys' fees, court costs and expenses relating to that litigation if that
litigation is not brought due to Escrow Agent's gross negligence or willful
misconduct hereunder. Seller and Purchaser shall be jointly and severally
obligated to indemnify Escrow Agent for all such attorneys' fees, court costs
and expenses. To the extent that Escrow Agent holds any funds under the terms of
this Agreement, the parties agree that the Escrow Agent may charge to and
collect from such funds such attorneys' fees, court costs, and expenses as they
are incurred by Escrow Agent hereunder.

8. RELEASE UPON PAYMENT. Payment and/or delivery of the Deposit and applicable
interest so held in escrow hereunder by Escrow Agent, in accordance with the
terms, conditions and provisions of this Escrow Agreement, shall Mly and forever
discharge and exonerate Escrow Agent hereunder from any and all further
liability or obligation of any nature or character, at law or in equity, to the
parties hereto and under this Agreement.

9. SUBSTITUTION OR RESIGNATION OF ESCROW AGENT. Seller and Purchaser may appoint
a substitute escrow agent hereunder in place of Escrow Agent by giving their
joint written notice of such appointment to Escrow Agent and such substitute
escrow agent at least fifteen (15) days prior to the effective date of such
substitution. Escrow Agent may resign upon thirty (30) days written notice to
Seller and Purchaser. If a successor escrow agent is not appointed jointly by
Seller and Purchaser within such 30-day period, Escrow Agent may petition a
court to name a successor. The provisions of Section 7.2. hereof shall be
equally applicable with respect to all costs and expenses incurred by Escrow
Agent in connection with such action under this Section 9.

10. NOTICE. Any notice shall be in writing and deemed duly given when delivered
in person (with receipt therefor) or sent by overnight courier, or registered or
certified mail (postage prepaid, return receipt requested) to the parties as
follows:

          N. To Seller:

               Unicorn Wisconsin LLC

                                       36

<PAGE>

               c/o 1370 Piccard Drive
               Suite 200
               Rockville, MD 20850
               Attention: Reuven Uberman
               Telephone: (301) 417-0300
               Facsimile: (301) 417-0507

               With Copies to:

               Donald N. Sperling, Esquire
               Beth H. McIntosh, Esquire
               Stein, Sperling, Bennett, De Jong,
               Driscoll & Greenfeig, P.C.
               25 West Middle Lane
               Rockville, MD 20850

          O.   To Purchaser:

               Columbia Equity Trust, Inc.
               1750 H Street, NW, Suite 500
               Washington, DC 20006
               Attention: Oliver T. Carr, III
               Telephone: (202) 303-3060
               Facsimile: (202) 303-3078

               With copies to:

               Hunton & Williams LLP
               1900 K Street, NW, Suite 1200
               Washington, DC 20006
               Attention: John M. Ratino
               Telephone: (202) 778-2221
               Facsimile: (202) 778-2201

          P.   To Escrow Agent:

               Commonwealth Land Title Insurance Company
               1015 15th Street, NW, Suite 300
               Washington, DC 20005
               Attention: Sarah E. Webb
               Telephone: (202) 312-5119
               Facsimile: (202) 737-4108

11. MISCELLANEOUS.

          11.1. This Agreement shall inure to the benefit of and shall be
binding upon the parties hereto and their respective heirs, personal
representatives, successors and assigns.

                                       37

<PAGE>

          11.2. This Agreement shall be construed, enforced and interpreted
under the laws of ________________________, without regard to principles of
conflict of laws.

          11.3. Time shall be of the essence for all purposes in construing and
applying the provisions of this Agreement.

          11.4. As used herein the plural shall include the singular, the
singular the plural, and the use of any gender shall be applicable to all
genders.

12. This Escrow Agreement may be executed in counterparts, each of which shall
be deemed an original, but all of which shall constitute one and the same
instrument. This Escrow Agreement may not be modified or amended in any way
except by a writing signed by Seller and Purchaser and acknowledged by Escrow
Agent. All written amendments to the Contract signed by Seller and Purchaser and
which may directly or indirectly alter or affect any of the provisions of this
Agreement shall be subject to written approval by Escrow Agent.

                                       38

<PAGE>

IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be duly
executed as of the date set forth above.

PURCHASER: COLUMBIA EQUITY TRUST, INC.

By:
    ----------------------------------
Name and Title
               -----------------------
Date:
      --------------------------------

SELLER: UNICORN WISCONSIN, LLC

By:
    ----------------------------------
Title:
       -------------------------------
Date:
      --------------------------------

ESCROW AGENT:
COMMONWEALTH LAND TITLE
INSURANCE COMPANY

By:
    ----------------------------------
Title:
       -------------------------------
Date:
      --------------------------------

                                       39

<PAGE>

                                  EXHIBIT 2(C)

                             VACANCY ACKNOWLEDGEMENT

          THIS VACANCY ACKNOWLEDGEMENT is made this ____ day of February, 2006,
by ATHENA WISCONSIN, LLC, a Delaware limited liability company ("Athena") and
UNICORN WISCONSIN, LLC, a Delaware limited liability company ("Unicorn"), for
the benefit of COLUMBIA EQUITY TRUST, INC., a Maryland corporation (the
"Purchaser").

          WHEREAS, Athena, Unicorn and Chicago Title Insurance Company are
parties to that certain Tenant Vacancy Escrow Agreement dated as of April 30,
2003 (the "Escrow Agreement") (All capitalized terms not otherwise defined
herein shall have the meanings set forth in the Escrow Agreement); and

          WHEREAS, the Purchaser and Unicorn have entered into an Agreement of
Purchase and Sale with Seller dated December __, 2005 (the "Purchase
Agreement"), wherein Purchaser has agreed to purchase the office building
located at 2233 Wisconsin Avenue, N.W., Washington, DC; and

          WHEREAS, Purchaser is unwilling to close on the purchase of the
Property unless Athena and Unicorn certify, acknowledge, and agree as to the
matters set forth herein.

          NOW, THEREFORE, with the understanding that the Purchaser will rely
thereon, the Athena and Unicorn hereby certify, acknowledge and agree as
follows:

          1. The outstanding amount of funds ("Funds") held under the Escrow
Agreement on the date hereof is $____________.

          2. The Tenant vacated all of the Tenant's Space on or before August
31, 2005 except for Suite 214 which Tenant held over in until October 31, 2005
and Athena is not entitled to credit for any Holdover Rentals except as
previously paid to Athena.

          3. As of the date hereof, neither the Tenant nor its designee has
sublet, leased or relocated to any space in the Building which was not part of
Tenant's Space on the date of the Escrow Agreement.

          4. Athena is not entitled to any of the Funds, to make payment on or
secure payment on the Contingent Note or otherwise, except pursuant to the
express terms of the Escrow Agreement.

          5. Athena and Unicorn have received all disbursements due to each of
them under the Escrow Agreement with respect to the Tenant Space consisting of
______ RSF that has been leased to Georgetown University, Quatt, Cornerstone and
McKinley (the "Leased Tenant Space").

                                       40

<PAGE>

          5. Neither Athena nor Unicorn have received, nor are either of them
due, any disbursements under the Escrow Agreement with respect to ______ RSF of
Tenant Space, consisting of all of the Tenant Space other than the Leased Tenant
Space (the "Remaining Tenant Space").

          6. As of the date hereof, Unicorn has paid (in the case of Category A)
or incurred (in the case of Category D) in the aggregate at least $22.22 per RSF
of Permitted Costs for each RSF of the Remaining Tenant Space.

          7. To the best of our information, knowledge and belief as of the date
hereof, no set of facts or circumstances exists which would constitute a default
under, or would but for the passage of time and/or the giving of notice
constitute a default under, the terms, provisions or conditions of the Escrow
Agreement on behalf of any party thereto.

          WITNESS the following hands and seals as of the day and year first
above written.

Attest:                                 ATHENA WISCONSIN, LLC, a
                                        Delaware limited liability company

                                        By: THE ATHENA GROUP, LLC, a
                                            Maryland limited liability company

By:                                     By:                               (SEAL)
    ---------------------------------       -----------------------------
Print Name:                             Print Name
            -------------------------              -----------------------------
Title:                                  Title:
       ------------------------------          ---------------------------------

[CORPORATE SEAL]

                                        UNICORN WISCONSIN, LLC a
                                        Delaware limited liability company

                                        By: Unicorn Wisconsin Management, Inc.,
                                            a Delaware corporation

By:                                     By:                               (SEAL)
    ---------------------------------       -----------------------------
Print Name:                             Print Name
            -------------------------              -----------------------------
Title:                                  Title:
       ------------------------------          ---------------------------------

                                [CORPORATE SEAL]

                                       41

<PAGE>

                                    EXHIBIT D

                                    RENT ROLL

                                       42

<PAGE>

                                    EXHIBIT E

                             EXISTING LOAN DOCUMENTS

                                       43

<PAGE>

                                    EXHIBIT F

                                  GROUND LEASE

                                       44

<PAGE>

                                    EXHIBIT G

                          SCHEDULE OF SERVICE CONTRACTS

                                       45

<PAGE>

                                    EXHIBIT H

                        GROUND LESSOR CONSENT AND WAIVER

                                       46

<PAGE>

                                    EXHIBIT I

                             FORM OF TENANT ESTOPPEL

                          TENANT'S ESTOPPEL CERTIFICATE

                                                                  ________, 2005

Columbia Equity Trust, Inc. ("PURCHASER")
1750 H Street, NW
Suite 500
Washington, D.C. 20006

          RE: BUILDING NAME: ____________________________
              ADDRESS:       ____________________________ (THE "PROPERTY")

Ladies and Gentlemen:

     It is our understanding that __________________, a __________________
("SELLER") proposes to transfer the ownership of the Property to Purchaser. As a
condition precedent of Purchaser acquiring the Property, Seller, Purchaser, and
[PURCHASER'S MORTGAGE LENDER] ("LENDER") have required this certification of the
undersigned.

     The undersigned, as Tenant, under that certain Lease Agreement, dated
__________________ (the "LEASE"), for certain premises at the Property (the
"PREMISES"), made with Seller, as Landlord, hereby ratifies the Lease and
certifies to Seller, Purchaser and Lender that:

     1.   The current annual Basic Rent payable pursuant to the terms of the
          Lease is $__________ PER ANNUM; and further, additional rental
          pursuant to the Lease is payable as follows: Tenant pays its pro-rata
          share of Excess Expenses in excess of the EXPENSE STOP OF $__________
          PER SF [OR BASE YEAR OF _______]; and

     2.   The Lease is in full force and effect and has not been assigned,
          modified, supplemented or amended in any way except as noted above;
          and

     3.   A true and correct copy of the Lease is attached hereto as Exhibit A.
          The Lease represents the entire agreement between Seller and Tenant as
          to the leasing of the Premises. All capitalized terms used herein but
          not defined shall be given the meaning assigned to them in the Lease;
          and

     4.   On this date there are no existing defenses or offsets, claims or
          counterclaims which the undersigned has against the enforcement of the
          Lease by Seller; and

     5.   No rental has been paid in advance and no security has been deposited
          with Seller except for a security deposit in the amount of
          $____________ [WHICH DEPOSIT IS IN THE FORM OF AN IRREVOCABLE LETTER
          OF CREDIT]; and

                                       47

<PAGE>

     6.   The total rentable floor area of the Premises is __________ SQUARE
          FEET; and

     7.   On the date of this certification there are no existing breaches or
          defaults by Seller or Tenant under the Lease that are known to Tenant;
          and

     8.   The term of the Lease commenced on __________. The Rent Commencement
          Date under the Lease was __________. The Lease will expire on
          __________. The Tenant has no option to purchase all or any part of
          the Property or, except as expressly set forth in the Lease, any
          option to terminate or cancel the Lease. The Lease provides for ___
          (__) ___-YEAR EXTENSION OPTION; and

     9.   Tenant has accepted possession of the Premises and there are no
          outstanding Landlord obligations to perform tenant improvements.

     10.  Tenant has not transferred, assigned, or sublet any portion of the
          Premises nor entered into any license or concession agreements with
          respect thereto except as follows (if none, please state "none"):
          None.

     11.  All monthly installments of Basic Rent and Excess Expenses have been
          paid when due through __________, 2005. The current monthly
          installment of BASIC RENT IS $__________ and the current monthly
          installment of EXCESS EXPENSES IS $__________.

     12.  Tenant's current address for notices under the Lease is:

          __________________________

          __________________________

          __________________________

          Attn: ____________________

     Tenant acknowledges that this certificate may be delivered to Purchaser,
Lender and their respective successors and assigns, and acknowledges that such
persons will be relying upon the statements contained herein in acquiring the
Property or disbursing loan advances or making a new loan secured by the
Property and that receipt of this certificate by Lender and Purchaser is a
condition of disbursing loan advances or making such loan or acquiring the
Property, respectively. Without limitation, any entity formed by Purchaser to
purchase the Property may rely upon this Certificate.

     IN WITNESS WHEREOF, the undersigned has caused this certificate to be
executed as of the ________ day of _____________, 2005.

                                                                        , a
                                        --------------------------------
                                                                        , Tenant
                                        --------------------------------

                                        By
                                           -------------------------------------
                                        Its
                                            ------------------------------------

                                       48

<PAGE>

                   Exhibit A to Tenant's Estoppel Certificate

                                      Lease

<PAGE>

                                    EXHIBIT J

              ASSIGNMENT AND ASSUMPTION OF VACANCY ESCROW AGREEMENT

                                      -50-
<PAGE>

                                    EXHIBIT K

                    ASSIGNMENT AND ASSUMPTION OF GROUND LEASE

     THIS ASSIGNMENT AND ASSUMPTION OF LEASEHOLD ESTATE (the "Assignment) is
made and entered into as of the ___ day of _________, 2005, by and between
UNICORN WISCONSIN, LLC, a Delaware limited liability company ("Assignor"), and
____________________________________ duly qualified to transact business in the
District of Columbia ("Assignee").

                                    RECITALS

     WHEREAS, Seller is the owner of a leasehold interest under that certain
Lease dated December 21, 1959, recorded among the land records of the District
of Columbia (the "LAND RECORDS") on December 28, 1959, as Instrument No. 40566
in Liber 11360 at folio 70, from Mary A.W. Holland and Robert D. Weaver
(predecessors in interest to Thomas W. Holland, Robert M. Holland, Mary
Charlotte Parr and Margaret W. Krull; collectively, the "GROUND LESSOR") to
Norbick Realty Company, as predecessor to Mortgagor, as amended and assigned
pursuant to: (i) that certain Amendment to Lease, dated February 8, 1963,
recorded February 14, 1963, as Instrument No. 4952 in Book 11949 at folio 385 of
the Land Records; (ii) that certain Amended Lease dated December 31, 1963,
recorded on June 18, 1964, as Instrument No. 20584 in Liber 12228 at folio 73 of
the Land Records; (iii) that certain Assignment of Leasehold Interest dated
August 8, 1966, recorded on August 15, 1966, as Instrument No. 26678 in Liber
12654 at folio 196 of the Land Records; (iv) that certain Assignment of
Leasehold Interest dated August 1, 1966, recorded on August 15, 1966, as
Instrument No. 26679 in Liber 12654 at folio 199 of the Land Records; (v) that
certain Amendment to Lease dated May 23, 1980, recorded May 30, 1980, as
Instrument No. 17500 of the Land Records; (vi) that certain Assignment of
Leasehold dated January 10, 1984, recorded January 11, 1984, as Instrument No.
1028 of the Land Records; (vii) that certain Assignment of Leasehold to 2233
Wisconsin Avenue Associates dated September 28, 1984, recorded December 31,
1984, as Instrument No. 47361 of the Land Records; (viii) that certain
Assignment of Leasehold to The Georgetown Building Associates Limited
Partnership dated March 6, 1986, recorded March 7, 1986, as Instrument No. 9580
of the Land Records; (ix)that certain Substitute Trustee's Assignment of
Leasehold Interest, dated January 12, 2000, recorded on January 13, 2000, as
Instrument Number 2000004734 of the Land Records; (x) that certain Assignment of
Leasehold Interest, dated December 14, 2000, by KeyKey Realty, Inc., a District
of Columbia corporation, as Assignor, to Athena Wisconsin LLC, a Delaware
limited liability company ("ATHENA"), as Assignee, recorded on December 18, 2000
as Instrument Number 2000115036 of the Land Records; (xi) that certain Amendment
to Amended Lease dated December 15, 2000, recorded December 18, 2000, as
Instrument No. 2000115037 of the Land Records; (xii) that certain assignment of
the Ground Lease by Athena to Mortgagor, to be recorded in the Land Records
prior to the recording of this Mortgage; (xiii) that certain Second Amendment to
Ground Lease dated on or about the date hereof, recorded in the Land Records
_________________, which Ground Lease covers certain real property located at
2233 Wisconsin Avenue N.W., Washington, D.C. as more particularly described on
Exhibit A annexed hereto, (the "LAND").

                                      -51-

<PAGE>

     WHEREAS, Assignor and Assignee entered into that certain Agreement of
Purchase and Sale Agreement dated ________________ (the "Sale Agreement")
pursuant to which the Assignee has agreed to acquire from Assignor all of
Assignor's interest in the Ground Lease; and

     WHEREAS, Assignor and Assignee desire to evidence in writing the assignment
by Assignor to Assignee of all of Assignor's right, title and interest under the
Ground Lease and the assumption by Assignee of all obligations, duties and
covenants thereunder arising from and after the effective date of this
Assignment.

     NOW THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, Assignor and Assignee hereby agree
as follows:

                                    AGREEMENT

     1. Assignment and Assumption. Assignor hereby irrevocably assigns, sets
over, transfers, and conveys to Assignee all of Assignor's right, title and
interest in and to the Ground Lease which assignment shall be effective from and
after the date hereof for the remainder of the term of the Ground Lease.
Assignee hereby accepts this Assignment and the rights granted herein. Assignee
hereby expressly assumes, for itself and its successors, assigns and legal
representatives, the Ground Lease and all of the obligations and liabilities,
fixed and contingent, of Assignor thereunder accruing from and after the date
hereof with respect to the Ground Lease and agrees to (a) be fully bound by all
of the terms, covenants, agreements, provisions, conditions, obligations and
liability of Assignor thereunder, which accrue from the date hereof, and (b)
keep, perform and observe all of the covenants and conditions contained therein
on the part of Assignor to be kept, performed and observed, from and after the
date hereof.

     2. General Provisions.

          a. Successors. This Assignment shall be binding upon and inure to the
benefit of the parties hereto and their respective heirs, legal representatives,
successors and assigns.

          b. Counterparts. This Assignment may be executed in as many
counterparts as may be deemed necessary and convenient, and by the different
parties hereto on separate counterparts, each of which, when so executed, shall
be deemed an original, but all such counterparts shall constitute one and the
same instrument.

          c. Governing Law. This Assignment and the legal relations of the
parties hereto shall be governed by and construed and enforced in accordance
with the laws of the District of Columbia without regard to its principals of
conflicts of law.

          d. Special Provisions. This Assignment shall not merge with or limit,
or otherwise expand or restrict, any provision of the Sale Agreement. The
parties expressly recognize and agree that the provisions of the Sale Agreement
shall govern and control the rights and obligations of the parties thereto with
respect to all matters described therein, including, without limitation, the
acknowledgement that this Assignment is being expressly made without any
representations and warranties except as may be expressly set forth in the Sale
Agreement.

                                      -52-

<PAGE>

     IN WITNESS WHEREOF, this Assignment was made and executed as of the date
first written above.

                                        ASSIGNOR:

                                        UNICORN WISCONSIN, LLC, a Delaware
                                        limited liability company

                                        By: Unicorn Management, Inc, a Delaware
                                            corporation, its manager

                                        By:                               (Seal)
                                            -----------------------------
                                            Reuven Uberman, President

                                        ASSIGNEE:

                                        ----------------------------------------

                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------
                                        Date:
                                              ----------------------------------

                        [ACKNOWLEDGMENTS BEGIN NEXT PAGE]

                                      -53-

<PAGE>

District of Columbia, to-wit:

     I, the undersigned, a Notary Public in and for the District of Columbia, DO
HEREBY CERTIFY that Reuven Uberman who is personally well known to me to be the
person(s) named as President of UNICORN MANAGEMENT, INC. a Delaware limited
liability company, on behalf of UNICORN WISCONSIN LLC, a Delaware limited
liability company, the Assignor in the aforegoing and annexed Assignment and
Assumption of Leasehold Interest bearing date on the ______ _day of ___________,
2005, who did personally appear before me in said District, and by virtue of the
authority thereby conferred upon him/her acknowledged the same to be the act and
deed of the said UNICORN MANAGEMENT, INC. in its capacity as manager /member of
UNICORN WISCONSIN LLC

     GIVEN under my hand and seal this ___ day of _______________, 2005.

                                        ----------------------------------------
                                        Notary Public

My Commission Expires:
(Notary Seal)

STATE OF                         )
                                 ) ss
COUNTY OF                        )

I, the undersigned, a Notary Public in and for the above jurisdiction, DO HEREBY
CERTIFY that _________________________________ _who is personally well known to
me to be the person(s) named as __________________________ of _________________,
a __________________________, the Assignee in the aforegoing and annexed
Assignment and Assumption of Leasehold Interest bearing date on the _______ day
of ____________, 2005, who did personally appear before me in said jurisdiction,
and by virtue of the authority thereby conferred upon him/her acknowledged the
same to be the act and deed of the said _______________________________.

     GIVEN under my hand and seal this __ day of _____________, 2005.

                                        ----------------------------------------
                                        Notary Public

My Commission Expires:

                                  (Notary Seal)

                                      -54-

<PAGE>

                                    EXHIBIT L

               FORM OF ASSIGNMENT AND ASSUMPTION OF TENANT LEASES

     THIS ASSIGNMENT AND ASSUMPTION OF OCCUPANCY LEASES (the "Assignment") is
made effective as of __________, 2005, by and between UNICORN WISCONSIN, LLC, a
Delaware limited liability company ("Assignor"), and ________________________
duly qualified to transact business in the District of Columbia ("Assignee").

                                   WITNESSETH:

     WHEREAS, contemporaneously with the execution hereof, Assignee has
purchased from Assignor, and Assignor has sold to Assignee, all of Assignor's
interest in certain real property described on Exhibit A attached hereto and
made a part hereof, and the buildings and other improvements thereon (the
"Property"), as being more fully described in that certain Agreement of Purchase
and Sale dated __________________, 2005 by and between Assignor as Seller and
Assignee as Purchaser (the "Agreement"); and

     WHEREAS, contemporaneously with such sale, Assignor desires to assign to
Assignee all of Assignor's interest in and to all Lease Agreements affecting the
Property, a schedule of which being attached hereto as Exhibit B and made a part
hereof (the "Leases"), and Assignee desires to accept such assignment and assume
the obligations of lessor which first arise under the Leases on and after the
date hereof.

     NOW, THEREFORE, in consideration of the premises and other good and
valuable consideration, the receipt and sufficiency of which are acknowledged,
Assignor and Assignee hereby agree as follows:

     3. Subject to the terms, covenants, conditions, and provisions of the
Leases and this Assignment, Assignor hereby transfers, conveys, and assigns to
Assignee all of its right, title, and interest as landlord in, to and under the
Leases.

     4. Assignee hereby accepts the transfer, conveyance, and assignment of the
Leases and those security deposits received this date from Assignor, a schedule
of which also being attached hereto as Exhibit C, and subject to the terms of
the Agreement, assumes all rights, duties, obligations, and liabilities of
Assignor under the Leases accruing after the Closing (as defined in the
Agreement).

     5. This Assignment shall not merge with or limit, or otherwise expand or
restrict, any provision of the Agreement. The parties expressly recognize and
agree that the provisions of the Agreement shall govern and control the rights
and obligations of Assignor and Assignee with respect to all matters described
therein, including, without limitation, the acknowledgment that this Assignment
is being expressly made without any representations and warranties by Assignor,
except as otherwise expressly set forth in the Agreement.

     6. This Assignment shall be binding upon and shall inure to the benefit of
Assignor, Assignee, and their respective legal representatives, heirs,
successors, and assigns.

                                      -55-

<PAGE>

     7. This Assignment may be executed in any number of counterparts, all of
which taken together shall constitute one and the same instrument.

     IN WITNESS WHEREOF, each of Assignor and Assignee has caused this
Assignment and Assumption to be executed by its duly authorized representative.

     IN WITNESS WHEREOF, this Assignment was made and executed as of the date
first written above.

                                        ASSIGNOR:

                                        UNICORN WISCONSIN, LLC, a Delaware
                                        limited liability company

                                        By: Unicorn Management, Inc, a Delaware
                                            corporation, its manager

                                        By:                              (Seal)
                                            -----------------------------
                                            Reuven Uberman, President

                                        ASSIGNEE:

                                        ----------------------------------------

                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------
                                        Date:
                                              ----------------------------------

                        [ACKNOWLEDGMENTS BEGIN NEXT PAGE]

                                      -56-

<PAGE>

District of Columbia, to-wit:

     I, the undersigned, a Notary Public in and for the District of Columbia, DO
HEREBY CERTIFY that Reuven Uberman who is personally well known to me to be the
person(s) named as President of UNICORN MANAGEMENT, INC. a Delaware limited
liability company, on behalf of UNICORN WISCONSIN LLC, a Delaware limited
liability company, the Assignor in the aforegoing and annexed Assignment and
Assumption of Leasehold Interest bearing date on the ______ _day of ___________,
2005, who did personally appear before me in said District, and by virtue of the
authority thereby conferred upon him/her acknowledged the same to be the act and
deed of the said UNICORN MANAGEMENT, INC. in its capacity as manager/member of
UNICORN WISCONSIN LLC

     GIVEN under my hand and seal this ___ day of _______________, 2005.

                                        ----------------------------------------
                                        Notary Public

My Commission Expires:
(Notary Seal)

STATE OF                         )
                                 ) ss
COUNTY OF                        )

I, the undersigned, a Notary Public in and for the above jurisdiction, DO HEREBY
CERTIFY that _________________________________ _who is personally well known to
me to be the person(s) named as __________________________ of _________________,
a __________________________, the Assignee in the aforegoing and annexed
Assignment and Assumption of Leasehold Interest bearing date on the _______ day
of ____________, 2005, who did personally appear before me in said jurisdiction,
and by virtue of the authority thereby conferred upon him/her acknowledged the
same to be the act and deed of the said _______________________________.

     GIVEN under my hand and seal this ___ day of _______________, 2005.

                                        ----------------------------------------
                                        Notary Public

My Commission Expires:

                                  (Notary Seal)

                                      -57-

<PAGE>

                                    EXHIBIT M

    FORM OF ASSIGNMENT AND ASSUMPTION OF SERVICE CONTRACTS AND ASSIGNMENT OF
                       ASSIGNABLE PERMITS AND INTANGIBLES

     THIS ASSIGNMENT AND ASSUMPTION OF SERVICE CONTRACTS (the "Assignment") is
made effective as of __________, 2005, by and between UNICORN WISCONSIN, LLC, a
Delaware limited liability company ("Assignor"), and __________________________
duly qualified to transact business in the District of Columbia ("Assignee").

                                   WITNESSETH:

     WHEREAS, contemporaneously with the execution hereof, Assignee has
purchased from Assignor, and Assignor has sold to Assignee, all of Assignor's
interest in certain real property described on Exhibit A attached hereto and
made a part hereof, and the buildings and other improvements thereon (the
"Property"), as being more fully described in that certain Agreement of Purchase
and Sale dated ________________, 2005 by and between Assignor as Seller and
Assignee as Purchaser (the "Agreement"); and

     WHEREAS, contemporaneously with such sale, Assignor desires to assign to
Assignee all of Assignor's interest in and to all of the service contracts
affecting the Property, a schedule of which being attached hereto as Exhibit B
and made a part hereof (the "Contracts"), and Assignee desires to accept such
assignment and assume the obligations of lessor which first arise under the
Leases on and after the date hereof.

     NOW, THEREFORE, in consideration of the premises and other good and
valuable consideration, the receipt and sufficiency of which are acknowledged,
Assignor and Assignee hereby agree as follows:

     8. Subject to the express terms and provisions of the Contracts, Assignor
does hereby transfer and assign unto Assignee all of its right, title and
interest under the Contracts and Assignee hereby assumes and accepts such
transfer, assignment and subject to the terms of the Agreement, assumes all
rights, duties, obligations, and liabilities of Assignor under the Contracts
accruing after the Closing (as defined in the Agreement).

     9. This Assignment shall not merge with or limit, or otherwise expand or
restrict, any provision of the Agreement. The parties expressly recognize and
agree that the provisions of the Agreement shall govern and control the rights
and obligations of Assignor and Assignee with respect to all matters described
therein, including, without limitation, the acknowledgment that this Assignment
is being expressly made without any representations and warranties by Assignor,
except as otherwise expressly set forth in the Agreement.

     10. This Assignment shall be binding upon and shall inure to the benefit of
Assignor, Assignee, and their respective legal representatives, heirs,
successors, and assigns.

     11. This Assignment may be executed in any number of counterparts, all of
which taken together shall constitute one and the same instrument.

                                      -58-

<PAGE>

     IN WITNESS WHEREOF, each of Assignor and Assignee has caused this
Assignment and Assumption to be executed by its duly authorized representative.

                                        ASSIGNOR:

                                        UNICORN WISCONSIN, LLC, a Delaware
                                        limited liability company

                                        By: Unicorn Management, Inc, a Delaware
                                            corporation, its manager

                                        By:                              (Seal)
                                            -----------------------------
                                            Reuven Uberman, President

                                        ASSIGNEE:

                                        ----------------------------------------

                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------
                                        Date:
                                              ----------------------------------

                        [ACKNOWLEDGMENTS BEGIN NEXT PAGE]

                                      -59-

<PAGE>

District of Columbia, to-wit:

     I, the undersigned, a Notary Public in and for the District of Columbia, DO
HEREBY CERTIFY that Reuven Uberman who is personally well known to me to be the
person(s) named as President of UNICORN MANAGEMENT, INC. a Delaware limited
liability company, on behalf of UNICORN WISCONSIN LLC, a Delaware limited
liability company, the Assignor in the aforegoing and annexed Assignment and
Assumption of Leasehold Interest bearing date on the _______ day of ___________,
2005, who did personally appear before me in said District, and by virtue of the
authority thereby conferred upon him/her acknowledged the same to be the act and
deed of the said UNICORN MANAGEMENT, INC. in its capacity as manager/member of
UNICORN WISCONSIN LLC

     GIVEN under my hand and seal this ___ day of _______________, 2005.

                                        ----------------------------------------
                                        Notary Public

My Commission Expires:
(Notary Seal)

STATE OF                         )
                                 ) ss
COUNTY OF                        )

I, the undersigned, a Notary Public in and for the above jurisdiction, DO HEREBY
CERTIFY that _________________________________ _who is personally well known to
me to be the person(s) named as __________________________ of _________________,
a __________________________, the Assignee in the aforegoing and annexed
Assignment and Assumption of Leasehold Interest bearing date on the _______ day
of ____________, 2005, who did personally appear before me in said jurisdiction,
and by virtue of the authority thereby conferred upon him/her acknowledged the
same to be the act and deed of the said _______________________________.

     GIVEN under my hand and seal this ___ day of _______________, 2005.

                                        ----------------------------------------
                                        Notary Public

My Commission Expires:

                                  (Notary Seal)

                                      -60-

<PAGE>

                                    EXHIBIT N

                              FORM OF BILL OF SALE

     For valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, UNICORN WISCONSIN, LLC, a Delaware limited liability company
("Seller"), hereby conveys to _______________________________ ("Purchaser"), all
of Seller's right, title and interest in and to those certain items of personal
property described on Exhibit A attached hereto and made a part hereof (the
"Personal Property") relating to certain real property known as 2233 Wisconsin
Avenue, N.W., Washington, D.C.

     Seller has not made and does not make any express or implied warranty or
representation of any kind whatsoever with respect to the Personal Property,
including but not limited to: title; merchantability of the Personal Property or
its fitness for any particular purpose; the design or condition of the Personal
Property; the quality or capacity of the Personal Property; workmanship or
compliance of the Personal Property with the requirements of any law, rule,
specification or contract pertaining thereto; patent infringement or latent
defects. Purchaser accepts the Personal Property on an "AS IS, WHERE IS" basis.

IN WITNESS WHEREOF, Seller has caused this instrument to be executed and
delivered as of this ___ day of __________________, 2005.

                                        SELLER:

                                        UNICORN WISCONSIN, LLC, a
                                        Delaware limited liability company

                                        By: Unicorn Management, Inc, a Delaware
                                            corporation, its manager

                                        By:            (Seal)
                                            -----------------------------
                                              Reuven Uberman, President

                                      -61-

<PAGE>

                                    EXHIBIT O

                           LIST OF INSURANCE POLICIES

                                      -62-<PAGE>
                                                                   Exhibit 10.22

                     SUMMARY OF 2005 CASH INCENTIVE BONUSES
                          PAYABLE TO EXECUTIVE OFFICERS

         On March 9, 2006, the Nominating, Corporate Governance and Compensation
Committee of the Company's Board of Directors determined and approved 2005 cash
incentive bonuses payable to each of the Company's executive officers. The 2005
cash incentive bonuses, which were ratified by the Company's Board on the same
dates, are summarized in the following table:

<TABLE>
<CAPTION>
         Name                                         2005 Cash Incentive Bonus
         ----                                         -------------------------
         <S>                                          <C>
         Oliver T. Carr, III                                   $50,000
           Chairman, President and CEO

         John A. Schissel                                      $40,000
           EVP and CFO

         Clinton D. Fisch                                      $22,750
           SVP and Director of Acquisitions

         Christian H. Clifford                                 $22,750
           SVP and Director of Asset Management

         John M. Novack                                        $27,000
           SVP and CAO
</TABLE>

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00100-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00100-of-00352.parquet"}]]