Dihedral angle

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

Inorganic–organic hybrid compounds based on face-sharing octahedral [PbI3]∞ chains: self-assemblies, crystal structures, and ferroelectric, photoluminescence properties

Abstract: Eight inorganic–organic hybrid compounds with a formula of [R-Bz-1-APy][PbI3] (R-Bz-1-APy+ = mono-substituted benzylidene-1-aminopyridinium Schiff base derivative; R = m-CN (1), m-CH3 (2), H (3), p-F (4), p-Cl (5), p-Br (6), o-Cl (7), o-Br (8)) have been synthesized and characterized structurally. The common characteristic of the crystal structures of 1–8 is that the inorganic components form straight and face-sharing octahedral [PbI3]∞ chains and the Schiff base cations surround the [PbI3]∞ chains to form molecular stacks. The substituent (R) on the phenyl ring of the Schiff base cation clearly influences the packing structures of 1–8, and the hybrid compound crystallizes in the space groupP63 when R = CN (1) in the meta-position of the phenyl ring, and in a central symmetric space group when R is in the ortho- or para-position of the phenyl ring. The conformation of the Schiff base cation is related to the R position, and the dihedral angle between the phenyl and pyridyl rings increases in the order of para- < meta- < ortho-position substitution of the phenyl ring. The long molecular axis of the Schiff base cation adopts a manner approximately parallel to the straight inorganic [PbI3]∞ chain in the para-substituted hybrid compounds, and perpendicular to the straight inorganic [PbI3]∞ chain in the ortho-substituted hybrid compounds. 1 is second harmonic generation (SHG) active with a comparable response as that of urea and also exhibits ferroelectricity with larger Ps and Pr values; 1–8 emit multi-band luminescence in the 300–650 nm regions under the excitation of ultraviolet light.

The NMR solution structure of the pheromone Er-11 from the ciliated protozoan Euplotes raikovi.

Abstract: The 3-dimensional structure of the pheromone Er-1 isolated from the ciliated protozoan Euplotes raikovi has been determined in aqueous solution by 1H NMR spectroscopy. The structure of this 40-residue protein was calculated with the distance geometry program DIANA on the basis of 503 upper distance constraints derived from nuclear Overhauser effects and 77 dihedral angle constraints derived from spin-spin coupling constants, and refined by restrained energy minimization with the program OPAL. The Er-1 solution structure is represented by a group of 20 conformers with an average RMS deviation relative to the mean structure of 0.55 A for the backbone atoms N, C alpha, and C', and 0.93 A for all heavy atoms of the complete polypeptide chain, residues 1-40. The molecular architecture is dominated by an up-down-up bundle of 3 alpha-helices formed by residues 2-9, 12-19, and 24-33. Although this core part coincides closely with the previously determined structure of the homologous pheromone Er-10, the C-terminal peptide segment adopts a novel conformation. This is of interest in view of previous suggestions, based on sequence comparisons, that this molecular region may be important for the different specificity of receptor recognition by different pheromones.

Infrared Spectra and Photochemistry of Matrix-Isolated Pyrrole-2-carbaldehyde

Abstract: Monomeric pyrrole-2-carbaldehyde (P2C) was isolated in low-temperature argon and xenon matrices, and its UV-induced photochemistry was studied. The structures of the reagent as well as the reaction photoproducts were characterized by FTIR spectroscopy. Interpretation of the experimental results was assisted by theoretical calculations carried out at the MP2 and DFT (B3LYP) levels with the 6-311++G(d,p) basis set. The compound can assume two conformations, cis and trans, regarding the orientation of the N-C-CdO dihedral angle. The cis form is the conformational ground state, being more stable than the trans by ca. 15 kJ mol -1 . The relative stability of the two conformers was analyzed based on the comparison of their structures and using the natural bond orbital method. In agreement with the calculations, only the signature of the cis conformer was found in the experimental FTIR spectra of matrix-isolated P2C monomers. UV irradiation (λ > 235 nm) readily converts the cis-P2C into the trans-P2C form, and a photostationary equilibrium is established where the [cis]/[trans] ratio is ca. 3.3:1 in both Ar and Xe. Upon prolonged irradiation, P2C slowly undergoes photolysis to [pyrrole + CO]. In matrices, pyrrole and CO form associates of different geometry, which could be characterized based on their vibrational signatures.

Solution structure of phenol hydroxylase protein component p2 determined by nmr spectroscopy

Abstract: Phenol hydroxylase from Pseudomonas sp. CF600 is a member of a family of binuclear iron-center-containing multicomponent oxygenases, which catalyzes the conversion of phenol and some of its methyl-substituted derivatives to catechol. In addition to a reductase component which transfers electrons from NADH, optimal turnover of the hydroxylase requires P2, a protein containing 90 amino acids which is readily resolved from the other components. The three-dimensional solution structure of P2 has been solved by 3D heteronuclear NMR spectroscopy. On the basis of 1206 experimental constraints, including 1060 distance constraints obtained from NOEs, 70 phi dihedral angle constraints, 42 psi dihedral angle constraints, and 34 hydrogen bond constraints, a total of 12 converged structures were obtained. The atomic root mean square deviation for the 12 converged structure with respect to the mean coordinates is 2.48 A for the backbone atoms and 3.85 A for all the heavy atoms. This relatively large uncertainty can be ascribed to conformational flexibility and exchange. The molecular structure of P2 is composed of three helices, six antiparallel beta-strands, one beta-hairpin, and some less ordered regions. This is the first structure among the known multicomponent oxygenases. On the basis of the three-dimensional structure of P2, sequence comparisons with similar proteins from other multicomponent oxygenases suggested that all of these proteins may have a conserved structure in the core regions.