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991.
Reduction potentials of arylxenon(II) tetrafluoroborates have been measured by cyclic voltammetry method on platinum disc and ultramicro electrodes. The electrochemical properties of the arylxenon(II) tetrafluoroborates are quite different to those of corresponding arylperfluoralkyliodine(III) salts. 相似文献
992.
K. D. Sen T. V. Gayatri R. Krishnaveni M. Kakkar Helge Toufar Geert O. A. Janssens Bart G. Baekelandt Robert A. Schoonheydt Wilfried J. Mortier 《International journal of quantum chemistry》1995,56(4):399-408
The average local electrostatic potential function, V(r)/ ρ(r), is calculated for 87 atoms, Li-Ac, in the ground state using the nonrelativistic average-over-configuration numerical Hartree-Fock density. It is found empirically that in a given atom the shell boundaries are expressed as the successively increasing maxima in V(r)/ ρ(r) and the outermost maximum presents good approximate estimates of the core-valence separation in atoms. The likeness in behavior of V(r)/ ρ(r) at each shell boundary with the maximum hardness principle is discussed. The single-exponent-fit parameters for the electron density in the valency region are provided for all atoms. © 1995 John Wiley & Sons, Inc. 相似文献
993.
Lan Liu Robert B. Pansu Jean Faure Jacques Roncin Bernard Arrio René Lapouyade 《Research on Chemical Intermediates》1995,21(7):765-775
The phase transition of dihexadecyl phosphate (DHP) bilayered disks has been studied using EPR spectroscopy. In the acid form
of DHP, a phase transition temperature exists, that we have monitored through the spin-spin interaction between the nitroxide
molecules at high concentration (8%) in DHP bilayers. This spin-spin interaction is due to the gathering of solutes in a fluid
defect of the membrane: the border. The fluorescence quenching of two probes by the nitroxide stearic acids in DHP bilayers
has been studied by stationary and time-resolved fluorescence measurements. The quenching process is mainly static. Both magnetic
and fluorescent probes are localized in the periphery of the bilayered disks.
An erratum to this article is available at . 相似文献
994.
Robert van Leeuwen Oleg Gritsenko Evert Jan Baerends 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1995,33(4):229-238
In this work we analyze the exchange-correlation potentialv xc within the Kohn-Sham approach to density functional theory for the case of atomic systems. The exchange-correlation potential is written as the sum of two potentials. One of these potentialsv xc,scr is the long-range. Coulombic potential of the coupling constant integrated exchange-correlation hole which represents the screening of the two-particle interactions due to exchange-correlation effects. The other potentialv xc,scr resp contains the functional derivative with respect to the electron density of the coupling constant integrated pair-correlation function representing the sensitivity of this exchange-correlation screening to density variations. As explicit expression of the exchange-part of this functional derivative is derived using an approximation for the Greens function of the Kohn-Sham system and is shown to display a distinct atomic shell structure. The corresponding potentialv xc,scr resp has a clear step structure and is constant within the atomic shells and changes rapidly at the atomic shell boundaries. Numerical examples are presented for the Be and Kr atoms using the Optimized Potential Model (OPM). 相似文献
995.
Göran Gellerstedt Eva-lisa Lindfors Maria Pettersson Danielle Robert 《Research on Chemical Intermediates》1995,21(3-5):441-456
The reactions between chlorine dioxide and the residual lignin in oxygen-bleached softwood kraft pulps have been studied. In a first series, isolated lignin samples have been subjected to chlorine dioxide oxidation at different pH values and subsequently analysed by oxidative degradation and elemental analysis. Different analytical techniques have also been employed to follow the gradual chemical changes in lignins isolated from kraft pulps after each of the bleaching stages in the OD(EOP)DD sequence. The results demonstrate that, in order to minimize chlorination of the lignin, the first chlorine dioxide stage should be carried out at a pH around or above three. At this pH level, a high degree of lignin oxidation is also achieved. A certain (mono)-chlorination of the lignin in the first D stage cannot be avoided, but this chlorine is to a large extent removed in the later bleaching stages. The efficient and non-selective oxidation of the various phenolic lignin end groups by chlorine dioxide is clearly illustrated by the analytical data. Moreover,13C NMR reveals that reduced lignin structures formed during the kraft cook survive the oxidative bleaching stages to a large extent. 相似文献
996.
997.
998.
Robert J. Maxwell Alan R. Lightfield Alida A. M. Stolker 《Journal of separation science》1995,18(4):231-234
An in-line collector assembly designed for use in supercritical fluid extraction (SFE) vessels is described. This assembly enables solutes extracted by supercritical fluids (SF) to be retained in-line on standard solid phase extraction (SPE) columns. The assembly consists of a standard 1 mL or 3 mL SPE column fitted into a specially fabricated Teflon© sleeve. The SPE column-Teflon sleeve assembly is inserted into the SFE vessel followed by the sample matrix. This unit forms a leak-tight seal with the vessel's end-cap up to pressures of 680 bar. The choice of sorbents used in the in-line SPE columns is dependent upon the properties of the solute in the supercritical state. After SFE is completed, the SPE column is removed and the solutes are recovered in 1–2 mL of the eluting solvent. No further clean-up is normally required prior to chromatographic analysis of the analyte. A comparison was made of recoveries by in-line and off-line (after SF decompression) techniques for the SFE of three anabolic steroids in fortified chicken liver. The HPLC chromatograms of the steroids from the off-line SPE columns were too complex for quantitation, because of coeluting artifacts, whereas chromatograms obtained from in-line SPE columns were free from UV-absorbing interferences and were easily quantified. 相似文献
999.