ESR study on carboxymethyl chitosan radicals in an aqueous solution

Saiki, Seiichi; Nagasawa, Naotsugu; Hiroki, Akihiro; Morishita, Norio; Tamada, Masao; Muroya, Yusa*; Kudo, Hisaaki*; Katsumura, Yosuke*

Carboxymethyl chitosan (CMCTS) is one kind of polysaccharide derivatives and has a good water-solubility. At a high concentrated aqueous solution, CMCTS forms gel by ionizing irradiation, though polysaccharide derivatives are generally radiation-degradation type. In general, OH radical, which is one of main water radiolysis products and very oxidative species, is said to induce crosslinking reaction of polymer solution. The purpose of this study is to understand the radiation-crosslinking mechanism of CMCTS at a high concentrated aqueous solution. In this study, identification of CMCTS radical produced by reaction with OH radical was introduced. CMCTS radical in an aqueous solution was observed directly by ESR method using photolysis of hydrogen peroxide. The ESR spectra have a large doublet split and small triplet split like [Triplet Doublet]. However, some species seemed to be overlapped on ESR spectra, because right-and-left triplet spectra are not equiform. Compared with some radicals, which have analogical structure to CMCTS, about hyperfine coupling constant, [Triplet Doublet], assigned as radical on carboxymethyl group linked to C6, and [Doublet], assigned as radical on carboxymethyl group linked to C2 or C3, were isolated from ESR spectra of experimental results. In conclusion, these spectra were identified as radicals located on secondary carbon of carboxymethyl groups.