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Dihedral angle

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


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TL;DR: In this paper, a soft mode has been observed in biphenylhl0 (hydrogenated) by Raman spectroscopy below T c = 40 K, corresponding to a doubling of b parameter only, and not to the doubling of a and b, as was found for p-terphenyl and p-quaterphenyl.
Abstract: Recently a soft mode has been observed in biphenylhl0 (hydrogenated) by Raman spectroscopy below T c = 40 K. The structural phase transition in biphenyld l0 (deuterated) has been investigated by neutron diffraction. Surprisingly, superlattice reflections appeared below 40 K, corresponding to a doubling of the b parameter only, and not to the doubling of a and b, as was found for p-terphenyl and p-quaterphenyl. The torsion angle between the planes of the phenyl groups is about 10 °, and is in opposite directions for two neighbouring molecules along b. The intensity of the superlattice reflections shows a linear behaviour with temperature, in agreement with Landau theory.

109 citations

Journal ArticleDOI
TL;DR: Comparison of LMP2-calculated inter-ring torsion potentials for a series of substituted stilbenes and bithiophenes to those calculated using standard classical force fields are compared and adjustments to the OPLS-2005 force field are implemented in order to improve its ability to model conjugated polymers.
Abstract: The modeling of the conformational properties of conjugated polymers entails a unique challenge for classical force fields. Conjugation imposes strong constraints upon bond rotation. Planar configurations are favored, but the concomitantly shortened bond lengths result in moieties being brought into closer proximity than usual. The ensuing steric repulsions are particularly severe in the presence of side chains, straining angles, and stretching bonds to a degree infrequently found in nonconjugated systems. We herein demonstrate the resulting inaccuracies by comparing the LMP2-calculated inter-ring torsion potentials for a series of substituted stilbenes and bithiophenes to those calculated using standard classical force fields. We then implement adjustments to the OPLS-2005 force field in order to improve its ability to model such systems. Finally, we show the impact of these changes on the dihedral angle distributions, persistence lengths, and conjugation length distributions observed during molecular dy...

109 citations

Journal ArticleDOI
TL;DR: In this article, a survey of over 50 crystal structures indicates that both imino acid and peptide derivatives of proline populate ring conformers consistent with the torsional potentials about single bonds.
Abstract: A survey of over 50 crystal structures indicates that both imino acid and peptide derivatives of proline populate ring conformers consistent with the torsional potentials about single bonds. In both cases, lower barriers for rotation about CN bonds relative to those about CC bonds favor smaller values for dihedral angles about the former bonds. In peptides a minimum in the torsional potential about CN bonds occurs at zero dihedral angle, further favoring small angles. The pyrrolidine-ring dihedral angles of the proline compounds in the solid state obey a cyclopentane-type pseudorotation function. Thus the puckering of the five-membered ring can be quantitatively described by two parameters. Consistent with small dihedral angles about CN bonds, Cβ and/or Cγ are puckered out of the mean plane of the ring in nearly all of the nonstrained compounds. Utilizing the consistent force-field method of Lifson and coworkers [see A. Warshel, M. Levitt, and S. Lifson (1970) J. Mol. Spectrosc.33, 84] the intramolecular energy of five proline peptides was minimized with respect to all internal coordinates. In addition, the energy surface near minima was explored by constraining a particular dihedral angle and reminimizing the energy with respect to all remaining variables. In linear peptides two types of pyrrolidine-ring conformers have identical predicted energies. In the cyclic dipeptide cyclo (Pro-Gly) one of the ring conformers is favored by about 3 kcal/mol, while the cyclic tripeptide cyclo(Pro-Gly-Gly) favors the other conformer by a comparable margin. In agreement with observations in the solid state and in solution, Cβ and/or Cγ are puckered in the predicted conformers. A correlation between proline Φ and the details of the puckered conformation was predicted and found to match precisely conformers observed in crystals. For the diamides N-acetyl-L-proline-N′-methyl-amide and N-acetyl-L-proline-N′,N′-dimethylamide (AcProMe2A) 30% and 60% cis acetyl peptide bonds were predicted in good agreement with observations in nonpolar solvents for the respective compounds. The conformational distributions with respect to proline Ψ are also in accord with experimental observations. For AcProMe2A, a model for a -Pro-Pro-sequence in a peptide chain, this study is the first to predict stable conformers for proline Ψ either ca. −50° or 140° for both cis and trans peptides.

109 citations

Journal ArticleDOI
TL;DR: The relative orientation of the two magnetic orbitals, the CuII d’ x 2-y‬2 orbital and the half-occupied π orbital of the tyrosyl radical, is the key to answering the question in the title.
Abstract: The relative orientation of the two magnetic orbitals, the CuII d x 2-y 2 orbital and the half-occupied π orbital of the tyrosyl radical, is the key to answering the question in the title. The arrangement shown (CuII -O-C bond angle of about 130° and a dihedral angle of about 90° between the x,y plane of the CuII polyhedron and the tyrosyl ring plane) leads to an overlap of the orbitals, which results in a singlet ground state.

109 citations

Journal ArticleDOI
TL;DR: In this paper, the frequency of the so-calledamide I band (amide C=O stretching vibration, vC=O) of proteins is discussed in terms of the dihedral angles of the various secondary structures present within proteins.
Abstract: The frequency of the so-called "amide I" band (amide C=O stretching vibration, vC=O) of proteins is discussed in terms of the dihedral angles of the various secondary structures present within prot...

108 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023203
2022473
2021160
2020195
2019193
2018216