Another approach to inventing new catalysts, known as "biomimetics", involves copying the active sites of enzymes of interest. The approach is as follows. When looking for catalysts for a given reaction, it may make sense to look at how nature does it. The detailed study (chemical mechanism, structure) of a metallo-enzyme, if it exists, catalyzing the targeted reaction, makes it possible to characterize on an atomic scale the active site of this enzyme, i.e. the site where substrates are activated and transformed. This information can be used to synthesize a metal complex that faithfully reproduces the active site. Chemists have long since demonstrated their ability to synthetically reproduce pieces of enzymes. It should be noted that this approach implies that all that needs to be done is to copy the active site, disregarding the rest of the polypeptide chain. Numerous results have shown this assumption to be justified, even if the protein environment obviously provides the enzyme with properties that will not be found in the biomimetic catalyst. These new molecular objects can not only provide original catalysts, but also unique tools for studying some of the properties of copied enzymes (mechanisms, reaction intermediates, etc.).
This biomimetic chemistry approach is again illustrated in the lecture in the context of the search for catalysts for the decomposition of water into oxygen and hydrogen. Several polynuclear manganese complexes, remarkably reproducing the water oxidation site in photosystem II, and very interesting binuclear iron or nickel-iron complexes, reproducing the active site of hydrogenases, have been prepared and studied in recent years. Their synthesis, structure and activity are discussed.
