Phosphorylation of chitin and chitosan: A review on its significance and various synthesis routes

Over the past few decades, chitin and chitosan, value-added biopolymers obtained majorly from seafood wastes, have been extensively evaluated and utilized for their application in plenty of domains such as biomedical, pharmaceutical, agricultural, food processing industries, fuel cells, wastewater curing, and flame retardants. A vast number of physical, chemical, and enzymatic approaches have been followed to improve the biological activities, biocompatibility, and physicochemical properties of chitin and chitosan. Among the innumerable modifications, this article focuses primarily on the importance of phosphorylation, as it intensifies not only water solubility but also tissue regeneration, flame retardation, ionic conductivity, metal chelation, and drug-carrying abilities. Furthermore, the aim of this review is to thoroughly assess various techniques that involve the use of phosphorylating agents such as phosphoric acid, phosphorus acid, phosphorus oxychloride, phosphorus pentoxide, and the grafting method to synthesize phosphorylated derivatives of chitin and chitosan, so that a clear vision can be provided to the reader aimed at choosing a best-fit method for phosphorylation.