Preorganization and reorganization as related factors in enzyme catalysis: the chorismate mutase case

In this paper a deeper insight into the chorismate-to prephenate-rearrangement, catalyzed by Bacillus subtilis chorismate mutase, is provided by means of a combination of statistical quantum mechanics/molecular mechanics simulation methods and hybrid potential energy surface exploration techniques. The main aim of this work is to present an estimation of the preorganization and reorganization terms of the enzyme catalytic rate enhancement. To analyze the first of these, we have studied different conformational equilibria of chorismate in aqueous solution and in the enzyme active site. Our conclusion is that chorismate mutase preferentially binds the reactive conformer of the substrate--that presenting a structure similar to the transition state of the reaction to be catalyzed--with shorter distances between the carbon atoms to be bonded and more diaxial character. With respect to the reorganization effect, an energy decomposition analysis of the potential energies of the reactive reactant and of the reaction transition state in aqueous solution and in the enzyme shows that the enzyme structure is better adapted to the transition structure. This means not only a more negative electrostatic interaction energy with the transition state but also a low enzyme deformation contribution to the energy barrier. Our calculations reveal that the structure of the enzyme is responsible for stabilizing the transition state structure of the reaction, with concomitant selection of the reactive form of the reactants. This is, the same enzymatic pattern that stabilizes the transition structure also promotes those reactant structures closer to the transition structure (i.e., the reactive reactants). In fact, both reorganization and preorganization effects have to be considered as the two faces of the same coin, having a common origin in the effect of the enzyme structure on the energy surface of the substrate.     

Multicomponent analysis with a computerized flow injection system using LED photometric detection

An original computer-controlled solid-state photometer has been developed and its potential for simultaneous multicomponent flow-injection analysis of binary and ternary mixtures is demonstrated. The device is simple in construction. Its principle of operation is based on rapid sequential measurements of the absorbance of the complexes formed by the analytes with chromogenic reagents at the wavelengths corresponding to the emission maxima of three light emitting diodes (563, 580 and 638 nm).     

Pervaporative transport modelling in a ternary system: ethyltertiarybutylether/ethanol/polyurethaneimide

The study deals with the analysis of diffusion and mass transfer modelling during pervaporation in a true ternary system involving a polar liquid mixture (ETBE/EtOH) and a polar block copolymer (polyurethaneimide or PUI). A survey of methods of pervaporative transfer modelling in ternary systems is first developed. From differential permeation experiments carried out with both pure liquids, it appears that both permeants obey a Fickian law. Moreover, the diffusional behaviour is consistent with Long's model, which has thus been assumed for the related ternary system. An extension of the Brun's model is then derived, which takes into account the diffusion coupling as well the significant deviation from sorption ideality. From a practical point of view, the calculated values of fluxes show generally good agreement with the experimental results, although a small deviation occurs for mixtures of low ethanol content. Diffusion coefficients of both pure solvents corresponding to transient or steady state are compared. A very good agreement is found for the aprotic permeant (ETBE). whereas the diffusion coefficient of ethanol in transient state is only the quarter of the value corresponding to steady state. The results are discussed in comparison with related investigations in the literature, involving specific liquid-polymer interactions.     

~(13)C代谢通量分析

代谢通量分析(metabolic flux analysis,MFA)是通过确定代谢网络中代谢流分布来表征细胞代谢状态的强有力的工具。鉴于计量学代谢通量分析在处理复杂代谢网络时表现出的局限性,发展了以13C标记实验为基础的13C MFA。本文介绍了13C MFA的原理与方法,总结和评述了13C MFA在实验与数据分析方面的最新进展以及MFA在功能基因组研究中的重要地位,同时对代谢通量分析的发展前景进行了展望。     

Full multinuclear resonance analysis of 4-amino-1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane

The complete assignment of 19F, 1H and 13C NMR spectra for a monosubstituted octafluoro[2.2]paracyclophane derivative is described for the first time. The unambiguous assignments were achieved through the combination of 19F--1H HOESY, 1H COSY and 19F COSY techniques and then further confirmed employing a complementary approach using a Karplus-dependent 3JCF interaction. Interesting aspects of the coupling patterns for various JHH, JHF, JCF and JFF interactions are also discussed.     

层状LiMnO2的固相合成及电化学性能

以Mn₂O₃和氢氧化锂为原料，通过焙烧合成出o-LiMnO₂。用X射线衍射和扫描电镜对不同温度下合成的粉末样品进行了表征，并研究了材料的电化学性能。通过对不同温度条件下烧结样品的晶胞参数、布拉格(110)晶面峰半高宽及电化学性能研究发现：600 ℃下合成样品的半高宽最大，堆垛层错率高，同时电化学性能也最好，首次放电容量达到156 mAh·g^-1，20次循环后仍保持在140 mAh·g^-1以上。中高温固相合成的o-LiMnO₂材料，在晶粒范围大小相近时，材料电化学性能与材料堆垛层错率相关。     

Determination of Aroma Compounds in Blackberry by GC/MS Analysis

The aromatic composition of five blackberry cultivars (Bursa 2, Navaho, Nessy, Chester Thornless, and Jumbo) was studied. The Im-SPME (Immersion Solid Phase Micro Extraction) extraction technique was applied and the samples were analyzed by GC/MS. Furfural and its derivatives were found to be the major aromatic compounds and 5-hydroxymethylfurfural was the most abundant compound in all the blackberry varieties.     

Thermoanalytical study of nucleating effects in polypropylene composites

Nucleating and transcrystallization behaviour of additives in engineering PP composites and the effect of modified interfacial structure is the subject of this series of papers. The first part concentrates on polypropylene/liquid crystalline polyester blends. Increased crystallisation temperature and degree of crystallinity of polypropylene is characteristic to the blends containing different amount of LCP additive. Transcrystallization process governs the formation of crystalline structure in these systems in course of isothermal crystallisation at 132C. The nucleating effect of LCP gives rise to more uniform crystalline structure in the polypropylene phase.The financial support of the OTKA 014194 is acknowledged with gratitude.     

CuO/Ce-Zr-La-O催化剂的表征及CO氧化活性

采用柠檬酸溶胶-凝胶法制备的Ce-Zr-La-O固溶体为载体，制备CuO／Ce-Zr-La-O催化剂，用XRD，Raman，TPR等实验技术对Ce-Zr-La-O固溶体及CuO／Ce-Zr-La-O的物相、Redox性能进行了表征。实验结果表明，Ce0.7Cr0.3-yLayO固溶体的还原性能与La含量有关，适量的La能促进固溶体的氧化还原。CuO的负载量为6％时，CuO／Ce0．7Zr0.15La0.15O的活性最高，高分散且与载体相互作用的CuO是CO氧化活性相。     

稀土铜硫化合物TbCuS2的合成和晶体结构

Terbium copper disulfide, TbCuS₂, has been synthesized in the reaction of the elements in a KI flux at 850 ℃. The compound crystallizes in space group P2₁/c of the monoclinic system with four formula units in a cell of dimensions of a= 0.639 3(1) nm, b=0.702 5(1) nm, c=0.670 8(1) nm, β=98.097(4)°, and V=0.298 3(1) nm³ at 153 K. The structure comprises two-dimensional ²_∞[CuS₂] layers along [100] separated by the Tb atoms. In the structure, each Tb and Cu atoms are coordinated to seven and four S atoms, respectively. CSD: 415490.