Chemistry World Podcast -July 2011
1:03 - Electron remains stubbornly spherical
4:15 - Chemical 'Scotch Tape' separates carbon nanotubes
7:42 - Robert Mulvaney is in the British Antarctic Survey cold room talking about what the chemistry of ice can tell us about the atmosphere of the past
14:50 - Coin isotopes unravel ancient inflation riddle
17:28 - Polymer caterpillar crawls in humid weather
20:40 - What do you do when you need a new catalyst for a reaction? Ask David Baker to design you an enzyme to do it
28:03 - Materials 'sandwich' superconductors
30:15 - Swimming with sensors
32:35 - Trivia - How many elements are there on the periodic table?
(Promo)
Brought to you by the Royal Society of Chemistry, this is the Chemistry World Podcast.
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Interviewer - Chris Smith
(Promo)
Brought to you by the Royal Society of Chemistry, this is the Chemistry World Podcast.
(End Promo)
Interviewer - Chris Smith
Hello welcome to the July 2011 edition of the Chemistry World podcast. With us this month are Phil Broadwith, Mike Brown and Patrick Walter and they're here to talk about the shapes of electrons, explosives detecting wet suits and even DIY enzymes.
Interviewee- David Baker
You give me a new reaction and I can very rapidly generate active site models which are accurate and then build proteins, which contain those active sites to give a very good starting point for a directed evolution methods for example.
Interviewer - Chris Smith
David Baker, with a way to design enzymes from scratch. He'll be with us later in the show. My name is Chris Smith, and this is the Chemistry World podcast.
(Promo)
The Chemistry World Podcast is brought to you by the Royal Society of Chemistry. Look us up online at chemistryworld dot org.
(End Promo)
(1:03 - Electron remains stubbornly spherical)
Interviewer - Chris Smith
What is round, in fact we now know it's extremely round and measures less than a billionth of a millimetre across. Phil.
Interviewee - Phillip Broadwith
Okay Chris, well obviously we can't actually see electrons, but the standard model of physics tells us that the electrons should be absolutely spherical. However, if you consider some of the other more alternative theories that include other particles that are predicted to exist, that gives us a slightly sort of off-spherical, slightly ovoid shape of an electron, but we don't really know how to tell which is which, because the difference between the two is way smaller than anything that we can possibly measure.
Interviewer - Chris Smith
So how come scientists then get to the bottom of that to work out if an electron is truly round, therefore some of the theories are right or if it's not round, it's an ovoid or something and therefore other sets of theories could be right.
Interviewee - Phillip Broadwith
Well, what you need to do Chris is to measure the electric dipole moment of the electron, which is the.
Interviewer - Chris Smith
Which is what?
Interviewee - Phillip Broadwith
Which is the distribution of electric charge across the surface of the electron, and you can do that with some fancy jiggery pokery with lasers using a ytterbium fluoride and that's exactly what a team lead by Ed Heinz at Imperial College in London has done to a degree of accuracy about one and half times better than anyone has ever done before, which gets just about down to the level, where some of those theories would start to predict this kind of slight oval shape of the electron.
Interviewer - Chris Smith
One staffer did here that group put forward was that they've done this to within a precision of if you were to scale the electrons, the size of a solar system, then they've made measurements which is sufficiently precise that they would be right to within the width of a human hair or that sort of scale, which is tremendous, I mean it's incredible. But how did they actually do the experiment?
Interviewee - Phillip Broadwith
Okay. So what they've actually done is take some ytterbium fluoride molecules, prepared them with their spins. So their spins are all aligned, whack them with the big laser and apply an electric field and if the direction of the spin on the ytterbium fluoride changes, then that would indicate some kind of electrical dipole moment measure Unfortunately or fortunately, depending on which branch of physics you prefer, the answer that they've come up is that it's still a hundred percent spherical.
Interviewer - Chris Smith
And what are the implications of that, obviously we can't rewrite the physics rule book right now because they didn't find that it was a funny shape. What are the implications are you going to find?
Interviewee - Phillip Broadwith
Okay, well not only is this a more accurate measurement, it's a slightly improved method and what the group is saying is that this should be the first of a series of ever-increasingly accurate measurements that we can do in the near future to get closer and closer to narrowing down where this theory breaks down.
Interviewer - Chris Smith
Okay. Don't hold your breath. I think I heard Jony Hudson, who is one of those researchers say it took him 10 years to actually get the result that they did. So I guess it will be another 10 years before they can do with anything bigger, because it was a pretty pretty hard experiment to do from what they tell me.
Interviewee - Phillip Broadwith
Yeah, well we'll see how that goes I think.
(4:15 - Chemical 'Scotch Tape' separates carbon nanotubes)
Interviewer - Chris Smith
Okay. Well here's something with a little bit more traction perhaps scotch tape, but this is selective scotch tape Mike. So funny.
Interviewee - Mike Brown
Yeah that's right, so here we're talking about a chemical scotch tape, so we all know about cello tape or scotch tape, where you stick things together, like cardboard boxes and things. Now we're talking about sticking single walled carbon nanotubes to a chemical scotch tape.
Interviewer - Chris Smith
And how does this work? How did they make this and why is it useful?
Interviewee - Mike Brown
Okay so at the moment, single-walled nanotubes are useful in nanoelectronics because of their conductivity and things like that but with current technologies, you basically get a mixture of metallic and semiconducting single-walled nanotubes at the moment and these decrease the efficiency and the use of devices that you're going to make.
Interviewer - Chris Smith
Per se, you haven't got a homogeneous population that you are using, so if you get just the ones to do one and ignore the ones you don't
Interviewee - Mike Brown
Yeah that's basically it, yeah. You get a better device. So Jin Zhang has a led team at Peking University and they've been looking at how they can separate them, still keeping them intact, but separate them easily and cheaply and what they've come up with are these chemical scotch tapes. So what they needed was a flexible tape, so they've used a flexible polymer called PDMS and what they've realised is that you can functionalise the polymer. In this case, they've got an A tape which is functionalised with amines and a P tape which is functionalised with phenyl groups. And depending on which one you stick to the nanotube sample, you can peel off different ones. So the A tape removed semiconducting single-wall nanotubes and the P tape removes metallic single-wall nanotubes. So depending on which ones you want, you can peel off the other ones and then you're left with a pure sample of the nanotubes you want for your device.
Interviewer - Chris Smith
Is this easy to make this stuff?
Interviewee - Mike Brown
Yeah, so what the authors have said is it could be used in any lab where you want to separate nanotubes and it is pretty easy to make, all you do is functionalise your polymer substrate and you can make these and the good thing about these is you can separate mixtures of long and short nanotubes without the nanotubes breaking which is the main thing. You need to have an undamaged sample to be able to take it on to make your nanoelectronic device.
Interviewer - Chris Smith
And when you actually use the tape, is it literally a case of if you sprinkle on the nanotubes onto the tape and then give it a shake and what doesn't get stuck is what you want.
Interviewee - Mike Brown
Well, you start with the surface with your nanotube sample on the actual surface and then you actually apply the tape to the surface. So instead of sprinkling onto the tape, you're actually sticking it on.
Interviewer - Chris Smith
Do you not miss any, are there not any that might be on the surface that don't quite seal the tape and get picked up?
Interviewee - Mike Brown
Well I think you have to make sure that the tape covers the complete sample. I mean, they're working on square samples, and they're covering the whole sample with the tape. So, yeah, as long as you don't miss some, then you're going to get a pure sample.
Interviewer - Chris Smith
I suppose, anything is better than the mixture you would have to start with, that you would have to live with.
Interviewee - Mike Brown
Yeah that's right. They're looking at scaling up this as well in the future and making the functionality even better, so that it's even tighter bound to the tape.
Interviewer - Chris Smith
Tempting to speculate that they've got that one wrapped up. Thank you Mike.
(7:42 - Robert Mulvaney is in the British Antarctic Survey cold room talking about what the chemistry of ice can tell us about the atmosphere of the past)
I'm off to Antarctica now. Well sort of. Here is Robert Mulvaney.
Interviewee - Robert Mulvaney
We're in the cold room or the cold laboratory of British Antarctic survey. As you can see here, I've got on the shelf, a range of tubes - they're all full of ice cores that we've collected in Antarctica. What I do is I go to Antarctica, I spend two to three months in the field and I drill deep into the Antarctic ice sheet and recover a core, all right through from the surface to as deep as I can get to bring back that back to the lab here, where I process the ice. It then goes through to the instruments in the laboratory next door and they measure a range of things that tells us about how the climate and the atmosphere has been evolving over many, many thousands of years.
Interviewer - Chris Smith
So talk us through the science behind that then? What're you actually looking in the ice for and how does the story of earth's past climate gets laid down in that?
Interviewee - Robert Mulvaney
What you need to know first of all is any ice that falls in the Central Antarctica are the same in Greenland, it doesn't melt. So from one year to the next it just builds up and builds up and builds up. So when we drill down into the ice, we're drilling down a continuous record into the past. Now what I do when I get back here; one of the first things I do, is I measure the isotopic composition of the water molecules. So water is H2O, we measure the heavy and light isotopes of oxygen, that's they're called oxygen 16 and oxygen 18 and the heavy and light isotopes of hydrogen that's hydrogen and deuterium. And the ratio of the heavy and light isotopes tell us about temperature, the amount of energy that you need to lift a heavier isotope out of the ocean and transport it to the point where it falls as snow on our drilling site, is related to the temperature. So the warmer the climate, the more of the heavier isotope we see.
Interviewer - Chris Smith
You immediately get it clear as to what the temperature on earth was like when the water that was evaporated to make that ice was first lifted out of the ocean. What about what else was going on in the atmosphere is that recorded in the ice too?
Interviewee - Robert Mulvaney
Well, if I take a little slice of the ice here and show it to you, you can see that these little tiny bubbles of air trapped in the ice. Now these are little tiny bubbles of the actual atmosphere of the past. So we're not here now measuring something that tells us about something else. So when we measure the isotopes of water, they're what we call a proxy, they tell us about something, they tell us about some temperature. But if we take the air out of these bubbles, these are the actual air that was circulating the planet in the past. So we can reconstruct things like the record of carbon dioxide and methane and the major greenhouse gases and see how they've evolved through time.
Interviewer - Chris Smith
And how far back in time, can this clock go?
Interviewee - Robert Mulvaney
Traditionally past tends to measure to draw fairly shallow cores but actually it's fairly shallow, it's up to about a 1000 meters or a recent 1000 meter core in a place called Berkner Island, like it goes about 150 thousand years, but we've been involved in a number of other bigger programs. Perhaps the biggest was the European Project for Ice Coring, EPICA. That went back through the ice sheet down to about 3200 metres and brought us back to 800 thousand years of records, so 800 thousand years and in that 800 thousand years, we could see we had eight glacial cycles, eight times that have been in and out of an ice age through that period of time.
Interviewer - Chris Smith
And what is this revealing when you begin to analyse those bubbles and ask what is in them? What do you see?
Interviewee - Robert Mulvaney
We quite clearly see how the climate is changing so we can see the slow progression into an ice age and then the rapid exit from an ice age into a warm period. But all through that time, we can see how closely the carbon dioxide and the methane matches the temperature and they're very very close in deed. But the other thing is we can see what levels we'd expect in a normal or unperturbed atmosphere. So if you like, if you go back through that last 800 thousand years, then normally in an ice age, we'd expect to see somewhere around about a 190 part per million of carbon dioxide in the atmosphere, its about a 190. And if you go to a warm period, we'd expect to see somewhere around about 290 parts per million. So all of the interglacial, all the warm periods up until present has always been about 290 parts per million. But of course in the atmosphere today, we're close to 390 parts per million. So we're already hundred parts per million above what we'd have actually seen in the last 800 thousand years. So that's what gives us some sort of belief that when we look at the changes that we see in the atmosphere at the moment, they're outside the range of natural climate and atmosphere system.
Interviewer - Chris Smith
So we're adding CO2 to the equation now, because we're actually liberating it into the atmosphere. So what are indicators that these have some kind of effect?
Interviewee - Robert Mulvaney
Well, first of all, we should be sure that what we're adding to the atmosphere is coming from the fossil fuels and not from some natural cycling of the carbon dioxide. Now if you imagine carbon dioxide in the atmosphere it's either been released into the atmosphere or absorbed back by the oceans and by the forest systems. Now that's effectively the same carbon dioxide cycling through the system, now that same carbon dioxide cycling through the system and it doesn't tend to change the isotopic composition of the carbon in that carbon dioxide. But what we're seeing at the moment is that the carbon isotope signature in the carbon dioxide in the atmosphere at the moment is starting to move away from the long term mean if you like. And it's starting to move more towards the carbon isotope signature of fossil fuels. So that's what gives us confidence of the carbon dioxide in the atmosphere is not from a natural source, it's from fossil fuels.
Interviewer - Chris Smith
Can we have a look at some of these ice cores?
Interviewee - Robert Mulvaney
Yes, what we've got here, we've got quite a few on the shelf here, this one from a place called Dyer Plateau as you can see, its called Dyer90. This ice was drilled in 1990. What I pulled out for you there, is a piece of core, it's already been processed as you can see. They've already taken one of the part of the edge off it, but it's about I'd say a 100 millimetres in diameter and about a meter long. This part I'm holding up for you is actually a piece of shallow ice; it's only 45 meters deep. You can see sort of light fairly porous, as I hold it. I'll just get another piece out from deeper in the ice. You can see now, if I just take this little slice out of this core here, this has come from quite a bit deeper, but you can see it's come from the sort of fairly wide looking porous medium to something that's much more glassy and I think it's quite clear you can see the air bubbles in it and if I just started to warm it up with a bit of luck what we might hear is the bubbles starting to explode, let's see if we can get that going.
Interviewer - Chris Smith
Would that reflect the pressure? This was under when it was made.
Interviewee - Robert Mulvaney
This piece of ice is from about 233 meters down in the ice.
Interviewer - Chris Smith
So how old is that?
Interviewee - Robert Mulvaney
This is not that old. This is about only about a 1000 meters, so thousand years old at this site.
Interviewer - Chris Smith
It is quite hard to warm things up in here. What temperature is it in this room?
Interviewee - Robert Mulvaney
It's minus 25 in here. And this piece I've just taken it out at minus 25 and I'm holding it between my hands to melt it, I don't if you can hear that
Interviewer - Chris Smith
I'll certainly can with my ears. I don't know if the micro is picking that up, but there's a cracking noise. Definitely
Interviewee - Robert Mulvaney
What that crackling is that the ice is under pressure, so for every 10 meters down, we go into the ice sheet there is an extra one atmosphere of pressure, so with 233 meters down, about 23 extra atmospheres of pressure there.
Interviewer - Chris Smith
So let me ask you a few things about the practical aspects of actually going and getting this material because it's pretty cold in this cold room. Antarctica is a lot colder than this though, isn't it?
Interviewee - Robert Mulvaney
We're there in the summer, and the lot of the sites that we were working at during the summer about this sort of temperature, but to be honest it's really when the wind comes, if you got wind on top of the temperature, that when it really gets cold. But yeah we're dressed well, well looked after. We do all our drilling under cover, so we're not out in the open. So it is uncomfortable, but yeah you get used to it.
Interviewer - Chris Smith
These scientists are built of stern stuff. That's was Robert Mulvaney from the British Antarctic Survey. And now from the white stuff to silver stuff and a history lesson. Patrick.
(14:50 - Coin isotopes unravel ancient inflation riddle)
Interviewee - Patrick Walter
Well I'm sure everyone's heard of the great Price Revolution of the 16th and 17th century.
Interviewer - Chris Smith
Actually, no I haven't.
Interviewee - Patrick Walter
Perhaps if you haven't then it was period of high inflation across Western Europe and there have been various competing theories as to why this is. And one of the most influential ones was that Spain was being flooded by silver that was coming from Mexico and mines in the Andes as well.
Interviewer - Chris Smith
Okay and so how can you get to the bottom of whether that was true or not?
Interviewee - Patrick Walter
So metals like silver have different isotopic ratios depending on where they're mined.
Interviewer - Chris Smith
Do you mean, as in there are contaminants in the silver which are different isotopes or the silver metal itself comes in different flavours of isotopes.
Interviewee - Patrick Walter
Well it's not the contaminants in the metal; it's different isotopes. So there are two different stable isotopes, naturally occurring isotopes of silver. This is the silver 107 and silver 109.
Interviewer - Chris Smith
So how can they be used to answer this question?
Interviewee - Patrick Walter
As they both have a different isotope signal, you can use mass spectrometry to distinguish between the different isotopes. So you can actually pick out which is which and you can tell European silver, Spanish silver from silver mined in Mexico or the Andes.
Interviewer - Chris Smith
Oh! Ingenious. So basically if you look at the silver that was allegedly around at that time and it's got a Mexican hallmark to it chemically speaking, that strongly argues that it was this influx of silver from South America that was driving inflation.
Interviewee - Patrick Walter
Yeah.
Interviewer - Chris Smith
And what did they find?
Interviewee - Patrick Walter
So, during the price revolution on 1520 to 1650, it turns out there was very little Mexican or Andean silver actually entering Spain.
Interviewer - Chris Smith
Oh! So it can't have been that that was driving this big inflation then?
Interviewee - Patrick Walter
No it appears that Mexican and Andean silver didn't start flooding the Spanish market until 1700s.
Interviewer - Chris Smith
So if it wasn't the silver, what was it?
Interviewee - Patrick Walter
Well, there are various different theories. This was coming shortly after the Black Death that spread all across Europe and decimated the population by perhaps as much as a half. And during the massive, during the quick recovery from this, as the population once again rose, demand on food increased and as demand on food increased, prices went up and there were various other possible factors. Spain was at war with the Netherlands, had a lot of debt to payoff, so that this partly explains why the inflation might have increased in Spain for instance.
Interviewer - Chris Smith
Sounding highly reminiscent of the situation today, isn't it?
Interviewee - Patrick Walter
Indeed.
(17:28 - Polymer caterpillar crawls in humid weather)
Interviewer - Chris Smith
Anyway let's look at something slightly different. Thank you for that Patrick. Mike tell us about this caterpillar, which crawls and you can see it but it's not real caterpillar, it's a chemical.
Interviewee - Mike Brown
Yeah, so, on the show we've talked a lot about molecular motors and molecular DNA walkers and things like that, but this is a polymer based device, you can actually see walking across a surface.
Interviewer - Chris Smith
Okay.
Interviewee - Mike Brown
And it's a polymer that moves in response to humidity. So when it's dry, when the air is dry, in this case nitrogen is dry, its relaxed state, it's lying down and when there's humidity around, then actually it gets up basically and they move.
Interviewer - Chris Smith
Changes shapes.
Interviewee - Mike Brown
Yeah changes shape, so the motion of it getting up kind of moves it across the surface.
Interviewer - Chris Smith
How does it get any kind of friction with the surface then?
Interviewee - Mike Brown
Okay, so the surface that it's on is pretty rough and grooved and so it's like ridges. It has claws on the bottom of its feet as well and so these kind of lock into the grooves and that gives it its direction really. The device is quite simple. It's a hydrogel which absorbs water. And it expands in response to rising humidity and it's got two supports. So it's a hydrogel strip and then on each end, it has these harder polymers, which are inert to humidity, so they're the feet. And as we said earlier it stands on a rough surface. So the team at Jilin University in China have been changing the humidity of nitrogen that they pass across it from a 11% to 40% and they've been observing the changes in the polymer as it does and it actually moves rather like a caterpillar would, where it picks up its back and you get an arched back and then it moves forwards.
Interviewer - Chris Smith
Why is this useful? What's the point?
Interviewee - Mike Brown
On the one hand, it's quite fun to see, you know, just a polymer that allows something to move across the surface, albeit, it's moving because of the rough surface. But the team do say that, you know, you could use it as a humidity sensor. One thing that I forgot to mention earlier is that the polymer is pretty strong and it can actually carry a load a hundred twenty times heavier than itself.
Interviewer - Chris Smith
So you could use it like some kind of switch. You could actually make it do some work in the course of making these movements, so it could actually be useful humidity detector or something capable of registering some kind of output.
Interviewee - Mike Brown
Yeah, yeah that's right. They also speculate that in the future, they could create a similar device which changes in response to a chemical or heat or light as well. So there's a wide variety of ways that the research could go forward.
Interviewer - Chris Smith
But not backwards at the moment.
Interviewee - Mike Brown
But not backwards because the ridges in the surface wouldn't allow it yeah, that's right Chris.
Jingle
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Interviewer - Chris Smith
You're listening to Chemistry World with me Chris Smith. And still to come, a way to pick up pollutants with your wet suit.
(20:40 - What do you do when you need a new catalyst for a reaction? Ask David Baker to design you an enzyme to do it)
First though, what do you do if you got a chemical reaction you want catalysed. The answer is: you talk to this man. David Baker.
Interviewee - David Baker
The problem is really a challenge that's posed by the almost miraculous ability of naturally occurring enzymes to catalyse reactions and with very, very high efficiencies and in principle if we understood the mechanisms by which naturally occurring enzymes catalyse the whole vast myriad of reactions that go on in our bodies and elsewhere, we should be able to make new catalysts, that catalyse reactions that are of interest to humans now, that nature didn't really ever care about during evolution, so never generated catalysts for.
Interviewer - Chris Smith
You make yourself sound very simple. But I mean, if you just take a snapshot of catalyst, these enzymes, they're proteins and even the very small one is made up of say a hundred amino acids, which means that's 20 to the power of 100 possible isomers that you could make with that protein. So it's not trivial to say we'll just put such acids that's how this molecule does what it does.
Interviewee - David Baker
Yeah, that's absolutely right. It's not at all trivial. Not only are there huge number of possible sequences, but if you choose one sequence that you've designed, that you expect will fold up to a particular structure, which will have a geometry compatible catalysis, that's just one possible structure that sequence could adopt in even larger sea of other possible conformations that could adopt, which wouldn't be catalytic, so we have to pick out the right sequence and that sequence has to fold up to exactly the right structure and not to any other.
Intervie
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