FeMoco

Other names: iron-molybdenum nitrogenase cofactor

Fe₇MoS₉C

48/50 rare

"FeMoco" is short for "FeMo cofactor", referring to the cofactor site of the iron-molybdenum nitrogenase enzyme used by rhizobia bacteria in the roots of leguminous plants to fix atmospheric nitrogen into bioavailable ammonia. (Some other nitrogenase enzymes feature iron-iron "FeFe" or vanadium-iron "VFe" cofactors.) These enzymes, through reactivity mediated at these cofactors, are among the only biological systems capable of cleaving the incredibly strong N≡N triple bond – a feat they accomplish at atmospheric pressure and room temperature, where the industrial Haber-Bosch process requires hundreds of atmospheres of pressure and hundreds of degrees of heat. When the cofactor was first characterized crystallographically, the identity of the central atom was unknown and it was briefly referred to in the literature as "Atom X". Much effort was bent towards elucidating the identity of this mystery atom, as it was thought its identity might be the key to deciphering the amazing nitrogen reduction capacity of nitrogenase, unlocking revolutionary new routes towards cheaper and cleaner synthesis of artificial fertilizers. When "Atom X" was definitively shown by ¹³C isotope labeling and X-ray spectroscopy to be a highly unusual hexavalent carbide ion with an apparently purely structural role, in the words of Nobel laureate Richard Schrock, "We all had to sit down and have a drink."