[1] the signal from Ta6Br12 is enormous and one will typically focus on low resolution (below 7 Å) so radiation sensitivity can be handled by a fairly low dose data collection We collected several data sets with Ta6Br12(2+) on the Na+,K+-ATPase (Morth JP et al. 2007) and found that although we got the strongest anom. diff. Fourier peaks from a data set collected on the Ta peak, we got far better SAD phases from a data set collected on the high-energy remote wavelength. This I think is also often observed for SeMet.
[2] With a loosely bound ionic compound like Ta6Br12(2+) you will tend to loose occupancy if you backsoak. 1 mM normally works fine for initial screening to see if it will form a useful derivative - then you can always play with parameters later Poul On 04/10/2010, at 18.28, Francis E Reyes wrote: > Hi all > > I'm reading a recent review by Elspeth Garman regarding radiation damage > (Acta Cryst D) and in this she mentions two ideas regarding metal centers: > > [1] They (The metal complexes themselves) are quickly reduced > > [2] Their absorption causes localized heating in the crystal. (This causes > the temp to increase above freezing thus allowing OH radicals to diffuse). > > How is it that people can phase off of TaBr considering [1]? Presumably as > TaBr is absorbing x-ray's whatever anomalous signal that was present at the > beginning of the collection is either absent/significantly altered by the > time data collection is complete? > > Regarding [2], is TaBr usually backsoaked (into cryoprotectant not containing > TaBr) to reduce it's concentration in the crystal to highly occupied sites? > It would seem to me that having a crystal soaked with TaBr would cause more > heating than one backsoaked. > > > > Thanks > > F > > > > --------------------------------------------- > Francis E. Reyes M.Sc. > 215 UCB > University of Colorado at Boulder > > gpg --keyserver pgp.mit.edu --recv-keys 67BA8D5D > > 8AE2 F2F4 90F7 9640 28BC 686F 78FD 6669 67BA 8D5D
