A new mechanism of acyl group transfer in the reaction catalyzed by D-glyceraldehyde-3-phosphate dehydrogenase

D-Glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) catalyzes the oxidative phosphorylation of its substrate in a two-step reaction. Asa result of the first, oxidativestep, the covalent intermediate where in 3-phosphoglyceroyl moiety is bound to Cys149 of the active center is subjected to nucleophilic attack by inorganic phosphate, but remains resistant to hydrolytic decomposition. This ensures tight coupling of oxidation with phosphorylation in glycolysis. In this article, we present the experimental evidence for the conversion of GAPDH into a form capable of performing the reaction in the absence of inorganic phosphate. The structural basis for this conversion is the oxidation of a cysteine residue (probably Cys 153) into a sulfenic acid derivative under mild conditions to affect the integrity of the essential Cys 149. As a result, an intram olecular transfer of 3-phosphoglyceroyl group from the active center Cys 149 to Cys 153 becomes possible with subsequent hydrolysis of the sulfenyl carboxylate intermediate.     

Sol–gel combustion synthesis of chromium doped yttrium aluminum perovskites

A water-based sol–gel combustion synthesis was optimized in order to achieve pure yttrium aluminium perovskite (YAlO₃, YAP). The method involved three main steps: xerogel formation, combustion treatment and calcination of the combusted precursors. TG DTA, FTIR and XRPD, used to investigate the precursor phase evolution, confirmed the strong influence of gel synthesis conditions, combustion temperature and calcination rate on YAP purity. Both stoichiometry and kinetics control during all the preparation steps are crucial in order to avoid the formation of undesired Y₃Al₅O₁₂ (YAG) and Y₄Al₂O₉ (YAM) stable phases. This method allowed to synthesize, for the first time from an aqueous sol–gel process, single phase samples of YAP. A series of samples with composition: YAl_(1−x)Cr_(x)O₃ where x is 0, 0.035, 0.135, 0.250, 0.500, 0.750 was obtained. A consistent decrease of calcination temperature, with respect to conventional solid state synthesis, was achieved by sol–gel combustion, avoiding polyphase materials even without the use of mineralizers. This is an important result in several applications like the synthesis of ceramic pigments.     

The effect of Co(II)‐mediated catalytic chain transfer on the emulsion polymerization kinetics of methyl methacrylate

The effect the catalytic chain transfer agent, bis[(difluoroboryl) dimethylglyoximato] cobalt(II) (COBF), on the course of the ab initio emulsion polymerization of methyl methacrylate, and the product properties in terms of the molecular weight distribution were investigated. The emulsion polymerization kinetics have been studied with varying surfactant, initiator, and COBF concentrations. The experimentally determined average number of radicals per particle strongly depends on the concentration of COBF and proves to be in good agreement with the results of model calculations. The apparent chain transfer constant, determined up to high conversion, is in excellent agreement with the predicted value based on a mathematical model based on COBF partitioning and the Mayo equation. The results of this work enhance the fundamental understanding of the influence a catalytic chain transfer agent has on the course of the emulsion polymerization and the control of the molecular weight distribution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5078–5089, 2009     

Catalytic decomposition of hydrogen peroxide by Cu/M heterobimetallic complexes (M = Mn, Zn) with Schiff bases in the presence of electrolytes

A study was carried out on the effect of electrolytes KCl, CaCl₂, MnCl₂, ZnCl₂, CuCl₂, KNO₃, Ca(NO₃)₂, Mn(NO₃)₂, Zn(NO₃)₂, and Cu(NO₃)₂ on the kinetics of the decomposition of H₂O₂ catalyzed by [Cu(L¹/L²)][MCl₄] complexes (M = Zn, Mn; L¹ is 4,6,6-trimethyl-1,9-diamino-3,7-diaza-3-nonene, L² is 1,15-dihydroxy-7,9,9-trimethyl-3,6,10,13-tetraaza-6-pentadecene). The chloride ions were found to reversibly inhibit the catalyst. The major kinetic characteristics of this reaction were obtained using a mathematical model taking account of the reversible and irreversible inhibition of the catalyst. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 4, pp. 240–247, July–August, 2008.     

Synchronously synthesizing and immobilizing porphyrins on crosslinked polystyrene microspheres and preliminary study on catalytic activity of supported metalloporphyrins

A novel method for immobilizing porphyrins as well as metalloporphyrins (MPs) on polymeric supports was found, and it is the way to synchronously synthesize and immobilize porphyrins on polymeric microspheres. By using 4‐hydroxybenzaldehyde (HBA)‐bound crosslinked polystyrene (CPS) microspheres, pyrrole, and benzaldehyde in a solution as co‐reactants and through the Adler's reaction between solid–liquid phases, it was successfully realized to simultaneously synthesize and immobilize phenyl porphyrin (PP) on CPS microspheres, resulting in PP‐supported microspheres PP–CPS. With the same method, substituted PPs, 4‐chlorophenyl porphyrin (CPP) and 4‐nitrophenyl porphyrin (NPP), were also successfully immobilized on CPS microspheres by using substituted benzaldehydes, 4‐chlorobenzaldehyde and 4‐nitrobenzaldehyde, as one reactant in the solution, respectively, and other two porphyrin‐supported microspheres, CPP–CPS and NPP–CPS, were obtained. The effects of various factors on the process of synchronously synthesizing and immobilizing porphyrins on CPS microspheres were mainly studied. Further, the coordination reaction of cobalt salt with PP–CPS as well as CPP–CPS and NPP–CPS was conducted, forming three solid catalysts, CoPP–CPS, CoCPP–CPS, and CoNPP–CPS. The catalytic properties of these catalysts in the catalytic oxidation of ethylbenzene to acetophenone by dioxygen were preliminarily examined. The experimental results indicate that the Adler's reaction between solid–liquid phases, namely the reaction between HBA‐bound CPS microspheres and pyrrole as well as free benzaldehyde or analogs in the solution can favorably be carried out. For this process, the fitting protonic acid catalyst is p‐nitrobenzoic acid and appropriate solvent is dimethyl sulfoxide (DMSO). By comparison, the process of preparing CPP–CPS microspheres is easier to be carried out. The obtained three solid catalysts can effectively catalyze the oxidation of ethylbenzene to acetophenone by dioxygen. In comparison, the catalytic activity of CoNPP–CPS is the highest. Copyright © 2009 John Wiley & Sons, Ltd.     

Copper complexes as chemical nucleases

Redox active mononuclear and binuclear copper(II) complexes have been prepared and structurally characterized. The complexes have planar N-donor heterocyclic bases like 1,10-phenanthroline (phen), dipyridoquinoxaline (dpq) and dipyridophenazine (dppz) ligands that are suitable for intercalation to B-DNA. Complexes studied for nuclease activity have the formulations [Cu(dpq)₂(H₂O)] (ClO₄)₂.H₂O (1), [CuL(H₂O)₂(μ-ox)](ClO₄)₂ (L = bpy,2; phen,3; dpq,4; and dppz,5) and [Cu(L)(salgly)] (L = bpy,6; phen,7; dpq,8; and dppz,9), where salgly is a tridentate Schiff base obtained from the condensation of glycine and salicylaldehyde. The dpq complexes are efficient DNA binding and cleavage active species. The dppz complexes show good binding ability but poor nuclease activity. The cleavage activity of thebis-dpq complex is significantly higher than thebis-phen complex of copper(II). The nuclease activity is found to be dependent on the intercalating nature of the complex and on the redox potential of the copper(II)/copper(I) couple. The ancillary ligand plays a significant role in binding and cleavage activity.     

Comparison of Combustion Models and Assessment of Their Applicability to the Simulation of Premixed Turbulent Combustion in IC-Engines

In order to simulate the turbulent combustion process occurring in spark-ignition (IC) engines, it is necessary to provide suitable and numerically economical models, the latter being particularly important in the application to industrial problems. Moreover, these models must deliver sufficiently accurate results for the unsteady operation of spark combustion engines, concerning variable geometries, temperatures, pressures and charge development in different configurations. In this work different turbulent combustion models for premixed hydrocarbon combustion are compared with respect to their ability to accurately predict the propagation of turbulent perfectly premixed flames. As a first configuration a cylinder of constant volume was studied. Transient calculations were used to simulate the propagation of the turbulent flame and to evaluate the resulting turbulent burning velocity. These calculations were performed for a perfect mixture of air and hydrocarbons at stoichiometric mixture and different initial conditions concerning pressure, temperature and turbulence intensity. As a second configuration a stationary turbulent bunsen-type flame with methane fuel was used to validate the turbulent combustion model of [Lindstedt and Vaos, Combust. Flame 116 (1999) 461] at different pressures. Calculated results were then compared to experimental data of [Kobayashi, Tamura, Maruta and Niioka. In: Proceedings of the 26th Symposium on Combustion, 1996, p. 389] and show excellent agreement for the turbulent burning velocity at several pressure levels using only a single set of model parameters.     

The composition-explicit distillation curve technique: Relating chemical analysis and physical properties of complex fluids

The analysis of complex fluids such as crude oils, fuels, vegetable oils and mixed waste streams poses significant challenges arising primarily from the multiplicity of components, the different properties of the components (polarity, polarizability, etc.) and matrix properties. We have recently introduced an analytical strategy that simplifies many of these analyses, and provides the added potential of linking compositional information with physical property information. This aspect can be used to facilitate equation of state development for the complex fluids. In addition to chemical characterization, the approach provides the ability to calculate thermodynamic properties for such complex heterogeneous streams. The technique is based on the advanced distillation curve (ADC) metrology, which separates a complex fluid by distillation into fractions that are sampled, and for which thermodynamically consistent temperatures are measured at atmospheric pressure. The collected sample fractions can be analyzed by any method that is appropriate. The analytical methods we have applied include gas chromatography (with flame ionization, mass spectrometric and sulfur chemiluminescence detection), thin layer chromatography, FTIR, corrosivity analysis, neutron activation analysis and cold neutron prompt gamma activation analysis. By far, the most widely used analytical technique we have used with the ADC is gas chromatography. This has enabled us to study finished fuels (gasoline, diesel fuels, aviation fuels, rocket propellants), crude oils (including a crude oil made from swine manure) and waste oils streams (used automotive and transformer oils). In this special issue of the Journal of Chromatography, specifically dedicated to extraction technologies, we describe the essential features of the advanced distillation curve metrology as an analytical strategy for complex fluids.     

Influence of annealing temperature on morphological and magnetic properties of La0.9Sr0.1MnO3

The nanocrystalline samples of La_0.9Sr_0.1MnO₃ (LSMO) have been prepared by the combustion method. The thermo gravimetric analysis of precursor was carried out. The X-ray diffraction study confirms the rhombohedral crystal structure without any other impurity phases. The morphology and magnetic properties change with annealing temperature. The saturation magnetization increases linearly and coercivity of the nanoparticles varies significantly as annealing temperature increases. The maximum saturation magnetization and lower coercivity found for the sample heat treated at 1200 °C are 52.5 emu/g and 10.7 Oe respectively.     

有旋和无旋气固两相湍流的不同结构

了解有旋和无旋突扩气粒两相详细湍流结构对控制燃料-空气混合、火焰稳定以及燃烧污染物生成很重要.周力行等曾经对其中的两相时平均流场和湍流特性进行过雷诺平均的RANS模拟和测量的研究,但是BANS模拟不能给出详细的两相湍流的瞬态结构.本文建立了二阶矩两相亚网格尺度应力模型,对有旋和无旋同轴突扩气粒两相流动进行了双流体大涡模...