Activation Thermodynamics and H/D Kinetic Isotope Effect of the H_(ox) to H_(red)H~+ Transition in [FeFe] Hydrogenase

摘要

Molecular complexes between CdSe nano-crystals and Clostridium acetobutylicum [FeFe] hydrogenase I (CaI) enabled light-driven control of electron transfer for spectroscopic detection of redox intermediates during catalytic proton reduction. Here we address the route of electron transfer from CdSe→CaI and activation thermodynamics of the initial step of proton reduction in CaI. The electron paramagnetic spectroscopy of illuminated CdSe:CaI showed how the CaI accessory FeS cluster chain (F-clusters) functions in electron transfer with CdSe. The H_(ox)→H_(red)H~+ reduction step measured by Fourier-transform infrared spectroscopy showed an enthalpy of activation of 19 kJ mol~(-1) and a ~2.5-foId kinetic isotope effect. Overall, these results support electron injection from CdSe into CaI involving F-clusters, and that the H_(ox)→H_(red)H~+ step of catalytic proton reduction in CaI proceeds by a proton-dependent process.