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Structural polysaccharide chemistry with analytical applications to lemon gum Gibney, Kelly Blair

Abstract

A gas chromatographic method has been developed whereby the following compounds may be determined quantitatively and simultaneously: ethylene glycol, glycerol, erythritol, threitol, arabinose, xylose, mannose, galactose and glucose. These products correspond to the constituent parts of periodate oxidized, borohydride reduced polysaccharides. Quantitative analysis of the fractions obtained on total and partial hydrolysis of such polyalcohols provides a new and powerful analytical tool in polysaccharide chemistry. Optimum conditions for the Smith degradation of a polysaccharide have been illustrated by a detailed analysis of lemon gum. A new method for the reduction of uronic acids in poly- and oligosaccharides has been developed. Reduction can be carried out after only esterification of the uronic acids. Reaction at this stage avoids possible degradation or fractionation during esterification and subsequent saponification of polysaccharide hydroxyl groups. Good levels of reduction [75%] have been achieved with reduction of highly branched lemon gum. Silylated polyhydroxy compounds and galacturonic acid were examined by proton magnetic resonance spectroscopy. The trimethylsilyl [TMS] protons of such ethers and esters show good separation from one another. Analysis of the trimethylsilyl proton peaks provides information concerning the number and degree of subsitution of hydroxyl and acid functions present in the parent molecule. Signal strength due to the nine protons on each trimethylsilyl group provides a chemical means of signal enhancement. Analysis was carried out on 2 mg. of a minor TMS glucofuranose derivative. Lemon gum has been analysed by the method of Lindberg et al [8l]. Analysis of lemon gum is the first example of the application of partially methylated alditol acetate mass spectroscopy to a plant gum. The results of this analysis are in good agreement with previous analysis of this gum.

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