title: Photoinduced intramolecular tryptophan oxidation and excited-state behavior of [Re(L-AA)(CO)3(α-diimine)](+) (L = pyridine or imidazole, AA = tryptophan, tyrosine, phenylalanine).
abstract: Re(I) carbonyl-diimine complexes [Re(L-AA)(CO)(3)(N,N)](+) (N,N = bpy, phen) containing an aromatic amino acid (AA), phenylalanine (Phe), tyrosine (Tyr), or tryptophan (Trp), linked to Re by a pyridine-amido or imidazole-amido ligand L have been synthesized and their excited-state properties investigated by nanosecond time-resolved IR (TRIR) and emission spectroscopy. Near-UV optical excitation populates a Re(I)(CO)(3)→N,N (3)MLCT excited state *[Re(II)(L-AA)(CO)(3)(N,N(•-))](+). Decay to the ground state (50-300 ns lifetime) is the only excited-state deactivation process observed in the case of Phe and Tyr complexes, whereas the Trp-containing species undergo a Trp(indole)→*Re(II) electron transfer (ET) producing a charge-separated (CS) state, [Re(I)(L-Trp(•+))(CO)(3)(N,N(•-))](+). The ET occurs with a 8-40 ns lifetime depending on L, N,N, and the solvent. The CS state is characterized by ν(CO) IR bands shifted to lower wavenumbers from their respective ground-state positions and two bands at 1278 and 1497 cm(-1) tentatively attributed to Trp(•+). The amido bridge is affected by both the MLCT excitation and the subsequent ET, manifested by the shifts and intensity changes of the amide-I IR band at about 1680 cm(-1). The CS state decays to the ground state by a N,N(•-)→Trp(•+) back-ET the rates of which are comparable to those of the forward ET, 30-60 ns. This study independently demonstrates that Trp can act as an electron-hopping intermediate in photodriven ET systems based on Re-labeled proteins and supramolecules. Photoinduced ET in Trp-containing Re complexes also can be used to generate Trp(•+) and investigate its spectral properties and reactivity.
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, United Kingdom.
authors.forename: Ana María
authors.initials: AM
authors.lastname: Blanco-Rodríguez
authors.forename: Mike
authors.initials: M
authors.lastname: Towrie
authors.forename: J
authors.initials: J
authors.lastname: Sýkora
authors.forename: Stanislav
authors.initials: S
authors.lastname: Záliš
authors.forename: Antonín
authors.initials: A
authors.lastname: Vlček
mesh_terms: D002248:Carbon Monoxide / Q000737:chemistry; D007093:Imidazoles / Q000737:chemistry; D007097:Imines / Q000737:chemistry; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010084:Oxidation-Reduction; D010649:Phenylalanine / Q000737:chemistry; D055668:Photochemical Processes; D011725:Pyridines / Q000737:chemistry; D011789:Quantum Theory; D012211:Rhenium / Q000737:chemistry; D013237:Stereoisomerism; D014364:Tryptophan / Q000737:chemistry*; D014443:Tyrosine / Q000737:chemistry
chemical_list: D007093:Imidazoles; D007097:Imines; D009942:Organometallic Compounds; D011725:Pyridines; D014443:Tyrosine; D010649:Phenylalanine; D012211:Rhenium; C029899:imidazole; D002248:Carbon Monoxide; D014364:Tryptophan; C023666:pyridine