Chitin and chitosan preparation from marine sources. Structure, properties and applications

Abstract

This review describes the most common methods for recovery of chitin from marine organisms. In depth, both enzymatic and chemical treatments for the step of deproteinization are compared, as well as different conditions for demineralization. The conditions of chitosan preparation are also discussed, since they significantly impact the synthesis of chitosan with varying degree of acetylation (DA) and molecular weight (MW). In addition, the main characterization techniques applied for chitin and chitosan are recalled, pointing out the role of their solubility in relation with the chemical structure (mainly the acetyl group distribution along the backbone). Biological activities are also presented, such as: antibacterial, antifungal, antitumor and antioxidant. Interestingly, the relationship between chemical structure and biological activity is demonstrated for chitosan molecules with different DA and MW and homogeneous distribution of acetyl groups for the first time. In the end, several selected pharmaceutical and biomedical applications are presented, in which chitin and chitosan are recognized as new biomaterials taking advantage of their biocompatibility and biodegradability.

Figure 1

Chemical structure of chitin and chitosan

Figure 2

¹³C NMR spectra for (A) chitin and chitosans (B) obtained by homogeneous reacetylation DA = 0.60; (C) commercial chitosan from Pronova DA = 0.2; (D) fully deacetylated chitin. Reproduced with permission from [90]. Copyright 2000 American Chemical Society.

Figure 3

¹H-NMR spectrum of chitosan with DA~0.06 in D₂O at pH~4, T = 85 °C and polymer concentration 5 g/L. Signals at 4.9 ppm is for H-1 of d-glucosamine unit, at 4.7 ppm is for H-1 of N-acetyl-d-glucosamine, at 3.2 ppm is for H-2 and at 2.1 ppm is for -CH₃ of the acetyl group allowing to get DA.