ABSTRACT

Dihydrogen (H2) has long been viewed as a future fuel-the compelling point being that it can be produced, continually, by recruiting the two most abundant resources on earth, sunlight and water! Visionary articles, not the least those written from an electrochemist’s viewpoint [1], have long proposed a key role for H2 in solving the looming energy problem, and despite its shortcomings in storability and energy density (which are mainly restricted to its use as a fuel for vehicles), H2 is being taken increasingly seriously. It is less widely known that H2 plays a vital role in microbiology, where it is not only a by-product of nitrogen xation ( ammonia production) by nitrogenase, but also rapidly produced and oxidized by another class of metalloenzyme, known as hydrogenases, that contain Fe or Fe with Ni at their catalytic centers. Hydrogenases are found in a wide range of microbes ranging from notable pathogens such as Salmonella to photosynthetic bacteria and green algae [2]. There is considerable interest in genetically engineering strains of photosynthetic microorganisms to produce H2 in place of most of the starch or lipids that are normally accumulated, particularly if H2 can be continuously removed-thus avoiding the need for harvesting and extraction [3-5]. However, not only is the microbiology extremely complicated, but the hydrogenases responsible for producing H2 tend to be inactivated by the O2 that is produced simultaneously. In addition to understanding how the enzymes work, there is great interest in mimicking their action with robust synthetic analogs [6, 7].