A De Novo‐Designed Artificial Metallopeptide Hydrogenase: Insights into Photochemical Processes and the Role of Protonated Cys
Sreya Malayam Parambath, Ashley E. Williams, Leigh Anna Hunt, Dhanashree Selvan, Nathan I. Hammer, Saumen Chakraborty
Abstract
Abstract Hydrogenase enzymes produce H 2 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 H 2 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 Ni I ‐peptide and protonation of the Ni II −H − intermediate (Ni−R) by a Cys (p K a ≈6.4) to produce H 2 .