Cobaloxime-Based
Artificial Hydrogenases
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Abstract
Cobaloximes are popular H<sub>2</sub> evolution molecular catalysts but have so far mainly been studied
in nonaqueous conditions. We show here that they are also valuable
for the design of artificial hydrogenases for application in neutral
aqueous solutions and report on the preparation of two well-defined
biohybrid species via the binding of two cobaloxime moieties, {Co(dmgH)<sub>2</sub>} and {Co(dmgBF<sub>2</sub>)<sub>2</sub>} (dmgH<sub>2</sub> = dimethylglyoxime), to apo <i>Sperm-whale</i> myoglobin
(<i>Sw</i>Mb). All spectroscopic data confirm that the cobaloxime
moieties are inserted within the binding pocket of the <i>Sw</i>Mb protein and are coordinated to a histidine residue in the axial
position of the cobalt complex, resulting in thermodynamically stable
complexes. Quantum chemical/molecular mechanical docking calculations
indicated a coordination preference for His93 over the other histidine
residue (His64) present in the vicinity. Interestingly, the redox
activity of the cobalt centers is retained in both biohybrids, which
provides them with the catalytic activity for H<sub>2</sub> evolution
in near-neutral aqueous conditions