Deformation density peptides

Figures 6 and 7 give respectively the experimental and theoretical static deformation density in the planes of the C3=C4 double bond and of one of the two peptide links, calculated with the two basis sets, as well as their difference.

Figure 7. Static deformation densities in one peptide plane of AcPhe Experiment (a), basis set I (b), basis set II (c), (c) - (b) = (d). (continued)...

Because electron density is a local property, electron density studies of the peptide-like molecules show that the nonspherical part of the deformation density (i.e the P]m parameters of Eq. 8) remain essentially the same for a given atom in the same environment (the peptide residue, a phenyl ring, a methyl group...) [29], The same observation was made for porphyrin ligands [30] and by Brock, Dunitz, and Hirshfeld [37] for naphthalene and anthracene type molecules. All these observations suggest that the multipole parameters are highly transferrable from one atom to a chemically similar atom in different molecules and crystals. A key question is is it possible to determine for each chemical type of a given atom a small set of pseudoatom multipole parameters, and can such parameters be used to calculate electrostatic properties of new molecules To answer this question [29], two accurate but low resolution X-ray data sets (sin 0/Xmax = 0.65 A-1) were... 

Figure 11. Low temperature (110 K), low resolution (0.65 A-1, sin0A) experimental deformation density in the planes of a peptide residue (a) and of a phenyl ring (b) for Pyr-Phe-Pro-tMe using P/m transferability. Contours as in Figure 6.

The experimental deformation density obtained are shown on Figures 11 and 12 which represent the deformation density of a peptide residue and of a benzene ring temperature at 110 K and at room temperature, respectively. 

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