Maybe all those highly disordered bromides (and rubidium ions) would be difficult to model and would push up the R factors? From the point of view of SAD or MAD phasing, a large number of partially occupied sites might be difficult to find. The highly disordered sites might also create an anomalous signal at low resolution that would interfere with the signal from the more ordered sites that one would like to use for phasing (we suspect that we may have been thwarted by this in a recent sulfur-SAD experiment that was crystallized from a high NaCl concentration).
George On Thu, Jun 16, 2011 at 10:38:41AM -0500, Jacob Keller wrote: > Yes! Although the Rb edge might be a little tricky to get to, but the > extra density would probably show up. Also, does Rb substitute well > for Na? > > Rb: > Edge keV A > K 15.1997 0.8157 > > I was thinking that perhaps the reason that solvent HAs were not used > historically is that perhaps at RT they would induce a lot of > secondary radiation damage due to diffusion of radicals, whereas at > cryo temperatures that would not be such an issue? > > Anyway, one would think these substitutions would always be > worthwhile, and their power could be greatly enhanced by doing SIRAS > against Cl if need be. > > JPK > > > > On Thu, Jun 16, 2011 at 10:22 AM, Edward A. Berry <ber...@upstate.edu> wrote: > > Better yet, RbBr? and pH MES, MOPS, and HEPES with RbOH? > > I haven't checked the price. > > > > Jacob Keller wrote: > >> > >> Is there any reason why crystallographers have not routinely > >> substituted NaBr for NaCl in protein crystallization stocks, or even > >> pH'd their TRIS with HBr, if there is no NaCl? Wouldn't it make a lot > >> of sense, since there would always be a possibility for a Br- > >> derivative, and the price difference is pretty small? Also, a data set > >> at the Br- peak would always be able to distinguish "heavy H2O" from > >> weak halide sites once the structure was solved, even if the sites > >> were not good enough for phase determination themselves. > >> > >> JPK > >> > >> On Wed, Jun 15, 2011 at 7:35 AM, Stephen Graham<sc...@cam.ac.uk> wrote: > >>> > >>> You might also want to try: > >>> > >>> http://www.ncbi.nlm.nih.gov/pubmed?term=12499536 > >>> > >>> Cheers, > >>> > >>> Stephen > >>> > >>> On 15 June 2011 02:09, Robbie Joosten<robbie_joos...@hotmail.com> wrote: > >>>> > >>>> Hi Wolfram, > >>>> > >>>> This was an early study on the subject: > >>>> http://www.ncbi.nlm.nih.gov/pubmed/8594192 > >>>> The software is still accessible via the STAN server. > >>>> > >>>> Cheers, > >>>> Robbie > >>>> > >>>>> Date: Tue, 14 Jun 2011 17:51:21 -0400 > >>>>> From: wtem...@gmail.com > >>>>> Subject: [ccp4bb] non-waters among structured solvent atoms > >>>>> To: CCP4BB@JISCMAIL.AC.UK > >>>>> > >>>>> Dear colleagues, > >>>>> following a discussion in our lab, I have volunteered to dig out > >>>>> articles from the literature about erroneous assignments of non-water > >>>>> entities such as metal ions, halides in protein models. For example I > >>>>> have the faint recollection that data mining of the PDB for suspect > >>>>> "water" assemblies matching the geometry of coordinated cations has > >>>>> previously been described. But none of my google searches has turned > >>>>> up the references I was looking for. Could someone point me in the > >>>>> right direction, please? > >>>>> Many thanks, > >>>>> Wolfram Tempel > >>>> > >>> > >>> > >>> > >>> -- > >>> Dr Stephen Graham > >>> 1851 Research Fellow > >>> Cambridge Institute for Medical Research > >>> Wellcome Trust/MRC Building > >>> Addenbrooke's Hospital, Hills Road > >>> Cambridge, CB2 0XY, UK > >>> Phone: +44 1223 762 638 > >>> > >> > >> > >> > >> -- > >> ******************************************* > >> Jacob Pearson Keller > >> Northwestern University > >> Medical Scientist Training Program > >> cel: 773.608.9185 > >> email: j-kell...@northwestern.edu > >> ******************************************* > >> > > > > > > -- > ******************************************* > Jacob Pearson Keller > Northwestern University > Medical Scientist Training Program > cel: 773.608.9185 > email: j-kell...@northwestern.edu > ******************************************* > -- Prof. George M. Sheldrick FRS Dept. Structural Chemistry, University of Goettingen, Tammannstr. 4, D37077 Goettingen, Germany Tel. +49-551-39-3021 or -3068 Fax. +49-551-39-22582
