1H MRS detection of glycine residue of reduced glutathione in vivo

Glutathione (GSH) is a powerful antioxidant found inside different kinds of cells, including those of the central nervous system. Detection of GSH in the human brain using ¹H MR spectroscopy is hindered by low concentration and spectral overlap with other metabolites. Previous MRS methods focused mainly on the detection of the cysteine residue (GSH-Cys) via editing schemes. This study focuses on the detection of the glycine residue (GSH-Gly), which is overlapped by glutamate and glutamine (Glx) under physiological pH and temperature. The first goal of the study was to obtain the spectral parameters for characterization of the GSH-Gly signal under physiological conditions. The second goal was to investigate a new method of separating GSH-Gly from Glx in vivo. The characterization of the signal was carried out by utilization of numerical simulations as well as experiments over a wide range of magnetic fields (4.0–14 T). The proposed separation scheme utilizes J-difference editing to quantify the Glx contribution to separate it from the GSH-Gly signal. The presented method retains 100% of the GSH-Gly signal. The overall increase in signal to noise ratio of the targeted resonance is calculated to yield a significant SNR improvement compared to previously used methods that target GSH-Cys residue. This allows shorter acquisition times for in vivo human clinical studies.     

Pyroelectric effects in magnetoelectric multilayer composites

Magnetoelectric and pyroelectric properties have been investigated in heterostructures of nickel zinc ferrite (NZFO)-lead zirconate titanate (PZT) and lanthanum calcium manganite (LCMO)-PZT. The magnetoelectric (ME) coupling, mediated by mechanical strain, is found to be two orders of magnitude stronger in NZFO-PZT than in LCMO-PZT. The pyroelectric effect is investigated by measuring the current through the sample as the temperature is varied at 0.1 K/s. For NZFO-PZT the pyroelectric coefficient is in the range 0.2-15 nC/cm² K, depending on the temperature. A much weaker current is observed in LCMO-PZT. A reversal in the current direction is detected when the thermal cycle is switched from heating to cooling. The pyroelectric coefficient is found to scale with the strength of ME interactions. A clear correlation between pyroelectric current and ME interactions is evident from the results.     

Ionic Liquid–Liquid Extraction and Supported Liquid Membrane Analysis of Lipophilic Wood Extractives from Dissolving-Grade Pulp

In this study, the extraction of lipophilic wood extractives from dissolving pulp samples using ionic liquid–liquid extraction and a two phase hollow fibre supported liquid membrane was investigated. Ionic liquids are capable of dissolving a range of organic and polymeric compounds and are biodegradable, with a negligible vapour pressure. Pulp samples were dissolved in a suitable amount of molten 1-butyl-3-methylimidazolium chloride to give 5 % cellulose solution. Pure cellulose was regenerated by adding water and filtered off. The ionic liquid-aqueous filtrate was first extracted for lipophilic extractives using liquid–liquid extraction. Then, a two phase hollow fibre supported liquid membrane extraction of lipophilic extractives was performed to extract the derivatized compounds prior to analysis by gas chromatography mass spectrometry. The operational parameters of this sample preparation approach were optimised using sterols and fatty acid methyl esters. The variation of enrichment factors and extraction efficiency with respect to liquid membrane, extraction time, stirring speed and sample pH were observed and used to get the optimal parameters. The approach was used in the analysis of oxygen bleached dissolving pulp samples in which main compounds identified were fatty acids, sterols, fatty alcohols, steroid hydrocarbons and ketones. These compounds were similar to those obtained using molecular solvent extraction method, which indicated the absence of chemical reaction between extractives and ionic liquid used.

     

Reduction of silicon halides and alkoxides with diisobutylaluminum hydride. Stereochemistry-rate law correlations for the SNiSi and SN2Si mechanisms

Stereochemistry-rate law correlations are given for the reduction of R₃Si*X compounds with i-Bu₂ AlH in either and n-hexane.     

57Fe NMR study of a spatially modulated magnetic structure in BiFeO3

The ⁵⁷ Fe spin echo spectra were studied in local magnetic fields of a BiFeO₃ ferroelectric antiferromagnet over the temperature range 77–304 K. The line shape analysis confirmed the presence of a spatially modulated, incommensurate cycloidal spin structure in BiFeO₃ and allowed the actual spin distribution to be reproduced throughout the cycloid length. The distribution was found to be essentially anharmonic. The modulated structure is stable over the whole temperature range studied. The cycloid wave becomes more harmonic with temperature elevation.