Document:

Exhibit 10.16

NEITHER THESE SECURITIES NOR THE COMMON STOCK ISSUABLE UPON EXERCISE HEREOF HAVE
BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 OR ANY APPLICABLE STATE
SECURITIES LAWS. THEY MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED OR HYPOTHECATED
OR OTHERWISE TRANSFERRED IN THE ABSENCE OF A REGISTRATION STATEMENT IN EFFECT
WITH RESPECT TO THE SECURITIES UNDER SUCH ACT OR AN EXEMPTION THEREFROM. ANY
SUCH TRANSFER MAY ALSO BE SUBJECT TO APPLICABLE STATE SECURITIES LAWS.

                           HUDSON TECHNOLOGIES, INC.

                     Warrant for the Purchase of Shares of
                                  Common Stock

                                                                  _______ Shares

FOR VALUE RECEIVED, HUDSON TECHNOLOGIES, INC., a New York corporation (the
"Company"), hereby certifies that [___________] or registered assigns (the
"Holder") is entitled to purchase from the Company, subject to the provisions of
this Warrant (the "Warrant"), at any time on or after ___________, 200_ (the
"Initial Exercise Date") [insert the date which is the earlier of (i) the first
anniversary of the date of issuance of Holder's 10% Subordinated Convertible
Promissory Note ("Convertible Note") and (ii) the consummation of an Equity
Offering (as defined in the Company's proxy statement dated November 20, 2002)
by the Company], and prior to 5:00 P.M., New York City time, on or prior to
_________, 200_ (the "Termination Date") [the date which is the fifth
anniversary of the Initial Exercise Date], ____________________ (________) fully
paid and non-assessable shares of the Common Stock, $.01 par value, of the
Company ("Common Stock") [equal to 10% of the number of shares of Common Stock
into which the Holder's Convertible Note was convertible on its issue date], at
an initial exercise price of $[____] [equal to 110% of the lesser of the
conversion rate of the Holder's Convertible Note (i) as of its issue date, or
(ii) as of the date this Warrant is issued] per share of Common Stock (the
"Initial Per Share Exercise Price"). The number of shares of Common Stock to be
received upon exercise of this Warrant and the price to be paid for each share
of Common Stock are subject to possible adjustment from time to time as
hereinafter set forth. The shares of Common Stock or other securities or
property deliverable upon such exercise as adjusted from time to time is
hereinafter sometimes referred to as the "Warrant Shares." The exercise price of
a share of Common Stock in effect at any time and as adjusted from time to time
is hereinafter sometimes referred to as the "Per Share Exercise Price." The Per
Share Exercise Price is subject to adjustment as hereinafter provided.

Exercise of Warrant.

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This Warrant may be exercised in whole or in part, at any time by its holder
commencing on the Initial Exercise Date and prior to the Termination Date by
presentation and surrender of this Warrant, together with the duly executed
subscription form and representations and warranties attached at the end hereof,
at the address set forth in Subsection 7(a) hereof, together with payment, by
certified or official bank check or wire transfer payable to the order of the
Company, of the product of (x) the Per Share Exercise Price multiplied by (y)
the number of shares of Common Stock subject to (1) this Warrant or (2) the
proportionate part thereof if exercised in part.

If this Warrant is exercised in part only, the Company shall, upon presentation
of this Warrant upon such exercise, execute and deliver (along with the
certificate for the Warrant Shares purchased) a new Warrant evidencing the
rights of the Holder hereof to purchase the balance of the Warrant Shares
purchasable hereunder upon the same terms and conditions as herein set forth.
Upon proper exercise of this Warrant, the Company promptly shall deliver
certificates for the Warrant Shares to the Holder duly legended as authorized by
the subscription form. No fractional shares or scrip representing fractional
shares shall be issued upon exercise of this Warrant; provided that the Company
shall pay to the holder of the Warrant cash in lieu of such fractional shares.

            Reservation of Warrant Shares; Fully Paid Shares; Taxes.

The Company hereby represents that it has, and until expiration of this Warrant
agrees that it shall, reserve for issuance or delivery upon exercise of this
Warrant, such number of shares of Common Stock as shall be required for issuance
and/or delivery upon exercise of this Warrant in full, and agrees that all
Warrant Shares so issued and/or delivered will be validly issued, fully paid and
non-assessable, and further agrees to pay all taxes and charges (other than
income taxes) that may be imposed upon such issuance and/or delivery. The
Company shall not, however, be required to pay any tax which may be payable in
respect of any transfer involved in the issue or delivery of Common Stock (or
other securities or assets) in a name other than that in which this Warrant is
registered, and no such issue or delivery shall be made unless and until the
person requesting such issue has paid to the Company the amount of such tax or
has established, to the satisfaction of the Company, that such tax has been paid
or need not be paid.

                          Protection Against Dilution.

Except with respect to the securities set forth in paragraph (b) below, in case
the Company shall at any time after the date hereof issue or sell any shares of
Common Stock, including shares held in the Company's treasury, or shall issue
any options, rights or warrants to subscribe for shares of Common Stock or other
equity or debt securities exercisable into or exchangeable for shares of Common
Stock (each, an "Additional Issuance"), for a consideration per share less than
the Per Share Exercise Price then in effect, the Per Share Exercise Price shall
be adjusted immediately thereafter such that it shall equal the consideration
per share received by the Company for the securities issued in such Additional
Issuance. Such adjustment shall be made successively whenever such an Additional
Issuance is made for consideration per share below the Per Share Exercise Price
then in effect.

The adjustment of the Per Share Exercise Price set forth in paragraph (a) above
shall not apply to options granted by the Company pursuant to
stockholder-approved option plans of the Company nor to the issuance of Common
Stock upon exercise of such options or upon the exercise of options, warrants or
other securities exercisable for or exchangeable into Common Stock outstanding
immediately prior to the date of this Warrant or the conversion of convertible
debt of the Company outstanding immediately prior to the date of this Warrant.

In case the Company shall hereafter (i) pay a dividend or make a distribution on
its Common Stock in shares of Common Stock, (ii) subdivide its outstanding
shares of Common Stock into a greater number of shares or (iii) combine its
outstanding shares of Common Stock into a smaller number of shares (each of (i)
through (iii) an "Action"), then the Per Share Exercise Price shall be adjusted
to be equal to the product of (i) a fraction, the numerator of which is the
number of shares of Common Stock outstanding immediately prior to such Action
and the denominator of which is the number of shares of Common Stock outstanding
immediately following such Action, multiplied by (ii) the Per Share Exercise
Price immediately prior to such Action. An adjustment made pursuant to this
Subsection 3(a) shall become effective immediately after the record date in the
case of a dividend or distribution and shall become effective immediately after
the effective date in the case of a subdivision, combination or
reclassification.

Whenever the Per Share Exercise Price is adjusted pursuant to subsection 3(a),
the number of Warrant Shares issuable upon payment of the adjusted Per Share
Exercise Price shall be adjusted to be equal to the product of the number of
Warrant Shares issuable upon payment of the adjusted Per Share Exercise Price
immediately prior to such adjustment multiplied by a fraction, the numerator of
which shall be the Per Share Exercise Price payable immediately prior to such
adjustment and the denominator which shall be the Per Share Exercise Price
payable immediately after such adjustment.

In the event of any capital reorganization or reclassification, or any
consolidation or merger to which the Company is a party other than a merger or
consolidation in which the Company is the continuing corporation, or in case of
any sale or conveyance to another entity of the property of the Company as an
entirety or substantially as an entirety, the Holder of this Warrant shall have
the right thereafter to receive on the exercise of this Warrant the kind and
amount of securities, cash or other property which the Holder would have owned
or have been entitled to receive immediately after such reorganization,
reclassification, consolidation, merger, statutory exchange, sale or conveyance
had this Warrant been exercised immediately prior to the effective date of such
reorganization, reclassification, consolidation, merger, statutory exchange,
sale or conveyance and in any such case, if necessary, appropriate adjustment
shall be made in the application of the provisions set forth in this Section 3
with respect to the rights and interests thereafter of the Holder of this
Warrant to the end that the provisions set forth in this Section 3 shall
thereafter correspondingly be made applicable, as nearly as may reasonably be,
in relation to any shares of stock or other securities or property thereafter
deliverable on the exercise of this Warrant. The above provisions of this
Subsection 3(e) shall similarly apply to successive reorganizations,
reclassifications, consolidations, mergers, statutory exchanges, sales or
conveyances. The issuer of any shares of stock or other securities or property
thereafter deliverable on the exercise of this Warrant shall be responsible for
all of the agreements and obligations of the Company hereunder. A

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sale of all or substantially all of the assets of the Company for a
consideration consisting primarily of securities shall be deemed a consolidation
or merger for the foregoing purposes.

Whenever the Per Share Exercise Price is adjusted as provided in this Section 3
and upon any modification of the rights of a Holder of Warrants in accordance
with this Section 3, the Chief Financial Officer, or equivalent officer, of the
Company shall prepare a certificate setting forth the Per Share Exercise Price
and the number of Warrant Shares after such adjustment or the effect of such
modification, a brief statement of the facts requiring such adjustment or
modification and the manner of computing the same and cause copies of such
certificate to be mailed to the Holder.

                            Limited Transferability.

This Warrant may not be sold, transferred, assigned or hypothecated by the
Holder except in compliance with the provisions of the Act and the applicable
state securities "blue sky" laws, and is so transferable only upon the books of
the Company which it shall cause to be maintained for such purpose. The Company
may treat the registered Holder of this Warrant as he or it appears on the
Company's books at any time as the Holder for all purposes. The Company shall
permit any Holder of a Warrant or his duly authorized attorney, upon written
request during ordinary business hours, to inspect and copy or make extracts
from its books showing the registered holders of Warrants. All Warrants issued
upon the transfer or assignment of this Warrant will be dated the same date as
this Warrant, and all rights of the holder thereof shall be identical to those
of the Holder.

Loss, etc., of Warrant. Upon receipt of evidence satisfactory to the Company of
the loss, theft, destruction or mutilation of this Warrant, of indemnity
reasonably satisfactory to the Company and, if requested by the Company, of a
bond reasonably satisfactory to the Company, if lost, stolen or destroyed, and
upon surrender and cancellation of this Warrant, if mutilated, the Company shall
execute and deliver to the Holder a new Warrant of like date, tenor and
denomination.

Status of Holder. This Warrant does not confer upon the Holder any right to vote
or to consent to or receive notice as a stockholder of the Company, as such, in
respect of any matters whatsoever, or any other rights or liabilities as a
stockholder, prior to the exercise hereof.

Notices. No notice or other communication under this Warrant shall be effective
unless, but any notice or other communication shall be effective and shall be
deemed to have been given if, the same is in writing and is mailed by
first-class mail, postage prepaid, addressed to:

the Company at 275 North Middletown Road, Pearl River, New York 10965 or such
other address as the Company has designated in writing to the Holder; or the
Holder at:

[Address]
Attn: [Name]

or such other address as the Holder has designated in writing to the Company.

                                    Headings.

The headings of this Warrant have been inserted as a matter of convenience and
shall not affect the construction hereof.

                                 Applicable Law.

This Warrant shall be governed by and construed in accordance with the laws of
the State of New York without giving effect to principles of conflicts of law
thereof.

            IN WITNESS WHEREOF, _____________ acting for and on behalf of the
Company, has executed this Warrant as of December , 2002.

                                            HUDSON TECHNOLOGIES, INC.

                                            By:_________________________________
                                                Name:
                                                Title:

<PAGE>

                                  SUBSCRIPTION

The undersigned, ____________________________, pursuant to the provisions of the
foregoing Warrant, hereby elects to exercise the within Warrant to the extent of
purchasing _____________________ shares of Common Stock of Hudson Technologies,
Inc. thereunder and hereby makes payment of $_______________ by certified or
official bank check in payment of the exercise price therefor.

Dated:_______________                       Signature:__________________________

                                            Address:____________________________

<PAGE>

                         REPRESENTATIONS AND WARRANTIES

The undersigned Holder, in connection with the exercise of this Warrant, hereby
represents and warrants to Hudson Technologies Inc. (the "Company") as follows:

The Holder is acquiring the Warrant Shares for its own account, for investment
purposes only and not with a view towards or in connection with public sale or
distribution thereof. The Warrant Shares may not be offered for sale, sold or
otherwise transferred except pursuant to an effective registration statement
under the Act and in compliance with the applicable securities laws of any state
or other jurisdiction, or pursuant to an opinion of counsel satisfactory to the
Company that such registration is not required and such compliance has been
obtained. The Company may affix an appropriate legend to any certificate(s)
representing the Warrant Shares to reflect the foregoing.

The Holder understands that the Warrant Shares are being offered and sold by the
Company in reliance on an exemption from the registration requirements of the
Securities Act and equivalent state securities and "blue sky" laws, and that the
Company is relying upon the accuracy of, and the compliance by the Holder with
its representations and warranties set forth in this letter, in determining the
availability of such exemption and the eligibility of the Holder to acquire the
Warrant Shares.

The Holder acknowledges that it has had access to the reports and other
documents filed by the Company with the Securities and Exchange Commission
pursuant to the Securities Exchange Act of 1934, as amended, and that it has
been given an opportunity to ask questions of, and to receive answers from, the
Company's management personnel concerning the Company's business and the Warrant
Shares. The Holder has been provided access to all materials relating to the
business, financial position and results of operations of the Company, and all
other materials requested by the Holder by enable it to make an informed
investment decision with respect to the acquisition of the Warrant Shares. The
Holder has such knowledge and experience in financial and business matters that
he is capable of evaluating the merits and risks of an investment in the
Company's securities.

The Holder is, and upon exercise of the Warrant will be, (i) either (A) an
"accredited investor" within the meaning of Rule 501 of Regulation D under the
Securities Act, or (B) a Person that meets the alternative investor suitability
standard established by the Company as set forth in the confidential private
offering memorandum dated as of December __, 2002, (ii) experienced in making
investments of the kind represented by the Warrant Shares, and (iii) capable, by
reason of its business and financial experience, of evaluating the relative
merits and risks of an investment in the Warrant Shares.

The Holder understands that an investment in the Warrants involves a high degree
of risk, and has the financial ability to bear the economic risk of this
investment in the Warrants, including a complete loss of such investment. The
Holder has adequate means for providing for its current financial requirements
and has no need for liquidity with respect to this investment.

Dated:_______________                       Signature:__________________________

                                            Address:____________________________

<PAGE>

                                   ASSIGNMENT

FOR VALUE RECEIVED _______________________________________ hereby sells, assigns
and transfers unto _____________________________________ the foregoing Warrant
and all rights evidenced thereby, and does irrevocably constitute and appoint
_____________________________, attorney, to transfer said Warrant on the books
of Hudson Technologies, Inc.

Dated:_______________                       Signature:__________________________

                                            Address:____________________________

<PAGE>

                               PARTIAL ASSIGNMENT

FOR VALUE RECEIVED __________________________ hereby assigns and transfers unto
_________________________ the right to purchase __________ shares of the Common
Stock, $.01 par value per share, of Hudson Technologies, Inc. covered by the
foregoing Warrant, and a proportionate part of said Warrant and the rights
evidenced thereby, and does irrevocably constitute and appoint
__________________________, attorney, to transfer that part of said Warrant on
the books of Hudson Technologies, Inc.

Dated:_______________                       Signature:__________________________

                                            Address:____________________________Exhibit 10.1

                                 PROMISSORY NOTE

$50,000.00                                                        March 26, 2003
                                                           San Diego, California

      1. Obligation. Plexus Vaccine Inc., a California corporation ("Plexus"),
hereby unconditionally promises to pay, in lawful money of the United States of
America, to the order of SIGA Technologies, Inc., a Delaware corporation
("SIGA"), the principal sum of $50,000, together with interest thereon at the
rate of six percent (6%) per annum, at the Maturity Date (defined below), at the
principal place of business of SIGA, New York City, New York. If Plexus fails to
pay any amounts due under this Note when due, interest shall accrue from the due
date until the date of payment at a rate of ten percent (10%) per annum, or to
the extent permitted by applicable law.

      2. Maturity Date. The principal and accrued interest due under this Note
shall become due and payable in full on the earliest of (i) the acquisition by
SIGA of substantially all of the assets of Plexus, (ii) three months following
the date when SIGA gives written notice to Plexus that SIGA does not intend to
proceed with the purchase of Plexus' assets, for reasons other than a default by
Plexus, (iii) ten days following a date when SIGA gives written notice to Plexus
that SIGA does not intend to proceed with the purchase of Plexus' assets, due to
a default by Plexus under the Plexus obligations set forth in the Asset Purchase
Agreement which the parties contemplate to be entered into within the next
several weeks, or (iv) November 30, 2003 (with the earliest of the foregoing
dates being the "Maturity Date" under this Note).

      3. Accelerated Maturity.

            (a) In the event Plexus makes an assignment for the benefit of
creditors, or appoints a receiver for all or substantially all of the Plexus
assets, or files a petition in bankruptcy or other similar proceedings for the
relief of debtors, or a creditor files a petition for bankruptcy of Plexus, then
upon the occurrence of any such event, the entire unpaid balance of principal
and accrued interest shall immediately become due and payable.

            (b) In the event Plexus undertakes any transaction involving the
consolidation or merger of Plexus with or into any individual, partnership,
limited liability company, venture, unincorporated association, organization,
syndicate, corporation, trust or trustee, executor, administrator or other legal
or personal representative or any government or any agency or political
subdivision thereof (a "Person") other than SIGA or the sale or conveyance to
any Person other than SIGA of all or substantially all of the assets of Plexus,
then upon the occurrence of any such event, the entire unpaid balance of
principal and accrued interest shall immediately become due and payable.

      4. Representations and Warranties. Plexus hereby represents and warrants
to SIGA:

            a. Enforceable Obligations. This Note has been duly executed and
delivered on behalf of Plexus, and constitutes the legal, valid and binding
obligation of Plexus, enforceable against it in accordance with its terms.

            b. No Legal Bar. The execution, delivery and performance of this
Note and the consummation of the transactions contemplated hereby, do not and
will not (i) violate any law, treaty, rule, regulation, right, privilege,
qualification or license or determination of an arbitrator or a court or other
governmental authority, in each case applicable to or binding upon Plexus or any
of its property or to which Plexus or any of its property is subject, or (ii)
conflict with or result in a breach of the terms or provisions of, or constitute
a default under, or result in the creation of any lien or other encumbrance
under any contractual obligation of the Plexus.

<PAGE>

      5. Cost of Collections. If this Note is not paid when due, whether at
maturity or by acceleration, Plexus promises to pay all reasonable costs
incurred by SIGA in collecting the amounts due and payable under this Note,
including reasonable attorney's fees and expenses.

      6. Waiver. Plexus hereby waives diligence, demand, presentment, protest
and notice of any kind, release, surrender or forbearance or other indulgence,
without notice.

      7. Modification. This Note may not be changed, modified, or terminated
orally, but only by an agreement in writing signed by the party to be charged.

      8. Governing Law. IN THE EVENT OF ANY LITIGATION WITH RESPECT TO THIS
NOTE, PLEXUS KNOWINGLY AND VOLUNTARILY WAIVES (TO THE EXTENT PERMITTED BY
APPLICABLE LAW) THE RIGHT TO A TRIAL BY JURY AND THE DEFENSES OF FORUM NON
CONVENIENS AND IMPROPER VENUE. THIS NOTE SHALL BE GOVERNED BY AND CONSTRUED IN
ACCORDANCE WITH THE LAWS OF THE STATE OF DELAWARE WITHOUT REGARD TO PRINCIPLES
OF CONFLICT OF LAWS AND SHALL BE BINDING UPON THE SUCCESSORS AND ASSIGNS OF
PLEXUS AND INURE TO THE BENEFIT OF SIGA AND ITS SUCCESSORS AND ASSIGNS. If any
item or provision of this Note shall be held invalid, illegal or unenforceable,
the validity of all other terms and provisions herein shall in no way be
affected thereby.

                                    PLEXUS VACCINE INC.

                                    By: /s/ Susan Burgess
                                        ----------------------------------------
                                    Name: Susan Burgess
                                    Title: President and Chief Executive Officer

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