modelling metal-sulfur clusters

Harry Powell hrp1000 at
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 been replaced by [2Ga-2S].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.

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

More information about the Xtal-log mailing list