On Thursday 28 February 2008 19:54, Sun Tang wrote:
> Dear All,
>
> In my structures, I want to assign Mn or Ca ions for some densities.
> But when I did not have anomalous density in CCP4i.
[snip]
> I collected the data at the wavelength of 1 A.
Mn has only about 1e of anomalous scattering (f") power at 1A.
Ca has essentially 0.
So you should not expect to see any peaks in your map.
> Do I need to adjust the wavelength to maximize the anomalous signal from Mn
> or Ca?
Yes.
To distinguish between them you would need to select an X-ray energy
between their respective K-absorption edges.
You can use the X-ray Anomalous Scattering server to help you:
http://skuld.bmsc.washington.edu/scatter/AS_form.html
This will tell you that you would need an X-ray energy less than the Mn K-edge
at 6.5390 keV (1.8961 Angstrom)
http://skuld.bmsc.washington.edu/scatter/AS_periodic.html
> I am not sure whether I was correct. The following was what I did:
>
> I processed the data with HKL2000 and select anomalous signal in scaling.
> In CCP4i, I selected "Run FFT-Creat Map" in the "Map& Mask Utilities". I
> select "O format to cover asymmetric unit" and "Plot section on Z axis from 0
> to 1 in steps on 10". All others were by default values. I display in ono10.
>
> I collected the data at the wavelength of 1 A. Do I need to adjust the
> wavelength to maximize the anomalous signal from Mn or Ca?
>
> Any ideas and suggestions are greatly appreciated!
>
> Sun Tang
>
--
Ethan A Merritt
Biomolecular Structure Center
University of Washington, Seattle 98195-7742
