Natural Xylan Research Articles

The relation between monosaccharide composition and specific optical rotation of galactomannans from plant seeds

An equation based on the principle of optical superposition, and derived by Marchessault and his co-workers for native xylans, has been applied in an adapted form to galactomannans isolated from seeds of angiospermous plant species. The specific rotations for aqueous solutions of the galactomannans obey the relationship with the ratio between the monosaccharide components of the galactomannans required by the equation. Similar relationships exist for the optical rotations of solutions of galactomannans in alkali and of methylated galactomannans in chloroform. Within naturally related groups of galactomannan-containing plant species, the mannose-to-galactose ratios of the polysaccharides vary between relatively narrow limits.

Correlation of chemical composition and optical rotation of water-soluble galactomannans

A quantitative relationship can be obtained between the rotatory power and the molar ratio mannose/galactose for galactomannans having a structure consisting of a backbone of β-(1 → 4)-linked d-mannopyranose units with side chains of α-(1 → 6)-linked d-galactopyranose residues, by using an equation based on the principle of optical superposition and derived originally by Timell for native xylans. By adopting the usually accepted errors for the determination of optical rotations (±5° for polysaccharides) and the percentages of the sugar units (±5%), the natural, water-soluble galactomannans can be grouped into two classes, namely, those for which the differences between the experimental and calculated rotations lie in the range of the experimental error, and those for which the above differences are higher than the experimental error. For the last class, the existence of structural details not considered in the basic pattern used for the correlation is suggested.

CORRELATION OF CHEMICAL COMPOSITION AND OPTICAL ROTATION OF NATIVE XYLANS

The principle of optical superposition has been used to derive an equation relating the specific rotations of native xylans with their content of 4-O-methylglucuronic acid and/or arabinofuranose residues. The equation is in good agreement with literature data for the 4-O-methylglucuronoxylans and the arabinoxylans. Based on this correlation, an α-L-linkage is suggested for the arabinofuranose residues in various arabinose-containing xylans. Literature rotations for the 4-O-methylglucuronoarabinoxylans are consistently greater than values predicted by the equation. Finally, the rotatory dispersion behavior of acidic and neutral xylans is examined.