Design and Function of Molecular Complex Sensors Based on Supramolecular Structure

本研究报道了荧光探针/环糊精（CyD）配合物在水中识别离子和分子的超分子功能。研究了具有不同烷基间隔长度的苯并-15-冠-5氟离子团Cn-15C5 (n=1,3,5)，建立了用于识别水中碱金属离子的超分子Cn-15C5/γ-CyD配合物传感器。在有机溶液中，C3-15C5以1:1的络合物形式表现出适度的Na^+选择性。然而，C3-15C5/γ-CyD配合物在水中选择性地响应K^+离子，并表现出芘二聚体的发射。对水中γ-CyD包合物的平衡分析表明，二聚体发射的主要成分是C3-15C5与K^+和γ-CyD的2:1:1配合物。虽然C5-15C5/γ-CyD配合物的K^+敏感性与C3-15C5/γ-CyD配合物相当，但它对Na^+也有响应。具有最短亚甲基间隔的氟离子团C1-15C5在γ-CyD的存在下对碱金属阳离子无响应。因此，响应函数受Cn-15C5的烷基间隔长度的强烈影响，C3-15C5/γ-CyD配合物在水中具有最高的K^+选择性。硼酸氟离子载体C4-PB/β-CyD复合物结合糖并在水中产生增强的荧光发射。C4-PB/β-CyD配合物的ph -荧光谱显示，随着硼酸盐共轭碱的形成，荧光强度增加。加入果糖后，表观pK_a降低到较低的pH，导致中性pH下荧光增强。糖结合后C4-PB/β-CyD复合物的荧光发射响应似乎是由于抑制了芘供体到三芳基硼酸受体的光诱导电子转移（PET）。

This study reports the supramolecular function of fluorescent probe/cyclodextrin (CyD) complexes for ion and molecule recognition in water. Benzo-15-crown-5 fluoroionophores, Cn-15C5 (n=1,3,5), with different alkyl spacer lengths were first examined to develop supramolecular Cn-15C5/γ-CyD complex sensors for alkali metal-ion recognition in water. In organic solutions, C3-15C5 shows moderate Na^+ selectivity based on 1:1 complex formation. However, the C3-15C5/γ-CyD complex is found to selectively respond to K^+ ion in water and to exhibit pyrene dimer emission. An equilibrium analysis of the γ-CyD inclusion complexes in water reveals that the major component for the dimer emission is a 2:1:1 complex of C3-15C5 with K^+ and γ-CyD. Although the K^+ sensitivity of the C5-15C5/γ-CyD complex is comparable to that of the C3-15C5/γ-CyD complex, it also responds to Na^+. The fluoroionophore C1-15C5, which has the shortest methylene spacer, exhibits no response to alkali metal cations in the presence of γ-CyD. Thus, the response function is strongly affected by the alkyl spacer length of Cn-15C5, and the highest K^+ selectivity in water is obtained for the C3-15C5/γ-CyD complex. The boronic acid fluoroionophore C4-PB/β-CyD complex binds sugars and produces increased fluorescence emission in water. A pH-fluorescence profile for the C4-PB/β-CyD complex reveals that the fluorescence intensity increases upon the formation of the boronate conjugate base. Upon the addition of fructose, the apparent pK_a decreases to a lower pH, resulting in increased fluorescence at neutral pH. The fluorescence emission response of the C4-PB/β-CyD complex upon sugar binding appears to be due to suppression of the photoinduced electron transfer (PET) from the pyrene donor to the trigonal arylboronic acid acceptor.