What is the degree of acetylation?

From ChitosanWiki
Jump to: navigation, search

The degree of acetylation (abbreviated as DA) describes the relative amount of N-acetylglucosamine residues within a chitosan molecule, given in percent. For a chitosan molecule consisting of n GlcNAc residues and m glucosamine residues, i.e. a chitosan with the formula GlcNAcnGlcNm, the degree of acetylation would be [(n / (n + m)] x 100]%. Unfortunately, chitosans are often described by giving their degree of deacetylation (abbreviated DDA), as chitosans are typically produced from chitin by partial deacetylation, easily leading to confusion. Of course, DDA and DA are related to each other by the formula DA + DDA = 100. In order to avoid misunderstandings, the term fraction of acetylation (abbreviated FA) has been introduced, which varies between 0 and 1 and which is calculated as DA/100 or n / (n + m). The degree of acetylation of natural chitosans in the cell walls of Zygomycete fungi has been recorded as being in the range of 10 to 50%. There are no commonly accepted definitions for the terms "low DA", "medium DA" or "high DA" chitosans. It is important to realise that like the degree of polymerization of a chitosan sample, the degree of acetylation is always an average value as chitosan samples (like any polymer or biopolymer sample) are always mixtures of molecules with different degrees of acetylation. However, unlike the polydispersity index which is a measure of the molecular weight distribution of a sample, there is no such value for the degree of acetylation as there is no analytical technique to determine the distribution of degrees of acetylation in a chitosan sample. The degree of acetylation is probably the single most important parameter influencing the biological activities of chitosan polymers, and it also influences their material properties.