Absorption characteristics of the semiquinone free radicals formed by one-electron reduction of quinizarin (QH2), 5-methoxyquinizarin (MQH2) and quinizarin 2-sulphonate (QSH2) have been studied by pulse radiolysis in a mixed solvent system consisting of water, isopropyl alcohol and acetone. Second-order rate constants have been determined for the reactions of (CH3)2ĊOH with the quinones, of the semiquinones
在由
水组成的混合溶剂系统中,通过脉冲辐解研究了通过
奎宁素(QH 2),5-甲氧基奎尼嗪(MQH 2)和奎尼嗪林2-
磺酸(QSH 2)的单电子还原形成的半醌自由基的吸收特性。,
异丙醇和
丙酮。对于(CH 3)2 = OH与醌,半醌与O 2以及半醌彼此的反应,已经确定了二阶速率常数。单电子还原电位(vs. NHE)对于QH 2为E 1 7 = –269 mV ,对于MQH 2为–333 mVQSH 2为–298 mV 。它们根据母体醌和半醌的p K a值随pH而变化。自由基在大约5-11的pH范围内是稳定的。稳定常数是在pH8.5最高(ķ小号为QH≈0.09)2,在pH≈9.5 QSH 2(ķ小号≈10)和pH≈10.8 MQH 2(ķ小号分别≈4.8),。计算半醌的单电子还原电位和醌的双电子还原电位分别为E 2 7 = –188,–192和–216 mV,以及E m 7对于QH 2,MQH 2和QSH