Determination of invariant reflection phases by four-beam X-ray diffraction

The extension of the phases of the structure factors of the organic crystal C(25)H(25)NO(2) from 77 starting individual phases using the maximum-entropy method is reported. These starting phases were determined from 90 experimental triplet phases calculated from 215 measured psi-scan three-beam and four-beam diffraction profiles obtained with a rotating-anode X-ray source, where the psi scans were around the reciprocal-lattice vectors of the 001, 002 and 003 reflections. The extension of the structure factors with phase values was carried out using the maximum-entropy method for 2040 measured two-beam Bragg diffraction intensities with 77 starting phases and the symmetry of the space group as the constraints. Use of structure-factor triplets as constraints for entropy maximization was also attempted. The minimum chi(2) criteria were applied to the maximum-entropy extrapolation to discern the best phase set to be used as the new constraints for the next step of generating new phases. With this phase-extension procedure, more than 100 phases were determined and an electron-density map at 1.97 A was deduced.

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Multiple diffraction data analysis for macromolecular crystals in stereoscopic multibeam imaging

Chao

Hung

Huang

et al. 2001

Acta Cryst Sect A

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A detailed analysis of multiple diffraction data collected by the stereoscopic multibeam imaging technique from a tetragonal lysozyme crystal is reported. Calculations based on the dynamical theory are employed to account for diffraction profiles obtained with Bragg‐angle scan in stereoscopic imaging and the conventional azimuthal scan in Renninger arrangement. The formation of a multibeam intensity profile and the relationship and mutual influence between the two scans are investigated. A simple practical method of quantitative estimation of the reflection phases of structure‐factor multiplets from the experimental data obtained with two inversion‐symmetry‐related diffractions is proposed. The procedures for data handling and for distinguishing `partial' diffraction images from `full' diffraction images are also developed considering multibeam diffraction geometry and experimental conditions. These procedures thus provide a practical way of reconstructing diffraction profiles for experimental phase determination for macromolecular crystals.

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Determination of invariant reflection phases by four-beam X-ray diffraction

Cited by 3 publications

References 9 publications

Enhanced coherent interaction in four-beam X-ray interference in crystals: a solution to the X-ray phase problem using weak four-beam diffraction

Enhanced coherent interaction in four-beam X-ray interference in crystals: a solution to the X-ray phase problem using weak four-beam diffraction

Phase determination and extension using X-ray multiple diffraction and the maximum-entropy method

Multiple diffraction data analysis for macromolecular crystals in stereoscopic multibeam imaging

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