Over the last 15 years, a plethora of research has provided major insights into the structure and function of hydrogenase enzymes. This has led to the important development of chemical models that mimic the inorganic enzymatic co-factors, which in turn has further contributed to the understanding of the specific molecular features of these natural systems that facilitate such large and robust enzyme activities. More recently, efforts have been made to generate guest-host models and artificial hydrogenases, through the incorporation of transition metal-catalysts (guests) into various hosts. This adds a new layer of complexity to hydrogenase-like catalytic systems that allows for better tuning of their activity through manipulation of both the first (the guest) and the second (the host) coordination sphere. Herein we review the aforementioned advances achieved during the last 15 years, in the field of inorganic biomimetic hydrogenase chemistry. After a brief presentation of the enzymes themselves, as well as the early bioinspired catalysts, we review the more recent systems constructed as models for the hydrogenase enzymes, with a specific focus on the various strategies employed for incorporating of synthetic models into supramolecular frameworks and polypeptidic/protein scaffolds, and critically discuss the advantages of such an elaborate approach, with regard to the catalytic performances. evolving systems with enhanced activity, it has also recently provided a novel and exciting route for the direct and facile activation of native [FeFe] hydrogenases [10,11].
HydrogenasesCharacterization of certain living organisms, such as archaea, bacteria, cyanobacteria and algae, has led to the exciting discovery that hydrogen can be either produced or utilised as a source of low-potential electrons within living cells participating in a global H 2 cycle [12].Bacteria such as Ralstonia eutropha (a facultative chemolithoautotrophic organism) provide a good example of this as they are able to use hydrogen as their sole source of energy [13].Another example comes from micro-algaea such as Chlamydomonas reinhardtii, which under certain conditions is able to use sunlight to transiently drive the reverse reaction, i.e. extracting electrons from water and using them to reduce protons into hydrogen [14]. Finally, methanogens such as Methanobacterium thermoautotrophicum are able to exploit the reducing power of H 2 to produce CH 4 from CO 2 [15]. This chemical activity is made possible through the expression of fascinating metalloenzymes called hydrogenases [13,16,17]. There are two classes of hydrogenmetabolizing enzymes, the [NiFe]-and [FeFe]-hydrogenases, which catalyse these reactions without any overpotential [18] and at very high rates (one molecule of hydrogenase produces between 1500 to 20000 molecules of H 2 per second at pH 7 and 37 °C in water) [3,19,20]. A third class, [Fe]-hydrogenase or Hmd (Hydrogen-forming methylene-tetrahydromethanopterin dehydrogenase), is only found in archaea methanogens and requires the use of a...
