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This seems to be the consensus and something I wasn't aware of. Curious that I haven't run into this before! On 03/03/2016 10:00 AM, SHEPARD William wrote: > Hi Paul, > > The bromine-carbon bonds are notoriously sensitive to X-rays. So the all bromines might be knocked off before you have a complete data set. As this is site specific radiation damage, the first thing to try is lowering the dose of x-rays. > > Cheers, > Bill > > > > ________________________________ > From: CCP4 bulletin board [[log in to unmask]] on behalf of Paul Paukstelis [[log in to unmask]] > Sent: 03 March 2016 15:06 > To: [log in to unmask] > Subject: Re: [ccp4bb] cacodylate and anomalous > > We are actually working on oligonucleotides that have been brominated (we have two derivatives with bromines at different positions). > > --paul > > On 03/03/2016 08:47 AM, Finke Aaron (PSI) wrote: > Sorry, not cysteines alone, but cysteine in the presence of a reducing agent like DTT, or even BME. See here: <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3797521/> http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3797521/ > > > ------------------------------------------ > Dr. Aaron Finke > Postdoctoral Fellow > Swiss Light Source > WSLA/214 > 5232 Villigen PSI > Switzerland > phone: +41 56 310 5652 > e-mail: <mailto:[log in to unmask]> [log in to unmask]<mailto:[log in to unmask]> > > On Mar 3, 2016, at 14:44, Aaron Finke <<mailto:[log in to unmask]>[log in to unmask]<mailto:[log in to unmask]>> wrote: > > Dear Paul, > > Have you tried phasing on arsenic? Cysteine can reduce cacodylate and bind the dimethylarsine, and actually I’ve had a few instances where the As signal was more than sufficient for SAD phasing. > > Cheers, > Aaron > > > ------------------------------------------ > Dr. Aaron Finke > Postdoctoral Fellow > Swiss Light Source > WSLA/214 > 5232 Villigen PSI > Switzerland > phone: +41 56 310 5652 > e-mail: <mailto:[log in to unmask]> [log in to unmask]<mailto:[log in to unmask]> > > On Mar 3, 2016, at 13:56, Paul Paukstelis <[log in to unmask]<mailto:[log in to unmask]>> wrote: > > I've seen some indications that cacodylate buffers can cause problems for SAD/MAD experiments. My initial impression was that this was just from the cacodylate leading to fluorescence spectra that shifts the apparent peak to lower energy. We've solved a number of SAD structures (Br) in crystals grown in cacodylate buffer, but only recently have we run into a case that appears to have decent anomalous signal, but has proved difficult to find a reasonable solution. Is there some other effect that cacodylate might be having, or is this likely just the case of poor energy choice and/or poorly ordered scatterers? > > >