skip to main content


Title: A De Novo‐Designed Artificial Metallopeptide Hydrogenase: Insights into Photochemical Processes and the Role of Protonated Cys
Abstract

Hydrogenase enzymes produce H2gas, 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 tandema/dpositions 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 H2photocatalytically, 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−Hintermediate (Ni−R) by a Cys (pKa≈6.4) to produce H2.

 
more » « less
Award ID(s):
1757220
PAR ID:
10224130
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
ChemSusChem
Volume:
14
Issue:
10
ISSN:
1864-5631
Page Range / eLocation ID:
p. 2237-2246
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    De novo metalloprotein design involves the construction of proteins guided by specific repeat patterns of polar and apolar residues, which, upon self‐assembly, provide a suitable environment to bind metals and produce artificial metalloenzymes. While a wide range of functionalities have been realized in de novo designed metalloproteins, the functional repertoire of such constructs towards alternative energy‐relevant catalysis is currently limited. Here we show the application of de novo approach to design a functional H2evolving protein. The design involved the assembly of an amphiphilic peptide featuring cysteines at tandema/dsites of each helix. Intriguingly, upon NiIIaddition, the oligomers shift from a major trimeric assembly to a mix of dimers and trimers. The metalloprotein produced H2photocatalytically with a bell‐shape pH dependence, having a maximum activity at pH 5.5. Transient absorption spectroscopy is used to determine the timescales of electron transfer as a function of pH. Selective outer sphere mutations are made to probe how the local environment tunes activity. A preferential enhancement of activity is observed via steric modulation above the NiIIsite, towards the N‐termini, compared to below the NiIIsite towards the C‐termini.

     
    more » « less
  2. Thorp, Holden (Ed.)

    Ancestral metabolic processes involve the reversible oxidation of molecular hydrogen by hydrogenase. Extant hydrogenase enzymes are complex, comprising hundreds of amino acids and multiple cofactors. We designed a 13–amino acid nickel-binding peptide capable of robustly producing molecular hydrogen from protons under a wide variety of conditions. The peptide forms a di-nickel cluster structurally analogous to a Ni-Fe cluster in [NiFe] hydrogenase and the Ni-Ni cluster in acetyl-CoA synthase, two ancient, extant proteins central to metabolism. These experimental results demonstrate that modern enzymes, despite their enormous complexity, likely evolved from simple peptide precursors on early Earth.

     
    more » « less
  3. Abstract

    Addition of sub‐stoichiometric quantities of PEt3and diphenyl disulfide to a solution of [Ni(1,5‐cod)2] generates a mixture of [Ni3(SPh)4(PEt3)3] (1), unreacted [Ni(1,5‐cod)2], and [(1,5‐cod)Ni(PEt3)2], according to1H and31P{1H} NMR spectroscopic monitoring of the in situ reaction mixture. On standing, complex1converts into [Ni4(S)(Ph)(SPh)3(PEt3)3] (2), via formal addition of a “Ni(0)” equivalent, coupled with a CS oxidative addition step, which simultaneously generates the Ni‐bound phenyl ligand and the μ3‐sulfide ligand. Upon gentle heating, complex2converts into a mixture of [Ni5(S)2(SPh)2(PEt3)5] (3) and [Ni8(S)5(PEt3)7] (4), via further addition of “Ni(0)” equivalents, in combination with a series of C–S oxidative addition and CC reductive elimination steps, which serve to convert thiophenolate ligands into sulfide ligands and biphenyl. The presence of14in the reaction mixture is confirmed by their independent syntheses and subsequent spectroscopic characterization. Overall, this work provides an unprecedented level of detail of the early stages of Ni nanocluster growth and highlights the fundamental reaction steps (i.e., metal atom addition, CS oxidative addition, and CC reductive elimination) that are required to grow an individual cluster.

     
    more » « less
  4. Abstract

    We report a nickel complex for catalytic oxidation of ammonia to dinitrogen under ambient conditions. Using the aryloxyl radical 2,4,6‐tri‐tert‐butylphenoxyl (tBu3ArO⋅) as a H atom acceptor to cleave the N−H bond of a coordinated NH3ligand up to 56 equiv of N2per Ni center can be generated. Employing theN‐oxyl radical 2,2,6,6‐(tetramethylpiperidin‐1‐yl)oxyl (TEMPO⋅) as the H‐atom acceptor, up to 15 equiv of N2per Ni center are formed. A bridging Ni‐hydrazine product identified by isotopic nitrogen (15N) studies and supported by computational models indicates the N−N bond forming step occurs by bimetallic homocoupling of two paramagnetic [Ni]−NH2fragments. Ni‐mediated hydrazine disproportionation to N2and NH3completes the catalytic cycle.

     
    more » « less
  5. Abstract

    We report a nickel complex for catalytic oxidation of ammonia to dinitrogen under ambient conditions. Using the aryloxyl radical 2,4,6‐tri‐tert‐butylphenoxyl (tBu3ArO⋅) as a H atom acceptor to cleave the N−H bond of a coordinated NH3ligand up to 56 equiv of N2per Ni center can be generated. Employing theN‐oxyl radical 2,2,6,6‐(tetramethylpiperidin‐1‐yl)oxyl (TEMPO⋅) as the H‐atom acceptor, up to 15 equiv of N2per Ni center are formed. A bridging Ni‐hydrazine product identified by isotopic nitrogen (15N) studies and supported by computational models indicates the N−N bond forming step occurs by bimetallic homocoupling of two paramagnetic [Ni]−NH2fragments. Ni‐mediated hydrazine disproportionation to N2and NH3completes the catalytic cycle.

     
    more » « less