Chemical characteristics of dehydro-L-ascorbic acid
Chemical characteristics of dehydro-L-ascorbic acid
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DOI：
10.1271/bbb.64.1651
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发表时间：
2000-08-01
影响因子：
1.6
通讯作者：
Nishikawa, Y
中科院分区：
文献类型：
--
作者：
Kurata, T;Nishikawa, Y
脱氢- l -抗坏血酸（DAA）在水溶液中主要以C2水合双环形式(5)存在，单环形式的DAA(3)是AA氧化后的预期反应产物，但尚未通过核磁共振光谱观察到。采用半经验分子轨道法（MOPAC）研究了3生成5的机理和5的稳定性。结果表明，质子化反应是形成5的关键步骤，因此，在中性或微碱性的生理条件下，5的形成更为困难。然而，通过核磁共振证实，即使在非常接近生理条件的中性或微碱性状态下，酶促氧化AA后水溶液中存在的DAA的优势形态也被证实为5，尽管不能完全排除其他极低浓度DAA的存在可能性。
Dehydro-L-ascorbic acid (DAA) exists mainly in its C2 hydrated bicyclic form (5) in an aqueous solution, and monocyclic DAA (3), which is the expected reaction product immediately after the oxidation of AA, has not been observed by NMR spectroscopy, The formation mechanism for 5 from 3 and the stability of 5 were examined by the semi-empirical molecular orbital method (MOPAC). It was indicated that the protonation reaction was the key step in the formation of 5, therefore, the formation of 5 Is thought to be more difficult under physiological conditions which mostly involve in the neutral or slightly alkaline state. However, by NMR, it was confirmed that, even In a neutral or slightly alkaline state very close to physiological conditions, the predominant form of DAA existing in an aqueous solution immediately after the enzymatic oxidation of AA was confirmed to be 5, although the possible existence of other farms of DAA at very low concentrations could not be completely excluded.