Topic
Dihedral angle
About: Dihedral angle is a research topic. Over the lifetime, 15718 publications have been published within this topic receiving 174904 citations.
Papers published on a yearly basis
Papers
More filters
TL;DR: In this paper, the structures of the [Ru(CO) 2 (μ-OOCCH 3 )L} 2 ] with L = P n Bu 3, P t Bu 3 or P i Pr 3 have been determined and their catalytic activity tested in the hydrogenation of internal and terminal olefins, of the carbonyl double bond and of both free and esterified carboxylic groups.
66 citations
TL;DR: This research demonstrates that stable isotope labeling provides specific advantages for the NMR investigation of paramagnetic molecules, as the small magnetic moment of heteronuclei minimizes the paramagnetic influence of unpaired electrons.
Abstract: The reduced high-potential iron sulfur protein I from Ectothiorhodospira halophila which contains the [4Fe-4S]2+ polymetallic center has been fully labeled with 15N and 13C. The protein is paramagnetic, the nuclear relaxation times of nuclei close to the paramagnetic ion are drastically shortened and some strategic dipolar connectivities are lost. Notwithstanding, the solution structure has been reported [Banci, L., Bertini, I., Eltis, L. D., Felli, I. C., Kastrau, D. H. W., Luchinat, C., Piccioli, M., Pierattelli, R. & Smith, M. (1994)Eur. J. Biochem. 225, 715–7251. We have performed classical HNHA, HNCA soft-COSY, soft-HCCH E. COSY and 15N-1H correlated NOESY experiments in order to obtain a set of 3J scalar coupling constants. Some experiments have been optimized to counterbalance the effect of paramagnetism. From heteronuclear single-quantum experiments preceded by a 180° pulse and variable delay times, the non-selective magnetization recovery has been followed from which the contribution to dipolar relaxation of nuclei due to the interaction with the paramagnetic metal ions (pppara) has been estimated. Finally, the intensities of NOEs have been corrected for the presence of paramagnetic metal ions and these corrected values together with 3J values and φpara data have been used to obtain a well defined solution structure. The aim is that of obtaining a structure with enough constraints to be well resolved all over the protein, including the vicinity of the paramagnetic metal cluster, which is anchored to the protein through the φpara constraints. In total, 1226 corrected NOESY crosspeaks (of which 945 were found to be meaningful), 37 one-dimensional NOEs,39 3JHNHα and 37 3JHNC′ (providing 45 φ dihedral angle constraints) 54 3JHαHβ and 31 3JNHβ (providing 26 χ1 dihedral angle constraints), 4 χ2 dihedral angle constraints of the coordinated cysteines, obtained from the hyperfine shifts of the βCH protons, and 58 φpara constraints, have been used for structure calculation. Restrained molecular dynamics simulations have also been performed to provide the final family of structures. This research demonstrates that stable isotope labeling provides specific advantages for the NMR investigation of paramagnetic molecules, as the small magnetic moment of heteronuclei minimizes the paramagnetic influence of unpaired electrons.
66 citations
TL;DR: In this article, a preliminary analysis has been performed for a sample of magnesia based on a three-parameter description of grain boundaries using an extended form of orientation imaging microscopy (OIM) and electron back scatter diffraction.
Abstract: Measurement of the geometry of triple junctions between grain boundaries in polycrystalline materials generates large sets of dihedral angles from which maps of the grain boundary energy may be extracted. A preliminary analysis has been performed for a sample of magnesia based on a three-parameter description of grain boundaries. An extended form of orientation imaging microscopy (OIM) was used to measure both triple junction geometry via image analysis in the SEM and local grain orientation via electron back scatter diffraction. Serial sectioning with registry of both in-plane images and successive sections characterizes triple junction tangents from which true dihedral angles are calculated. We apply Herring's relation at each triple junction, based on the assumption of local equilibrium at the junction. By limiting grain boundary character to a (three parameter) specification of misorientation for the preliminary analysis, we can neglect the torque terms and apply the sine law to the three boundaries. This provides two independent relations per triple junction between grain boundary energies and dihedral angles. Discretizing the misorientation and employing multiscale statistical analysis on large data sets allows (relative) grain boundary energy as a function of boundary character to be extracted from triple junction geometry. A similar analysis of thermal grooves allows the anisotropy of the surface energy to be measured in MgO.
66 citations
TL;DR: The solution structure of the 39-residue peptide margatoxin, a scorpion toxin that selectively blocks the voltage-gated potassium-channel Kv1.3, has been determined by NMR spectroscopy.
Abstract: The solution structure of the 39-residue peptide margatoxin, a scorpion toxin that selectively blocks the voltage-gated potassium-channel Kv1.3, has been determined by NMR spectroscopy. The toxin was isotopically labeled with 13C and 15N and studied using two-dimensional homonuclear and three- and four-dimensional heteronuclear NMR spectroscopy. The final structure was determined using 501 constraints, comprising 422 NOE constraints, 60 dihedral angle constraints, 9 disulfide constraints, and 10 hydrogen bond constraints. Structures were initially determined with the program PEGASUS and subsequently refined with X-PLOR. The average rms deviation from a calculated average structure for the backbone atoms of residues 3-38 is 0.40 A. A helix is present from residues 11 to 20 and includes two proline residues at positions 15 and 16. A loop at residues 21-24 leads into a two-strand antiparallel sheet from residues 25 to 38 with a turn at residues 30-33. Residues 3-6 run adjacent to the 33-38 strand but do not form a canonical beta-strand. The two additional residues of margatoxin, relative to the related toxins charybdotoxin and iberiotoxin, insert in a manner that extends the beta-sheet by one residue. Otherwise, the global structure is very similar to that of these two other toxins. The longer sheet may have implications for channel selectivity.
65 citations
TL;DR: In this paper, three dinuclear complexes were prepared in which Cr(CO) 2 (PPh 3 ) moieties are connected through biphenyl linkages, and each monocation was shown by IR spectroscopy to be trapped-valent.
Abstract: Three dinuclear complexes were prepared in which Cr(CO) 2 (PPh 3 ) moieties are connected through biphenyl linkages. The dihedral (twist) angle of the two arenes in the biphenyl decreases from 100 to 17 to 0 o as the bridging ligand is changed from biphenyl-2,2'-dicarboxylic acid dimethyl ester to dihydrophenanthrene to fluorene. All three compounds are oxidized in two reversible one-electron steps with a voltage separation of ca. 260 mV. Each monocation is shown by IR spectroscopy to be trapped-valent. ESR spectroscopy in frozen glasses gives the same result. IR sampling of the dications is achieved by low-temperature flow electrochemical experiments
65 citations