壳聚糖在水溶液中的辐射降解反应

STUDIES ON RADIATION DEGRADATION OF CHITOSAN IN AQUEOUS SOLUTIONS

研究了壳聚糖在CH3COOH/NaCl缓冲溶液均相体系下的辐射降解反应,给出了H2O2、异丙醇、pH、样品初始分子量等因素对壳聚糖降解的影响,探讨了实验条件下溶液中不同自由基对壳聚糖降解的作用,并对辐照前后壳聚糖的结构进行了表征.结果表明,酸性条件下,壳聚糖的降解主要由.H和.OH自由基共同作用引起,加入H2O2或者通入N2O都能够略微提高.OH自由基浓度,对壳聚糖的降解有促进作用.加入异丙醇后,由于同时降低了.H和.OH自由基浓度,导致壳聚糖降解缓慢.当溶液的pH接近中性后,对壳聚糖的降解起主要作用的为.OH自由基,加入H2O2或者通入N2O都会增加.OH自由基的浓度,从而明显提高壳聚糖的降解速率.此外,研究发现低分子量的壳聚糖具有较快的降解速率.样品的UV、FTIR分析表明,辐照后除在壳聚糖分子链端生成羰基外,壳聚糖主链结构未见变化,脱乙酰度也没有显著改变,显示出辐射降解是一种有效的控制壳聚糖分子量方法.

Chitosan dissolved in CH3COOH/NaCl aqueous solution was irradiated at various conditions, and the influence of H2O2, N2O, isopropanol, pH and molecular weight of chitosan on the radiation degradation of chitosan in aqueous solutions was investigated. In acidic solutions （pH = 3 ）, the degradation of chitosan in aqueous solutions might be attributed to the interaction with both · H and · OH radicals. The degradation of chitosan was slightly faster in the presence of H2O2 or N2O, because the concentrations of · OH radicals increased slightly. The degradation of chitosan was inhibited obviously after adding isopropanol, due to the decrease of both ·H and · OH radicals in the presence of isopropanol. With the pH of the solution approaching neutral, the concentration of · H decreased and the·OH radicals increased rapidly with the presence of H2O2 or N2O. The chain scission of chitosan was promoted significantly after adding H2O2 or saturated with N20. In addition, it was found that the rate constant of radiation degradation of chitosan increased with the decrease of molecular weight of chitosan. UV and FFIR analyses of radiation-degraded chitosan manifested that except for carbonyl groups generated at the ends of molecular chains, no obvious change in the main chain structure of radiation-degraded chitosan, comparing with unirradiated chitosan. Therefore, gamma irradiation can be expected as an effective way to control the molecular weight of chitosan without obvious change in its backbone structure.