Periodic Reporting for period 1 - DANHIMC (Development and Application of Novel Hydrogenase-Inspired Mn Complexes)
Reporting period: 2018-03-01 to 2020-02-29
Nature has its own way to do similar hydrogenation reactions. Hydrogenases are biological catalysts for the production and activation of H2. There are three types of hydrogenases: [NiFe]-hydrogenase, [FeFe]-hydrogenase, and [Fe]-hydrogenase. The [Fe]-hydrogenase is found in some methanogenic archaea growing on H2 and CO2. The enzyme catalyzes the reaction of methenyltetrahydromethanopterin (methenyl-H4MPT+) with H2 to form methylenetetrahydromethanopterin (methylene-H4MPT) and H+. The reaction is rapid under 1 atmosphere of H2 at room temperature, with turnover frequencies of 100-200 per second. Thus, [Fe]-hydrogenase might be considered as an excellent hydrogenation catalyst for unsaturated organic substrates.
Impressed by the high activity of [Fe]-hydrogenase and considering its base metal nature, we plan to learn from this natural hydrogenase for new base metal dependent hydrogenation catalysts development. On the other hand, the limited activities from reported Fe based mimic models force us to reconsider the choice of metal center. Inspired by the vast development of Mn hydrogenation catalysts in recent years and given that Mn(I) and Fe(II) are isoelectronic, we decided to combine [Fe]-hydrogenase and Mn(I) together. Moreover, we expect our new biomimetic synthetic models will provide insights on this enzyme’s working mechanism and result in even better catalytic performance.
As a result, we managed to synthesize some novel Mn(I) based complexes mimicking natural [Fe]-hydrogenase. These complexes not only showed the highest catalytic activities among all the known analogous mimic models, but also delivered useful hydrogenation systems for various substrates. At the same time, semi-synthetic artificial [Mn]-hydrogenases were constructed with enhanced activity and gave insights for mechanism study.
Except for hydrogenation catalyst development, these new Mn(I) based mimic models were also subjected to semi-synthetic hydrogenases constructions. Complex 1 was successfully transferred into the apo-enzyme of [Fe]-hydrogenase to deliver the first hydrogenase incorporating a Mn metal center. Encouragingly, this new [Mn]-hydrogenase not only retained the original catalytic functionality of [Fe]-hydrogenase, but also showed 25% activity higher than that of analogous semi-synthetic Fe based hydrogenase. These findings demonstrated that hydrogenases based on a Mn active site are viable and there are great potentials in creating better-than-nature artificial hydrogenases through our biomimetic synthesis/reconstitution strategy. The higher activity of this Mn mimic model over Fe models also proved our strategy of using non-natural metal center feasible.