modelling metal-sulfur clusters

Chetlen Crossnoe cc691077 at
Thu Apr 8 15:06:11 EST 1999

Hi all,

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been replaced by [2Ga-2S].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.

Has anyone had experience modelling these clusters?  Did you use
scattering factors for S-, or did you let the difference be made up for
in the B-factor or occupancy?  Does it matter?



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