Electron Spin in Metalloprotein Electron Transfer

描述(由申请人提供)：在金属蛋白的活性部位存在多个电子耦合的金属离子使这种体系的电子结构具有独特性。这项提案中描述的研究将确定这些电子特征在其功能中发挥作用的程度。更具体地说，这项工作将考察电子自旋极化对电子转移反应的影响，特别是与几种铁-氧和铁-硫金属蛋白活性中心相关的电子转移反应。这将通过在从简单的配位化合物到活性中心的结构模型再到表面修饰的铁硫蛋白等系统上进行的合成、物理和计算化学的融合来实现。这项研究将分几个阶段进行。首先，在先前结果的基础上，将合成几个允许以受控和系统的方式调制电子自旋的模型系统。时间分辨光谱研究，结合变温磁性测量，将被用来量化这些体系的电子结构和电子转移动力学。这些研究将提供第一个明确的实验数据，详细说明电子自旋极化对涉及生物重要金属团簇的电子转移反应的影响。然后将寻求更复杂的系统，包括但不限于，(1)铁-硫/卟啉组件，以研究亚硫酸盐还原酶模型中的电子转移动力学；(2)Ru修饰的铁-硫蛋白质(例如，HIPIP)，以评估活性中心簇内可热访问的激发自旋态对于基于蛋白质的电子转移的作用；以及(3)施主/簇/受体组件，以实现通过簇的电子转移，研究自旋态调制对于门控金属蛋白活性中心的电子迁移的可能作用。这项工作将极大地促进我们对与金属蛋白电子转移有关的机制问题的理解，通过对其活性中心的电子结构的内在但未被探索的方面的研究。

DESCRIPTION (provided by applicant): The presence of multiple electronically coupled metal ions in the active sites of metalloproteins imparts unique character to the electronic structures of such systems. The research described in this proposal will determine the extent to which these electronic features play a role in their function. More specifically, this work will examine the influence of electron spin polarization on electron transfer reactions, in particular those relevant to the active sites of several iron-oxo and iron-sulfur metalloproteins. This will be achieved through a confluence of synthetic, physical, and computational chemistries performed on systems ranging from simple coordination compounds to structural models of active sites to surface-modified iron-sulfur proteins. The research will be developed in several stages. First, building on previous results, several model systems will be synthesized that allow for the modulation of electron spin in a controlled and systematic fashion. Time-resolved spectroscopic studies, in conjunction with variable-temperature magnetic measurements, will then be employed to quantify both the electronic structures and electron transfer kinetics of these systems. These studies will provide the first unambiguous experimental data detailing the influence electron spin polarization has on electron transfer reactions involving biologically important metal clusters. More complex systems will then be pursued including, but not limited to, (1) iron-sulfur/porphyrin assemblies to study electron transfer kinetics in models of sulfite reductase; (2) Ru-modified iron-sulfur proteins (e.g., HiPIP) to assess the role of thermally accessible excited spin states within the active-site cluster for protein-based electron transfer; and (3) donor/cluster/acceptor assemblies to effect through-cluster electron transfer, examining the possible role of spin-state modulation for the gating of electron migration in metalloprotein active sites. This work will significantly advance our understanding of mechanistic issues related to metalloprotein electron transfer through its examination of an intrinsic but unexplored aspect of the electronic structure of their active sites.