Quinones are widely distributed compounds in nature. Of these, ortho-quinones are found to be involved in the pathogenic mechanism of Parkinson's disease, in oxidative deaminations to free-radical redox reactions, and as intermediates in the pathways implicated in the carcinogenicity of 2,3- and 3,4-catechol estrogens. Addition of MgCl2 to solutions of the hydrophobic ortho-quinones, 1,10-phenanthroquinone (PHQ) and beta-lapachone (LQ) enhances ascorbate oxidation in the absence or presence of large unilamellar vesicles (LUVs) of the neutral lipid dimyristoylphosphatidylcholine (DMPC), although initial rates of ascorbate oxidation are smaller in the presence of lipid as compared to its absence. Addition of this salt to solutions of the para-quinone 1,4-naphthoquinone (NQ) did not affect the ascorbate rate of oxidation in the absence or presence of DMPC. Addition of MgCl2 to semiquinone solutions of PHQ or LQ in the presence or absence of DMPC increases semiquinone stability, as detected from the semiquinone disproportionation equilibrium displacement to semiquinone formation. Furthermore, MgCl2 increases the partition of the ortho-semiquinones into the aqueous phase, although no such effect is observed for the semiquinone of NQ. For all the quinones under study, smaller rates of ascorbate oxidation and of semiquinone equilibrium concentration occur in the presence of negatively charged LUVs composed of an equimolar mixture of DMPC and dimyristoylphosphatidic acid DMPA. Ascorbate oxidation rate enhancements correlate with an increase in semiquinone concentration with addition of MgCl2, in the absence or presence of neutral lipid. This observation favors the proposition that ascorbate oxidation rate increases are caused by semiquinone thermodynamic stabilization. Thus, the ascorbate oxidation rate enhancement by MgCl2 in solutions containing hydrophobic ortho-quinones is still possible in systems with hydrophobic environments analogous to that of DMPC.

中文翻译：

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邻醌增强抗坏血酸氧化。脂质电荷和镁阳离子的综合作用

醌类是自然界中分布广泛的化合物。其中，发现邻苯醌参与帕金森病的发病机制、氧化脱氨作用到自由基氧化还原反应，以及作为与 2,3- 和 3,4-邻苯二酚致癌性有关的途径的中间体雌激素。在中性脂质二肉豆蔻酰磷脂酰胆碱 (DMPC) 的大单层囊泡 (LUV) 存在或不存在的情况下，将 MgCl2 添加到疏水性邻醌、1,10-菲醌 (PHQ) 和 β-拉帕酮 (LQ) 的溶液中可增强抗坏血酸的氧化，尽管与不存在脂质相比，存在脂质时抗坏血酸氧化的初始速率较小。将这种盐加入对醌 1 的溶液中，在不存在或存在 DMPC 的情况下，4-萘醌 (NQ) 不影响抗坏血酸的氧化速率。在存在或不存在 DMPC 的情况下，将 MgCl 2 添加到 PHQ 或 LQ 的半醌溶液中会增加半醌稳定性，如从半醌歧化平衡位移到半醌形成中检测到的。此外，MgCl2 增加了邻半醌在水相中的分配，尽管对 NQ 的半醌没有观察到这种影响。对于正在研究的所有醌，在由 DMPC 和二肉豆蔻酰磷脂酸 DMPA 的等摩尔混合物组成的带负电荷的 LUV 存在下，发生较小的抗坏血酸氧化和半醌平衡浓度。抗坏血酸氧化速率的提高与加入 MgCl2 后半醌浓度的增加有关，在不存在或存在中性脂质的情况下。该观察结果支持抗坏血酸氧化速率增加是由半醌热力学稳定性引起的命题。因此，在疏水环境类似于 DMPC 的系统中，MgCl2 在含有疏水邻醌的溶液中提高抗坏血酸氧化速率仍然是可能的。