IMAGING PLATE DATA PROCESSING FOCUSED ON CHEMICAL CRYSTALLOGRAPHY. T. Higashi, Rigaku Corporation, 3-9-12 Matsubara-chi, Akishima-shi, Japan 196

Rapid data collection using an area detector developed for protein crystallography is now successfully applied to small molecule crystallography, especially when crystals are unstable. As far as imaging plate data processing is concerned, however, software strategy suited to chemical crystallography is not yet completed.

In a physical sense, diffraction phenomena do not discriminate small molecule or macromolecule crystals, difference is just size of cell dimensions, ie. a protein data acquisition method can be straightforwardly applicable to small molecules, except a few points.

1) Alpha-1 alpha-2 splitting of spots, resulting in re-consideration of a measurement box. One solution could be superposition of two separated spot boxes. Local profile fitting of DENZO may compensate it to some extent, or a dynamic box based on the seed-skewness method would be another possibility.

2) Less dense reciprocal lattice points, causing sometimes difficulty in indexing. Real space indexing would be a solution. On the other hand, an area detector loses benefits of four-circle diffractometry in the points.

1) Less accurate cell constants, arising from rough estimation of diffraction geometry. Direct two-theta measurement of reflections, calibrated with a standard powder sample, may be required.

2) No experimental absorption correction, such as a psi-scan method, available. Since easy DIFABS correction is banned in Acta Crystallographica, an alternative method is highly required. Discussed will be some solutions to those problems.