摘要:

AbstractSeveral numerical integration schemes for the evaluation of matrix elements in density functional theory calculations have been studied and compared by computational practice. The best scheme was found to be the combination of the atomic partition [function proposed by Becke with the scaled generalized Gauss‐Laguerre quadrature formula for radial integration suggested by Yang, which achieve the highest convergence rate to the numerical integration. With the same number of integration points, the accuracy of the calculated results by this scheme is higher by 1 to 2 orders of magnitudes than that by other schemes. The reason for achieving higher accuracy by this scheme has been proposed preliminaril

ISSN:1001-604X    

DOI:10.1002/cjoc.19960140402

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThe effect of Cu2+on the triple‐stranded helical structure of poly(A:2I) was studied by means of circular dichroism spectral method with the help of ultraviolet spectral and ethidium bromide fluorescence probe methods. It was found that Cu2+destabilizes the structure of the triple helix poly(A:2I) and induces its structural transformations, meanwhile, the transformations can be partially reversed by a higher NaCl concentration. The structural transformations may be expressed by the following scheme: poly(A:2I)·poly(A:I) + poly (I) · poly(A) + 2pol

ISSN:1001-604X    

DOI:10.1002/cjoc.19960140403

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractMetalloporphyrins and crown ether groups were simultaneously supported on chloromethylated polystyrene resin to produce a series of polymer‐supported catalysts. The synthesis of these catalysts has been studied. The influence of pH, concentrations of NaOCl and phase transfer catalysts on the epoxidation of styrene catalyzed by these catalysts has also been investigated. The experimental results show that manganese(III) porphyrin bound to chloromethylated polystyrene which bears crown ether groups is effective catalysts for the epoxidation of styrene by sodium hypochlorite. The introduction of crown ether groups increases the catalytic efficiency of supported metalloporphyrins. The kinetics of epoxidation catalyzed by supported manganese(III) porphyrins obeys Michaelis‐Menten equation—the characteristic of enzyme‐driven r

ISSN:1001-604X    

DOI:10.1002/cjoc.19960140404

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThe structures of singlet stannylenoid H2SnLiF have been examined byah initioMO theory. Four equilibrium states and three transition states of isomerization reaction are located. The calculation shows that the p‐complex 1 is the most stable and experimentally detectable. The other three species, three‐membered ring 2, s̀‐complex 3 and tetrahedron 4, are also local minima on the potential energy surface, but are higher in

ISSN:1001-604X    

DOI:10.1002/cjoc.19960140405

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThe optical effects of the adsorption of eosin on the colloidal silver particle have been investigated in aqueous solutions. It was found that upon adsorption the fluorescence of eosin was effectively quenched. This was explained as the photoinduced interfacial electron transfer from the excited singlet state of eosin to the silver particle. Decreasing pH of the solution favors the adsorption of eosin and so enhances the fluorescence quenching. For comparison, the fluorescence quenching in reverse micelles was also investigated. The quenching behavior was much different from that mediated in aqueous solution. This was attributed to the unique microenvironment of reverse micelles.

ISSN:1001-604X    

DOI:10.1002/cjoc.19960140406

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractThe Clar covering polynomial of hexagonal systems is a recently proposed1,2concept which contains much more topological properties of condensed aromatic hydrocarbons, such as Kekulé structure count, Clar number, first Herndon number,etc.It is shown that this polynomial can be used for calculating the resonance energy of condensed aromatic hydrocarbons with better accuracy

ISSN:1001-604X    

DOI:10.1002/cjoc.19960140407

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractFour new heterotrinuclear complexes have been synthesized and characterized, namely {[Ni(L)2]2[Cu(opba)]}(ClO4)2, where opba denoteso‐phenylenebis(oxamato) and L stands for 1,10‐phenanthroline(phen) (1), 5‐nitro‐l,10‐phenanthroline(NO2‐phen) (2), 2,2′‐bipyridyl(bpy) (S) and 4,4′‐dimethyl‐2,2′‐bipyridyl(Me2bpy) (4). The temperature dependence of the magnetic susceptibility of {[Ni(phen)2]2[Cu(opba)]}(ClO4)23H2O has been studied in the 4–300 K range, giving the exchange integralJ—109 cm−1. The HMTvs. Tplot exhibits a minimum at about 100 K, characteristic of this kind of coupled polymetallic complex with an

ISSN:1001-604X    

DOI:10.1002/cjoc.19960140408

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractWith the aspect of equivalent diffusion layer an analytical chronoamperometric current equation on an oblate hemispheroid microelectrode for reversible electrochemical condition is derived. To verify this equation the chronoammograms have been obtained with benzoquinone in McIlvaine buffer solution (pH 7.0) at a mercury oblate hemispheroid microelectrode. The experimental results agree with the theoretical conclusions.

ISSN:1001-604X    

DOI:10.1002/cjoc.19960140409

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractAn analytical expression describing voltammetric behaviors responses at microdisk electrode for various diffusion conditions and degrees of reversibility is reported in this paper. Results of theoretical calculation made it possible to use cyclic voltammetry to evaluate heterogeneous rate constants under intermediate diffusion conditions. At relatively low scan rate, the distortion of current‐voltage can be reduced due to small iR drops and charging current. The effects of transfer coefficient, α, kinetic parameter, λ(=k0r/4D), and switching potential, εs, on potential peak separation are discussed in detail. The relationship obtained in this paper between potential peak separation and λ is in good agreement with that in Ref. 14, whose authors have got their results by using digital simulation technique. After the experiment of Fe(CN)4–6oxidation,k0and α were obtained by the theory of this paper. The result agrees with that in

ISSN:1001-604X    

DOI:10.1002/cjoc.19960140410

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY

摘要:

AbstractA mixed stationary phase of modified β‐cyclodextrin, 2,6‐di‐O‐butyl‐3‐O‐butyryl‐β‐cyclodextrin (phase A), and SE‐54 (phase B) was used for enantiomeric separation of α‐phenylethylamine,o,m,p‐methyl ando,m,p‐methoxy‐substituted analogs. The composition of mixed phase was selected by comparison of each calculated αmin(=(γm,i+1)/(γm,i)), the relative retention values of the most adjacent peaks, and γm, last, the relative retention values of the last eluting peak at each preselected ratio. Values of γ,i, a calculated by derived equations were in good agreement with the experimental results obtained with two specified mixed phases. All solutes investigated were almost baseline separated at a predicted composition of phase A and phase

ISSN:1001-604X    

DOI:10.1002/cjoc.19960140411

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1996

数据来源: WILEY