What are chitosans?
Chitosans, like chitin, are natural biopolymers, i.e. large molecules build of many small molecules (the monomers). Chitosans, like chitin, belong to the class of polysaccharides (complex sugars) build of many monosaccharide units (simple sugars), namely glucosamine and N-acetylglucosamine residues linked via β-1,4-glycosidic linkages. The total number of monomeric units in a chitosan polymer (the degree of polymerization) can vary, and so can the ratio of the two monomeric units (the degree of acetylation). The distribution of the acetylated units within the polymer (the pattern of acetylation) is invariably random in today's commercially produced chitosans due to the chemical production processes, but the pattern of acetylation in naturally occurring chitosans (which are produced from chitin by the enzyme chitin de-N-acetylase) is unknown at present. Due to the presence of positive charges at the free amino groups of the glucosamine units, chitosans can be soluble at slightly acidic pH values (below pH 6). These properties make them well suited for a plethora of potential applications. The border between chitin and chitosan is not a sharp one (unless the term chitin is strictly reserved for fully acetylated polymers with a degree of acetylation of 100%). In practice, polymers that are insoluble in dilute acid are considered chitin while acid-soluble ones are defined as chitosans. The border between the two depends on the degree of acetylation of the molecule, it is somewhere in the range of a degree of acetylation of 75%.