Interfacial Supramolecular Structures of Amphiphilic Receptors Drive Aqueous Phosphate Recognition
Interfacial Supramolecular Structures of Amphiphilic Receptors Drive Aqueous Phosphate Recognition
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DOI：
10.1021/jacs.9b02148
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发表时间：
2019-05-15
影响因子：
15
通讯作者：
Allen, Heather C.
中科院分区：
文献类型：
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作者：
Neal, Jennifer F.;Zhao, Wei;Allen, Heather C.
磷酸盐修复对于防止淡水沃茨富营养化和维持水质具有重要意义。去除磷酸盐的一种方法涉及利用分子受体。然而，我们对水溶液和水界面阴离子识别的理解还不发达，表面固定化受体的合理设计在很大程度上仍有待探索。在这里，我们评估了驱动力控制磷酸盐结合锚定在空气-水界面的基本两亲性受体。我们设计了具有中性硫脲、带正电荷的胍盐和硫脲盐单元的生物灵感受体，这些单元都形成了朗缪尔单分子层。磷酸盐结合进行了定量研究，使用表面压力面积等温线和红外反射吸收光谱（IRRAS）。该同源系列内的受体在官能团、电荷和烷基链数目方面不同，以帮助区分影响水界面处阴离子识别的基本组分。带有两个烷基链的两个带电受体各自显示出强的磷酸盐亲和力和10（3）和10（1）倍的抗Hofmeister选择性，分别超过氯化物。中性硫脲和单链胍受体没有绑定磷酸盐，揭示了静电相互作用和超分子组织的重要性。一致地，在高离子强度下的电荷屏蔽减弱结合。光谱的结果证实磷酸盐结合的双烷基链胍受体，而表面压力等温线的结果单独显示出最小的变化，从而强调了界面光谱的重要性。我们发现，结合位点的身份，带电的双电层，和超分子的超结构所产生的界面结合都影响。这些详细的见解磷酸盐识别在水界面提供了一个基础，开发有效的受体磷酸盐捕获。
Phosphate remediation is important for preventing eutrophication in fresh waters and maintaining water quality. One approach for phosphate removal involves the utilization of molecular receptors. However, our understanding of anion recognition in aqueous solution and at aqueous interfaces is underdeveloped, and the rational design of surface-immobilized receptors is still largely unexplored. Herein, we evaluated the driving forces controlling phosphate binding to elementary amphiphilic receptors anchored at air-water interfaces. We designed biologically inspired receptors with neutral thiourea, positively charged guanidinium, and thiouronium units that all formed Langmuir monolayers. Phosphate binding was quantitatively examined using surface pressure-area isotherms and infrared reflection-absorption spectroscopy (IRRAS). The receptors within this homologous series differ in functional group, charge, and number of alkyl chains to help distinguish the fundamental components influencing anion recognition at aqueous interfaces. The two charged receptors bearing two alkyl chains each displayed strong phosphate affinities and 10(3)- and 10(1)-fold anti-Hofmeister selectivity over chloride, respectively. Neutral thiourea and the single-chain guanidinium receptor did not bind phosphate, revealing the importance of electrostatic interactions and supramolecular organization. Consistently, charge screening at high ionic strength weakens binding. Spectroscopic results confirmed phosphate binding to the double alkyl chain guanidinium receptor, whereas surface pressure isotherm results alone showed a minimal change, thus emphasizing the importance of interfacial spectroscopy. We found that the binding site identity, charged interface created by the electrical double layer, and supramolecular superstructure all affect interfacial binding. These detailed insights into phosphate recognition at aqueous interfaces provide a foundation to develop efficient receptors for phosphate capture.