Ruthenium polypyridyl complexes hopping at anionic lipid bilayers through a supramolecular bond sensitive to visible light.
The new ruthenium complex [Ru(terpy)(dcbpy)(Hmte)](PF(6))(2) ([2](PF(6))(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)(OH(2))](2+) ([1](2+)), with a second-order rate constant of 0.025 s(-1) M(-1) at 25 °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 thioether-cholesterol 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 °C, thus achieving light-triggered hopping of the metal complex at the water-bilayer interface.
Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, Leiden, 2300 RA, The Netherlands.
Azadeh
A
Bahreman
Bart
B
Limburg
Maxime A
MA
Siegler
Roman
R
Koning
Abraham J
AJ
Koster
Sylvestre
S
Bonnet
D000838:Anions / Q000737:chemistry*; D056831:Coordination Complexes / Q000737:chemistry*; D018360:Crystallography, X-Ray; D008024:Ligands; D008027:Light; D008051:Lipid Bilayers / Q000737:chemistry*; D015394:Molecular Structure; D010777:Photochemistry; D011725:Pyridines / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*
D000838:Anions; D056831:Coordination Complexes; D008024:Ligands; D008051:Lipid Bilayers; D011725:Pyridines; D012428:Ruthenium