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Nitrogen fixation

2007 Schools Wikipedia Selection. Related subjects: General Biology; General
Chemistry

   Nitrogen fixation is the process by which nitrogen is taken from its
   relatively inert molecular form (N[2]) in the atmosphere and converted
   into nitrogen compounds useful for other chemical processes (such as,
   notably, ammonia, nitrate and nitrogen dioxide) .

   Nitrogen fixation is performed naturally by a number of different
   prokaryotes, including bacteria, and actinobacteria certain types of
   anaerobic bacteria. Microorganisms that fix nitrogen are called
   diazotrophs. Some higher plants, and some animals ( termites), have
   formed associations with diazotrophs.

   Biological nitrogen fixation was discovered by the Dutch microbiologist
   Martinus Beijerinck.

Biological Nitrogen Fixation

   Biological Nitrogen Fixation (BNF) occurs when atmospheric nitrogen is
   converted to ammonia by a pair of bacterial enzymes called nitrogenase
   . The formula for BNF is:

          N[2] + 8H^+ + 8e^− + 16 ATP → 2NH[3] + H[2] + 16ADP + 16 P[i]

   Although ammonia (NH[3]) is the direct product of this reaction, it is
   quickly ionized to ammonium (NH[4]^+). In free-living diazotrophs, the
   nitrogenase-generated ammonium is assimilated into glutamate through
   the glutamine synthetase/glutamate synthase pathway.

   In most bacteria, the nitrogenase enzymes are very susceptible to
   destruction by oxygen (and many bacteria cease production of the enzyme
   in the presence of oxygen) . Low oxygen tension is achieved by
   different bacteria by: living in anaerobic conditions, respiring to
   draw down oxygen levels, or binding the oxygen with a protein (e.g.
   leghaemoglobin) . The great majority of legumes have this association,
   but a few genera (e.g., Styphnolobium) do not.

Non-leguminous nitrogen fixing plants

   Plants from many other families have similar associations, including: *
   Lobaria lichen and some other lichens
     * Mosquito fern (Azolla species)
     * Cycads
     * Gunnera
     * Alder (Alnus species)
     * Ceanothus (Ceanothus species)
     * Wax myrtle (Myrica species)
     * Mountain-mahogany (Cercocarpus species)
     * Bitterbrush (Purshia tridentata)
     * Buffalo berry (Shepherdia argentea)
     * Ironwood (Casuarina species), Sheoak (Allocasuarina species), and
       other genera in the Casuarinaceae

Chemical nitrogen fixation

   Nitrogen can also be artificially fixed for use in fertilizer,
   explosives, or in other products. The most popular method is by the
   Haber process. This artificial fertilizer production has achieved such
   scale that it is now the largest source of fixed nitrogen in the
   Earth's ecosystem.

   The Haber process requires high pressures and very high temperatures
   and active research is committed to the development of catalyst systems
   that convert nitrogen to ammonia at ambient temperatures. The first
   dinitrogen complex was discovered in 1965 based on ammonia coordinated
   to ruthenium ([Ru(NH[3])[5](N[2])]^2+) This discovery was followed by
   the first example of homolytic cleavage of nitrogen by a molybdenum
   complex to two equivalents of a triple bonded MoN complex (1995). The
   first catalytic system converting nitrogen to ammonia at room
   temperature and 1 atmosphere was discovered in 2003 and is based on
   another molybdenum catalyst, a proton source and a strong reducing
   agent .
   Synthetic nitrogen reduction Yandulov 2006
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