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Dear Sara, depending on the wavelength at which your data was collected, you should get an anomalous signal for the Cd and the S atoms in your structure. You should then be able to estimate the occupancy of the Cd based on the peak height and the peak heights of the S-atoms in the anomalous difference Fourier map. See for instance Acta D58, 1407-1412 (2002). If the data collection wavelength is too short or your anomalous are not complete enough, I would suggest to collect some data at a longer wavelength (1.5 A or longer depending on which facilities you have access to). This should resolve the problem. Cheers, Manfred. ******************************************************************** * * * Dr. Manfred S. Weiss * * * * Team Leader * * * * EMBL Hamburg Outstation Fon: +49-40-89902-170 * * c/o DESY, Notkestr. 85 Fax: +49-40-89902-149 * * D-22603 Hamburg Email: [EMAIL PROTECTED] * * GERMANY Web: www.embl-hamburg.de/~msweiss/ * * * ******************************************************************** On Mon, 20 Mar 2006, Sara Elizabeth Cnudde wrote: > *** For details on how to be removed from this list visit the *** > *** CCP4 home page http://www.ccp4.ac.uk *** > > > > Hi, > > I have a structure that I'm refining that I believe has a metal site in > which 50% of the time it's occupied by cadmium and the other 50% of the time > this same site is occupied by magnesium. How can I really tell if this is > true? If I put Mg in with 100% occupancy I see a lot of density in my > fo-fc map contoured at 3 sigma indicating that this is incorrect. However, > if I put in Cd with 50% occupancy I no longer see this density but if the Cd > has 100% occupancy I see density in the fo-fc map contoured at -3 sigma. > > Thanks, > > Sara > >
