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首页> 外文期刊>Inorganic Chemistry: A Research Journal that Includes Bioinorganic, Catalytic, Organometallic, Solid-State, and Synthetic Chemistry and Reaction Dynamics >Ruthenium bisbipyridine complexes of horse heart cytochrome c: Characterization and comparative intramolecular electron-transfer rates determined by pulse radiolysis and flash photolysis
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Ruthenium bisbipyridine complexes of horse heart cytochrome c: Characterization and comparative intramolecular electron-transfer rates determined by pulse radiolysis and flash photolysis

机译:马心脏细胞色素c的钌双联吡啶配合物:脉冲辐射分解和快速光解法测定的表征和比较分子内电子传输速率

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摘要

The reaction of [Ru(bpy)(2)L(H2O)](2+) (bpy = 2,2'-bipyridine, L = imidazole, water) with reduced horse heart cytochrome c results in coordination of [Ru-II(bpy)(2)L] at the His 33 and His 26 sites. Coordination at the His 33 site gave a diastereomeric [Ru-II(bpy)(2)L]-His-cyt c(II) mixture favoring the Il-Ru form regardless of the substituent on the bipyridine ligands, while substitution at the more buried His 26 site gave an isomeric distribution that varies according to the substituent on the bipyridine ligands. The diastereomeric aquoproteins (L = H2O) are distinguished by their redox potentials and their conversion to the corresponding fluorescent imidazole proteins. Intramolecular electron transfer between the reduced ruthenium bipyridine and cyt c(III) in [Ru-II(bpy(.))(bpy)L]-His33-cyt c(II) was determined by reductive pulse radiolysis using the aqueous electron as a reducing agent, k(ret) = (2.0 +/- 0.3) x 10(5) s(-1), and k(ret) is independent of the sixth ligand L = H2O imidazole. In addition, the rate constant for intramolecular electron transfer from cyt c(II) to the ruthenium(III) center in [Ru-III(bpy)(2)L]-His33-cyt c(II)) was determined by oxidative pulse radiolysis using azide and carbonate radicals. This rate is very sensitive to the nature of the sixth ligand. When L = H2O, the intramolecular electron-transfer rate for the major diastereomer Lambda-cis-[Ru-III (bpy)(2)(H2O)]-His33-cyt c(II) is k = 1.1 x 10(4) s(-1) and is independent of pH between 5.6 and 8.3. The minor Delta-cis-[Ru-III(bpy)(2)(H2O)]-His33-cyt c(II) isomer has pH-dependent electrochemistry and a lower rate of intramolecular electron transfer. Complete conversion from L = H2O to L = imidazole is slow, requiring more than 7 days in 1 M imidazole. A lower limit (k > 2 x 10(6) s(-1)) for the intramolecular electron-transfer rate constant in [Ru-III(bpy)(2)(L)]-His33-cyt c(II), L = imidazole, could be obtained by pulse radiolysis in the absence of the slower reacting aquo species. This observation is in agreement with the value of 3 x 10(6) s(-1) measured by flash photolysis. Earlier pulse radiolysis experiments primarily measured the aquoligated ruthenium protein, while the flash photolysis experiments measured the imidazole-ligated fraction because it is the only species oxidatively quenched in the photoinduced reactions. Intramolecular electron-transfer reactions for a new series of ruthenium bipyridine complexes, [Ru(dabpy)(2)L]-His33-cyt c proteins (dabpy = 4,4'-diamino-2,2'-bipyridine ) (L imidazole, pyridine, isonicotinamide and pyrazine), proceed with lower driving force, resulting in slower rate constants amenable to measurement by oxidative pulse radiolysis. The electron-transfer rate constants for this series spanned a wide range of the Marcus log k vs Delta G plot. [References: 23]
机译:[Ru(bpy)(2)L(H2O)](2+)(bpy = 2,2'-联吡啶,L =咪唑,水)与还原的马心脏细胞色素c的反应导致[Ru-II (bpy)(2)L]在他的33和26个地点。在His 33位点的配位得到了非对映异构的[Ru-II(bpy)(2)L] -His-cyt c(II)混合物,无论联吡啶配体上的取代基如何,都具有Il-Ru形式,而在更多位置处具有取代基埋藏在他的26位上的异构体的分布随联吡啶配体上的取代基而变化。非对映体水基蛋白(L = H2O)的特征在于其氧化还原电势及其转化为相应的荧光咪唑蛋白的能力。通过还原性脉冲辐射分解,使用水电子作为离子,测定还原的钌联吡啶与[Ru-II(bpy(。))(bpy)L] -His33-cyt c(II)中的cyt c(III)之间的分子内电子转移。还原剂,k(ret)=(2.0 +/- 0.3)x 10(5)s(-1),k(ret)与第六个配体L = H2O咪唑无关。此外,通过氧化脉冲确定分子内电子从cyt c(II)转移到[Ru-III(bpy)(2)L] -His33-cyt c(II))中的钌(III)中心的速率常数。使用叠氮化物和碳酸盐自由基进行辐射分解。该速率对第六配体的性质非常敏感。当L = H2O时,主要非对映异构体Lambda-cis- [Ru-III(bpy)(2)(H2O)]-His33-cyt c(II)的分子内电子转移速率为k = 1.1 x 10(4) s(-1),且不受pH值介于5.6和8.3之间的影响。较小的Delta-顺式-[Ru-III(bpy)(2)(H2O)]-His33-cyt c(II)异构体具有pH依赖的电化学性质,且分子内电子转移的速率较低。从L = H2O到L =咪唑的完全转化很慢,在1 M咪唑中需要7天以上。 [Ru-III(bpy)(2)(L)]-His33-cyt c(II)中分子内电子传递速率常数的下限(k> 2 x 10(6)s(-1)), L =咪唑,可通过在不发生较慢反应的水族物种的情况下通过脉冲辐射分解获得。该观察结果与通过快速光解法测得的3 x 10(6)s(-1)值一致。较早的脉冲辐射分解实验主要测量水合钌蛋白,而快速光解实验则测量与咪唑连接的馏分,因为它是光诱导反应中唯一被氧化猝灭的物质。一系列新的钌联吡啶配合物[Ru(dabpy)(2)L] -His33-cyt c蛋白(dabpy = 4,4'-diamino-2,2'-bipyridine)(L咪唑)的分子内电子转移反应(例如吡啶,异烟酰胺和吡嗪),以较低的驱动力进行,导致较慢的速率常数,该速率常数适合通过氧化脉冲辐射分解进行测量。该系列的电子传输速率常数涵盖了Marcus log k与Delta G曲线的较大范围。 [参考:23]

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