Photoinduced Intramolecular Tryptophan Oxidation and Excited-State Behavior of [Re(L-AA)(CO) 3 (α-diimine)] + (L = Pyridine or Imidazole, AA = Tryptophan, Tyrosine, Phenylalanine)
2011; American Chemical Society; Volume: 50; Issue: 13 Linguagem: Inglês
10.1021/ic200252z
ISSN1520-510X
AutoresAna María Blanco‐Rodríguez, Michael Towrie, Jan Sýkora, Stanislav Záliš, Antonı́n Vlček,
Tópico(s)Free Radicals and Antioxidants
ResumoReI 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 ReI(CO)3→N,N 3MLCT excited state *[ReII(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)→*ReII electron transfer (ET) producing a charge-separated (CS) state, [ReI(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.
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