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991.
I. I. Zakharov O. V. Voroshina A. N. Startsev 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(7):1083-1087
The density functional theory (DFT) with the B3P86 hybrid exchange-correlation functional was used to calculate the molecular and electronic structure of the Mo12S24 macromolecule as a single MoS2 layered structure slab. Calculations with geometry optimization are indicative of insignificant relaxation of the coordinatively unsaturated Mo and S atoms, which corresponds with the literature DFT data on the MoS2 single slab obtained with periodic boundary conditions. The calculated forbidden band width (0.85–0.98 eV) is comparable with its experimental value (1.30 eV) and the results of DFT calculations of MoS2 with periodic boundary conditions (0.89 eV). An analysis of the electronic state of the surface Mo centers in the Mo12S24 macromolecule showed that these centers were reduced to a greater degree than the Mo(IV) atoms in the bulk. The adsorption complex between the Mo12S24 macromolecule and six H2S molecules was calculated to characterize the adsorption ability of the coordinatively unsaturated Mo centers. The structure and energy characteristics of the adsorption complex corresponded to weak donor-acceptor interaction between the π lone pair of H2S and the surface (reduced) Mo centers. The suggestion was made that the active center of the catalytic cycle of thiophene hydrodesulfurization should induce the oxidative addition of H2 followed by the occlusion of hydrogen into the MoS2 matrix. 相似文献
992.
LDPE and its blend with cellulose, obtained by extrusion, were UV-irradiated with different doses or biodegraded in soil up to 1 year. Simultaneously, the same samples were 1 year biodegraded after 20 h UV pre-irradiation in the same conditions. The course of photo- and biodegradation was monitored by estimation of average molecular weights and polydispersity, gel amount, changes of PE crystallinity and mechanical properties. Moreover, the biodegradation degree was calculated on the basis of carbon dioxide evolved and surface morphological changes were observed by SEM. It was found that biodegradation of PE + cellulose is hampered by intermolecular crosslinking of both components. Although, the rate of decomposition of PE + cellulose blends is low it is enough for disintegration of such materials in the natural environment. 相似文献
993.
A simple, specific, rapid and sensitive spectrophotometric method has been developed for the assay of clotrimazole, in bulk drug and its pharmaceutical preparations. This method is based on the ion-pair complex reaction of clotrimazole and methyl orange in aqueous methanol, and in the presence of citric acid. The chromogen, being extractable with chloroform, could be measured quantitatively at 422 nm. All variables were studied to optimize the reaction conditions. Regression analysis of beer's plot showed good correlation in a general concentration range of 2-14 mu/ml. The proposed method has been successfully applied for the analysis of the bulk drug and its dosage forms such as powder, vaginal tablets, topical solution and creams. No interference was observed from betamethasone dipropionate (Lotriderm cream) or dexamethasone acetate and azidamphenicol (Baycuten cream) or other common pharmaceutical adjuvants. In addition, this method was also found to be specific for the analysis of clotrimazole in the presence of its hydrolytic products as well as imidazole, as a possible impurity. 相似文献
994.
L. N. Sobenina A. I. Mikhaleva M. P. Sergeeva D. -S. D. Toryashchinova O. B. Kozyreva B. A. Trofimov 《Chemistry of Heterocyclic Compounds》1996,32(1):43-47
Condensation of pyrrole-2-dithiocarboxylates with CH acids containing ester groups, in the KOH-DMSO system, was used to prepare previously unknown 1-alkylthio-3H pyrrolizin-3-ones. The latter, treated with secondary amines, are readily converted to the corresponding 1-amino derivatives. 相似文献
995.
The interplay between electronic and geometric structure is investigated for covalently bonded phosphorus clusters. We use a modification of the molecular dynamics/ density functional (MD/DF) method of Car and Parrinello, describing the electronic structure by a simplified linear combination of atomic orbitals (LCAO) approach. The results show clearly the tendency of phosphorus to threefold coordination, and substantial variations in bond angles lead to a large variety of isomers. 相似文献
996.
1-Methyl-1-(-haloethyl)-1,2,3,4-tetrahydroquinoxalinium salts were synthesized and the dependence of the hydrolysis and cyclization rate constants on the acidity of the medium and presence of halide was found. It was determined that the monocations of tetrahydroquinoxalines participate in the formation of the benzo[b]-1,4-diazabicyclo[2.2.2]octene system, since blocking the free electron pair of the tertiary nitrogen atom with a methyl substituent significantly accelerates the cyclization and suppresses the hydrolytic side reaction.For Communication 17, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 372–378, March, 1989. 相似文献
997.
A new technique is presented for study of the thermal behaviour of materials. Experimental and theoretical bases are established for the limiting temperatures of thermal decomposition of different polymers.
Zusammenfassung Es wird ein neues Verfahren zur Untersuchung des thermischen Verhaltens von Stoffen. vorgestellt. Es wurden experimentelle und theoretische Grundlagen zur Bestimmung von thermischen Zersetzungstemperaturen verschiedener Polymere erstellt.
. .相似文献
998.
Beller M Thiel OR Trauthwein H Hartung CG 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(14):2513-2522
A new catalytic amination of aromatic olefins with anilines is presented. In a domino reaction, substituted quinoline derivatives are obtained in the presence of cationic rhodium complexes, such as [Rh(cod)2]BF4, and PPh3. Ethylbenzene is formed as a by-product in this new oxidative reaction. The first transition metal catalyzed anti-Markovnikov hydroamination of styrene with anilines occurs as a side reaction. Mechanistic investigations strongly support the regioselective oxidative amination of styrene as the key reaction step. 相似文献
999.
As the first part of our studies on counter-current chromatography, the methodology for selecting suitable solvent systems was established based on detailed investigations of solubility and partition coefficients (log K) of macrolide antibiotic analogues. The solubility of two important macrolides, ascomycin and FK-506, was measured in a series of common solvents, where their polarities were ranked with dielectric constants. The partition coefficients of the two macrolides were compared in various binary, ternary, quaternary solvent systems. Hexane-tert.-butyl methyl ether-methanol-water system was selected based on suitable log K of solutes and hydrogen-bonding properties of solvents. In the further optimisation of composition proportions in the multicomponent solvent system, hexane-tert.-butyl methyl ether-methanol-water (1:3:6:5) showed the best solvent selectivity by giving the most prominent difference of partition coefficient (delta log K) between ascomycin and FK-506. With this solvent system, a baseline preparative separation of these two very closely related 23-membered macrolide antibiotics was successfully achieved by employing the newly introduced Quattro counter-current chromatograph. 相似文献
1000.
T. Kluge D. Pankonin O. Brede 《Journal of Radioanalytical and Nuclear Chemistry》1998,232(1-2):103-105
The rate constants of the reactions of the radicals OH? and Cl2 ?? with α-pinene determined by pulse radiolysis in aqueous solution are given. The reaction of Cl? with α-pinene has been studied by laser photolyis in CCl4 solution. Furthermore, the rate constants of the reactions of the formed organic radicals with oxygen as well as those of the deactivation of all radicals were determined. 相似文献