新法构建25-羟基油菜甾体的侧链

油菜甾体例如油菜甾醇内酯(1a)和24-表油菜甾醇内酯(2a)是一族新型的甾体植物生长激素(植物生长调节剂).它们具有提高植物生长调节和应变的活性并具有农作物增产效果,已愈益受到国际上的广泛重视[1].     

Synthesis and Biological Activity of Cyanoethyl Derivatives of Fusidic Acid

3,11-Dihydroxy and 3,11-dioxo triterpenoids of the fusidane series reacted with acrylonitrile in 1,4-dioxane in the presence of alkali and phase-transfer catalyst to give mono- and bis(2-cyanoethoxy) and 2-cyanoethyl derivatives. The reaction with 3,11-dioxo analog afforded 2,2-disubstituted derivative as a result of addition of two cyanoethyl groups to the α-position with respect to the C³=O carbonyl group. The isolated compounds were screened for antibacterial and antifungal activities.

     

A Film-Pore-Surface Diffusion Model for the Adsorption of Acid Dyes on Activated Carbon

The sorption of acid dyes from aqueous effluents onto activated carbon has been studied. The effects of initial dye concentration and activated carbon mass on the rate of Acid Blue 80, Acid Red 114 and Acid Yellow 117 removal have been investigated. A three-resistance mass transport model based on film, pore and surface diffusion control has been applied to model the concentration decay curves. The model incorporates an effective diffusion coefficient D _eff, which is dependant on the equilibrium solid phase concentration or fractional surface coverage. The results of the film-pore-surface diffusion model are compared with the data obtained from the basic film-pore diffusion model. It has been found that the film-pore-surface diffusion model provides a major improvement over the data correlated by the film-pore diffusion model. Also, the relationship between surface diffusion and fractional surface coverage has been investigated for the adsorption of acid dyes on activated carbon.     

A Film-Pore-Surface Diffusion Model for the Adsorption of Acid Dyes on Activated Carbon

The sorption of acid dyes from aqueous effluents onto activated carbon has been studied. The effects of initial dye concentration and activated carbon mass on the rate of Acid Blue 80, Acid Red 114 and Acid Yellow 117 removal have been investigated. A three-resistance mass transport model based on film, pore and surface diffusion control has been applied to model the concentration decay curves. The model incorporates an effective diffusion coefficient D _eff, which is dependant on the equilibrium solid phase concentration or fractional surface coverage. The results of the film-pore-surface diffusion model are compared with the data obtained from the basic film-pore diffusion model. It has been found that the film-pore-surface diffusion model provides a major improvement over the data correlated by the film-pore diffusion model. Also, the relationship between surface diffusion and fractional surface coverage has been investigated for the adsorption of acid dyes on activated carbon.     

Ribosomal Incorporation of Aromatic Oligoamides as Peptide Sidechain Appendages

Derivatives of 4‐aminomethyl‐l ‐phenylalanine with aromatic oligoamide foldamers as sidechain appendages were successfully charged on tRNA by means of flexizymes. Their subsequent incorporation both at the C‐terminus of, and within, peptide sequences by the ribosome, was demonstrated. These results expand the registry of chemical structures tolerated by the ribosome to sidechains significantly larger and more structurally defined than previously demonstrated.     

Regiospecific Synthesis of Dioxabicyclooctanes Containing a Terminal Prenyl Sidechain

A Wittig reaction employing the ylide generated from isopropyl triphenylphosphonium bromide with THP-protected aldol intermediate 8 constitutes the key step in a regiospecific synthesis of olefin 1 in the total synthesis of zoapatanol analogue 2a.     

A Branched Pore Model Analysis for the Adsorption of Acid Dyes on Activated Carbon

A new branched-pore adsorption model has been developed using an external mass transfer coefficient, K _f, an effective diffusivity, D _eff, a lumped micropore diffusion rate parameter, K _b, and the fraction of macropores, f, to describe sorption kinetic data from initial adsorbent-adsorbate contact to the long-term adsorption phase. This model has been applied to an environmental pollution problem—the removal of two dyes, Acid Blue 80 (AB80) and Acid Red 114 (AR114), by sorption on activated carbon. A computer program has been used to generate theoretical concentration-time curves and the four mass transfer kinetic parameters adjusted so that the model achieves a close fit to the experimental data. The best fit values of the parameters have been determined for different initial dye concentrations and carbon masses. Since the model is specifically applicable to fixed constant values of these four parameters, a further and key application of this project is to see if single constant values of these parameters can be used to describe all the experimental concentration-time decay curves for one dye-carbon system.The error analysis and best fit approach to modeling the decay curves for both dye systems show that the correlation between experimental and theoretical data is good for the fixed values of the four fitted parameters. A significantly better fit of the model predictions is obtained when K _f, K _b and f are maintained constant but D _eff is varied. This indicates that the surface diffusivity may vary as a function of surface coverage.     

A New Hybrid Model of Amino Acid Substitution for Protein Functional Classification

In recent years, methods of protein sequences analysis have been gradually evolved into two directions: One is based on the models of probability and statistics1-4; the other is based on the digital signal processing technologies 5-8. The latter mainly converts the protein character sequences into digital signals and uses some signal processing methods to analyze them, i.e., fast Fourier transform (FFT). However, it is still unsolved how to characterize the protein sequences accurately with …     

The Effect of Molecular Weight on the Thermal Properties of Polystyrene-Based Sidechain Liquid-Crystalline Polymers

Abstract

Sidechain liquid-crystalline polymers were prepared by the derivatization of three poly(4-hydroxystyrene) fractions of different molecular weights (M_w = 1.0 × 10⁴, 2.2 × 10⁴ and 3.0 × 10⁴). 4-Cyanoazobenzene and 4-cyanobiphenyl were incorporated as mesogenic groups with ether-linked methylene spacers of varying length. The polymers all exhibited a smectic A phase, with the exception of the propyl member of the cyanobiphenyl series for which no liquid-crystalline behavior was observed. For short spacers the thermal properties were insensitive to molecular weight changes in the backbone, whereas small but consistent differences in the transition temperatures and entropies were observed as the number of methylene groups in the spacer increased.     

A Supramolecular Model for the Co-Catalytic Role of Nitro Compounds in Brønsted Acid Catalyzed Reactions

Nitro compounds are known to change reaction rates and kinetic concentration dependence of Brønsted-acid-catalyzed reactions. Yet, no mechanistic model exists to account for these observations. In this work, an atomistic model for the catalytically active form for an alcohol dehydroazidation reaction is presented, which is generated by DFT calculations and consists of an H-bonded aggregate of two molecules of Brønsted acid and two molecules of nitro compound. The computed O−H stretching frequencies for the aggregate indicate they are stronger acids than the individual acid molecules and serve as predictors for experimental reaction rates. By applying the model to a chemically diverse set of potential promoters, it was predicted and verified experimentally that sulfate esters induce a similar co-catalytic effect. The important implication is that Brønsted-acid catalysis must be viewed from a supramolecular perspective that accounts for not only the pK_a of the acid and the bulk properties of a solvent, but also the weak interactions between all molecules in solution.     

Lewis Acid Catalyzed Transfer Hydromethallylation for the Construction of Quaternary Carbon Centers

The design and gram‐scale synthesis of a cyclohexa‐1,4‐diene‐based surrogate of isobutene gas is reported. Using the highly electron‐deficient Lewis acid B(C₆F₅)₃, application of this surrogate in the hydromethallylation of electron‐rich styrene derivatives provided sterically congested quaternary carbon centers. The reaction proceeds by C(sp³)?C(sp³) bond formation at a tertiary carbenium ion that is generated by alkene protonation. The possibility of two concurrent mechanisms is proposed on the basis of mechanistic experiments using a deuterated surrogate.     

A Diffusion-Kinetic Model for Radiation-Chemical Transformations of Oxalic Acid and Oxalate Ions in Aqueous Solutions

A diffusion-kinetic model for the radiation-chemical degradation of oxalic acid and oxalates in aqueous solutions was developed. The model adequately describes published data on the formation of H₂, H₂O₂, and CO₂ over wide ranges of acid concentrations and pH values.__________Translated from Khimiya Vysokikh Energii, Vol. 39, No. 4, 2005, pp. 250–254.Original Russian Text Copyright © 2005 by Gordeev, Ershov, Kosareva.     

硅胶自水溶液中吸附丙酸和丁酸的计量置换吸附模型

实验研究了硅胶在293、303和313 K下,从水溶液中对丙酸和丁酸的吸附.发现该吸附服从液 固吸附中的计量置换吸附模型（SDM A）.根据吸附模型的线性参数研究了吸附热力学和吸附机理.该吸附是一个自发的、放热的熵减少过程.丁酸的标准吸附自由能比丙酸大,而标准吸附焓比丙酸小.推导出了实验条件下吸附自由能变化的计算公式.     

硅胶自环己烷溶液中吸附苯甲酸和苯的计量置换吸附模型

在293~313 K温度范围, 研究了硅胶在环己烷溶液中对苯甲酸和苯的吸附. 发现苯甲酸能非常好地服从计量置换吸附模型(SDM-A). 在用SDM-A处理苯的吸附时, 出现折线形的吸附等温线, 折线的转折点正好是单分子层吸附与多分子层吸附的分界点. 基于SDM-A, 研究了吸附热力学, 建立了吸附热力学的计算公式. 发现在环己烷溶液中苯甲酸被硅胶吸附是自发的、放热的熵增大过程, 而苯被吸附是自发的放热的熵减少过程, 苯甲酸的吸附自由能大于苯, 而吸附焓小于苯, 这是因为苯甲酸有更大的亲吸附剂作用和疏溶剂作用的结果.     

Azido Homoalanine is a Useful Infrared Probe for Monitoring Local Electrostatistics and Sidechain Solvation in Proteins

The use of IR probes to monitor protein structure, deduce local electric field, and investigate the mechanism of enzyme catalysis and protein folding has attracted increasing attention. Here, the azidohomoalanine (Aha) is considered as a useful IR probe. The intricate details of the distinct effects of backbone peptide bonds and H-bonded water molecules on the azido stretch mode of the IR probe Aha were revealed by carrying out QM/MM MD simulations of two variants of the protein NTL9, NTL9-Met1Aha and NTL9-Ile4Aha and comparing the resulting simulated IR spectra with experiments.     

草酸电解合成乙醛酸连续化工艺研究

针对传统草酸电解生产乙醛酸工艺只能间歇循环的缺陷,本文提出模拟连续化实验方案,并分别设计阴极冷却反应器和阴极冷却固定床反应器,探讨连续化实验的可行性.另外还考察了草酸饱和度和温度工艺参数对反应的影响.实验表明,保持草酸过饱和和利用变温操作可在反应停留时间(30m in)内于连续化反应过程中得到分别含有3.76%和3.66%乙醛酸的反应液,因此阴极冷却固定床反应器可望实现草酸电解还原乙醛酸的连续化生产.     

复杂样品近红外光谱定量分析模型的构建方法

针对复杂样品近红外光谱分析中校正集的设计问题, 探讨了标准样品参与复杂样品建模的可行性. 通过标准样品和复杂基质样品共同构建的偏最小二乘(PLS)模型, 考察了波段筛选和建模参数对预测结果的影响. 结果表明, 采用PLS方法建立定量模型时, 校正集样品性质应该尽量与预测集样品相似, 当样品的性质相差较大时, 适当增加校正集样品的差异性可使模型具有更强的预测能力. 同时, 波段优选对提高预测结果的准确性具有重要的意义.     

A New Fluorimetric Method for the Determination of Ascorbic Acid

Abstract

The fluorescent reaction between ascorbic acid(AA) and 2-cyanoacetamide was studied. The experimental results showed that AA can react with 2-cyanoacetamide at pH 12.9–13.3, and form a fluorescent product, which emitted strong fluorescence. The fluorescence intensity was measured at excitation and emission wavelengths of 329 and 380nm, respectively. A linear relationship was obtained between the fluorescence intensity and AA concentration in the range of 0.1–50μg/ml, the regression coefficient is 0.9994, and the detection limit of AA is 0.03μg/ml. (signal-to-noise=3).