Dihedral angle

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

Helix-coil transitions of amino-acid homo-oligomers in aqueous solution studied by multicanonical simulations

Abstract: Helix-coil transitions of homo-oligomers in aqueous solution are studied by multicanonical Monte Carlo simulations. The solvation effects are represented by the sum of the terms that are proportional to the solvent-accessible surface area of the atomic groups. Homo-oligomers of length 10 are considered for three characteristic amino acids, alanine, valine, and glycine, which are helix former, helix indifferent, and helix breaker, respectively. We calculated as a function of temperature the distributions of the backbone dihedral angles, the average values of total energy, and its component terms of the homo-oligomers. It is shown that for homo-alanine, the helix-coil transition exists and that the transition temperature in water is considerably lower than in gas phase, which implies that the effects of solvation tend to reduce helical content. Moreover, the helix propagation parameter s and nucleation parameter σ of the Zimm-Bragg model were calculated. The s values that were obtained from the simulations in aqueous solution are in remarkable agreement with the experimental results.

Molecular Theory of the Helix‐Coil Transition in Polyamino Acids. II. Numerical Evaluation of s and σ for Polyglycine and Poly‐l‐alanine in the Absence (for s and σ) and Presence (for σ) of Solvent

Abstract: The Zimm–Bragg parameters s and σ for the helix‐coil transition in polyglycine and poly‐l‐alanine are calculated in terms of molecular quantities, based on our earlier formulation which is modified here to take effects at junctions between helical and coil sequences into account more properly The statistical weight of a helical sequence is computed for both regular and nonregular helices In the latter, the dihedral angles φ and ψ (and χ for alanine) near the ends of helical sequences differ from those in the interior; this diffuseness, which extends over about five residues at each end, reduces the values of σ by a factor of 1000−1008 The dihedral angles and the corresponding conformational energies of both regular and nonregular helices are obtained by energy minimization The entropy factor in the statistical weight of a helical sequence consisting of j residues [(j + 1) peptide units] is obtained from the second derivatives of the energy surface in the 2j‐dimensional space for both regular and non

New 6,6′-disubstituted-binaphthol derivatives as chiral dopants: Synthesis and temperature dependence of molecular conformations

Abstract: A number of new chiral binaphthol (BN) derivatives with different substituents R,R′ in the 6,6′-positions in open (BN-diethylethers) and bridged forms (BN-acetals) have been synthesized. The syntheses of the chiral 6,6′-disubstituted-2,2′-diethoxy-1,1′-binaphthyls (R,R′ = -CH'CHCHO, -CH'CH-(p-BrPh), -CH'CH-(p-CHOPh)) and the chiral 9,14-disubstituted-dinaphtho [2,1-d:1′,2′-f][1,3] dioxepins with R,R′ = -CH'CH-(p-BrPh), -CH'CH-(p-CHOPh) are reported for the first time. The possible liquid crystalline properties and molar twisting powers (βM) in three different nematic liquid crystals (LCs) of the BN derivatives were investigated. Derivatives with spatially extended substituents in the 6,6′-positions (e.g. styryl or vinyl) show unusually high molar twisting power (up to 124.5μm−1). A direct correlation between the magnitude of βM and the length of the substituents was found. Bridged forms, in which the dihedral angle θ between the naphthyl moieties is ≊ 54°, show higher twisting power than the corr...