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，沿着八面体的一个轴被拉长（“Jahn-Teller效应”）。这种畸变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）。我们发现一种不同的、压缩的分子结构可以被施加到一个八面体铜（II）配合物上，这个八面体铜（II）配合物经过了适当的设计。这是第一个具有这种性质的铜（II）分子化合物。两种类型的扭曲结构（伸长和压缩）可以很容易地区分上述EPR方法。重要的是，我们的结果表明，我们的一些化合物的姜-泰勒扭曲可能会在响应外部刺激时发生改变。我们正在申请并尝试做到这一点，通过设计一种铜化合物，当第二个客体分子与它结合时，它的结构扭曲可能会改变。如果成功，我们将为客体物种制作一个化学传感器，可以用EPR测量。基于我们早期的工作，我们设计了两个铜（II）配合物来做到这一点。一种是与羧酸客体相互作用，包括一些肽。另一种被设计用来结合碱金属离子，特别偏爱Cs+。通过EPR滴定，以及类似的镍（II）和锌（II）复合物宿主的紫外/可见和核磁共振滴定，我们将证明这些客体是否与我们的化合物结合，如果是的话，它们是否触发铜报告中心的EPR光谱的预期变化。对于大小和形状正确的客体物种，EPR响应应该是选择性的。这将是EPR探测主客绑定的一个非常新颖的用途。

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.