Chemistry Update - Mosquitoes, Bubbles and Superconductors

01 June 2008

Interview with

Mark Peplow, Chemistry World

Chris - What's all this about computers designing new ways to ward of mosquitoes?

A mosquito biting a fingerMark - This is fantastic. The chemical compound, DEET is the gold standard in insect repellents. The University of Florida scientists have trained a computer to come up with even better repellents. Basically they took an artificial neural network which is kind of a computer programme that's trained to recognise patterns in huge, complex sets of data. They let it loose on the US Department of Agriculture's database of insect repellents. 60 years' worth of data, 40,000 chemical structures. It slowly learned, with some help from the scientists, how to relate the structure of the compound, the position of atoms to its activity as an insect repellent. Then they gave it 2000 new chemical structures, many of which had never been created, to have a look at. It picked out 11 previously known molecules and 23 completely new and had to be synthesised. When the chemists actually made these molecules and tested them next to DEET they found they were much better in some cases. They were active for 73 days as opposed to 17.5 days.

Chris - Could they be applied to the skin safely without risk to health?

Mark - Certainly the quickest way to try these things is to try them on your skin. Indeed, the fearless chemists did try these out with little swabs, patches with this chemical absorbed - stuck onto their skin. This is obviously a little way from being a new insect repellent going on the market. They have identified the best seven compounds which are now under further study.

Chris - It's very exciting because mosquitoes are responsible for spreading so many diseases. Incidentally on of those chemists who tested it is just having his other arm removed as we speak. There's another interesting thing here about bubbles that can last for donkey's years.

Macro photograph of bubbles in a fizzy drinkMark - A year at least. Gas bubbles are an essential part of everything from ice cream, foams, paint. The size of the bubbles really affects their properties. The trouble is that bubbles less than a micrometre in size, just a millionth of a metre, are really hard to make. The trouble is smaller bubbles tend to aggregate and merge into bigger ones. Now a group of scientists at Unilever, the people who make everything from paint to ice cream to washing powder, teamed up with people from Harvard University. They found a way to make microbubbles that last longer than a year. Basically they've used a really clever mix of surfactants. They're often used in detergents to keep oil, grease and water apart. These are molecules that look kind of like little tadpoles. They have a water-loving head and a fat-loving tail. These tadpole molecules all line up in a big sphere and actually encapsulate and stabilise these microbubbles.

Chris - So it would mean better paints, better ice cream?

Mark - Exactly. If you think about it beer is a good example. If you think about the difference in taste between Guinness and the lager a lot of it is to do with the feel of it on your tongue. You have really big fat bubbles in lager and tiny little microbubbles in Guinness so all these things are very important for the chemists that make, like I said, everything from ice cream to paint.

Chris - Thank you, Mark. Lastly, superconductors. This is really big business. We've heard about data centres consuming enormous amounts of energy and being very bad for the environment but superconductors are a way of potentially alleviating that problem if we can find a way to make them work.

Mark - It's one of the challenges which is, I think, up there alongside developing fusion power. Superconductors carry electricity with no resistance at all. There are already many small-scale uses for them. If you could use them on a very large scale replacing cables on a power grid you could transform the way we use energy. Resistance takes up about 10% of power that's pumped into the American grid, for example. The trouble is superconductivity only switches on at very low temperatures. About 20 years ago scientists found some copper-based compounds which are our best candidates for high temperature superconductors. They start doing that at -135 degrees.

Chris - But it's still -135 degrees.

Mark - It's still pretty chilly. The trouble is progress stalled at that stage and no one knows how they work and for a decade no one's been able to improve much on that temperature. In the last three months about half a dozen different groups in China and Japan have made really rapid progress with a completely different set of compounds. Instead of copper and oxygen atoms in these compounds they have iron and arsenic. There's a smattering of other elements which they've been tweaking: lanthanum, samarium. Exotic things. Already in three months they've seen a 30 degree improvement in these compounds which in the field is quite a significant improvement. That superconducting temperature, that threshold temperature is still at -218 so it's a long way from being practical but they key thing is it's revitalised a field where physicists had been banging their head against the wall for ten years, making very little progress. Crucially these are the best alternative candidates you can actually compare to. No one really knows how these materials really work. If you've got one set of copper-based compounds you can now compare them to these new iron compounds and try and work out how they're functioning.

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