ZnO:Mn as a member of II-VI:Mn family

ZnO:Mn thin films are grown by the metal organic chemical vapor deposition technique. Mn (x) varies in the 0<x<0.44 range. Vegard’s law has been verified for the lattice parameters. Electron paramagnetic resonance (EPR) measurements prove the substitutional incorporation of Mn²⁺ on zinc sites. The behavior of the EPR line width regarding temperature is discussed. All ZnO:Mn layers show antiferromagnetic interaction and a J₁/k_B=-15 K effective exchange constant. The optical band gap of ZnO:Mn increases with the manganese concentration. Raman spectroscopy reveals a Mn-related scattering band. PACS 71.55.Gs; 75.50.Pp; 61.10.Nz; 76.30.Fc; 75.30.Et; 78.40.-q     

Sensitive method of detection, quantitation and purification of peptides using pre-column derivatization with phenyl isothiocyanate

A sensitive method for the detection, quantitation and purification of peptides is described. The method is based on pre-column derivatization of peptides with phenyl isothiocyanate to form phenylthiocarbamoyl derivatives (PTC peptides). The derivatized peptides are analysed by reversed-phase high-performance liquid chromatography on a Zorbax ODS column (5 micron) and detected at 269 nm with a sensitivity limit of 1-5 pmol. The technique was utilized for the separation of a mixture of closely related synthetic peptides. The eluted PTC peptides were collected with an average recovery yield of 75% as determined by amino acid analysis. This method of separation of PTC peptides was also combined with the determination of the complete structure of recovered PTC-dynorphin A-(1-13) using the solid-phase sequenator (Sequemat). The advantages of the derivatization method are the rapidity and completeness of the reaction, the stability of the product, the sensitivity and specificity of the detection of derivatized peptides and the compatibility of the technique with subsequent analytical procedures. A particular application of this method was exemplified by the dosage of enkephalins secreted from perfused bovine adrenal glands.     

Direct determination of calcium,copper, iron,magnesium, manganese and zinc in amniotic fluid samples using inductively coupled plasma-atomic emission spectrometry

An inductively coupled plasma-atomic emission spectrometric method is reported for the determination of calcium, copper, iron, manganese, magnesium and zinc. Samples are introduced directly when a sheath gas device is used. An external calibration procedure is used. The standards are prepared in a matrix composed of 0.5% (w/v) albumin and 0.76% (w/v) sodium chloride. The procedure was evaluated with a standard reference material (NBS SRM 909 Human Serum); all the values obtained are in agreement with the certified values. Results obtained for the determination of zinc, calcium, magnesium, copper, iron and manganese in amniotic fluid samples are reported.     

Regioselective 1–4 addition of acyl and equivalents to α-enones

2-lithio-1,3-dithianes, bis(phenylthio)alkyllithiums and bis(methylseleno)alkyllithiums add 1–4 to α-enones if HMPT is present in the medium prior to the addition of enones. Most of the reactions occur under kinetic control.     

Stéréosélectivité et régiosélectivité de la réduction des cyclopropènes-2,3 et méthylène-2 cyclopropanes fonctionalisés en position 1

Reduction of 2 cyclopropenyl esters and alcohols with lithium aluminium hydride is selective; at low temperatures (0°) the double bond is not reduced, but at higher temperatures (65°) the reduction is complete and only the cyclopropylmethanol is obtained. The reduction of the double bond is regioselective (the most stable carbanion is formed) and stereospecific (the hydride attack on the double bond occurs cis to the functional group). This stereospecificity can be explained through the initial formation of an alkoxylaluminium hydride followed by an intramolecular reduction of the double bond. Similar results have been obtained in the reduction of functionalised methylenecyclopropanes.     

Novel one step synthesis of epoxides from β-hydroxy-selenides and sulfides

Epoxides are stereoselectively prepared in one step from β-hydroxy selenides and β-hydroxy sulfides in a process which involves dichlorocarbene     

Synthesis and electronic characterization of bipyridine dithiolate rhodium(III) complexes

Five new mixed diimine 1,1'-dithiolate or dithiocarbamate ligand complexes of the form [Rh(bpy)2(SS)][PF6]n, where bpy = 2,2'-bipyridine and SS = various substituted dialkyldithiocarbamates or 1,1'-dithiolates, were synthesized from cis-[Rh(bpy)2(OTf)2][OTf]. The triflate ligands are easily displaced by other ligands and allow these syntheses to proceed in high yields (80-90% overall) under relatively mild reaction conditions and to give high purity products. Electrochemistry shows irreversible two-electron reduction of Rh(III) to Rh(I) and a concomitant loss of one bipyridine ligand; this is followed by reversible one-electron reduction of the remaining 2,2'-bipyridine ligand. The electronic characterizations of these complexes are consistent with significant delocalization of the sulfur electron density onto the empty metal d orbitals. The 1,1'-dithiolate ligands induce larger red shifts in the absorption and emission spectra than the dithiocarbamates as the 1,1'-dithiolates have a more extensive conjugation system.     

Molecular weight determination of vinylidene chloride copolymers by gel-permeation chromatography and viscometry

This is the first report on the characterization of several pairs of random copolymers of vinylidene chloride by gel-permeation chromatography in conjunction with viscometry. Such copolymers have not previously Received much attention, so we first determined the individual viscosity–molecular weight relationship. The K–a values were compared with known values for the parent homopolymers. We then derived calibration curves (different for each composition) and the calculation of the average molecular weight. These results are compared to those obtained by direct methods, without fractionation, and to kinetic observations. This method avoids misinterpretation of viscosity data and elution volume. Chromatograms may indicate heterogeneity of the compounds as related to polymerization conditions.