Sequential Proton Coupled Electron Transfer (PCET): Dynamics Observed over 8 Orders of Magnitude in Time

Luke Macaleese (1) , Sylvain Hermelin (2) , Krystel El Hage (3) , Pierre Chouzenoux (1) , Alexander Kulesza (1) , Rodolphe Antoine (1) , Luigi Bonacina (2) , Markus Meuwly (3) , Jean-Pierre Wolf (2) , Philippe Dugourd (1)

1 ILM - Institut Lumière Matière [Villeurbanne]
2 GAP - Group of Applied Physics [Geneva]
3 Department of Chemistry [Basel]

Charge transfer mechanisms lay at the heart of chemistry and biochemistry. Proton coupled electron transfers (PCET) are central in biological processes such as photosynthesis and in the respiratory chain, where they mediate long-range charge transfers. These mechanisms are normally difficult to harness experimentally due to the intrinsic complexity of the associated biological systems. Metal-peptide cations experience both electron and proton transfers upon photoexcitation, proving an amenable model system to study PCET. We report on a time-resolved experiment designed to follow this dual charge transfer kinetics in [HG₃W+Ag]⁺ (H = histidine, G = glycine, W = tryptophan) on time scales ranging from femtoseconds to milliseconds. While electron transfer completes in less than 4 ps, it triggers a proton transfer lasting over hundreds of microseconds. Molecular dynamics simulations show that conformational dynamic plays an important role in slowing down this reaction. This combined experimental and computational approach provides a view of PCET as a single phenomenon despite its very wide time-domain span.

Mots clés: photo-triggered charge transfer; metal-peptide complex; electron and proton transfer; tryptophan-containing peptide; Pump-probe spectroscopy; action spectroscopy

Domaines: Chimie; Physique [physics]

Luke Macaleese, Sylvain Hermelin, Krystel El Hage, Pierre Chouzenoux, Alexander Kulesza, et al.. Sequential Proton Coupled Electron Transfer (PCET): Dynamics Observed over 8 Orders of Magnitude in Time. Journal of the American Chemical Society, 2016, 138 (13), pp.4401-4407. ⟨10.1021/jacs.5b12587⟩. ⟨hal-01344620⟩