Composition-controlled synthesis of bimetallic gold-silver nanoparticles

This paper reports findings of an investigation of the synthesis of monolayer-capped binary gold-silver (AuAg) bimetallic nanoparticles that is aimed at understanding the control factors governing the formation of the bimetallic compositions. The synthesis of alkanethiolate-capped AuAg nanoparticles was carried out using two related synthetic protocols using aqueous sodium borohydride as a reducing agent. One involves a two-phase reduction of AuCl(4)(-), which is dissolved in organic solution, and Ag(+), which is dissolved in aqueous solution. The other protocol involves a two-phase reduction of AuCl(4)(-) and AgBr(2)(-), both of which are dissolved in the same organic solution. AuAg nanoparticles of 2-3 nm core sizes with different compositions in the range of 0-100% Au have been synthesized. The two synthetic routes were compared in terms of bimetallic composition and size properties. Our new findings have allowed us to establish the correlation between synthetic feeding of metals and metal compositions in the bimetallic nanoparticles, which have important implications to the exploration of gold-based bimetallic nanoparticles for constructing sensing and catalytic nanomaterials.     

Dispersed fluorescence spectroscopy of primary and secondary alkoxy radicals

Dispersed fluorescence (DF) spectra of 1-propoxy, 1-butoxy, 2-propoxy, and 2-butoxy radicals have been observed under supersonic jet cooling conditions by pumping different vibronic bands of the B-X laser induced fluorescence excitation spectrum. The DF spectra were recorded for both conformers of 1-propoxy, three conformers of the possible five of 1-butoxy, the one possible conformer of 2-propoxy, and two conformers of the possible three of 2-butoxy. Analysis of the spectra yields the energy separations of the vibrationless levels of the ground X and low-lying A electronic state as well as their vibrational frequencies. In all cases, the vibrational structure of the DF spectra is dominated by a CO stretch progression yielding the nuCO stretching frequency for the X state and in most cases for the A state. In addition to the experimental work, quantum chemical calculations were carried out to aid the assignment of the vibrational levels of the X state and for some conformers the A state as well. Geometry optimizations of the different conformers of the isomers were performed and their energy differences in the ground states were determined. The results of the calculation of the energy separations of the close-lying X and A states of the different conformations are provided for comparison with the experimental observations.     

Development of a miniature simultaneous MPT spectrometer

An unique miniature simultaneous microwave plasma torch (MPT) atomic emission spectrometer employing linear UV intensified charge-coupled device (ICCD) array detector has been developed and studied preliminarily. The detection limits and precisions of the spectrometer for Ag, Al, Ba, Ca, Cr, Cu, Fe, Mg, Mn, Sr and V by using different CCD exposure times have been determined. An analysis of a practical sample has been carried out. The preliminary results demonstrate that such simultaneous spectrometer has advantages of saving sample and time, especially suitable for use as detector for chromatography and in combination with flow injection systems. Taking analytical figures of merit and portability into accounts, the miniature simultaneous MPT system will have extended application areas and greater competition potential as compared with commercialized scanning MPT spectrometers.     

Thermoregulated Liquid/Liquid Biphasic Catalysis and Its Application

A brief overview of our recent research results of thermoregulated liquid/liquid biphasic catalysis is presented. Emphasis is given to the general principles of thermoregulated phase-transfer catalysis (TRPTC) and thermoregulated phase-separable catalysis (TPSC). In addition, the applications of TRPTC and TPSC in biphasic catalysis are also discussed. The introduction of TRPTC to biphasic system is free from the shortcomings of classical aqueous/organic two-phase catalysis, in which the application scope is restrained by the water solubility of the substrate. Meanwhile, TPSC provides a very simple and reliable way to deal with the separation of catalyst in homogeneous catalysis. The common advantages of TRPTC and TPSC are characterized by homogeneous catalysis coupled with convenient biphasic separation.     

A comparison of acetyl- and methoxycarbonylnitrenes by computational methods and a laser flash photolysis study of benzoylnitrene

Density functional theory (DFT), CCSD(T), and CBS-QB3 calculations were performed to understand the chemical and reactivity differences between acetylnitrene (CH(3)C(=O)N) and methoxycarbonylnitrene (CH(3)OC(=O)N) and related compounds. CBS-QB3 theory alone correctly predicts that acetylnitrene has a singlet ground state. We agree with previous studies that there is a substantial N-O interaction in singlet acetylnitrene and find a corresponding but weaker interaction in methoxycarbonylnitrene. Methoxycarbonylnitrene has a triplet ground state because the oxygen atom stabilizes the triplet state of the carbonyl nitrene more than the corresponding singlet state. The oxygen atom also stabilizes the transition state of the Curtius rearrangement and accelerates the isomerization of methoxycarbonylnitrene relative to acetylnitrene. Acetyl azide is calculated to decompose by concerted migration of the methyl group along with nitrogen extrusion; the free energy of activation for this concerted process is only 27 kcal/mol, and a free nitrene is not produced upon pyrolysis of acetyl azide. Methoxycarbonyl azide, on the other hand, does have a preference for stepwise Curtius rearrangement via the free nitrene. The bimolecular reactions of acetylnitrene and methoxycarbonylnitrene with propane, ethylene, and methanol were calculated and found to have enthalpic barriers that are near zero and free energy barriers that are controlled by entropy. These predictions were tested by laser flash photolysis studies of benzoyl azide. The absolute bimolecular reaction rate constants of benzoylnitrene were measured with the following substrates: acetonitrile (k = 3.4 x 10(5) M(-1) (s-1)), methanol (6.5 x 10(6) M(-1) s(-1)), water (4.0 x 10(6) M(-1) s(-1)), cyclohexane (1.8 x 10(5) M(-1) s(-1)), and several representative alkenes. The activation energy for the reaction of benzoylnitrene with 1-hexene is -0.06 +/- 0.001 kcal/mol. The activation energy for the decay of benzoylnitrene in pentane is -3.20 +/- 0.02 kcal/mol. The latter results indicate that the rates of reactions of benzoylnitrene are controlled by entropic factors in a manner reminiscent of singlet carbene processes.     

Use of N-N bond stereodynamics in ring-closing metathesis to form medium-sized rings and macrocycles

A unique strategy based on double ring-closing metathesis for the formation of a 14-membered macrocyclic enamide has been developed. This strategy hinges upon the well-known stereodynamic and conformational behavior of N-substituted diacylhydrazines, which promotes an effective ring-closing metathesis of hydrazine-derived dienes and enynes to form 8- to 14-membered rings.     

Phosphorous,nitrogen, and molybdenum ternary co-doped TiO2: preparation and photocatalytic activities under visible light

P, N, and Mo ternary co-doped nano TiO₂ photocatalysts ((P, N, Mo)-TiO₂) were prepared by a single step sol–gel method, which show much enhanced photocatalytic activities over Mo-TiO₂, (P, N)-TiO₂, un-doped TiO₂ and Degussa P25 under visible light irradiation. The degradation rate of 0.72Mo–P-TiO₂ is as high as 65.3%, which is about 6.7 times of that of Degussa P25. Possible reasons for the improvement of photocatalytic activities were analyzed.     

新型苯并噁唑侧基聚酰亚胺的合成、结构与性能研究

为了改善聚酰亚胺的不溶不熔性, 一类可溶性苯并噁唑侧基聚酰亚胺树脂被成功制备. 从合成的新型二元胺单体出发, 制备了侧链为邻羟基苯胺酰胺结构的聚酰亚胺体系, 进一步催化环化邻羟基苯胺酰胺为苯并噁唑结构, 并对这两类不同结构的聚合物树脂进行了红外光谱的结构表征, 以及最终成膜的力学性能和耐热性能测试. 研究结果表明: 苯并噁唑侧基聚酰亚胺的力学性能优于相应的主链型聚酰亚胺, 且TGA分析表明, 其初始分解温度高达597 ℃, 有望用于航空航天方面高强、高模、耐高温的结构材料.     

钯催化合成嘧啶核苷衍生物的研究进展

嘧啶核苷衍生物在药物化学、生物探针和核酸化学的研究中具有重要的作用, 金属催化碳碳的形成广泛应用于嘧啶核苷衍生物的合成. 综述了钯催化的Sonogashira反应、Stille反应、Heck反应以及Hiyama反应在嘧啶类核苷衍生物合成中的应用.     

N,N-二取代甘氨酸四乙酰基葡萄糖酯的合成与表征

在碳酸钾和十六烷基三甲基溴化铵存在下, 将N-(N-乙酰基-N-芳氨基乙酰基)-N-芳氨基乙酸与全乙酰化α-溴代葡萄糖反应合成出了7个新的N,N-二取代甘氨酸四乙酰基葡萄糖酯(5a～5g), 并利用IR, 1H NMR, MS和元素分析对其结构进行了表征.