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I'm cross posting this on CCP4 and SA_scat, so sorry if you get two
copies.
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
worry.
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
MacCHESS
Cornell
