Molybdenum Fixes Nitrogen

Molybdenum's odd-sounding name comes from its resemblance to lead ores. That makes three elements: plumbum (lead), carbon (plumbago), and now molybdenum named after lead. Perhaps it's not so much the color as the texture:

Native ore: MoS₂

Native plumbago (graphite)

Native lead (Galena, PbS)

Molybdenum's role in life is anything but leaden. Mo is in nitrogenase, an enzyme absolutely essential for life. Nitrogenase-containing bacteria "fix" nitrogen, turning thin air into solid plant food (ammonium), a feat no less remarkable than photosynthesis. The bacteria in turn get first dibs on the sugars made by the plants in perfect symbiosis.

If artificial photosynthesis is cool--making sugars and fuels from CO₂--nitrogen fixation is even more exciting because we're about a third of the way there.*  Bacteria make about 2/3 of the world's fixed nitrogen, and the ancient Haber-Bosch process does the rest.  The Haber-Bosch process, first developed in 1913, enabled Germany to fight the First World War. Today it helps feed about a third of the world's population but it also consumes about 1-2 % of the world's annual energy supply. We can do even better, perhaps by learning from nature.

Nitrogenase manages to fix nitrogen under much milder conditions than Haber-Bosch, though like many natural processes, the yield is diffuse and unusable industrially. Molybdenum's connection to nitrogen fixation was first noted in 1930 when bacteria raised on ammonia showed no need for the element while those raised on nitrogen did (before the enzyme nitrogenase had even been identified). When nitrogenase was found, the next step was to crystallize it and determine its structure. This happened in 1992, at a time when molybdenum and the heavier tungsten were already famous for loosely binding things like H₂ and N₂ in synthetic tungsten compounds. Some thought perhaps nature had gotten there first. Alas, the structure gave few clues as to where and how nitrogen is activated, except that it happened stepwise, using protons and electrons instead of H₂.

Another really cool thing about the nitrogenase X-ray crystal structure was the revelation of a mystery element "X" which could be either a C, an N, or an O atom. Several contact points surround the mystery element X which makes that a "Texas" atom.  More recent work, published last year in Science, says it is carbon (link). More on that later.
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*There are vanadium-dependent nitrogenases which convert CO to alkanes--just like Fischer-Tropsch catalysts do: link  That would be so cool if the X-factor were a Texas carbide.

The Language of Chemistry

Original

Beginning students of chemistry encounter chemical symbols which bear little resemblance to their English names. The roots of several common and especially more historical elements caught my fancy, just as other Latin words buried in English did earlier. link

Several names and symbols come from Latin:

• Sb stands for antimony which comes from the Latin Stibium. The Italians still call antimony stibio. We did too until the Middle Ages. link

• Cu for copper comes from Cuprum, which is related to the word Cyprus, an ancient source of copper for the Romans.

• Fe for iron comes from Ferrum. The Italians call their railroads la ferrovia and Spanish calls hardware ferreteria (cf. bilingual signs at Home Depot). English has the vestigial word, farrier.

• Au for gold comes from Aurum.  We've lost that word in English except for some pretentious words like aureate, aurelia, aureole and the like.

• Pb for lead comes from Plumbum. There are lots of English cognates, including plumbago, plumbing, plumb lines and plumb bobs.

• Hg for mercury comes from hydrargyrum. That's confusing because at first glance it could be water-silver. But "hydra" is more generic and means liquid. Mercury used to be called quicksilver which sort of conveys the same notion as hydrargyrum.

• Ag for silver comes from Argentum. The French still call money l'argent.

A couple names look like Latin but are neologisms coined by Sir Humphry Davy:

• K for potassium comes from Kalium which derives from Arabic al-kali.

• Na for sodium comes from Natrium. The Germans still use both words Natrium and Kalium; they never adopted sodium and potassium. I guess they weren't as impressed with Davy as we were.

Also:

• Sn for tin comes from the Latin Stannum. There is some irony here.  The word Stannum is Latin but appears to derive from Irish or Welsh. The Romans got their tin from the British Isles.  Tin is still mined in Cornwall.

• W for Tungsten comes from an older name, Wolfram, which is still used by the Germans. Tungsten derives from Swedish tung heavy + sten stone.