Subject: Summary:radical cations in solution(2)

From: Jenny <[email-masked]>
Date: Tue, 10 Dec 1996 09:34:44 +0100

Dear CCLers,

         I thank Ernest Chamot for the useful information.

I have submitted the following query:       

>I am interested in the calculation of  minimum energy conformations of a
radical cation (17 heavy atom: C, O, N) in solution (water).
>Can continuum solvation models be used to  investigate geometries and
relative energies of different conformers?
>Is AMSOL a good choice?

        third reply

I think you're in luck!  It turns out that the newer continuum solvation
models, (those that realistically model charges at the solvent accessible
surface instead of just assuming a spherical cavity) are capable of
reproducing some subtle effects of solvation, including geometry changes
that would seem to require explicit solvent-solute interaction.  For your
particular interest, ie. radical ions, Cramer and Truhlar's solvation models
(SM2 and later, in AMSOL) have proven particularly effective, as has Klamt's
COSMO model (in MOPAC 93).  Chris Cramer and Sue Barrows had a paper in the
first Electronic Computational Chemistry Conference, "Predicting
Regioselectivity in the Reduction of Polynitroaromatics in Aqueous
Solution," in which the charge distribution and geometries of the nitro
groups  in the radical anions of various polynitroaromatics were correctly
predicted to differ from "gas" phase modeling, and reproduced experimental
reduction patterns.  This has subsequently been published as:

University of Minnesota Supercomputer Institute Research Report UMSI 96/112
May 1996; Factors Controlling Regioselectivity in the Reduction of
Polynitroaromatics in Aqueous Solution; S. Barrows, C. Cramer, D. Truhlar,
M. Elovitz, & E. Weber

I reproduced the calculations in the ECCC paper with the COSMO model in
MOPAC 93 and found it to work just as well as SM2 on the radical anions.

Henry Rzepa has also used the COSMO model to calculate redox potentials by
modeling solvated quinones and hydroquinones:

 H. Rzepa & G. Suner, J. Chem. Soc., Chem. Comm. 1743 (1993)

Hopefully, success in modeling solvated radical anions will translate in to
success in modeling radical cations as well.  Good luck. 

EC
---
Ernest Chamot
Chamot Labs, Inc.
530 E. Hillside Rd.
Naperville, Illinois 60540
(630)637-1559
[email-masked]
http://www.xnet.com/~chamotlb

Best Regards

Jenny Migliavacca
Institut de Chimie Therapeutique
Ecole de Pharmacie
Universite de Lausanne                    
CH-1015 Dorigny-Lausanne
Tel:	 021 / 692.45.29
Fax: 	021 / 692.45.05
Email:	[email-masked]

---

From: Chris Cramer <[email-masked]>
Date: Tue, 10 Dec 1996 12:07:52 -0600 (CST)

> 
>          I thank Ernest Chamot for the useful information [about prior
>   study on continuum solvation of radical anions of nitroaromatics].
> 
   for the record, that's now Environmental Science & Technology, 30 (1996)
3028-3038. It's also online at ACS's website for ES&T, but their server
appears to be down at the moment, so all I can do is give you the top
address, http://pubs.acs.org (it's about four links to the paper at that
point, through Journals, ES&T, proper issue (#10) etc.) 

Those of you interested in Web development will find that the beautiful 
color pictures we published as part of this study were included in the 
journal (where we paid through the nose for them, thank you EPA
collaborators) but were reproduced as (illegible) grayscale in the on-line 
version (where we'd have been only too happy to send our color .jpeg's if 
we'd been informed of electronic publishing plans). Feel free to send a 
comment to ACS on the helpful form provided . . .

CJC
-- 

Christopher J. Cramer
University of Minnesota
Department of Chemistry
207 Pleasant St. SE
Minneapolis, MN 55455-0431
--------------------------
Phone:  (612) 624-0859 || FAX:  (612) 626-7541
[email-masked]
http://pollux.chem.umn.edu/~cramer