微生物多糖可德胶的区域选择性取代及其衍生物的功能性和流变学研究

Polysaccharides are important natural biopolymers with special conformation and structures, functions and physicochemical properties. Chemical modification of polysaccharides to improve their functionality and find their industrial applied prospect have attracted great interests in scientific and industrial fields. The aim of the project is to develop a series of novel and functional ester and ether derivatives from the microbial polysaccharide of bioactive curdlan, a beta-1, 3-glucan, different from beta-1, 4-glucan of cellulose and alpha-1, 4-glucan of starch, by using regioselective substitution, and thereby study their molecular conformation, rheological properties and structure-property relationship. The driving force and mechanism of conformation change will be clarified by investigating the influence of regioselective substitution at different positions in anhydroglucose unit on the triple-helix dissociation and single-helix self-assembly behaviour of curdlan. We will also investigate the effect of degree of substitution and distribution of substitution on the molecular conformation and properties, and further elaborate the gelation mechanism and solution behaviour of curdlan. To meet the needs of the national economic development and the requirements of industrial applications, new functionalities of the regioselectively substituted curdlan derivatives, especially rheological properties such as thickening, emulsification, and interfacial activity/viscoelasticity that native curdlan does not possess and have tremendous practical values largely and widely in many industrial fields will be explored. The structure-property relationship of regioselectively substituted curdlan derivatives will provide theoretical basis and technical support for the development and new applications of microbial polysaccharide derivatives.

多糖是一类十分重要的天然大分子，具有独特的构象结构、功能以及物化性质。对多糖进行化学改性以提高其功能性和发掘其工业应用前景一直广受关注。本项目拟采用区域选择性取代方法，发展一类有别于beta-1, 4型纤维素和alpha-1, 4型淀粉的，基于具有生物活性的beta-1, 3型葡聚糖可德胶的典型功能性酯类和醚类新产物，并研究其分子构象、流变学性质及构效关系。通过揭示不同位点取代对螺旋结构解离和自组装的影响，阐明分子构象变化的机理；通过精确调控取代分布和取代度揭示不同取代方式对分子构象和性能的影响，阐明凝胶机理和溶液行为。服务于国民经济发展和相关工业化应用的需求，发掘可量大面广应用的可德胶衍生物的新功能，特别是从流变学角度发掘原可德胶不具有的、有重大应用价值的增稠性、乳化性、界面活性和粘弹性，建立可德胶衍生物结构与性能之间的关系，为新型微生物葡聚糖衍生物的开发和应用提供理论依据和技术支持。

化学改性和分子构象研究是多糖大分子研究和应用发展的重要内容，分子构象和性能有本质的内在关系。通过化学改性，可改善多糖的既有性质或赋予其新功能，而既有性能的提高或新功能的获得又与改性导致的分子构象及构象变化密切相关。可德胶多糖是具有独特流变学性质和生物活性的葡聚糖，对其化学修饰可以诱导修饰位点附近的构象变化，从而影响其独特的理化性质和生物活性。本项目着重开展了多糖化学改性特别是可德胶多糖的羧甲基化和烷基化研究，合成了一系列不同分子量、不同取代度、不同取代分布的多糖衍生物。通过多种技术手段，详细研究了这些改性产物的结构、溶液和凝胶的流变学性质和生物相容性；系统分析了不同醚化可德胶衍生物的区域取代以及取代导致的不同分子构象和构象变化，揭示了多糖衍生物特别是可德胶衍生物构效关系的本质性影响因素和规律；从流变学角度发掘了有重要应用价值的增稠性、乳化性、界面活性和粘弹性性质，建立起了衍生物结构与性能之间的关系；提出了有别于可德胶物理交联凝胶传统制备方法的新方法和新机理；揭示了多糖分子结构参数-流变学性质-功能特性之间的关系和规律，并在多个领域开展了多糖及其衍生物作为的应用研究，以期为工业化实际应用提供坚实的理论依据和技术支持。