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111.
S. Padmaja V. Ramakrishnan J. Rajaram J. C. Kuriacose 《Journal of Chemical Sciences》1988,100(4):297-303
The borate radical is produced by the flash photolysis of an aqueous alkaline solution of NaBO2 and K2S2O8. The absorption spectrum of the transient borate radical shows two maxima. The self decay of this radical is second order.
Rate constants for the reactions of this radical with some organic substrates have been determined. 相似文献
112.
Fabio E. Penotti 《International journal of quantum chemistry》2006,106(5):1153-1159
Nonorthogonal single‐configuration and multiconfiguration ab initio calculations are carried out on the BeH2 molecule in its equilibrium (D∞h) geometry, using a highly optimized even‐tempered Slater‐type orbital (STO) basis set. The results are used as a basis for a discussion of the electronic structure of the molecule in modern‐VB terms. A value of Re = 1.329 Å is obtained. Values are also obtained for the symmetric‐stretch harmonic frequency (2053 cm?1), electric quadrupole moment (?5.60 Buckingham), and nuclear quadrupole coupling constants (?3.59 MHz for 9Be and 0.0915 MHz for 2H). © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
113.
The finite field approach has been implemented in the periodic ab initio CRYSTAL program and been used for calculating the dielectric constants of crystalline LiF and MgO (FCC structure) and BeO (wurtzite structure). To maintain the periodicity along the applied field direction, a "sawtooth" potential is used in conjunction with a supercell scheme. Supercells four to five times longer than the primitive cell in the direction of the applied field provide well-converged results. The influence of the computational parameters is discussed. An alternative scheme has also been implemented, for inner check, that consists of applying a static electric field to a slab of increasing thickness in the direction orthogonal to the surface; the dielectric response at the center of the slab is shown to converge rapidly to the bulk value evaluated with the sawtooth field. The method is accurate and permits the determination of nonlinear corrections to the dielectric constant. When used in conjunction with the local density approximation (LDA) scheme, it provides for the dielectric constant of the three above-mentioned compounds values close to those recently obtained with a time-dependent density functional theory approach. 相似文献
114.
A. D. Smirnov 《Journal of Structural Chemistry》2003,44(5):757-762
The vibrational, rotational, and centrifugal constants have been calculated for the ground electronic states of KRb and RbCs molecules. The calculation is performed using the semiempirical potential curves constructed in a wide range of internuclear distances. The estimated spectroscopic constants are compared with experimental data. 相似文献
115.
Andrei A. Gakh Bobby G. Sumpter Donald W. Noid Richard A. Sachleben Bruce A. Moyer 《Journal of inclusion phenomena and macrocyclic chemistry》1997,27(3):201-213
A computational neural network method was used for the prediction of stability constants of simple crown ether complexes. The essence of the method lies in the ability of a computer neural network to recognize the structure-property relationships in these host-guest systems. Testing of the computational method has demonstrated that stability constants of alkali metal cation (Na+, K+, Cs+)-crown ether complexes in methanol at 25 °C can be predicted with an average error of ±0.3 log K units based on the chemical structure of the crown ethers alone. The computer model was then used for the preliminary analysis of trends in the stabilities of the above complexes. 相似文献
116.
Preparation of Silver Nanoparticles through Alcohol Reduction with Organoalkoxysilanes 总被引:1,自引:0,他引:1
Hoe Jin Hah Sang Man Koo Sang Hoon Lee 《Journal of Sol-Gel Science and Technology》2003,26(1-3):467-471
Silver nanoparticles of narrow size distribution were prepared through the chemical reduction in an alcohol solution with several organoalkoxysilanes. In this system, organoalkoxysilanes served as a stabilizer, protecting silver nanoparticles from aggregation. The changes in size and morphology of colloidal silver nanoparticles were investigated with the addition of organoalkoxysilanes such as 3-aminopropyltriethoxysilane (APS), methyltriethoxysilane (MTS), phenyltrimethoxysilane (PTS), vinyltriethoxysilane (VTS), and 3-glycidoxypropyltrimethoxysilane (GPS) as stabilizers. The organic functional groups of organoalkoxysilanes interact with silver ions and clusters, which stabilize silver nanoparticles in the system. The silver nanoparticles obtained were characterized with transmission electron microscopy (TEM), UV-vis spectroscopy, etc. 相似文献
117.
Cobas JC Constantino-Castillo V Martín-Pastor M del Río-Portilla F 《Magnetic resonance in chemistry : MRC》2005,43(10):843-848
(1)H NMR scalar coupling constants are a rich source of information on molecular structure, but their extraction from spectra can be less than straightforward. Previous approaches to J extraction include methods proposed by Hoye, Golotvin, and the 'modified J-doubling' method. Here we describe the ACCA method, currently implemented in the NMR package MestReC, which allows a high degree of automation in the extraction of coupling patterns even in the case of complex multiplets with sublinewidth splitting. The new approach is illustrated by application to strychnine, for which it has detected previously unreported couplings. 相似文献
118.
M. I. El-Barghouthi N. A. Masoud J. K. Al-Kafawein M. B. Zughul A. A. Badwan 《Journal of inclusion phenomena and macrocyclic chemistry》2005,53(1-2):15-22
The solubility of risperidone (Risp) in aqueous buffered cyclodextrin (CD) solution was investigated for α-, β-, γ- and HP-β-CD. The effects of pH, ionic strength and temperature on complex stability were also explored. Neutral Risp tends to form
higher order complexes (1:2) with both β- and HP-β-CD, but only 1:1 type complexes with α-, and γ-CD. The tendency of Risp to complex with cyclodextrins is in the order β-CD > HP-β-CD > γ-CD > α-CD. The 1:1 complex formation constant of Risp/HP-β-CD increases with increasing ionic strength in an opposite trend to the inherent solubility (S
0) of Risp, thus indicating significant hydrophobic effect. The hydrophobic effect contributes to the extent of 72% towards
neutral Risp/HP-β-CD complex stability, while specific interactions contribute only 4.7 kJ/mol. Thermodynamic studies showed that 1:1 Risp/HP-β-CD complex formation is driven by a favorable enthalpy change (ΔH
0=−31.2 kJ/mol, ΔS
0=−7 J/mol.K) while the 1:2 complex is largely driven by entropy changes (ΔH
0=−5.0 kJ/mol, ΔS
0=42 J/mol.K). Complex stability was found to vary with pH, with a higher formation constant for neutral Risp. Molecular mechanical
computations using MM (atomic charges and bond dipole algorithms) and Amber force fields, which were carried out to explore
possible sites of interactions between Risp and CDs and to rationalize complex stoichiometry, produced similar results concerning
optimal inclusion complex geometries and stoichiometries. 相似文献
119.
T. P. Elango V. Ramakrishnan S. Vancheesan J. C. Kuriacose 《Journal of Chemical Sciences》1984,93(1):47-52
Rate constants for the reaction of carbonate radical with aniline and some parasubstituted anilines have been determined by
the flash photolysis technique. Using σ+ para values the rate constants at pH 8.5 correlate very well with the Hammett equation yielding ρ= − 1. The carbonate radical oxidises aniline giving the anilino radical. The products so formed have been identified through
studies under conditions of continuous irradiation. 相似文献
120.
Michael Dolg 《Theoretical chemistry accounts》2005,114(4-5):297-304
Energy-consistent relativistic pseudopotentials for 3d-transition metals Sc to Ni based on modified valence energies are proposed. The pseudopotentials are adjusted at the finite
difference level within the intermediate coupling scheme with respect to multi-configuration Dirac–Hartree–Fock data based
on the Dirac–Coulomb Hamiltonian with an estimate of the Breit contributions in quasidegenerate perturbation theory. Typically
a few hundred to thousand J levels arising from about 35 to 40 configurations ranging from the anion down to the highly charged
cation are considered as references. It is shown that introducing a small common energetic shift of all valence energies reduces
the errors in the parameter adjustment considerably. Results of highly correlated atomic and molecular test calculations using
large basis sets and basis set extrapolation techniques are presented.
To be submitted to Theoretical Chemistry Accounts (special volume on the occasion of Prof. Dr. H. Stoll's 60th birthday) 相似文献