Operation of an Oxygen Gas Diffusion Electrode in a Hybride Fuel Cell

The paper is devoted to the operation of a hybride fuel cell (i.e. in the course of simultaneous electrosynthesis of a chemical product), in particular, the polarization characteristic of an oxygen electrode and the ratio of the produced electric energy to the amount of the produced target product. An equation for the dependence of the polarization of an oxygen gas diffusion hydrophobized electrode of a hydrogen-oxygen fuel cell on the concentration of the produced electroactive soluble product H₂O₂ in an inner-kinetic regime is suggested. It is established that the polarization variation does not depend on its initial magnitude but does depend on the concentration of the target product and the ratio between currents of the side and target reactions. The ratio of the produced electric energy to the amount of the produced target product is found to depend on the concentration of the produced target product, the electrode polarization, and the ratio between exchange currents of the side and target reactions.     

A note on electrolysis with forced convection at large peclet number in a channel and an excess of supporting electrolyte

Electrolysis of an aqueous solution of a metal salt with an excess of supporting electrolyte flowing in a two-dimensional channel is considered. The reaction kinetics is modeled by a Butler-Volmer law. The metal electrodes are symmetrically flush mounted in the channel walls, which are otherwise electrically insulating. Using the perturbation scheme originally proposed by Levich for electrolytes with an excess of supporting electrolyte, a solution in closed form, involving the root of a transcendental algebraic equation, is obtained for the polarization curve. For small and large values of the potential difference between the electrodes, explicit expressions for the polarization curve and the distributions of electric current and concentration on the electrodes are obtained. Particular attention is given to the conditions prevailing during the asymptotic approach to the limiting current. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 4, pp. 508–517. The text was submitted by the authors in English.     

Kinetic release of triptolide after injection of renal-targeting 14-succinyl triptolide-lysozyme in a rat kidney study by liquid chromatography/mass spectrometry

Triptolide (TP) is one of the most important biologically active components of the Chinese herb Tripterygium wilfordii Hook f (TWHf). A novel high-performance liquid chromatography/mass spectrometry (LC/MS) method was developed to study the kinetic release of TP after intravenous injection of the newly synthesized 14-succinyl triptolide-lysozyme (TPS-LZM). The method was validated in terms of selectivity, linearity, precision, accuracy, stability, limit of detection (LOD) and limit of quantification (LOQ). The calibration curve was linear over the concentration range 0.5-400.0 ng/g. The mean recovery of triptolide from spiked samples, in a concentration range of 0.5-400.0 ng/g, was 91.84% (RSD = 3.69%, n = 3). The intra- and inter-assay coefficients of variation were less than 6.38%. The method with simple sample pretreatment and being highly specific and precise, can be used for analysis of triptolide release in rat kidney after intravenous injection of renal-targeting TPS-LZM conjugate. The results showed that, as compared with free TP, TPS-LZM could significantly increase the concentration and prolong the action time of TP in the kidney.     

The possibility of a truly absolute method of spectrographic analysis

A quantitative expression is given for the relation between the concentration of an element in a sample and the line intensity when a low current d.c. carbon arc with anode excitation is employed. With this equation, the concentration of an element can be determined without previous establishment of a working curve.     

Polarization Curve of a Porous Hydrophobized Electrode for Electrosynthesis Involving a Side Electrochemical Reaction

A polarization curve, suggested for electrosynthesis in a porous hydrophobized electrode operating in an inner-kinetic mode at a current efficiency for the target product below 100%, depends on the balance between exchange currents and slopes of the side and target reactions and the difference between the equilibrium potential of the side reaction and the steady-state electrode potential. At different slopes of the side and the target reactions, the current efficiency depends on the polarization. Experimental and calculated data satisfactory agree.     

Upper and lower bounds for a serial dilution test

A Poisson-binomial model estimates the concentration of a target microbe from a serial dilution test. The maximum likelihood procedure gives an equation whose solution equals the estimate of the concentration. This paper gives bounds for the solution to this equation that require only minimal calculations.     

中药活性成分对血栓素A2受体抑制作用的分子模拟

中药中黄酮类化合物和白藜芦醇等活性成分对血栓素A2受体具有抑制作用,但具体机理不详.本研究通过同源模建方法,以墨鱼视紫红质蛋白为模板,构建血栓素A2受体的蛋白质结构模型.并使用分子对接方法研究中药活性成分白藜芦醇和芹菜苷元与血栓素A2受体模型的作用方式,据此建立药效团模型,筛选其他潜在的血栓素A2受体抑制剂.结果表明:白藜芦醇等中药活性成分能与血栓素A2受体活性口袋中的残基发生氢键作用,结合方式与血栓素相似.血栓素与Ser201、Leu198、Arg295和Thr298发生氢键作用,白藜芦醇等活性成分与Ser201、Leu198和Arg295发生氢键作用.建立的药效团模型由7个药效元素以及排斥性空间元素组成,经测试对高活性的血栓素A2受体抑制剂有比较好的选择性.使用该药效团模型对中药天然产物数据库进行筛选,命中了一批可能具有血栓素A2受体抑制作用的活性化合物.其中一些已经报道有抑制血小板凝聚活性.本研究表明血栓素A2受体可能是活血化瘀类中药的一个潜在的靶点.     

Kinetic substrate quantification by fitting the enzyme reaction curve to the integrated Michaelis–Menten equation

The reliability of kinetic substrate quantification by nonlinear fitting of the enzyme reaction curve to the integrated Michaelis-Menten equation was investigated by both simulation and preliminary experimentation. For simulation, product absorptivity epsilon was 3.00 mmol(-1) L cm(-1) and K(m) was 0.10 mmol L(-1), and uniform absorbance error sigma was randomly inserted into the error-free reaction curve of product absorbance A(i) versus reaction time t(i) calculated according to the integrated Michaelis-Menten equation. The experimental reaction curve of arylesterase acting on phenyl acetate was monitored by phenol absorbance at 270 nm. Maximal product absorbance A(m) was predicted by nonlinear fitting of the reaction curve to Eq. (1) with K(m) as constant. There were unique A(m) for best fitting of both the simulated and experimental reaction curves. Neither the error in reaction origin nor the variation of enzyme activity changed the background-corrected value of A(m). But the range of data under analysis, the background absorbance, and absorbance error sigma had an effect. By simulation, A(m) from 0.150 to 3.600 was predicted with reliability and linear response to substrate concentration when there was 80% consumption of substrate at sigma of 0.001. Restriction of absorbance to 0.700 enabled A(m) up to 1.800 to be predicted at sigma of 0.001. Detection limit reached A(m) of 0.090 at sigma of 0.001. By experimentation, the reproducibility was 4.6% at substrate concentration twice the K(m), and A(m) linearly responded to phenyl acetate with consistent absorptivity for phenol, and upper limit about twice the maximum of experimental absorbance. These results supported the reliability of this new kinetic method for enzymatic analysis with enhanced upper limit and precision.     

Analysis of Gibbs adsorption equation and thermodynamic relation between Gibbs standard energies of adsorption and micellization through a surface equation of state

The calculation of surface molecular areas through Gibbs adsorption equation has been questioned in some early works on the belief that these areas have been obtained from the apparently constant slope of the surface tension vs. logarithm of concentration curve along the entire region at which surface tension declines rapidly as the concentration increases. This premise leads to consider that Gibbs equation predicts that surface saturation is reached at the beginning of this region. However, through an analysis of the forementioned curve in accordance to Gibbs equation, it can be easily shown that surface saturation is attained at the end of the region. On the other hand, based on a thermodynamic model, it is also shown that the adsorption process, and thus, surface saturation, proceeds before micellization.     

Combined STM and FTIR characterization of terphenylalkanethiol monolayers on Au(111): effect of alkyl chain length and deposition temperature

Self-assembled monolayers (SAMs) of 4,4'-terphenyl-substituted alkanethiols C6H5(C6H4)2(CH2)n-SH (TPn, n = 1-6) on Au (111) substrates were studied using scanning tunneling microscopy (STM) and infrared reflection absorption spectroscopy (IRRAS). When the SAMs were prepared at room temperature (RT, 298 K), TPn films (except TP2) exhibit an odd-even effect regarding both molecular orientation and packing density. For all investigated films, STM data reveals the presence of a large degree of lateral order. In the case of odd-numbered TPns, the films revealed a (2 square root(3) x square root(3))R30 degree molecular arrangement. For the even-numbered TP4 and TP6 SAMs, a c(5 square root(3) x 3) rectangular unit cell was found. The packing density for the even-numbered TPn SAMs is 25% lower than that for the odd-numbered TPn SAMs. When the SAMs were prepared at 333 K, the even-numbered SAMs were found to form structures with a significantly lower packing density. In the case of TP2, instead of the (2 square root(3) x square root(3))R30 degree structure formed at room temperature, a c(5 square root(3) x 3) structure was observed. For TP6 SAMs, the room-temperature c(5 square root(3) x 3) structure was replaced by a (6 square root(3) x 2 square root(3))R30 degree structure.     

Estimation of the standard uncertainty of a calibration curve: application to sulfur mass concentration determination in fuels

The construction of a calibration curve using least square linear regression is common in many analytical measurements, and it comprises an important uncertainty component of the whole analytical procedure uncertainty. In the present work, various methodologies are applied concerning the estimation of the standard uncertainty of a calibration curve used for the determination of sulfur mass concentration in fuels. The methodologies applied include the GUM uncertainty framework, the Kragten numerical method, the Monte Carlo method (MCM) as well as the approximate equation calculating the standard error of prediction. The standard uncertainty results obtained by all methodologies agree well (0.172?C0.175?ng???L^?1). Aspects of inappropriate use of the approximate equation of the standard error of prediction, which leads to overestimation or underestimation of calculated uncertainty, are discussed. Moreover, the importance of the correlation between calibration curve parameters (slope and intercept) within GUM, MCM and Kragten approaches is examined.     

水中总磷和总氮含量的离子色谱测定法

采用紫外光-臭氧氧化结合离子色谱法对氧化消解后的水样同时进行总磷和总氮的测定。配制Na2CO3/NaHCO3淋洗液,采用1 mL定量环,大体积直接进样。在优化工作条件下,总磷在0.05～5.00 mg/L,总氮在0.10～10.0 mg/L范围内线性良好,线性相关系数分别为0.9999和0.9998,总磷和总氮检出限为分别3.60和4.57μg/L;总磷和总氮的检测相对标准偏差(RSD)分别低于4.9%和4.1%,总磷加标回收率为95.0%～105.0%,总氮加标回收率为93.0%～103.0%。自然环境水样检测与真实值相对偏差小于4.2%。本方法选择性好,灵敏度高,精密度和准确度高,用于实际水样中总磷和总氮含量测定的结果与国标法(GB11894-89,GB11893-89)基本一致     

用TNT的{D,ρ0}实验数据对爆轰的ZND理论的检验

爆轰产物中或多或少含有固态碳,一相的排平物态方程被推广为两相的之后,以某种炸药的一条已知等熵线为参考曲线,就可以用来估算其各种初始装药密度下的爆轰参数.用产物中含碳量较多的TNT的{D,ρ0}实验数据与理论估算值相比较,可以对爆轰的ZND理论的假设进行检验.检验的结果再一次表明,爆轰的ZND理论的假设是成立的,并且排平物态方程是恰当的爆轰产物的物态方程.     

Distribution of a Soluble Product During Its Electrosynthesis in the Porous Hydrophobic Electrode

The distribution of the concentration of a product, which is soluble in the electrolyte, inside a porous hydrophobic electrode is calculated. During the electrosynthesis under inner-kinetic conditions, the electrode obeys regularities observed in hydrophobic electrodes of fuel cells. The product distribution depends mainly on the polarization at the electrode front, the electrolyte conductivity, and the diffusion coefficient, and slightly depends on the electrode structure. An approximate equation describing the distribution of the product concentration inside the electrode is suggested.     

Factorizing of a concentration function for the mean activity coefficients of aqueous strong electrolytes into individual functions for the ionic species

The concentration curve of mean activity coefficients to the required power was approximated by a product function. The product function parameters were optimized by experimental data for the mean activity coefficients using a nonlinear regression model. Assuming that the product function parameters can be determined, the factor functions are clearly known. The mathematical complexity and a concept solution are presented. Clear, reliable results were obtained with the help of asymptotic theory when corresponding approximations were used. The method described makes it possible to split the experimentally determinable concentration curve of the mean activity coefficients to the required power in individual factor functions of complementary ion species, [`(g)]<sub>\textC</sub>(m) {\bar{\gamma }_{\text{C}}}(m) and [`(g)]_\textA(m) {\bar{\gamma }_{\text{A}}}(m) . The results are verified by comparing them with experimentally determined quotients of single-ion activity coefficients of ternary systems. The calculated individual parts for single-ion species are plausible and show a characteristic, typical concentration curve for cations as well as for anions. They correlate with the ion parameters.     

Quantitative analysis of essential oils in perfume using multivariate curve resolution combined with comprehensive two-dimensional gas chromatography

The use of multivariate curve resolution (MCR) to build multivariate quantitative models using data obtained from comprehensive two-dimensional gas chromatography with flame ionization detection (GC × GC-FID) is presented and evaluated. The MCR algorithm presents some important features, such as second order advantage and the recovery of the instrumental response for each pure component after optimization by an alternating least squares (ALS) procedure. A model to quantify the essential oil of rosemary was built using a calibration set containing only known concentrations of the essential oil and cereal alcohol as solvent. A calibration curve correlating the concentration of the essential oil of rosemary and the instrumental response obtained from the MCR-ALS algorithm was obtained, and this calibration model was applied to predict the concentration of the oil in complex samples (mixtures of the essential oil, pineapple essence and commercial perfume). The values of the root mean square error of prediction (RMSEP) and of the root mean square error of the percentage deviation (RMSPD) obtained were 0.4% (v/v) and 7.2%, respectively. Additionally, a second model was built and used to evaluate the accuracy of the method. A model to quantify the essential oil of lemon grass was built and its concentration was predicted in the validation set and real perfume samples. The RMSEP and RMSPD obtained were 0.5% (v/v) and 6.9%, respectively, and the concentration of the essential oil of lemon grass in perfume agreed to the value informed by the manufacturer. The result indicates that the MCR algorithm is adequate to resolve the target chromatogram from the complex sample and to build multivariate models of GC × GC-FID data.     

Integrated rate equation considering product inhibition and its application to kinetic assay of serum ethanol.

Kinetic assay of serum ethanol was investigated by predicting maximal product absorbance at 340 nm (A(mk)) through fitting to the yeast alcohol dehydrogenase reaction curve with the integrated rate equation, taking into account product inhibition in the presence of semicarbazide. Predicted A(mk) linearly responded to the preset constant of steady-state concentration of acetaldehyde (C(ald)). An exponential correlation function was established between desired C(ald) and putative A(mk) for authentic ethanol. For unknown samples, iterative fitting to reaction curve till preset constant C(ald) and resultant A(mk) satisfied this exponential correlation function yielded A(mk) with variation coefficient <4.3%. Variations in enzyme activity, data range and kinetic parameters showed negligible effects. The recovery was consistent to 100% with resistance to methanol and isopropanol. The upper limit of linear response for A(mk) was about 40 times of the lower limit. These results indicated that this kinetic method was reliable for serum ethanol assays with obvious advantages.     

Study on the capacities,heats of dilution and properties of concentrated potassium carnallite solutions at 298.15 K

The heats of dilution of the infinitesimally dilute potassium carnallite solutions at 298.15 K have been studied by continuous titration from 1.8942 to 0.01044 mol·kg^?1, and an equation for the curve of heats of dilution has been fitted. It was shown that the enthalpy of dilution for the same concentration of the carnallite solution is equal to the sum of those of KCl and MgCl₂ solutions. The equation for the curve of enthalpy of dilution corresponds to that of natural carnallite.     

正常拖尾色谱峰的塔板模型表达式

得到了描述正常拖尾色谱峰的塔板模型表达式,根据这一表达式,正常的色谱流出曲线应是非对称的拖尾峰,而对称的高斯型分布函数是对塔板模型进行近似处理的结果。和扩散模型的色谱流出曲线方程相比,二者在形式上完全相同,因此,尽管塔板模型和扩散模型的机理不同,但它们对于色谱流出曲线的数学描述是完全相同的。     

Determination of drug-protein interactions by microdialysis coupled with liquid chromatography and electrochemical detection based on a nickel hexacyanoferrate modified electrode

Microdialysis sampling coupled with liquid chromatography-electrochemical detection (LC-ED) was developed and applied to determine the interaction of thiopurine (TP) with bovine serum albumin (BSA). A nickel hexacyanoferrate (NiHCNFe) modified electrode was fabricated and used as the working electrode in LC-ED for the determination of TP. Cyclic voltammetric experiments demonstrate that this chemically modified electrode (CME) can effectively catalyze the electrooxidation of TP. The mechanism of the catalytic oxidation of TP at the CME involves an 'EC' process. In the LC-ED, the CME also shows good stability and reproducibility for the determination of TP. The limit of detection is 5.0 x 10(-7) mol l(-1) for 6-TP with a signal-to-noise ratio of 3. The utility of microdialysis as a quantitative sampling technique for in vitro studies of drug-protein interactions was studied. The microdialysis experiments were performed in phosphate buffer solution (pH 7.4) containing different molar ratios of the drug and protein at 37 degrees C. The collected microdialysis sample with unbound TP was analyzed at the NiHCNFe CME in the LC-ED. The relative recovery of TP determined in vitro is 18.3% at a perfusion rate of 1.0 microl min(-1) and the RSD is about 2.1%. The association constant and the number of binding sites on a BSA molecule calculated with the Scatchard equation are 3.72 x 10(-3) (1 mol(-1)) and 1.51, respectively. This method provides a fast, sensitive and simple technique for the study of drug-protein interactions.