Hello Eddie, I believe this article from Robert Huber and coauthors was the first to discuss dynamical effects in a protein crystal:- Acta Cryst. <https://journals.iucr.org/b> (1980). B*36* <https://journals.iucr.org/b/contents/backissues.html>, 621-627 Greetings, John
On Thu, May 28, 2020 at 4:44 PM 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 > > Phone: (716) 898 8631 Fax: (716) 898 8660 > > Skype: eddie.snell Email: esn...@hwi.buffalo.edu > > Webpage: https://hwi.buffalo.edu/scientist-directory/snell/ > > [image: 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 > > > ------------------------------ > > 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 > -- Professor John R Helliwell DSc ######################################################################## 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/
