I have seen similar ripples with S-methylmercury cysteine - and an 80
sigma peak for Hg is not that surprising! Anisotropic refinement was
not helpful in reducing the ripples, as it is indeed a summation
problem. It's a good idea to refine occupancy of the Hg, though, and to
look for dual conformations of the cysteines.
best wishes
kmj
Klemens Wild wrote:
Dear friends of the Fourier transform,
I am refining a structure with 2 adjacent Hg atoms bound to cysteines of
different monomers in the crystal contacts, which means I need to refine
them as well. While the structure nicely refines (2.2 A data), I do not
get rid of negative density ripple layers next to them (-10 sigmas). My
question: is this likely due to anistropy of the soft mercury atoms
(anisotropic B refinement decreases the ripples) or is this likely a
summation truncation effect prominent for heavy atoms? Can I just
anistropically refine the mercuries while I keep the rest isotropic?
Never saw this in a PDB. Suggestions are very welcome.
Greetings
Klemens Wild
