ESR study on carboxymethyl chitosan radicals in an aqueous solution

水溶液中におけるカルボキシメチルキトサンラジカルのESR測定に関する研究

佐伯 誠一; 長澤 尚胤; 廣木 章博; 森下 憲雄; 玉田 正男; 室屋 裕佐*; 工藤 久明*; 勝村 庸介*

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

水溶性の多糖類誘導体であるカルボキシメチルキトサン(CMCTS)は10%以上の濃厚水溶液で放射線照射により橋かけ反応を起こしゲルが形成される。しかし、放射線橋かけ反応機構の詳細については明らかではなく、放射線照射後に生成する多糖ラジカルの同定も詳細にはなされていない。そこで、水の放射線分解生成物であるOHラジカルとの反応により生成したCMCTSラジカルを高速流通法を用いた電子スピン共鳴(ESR)測定法により同定した。その結果、水溶液中におけるCMCTSラジカルを直接観測でき、生成する多糖ラジカルは、CMCTSのカルボキシメチル基の第2級炭素上にラジカルであると同定した。

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.