In vitro nitrogen fixation

Interest in the molecular structures of molybdenum and tungsten complexes, particularly in those containing N-donor ligands, is enhanced by the occurrence of molybdenum in the enzyme nitrogenase. It is possible that the stereochemistry of these metals may be of importance in understanding processes of in vivo and in vitro nitrogen-fixation. 

Syrtsova, L.A., Druzhinin, S. Yu., Khramov, A. V., and Moravsky, A.P. (1995) Photostimulation of nitrogenase reaction in vitro for investigation of nitrogenase mechanism action Curr. Plant Sci. Biotechnol. Agric. 27 (Nitrogen Fixation Fundamentals and Applicaaaation. 

The Fixation of Carbon Dioxide and Nitrogen.—As reduced carbon compounds are convenient fuels, the possibility of achieving the reductive fixation of COa in vitro is appealing, if remote. There are very few data on photochemical reactions involving carbon dioxide, for it has no low-lying excited states and has not historically been of much interest to the photochemist. However, what appears to be the first example of photofixation of COa in a non-biological system has been briefly reported.18 Photoirradiation (with a high-pressure mercury lamp) of phenanthrene in the presence of an amine and C02 in a polar solvent (MeaSO or HCONMea) yielded 9,10-dihydrophenanthrene-9-carboxylic acid, in unspecified quantum yield. The mechanism appears to involve formation of COaT by electron transfer from the photoexcited amine, followed by attack of COaT on position 9 of phenanthrene. Similar reductive carboxylation of anthracene, pyrene, naphthalene, and biphenyl was observed. 

The Fe protein is, however, capable of being reduced by two electrons in vitro and then transferring two electrons in one step to the MoFe protein with the hydrolysis of only two molecules of MgATP (42), an obvious saving in energy. It is not yet clear whether the Fe protein acts as either a one-electron donor or a two-electron donor during nitrogen fixation within the bacterial cell. 

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