CHEMICAL MODELS FOR BIOLOGICAL ELECTRON TRANSFER

许多生物学过程在很大程度上依赖于电子 转移：氧化磷酸化，光合作用和氧化还原 金属酶的反应仅举几例。 如果基本 这些系统的理解是要实现，其显着的 必须解释效率和选择性。 的距离 氧化还原位点之间的分离和 电子转移反应被认为在 控制电子转移的速率。 该提案提出 一项广泛的研究计划，旨在探索 距离和驱动力对热电子速率的影响 金属之间的转移。 为此，一系列双核金属 将在桥连配体存在的地方制备配合物 饱和的结构，刚性地保持两种金属， 距离，并且该距离可以系统地 各种各样。 此外，复合物的设计使得 已知两种金属的还原电位的差异， 也可以改变。 有两种一般方法， 提出了 (A)在第一个系统中，一系列Ru 2和Os 2 联吡啶络合物将用于间接探测 通过研究电子转移的物理机制， 性质（价间电荷转移跃迁， 平衡常数，电子离域， 耦合）的混合价态（M-M+）。 (B)在第二 通过这种方法，可以合成出一系列钌-锇联吡啶配合物， 用于直接测量电子之间的转移速率 金属，以探测距离对速率的影响， 固定电位 此外，通过改变取代基， 结合到每个金属的联吡啶配体， 将改变两个金属位点以研究（1） 氧化还原不对称性对混合价态性质的影响 和（2）确定作为以下函数的电子转移速率： 驱动力恒定距离。 有许多 距离和驾驶效应的理论处理 力的物理性质的混合价络合物和 电子转移的速率。 通过此获得的数据 总体方法将提供几个严格的实验测试 这些理论。 只有通过系统的调查 的结构确定的双核金属配合物桥连的非- 共轭配体，一个准确的图片将出现的 距离和驱动力在决定 混合价态性质与电子速率 金属之间的转移。

A number of biological processes depend critically upon electron transfer: oxidative phosphorylation, photosynthesis and the redox reactions of metalloenzymes to name just a few. If a basic understanding of such systems is to be achieved, their remarkable efficiency and selectivity must be explained. The distance of separation between redox sites and the driving force of the electron transfer reaction are thought to play crucial roles in controlling the rate of electron transfer. This proposal presents an extensive program of research designed to probe the effects of distance and driving force on the rates of thermal electron transfer between metals. To that end, a series of binuclear metal complexes will be prepared where the bridging ligands are saturated structures that rigidly hold the two metals a defined distance apart and where that distance can be systematically varied. In addition, the complexes have been designed so that the difference in reduction potentials of the two metals is known and can also be changed. Two general approaches have been presented. (A) In the first system, a series of Ru2 and Os2 bipyridyl complexes will be used to indirectly probe the mechanism of electron transfer by studying the physical properties (intervalence charge transfer transitions, comproportionation constant, and electronic delocalization and coupling) of the mixed valence (M---M+) states. (B) In the second approach, a series of Ru---Os bipyridyl complexes will be employed to directly measure rates of electron transfer between the metals so as to probe the effect of distance on the rate at a fixed potential. In addition, by changing the substituents on the bipyridyl ligands bound to each metal, the reduction potentials of the two metal sites will be varied in order to study (1) the effect of redox asymmetry on the properties of the mixed valence states and (2) to determine the rate of electron transfer as a function of driving force at constant distance. There have been numerous theoretical treatments of the effects of distance and driving force on the physical properties of mixed valence complexes and on the rate of electron transfer. The data obtained through this overall approach will provide several stringent experimental tests of these theories. It is only through the systematic investigation of structurally defined binuclear metal complexes bridged by non- conjugated ligands that an accurate picture will emerge of the role played by distance and driving force in determining the properties of mixed valence states and the rate of electron transfer between metals.