Two types of bisurea receptors, containing either 2,6-substituted phenyl or 2,6-substituted pyridine, are prepared, and their anion binding properties are investigated. Compared with the phenyl bisurea receptors, the pyridine bisurea receptors can be more easily converted to a cis–cis conformation from a trans–trans conformation, providing a cavity that more closely matches the volume of a fluoride ion and increasing the number of NH sites bound to the fluoride ion. As a result, the pyridine bisurea in cis–cis conformation shows stronger affinity and higher selectivity to fluoride ions, which is supported by crystal structure analysis and NMR titration experiments. Through DFT calculations, a mechanism of fluoride ion induced conformational changes of pyridine bisurea receptors is proposed, and the energy barriers of conformational changes for both types of receptors are determined.

中文翻译：

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阴离子结合和氟离子诱导的Bisurea受体构象变化

制备了两种含有2，6-取代的苯基或2，6-取代的吡啶的Bisurea受体，并研究了它们的阴离子结合特性。与苯基Bisurea受体相比，吡啶Bisurea受体可以更容易地从反式-反式构象转变为顺式-顺式构象，从而提供一个与氟离子的体积更紧密匹配并增加结合的NH位点的空腔氟离子。结果，吡啶的双氨氮处于顺式–顺式构象表明对氟离子具有更强的亲和力和更高的选择性，这由晶体结构分析和NMR滴定实验证实。通过DFT计算，提出了氟离子诱导吡啶双surea受体构象变化的机理，并确定了两种受体构象变化的能垒。