Hi Bill, On Apr 2, 2008, at 10:58 PM, William G. Scott wrote:
I've got what appears to be an inner-sphere interaction between Mg++ and the N7 of a G. The mode of binding is the same as what is observed at this site for Mn++, confirmed with anomalous data. Our resolution is 1.6 Å, so I am reasonably confident this is right. However, my chemist's viewpoint is that Mg++ is too hard and N is too soft for this to happen.
I would also be hesitant.
Since Mg++ has the same number of electrons as water and no useful absorbance, it seems assigning them based on hydration geometry and bond distances is the only hope.
One can often see magnesium ions in anomalous-difference fouriers with good home-source data. Since you appear to have very good diffraction and your magnesium is most definitely relatively well ordered (if it is a magnesium..) I think it is worth a try to carefully collect a data set using a wavelength around 1.5-1.6 Å (or simply your home source depending on how good it is).
Cheers, Martin . B. Martin Hallberg, PhD Assistant professor Department of Cell and Molecular Biology Medical Nobel Institute Karolinska Institutet Nobels väg 3 SE-171 77 Stockholm Sweden
