Understanding dissolution process of chitin crystal in ionic liquids: theoretical study

Abstract

Chitin is a promising biomass resource and has high potential for industrial applications owing to its huge annual production in nature. However, it exhibits poor processability and solubility due to its very stable and crystalline character. Recently, ionic liquids (ILs) have attracted attention as solvents for structural polysaccharides - for example, 1-allyl-3-methylimidazolium bromide (AMIMBr) has been found to dissolve chitin. As few ILs are known to dissolve chitin, little research has been conducted on the dissolution mechanism involved. In this study, we have adopted a molecular dynamics (MD) approach to study the dissolution of chitin crystals in imidazolium-based ILs. The MD simulation in AMIMBr has demonstrated that the dissolution process involved peeling of chitin chains from the crystal surface, with Br- cleaving the chitin hydrogen bonds, and AMIM+ preventing a return to the crystalline phase after the peeling. By contrast, in imidazolium acetates, which has also been reported to dissolve chitin, although the molecular chains are peeled off, the peeled chains occasionally return to the crystalline phase. Furthermore, the MD trajectory analysis has revealed that the solubility of chitin is well correlated with the number of intermolecular hydrogen bonds by acetamido groups in the chitin crystal. It has been experimentally proven that mixing a small amount of 2-bromoethyl acetate, as a bromide generator, with 1-allyl-3-methylimidazolium chloride can enhance chitin solubility, which supports the dissolution mechanism indicated by the above theoretical results.

Progress in Catalytic Conversion of Renewable Chitin Biomass to Furan-Derived Platform Compounds

“…As mentioned earlier, the large number of hydrogen bonds in chitin-based biopolymers lead to difficulties in the dissolution and degradation of chitin and chitosan. Ionic liquids exhibit the ability to cleave hydrogen bonds in polysaccharides and form new hydrogen bonds between anions and the hydroxyl groups of biopolymers, improving the dissolution [30,31].…”

Marine-Derived Polymers in Ionic Liquids: Architectures Development and Biomedical Applications

“…Therefore, acetate ions can be more effective than chloride or dimethylphosphate anions. Studies involving a molecular dynamics (MD) approach to evaluate the dissolution of chitin crystals in imidazolium-based ILs revealed that the solubility of chitin can be correlated with the number of intermolecular hydrogen bonds by acetamido groups in the chitin crystal [55]. The data also proved that mixing a small amount of 2-bromoethyl acetate, as a bromide generator, with (Amim)(Br)can enhance chitin solubility.…”

A review on chitosan and its development as pulmonary particulate anti-infective and anti-cancer drug carriers

“…The chitin is constituted of β (1→4) linked residues of N-acetyl-2-amino-2-deoxy- d -glucose and 2-amino-2-deoxy- d -glucose ( Elieh-Ali-Komi & Hamblin, 2016 ). It exhibits an extremely poor aqueous solubility due to its highly crystalline characteristics which are brought about via hydrogen bonding between the acetamido moieties ( Uto et al, 2018 ; Zhu et al, 2016 ). The partially deacetylated chitin is water-soluble ( Muzzarelli et al, 1999 ; Ying et al, 2011 ).…”