Document:

<PAGE>

                                                                   Exhibit 10.10

                                                              March 11, 2004

EarlyBirdCapital, Inc.
600 Third Avenue
33rd Floor
New York, New York 10016

                  Re:  Tremisis Energy Acquisition Corporation
                       ---------------------------------------

Gentlemen:

                  This letter will confirm the agreement of the undersigned to
purchase warrants ("Warrants") of Tremisis Energy Acquisition Corporation
("Company") included in the units ("Units") being sold in the Company's initial
public offering ("IPO") upon the terms and conditions set forth herein. Each
Unit is comprised of one share of Common Stock and two Warrants. The shares of
Common Stock and Warrants will not be separately tradeable until 90 days after
the effective date of the Company's IPO unless EarlyBirdCapital, Inc. ("EBC")
informs the Company of its decision to allow earlier separate trading.

                  The undersigned agrees that this letter agreement constitutes
an irrevocable order for EBC to purchase for the undersigned's account within
the forty-trading day period commencing on the date separate trading of the
Warrants commences ("Separation Date") up to 1,000,000 Warrants at market prices
not to exceed $0.65 per Warrant ("Maximum Warrant Purchase"). EBC (or such other
broker dealer(s) as EBC may assign the order to) agrees to fill such order in
such amounts and at such times as it may determine, in its sole discretion,
during the forty-trading day period commencing on the Separation Date. EBC
further agrees that it will not charge the undersigned any fees and/or
commissions with respect to such purchase obligation.

                  The undersigned may notify EBC that all or part of his
respective Maximum Warrant Purchase will be made by an affiliate of the
undersigned (or another person or entity introduced to EBC by the undersigned (a
"Designee")) who (or which) has an account at EBC and, in such event, EBC will
make such purchase on behalf of said affiliate or Designee; provided, however,
that the undersigned hereby agrees to make payment of the purchase price of such
purchase in the event that the affiliate or Designee fails to make such payment.

                  The undersigned agrees that neither he nor any affiliate or
Designee shall sell or transfer the Warrants until after the consummation of a
merger, capital stock exchange, asset acquisition or other similar business
combination with an operating business and acknowledges that, at the option of
EBC, the certificates for such Warrants shall contain a legend indicating such
restriction on transferability.

                                                     Very truly yours,

                                                     /s/ Lawrence S. Coben
                                                     -----------------------
                                                     Lawrence S. Coben<PAGE>
                                                                               .
                                                                               .
                                                                               .
                                                                    Exhibit 4.24
<Table>
<S>                                                                                     <C>
         COMMON STOCK                                                                           COMMON STOCK

        PAR VALUE $.10                                [PICTURE]                                    PAR VALUE $.10

NUMBER                                                                                                                    SHARES
M5359                                                                                                                    [      ]

         THIS CERTIFICATE IS TRANSFERABLE
             IN RIDGEFIELD PARK, NJ                                                 CUSIP 370021 10 7
               AND NEW YORK, NY                                              SEE REVERSE FOR CERTAIN DEFINITIONS

                                        GENERAL GROWTH PROPERTIES, INC.

                                INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE

         THIS CERTIFIES THAT

                                                  [SPECIMEN]

         IS THE OWNER OF

                             FULLY-PAID AND NON-ASSESSABLE SHARES OF THE COMMON STOCK OF

         General Growth Properties, Inc. transferable on the books of the Corporation by the holder hereof in
         person or by duly authorized attorney upon surrender of this certificate property endorsed.  This certificate
         is not valid unless countersigned by the Transfer Agent and registered by the Registrar.

         Witness the facsimile seal of the Corporation and the facsimile signatures of its duly authorized officers.

[SEAL]

                                           PAR VALUE CHANGED TO $.01

         Dated:

         COUNTERSIGNED AND REGISTERED:                                                        /s/ JOHN BURLESBAUM
         MELLON INVESTOR SERVICES LLC                                                       CHIEF EXECUTIVE OFFICER
                                                 TRANSFER AGENT
                                                 AND REGISTRAR,

         BY                                                                                   /s/ MARSHALL E. EISENBERG
                                                                                             SECRETARY

         AUTHORIZED SIGNATURE

[BANKNOTE CORPORATION OF AMERICA]
</Table>

<PAGE>

                        GENERAL GROWTH PROPERTIES, INC.

     The shares of Equity Stock represented by this certificate are subject to
restrictions on transfer for the purpose of the Corporation's maintenance of its
status as a real estate investment trust under the Internal Revenue Code of
1986, as amended (the "Code"). No Person may (1) Beneficially Own or
Constructively Own shares of Equity Stock in excess of 7.5% (or such other
percentage as may be determined by the Board of Directors of the Corporation) of
the value of the outstanding Equity Stock of the Corporation unless such Person
is an Existing Holder (in which case the Existing Holder Limit shall be
applicable); or (2) Beneficially Own Equity Stock which would result in the
Corporation being "closely held" under Section 856(h) of the Code. Any Person
who attempts to Beneficially Own or Constructively Own shares of Equity Stock in
excess of the above limitations must immediately notify the Corporation in
writing. If the restrictions above are violated, the shares of Equity Stock
represented hereby will be transferred automatically and by operation of law to
a Trust and shall be designated Shares-in-Trust. All capitalized terms in this
legend have the meanings defined in the Corporation's Amended and Restated
Certificate of Incorporation, as the same may be further amended from time to
time, a copy of which, including the restrictions on transfer, will be sent
without charge to each stockholder who so requests.

     This certificate also evidences and entitles the holder hereof to certain
Rights as set forth in a Rights Agreement between General Growth Properties,
Inc. and Mellon Investor Services LLC, as successor to Norwest Bank Minnesota,
N.A., as Rights Agent, dated as of November 18, 1998 (as amended, the "Rights
Agreement"), the terms of which are hereby incorporated herein by reference and
a copy of which is on file at the principal executive offices of General Growth
Properties, Inc. Under certain circumstances, as set forth in the Rights
Agreement, such Rights will be evidenced by separate certificates and will no
longer be evidenced by this certificate. General Growth Properties, Inc. will
mail to the holder of this certificate a copy of the Rights Agreement without
charge after receipt of a written request therefor. Under certain circumstances,
Rights that are or were acquired or beneficially owned by Acquiring Persons (as
defined in the Rights Agreement) may become null and void.

     The Corporation will furnish to any stockholder upon request and without
charge a statement of the designations, preferences, limitations and relative
rights of the shares of each class or series authorized to be issued, so far as
they have been determined, and the authority of the Board of Directors to
determine the relative rights and preferences of subsequent classes or series.
Such requests may be made to the Secretary of the Corporation.

     The following abbreviations, when used in the inscription on the face of
this certificate, shall be construed as though they were written out in full
according to applicable laws or regulations:

<Table>
        <S>                                             <C>
        TEN COM -- as tenants in common                 UNIF GIFT MIN ACT -- _____________ Custodian ___________
                                                                                (Cust)                 (Minor)
        TEN ENT -- as tenants by the entireties                              under Uniform Gifts to Minors

        JT TEN  -- as joint tenants with right of                            Act __________________
                   survivorship and not as tenants                                     (State)
                   in common
</Table>

     Additional abbreviations may also be used though not in the above list.

  For value received, __________________ hereby sell, assign and transfer unto

PLEASE INSERT SOCIAL SECURITY OR OTHER
   IDENTIFYING NUMBER OF ASSIGNEE
[                                    ]

--------------------------------------------------------------------------------
   PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS INCLUDING ZIP CODE OF ASSIGNEE

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

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

--------------------------------------------------------------------------------
shares of common stock represented by the within Certificate, and do hereby
irrevocably constitute and appoint ___________________________________ Attorney
to transfer the said stock on the books of the within named Corporation with
full power of substitution in the premises.

Dated:

SIGNATURE GUARANTEED:

------------------------------------------------
NOTICE: THE SIGNATURE(S) SHOULD BE GUARANTEED BY
AN ELIGIBLE GUARANTOR INSTITUTION (BANKS,
STOCKBROKERS, SAVINGS AND LOAN ASSOCIATIONS AND
CREDIT UNIONS WITH MEMBERSHIP IN AN APPROVED
SIGNATURE GUARANTEE MEDALLION PROGRAM)
PURSUANT TO S.E.C. RULE 17Ad-15.

Signature:
          -------------------------------------------------------------

Signature:
          -------------------------------------------------------------

NOTICE: The signature to this assignment must correspond with the name
as written upon the face of the certificate in every particular, without
alteration or enlargement, or any change whatever.

<PAGE>

<Table>
<S>                                                                                     <C>
         COMMON STOCK                                                                           COMMON STOCK

        PAR VALUE $.10                                [PICTURE]                                    PAR VALUE $.10

NUMBER                                                                                                                    SHARES
M5360                                                                                                                    [      ]

         THIS CERTIFICATE IS TRANSFERABLE
             IN RIDGEFIELD PARK, NJ                                                 CUSIP 370021 10 7
               AND NEW YORK, NY                                              SEE REVERSE FOR CERTAIN DEFINITIONS

                                        GENERAL GROWTH PROPERTIES, INC.

                                INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE

         THIS CERTIFIES THAT

                                                  [SPECIMEN]

         IS THE OWNER OF

                             FULLY-PAID AND NON-ASSESSABLE SHARES OF THE COMMON STOCK OF

         General Growth Properties, Inc. transferable on the books of the Corporation by the holder hereof in
         person or by duly authorized attorney upon surrender of this certificate property endorsed.  This certificate
         is not valid unless countersigned by the Transfer Agent and registered by the Registrar.

         Witness the facsimile seal of the Corporation and the facsimile signatures of its duly authorized officers.

[SEAL]

                                           PAR VALUE CHANGED TO $.01

         Dated:

         COUNTERSIGNED AND REGISTERED:                                                        /s/ JOHN BURLESBAUM
         MELLON INVESTOR SERVICES LLC                                                       CHIEF EXECUTIVE OFFICER
                                                 TRANSFER AGENT
                                                 AND REGISTRAR,

         BY                                                                                   /s/ MARSHALL E. EISENBERG
                                                                                             SECRETARY

         AUTHORIZED SIGNATURE

[BANKNOTE CORPORATION OF AMERICA]
</Table>

<PAGE>

                        GENERAL GROWTH PROPERTIES, INC.

     The shares of Equity Stock represented by this certificate are subject to
restrictions on transfer for the purpose of the Corporation's maintenance of its
status as a real estate investment trust under the Internal Revenue Code of
1986, as amended (the "Code"). No Person may (1) Beneficially Own or
Constructively Own shares of Equity Stock in excess of 7.5% (or such other
percentage as may be determined by the Board of Directors of the Corporation) of
the value of the outstanding Equity Stock of the Corporation unless such Person
is an Existing Holder (in which case the Existing Holder Limit shall be
applicable); or (2) Beneficially Own Equity Stock which would result in the
Corporation being "closely held" under Section 856(h) of the Code. Any Person
who attempts to Beneficially Own or Constructively Own shares of Equity Stock in
excess of the above limitations must immediately notify the Corporation in
writing. If the restrictions above are violated, the shares of Equity Stock
represented hereby will be transferred automatically and by operation of law to
a Trust and shall be designated Shares-in-Trust. All capitalized terms in this
legend have the meanings defined in the Corporation's Amended and Restated
Certificate of Incorporation, as the same may be further amended from time to
time, a copy of which, including the restrictions on transfer, will be sent
without charge to each stockholder who so requests.

     This certificate also evidences and entitles the holder hereof to certain
Rights as set forth in a Rights Agreement between General Growth Properties,
Inc. and Mellon Investor Services LLC, as successor to Norwest Bank Minnesota,
N.A., as Rights Agent, dated as of November 18, 1998 (as amended, the "Rights
Agreement"), the terms of which are hereby incorporated herein by reference and
a copy of which is on file at the principal executive offices of General Growth
Properties, Inc. Under certain circumstances, as set forth in the Rights
Agreement, such Rights will be evidenced by separate certificates and will no
longer be evidenced by this certificate. General Growth Properties, Inc. will
mail to the holder of this certificate a copy of the Rights Agreement without
charge after receipt of a written request therefor. Under certain circumstances,
Rights that are or were acquired or beneficially owned by Acquiring Persons (as
defined in the Rights Agreement) may become null and void.

     The Corporation will furnish to any stockholder upon request and without
charge a statement of the designations, preferences, limitations and relative
rights of the shares of each class or series authorized to be issued, so far as
they have been determined, and the authority of the Board of Directors to
determine the relative rights and preferences of subsequent classes or series.
Such requests may be made to the Secretary of the Corporation.

     The following abbreviations, when used in the inscription on the face of
this certificate, shall be construed as though they were written out in full
according to applicable laws or regulations:

<Table>
        <S>                                             <C>
        TEN COM -- as tenants in common                 UNIF GIFT MIN ACT -- _____________ Custodian ___________
                                                                                (Cust)                  (Minor)
        TEN ENT -- as tenants by the entireties                              under Uniform Gifts to Minors

        JT TEN  -- as joint tenants with right of                            Act __________________
                   survivorship and not as tenants                                     (State)
                   in common
</Table>

     Additional abbreviations may also be used though not in the above list.

  For value received, __________________ hereby sell, assign and transfer unto

PLEASE INSERT SOCIAL SECURITY OR OTHER
   IDENTIFYING NUMBER OF ASSIGNEE
[                                    ]

--------------------------------------------------------------------------------
   PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS INCLUDING ZIP CODE OF ASSIGNEE

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

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

--------------------------------------------------------------------------------
shares of common stock represented by the within Certificate, and do hereby
irrevocably constitute and appoint ___________________________________ Attorney
to transfer the said stock on the books of the within named Corporation with
full power of substitution in the premises.

Dated:

SIGNATURE GUARANTEED:

------------------------------------------------
NOTICE: THE SIGNATURE(S) SHOULD BE GUARANTEED BY
AN ELIGIBLE GUARANTOR INSTITUTION (BANKS,
STOCKBROKERS, SAVINGS AND LOAN ASSOCIATIONS AND
CREDIT UNIONS WITH MEMBERSHIP IN AN APPROVED
SIGNATURE GUARANTEE MEDALLION PROGRAM),
PURSUANT TO S.E.C. RULE 17Ad-15.

Signature:
          -------------------------------------------------------------

Signature:
          -------------------------------------------------------------

NOTICE: The signature to this assignment must correspond with the name
as written upon the face of the certificate in every particular, without
alteration or enlargement, or any change whatever.

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