Not true. For MAD and SIRAS you still have to try both hands of the heavy atom substructure (unless the heavy atom arrangement is itself centrosymmetric, then both hands are correct).
Maybe I should also mention for completeness, that for the space groups I41, I4122 and F4122 the heavy atoms have to be inverted at a point that is not at the origin (e.g. x, y, z -> 1-x, 0.5-y, 0.25-z for I4122). Fortunately SHELXE and some other programs know this and apply the correct inversion automatically. George 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 On Fri, 20 Aug 2010, Jacob Keller wrote: > > > > > > MAD and SIRAS will in general behave like SAD. However if your isomorphous > > difference is large and the anomalous signal is lost in the noise, they > > might be dominated by it and so tend to behave more like SIR. > > > > > I thought that MAD and SIRAS had no hand ambiguity--not true? > > Jacob Keller >
