The As K edge is at 11.87 keV (1.04 A). If you have a MAD beamline, you
can use this for phasing, rather than worry about the As interfering
with phasing from other elements.
If you also have other anomalous elements in there, using multiple
wavelengths can help in phasing; you can add an in-between wavelength
above one edge but below the other. The Br K edge is 13.47 keV (0.92 A)
so there should be no problem differentiating it from As.
Do you also have Zinc in your mother liquor? Cacodylate will form some
interesting complexes with zinc.
On 03/03/16 07:56, Paul Paukstelis wrote:
> I've seen some indications that cacodylate buffers can cause problems
> for SAD/MAD experiments. My initial impression was that this was just
> from the cacodylate leading to fluorescence spectra that shifts the
> apparent peak to lower energy. We've solved a number of SAD structures
> (Br) in crystals grown in cacodylate buffer, but only recently have we
> run into a case that appears to have decent anomalous signal, but has
> proved difficult to find a reasonable solution. Is there some other
> effect that cacodylate might be having, or is this likely just the
> case of poor energy choice and/or poorly ordered scatterers?
--
=======================================================================
All Things Serve the Beam
=======================================================================
David J. Schuller
modern man in a post-modern world
MacCHESS, Cornell University
[log in to unmask]
|