Standard potential of the silver-silver chloride electrode in 10, 20, and 40 wt.% ethanol/water solvents at 25, 0, −5, and −10°C

In order to facilitate the measurement of thermodynamic quantities at temperatures below 0°C in ethanol/water solvents, the standard potential of the silver-silver chloride electrode in 10, 20, and 40 wt.% ethanol has been determined at 25, 0, ?5, and ?10°C. Electromotive force measurements of cells of the type $$Pt;H_2 (g)|HCl(m) in EtOH/H_2 O|AgCl;Ag$$ were used. The potentials found at 25°C were in good agreement with earlier results. Mean activity coefficients for hydrochloric acid in the three mixed solvents were derived.     

Spectrophotometric determination of mebeverine hydrochloride

Three simple, sensitive and reproducible visible spectrophotometric methods (A-C) for the determination of mebeverine hydrochloride (MVH) in bulk samples and pharmaceutical formulations are described. Methods A and B are based on the formation of ion-association complexes between the drug and fast green FCF (FGFCF, _max 625 nm) or bromothymol blue (BTB, _max 405 nm). Method C is based on the formation of a molecular complex between the drug and cobalt thiocyanate (CTC, _max 625 nm). Regression analysis of Beer's plots showed good correlation in the concentration ranges 2–40, 2–25 and 100–600 g/ml for methods A, B and C respectively. No interference was observed from the usually existing additives in pharmaceutical formulations and the applicability of the methods was examined by analysing tablets containing MVH. Standard deviations were typically 0.75 mg per dose (RSD: 0.25–0.5%). Recoveries were 99.0–100.2%.     

Core-modified expanded porphyrins with large third-order nonlinear optical response

The third-order nonlinear optical response through measurement of two-photon absorption cross-sections (TPACS) for aromatic core-modified expanded porphyrin analogues by a femtosecond open aperture Z-scan method is reported. The values reported here are among the largest known so far in the literature for any organic molecules.     

Determination of uranium(VI) in monazite sand

The design and characterization of an argon segmented-solid phase extraction system is described. A 200 ul volume micro-column has been constructed for the preconcentration of rare earth elements (REEs) from salt matrices containing uranium. An inductively coupled plasma atomic emission spectrometer has been utilized for simultaneous detection of Sr, Y and the REEs (namely Ce, Eu, La, Nd, Pr, Sm) at levels ranging from 5- to 2000 ppm in LiC1/KCl samples containing U. Preconcentration factors of 100 fold have been demonstrated. The precision, linear dynamic range and column performance of the system will be presented.     

Preparation of ion exchange resin based elemental standards for use in activation analysis

Various methods of preparing standards for activation analysis have been reported in the literature. This paper describes the feasibility of preparing ion exchange resin based standards containing predetermined levels of ions. Using a solution of known initial concentration of the ion, and given the value of its distribution coefficient, it is possible to predict the resin concentration that will be obtained. Resins containing ppm levels of copper and manganese have been prepared and their stabilities evaluated over a period of time. The feasibility of preparing a multielement standard has been studied with five rare earth elements (La, Ce, Sm, Eu and Dy).     

Spectrophotometric determination of arsenic by molybdenum blue method in zinc-lead concentrates and related smelter products after chloroform extraction of iodide complex

The most popular and widely applied method for determination of arsenic in ore concentrates is by spectrophotometry of arsenomolybdic acid reduced to molybdenum blue. While applying this method, several authors have developed procedures which varied in the decomposition, separation of arsenic and in the final colour development. Data regarding interference from germanium is inadequate. The present paper describes a procedure, which combines the best features of the previous procedures and is simple, less time consuming and interference-free compared to earlier procedures. This method has been applied to zinc-lead concentrates and related smelter products.     

Thermodynamic Constants of Glycyl Peptides: Solvation and Buffers for the Physiological pH Range

The pK ₂ values for the dissociation of the NH ₃ ⁺ charge center of the glycyl peptides, e.g., glycyl-D-asparagine, glycyl-DL-serine, glycyl-L-leucine, and glycyl-DL-methionine have been determined at 10 temperatures in the range 5–50°C by measurements of the emf of cells without liquid junction, utilizing hydrogen electrodes and silver–silver bromide electrodes. The thermodynamic quantities, H ^o, C _p ^o and S ^o were calculated from the temperature coefficients of the dissociation constants. The pK ₂ values at 25°C are 8.268 (glycyl-D-asparagine), 8.277 (glycyl-DL-serine), 8.323 (glycyl-L-leucine), and 8.408 (gly-cyl-DL-methionine). These values show that changes in the substituents on the -carbon atom have very little effect on the dissociation of the NH ₃ ⁺ , with the possible exception of glycyl-DL-methionine. The suitability of these compounds as buffers in the physiologically important pH range 7–9 is of interest. The thermodynamics of the solute–solvent interaction is interpreted in terms of a mixture model. The peptides chosen for study include both polar and nonpolar substituents.     

Formation and isolation of an iron-tripyrrole complex from heme degradation

Addition of dioxygen to a solution of (py)2Fe(OEPO) (1) (where OEPO is the trianion of octaethyloxophlorin) in pyridine-d5 at 23 degrees C results in a series of oxidative changes that have been followed by 1H NMR spectroscopy. After 4 h, the resonances of 1 have vanished, while several sets of new resonances have developed. The most intense of these are identified as belonging to (py)2FeIII(OEB) (2) by comparison with the previously obtained spectrum of this species, which contains a ring-opened tetrapyrrole. After the sample was left standing for 1 day, further changes occur which produce a sample that is stable, because 1H NMR spectroscopic examination reveals no further changes on continued exposure to dioxygen or air. The product, (py)2FeIII(HETP) (3), where HETP is the dianion of a hexaethyltripyrrole, has been converted into (n-Bu4N)[ClFeIII(HETP)] by treatment with tetra(n-butyl)ammonium chloride. Red (n-Bu4N)[ClFeIII(HETP)] has been isolated and characterized by single-crystal X-ray diffraction.     

Photophysical behaviour of 4-(imidazole-1-yl) phenol and its complexation with beta-cyclodextrin in ground and excited states

This paper mainly dwells on photophysics of 4-(imidazole-1-yl) phenol (IDP) in different solvents and temperatures from the investigations of absorption, emission and laser flash photolysis and also on the nature of complexation with beta-cyclodextrin (CD) in ground and excited states. IDP makes 1:1 inclusion complex with beta-CD in ground, excited singlet and also in triplet states. The orientation of complex could be ascertained as imidazole moiety stays inside the cavity with phenol moiety stays in the bulk. A proposed energy level scheme unveils that vibronic interaction and spin-orbit interaction are found to be active differently in aprotic and protic solvents.     

Crystal and molecular structure of isogarcinol

The controversy with regard to the structures of the closely related polyisoprenylated phenolic compounds, garcinol, isogarcinol, camboginol, cambogin, xanthochymol and isoxanthochymol is cleared by X-ray crystallographic analysis of the naturally occurring isogarcinol. The unusual UV spectral characteristics of the chromophore of isogarcinol are discussed.