Nicolas Henning, Yuan Bin, Xu Jiangfei, Zhang Xi, Schönhoff Monika
University of Muenster, Institute of Physical Chemistry, Correnstraße 28/30, 48149 Münster, Germany.
Key Laboratory of Organic Optoelectronics & Molecular Engineering, Department of Chemistry, Tsinghua University, Beijing 100084, China.
Polymers (Basel). 2017 Dec 16;9(12):719. doi: 10.3390/polym9120719.
A water-soluble, anionic pillar[6]arene derivative (WP6) is applied as monomeric building block for the layer-by-layer self-assembly of thin polyelectrolyte multilayer films, and its pH-dependent host⁻guest properties are employed for the reversible binding and release of a methylviologen guest molecule. The alternating assembly of anionic WP6 and cationic diazo resin (DAR) is monitored in-situ by a dissipative quartz crystal microbalance (QCM-D). In solution, the formation of a stoichiometric inclusion complex of WP6 and cationic methylviologen (MV) as guest molecule is investigated by isothermal titration calorimetry and UV-vis spectroscopy, respectively, and attributed to electrostatic interactions as primary driving force of the host⁻guest complexation. Exposure of WP6-containing multilayers to MV solution reveals a significant decrease of the resonance frequency, confirming MV binding. Subsequent release is achieved by pH lowering, decreasing the host⁻guest interactions. The dissociation of the host⁻guest complex, release of the guest from the film, as well as full reversibility of the binding event are identified by QCM-D. In addition, UV-vis data quantify the surface coverage of the guest molecule in the film after loading and release, respectively. These findings establish the pH-responsiveness of WP6 as a novel external stimulus for the reversible guest molecule recognition in thin films.
一种水溶性阴离子柱[6]芳烃衍生物（WP6）被用作构建超薄聚电解质多层膜逐层自组装的单体结构单元，其pH依赖的主客体性质被用于甲基紫精客体分子的可逆结合与释放。通过耗散石英晶体微天平（QCM-D）原位监测阴离子WP6和阳离子重氮树脂（DAR）的交替组装。在溶液中，分别通过等温滴定量热法和紫外-可见光谱研究了WP6与作为客体分子的阳离子甲基紫精（MV）形成化学计量比包合物的情况，并将其归因于静电相互作用作为主客体络合的主要驱动力。将含WP6的多层膜暴露于MV溶液中，共振频率显著降低，证实了MV的结合。随后通过降低pH值实现释放，降低主客体相互作用。通过QCM-D确定主客体络合物的解离、客体从膜中的释放以及结合事件的完全可逆性。此外，紫外-可见数据分别量化了加载和释放后膜中客体分子的表面覆盖率。这些发现确立了WP6的pH响应性作为薄膜中可逆客体分子识别的一种新型外部刺激。
