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

Abstract

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 phototriggered electron transfer between triarylamine and Ru(iii) is complete within 10 ns, thus highlighting the potential of such artificial metalloenzymes to perform photoredox catalysis.

Rational design of metalloenzymes: From single to multiple active sites

“…In vitro studies further showed that biot-Ru-SAV mut has a catalytic efficiency 2-fold that of biot-Ru-SAV peri , with increasing kcat and decreasing KM values, respectively. In another study, Wenger, Ward, and co-workers [161] Cu center with an electron transfer function. Together with previous achievements [153], these studies show that the biotin-steptavidin system is well-exploited for design of novel metalloenzymes with diverse functions.…”

Streptavidin as a Scaffold for Light‐Induced Long‐Lived Charge Separation

“…The ruthenium(II) complex [Ru(bpy) 2 (phenNHCOCH 2 Br)](PF 6 ) 2 , the biotinylated supramolecular binding partner triarylamine Biot-TAA,a nd the reference triarylamine TAA-NH 2 were synthesized as previously described (Figure 1). [50] The alkoxy-amine containing methyl viologen analogue aMV 2 + + was synthesized in four steps, as detailed in the Supporting Information (Scheme S1 andF igures S1-S7). As previously demonstrated, [50] the dyad bearing the ruthenium photosensitizer covalently anchored at position K121C of Sav displayed the highest quantum yield of the oxidized Biot-TAA.W et hus selected K121C Sav as as tarting scaffold fora ll mutagenesis studies reported herein.I nspection of the X-ray structure of the mature S112A Sav (pdb code:3 PK2) [54] revealed ad isordered N-terminus (i.e., residues 2-12, ASMTGGQQMGR).…”

“…[50] The alkoxy-amine containing methyl viologen analogue aMV 2 + + was synthesized in four steps, as detailed in the Supporting Information (Scheme S1 andF igures S1-S7). As previously demonstrated, [50] the dyad bearing the ruthenium photosensitizer covalently anchored at position K121C of Sav displayed the highest quantum yield of the oxidized Biot-TAA.W et hus selected K121C Sav as as tarting scaffold fora ll mutagenesis studies reported herein.I nspection of the X-ray structure of the mature S112A Sav (pdb code:3 PK2) [54] revealed ad isordered N-terminus (i.e., residues 2-12, ASMTGGQQMGR). These residues were modeled using Yasara [55] and possesseda na-helicals tructure.…”

“…In a recent study, we covalently anchored [Ru(bpy) 2 (phenNHCOCH 2 Br)](PF 6 ) 2 (bpy=2,2′‐bipyridine, phen=phenanthroline) to four different Sav isoforms bearing a single cysteine residue per monomer (Figure ). Upon addition of a biotinylated triarylamine Biot‐TAA , acting as electron donor, and excess methyl viologen MV 2+ as external electron acceptor, we could characterize, by transient absorption spectroscopy, the formation of charge‐separated species by photoinduced electron transfer.…”

“…[23,[29][30][31][32][33] In a related context, several studies on the luminescence properties of (strept)avidin-embedded biotinylated d 6 -metal complexes, including ruthenium(II) polypyridines, [34][35][36][37] rhenium(I) tricarbonyl diimines, [38][39][40][41][42] and cyclometalated iridium(III) complexes [43][44][45][46][47][48] suggest that such protein-based systems are well-suited for the generationo fp hoto-induced chargeseparation. [49] In ar ecent study, [50] we covalently anchored [Ru(bpy) 2 (phenNHCOCH 2 Br)](PF 6 ) 2 (bpy = 2,2'-bipyridine, phen = phenanthroline) to four different Sav isoformsb earing as ingle cysteine residue per monomer( Figure 1). Upon addition of ab iotinylated triarylamine Biot-TAA,a cting as electron donor,a nd excessm ethyl viologen MV 2 + + as externale lectron acceptor, we could characterize, by transienta bsorption spectroscopy, the formation of charge-separated species by photoinduced electron transfer.…”