Free radical-induced chitosan depolymerized products protect calf thymus DNA from oxidative damage.

Low molecular weight chitosan (LMWC) and chitooligosaccharides (COs), obtained by persulfate-induced depolymerization of chitosan showed scavenging of OH. and O2.- radicals and offered protection against calf thymus DNA damage. Over 85% inhibition of free radicals and DNA protection were observed. LMWC (0.05 micromol) showed a strong inhibitory activity compared to COs (3.6 micromol). Further, LMWC showed calf thymus DNA condensation reversibly giving stability, as evident from CD, TEM and melting curves (Tm). A fluorescence study suggests the binding of LMWC in the minor groove, forming H-bonds to the backbone phosphates without distorting the double helix structure.