Gas-stirred solvent extraction with propylene carbonate for separation and direct polarographic determination of thallium (III)

Gas-stirred propylene carbonate (PC) extraction can be performed by bubbling nitrogen without loss of volume. This extraction technique has proved to be highly useful for the separation and subsequent direct polarographic estimation of Tl(III) in the recovered PC phase. Tl(III) can be determined by differential-pulse polarography over the concentration range of 0.4 10 g ml^–1 without any interferences due to most metal ions such as Pb(II), Bi(III), Cu(II), Sb(III) and As(III). This proposed technique would be possible to use as a simple extraction step prior to the final estimation by instrumental method of analysis such as atomic absorption spectrometry or spectrophtometry.     

Kinetic studies of ion-exchange of cobalt(II) and nickel(II) on a resin loaded with 5-sulpho-8-quinolinol

The mechanism of ion-exchange of cobalt(II) and nickel(II) on a resin loaded with 5-sulpho-8-quinolinol has been studied, and the chelate-forming reaction in the resin matrix shown to be rate-determining. The observed rate seems to be related to the rate of water-exchange with the metal ion in the aqueous phase, suggesting that complexation in the resin matrix may proceed according to the Eigen mechanism.     

Preparation of chiral stationary phase via activated carbamate intermediate for liquid chromatographic optical resolution

Summary Chiral stationary phases (CSPs) for liquid chromatography were prepared by the way of an activated carbamate intermediate. The amino group of aminopropylsilyl silica gel was first activated by carbamylation with disuccinimido carbonate (DSC). The obtained activated carbamate silica gel (ACsil) proved useful as an intermediate for the preparation of urea-type CSPs. The reaction of ACsil with (S)- of (R)-1-(α-naphthyl)-ethylamine gave naphthylethylurea type CSPs. These CSPs were also obtained directly from aminopropylsilyl silica gel by its reaction with optically active (S)- or (R)-succinimido 1-(α-naphthyl)ethyl carbamate (SINEC). Several phenylthiohydantoin amino acid enantiomers and p-bromophenylcarbamyl amino acid enantiomers were resolved on the CSPs by elution with aqueous mobile phase.     

Enhancement of electronic excitation energy transfer in the colloidal crystals of colloidal silica suspensions doped with fluorescent dyes

The efficiency of electronic excitation energy transfer from photo-excited rhodamine 110 (Rh110, energy donor) to rhodamine B (RhB, energy acceptor) in an exhaustively deionized colloidal silica suspension has been studied. This colloidal suspension shows Bragg reflection due to the formation of colloidal crystals and the Bragg-peak wavelength is controllable by the volume fraction of the silica spheres. When the Bragg-peak wavelength matches with the fluorescence band of Rh110, a depletion was observed in the Rh110 fluorescence spectrum. This means the fluorescence of Rh110 is partially trapped due to the Bragg reflection inside the crystal lattice. In the coexistence of RhB, the enhancement of RhB fluorescence intensity was observed. These facts clearly indicate the trapped photon energy of Rh110 is efficiently transferred to RhB within the colloidal crystals. The quantitative measurements showed that the enhancement of the transfer efficiency is 20% (or slightly more) in the present experimental conditions.     

Electrode reaction of zinc ions at a dropping mercury electrode in ammonium sulphate solutions

The electrode reaction of Zn(II) at a DME in aqueous solutions of (NH₄)₂SO₄ has been studied by d.c. and square-wave polarography at 25.0±0.1°C. The electrochemical kinetic parameters for the reaction are determined. The appearance of the second wave in the square-wave polarogram has been attributed to the low values of the rate parameter and the transfer coefficient.     

Synthesis and application of chiral bisphosphines through lithiation-conjugate addition tandem cyclization of chiral alpha,beta,psi,omega-unsaturated bisphosphine oxide

Upon treatment with lithium diisopropylamide achiral and chiral alpha,beta,psi,omega-unsaturated bisphosphine oxides underwent lithiation-conjugate addition tandem cyclization to afford the corresponding endo-alpha,beta-unsaturated cyclic bisphosphine oxides; sequential stereoselective reduction of the cyclized bisphosphine oxide gave the corresponding trans- and cis-bisphosphines that were successfully applicable in a catalytic asymmetric hydrogenation as chiral bisphosphine ligands.     

Mass spectral study on thiazolo[3,2-a]benzimidazoles. Studies on heterocyclic compounds. IV

Condensation of α-halocarbonyl compounds and 2-mercaptobenzimidazole gives thiazolo-[3,2-a]benzimidazoles. This condensation occurred at the mercapto group of the benzimidazole followed by cyclization to form the thiazole ring. This was confirmed by the examination of the mass spectra of 2- and 3-methylthiazolo[3,2-a]benzimidazoles, 2- and 3-phenylthiazolo[3,2-a]-benzimidazoles, and their derivatives.     

Formation of non-racemic E- and Z-olefins based on discrimination of enantiotopic carbonyl groups in α-diketones by a chiral phosphonate reagent

A chiral HWE reagent reacted with an alternative carbonyl group of meso-α-diketones of bicyclo[2.2.1] system to give non-racemic (Z)- and (E)-olefins, respectively.     

Spectrofluorimetric assay for acyl CoA-cholesterol acyltransferase

A sensitive assay for acyl CoA-cholesterol acyltransferase (EC 2.3.1.26) in rat liver microsomal and mitochondrial preparations is described. The lowered cholesterol concentration in the enzyme reaction with oleoyl CoA is determined spectrofluorimetrically by using the cholesterol oxidase/peroxidase/p-hydroxyphenylpropionic acid system. The assay requires as little as 20 μg of protein in the enzyme preparation.