Thermodynamic and kinetic considerations for the reaction of semiquinone radicals to form superoxide and hydrogen peroxide.
Thermodynamic and kinetic considerations for the reaction of semiquinone radicals to form superoxide and hydrogen peroxide.
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DOI：
10.1016/j.freeradbiomed.2010.05.009
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发表时间：
2010-09-15
影响因子：
7.4
通讯作者：
Buettner, Garry R.
中科院分区：
文献类型：
--
作者：
Song, Yang;Buettner, Garry R.
醌/半醌/氢醌三联体（Q/SQ·−/H2 Q）代表了一类在广泛的生物过程中具有重要意义的化合物。这些氧化还原电对在中性pH水溶液中的半电池还原电位E°′为理解该三元组的热力学和动力学特征及其在体内的相关化学和生物化学提供了一个窗口。醌环上的取代基可以显著地影响“环上”的电子密度，从而显著地改变E°′。醌的E°′控制半醌与分子氧形成超氧化物的反应。在近中性pH下，氢醌的pKa是这些三元组成员的芳环中的电子密度（亲电性）的突出指标，因此是预测单电子和双电子对的半电池还原电位的极好工具，这又允许估计这些三元组的反应的速率常数。例如，H2 Q的pKa越高，还原电位越低，SQ·−与分子氧反应形成超氧化物的速率常数越高。然而，对苯二酚自氧化由去离子对苯二酚的浓度控制;因此，pKa越低，对自氧化的H2O越不稳定。催化剂，例如，金属和醌，可以加速氧化过程;通过去除超氧化物和增加醌的形成速率，超氧化物歧化酶可以加速氢醌的氧化，从而增加过氧化氢的流量。醌的主要反应是通过迈克尔加成与亲核试剂反应，例如与硫醇和胺反应。这些加成反应的速率常数也与E°′有关。因此，对苯二酚和E°′的pKa是这些三元组的化学性质的中心。
The quinone/semiquinone/hydroquinone triad (Q/SQ•−/H2Q) represents a class of compounds that has great importance in a wide range of biological processes. The half-cell reduction potentials of these redox couples in aqueous solutions at neutral pH, E°′, provide a window to understanding the thermodynamic and kinetic characteristics of this triad and their associated chemistry and biochemistry in vivo. Substituents on the quinone ring can significantly influence the electron density “on the ring” and thus modify E°′ dramatically. E°′ of the quinone governs the reaction of semiquinone with dioxygen to form superoxide. At near-neutral pH the pKa's of the hydroquinone are outstanding indicators of the electron density in the aromatic ring of the members of these triads (electrophilicity) and thus are excellent tools to predict half-cell reduction potentials for both the one-electron and two-electron couples, which in turn allow estimates of rate constants for the reactions of these triads. For example, the higher the pKa's of H2Q, the lower the reduction potentials and the higher the rate constants for the reaction of SQ•− with dioxygen to form superoxide. However, hydroquinone autoxidation is controlled by the concentration of di-ionized hydroquinone; thus, the lower the pKa's the less stable H2Q to autoxidation. Catalysts, e.g., metals and quinone, can accelerate oxidation processes; by removing superoxide and increasing the rate of formation of quinone, superoxide dismutase can accelerate oxidation of hydroquinones and thereby increase the flux of hydrogen peroxide. The principal reactions of quinones are with nucleophiles via Michael addition, for example, with thiols and amines. The rate constants for these addition reactions are also related to E°′. Thus, pKa's of a hydroquinone and E°′ are central to the chemistry of these triads.
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影响因子：
2.9
作者：
CORNELL, BA;KENIRY, MA;WESTERMAN, PW
通讯作者：
WESTERMAN, PW
影响因子：
5.1
作者：
BRUNMARK, A;CADENAS, E
通讯作者：
CADENAS, E
影响因子：
4.1
作者：
Amaro, AR;Oakley, GG;Robertson, LW
通讯作者：
Robertson, LW
影响因子：
15
作者：
BISHOP, CA;TONG, LKJ
通讯作者：
TONG, LKJ
DOI：
10.1016/0748-5514(86)90127-3
发表时间：
1986-01-01
期刊：
Journal of Free Radicals in Biology and Medicine
影响因子：
--
作者：
BUTLER J;HOEY B M
通讯作者：
HOEY B M