Dear Eddie, dear all According to ftp://ftp.ccp4.ac.uk/ccp4/newsletter/jun_95/, this article appeare in Newsletter June 95. It is mentioned in the table of contents, "Correction on perfection: primary extinction correction in protein crystallography" by Polykarpov and Sawyer. Unfortunately, the article itself is not there
Extinction is not the same as the dynamic effects that James mentioned, but this seems the closest match. Would anyone have a copy they can share with me? Thanks a lot! Best, Tim On Thu, 28 May 2020 15:43:00 +0000 Edward Snell <esn...@hwi.buffalo.edu> wrote: > This jogged my memory of a CCP4 newsletter article many years ago > covering kinematical versus dynamic scattering in protein crystals > and offering a correction that could be used. I think it was Lindsay > Sawyer and Igor Polikarpov in the late 90’s. I apologize if I have > the authors wrong but I thought it was a commentary well ahead of its > time and with modern sources and low noise detectors, I am wondering > if anyone has revisited this? Protein crystals are remarkably high > quality until you cryocool them. Serial methods combined with > instrument capabilities may rate a revisit to the use of the > kinematical approximation versus application of dynamical theories? > Certainly the computational power is available. > > Just my 2 cents for the day. > > Best, > > Eddie > > > Edward Snell Ph.D. > > Director of the NSF BioXFEL Science and Technology Center > President and CEO Hauptman-Woodward Medical Research Institute > BioInnovations Chaired Professorship, University at Buffalo, SUNY > 700 Ellicott Street, Buffalo, NY 14203-1102 > hwi.buffalo.edu<http://hwi.buffalo.edu/> > Phone: (716) 898 8631 Fax: (716) 898 8660 > Skype: eddie.snell Email: > esn...@hwi.buffalo.edu<mailto:esn...@hwi.buffalo.edu> Webpage: > https://hwi.buffalo.edu/scientist-directory/snell/ [hwilogo] > Heisenberg was probably here! > > > > From: CCP4 bulletin board <CCP4BB@JISCMAIL.AC.UK> On Behalf Of James > Holton Sent: Thursday, May 28, 2020 11:34 AM > To: CCP4BB@JISCMAIL.AC.UK > Subject: Re: [ccp4bb] Strange Pseudosymmetry Effects > > Be careful with electron diffraction and apparent absence violations. > It is possible these weak spots are simply due to multiple > scattering. If so, you would see them relatively stronger with > larger crystals,but much weaker relative to the strong reflections > when the crystal is smaller. Do you? > > -James Holton > MAD Scientist > On 5/27/2020 6:49 PM, Jessica Bruhn wrote: > Hello, > > I am wondering if pseudosymmetry can cause weak reflections that > mimic the doubling of one unit cell axis' length. Has anyone seen > something like this before? > > I am processing data from a small molecule sample collected with > electron diffraction from multiple crystals. For the b axis, it is > not clear if the length should be 10A or 20A. There are spots with > the correct spacing for b=20A, but every other spot seems weaker than > the spots along k if I choose b=10A (this extends beyond (0,k,0)). I > am unable to phase the b=20 data. I have solved this structure in P1 > with b=10 and found four molecules in the ASU and in P212121 with > b=10 resulting in one molecule in the ASU. In P1, three of the four > molecules adopt the same conformation, but the fourth molecule is in > an alternate conformation that causes only ~1/2 of the molecule to be > consistent with the first three. In P212121 I see density for part of > this alternative conformation, but the full molecule in this > alternate conformation cannot pack properly in P212121. Based on > these results and some orthogonal data, I think I should refine the > solution in P1 with b=10. Does it seem reasonable that pseudosymmetry > is causing these weak reflections along k hinting at a doubling of > the b axis? > > Thanks in advance! > > Best, > Jessica > > -- > Jessica Bruhn, Ph.D > Principal Scientist > NanoImaging Services, Inc. > 4940 Carroll Canyon Road, Suite 115 > San Diego, CA 92121 > Phone #: (888) 675-8261 > www.nanoimagingservices.com<http://www.nanoimagingservices.com> > > ________________________________ > > To unsubscribe from the CCP4BB list, click the following link: > https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 > > > ________________________________ > > To unsubscribe from the CCP4BB list, click the following link: > https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 > > ######################################################################## > > To unsubscribe from the CCP4BB list, click the following link: > https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 > > This message was issued to members of www.jiscmail.ac.uk/CCP4BB, a > mailing list hosted by www.jiscmail.ac.uk, terms & conditions are > available at https://www.jiscmail.ac.uk/policyandsecurity/ -- -- Tim Gruene Head of the Centre for X-ray Structure Analysis Faculty of Chemistry University of Vienna Phone: +43-1-4277-70202 GPG Key ID = A46BEE1A ######################################################################## To unsubscribe from the CCP4BB list, click the following link: https://www.jiscmail.ac.uk/cgi-bin/webadmin?SUBED1=CCP4BB&A=1 This message was issued to members of www.jiscmail.ac.uk/CCP4BB, a mailing list hosted by www.jiscmail.ac.uk, terms & conditions are available at https://www.jiscmail.ac.uk/policyandsecurity/
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