Spectrophotometric Determination of Prochlorperazine Maleate in Pure and Pharmaceutical Preparations

 Prochlorperazine maleate reacts with 1-naphthylamine and sodium nitrite, after heating for 110 s at 80 °C to give an orange red colour having maximum absorbance at 460 nm. The reaction is selective for prochlorperazine maleate with 0.01 mg/mL as visual limit of quantitation and provides a basis for a new spectrophotometric determination. The colour reaction obeys Beer’s law from 0.01 mg/10 mL to 0.33 mg/10 mL of prochlorperazine maleate and the relative standard deviation is 0.68%. The quantitative assessment of tolerable amounts of other drugs is also studied. Received September 22, 2000. Revision June 19, 2001     

Spectrophotometric Determination of Phenytoin Sodium in Pure and Pharmaceutical Preparations

 Phenytoin sodium reacts with o-nitrobenzoic acid in alkaline media after heating for 10 minutes at 70 °C, to give a red coloured complex having maximum absorbance at 510 nm. The reaction is selective for phenytoin sodium with 0.01 mg/10 mL as visual limit of quantitation and provides a basis for a new spectrophotometric determination. The colour reaction obeys Beer’s law from 0.01 mg to 3 mg/10 mL of phenytoin sodium and the relative standard deviation is 0.29%. The quantitative assessment of tolerable amounts of other drugs is also studied. Received May 2, 2000. Revision May 11, 2001.     

Determination of Periodate by Fluorescence Quenching of Tetraiodofluorescein

 The fluorometric determination of periodate with tetraiodofluorescein has been developed. Under the optimum conditions responses were linear between 4.0×10⁻⁷ ∼ 1.0 × 10⁻⁵ mol/L of periodate. The detection limit was 1.0 × 10⁻⁷ mol/L corresponding to a signal to noise ratio of 2. The proposed method was applied to the determination of periodate in artificial fresh water and kelp sample with good results. Received March 20, 2001 Revision December 19, 2001     

Study on the Catalytic Determination of Vanadium (V) Using the Rhodamine 6G-Periodate Redox Reaction and its Analytical Application

 A fluorescence quenching method for the determination of vanadium (V) based on the vanadium- catalyzed oxidation of rhodamine 6G (R6G) with periodate in the presence of ethylenediaminetetraacetic acid disodium salt (EDTA) in sulfuric acid medium is described. The fluorescence was measured with excitation and emission wavelengths of 525 and 555 nm, respectively. The calibration graph for vanadium (V) had linear ranges of 3.0 × 10⁻⁹–1.5 × 10⁻⁸ mol/l and 1.5 × 10⁻⁸–4.0 × 10⁻⁸ mol/l, respectively. The detection limit was 1.7 × 10⁻⁹ mol/l. The proposed method was successfully applied to the determination of vanadium (V) in river water, rain water and cast iron samples. Received June 29, 2001 Revision October 9, 2001     

In situ Fourier transform IR spectroscopy and variable-temperature wide-angle X-ray diffraction studies on the crystalline transformation of melt-crystallized nylon 12 12

 The crystalline transformation in nylon 12 12 was monitored by variable-temperature wide-angle X-ray diffraction during heating, isothermal and cooling processes. It could be found that the α phase of the sample transforms into a γ phase at about 130 °C if the sample is heated from room temperature to a high temperature, which is the so-called Brill transition temperature. In addition, nylon 12 12 was found to crystallize into the γ phase when isothermally crystallized at high temperature from the melt. Upon further cooling from the crystallization temperature to room temperature, the reverse transition from the γ phase to the α phase can be detected. Furthermore, in situ Fourier transform IR spectroscopy was also used to study the Brill transition of nylon 12 12 samples on both heating and cooling. It is interesting that the hydrogen-bond strength in nylons decreases dramatically and that some Brill bands of nylon 12 12 disappear abruptly during the Brill transition on heating. Received: 3 April 2001 Accepted: 28 July 2001     

Production of submicron-sized poly(methyl methacrylate) particles by dispersion polymerization with a poly(dimethylsiloxane)-based azoinitiator in supercritical carbon dioxide

 Submicron-sized, comparatively monodisperse poly (methyl methacrylate) particles were produced by dispersion polymerization of methyl methacrylate with a poly(dimethylsiloxane)-based azoinitiator in supercritical carbon dioxide at 30 MPa for 24 h at 65 °C. The initiator operated not only as a radical initiator but also as a colloidal stabilizer, and was named an “inistab”. Received: 13 February 2001 Accepted: 20 June 2001     

Spectrophotometric reaction rate method for the determination of molybdenum by its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide

A kinetic spectrophotometric method for the determination of molybdenum is based on its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide. The decrease of the absorbance of pyrogallol red in the presence of hydrogen peroxide with time from 0.5 to 4.5 min is proportional to the concentration of Mo(VI) over the range 0.010–0.500 μg/mL. The limit of detection is 0.008 μg Mo/mL. The precision and the effect of the presence of more than forty ions on the molybdenum determination are reported. Probable interferences are completely removed by a cation exchange resin. The procedure was successfully applied to the determination of molybdenum in plant materials and steels. Received: 28 April 1997 / Revised: 16 June 1997 / Accepted: 18 June 1997     

Formulas and numerical table for the radial part of overlap integrals with the same screening parameters of Slater-type orbitals

 The numerical properties of the radial part of overlap integrals with the same screening parameters in the form of polynomials in p = ξR over Slater-type orbitals have been studied and obtained by using three different methods. For that purpose, the characteristics of auxiliary functions were used first, then Fourier transform convolution theorem, and recurrence relations for the basic coefficients of A ^s _{n l λ, n ′ l ′λ} were used. The calculations of the radial part of overlap integrals with the same screening parameters were made in the range 1 ≤ n ≤ 75, 1 ≤ n′ ≤ 75, and 10⁻⁶ ≤ p. Received: 18 January 2001 / Accepted: 5 April 2001 / Published online: 27 June 2001     

Spectrophotometric reaction rate method for the determination of molybdenum by its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide

A kinetic spectrophotometric method for the determination of molybdenum is based on its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide. The decrease of the absorbance of pyrogallol red in the presence of hydrogen peroxide with time from 0.5 to 4.5 min is proportional to the concentration of Mo(VI) over the range 0.010–0.500 μg/mL. The limit of detection is 0.008 μg Mo/mL. The precision and the effect of the presence of more than forty ions on the molybdenum determination are reported. Probable interferences are completely removed by a cation exchange resin. The procedure was successfully applied to the determination of molybdenum in plant materials and steels. Received: 28 April 1997 / Revised: 16 June 1997 / Accepted: 18 June 1997     

Preparation and properties of uniform praseodymium-doped ceria colloidal particles

 A procedure to prepare submicrometre spherical particles of Pr(III), Ce(III) or Pr(III)-doped C(III) hydroxycarbonates with narrow size distribution is reported. The particles were obtained by aging aqueous solutions of Pr(III) chloride and/or Ce(III) nitrate in the presence of urea at 100 °C for 2 h. The effect of Pr and/or Ce salt concentrations in the starting solutions on the size, shape and composition of the precipitated particles is reported. The thermal behaviour of the basic carbonates up to decomposition into the metal oxides was followed by differential thermal and thermogravimetric analyses, X-ray diffraction, IR spectroscopy and transmission electron microscopy. All the systems were also characterized by their electrokinetic behaviour (determination of isoelectric point) and specific surface areas. The colour of the powders was also evaluated as a function of the Pr content and temperature and was compared with previous results on red pigments of similar composition. Received: 30 May 2001 Revised: 17 September 2001 Accepted: 20 September 2001     

Spectrophotometric Determination of Dithionite in Household Commercial Formulations Using Naphthol Yellow S

 A rapid and quantitative procedure for the determination of dithionite based on the reduction of naphthol yellow S in ammonia containing solution and measurement of the absorbance of the product formed at 502 nm is described. The mechanism of the reaction is discussed and its analytical application is shown to be possible in a concentration range of dithionite between 16.7 and 133.1 mg l⁻¹ (1.3 × 10⁻⁴ and 1.04 × 10⁻³ mol l⁻¹). The procedure was applied to the determination of dithionite in commercial formulations used in the household. In a 0.5 g sample of decolorant, dithionite was found to be present at concentrations between 25 and 35% (w/w), which can be determined without interference of its decomposition products. The results are shown to be in good agreement with those of polarographic determinations. Received April 26, 2001. Revision August 2, 2001.     

Construction and Evaluation of a Promazinium Cation-Selective Electrode

 The construction of a plasticised PVC matrix-type promazinium cation-selective membrane electrode and its use in the potentiometric determination of promazine hydrochloride in pharmaceutical preparations are described. It is based on the use of the ion-associate species, formed by promazinium cation and tetraphenylborate (TPB) counter ion. The basic electrode performance characteristics are evaluated according to IUPAC recommendations. It exhibited a linear response for 1 × 10⁻²−1 × 10⁻⁵ M of promazine hydrochloride solutions with a cationic Nernstian slope over the pH range 2–6. Common organic and inorganic cations showed negligible interference. Direct potentiometric determination of 1 × 10⁻²−1 × 10⁻⁵ M aqueous promazine hydrochloride using this membrane electrode system showed an average recovery of 99.5% with a mean standard deviation of 1.5%. This electrode was successfully used for monitoring the titration of promazine hydrochloride with sodium tetraphenyl borate and for determining promazine hydrochloride in ampoules. Received June 15, 2001 Revision November 6, 2001     

Release of cationic drugs from loaded clay minerals

The adsorption of promethazine chloride [10-(2-dimethylammonium propyl) fenothiazine chloride] and buformin hydrochloride (1-butylbiguanidine chloride) on montmorillonite was studied in previous work. The present article focuses on the desorption of these molecules from their organocomplexes in a medium of artificial intestinal juice (pH 7.0 ± 0.1) at the temperature of the human body (37 ± 0.5 °C). The desorption was investigated by kinetic studies, basal spacing measurements and Fourier transform IR studies. Important quantitative differences were observed: buformin, which adsorbed in a monolayer coverage, exhibited a very high desorption rate, whereas promethazine formed a pseudotrilayer arrangement and showed a lower dissolution rate. Received: 20 January 2001 Accepted: 8 March 2001     

Local-orbital-based correlated ab initio band structure calculations in insulating solids: LiF

 A local-orbital-based ab initio approach to calculate correlation effects on quasi-particle energies in insulating solids is presented. The use of localized Wannier-type Hartree–Fock orbitals allows correlation effects to be efficiently assessed. First a Green's function approach based on exact diagonalization is introduced and this is combined with an incremental scheme, while subsequently different levels of perturbative approximations are derived from the general procedure. With these methods the band structure of LiF is calculated and good agreement with experiment is found. By comparing the different approximations proposed, including the exact diagonalization procedure, their relative quality is established. Received: 25 June 2001 / Accepted: 31 August 2001 / Published online: 19 December 2001     

A new look at the reduced-gradient-following path

 The mathematical structure of the reduced-gradient-following (RGF) path introduced by Quapp et al. (1988 J. Comput. Chem. 19:1087) is reviewed and analyzed. We report two new algorithms to evaluate the RGF path. The RGF path is also compared mathematically and computationally with the gradient extremals path. An example of the evaluation of the RGF path is also reported. Received: 21 May 2001 / Accepted: 27 September 2001 / Published online: 9 January 2002     

The aggregation of sodium dehydrocholate in water

 We used a battery of different methods to study the association in aqueous sodium dehydrocholate (NaDHC) solutions. This salt associates by a stepwise mechanism. Below (9.6 ± 4.2) × 10⁻⁴ mol dm⁻³ there is a molecular solution with some strongly insoluble dehydrocholic acid produced by hydrolysis. Between (9.6 ± 4.2) × 10⁻⁴ and (5.2 ± 2.2) × 10⁻³ mol dm⁻³, an aggregate similar to acid soap (NaDHC.HDHC) appears and its amount and the aggregate's size increase with concentration. At =(2.20 ± 0.85) × 10⁻² mol dm⁻³ the aggregates formed have properties usually associated with true micelles, such as solubilisation of water-insoluble dyes. These aggregates increase in size with concentration and change their shape at 8 × 10⁻² mol dm⁻³, giving nonsymmetrical aggregates. The changes in the solution physicochemical properties at these concentrations may be misinterpreted and this explains the different values of the critical micelle concentration reported in the literature for substances with similar structure, such as bile salts. Received: 14 May 2001 Accepted: 10 August 2001     

Concerning the Absorption and Photochemical Properties of an ω-4-Dimethylaminobenzal Hypericin Derivative

Summary.  A hypericin derivative containing ω,ω ′-4-dimethylaminobenzal residues was shown to undergo an intramolecular [2 + 2] cycloaddition upon irradiation leading to a cyclobutane derivative whose main absorption band is hardly shifted as compared to hypericin. The corresponding ω-substituted derivative displayed a 34 nm bathochromic shift and a strongly reduced fluorescence quantum yield rendering it a nice candidate for a photodynamic therapy agent. Unfortunately, however, it produced virtually no photosensitized active oxygen species, making it thus unsuited for this purpose. Received July 11, 2001. Accepted July 18, 2001     

Comparison of solvent reaction field representations

 Alternative ways are examined for representing a reaction field to treat the important effects of long-range electrostatic interaction with a solvent in electronic structure calculations on the properties of a solute. Several extant boundary element methods for approximate representation of the solvent reaction field in terms of surface charge distributions are considered, and analogous new methods for approximate representation in terms of surface dipole distributions are introduced. Illustrative computational results are presented on representative small neutral and ionic solutes to evaluate the relative accuracy of various methods. Received: 2 July 2001 / Accepted: 10 September 2001 / Published online: 19 December 2001     

Molecular Schrödinger–Riccati calculations. Test for the hydrogen-ion molecule

 The hydrogen-ion molecule has been used as a test system for the application of the Schr?dinger–Riccati formulation to molecular calculations. Some of the points discussed are the characteristics (quasiconstancy of the local energies, size, number of points) of the sampling region to be chosen, the dependence on the starting function, the precision of the calculations, and the excellent behaviour of the predicted function (by comparison to an accurate function). Received: 1 May 2001 / Accepted: 25 July 2001 / Published online: 11 October 2001     

Preparation and Crystal Structure of K2Ag12Te7

Summary.  Single crystals of K₂Ag₁₂Te₇ (a = 11.460(2), c = 4.660(1) ?; V = 530.01 ?³; space group: P6₃/m; Z = 1) were synthesized under hydrothermal conditions at 250°C in concentrated aqueous KOH solution from elementary silver and tellurium. The crystal structure is characterized by trigonal prismatic KTe₆ polyhedra, connected via two common faces to KTe₃ rods parallel to [001]. These rods are combined by two crystallographically independent Ag atoms, each coordinated to four Te and three Ag atoms (Ag–Te and Ag–Ag < 3.1 ?) to a framework of the formula (K₂Ag₁₂Te₆)^2 + and with channels parallel to the sixfold axis. These channels are statistically occupied by one further Te atom per unit cell, distributed over two independent positions. Received May 17, 2001. Accepted (revised) July 3, 2001