Perhaps I misunderstood Jacob's original question, but it seems like two different phenomena are being discussed here. My read of Jacob's original question was, roughly, shouldn't we observe non-Bragg, powder-like scattering from a well-ordered macromolecular crystal due to the abundance of ~ 1 Å interatomic distances? In my opinion, the answer is "no" unless translational periodicity is violated. When translational periodicity is violated (as it is to some extent in all real crystals), then the non-Bragg (diffuse) scatter can contain many features, as it is the Fourier transform of the variance-covariance function for all disorder in the unit cell. If I misunderstood Jacob's original question, my apologies. Best regards, Mark
Mark A. Wilson Associate Professor Department of Biochemistry/Redox Biology Center University of Nebraska N118 Beadle Center 1901 Vine Street Lincoln, NE 68588 (402) 472-3626 [email protected] Jacob Keller <[email protected]> Sent by: CCP4 bulletin board <[email protected]> 05/09/2012 12:22 PM Please respond to Jacob Keller <[email protected]> To [email protected] cc Subject Re: [ccp4bb] Powder Rings in Single Crystals Yes, I just looked up the paper--seems right on topic--a powder-type ring at ~4.2 Ang, corresponding to Calpha-Calpha distances! But no 1.2-1.5 Ang ring, from what I saw. Maybe it gets swamped out by other things. I am thinking that the variety/distribution of bonds/distances of length 1-3 Ang in the crystal/mother liquor combo is so high/broad that you can't see them anymore. I wonder whether when people soak in various heavy atom clusters, they see powder rings for the HA-HA distances in the unbound clusters? JPK On Wed, May 9, 2012 at 11:51 AM, Philip Kiser <[email protected]> wrote: Hey Jacob, There was a paper by Robert M. Blessing et al (Acta Cryst D 1996) that at least partially attributed the diffuse ring that one sees around 3-4 A to something similar to what you are describing (scattering between amide oxygen and nitrogen for example). Philip -- ******************************************* Jacob Pearson Keller Northwestern University Medical Scientist Training Program email: [email protected] *******************************************
