Synthesis and stereochemical studies of 6-substituted 1H,3H,6H,7aH-3,3-dimethylimidazo-[1,5-c]thiazol-5-one-7-thiones

The reaction of (4S)-5,5-dimethyl-4-thiazolidine-carboxylic acid 1 with alkyl and aryl isothiocyanates 2 gave bicyclic thiohydantoins 3 . The (2R,4S)- and (2S,4S)-mixtures of 2-substituted 5,5-dimethyl-4-thiazolidine-carboxylic acids 4 and 8 containing two centers of chirality in the analogous reaction afforded thiohydantoins 7 and 10 , respectively, with (1R)-configuration. In some cases we managed to isolate the thioureido acid intermediates 6 and 9 or their triethylamine salts which afforded the corresponding bicycles 7 and 10 under thermal cyclization or acidification. The stereochemistry has been elucidated by high resolution ram studies, optical rotation measurements and X-ray crystallography.     

Preparation and investigation of structural and photocatalytic properties of phosphate modified titanium dioxide

A series of high surface area titanium dioxide samples (P-TiO₂) with varying phosphate content have been prepared by the sol–gel technique. The structural characterization of the samples included X-ray powder diffraction, diffuse reflectance infrared and UV–vis spectroscopy (DRIFT and UV–vis–DR), and nitrogen adsorption measurements. The structural properties of the P-TiO₂ samples significantly changed with the phosphate content and calcination temperature. According to XRD data the presence of phosphate shifts the anatase rutile phase transition to higher temperatures, revealing that phosphate improves the thermal stability of the samples. The specific surface area and the semiconductor band gap energy increase with the phosphate content.

The photocatalytic activity of TiO₂ and P-TiO₂ was studied by phenol degradation in liquid phase. A small amount of phosphate of the catalysts increases the photocatalytic activity, but further increase of the P/Ti molar ratio (above 0.01), leads to a considerable loss in activity. The optimal calcination temperature of P-TiO₂ was 300–500 °C. The phenol conversion rate is highest with catalysts calcined at 700 °C, but phenol does not degrade to carbon dioxide.     

An efficient reagent for the phosphorylation of deoxyribonucleosides, DNA oligonucleotides, and their thermolytic analogues

[reaction: see text] The phosphoramidite 11 was prepared in three steps from methyl 2-mercaptoacetate and demonstrated efficiency in the synthesis of conventional 5'-/3'-phosphate/thiophosphate monoester derivatives of 2'-deoxyribonucleosides and DNA oligonucleotides. Moreover, the use of 11 has enabled the preparation of the dinucleoside phosphorothioate analogue 26 in high yields (>95%) with minimal cleavage (<2%) of the thermolytic thiophosphate protecting group.     

Analytical control of silica glass production. Voltammetric determination of titanium and iron in raw materials and silica glass samples

Adsorptive stripping voltammetric (AdSV) methods are presented for the determination of titanium and iron in quartz and silica glass samples obtained after pressure decomposition. Mandelic acid and catechol were used as complexing agents for titanium and iron, respectively. The method for titanium determination is based on the catalytic effect of chlorate ions. An insoluble residue remaining after decomposition of quartz and silica glass samples in HF+H2SO4 mixture was checked by energy-dispersive X-ray analyses. ET-AAS was applied as a reference method to AdSV measurements.     

Adsorption and microcalorimetric investigations ofn-butylamine intercalation in α- and γ-zirconium phosphates

The intercalation process ofn-butylamine was investigated. The adsorption ofn-butylamine in interlamellar space had stepwise character in case of both crystalline forms of zirconium phosphate. The intercalatedn-butylamine existed at low concentration as bilayered complex. The reaction heat was determined by a microcalorimetric method. It was found that about 90% of it refers to the neutralization ofn-butylamine and only about 10% is related with surface adsorption (ion exchange). The steps of adsorption are 6.0 J/g and 1.0 J/g reaction heat values, respectively. The enthalpy balance of total process in dilute solution system (c ₀=3.0 vol%) is 14.67 kJ/mol. The calculated value for ion adsorption (exchange) was 1.37 kJ/mol.     

Formation of (E) 1-alkoxy-1,3-butadienes from corresponding propargyl ethers; vicarious nucleophilic substitution in alkoxyallenes

Propargyl ethers treated with dimsyl anion in DMSO at 80-100°C undergo terminal methylenation to afford corresponding (E) 1-alkoxy-1,3-butadienes. The reaction proceeds via an alkoxy-allene.     

Mechanistic Study on the Oxidation of Promazine and Chlorpromazine by Hexaimidazolcobalt(III) in Acidic Aqueous Media

The kinetics of the oxidation of promazine and chlorpromazine by hexaimidazolcobalt(III) were studied in the presence of a large excess of cobalt(III) and H⁺ ions using u.v.–vis. spectroscopy ([Co^III] = (1–6) × 10⁻³ m, [ptz] = (2.5–10) × 10⁻⁵ m, [H⁺] = 0.05–0.8 m, I = 1.0 m (H⁺, Na⁺, Cl⁻), T = 333–353 K, l = 1 cm). In each case, the reversible reaction leads to formation of cobalt(II) species and a stable cationic radical. A linear dependence of the pseudo-first-order rate constant (k_obs) on [Co^III] with a non-zero intercept was established for both phenothiazine derivatives. A marked difference in the observed reaction rate for promazine and chlorpromazine is associated with the difference in its ability to undergo oxidation and is consistent with a trend in the redox potential changes for these reductants. The activation parameters for reactions studied were determined. Mechanistic consequences of all the results are discussed.     

Simple Method for Simultaneous Determination of Selenium and Arsenic in Human Hair by Means of Atomic Fluorescence Spectrometry with Hydride Generation Technique

This study describes a simple, rapid and reliable method for simultaneous determination of selenium and arsenic in human hair by means of atomic fluorescence spectrometry combined with a hydride generation technique (HG-AFS). The procedure developed encompasses microwave digestion of a sample in the nitric acid environment only. The interferences caused by nitrous oxides are eliminated by removing a gas from above the digested solution with a stream of argon. The sample is then chemically treated in a flow-through hydride generation system and exposed to measurements in a double-channel atomic fluorescence spectrometer. The method permits determining both analytes in the linear range of 0.5–100µgL^–1 with a detection limit equal to 0.2µgL^–1, as well as with very good repeatability not exceeding 1% for Se and 2% for As. No mutual interferences from either of the analytes in the concentrations ranges matching the hair composition were found. The method was verified in terms of accuracy with the use of a reference material and then applied to the analysis of the natural samples of human hair.     

Mutual Solubilities of Water and Alkanes

Summary.  The evaluation of mutual solubility data for systems water with n-alkanes, isoalkanes, and cycloalkanes along the three phase line is reported and a formula for the prediction of solubility of alkanes in water is developed. Then a cubic equation of state with an added term, which accounts for hydrogen bonding is used for correlation of liquid–liquid equilibrium data and for prediction of solubility of water in hydrocarbons using alkane in water solubility data. Comparison of the predicted and experimental solubilities is performed using all accessible experimental data. With this approach it is possible to predict the solubilities of water in alkanes with good accuracy over the temperature range up to about 20 K below critical temperature. Solubility of alkanes in water can also be calculated using experimental data for solubility of water in alkanes but results of these calculations are more sensitive to experimental errors of the data. Corresponding author: E-mail: macz@ichf.edu.pl Received August 5, 2002; accepted (revised) September 13, 2002 Published online March 13, 2003 RID="a" ID="a" Dedicated to Prof. Dr. H. Gamsj?ger on the occasion of his 70^th birthday anniversary     

Magnon spectrum and curie temperature of doped ferromagnetic semiconductors

The influence of a partially filled conduction band on the magnetic properties of ferromagnetic semiconductors is studied within the framework of thes-f model. Allowing for magnon scattering to arbitrary order in the form of virtual electron- holecreation the magnon spectral density is derived, from which one gets magnon energies which are substantially renormalized by the presence of conduction electrons. In particular it is shown how the quasiparticle structure of the electronic excitation energies [4, 5] leads to scattering corrections in the magnon spectrum. These corrections are always negative and reduce the positive mean field part, which is proportional to the electron densityn. The calculated magnon spectrum is then used to determine the strikingn-dependence of the Curie-temperatureT _c of Gd-doped EuO and EuS.