Electron Spin in Metalloprotein Electron Transfer

描述（由申请人提供）：在金属蛋白的活性位点中存在多个电子偶联的金属离子赋予了此类系统的电子结构独特的特征。本提案中所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，这项工作将研究电子自旋极化对电子转移反应的影响，特别是那些相关的几个铁氧和铁硫金属蛋白的活性位点。这将通过在从简单的配位化合物到活性位点的结构模型再到表面改性的铁硫蛋白质的系统上进行的合成，物理和计算化学的融合来实现。研究将分几个阶段进行。首先，建立在以前的结果，几个模型系统将被合成，允许在一个控制和系统的方式调制电子自旋。时间分辨光谱研究，结合变温磁测量，然后将被用来量化这些系统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电子转移反应的影响，涉及生物学上重要的金属簇。然后将追求更复杂的系统，包括但不限于：（1）铁-硫/卟啉组装体，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（例如，HiPIP）来评估活性位点簇内的热可接近的激发自旋态对于基于蛋白质的电子转移的作用;以及（3）供体/簇/受体组件来实现通过簇的电子转移，检查自旋态调制对于金属蛋白活性位点中的电子迁移的门控的可能作用。这项工作将显着推进我们的理解有关的金属蛋白质电子转移的机制问题，通过其检查的一个内在的，但未开发的方面，其活性位点的电子结构。

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.