April 2007

Chemistry World Podcast - April 2007

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Brought to you by the Royal Society of Chemistry: The Chemistry World podcast.

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Interviewer - Chris Smith

Hello and welcome to the Chemistry World podcast, this is episode number 7 with Chemistry World''s editor Mark Peplow... 

Interviewee - Mark Peplow

Hello!

Interviewer - Chris Smith

With Deputy Editor Bea Perks... 

Interviewee - Bea Perks

Hello!

Interviewer - Chris Smith

And science correspondents, Victoria Gill... 

Interviewee - Victoria Gill

Hello!

Interviewer - Chris Smith

And Richard Van Noorden...

Interviewee - Richard Van Noorden

Hello!

Interviewer - Chris Smith

And also with me Chris Smith.   This month what our ancient relatives tell us about where we get our taste for dairy.

Interviewee - Bea Perks

Mark Thomas and colleagues at University College London got some Neolithic skeletons and investigated their genetics and discovered that they were not able to digest lactose.

Interviewer - Chris Smith

Also a clever chemical trick to track migrating birds, which might help public health teams to keep tabs on avian flu.

Interviewee - Laura Font

They wanted to know if we could analyze the strontium isotopes in bird's feathers to track migration path, then if we know that there is species that can potentially carry bird flu, then we will manage to find the origin of bird's carriers of the flu.

Interviewer - Chris Smith

And how scientists created the perfect antireflective coating?

Interviewee - Mark Peplow 

Strictly speaking, it's the world's least reflective coating.   So if you have that on say on an opaque material, it ultimately makes for the blackest material known to science.

Interviewer - Chris Smith

That's all on the way, but cast your mind back first, to the last month's program when the diet conscious Chemistry World podcast listener, Sabina wanted to know why the healthy option isn't always the tastiest option.

Interviewee - Sabina

Just wondering, could you tell me why is it that sodium chloride or table salt tastes so different to potassium salt?

Interviewer - Chris Smith

No idea!!   Well luckily, we've got the answer and it's coming up shortly.   But first this week from the taste of salt to the taste of milk and whether or not we can tolerate it.   A sizable proportion of the world's population can't and that's because they lack a digestive enzyme called lactose, which breaks down the lactose sugar, which is in high concentrations in cow's milk.   The lucky ones amongst us who do posses that enzyme are mainly all Northern Europeans, but where do we get it from?   Well it turns out that keeping cows in the first place probably triggered it to evolve, because DNA from our ancient relatives shows that they were initially lactose intolerant.   Bea, tell us more.

Interviewee - Bea Perks

Apparently there's been a bit of debate for sometime about whether lactose tolerance developed as a result of the fact that we were dairy farmers or the fact that we could digest milk made us then realize that we may as well start becoming dairy farmers and so what's happened here is Mark Thomas and colleagues at University College London got some Neolithic skeletons and investigated their genetics and discovered that they were not able to digest lactose.

Interviewer - Chris Smith

When you say they got skeletons, how old were these specimens?

Interviewee - Bea Perks

So they were Neolithic Europeans.   They were about 7 to 8000 years old.

Interviewer - Chris Smith

So, you can get reasonable DNA from them?

Interviewee - Bea Perks

Apparently so, yes.

Interviewer - Chris Smith

And they didn't carry the gene.

Interviewee - Bea Perks

And they didn't carry the gene but it was known that pasture farming had begun.

Interviewer - Chris Smith

Where did these items come from? Where these actually Britain?

Interviewee - Bea Perks

No, They were dotted around Northern Europe, apparently in Southern Europe, and I really didn't know this, apparently in southern Europe 80% of people are lactose intolerant.

Interviewer - Chris Smith

It's like the Americans, because have they looked at other skeletons of similar age but from other parts of the world to get this comparison?

Interviewee - Bea Perks

They haven't looked at, I don't think they've looked at exactly the same age skeletons, but they do know that lactose intolerance is the norm in fact.   I mean, if anything Northern Europeans are bit unusual, we're a bit unusual, that we can digest milk, Africans don't, Asians don't by and large.

Interviewer - Chris Smith

But you find people keeping cows and milking cows in other countries apart from European countries where this gene is found.   So how do you explain that, if it's that, that provoked us to become dairy farmers?

Interviewee - Bea Perks

Well, apparently and I don't know an awful lot about dairy products, but apparently yoghurt and cheese are okay -- you don't need to be lactose tolerant.

Interviewer - Chris Smith

So, people went for the yoghurt before they went just for the milk.

Interviewee - Bea Perks

Exactly! Well exactly! And if you think about in Africa, so they do eat yoghurt, they don't drink milk.

Interviewer - Chris Smith

Well, that's certainly food for thought, but here's another even bigger item of food for thought.   So what's this about obesity then? Victoria.

Interviewee - Victoria Gill

Right!   Well, this is a study that's come out of the University of Oregon.   They basically answered the question of why people who are obese continue to eat too much.   The thing is that when people become fatter their fat cells produce a hormone called leptin and that sends signals to an area of the brain called the hypothalamus, which is the area of the brain that controls appetite, that stimulates chemical signalling that stops you from eating that suppresses your appetite.

Interviewer - Chris Smith

Strictly it doesn't work because people that are very, very fat have much higher leptin levels than I do and they often have a much bigger appetite than I do as well.

Interviewee - Victoria Gill

Exactly.   So, what this study has done has used a mouse model, thin mice and fat mice that have been fed a high-fat diet and they tested them by giving them leptin and seeing how they respond and sure enough the fatter mice have less of a response to leptin, it doesn't suppress their appetite.   This theory has been around for a while, but what this group wanted to do was find out why these mice are leptin resistant.   If we can find out why these animals are leptin resistant, then may be we can look into some of the stumbling blocks that have prevented us from creating good obesity drugs in the past.

Interviewer - Chris Smith

And have they got some clues as to what the basis of that resistance is now then?

Interviewee - Victoria Gill

Yes, they have.   It's a little contentious, but what they've done is they fed these mice a high fat diet and some of them with a low fat diet.   After giving them leptin and testing them for their response, they've taken the hypothalamus out of these mice and they've tested them to see what chemicals are there and they found that this protein signalling compound called Socs-3, there's a lot of it in the hypothalamus of these fatter mice, so they think that this particular protein is what's blocking the activity of leptin in these leptin-resistant obese mice.

Interviewer - Chris Smith

And the logical question, if you therefore block it, does this make these fat mice turn into thin mice, have they've been able to do that?

Interviewee - Victoria Gill

That's the next step.   We were talking to Michael Cowley, who is leader of this research group and he's pretty convinced that this shows that if they can figure out how to block Socs-3, then they can get on with designing a drug that will interfere with this leptin resistance and therefore you'll be able to anchor the chemical signalling in obese people's brains and design a decent appetite suppressing drug.

Interviewer - Chris Smith

Thanks Victoria.   Well, from a bulging waistline to an expanding carbon footprint now, because third world countries are exploiting a loophole in the Kyoto protocol, to make money out of pollution.   It's called the CDM or Clean Development Mechanism and it works by allowing industrialized countries to meet their greenhouse gas reduction targets by paying for emission cutting projects in developing nations.   But many of these countries are producing large amounts of CFC-like agents, which are actually very cheap and easy to get rid off, but they are being traded for carbon credits, which are worth a fortune in comparison, so perversely these countries are being rewarded for being bad.   Michael Wara is a San Francisco based climate change lawyer.

Interviewee - Michael Wara

The Clean Development Mechanism is a way for developing countries to reduce their emissions of greenhouse gases and then sell those emissions reductions to countries that have caps in the Kyoto protocol, so countries like the UK or the broader EU or Japan or Canada.   And what has happened in the CDM, which no one really expected, but it's nevertheless come to pass is that rather than producing emissions reductions through investment in clean energy, the vast majority of reductions are coming from industrial gas plants that they make relatively obscure products like HCFC-22.

Interviewer - Chris Smith

This is a refrigerant, isn't it?

Interviewee - Michael Wara

It's a refrigerant, yeah, in mobile air conditioners like in your car or in an air conditioner you put in your window and there's a lot of demand for such things like that in developing economies right now, but in the developed world capture of the greenhouse gas emissions from these plants is done voluntarily because it's very inexpensive to do, it costs something on the order of 10 cents per ton CO2.   In contrast, because of the incentives created by the Clean Development Mechanism, plants in the developing world insist on receiving a payment for that reduction and the payments is typically $10 per ton.   So they invest 10 cents per ton, they get $10 per ton back.

Interviewer - Chris Smith

And how much would it actually cost to get rid of it?

Interviewee - Michael Wara

My estimate is less than a 100 million dollars for the entire plant.

Interviewer - Chris Smith

Okay and how much actually gets spent by first world countries paying third world countries to do this?

Interviewee - Michael Wara

On the order of 7 billion dollars.

Interviewer - Chris Smith

So there's a incentive for a third world country to produce this stuff because they know that its lucrative because they can flock the idea of getting rid of it to the first world and get loads of revenue.

Interviewee - Michael Wara

Yeah, in fact the sale of the credits is more profitable than the sale of the products, refrigerant gas, at this point in time.   So, there are some real perverse incentives there and the governing body of the Clean Development Mechanism has made some substantial efforts to try to control that problem, but what they haven't been able to deal with is the fact that this incredibly low cost, very profitable, emission reduction scheme has basically diverted all of the climate related investments away from clean energy projects in the developing world, which in the long run are far more important for developing a solution to climate change and I think that's in a way the deeper problem here.

Interviewer - Chris Smith

Can we fix this, Michael, because this is obviously a very serious issue -- these countries that are actually guilty of this are also exempt aren't they, because there are upcoming countries, from other kinds of caps and things.

Interviewee - Michael Wara

Yeah, they don't have a cap under the Kyoto protocol and so this Clean Development Mechanism is the main way that those countries are involved in addressing climate change.   I think that the most important thing that could be done would be to remove the really bad gases for climate change from the Clean Development Mechanism, make the CDM more like the EU ETS where only carbon dioxide is traded.

Interviewer - Chris Smith

And this would mean that these people could no longer sell the fact that they are reducing the amounts of this and therefore would no longer be profitable and this would actually put the money back into alternative projects.

Interviewee - Michael Wara

That's right and I think in conjunction with that change it would be important for the governments that are signatory to the Kyoto agreement to negotiate additional agreement to abate those gases, to spend the 100 million dollars to capture all of those refrigerant pollutants, but to do that outside of a market mechanism and to focus the market on where you can do the most good, with energy.

Interviewer - Chris Smith

Can you see that happening?

Interviewee - Michael Wara

I think its becoming an increasing possibility-- the level of criticism of these projects is even generating movements on the part of some of the carbon market participants who have made lots of money from them for change because ultimately the integrity of the carbon market and its environmental credibility are really important to its future and these projects call that into question.

Interviewer - Chris Smith

Michael Wara on why the CDM needs an overhaul.   Now on the way, why cold fusion could be back on the menu and how scientists have made the world's darkest material.   But first silicon's days, as our preferred material for making microchips, could well be numbered then, Richard.

Interviewee - Richard Van Noorden

Yes Chris.   Well a few weeks ago, we saw the announcement of the first ever graphene transistors.   A Transistor is the thing that switch current back and forth and so far they've all been made of silicon which is great, but if we want to pack more in a chip, we need to get them smaller and smaller, silicon won't be up to the job in a few years from now, so instead we're turning to graphene -- the single layer of carbon atom, its like one layer of graphite.   These are pretty amazing materials, electrons travel through them in pretty interesting ways and now Andre Geims group at the University of Manchester have announced that they've actually managed to cut ribbons of graphene into different shapes, controlling electron flow so that the whole thing switches electrons back and forth like a transistor does.

Interviewer - Chris Smith

But why should graphene be any better than silicon, they're both, after all, chemicals?

Interviewee - Richard Van Noorden

Well, when silicon gets to these kinds of nanometre widths that these ribbons are, it actually decomposes and oxidizes.   The carbon-carbon bonds in graphene is so strong that the honeycomb lattice remains stable, even when the ribbons are really thin and that's why you can't use silicon for these tiny transistors, but you can use graphene.

Interviewer - Chris Smith

But silicon is the material of choice, because it's really easy to work it.   We can etch it; we can produce just the right shapes and sizes we want, at the moment for the present demands of technology.   Can we do the same with graphene in order to achieve, what's being achieved with silicon and therefore is this a reasonable replacement?

Interviewee - Richard Van Noorden

At the moment we certainly can't.   People are trying to deposit graphene onto wafers and to try and etch it in the same way as you can with silicon, but it's just not happening.   The way you make graphene at the moment is actually rubbing it with a bit of cellotape and then with some pencil you get these little thin flakes, some of which are one layer thick and chemists are trying to deposit it from vapour, which might be more controllable way of doing it and one of the team members here said that when they cut graphene into these ribbons to make the transistors it was unreliable, some of them worked, some of them didn't, but they are confident that when it comes to something like, I don't know 2025, when there'll be real problems with packing silicon transistors smaller and smaller, then that's when graphene might come into its own.

Interviewer - Chris Smith

So how has Andre Geims group actually made their little ribbons?   How did they get them produce it, is that the same way with the cellotape and a pencil?

Interviewee - Richard Van Noorden

Yeah and then they've got to sculpt them with conventional lithography techniques and what they've done is they've got two electrodes, 5 nanometre thick ribbons of graphene and in the middle, they've got what's called a quantum dot; it's like a barrier that controls the electron flow.   This is called a single electron transistor.   Its switches and allows one electron back and forth and people had earlier said they tried to make graphene transistors but using a, sort of, gate that control the electric field flow and the electrode placed above a graphene strip, much more conventional transistor.   Problem with that was when you switched it off, the current kept flowing so it couldn't be switched ON and OFF cleanly.   That's why these are really the first practical graphene transistors to be demonstrated.

Interviewer - Chris Smith

Well, sticking with the very small -- from transistors to viral particles and there's an interesting breakthrough in understanding how HIV gets into cells, Victoria.

Interviewee - Victoria Gill

Yeah, this group in the Netherlands have, discovered a protein that's expressed on the surface of immune cells in the mucosa that is a natural barrier to HIV.   It binds HIV and the bound HIV is taken up inside these large immune cells which are called Langerhans cells, they are macrophages and once HIV is bound by this Langerin protein, it is taken up inside the macrophages and degraded by little granules inside these cells.

Interviewer - Chris Smith

So the obvious question is if we've all got this, then why do we still catch HIV?

Interviewee - Victoria Gill

Well, it's obviously not the only protein and these aren't the only immune cells that the HIV is meeting when it gets to the mucosa.   What this team thinks is that all the cells, the immune cells that express lots of different proteins on their surfaces, when they meet HIV, they pick it up and then they transmit it to the T cells.   It's the T cells, the helper immune cells that HIV attacks and destroys, which is how it breaks down your immune system and what they think is that it's just this one particular protein that has this anti-HIV effect that acts as a natural barrier to it, so on its own and in natural transmission, the rest of the proteins and other immune cells would have enough of an effect for HIV to be able to transmit, but what's exciting about this is that this helps us to understand why the microbicide gels which are gels that women can use to protect themselves against HIV without the need for other barrier methods.   These have been tested in clinical trials in Africa and the results from those have been extremely disappointing.   They have actually stopped these tests because they've found that these gels are increasing the rate of transmission of HIV.   Now what this group thinks is that they might have come up with a reason for why this is happening.   If these microbicide gels that are trying to activate and stimulate the activity of these immune cells, these early immune cells in the mucosa, if they're activating and stimulating these Langerhans cells that will reduce the amount of this Langerin protein that is expressed on the surface of these cells, so if you reduce the amount of Langerin, you reduce the amount of natural barrier to HIV transmission, so you will increase the rate of transmission.   So they think that if you can test these microbicide gels to see if they have this effect on Langerhans cells then you might be able to create an improved and functional microbicide against HIV transmission.

Interviewer - Chris Smith

Thanks Victoria and now to a clever chemical tracking trick.   Durham University's Laura Font found a way to use the ratio of different isotopes of strontium to track the migration patterns of birds.   This ratio varies geographically so reading it from a bird's feathers tells you where that bird must have just come from which could help in controlling the spread of avian flu.

Interviewee - Laura Font

We've been developing a technique to measure strontium isotopes in birds' feathers because these biologists in the Department of Biology of Durham University, they came to us with the problem and basically they wanted to know if we would analyze the strontium isotopes in birds' feathers to track migration paths because this type of work has been done.   Well, this type of analysis has been done in using bones of birds but obviously you have to capture the birds and kill it and then get, you know, substract the bone sample.

Interviewer - Chris Smith

So what's the, sort of, scientific bases for using a) strontium and b) feathers?

Interviewee - Laura Font

Because the strontium ratios that we analyzed in rock samples, they are very characteristic of the different ecologies and also of the age of the rock, so then if a bird is in a particular environment where there is particular type of rock then this ratio that is in this environment will be in, as well in the tissues of the bird because the ratios of the rock will be explained in a very easy way will be trespassed through the soil and then the plants and then all the insects that eat these plants and then the bird will eat these insects or snails and then the same ratio will go through this trophic chain.

Interviewer - Chris Smith

And the levels in the bird will change rapidly enough in order to make this sensitive and get into the feathers, will they?

Interviewee - Laura Font

Well, basically because we measure the ratio these won't change because this thing is indicative of the source then it will be the same in all the tissues of the birds.

Interviewer - Chris Smith

And why do you use feathers?

Interviewee - Laura Font

Because the migratory birds, they change the feathers, when they are in the winter location and in the summer location, they will change these feathers, you know, in each season, so then each feather will reflect the ratios in the winter location or when they move to the summer location.

Interviewer - Chris Smith

So, you can get a pretty accurate picture of where the bird has been where it has come from and then gone to.   These amounts of strontium must be absolutely tiny in the feathers, how do you actually measure it?

Interviewee - Laura Font

We use this special technique with microcolumns with a special wavelength and then we dissolve the feather we pass it through this small columns and then we collect the strontium fraction and then we load the solution on filaments and then we analyze it with thermal ionisation mass spectrometer.

Interviewer - Chris Smith

And that gives you a picture of what the relative ratios are?

Interviewee - Laura Font

Well Yes.   That gives your value then you'll have to analyze soils and look at the geology of the areas where, you know, you've seen that these birds spend the winters and the summers.

Interviewer - Chris Smith

This is very useful for people that happen to like looking where birds have come and gone but there must be some important medical and scientific principals which would benefit from this, I can think immediately where we're worried about avian flu.

Interviewee - Laura Font

Avian flu, yes, because if we manage to define very well the migration routes of migratory birds then if we know that there is a species that can potentially carry bird flu then if we manage to characterize these migration paths then we will manage to find the origin of birds carriers of the flu.

Interviewer - Chris Smith

Durham's Laura Font describing how the strontium isotopes in bird's feathers can tell you where it has been.   In just a moment we'll be hearing why the concept of cold fusion is coming back into fashion.   But first Mark, what's this about the world's blackest material.

Interviewee - Mark Peplow

Yeah! That's right, strictly speaking it's the world's least reflective coating.   So if you have that on say an opaque material it ultimately makes for the blackest material known to science.   Now the way that they made this is using a cunning property of materials called their refractive index that determines how fast light can travel through a material and it is the thing ultimately that's going to determine how reflective something is.   When you have light going through air and hitting material, the bigger the difference between the refractive indices of air and material the more reflection you're going to get.   So for instance, diamond has a refractive index of 2.4 in comparison to air's 1, so it's quite sparkling, what the scientists have done led by Fred Schubert of Rensselaer Polytechnic Institute in New York,   they have actually made a material that has a refractive index of 1.05, so it is very close to air's value of 1.

Interviewer - Chris Smith

So it does not actually reflect very much?

Interviewee - Mark Peplow

That's right, it hardly reflects at all.   The really cunning thing that they've done -- this is just the first layer, it is made out of a tiny silica nanorods, they are tiny silica cylinders which are about 2000 times thinner than the human hair.   They've arranged those on the surface but that's just the first layer; they have a total of 5 layers, where each layer successively has a slightly higher refractive index.   That means at each stage very little light is being reflected ultimately they put that on top of a material called aluminium nitride, now this is a material that's being investigated for use in light emitting diodes and they reason that if you can reduce reflection down as much as possible you can actually increase the efficiency of these LEDs because more light will get out rather than being bounced around through reflections.

Interviewer - Chris Smith

Are there any other applications that you could see this being employed as a useful non-reflective dark surface?

Interviewee - Mark Peplow

Well, they're also hoping that if you look at say solar cells and you obviously don't want to lose any sunlight at all through reflection, you don't want the sunlight literally bouncing off your solar cell what you want is for all of that sunlight to be absorbed, so they reckon a coating of this on solar cells may also help to improve the efficiency of those devices as well.

Interviewer - Chris Smith

Thanks Mark and Richard what's this about cold fusion being back on the menu.  

Interviewee - Richard Van Noorden

I think most chemists would probably rather forget about cold fusion altogether after Pons and Fleischmann's 1989 big descriptions that they could achieve cold fusion in the test tube at room temperature, they could get deuterium nuclei to fuse together they claimed in a simple electrochemical cell, but you know years after that lots of experiments from other research have seemed to show that their results couldn't be replicated and something was wrong somewhere.   Nonetheless, a few researchers have kept going and intriguingly at the ACS, American Chemical Society Conference there is a whole session organized just on cold fusion, which is extremely unusual and one cold fusion devotee told me it hasn't happened as far back as he could remember.   Now cold fusion enthusiasts are saying this really does point to revival in cold fusion fortunes and they're particularly interested in a group of researchers at the American Space and Naval Warfare System Centre in San Diego where researchers say they've claimed realm of evidence for nuclear reactions occurring in a system quite similar to the 1989 cell with a few improved materials and then indeed they've got other groups who are trying to replicate their research and they've published papers in Naturwissenschaften.

Interviewer - Chris Smith

So they're looking for stray neutrons and things that would be evidence that this is taking place.

Interviewee - Richard Van Noorden

Yeah, they are looking for things like gamma rays, alpha particles and they're using conventional thin films that nuclear physicists use to show evidence of nuclear reactions.   Now of course a lot of people are disagreeing with this saying that it is just the old monsoons recycled; nonetheless cold fusion enthusiasts feel they might start to get their research published in respected journals like Physical Review Letters which would really mark a real change in how the subject was perceived by other scientists.

Interviewer - Chris Smith

Do you believe it?

Interviewee - Richard Van Noorden

I really couldn't say Chris.   It's always edgy talking to people about cold fusion because this is such a polarized opinion, I talked to Martin Fleischmann who did the original experiments in 1989 and he said "sometimes you just can't get people to believe it" and although he felt, you know, may be he would be vindicated he said "my optimism is tampered by realism", w