Poly(ethylene glycol)-supported nitroxyls: branched catalysts for the selective oxidation of alcohols

Nitroxyl radicals such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) are highly selective oxidation catalysts for the conversion of primary alcohols into the corresponding aldehydes. In this study, direct tethering of TEMPO units onto linear poly(ethylene glycol) (PEG) has afforded macromolecular catalysts that exhibit solubility in both aqueous and organic solvents. Recovery of the dissolved polymer-supported catalyst has been carried out by precipitation with a suitable solvent such as diethyl ether. The high catalyst activities and selectivities associated traditionally with nitroxyl-mediated oxidations of alcohols are retained by the series of "linker-less" linear PEG-TEMPO catalysts in which the TEMPO moiety is coupled directly to the PEG support. Although the selectivity remains unaltered, upon recycling of the linker-less polymer-supported catalysts, extended reaction times are required to maintain high yields of the desired carbonyl compounds. Alternatively, attachment of two nitroxyl radicals onto each functionalized PEG chain terminus via a 5-hydroxyisophthalic acid linker affords branched polymer-supported catalysts. In stark contrast to the linker-less catalysts, these branched nitroxyls exhibit catalytic activities up to five times greater than 4-methoxy-TEMPO alone under similar conditions. In addition, minimal decrease in catalytic activity is observed upon recycling of these branched macromolecular catalysts via solvent-induced precipitation. The high catalytic activities and preservation of activity upon recycling of these branched systems is attributed to enhanced regeneration of the nitroxyl species as a result of intramolecular syn-proportionation.     

Aerobic oxidation of alcohols to carbonyl compounds mediated by poly(ethylene glycol)-supported TEMPO radicals

Two poly(ethylene glycol)-supported TEMPO (PEG-TEMPO) has been successfully applied as soluble, recyclable catalysts in the chemoselective oxidation of primary and benzylic alcohols with molecular oxygen in the presence of Co(NO₃)₂ and Mn(NO₃)₂ as co-catalysts (Minisci's conditions). Under those conditions, secondary alcohols are also oxidized to ketones, although usually in lower yields. The insertion of a spacer between the PEG moiety and TEMPO has beneficial effects on both the activity and ease of recovery of the supported catalyst.     

Reductive carbonylation of nitrobenzene over Pd/Fe/I2/Py and Pd/C/Fe/I2/Py catalytic systems

A simple catalytic system containing metallic palladium, iron and iodine has been shown to be very active in the carbonylation of nitrobenzene to carbamate. The influence of the components of the catalytic system studied on its selectivity and activity has been established. It has been found that the catalytic activity of palladium supported on carbon (using both lignite coal and bituminous coal) was not lower than the activity of metallic palladium. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study on catalytic oxidation of planar binuclear copper phthalocyanine on 2-mercaptoethanol

Mononuclear copper phthalocyanine (CuPc) and binuclear copper phthalocyanine (Cu2Pc2) were synthesized by the phenylanhydride-urea route, and their catalytic oxidation activity on 2-mercaptoethanol was studied. Based on the experimental results, a catalytic mechanism of Cu2Pc2 on 2-mercaptoethanol has been proposed. Furthermore, the effects of pH, Cu2Pc2 concentration, and temperature on the catalytic oxidation activity were evaluated. The results showed that CuPc has no catalytic activity, while Cu2Pc2 has high catalytic oxidation activity towards 2-mercaptoethanol with the optimal activity at pH 11. The reaction can further be enhanced by increasing Cu2Pc2 concentration and temperature, due to its endothermic characteristics.     

Palladium nanoparticles in aqueous solution: Preparation,properties, and effect of their size on catalytic activity

A method has been developed for the preparation of palladium nanoparticles with different sizes of up to 7 nm via the reduction of Pd(II) ions with hydrogen in an aqueous solution on seed metal nanoparticles (2.5 nm). The effect of the size of nanoparticles on their catalytic activity in methyl viologen reduction with molecular hydrogen in an alkaline medium has been studied. It has been found that the specific catalytic activity of palladium nanoparticles is independent of their size.     

Significantly enhancing catalytic activity of tetrahexahedral Pt nanocrystals by Bi adatom decoration

Tetrahexahedral Pt nanocrystals (THH Pt NCs) bounded by high-index facets possess a high density of active sites and display therefore a higher catalytic activity in comparison with those enclosed by low-index facets. In the current communication, we report, for the first time, the decoration of THH Pt NC surfaces by using Bi adatoms and have demonstrated that the catalytic activity of the Bi decorated THH Pt NCs toward HCOOH electrooxidation has been drastically enhanced in comparison with bare THH Pt NCs. It has also been revealed that the catalytic activity of Bi decorated THH Pt NCs for all coverages investigated always exhibits a higher catalytic activity that is about double that of Bi decorated Pt nanospheres. The study is of great importance regarding both fundamentals and applications.     

The study and application of biomimic peroxidase ferric 2-hydroxy-1-naphthaldehyde thiosemicarbazone (Fe(III)-HNT)

Ferric 2-hydroxy-1-naphthaldehyde thiosemicarbazone (Fe(III)-HNT) has been synthesized and used to mimic the active group of horseradish peroxidase (HRP). The catalytic characteristics of this mimic-enzyme catalyst in the oxidation reaction of ascorbic acid with hydrogen peroxide has been studied. The experimental results showed that this peroxidase model compound has similar catalytic activity that of HRP. The catalytic activity of Fe(III)-HNT has been compared with those of HRP and common mimic-enzymes, metalloporphyrins (e.g. metal tetrakis(sulphophenyl)porphyrin (Me-TPPS(4))). Though the catalytic activity of Fe(III)-HNT is 75% of that of HRP, it can be used as a new kind of mimic-enzyme catalyst in determination of trace H(2)O(2). By coupling this mimetic catalytic reaction with the catalytic reaction of glucose oxidase, glucose can be determined indirectly. Under experimental conditions the linear relationship between DeltaA(265) and glucose concentration was in the range of 2.0-40.0 mug ml(-1), The correlation coefficient (r) was 0.9996. The R.S.D. (P=0.05, n=6) was 0.24%. The detection limit was determined to be 0.238 mug ml(-1). It was applied successfully to the determination of glucose in normal human and diabetic urine. The values of determination by the proposed method were compared with those of a routine method (enzymic glucose determination) applied in an hospital clinical laboratory. The agreement was very good.     

Are amines basic or nucleophilic catalysts for oxirane ring opening by proton-donating nucleophiles?

The behavior of amines as catalysts for oxirane acidolysis and phenolysis has been studied using kinetic methods. The apparent catalytic and noncatalytic reaction rate constants have been estimated. It has been demonstrated that the noncatalytic pathway has almost no effect on the apparent reaction rate constant. In order to determine the character of the behavior of amines (bases/nucleophiles) in this reaction, their reactivity has been analyzed within the conceptions of basic and nucleophilic mechanisms of catalysis. Based on the quantitative amine structure—catalytic activity correlation, it has been shown by comparing the values of correlation coefficients (r) of equations describing mechanisms for various reaction systems that, in the reactions of oxiranes with proton donors (carboxylic acids and phenols), the catalytic activity of tertiary amines/pyridines is determined by their nucleophilicity rather than basicity.     

新癌药物的电化学研究1: 一种Fe(III) Schiff碱配合物的基本电化学性质及其与DNA的相互作用

研究了一种自合成的Schiff碱配合物的电化学行为及其与氧和DNA的相互作用。发现此种Schiff碱配合物能与氧发生相互作用而具有吸氧功能, 并对氧的电还原有催化作用, 同时还发现dsDNA能与此种Schiff碱配合物发生较强的相互作用, 特别是Fe(II)Schiff碱配合物更易与dsDNA结合。     

Co-B非晶态合金超细微粒的热稳定性与催化性能研究

利用化学还原法制备了Co—B非晶态合金超细微粒，用电感耦合等离子体光谱(ICP)、电子显微镜(TEM)、X射线粉末衍射(XRD)、BET、表面积测试及X光电子能谱(XPS)等手段对新鲜样品及经过不同温度热处理后的样品进行了表征，并用微型催化反应装置评价其CO H2催化性能．结果表明，经过热处理后的样品不仅其表面组成和结构状态发生了变化，而且其催化性能也发生了明显变化，同时还表明非晶态Co—B合金超细微粒具有比其晶态更高的催化活性和独特的选择性。     

Synthesis, characterization and structures of 2-(3,5-dimethylpyrazol-1-yl)ethylseleno derivatives and their probable glutathione peroxidase (GPx) like activity

A series of 2-(3,5-dimethylpyrazol-1-yl)ethylseleno derivatives has been synthesized. The glutathione peroxidase like catalytic activity of these compounds has been studied in a model system, in which reduction of hydrogen peroxide with dithiothreitol (DTT(red)), in the presence of an organoselenium compound was investigated by (1)H NMR spectroscopy. All these compounds exhibit GPx like catalytic activities and the catalytic reaction proceeds through a selenoxide intermediate, identified by (77)Se{(1)H} NMR spectroscopy.     

钙钛矿型化合物催化氧化性能与d电子构型关系的研究

我们用活性评价、磁性测定、原子吸收光谱、TPR(程序升温还原)、TPSR(程序升温表面反应)、XRD等手段研究了以共沉淀和混合法制备的LaMO2(M为从钛到铜的八个过渡金属离子)钙钛矿型化合物对CH4和CO的催化氧化性能。结果表明, 随M离子的d电子数增多, 催化剂的催化氧化活性呈现三峰变化模式并与表面氧结合能及TPSR活性氧物种分布规律一致。根据磁性分析了M离子d电子组态, 对活性的三峰现象作了说明。比较了不同方法对催化剂上氧物种的表征效果。考察了在氧化还原气氛下M离子价态变化规律。根据实验结果讨论了催化剂上活性氧物种分布。     

Synthesis and characterization of polyaniline: nanospheres,nanorods, and nanotubes—catalytic application for sulfoxidation reactions

The synthesis of nanostructured polyaniline (PANI) with different morphologies by simple alkali‐guided template‐free method followed by doping them with vanadium has been described. The synthesized polyaniline nanoparticles have been well characterized by various techniques. Further, the catalytic activity of the undoped and doped PANI nanostructures for selective oxidation of sulfides to sulfoxides in water has been studied. It was observed that the special morphology of nanostructures plays an important role in enhancement of catalytic activity. Vanadium‐doped PANI nanotubes and nanorods showed higher activity and selectivity than nanospheres. The catalyst has been reused for five consecutive cycles with consistent activity. Copyright © 2008 John Wiley & Sons, Ltd.     

PNPP catalytic hydrolysis by mono- and binuclear transition-metal complexes with polyether-bridged dihydroxamic acids

Polyether-bridged dihydroxamic acids and their mono- and binuclear copper(II), and cobalt(II) complexes have been synthesized and employed as models to mimic hydrolase in the catalytic hydrolysis of p-nitrophenyl picolinate (PNPP). The kinetics and the mechanism of PNPP hydrolysis have been investigated. The kinetic mathematical model of PNPP cleavage by the complexes has been proposed. The effects of the different central metal ion, mono- and binuclear metal, the pseudo-macrocyclic polyether constructed by the polyethoxy group in complexes, and reactive temperature on the rate of PNPP catalytic hydrolysis have been examined. The results show that the transition-metal dihydroxamates exhibit high catalytic activity in the PNPP hydrolysis; the rate of the PNPP hydrolysis increases with the increase in pH of the buffer solution; the catalytic activity of binuclear complexes is higher than that of mononuclear complexes; the catalytic activity of copper(II) complex is about four times that of the cobalt(II) complex; the pseudo-macrocyclic polyether can synergetically activate H₂O coordinated to the metal ion with the central metal ion together and promote the PNPP catalytic hydrolysis.     

Hydrodesulfurization catalysts P-Mo-W/γ-Al2O3: Characterization and catalytic activity

P-Mo-W/γ-Al₂O₃ catalysts with various Mo and W contents have been synthesized. The parameters of the porous structure of their sulfide and oxide forms have been determined. The geometric parameters of the active phase of the sulfide catalysts have been calculated using high-resolution transmission electron microscopy data. The catalytic activity has been estimated in dibenzothiophene (DBT) hydrodesulfurization (HDS). The reaction under the conditions examined proceeds mainly as direct hydrodesulfurization. The catalytic activity has been correlated with the Mo/W molar ratio and with the proportions of edge and corner sites.     

Selective oxidation of sulfides and oxidative bromination of organic substrates catalyzed by polymer anchored Cu(II) complex

A new polymer-anchored Cu(II) complex has been synthesized and characterized. The catalytic performance of the complex has been tested for the oxidation of sulfides and in oxidative bromination reaction with hydrogen peroxide as the oxidant. Sulfides have been selectively oxidized to the corresponding sulfoxides in excellent yields and in the presence of KBr as the bromine source, organic substrates have been selectively converted to mono bromo substituted compounds using polymer-anchored Cu(II) catalyst. This catalyst showed excellent catalytic activity, high selectivity, and recyclability. The polymer-anchored Cu(II) catalyst could be easily recovered by filtration and reused more than five times without appreciable loss of its initial activity.     

杂多酸(盐)及单缺位磷钨杂多化合物在醇类氧化反应中的催化活性

在相转移条件下,研究了杂多化合物在苄醇,环己醇氧化反应中的催化活性.六种Keggin结构杂多酸的催化活性按GeMo~12(H~4GeMo~12O~40的简写,其余类推,PW~12,PMo~12,SiMo~12,GeW~12,SiW~12顺序下降,杂多酸中的质子可分别被其它阳离逐渐取代而达到酸性修饰. H~3PW~12O~40随着其质子逐步被Na^+取代,酸性下降,催化活性大大提高;杂多酸(盐)的催化活性随体系pH值的改变将发生奇妙剧烈的变化;单缺位杂多化合物显示出较饱和杂多酸(盐)更高催化活性.溶剂对催化活性有明显影响.     

Mn(Ⅲ)-四芳基卟啉与高碘酸四丁基铵催化羧酸的氧化脱羧:金属、取代基和轴向阴离子配体的影响

锰四芳基卟啉与高碘酸四丁基铵(n-Bu4NIO4)和咪唑(ImH)组合,为羧酸氧化脱羧提供了一个有效的催化剂体系.中位含有吸电子基团和/或大体积芳基的中位-四芳基卟啉使金属卟啉的活性降低.咪唑的存在和金属中心的选择对金属卟啉的催化性能起关键性作用,催化体系中的反离子也有重要影响.Mn(TPP)CN/n-Bu4NIO4/ImH体系的催化活性最好.二苯基乙酸的氧化脱羧可能涉及高价的含氧锰物种与反应物间的相互作用,提出了可能的反应机理.     

硅胶功能化的N-丙哌嗪固载钯纳米粒子作为有效的多相催化剂用于氰化反应(英文)

An efficient heterogeneous Pd catalytic system has been developed, based on immobilization of Pd nanoparticles (PNPs) on a silica-bonded N-propylpiperazine (SBNPP) substrate. The SBNPP substrate effectively stabilizes the PNPs and improves their stability against aggregation. The catalytic activity of this catalyst was investigated in the cyanation of aryl halides with K4[Fe(CN)6 ] as the cyanide source. The catalyst could be recycled several times without appreciable loss of catalytic activity.     

Yolk-shell gold nanoparticles as model materials for support-effect studies in heterogeneous catalysis: Au, @C and Au, @ZrO2 for CO oxidation as an example

The use of nanostructured yolk-shell materials offers a way to discriminate support and particle-size effects for mechanistic studies in heterogeneous catalysis. Herein, gold yolk-shell materials have been synthesized and used as model catalysts for the investigation of support effects in CO oxidation. Carbon has been selected as catalytically inert support to study the intrinsic activity of the gold nanoparticles, and for comparison, zirconia has been used as oxidic support. Au, @C materials have been synthesized through nanocasting using two different nonporous-core@mesoporous-shell exotemplates: Au@SiO(2)@ZrO(2) and Au@SiO(2)@m-SiO(2). The catalytic activity of Au, @C with a gold core of about 14 nm has been evaluated and compared with Au, @ZrO(2) of the same gold core size. The strong positive effect of metal oxide as support material on the activity of gold has been proved. Additionally, size effects were investigated using carbon as support to determine only the contribution of the nanoparticle size on the catalytic activity of gold. Therefore, Au, @C with a gold core of about 7 nm was studied showing a less pronounced positive effect on the activity than the metal oxide support effect.