Radical adducts formation mechanism of CH3CO2○ and CH3CO3○ realized decomposition of chitosan by plasma catalyzed peracetic acid

High-molecular-weight chitosan has limited applications due to unsatisfactory solubility and hydrophilicity. Discharge plasma coupled with peracetic acid (PAA) oxidation ("plasma+PAA") realized fast depolymerization of high-molecular-weight chitosan in this study. The molecular weight of chitosan rapidly declined to 81.1 kDa from initial 682.5 kDa within 60 s of "plasma+PAA" treatment, and its reaction rate constant was 12-fold higher than single plasma oxidation. Compared with O-1(2), circle CH3, CH3O2 center dot, and O-2 circle(-), CH3CO2 circle and CH3CO3 circle played decisive roles in the chitosan depolymerization in the plasma+PAA system through mechanisms of radical adduct formation. The attacks of CH3CO2 circle and CH3CO3 circle destroyed the beta-(1,4) glycosidic bonds and hydrogen bonds of chitosan, leading to generation of low-molecular-weight chitosan; the main chain structure of chitosan was not changed during the depolymerization process. Furthermore, the generated low-molecular-weight chitosan exhibited greater antioxidant activities than original chitosan. Overall, this study revealed the radical adduct formation mechanisms of CH3CO2 circle and CH3CO3 circle for chitosan decomposition, providing an alternative for fast depolymerization of high-molecular-weight chitosan.