Hello Actually, if the home source uses a copper tube, neither copper nor zinc have much of an anomalous signal at that wavelength (the energy is below the absorption edge for both). The best way is to check the location of the absorption edge at the synchrotron. Cu+ and Cu++ can be distinguished this way, but make sure the absorption scan is done before you collect data since copper(II) can be photoreduced to copper(I) in the synchrotron x-ray beam. Whether or not you can get a clue from geometry depends upon the resolution of the structure.
Sue On Jul 24, 2012, at 10:22 AM, Nat Echols wrote: > On Tue, Jul 24, 2012 at 10:14 AM, Haytham Wahba <haytham_wa...@yahoo.com> > wrote: >> 1- if i have anomalous peak of unknown heavy atom, How can i identify this >> heavy atom in general. (different methods) >> >> 2- in my case, i see anomalous peak in heavy atom binding site (without any >> soaking). preliminary i did mass spec. i got Zn++ and Cu, How can i know >> which one give the anomalous peak in my protein. >> >> 3- there is way to know if i have Cu+ or Cu++. > > You may be able to identify the element based on the coordination > geometry - I'm assuming (perhaps incorrectly) that it is actually > different for Cu and Zn. Marjorie Harding has written extensively on > the geometry of ion binding: > > http://tanna.bch.ed.ac.uk/ > > The only way to be certain crystallographically, if you have easy > access to a synchrotron, is to collect data above and below the K edge > of any candidate element, and compare the difference maps. (For > monovalent ions it is more complicated, since they don't have > accessible K edges.) On a home source, Cu should have a larger > anomalous map peak, but I'm not sure if this will be enough to > identify it conclusively. > > -Nat Dr. Sue A. Roberts Dept. of Chemistry and Biochemistry University of Arizona 1041 E. Lowell St., Tucson, AZ 85721 Phone: 520 621 8171 or 520 621 4168 s...@email.arizona.edu http://www.cbc.arizona.edu/xray or http://www.cbc.arizona.edu/facilities/x-ray_diffraction
