Chemistry World podcast - March 2012
0:37- Calculations find a quadruple carbon-carbon bond
4:18- Graphene sheets are made irridescent and superhydrophobic
7:10- Paul Kelly discusses an accidental discovery that led to a novel fingerprinting method
14:20- Cooperative chemistry gives rotaxanes with multiple rings in surprisingly high yield
16:35- The toughest fibres ever made
20:42- Norbert Jakubowski on the highly sensitive techniques used to detect metals for toxicity and diagnostic measurements
26:25- The instant detection of ecstasy
29:33- A magnetic soap
32:53- Trivia - the largest ever sodium water experiment?
(Promo)
Brought to you by the Royal Society of Chemistry, this is the Chemistry World Podcast.
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Interviewer - Chris Smith
This month we're meeting head-on the toughest substance ever made and a clever way to fingerprint the formerly unfingerprintable. Hello, I am Chris Smith and with me for this month's Chemistry World are Phil Broadwith, Andrew Turley and Laura Howes.
(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)
(0:37 - Calculations find a quadruple carbon-carbon bond)
Interviewer - Chris Smith
And to kick us off, you've heard of single carbon-carbon bonds, you've met double bonds and probably also triple bonds, but no one expected that we might start considering a quadruple carbon bond, Phil.
Interviewee - Phillip Broadwith
If you were to draw the molecule C2, you know, with two carbon atoms then classically according to the sort of the valence bond picture, that we're all taught at school, you'd draw two bonds between the carbon.
Interviewer - Chris Smith
What about three if you had say acetylene because there are three, three bonds.
Interviewee - Phillip Broadwith
Yeah, so acetylene, you would normally have three bonds but that also has hydrogens bonded on the end and when you take those hydrogens away because of the way that we think of electrons being arranged that kind of ends out being a double bond. That's again as I say in the classical view of bonding, but what Sason Shaik and his colleagues at the Hebrew University of Jerusalem in Israel have done is kind of take a slightly different view of bonding and kind of looked at what is a bond anyway because, you know, we draw lines on paper but what do they actually mean and they said well, you know, a carbon atom has four valence electrons so why can't it make four bonds.
Interviewer - Chris Smith
Why indeed, so what did they find?
Interviewee - Phillip Broadwith
Okay, well they did some complicated calculations and came up with a model that has three kind of classical bonds in the same way that acetylene would as we'd said and then there are two electrons left and those electrons are arranged in orbitals that point directly out of the ends of the molecule, sort of kind of directly away from each other.
Interviewer - Chris Smith
So, you'd think that they'd be so far away that they wouldn't actually interact because they'd be pointing away from each other.
Interviewee - Phillip Broadwith
Yeah, exactly but what the calculations say that the group has done to show is that actually there is an interaction between those two electrons and they do pair up in a way that gives a lowering in energy of the whole system, so what you could formally call a bond admittedly it's not strong as a normal single or double bond but it is about somewhere between 11.6 and 14.8 kilocalories per mole.
Interviewer - Chris Smith
So why can't those two electrons that are pointing outwards from the end of the molecule just be bent around into the middle so that they do talk to each other and establish a proper covalent bond, what's stopping that happening?
Interviewee - Phillip Broadwith
The way we kind of think of bonding is through orbitals that are on the atoms overlapping with each other and those orbitals because of the way that they're defined through quantum mechanics whatever point in very specific directions, so they can only overlap with each other to make bonds if they point in the same direction or if they point towards each other to a certain degree. Now if you've got two orbitals that point directly out from each other that can't really happen in the same way as we would normally think about it happening, but what the calculations have shown is that there is still some interaction between those two electrons.
Interviewer - Chris Smith
And apart from in itself being an interesting finding, does this fundamentally change how we regard this aspect of chemistry or are there any other aspects of chemistry which now we are going to have to rethink because of this finding?
Interviewee - Phillip Broadwith
In terms of textbook chemistry, nobody says that you know you can have quadruple bonds between non metals that are at the top end of the periodic table and to be honest I don't think we're going to start teaching chemistry at school to include this kind of theory, but if you want to get really into these particular kinds of molecules and really explain their reactivity, then it only really matches up with the experimental data if you look at a bonding picture, which is more like this kind of quadruple bond than the kind of standard double bond that you would see in a text book.
(4:18 - Graphene sheets are made irridescent and superhydrophobic)
Interviewer - Chris Smith
Indeed, well let's stick with carbon and a form which is getting enormous attention increasingly now Graphene, what have you got for us on this aspect Laura, sparkly graphene.
Interviewee - Laura Howes
Irridescent graphene oxide really. This is a beautiful looking material which is superhydrophobic What Yong-Lai Zhang at Jilin University in China has done is taken graphene oxide so that's the oxidized version of graphene, so it's still a flat sheet that there are oxygen sort of sticking up from the sheet, and then they have used lasers to micropattern it, so they've put these two laser beams onto the surface and that's created an interference pattern which has made almost sort of like a corrugated sheet of a graphene oxide.
Interviewer - Chris Smith
So, you get almost like pillars sticking out and then there are ridges and valleys on them?
Interviewee - Laura Howes
Ridges and valleys exactly, and these ridges and valleys what gives you the iridescence which is why we're saying it's so beautiful, but it also gives you these superhydrophobic properties we have talked about that before how microstructures can do that.
Interviewer - Chris Smith
So, you put a droplet of water on that, it's presumably going to balance on the pillars on the ridges because the oxygen stuck there sticking up is going to interact with the water.
Interviewee - Laura Howes
Yeah, so there's an interesting sort of balance here, so the nanostructure means that you're going to get beading which is the superhydrophobic effect, but because there are still these oxygen atoms sticking up from the surface, there'll be some sort of hydrophilicity, some sort of hydrogen bonding.
Interviewer - Chris Smith
So, it's both hydrophobic and hydrophilic all at once.
Interviewee - Laura Howes
All at once and so you end up getting as little beads of water on a surface but if you turn the surface upside down the beads of water stay there.
Interviewer - Chris Smith
It stays there. Wow! Apart from being beautiful what can you do with them? There must be applications for that.
Interviewee - Laura Howes
Sure, I mean obviously the immediate applications spring to mind are when you talk about microfluidics, when you talk about controlling water or keeping small amounts of water in specific places, and other aspects that they talk about is maybe looking at cell cultures. So if you're trying to do cell cultures and keep your cells in particular areas then you could start doing interesting things there as well.
Interviewer - Chris Smith
Can you turn the effect on and off, is there any way that you could apply an electrical current to strengthen or weaken the effect?
Interviewee - Laura Howes
To flatten it, I don't know and I'm not sure they've looked at it but one thing they've started to apply is because you've got this structural colour you could potentially start using the structural colour as some sort of sensor to monitor or detect things as well as keeping your water in one place.
Interviewer - Chris Smith
Because the ridges and patterns produced an interference pattern.
Interviewee - Laura Howes
Yes.
Interviewer - Chris Smith
With light coming in.
Interviewee - Laura Howes
Yeah, so because you've used lasers and you've made this patterns which is sort of I think the ridge is kind of about two micrometers apart, so that's similar to the wavelength of light and so it just works like a diffraction grating, it separates how your lighting it and you get these beautiful colours.
(7:10 - Paul Kelly discusses an accidental discovery that led to a novel fingerprinting method)
Interviewer - Chris Smith
Amazing stuff, thank you Laura. For over a century fingerprints have been helping forensic teams to solve crimes. That led to use of a range of techniques including even superglue vapour to lift prints from various surfaces, but the results and the situations that they work under aren't ideal which is what made a serendipitous discovery by Loughborough scientist Paul Kelly, so exciting.
Interviewee - Paul Kelly
What we wanted to do was looked at the chemistry of this rather strange small molecule disulphur dinitride which is rather odd in the sense that it's only got four atoms in it. It's in a square-ring arrangement and as you might imagine with something like that it takes extremely strained and wants to polymerize and that's been known for many, many decades. Now because the polymer is generated that way it behaves as a metallic conductor. So we wanted to get into some aspect of this. So we were looking at working with zeolite systems, putting this small molecule within the pores of the zeolite and hoping that it would polymerize up and so therefore we would generate, if you like, a molecular wire within a zeolite system. What we found was that when you were exposing this small molecule to the zeolite systems within one of our vacuum chambers, the little sample vial that you have poled the zeolite in would come out with a fingerprint developed on it and even though people have been doing fingerprints for many, many decades it was still important to try to address some key issues regarding problem media and so on.
Interviewer - Chris Smith
So what did the fingerprints that were developing incidentally like this look like?
Interviewee - Paul Kelly
The polymer itself is dark blue black in colour, it was pretty obvious what you had straight away on the glass of the vial, you would see the fingerprints picked out in this dark blue material.
Interviewer - Chris Smith
What about if you washed off the glassware, was it particularly robust and resilient this signal or was it relatively easy to perturb the fingerprint?
Interviewee - Paul Kelly
That depends on what media we're talking about because the subsequent work that we have done shows that if you were to wash some media beforehand and get rid of the fingerprint before exposing it to S2N2, you don't really get any joy but what we've shown is that on certain media particularly metals there is a corrosion signature left over by the washed off fingerprint and so when exposed to S2N2 you also get the fingerprint still picked up even though paradoxically it's not actually physically there anymore.
Interviewer - Chris Smith
Looking what's in a fingerprint there's going to be some sweat there, there'll be some metal ions in the sweat, there will be proteins and there will be fats. So actually pretty much all aspects of chemistry roping for investigation, it could be anything, but what aspects of the reactivity the disulphur dinitride could actually be doing this.
Interviewee - Paul Kelly
It's hard to know because it's usual molecule as I say one that in many ways hasn't been studied in terms of its general chemistry and if you like as much as many other main group systems has been studied in the context of polymerizing because as I say there's really nice properties to the polymer when you get it. But direct sort of fundamental chemistry studies on it had been fewer and further between, even ccompares to some relative material such as the tetrasulphur tetranitride. So one problem is it's actually rather difficult to, necessarily from first principles sort of fathom what direct chemical interaction you actually could have from this material. The other point to bear in mind of course is that when it's reacting or when it's generating an image in a situation where the print has been removed from the metal surface then you don't have a chemical reaction happening . you can't do because there's no chemistry there to occur, this must be a physical process on the surface of the metal and somehow this thing is relating though, recognizing the factor that there is a change to surface of the metal and responding accordingly by polymerizing where the print was, where the small corrosion signature is.
Interviewer - Chris Smith
So, what can this do that's we can't do with traditional existing forensic techniques, what does it add?
Interviewee - Paul Kelly
There's a couple of things; one that I guess on its potential and that it relates to what you might call problem media but where you actually have extant prints, so where you would have that the print is definitely there, some chemical residue the print is there but it's all on a surface that is actually traditionally very difficult to get prints from, a classic example of that would be cotton or various textiles and we had some level of success on that front. But the other thing that it does that is different is it's chemically revealing those removed prints from a metal surface to the best of my knowledge, there is no chemical technique that can do that at the moment. There are instrumental techniques that allow you to show that kind of corrosion signature is there but because this is in a gas phase, you've got the opportunity to expose a large area of maybe a convoluted item in one full sweep
Interviewer - Chris Smith
So, is this actually in counter-fruition or the forensics people taking this technique and are applying it to crime scenes or is that tons of regulation and proof of concept to go through yet before you can say this is a done and dusted - excuse the pun, technique.
Interviewee - Paul Kelly
But what we have done is we had a lot of interaction with people, for example, what used to be HOSDB, the home Office Scientific Development Branch, but now is CAST. We've certainly had the interactions to show what we can do. One thing that we've been very careful to do thus far because I think of the synthetic background rather than the forensic background is to say, well look if you do this , this and this, this happens. In that sense, the ball is then in the forensic people's court, it's for them to say, well okay, that is actually applicable that's something that we want, that's something that could be usable in the correct circumstance.
Interviewer - Chris Smith
Given that you've had this level of success with this rather strange molecule, which you wouldn't have thought would have done this, has this tempted you to take things at a chemically a bit similar and see if you can extend the repertoire of fingerprinting or the sensitivity and so on into a regime or realm that we wouldn't previously have thought would be possible.
Interviewee - Paul Kelly
I think the answer to that is that there is a moral to the story here, which is that you wouldn't have particularly expected that system to do what it does and the moral therefore is what other main group, compounds, one of the other main group, the binary systems for example, could possibly do this, not just in terms of fingerprints but for other forensic aspects as well. One problem with that is there is a little bit of a disparity between the forensic community and certainly what you would broadly class as an inorganic chemistry community and they don't particularly talk to each other. So, in a sense if there's something that comes from this, aside the actual technique itself, it might be hopefully this idea that's a bit more of a meeting of minds between those two different communities, there's clearly a crossover possibility there. There has to be.
(14:20 - Cooperative chemistry gives rotaxanes with multiple rings in surprisingly high yield)
Interviewer - Chris Smith
Loughborough chemist, Paul Kelly. And now to one of the toughest substances ever made, after Laura first introduces us to the world of polyrotaxanes.
Interviewee - Laura Howes
Rotaxane is a molecule which involves a long axle or dumb-bell shaped molecule and then it has circular molecules that clip around it. These could be made into sort of molecular motors for instance, but you could also make polyrotaxanes which have multiple rings clipping around the dumb-bell. What this work from Fraser Stoddart's lab at Northwestern University in the States has done has made a really big polyrotaxane molecule, which has 20 rings around it.
Interviewer - Chris Smith
Why is this a breakthrough? What's different or special here?
Interviewee - Laura Howes
Well the really special thing is them, actually they manage to do it (15.07) or at least they managed to do with such good yields, they've managed to do this in one pop and actually get 90% yield out of it. This is a really nice introduction to (15.18) covalent chemistry and looking at pi-bonds because the way they've done this is they've used pi-stacking. So, each of these circular molecules has aromatic rings on it and if they start stacking up, you get pi- stacking and make much bigger, more complicated molecules and really start to think about really interesting applications. The original application that they're actually thinking of was to make molecular wires, using this pi- stacking to make the molecules rigid and therefore they could use them as molecular wires and that's one of the things that Fraser Stoddart told me they're going to be looking at, trying to make self-assembling wires that they can then sort of start connecting up into circuits.
Interviewer - Chris Smith
Why do they think the efficiency is so high? Why did they get in the 90% yield?
Interviewee - Laura Howes
So, the 90% yield is, as I mentioned before is to do with this pi-stacking. But I think what happens is if the first ring snaps on and the second ring snaps on and then it just starts to ramp up and up, so they think it's sort of a stepwise process; you get one and then you get another and then just causes it to zips up and gets to a certain stage, they like to actually to doing up a co-zip, so you start to up this a bit fiddly and then and you start to pull up the zip and once you get to a certain amount and everything is aligning, it just zips up really quickly
(16:35 - The toughest fibres ever made)
Interviewer - Chris Smith
And off you go. And on the subject of wires, which I was saying is one possible application, something a bit like a wire, spider thread, Andrew tell us about this breakthrough with regard to a molecule that's potentially one of the toughest materials we have made.
Interviewee - Andrew Turley
Yeah, so this group has developed this strongest or more specifically the toughest fibres ever they say, they don't know if anything tougher. We all know about spider silk - this is very tough. What they're interested in doing is recreating some of the toughness of spider silk, but doing it artificially, spiders are very difficult to manipulate, it's very hard to get them to produce spider silk altogether for your purposes, so is it possible to mimic what they do synthetically.
Interviewer - Chris Smith
So, if they can't get spiders to do it, you need the test tubes do it for you. What is the solution?
Interviewee - Andrew Turley
So, the solution that Seon Jeong Kim, and his colleagues at at Hanyang University in Korea have come up with is to use a combination of graphene and carbon nanotubes. So it's this combination of something that is kind of a 2D sheet which is the graphene, and a 1D strand, which is the carbon nanotubes. People have previously used both of these but in isolation and the carbon nanotubes in particular produce a very, very strong fibre, but carbon nanotubes are very, very expensive and so you can bring the cost right down if you mix in some graphene and as an extra benefit, the graphene actually makes it even stronger.
Interviewer - Chris Smith
So if were to zoom in on this with a really powerful microscope, having mixed together some flakes of graphene and some of these nanotubes, what would it look like?
Interviewee - Andrew Turley
What happens is the graphene flakes align and it's that alignment that gives you the toughness. The definition of toughness is the energy needed to cause the material to fracture. The way these flakes were aligned, they deflect away the pressure on them, the force on them and they deflect it into the sort of more squidgy polymer type material, the matrix surrounding all of this and as well the one dimensional fibres that sort of coil and twist around, around the flakes.
Interviewer - Chris Smith
So if you had a bullet coming in, it would be rather like the crumple zone on car, you would turn all of the nice metal which is in a straight line into lots of ripples, basically the sheets of graphene, connected by the nanotubes do the same thing, they deform and therefore the energy gets dissipated through the molecule.
Interviewee - Andrew Turley
Yes, it's that exactly. You want to take the force away from the impact.
Interviewer - Chris Smith
So this is a proof of concept. The molecule is synthesizable or at least the sandwhich, the molecular sandwhich can easily be made? Is it practical to try and turn that into a bullet proof vest or something similar?
Interviewee - Andrew Turley
It seems like this fibre is pretty good in terms of practical applications. Obviously when you're talking about practical applications, it needs to be fine tuned. So there's a range of different properties that you'd want. This group has focussed particularly on toughness, but the fibre they've produced is flexible and it can be manipulated in the same way as you'd expect for weaving a fabric. At the moment, it's not very strong when you stretch it and that's something that they would, they want to work on in the future. With any of these kind of things, it's the combination of properties that will make something like this a commercial success.
Interviewer - Chris Smith
And is this a surmountable problem? What would they need to do to the recipe or what would they need to add in order to get around this toss-up between strength and toughness?
Interviewee - Andrew Turley
Well, the combination materials has got various elements by varying those, they could probably change a wide range of characteristics. There's a polymer matrix that surrounds the carbon nanotubes and the graphene flakes and then the ratio of the flakes to the nanotubes is something that perhaps they could alter as well. So, there's probably a range of different things they can do by altering the components and their ratios.
Interviewee - Chris Smith
Andrew Turley with the molecular equivalent of a chemical crumple zone.
Jingle
Interviewer - Chris Smith
You're listening to Chemistry World with me Chris Smith. Still to come, how scientists have made magnetic soap and the biggest metallic sodium and water experiment ever, 10 tons of this stuff. Before that though, and on the subject of metals, here's a man with a detecting technique so sensitive that he can pick up metal ions glued onto antibodies in order to examine the biochemistry of individual cells.
(20:42 - Norbert Jakubowski on the highly sensitive techniques used to detect metals for toxicity and diagnostic measurements)
Interviewee - Norbert Jakubowski
My name is Norbert Jakubowski, I'm working at a Federal Institute for Materials Research and Testing in Berlin in Germany and here our main duty is to analyze metals at extremely low levels in industrial products or in the environment, but also in bio-systems and we have the most sensitive instrumentation at hand. One of these is inductively coupled plasma mass spectrometry and it is playing an important role for metal analysis. It allows us to detect metals down to nanogram per millilitre levels or even below.
Interviewer - Chris Smith
Can you get a handle on with this sort of technique then, the question of whether all metals in all forms are all bad or whether, as I think is becoming more clear, more recently some metals in some forms are bad, but the same metals in other forms, other oxidation states may not be, can you discriminate?
Interviewee - Norbert Jakubowski
Yes, I can give you a very nice example. About already 30 years we have started to investigate chromium. Chromium 3 is an oxidation state which is essential for human beings and for animals and plants, but the chromium in the oxidation state 6 can damage the DNA, thus can cause cancerogenic effects and can cause mutations and can possibly also induce cancer. That's the one at the same element can have positive effects, so it is needed for our health, but another oxidation state of the same metal can cause for instance cancer.
Interviewer - Chris Smith
How does this technique that you're using actually discriminate between these different oxidation states of the chemicals, which is enabling you to make these amazing discoveries that the same stuff can be as you say two phased, on the one hand quite nasty, on the other hand, absolutely essential for life?
Interviewee - Norbert Jakubowski
For this we couple our atomic detectors with a special separation techniques for instance, high pressure liquid chromatography which then are separating these species of interest. So we started at the beginning to learn to separate these toxic compounds, but later we found a better way to investigate toxic biomolecules by using antibodies which are directed against specific compounds. Metal detect antibodies, they can then measure these substances in a tissue sample, by just measuring a fingerprint of these biomarkers, we can identify even if organism is stressed by chemicals.
Interviewer - Chris Smith
What about making diagnoses as well, because if I would hand you a histopathological slide, say a biopsy from a liver or something, or an organ where I suspect that there may be cancer developing there. Could you step cell by cell across that and then say, yes there are signs and features in here, where by these cells in these discrete area are showing the characteristics of evolving a cancer.
Interviewee - Norbert Jakubowski
So, we're using here again the same trick. We apply antibodies, which are tagged by a metal and these antibodies are specific for a cancer biomarker and then we can use laser ablation system as a sample introduction system for ICPMS for Inductively Coupled Plasma-Mass Spectrometry, to measure the metal distribution in the tissue samples and now we can apply many of these biomarkers tagged with different metals, that means we can measure many biomarkers at the same time in the tissue sample. This technology is so sensitive we can go even into a cell; that means we can image a single cell. If we have only one metal
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