Thermal behaviour of anhydrous, dihydrate and (2/1) ethanol forms of 1-O-α- -glucopyranosyl- -mannitol

The melting points of anhydrous 1-O-α- -glucopyranosyl- -mannitol, 1-O-α- -glucopyranosyl- -mannitol dihydrate and a new compound, 1-O-α- -glucopyranosyl- -mannitol-ethanol (2/1) were determined using differential scanning calorimetry. The melting onset values were 169.2 (3), 104.3 (18) and 158.7 (9), respectively, and the melting peak values were 171.4 (5), 107.9 (15) and 160.1 (6), respectively. 1-O-α- -glucopyranosyl- -mannitol dihydrate and 1-O-α- -glucopyranosyl- -mannitol-ethanol (2/1) decompose to anhydrous form when heated at slow heating rates.According to TG-FTIR measurements, 1-O-α- -glucopyranosyl- -mannitol-ethanol (2/1) lost its ethanol in the 110–190°C range, and 1-O-α- -glucopyranosyl- -mannitol dihydrate lost its crystal water in the 60–210°C range. After removal of ethanol and crystal water, both decomposed in air totally as carbohydrates usually do, forming lower hydrocarbons with OH-groups, CO₂ and H₂O.     

Evolved Gas Analysis of Some Solid Fuels by TG-FTIR

FTIR spectrometry combined with TG provides information regarding mass changes in a sample and permits qualitative identification of the gases evolved during thermal degradation. Various fuels were studied: coal, peat, wood chips, bark, reed canary grass and municipal solid waste. The gases evolved in a TG analyser were transferred to the FTIR via a heated teflon line. The spectra and thermoanalytical curves indicated that the major gases evolved were carbon dioxide and water, while there were many minor gases, e.g. carbon monoxide, methane, ethane, methanol, ethanol, formic acid, acetic acid and formaldehyde. Separate evolved gas spectra also revealed the release of ammonia from biomasses and peat. Sulphur dioxide and nitric oxide were found in some cases. The evolution of the minor gases and water parallelled the first step in the TG curve. Solid fuels dried at 100°C mainly lost water and a little ammonia. This revised version was published online in August 2006 with corrections to the Cover Date.     

Formation of the main degradation compounds from arabinose,xylose, mannose and arabinitol during pyrolysis

The thermochemical behaviour of sugars (D- and DL-arabinose, D- and DL-xylose and D-mannose) and sugar alcohol (D- and DL-arabinitol) was investigated by TG and pyrolysis-gas chromatography with mass-selective detection (Py-GC/MSD). The temperature of pyrolysis was 500 and 550°C. The TG-curves were measured both in air and nitrogen atmospheres, from 25 to 700°C with the heating rate of 2°C min^-1. In each case, the main pyrolysis products were classified into the following compound groups: (i) furanes, (ii) pyranes, (iii) cyclopentanes, (iv) cyclohexanes, (v) anhydroglucopyranoses, (vi) dianhydroglucopyranoses and (vii) saturated fatty acids. For example, the main peaks of the chromatograms of pentoses (arabinose, xylose), hexose (mannose) and sugar alcohols (arabinitols) were different. The greatest peak of pentoses in gas-chromatogram was 2-furancarboxaldehyde and that of hexose was (2H)-furan-3-one. The greatest peak of arabinitols at pyrolysis temperature of 500°C was furan methanol and at 550°C a-angeligalactone. 5-hydroxymethyl-2-furan carboxaldehyde was found only in the pyrolysis of D-mannose (hexose). The former study showed that it was not found in pyrolysis of pentoses. The amount of CO₂ and H₂O was not determined. This revised version was published online in July 2006 with corrections to the Cover Date.     

Design,synthesis, and evaluation of gluten peptide analogs as selective inhibitors of human tissue transglutaminase

Recent studies have implicated a crucial role for tissue transglutaminase (TG2) in the pathogenesis of Celiac Sprue, a disorder of the small intestine triggered in genetically susceptible individuals by dietary exposure to gluten. Proteolytically stable peptide inhibitors of human TG2 were designed containing acivicin or alternatively 6-diazo-5-oxo-norleucine (DON) as warheads. In biochemical and cell-based assays, the best of these inhibitors, Ac-PQP-(DON)-LPF-NH(2), was considerably more potent and selective than other TG2 inhibitors reported to date. Selective pharmacological inhibition of extracellular TG2 should be useful in exploring the mechanistic implications of TG2-catalyzed modification of dietary gluten, a phenomenon of considerable relevance in Celiac Sprue.     

The sorption and desorption of water in lactitols

Summary Anhydrous lactitols (A1, α- and β-lactitol), lactitol monohydrate, lactitol dihydrate and lactitol trihydrate were kept for varying times in atmospheres of different relative humidity at 20°C in equivalent size plastic desiccators. The relative humidities (8-95%) were maintained with saturated salt solutions and drying agents (silica gel and phosphorous pentoxide). The composition of the samples was monitored by thermogravimetry, differential scanning calorimetry and X-ray powder diffraction. According to these measurements both lactitol monohydrate and lactitol dihydrate were substantially stable under the conditions used. Lactitol monohydrate converts to lactitol dihydrate at the highest relative humidity used. All phases of anhydrous lactitol convert into a form of lactitol monohydrate but not to lactitol dihydrate, even at the highest relative humidity used. At a high relative humidity lactitol trihydrate easily loses part of its crystal water and converts partly to lactitol dihydrate. At a lower relative humidity, the phase forming from trihydrate is difficult to identify.     

Formation of the main gas compounds during thermal analysis and pyrolysis: Betaine and betaine monohydrate

The thermochemical behaviour of betaine and betaine monohydrate was investigated under two degradation conditions. Betaine was heated up to 700°C at 10°C min^–1 in air and nitrogen flows and the evolved gas was analysed with the combined TG-FTRIR system. The evolved gas from betaine pyrolysis at 350 and 400°C was analysed by gas chromatography using mass-selective detection (Py-GC/MSD). In addition, the electron impact mass spectra of betaine and betaine monohydrate were measured.Esterification is one of the most important pyrolytic processes involving beta- ines. Even glycine betaine can change to dimethylglycine methyl ester via intermolecular transalkylation by heating. Trimethylamine, CO₂, and glycine esters were the main degradation products. Small amounts of ester type compounds evolved both in pyrolysis and with TG-FTIR. The monohydrate lost water between 35 and 260°C while the main decomposition took place at 245-360°C. The residual carbon burnt in air to CO₂ up to a temperature 570°C.This revised version was published online in November 2005 with corrections to the Cover Date.     

Infrared evolved gas analysis during thermal investigation of lanthanum, europium and samarium carbonates

The characterisation of rare earth elements carbonates (REECs) was performed by thermal analysis (TG-DTG) combined with simultaneous infrared evolved gas analysis-Fourier transform infrared (EGA-FTIR) spectroscopy. The TG-DTG curves were obtained using the Perkin-Elmer PC series TGA-7 thermogravimetric analyser in the temperature range 25-800 °C both in dynamic air and nitrogen atmosphere.La₂(CO₃)₃·nH₂O, Eu₂(CO₃)₃·nH₂O and Sm₂(CO₃)₃·nH₂O were analysed, the dehydration and decarbonation steps were investigated and the water content was calculated. The trace rare earth elements in lanthanum, europium and samarium carbonates were determined by Philips PU 7000 inductively coupled plasma atomic emission spectrometry (ICP-AES) and the concentration of REE ranged from 6.2×10⁻⁵ to 4.2×10⁻⁴% (w/w).     

Influence of drying to the structure of lactitol monohydrate

The purpose of this study is to find out the effect of the crystal water content on the crystal structure of lactitol monohydrate. Crystal water was removed by drying over silicagel at 40°C and by using phosphorus pentoxide as drying agent at 20°C. The amouts of water removals were identified by thermogravimetry, the melting points and the heat of fusions were calculated from the results of differential scanning calorimetry measurements and the structure of samples were identified by X-ray powder diffraction method. Over 23 w/w% of total water content could removed by gently drying until significant structural changes could be detected. The melting point of anhydrous lactitol obtained by drying lactitol monohydrate was 120°C and the melting enthalpy was 102 J g^?1 when measured with heating rate 10°C min^?1 by DSC.