Dihedral angle

About: Dihedral angle is a research topic. Over the lifetime, 15718 publications have been published within this topic receiving 174904 citations.

Chemistry of organosilicon compounds. 300. .sigma..pi.* Orthogonal intramolecular charge-transfer (OICT) excited states and photoreaction mechanism of trifluoromethyl-substituted phenyldisilanes

Abstract: Photophysical and photochemical properties of phenyldisilanes having a trifluoromethyl substituent on a benzene ring as one of the most suitable substituents for stabilization of the OICT (σπ * orthogonal intramolecular charge-transfer) state were investigated in detail. The OICT mechanism for CT fluorescence in nonpolar solvents was supported by the remarkable dependence of absorption and fluorescence spectra of trifluoromethyl-substituted phenyldisilanes on the dihedral angle between benzene pπ orbital and the SiSi a bond

On the use of conformationally dependent geometry trends from Ab Initio dipeptide studies to refine potentials for the empirical force field CHARMM

Abstract: Previous 4-21G ab initio geometry optimizations of various conformations of the model dipeptides (N-acetyl N'methyl amides) of glycine (GLY) and the alanine (ALA) have been used to help refine the empirical force constants and equilibrium geometry in the CHARMM force field for peptides. Conformationally dependent geometry trends from ab initio calculations and positions of energy minima on the ab initio energy surfaces have been used as guides in the parameter refinement, leading to modifications in the bond stretch, angle bending, and some torsional parameters. Preliminary results obtained with these refined empirical parameters are presented for the protein Crambin. Results for the cyclic (Ala-Pro-DPhe)2 are compared with those from other calculations. It seems that the dihedral angle fit achieved by the new parameters is significantly improved compared with results from force fields whose derivation does not include ab initio geometry trends.

Origin and consequences of steric strain in the rhodopsin binding pocket.

Abstract: To study the origin and the effects of steric strain on the chromophore conformation in rhodopsin, we have performed quantum-mechanical calculations on the wild-type retinal chromophore and four retinal derivatives, 13-demethyl-, 10-methyl-13-demethyl-, 10-methyl-, and 9-demethylretinal. For the dynamics of the whole protein, a combined quantum mechanics/molecular mechanics method (DFTB/CHARMM) was used and for the calculation of excited-state properties the nonempirical CASSCF/CASPT2 method. After relaxation inside the protein, all chromophores show significant nonplanar distortions from C10 to C13, most strongly for 10-methylretinal and least pronounced for 9-demethylretinal. In all five cases, the dihedral angle of the C10−C11C12−C13 bond is negative which attests to the strong chiral discrimination exerted by the protein pocket. The calculations show that the nonplanar distortion of the chromophore, including the sense of rotation, is caused by a combination of two effects: the fitting of both ends t...

The Conformations of 2-Phenylpropionaldehyde and Some Aliphatic Ketones. The Possible Importance of the CH/π and CH/n Interactions in Determining the Molecular Geometry of a Mobile System

Abstract: The conformations have been studied by means of NMR spectroscopy, largely by the computer simulation of the lanthanoid-induced shifts, for a series of aliphatic carbonyl compounds with the following structures: CH3CH(C6H5)CO–R; R=H, CH3, C2H5, i-C3H7, and t-C4H9. It has been suggested that two rotamers are important in the conformational equilibria of these ketones, in which the R–C–C–C6H5 dihedral angle is ca. 30° and ca. 90°. The relative stability of the above two rotamers has been found to depend on the nature of the alkyl group, R. The results have been discussed in light of the possible weak attractive forces, the CH/π and CH/n interactions.