The Molecular Structure and Conformational Dynamics of Chitosan Polymers: An Integrated Perspective from Experiments and Computational Simulations

Abstract

Chitosan is a semi-synthetic linear copolymer composed of a variable number of β-(1-4) linked units of 2-acetamide-2-deoxy-β-d-glucopyranose (GlcNAc) and 2-amino-2-deoxy-β-d-glycopyranose (GlcN) [1]. The two monomers differ with respect to the C2-substituent in the sugar ring, which is either an amino or acetamide group (Figure 1). Chitosan is obtained via the alkaline deacetylation of chitin. However, the deacylation reaction hardly proceeds completely in a normal heterogeneous reaction, leading to a random distribution of GlcNAc and GlcN residues in the chitosan polymer [2, 3]. The degree of acetylation of a polymer is a measure of the average number of GlcNAc per 100 chitosan monomers in percentile unit. The degree of acetylation governs important physical-chemical properties of the chitosan polymer such as solubility and conformation, being critical for the effectiveness of various technological applications [4-6]. The threshold for the conversion of chitin into chitosan depends on the solubility of the oligosaccharide in a slightly acid solution (0,1 mol/L of acetic acid). Conventionally, chitin polymers with a level of acetylation below 50% is considered as chitosan. The level of protonated amino groups in the glucosamine monomers dictates the solubility of chitosan, conferring the cationic nature to the polymer