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81.
A method is presented to reduce the memory requirement of normal mode analysis applied to systems containing two or more large proteins when these systems exhibit symmetry properties. We use a rigid geometry model (i.e., only the dihedral angles of the polypeptide chain are considered as variables). This model allows a reduction by a factor of 8 on average of the number of variables with a concomitant freezing of the high-frequency modes. The symmetry properties of the system are used to reduce further the number of variables that must be considered in the computation. Application of group theory leads to a factorization of the matrices of interest (the coefficient and the Hessian matrices) into independent blocks along the diagonal. The initial, reducible representation is thus transformed into a number of irreducible representations of smaller dimensions. In the case of the C2 symmetry group, the method leads to a reduction of the size of the matrices that must be manipulated during the computation (coefficient matrix, Hessian matrix, and eigenvectors matrix) by a factor of 256 compared with the usual normal mode analysis in Cartesian coordinate space. The method is particularly well adapted to the study of the dynamics of oligomeric proteins because these proteins often display symmetry properties (e.g., virus coat proteins, immunoglobulins, hemoglobin, etc.). In favorable cases, in conjunction with X-ray diffuse scattering data, the study of systems showing allosteric properties might be considered. © 1994 by John Wiley & Sons, Inc. 相似文献
82.
Ludovic Jean 《Tetrahedron letters》2006,47(13):2141-2145
The first systematic screening of chiral phosphines in the cycloaddition reaction between 2,3-butadienoates and arylimines has led to the identification of fairly efficient catalysts. 2-Aryl-3-pyrrolines have been obtained with enantiomeric excesses up to 64%. In one instance, the enantiomeric excess could be increased to 91% ee by combining the enantioselective cyclization reaction with a crystallization step. 相似文献
83.
Jean M. J. Tronchet Bernard Gentile Alain P. Bonenfant Olivier R. Martin 《Helvetica chimica acta》1979,62(3):696-699
Further examples of O-isopropylidenaldehydosugars in the furanose series Formyl-bearing furanose derivatives 1–3 (α-D -xylo or α-D -erythro configurations) and 5–8 (configurations α-D -ribo, α-D -lyxo, β-L -threo and D -arabino) have been prepared by classical synthetic steps and their properties mainly spectroscopic, reported. The coupling constant between the formyl and the vicinal proton is always small. Like other members of the series, these new aldehydosugars constitute very useful and flexible synthetic intermediates. 相似文献
84.
Marfisi S Rodríguez MP Alvarez G Celis MT Forgiarini A Lachaise J Salager JL 《Langmuir : the ACS journal of surfaces and colloids》2005,21(15):6712-6716
Commercial ethoxylated nonionic surfactant mixtures containing alcohol cosurfactant exhibit a three-phase behavior whose formulation strongly varies with the water/oil ratio. As a consequence, a change in water/oil ratio can result in a sequence of up to three different emulsion inversion processes, through a combination of formulation and composition effects. 相似文献
85.
We describe a versatile, efficient method for the preparation of ether analogues of (S,S)-lysobisphosphatidic acid (LBPA) and its enantiomer from (S)-solketal. Phosphorylation of a protected sn-2-O-octadecenyl glyceryl ether with 2-cyanoethyl bis-N,N-diisopropylamino phosphine and subsequent deprotection generated the bisether LBPA analogues. By simply changing the sequence of deprotection steps, we obtained the (R,R)- and (S,S)-enantiomers of 2,2'-bisether LBPA. An ELISA assay with anti-LBPA monoclonal antibodies showed that the bisether LBPAs were recognized with the same affinity as the natural 2,2'-bisoleolyl LBPA. [reaction: see text] 相似文献
86.
Bosman AW Vestberg R Heumann A Fréchet JM Hawker CJ 《Journal of the American Chemical Society》2003,125(3):715-728
A new strategy for the preparation of functional, multiarm star polymers via nitroxide-mediated "living" radical polymerization has been explored. The generality of this approach to the synthesis of three-dimensional macromolecular architectures allows for the construction of nanoscopically defined materials from a wide range of different homo, block, and random copolymers combining both apolar and polar vinylic repeat units. Functional groups can also be included along the backbone or as peripheral/chain end groups, thereby modulating the reactivity and polarity of defined portions of the stars. This modular approach to the synthesis of three-dimensional macromolecules permits the application of these tailored materials as multifunctional hosts for hydrogen bonding, nanoparticle formation, and as scaffolds for catalytic groups. Examples of applications of the functional stars in catalysis include their use in a Heck-type coupling as well as an enantioselective addition reaction. 相似文献
87.
E. M. Azaroual P. Luc R. Vetter 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1992,24(2):161-164
The use of an effusive beam of titanium atoms crossed with a CW single-mode tunable dye laser has allowed the high-resolution, Doppler-free study of the isotope shifts between50Ti,48Ti and46Ti, for seven 3d
2 4s
2 a3
F
J
3d
2 4s 4p z
5
D
J
, visible transitions of Ti I. The measurements show without ambiguity the existence of a non-negligible field shift. Using the values of the nuclear radii of titanium (coming from muonic X-ray measurements), it is possible to determine the respective values of the field and mass shifts. 相似文献
88.
Hans‐Ruedi Mürner Rosario Scopelliti Jean‐Claude G. Bünzli 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(8):m434-m435
In the title compound, [TbCl(C27H35N3)2(H2O)](ClO4)2·2C2H6O, the TbIII ion has a coordination number of eight, composed of two tridentate substituted‐terpyridine ligands, a water molecule and a bound Cl? anion. The first coordination shell can be described as a distorted bicapped trigonal prism. The dihedral angles between pyridine rings belonging to the same tpy ligand range from 5.2 (5) to 16.8 (5)°. 相似文献
89.
Regioselectivite de la reaction des dialkyl cuprates de magnesium sur des aldehydes α,β-ethyleniques
Monique Bourgain-Commerçon Jean-Pierre Foulon Jean François Normant 《Journal of organometallic chemistry》1982,228(3):321-326
Various magnesium organocuprates give conjugative addition products with α,β-ethylenic aldehydes, and even with acrolein. The enolates may be trapped with bromine or trimethylsilyl chloride. 相似文献
90.
The ultraviolet absorption spectrum of the neopentyl peroxy radical (CH3)3CCH2O2, and the kinetics and products of its self reaction have been studied in the gas phase at 298 K. Absorption cross sections were quantified over the wavelength range 230–290 nm. The measured cross section at 250 nm was; Errors represent statistical (2σ) together with our estimate of potential systematic errors(15%). The kinetics of the decay of the UV absorption following the generation of the neopentyl peroxy radicals was complicated by the rapid decomposition of the (CH3)3CCH2O radicals formed in channel (4a). By measuring the yield of t-butyl peroxy radicals, the branching ratio k4a/(k4a + k4b) was determined to be 0.39 ± 0.03. The rate constant for the self reaction of neopentyl peroxy radicals was k4 = (1.07 ± 0.22) × 10?12 cm3 molecule?1 s?1. Quoted errors represent 2σ. These results are discussed with respect to the available literature data. © John Wiley & Sons, Inc. 相似文献