Heterogeneously deacetylated chitosans possess an unexpected regular pattern favoring acetylation at every third position

Abstract

Chitosans are promising natural polymers with diverse industrial, medical and agricultural applications, but their properties and bioactivities depend on their structural characteristics, including their pattern of acetylation (PA). Chitosans produced by homogeneous deacetylation or chemical N-acetylation are assumed to have a random PA, but almost all commercially available chitosans are heterogeneously deacetylated, and whether they possess a random or block-wise PA has been the subject of a decades-long debate. Here we used a novel combination of analytical tools to address this unanswered question and found that both assumptions are wrong. Our combination of in vitro experiments and in silico modeling surprisingly revealed a more regular PA in heterogeneously deacetylated chitosans, with acetylated units overrepresented at every third position in the polymer chain. This unanticipated regular PA increases the elicitation activity of chitosans in plants compared to a random PA, and also generates different product profiles and distributions in enzymatic and acid hydrolysates. A regular PA may be beneficial for some applications but detrimental for others. Researchers in academia and in industries that use chitosans should therefore be aware that today’s commercial chitosans differ fundamentally from enzymatically produced natural chitosans and niche products produced by homogeneous deacetylation or N-acetylation.