Title: Amino acid modified Ni catalyst exhibits reversible H₂ oxidation/production over a broad pH range at elevated temperatures

Abstract

Hydrogenases interconvert H₂ and protons at high rates and with high energy efficiencies, providing inspiration for the development of molecular catalysts. Studies designed to determine how the protein scaffold can influence a catalytically active site has led to the synthesis of amino acid derivatives, [Ni(P^Cy₂N^{Amino acid}2)₂]²⁺ (CyAA), of [Ni(P^R₂N^R'₂)₂]²⁺ complexes. It is shown that these CyAA derivatives can catalyze fully reversible H₂ production/oxidation, a feature reminiscent of enzymes. The reversibility is achieved in acidic aqueous solutions, 0.25% H₂/Ar, and elevated temperatures (tested up to 348 K) for the glycine (CyGly), arginine (CyArg), and arginine methyl ester (CyArgOMe) derivatives. As expected for a reversible process, the activity is dependent upon H₂ and proton concentration. CyArg is significantly faster in both directions than the other two derivatives (~300 s^-1 H₂ production and 20 s^-1 H₂ oxidation; pH = 1, 348 K). The significantly slower rates for CyArgOMe (35 s^-1 production and 7 s^-1 oxidation) compared to CyArg suggests an important role for the COOH group during catalysis. That CyArg is faster than CyGly (3 s^-1 production and 4 s^-1 oxidation under the same conditions) suggests that the additional structural features imparted by the guanidinium groups facilitate fast and reversible H₂ addition/release. Furthermore,more » these observations demonstrate that appended, outer coordination sphere amino acids work in synergy with the active site and can play an equally important role for synthetic molecular electrocatalysts as the protein scaffold does for redox active enzymes.« less

Authors:

Dutta, Arnab ^[1]; DuBois, Daniel L. ^[1]; Roberts, John A. S. ^[2]; Shaw, Wendy J. ^[1]

---

+ Show Author Affiliations

1. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States); REC Silicon, Moses Lake, WA (United States)

Publication Date:

Mon Nov 03 00:00:00 EST 2014

Research Org.:

Pacific Northwest National Laboratory (PNNL), Richland, WA (United States). Environmental Molecular Sciences Laboratory (EMSL)

Sponsoring Org.:

USDOE

OSTI Identifier:

1166832

Report Number(s):

PNNL-SA-104694
Journal ID: ISSN 0027-8424; 44681; KC0302010

Grant/Contract Number:  

AC05-76RL01830

Resource Type:

Accepted Manuscript

Journal Name:

Proceedings of the National Academy of Sciences of the United States of America

Additional Journal Information:

Journal Volume: 111; Journal Issue: 46; Journal ID: ISSN 0027-8424

Publisher:

National Academy of Sciences, Washington, DC (United States)

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; reversible H2 oxidation/production catalysis; bioinspired catalyst; outer coordination sphere; homogeneous electrocatalysis; hydrogenase mimics; Environmental Molecular Sciences Laboratory; amino acid catalysts; outer coordination; sphere