First-principles theory for the H + H2O, D2O reactions

A full quantum dynamical study of the reactions of a hydrogen atom with water, on an accurate ab initio potential energy surface, is reported. The theoretical results are compared with available experimental data for the exchange and abstraction reactions in H + D2O and H + H2O. Clear agreement between theory and experiment is revealed for available thermal rate coefficients and the effects of vibrational excitation of the reactants. The excellent agreement between experiment and theory on integral cross sections for the exchange reaction is unprecedented beyond atom-diatom reactions. However, the experimental cross sections for abstraction are larger than the theoretical values by more than a factor of 10. Further experiments are required to resolve this.     

Transition-state models and hydrogen-isotope effects. Kinetic isotope effects provide a sensitive test for detailed models of reacting systems

The transition-state theory of chemical kinetics, coupled with relatively crude methods of constructing potential-energy surfaces for reacting systems, has great utility in the forecasting of kinetic properties. In particular, it permits prediction of the effect of isotopic substitution on rate constants, and comparison of these predictions with experimental data provides a particularly sensitive test for the combination of potential-energy surface and transition-state theory. More rigorous tests of each of these factors depend on future developments in quantum chemistry, in studies of chemical reactions in molecular beams, and in detailed trajectory calculations of scattering processes.     

Flow of mantle fluids through the ductile lower crust: helium isotope trends

Heat and mass are injected into the shallow crust when mantle fluids are able to flow through the ductile lower crust. Minimum 3He/4He ratios in surface fluids from the northern Basin and Range Province, western North America, increase systematically from low crustal values in the east to high mantle values in the west, a regional trend that correlates with the rates of active crustal deformation. The highest ratios occur where the extension and shear strain rates are greatest. The correspondence of helium isotope ratios and active transtensional deformation indicates a deformation-enhanced permeability and that mantle fluids can penetrate the ductile lithosphere, even in regions where there is no substantial magmatism. Superimposed on the regional trend are local, high 3He/4He anomalies indicating hidden magmatic activity and/or deep fluid production with locally enhanced permeability, identifying zones with high resource potential, particularly for geothermal energy development.     

H_2O_2/Fe~(2+)体系处理难降解废水的动力学模型研究进展

概述了H2O2/Fe2+体系(Fenton)处理难降解废水中有关反应动力学模型的研究进展,包括一级、二级动力学模型、反应级数推导模型、稳态假设动力学模型和反应因素相关模型,并对Fenton法处理难降解废水的动力学模型发展趋势进行了展望。     

An Accurate Quantum Monte Carlo Calculation of the Barrier Height for the Reaction H + H2 rarr H2 + H

An improved quantum Monte Carlo method has been used to calculate the classical barrier height for the hydrogen exchange reaction H + H(2) --> H(2) + H with accuracies greater than previously attained. The method is exact in that, except for the easily estimated Monte Carlo statistical or sampling error, it requires no mathematical approximations or physical approximations beyond those of the Schr?dinger equation. The minimum in the barrier, occurring for the collinear nuclear configuration with the protons separated by 1.757 bohrs, was found to be 9.61 +/- 0.01 kilocalories per mole above H + H(2).     

Sequence-specific isotope effects on the cleavage of DNA by bleomycin

Bleomycin is a metal- and oxygen-dependent DNA cleaver. The chemistry of DNA damage has been proposed to involve rate-limiting abstraction of the 4'-hydrogen. A DNA fragment has been prepared that contains [4'-2H]thymidine residues of high isotopic content. Primary kinetic isotope effects have been directly observed at individual thymidine residues with DNA sequencing technology.     

Enzyme-catalyzed reactions of the carcinogen N-hydroxy-2-fluorenylacetamide with nucleic acid

A protein fraction obtained by gel filtration of a 105,000g supernatant of rat liver catalyzes three reactions of the hepatocarcinogen N-hydroxy-2-fluorenylacetamide with nucleic acid. Cofactor requirements and isotopic studies suggest that the reactive intermediates involved may be N-2-fluorenylhydroxylamine, and phosphate and sulfate esters of N-hydroxy-2-fluorenylacetamide.     

双氧水对鼻咽癌细胞生长特性的影响及其机制的初步研究

目的:观察H2O2对人低分化鼻咽癌细胞(CNE-2Z)生长、增殖能力的影响,并探讨其可能机制。方法:用M TT及平板克隆形成实验、W estern B lot等检测H2O2诱导CNE-2Z后增殖能力、EGR-1、p53、p16、Cyclin D1的表达。结果:不同浓度H2O2可不同程度地抑制CNE-2Z细胞的生长增殖能力,同一时间点各实验组细胞抑制率相比差异有统计学意义,抑制率与H2O2浓度间表现出明显的剂量-效应关系。平板克隆形成实验的抑制率较M TT更明显。CNE-2Z无EGR-1、p16蛋白表达,可见p53、Cyclin D1蛋白表达;诱导培养后EGR-1、p53、Cyclin D1蛋白表达明显增加。结论:一定浓度的H2O2能抑制CNE-2Z细胞生长,其作用可能与EGR-1及p53蛋白表达增强有关;Egr-1基因在CNE-2Z中具有可诱导性,在肿瘤治疗中有一定的应用前景。     

Detection and Characterization of the Cumulene Carbenes H2C5 and H2C6

Two cumulene carbenes, H2C5 and H2C6, were detected in a supersonic molecular beam by Fourier transform microwave spectroscopy. Their rotational and leading centrifugal distortion constants were determined with high accuracy, such that the entire radio spectrum can now be calculated. Like the known carbenes H2C3 and H2C4, both molecules have singlet electronic ground states and linear carbon-chain backbones. They can be produced in sufficiently high concentrations in the laboratory that their electronic spectra, expected to lie in the visible, should be readily detectable by laser spectroscopy. The microwave spectra of other, more exotic isomers may be detectable as well.     

Rate constants for the reactions of hydroxyl and hydroperoxyl radicals with ozone

Chain decomposition of ozone by hydroxyl and hydroperoxyl radicals has been observed. The rate constant at 3000 degrees K for OH + O(3)-->HO(2) + O(2) is 8 x 10(-14) cubic centimeters per second. The rate constant for HO(2) + O(3)--> OH + 2O(2), is 3 x 10(-15) cubic centimeters per second. These results have implications concerning stratospheric ozone.     

Possible mechanism for the antiarrhythmic effect of helium in anesthetized dogs

Breathing a mixture of 75 percent helium and 25 percent oxygen instead of 75 percent nitrogen and 25 percent oxygen reduced the occurrence of dangerous cardiac arrhythmias after ligation of the circumflex coronary artery in open-chest dogs anesthetized with pentobarbital. In dogs not subjected to circumflex ligation, the sensitivity of blood pressure, heart rate, and extrasystoles to epinephrine injected intravenously was not altered by the substitution of helium for nitrogen; however, helium did reduce the baseline heart rate and the concentration of endogenous plasma catecholamines. The antiarrhythmic effect of helium may thus be mediated by changes in sympathetic activity.     

Bimetallic system for nitrogen fixation: ruthenium-assisted protonation of coordinated N2 on tungsten with H2

Treatment of the tungsten dinitrogen complex cis-[W(N2)2(PMe2Ph)4] (Me = methyl, Ph = phenyl) with an equilibrium mixture of [RuCl(dppp)2]X and trans-[RuCl(eta2-H2)(dppp)2]X [X = BF4, PF6, or OSO2CF3; dppp = 1,3-bis(diphenylphosphino)propane] under 1 atmosphere of dihydrogen at 55 degrees Celsius for 24 hours gave NH3 in moderate yield. The same reaction in the presence of acetone produced acetone azine in high yield. None of these reactions proceeded in the absence of dihydrogen.     

甘草主要成分抗H9N2亚型流感病毒作用研究

利用H9N2亚型流感病毒鼠肺适应株感染小鼠,以肺指数抑制率、肺组织病毒滴度、死亡保护率和生命延长率为评价指标,研究了甘草酸单铵盐、甘草次酸、甘草黄酮等甘草中3种主要成分和甘草粗提物对感染H9N2亚型流感病毒小鼠的防治效果.结果表明,甘草粗提物及甘草酸单铵盐口服均能显著抑制H9N2亚型流感病毒鼠肺适应株引起的小鼠肺炎实变(P<0.01),甘草粗提物20 mg/kg组能明显延长流感病毒感染小鼠的生存时间.     

过氧化氢光催化脱色甲基橙溶液的研究

本文在H2O2存在下用紫外灯照射对甲基橙溶液进行光催化脱色。结果表明,甲基橙溶液的脱色率随着H2O2的增加而增加,但存在一个最佳值。当甲基橙浓度低于25 mg/L时,反应为假一级,当甲基橙浓度高于100 mg/L时,反应为零级;但是不符合Langmuir-Hinshewood动力学模型。脱色率在酸性条件下比碱性条件高。日光照射下对实际染料废水的脱色效果好。     

双氧水处理对甜菜种子发芽的影响

双氧水浸种处理叶甜菜和根甜菜种子 ,可明显提高种子的发芽率、发芽势及发芽指数。叶甜菜以浓度 2 %～ 5%的双氧水处理为宜 ,根甜菜以浓度 3%的双氧水处理为宜 ;对贮期较长的种子则以浓度 5%的双氧水处理为佳。叶甜菜和根甜菜均不宜贮藏较长时间     

First-principles theory for the H + CH4 --> H2 + CH3 reaction

A full-dimensional quantum dynamics simulation of a hydrogen atom reacting with methane on an accurate ab initio potential energy surface is reported. Based on first-principles theory, thermal rate constants are predicted with an accuracy comparable to (or even exceeding) experimental precision. The theoretical prediction is within the range of the significantly varied experimental rate constants reported by different groups. This level of accuracy has previously been achieved only for smaller, three-or four-atom reactive systems. Comparison with classical transition state theory confirms the importance of quantum mechanical tunneling for the rate constant below 400 kelvin.     

钯修饰电极的制备及其对H_2O_2的电催化还原作用研究

[目的]研究钯化学修饰电极在H2O2检测中的应用。[方法]采用循环伏安法制备了钯修饰的复合陶瓷碳电极(Pd/CCE),研究了该修饰电极对H2O2的电催化性能。[结果]在含有PdCl2.2H2O的H2SO4溶液中(pH 1.2),控制扫描电位范围为0～1.0 V(vs.SCE)连续扫描40圈时制得的Pd/CCE修饰电极对H2O2具有较强的电催化活性,安培法检测H2O2的线性范围为6.0×10-5～1.0×10-2mol/L,检出限为2.2×10-5mol/L(3Sb)。[结论]直接电沉积得到的钯修饰电极,可实现较低电位下测定H2O2,且电极具有制作简单、价格低廉、响应时间短和表面容易更新等特点。     

Physical Chemistry of the H2SO4/HNO3/H2O System: Implications for Polar Stratospheric Clouds

Polar stratospheric clouds (PSCs) play a key role in stratospheric ozone depletion. Surface-catalyzed reactions on PSC particles generate chlorine compounds that photolyze readily to yield chlorine radicals, which in turn destroy ozone very efficiently. The most prevalent PSCs form at temperatures several degrees above the ice frost point and are believed to consist of HNO(3) hydrates; however, their formation mechanism is unclear. Results of laboratory experiments are presented which indicate that the background stratospheric H(2)SO(4)/H(2)O aerosols provide an essential link in this mechanism: These liquid aerosols absorb significant amounts of HNO(3) vapor, leading most likely to the crystallization of nitric acid trihydrate (NAT). The frozen particles then grow to form PSCs by condensation of additional amounts of HNO(3) and H(2)O vapor. Furthermore, reaction probability measurements reveal that the chlorine radical precursors are formed readily at polar stratospheric temperatures not just on NAT and ice crystals, but also on liquid H(2)SO(4) solutions and on solid H(2)SO(4) hydrates. These results imply that the chlorine activation efficiency of the aerosol particles increases rapidly as the temperature approaches the ice frost point regardless of the phase or composition of the particles.     

稻谷陈化过程中维生素B1、B2变化的动力学研究

为进一步了解稻米在陈化过程中维生素营养品质的变化趋势，尽量减少其损失和改善粮食维生素营养品质，采用人工陈化法，对稻米陈化过程中维生素B1、B2含量变化的动力学特征进行了研究。结果表明，陈化过程中稻米维生素B1和维生素B2含量损失严重，以45℃储藏约150d，维生素B1含量损失为74％，维生素B2含量损失67％；在45℃时，维生素B1的酶催化反应速率方程为1／V=41．807／C 65．211；维生素B2的酶催化反应速率方程为1／V=58．523／C 33．751。维生素B2的解离速率是维生素B1的两倍。储藏温度是严重影响稻米维生素含量的因素之一。