I’ve always been a huge fan of alternative biochemistries. Because as marvellous as we terrestrial lifeforms are with our amino acids and our sugar phosphate self-replicating polymers, there’s got to be more than one way to skin this particular catfish★. Enter Lee Cronin, a scientist based at the University of Glasgow who’s attempting to create just such a thing.
It’s a curious idea really. Almost frankensteinian, in a sense. Cronin’s aim is to create cell-like bubbles made from polyoxometalates, which he hopes will one day be able to reproduce and even evolve. Synthetic, inorganic life forms. Cronin is even quoted as saying, “I am 100 per cent positive that we can get evolution to work outside organic biology.” I share his enthusiasm on the fact that it can work, but the fact that he’s actually attempting to make it work is really quite staggering!
The polyoxometallates he’s using are based on oxygen and phosphorus, with various different types of metal (Tungsten being amongst them, apparently) being used to combine with them. The molecules themselves then self-assemble into cell-like structures in solution♦. He accomplishes this by creating salt solutions, once containing large metal oxide anions, and the other containing large organic cations. When mixed together the large ions, metal oxide and organic, combine together and precipitate out of solution, forming shell-like structures. The image above is a microscope image of one of these cell-like bubbles, this one containing a smaller bubble within it, mimicking the internal compartments of living cells. Artificial organelles, if you will.
The interesting thing here is that if these things really do self assemble this way, then that bolsters the idea of something like this occurring naturally elsewhere. When life formed on Earth, it obviously didn’t have any scientists tinkering with it and making sure everything went according to plan♣. It was just a messy soup of chemicals. Anything which couldn’t form by itself would not have formed at all. Self-organisation (presumably) allowed lipids to form into bilayers and cell membranes for Earth life. Apparently self-organisation also allows polyoxometalates to do something similar in Cronin’s lab.
These metal-oxide based bubbles have been dubbed iCHELLs (short for inorganic chemical cells), and with some fine tuning of the precise chemical precursors used, they can actually be made to act like real cell membranes. It’s fairly intuitive really, seeing as whatever properties a small molecule has are passed onto any larger structure they become a part of. Use a small molecule with a hole in it, and get a porous cell wall. Further fine tuning, and you become able to carefully control how the cell behaves. Chemically speaking, that is.
The research group is even working on ways to use photosensitive dyes to split water into ions and electrons, and set up a proton gradient across one of the iCHELL membranes, to mimic photosynthesis. Could they really create an artificial cell powered by photosynthesis? Think what a leap that would be for nanotechnology!
On a final note, Cronin is attempting to introduce his iCHELLs into different chemical environments, in order to see which survive and which don’t. If an iCHELL is broken down by a different pH, it’s considered to have died, leaving behind the more adaptable and more healthy iCHELLs to continue the miniature Darwinian experiment. Apparently, though he hasn’t released any specifics, Cronin is quoted as saying that “I think we have just shown the first droplets that can evolve.” Curiouser and curiouser. I’d be interested to see what might be published from this study…
Personally, my immediate thought (aside from the general elation that someone is actually working on alternative biochemistries in the lab!) is into what the chemical composition of those iCHELL membranes actually is. And I mean in detail. I’ll admit that I haven’t read the papers yet (I don’t have access to them at home), but certain metals would be particularly favourable from an astrobiological viewpoint. For instance, ageing carbon stars tend to be rich in certain metals like Vanadium and Zirconium. Metals created in a type of stellar fusion called the s-process. Stars with spectra showing Titanium oxide are not uncommon. If any of these s-process metals prove to be particularly successful in Cronin’s iCHELLs, then I’d be very interested indeed.
Ageing bloated red giants constantly puff material off into space. Hot stardust cooling slowly in the night. Perhaps the ash from one of these elder stars may be the cause of life taking hold somewhere. What a happy thought!
Source: New Scientist
Image Credits: Microscope images – Cronin Group, Uni. Glasgow
“Mercury” – Mercury metal droplets and puddle – Cyberchemist @ Flickr
Publications: Cooper et al 2011, Miras et al 2010
★ I know the actual proverb is that there’s more than one way to skin a cat, but I’m rather fond of cats, so that’s an image I’d rather do without. Besides, apparently the expression was originally about catfish who, as it happens, are notoriously difficult to prepare for cooking. Ok, I should stop offending the vegetarian contingent of my readership now. Oh, and while we’re on the subject of proverbs, I hasten to add that I do know the true phrase is “testing one’s mettle”, but the pun doesn’t work with that spelling!
♦ Which would presumably be a process of supramolecular self-assembly…?
♣ Or perhaps it did, who am I to know? Somehow though, I have a feeling we aren’t living in a four billion year old petri dish.