Inorganic–Organic Hybrid Vesicles with Counterion- and pH-Controlled Fluorescent Properties

Two inorganic–organic hybrid clusters with one or two covalently linked pyrene fluorescent probes, [(n-C4H9)4N]2[V6O13{(OCH2)3C(NH(CO)CH2CH2CH2C16H9)}{(OCH2)3C–(NH2)}] ((TBA+)21) and [(n-C4H9)4N]2[V6O13{(OCH2)3C(NH(CO)CH2CH2CH2C16H9)}2] ((TBA+)22), respectively, are synthesized from Lindqvist type polyoxometalates (POMs). The incorporation of pyrene into POMs results in amphiphilic hybrid molecules and simultaneously offers a great opportunity to study the interaction between hybrid clusters and their counterions. 2D-NOESY NMR and fluorescence techniques have been used to study the role of counterions such as tetrabutyl ammonium (TBA) in the vesicle formation of the hybrid clusters. The TBA+ ions not only screen the electrostatic repulsions between the POM head groups but also are involved in the hydrophobic region of the vesicular structure where they interrupt the formation of pyrene excimers that greatly perturbs the luminescence signal from the vesicle solution. By replacing the TBA+ counterions with protons, the new vesicles demonstrate interesting pH-dependent fluorescence properties.

本研究以林德奎斯特型多金属氧酸盐（Lindqvist type polyoxometalates, POMs）为起始原料，合成了两款分别共价连接一个或两个芘荧光探针的无机-有机杂化簇，其化学式分别为[(n-C4H9)4N]2[V6O13{(OCH2)3C(NH(CO)CH2CH2CH2C16H9)}{(OCH2)3C–(NH2)}]（记为(TBA+)21）与[(n-C4H9)4N]2[V6O13{(OCH2)3C(NH(CO)CH2CH2CH2C16H9)}2]（记为(TBA+)22）。将芘基团引入多金属氧酸盐骨架可得到两亲性杂化分子，同时为探究杂化簇与其抗衡离子之间的相互作用提供了理想的研究契机。研究人员采用二维核奥弗豪泽效应谱核磁共振（2D-NOESY NMR）与荧光技术，探究了四丁基铵（tetrabutyl ammonium, TBA）这类抗衡离子在杂化簇囊泡形成过程中的作用。四丁基铵阳离子不仅能够屏蔽多金属氧酸盐头部基团间的静电排斥作用，还可嵌入囊泡结构的疏水区域，在此区域内其会干扰芘激基缔合物的形成，进而显著扰动囊泡溶液的发光信号。将体系中的四丁基铵抗衡离子替换为质子后，所得新型囊泡展现出有趣的pH依赖荧光特性。