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 have led to the synthesis of amino acid derivatives of [Ni(PR 2NR' 2)2]2+ complexes, [Ni(PCy 2 N2 Amino acid)2]2+ (CyAA). It is shown that these CyAA derivatives can catalyze fully reversible H2 production/oxidation at rates approaching those of hydrogenase enzymes. The reversibility is achieved in acidic aqueous solutions (pH = 0-6), 1 atm 25% H2/Ar, and elevated temperatures (tested from 298 to 348 K) for the glycine (CyGly), arginine (CyArg), and arginine methyl ester (CyArgOMe) derivatives. As expected for a reversible process, the catalytic activity is dependent upon H2 and proton concentrations. CyArg is significantly faster in both directions (∼300 s-1 H2 production and 20 s-1 H2 oxidation; pH = 1, 348 K, 1 atm 25% H2/Ar) than the other two derivatives. The slower turnover frequencies for CyArgOMe (35 s-1 production and 7 s-1 oxidation under the same conditions) compared with 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) suggests that the additional structural features imparted by the guanidinium groups facilitate fast and reversible H2 addition/release. These observations demonstrate that outer coordination sphere amino acids work in synergy with the active site and can play an important role for synthetic molecular electrocatalysts, as has been observed for the protein scaffold of redox active enzymes.
| Original language | English |
|---|---|
| Pages (from-to) | 16286-16291 |
| Number of pages | 6 |
| Journal | Proceedings of the National Academy of Sciences of the United States of America |
| Volume | 111 |
| Issue number | 46 |
| DOIs | |
| Publication status | Published - Nov 18 2014 |
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Keywords
- Amino acid catalysts
- Homogeneous electrocatalysis
- Hydrogenase mimics
- Outer coordination sphere
- Reversible catalysis
ASJC Scopus subject areas
- General
Cite this
Amino acid modified Ni catalyst exhibits reversible H2 oxidation/production over a broad pH range at elevated temperatures. / Dutta, Arnab; DuBois, Daniel L; Roberts, John; Shaw, Wendy J.
In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 111, No. 46, 18.11.2014, p. 16286-16291.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Amino acid modified Ni catalyst exhibits reversible H2 oxidation/production over a broad pH range at elevated temperatures
AU - Dutta, Arnab
AU - DuBois, Daniel L
AU - Roberts, John
AU - Shaw, Wendy J.
PY - 2014/11/18
Y1 - 2014/11/18
N2 - 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 have led to the synthesis of amino acid derivatives of [Ni(PR 2NR' 2)2]2+ complexes, [Ni(PCy 2 N2 Amino acid)2]2+ (CyAA). It is shown that these CyAA derivatives can catalyze fully reversible H2 production/oxidation at rates approaching those of hydrogenase enzymes. The reversibility is achieved in acidic aqueous solutions (pH = 0-6), 1 atm 25% H2/Ar, and elevated temperatures (tested from 298 to 348 K) for the glycine (CyGly), arginine (CyArg), and arginine methyl ester (CyArgOMe) derivatives. As expected for a reversible process, the catalytic activity is dependent upon H2 and proton concentrations. CyArg is significantly faster in both directions (∼300 s-1 H2 production and 20 s-1 H2 oxidation; pH = 1, 348 K, 1 atm 25% H2/Ar) than the other two derivatives. The slower turnover frequencies for CyArgOMe (35 s-1 production and 7 s-1 oxidation under the same conditions) compared with 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) suggests that the additional structural features imparted by the guanidinium groups facilitate fast and reversible H2 addition/release. These observations demonstrate that outer coordination sphere amino acids work in synergy with the active site and can play an important role for synthetic molecular electrocatalysts, as has been observed for the protein scaffold of redox active enzymes.
AB - 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 have led to the synthesis of amino acid derivatives of [Ni(PR 2NR' 2)2]2+ complexes, [Ni(PCy 2 N2 Amino acid)2]2+ (CyAA). It is shown that these CyAA derivatives can catalyze fully reversible H2 production/oxidation at rates approaching those of hydrogenase enzymes. The reversibility is achieved in acidic aqueous solutions (pH = 0-6), 1 atm 25% H2/Ar, and elevated temperatures (tested from 298 to 348 K) for the glycine (CyGly), arginine (CyArg), and arginine methyl ester (CyArgOMe) derivatives. As expected for a reversible process, the catalytic activity is dependent upon H2 and proton concentrations. CyArg is significantly faster in both directions (∼300 s-1 H2 production and 20 s-1 H2 oxidation; pH = 1, 348 K, 1 atm 25% H2/Ar) than the other two derivatives. The slower turnover frequencies for CyArgOMe (35 s-1 production and 7 s-1 oxidation under the same conditions) compared with 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) suggests that the additional structural features imparted by the guanidinium groups facilitate fast and reversible H2 addition/release. These observations demonstrate that outer coordination sphere amino acids work in synergy with the active site and can play an important role for synthetic molecular electrocatalysts, as has been observed for the protein scaffold of redox active enzymes.
KW - Amino acid catalysts
KW - Homogeneous electrocatalysis
KW - Hydrogenase mimics
KW - Outer coordination sphere
KW - Reversible catalysis
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U2 - 10.1073/pnas.1416381111
DO - 10.1073/pnas.1416381111
M3 - Article
VL - 111
SP - 16286
EP - 16291
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
SN - 0027-8424
IS - 46
ER -