Hartings Matthew R, Kurnikov Igor V, Dunn Alexander R, Winkler Jay R, Gray Harry B, Ratner Mark A
Beckman Institute, California Institute of Technology, Pasadena, CA 91125.
Coord Chem Rev. 2010 Feb 1;254(3):248-253. doi: 10.1016/j.ccr.2009.08.008.
We report a quantitative theoretical analysis of long-range electron transfer through sensitizer wires bound in the active-site channel of cytochrome P450cam. Each sensitizer wire consists of a substrate group with high binding affinity for the enzyme active site connected to a ruthenium-diimine through a bridging aliphatic or aromatic chain. Experiments have revealed a dramatic dependence of electron transfer rates on the chemical composition of both the bridging group and the substrate. Using combined molecular dynamics simulations and electronic coupling calculations, we show that electron tunneling through perfluorinated aromatic bridges is promoted by enhanced superexchange coupling through virtual reduced states. In contrast, electron flow through aliphatic bridges occurs by hole-mediated superexchange. We have found that a small number of wire conformations with strong donor-acceptor couplings can account for the observed electron tunneling rates for sensitizer wires terminated with either ethylbenzene or adamantane. In these instances, the rate is dependent not only on electronic coupling of the donor and acceptor but also on the nuclear motion of the sensitizer wire, necessitating the calculation of average rates over the course of a molecular dynamics simulation. These calculations along with related recent findings have made it possible to analyze the results of many other sensitizer-wire experiments that in turn point to new directions in our attempts to observe reactive intermediates in the catalytic cycles of P450 and other heme enzymes.
我们报告了对通过结合在细胞色素P450cam活性位点通道中的敏化剂导线进行远程电子转移的定量理论分析。每条敏化剂导线由对酶活性位点具有高结合亲和力的底物基团组成，该基团通过桥连脂肪族或芳香族链与钌二亚胺相连。实验表明，电子转移速率对桥连基团和底物的化学组成都有显著依赖性。通过结合分子动力学模拟和电子耦合计算，我们表明通过全氟芳香族桥的电子隧穿是由通过虚拟还原态增强的超交换耦合促进的。相比之下，通过脂肪族桥的电子流动是通过空穴介导的超交换发生的。我们发现，少数具有强供体-受体耦合的导线构象可以解释以乙苯或金刚烷终止的敏化剂导线的观测电子隧穿速率。在这些情况下，速率不仅取决于供体和受体的电子耦合，还取决于敏化剂导线的核运动，因此需要在分子动力学模拟过程中计算平均速率。这些计算以及相关的最新发现使得分析许多其他敏化剂导线实验的结果成为可能，这些结果反过来又为我们观察P450和其他血红素酶催化循环中的反应中间体的尝试指明了新的方向。
