Light-driven electron injection from a biotinylated triarylamine donor to [Ru(diimine)3]2+-labeled streptavidin

Electron transfer from a biotinylated electron donor to photochemically generated Ru(III) complexes covalently anchored to streptavidin is demonstrated by means of time-resolved laser spectroscopy. Through site-selective mutagenesis, a single cysteine residue was engineered at four different positions on streptavidin, and a Ru(II) tris-diimine complex was then bioconjugated to the exposed cysteines. A biotinylated triarylamine electron donor was added to the Ru(II)-modified streptavidins to afford dyads localized within a streptavidin host. The resulting systems were subjected to electron transfer studies. In some of the explored mutants, the photo-triggered electron transfer between triarylamine and Ru(III) is complete within 10 ns, thus highlighting the potential of such artificial metalloenzymes to perform photoredox catalysis.