Infrared determination of calcium or lithium nitrate in acetone solution determination of calcium or lithium in the presence of strontium or barium

A method is proposed for the infrared determination of calcium or lithium in the presence of strontium or barium. A mixture of the nitrates is treated with acetone which dissolves only the calcium or lithium nitrate. The strontium or barium nitrate is filtered off. The nitrate is evaporated to about 2 ml with a stream of dry air and then diluted to 5 ml with acetone. The infrared spectrum is scanned from 860 to 800 cm(-1) and the nitrate peak at 824 cm(-1) for calcium and 827 cm(-1) for lithium is measured. The recommended range is 1-80 mg of calcium or lithium nitrate in the presence of up to about 200 mg of strontium or barium nitrate.     

Stacking design of inverse perovskites: the systems (Sr3-xBaxN)E, E = Bi, Sb

The first representatives of 4H (BaMnO3-type structure, P63/mmc, Z = 4) and 9R (BaMnO3-type structure, Rm, Z = 9) inverse Perovskite phases are presented. The phases are obtained within the solid solutions (Sr3-xBaxN)E with E = Bi, Sb. The crystal structures and homogeneity ranges were studied by combined X-ray and neutron diffraction as well as chemical analyses. The cubic Perovskite phase with Bi (Sb) is stable in the range of 0.00 < or = x < or = 0.90(5) (0.00 < or = x < or = 1.30(5)), the 4H variant is stable for 1.55(5) < or = x < or = 2.10(5) (1.85(5) < or = x < or = 2.45(5)), the 9R structure is stable for 2.50(2) < or = x < or = 2.55(2) (2.56(2) < or = x < or = 2.60(2)), and the 2H phase is stable for 2.75(5) < or = x < or = 3.00 (2.80(5) < or = x < or = 3.00). Ba occupies preferable sites in the hexagonal stacking of close packed layers of alkaline earth metal ions and E3-; Sr is mainly located in cubic stacked layers. The phase order upon going from cubic (Sr3N)E to 2H-type (Ba3N)E concomitant to the pronounced Sr/Ba partial order can, in general, be rationalized considering the Coulomb repulsion of nitride ions, as well as the size and charge density of the alkaline earth metal ions.     

Tox-match/pharm-match prediction of toxicological and pharmacological features by using optimal substructure coding and retrieval systems

The computer program TOX-MATCH/PHARM-MATCH allows prediction of toxicological or pharmacological features based on a reverse search strategy. The program has a library of model chemical structure toxicophores or pharmacophores in a tree structure using a special chemical coding method (based on topology, topography, and graph theory). Graph theory has proven particularly efficient for coding and retrieval of polynuclear aromatic hydrocarbons. The library of model pharmacophores or toxicophores is then followed by a library of the toxicological or pharmacological triggering events (usually biochemical) caused by each model toxicophore or pharmacophore, the subsequent physiological events (also usually biochemical) and the observed physiological signs and symptoms of each species. An unknown sample is input (also in the special chemical coding), and the model toxicophore or pharmacophore is compared with the sample compound to see how close the match is (reverse search). This program is open-ended and extremely versatile and can be used for any toxicological or pharmacological problem.     

A method,based on statistical moments,to evaluate the kinetic parameters involved in unstable enzyme systems

The evaluation of individual rate constants involved in any reaction mechanism of an enzymatic systems first requires experimental monitoring of the time course of the concentration or product rate creation or of any enzyme species. The experimental progress curves obtained must then be fitted to the corresponding theoretical symbolic equation. Nevertheless, in some cases, e.g. when the equation involves two or more exponential terms, this fit is not easy and sometimes impossible. Simplification of the equation is usually required by assuming, for example, that the system has reached the steady-state, assuming an initial steady-state of a segment in the scheme of the reaction mechanism or assuming rapid equilibrium in one or more of the reversible steps, if there are any. But, obviously, simplified equations produce either fewer individual rate constants or global constants consisting of algebraic associations of individual rate constants or individual rate constants or global constants that might considerably differ from the real ones due to the approaches made. In this contribution, we suggest an alternative procedure for evaluating the rate constants of enzyme reactions corresponding to enzyme systems where one or more of the species involved is unstable or where one or more of the enzyme species is irreversibly inhibited, or both. The procedure is based on the numerical determination of statistical moments from experimental time progress curves. The fitting of these experimentally obtained moments to the corresponding theoretical expressions allows us, in most cases, to evaluate of all of the rate constants involved, with only a small error. To verify the goodness of the suggested procedure, it was applied to an unstable enzyme system which had previously been analysed with other methods. Finally, it is indicated how this procedure could also be extrapolated for application to any stable or unstable enzyme system.     

Coprecipitation of uranium and thorium with barium sulfate

The coprecipitation behaviour of uranium or thorium with barium sulfate is investigated from the variation of yields with uranium or thorium concentration, acid and acidity, and amount of sodium and/or potassium sulfate. Uranium or thorium in quantities less than 1.5 mg is quantitatively coprecipitated with barium (5.9 mg) sulfate when using an optimum conditions. The chemical form of uranium in barium sulfate precipitates is discussed by determination of mole ratio of potassium to uranium.     

关于统计学中一个新兴化学分支学科的建立、定义和教育

本文追溯了统计学发展、建立中的大事, 陈述了它的定义及其化学分支发展、建立的梗概; 鉴于化学界对该新兴化学分支学科的名称长期存在争议, 提出了以化学统计学而不以化学计量学为该学科名称的理由, 把化学统计学定义为一个研究有关数据的收集或产生、描述、分析、综合和解释, 以获得新化学知识或信息的学科; 阐明了许多公认属于统计学的方法, 如显著性检验、方差分析、回归和相关, 以及一些尚未认定属于统计学的方法, 如模型建立、蒙特卡罗方法、傅立叶变换和人工神经网络, 都含有统计学5 个内涵中的一个或多个; 探讨了化学统计学家成长的模式, 认为当务之急是把化学统计学纳入化学专业的教学计划, 以培养懂统计学的化学家。     

Assessing the reproducibility of an analytical method

The reproducibility of a validated analytical method may require reassessment because of various reasons, such as the transfer between laboratories or companies, changes in the instruments or software platforms (or both), or changes in critical reagents, among others. This paper is a demonstration of an assay bridging study in evaluating reproducibility. The approach is simple but very informative and offers many advantages over existing approaches.     

An integration method of enzyme analysis

The application of an integration method of kinetic analysis to first-order and second-order reactions is discussed with particular emphasis on enzyme analyses. Transducer signals or concentrations of products or substrates are integrated for a Fixed time and the net integral of the increased or decreased signal or concentration is related to the initial substrate or enzyme concentration. Equations are developed describing the dependence of the integrals on enzyme and substrate concentrations for first- and second-order reactions, and examples are presented illustrating different cases. The application of this method to complicated enzymatic systems is discussed.     

Die erlangungsfähigkeit des gleichgewichtes in systemen,die aus flüssigkeit und wenigstens aus einer festen phase gebildet sind

The difficulties associated with the precise determination of the freezing temperature of different systems containing one, two, or several solid phases are discussed. The “thermal sensitivity test” is suggested for testing whether the precision with which the thermodynamic liquid-solid phase equilibrium, is restored is quite satisfactory.The static method makes it possible to introduce or to remove very small quantities of heat and to observe whether or not the restoration of the phase equilibrium takes place. If a kinetic method is applied, the “thermal sensitivity” of the system may be tested by comparing the solidification and the melting curves determined at different crystallization or melting velocities.     

A new method for “ferrous iron” and “excess oxygen” in rocks, minerals, and oxides

A new method is given whereby oxygen excess or deficiency in many minerals and oxides may be simply determined. The method depends on the stability in phosphoric acid-pyrophosphate mixtures of both Mn^III and Mn^II. The sample is dissolved in a phosphoric acid mixture containing excess Mn^II, with or without the addition of standard oxidant, and Mn^III remaining in solution or produced by reaction with the sample is titrated with ferrous ammonium sulphate, using barium diphenylamine sulphate as indicator. The method is useful in many cases where existing methods are inapplicable or unsatisfactory. Accurate results can be obtained using relatively small samples.     

Determination of trace elements in inorganic and organic materials by x-ray fluorescence spectroscopy

A new, almost universally applicable method for the trace analysis of inorganic and organic materials is described. The trace element (or elements) together with a suitable coprecipitating element is isolated from interfering elements by precipitation with a suitable organic or inorganic precipitant. The precipitate is then filtered on a paper disk and the collected trace element (or elements) is determined by X-ray analysis.     

含有机硅多嵌段及其接枝共聚物的表面组成

利用ＸＰＳ对聚二甲基硅氧烷与聚砜或／和聚对羟基苯乙烯组成的二元和三元多嵌段和接枝共聚物及其共混物进行了研究。结果表明溶液成果的聚合物样品的表面都存在有机硅富集，共混物的表面富集程度等于接枝共聚物，更高于多嵌段共聚物，讨论了有机硅含量和键接结构对有机硅表面富集的影响。     

Structure and speciation in hydrous silica melts. 2. Pressure effects

The effect of pressure on structure and water speciation in hydrated liquid silica is examined over a range of temperatures and compositions. The Feuston-Garofalini (FG) potential is used in isobaric-isothermal Monte Carlo simulations carried out at four pressures (0.25, 1.0, 2.5, and 10 GPa) for seven temperatures (2000 < or = T < or= 9000 K) and five compositions (0.0 < or = x_w < or = 0.4). The FG potential yields a stable melt phase for p > or = 1.0 GPa and/or x_w < or = 0.1 for all temperatures. The volume minimum seen in previous simulations of pure and hydrated liquid silica using the FG potential persists up to 2.5 GPa but is no longer evident at 10 GPa. This is correlated with gradual structural changes of the liquid up to 2.5 GPa and with more significant changes at 10 GPa. Even at high overall concentrations of water (x_w = 0.4), only about 2% of oxygen atoms are present as molecular water species at the lowest temperature. This percentage decreases with increasing pressure and temperature.     

Propane‐1,2‐diols from Dilactides,Oligolactides, or Poly‐L‐lactic Acid (PLLA): From Plastic Waste to Chiral Bulk Chemicals

The preparation of racemic or enantioenriched propane‐1,2‐diol from dilactides, oligolactides, or poly‐L ‐lactic acid (PLLA) is described. The transformation is carried out as tandem reactions in MeOH, covering hydrolysis and subsequent hydrogenation by using copper chromite as a catalyst. The starting material present undesired side products of the PLLA synthesis or PLLA waste.     

Lactones. Part 16: Lactonization of γ,δ-epoxy esters with p-toluenesulfonic acid monohydrate

The reaction of cyclic γ,δ-epoxy esters with p-toluenesulfonic acid monohydrate is described. The reaction carried out in benzene or methylene chloride gave tosyloxy lactones as product. The ethoxy or methoxy lactones were obtained when ethanol or methanol were used as solvent. A mechanism of this lactonization is proposed.     

Synthèse de nouvelles amidines bicycliques . Dérivés de la pyrimidine,de la quinazoline et de la diazépine-1,3

The synthesis of pyrrolo[1,2-α] pyrimidines is described. Several homologous compounds contain pyridine or azepine instead of pyrrole ring. They are obtained by cyclization of iminolactams with β-ketoesters, αβ-unsaturated esters, aldehydes or ketones, or diketene. The possibility of obtaining isomers is discussed.     

Two OPEEs (organic phase enzyme electrodes) used to check the percentage water content in hydrophobic foods and drugs.

The development and optimization of an analytical method using enzymatic biosensors able to operate in organic solvents [organic phase enzyme electrodes (OPEEs)] for the determination of the water content in food fats (butter, margarine) or pharmaceutical or cosmetic ointments is described. The method is based on the increase in enzymatic activity which is related to the increase in the percentage water content in the organic phase into which the biosensor is dipped. The enzymes used to assemble the biosensors were tyrosinase or catalase, the substrates were phenol or p-cresol and tert-butyl hydroperoxide, respectively, and the organic solvents were acetonitrile or dioxane. A gas diffusion amperometric electrode for oxygen measurement was used as electrochemical transducer. The results were compared with those obtained applying the Karl Fischer method to the same food or drug matrices. The correlations among the two methods proved satisfactory, as the difference in the computed values of water content was never higher than 7%. Also, the precision of measurements was acceptable (RSD < 6%) in all the analyses of real matrices.     

Studies on the extraction and determination of metal salts with isobutyl methyl ketone-XIII Extraction of thorium and uranium

The work deals with the extraction of thorium or uranium from hydrochloric, perchloric, sulphuric or nitric acid solutions of various concentrations, or from mixed acid solutions, by means of isobutyl methyl ketone. When the extraction is made from 5-8M hydrochloric acid that is 10M in lithium chloride or from 7-8M hydrochloric acid that is 1M in magnesium chloride, uranium is extracted quantitatively (>99%), whereas thorium is hardly extracted at all.     

Approaches to Total Synthesis of Heterocyclic Steroidal Systems

In heterocyclic steroids the carbon atoms of the steroid skeleton (positions I to 17) are replaced in part by hetero atoms. The term generally denotes compounds containing one or two nitrogen, oxygen, and/or sulfur atoms. The part of the molecule containing the hetero atom is either introduced as a preformed unit or is constructed by stepwise synthesis. The examples given in the present article contain the hetero atoms in ring A, ring B, between rings A and B, and/or between rings C and D.     

Spectrophotometric determination of some phenothiazine derivatives and opipramol with chloramine-T

This paper describes a spectrophotometric method for the assay of phenothiazines (and also opipramol, which is similar but contains a C=C linkage instead of the S atom of the phenothiazines) as the pure drug or in tablets or solutions for injection. The colour is produced by heating a solution of the drug or drug preparation with a solution of chloramine-T. The coloured product can be extracted into chloroform before the colour measurement or the whole process carried out in ethanol solution, the colour of which is then measured.