Control of nanospaces with molecular devices

Abstract

Cavitands and capsules define nanoliter spaces for recognition, isolation and reactions of small molecules. These systems are usually self-assembled and factors such as solvent size, stoichiometry, and packing factors determine what goes into the spaces. Here we examine two switching devices to control what and when guests get in and out of these hosts: bipyridyl-metal chelation and azobenzene photoisomerization. The effects are reversible by treatment with conventional chelating agents and brief heating, respectively. Accordingly, it is possible to trigger reactions that take place within a cylindrical capsule by light, even though the reaction process is not photochemical by nature. Likewise the presence of metals can regulate reactions without acting as direct catalysts.

Electrochemically Driven Cup‐and‐Ball CuI and CuII Complexes

“…However, even with a reinforced intramolecular coordination of the hydroxy ligand, substitution at the endo site is still possible in the two redox states. The coordinating ability of L OH confirms that a redox switch at a metal cation can be activated if the affinity of a receptor for a guest is adequately tuned 22. In previous studies, it has been demonstrated that the control of molecular recognition in a cavity could be triggered by using a chemical,9a photochemical,9b or redox stimulus 6b.…”

“…The coordinating ability of L OH confirms that a redox switch at a metal cation can be activated if the affinity of a receptor for a guest is adequately tuned. [22] In previous studies, it has been demonstrated that the control of molecular recognition in a cavity could be triggered by using a chemical, [9a] photochemical, [9b] or redox stimulus. [6b, c, d] In this work, we coupled a redox stimulus with molecular recognition to induce motion in a molecular machine by switching the position of an internal ligand (endo/exo).…”

Photolariats: synthesis, metal ion complexation and photochromism

“…The return cis-to-trans transformation can be achieved thermally or by visible irradiation. In this way, different hosts such as cavitands and capsules can be rendered photoactive and more specifically the miniscule internal (yoctolitre) spaces available for chemical encapsulation can be controlled, which can ultimately lead to recognition, sequestration and reactivity of small molecules, depending on the host (9,10). Among different manifestations of azobenzene in supramolecular hosts, one of the most successful implementations was the development of photocrowns where an azobenzene unit was directly incorporated in the macrocyclic host or in 'butterfly' variants (7, 11 15).…”

Reversible switching between self-assembled homomeric and hybrid capsules

“…Earlier, we reported several reversible switches for container molecule complexes. [20][21][22][23][24][25] Typically, long guests such as azobenzene derivatives are well encapsulated by the homomeric cylindrical assembly 2.2 and smaller guests tend to favor hybrid capsule 1.2 (Fig. 1).…”