Chitosan stability in acetic acid-permanganate solutions: Spectroscopic and viscometric approach

Spectroscopic and viscometric investigations of oxidative degradation of chitosan as a biodegradable and sustainable macromolecule by permanganate (MnO₄^-) have been studied in aqueous media. The fast decay of absorbance at 525 nm revealed the cleavage of glycosidic linkage of chitosan, leads to the formation of lower molecular mass chitosan oligomers. Formation of a coordination biopolymer complex between chitosan and MnO₄^- prior to the rate determining step was observed at lower concentration of oxidant for ca. 6 min. The activation energy, enthalpy of activation, and entropy of activation found to be 95.6 kJ/mol, 91.0 kJ/mol, and 20.9 JK^-1 mol^-1, respectively, for the redox reaction. The degraded chitosan was characterized by Fourier transform infra-red (FT-IR) spectroscopy. A viscometric study was carried out to assess the stability as well as molecular weight determination of chitosan solutions in acetic acid, and MnO₄^-. The viscosity of chitosan was decreased (from 50 cp to 40 cp) slowly in acetic acid within 30 min of storage time. Chitosan was unstable with MnO₄^- solution and viscosity decreased very sharply. The viscosity date of molecular weight changes was used to calculate the average number of chain scission and degradation rate. The low-molecular weight chitosan could be generated rapidly with KMnO₄ for biological applications.