等离子体降解对壳聚糖分子结构影响及功能活性调控机理研究

Chitosan is the only alkaline amino polysaccharide in the natural world. However, high viscosity and low solubility limit its applications. The key resolution of the problem is the modification of the molecular structure of chitosan by the degrading treatment. Thus the development of an efficient process for degrading chitosan is of great interest. In our previous studies, we found that plasma process can significantly contribute to the properties and functionalities of chitosan, and we draw conclusions that the formation of a reactive species（•OH,•O,•H, et al.）played an important role. Based on the results of previous studies, we will study the effect of the distance between the electrodes and initial pH on the molecular structure of chitosan (e.g., molecular weight of chitosan and its distribution, molecule chain structure, reactive groups, and conformation). Base on the research of relationship between the biological activities of chitosan (e.g., antioxidant and antimicrobial activity) and its molecular structure, the key molecular structure effecting the biological activities of chitosan by plasma degradation will be confirmed. Moreover, we will investigate the major reactive species of chitosan degradation, and analyze the effect of the major reactive species on the key molecular structure and its reaction pathways, and reveal the regulation mechanisms of biological activities of chitosan under plasma process. All the studies will is useful for the application of chitosan and the preparation of oligochitosan.

壳聚糖是唯一的天然碱性氨基多糖。但是，黏度高、水溶性差等特性严重限制了其应用，对壳聚糖分子结构降解改性成为解决问题的关键，开发一种可行的壳聚糖降解技术已成为研究热点。申请人前期研究发现，脉冲放电等离子体技术对壳聚糖应用特性和功能活性具有显著的促进作用，且可能与诱导活性氧（•OH、•O、•H等）生成有关。本项目重点围绕壳聚糖分子结构（分子量及其分布范围、主链结构、活性基团和构象），以在脉冲放电等离子体降解中起关键作用的极板间距和pH值为降解因素，研究降解对壳聚糖分子结构的影响规律；通过壳聚糖功能活性（抗氧化、抑菌）与其分子结构变化的构效关系，明确降解改善壳聚糖功能活性的关键活性特征结构；通过确定对降解起主要作用的主效活性氧，并探讨主效活性氧对关键活性特征结构的影响规律及其产生途径，揭示脉冲放电等离子体技术对壳聚糖功能活性调控机理。该研究对壳聚糖应用及可控制备高功能活性低聚壳聚糖具有重要意义。

对壳聚糖降解处理可以显著改善壳聚糖功能活性，将脉冲放电等离子体处理技术应用于壳聚糖降解处理，可以很好的解决当前降解技术存在的污染严重、成本高的问题。本项目研究不同降解关键因素（降解时间、pH值、极板间距）条件下，壳聚糖分子结构与功能活性变化的相关性，筛选出与壳聚糖功能活性相关的关键活性特征结构；通过研究降解过程中，活性氧（•OH、H2O2、•O、•OH、水合电子）的产率和活性氧屏蔽剂对降解效果的影响程度，确定起主要降解作用的主效活性氧，并通过研究主效活性氧屏蔽剂对关键活性特征结构的影响规律，揭示关键活性特征结构作用机理和调控途径。结果表明，壳聚糖分子量、结晶结构、分子构象为关键活性特征结构，特别是分子量；•OH、H2O2和•O为主效活性氧，•O降解作用高于•OH；活性自由基的产生途径可能有：（1）水合电子分解水分子产生，（2）通过脉冲放电等离子体物理效应（紫外、超声波）分解水分子产生，（3）通过Fenton's反应产生；对于活性官能基团和结晶结构，•O屏蔽剂1,4-苯醌是主要调控途径，对于壳聚糖分子量和分子构象，•OH屏蔽剂叔丁醇和H2O2屏蔽剂MnO2是主要调控途径。本研究成果可以为脉冲放电等离子体制备高功能活性低聚糖壳聚糖提供基础数据与参考，对壳聚糖产业发展具有重要意义。