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Yes, but at 1.54 A or 8.0 kev, according to the info at
http://skuld.bmsc.washington.edu/scatter/data/P.dat
f" is about 0.44 electrons. I had looked at that many
times in the past and decided it was just not practical.
Now with your encouragement I see that 0.44 is only a
little lower than S at the same wavelength, 0.56; and
greater than S at 1 A (.25 e).
If I can see good S peaks in synchrotron data at 1A
I should be able to locate well-ordered phospholipids.
Trouble is these crystals are not lysozyme, data is
not extremely accurate, and radiation damage at long
wavelengths is very severe. Still its worth a try!
Ed
Jim Pflugrath wrote:
As we all know, the diffraction intensities do not have to be measured at an
absorption edge to detect a useful anomalous signal: there is almost always
anomalous scattering at any wavelength you choose. It's just a matter of
measuring it.
And a single wavelength often suffices. So one can do a SAD experiment
within a broad range of wavelengths (for instance: 1.54 Angstrom) and phase
on the signal from S, Cl, Ca, and other atoms. The literature is full of
such instances.
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of
Edward Berry
Sent: Friday, November 10, 2006 4:56 PM
To: Richard Gillilan
Cc: CCP4
Subject: Re: [ccp4bb]: MAD at very low energy?
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Richard Gillilan wrote:
I know that some work has been done on phasing from Sulfur (2.47 keV).
Does anyone know of work on
phasing from P, Cl, Ar, K, or Ca?
Are there any very important systems that might benefit from MAD in
range 2-5 keV?
P anomalous signal would be very useful for identifying
phospholipids in membrane protein structures, and ATP
and other nucleotides in enzymes - but I understand it
is completely impractical?
Ed
