premjan

is there any possibility of ever using sunlight (e.g. a photosynthetic process) to capture atmospheric nitrogen into a nitrogen compound such as ammonia or hydrazine or something more complex and kicking off a cycle of nitrogenous organic chemistry of some kind?

HRG

Don't think so. 1) The N-N triple bound is hard to break; IIANM a single solar photon can't do it. 2) Unlike C, N cannot form chains.

Regards, HRG.

Sven

First, an answer to premjan's question. Nitrogen is indeed metabolized by some bacteria, but not using sunlight as far as I know. This is in fact a very important resource of organic compounds containing nitrogen, such as amino acids. Just google for nitrogenase.

Then, a comment on HRG's second point:
Nitrogen can indeed form chains. The problem is that they are very short (up to four nitrogen atoms, I think) and very unstable. I've no idea if environmental conditions are possible for which the chains are longer and more stable, but I think it's unlikely.

premjan

Sven, thanks for picking up this dormant thread. I found out that nitrogenase contains Molybdenum (and some Fe). The other two star molecules that I have read something about are chlorophyll and hemoglobin (ok, apart from the usual suspects such as DNA/RNA/cellulose/chitin and the like).

nitrogenase: Mo,Fe
Chlorophyll: Mg
Hemoglobin: Fe

Seems like the metal atoms play a key role in these chemicals. I remember reading an Asimov science fiction story about the poisonous properties of a chemical called aureoglobin. Would substituting gold for iron do anything in your knowledge?

What are the other star molecules you could discuss off the top of your head? we could start an informative thread about those.

Peez

FWIW, Robert O'Connor has an interesting and apparently well-researched essay on alien life forms in science fiction: Xenobiology 101.

Peez

Sven

Yes. Metal atoms play a key role in many (most? all?) enzymes.

Gold most certainly would not work in hämoglobin (German spelling) - because the porphyrin ring in which the metal atom is located binds much better to iron than to gold (because of size and electronic reasons) and because oxygen (as far as I know) binds poorly to gold. Biochemistry using gold would work much better with sulfur than with oxygen.

I would not call porphyrin a "star molecule". And porphyrin is only the basic compound, it's modified much in different enzymes. For example, take a look at Vitamin B12 (or at Cobalamins in general). The porphyrin is modified that much that it's now called "Corrin" and it has a cobalt atom as the active center. Some of the Cobalamins are very interesting for another reason: They are the only biological compounds (at least that I know of) which contain a metal-carbon bond (usually, the metal is bound by nitrogen, oxygen, or sulfur).

Al Chemist

There are also larger macrocycles which, like porphyrin, are based on pyrrole rings -- these include things like texaphyrin (http://www.cm.utexas.edu/texaphyrin.html) and sapphyrin. These macrocycles have larger cavities which can accomodate larger metals, but as far as I know, these are produced only in the lab (at least so far).

premjan

B12 does not appear to have any metal-carbon bonds (Co is pentavalent!)

Coragyps

Metal-carbon bonds are rare or totally absent in biomolecules. All the metals in my body that I can think of at the moment are coordinated ("bonded" but maybe not as permanantly as a full covalent bond) by nitrogen and/or sulfur and/or oxygen, which in turn are held there by a largely carbon framework. Sven said "some of the cobalamins" - I'd be interested to see which have C-metal bonds, too.

All the C-metal bonded compounds I ever fooled with would either 1) kill you with their mercury content or 2) spontaneously catch fire in air.

DNAunion

Your question is unclear. One could say that biology already has nitrogenous organic chemistry: two of the four key organic compounds - nucleic acids and proteins - all contain nitrogen, and so do many phospholipids, a third of the four major organic compounds.

Instead of an organic chemistry, do you mean a biological chemistry based on nitrogen?