From chemistry-request ^at^ ccl.net Thu Mar 4 15:08:18 2004 Received: from copland.udel.edu (copland.udel.edu [128.175.13.92]) by server.ccl.net (8.12.8/8.12.8) with ESMTP id i24K8Hd4032621 for ; Thu, 4 Mar 2004 15:08:18 -0500 Received: from [128.175.138.90] ([128.175.138.90]) by copland.udel.edu (8.12.10/8.12.10) with ESMTP id i24K9s8L005273 for ; Thu, 4 Mar 2004 15:09:55 -0500 (EST) Message-Id: <200403042009.i24K9s8L005273.-at-.copland.udel.edu> X-Mailer: Microsoft Outlook Express Macintosh Edition - 4.5 (0410) Date: Thu, 04 Mar 2004 15:00:03 -0500 Subject: relative stabilities in water: zwitterion vs anion From: "Olga Dmitrenko" To: chemistry.-at-.ccl.net Mime-version: 1.0 X-Priority: 3 Content-type: multipart/alternative; boundary="MS_Mac_OE_3161257203_838915_MIME_Part" X-Spam-Score: 1.7 HTML_FONT_FACE_ODD,MIME_LONG_LINE_QP,SPAM_PHRASE_03_05 X-Scanned-By: MIMEDefang 2.37 > THIS MESSAGE IS IN MIME FORMAT. Since your mail reader does not understand this format, some or all of this message may not be legible. --MS_Mac_OE_3161257203_838915_MIME_Part Content-type: text/plain; charset="ISO-8859-1" Content-transfer-encoding: quoted-printable Dear CCLers, The molecule I am studying is bifunctional and can exist in aqueous solutions as zwitterion or anion depending on pH. I am trying to compare the energies of zwitterionic and anionic forms by optimizations of the following H-bonded systems put into water media (using COSMO model): 1) zwitterion/OH- and anion/H2O - this system has net charge =B3-1=B2 2) zwitterion/H2O and anion/H3O+ - this system is neutral, which is better > from the computational point of view. I=B9ve got VERY different results. In case #1, the anionic form of my molecul= e was more stable. In the second case, the zwitterion was the preferred form. I feel that this is a wrong approach, but I can not compare directly the energies of zwitterion and anion because of different number of atoms. I would greatly appreciate if someone will point out the publications which rise similar questions. Best regards, Olga --MS_Mac_OE_3161257203_838915_MIME_Part Content-type: text/html; charset="ISO-8859-1" Content-transfer-encoding: quoted-printable relative stabilities in water: zwitterion vs anion Dear CCLers,

The molecule I am studying is bifunctional and can exist in aqueous solutio= ns as zwitterion or anion depending on pH.
 I am trying to compare the energies of zwitterionic
and anionic forms by optimizations of the following H-bonded systems put in= to water media (using COSMO model):

1) zwitterion/OH-  and anion/H2O    - this system has n= et charge =B3-1=B2
2) zwitterion/H2O and anion/H3O+  - this system is neutral, which is b= etter from the computational point of view.

I=B9ve got VERY different results. In case #1, the anionic form of my molecul= e was more stable. In the second case, the zwitterion was the preferred form= .
I feel that this is a wrong approach, but I can not compare directly the en= ergies of zwitterion and anion because of different number of atoms.

I would greatly appreciate if someone will point out the publications which= rise similar questions.

Best regards,
Olga
 --MS_Mac_OE_3161257203_838915_MIME_Part--