Crystallographic structure refinement properties

The crystallographic structure refinement approach suggested is based on the viability of a fuzzy and additive density fragmentation technique. Ultimately, the fundamental quantum mechanical properties of density functionals justify the fuzzy fragmentation procedure, and the very same fundamental properties also suggest new approaches to local electron density shape analysis. These possibilities have relevance both to crystallographic structure refinement as well as to a density-based interpretation of the chemical properties of functional groups and other local... 

As an alternative approach to solution-state NMR methods, which are ineffective with lipid bilayer samples, solid-state NMR methods have been refined sufficiently to permit structural details to be obtained for membrane-embedded peptides and proteins. This usually requires isotopic enrichment, either through chemical synthesis or biosynthetic incorporation in expressed peptides and proteins. In the absence of routine X-ray crystallographic structural studies for these molecules, solid-state NMR spectroscopy has the potential to be a powerful and unique approach to determining the structures and describing the dynamics and functions of membranes and membrane-bound proteins. In addition, solid-state NMR spectroscopy has been widely used to describe lipid structure, dynamics and phase properties. Thus, solid-state NMR experiments can be... 

The radial deformation of the valence density is accounted for by the expansion-contraction variables (k and k ). The ED parameters P, Pim , k, and k are optimized, along with conventional crystallographic variables (Ra and Ua for each atom), in an LS refinement against a set of measured structure factor amplitudes. The use of individual atomic coordinate systems provides a convenient way to constrain multipole populations according to chemical and local symmetries. Superposition of pseudoatoms (15) yields an efficient and relatively simple analytic representation of the molecular and crystalline ED. Density-related properties, such as electric moments electrostatic potential and energy, can readily be obtained from the pseudoatomic properties [53]. 

Spectral and X-ray crystallographic data are described in Ref. 1 and in Infrared Data Correlations with Chemical Structure NMR Data Correlation with Chemical Structure and NMR Refinement. For toxicology and biological properties or environmental and hazard or reaction data refer to Chemical Safety Information Databases or Environmental Information Databases. Chemical and physical properties databases will be presented in this article. 

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