How Is the Oxidation Related to the Tautomerization in Vitamin B9?
How Is the Oxidation Related to the Tautomerization in Vitamin B9?
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氧化与维生素 B9 的互变异构有何关系？
DOI：
10.1021/acs.jpca.1c06678
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
Yamazaki Shoko
中科院分区：
文献类型：
--
作者：
Yamabe Shinichi;Tsuchida Noriko;Yamazaki Shoko
采用密度泛函理论研究了维生素B 9 [叶酸（FA）]中内酰亚胺-内酰胺互变异构与自由基清除反应之间的关系。6-甲基蝶呤也被用于详细分析各种反应路径。对于蝶呤，与两个水分子（n= 2）的互变异构化的过渡态被计算为最低的活化能。即使加入了外层水分子，n = 2的质子转移回路也保持不变（没有中断），n= 2 + 2，2 + 4，2 + 8和2 + 14。在6-甲基蝶呤+（H2O）2+ HO·的氧化反应中，HO·的自由基性质随着C-O → H → O → H → O → H → OH质子转移而沿着转移到蝶呤环上。对于氧化剂（OX·）= HO·、Cl_3C-O_2·、N_3·或SO_4-·，通常得到电子转移（蝶呤环→ OX·）和伴随的质子通过水二聚体转移的模式。排除了氢原子转移机理。两种含有FA分子内−C（NOO）-OH···N氢键的褶皱构象的稳定性与线性构象相似。计算了三种构象异构体的互变异构和氧化反应。
The relationship between the lactim–lactam tautomerization and the free-radical scavenging reaction in vitamin B9 [folic acid (FA)] was investigated by density functional theory calculations. 6-Methylpterin was also adopted for the detailed analyses of various reaction paths. For pterin, the transition state of the tautomerization with two water molecules (n= 2) was calculated to be of the lowest activation energy. The proton-transfer circuit ofn= 2 is retained (not broken) even with the addition of outer water molecules,n= 2 + 2, 2 + 4, 2 + 8, and 2 + 14. At the oxidation of the system composed of 6-methylpterin + (H2O)2+ HO•, the radical character of HO•is directly transmitted to the pterin ring along with the C–O → H → O → H → O → H → OH proton transfer. The patterns of the electron transfer (pterin ring → OX•) and the concomitant proton transfer via the water dimer were commonly obtained for the oxidant (OX•) = HO•, Cl3C–O2•, N3•, or SO4–•. The hydrogen atom transfer mechanism was ruled out. Two conformations of the puckered form with the −C(═O)–OH···N intramolecular hydrogen bonds of FA were found to have the stability similar to that of the linear conformer. Both the tautomerization and the oxidation were calculated to occur competitively in the three conformers.
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