Metal/metal and metal/nitroxyl-labeled compounds for the development of EPR-based distance measurement techniques

电子顺磁共振(EPR)技术已经成为非常有用的工具来解释(生物)大分子的结构及其在无序的自然状态下的组装。一种单元内应用程序即将出现。为此目的，对感兴趣的分子进行选择性自旋标记。在很长一段时间里，这都是用氮氧基来完成的。直到最近，Gd(III)才成为人们关注的焦点。该项目的一个主要目标是鉴定具有特定EPR技术(PULSE和CW EPR)所需的光谱性质的Gd(III)配合物，并将它们开发成现成的自旋标记，用于蛋白质的定点自旋标记。为了使基于Gd的自旋标记的潜力以及新开发的基于Gd的EPR技术的潜力发挥出来，将制备类型为Gd-间隔-Gd和Gd-间隔-氮氧基的化合物。间隔物将两个自旋标记保持在定义明确的、可调的距离。这些化合物将是水溶性的，以便在与研究生物分子时相同的条件下进行EPR实验。以铜(II)和锰(II)为自旋标记物的模型化合物被列为本项目的合成目标。这使得对应用于顺磁金属离子与相同或不同类型的第二顺磁金属离子或与氮氧基自由基相互作用的EPR光谱技术进行了更广泛的基础探索，这是自旋标记金属蛋白遇到的情况。

Electron paramagnetic resonance (EPR) techniques have become very useful tools to elucidate the structure of (bio)macromolecules and their assemblies in a disordered, native state. An in-cell application is on the horizon. For this purpose the molecules of interest are site-selectively spin labeled. For a long time this was done with nitroxyl radicals. Only recently Gd(III) came into focus as a spin label. One major objective of this project is to identify Gd(III) complexes having the spectroscopical properties required for a specific EPR technique (pulse and cw EPR) and developing them into ready-made spin labels for site-directed spin labeling of proteins. To sound the potential of Gd-based spin labels as well as those of the newly developing Gd-based EPR techniques compounds of the type Gd-spacer-Gd and Gd-spacer-nitroxyl will be prepared. The spacer keeps the two spin labels at a well-defined, tunable distance. The compounds will be water soluble to allow EPR experiments under conditions identical to those when biomolecules are studied. Model compounds with Cu(II) and Mn(II) as spin labels are included as synthetic targets in our project. This enables a broader fundamental exploration of EPR spectroscopical techniques that are applied to paramagnetic metal ions interacting with a second paramagnetic metal ion of the same or different kind or with a nitroxyl radical, a situation met with spin-labeled metallo-proteins.