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181.
Bagiyan G. A. Koroleva I. K. Soroka N. V. Ufimtsev A. V. 《Russian Chemical Bulletin》2003,52(5):1135-1141
Side self-oxidation of thiols was studied. It was found that these reactions in neutral and alkaline solutions are induced by impurities of variable-valence metals. The ability of transition metals to catalyze oxidation of thiols changes in the order Cu > Mn > Fe > Ni Co. The plot of the self-oxidation rate vs. pH passes through a maximum whose position on the pH scale depends on both the nature of metal and the structure of the thiol oxidized. For thiols having different structures, the kinetic orders in reactions catalyzed by copper ions differently vary with pH, which is apparently associated with the formation of complexes possessing different catalytic activity. 相似文献
182.
183.
Using Monte Carlo molecular dynamics, a new, careful study is made of the approach of the trajectory of a typical particle in a hard sphere fluid to that of a Brownian particle, discussed before by Powles and Quirke and Rapaport. The apparent fractal dimension of the trajectory, as a function of reduced length scale,(), characterizes the transition from mechanical to Brownian motion and differs markedly from 2 in all present computer simulations. 相似文献
184.
We use a driving field, of the type first suggested by Evans, to generate a steady heat current in the simplest possible system, a two-dimensional periodic fluid of three hard disks. Hard-disk motion equations can be conveniently derived from repulsive constant-force or linear-force potentials by considering the infinitely repulsive limit of these potentials. We show that the isoenergetic and isokinetic forms of the nonequilibrium equations of motion generate steady-state heat conductivities differing by terms of order 1/N, whereN is the number of particles. The resulting conductivities appear to vary as the logarithm of the driving field strength. Even at low fields, the three-body periodic-system results lie well below Enskog's infinite-system prediction. 相似文献
185.
186.
Sevim?Hamamci Veysel?T.?YilmazEmail author William?T.?A.?Harrison 《Structural chemistry》2005,16(4):379-383
The first silver(I) complex of saccharinate (sac) with pyridine (py), [Ag(sac)(py)]n has been synthesized and characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffractometry. The complex crystallizes in chiral, trigonal space group P3121 (No. 152) with unit cell parameters of a = 11.2605(2) Å, c = 17.3300(4) Å, V = 1903.02(6) Å3 and Z = 6. [Ag(sac)(py)]n contains monomeric [Ag(sac)(py)] units linked into infinite helices by way of Ag⋅sAg interactions [d(Ag⋅sAg) = 2.909(2) and 2.985(1) Å]. The distorted square-planar environment of Ag is completed by an N-bonded sac [Ag—N = 2.084(2) Å] and a py molecule [Ag—N = 2.116(2) Å]. The Nsac—Ag—Npy angle is 173.85(10)∘. The one-dimensional chains are crosslinked by C—H⋅sO interactions involving the carbonyl and sulfonyl O atoms of sac and aromatic-ring hydrogen atoms of both sac and py. The thermal stability of the title complex was investigated using thermogravimetry and differential thermal analysis in a static atmosphere of air. The first decomposition stage between 90 and 160∘C corresponds to removal of the py molecule in a single stage, while the degradation of the sac moiety occurs at two stages in the temperature range 370–515∘C, giving an end product of metallic Ag. 相似文献
187.
Elisa Brivio Alessandro Ceriotti Roberto Della Pergola Luigi Garlaschelli Mario Manassero Mirella Sansoni 《Journal of Cluster Science》1995,6(2):271-287
Redox condensation of [Ru3H(CO)11]- with Ni(CO)4, in tetrahydrofuran solution, under a nitrogen atmosphere, yields the tetranuclear anion [NiRuH(CO)11)-. Subsequent deprotonation with Bu'OK in acetonitrile solution leads to the formation of the related dianion. Both anions have been characterized by spectroscopic techniques, elemental analysis and single crystal X-ray diffraction. [PPh4][NiRu3H(CO)12] crystallizes in the triclinic space group PI with unit cell dimensionsof a = 11.842(2) Å,b = 12.335(3) Å, c = 13.3080) Å,a = 91.89(2)°, = 93.35(1)°,y = 96.41(2)°, Z = 2, V= 1926.9(7) Å'. The NiRu3, metal core of the molecule defines a distorted tetrahedron with nine terminal and three edge bridging carbonyl groups. The hydrido ligand was located by difference Fourier techniques and was found to bridge the NiRu2 basal triangle at a distance of 0.88(6) A from this plane. Selected average distances and angles are: Ru-Ru = 2.839 Å, Ru-Ni = 2.640 Å, Ru-C, = 1.910 A,Ru-C
b
= 2.084 Å, Ni-C
b
= 2.022 Å, Ru-H = 1.77 Å, C-0, = 1.135 Å, C-O
b
= 1.159 Å, M-C-O, = 176.3°,M-C--O
b
= 139.3°;other distances are: Ni-C1 = l.758(7) Å, Ni-H= 1.85(7) Å. [NEt4]2[NiRu3(CO)12] crystallizes in the orthorhombic space group Pnma (no. 62) with unit cell dimensions ofa=20.247(5) Å,b = 15.038(4)Å,c = 12.079(3) Å, Z=4, V=3678(2) A'. The molecule contains a tetrahedral NiRu3 core with eight terminal and four edge bridging carbon monoxide groups which bridge the three Ni-Ru and one Ru-Ru bond. Average distances and angles are: Ru -Ru =2.3050A Ru-Ni 2.648 Å, Ru-C
t
= 1.878 Å, Ru-C
b
2.045 Å, Ni-C
b
= 2.055 Å, C-O
t
= 1.145 Å, C-01,=1.157 Å, M-C-O,= 176.9°, M-C-O
b
= 138.6°; other distance is: Ni-C
t
= 1.754(10) Å,t = terminal,b = bridging. 相似文献
188.
José Glaüco Ribeiro Tostes 《Theoretical chemistry accounts》1981,59(3):229-235
Certain features of the chemist's molecular structure model, viz. size and shape, are retrieved even in the best non-adiabatic variational calculations thus far carried out for ground states of H
2
+
and H2. Those features do not conflict with the full symmetry of exact molecular eigenstates, once they are properly understood as correlation effects. 相似文献
189.
Parameterization of peptide 13C carbonyl chemical shielding anisotropy in molecular dynamics simulations. 总被引:1,自引:0,他引:1
Daniel M Jordan K Maria Mills Ioan Andricioaei Akash Bhattacharya Kim Palmo Erik R P Zuiderweg 《Chemphyschem》2007,8(9):1375-1385
NMR chemical shielding anisotropy (CSA) relaxation is an important tool in the study of dynamical processes in proteins and nucleic acids in solution. Herein, we investigate how dynamical variations in local geometry affect the chemical shielding anisotropy relaxation of the carbonyl carbon nucleus, using the following protocol: 1) Using density functional theory, the carbonyl (13)C' CSA is computed for 103 conformations of the model peptide group N-methylacetamide (NMA). 2) The variations in computed (13)C' CSA parameters are fitted against quadratic hypersurfaces containing cross terms between the variables. 3) The predictive quality of the CSA hypersurfaces is validated by comparing the predicted and de novo calculated (13)C' CSAs for 20 molecular dynamics snapshots. 4) The CSA fluctuations and their autocorrelation and cross correlation functions due to bond-length and bond-angle distortions are predicted for a chemistry Harvard molecular mechanics (CHARMM) molecular dynamics trajectory of Ca(2+)-saturated calmodulin and GB3 from the hypersurfaces, as well as for a molecular dynamics (MD) simulation of an NMA trimer using a quantum mechanically correct forcefield. We find that the fluctuations can be represented by a 0.93 scaling factor of the CSA tensor for both R(1) and R(2) relaxations for residues in helix, coil, and sheet alike. This result is important, as it establishes that (13)C' relaxation is a valid tool for measurement of interesting dynamical events in proteins. 相似文献
190.
V. P. Solov’ev N. V. Kireeva A. Yu. Tsivadze A. A. Varnek 《Journal of Structural Chemistry》2006,47(2):298-311
The method of substructural molecular fragments based on representation of the molecular graph by ensembles of fragments and involving calculations of those contributions to the given property is applied to the modelling of stability constants of the complexes of strontium(II) with organic ligands in water. Reliability of predictions of developed structure-property models was examined using three different test sets of structurally diverse ligands. The obtained models have been used for generation and screening of combinatorial library of virtual ligands. Some hypothetical efficient Sr(II) binders were suggested. 相似文献