Topic
Conformational isomerism
About: Conformational isomerism is a research topic. Over the lifetime, 11563 publications have been published within this topic receiving 199312 citations.
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46 citations
TL;DR: CNDO and ab initio calculations on the dimethyl phosphate monoanion demonstrate that geometry optimization can dramatically alter the relative energies of the conformational isomers of the phosphate ester with geometry optimization (particularly of the diester RO-P-OR bond angle).
46 citations
TL;DR: The results can be interpreted with a model that considers the structure of a folded protein as resulting from packing imperfectly complementary parts, with a requirement of an overall low energy.
Abstract: We analyze packing imperfections in globular proteins as reflected in deviations of torsion angles from the equilibrium values for the isolated side chains. The distribution of conformations of methionine and lysine residues in a database of high-resolution structures is compared with energies of model compounds calculated with high-level quantum-mechanics. The distribution of the C–C and C–S torsion angles (χ3) correlates well with the Boltzmann factor of the torsion energy, exp(−βE) of the model compounds C2H5—C2H5 and C2H5—S—CH3. An exponential relation was again found between the relative occurrence of g+, g− and t conformations for Cα—Cβ bonds in long side chains and the energy differences of rotamers of α-amino n-butyric acid, when dependence on backbone conformation was taken into account. The distribution of all 27 rotamers of methionine was correlated with the energy differences between the model’s rotamers, corrected for clashes with nearby residues, the correlation being good for a set with backbone in the β-conformation, but less clear for backbone α-conformation. In all correlations, the value of the coefficient β corresponds to a temperature of circa 300 K. These results can be interpreted with a model that considers the structure of a folded protein as resulting from packing imperfectly complementary parts, with a requirement of an overall low energy. Compromises are required to optimize the fit of nonbonded contacts with surrounding groups, and side chains assume conformations away from the energy minimum. An exponential distribution is a most probable distribution, and this can be established easily under conditions other than thermal equilibrium.
46 citations
TL;DR: For 3- trans and 3- cis isomers of 1,3,5-hexatriene, structure parameters of not only the stable but also less stable conformers have been optimized by restricted Hartree-Fock calculations at the 6-31G level.
46 citations
TL;DR: Unexpected and dramatic sensitivity of the dichroic-parameter profile to the methyl rotation, both in the core and valence states, has been found.
Abstract: The B-spline density-functional method has been applied to the conformers of the (1R, 2R)-1,2-dibromo-1,2-dichloro-1,2-difluoroethane molecule. The cross section, asymmetry, and dichroic parameters relative to core and valence orbitals, which do not change their nature along the conformational curve, have been systematically studied. While the cross section and the asymmetry parameter are weakly affected, the dichroic parameter appears to be rather sensitive to the particular conformer of the molecule, suggesting that this dynamical property could be a useful tool for conformational analysis. The computational method has also been applied to methyl rotation in methyloxirane. Unexpected and dramatic sensitivity of the dichroic-parameter profile to the methyl rotation, both in the core and valence states, has been found. Boltzmann averaging over the conformers reproduces quite closely the profiles previously obtained for the minimum-energy conformation, which is in good agreement with the experimental results.
46 citations