Studies on acetylation patterns of different chitosan preparations

Abstract Chitosan is a biopolymer which physicochemical characteristics like fraction of acetylation ( F A ) and molecular weight ( M W ) depend strongly on preparation conditions. Furthermore, the orientation of acetyl groups along the chain may adopt different patterns like an alternating, random or a block-wise pattern depending on preparations conditions. However, a reliable determination of the pattern of acetylation of unknown chitosan preparations – as a single parameter P A – is crucial for structure–activity-analysis dealing with biological systems. In this study, an improved method for pattern determination using 13 C-NMR data of commercial de- N -acetylated and lab-made re- N -acetylated chitosan samples is shown. Results indicated a random-dominated pattern ( P A 0.5–1.5) for all 32 samples although different process conditions were used during production of the samples. No evidence for the existence of a clear block-wise or clear alternating chitosan preparation was found. For the first time it could be shown that pattern of acetylation correlates with F A exponentially P A = 1.11 − 0.58 · e - F A 0.13 .