Computer Simulation of Binary Platinum–Cobalt Nanoclusters Interaction with Oxygen

On the basis of the quantum-chemical method of density functional theory (DFT) in cluster approximation binary nanoclusters of platinum-cobalt are simulated and their interactions with molecular and atomic oxygen are calculated. It was shown that a binary nanocluster Pt₃₇Co₁₈, constructed of platinum atom outer shell, has the lowest adsorption heat for both molecular and atomic oxygen. This may contribute favorably to accelerate oxygen reduction on catalytic electrodes. The results obtained are in good satisfaction with known experimental and theoretical data, indicating the perspectives of the proposed approximation for theoretical search of chemical composition and structure of effective binary nanocatalysts with platinum as cathode materials in low temperature membrane fuel cells.     

Study on Determination of Chemical Oxygen Demand in Water with Ion Chromatography

A new method for determining chemical oxygen demand （COD） value in water using ion chromatography coupled with nano TiO2-K2S2O8 co-existing system was described. The photocatalytic oxidation system and nano TiO2-K2S2O8 co-existing system could degrade the organic compounds in water. All sulfur-containing species in the reactive solution were eventually transformed to sulfate which could be determined by conductivity detector in ion chromatography. The change of conductivity of sulfate was proportional to COD value. The optimal experimental conditions and the mechanism of the detection were discussed. The application range was 10.0-300.0 mg·L^-1 and the lowest limit of detection was 3.5 mg·L^-1. It was considered that the value obtained could be reliably correlated with the COD value obtained using the conventional methods.     

Dielectric Study of Charge-transfer Complexes in Binary and Ternary Systems at 35°C

Abstract

The measurements of dielectric constant of a number of binary and ternary mixtures of butyl acetate, butyl alcohol, quinoline, pyridine and o-cresol in carbon tetrachloride and benzene have been made at 35°C. Molecular interaction of these aromatic compounds have been studied in terms of variations in parameters; ‘dipole moment’ (μ), ‘interaction dielectric constant’ (δ?), ‘molecular polarisation’ (P) and ‘excess polarisation’ (P_E ). The dipole moment has been calculated using Hysken's method, the interaction dielectric constant utilizing the equation of ideal mole fraction law and excess polarisation using the theory of Erap and Glasstone. The positive values of δ?₁₂ for binary mixtures of quinoline and butyl acetate in carbon tetrachloride and benzene have been attributed to the formation of charge transfer complexes. The negative values of δ?₁₂ and δ?₁₂₃ with pyridine suggest that charge transfer interaction is weakened by pyridine in its binary and ternary mixtures. The plot between the excess polarisation value and the product of mole fractions yielded a straight line passing through the origin showing the formation of charge transfer complexes.     

Reactions of Initiation and Reinitiation in Polymerization Mediated by Organoborane–Oxygen Systems

The kinetics and mechanism of initiation and reinitiation reactions in the polymerization of methyl methacrylate mediated by the ammonia–tripropylborane–oxygen and 2-isopropyl-2-boraadamantane–oxygen systems are studied by ESR spectroscopy using C-phenyl-N-tert-butylnitrone and 2-methyl-2-nitrosopropane as spin traps. It is shown that alkyl and alkoxyl radicals are the main initiating radicals and the rate of initiation is directly proportional to the concentration of oxygen. Two mechanisms of radical formation are valid in the postpolymerization of methyl methacrylate at room temperature under vacuum. The first one (which is predominant) is the decomposition of poly(methyl methacrylate)–boroxyl macromolecules, i.e., the reinitiation of polymerization; the second one (additional during the first 30 min of the process) is the decomposition of borane peroxide compounds accumulated during the stage of oxidation.     

Liebig–Denigès Method of Cyanide Determination: A Comparative Study of Two Approaches

The paper compares two approaches to the simulated argentometric titration of cyanide with the use of the modified Liebig?CDenigès (L-D) method, carried out according to GATES and applied with (1) classical and (2) pH-static titrations. Both approaches are discussed thoroughly and the results obtained from calculations are presented graphically. The calculations are performed with the use of an iterative computer program, based on charge and concentration balances and expressions for equilibrium constants, providing all physicochemical knowledge of the dynamic system in question. This way, physicochemical knowledge on complex electrolytic systems can be gained during the analytical procedure, i.e., the physicochemical and analytical knowledge are interrelated. The simulations follow the analytical procedures applied in experimental titrations and so provide an example of searching for the best a priori conditions for the quantitative analysis of cyanide. The computer program for pH-static titrations (described in this paper) enables one to carry out the simulation procedures with different preliminary data (concentrations, volumes).     

DSC Study of the Postdenaturated Structures in Biopolymer–water Systems

The temperature dependences of heat capacity for water–denaturated biopolymer (globular proteins, collagen and DNA) were measured in a wide range of temperatures (0–140°C) and water content of the systems. It has been shown that thermally denaturated globular proteins (lysozyme, myoglobin and catalase) are able to form the thermoreversible heat-set structures under the certain conditions studied. The additional endothermal maximum observed is the calorimetric manifestation of the phase transition related to the melting of these thermotropic non-native structures. The melting gels are completely formed just after denaturation during relatively short time and only their prolonged state at T>T _d leads to their transformation to thermoirreversible non-melting ones. The post denaturated structures from water-denaturated protein (Mb, Lys and RN-ase) systems with a different amount of free water were also studied. The thermoreversible cold-set gels are formed from both water-denaturated DNA and water-denaturated collagen systems. These thermotropic structures are metastable. A spatial gel network of both collagen and DNA is formed from the native-like renaturated structures. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparative Study of the Use of Flow-Through Systems with and without Air Segmentation for Determination of Phenols by Solid-Phase Microextraction–Gas Chromatography

Two procedures have been evaluated for SPME of phenols from liquids—flow-through extraction and a system based on flow-through extraction in which the sample stream is segmented with air bubbles. For testing the segmented flow-through procedure, free and derivatized phenols were absorbed directly from an aqueous solution by means of an 80-m polyacrylate fiber and a 100-m polydimethylsiloxane fiber, respectively. The amounts of analytes absorbed by the fibers, and the precision achieved, were compared for the two procedures. The results indicated extraction, including that of the more volatile phenols, was better when the air-segmented flow-through extraction cell was used.     

Nature of a Positive Anodic Peak in the Stripping Voltammogram of Binary Platinum–Metal Systems

The effect of platinum on the electrodeposition of cadmium, lead, copper, and mercury at the surface of a solid electrode was studied by stripping voltammetry. It was shown that an additional current peak in the anodic voltammogram corresponded to the metal ionization to support electrolytic platinum.     

Ultrasonic and Volumetric Study of N–H Bond Complexes in Binary Mixtures

Experimental values of the density and ultrasonic velocity have been measured for binary mixtures of butylamine with 1-butanol and with tert-butanol at temperatures of 293.15, 303.15 and 313.15 K over the entire mole fraction range. From these data, the excess molar volumes, deviations in isentropic compressibility, excess internal pressures, and excess molar enthalpies have been calculated. All of the excess functions were fitted to Redlich-Kister polynomial relations to estimate the adjustable parameters along with the standard deviations of the fits. The variations of these excess functions with mole fraction of butylamine have been examined. The changes in these parameters with composition suggest that the interaction between butylamine and 1-butanol is strong, whereas its interaction with tert-butanol is weak. Further, the partial molar volumes and partial molar compressibilities at infinite dilution have also been evaluated since these parameters provide better insight for studying intermolecular interactions.     

Study on Isoelectric Point of Magnesium Aluminum Hydroxide

Isoelectricpoint(IEP)valuesareInaiulyforbytheprOpeniesandcomposihonOfmetalions,thcyindicaethemagnitudeofrmnityofmetalionsf0releCtrn.TheeffodofIEPofmagncsiumabonumhydroaldeonthepropeniesandcomposihonofmetalionsarediscussedinthispaPer.Experimentall.PreparationofmagnesiumaltalnumhydrokidePOsihvesol.ThepreParationmethodreferredtoref[41.2.MeasurementS0ftheelmphoreticmobilityTheelectrophorehcmobilihesweredetetrinedwithDXD-IIm0delInieroelCCtfophoresisapparatUs.at1hei0nicstrengthof0.OOland…     

Study on Phase Equilibrium Properties for CO_(2+) Cosolvent Binary Systems

Recently, the application of supercritical fluid technology is very interested, and it is applied in many areas for its special properties. The performance of supercritical fluid (SCF) as a solvent can be greatly affected by addition of an entrainer to the system. An entrainer can be added to a supercritical fluid to enhance its solvent strength and/or selectivity. Critical point data for these dilute supercritical fluid-cosolvent systems are imperative for the design of efficient separation …     

Determination of Memantine in Human Plasma by LC–MS–MS: Application to a Pharmacokinetic Study

A sensitive and selective liquid chromatography–tandem mass spectrometry method for the determination of memantine was developed and validated over the linearity range 0.1–25 ng mL^?1 with 0.5 mL of plasma using procainamide as the internal standard. This analysis was carried out on a Cosmosil 5C₁₈-MS column and the mobile phase was composed of methanol: 0.5% formic acid (50:50, v/v). Detection was performed on a triple–quadrupole tandem mass spectrometer using positive ion mode electrospray ionization and quantification was performed by multiple reaction monitoring mode. The MS–MS ion transitions monitored were m/z 180 → 107 and 236 → 163 for memantine and procainamide, respectively. The between- and within-day precision was less than 10.9% and accuracy was less than 2.5%. The lower limit of quantification (LLOQ) was 0.1 ng mL^?1. The method proved to be accurate and specific, and was applied to the pharmacokinetic study of memantine in healthy Chinese volunteers.     

Adsorption Chronopotentiometric Determination of Aluminum in Drinking Waters by Cupferron

1.IntroductionAluminumisknowntobetoxictothecentfalnervoussystem.AlotofAl-relatedhumandisordershavebeenreported'.InChina,aluminumsaltsarewidelyusedindrinkingwaterpurificationandAlpotsareusuallyutilizedforstoringdrinkingwaters.Therefore,thedeterminationofAlindrinkingwatersisessentialforevaluatingitsbiologicaleffect.NumerousanalyticalapproacheshavebeendevelopedincludingAAS,ICP-AES,spectrophotometry,fluorescenceandelectyochemicaltechniques.Amongthemthemostsensitivetechniqueisadsorptivestripp…     

Thermal Analysis of Binary Systems. Explosive – lead compound

The thermal decomposition of explosives: pentaerythrol tetranitrate (PETN), 2,4,6-trinitrotoluene(TNT), cyclo-1,3,5-trimethylene-2,4,6-trinitroamine (RDX) and their two-component mixtures with 40% of lead compounds [PbO, Pb₃O₄, Pb(NO₃)₂] were performed. The simple method of determination of stability changes in the mixtures described above, in comparison with pure explosives was presented. The lead oxides accelerated significantly the thermal decomposition of explosives. Pb(NO₃)₂ acts as a catalyst in the mixture containing TNT degradation, but not in a case of PETN and RDX. This revised version was published online in August 2006 with corrections to the Cover Date.     

Temperature and Oxygen Partial Pressure Dependences of the Surface Tension of Liquid Sn–Ag and Sn–Cu Lead-free Solder Alloys

Summary. Temperature dependence of the surface tension of liquid Sn–Ag and Sn–Cu base lead-free solder alloys and oxygen partial pressure dependence of liquid Sn–Ag alloy were evaluated using the experimental data obtained, respectively, by the constrained drop method and the sessile drop method in the previous studies [1, 2]. The temperature dependences of the surface tension have maximum positive values when the mol fraction of Ag and Cu is about 0.7, while those for pure liquid Sn, Ag, and Cu have negative values. The calculated values based on Butler’s equations were found to be in reasonable agreement with those of the experimental data. The oxygen partial pressure dependences of the surface tension of liquid Sn–Ag alloys at 1253 K have a minimum value when the mol fraction of Ag is about 0.9 and the oxygen partial pressure is less than about 10⁻¹³ atm. From this, it is considered that the oxygen adsorption increased by adding Ag to Sn when the mol fraction of Ag is less than 0.9.     

Spectroscopic Probe–Aluminum(III)–Chrome Azure S Enhanced Determination of Serum Albumin in Microemulsion Medium

Abstract

The sensitizing effect of spectroscopic probe and microemulsion media on the determination of serum albumin by spectrometry was developed. The main factors affecting the determination were investigated in detail. The results showed that serum albumin reacted with spectroscopic probe Al(III)‐CAS to form a blue complex at pH=3.0 in the p‐octyl polyethyleneglycolphenyether microemulsion (Triton X‐100‐M). The λ_max=641 nm, and Beer's law was obeyed in the range of 0.0 and 35.0 µg · ml^?1 for bovine serum albumin (BSA). The sensitizing effect of spectroscopic probe in Triton X‐100-M microemulsion was higher than that in aqueous media. The proposed method has been used to determine protein in serum with satisfactory results.     

Validated Stability-Indicating HPLC–DAD Determination of the Antihypertensive Binary Mixture of Carvedilol and Hydrochlorothiazide in Tablet Dosage Forms

A simple and selective HPLC with diode array detection stability-indicating method was developed for the simultaneous determination of the antihypertensive drugs carvedilol (CRV) and hydrochlorothiazide (HCT) in their combined formulations. Effective chromatographic separation was achieved using Zorbax SB-C8 column (4.6 × 250 mm, 5 μm) with gradient elution of the mobile phase composed of 0.025 M phosphoric acid and acetonitrile at a flow rate of 1 mL min^?1. The multiple wavelength detector was set at 242 nm for measurement of CRV and 271 nm for HCT. Quantification was based on measuring the peak areas. The cited drugs were resolved with retention times 4.9 and 6.7 min for HCT and CRV, respectively. Analytical performance of the proposed HPLC procedure was thoroughly validated with respect to system suitability, linearity, ranges, precision, accuracy, specificity, robustness, detection and quantification limits. The linearity ranges were 5–300 and 5–200 μg mL^?1 for CRV and HCT, respectively, with correlation coefficients >0.9996. Both drugs were subjected to stress conditions of acidic and alkaline hydrolysis, oxidation, photolysis and thermal degradation. The proposed method proved to be stability-indicating by resolution of the drugs from their forced degradation products. Moreover, specificity of the method was verified by resolution of both drugs from more than 20 pharmaceutical compounds of various medicinal categories. The validated HPLC method was applied to the analysis of the cited antihypertensive drugs in their combined tablet dosage forms. The proposed method made use of DAD as a tool for peak identity and purity confirmation.     

Validated Stability-Indicating HPLC–DAD Determination of the Antihypertensive Binary Mixture of Carvedilol and Hydrochlorothiazide in Tablet Dosage Forms

A simple and selective HPLC with diode array detection stability-indicating method was developed for the simultaneous determination of the antihypertensive drugs carvedilol (CRV) and hydrochlorothiazide (HCT) in their combined formulations. Effective chromatographic separation was achieved using Zorbax SB-C8 column (4.6 × 250 mm, 5 μm) with gradient elution of the mobile phase composed of 0.025 M phosphoric acid and acetonitrile at a flow rate of 1 mL min⁻¹. The multiple wavelength detector was set at 242 nm for measurement of CRV and 271 nm for HCT. Quantification was based on measuring the peak areas. The cited drugs were resolved with retention times 4.9 and 6.7 min for HCT and CRV, respectively. Analytical performance of the proposed HPLC procedure was thoroughly validated with respect to system suitability, linearity, ranges, precision, accuracy, specificity, robustness, detection and quantification limits. The linearity ranges were 5–300 and 5–200 μg mL⁻¹ for CRV and HCT, respectively, with correlation coefficients >0.9996. Both drugs were subjected to stress conditions of acidic and alkaline hydrolysis, oxidation, photolysis and thermal degradation. The proposed method proved to be stability-indicating by resolution of the drugs from their forced degradation products. Moreover, specificity of the method was verified by resolution of both drugs from more than 20 pharmaceutical compounds of various medicinal categories. The validated HPLC method was applied to the analysis of the cited antihypertensive drugs in their combined tablet dosage forms. The proposed method made use of DAD as a tool for peak identity and purity confirmation.

     

AB Initio MO Study of P--Si π Systems: Structures and Energies

The origin of the relative stability of isomers of 1,2-diphosphinodisilene and related compounds is discussed. The geometries of 18 isomers of (H 2 X)HE=EH(XH 2 ), (H 2 X)HE=EH(XH 2 ) 2+ , and HX=EH--HE=XH (E = C, Si; X = P, N) have been optimized at the MP2/6-311++G(d,p) level of theory. Since nitrogen and phosphorus have lone-pair electrons, six electrons can delocalize in four orbitals of (H 2 X)HE=EH(XH 2 ) (6e/4o), while four electrons can delocalize in four orbitals of (H 2 X)HE=EH(XH 2 ) 2+ and HX=EH--HE=XH (4e/4o). To examine the interaction that governs the structure and relative stability of their cis and trans (or cisoid and transoid) isomers, the ~ - * delocalization energies and isodesmic reaction energies of the compounds were calculated. It is concluded that the ~ - * delocalization affects the bending structure of disilene derivatives, and phosphorus substituents prefer 2e/4o and 4e/4o systems.