BIO-ANTIOXIDATION MECHANISM AND PHSIOLOGICAL FUNCTION OF L-ASCORBIC ACID

L抗坏血酸又称维生素C，是一种必需的水溶性营养素，广泛参与胶原蛋白的合成、芳香氨基酸的代谢、脂质代谢、免疫系统的激活和细胞增殖。然而，AsA的生物学功能的详细机制仍不清楚。此外，由于其极强的还原性能，ASA被广泛用作食品储存和加工中的抗氧化剂。近年来，有关抗氧化功能与生物功能之间关系的研究报道较多，但对二者之间关系的详细描述尚不清楚。为了阐明AsA的生物学功能和抗氧化功能之间的详细关系，我们采用了实验和计算化学的方法来阐明这些悬而未决的问题。首先，计算了ASA及其相关化合物的优化结构，并通过半经验分子轨道计算得到了电子密度、偶极矩、生成热等物理化学参数。阐明了AsA分子与三重态氧分子的自氧化反应机理。对不同的自氧化产物苏氨酸和草酸进行了鉴定，证实了ASA在自氧化过程中产生了超氧阴离子，并在此基础上提出了一种新的ASA自氧化机理。

L-Ascorbic Acid(ASA), which is also called Vitamin C, is an essential water soluble nutrient, and is widely known to be involved in the blo-synthesis of collagen, metabolism of aromatic amino acids, lipid metabolism, activation of immune system and cell multiplication. However, the detailed mechanism of the biological function of ASA is still unknown. Furthermore, ASA is widely used as antioxidant in food storage and processing making use of its very strong reducing property. Recently, there have been many reports which describe the relationship between the antioxidant function and biological function, however the details of their relationship is still unclear. In order to clarify the detailed correlation between the biological function and antioxidant function of ASA, both experimental and computational chemical methods were applied to elucidate these unresolved problems. First, the optimized structures of ASA and its related compounds were calculated, and other various physico-chemical parameters, such as electron densities, dipole moment, heat of formation etc., were obtained by semi-empirical molecular orbital calculations. The auto-oxidation reaction mechanism of ASA molecule with triplet oxygen molecule was also clarified. Identification of various auto-oxidation products including threonic acid and oxalic acid were made and confirmation of the production of super-oxide anion during the auto-oxidation of ASA was also made, Based on the results obtained in this study, a new auto-oxidation mechanism of ASA was proposed.