Structural and conformational changes on chitosan after green heterogeneous synthesis of phenyl derivatives

AGUIRRE-PRANZONI, CELESTE; GARCÍA, MARÍA G.; OCHOA, NELIO A.

CARBOHYDRATE POLYMERS

ELSEVIER SCI LTD

Año: 2023 p. 1 - 33

0144-8617

Four aromatic acid compounds: benzoic acid (Bz), 4-hydroxyphenylpropionic acid (HPPA), gallic acid (GA) and 4-aminobenzoic acid (PABA) were covalently bonded to chitosan in order to improve water solubility at neutral pH. The synthesis was performed via a radical redox reaction in heterogeneous phase by employing ascorbic acid and hydrogen peroxide (AA/H2O2) as radical initiators in ethanol. The analysis of chemical structure and conformational changes on acetylated chitosan was also the focus of this research. Grafted samples exhibited as high as 0.46 molar degree of substitution (MS) and excellent solubility in water at neutral pH. Results showed a correlation between the disruption of C3-C5 (O3…O5) hydrogen bonds with increasingsolubility in grafted samples. Spectroscopic techniques such as FT-IR and 1H- and 13C C-NMR showed modifications in both glucosamine and N-Acetyl-glucosamine units by ester and amide linkage at C2, C3 and C6 position, respectively. Finally, loss of crystalline structure of 2-helical conformation of chitosan after grafting was observed by XRD and correlated with 13C CP-MAS-NMR analyses.