Spectroscopic characterization and assignment of reduction potentials in the tetraheme cytochrome C554 from Nitrosomonas europaea

The tetraheme cytochrome c(554) (cyt c(554)) from Nitrosomonas europaea is an essential electron transfer component in the biological oxidation of ammonia. The protein contains one 5-coordinate heme and three bis-His coordinated hemes in a 3D arrangement common to a newly characterized class of multiheme proteins. The ligand binding, electrochemical properties, and heme-heme interactions are investigated with M?ssbauer and X- and Q-band (parallel/perpendicular mode) EPR spectroscopy. The results indicate that the 5-coordinate heme will not bind the common heme ligands, CN(-), F(-), CO, and NO in a wide pH range. Thus, cyt c(554) functions only in electron transfer. Analysis of a series of electrochemically poised and chemically reduced samples allows assignment of reduction potentials for heme 1 through 4 of +47, +47, -147, and -276 mV, respectively. The spectroscopic results indicate that the hemes are weakly exchange-coupled (J approximately -0.5 cm(-)(1)) in two separate pairs and in accordance with the structure: hemes 2/4 (high-spin/low-spin), hemes 1/3 (low-spin/low-spin). There is no evidence of exchange coupling between the pairs. A comparison of the reduction potentials between homologous hemes of cyt c(554) and other members of this new class of multiheme proteins is discussed. Heme 1 has a unique axial N(delta)-His coordination which contributes to a higher potential relative to the homologous hemes of hydroxylamine oxidoreductase (HAO) and the split-Soret cytochrome. Heme 2 is 300 mV more positive than heme 4 of HAO, which is attributed to hydroxide coordination to heme 4 of HAO.     

一类高喜树碱化合物的新型合成方法

本文以溴乙酸叔丁酯与9-羟基喜树碱反应,引入了羧酸官能团,能很方便地合成一系列高喜树碱酰胺化合物。本路线摈弃了磷酸酯等保护基团,路线简洁,收率提高,羧酸官能团起到了提高喜树碱溶解度的作用,便于后面反应的进行和产物纯化。     

Thermal Degradation and Kinetic Studies of New Flame-Retardant Phosphorus-Containing Polymers with Liquid Crystalline Properties

In this study, two new thermotropic liquid crystalline phosphorus-containing polymers were prepared by polycondensation reaction of 1,4-phenylene-bis((6-oxido-6H-dibenz[c,e][1,2]oxaphosphorinyl)carbinol) with two different phosphonic dichlorides, namely ethyl dichlorophosphate and phenyl dichlorophosphate. The polymers were characterized by means of FT-IR, ¹H NMR, differential scanning calorimetry, polarized light microscopy, wide-angle X-ray diffraction, and thermogravimetric analysis. Thermogravimetric analysis was performed in nitrogen atmosphere by heating the samples over a range of temperatures from 25° to 700°C using five different heating rates. The kinetic processing of data was achieved using the Freeman-Carroll, ASTM E1641, and Kissinger methods.     

Kinetic Studies of the Thermal Decomposition of KDNBF, a Primer for Explosives

KDNBF (potassium 4,6-dinitrobenzofuroxan) has been used as a primer explosive in igniters and detonators for many years. Considerable information about the sensitivity of KDNBF to various stimuli, such as impact, friction, shock and electrostatic charge, is known. However, the thermal sensitivity of KDNBF has been relatively unexplored. Hence, there is very little information available concerning the fundamental thermal properties of KDNBF. Therefore, as part of an extensive thermal hazard assessment, DSC, TG, accelerating rate calorimetry (ARC) and heat flux calorimetry (HFC) measurements have been undertaken on KDNBF. The results demonstrate that KDNBF decomposes via a multi-step exothermic process directly from the solid state. The decomposition process does not appear to depend on the nature of the atmosphere, except in the final stage of the TG decomposition in air, where remaining carbonaceous material is converted to CO₂. The first stage of the decomposition is sufficiently rapid that ignition occurs if too large a sample is used. Dynamic and isothermal methods were used to obtain the kinetic parameters and a range of activation energies were obtained, depending on the experimental conditions. The kinetic results have been analyzed in terms of various solid state decomposition models. This revised version was published online in August 2006 with corrections to the Cover Date.     

Modulation of the ligand-field anisotropy in a series of ferric low-spin cytochrome c mutants derived from Pseudomonas aeruginosa cytochrome c-551 and Nitrosomonas europaea cytochrome c-552: a nuclear magnetic resonance and electron paramagnetic resonance study

Cytochromes of the c type with histidine-methionine (His-Met) heme axial ligation play important roles in electron-transfer reactions and in enzymes. In this work, two series of cytochrome c mutants derived from Pseudomonas aeruginosa (Pa c-551) and from the ammonia-oxidizing bacterium Nitrosomonas europaea (Ne c-552) were engineered and overexpressed. In these proteins, point mutations were induced in a key residue (Asn64) near the Met axial ligand; these mutations have a considerable impact both on heme ligand-field strength and on the Met orientation and dynamics (fluxionality), as judged by low-temperature electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) spectra. Ne c-552 has a ferric low-spin (S = 1/2) EPR signal characterized by large g anisotropy with g(max) resonance at 3.34; a similar large g(max) value EPR signal is found in the mitochondrial complex III cytochrome c1. In Ne c-552, deletion of Asn64 (NeN64Delta) changes the heme ligand field from more axial to rhombic (small g anisotropy and g(max) at 3.13) and furthermore hinders the Met fluxionality present in the wild-type protein. In Pa c-551 (g(max) at 3.20), replacement of Asn64 with valine (PaN64V) induces a decrease in the axial strain (g(max) at 3.05) and changes the Met configuration. Another set of mutants prepared by insertion (ins) and/or deletion (Delta) of a valine residue adjacent to Asn64, resulting in modifications in the length of the axial Met-donating loop (NeV65Delta, NeG50N/V65Delta, PaN50G/V65ins), did not result in appreciable alterations of the originally weak (Ne c-552) or very weak (Pa c-551) axial field but had an impact on Met orientation, fluxionality, and relaxation dynamics. Comparison of the electronic fingerprints in the overexpressed proteins and their mutants reveals a linear relationship between axial strain and average paramagnetic heme methyl shifts, irrespective of Met orientation or dynamics. Thus, for these His-Met axially coordinated Fe(III), the large g(max) value EPR signal does not represent a special case as is observed for bis-His axially coordinated Fe(III) with the two His planes perpendicular to each other.     

Isothermal and Non-Isothermal Techniques in Kinetic Studies of Reactions in a Photoactive Molecular Material

The kinetics of thermally driven reactions in a crystalline photochromic solid, 1-methyl-2,4,4,6-tetraphenyl-1,4-dihydropyridine (DHP), has been studied. The processes have been monitored by measuring the isothermal bleaching of coloured species produced upon UV irradiation of DHP, and by measuring the heat flow in non-isothermal differential scanning calorimetry experiments. Signatures of two processes were detected; a combination of quantum-chemical calculations and spectroscopic measurements allowed us to attribute them to reactions occurring in the photochromic system.     

Studies on the Amination of Aryl Chlorides with a Monoligated Palladium Catalyst: Kinetic Evidence for a Cooperative Mechanism

Combined spectroscopic, crystallographic, and kinetic studies of the mechanism of aromatic amination with the efficient dinuclear Pd precatalyst [Pd₂Cl(μ‐Cl)PtBu₂(Bph‐Me)] (Bph‐Me=2′‐methyl‐[1,1′‐biphenyl]‐2‐yl) have revealed overlapping, yet cooperative, mechanistic scenarios, the relative weights of which are strongly influenced by the products formed as the reaction proceeds. The stability and evolution of the precatalyst in solution has been studied and several metalation pathways that point to a single monoligated intermediate have been identified. Our work sheds light on the nature of the catalytic species involved in the process and on the structure of the corresponding catalytic network.     

A Highly Active Bidentate Magnesium Catalyst for Amine-Borane Dehydrocoupling: Kinetic and Mechanistic Studies

A magnesium complex ( 1 ) featuring a bidentate aminopyridinato ligand is a remarkably selective catalyst for the dehydrocoupling of amine-boranes. This reaction proceeds to completion with low catalyst loadings (1 mol %) under mild conditions (60 °C), exceeding previously reported s-block systems in terms of selectivity, rate, and turnover number (TON). Mechanistic studies by in situ NMR analysis reveals the reaction to be first order in both catalyst and substrate. A reaction mechanism is proposed to account for these findings, with the high TON of the catalyst attributed to the bidentate nature of the ligand, which allows for reversible deprotonation of the substrate and regeneration of 1 as a stable resting state.     

Polymerization of Methylene Dichloride and Sodium Tetrasulfide: Synthesis and Kinetic Studies

The kinetics of the condensation polymerization of a novel polysulfide polymer based on methylene dichloride and sodium tetrasulfide is studied. The results of the experiments indicated that the reaction order is two. The activation energy obtained from the Arrhenius plot is 1.879 kcal mol^?1, and the pre-exponential frequency factor is A = 27.11 min^?1 at temperature range of 40～60°C. The polymer is characterized by using Fourier transform-infrared and CHN analysis. Thermal properties were evaluated by differential scanning calorimetry. The TGA-DTA was used to find out the thermal stability of polymer. The solvent resistance of the polymer was investigated by the swelling method.

Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file.     

傅-克酰基化反应的机理及动力学研究进展

总结了傅-克酰基化反应提出以来,化学工作者对该反应的机理方面的研究,包括动力学研究、中间体结构和性质的.提出傅-克反应机理目前存在的疑问及机理动力学的发展方向.     

Isolation of Natural Colorants from Lagerstroemia indica:Kinetic and Adsorption Studies

The color components extracted and isolated from the fruits of Lagerstroemia indica were characterized by NMR, mass, IR and UV/visible spectral techniques. The bio‐colorants isolated were found to be quercetin and apigenin. The dyed samples exhibited good colour fastness to washing and perspiration. CIE Lab values have also been evaluated. The rate of dyeing was higher at higher temperature. The thermodynamic parameters were evaluated using Arrhenius plot. The positive value of enthalpy change (ΔH^≠) indicated endothermic nature of adsorption, the high negative entropy (ΔS^≠) revealed that the color components adsorb more orderly on silk and the positive value of free energy (ΔG^≠) validated the strong affinity between adsorbent and adsorbate. Adsorption study was carried out based on the model proposed by Langmuir, Freundlich, Tempkin and Pyzhev isotherm to account for the observed results. The Freundlich isotherm was found to fit best with high regression coefficient. The colorants obtained from Lagerstroemia indica fruit could form a potential source as a dye for textile dyeing.     

A Protocol for the Estimation of Parameters in Process Models: Case Studies with Polymerization Scenarios

Summary: As our understanding of chemical processes increases, the complexity of the models developed to describe them also increases. In most cases the equations are nonlinear in the inputs and parameters, and must be solved numerically. At present in estimating parameters for large process models, there are two shortcomings in the existing knowledge about (multiresponse) parameter estimation. The first is, how effective is the present parameter estimation methodology when applied to large models, and the second is, can any advantage be gained from considering the parameter estimation problem as a whole. This paper will address these questions, by revisiting the various steps of a parameter estimation protocol. There is little discussion in the literature as to how all the steps for parameter estimation are related. In the development of this protocol all of the steps for parameter estimation will be revisited: parameter sensitivity analysis, statistical design of experiments, estimation of parameters and confidence regions. By considering all these steps as a whole the overall parameter estimation procedure can be more efficient and some pitfalls, such as local optima and incorrect confidence regions, may be dealt with in an appropriate manner. To illustrate the application of the protocol, two case studies related to polymerization models are presented. These case studies illustrate some of the problems that may be encountered in the parameter estimation process and how the proposed protocol can aid in overcoming them.

Plot of conversion versus time for the copolymerization of styrene/methyl methacrylate.     

Adsorption of Malachite Green by Diatomite: Equilibrium Isotherms and Kinetic Studies

The utilization of diatomite as potential adsorbent to remove malachite green (MG) from aqueous solution was developed. The characterization of the diatomite was evaluated by scanning electron microscope (SEM) and Brurauer Emmerr Teller (BET). The operating variables of pH, diatomite mass, initial MG concentration, and adsorption reaction time were studied. The equilibrium, kinetics, and thermodynamic parameters were investigated as well. It was found that the diatomite was composed of integral and almost circle sieve tray with lots of small pores on it, which afforded the diatomite high specific surface area of 46.09 m² g^?1. The optimum pH and reaction time were 7 and 90 minutes, respectively. The MG removal increased accordingly as the diatomite mass increased. The isotherm results showed that the equilibrium data were fitted to Langmuir model better, indicating the MG adsorption was better characterized by mono-layer. The maximum mono-layer capacity obtained from Langmuir was 23.64 mg g^?1 at 25°C. The kinetic studies indicated that experiment data followed pseudo-second-order model better. It also revealed that intraparticle diffusion was not the only rate-controlling step. The thermodynamic results concluded that the adsorption process was endothermic and more favorable at high temperature. Researches confirmed the applicability of diatomite as an efficient adsorbent and low-cost process to remove hazardous materials.     

聚苯乙烯非均相催化加氢吸附动力学及反应动力学研究

采用以表面具有贯穿大孔的二氧化硅空心微球为载体制备的负载型钯催化剂（Pd/SHMs）,对聚苯乙烯（PS）在非均相加氢催化剂上的吸附及加氢反应行为进行了系统研究,得到了吸附和反应动力学模型,并对部分加氢产物进行了详细分析.结果表明随着温度的升高,PS吸附量逐渐增加,且达到饱和吸附时间也随之增长,确定了PS非均相加氢为1级反应,活化能为58.3 kJ·mol^-1.将不同加氢度的样品进行分离提纯分析,结果显示PS的部分加氢产物都是由较高加氢转化率（85%左右）和较低加氢转化率（25%左右）的PS组成,证明PS非均相加氢存在二次吸附和竞争吸附加氢的现象,即服从“Blocky”机理.此工作为PS催化加氢吸附及反应过程的研究奠定基础,也为理解其他聚合物在非均相催化剂上的吸附及反应行为提供帮助.     

Supramolecular Chemistry in Microflow Fields: Toward a New Material World of Precise Kinetic Control

Constructing new and versatile self‐assembling systems in supramolecular chemistry is much like the development of new reactions or new catalysts in synthetic organic chemistry. As one such new technology, conventional supramolecular assembly systems have been combined with microflow techniques to control intermolecular or interpolymer interactions through precise regulation of a flowing self‐assembly field. The potential of the microflow system has been explored by using various simple model compounds. Uniform solvent diffusion in the microflow leads to rapid activation of molecules in a nonequilibrium state and, thereby, enhanced interactions. All of these self‐assembly processes begin from a temporally activated state and proceed in a uniform chemical environment, forming a synchronized cluster and resulting in effective conversion to supramolecules, with precise tuning of molecular (or polymer) interactions. This approach allows the synthesis of a variety of discrete microstructures (e.g., fibers, sheets) and unique supramolecules (e.g., hierarchical assemblies, capped fibers, polymer networks, supramolecules with time‐delayed action) that have previously been inaccessible.     

Determination of Sulfide in Spring and Wastewater by a New Kinetic Spectrophotometric Method

A simple, rapid, and sensitive method has been developed for the determination of trace amounts of sulfide based on its reaction with thionine. The reaction is monitored spectrophotometrically by measuring the decreasing absorbance of the dyestuff at 600 nm by the fixed time method. After optimization of the measuring conditions the calibration curves were found linear up to 38.0 ppm (four regions), and the theoretical limit of detection was 0.076 ppm and the relative standard deviation for determination of 1.0 ppm sulfide (n = 10) was found to be 2.7%. The proposed method was applied successfully to the determination of sulfide in spring water and wastewater samples.     

Synthesis of a New pH-Dependent Ligand: Conformational and Complexation Studies

A new macrocyclic ligand, 3, which exhibits pH-induced conformational changes, has been prepared. This ligand consists of a crown ether derived from a trans-anti-trans 1,2,4,5-tetrasubstituted cyclohexane. Due to the stereochemistry of the substituents on the carbocyclic ring, two different low-energy conformations of the crown ether are possible. Ligand 3 has been studied in solution by ¹H NMR spectroscopy at different values of pH and temperature, showing that the conformation of the crown ether, and thus its complexing ability, is strongly pH-dependent. The solid-state structure of the ligand has been determined by X-ray diffraction.     

Investigation of Growth Conditions for the Expansion of Porcine Mesenchymal Stem Cells on Microcarriers in Stirred Cultures

The extensive use of mesenchymal stem cells (MCS) in tissue engineering and cell therapy increases the necessity to improve their expansion. Among these, porcine MCS are valuable models for tissue engineering and are classically expanded in static T-flasks. In this work, different processes of stirred cultures were evaluated and compared. First, the effect of glucose, glutamine, antioxidant, and growth factors concentrations on porcine MSC expansion were analyzed in a suitable medium by performing kinetic studies. Results showed that a lower glucose concentration (5.5 mM) enabled to increase maximal cell concentration by 40 % compared with a higher one (25 mM), while addition of 2 to 6 mM of glutamine increased maximal cell concentration by more than 25 % compared with no glutamine supplementation. Moreover, supplementation with 1 μM thioctic acid increased maximal cell concentration by 40 % compared with no supplementation. Using this adapted medium, microcarriers cultures were performed and compared with T-flasks expansion. Porcine MSC were shown to be able to proliferate on the five types of microcarriers tested. Moreover, cultures on Cytodex 1, Cytopore 2, and Cultispher G exhibited a MSC growth rate more than 40 % higher compared with expansion in T-flasks, while MSC metabolism was similar.