低分子质量右旋糖酐的氧化改性及其理化特性

Oxidative Modification of Low Molecular Mass Dextran and Physicochemical Properties of Oxidized Dextran

以低分子质量右旋糖酐(m_w 5 400 Da)为原料在碱性条件下通过NaClO-NaBr将其氧化并对氧化后的产物进行理化性质分析。结果表明,随着氧化剂用量的增加,羧基含量逐渐增加,羧基质量分数的变化范围为0.05%～0.8%。高效液相色谱分析显示,右旋糖酐在氧化过程中随着氧化剂用量的增加会发生一定的降解。随着NaClO用量逐渐增加,氧化程度逐渐增加,NaClO过量使用,则氧化产物降解加剧。氧化的发生会破坏右旋糖酐的晶体结构,使其结晶区逐渐变为无定型区。核磁共振碳谱表明氧化产物的结构随着氧化剂的用量的增加氧化反应不仅发生在C1的半缩醛羟基上,还会发生在葡萄糖环的其他碳上。氧化改性提高了右旋糖酐的水溶性并且得到的产物具有良好的热稳定性。本研究在碱性条件下利用NaClO-NaBr将右旋糖酐中的羟基氧化为羧基,揭示了氧化产物理化性质的变化规律,研究结果为生物多糖的氧化改性提供了参考依据。

In the current work, low molecular mass dextran （with a molecular mass of 5 400 Da） was oxidized by NaClO-NaBr in a basic environment. The content of carboxyl groups gradually increased from 0.05% to 0.8% with increasing oxidant dosage. HPLC analysis indicated that dextran was degraded during the course of oxidation. Moreover, the degree of oxidation gradually increased with the increase of NaClO dosage, whereas the oxidized products were partly degraded into oligosaccharides when the dosage of NaClO was excessive. During the oxidation process the crystalline structures were gradually transformed into amorphous states. Structural characterization by 13C nuclear magnetic resonance （NMR） demonstrated that NaClO-NaBr oxidized the hemiacetal hydroxyl groups at the C1 position and other C positions of the glucose ring into carboxyl groups. This modication improved dextran solubility and the oxidized dextran exhibited good thermal stability. The oxidation of the hydroxyl groups of dextran into carboxyl groups under basic condition and the resulting changes in the physicochemical and structural properties of dextran provide a foundation for the oxidative modification of polysaccharides.