Subject: Re: CCL:Effect of oxidation on electron density

From: Mikael Johansson <mpjohans -()- pcu.helsinki.fi>
Date: Wed, 20 Apr 2005 14:27:24 +0300 (EEST)

Hello Noel and All!

On Tue, 19 Apr 2005, Noel O'Boyle wrote:

> I am using Gaussian03 and have calculated the electron density of the
> molecule in its oxidised state (at the geometry of the native state) and
> subtracted this from the electron density of the molecule in its native
> state.
>
> However, I have just noticed that the total spin density of the oxidised
> molecule gives an almost identical picture. Is this true in general? (I
> don't have a good understanding of what the total spin density shows.)

No. Spin density and total electron density difference are two different 
and more or less independent creatures, though they _can_ be located to 
similar regions of the molecule (as apparently for you). Spin density is 
much more free to change after, for example, oxidation/reduction. The 
electron density is much more restricted as it is bound by classical 
electrostatic forces.

I've done some studies comparing electron and spin density changes during 
oxidation/reduction of iron porphyrins [1-3]. Perhaps they are of some 
interest.

Have a nice day,
     Mikael J.
     http://www.helsinki.fi/~mpjohans/

[1] M.P. Johansson, M.R.A. Blomberg, D. Sundholm, M. Wikström, "Change in
     electron and spin density upon electron transfer to haem", Biochim.
     Biophys. Acta - Bioenergetics 1553 (2002) 183-187.
[2] M.P. Johansson, D. Sundholm, G. Gerfen, M. Wikström, "The Spin
     Distribution in Low-Spin Iron Porphyrins", J. Am. Chem. Soc. 124
     (2002) 11771-11780
[3] M.P. Johansson, D. Sundholm, "Spin and charge distribution in iron
     porphyrin models: A coupled cluster and density-functional study",
     J. Chem. Phys. 120 (2004) 3229-3236.