Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK.
J Am Chem Soc. 2012 Jul 18;134(28):11533-41. doi: 10.1021/ja302213r. Epub 2012 Jul 3.
The synthesis and anion binding properties of a new family of fluorescent halogen bonding (XB) macrocyclic halo-imidazolium receptors are described. The receptors contain chloro-, bromo-, and iodo-imidazolium motifs incorporated into a cyclic structure using naphthalene spacer groups. The large size of the iodine atom substituents resulted in the isolation of anti and syn conformers of the iodo-imidazoliophane, whereas the chloro- and bromo-imidazoliophane analogues exhibit solution dynamic conformational behavior. The syn iodo-imidazoliophane isomer forms novel dimeric isostructural XB complexes of 2:2 stoichiometry with bromide and iodide anions in the solid state. Solution phase DOSY NMR experiments indicate iodide recognition takes place via cooperative convergent XB-iodide 1:1 stoichiometric binding in aqueous solvent mixtures. (1)H NMR and fluorescence spectroscopic titration experiments with a variety of anions in the competitive CD(3)OD/D(2)O (9:1) aqueous solvent mixture demonstrated the bromo- and syn iodo-imidazoliophane XB receptors to bind selectively iodide and bromide respectively, and sense these halide anions exclusively via a fluorescence response. The protic-, chloro-, and anti iodo-imidazoliophane receptors proved to be ineffectual anion complexants in this aqueous methanolic solvent mixture. Computational DFT and molecular dynamics simulations corroborate the experimental observations that bromo- and syn iodo-imidazoliophane XB receptors form stable cooperative convergent XB associations with bromide and iodide.
描述了一类新型荧光卤键（XB）大环卤代咪唑鎓受体的合成及阴离子结合性能。这些受体含有氯、溴和碘代咪唑基元，通过萘间隔基整合到环状结构中。碘原子取代基的大体积导致碘代咪唑烷的反式和顺式构象得以分离，而氯代和溴代咪唑烷类似物则表现出溶液动态构象行为。顺式碘代咪唑烷异构体在固态下与溴化物和碘化物阴离子形成新颖的二聚体等结构 XB 配合物，具有 2:2 的化学计量比。溶液相 DOSY NMR 实验表明，在水溶剂混合物中，碘识别通过协同收敛的 XB-碘 1:1 化学计量结合发生。在竞争的 CD(3)OD/D(2)O（9:1）水溶剂混合物中，用各种阴离子进行的 (1)H NMR 和荧光光谱滴定实验表明，溴代和顺式碘代咪唑烷 XB 受体分别选择性地结合碘化物和溴化物，并通过荧光响应专门感知这些卤化物阴离子。质子化、氯代和反式碘代咪唑烷受体在这种水-甲醇溶剂混合物中被证明是无效的阴离子配合物。计算 DFT 和分子动力学模拟证实了实验观察结果，即溴代和顺式碘代咪唑烷 XB 受体与溴化物和碘化物形成稳定的协同收敛 XB 缔合。
