Studies on acetylation patterns of different chitosan preparations

Chitosan is a biopolymer which physicochemical characteristics like fraction of acetylation (FA) and molecular weight (MW) 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 PA – is crucial for structure–activity-analysis dealing with biological systems. In this study, an improved method for pattern determination using 13C-NMR data of commercial de-N-acetylated and lab-made re-N-acetylated chitosan samples is shown. Results indicated a random-dominated pattern (PA 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 FA exponentially PA=1.11−0.58·e-FA0.13.