<PAGE>
                                                                Exhibit 10.94

                                      1


                            ASSIGNMENT OF COLLATERAL

                     (AVENUE ASSOCIATES LIMITED PARTNERSHIP)

      THIS ASSIGNMENT OF COLLATERAL (hereinafter referred to as the
"Assignment") is made as of the 27 day of October, 1997, by STICHTING
PENSIOENFONDS VOOR DE GEZONDHEID, GEESTELIJKE EN MAATSCHAPPELIJKE BELANGEN
(hereinafter referred to as "Assignor") in favor of Cornerstone Properties Inc.
(hereinafter referred to as "Assignee").

                              W I T N E S S E T H :

      WHEREAS, Assignor is the recipient and owner of the promissory note and
collateral security documents described on Exhibit A attached hereto and by this
reference incorporated herein (the "Collateral"); and

      WHEREAS, pursuant to that certain Loan Purchase Agreement dated as of
August 18, 1997, between Assignor and Assignee, Assignor has agreed to transfer
all of its right, title and interest in and to the Collateral to Assignee.

      NOW, THEREFORE, for and in consideration of the exchange of good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged by the parties hereto, the parties hereto covenant and agree as
follows:

      I. Assignor hereby irrevocably transfers, assigns, grants, bargains,
sells, conveys, remises, releases, warrants, set over and confirms unto Assignee
for its benefit and the benefit of its successors and assigns, all of its right,
title and interest in and to the Collateral without recourse or warranty except
as provided for and set forth in that certain Loan Purchase Agreement dated as
of August 18, 1997, executed by and between Assignee and Assignor.

      II. Upon the request of Assignee, Assignor shall execute and deliver to
Assignee such further instruments as Assignee may deem reasonably necessary to
effectuate this Assignment.

      III. This Assignment shall bind and inure to the benefit of the Assignor
and Assignee and their respective heirs, successors and assigns.

      IV. Nothing in this Assignment shall be construed to give to any person
other than Assignee its successors and assigns any legal or equitable right,
remedy or claim under this Assignment, and this Assignment shall be held for the
sole and exclusive benefit of Assignee and its successors and assigns.

      V. This Assignment shall be governed by, construed and enforced in
accordance with the laws of the District of Columbia.
<PAGE>

                                      2


      IN WITNESS WHEREOF, Assignor and Assignee have executed or caused to be
executed this Assignment under seal, as of the date and year first above
written.

                           ASSIGNOR:

                           STICHTING PENSIOENFONDS VOOR DE
                           GEZONDHEID, GEESTELIJKE EN
                           MAATSCHAPPELIJKE BELANGEN

                           By: /s/
                               ---------------------------
                           Name: Jan H.W.R. van der Vlist
                                 -------------------------
                           Title: Attorney-in-fact
                                  ------------------------
                           By: /s/
                               ---------------------------
                           Name: Anneke C. van de Puttelaar
                                 -------------------------
                           Title:
                                  ------------------------

                           ASSIGNEE:
                           CORNERSTONE PROPERTIES INC.

                           By: /s/
                               ---------------------------
                           Name: John S. Moody
                                 -------------------------
                           Title: President
                                  ------------------------

                           By: /s/
                               ---------------------------
                           Name: Rodney S. Dimock
                                 -------------------------
                           Title: Executive Vice President
                                  ------------------------
<PAGE>

STATE OF NEW YORK )
                  )     ss.:
COUNTY OF NEW YORK)

            Subscribed, sworn to and acknowledged before me by Anneke C. Van de
Puttelaar, _________ of STICHTING PENSIOENFONDS VOOR DE GEZONDHEID, GEESTELIJKE
EN MAATSCHAPPELIJKE BELANGEN this 27 day of October, 1997.

                                    /s/
                                    ----------------
                                    Notary Public

My Commission Expires:  February 21, 1999       Michael L. Perry
                        ------------------      Notary Public, State of New York
                                                No. O1PE50393S8

STATE OF NEW YORK )
                  )     ss.:
COUNTY OF NEW YORK)

            Subscribed, sworn to and acknowledged before me by Jan M.W.R. Van
der Vlist, __________ of STICHTING PENSIOENFONDS VOOR DE GEZONDHEID, GEESTELIJKE
EN MAATSCHAPPELIJKE BELANGEN this 27 day of October, 1997.

                                    /s/
                                    ----------------
                                    Notary Public

My Commission Expires:  February 21, 1999       Michael L. Perry
                        ------------------      Notary Public, State of New York
                                                No. O1PE50393S8
<PAGE>

STATE OF NEW YORK )
                  )     ss.:
COUNTY OF NEW YORK)

            Subscribed, sworn to and acknowledged before me by John S. Moody,
President of Cornerstone Properties Inc., this 27 day of October, 1997.

                                    /s/
                                    ----------------
                                    Notary Public

My Commission Expires:  February 21, 1999       Michael L. Perry
                        ------------------      Notary Public, State of New York
                                                No. O1PE50393S8

STATE OF NEW YORK )
                  )     ss.:
COUNTY OF NEW YORK)

            Subscribed, sworn to and acknowledged before me by Rodney C. Dimock,
Executive Vice President of Cornerstone Properties Inc., this 27 day of
_____________, 1997.

                                    /s/
                                    ----------------
                                    Notary Public

My Commission Expires:  February 21, 1999       Michael L. Perry
                        ------------------      Notary Public, State of New York
                                                No. O1PE50393S8
<PAGE>

VIRGINIA:

                   IN THE CLERK'S OFFICE OF THE CIRCUIT COURT

            This certificate was presented, and with the Certificate annexed,
admitted to record on _______________ at ______________ o'clock __.m.

            Clerk's fees: $____________ have been paid.

                  Attest:___________________________________, Deputy Clerk
<PAGE>

                                   EXHIBIT A

1.    Promissory Note dated as of July 15, 1987, executed by Avenue Associates
      Limited Partnership ("AALP") in favor of DIHC Finance Corporation
      ("DIFCO") in the original principal amount of $188,491,750; as assigned by
      DIFCO to Stichting Pensioenfonds voor de Gezondheid, Geestelijke en
      Maatschappelijke Belangen ("PGGM") pursuant to that certain Assignment of
      Loan Documents dated as of November 15, 1992.

2.    Deed of Trust and Security Agreement dated as of July 15, 1987, executed
      by AALP in favor of Michael J. Shea, as Trustee for DIFCO, recorded June
      17, 1987 as Instrument No. 38127, among the Land Records of the District
      of Columbia; as amended by that certain Spreader Amendment to Deed of
      Trust and Security Agreement and Assignment of Lessor's Interest in Leases
      dated as of June 13, 1988, executed by and between AALP, DIFCO and Michael
      J. Shea, recorded June 24, 1988, as Instrument No. 34236, aforesaid
      records; as further amended by that certain First Amendment to Deed of
      Trust dated as of July 15, 1987, executed by and between AALP, Michael J.
      Shea and DIFCO, recorded October 18, 1988, as Instrument No. 57570,
      aforesaid records; as further amended by that certain Second Amendment to
      Deed of Trust dated as of July 15, 1987, executed by and between AALP,
      Michael J. Shea and DIFCO, recorded May 23, 1989, as Instrument No. 28528,
      aforesaid records; as further amended by that certain Third Amendment to
      Deed of Trust dated as of July 15, 1987, executed between AALP, Michael J.
      Shea and DIFCO, recorded November 29, 1989, as Instrument No. 66305,
      aforesaid records; and as assigned by DIFCO to PGGM pursuant to that
      certain Assignment of Loan Documents dated as of November 15, 1992.

3.    Assignment of Lessor's Interest in Leases dated as of July 15, 1987,
      executed by AALP in favor of DIFCO, recorded July 17, 1987, as Instrument
      No. 38128, aforesaid records; as assigned by DIFCO to PGGM pursuant to
      that certain Assignment of Loan Documents dated as of November 15, 1992.

4.    Assignment of Borrower's Interest in Construction Contract Documents dated
      as of July 15, 1987, executed by AALP in favor of DIFCO; as assigned by
      DIFCO to PGGM pursuant to that certain Assignment of Loan Documents dated
      as of November 15, 1992.

5.    Building Loan Agreement dated as of July 15, 1987, executed by and between
      AALP and DIFCO; as amended by that certain First Amendment to Building
      Loan Agreement dated as of January 27, 1989; as further amended by that
      certain Second Amendment to Building Loan Agreement dated as of April 17,
      1991; and as assigned by DIFCO to PGGM pursuant to that certain Assignment
      of Loan Documents dated as of November 15, 1992.
<PAGE>

6.    Subordination Agreement executed by and between PADC, Robert Acker,
      Charles Duke and DIFCO; as assigned by DIFCO to PGGM pursuant to that
      certain Assignment of Loan Documents dated as of November 15, 1992.

7.    Agreement to Subordinate executed by and between PADC and DIFCO; as
      assigned by DIFCO to PGGM pursuant to that certain Assignment of Loan
      Documents dated as of November 15, 1992.

8.    Sixteen consecutively numbered Amendments to Deed of Trust executed by
      Avenue Associates in favor of Michael Shea, as trustee for DIFCO; as
      assigned by DIFCO to PGGM pursuant to that certain Assignment of Loan
      Documents dated as of November 15, 1992.

9.    Escrow Agreement executed by and between AALP, DIFCO, and Commercial
      Settlements concerning the sixteen consecutively numbered Amendments to
      the Deed of Trust; as assigned by DIFCO to PGGM pursuant to that certain
      Assignment of Loan Documents dated as of November 15, 1992.

10.   Borrower's Affidavit executed by T. Christopher Roth in favor of DIFCO,
      Chicago Title Insurance Company, Commonwealth Land Title Insurance Company
      and Ticor Title Insurance Company; as assigned by DIFCO to PGGM pursuant
      to that certain Assignment of Loan Documents dated as of November 15,
      1992.

11.   Letter from Western Associates to Market Square Associates approving the
      loan by DIFCO to Market Square Associates; as assigned by DIFCO to PGGM
      pursuant to that certain Assignment of Loan Documents dated as of November
      15, 1992.

12.   Opinion Letter from Jones, Day, Reavis & Pogue to DIHC Market Square and
      DIFCO concerning loans; as assigned by DIFCO to PGGM pursuant to that
      certain Assignment of Loan Documents dated as of November 15, 1992.
<PAGE>

                                     ALLONGE

                               ENDORSEMENT OF NOTE

                     (AVENUE ASSOCIATES LIMITED PARTNERSHIP)

      Pay to the order of CORNERSTONE PROPERTIES INC. (the "Assignee") without
recourse or warranty except as provided for and set forth in that certain Loan
Purchase Agreement dated as of August 18, 1997 executed by and between Stichting
Pensioenfonds voor de Gezondheid, Geestelijke en Maatschappelijke Belangen and
Assignee.

                                          STICHTING PENSIOENFONDS VOOR
                                          DE GEZONDHEID, GEESTELIJKE EN
                                          MAATSCHAPPELIJKE BELANGEN

                                          By: /s/
                                              ----------------------------
                                          Name: Jan H.W.R. van der Vlist
                                                --------------------------
                                          Title: Attorney-in-Fact
                                                 -------------------------

                                          By: /s/
                                              ----------------------------
                                          Name: Anneke C. van de Puttelaar
                                                --------------------------
                                          Title: Attorney-in-fact
                                                 -------------------------

                                    DATE:   October __, 1997