Functionalization of cellulosic materials by TEMPO-mediated oxidation under aqueous media

答：在TEMPO介导的氧化过程中，必须尽可能地控制纤维素的解聚，以制备不同分子量的水溶性纤维素酸(β-1，4-连接的聚葡萄糖醛酸)。然后通过改变加入试剂的组合，研究了不同条件下纤维素酸在氧化过程中的解聚机理。以水相GPC柱为色谱柱，0.1N氯化钠为洗脱液，用尺寸排除色谱法测定产物的相对分子质量。结果表明，在由TEMPO和NaBRO组成的氧化介质中，氧化过程中生成的一些自由基可能会导致明显的解聚。在氧化介质中加入自由基清除剂叔丁基苯酚可以在一定程度上避免解聚反应的发生，而氯化镁和次亚硫酸钠均无此作用。C.以分子量较大的再生纤维素TempO为起始原料，如铜铵溶液中空纤维，可制得相对分子质量较高的纤维素酸。D.α-甲壳素、β-甲壳素、直链淀粉、支链淀粉、柯德兰和普鲁兰的C6伯羟基通过TEMPO催化氧化生成相应的水溶性多糖醛酸，纤维素酶将纤维素酸降解为葡萄糖醛酸，使纤维素酸兼具生物降解性和生物降解性。

A.Depolymerization of cellulose during the TEMPO-mediated oxidation must be controlled as possible in order to prepare water-soluble cellouronic acid (β-1, 4-linked polyglucuronic acid) having various molecular weights. Then depolymerization mechanism of cellouronic acid during the oxidation was studied under various conditions by changing combinations of the reagents added. Molecular weights of the products were determined by size exclusion chromatography using aqueous GPC columns and 0.1N NaCl as an eluent. The results showed that some radicals formed in the oxidation medium consisting of TEMPO and NaBrO during the oxidation were likely to bring about remarkable depolymerization. β-Elimination had little influence on the depolymerization.B.The addition of t-butylphenol as a radical scavenger to the oxidation medium could avoid the depolymerization to some extent, although neither MgCl_2 nor sodium dithonite had the effect.C.When higher molecular weight regenerated celluloses, such as hollow fibers prepared from linters by cupriammonium solutions, were used as the starting materials for the TEMPO-mediated oxidation, correspondingly higher molecular weight cellouronic acids were prepared.D.α-Chitin, β-chitin, amylose, amylopectin, curdlan and pullulan were selectively oxidized at their C6 primary hydroxyl groups to give the corresponding water-soluble polyuronic acids quantitatively by the TEMPO-mediated oxidation.E.Cellouronic acid was hydrolyzed to glucuronic acid by crude cellulase treatments, and thus cellouronic acid had both biodegradability and biometabolizability.