Working Supramolecular Machines Trapped in Glass and Mounted on a Film Surface

Abstract

The concept of a macroscopic machine can be realized [1] in solution at a supramolecular level in complexes where the self-assembly [2] of the components can be reversed upon quelling temporarily the molecular recognition that exists between the matching components. Thus, a supramolecular machine can be defined as an assembly of two or more molecular components designed to perform mechanical-like motions with respect to each other in response to some energy supplyÐfor example, chemical, electrochemical, or photo-chemicalÐthat can be switched on and off at will. One of the most highly investigated classes of supramolecular machines [1,3] are those based on the complexes known as pseudorotaxanes. [4] The reason for this is that the dethreading and rethreading movements of a thread through the center of a ring are reminiscent of the action of a linear motor. Numerous artificial supramolecular machines, [1] based on pseudorotaxanes, [4] exist that can be induced to undergo coconformational change [5] by chemical, [6] electrochemical, [7] and photochemical [8±10] means. They have been demonstrated [1] to operate efficiently in solution, albeit in an incoherent manner. In order to realize the full potential of these supermolecules in a machine-shop setting, they have to be organized at interfaces [11] or deposited on surfaces [12] so that they can be made to operate in unison. Herein we describe two solid-state supramolecular machines in action: one in which the machines are trapped physically in a rigid, nanoporous, optically transparent matrix, and the other in which[9] a) Single-crystal X-ray experiments were performed on either a Nonius kappaCCD diffractometer (1) or a Bruker SMART1000 CCD diffractometer (2,3) both equipped with an Oxford Cryosystems openflow cryostat (graphite-monochromated Mo Ka radiation, l 0.71073 ). All structures were solved by direct methods [11] and all non-hydrogen atoms were located by using subsequent difference Fourier methods. [12] b) Crystals of 1 were grown by the following procedure: Lanthanum triflate hydrate (0.029 g, 5 Â 10 À5

Stimuli-Responsive Drug-Delivery Systems Based on Supramolecular Nanovalves

“…Taking into account the improvement of biocompatibility and highly ordered porosity of MOFs, we built up a multifunctional Fe 3 O 4 @MOF core-shell nanocomposite integrated with stimulus responsiveness, sustained drug release, and magnetic resonance imaging (MRI) in one platform. 36 The Fe 3 O 4 @MOF material was prepared by coating UiO-66 Zr-MOF shell on Fe 3 O 4 core to produce Fe 3 O 4 @UiO-66-NH 2 composites assisted by an in situ growth method, and water-soluble pillar [6]arene (WP6) was then installed on 1-(6-bromohexyl) pyridinium bromide (Py) stalks-modified and 5-Fu-encapsulated core-shell nanocomposites through forming a bulky pseudorotaxanes structure. Significantly, the movable WP6-gated Fe 3 O 4 @UiO-66@WP6 material endowed the theranostic nanoplatform with multiple responsiveness toward pH, temperature, and competitive agents due to the dynamic hostguest binding.…”

“…In the same year, we continued in fabricating another pH/temperature dual-responsive pillar [6]arene-valved nanoplatform for multimodal chemo-photothermal therapy with desirable targeting ability ( Figure 5). 67 In light of the layer-by-layer assembly strategy and surface engineering concept, different modular components possessing specific functions were utilized, for example, polypyrrole NPs (PPy NPs) with desirable photothermal conversion capability performed as cores, UiO-66 MOF scaffolds bearing high drug-loading capacity served as shells, and folic acid conjugated polyethyleneimine (PEI-Fa) acted as active targeting entity in the outermost layer via electrostatic interactions.…”

“…1,2 The past few decades have marked the advent of artificial molecular machines and smart supramolecular devices equipped with fascinating mechanical and reversible properties and capable of desirable stimuli responsiveness based on macrocyclic chemistry and host-guest chemistry, and accordingly great impetus has been given to the development of materials science, such as biomedical materials. [3][4][5][6] One appealing type of supramolecular assemblies refers to the gated devices serving for the security and escape of cargos. 7,8 As an essential player in supramolecular chemistry, reversible non-covalent interactions-which include electrostatic interactions, p-p stacking interactions, hydrophobic effects, van der Waals interactions, and hydrogen-bonding interactions-could effectively organize matching pieces together by molecular recognition to produce ordered supramolecular nanoarchitectures with tailorable size, morphology, and functions, such as micelles, nanoparticles (NPs), vesicles, and hydrogels.…”

A Pseudorotaxane on Gold: Formation of Self‐Assembled Monolayers, Reversible Dethreading and Rethreading of the Ring, and Ion‐Gating Behavior

“…To realize the full potential of these molecules, however, they need to be organized on surfaces so that they behave coherently. Nevertheless, few studies on self‐assembled monolayers (SAMs) of pseudorotaxanes on solid surfaces and their behavior have been reported 6. Herein we report a self‐assembled monolayer of a pseudorotaxane on gold and its machinelike behavior—reversible dethreading and rethreading of the ring.…”

Elektrochemische und photochemische Steuerung der Wirt‐Gast‐Komplexierung an Oberflächen

“…Die Photochemie ist eine einfache Methode zur Modulation supramolekularer Wechselwirkungen zwischen Komponenten molekularer Maschinen und somit attraktiv für die Steuerung der Selbstorganisation zueinander komplementärer Einheiten sowohl in Lösung als auch in der Festphase. Stoddart et al entwickelten photochemisch gesteuerte supramolekulare Maschinen auf der Grundlage von Pseudorotaxanen, die auf einer Sol‐Gel‐Oberfläche immobilisiert sind 24. In diesen Systemen kann eine bewegliche Ring‐Komponente unter dem Einfluss eines äußeren Reizes reversibel auf eine feststehenden Achse auf‐ und wieder abgefädelt werden kann.…”