Switching the Jahn-Teller Distortion of Copper(II) Compounds - Towards an EPR Reporter Group for Sensor Applications

八面体铜(II)化合物通常表现出强烈扭曲的分子结构，沿八面体的一个轴拉长(‘Jahn-Teller效应’)。这种失真反映在这些化合物所显示的光谱中，特别是电子顺磁共振技术(EPR，又名ESR)。我们发现，经过适当设计的八面体铜(II)络合物可以被施加不同的、压缩的分子结构。这是第一个具有这种性质的分子铜(II)化合物。通过前述EPR方法可以容易地区分两种类型的扭曲结构(拉长和压缩)。重要的是，我们的结果表明，我们的一些化合物的Jahn-Teller扭曲可能会因外部刺激而改变。我们正在申请尝试并做到这一点，通过设计一种铜化合物，当第二个客体分子与其结合时，其结构扭曲可能会改变。如果成功，我们将为客种制造一种化学传感器，可以通过EPR进行测量。为了做到这一点，我们在早期工作的基础上设计了两个铜(II)络合物。一种是与羧酸客体相互作用，包括一些多肽。另一种是设计用来结合碱金属离子，特别是对Cs+。通过EPR滴定，以及类似的镍(II)和锌(II)络合物主体的UV/Vis和核磁共振滴定，我们将证明这些客体是否与我们的化合物结合，如果是，他们是否会引发铜报告中心EPR光谱的预期变化。对于大小和形状正确的客种，EPR反应应具有选择性。这将是EPR探测主机：来宾绑定的一种非常新颖的用法。

Octahedral copper(II) compounds usually show a strongly distorted molecular structure, that is elongated along one axis of the octahedron (the 'Jahn-Teller effect'). This distortion is reflected in the spectra shown by these compounds, particularly with the Electron Paramagnetic Resonance technique (EPR, aka ESR). We have found that a different, compressed molecular structure can be imposed onto an octahedral copper(II) complex compound that has been suitably designed. These were the first molecular copper(II) compounds to have this property. The two types of distorted structure (elongated and compressed) can be readily distinguished by the aforementioned EPR method. Importantly, our results have implied that the Jahn-Teller distortion of some of our compounds might be switched in response to an external stimulus. We are applying to try and do this, by designing a copper compound whose structural distortion might be changed when a second, guest molecule bonds to it. If successful, we will have made a chemical sensor for the guest species, that can be measured by EPR. We have designed two copper(II) complexes, based on our earlier work, to do just that. One is intendeded to interact with carboxylic acid guests, including some peptides. The other is designed to bind alkali metal ions, with a particular preference for Cs+. Through EPR titrations, and UV/vis and NMR titrations of analogous nickel(II) and zinc(II) complex hosts, we will prove whether these guests bind to our compounds and, if so, whether they trigger the expected change in the EPR spectra of the copper reporter centres. The EPR response should be selective for guest species of the correct size and shape. This would be a very novel use of EPR to probe host:guest binding.