Dear Phil, Is the twin fraction varying? Can you correlate the variation of twin fraction with variations in crystal morphology or handling?
With constant perfect twinning you could try MIR using the phase determination method of Yates & Rees (Acta Cryst. (1987). A43, 30-36). I can't access the paper at the moment but if I remember it correctly you would need four good (i.e. independent) derivatives for a perfect twin. Best regards, Martin On May 13, 2011, at 11:28 AM, Phil Evans wrote: > We're trying to solve a 50% twin crystal by experimental phasing (SAD & > SIRAS) since molecular replacement hasn't worked. The crystals diffract very > well in apparent space group P62 2 2. A Hg derivative shows a strong apparent > anomalous signal (from half-dataset correlations etc), but we've failed to > solve it so far, nor even to decide the true space group. > > Has anyone out there successfully solved a 50% twin by experimental phasing? > Any suggestions or tips? It would be nice to know if we are not attempting > the impossible > > Phil Evans & Rich Suckling
