Reactivity of the gold/water interface during selective oxidation catalysis

The selective oxidation of alcohols in aqueous phase over supported metal catalysts is facilitated by high-pH conditions. We have studied the mechanism of ethanol and glycerol oxidation to acids over various supported gold and platinum catalysts. Labeling experiments with (18)O(2) and H(2)(18)O demonstrate that oxygen atoms originating from hydroxide ions instead of molecular oxygen are incorporated into the alcohol during the oxidation reaction. Density functional theory calculations suggest that the reaction path involves both solution-mediated and metal-catalyzed elementary steps. Molecular oxygen is proposed to participate in the catalytic cycle not by dissociation to atomic oxygen but by regenerating hydroxide ions formed via the catalytic decomposition of a peroxide intermediate.     

Heterogeneous catalysis: effect of an alternating electric field

Oxidation of carbon monoxide was studcied in a static reactor at 123 degrees +/- 1 degrees C, wtith NiO as catalyst. An alternating electric field of about 22,000 volts per centimeter, peak to peak, was applied normal to the catalytic Surfaces. The rate of oxidation was thereby enhanced by a factor of 6 at 100 cycles per second, with maximum enhancement at between 100 and 200 cycles per second.     

Selective chemical catalysis by an antibody

The immunoglobulin MOPC167, which binds the transition state analog p-nitrophenylphosphorylcholine with high affinity, catalyzed the hydrolysis of the corresponding carbonate 1. MOPC167 catalysis displayed saturation kinetics with catalytic constant (kcat) = 0.4 min-1 and Michaelis constant (Km) = 208 microM, showed substrate specificity, and was inhibited by p-nitrophenylphosphorylcholine. The rate of the reaction was first order in hydroxide ion concentration between pH 6.0 and 8.0. The lower limit for the rate of acceleration of hydrolysis by the antibody above the uncatalyzed reaction was 770. This study begins to define the rules for the generation of catalytic antibodies.     

The impact of nanoscience on heterogeneous catalysis

Most catalysts consist of nanometer-sized particles dispersed on a high-surface-area support. Advances in characterization methods have led to a molecular-level understanding of the relationships between nanoparticle properties and catalytic performance. Together with novel approaches to nanoparticle synthesis, this knowledge is contributing to the design and development of new catalysts.     

Stereochemical course of catalysis by the Tetrahymena ribozyme

The group I intron from Tetrahymena catalyzes phosphodiester transfer reactions on various RNA substrates. A modified RNA substrate with a phosphorothioate group in one stereoisomeric form at the site of reaction was synthesized in order to determine the stereochemical course of an RNA-catalyzed reaction. The reaction product was digested with a stereospecific nuclease to determine the configuration of the product phosphorothioate. The reaction occurs with inversion of configuration at phosphorus, implying an in-line pathway for the reaction.     

The mechanical response of gold substrates passivated by self-assembling monolayer films

Interfacial force microscopy has been used to show that a single layer of self-assembling molecules adsorbed on a gold substrate can prevent adhesion between gold and a tungsten probe. The passivated gold is able to elastically support large repulsive loads, with plots of load versus deformation closely following the Hertzian model. The gold shear-stress threshold for plastic deformation is determined to be approximately 1 gigapascal, which is in agreement with the theoretical value for the intrinsic gold-lattice stability.     

The dynamic energy landscape of dihydrofolate reductase catalysis

We used nuclear magnetic resonance relaxation dispersion to characterize higher energy conformational substates of Escherichia coli dihydrofolate reductase. Each intermediate in the catalytic cycle samples low-lying excited states whose conformations resemble the ground-state structures of preceding and following intermediates. Substrate and cofactor exchange occurs through these excited substates. The maximum hydride transfer and steady-state turnover rates are governed by the dynamics of transitions between ground and excited states of the intermediates. Thus, the modulation of the energy landscape by the bound ligands funnels the enzyme through its reaction cycle along a preferred kinetic path.     

Engineering enzyme specificity by "substrate-assisted catalysis"

A novel approach to engineering enzyme specificity is presented in which a catalytic group from an enzyme is first removed by site-directed mutagenesis causing inactivation. Activity is then partially restored by substrates containing the missing catalytic functional group. Replacement of the catalytic His with Ala in the Bacillus amyloliquefaciens subtilisin gene (the mutant is designated His64Ala) by site-directed mutagenesis reduces the catalytic efficiency (kcat/Km) by a factor of a million when assayed with N-succinyl-L-Phe-L-Ala-L-Ala-L-Phe-p-nitroanilide (sFAAF-pNA). Model building studies showed that a His side chain at the P2 position of a substrate bound at the active site of subtilisin could be virtually superimposed on the catalytic His side chain of this serine protease. Accordingly, the His64Ala mutant hydrolyzes a His P2 substrate (sFAHF-pNA) up to 400 times faster than a homologous Ala P2 or Gln P2 substrate (sFAAF-pNA or sFAQF-pNA) at pH 8.0. In contrast, the wild-type enzyme hydrolyzes these three substrates with similar catalytic efficiencies. Additional data from substrate-dependent pH profiles and hydrolysis of large polypeptides indicate that the His64Ala mutant enzyme can recover partially the function of the lost catalytic histidine from a His P2 side chain on the substrate. Such "substrate-assisted catalysis" provides a new basis for engineering enzymes with very narrow and potentially useful substrate specificities. These studies also suggest a possible functional intermediate in the evolution of the catalytic triad of serine proteases.     

胶体金免疫层析法检测猪旋毛虫病试验

用胶体金免疫层析试纸条检测10份猪旋毛虫病阳性样品,结果均为阳性;检测18份猪蛔虫病、12份猪囊虫病、11份猪细颈囊尾蚴病阳性样品和10份健康猪阴性样品,结果全部呈阴性;检测6份人工感染猪旋毛虫病阳性血清抗体滴度,结果与ELISA方法相一致。用该试纸条诊断旋毛虫病,特异性高,敏感性强,重复性和稳定性好,方法简便,快速实用。     

Organometallic chemistry in homogeneous catalysis

Many reactions catalyzed by soluble transition metal compounds proceed by way of organometallic intermediates, even though the original catalyst may be a simple salt. This generality is illustrated for three industrial syntheses of acetic acid that use homogeneous catalysts. Some developments in organometallic chemistry that may extend the utility of homogeneous catalysis are photoactivation of catalysts and the recognition of the importance of metallacyclic intermediates.     

Homogeneous catalysis in supercritical fluids

Supercritical fluids (SCFs), compounds heated and pressurized beyond the critical point, have many unusual properties. Homogeneous molecular catalysts, which have far greater control over selectivity than heterogeneous solid catalysts, are now being tested in SCFs, and early results show that high rates, improved selectivity, and elimination of masstransfer problems can be achieved. As industry moves away from toxic or environmentally damaging solvents, supercritical carbon dioxide may be an ideal replacement medium for nonpolar or weakly polar chemical processes. More than simply substitutes for nonpolar solvents, SCFs can radically change the observed chemistry. Supercritical carbon dioxide is also an excellent medium for its own fixation, as demonstrated by studies of its hydrogenation.     

Carbon compounds in interplanetary dust: evidence for formation by heterogeneous catalysis

Associations of carbonaceous material with iron-nickel alloy, carbides, and oxides were identified by analytical electron microscopy in ten unmelted chondritic porous micrometeorites from the earth's stratosphere. These associations, which may be interpreted in terms of reactions between a carbon-containing gas and catalytically active dust grains, suggest that some of the carbon in the chondritic porous subset of interplanetary dust was emplaced through heterogeneous catalysis.     

广东高等农业院校参与公益性农技推广人员培训的模式探索

农业现代化的发展和农业的创收在很大程度上取决于广大农技推广人员的科技水平.面对急需培训的农技推广人员队伍,在分析国内外高等农业院校参与公益性农技推广人员培训模式的基础上,提出依托广东高等农业院校成功的继续教育模式,建立农村远程培训的长效机制,建立农技人员培训网络平台,建设农技培训网络教学资源库,以及组织大型专题培训,普及推广现代农业技能等对策,从而解决目前培训模式中存在的时空限制、规模过小、互动性缺乏等问题.     

Mercury detection by means of thin gold films

The adsorption of elemental mercury vapor on a thin (several hundred angstroms) gold film produces resistance changes in the film. An instrument for the detection of mercury based on this phenomenon is simple and rapid and requires no chemical separations other than passage of the vapor sample through a few standard dry filters. The instrument is portable, and the technique is directly applicable to environmental problems and geochemical prospecting. The limit of detection of the prototype instrument is 0.05 nanogram of mercury.     

福建省城镇-交通系统的景观分隔效应

近年来,我国城市及交通基础设施建设的迅猛发展对区域生态功能造成了严重影响。城镇-交通网络的不断强化和扩展加剧了区域景观的破碎化并导致多种景观功能的退化。以2007年为研究基准年,采用跨边界有效栅格评价指标,借助地理信息技术,定量评估了福建省由城镇-交通网络引发的景观分隔效应。研究结果显示,面积大小位于0-15 km²的斑块数量最多。厦门、漳州、泉州3市小于300 km²的斑块面积及斑块数量分别所占比例率均高于南平、三明和龙岩3市。福建省有效栅格计算结果显示,全省景观破碎化呈现北轻南重、西轻东重的空间分布格局。沿海地区和交通干线周边破碎化明显高于其他地区。以地市为报告单位,福建省景观破碎化的空间分布呈现由西向东的梯度格局。景观破碎化最轻微地区(龙岩市、三明市、南平市有效栅格值处于679.2-939.0 km²之间)和最严重地区(厦门市、泉州市、漳州市的有效栅格值处于197.1-336.2 km²之间)形成鲜明对比。结果还显示,福建省厦门市、泉州市、漳州市的景观破碎化水平与欧洲发达国家如荷兰、比利时等接近;西部的三明市、北部的南平市则接近美国加利福尼亚。以县(市、区)为报告单位,全省景观破碎程度的空间分布从西至东呈现三级梯度。以瑞士Glarus州跨边界有效栅格值为参照,厦门、泉州和漳州3市所辖各县(市、区)的景观破碎化程度均高于Glarus。宁德、福州、莆田3市各县(市、区)则与Glarus基本持平。南平、三明、龙岩3市各县(市、区)则好于Glarus,其中,三明市和南平市各县(市、区)跨边界有效栅格值远大于Glarus。     

The structure of catalytically active gold on titania

The high catalytic activity of gold clusters on oxides has been attributed to structural effects (including particle thickness and shape and metal oxidation state), as well as to support effects. We have created well-ordered gold mono-layers and bilayers that completely wet (cover) the oxide support, thus eliminating particle shape and direct support effects. High-resolution electron energy loss spectroscopy and carbon monoxide adsorption confirm that the gold atoms are bonded to titanium atoms. Kinetic measurements for the catalytic oxidation of carbon monoxide show that the gold bilayer structure is significantly more active (by more than an order of magnitude) than the monolayer.