天然聚多糖的溶解机理及溶液性质

21世纪"绿色"化学已成为各国科学界和工业界研究与开发的方向.天然高分子中纤维素、甲壳素等聚多糖来源丰富,是重要的可再生资源,也是未来主要的化工原料之一.由于大量的分子内和分子间氢键,它们的溶解长期以来都是非常棘手的问题.另一方面,聚多糖的结构非常复杂,只有弄清楚其链构象和溶液性质,才可能进行合理的分子设计,实现其更好的应用.本文简要介绍了本课题组用碱/尿素水体系低温溶解纤维素和甲壳素等天然高分子的机理和溶液中分子链构象,以及活性多糖在水溶液中的链构象和溶液性质的研究进展.

Dissolution Mechanism and Solution Properties of Natural Polysaccharides

Naturalpolymers such as cellulose,chitin,chitosan and other fungi polysaccharides are derived from renewable resources,which is one kind of main chemical raw materials in the future.The numerous intermolecular and intramolecular hydrogen bonds have made their dissolution difficult in most common solvents.Moreover,their structures are very complex.Clarifying their chain conformation and solution properties is essential in designing their molecular structure,realizing more sophisticated applications.This article introduces the recent results about low temperature dissolution of cellulose,chitin and chitosanin in alkali/urea aqueous solution and their chain conformation and solution properties,as well as solution properties of the active polysaccharides.Cellulose can be dissolved in 7 wt％ NaOH-12 wt％ urea aqueous solution with precooling (-12 ℃) within 2 min,whereas chitin can be dissolved in a mixture of NaOH,urea and water atweight ratio of 11:4:85 at-30 ℃.The weight average molecular weight (Mw),radii of gyration (z),hydrodynamic radii ((Rh)z),the structure-sensitive parameter (ρ) and persistent length (q) values of the natural macromolecules were determined,indicating the worm-like stiff chain conformation of cellulose,chitin and chitosan.Furthermore,TEM,cryo-TEM and AFM images provide direct observation of the extended chain conformation and the visualized nanofibers constructed from the stiff chains in parallel aggregation in the aqueous solution.A water-soluble neutral polysaccharide (AF1) was extracted from A.auricula-judae was and identified as a high branched β-(1 →3)-D-glucan.AF1 was proved to exist as stiff chains in water,and as flexible chains in dimethylsulfoxide (DMSO).The high-branched glucan was used to self-assemble into hollow nanofibers with apparent average diameter of 92 nm.Lentinan,a β-(1→3)-D-glucan isolated from Lentinus edodes,exhibited good water solubility,and existed as a triple-helical conformation in the aqueous solution at 25 ℃.AFM images confirmed that the triple-helical chain conformation of lentinan with high Mw formed wormlike patterns in aqueous solution at 25 ℃.Water-insoluble polysaccharide (TM3a),extracted from sclerotia of Pleurotus tuber-regium,was identified as ahyperbranched β-D-glucan.The degree of branching of TM3a was 65.5％.The dependence of intrinsic viscosity (η]),radius of gyration ((S2)z1/2),and hydradynamic radius (Rh) on the weight-average molecular weight (Mw) was studied,indicating that TM3a existed as a compact chain conformation with a sphere-like structure in LiCl/DMSO solution.Furthermore,TEM image provided direct observation of the sphere-like pattern of the chain conformation.