Computer Simulation of the Structure of Porous Electrodes with an Immobilized Enzyme and Nanosized Support Particles

The efficiency of the operation of a porous electrode with an immobilized enzyme is defined, in particular, by a lucky structure of its active layer, which can contain nanosized particles of the support. The composites of such a kind are prepared with the aid of methods of colloidal chemistry. The aim of this particular investigation is to perform a computer simulation of processes of coagulation of particles of the support and their possible heterocoagulation with molecules of the enzyme. Algorithms of the formation of nanocomposite structures in solution are suggested. Calculations show that the concentration of the enzyme molecules in the nanocomposite structures cannot exceed a certain critical value. On the other hand, at a fixed value of the concentration of the enzyme molecules, the concentration of the support particles must not fall below a certain threshold quantity, which provides for the passing of current through the active layer. In order for all the enzyme molecules, rather than for a fraction of these, in the composite to take part in the process of bioelectrocatalysis, the concentration of support particles must be increased even higher, to an optimum value.__________Translated from Elektrokhimiya, Vol. 41, No. 6, 2005, pp. 738–747.Original Russian Text Copyright © 2005 by Chirkov, Rostokin.     

Self-aggregation and phase behavior of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers in aqueous solution

The phase behavior and aggregation properties of block copolymers of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (Pluronics, poloxamers) in aqueous solution have recently attracted much attention. Both experimental and theoretical studies are reviewed, not comprehensively, but with the focus on studies, partly cooperative, partly independent, performed by groups in Uppsala (light scattering and fluorescence), Roskilde (rheology and calorimetry), Risø (SANS), Graz (x-ray and speed of sound), and Lund (theoretical model calculations).The phase behavior of these copolymers is similar in many respects to that of conventional nonionic surfactants, with the appearance of hexagonal, cubic, and lamellar liquid crystalline phases at high concentrations. In the isotropic solution phase the critical concentration for micelle formation is strongly temperature dependent, and at a given concentration the monomer to micelle transition occurs gradually over a broad temperature range, partly due to the broad size polydispersity of both the PO- and EO-blocks. For some Pluronic copolymers a transition from globular to long rod-like micelles occurs above a transition temperature, resulting in a strong and sudden increase of viscosity and viscoelasticity of the solution.Size and aggregation numbers have been determined for the globular micelles in some cases, and also the rod-like micelles have been characterized. NMR and fluorescence measurements have provided further information on the properties of the micellar core and mantle. In combination, results from different measurements on the same Pluronics material indicate that the aggregation number of the micelles increases with the temperature, whereas the hydrodynmic radius varies much less. The PEO-mantle of the micelles seems to contract with increasing temperature. The core appears to contain appreciable amounts of PEO in addition to PPO (and also some water). The segregation between core and mantle is not as distinct as in normal micelles, a conclusion which is in line with the predictions from the model calculations.     

Orthokinetic Aggregation in Two Dimensions of Monodisperse and Bidisperse Colloidal Systems

Orthokinetic aggregation of colloids trapped at the air–liquid interface was studied by direct imaging in a couette cell. This method allowed us to follow the temporal evolution of both the cluster-mass distribution and the cluster structure at a shear rate where Brownian aggregation is suppressed. The interactions between the monodisperse latex particles floating at the air–liquid interface were controlled either by varying the electrolyte concentration or by creating a bidisperse system through the addition of small particles. The results show that the clusters in all of the systems are characterized by a high fractal dimension, indicating that the clusters are rearranged and densified by the shear. Kinetic analysis suggests that aggregation of monodisperse systems mainly proceeds through homogeneous aggregation, i.e., large clusters sticking to other large clusters. The bidisperse system, finally, with a size ratio around 10, favored a more heterogeneous aggregation among small and large clusters throughout the aggregation process; a slightly lower fractal dimension was observed compared to the strongly aggregated monodisperse system.     

Cyanex301的纯化及其特性

研究了用Ｃｙａｎｅｘ３０１［ＴＭ］铵盐在苯中重结晶以纯化Ｃｙａｎｅｘ３０１的方法，该法收率６２．４％，产品纯度＞９９％。测定了经纯化后产品的红外光谱，研究了纯化产品在－水正庚烷体系中的分配平衡及其在正庚烷中的缔合，浓度在０．２～１．０ｍｏ１／Ｌ范围，Ｃｙａｎｅｘ３０１主要以二聚形式存在。     

Bola型阴离子表面活性剂与溴化十二烷基三乙铵混合体系的表面性质与聚集行为

研究了具有简单结构的bola型阴离子表面活性剂二十酸二钠（C_(20)Na_2)与 阳离子型普通表面活性剂溴化十二烷基三乙铵（C_(12)Et_3）混合体系的表面性质 ，发现混合体系的cmc和γ_(cmc)比C_(12)Et_3单一体系未有显著降低。以负染色 ，FF-TEM，动态光散射（DLS）及粘度方法研究了混合体系的聚集行为，发现混合 体系中同时形成球形囊泡和管状聚集体，提出了产生这种聚集行为的机制。     

Molecular chaperones, folding catalysts, and the recovery of active recombinant proteins fromE. coli

The high-level expression of recombinant gene products in the gramnegative bacteriumEscherichia coli often results in the misfolding of the protein of interest and its subsequent degradation by cellular proteases or its deposition into biologically inactive aggregates known as inclusion bodies. It has recently become clear that in vivo protein folding is an energy-dependent process mediated by two classes of folding modulators. Molecular chaperones, such as the DnaK-DnaJ-GrpE and GroEL-GroES systems, suppress off-pathway aggregation reactions and facilitate proper folding through ATP-coordinated cycles of binding and release of folding intermediates. On the other hand, folding catalysts (foldases) accelerate rate-limiting steps along the protein folding pathway such as thecis/trans isomerization of peptidyl-prolyl bonds and the formation and reshuffling of disulfide bridges. Manipulating the cytoplasmic folding environment by increasing the intracellular concentration of all or specific folding modulators, or by inactivating genes encoding these proteins, holds great promise in facilitating the production and purification of heterologous proteins. Purified folding modulators and artificial systems that mimic their mode of action have also proven useful in improving the in vitro refolding yields of chemically denatured polypeptides. This review examines the usefulness and limitations of molecular chaperones and folding catalysts in both in vivo and in vitro folding processes.     

Synthesis, fluorescence and photoisomerization studies of azobenzene-functionalized poly(alkyl aryl ether) dendrimers

A series of azobenzene-functionalized poly(alkyl aryl ether) dendrimers have been synthesized and their photochemical and photophysical properties in solution and as thin films have been investigated. Although the photochemical behavior of the azodendrimers in solution indicated that the azobenzene units behave independently, very similar to the constituent monomer azobenzene unit, the properties of thin solid films of the dendrimers were distinctly different. The azodendrimers, AzoG1, AzoG2, and AzoG3 were observed to form stable supercooled glasses, which showed long-wavelength absorption and red emission characteristics of J-aggregates of the azobenzene chromophores. Reversible photoinduced isomerization of the azodendrimers in the glassy state is described.     

SO4●－自由基氧化酪氨酸反应中的溶剂效应

研究了水-乙腈混合溶液中SO4●－自由基氧化酪氨酸的反应.实验结果表明，SO4●－自由基氧化酪氨酸的反应机制不因乙腈的加入而改变，但所产生的瞬态粒子的动力学行为受到较大影响.随介质中乙腈体积分数的增加，SO4●－的衰变速率减慢而酪氨酸中性自由基（TyrO●）的衰变速率加快.我们认为这两种自由基所呈现出来的相反的溶剂效应是由于其所带电荷的不同.随介质中乙腈体积分数的增加，SO4●－氧化酪氨酸的反应速率减慢.这一实验结果意味着，在有机溶剂存在的情况下TyrO●/ TyrOH的氧化还原电势可能发生了变化，从而旁证了关于TyrO●/ TyrOH的氧化还原电势因酪氨酸从游离状态变到肽或蛋白质中而发生变化的推测.     

The structure of metallomicelles

The morphology of micelles formed by two novel metallosurfactants has been studied by small-angle neutron scattering (SANS) and small-angle-X-ray scattering (SAXS). The two surfactants both contain a dodecyl chain as the hydrophobic moiety, but differ in the structure of the head group. The surfactants are Cu(II) complexes of monopendant alcohol derivatives of a) the face-capping macrocycle 1,4,7-triazacyclanonane (tacn), and b) an analogue based upon the tetraazamacrocycle 1,4,7,10-tetraazacyclododecane. Here, neutron scattering has been used to study the overall size and shape of the surfactant micelles, in conjunction with X-ray scattering to locate the metal ions. For the 1,4,7,10-tetraazacyclododecane-based surfactant, oblate micelles are observed, which are smaller to the prolate micelles formed by the 1,4,7-triazacyclononane analogue. The X-ray scattering analysis shows that the metal ions are distributed throughout the polar head-group region, rather than at a well-defined radius; this is in good agreement with the SANS-derived dimensions of the micelle. Indeed, the same model for micelle morphology can be used to fit both the SANS and SAXS data.     

侧链型丙烯酸酯共聚物相变的正电子湮没谱研究

利用正电子湮没技术对侧链型热致高分子液晶丙烯酸酯共聚物进行了变温相变研究．除实验标识出样品的相变温度点外，根据试样中自由体积随温度的变化关系，对高分子液晶材料内部立链、侧链以及介晶基元的相变行为特点进行了探讨，并就与小分子液晶变化特点的一些不同做了解释．