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

细胞色素c氧化酶的结构从静态（结晶）的角度来看是相当众所周知的，但所有试图组装复合物，模拟CuA在这种酶或建立一个简化的等效电路在一个复杂的化学水平上，代表电子流从细胞色素c到CuA失败至今。应该注意的是，所有先前描述的具有CuA的某些选择性特征的化合物在突出的性质（例如结构和氧化还原化学）上偏离生物原型，因此必须显著改进以达到可以获得对生物电子传输的动力学方面的显著见解的阶段。我们将继续致力于改进具有双官能硫醇盐配体的CuA模型，同时也使用我们的新型三齿GuaphSetS系统，该系统具有建立蛋氨酸生物学要求的环境的潜力。结合位点的CuA通过激活他们的NSS'供体集的配位，这是不容易的其他配体在文献中描述。另一方面，一个新的焦点将被创建和导向光化学可激发的电子转移级联作为电子转移的等效电路图从细胞色素c到CuA，其中二价钌离子作为电子源，双核铜-硫醇盐配合物作为相应的电子汇。在不同的阶段结束时，模型的CuA网站的细胞色素，C氧化酶和N2 O还原酶的研究将出现在越来越复杂的阶段，这也将作为复杂化学水平上的简化等效电路的组成部分，对更好地理解动态和生物电子传输问题的动力学方面驱动的铜。除了经典的X射线结构分析方法和传统的表征光谱，（光谱）电化学和磁化学方法，我们将特别强调复杂的光谱技术，利用脉冲光学激光的杰出潜力，（脉冲式）自由电子激光器和（脉冲式）第三代同步加速器光源的时间分辨信息，以获得铜驱动的生物电子传输现象。在这种情况下，高分辨率的X射线吸收和发射发挥了核心作用，因为这些技术可以直接进入我们的复合物的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.