Dual Aperture Control on pH- and Anion-Driven Supramolecular Nanoscopic Hybrid Gate-like Ensembles

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• 作者：Rosa Casasú ; s ; Estela Climent ; M. Dolores Marcos ; Ramó ; n Martí ; nez-M&aacute ; ñ ; ez ; Fé ; lix Sancenó ; n ; Juan Soto ; Pedro Amoró ; s ; Joan Cano ; Eliseo Ruiz
• 刊名：Journal of the American Chemical Society
• 出版年：2008
• 出版时间：February 13, 2008
• 年：2008
• 卷：130
• 期：6
• 页码：1903 - 1917
• 全文大小：790K
• 年卷期：v.130,no.6(February 13, 2008)
• ISSN：1520-5126

文摘

The development of gate-like systems able to perform certain programmed functions is aninteresting way of taking chemistry to the frontiers of nanoscience. In relation to this field, we report acomplete study of the behavior of a pH-driven and anion-controlled nano-supramolecular gate-like ensembleobtained by anchoring suitable polyamines on the pore outlets of mesoporous materials of the type MCM-41 (solid N3-S). The release of an entrapped dye (Ru(bipy)₃²⁺) from the pore voids into the bulk solutionallows us to study the gating effect. A pH-driven open/close mechanism was observed that arises from thehydrogen-bonding interaction between amines at neutral pH (open gate) and Coulombic repulsions at acidicpH between closely located polyammoniums at the pore openings (closed gate). Molecular dynamicssimulations 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 (1mages/entities/onemacr.gif">1) plane of themages/gifchars/beta2.gif" BORDER=0 ALIGN="middle">-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 ofthe pore (fully open gate), whereas completely protonated amines (simulating a pH 2 or lower) result in aclear 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-controlledmechanism. This study was carried out by monitoring the dye released from the pore voids of the N3-Ssolid 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 × 10^-2 mol dm^-3). The choice of a certainanionic 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 remarkableanion-controllable response of the gate-like ensemble can be explained in terms of anion complex formationwith the tethered polyamines. These experimental studies are also in agreement with computationalsimulations with fluoride, chloride, iodide, and dihydrogen phosphate anions. In the model, larger anionspush the tethered polyamines toward the pore openings more efficiently, and therefore the pore aperturedecreases. The studies also show that, for anions showing a strong tendency to form hydrogen-bondingnetworks (e.g., phosphate), complete pore blockage was observed at acidic pH. Finally, selectivity patternshave been discussed in terms of kinetic rates of the liberation of the Ru(bipy)₃²⁺ dye from the amine-functionalized dye-containing material N3-S.