Dear all. I have recently solved a structure in-house, 2.8A, CuKa. I have a metal ion bound very obvious hepta-valent co-ordination, which would suggest either Ca or Mn. Neither was present in the crystallisation setup, but there was some Mg around, which has contaminants of both Ca & Mn. At 2.8A, I don't really think I can reliably discriminate between 2.15A & 2.36A distances to coordinating atoms ( http://tanna.bch.ed.ac.uk/newtargs_06.html). The B factors for refined Ca are 18, and Mn 30. The B-factors of coordinating atoms vary from... 18 > 30 - so no help there.
I have a nice clear 6sigma anomalous difference peak, but then, according to http://skuld.bmsc.washington.edu/scatter/ both Ca (f" ~1.3) and Mn (f" ~2.8) scatter anomalously at that wavelength. The obvious solution is go to a synchrotron and scan around the Mn edge and see what happens, however, whilst waiting for beam time, is there any way I could... oh I don't know, use the peak in my anomalous difference Fourier to figure out what anomalous signal would be required to generate a peak of that size - a sort of back-transform??? Is this do-able, and if so, how would one go about it? Cheers, Dave -- --------------------------------------- David Briggs, PhD. Father & Crystallographer www.dbriggs.talktalk.net iChat AIM ID: DBassophile --------------------------------------- Anyone who is capable of getting themselves made President should on no account be allowed to do the job. - Douglas Adams
