Versatile Supramolecular Nanovalves Reconfigured for Light Activation

Abstract

All autonomous machines share the same requirement—namely, they need some form of energy to perform their operations and nanovalves are no exception. Supramolecular nanovalves constructed from [2]pseudorotaxanes—behaving as dissociatable complexes attached to mesoporous silica which acts as a supporting platform and reservoir—rely on donor‐acceptor and hydrogen bonding interactions between the ring component and the linear component to control the ON and OFF states. The method of operation of these supramolecular nanovalves involves primarily the weakening of these interactions. The [2]pseudorotaxane [BHEEEN ⊂ CBPQT]4+ [BHEEEN ≡ 1,5‐bis[2‐(2‐(2‐hydroxyethoxy)ethoxy)ethoxy]naphthalene and CBPQT4+ ≡ cyclobis(paraquat‐p‐phenylene)], when this 1:1 complex is tethered on the surface of the mesoporous silica, constitutes the supramolecular nanovalves. The mesoporous silica is charged against a concentration gradient with luminescence probe molecules, e.g., tris(2,2′‐phenylpyridyl)iridium(III), Ir(ppy)3 (ppy = 2,2′‐phenylpyridyl), followed by addition of CBPQT·4Cl to form the tethered [2]pseudorotaxanes. This situation corresponds to the OFF state of the supramolecular nanovalves. Their ON state can be initiated by reducing the CBPQT4+ ring with NaCNBH3, thus weakening the complexation and causing dissociation of the CBPQT4+ ring away from the BHEEEN stalks on the mesoporous silica particles MCM‐41 to bring about ultimately the controlled release of the luminescence probe molecules from the mesoporous silica particles with an average diameter of 600 nm. This kind of functioning supramolecular system can be reconfigured further with built‐in photosensitizers, such as tethered 9‐anthracenecarboxylic acid and tethered [Ru(bpy)2(bpy(CH2OH)2)]2+ (bpy = 2,2′‐bipyridine). Upon irradiation with laser light of an appropriate wavelength, the excited photosensitizers transfer electrons to the near‐by CBPQT4+ rings, reducing them so that they dissociate away from the BHEEEN stalks on the surface of the mesoporous silica particles, leading subsequently to a controlled release of the luminescent probe molecules. This control can be expressed in both a regional and temporal manner by the use of light as the ON/OFF stimulus for the supramolecular nanovalves.

Enzyme-Responsive Intracellular Controlled Release Using Nanometric Silica Mesoporous Supports Capped with “Saccharides”

“…56,57 Zink and Stoddart prepared several gated materials triggered by redox inputs that were equipped with nanovalves based on rotaxanes and pseudorotaxanes containing redox active moieties. [58][59][60][61][62] Apart from the examples described above, which use redox-, light-and pH-triggered systems, some additional exploratory studies that use alternative external stimuli such as temperature 63 and the presence of certain anions 64 have also been reported. Another use of these hybrid gated nanomaterials deals with the development of new signaling protocols.…”

Zeolitic Imidazolate Framework-8 Capped Mesoporous Silica Nanoparticles for pH-Controlled Drug Release

“…Many studies have reported the design of responsive caps, such as nanoparticles, polymers, supramolecular assembles and biomolecules, to control drug release from MSN in response to different stimuli including pH, temperature, light, redox activation, enzymes, competitive binding, etc. [5][6][7][8][9][10][11][12][13] Of the stimuli previously reported, the construction of pH-triggered caps was one of the most efficient strategies for controlled drug release due to the different pH environment in cells, tissue or body. [14][15][16][17] For example, the interstitial or extracellular environment in tumors tends to be more acidic than the normal tissues, and the endosomes/lysosomes in cancer cells exhibit even lower pH values.…”

In vitro controlled release of cisplatin from gold-carbon nanobottles via cleavable linkages

“…In the realm of drug delivery, a sophisticated nanodelivery system, which is capable of storing and protecting drug molecules, controlling and regulating release of cargo molecules only at target site, is unequivocally desired. In this regard, release of the drugs or active agents from nanocontainers had been successfully demonstrated to be regulated in response to changes in redox potential, 17 pH, 18,19 temperature, 20 light, 21 and the presence of enzymes found in certain diseases. 22 The rate of release of the cargo molecules relies on the shape and geometrical properties of nanocontainers.…”