Dihedral angle

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

Influence of conformation on conductance of biphenyl-dithiol single-molecule contacts.

Abstract: The conductance of a family of biphenyl-dithiol derivatives with conformationally fixed torsion angle was measured using the scanning tunneling microscopy (STM)-break-junction method. We found that it depends on the torsion angle φ between two phenyl rings; twisting the biphenyl system from flat (φ = 0°) to perpendicular (φ = 90°) decreased the conductance by a factor of 30. Detailed calculations of transport based on density functional theory and a two level model (TLM) support the experimentally obtained cos2 φ correlation between the junction conductance G and the torsion angle φ. The TLM describes the pair of hybridizing highest occupied molecular orbital (HOMO) states on the phenyl rings and illustrates that the π−π coupling dominates the transport under “off-resonance” conditions where the HOMO levels are well separated from the Femi energy.

Influence of anionic ligands (X) on the nature and magnetic properties of dinuclear LCuDgX3.nH2O complexes (LH2 standing for tetradentate Schiff base ligands deriving from 2-hydroxy-3-methoxybenzaldehyde and X being Cl, N3C2, and CF3COO).

Abstract: The monometallic precursor L1Cu (L1H2 standing for 1,3-bis((3-methoxysalicylidene)amino)-2,2'-dimethylpropane) reacts with GdC13 x 6H2O to afford a dinuclear complex which crystallizes in the orthorhombic space group Pca2(1) (No. 29) in a cell having the dimensions a = 9.0246(11) A, b = 16.5198(14) A, c = 20.286(2) A, and Z = 4. Analysis of the structural data shows that it may be formulated as [L1CuCl2Gd(H2O)4]Cl x 2H2O. The cationic dinuclear unit possesses a CuO2Gd bridging core which is almost planar. The complex displays a ferromagnetic interaction (10.1 cm(-1) which is the largest yet reported for a structurally characterized dinuclear (Cu-Gd) complex. Lower magnetic interactions are observed for neutral L1CuGdX3 x H2O complexes (X = N3C2, CF3COO). Consideration of the magnetic and structural data obtained for various dinuclear (Cu-Gd) complexes leads to a correlation between the magnitude of the magnetic interaction and the exponential of the dihedral angle between the two halves of the CuO2Gd bridging core.

Molecular dynamics simulation of a smectic liquid crystal with atomic detail

Abstract: A molecular dynamics simulation of a sodium–decanoate/decanol/water system is reported. The system is treated in full atomic detail, with the exception of CH2 and CH3 groups that are considered to be ‘‘united atoms,’’ and is a refinement of a previous model membrane [Mol. Phys. 11, 1 (1983)]. The long‐range Coulomb interactions were included specifically. The order parameters of the chain units of the lipids and diffusion constants of components in the system calculated from the simulation agree well with those reported in experiments on this model membrane. The overall structure of the membrane shows considerable disorder, with a broad lipid–water interface, extending over approximately 1 nm. The distribution of the components is such that an almost complete charge cancellation occurs throughout the system, which is in contradiction with the generally assumed electrical double layer structure for membranes. A counterion condensation of 70% is observed. Both the translational and the rotational motions of water are slowed down compared to bulk water. The penetration of water into the hydrocarbon region of the membrane is substantial. Pair correlations of various atom pairs, and dihedral statistics and transition rates of the dihedrals in the lipids are reported. The distributions of chain segments of the lipids, of water molecules, and of sodium ions are compared with theoretical predictions.

Evaluation of backbone proton positions and dynamics in a small protein by liquid crystal NMR spectroscopy.

Abstract: NMR measurements of a large set of protein backbone one-bond dipolar couplings have been carried out to refine the structure of the third IgG-binding domain of Protein G (GB3), previously solved by X-ray crystallography at a resolution of 1.1 A. Besides the commonly used bicelle, poly(ethylene glycol), and filamentous phage liquid crystalline media, dipolar couplings were also measured when the protein was aligned inside either positively or negatively charged stretched acrylamide gels. Refinement of the GB3 crystal structure against the 13Cα−13C‘ and 13C‘−15N dipolar couplings improves the agreement between experimental and predicted 15N−1HN as well as 13Cα−1Hα dipolar couplings. Evaluation of the peptide bond N−H orientations shows a weak anticorrelation between the deviation of the peptide bond torsion angle ω from 180° and the angle between the N−H vector and the C‘−N−Cα plane. The slope of this correlation is −1, indicating that, on average, pyramidalization of the peptide N contributes to small devi...

Structural Genealogy of BEDT-TTF-Based Organic Conductors II. Inclined Molecules: θ, α, and κ Phases

Abstract: Overlap integrals between HOMO’s of two non-parallel BEDT-TTF (bis(ethylenedithio)tetrathiafulvalene) molecules have been calculated. As the dihedral angle between the molecular planes decreases fr...