Conjugation of kojic acid with chitosan

Direct and non-direct conjugation of kojic acid with chitosan was carried out according to the following approaches: (a) covalent binding of chlorokojic acid to chitosan via free amino groups, and (b) complexation of kojic acid with iron(III) bound to chitosan. Obtained products were analysed by organic elemental analysis and spectroscopic methods. The maximal degree of substitution was ∼0.2 mol/mol for the chitosan–kojic acid conjugates. The triple chitosan–FeO(OH)–kojate complex contained these components in the molar ratio of 1:0.48:0.07. UV–vis absorption, FT-IR and Raman spectra of the obtained products showed characteristic bands of bound kojic acid and thus confirmed that both ways of kojic acid binding were efficient. Solution 1H NMR and solid state 13C CP-MAS NMR spectra of the chitosan–kojic acid conjugates supported the predicted way of 4-oxypyranone binding to chitosan. UV–vis absorption spectra of the chitosan films subsequently modified with ferric chloride and kojic acid indicated that the ligand molecules are bound to peripheral iron(III) cations of FeO(OH) subcolloidal particles arranged on the surfaces of a film.