Catalytic mechanism of an abzyme displaying a beta-lactamase-like activity

A catalytic IgG (Ab2) displaying a beta-lactamase-like activity was previously obtained by using the antiidiotypic pathway: the particularity of this antibody is that it is a true antiidiotype of the beta-lactamase active site. We have previously demonstrated that this IgG has retained some of the structural information displayed by the beta-lactamase active site, evident from data that polyclonal anti-Ab2 antibodies (Ab3) recognize beta-lactamase. In this article, we investigated the catalytic mechanism of the abzyme compared to that of the enzyme. The experimental data allow us to hypothesize the catalytic residues required for catalysis.     

Thermodynamic Evaluation of Non-Equilibrium Compositions and Activity of Multicomponent Catalysts in Redox Reactions

The analysis of structural state and energetic properties of active catalyst component in oxide copper-containing catalytic system has been performed on the basis of comparing the data of thermochemical, X-ray diffraction and catalytic activity determinations. The analysis of thermochemical data obtained makes it possible to evaluate changes in lattice energy and the nearest coordination sphere energetic parameters of copper cations during the formation of solid solutions. The high degree of correlation of catalytic properties and the formation enthalpy of solid solutions can be explained by the fact that alongside with the factors influencing the catalytic activity it is the strength of cation—cation interaction that is the most important.This revised version was published online in November 2005 with corrections to the Cover Date.     

Gas transfer and water vapor condensation in cathode layers of air–hydrogen fuel cells

Model of heat and mass transfer in catalytic cathode layers of air–hydrogen fuel cells is developed on the basis of experimental data on the layers’ structure. The effect of carbon nanotubes is analyzed: their introducing into the catalytic layer increased the layer’s porosity. The derived analytical expressions allow estimating the carbon-nanotubes-content-dependence of the catalytic layer structure parameters, in particular, the gas channel characteristic dimensions and oxygen and water molecule diffusion coefficients. The simulation results showed that the adding of carbon nanotubes into the catalytic layer allows increasing the fuel cell power significantly, due to removal of limitations caused by water condensation process. The calculated results agree well with the previously obtained experimental data.     

Catalysis by supported gold: correlation between catalytic activity for CO oxidation and oxidation states of gold

X-ray absorption near-edge spectra and temperature-programmed oxidation and reduction data demonstrate that Au(I) and Au(0) are both present in working MgO-supported gold catalysts for CO oxidation. EXAFS data indicate gold clusters with essentially the same average diameter (about 30 A) in each catalyst sample. Thus, the results provide no evidence of an effect of gold cluster size on the catalytic activity, but both the catalytic activity and the surface concentration of Au(I) were found to decrease with increasing CO partial pressure (as Au(0) was increasingly formed), demonstrating that the catalytic sites incorporate Au(I).     

Role of the base and endogenous anions in “ligand-free” catalytic systems for the Suzuki–Miyaura reaction

UV spectroscopic studies combined with kinetic measurements for the Suzuki–Miyaura reaction catalyzed by “ligand-free” catalytic systems have demonstrated that the base is involved in the formation of the palladium complexes ensuring the occurrence of the transmetalation stage. It follows from UV monitoring data for the catalytic reaction involving aryl iodides that a considerable part of palladium during the process is in the form of Pd²⁺ acid complexes with endogenous anions and does not participate in the main catalytic cycle.     

The influence of modifying admixtures on the catalytic properties of the Ni<Subscript>3</Subscript>Al intermetallic compound in the conversion of methane with carbon dioxide

Catalytic systems based on the Ni₃Al intermetallic compound and modified with niobium and chromium were studied in methane reforming with carbon dioxide. The catalysts were prepared under self-propagating high-temperature synthesis conditions. The phase composition of the catalytic systems was studied by X-ray diffraction. The catalytic activity of the samples increased as the concentration of modifying admixtures decreased and was maximum at 2% concentrations of Nb and Cr. The scanning electron microscopy data showed that the catalytic systems experienced substantial structural changes, which caused catalytic activity loss with time.     

气相色谱法测定平衡催化裂化催化剂中碳元素含量

石油催化裂化反应中生成附着在催化剂表面的碳的单质或化合物会隔绝石油与催化剂的接触，从而使催化剂的选择性、活性降低．对平衡催化裂化催化剂中碳元素含量进行测定，可以有效地指导炼油厂的生产．通过对准确性、重复性的考察，表明燃烧和色谱测定法是平衡催化裂化催化剂中碳元素含量测定的有效方法之一．     

Mechanism of the catalytic carbonylation of aryl halides with a modified cobalt carbonyl

Investigation of the mechanism of the carbonylation of aryl halides in a catalytic system consisting of cobalt carbonyl, terminal olefin oxide, and base showed that this catalytic system activates aryl halides via a radical anion mechanism. The kinetic regularities of the process together with IR spectral data suggest reversible formation of the active catalytic complex under the reaction condition. The complex is a cyclic metal lactone, and it can form not only from olefin oxide but also from its methanolysis product, the corresponding glycol monomethyl ether.     

Construction and Activity of a New Catalytic System in the Hydrolysis of Bis(4‐nitrophenyl) Phosphate Ester

A new catalytic system containing an unsaturated heterocyclic nitrogen ligand and lanthanum(III) was constructed and used as a catalyst in the hydrolysis of bis(4‐nitrophenyl) phosphate ester (BNPP) in this work. The results indicated that this catalytic system showed greater catalytic activity in the hydrolysis of BNPP and better reproducibility and stability than other similar lanthanum(III) systems. The catalytic rate of the BNPP hydrolysis was about 10⁷‐fold faster than that of its spontaneous hydrolysis at the same conditions. Compared with the previous Cu(II) or Ni(II) complex containing the same ligand in the water, the activity of the macrocyclic La(III) complex increases ca. 10³‐fold for BNPP catalytic hydrolysis. The experimental data showed that the monohydroxy complex made of the heterocyclic nitrogen ligand and lanthanum(III) is the real active species as a catalyst in BNPP catalytic hydrolysis.     

尖晶石CuM2O4(M=Al、Fe、Cr)催化甲醇重整反应的特性

采用柠檬酸络合法,经900 ℃热处理制备了CuAl₂O₄、CuFe₂O₄和CuCr₂O₄三种尖晶石,并进行了甲醇重整性能评价。结合XRD、H₂-TPR、SEM和BET等表征,研究了铜基尖晶石的催化特性。结果表明,三种铜基尖晶石的形貌和大小有极大差异,表现出不同的催化性能,CuAl₂O₄尖晶石获得最优的稳定性和最低的CO选择性,CuFe₂O₄尖晶石上CO选择性最高且稳定性差,CuCr₂O₄尖晶石上石墨碳沉积最严重。根据长时间评价结果和表征数据发现,在反应气氛中铜基尖晶石不稳定,通过释放活性铜而起催化作用;同时铜的烧结长大与积炭现象共同影响催化性能。     

Catalytic Ignition of Light Hydrocarbons

Catalytic ignition refers to phenomenon where sufficient energy is released from a catalytic reaction to maintain further reaction without additional extemai heating. This phenomenon is important in the development of catalytic combustion and catalytic partial oxidation processes, both of which have received extensive attention in recent years. In addition, catalytic ignition studies provide experimental data which can be used to test theoretical hydrocarbon oxidation models. For these reasons, catalytic ignition has been frequently studied. This review summarizes the experimental methods used to study catalytic ignition of light hydrocarbons and describes the experimental and theoretical results obtained related to catalytic ignition. The role of catalyst metal, fuel and fuel concentration, and catalyst state in catalytic ignition are examined, and some conclusions are drawn on the mechanism of catalytic ignition.     

Copper-homoscorpionate complexes as active catalysts for atom transfer radical addition to olefins

Cu(I) complexes containing trispyrazolylborate ligands efficiently catalyze the atom transfer radical addition (ATRA) of polyhalogenated alkanes to various olefins under mild conditions. The catalytic activity is enhanced when bulky and electron donating Tpx ligands are employed. Kinetic data have allowed the proposal of a mechanistic interpretation that includes a Cu(II) pentacoordinated species that regulates the catalytic cycle.     

湿式氧化吡虫啉农药生产废水的MnOx-CeO2催化剂性能研究

采用共沉淀法制备了用于湿式氧化吡虫啉农药废水的MnOx-CeO2系列催化剂, 利用比表面测定仪(BET), X射线衍谢仪(XRD)和X射线光电子能谱(XPS)等对其进行了表征, 并研究了不同Mn/(Mn+Ce)摩尔比对催化剂表面形态的影响以及催化剂表面形态与活性之间的关系. BET和XRD表征结果表明, Mn/(Mn+Ce)摩尔比为0.6时, 催化剂晶粒尺寸最小, 比表面积最大. XRD和XPS表征结果显示, Mn和Ce氧化物之间存在明显的相互作用, 催化剂表面Mn的氧化态和化学需氧量(COD)随着组成的变化而变化, 当Mn/(Mn+Ce)摩尔比为0.7时, 催化剂表面出现高价锰氧化物, 而且其化学吸附氧最多. 用Mn/(Mn+Ce)摩尔比为0.7的MnOx-CeO2催化湿式氧化吡虫啉农药废水时, 当催化剂用量为4 g/L, 反应温度190 ℃, 进水pH为7.0, 氧分压1.6 MPa, 搅拌速度500 r/min, 反应60 min时, COD去除率最大为89.3%.     

Catalytic decomposition of peroxides by medicinal activated carbons

The catalytic properties of carbon hemosorbents were investigated in reactions of the decomposition of peroxide compounds simulating the peroxides of lipids. It was shown that SKN carbons have much higher catalytic activity than SKS or VAS-MU. A mechanism of the catalytic action of the carbons during hemocarboperfusion is proposed on the basis of theories of radical-chain degenerate branched processes. It is concluded that catalytic reactions must be taken into account in extracorporal detoxification. The mechanism that is given is in agreement with the experimental data according to the intensity of the EPR signal in the blood during ischemic heart disease and other pathologies.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 3, pp. 366–370, May–June, 1989.     

Spectroscopic Observation of Calcium‐Induced Reorientation of Cellobiose Dehydrogenase Immobilized on Electrodes and its Effect on Electrocatalytic Activity

Cellobiose dehydrogenase catalyzes the oxidation of various carbohydrates and is considered as a possible anode catalyst in biofuel cells. It has been shown that the catalytic performance of this enzyme immobilized on electrodes can be increased by presence of calcium ions. To get insight into the Ca²⁺‐induced changes in the immobilized enzyme we employ surface‐enhanced vibrational (SERR and SEIRA) spectroscopy together with electrochemistry. Upon addition of Ca²⁺ ions electrochemical measurements show a shift of the catalytic turnover signal to more negative potentials while SERR measurements reveal an offset between the potential of heme reduction and catalytic current. Comparing SERR and SEIRA data we propose that binding of Ca²⁺ to the heme induces protein reorientation in a way that the electron transfer pathway of the catalytic FAD center to the electrode can bypass the heme cofactor, resulting in catalytic activity at more negative potentials.     

氢气对正丁烷/空气混合物催化着火的热作用和化学作用

通过对正丁烷/氢气/空气混合物在Pt 催化表面的详细反应机理分析, 研究了氢气添加对正丁烷/空气混合物催化着火过程的影响. 研究发现, 在正丁烷/空气混合中添加氢气有助于正丁烷在更低的温度下实现催化着火, 而且不同的氢气添加量对混合物的着火温度和着火过程呈现不同的影响: 当氢气添加量较小时, 氢气的作用主要呈现为热影响; 而当氢气添加量较大时, 氢气的作用主要呈现为化学影响. 这些结果与实验结果是一致的. 本文进一步确定了发挥不同作用的氢气添加量的范围, 并分别对热作用和化学作用情况下的着火启动反应进行了动力学分析.     

Insights into the mechanism of N2O reduction by reductively activated N2O reductase from kinetics and spectroscopic studies of pH effects

Nitrous oxide reductase (N2OR) from Achromobacter cycloclastes (Ac) can be reductively activated with reduced methyl viologen over a broad range of pH. Activated Ac N2OR displays a complex activity profile as a function of the pH at which catalytic turnover is measured. Spectroscopic and steady-state kinetics data suggest that [H+] has multiple effects on both the activation and the catalytic reactions. These experimental results are in good agreement with previous theoretical studies, which suggested that the transition state is stabilized by H-bonding interactions between the active site and an N2O-derived intermediate bound to the catalytic CuZ cluster.     

Pd-Co-Mo electrocatalyst for the oxygen reduction reaction in proton exchange membrane fuel cells

The catalytic activity of carbon supported Pd-Co-Mo for the oxygen reduction reaction (ORR) in a single cell proton exchange membrane fuel cell (PEMFC) has been investigated at 60 degrees C and compared with data from commercial Pt catalyst and our previously reported Pd-Co-Au and Pd-Ti catalysts. The Pd-Co-Mo catalyst with a Pd:Co:Mo atomic ratio of 70:20:10 exhibits slightly higher catalytic activity like the Pd-Co-Au catalyst than the commercial Pt catalyst, but with excellent chemical stability unlike the Pd-Co-Au catalyst. The Pd-Co-Mo catalyst also exhibits better tolerance to methanol poisoning than Pt. Investigation of the catalytic activity of the Pd-Co-Mo system with varying composition and heat treatment temperature reveals that a Pd:Co:Mo atomic ratio of 70:20:10 with a heat treatment temperature of 500 degrees C exhibits the highest catalytic activity. Although the degree of alloying increases with increasing temperature from 500 to 900 degrees C as indicated by the X-ray diffraction data, the catalytic activity decreases due to an increase in particle size and a decrease in surface area.     

杂元素冠醚研究 Ⅷ．10─硫杂苯并－15－冠－5铂配合物催化硅氢化反应的研究

本文通过双（２－羟基乙基）硫酸与１，２一双（２’－对甲苯磺酞氧基乙氧基）苯缩合闭环，得到１０－硫杂苯并－１５－冠－５，后者再与氯亚铂酸钾反应得到标题配合物；同时研究了该配合物对烯烃与三乙氧基硅烷的硅氢加成反应的催化特性，并与硒、碲的类似配合物进行了比较．结果表明，此配合物是烯烃硅氢化反应的高效催化剂．     

开链冠醚类似物(Ⅱ)——4-氧安替比林为端基的含氮开链冠醚等效物的合成与研究

本文合成了11种以4-氧安替比林为端基的含氮开链冠醚类似物,通过元素分析和波谱鉴定了它们的结构.报道了4-羟基安替比林O-烷基化的新方法.相转移催化性能研究表明,它们可以作为液-液相或固-液相转移的良好催化剂。