Mössbauer study of spin-glass Fe x Zn1−x F2 system

⁵⁷Fe Mössbauer effect measurements in the diluted Ising antiferromagnet Fe _x Zn_1?x F₂ withx=0.25 andx=0.57 at temperatures between 4.2 and 55 K, are reported. DC suceptibility measurements show a spin-glass (SG) phase at low temperatures forx≤0.31. Our Mössbauer spectra show a phase transition to a SG state with antiferromagnetic order (AFSG) forx=0.25 and only antiferromagnetic order forx=0.57.     

Pulsed reactive crossed beam laser ablation of La0.6Ca0.4CoO3 using O: Where does the oxygen come from?

The composition of thin perovskite films, especially the oxygen content, is a crucial parameter which influences many physical properties, such as conductivity and catalytic activity. Films produced by pulsed laser deposition are normally annealed in an oxygen atmosphere after deposition to achieve a desired oxygen content. In pulsed reactive crossed beam laser ablation, no annealing step is necessary, but a fundamental question regarding this deposition technique is still open: where does the oxygen in the films come from?There are three possibilities, i.e. from the target, from the gas background, or from the gas pulse. To answer this question two experiments were performed: ¹⁸O₂ was used during the deposition process as background gas with ¹⁶O anions in the target and ¹⁶O₂ gas pulse, and a ¹⁸O₂ gas pulse with ¹⁶O from the target and background. These experiments revealed that the quantification of the oxygen origin is only possible, when no oxygen exchange occurs at the deposition temperature. The films are characterized after deposition by elastic recoil detection analysis (ERDA) to determine the ¹⁶O/¹⁸O ratio. Experiments with different oxidizing species in the gas pulse (N₂O and O₂) confirm that the oxidizing potential (N₂O > O₂) as well as the number of molecules are important.     

Cyanoethylation of azafluorenes and syntheses of alcohols containing an azafluorene fragment

Isomeric (with respect to the position of the nitrogen atom) azafluorenes were cyanoethylated. The resulting 9,9-bis(-cyanoethyl) derivatives were converted to the corresponding dibasic acids and their diesters. The latter were subjected to the Dieckmann reaction to obtain spiro compounds with azafluorene and cyclohexene fragments. The analogous spirans with 1,3-dioxalane and 1,3-dioxane rings were obtained from 3-methyl-2-azafluorenone.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1668–1672, December, 1982.     

Application of amperometric sol-gel biosensor to flow injection determination of glucose

A glucose biosensor with enzyme immobilised by sol–gel technology was constructed and evaluated. The glucose biosensor reported is based on encapsulated GOX within a sol–gel glass, prepared with 3-aminopropyltriethoxy silane, 2-(3,4-epoxycyclohexyl)-ethyltrimetoxy silane and HCl. A flow system incorporating the amperometric biosensor constructed was developed for the determination of glucose in the 1×10⁻⁴–5×10⁻³ mol l⁻¹ range with a precision of 1.5%. The results obtained for the analysis of electrolytic solution for iv administration and human serum samples showed good agreement between the proposed method and the reference procedure, with relative error <5%.     

Flow injection analysis of fluoride in electroplating baths with potentiometric detection

A high dispersion FIA system with a fluoride selective and a double junction reference electrode in cascade arrangement was developed for the determination of the fluoride content in chromium electroplating baths. The analyses of seven synthetic baths prepared in the laboratory and two samples provided by the industry gave results with a mean recovery value of 100.5%, and a mean variation coefficient of 1.6%. These data were better than those obtained by the EDTA complexometric titration, the reference technique, with a mean recovery of 94.0% and a mean variation coefficient of 7.5%. The sampling rate for the FIA manifold was 20 samples per hour. Received: 27 November 1997 / Revised: 24 February 1998 / Accepted: 1 March 1998     

Deprotection by electrolysis: Part I. The application of homogeneous redox catalysis to the study of the reduction of tosyl esters and amides

The mechanism of the cathodic cleavage of tosylate protecting groups from alcohols, amines and phenols in dimethylformamide has been probed using the technique of homogeneous redox catalysis. Some nine tosyl esters and six tosyl amides have been investigated and it is confirmed that these deprotection reactions occur by cleavage of the anion radicals. The formal electrode potentials for the couples, neutral molecule/anion radical, are reported and it is shown that the rate constants for the cleavage of the anion radicals lie in the range 10⁴ s^?1 to >10⁸ s^?1. Indeed for aromatic amines and phenols, the homogeneous charge transfer between the catalyst and the substrate becomes the rate determining step.     

Latex Fractionation by Sedimentation and Colloidal Crystallization: The Case of Poly(styrene-co-acrylamide)

Poly(styrene-co-acrylamide) (PS-AAM) latex was prepared, fractionated by sedimentation under gravity, and characterized by PCS, infrared spectra, secondary and backscattered electron imaging in the scanning electron microscope, and electron spectroscopy imaging in an analytical transmission electron microscope. Three latex fractions were obtained. The lower fraction was opalescent and its particles were the more uniform, concerning size, chemical composition, and topochemical features. This lower fraction was still further fractionated by zonal centrifugation in a density gradient, yielding two fractions with similar macrocrystal-forming abilities but different sizes and chemical compositions. These results confirm those previously obtained for the PS-HEMA latex. Copyright 2000 Academic Press.