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851.
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Calculations of localized molecular orbitals (LMO) and their energy levels for the cluster cores [MO3O4]4+, [MO3SO3]4+, [MO3OS3]4+, [Mo3S4]4+ and [MO3OCl3]5+ have been made by the use of energy-localized CNDO/2-LMO. The results of these LMO calculations show that the six-membered closed and continuous π-conjugated systems around the [MO3Y3] rings, each of which is formed from three synergically connected three-centered two-electron
π bonds, is the most significant feature of the electronic structure for the quasi-aromatic clusters [Mo3(μ3-Y)(μ-X)3]4+ (X, Y = O, S), and the size and electronegativity of the bridging Y atoms exhibit significant effects on the degree of quasi-aromaticity of these cluster compounds. For the non-aromatic reference cluster [Mo3OCl3]5+, the results of our calculations also show a bonding scheme with only one isolated
π bond, thus leading to the loss of quasi-aromaticity; and meanwhile, there is a pair of extra electrons localized on the apical molybdenum atom of the Mo3 triangle, thus with three Mo---Mo single bonds. 相似文献
854.
实验结果支持了血红素(Ha.)的单体(monomer)吸附态对分子氧起电催化还原作用的观点;并表明,H_2O_2的电催化还原主要是在Ha.的二聚体(dimer)吸附态上进行。Ha./电极对苯一步羟基化生成苯酚有电催化作用。 相似文献
855.
Thermally induced phase separation technique was utilized to fabricate biodegradable poly(l ‐lactic acid) (PLLA) macrocellular foams which were capable of being applied in tissue engineering. The block copolymer Pluronic F127 composed of (polyethyleneoxide)‐(polypropyleneoxide)‐(polyethyleneoxide) [(PEO)‐(PPO)‐(PEO)] was used as a porogen. Water/dioxane mixtures with different volume ratios were used as solvents. The addition of Pluronic F127 could induce an appearance of large pores (50–200 μm) besides small pores (10–20 μm) or a change from a solid–liquid phase separation to a liquid–liquid phase separation. The role of Pluronic F127 depends on the water/dioxane ratios in the PLLA/dioxane/water system. The X‐ray diffraction patterns and porosity measurement results showed that Pluronic F127 was crystallized and existed on the pore wall. The effect of Pluronic F127 on changing pore structure is attributed to the occurrence of the interaction of the lipophilic PPO blocks in Pluronic F127 with PLLA clews, consequently, this results in PLLA aggregation and early phase separation on cooling. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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2-(8-Quinolylazo)-7-phenylazochromotropic acid (QAPAC) has been synthesized by coupling diazotized 8-aminoquinoline with 2-phenylazochromotropic acid as well as by coupling diazotized aniline with 2-(8-quinolylazo)chromotropic acid. The properties of QAPAC and the spectrophotometric characteristics of some metal-QAPAC complexes are reported. 相似文献
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