Radical scavenging activity of 5-methylpyrrolidinone chitosan and dibutyryl chitin

This study compares the behaviour of 5-methylpyrrolidinone chitosan (MPC), a substituted hydrophilic polymer bearing free -OH and -NH2 groups, and dibutyryl chitin (DBC), a novel lipophilic O- and N-persubstituted chitin, toward free radicals. By means of EPR measurements their capacity of trapping radicals photochemically generated from PTOC esters was assessed. The fate of radicals inside the polysaccharides was checked on the basis of the structure of products obtained after photolysis and characterized by NMR spectroscopy. The experimental data clearly demonstrated that hydrophilic chitosans and persubstituted chitins possess remarkable radical blocking activity even though the nature of the process should be rather different between MPC and DBC. The DBC substrate hosts the radicals in protected and poorly reactive environment, whereas hydrophilic chitosan substrates favor a more rapid annealing of the radicals. MPC takes part in radical reactions with a consequent likely fragmentation of the polymer chain. A photochemical experiment carried out on chitosan confirmed the behaviour observed for MPC.