Dual aperture control on pH- and anion-driven supramolecular nanoscopic hybrid gate-like ensembles
Dual aperture control on pH- and anion-driven supramolecular nanoscopic hybrid gate-like ensembles
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DOI：
10.1021/ja0756772
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发表时间：
2008-02-13
影响因子：
15
通讯作者：
Ruiz, Eliseo
中科院分区：
文献类型：
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作者：
Casasus, Rosa;Climent, Estela;Ruiz, Eliseo
能够执行某些程序功能的门状系统的发展是将化学带到纳米科学前沿的一种有趣的方式。在这一领域，我们报道了一项完整的研究，通过在MCM-41型介孔材料（固体W-S）的孔出口上锚定合适的多胺，获得了ph驱动和阴离子控制的纳米超分子门状系综的行为。捕获的染料(Ru（bipy)3(2+)）从孔隙中释放到体溶液中，使我们能够研究门控效应。在中性pH下，胺之间的氢键相互作用（打开门）和在酸性pH下，位于孔口处的聚铵之间的库仑排斥作用（关闭门）产生了pH驱动的开/关机制。利用力场方法进行分子动力学模拟来解释ph驱动的开/闭机理。为此，以β -晶体石结构的（111）平面为基础，构建了介孔二氧化硅结构，其上含有大的六方纳米孔和锚定多胺。从这些计算中，可以观察到完全未质子化的胺对孔的覆盖程度很差（完全打开的门），而完全质子化的胺（模拟pH为2或更低）导致孔孔径明显缩小，这与实验结果一致。除了ph驱动的协议之外，也可以通过阴离子控制的机制来调制类似门的集成的打开/关闭。本研究通过监测一定pH下N3-S固体孔洞中存在不同结构尺寸和电荷的阴离子，包括氯化物、硫酸盐、磷酸盐和ATP (c -阴离子= 1 × 10（-2) mol dm(-3)）时的染料释放情况来进行。选择某种阴离子客体会导致不同的门状系综行为，根据pH值（硫酸盐和磷酸盐）的不同，从基本不起作用（氯化物）到完全（ATP）或部分孔隙堵塞。门状系综的显著阴离子可控响应可以解释为阴离子配合物与拴系多胺的形成。这些实验研究也与氟、氯、碘和磷酸二氢阴离子的计算模拟一致。在该模型中，较大的阴离子更有效地将拴系多胺推向孔口，因此孔口孔径减小。研究还表明，对于表现出强烈形成氢键网络倾向的阴离子（如磷酸盐），在酸性ph下观察到完全的孔隙堵塞。最后，根据Ru(bipy)(3)（2+）染料从胺功能化的含染料材料W-S中解放的动力学速率，讨论了选择性模式。
The development of gate-like systems able to perform certain programmed functions is an interesting way of taking chemistry to the frontiers of nanoscience. In relation to this field, we report a complete study of the behavior of a pH-driven and anion-controlled nano-supramolecular gate-like ensemble obtained by anchoring suitable polyamines on the pore outlets of mesoporous materials of the type MCM-41 (solid W-S). The release of an entrapped dye (Ru(bipy)3(2+)) from the pore voids into the bulk solution allows us to study the gating effect. A pH-driven open/close mechanism was observed that arises from the hydrogen-bonding interaction between amines at neutral pH (open gate) and Coulombic repulsions at acidic pH between closely located polyammoniums at the pore openings (closed gate). Molecular dynamics simulations using force field methods have been carried out to explain the pH-driven open/close mechanism. For this purpose, a mesoporous silica structure was constructed, taking as base the (111) plane of the beta-crystoballite structure on which large hexagonal nanopores and anchored polyamines were included. From these calculations, it was observed how completely unprotonated amines display poor coverage of the pore (fully open gate), whereas completely protonated amines (simulating a pH 2 or lower) result in a clear reduction of the pore aperture, in agreement with the experimental results. In additional to the pH-driven protocol, opening/closing of the gate-like ensemble can also be modulated via an anion-controlled mechanism. This study was carried out by monitoring the dye released from the pore voids of the N3-S solid at a certain pH in the presence of a range of anions with different structural dimensions and charges, including chloride, sulfate, phosphate, and ATP (C-anion = 1 X 10(-2) mol dm(-3)). The choice of a certain anionic guest results in a different gate-like ensemble behavior, ranging from basically no action (chloride) to complete (ATP) or partial pore blockage, depending on the pH (sulfate and phosphate). The remarkable anion-controllable response of the gate-like ensemble can be explained in terms of anion complex formation with the tethered polyamines. These experimental studies are also in agreement with computational simulations with fluoride, chloride, iodide, and dihydrogen phosphate anions. In the model, larger anions push the tethered polyamines toward the pore openings more efficiently, and therefore the pore aperture decreases. The studies also show that, for anions showing a strong tendency to form hydrogen-bonding networks (e.g., phosphate), complete pore blockage was observed at acidic pH. Finally, selectivity patterns have been discussed in terms of kinetic rates of the liberation of the Ru(bipy)(3)(2+) dye from the amine-functionalized dye-containing material W-S.