Cobaloxime-Based Artificial Hydrogenases

Abstract

Cobaloximes are popular H 2 evolution molecular catalysts, but have so far mainly been studied in non-aqueous 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) 2 } and {Co(dmgBF 2 ) 2 }(dmgH 2 = dimethylglyoxime) to apo Sperm-whale myoglobin (SwMb). All spectroscopic data confirm that the cobaloxime moieties are inserted within the binding pocket of the SwMb protein and are coordinated to a histidine residue in axial position of the cobalt complex, resulting in thermodynamically stable complexes. QC/MM docking calculations indicated 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 catalytic activity for H 2 evolution in near neutral aqueous conditions.

Computational, electrochemical, and spectroscopic studies of two mononuclear cobaloximes: the influence of an axial pyridine and solvent on the redox behaviour and evidence for pyridine coordination to cobalt(i) and cobalt(ii) metal centres

“…1), however, cobaloximes still continue to generate a lot of interest due to their high activity towards electrocatalytic proton reduction. 15,19,37–39 …”

Structural and electronic characterization of multi-electron reduced naphthalene (BIAN) cobaloximes

“…Furthermore, cobaloximes have been explored in conjunction with homogeneous photosensitizers, [25][26][27][28] as components in aqueous systems, [29][30][31] as a functional catalyst on vesicle membrane surfaces, 32 and used as part of an artificial hydrogenase in a hybrid SwMb system. 33 Moreover, increasingly elaborate ligand designs have been devised and studied. However, only marginal improvements over the most basic complexes have been realized.…”

Artificial hydrogenase: biomimetic approaches controlling active molecular catalysts

“…To develop cobaloxime-based catalysts in aqueous media, a process of embedding the active catalyst within the protein scaffold was explored to generate an artificial metalloenzyme. Two cobaloximes 11 and 12 were inserted into sperm whale myoglobin, a protein which is known to bind a variety of hydrophobic planar cofactor analogues (Figure 3a) [36]. The UV-vis absorption and EPR analysis of the resulting biohybrid indicates axial coordination of the His residue to the Co center.…”

“…The Co complexes noncovalently inserted into a protein matrix[36,37]. (b) Structure of cobalt myoglobin (PDB ID: 1YOH…”