modelling metal-sulfur clusters

Harry Powell hrp1000 at cus.cam.ac.uk
Fri Apr 9 04:17:42 EST 1999


> 
> We are trying to refine a ferredoxin in which the [2Fe-2S] cluster has
> been replaced by [2Ga-2S].  We are modelling gallium using scattering
> factors for Ga3+, but for sulfur are using scattering factors from
> elemental sulfurs (this is in both X-PLOR and SHELX).  Not surprisingly,
> we have a lot of positive difference density around the clusters, but it
> is particularly centered around the galliums.
> 

In SHELX, unless I knew I was dealing with an ionic compound, I'd be
tempted to use scattering factors for _neutral_ atoms - Ga[0] and S[0]; 
if you've got positive electron density around your gallium sites, it
indicates that you haven't put enough density there.

Harry
-- 
Dr Harry Powell, MRC Laboratory of Molecular Biology,
MRC Centre, Hills Road, Cambridge, CB2 2QH





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