CYCLIC VOLTAMMETRY STUDIES OF METALLOFLAVIN COMPLEXES IN AQUEOUS SOLUTION
CYCLIC VOLTAMMETRY STUDIES OF METALLOFLAVIN COMPLEXES IN AQUEOUS SOLUTION
复制标题
水溶液中金属黄素配合物的循环伏安法研究
DOI：
10.1002/chin.198202309
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发表时间：
1981
期刊：
影响因子：
--
通讯作者：
M. G. Dowling
中科院分区：
文献类型：
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作者：
M. Clarke;M. G. Dowling
报道了 10-甲基异咯嗪、3, 10-二甲基异咯嗪和核黄素的稳定四氨钌 (II) 配合物的电化学研究。虽然这些复合物的某些特性与金属稳定的黄酮半醌相似，但这些复合物最好配制为 Run-Fl0I，而不是 Rum-Fl·。黄素配体的还原通过两个连续的单电子步骤进行，而不是通过游离黄素在类似条件下表现出的明显的双电子过程进行。这似乎主要是由于完全还原的黄素的不稳定造成的。 pKa 值的测量通过分光光度法确定，并用于根据作为 pH 函数的实验还原电位数据进行推断。金属与异咯嗪环的 N-5 和 0-4 位的配位可调节黄素的酸碱行为，从而在发生电子转移而不同时发生质子转移的情况下出现不同的 pH 区域。当黄酮半醌络合物在 N1 位被 50% 质子化时，两个单电子黄素还原电势之间出现最小间隔。 Ru (II) 异常高的氧化电位表明金属向异咯嗪环提供了大量的电子密度。由于复合物的时间依赖性吸附和还原复合物解离后游离黄素的相互作用，存在几种类型的吸收现象。这些过程是从本体溶液氧化还原对中识别和辨别的。从蛋白质控制黄素氧化还原行为的可能机制方面讨论了结果。
Electrochemical studies of stable tetraammineruthenium (II) complexes of 10-methylisoalloxazine, 3, 10-dimethylisoalloxazine, and riboflavin are reported. While approximating metal-stabilized flavosemiquinones in some of their properties, these complexes are best formulated as Run-Fl0I rather than Rum-Fl·. The reduction of the flavin ligand is shown to proceed through two successive single-electron steps rather than by the apparent two-electron process exhibited by the free flavins under similar conditions. This appears to be largely dueto destabilization of the fully reduced flavin. Measurements of the pKa values were determined spectrophotometrically and are used toextrapolate from experimental reduction potential data as a function of pH. Coordination of the metal to the N-5 and 0-4 positions of the isoalloxazine ring modulates the acid-base behavior of the flavin so that distinct pH regions emerge where electron transfer occurs without simultaneous proton transfer. A minimum separation between the two one-electron flavin reduction potentials occurs when the flavosemiquinone complex is 50% protonated at the Nl position. An unusually high oxidation potential for the Ru (II) indicates substantial donation of electron density from the metal onto the isoalloxazine ring. Several types of absorption phenomena are present owing to time-dependent adsorptions of the complex and interactions of the free flavin following dissociation of the reduced complex. Such processes are identified and discerned form bulk solutionredox couples. The results are discussed in terms of possible mechanisms for protein control of flavin redox behavior.