Dihedral angle

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

Polysulfide anions II: structure and vibrational spectra of the S4(2-) and S5(2-) anions. Influence of the cations on bond length, valence, and torsion angle.

Abstract: The influence of the cations on bond length, valence, and torsion angle of S4(2-) and S5(2-) anions was examined in a series of solid alkali tetra- and pentasulfides by relating their Raman spectra to their known X-ray structures through a force-field analysis. The IR and Raman spectra of BaS4.H2O and the Raman spectra of (NH4)2S4.nNH3, gamma-Na2S4, and delta-Na2S5 are presented. The similarity of spectra of gamma-Na2S4 with those of BaS4.H2O suggests similar structures of the S4(2-) anions in these two compounds with a torsion angle smaller than 90 degrees. The variations of SS bond length, SSS valence angle, and dihedral angle of Sn2- anions are related to the polarization of the lone pair and electronic charge of the anion by the electric field of the cations. A correlation between the torsion angle and the SSS valence angle is shown as that previously reported between the length of the bond around which the torsion takes place and the dihedral angle value. These geometry changes are explained by the hyperconjugation concept and the electron long-pair repulsion.

Conformational Flexibility of Carbohydrates: A Folded Conformer at the φ Dihedral Angle of a Glycosidic Linkage

Abstract: The trisaccharide β-d-Glcp-(1→2)-β-d-Glcp-(1→3)-α-d-Glcp-OMe has been studied by Langevin dynamics (LD) simulations and NMR spectroscopy including measurement of transglycosidic 3JC,H coupling cons...

1H and 15N NMR assignment and solution structure of the SH3 domain of spectrin: comparison of unrefined and refined structure sets with the crystal structure.

Abstract: The assignment of the 1H and 15N nuclear magnetic resonance spectra of the Src-homology region 3 domain of chicken brain alpha-spectrin has been obtained. A set of solution structures has been determined from distance and dihedral angle restraints, which provide a reasonable representation of the protein structure in solution, as evaluated by a principal component analysis of the global pairwise root-mean-square deviation (rmsd) in a large set of structures consisting of the refined and unrefined solution structures and the crystal structure. The solution structure is well defined, with a lower degree of convergence between the structures in the loop regions than in the secondary structure elements. The average pairwise rmsd between the 15 refined solution structures is 0.71 +/- 0.13 A for the backbone atoms and 1.43 +/- 0.14 A for all heavy atoms. The solution structure is basically the same as the crystal structure. The average rmsd between the 15 refined solution structures and the crystal structure is 0.76 A for the backbone atoms and 1.45 +/- 0.09 A for all heavy atoms. There are, however, small differences probably caused by intermolecular contacts in the crystal structure.

New theoretical studies on the dihedral angle and energy barriers of biphenyl

Abstract: Using Hartree–Fock (HF), Moller–Plesset (MP2) and the B3LYP, B3PW91 and MPW1PW91 density functional (DF) methods, each combined with the 6-31G(d), 6-311G(d), 6-311+G(d), 6-311++G(d,p), cc-pVDZ amd cc-pVTZ basis sets, the geometry of biphenyl was optimized and the energy barriers at 0°, Δ E 0 , and 90°, Δ E 90 , were obtained. For the best basis sets (6-311++G(d,p) and cc-pVTZ), the DF methods lead to dihedral angles φ from 39 to 41° (44.4±1.2°) experimental), Δ E 0 's from 1.9 to 2.3 kcal/mol (the experimental estimate is 1.4±0.5 kcal/mol), and Δ E 90 's from 1.9 to 2.3 kcal/mol (the experimental estimate is 1.6±0.5 kcal/mol). With the MP2 method, however, the results depend drastically on the basis set. With cc-pVTZ, all three quantities are close to the DF values, but with the 6-311++G(d,p) basis set, φ is 47.7°, Δ E 0 4.4 kcal/mol and Δ E 90 1.6 kcal/mol. The MP2 method appears to show a trend towards a more coplanar conformation, expected for methods that include electron correlation, only with highly polarized basis sets.