Chemical synthesis of hexose polymers

Influence of ultrasonication and hydrolysis conditions in methylation analysis of bacterial homoexopolysaccharides

Homoexopolysaccharides (HoEPS) such as α-glucans and β-fructans are synthesized by lactic and acetic acid bacteria. Methylation analysis is an important and well-established tool for the structural analysis of these polysaccharides, however, multiple steps are required for polysaccharide derivatization. Because ultrasonication during methylation and the conditions during acid hydrolysis may influence the results, we investigated their role in the analysis of selected bacterial HoEPS. The results reveal that ultrasonication is crucial for water insoluble α-glucan to swell/disperse and deprotonate prior to methylation whereas it is not necessary for water soluble HoEPS (dextran and levan). Complete hydrolysis of permethylated α-glucans requires 2 M trifluoroacetic acid (TFA) for 60/90 min at 121 °C while levan is hydrolyzed in 1 M TFA for 30 min at 70 °C. Nevertheless, levan was also detectable after hydrolysis in 2 M TFA at 121 °C. Thus, these conditions can be used to analyze a levan/dextran mixture. However, size exclusion chromatography of permethylated and hydrolyzed levan showed degradation and condensation reactions at harsher hydrolysis conditions. Application of reductive hydrolysis with 4-methylmorpholine-borane and TFA did not lead to improved results. Overall, our results demonstrate that conditions used for methylation analysis have to be adjusted for the analysis of different bacterial HoEPS.

The Oligomerization of Glucose Under Plausible Prebiotic Conditions

The prebiotic origin of polysaccharides, the largest class of biopolymers by mass in extant biology, has seldom been investigated experimentally. Herein, we report on the acid-catalyzed condensation of aqueous solutions of glucose, a model monosaccharide, under plausible prebiotic conditions employing a wet-dry (night-day) protocol with 0.01 M HCl at 50 °C. This protocol leads to the formation of oligosaccharides containing up to eight monomeric units identified by high resolution mass spectrometry. The regio- and stereochemistry of the oligomeric acetal linkages, as well as the quantitative analysis of glucose conversion, are elucidated by combining 1H, 13C and 2D NMR spectroscopy. Ten out of eleven possible acetal linkages, including α- and β- anomers, have been identified with the α- and β- 1,6-acetals being the dominant linkages observed. In addition, the acid-catalyzed oligomerization of several glucose disaccharides such as cellobiose, maltose, and gentiobiose are presented along with an accompanying comparison with the corresponding oligomerization of glucose.

THE STRUCTURE OF A SYNTHETIC GLUCAN: I. GENERAL STRUCTURAL FEATURES

Only D-glucose was obtained on acid hydrolysis of the glucan. Periodate oxidation released formaldehyde, which was believed to arise from C6 of D-glucofuranose units. From the additional formaldehyde liberated from the borohydride-reduced glucan the degree of polymerization was estimated to be about 165. Complete hydrolysis of the derived polyalcohol gave glycerol, erythritol, D-glucose, and D-xylose. Partial hydrolysis gave glycerol, erythritol, and at least seven non-reducing oligosaccharides. Direct evidence for the existence of relatively large numbers of 1 → 6 and 1 → 4 linkages was found, together with smaller numbers of 1 → 2 linkages. The methylated glucan was freely soluble in chloroform – petroleum ether (5:95), and hydrolysis gave tetra, tri, di, and mono-O-methyl-D-glucoses in a 6:6:3:1 molar ratio.

The occurrence of isomaltose among the products of heating glucose in dilute mineral acid

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Sedimentation coefficients of small molecules: methods of measurement based on the refractive-index gradient curve; the sedimentation coefficient of polyglucose A

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