Nitrogen-fixing bacteria are able to convert dinitrogen (N2) to ammonia (NH3) under gentle conditions with the help of the enzyme nitrogenase. High-resolution structures have revealed that this enzyme contains iron-sulfur and iron-sulfur-molybdenum clusters in the active site. Can this biochemical process be traced back to a prebiotic mechanism of nitrogen reduction involving iron-sulfur compounds?
Dörr et al. report that ammonia can be made in low yield (0.1%) from dinitrogen in the presence of hydrogen disulfide (H2S) and freshly precipitated iron sulfide (FeS). The reaction conditions (atmospheric nitrogen pressure and 80°C) are comparable to those of the biological process and much milder than in previously reported ammonia syntheses. Commercially purchased or aged iron sulfide did not fix nitrogen, suggesting that the rugged surface of the freshly precipitated material provides a "library of Fe-S clusters" that are crucial for the reaction to take place. Given the large amounts of iron sulfide and hydrogen disulfide available on early Earth, a reaction similar to the one described may have played a role in the prebiotic formation of ammonia. -- JFU
Angew. Chem. Int. Ed. 42, 1540 (2003).
