PHOSPHORYLATED CHITOSAN: CHARACTERIZATION AND 3D POROUS NETWORK ASSEMBLING BY IONOTROPIC GELATION

Chitosan is the only cationic polysaccharide found in nature derived from biomass, which has several biological properties.1 However the solubility of chitosan is one of its main limitations, being insoluble at pH value above 6. Therefore, modification through phosphorylation is an alternative method to increase the water solubility and biological activity of the polysaccharide.2 In this work, the modification followed the method described by Nishi et al3 where the phosphorylation occurred only in the hydroxyl groups of chitosan, due to protection of amino group, that was proved by NMR and FTIR. In addition, the pKa value of amino group and phosphate groups was determined as 6.70 and 10.08, respectively. It was observed that phosphorylated chitosan is soluble in the range of pH 11.00 to 7.00 and partially soluble in pH values below 2.80, presenting a higher solubility than pure chitosan. The incorporation of phosphates into the chitosan structure allows the complexation with Ca2+ ions by ionotropic gelation, forming a 3D network due to the electrostatic interaction. The analysis of lyophilized phosphorylated chitosan by SEM/EDS showed the incorporation of calcium ions into the structure and its porous network.