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151.
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153.
Peter Politzer Katherine C. Leung James D. Elliott Shirley K. Peters 《Theoretical chemistry accounts》1975,38(2):101-107
Atomic charges calculated by the population analysis method for three types of semi-empirical wave functions have been compared with charges obtained by integrating the corresponding electronic density functions over individual atomic regions. It was found that the two sets of charges compare quite well for CNDO wave functions and for extended-Hückel functions which are in terms of orthogonalized basis orbitals. However only the CNDO charges are reasonably close to those obtained by integrating near-Hartree-Fock electronic density functions. 相似文献
154.
The addition of LiPh to Ar*SnCl (Ar* = C6H3-2,6-Trip2; Trip = C6H2-2,4,6-iPr3) at low temperature afforded the Sn(1)-Sn(III) species Ar*SnSnPh2Ar*, which exists in equilibrium with the Sn(II) compound Ar*SnPh. It is the first example of a room-temperature equilibrium of compounds involving main group elements in different oxidation states. 相似文献
155.
Jane S. Thomson John B. Green Ted B. McWilliams Shirley K.-T. Yu 《Journal of separation science》1994,17(6):415-426
An analytical method for differentiation of primary, secondary, and tertiary amines using exhaustive trifluoroacetylation prior to GC/MS has been developed. Using the conditions described in the report, most primary amines add two and secondary amines add one trifluoroacetyl group. In general, tertiary amines do not react. GC retention indices and relative GC/MS total ion current response factors for 102 trifluoroacetyl derivatives are reported. Examples of the application of the method to petroleum and coal liquid products are provided. Because of the limited thermal stability of the derivatives of primary amines, the method is applicable only to distillates boiling below 370 °C (700 °F). 相似文献
156.
An equivalent-cores-relaxation model is given for calculating atomic binding energies from orbital energies using only ground-state atomic properties. The agreement with experiment is excellent for the noble gases. On the basis of present knowledge of atomic relaxation, the phenomenon of “extra-atomic relaxation”, in which electronic charge is attracted toward a hole-state atom, is shown to have an important effect in lowering atomic core-level binding energies in condensed phases. This will affect the interpretation of most core-level binding energies measured to date. 相似文献
157.
A rapid spectrographic method was developed to analyze seven elements collected in glass fiber air filters, they were Cd, Pb, Ni, Zn, Sn, Ti and V. Direct excitation method was used for volatile elements while graphite powder was added for determining involatile elements like titanium and vanadium in a dc arc source. Limits of detection for analyzed elements were between 0.01-0.1.μg. This simple and sensitive method was employed to analyze samples from fifteen air sampling stations in different areas of Taiwan. 相似文献
158.
Misa V. Jovanovic Edward R. Biehl Patrice De Meester Shirley S. C. Chu 《Journal of heterocyclic chemistry》1984,21(5):1425-1429
The crystal structure of title compound, 4 , shows that the 10-aryl group is parallel to the plane bisecting the pyridobenzothiazine ring. This structure is in contrast to that normally found for phenothiazines substituted with electron-withdrawing substituents on the 10-phenyl ring. In those compounds, the 10-aryl group is perpendicular to the plane bisecting the phenothiazine ring. The esr spectrum of the cation radical of 4 shows that the radical is located on the hetero ring system which is opposite to that of the cation radical of 4′-dimethylamino-10-phenylphenothiazine in which the radical is located on the 10-aryl ring. 相似文献
159.
Gandini SC Itri R de Sousa Neto D Tabak M 《The journal of physical chemistry. B》2005,109(47):22264-22272
In this work, small-angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR) studies on the interaction of three anionic mesotetrakis (4-sulfonatophenyl) porphyrins, TPPS4, FeTPPS4, and ZnTPPS4, at concentrations in the 2-10 mM range, with micelles of the zwitterionic surfactant 3-(N-hexadecyl-N,N-dimethylammonium) propane sulfonate (HPS, 30 mM) at pH 4.0 and 9.0 are reported. The SAXS results demonstrate that, upon addition of all species of porphyrins, the HPS micelle of prolate shape reduces its axial ratio from 1.8 +/- 0.2 (in the absence of porphyrin) to 1.5 +/- 0.1. Such an effect is accompanied by a shrinking of the paraffinic shortest semiaxis from 22.5 +/- 0.5 A to 18.0 +/- 0.2 A. This shows that the micellar hydrophobic core is affected by porphyrin incorporation, independent of the type of porphyrin and pH. Concurrently, EPR results demonstrate an increase in the micellar packing as noticed from the increase in motional restriction for both nitroxides. Furthermore, increase of the porphyrin concentration induces the appearance of a repulsive interference function over the SAXS curve of zwitterionic micelles, which is typical of an interaction between surface-charged micelles. Such a finding gives strong evidence that the negatively charged porphyrin molecule must accommodate in the HPS micelle dipole layer close to the inner positive charges (near the hydrophobic core), inducing a surface charge (probably a negative one associated with the HPS sulfonate external groups) in the original zwitterionic (overall neutral) micelle. Such a porphyrin location is favored by both electrostatic and hydrophobic contributions, giving rise to binding constant values that are quite large compared to the binding of cationic drugs to HPS micelles (Caetano, W.; Barbosa, L. R. S.; Itri, R.; Tabak, M. J. Coll. Int. Sci. 2003, 260, 414). 相似文献
160.