Synthetic methods and applications of chitosan containing pyridylmethyl moiety and its quaternized derivatives: A review

Chitosan is a natural polysaccharide with non-toxic, biodegradable, and biocompatible properties. Subsequently, there has been much interest in chitosan and it has been widely used in many fields. However, its applications have only been shown in acidic medium because of its poor solubility in neutral and basic pH. To enhance the solubility, the physicochemical and biological properties and application, chemical modifications of chitosan were made. Quaternization is a popular means of modifying chitosan resulting in a water-soluble chitosan derivative with a wide pH range including neutral and basic conditions. This is due to a permanent positive charge on the polymer backbone. The N-arylation of chitosan, particularly the aromatic containing nitrogen atom, has gained increasing attention because it not only has a hydrophobic character, but it is also a hydrophilic and nucleophilic characters at nitrogen atom. Therefore, the focus was on the recent synthetic methods and applications of N-pyridylmethyl chitosan and its quaternized derivatives in this review. Moreover, the quaternization of chitosan and its derivatives with different synthetic routes and quaternizing agents were reviewed.