Cu-S complexes in the heart of biological electron transfer: the homodinuclear CuA site of Cytochrome-c oxidases and N2O reductases

从静态（结晶）的角度来看，细胞色素-c氧化酶的结构是相当众所周知的，但迄今为止，所有试图在这种酶内组装模仿CuA的复合物或在复杂化学水平上建立一个简化的等效电路（代表从细胞色素-c到CuA的电子流）的尝试都失败了。值得注意的是，所有先前描述的具有特定CuA选择性特征的化合物在结构和氧化还原化学等突出性质上都偏离了生物原型，因此必须进行显著改进，以达到可以获得生物电子传递动力学方面的重要见解的阶段。一方面，我们将继续致力于改进双功能硫化物配体的CuA模型，同时也使用我们的新型三叉GuaphSetS系统，这些系统有可能通过激活它们的NSS供体集来建立CuA蛋氨酸结合位点的生物学要求环境，这是文献中描述的其他配体无法获得的。另一方面，一个新的焦点将被创建并指向光化学可激发的电子转移级联，作为从细胞色素c到CuA的电子转移的等效电流图，其中二价钌离子作为电子源，双核铜硫酸盐配合物作为相应的电子汇。在研究的各个阶段，细胞色素c氧化酶和N2O还原酶的CuA位点模型将在越来越复杂的阶段出现，这也将作为复杂化学水平上简化等效电路的组成部分，为更好地理解由CuA驱动的生物电子传递问题的动力学和动力学方面做出决定性贡献。除了经典的x射线结构分析方法和传统的光谱、电化学和磁化学表征方法外，我们将特别强调复杂的光谱技术，以利用脉冲光学激光器、脉冲自由电子激光器和第三代同步加速器光源的突出潜力，获得铜驱动生物电子传输现象的时间分辨信息。在这种情况下，高分辨率x射线吸收和发射发挥了核心作用，因为这些技术允许直接访问我们的配合物的LUMO和HOMO状态。

The structure of cytochrome-c oxidase is fairly well known from a static (crystalline) point of view, but all attempts to assemble complexes that mimic CuA within this enzyme or to establish a simplified equivalent circuit on a complex chemical level that represents the flow of electrons from cytochrome-c to CuA failed so far. It should be noted that all previously described compounds with certain selective characteristics of CuA deviate from the biological archetype in prominent properties such as structure and redox chemistry, and thus must be improved significantly to arrive at a stage from which significant insights into dynamical aspects of the biological electron transport can be obtained.On the one hand, we will continue our work directed towards improved CuA models with bifunctional thiolate ligands and in parallel also use our novel tridentate GuaphSetS systems which have the potential to establish the biologically requested environment of the methionine-binding site of CuA by activating their NSS' donor sets a coordination which is not accessible by other ligands described in the literature.On the other hand, a novel focus will be created and directed towards photochemically excitable electron transfer cascades as equivalent circuit diagrams for the electron transfer from cytochrome-c to CuA, in which divalent ruthenium ions serve as electron sources and binuclear copper-thiolate complexes act as corresponding electron sinks.Over various stages to the end of the way, models for the CuA sites of cytochrome-c oxidases and of N2O reductases will emerge in increasing sophisticated stages which will also make decisive contributions as components of simplified equivalent circuits on a complex chemical level to a better understanding of dynamic and kinetic aspects of biological electron transport issues driven by CuA.Apart from classical methods of X-ray structure analysis and of conventional characterization by spectroscopic, (spectro)electrochemical and magneto-chemical methods, we will place particular emphasis on sophisticated spectroscopic techniques to make use of the outstanding potential of pulsed optical laser, (pulsed) free electron laser and of (pulsed) 3rd generation synchrotron sources in order to obtain time-resolved information on copper-driven biological electron transport phenomena. In this context, high-resolution X-ray absorption and emission play a central role as these techniques allow direct access to the LUMO and HOMO states of our complexes.