Molecular dynamics was used to study the hydration of superoxide (O). The Helmholtz free energy of hydration of O was estimated by the thermodynamic integration method. The diffusion of O and the water structure around O were also studied. Two water models were used in the calculations and the results were compared to experiments. 相似文献
The results of calculating the average polarizabilities, first and second hyperpolarizabilities and molar Kerr constants of C5H, C6H, 2-C10H, 2-C14H, C8H and C8H are reported. The main elements of our computational scheme are McWeeny's coupled Hartree–Fock perturbation theory and an extended basis CNDO wave function. It is shown that the studied anions have nonlinearities within the same order of magnitude as their respective uncharged parent molecules. The Kerr constants of these anions are analyzed and the contribution of the various terms is appraised. 相似文献
Ab initio molecular orbital theory with the STO -3G basis set is used to examine both charge and energy interactions in a series of meta- and para-substituted phenylborate anions and toluenes. Comparison of the results is made with data for substituted anilinium cations. It is concluded that whereas NH is a powerful σ acceptor, with essentially no π interaction, BH is primarily a π donor, and, to a slight extent only, a π donor. CH3 is indicated to be both a weak σ and π donor. Energies of interaction of BH and NH with a series of substituents are an order of magnitude larger than corresponding values for CH3. Interaction energies for BH are of opposite sign to those for NH. The results may be understood qualitatively using perturbation molecular orbital (PMO ) theory. 相似文献
Semiempirical molecular orbital calculations by the MNDO method are reported for sulfur rings and chains S3 through S8, for the corresponding dications, S through S, and for S. The MNDO method seems quite successful in predicting the geometries of neutral catenated sulfur molecules, even the unusual bond-length alternation and extent of coplanarity in cyclo-S7. In contrast to hydrocarbon rings, for which its prediction of strain is erratic, MNDO is consistent in its calculated strain energies in small cyclosulfur rings; unfortunately all the strain energies are overestimated by 70%. As a consequence of this error, the method must be considered unreliable in its predictions of structures for the dications S, since many of these ions could potentially exist as strained bicyclic systems. In addition, MNDO appears to have difficulty handling long, partial SS σ bonds, as are found to occur in S. It may be for this reason that MNDO predicts, apparently incorrectly, that the open-chain isomers of S are more stable than are any of the cyclic forms, at least for S to S. With respect to neutral Sn molecules, however, the MNDO predictions appear more reliable than ab initio molecular orbital (MO ) calculations using small basis sets without polarization functions and without configuration interaction (CI ). However, MNDO apparently underestimates by about a factor of two the strength of the three-electron π bonds present in the terminal links of sulfur diradical chains. 相似文献
The energy hypersurface for the system Li(H2O)–F(H2O) is investigated using the polarization model. A possible mechanism for the production of HF in this solution droplet is observed. 相似文献
The Hartree-Fock instablities of S2N2 are reported and compared with those of S3N and S4N. These unsaturated sulfur nitrogen planar rings are π electron rich and although the symmetry adapted HF solutions are singlet stable at the experimental bond lengths they become unstable with only a very modest increase in bond length. The broken symmetry solutions for S2N3, S3N, and S4N are of planar C2v type with one of the nitrogens stripped of its π electrons, producing a π hole. 相似文献
Using previously reported ab initio potentials of the intermolecular interaction energies of phospholipid (PL), Lysophosphatidyl Ethanolamine, with one Na+ ion and one water molecule, we performed Monte Carlo simulations for PL-water and PL-Na+-water systems. Water-water and PL-water interaction energetics of PL hydration sites are analyzed to understand, in a qualitative way, why the PL head part shows hydrophilicity and the tail part shows hydrophobicity. The interaction of Na+ with PL, as well as the interaction of water with PL, is visualized from the analysis of the hydration structures near PL, and the radial distribution functions are analyzed for selected hydration sites. The PL molecule shows much stronger interaction with Na+ than with water. The Na+ ion is likely to be strongly bound to PO, even to the extent of being trapped, whereas, for water, there exist two strong binding regions near NH and PO. Three water molecules near NH are much more strongly bound than four water molecules near the double-bonded oxygens of PO. The hydrogens of CH2 adjacent to NH show somewhat strong hydrophilicity, while the hydrogens of CH2 adjacent to PO does not show such characteristics. The CH2 groups at the PL tail part give repulsive interactions with water molecules, showing hydrophobicity. Water molecules near the PL tail are stabilized only by water-water interactions. 相似文献
On Ordered Perovskites with Cationic Vacancies. XI. Compounds of Type A B B □1/4WVIO6 ? A BIIB □W O24 with AII, BII = Ba, Sr Depending on the ionic radii of the two and three valent cations in the perovskites of type ABB □1/4WVIO6 ?; ABIIB □WO24 order disorder phenomena are present. The results of the x-ray and vibrational spectroscopic investigations as well as the diffuse reflectance spectra and the visible photoluminescence are reported. 相似文献
Dibromomethylsulfoniumsalts — Preparation and Crystal Structure The salts CH3SBrA? (A? = SbCl, AsF) were prepared by various routes and characterized by their Ramanspectra. CH3SBrAsF crystallized in the monoclinic space group P21/c with a = 770,5(4) pm, b = 942,4(12) pm, c = 1329,3(14) pm, β = 100,28(6)°, Z = 4. Distances and bond angles in the cation are as expected. 相似文献
Monte Carlo simulation results are presented for lattice models of uniform stars (one branch point of functionality f = 3), combs (two branch points, ? = 3,3) and brushes (two branch points ? = 3,4 and ? = 3,5). We estimate the critical exponent γ(?), the ratio g(?) = 〈S(?)〉/〈S(1)〉 (where 〈S(?)〉 is the mean-square radius of gyration of a structure having ? branches and N monomers), and the meansquare end-to-end branch lengths, as a function of the number and arrangement of branches. Comparisons with theoretical predictions and experimental data are made where possible, leading to a test of some predictions, and a suggestion concerning future experiments. 相似文献
19F NMR Spectroscopic Evidence and Calculation of the Statistical Formation of Mixed Cluster Anions [(Mo6Br Cl )F ]2?, n = 0 – 8 The complete system of the innersphere mixed clusters (Mo6BrCl)4+ is formed by exchange of innersphere bound Cli against outersphere bound Bra on tempering the solid [(Mo6Cl)Br] at 500°C for 16 h. After conversion with conc. HCl into (H3O)2[(Mo6BrCl)Cl] and precipitation of the outer Cla with AgBF4 in ethanol, treatment with tetrabutylammonium(TBA)fluoride yields (TBA)2 [(Mo6BrCl)F], a mixture of 22 different species. According to the sets of chemical equivalent fluorine atoms in total 55 19F nmr signals are expected, which are really observed in the high resolution 1D-19F-nmr spectrum. Using increments of chemical shifts, peak intensities and multiplet structures as well as the 2D-19F/19F-COSY spectrum the complete and unambiguous assignment of all resonances is achieved. From the measured integral intensities the distribution of the different compounds is determined, revealing statistical formation of the geometrical isomers. 相似文献
Aqueous sols of TiO2 (anatase, particle radius 25 Å) were excited with (347.1 nm)-laser light and the reaction of valence-band holes with halide ions (X = I?, Br?, Cl?) was investigated. Hole transfer takes place within the duration of the (10 ns)-laser pulse and results in the formation of anion radicals according to the sequence: The quantum yield of X increases in the order Cl < Br < I, attaining 0.8 for I at pH 1. It is affected by pH, halide concentration and the presence of a protective agent for the sol. RuO2 deposited onto TiO2 enhances markedly Cl and Br -formation, but has no effect on the yield of I. Laser-photolysis investigation of halide oxidation were also carried out with colloidal Fe2O3 (particle radius 600 Å). For I2?formation, the quantum yield exceeds 0.9 indicating almost quantitative hole scavenging by iodide. 相似文献
Ab initio molecular orbital (MO ) calculations for two series of sulfur–oxygen compounds are reported: the S(IV ) system of SO2, H2SO3, HSO, and SO, and the S(VI ) system of SO3, H2SO4, HSO, and SO. Geometries about the sulfur atoms were optimized using the STO -3G* basis set; energies at these geometries were computed by the STO ?3G and 44-31G basis sets both with and without five Gaussian d orbitals on S. The sulfur–oxygen bond lengths and the angles about the central atoms agree fairly well with experiment. The stabilization energy associated with the addition of the d orbitals was found to be a constant amount per bond (ca. 54 and 28 kcal mole?1 in the minimal and extended bases, respectively) in hypervalent compounds. The isomer HSO was predicted to be more stable than SO2(OH)?, but the reverse was true for HSO2(OH) compared to SO(OH)2. The deprotonation energies for the acids and the hydration energies for the oxides also were computed and discussed with reference to experimental data. 相似文献