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A De Novo‐Designed Artificial Metallopeptide Hydrogenase: Insights into Photochemical Processes and the Role of Protonated Cys
Ist Teil von
ChemSusChem, 2021-05, Vol.14 (10), p.2237-2246
Ort / Verlag
Germany: Wiley Subscription Services, Inc
Erscheinungsjahr
2021
Link zum Volltext
Quelle
Wiley Online Library - AutoHoldings Journals
Beschreibungen/Notizen
Hydrogenase enzymes produce H2 gas, which can be a potential source of alternative energy. Inspired by the [NiFe] hydrogenases, we report the construction of a de novo‐designed artificial hydrogenase (ArH). The ArH is a dimeric coiled coil where two cysteine (Cys) residues are introduced at tandem a/d positions of a heptad to create a tetrathiolato Ni binding site. Spectroscopic studies show that Ni binding significantly stabilizes the peptide producing electronic transitions characteristic of Ni‐thiolate proteins. The ArH produces H2 photocatalytically, demonstrating a bell‐shaped pH‐dependence on activity. Fluorescence lifetimes and transient absorption spectroscopic studies are undertaken to elucidate the nature of pH‐dependence, and to monitor the reaction kinetics of the photochemical processes. pH titrations are employed to determine the role of protonated Cys on reactivity. Through combining these results, a fine balance is found between solution acidity and the electron transfer steps. This balance is critical to maximize the production of NiI‐peptide and protonation of the NiII−H− intermediate (Ni−R) by a Cys (pKa≈6.4) to produce H2.
State of the artifice: An artificial Ni hydrogenase is designed within a coiled coil peptide, which produces H2 under light. Mechanistic studies employing time‐resolved kinetics, transient absorption spectroscopy, and pH‐titration experiments demonstrate that a suitable control of solution acidity needs to be maintained to maximize the yield of NiI‐peptide and to enable a Cys thiol to protonate the NiII−H− intermediate for optimal catalytic activity.