木质素天然聚多酚的结构设计和抗氧化活性构效关系研究

Lignin is the most abundant natural polyphenols which has been attracted more and more interests as an antioxidant for its low toxicity, bio-compatible and stabability. But its antioxidant acitivity is quite lower than the synthetic antioxidants. In recent years, the design and synthesis of novel, low toxicity and high efficiency of natural antioxidants from raw natural materials has become one of the hot spots in biomedical, chemistry, and pharmacopedics. This project focuses on the relationship between structure and antioxidant activity of lignin as an original antioxidant. The alkaline lignin and hydrolysis lignin are used as the primary sources with lignin models as references. The lignins are firstly treated by microwave oxidation and demethoxy to improve their chemical reactivity. And following they are modified by methylolation, Mannich reaction, sulfomethylation, carboxymethylation, sulfhydryl reaction, graft copolymerization and condensation to adjust their molecular structure including aliphatic hydroxyl groups, amine groups, sulfonic groups, carboxyl groups, sulfhydryl groups and alkyl chains. The influences of functional groups and molecular weight of lignins on the radical scavenging efficiency for oxyradicals, hydroxyl radicals, DPPH and protecting DNA are also investigated. The mechanisms of lignins for scavenging radicals should be clarified by investigating the dynamics of scavenging radicals. This research will lead to providing a serial lignin based antioxidants with low toxicity and high efficiency for the potential usages in food, cosmetics and pharmacopedics. It is very important to the high value added utilization of lignin as a biomass resource and is also meaningful for the sustainable development of our society and benefit to the environment.

木质素是储量最丰富的聚多酚生物质资源，作为天然抗氧化剂具有安全、低毒和稳定性好的优点。但木质素是一种高度交联、3D网状结构的复杂高分子，其氢原子转移能力和给电子能力弱，抗氧化活性难以与合成类抗氧化剂相比。本项目拟在前期研究基础上，采用化学手段对工业碱木质素、水解木质素进行系统的结构设计，研究其抗氧化构效关系，并以木质素模型化合物为参考对象。通过微波氧化、脱甲氧基化、羟甲基化、Mannich反应、磺甲基化、羧甲基化、巯基化、接枝共聚、缩合反应、配位反应等设计合成一系列木质素衍生物，探索环境友好的新型木质素天然聚多酚抗氧化剂的制备。采用化学体系法和模拟生物体系法对木质素衍生物的抗氧化活性进行综合评价和构效关系研究。研究结果将为新型木质素抗氧化剂在食品、保健品、医药品等领域的应用提供科学基础，为木质素的利用开辟一条新路径，对有效利用广西特色资源、环境保护、延长产业链和提高产品附加值等有重要意义。

研究和寻求对人体友好无毒的高效天然抗氧化剂已成为当今生物医学、化学、药剂学等领域的重要课题之一。木质素是储量最丰富的聚多酚生物质资源，作为天然抗氧化剂具有安全、低毒和稳定性好的优点。但木质素是一种高度交联、3D 网状结构的复杂高分子，其氢原子转移能力和给电子能力弱，抗氧化活性难以与合成类抗氧化剂相比。本项目着重采取化学手段对工业碱木质素、水解木质素进行系统的结构设计，通过微波氧化、酚化、Mannich 反应、 磺甲基化、羧甲基化、缩合反应、配位反应等设计合成一系列木质素衍生物，建立了木质素的改性路线。采用化学体系法（DPPH，ABTS，HRSA）和模拟生物体系法（抑制DNA的氧化损伤）对木质素衍生物的抗氧化活性进行综合评价和构效关系研究。研究结果表明木质素的酚羟基、分子量、取代基等对其抗氧化活性有重要影响：酚羟基对抗氧化活性有正向促进作用；分子量越小其抗氧化活性越高；引入供电子基团可促进其抗氧化活性，而斥电子基团则会降低其抗氧化活性。在碱木质素和水解木质素系列改性产物中，以酚化改性产物的抗氧化活性最高，尤其是碱催化酚化改性可在大大降低酚用量的情况下提高改性产物酚羟基的含量，其抗氧化活性达到了合成抗氧化剂BHA、BHT的水平。通过在不同溶剂体系中（中性、质子型和非质子型溶剂）的DPPH自由基清除动力学研究发现在质子型溶剂中与自由基的反应速率常数增加，证明木质素酚类的抗氧化机理属于氢原子转移机理，属于主抗型。由于木质素来源广泛，价格便宜，项目研究成果为木质素的高价值利用开辟了一条新路径，对有效利用木质素资源、环境保护、延长产业链和提高产品附加值等有重要意义。