Gene/Protein
Disease
Symptom
Drug
Enzyme
Compound
Pivot Concepts:
Gene/Protein
Disease
Symptom
Drug
Enzyme
Compound
Target Concepts:
Gene/Protein
Disease
Symptom
Drug
Enzyme
Compound
Query: EC:1.12.7.2 (
hydrogenase
)
3,522
document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)
The electrochemical reduction of CO
2
has been extensively investigated in recent years, with the expectation that a detailed mechanistic understanding could achieve the goal of finding a stable catalyst with high turnover frequencies and low reduction potentials. In the catalytic cycle of the carbon dioxide
hydrogenase
enzyme, it has been suggested that the reduced metal center reacts with CO
2
to form a carboxylate intermediate that is stabilized by hydrogen bonding using a histidine moiety in the second coordination sphere. Using the well-known fac-Re(I)bipyridine(CO)
3
Cl complex as a starting point, the bipyridine ligand was modified in the second coordination sphere with a
thiourea
tether that is known to form hydrogen bonds with carbonyl moieties. The resulting Re(I) catalyst was an excellent electrocatalyst for the selective reduction of CO
2
to CO, with a turnover frequency of 3040 s
-1
. The binding of CO
2
to the
thiourea
tether was observable by
1
H NMR, and NOE experiments showed that the hydrogen atoms of the
thiourea
group were labile. Further experiments indicated that the
thiourea
moiety is also a local proton source and addition of an external proton source actually inhibits catalysis. The absence of a kinetic isotope effect was explained through DFT calculations that showed that the proton invariably jumps to the nearest CO
2
oxygen atom to form a metal-carboxylic acid without going through any minimum or transition state. EPR and NMR spectroscopies were used to identify the various reduced intermediates. Thus, the
thiourea
tether in the second coordination sphere can bind CO
2
, stabilize carboxylic acid reaction intermediates, and directly act as a local proton source, leading to a significantly more active catalyst.
...
PMID:A Thiourea Tether in the Second Coordination Sphere as a Binding Site for CO
2
and a Proton Donor Promotes the Electrochemical Reduction of CO
2
to CO Catalyzed by a Rhenium Bipyridine-Type Complex. 3020 68
