Spectroscopic and conformational study of chitosan acid salts

The efficient procedure for preparation of chitosan acid salts in isopropyl alcohol under mild condition has been demonstrated. The salts were prepared by dissolving chitosan into ascorbic acid, p-amino benzoic acid and p-nitro benzoic acid, respectively, and then washed with an isopropyl/water mix-solvent. The prepared crystal salt and molecular conformation of modified chitosan derivatives are characterized by using ultraviolet, Fourier transform infrared (FTIR), ¹H nuclear magnetic resonance (NMR), X-ray diffraction and Circular dichroism (CD) techniques. The formation of salts was confirmed by FTIR (∼1,523–1,557 cm⁻¹) and NMR (∼7–8 ppm) with respect to the bonding between NH₂ group on chitosan and COOH group on acid. The CD spectra of chitosan salts showed negative at (253, 285 and 295 nm band) in chitosan ascorbic acid, p-amino benzoic acid and p-nitro benzoic acid salt respectively in DMSO, indicating that the polymer adopted a helical secondary structure. The polymers are highly soluble in a wide pH range, which opens new perspectives for the biomedical application of chitosan based-materials.