Study of chitosan and hydrophilic derivatives by time domain NMR

Abstract

Chitosan (Ch) is a linear copolymer obtained from natural source, frequently studied for biotechnological applications, but it has limited solubility over pH < pKa values. The derivatization of Ch chains, on the other hand, with hydrophilic chains of poly(ethylene glycol) or by -N(CH3)+ glicidiltrimetilamônio substituent insertion in the GlcN units, not only increases the solubility for Ch chains at neutral and alkaline pH, but also increases the bioavailability in vivo, biocompatibility, immunogenicity, antimicrobial activity and mucoadhesiveness, such properties especially useful for biomedical applications, particularly for bioactive delivery systems. The performance of Ch-based and derivatives biomaterial systems are often affected by structural parameters such as the average degree and distribution of block or random acetamido groups (GlcNAc units) and the average molar mass of polymer chains. Therefore, currently there are different techniques and analytical methods to characterize the influence of these parameters on the properties of Ch and derivatives in solution, as well as the ability of interaction of Ch chains with metal ions for biological and environmental applications. However, recently it was found that the relaxation processes (T1 and T2) of the solvent in Ch solutions, determined by Time Domain NMR (TD-NMR) is directly related to the colloidal properties of Ch. In this sense, this work aims to explore a systemic relationship between structure / colloid property and interaction with paramagnetic ions with Ch produced from USAD process with different structural and physicochemical characteristics, as well as for derivatives N-methoxypoly(ethylene glycol)-graft-chitosan (PCh) and N-(2-hydroxy) propyl-3-trimethylammonium chitosan (QCh) by simultaneous relaxation measurements in CWFP and CP-CWFP methods in order to correlate the values of T1 and T2 with the thermal stability, crystallinity, pH variation, viscosity, zeta potential and average hydrodynamic diameter distribution of macromolecules in solution. (AU)