Ruthenium Polypyridyl Complexes Hopping at Anionic Lipid Bilayers through a Supramolecular Bond Sensitive to Visible Light

TitleRuthenium Polypyridyl Complexes Hopping at Anionic Lipid Bilayers through a Supramolecular Bond Sensitive to Visible Light
Publication TypeJournal Article
Year of Publication2012
AuthorsBahreman, A., B. Limburg, M.A. Siegler, R. Koning, A.J. Koster, S. Bonnet
JournalChemistry-a European Journal
Date PublishedAug
ISBN Number0947-6539
Accession NumberISI:000307108100020
Keywordsalpha-cyclodextrin, azobenzene polymers, binding ability, bioinorganic chemistry, dithienylethene, host, hydrogel, ligand-l, liposomes, molecular machine prototypes, molecular motion, photochemical expulsion, photochemistry, recognition, supramolecular chemistry

The new ruthenium complex [Ru(terpy)(dcbpy)(Hmte)](PF6)2 ([2](PF6)2; dcbpy=6,6'-dichloro-2,2'-bipyridine, terpy=2,2';6',2-terpyridine, Hmte=2-(methylthio)ethanol) was synthesized. In the crystal structure, this complex is highly distorted, revealing steric congestion between dcbpy and Hmte. In water, [2]2+ forms spontaneously by reacting Hmte and the aqua complex [Ru(terpy)(dcbpy)(OH2)]2+ ([1]2+), with a second-order rate constant of 0.025 s-1?M-1 at 25?degrees C. In the dark, the Ru?S bond of [2]2+ is thermally unstable and partially hydrolyzes; in fact, [1]2+ and [2]2+ are in an equilibrium characterized by an equilibrium constant K of 151?M-1. When exposed to visible light, the Ru?S bond is selectively broken to release [1]2+, that is, the equilibrium is shifted by visible-light irradiation. The light-induced equilibrium shifts were repeated four times without major signs of degradation; the Ru?S coordination bond in [2]2+ can be described as a robust, light-sensitive, supramolecular bond in water. To demonstrate the potential of this system in supramolecular chemistry, a new thioethercholesterol conjugate (4), which inserts into lipid bilayers through its cholesterol moiety and coordinates to ruthenium through its sulfur atom, was synthesized. Thioether-functionalized, anionic, dimyristoylphosphatidylglycerol (DMPG), lipid vesicles, to which aqua complex [1]2+ efficiently coordinates, were prepared. Upon exposure of the Ru-decorated vesicles to visible light, the Ru-S bond is selectively broken, thus releasing [1]2+ that stays at the water-bilayer interface. When the light is switched off, the metal complex spontaneously coordinates back to the membrane-embedded thioether ligands without a need to heat the system. This process was repeated four times at 35?degrees C, thus achieving light-triggered hopping of the metal complex at the water-bilayer interface.


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