Figure 2.

Chemical structures of chitin and chitosan. (a) Chitin is a homo-polymer assembled of N-acetyl-D-glucosamine monomers (GlcNAc), covalently bound through β-(1-4)-glycosidic linkages. In nature, it occurs as a co-polymer comprised of both GlcNAc and non-acetylated D-glucosamine (GlcN) subunits, with a molar GlcNAc fraction > 50%. (b) Chitosan is the deacetylated derivative of chitin, defined by a ratio of GlcN to GlcNAc monomers of > 1,0. It exhibits solubility in aqueous acetic solvents. (c) Chitin has three different allomorphs, which differ in the orientation of the respective polymer chains within the micro-fibril macro structure. The most abundant and resilient α-chitin is formed by antiparallel aligned polysaccharide chains. In β-chitin, the sugar chains are ordered in a parallel manner, therefore exhibiting weaker intramolecular interactions. The γ-allomorph of chitin is characterized by a mixture of both antiparallel and parallel aligned chains, which leads to a polymer with fractions of higher and lower levels of crystallinity. The figure was created with BioRender.