Two separate crystals, but very similar data collection strategies P
On 04/10/2010, at 21.48, Jacob Keller wrote: > ----- Original Message ----- From: "Poul Nissen" <p...@mb.au.dk> > To: <CCP4BB@JISCMAIL.AC.UK> > Sent: Monday, October 04, 2010 2:21 PM > Subject: Re: [ccp4bb] Radiation damage with crystals containing metal centers > (TaBr people chime in?) > > > [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. > > > > > > Interesting phenomenon--has it been documented, I wonder? I wonder which > datasets were collected first? If the peak was collected first, as usual I > think, and one assumes an exponential decay of the resonant signal as a > function of radiation dose, it makes sense that the resonant signal would be > more constant after the first data set, where the decay curve would have > flattened out a bit. This would also be true for two consecutive data sets > collected at high energy. Also, I think the decay function itself is steeper > at the peak wavelength, leading to a less-internally-consistent data set at > the peak. Does this argument hold water? > > Jacob Keller
