Direct Phase Determination in the Electron Crystallography of Organic Compounds
Although other, more traditional, methods for determination of crystallographic phases have been often used with electron diffraction intensity data from organic crystals, direct phasing based on the probabilistic estimate of structure invariants has been found recently to be generally applicable for such structure analyses. New structure solutions include the lamellar packings of several phospholipids, a previously undetermined polymorph of an odd-chain paraffin, the solid solution of two paraffins, and the three-dimensional crystal structure of polyethylene. In some cases, low-dose high-resolution electron microscope images provide phase information useful for the elucidation of the total crystal structure, especially when the diffraction pattern is dominated by the scattering from a sublattice structure.
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