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My understanding of coherence is a constant phase relation between waves. Of course, this breaks down for inelastic scattering, but (in)coherence can also be described without any change in wavelength. Best regards, Dirk. Am 12.01.12 11:27, schrieb Bernhard Rupp (Hofkristallrat a.D.): > Does out of phase imply incoherent scattering? I though it means inelastic Compton scattering? > > -----Original Message----- > From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of Dirk Kostrewa > Sent: Thursday, January 12, 2012 1:58 AM > To: [log in to unmask] > Subject: Re: [ccp4bb] NMR review > > Dear Bernhard, > > Am 12.01.12 10:30, schrieb Bernhard Rupp (Hofkristallrat a.D.): >> Dear All, >> >> I read an interesting statement in an NMR review: >> >> ".... regions of a protein or >> DNA / RNA molecule that are ?exible in the crystal do not provide >> coherent X-ray scattering and hence do not contribute to the ?nal >> electron density map. Thus, for all intents and purposes, they can >> effectively be ignored." >> >> Besides that I was not aware that disorder across molecules implies >> incoherence in scattering, I think this is quite some strong tobacco >> coming from what is primarily a crystallization screening tool ;-) > That doesn't sound wrong to me: the flexible parts are at different relative positions in the unit cells and thus their "partial-structure scattering waves" do not have a constant phase relation to each other, i.e., they don't give a coherent contribution to the total scattering. > > But I don't agree to their conclusion, since disorder doesn't necessarily mean, that there won't be any interpretable electron density left. The floppy parts could still be interpreted at an effective lower resolution and thus will not be ignored. > > Maybe the authors were annoyed by a vanishing NMR signal because the macromolecule crystallized in the NMR test tube ;-) > > Best regards, > > Dirk. >> Cheers, BR >> >> PS: I am grappling with the meaning of resolution in NMR. I can see >> that it could be related to comparable data/parameter ratios, although >> I am even less clear about the weights of NMR restraint weights than in the case of MX... >> some cross-trained person out there who can explain? -- ******************************************************* Dirk Kostrewa Gene Center Munich Department of Biochemistry Ludwig-Maximilians-Universität München Feodor-Lynen-Str. 25 D-81377 Munich Germany Phone: +49-89-2180-76845 Fax: +49-89-2180-76999 E-mail: [log in to unmask] WWW: www.genzentrum.lmu.de *******************************************************