Morphological Structure of Cellulose

Abstract

The specific nature of the morphological structure of cellulose is defined primarily by its function within the cell wall. Having no mineral frame the substance surrounding the plant cell provides it with resistance against exposure to the considerable mass forces. This ability is realized by secretion of cellulose by the membrane of the plant cell as tightly packed fibrils, which afford something like a crystalline lattice. At the same time the fibrils providing cell strength are present in a complex relationship with the amorphous matrix of other polysaccharides, which are a rather complicated group of substances having specific features. Among them the most widespread are hemicelluloses comprising xylans—linear polymers of d-xylose binded by β-1,4-linkages with side chains of 4-O-methylglucuronic acid and (or) arabinose residues. Together with hemicelluloses the matrix comprises unbound pectins—polymers of methyl esters of galacturonic acid. Matrix of some plant species contain d-galactan, l-arabinan and other heteroglycans. Cellulose fibrils of the matrix interact strongly with protein—extensin containing a great amount of hydroxyproline. It is important that arabinose or galactose residues of hemicelluloses are bound by the glycoside bond with some hydroxyl groups of hydroxyproline [162] (proline is hydroxylated after its intercalation into the peptide chain). The formation and orientation of extensin as a rigid left-twisted helix may define the growth of cellulose macromolecules and direction of their ordering upon fibril formation.