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.     

Identification of hexose diastereomers by means of tandem mass spectrometry of oxocarbenium ions followed by neural networks analysis

The ion abundances in the tandem mass spectra of oxocarbenium ions generated from aldohexoses and ketohexoses under electrospray ionization conditions depend on their stereochemistry. The ratios of the abundances of two of the major ions m/z 85 and 91 are different in the aldohexoses and the ketohexoses. Principal component analysis (PCA) allowed visual differentiation of the hexose isomers. However, identification of an individual hexose was difficult. The data were subjected to neural network analysis (NNA) using a multilayer perceptron (MLP) model. The model was first trained using the data from the 11 hexoses and then used to identify the hexoses using fresh data acquired later. There was 100% identification of the various hexoses. The hexose units in methyl glucoside, mannoside and galactoside could also be identified accurately. The method can therefore be used for the characterization of hexose units from monosaccharides and glycosides.     

Two Efficient Syntheses of Protected 4‐Deoxy‐D‐lyxo‐hexose (4‐Desoxy‐D‐mannose)

The formation of four differently protected 4‐deoxy‐D‐lyxo‐hexose derivatives 7, 8, 12, and 14 is described. In the first procedure, a nucleophilic displacement of the allylic mesylate 4 by hydride was combined with a highly stereoselective osmylation of olefin 6 to afford diol 7. In the second radical procedure, tributyl tin hydride was substituted by the cheap and environmentally friendly hypophosphorous acid as a hydrogen donor in the reduction of xanthate 13 to 4‐deoxy lyxo‐hexose 14.     

L‐Valine assisted distinction between the stereo‐isomers of D‐hexoses by positive ion ESI tandem mass spectrometry

The binary mixtures of 7 hexoses and 20 amino acids were investigated by electrospray ionization ion trap mass spectrometry (ESI‐ITMS). The adduct ions of the amino acid and the hexose were detected for 12 amino acids but not for the other 8 amino acids which are basic acidic amino acids and amides. The ions of amino acid–hexose complexes were further investigated by tandem mass spectrometry (MS/MS), and some of them just split easily into two parts whereas the others gave rich fragmentation, such as the complex ions of isoleucine, phenylalanie, tyrosine, and valine. We found that hexoses could be complexed by two molecules of valine but only by one molecule of the other amino acids. Among seven kinds of valine–hexose complexes coordinated by potassium ion, the MS² spectra of the ion at m/z 453 yielded unambiguous differentiation. And the fragmentation ions are sensitive to the stereochemical differences at the carbon‐4 of hexoses in the complexes, as proved by the MS². Copyright © 2010 John Wiley & Sons, Ltd.     

Acidic Ultrafine Tungsten Oxide Molecular Wires for Cellulosic Biomass Conversion

The application of nanocatalysis based on metal oxides for biomass conversion is of considerable interest in fundamental research and practical applications. New acidic transition‐metal oxide molecular wires were synthesized for the conversion of cellulosic biomass. The ultrafine molecular wires were constructed by repeating (NH₄)₂[XW₆O₂₁] (X=Te or Se) along the length, exhibiting diameters of only 1.2 nm. The nanowires dispersed in water and were observed using high‐angle annular dark‐field scanning transmission electron microscopy. Acid sites were created by calcination without collapse of the molecular wire structure. The acidic molecular wire exhibited high activity and stability and promoted the hydrolysis of the glycosidic bond. Various biomasses including cellulose were able to be converted to hexoses as main products.     

Spectral Determination of the Structure of 5-Hydroxymethylfurfurylidene Barbituric Acid

5-hydroxymethylfurfural reacts with barbituric acid and forms a product with maximum absorbance at 395nm. Via UV-VIS and IR-spectra it becomes evident that in acidic conditions this compound has a conjugated system of bonds with a chynoide-like chromophore. In alkali conditions this chromophore breaks out and the solution is colorless. In this paper is reported a mechanism which is an attempt to explain the stages of this reaction.     

Polymerase‐Catalysed Incorporation of Glucose Nucleotides into a DNA Duplex

Active but unselective : Nucleoside triphosphates possessing glucose moieties (such as those depicted) instead of the natural furanose rings are recognised by the active sites of polymerases. Polymerases therefore seem to be very unspecific in their recognition patterns.