title: Metal ion, light, and redox responsive interaction of vesicles by a supramolecular switch.
abstract: Chemical, photochemical and electrical stimuli are versatile possibilities to exert external control on self-assembled materials. Here, a trifunctional molecule that switches between an "adhesive" and a "non-adhesive" state in response to metal ions, or light, or oxidation is presented. To this end, an azobenzene-ferrocene conjugate with a flexible N,N'-bis(3-aminopropyl)ethylenediamine spacer was designed as a multistimuli-responsive guest molecule that can form inclusion complexes with β-cyclodextrin. In the absence of any stimulus the guest molecule induces reversible aggregation of host vesicles composed of amphiphilic β-cyclodextrin due to the formation of intervesicular inclusion complexes. In this case, the guest molecule operates as a noncovalent cross-linker for the host vesicles. In response to any of three external stimuli (metal ions, UV irradiation, or oxidation), the conformation of the guest molecule changes and its affinity for the host vesicles is strongly reduced, which results in the dissociation of intervesicular complexes. Upon elimination or reversal of the stimuli (sequestration of metal ion, visible irradiation, or reduction) the affinity of the guest molecules for the host vesicles is restored. The reversible cross-linking and aggregation of the cyclodextrin vesicles in dilute aqueous solution was confirmed by isothermal titration calorimetry (ITC), optical density measurements at 600 nm (OD600 ), dynamic light scattering (DLS), ζ-potential measurements and cyclic voltammetry (CV). To the best of our knowledge, a dynamic supramolecular system based on a molecular switch that responds orthogonally to three different stimuli is unprecedented.
authors.affiliation: Organic Chemistry Institute and Graduate School of Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster (Germany).
authors.forename: Avik
authors.initials: A
authors.lastname: Samanta
authors.forename: Bart Jan
authors.initials: BJ
authors.lastname: Ravoo
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D003692:Delayed-Action Preparations / Q000737:chemistry; D005029:Ethylenediamines / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D008027:Light; D000075163:Metallocenes; D008670:Metals / Q000737:chemistry; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D047392:beta-Cyclodextrins / Q000737:chemistry*
chemical_list: D001391:Azo Compounds; D003692:Delayed-Action Preparations; D005029:Ethylenediamines; D005296:Ferrous Compounds; D007477:Ions; D000075163:Metallocenes; D008670:Metals; D047392:beta-Cyclodextrins; C009850:azobenzene; C031215:betadex; C004998:ferrocene
keywords: cyclodextrins; host-guest systems; molecular recognition; stimulus-responsive materials; vesicles