Vectorial Photoinduced Electron-Transfer and Charge Separation in a Zn(II)-Protoporphyrin−Bipyridinium Dyad Reconstituted Myoglobin
Vectorial Photoinduced Electron-Transfer and Charge Separation in a Zn(II)-Protoporphyrin−Bipyridinium Dyad Reconstituted Myoglobin
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Zn(II)-原卟啉-联吡啶二元体重构肌红蛋白中的矢量光诱导电子转移和电荷分离
DOI：
10.1021/ja983773k
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发表时间：
1999
影响因子：
15
通讯作者：
I. Willner
中科院分区：
文献类型：
--
作者：
V. Heleg;and Tobias Gabriel;I. Willner
对蛋白质中长程电子转移的理解一直是广泛的理论和实验研究的主题。发现蛋白质环境6和结构参数7内的供体-受体距离4，5控制蛋白质系统中的电子转移速率。在光合反应中心的供体-受体单元的独特组织导致矢量电子转移和有效的电荷分离。8以前的研究工作是针对模拟光合作用反应中心的分子9、10或超分子11供体-受体二联体、三联体等组装体的组织。由于空间紧密的氧化还原产物的快速重组，许多分子二联体或三联体的空间灵活性防止电荷分离。在蛋白质系统中固定分子二联体（或三联体）可以使供体-受体对在结构上刚性化并导致电荷分离。重构的脱血红素蛋白，例如，脱肌红蛋白，与光敏锌（II）-原卟啉IX和受体位点的蛋白质的位点特异性共价连接，产生结构上定义的供体-受体系统。5此外，据报道，用Co（II）-原卟啉IX作为电子受体/催化中心和发色团与蛋白质的共价连接重建脱血红素蛋白质，12例如脱血红素肌红蛋白或脱血红素，以产生用于受控电子转移的有组织的组装体。Hamachi和Shinkai提出了构建供体-受体系统的另一种方法13，14，包括用发色团修饰的Fe（III）-原卟啉IX重建脱辅基肌红蛋白。这种方法被进一步开发的重构脱辅基肌红蛋白与发色团醌二联体15 a或与功能化的锌（II）-原卟啉IX能够产生一个非共价的，超分子复合物与电子受体。15 b在这里，我们希望报告用Zn-（II）-原卟啉IX-双-N，N '-二烷基-4，4'-联吡啶鎓，Zn-（II）-PV 2+，供体-受体二分体重建脱辅基肌红蛋白。我们揭示了在Ru（NH 3）6 3+作为次级电子受体存在下的重构蛋白质模拟了光合反应中心的功能。脱辅基肌红蛋白用Zn（II）-PV 2+重构，（1），方案1。供体-受体重构蛋白质的光激发产生三重激发态。图1示出了作为时间的函数的三重态衰减。通过比较Zn（II）-PV 2+-Mb中的三重态衰减速率与缺少受体单元的Zn（II）-原卟啉重构肌红蛋白Zn（II）-P-Mb的三重态衰减速率（τ），我们计算出分子内电子转移猝灭速率常数（eq 1）为kq）1.55× 106 s-1。三重态的猝灭导致了内-
The understanding of long-range electron transfer in proteins has been the subject of extensive theoretical1 and experimental2, 3 research efforts. The donor-acceptor distances4, 5 within the proteins environmental6 and structural parameters7 were found to control the electron-transfer rates in the protein systems. The unique organization of the donor-acceptor units in the photosynthetic reaction center leads to vectorial electron transfer and effective charge separation. 8 Previous research efforts were directed to the organization of molecular9, 10 or supramolecular11 donor-acceptor dyad, triad, and so forth assemblies which mimic the photosynthetic reaction center. The steric flexibility of many of the molecular dyads or triads prevents charge separation due to the rapid recombination of the spatially intimate redox products. Immobilization of molecular dyads (or triads) in protein systems could structurally rigidify the donor-acceptor pairs and lead to charge separation. Reconstitution of apo-hemoproteins, eg, apomyoglobin, with the photoactive Zn (II)-protoporphyrin IX and site-specific covalent linkage of acceptor sites to the proteins, yield structurally defined donor-acceptor systems. 5 Also, reconstitution of apo-hemo proteins, 12 eg, apo-myoglobin or apohemoglobin, with Co (II)-protoporphyrin IX, acting as an electron acceptor/catalytic center and the covalent attachment of a chromophore to the protein was reported to yield organized assemblies for controlled electron transfer. An alternative approach to construct donor-acceptor systems was addressed by Hamachi and Shinkai13, 14 and includes the reconstitution of apo-myoglobin with a chromophore-modified Fe (III)-protoporphyrin IX. This approach was further developed by the reconstitution of apo-myoglobin with a chromophore-quinone dyad15a or with a functionalized Zn (II)-protoporphyrin IX capable of generating a noncovalent, supramolecular complex with an electron acceptor. 15b Here we wish to report on the reconstitution of apo-myoglobin with a Zn-(II)-protoporphyrin IX-bis-N, N′-dialkyl-4, 4′-bipyridinium, Zn-(II)-PV 2+, donor-acceptor dyad. We reveal that the reconstituted protein in the presence of Ru (NH3) 6 3+, as secondary electron acceptor, mimics functions of the photosynthetic reaction center.Apo-myoglobin was reconstituted with Zn (II)-PV 2+,(1), Scheme 1. Photoexcitation of the donor-acceptor reconstituted protein yields the triplet excited state. Figure 1 shows the triplet decay as a function of time. By comparison of the triplet decay rate in Zn (II)-PV 2+-Mb to the triplet decay of Zn (II)-protoporphyrin reconstituted myoglobin, Zn (II)-P-Mb, lacking the acceptor units (τ) 110 s-1) we calculated the intramolecular electron-transfer quenching rate constant, eq 1, to be kq) 1.55× 106 s-1. The quenching of the triplet-state leads to intra-