Development and Evaluation of a Kinetic‐Spectrophotometric Method for Determination of Arginine

A kinetic method for the determination of micro quantities of amino acid arginine (Arg) is described in this paper. The catalytic activity of cobalt in the reaction of oxidation of purpurin (1,2,4‐trihydroxy‐antraquinone, PP) by hydrogen peroxide in alkaline buffer solution decreases in the presence of micro quantities of arginine, because of the formation of the complex. Operating conditions for the successful determination of arginine were optimized. The optimized conditions yielded a theoretical detection limit of 1.45 μg mL^?1. Kinetic equations are proposed for the investigated process. The interference effects of certain foreign ions and amino acids upon the reaction rate were studied and removed in order to assess the selectivity of the method. The developed procedure was successfully applied to the determination of arginine in various pharmaceutical samples. The typical feature of this procedure is that determination can be carried out at room temperature and in a short analysis time. The newly developed method is simple, inexpensive and efficient for use in the analysis of a large number of samples.     

Electronic spectrum in a microscopical model for the Zn-doped CuO2 plane

We consider a microscopical model for the Zn-doped CuO₂ plane with Zn impurities being described as vacancies for the d-states on Cu sites. A reduction of the original p-d model to an effective one-band model results in the t-J model with vacancies for the spin 1/2 d-states at the Zn-sites. By employing the T-matrix formalism for the Green functions in terms of the Hubbard operators the density of electronic states (DOS) is calculated. Symmetry analysis of the perturbation matrix shows that in the system with d-type electronic wave functions additional DOS of d-, p- and s-types appear due to the perturbation of local energy levels and the interaction between nearest neighbors around the vacancy. The local and resonant state formation caused by Zn impurities is analyzed. Received 24 May 2000 and Received in final form 1 August 2000     

Kinetics and Mechanism of the Natural Mineral Marmatite Oxidation Process

Results obtained by the comparative investigations of the natural mineral marmatite (Zn,Fe)S (Stari Trg, Yugoslavia) oxidation process are presented in this paper. Determination of the oxidation process mechanism was done by thermal analysis methods: DTA-TG-DTG and DSC, while Mössbauer spectroscopy, X-ray and electronic microanalysis were used for phase composition determination of the products formed during the oxidation process. Kinetics of the process was defined for two temperature intervals 862–973 and 1023–1173 K, under isothermal conditions.     

Electron and ion mobilities in argon plasma with fluorine as additive

Results of the numerical evaluation of the electron and ion mobilities in plasmas from mixtures of argon and fluorine are given. The temperature dependence of the number densities of the components and their mobilities as a function of temperature for low-pressure (from 0.1 kPa to 1.0 kPa) and low-temperature (from 500 K to 5000 K) argon plasmas with 20% and 30% of added fluorine are evaluated. It is assumed that the system is kept under constant pressure and that a corresponding state of local themodynamical equilibrium is attained in it. The previously derived expression for the modified Debye radius, offering the possibility to treat the plasmas as weakly non-ideal in the whole temperature range, is used and the cut-off at the Landau length rather than at the smallest ionic radius is introduced. This alteration in the evaluation procedure gives different changes in the final numerical results for all the relevant quantities. It was found that the equilibrium plasma composition depends considerably on the presence of fluorine in the whole temperature range for both the pressures; the addition of fluorine significantly enhances the number densities of all relevant charged constituents. This fact influences the electron and ion collision frequencies as well as their mobilities.     

Relations between reflections in the unitary group and Hermitian hyperquadrics in the complex projective space

We consider the subgroup G(n) of the compact unitary group U(n) generated by reflections. By a reflection we mean an element R of U(n) such that R²=I and ?1 is a simple eigenvalue of R. It is easy to describe the relations between reflections of the form R₁R₂=R₃R₄. One of our main results is that these relations together with R²=I are the defining relations of G(n). Other results characterize the set of all shortest sequences R₁, R₂,…, R_m of reflections whose product is a fixed element of G(n).     

Favorski type rearrangement in the lead tetraacetate oxidation of enamines promoted by boron trifluoride

Favorski type rearrangement has been achieved in the lead tetraacetate oxidation of enamines in the presence of boron trifluoride etherate and alcohol.     

A LFER Kinetic Study of The Reaction of 5‐Substituted Orotic Acids with Diazodiphenylmethane

Linear free energy relationships (LFER) were applied to the kinetic data for the reaction of 5‐substituted orotic acids, series 1 , with diazodiphenylmethane (DDM) in N,N–dimethylformamide and compared with results obtained for 2‐substituted benzoic acids, series 2 . The correlation analysis of the kinetic data with σ substituent parameters was carried out using SSP (single substituent parameter) methods. From the sign and value of proportinality constant ρ, lower sensitivity to the substituent effect was obtained in series 1 , 0.876, than in the series 2 , 1.877. Evaluation of substituent “ortho‐effect” was performed using the Charton model, which includes the steric substituent parameter, and Fujita and Nishioka's model, which describes the total ortho‐effect as contribution of ordinary polar effect, the ortho‐steric and ortho‐polar effects. Results of correlations, obtained by using the Charton model, showed highest contribution of the polar effect, 0.861 vs. 2.101, whereas the steric effect is of lowest significance, 0.117 vs. 0.055, for series 1 and 2 , respectively. Also, a low negative value of coefficient with the steric effect, –0.08, obtained from the Fujita–Nishioka model indicated low steric effect, influencing a decrease of the reaction rate in series 1 . The structural and substituent effects were also studied by using the density functional theory method, and together with kinetic data, it gave a better insight into the influence of the effect of both geometry and substituent on the π?electron density shift induced reactivity of investigated acids.     

Solubility in K+-Na+-Mg 4 2− aqueous solution at T = 298.15 K

In the salt solubility predictions for K⁺-Na⁺-Mg ₄ ^2? aqueous solution the treatment of thermodynamic data of three-component systems at T = 298.15 K involved the application of the Extended Pitzer’s ion-interaction model for the pure and mixed electrolyte solutions and criteria of phase equilibrium. Osmotic coefficients data of three-component systems were revised according to recently published parameters of the solutions NaCl(aq) and KCl(aq) that served as reference standards in isopiestic measurements. Parameters of the extended ion-interaction model of K₂SO₄(aq) are determined by treatment of experimental and predicted values of osmotic coefficient in supersaturated region obtained by the Zdanovskii-Stokes-Robinson rule. Results of salt solubility prediction were compared to experimental solubility data from literature. The agreement between calculated and experimental solubility data in the systems K₂SO₄ + MgSO₄ + H₂O, Na₂SO₄ + MgSO₄ + H₂O, and Na₂SO₄ + K₂SO₄ + H₂O at T = 298.15 K, was excellent.