[SA_scat] protein SAXS in conc Zn soln

Richard Gillilan reg8 at cornell.edu
Thu Sep 7 15:11:09 BST 2006

I'm cross posting this on CCP4 and SA_scat, so sorry if you get two  

One of my users wants to do SAXS on a protein in a buffer containing  
concentrated Zn ions.
I did some simple calculations of contrast and the results make me  

water = 334 electrons/nm^3
protein = 430 electrons/nm^3

For saturated ZnCl2, I estimate 530 electrons/nm^3

He didn't specify what kind of Zn salt, but it seems that any  
addition of Zn to the buffer is going to initially decrease contrast.  
At best, in a very strong solution, there would be negative contrast  
about equal to water in magnitude.

Has anyone had experience of doing SAXS in concentrated heavy atom  
solutions? Did you have contrast problems?

Richard Gillilan

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