Chemistry World Podcast - December 2010
00:12- Introduction
01:26- Using host-guest chemistry as molecular velcro
04:45- Nanotubes defuse explosives
08:09- University of Bayreuth's Thomas Scheibel untangles the web of research on artificially reproducing the properties of spiders silk
16:18- Inhaled nanoparticles, from there to where?
20:15- World's smallest chromatography column
23:00- University of Western Ontario's Darcy O'Neil explains the chemistry behind making the perfect cocktail
29:45- Nanoparticles makes leaves glow
32:48- Molecular motors find reverse gear
(00:12 - Introduction)
(Promo)
Brought to you by the Royal Society of Chemistry, this is the Chemistry World Podcast.
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Interviewer - Chris Smith
Hello, welcome to the December 2010 edition of the Chemistry World podcast with Phil, Akshat Rathi and Mike Brown. This month where the nanoparticles in pollution end up in the body, how chemists can now put molecular motors into reverse and a nanotrick to make plants glow, why you might ask, well, the inventors don't actually know yet but it could prove perfect for Christmas time. So is this the end of faulty fairy lights? Also on the subject of the Festive Period open that drinks cabinet and grab your cocktail shaker.
Interviewee - Darcy O'Neil
So what it was is take sodium alginate and calcium chloride, add a flavour and mix with the alginate and then drop it into the calcium chloride bath and form these little spheres, so one of the things you could do with these lot of spheres is put them in a glass of champagne and they would move up and down and they go like a Lava lamp.
Interviewer - Chris Smith
And yes they are edible. That is molecular mixologist Darcy O'Neil on what Chemistry can bring to the cocktail bar. Hello I am 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)
(01:26 - Using host-guest chemistry as molecular Velcro)
Interviewer - Chris Smith
And we've got a sticky story to get us going, Phil.
Interviewee - Phillip Broadwith
Okay Chris, so we are talking about molecular recognition but in a macroscopic scale, so two kinds of molecules that recognize each other but can be used to stick large amounts of material together.
Interviewer - Chris Smith
How is this new, because we've known antibodies do that, for a long time we've found other molecules in nature streptavidin and biotin and so on, all these things do that. So what's new here?
Interviewee - Phillip Broadwith
Well, the new thing is that the molecules that are recognizing each other are then attached to a large polymer and you can take blobs of two different polymers, mix them together in a dish with some water and they'll stick together.
Interviewer - Chris Smith
Which sounds potentially useful, because you can make this to assemble into little machines or something?
Interviewee - Phillip Broadwith
Yeah absolutely, you can shape it into pretty much any shape you like and a lots of ways of processing polymers and then when you bring the right two polymers together they'll recognize each other and stick either reversibly or strongly enough so that they can't be pulled apart.
Interviewer - Chris Smith
Well that's easy stuff, now the hard part, how does it work?
Interviewee - Phillip Broadwith
Okay, so what Akira Harada from Osaka University in Japan has done has used host-guest chemistry. It's a well known phenomenon. You take a host molecule, in this case is a sort of doughnut shaped cyclodextrin with a very specific sized hole in the middle and a guest molecule that likes to sit inside that host and he has got two sizes of doughnut, one that's exactly the right size for a straight chain alkane like a butyl group and one that is exactly the right size to fit a much bulkier group like a tertiary butyl group or an adamantyl group in.
Interviewer - Chris Smith
And you would have the doughnut struck onto one type of polymer or species, the butyl the short bit on another one and when you mix them together the two would get, gluing the two big molecules together effectively.
Interviewee - Phillip Broadwith
Yep that's exactly right Chris and you can see the videos on our web site where you put all four different kinds of polymers, he has dyed them different colours so that you can identify which one is which, you mix it all around and the two sets pair up. So the larger doughnut goes with the tert-butyl guest and the smaller cyclodextrin donor goes with the narrower normal butyl guest.
Interviewer - Chris Smith
Is it reversible? Once it's in there, can you get it apart again?
Interviewee - Phillip Broadwith
Well, that depends on which interaction you use. In the case of the larger donor the beta-cyclodextrin, if you use a tertiary butyl guest then the interaction is weak enough to be reversible but if you use the slightly more bulky, slightly bigger adamantyl guest which is slightly bigger fits more exactly into the cyclodextrin hole, you get an interaction which is strong enough that the polymers pull themselves apart when you try and separate them rather than separating at the joint.
Interviewer - Chris Smith
As suggested earlier, one possibility would be to use something like this to build molecules where you want to build a small machine or something from a series of parts being added, but do they suggest any other possible applications in here and now, how we could use this?.
Interviewee - Phillip Broadwith
Well one thing that the authors have suggested is that it could be used for tissue engineering or wound healing or even just joining things together, if you coat two surfaces with the right types of polymers they will then stick together but only with their complimentary surface, so only when you get a molecular match, if you like.
Interviewer - Chris Smith
Science of the very small is very amazing, thank you Phil.
(04:45 - Nanotubes defuse explosives)
Interviewer - Chris Smith
And sticking with a very small, nanotubes that can diffuse explosives. This sounds Mike like a discovery that could well set the world of explosives alight it's a pun.
Interviewee - Mike Brown
Yeah that's right. We are talking about making explosives safer so that they can be used for different applications. So Benny Siegert and his colleagues at the National Centre for Scientific Research and the French-German Research Institute of Saint-Louis in France have been looking at how they can make explosive systems safer for military applications. So, they've taken the thermite reaction which is basically where a metal oxide is exposed to reducing metal like aluminium powder and there's an exothermic reaction that then occurs.
Interviewer - Chris Smith
Well, many people have relished seeing them at school.
Interviewee - Mike Brown
Yes, so what they're doing now is they're using a nanothermite reaction, so they are using metal oxide nanoparticles in the reaction which makes a bigger explosion.
Interviewer - Chris Smith
Because of surface area, why does it make the explosion more pronounced?
Interviewee - Mike Brown
Yes, basically there's more surface area to react with the aluminium powder, so the reaction is bigger. The problem is that these systems are so sensitive that they can't transport them in a military situation and they can't even transport them in the lab when they're making them, so what they're doing is that taking carbon nanofibers and they are putting the metal oxide which in this case is manganese oxide inside the carbon nanofibers and then the aluminium powder doesn't touch the manganese oxide. So then that can be transported to wherever it needs to be deployed into the field for example and then the way that you initiate the reaction, in the lab in this case, they're using a laser, carbon dioxide laser.
Interviewer - Chris Smith
And what does that do, attack the nanotube?
Interviewee - Mike Brown
Yeah, that basically makes the nanofibers disintegrate. So, the two reactants then mix and the reaction occurs but they also say that you can use a small battery with exploding wires such as platinum wire and you use a current to explode the platinum wire and then the reaction can occur.
Interviewer - Chris Smith
So how is this safer or better than the other one, just because it's much harder to trigger off externally?
Interviewee - Mike Brown
Yes, so you're basically taking a really exothermic reaction, but because it's so good as an explosive, you can actually afford to make it less sensitive. So, basically by protecting one of the reactions in nanofibers you're making it less sensitive so you can take it to where you need it to be and then disintegrate the nanofibers and then away goes.
Interviewer - Chris Smith
Are there any other applications, could you take the same science and apply it either to other kinds of explosives or a totally other kinds of reactions, so that you could use the same science elsewhere and it has a practical purpose in another field completely?
Interviewee - Mike Brown
Yes, the authors do talk about potential applications not necessarily for rockets and things like that in the military but using it for civilian applications such as airbags in cars, so you would combine the nanothermite with a gas generating compound to inflate the airbag in the car potentially you know an accident occurs and there's an impact.
Interviewer - Chris Smith
Because it's so quick, it works quite good.
Interviewee - Mike Brown
Because it's so quick, and yeah the gas will inflate the airbag.
Interviewer - Chris Smith
It really is an example of turning swords into power shears or even airbags, thank you very much Mike.
(08:09 - University of Bayreuth's Thomas Scheibel untangles the web of research on artificially reproducing the properties of spiders silk)
Interviewer - Chris Smith
On the subject of ammunitions and explosives bulletproof vests have saved countless lives but the materials used to make them aren't ideal. They tend to be bulky and it's hard to work them into flexible fabrics. So, the protection they offer is a bit limited but there is a substance, silk, that would work much better, if only we could discover healthy animals that make it like spiders actually do it. Well, we're getting close and largely thanks to the efforts of this man.
Interviewee - Thomas Scheibel
My name is Thomas Scheibel and I am currently leading the chair of biomaterials which is part of the engineering department at the University of Bayreuth in Germany. Silk is a very ancient material that is used by arthropods which includes insects, spiders, crabs, scorpions and all these kind of creatures and the very first usage of silk of probably in just protecting eggs. So, it has to withstand harsh environmental conditions and it has to have some mechanical properties and later on some animals especially spiders developed out of this ancient material something new, so not only for protecting but also for making something active with it, which is in case of spiders is hunting.
Interviewer - Chris Smith
And that's their webs of course.
Interviewee - Thomas Scheibel
Exactly webs, but there's also spiders that use for instance single fibres as sort of lasel, they're called the Bola spiders, so they've a sticky droplet at the end and they swing this single thread and they catch moths with it.
Interviewer - Chris Smith
I think glow worms do that too, they sort of secret sort of silken thread that they put little blobs of sticky stuff on it and then use their light to trap insects. Biomechanically, if you zoom on in silk, what would you see that gives it these amazing properties?
Interviewee - Thomas Scheibel
Well, we have to be a little bit cautious if we talk about properties of silks because they can differ quite significantly, so if you look under insects, what kind of properties their silk has, they can be, as I said protective for the eggs, or they can be protective during transformation from silkworm, for instance into the moth or they can be quite stiff materials like caddisflies, so they make egg-stocks, so stiff sticks at the end they locate the eggs and therefore the eggs are actually protected from predators to crawl around under leaf. So, they can have completely different mechanical properties and we see that also in spider's webs because a spider uses up to five different silk types to make a web. Some of them are stiff and very tough, they make the frame of the web and some of them are very elastic, they make the capture spiral, some of them are sticky to actually keep the prey inside and some are from sort of a cement and the cement is used to attach the web to the substratum like to the tree or to a rock or wherever the spider makes the webs.
Interviewer - Chris Smith
But they're all made of proteins, aren't they?
Interviewee - Thomas Scheibel
They are all made of proteins, so it's typically a protein core, there might be some other additives like sugars or lipids but these are really the minority. So, the specific properties of silks is originated in the proteins and the molecular setup of the proteins and they're actually huge proteins very big ones with repetitive units. So, they're small sequences, amino acid sequences that actually provide then crystallinity, so making a very strong structure. Some sequences make amphiphilic or amorphous structures, so, they actually are thought to gain some elasticity to the final structure and they're repeated all over again, hundreds or thousands of times. It looks quite simple but it's very hard to be mimicked in the entire length and this gives us some trouble. That's one part of the story and the other part is the processing the insects or the spiders make. So, making a solution of a protein and transform this soluble protein in to a solid thread within just fraction of a second.
Interviewer - Chris Smith
But can biology give us any clues, if you look at what a spider is actually doing in its spinnerets, how does it get this amazing polymer to form?
Interviewee - Thomas Scheibel
Chemically you start with a water soluble polymer and what you have to do is, to remove the solvent which is water quite quickly and you can do that by phase separation. So, actually the spider pumps certain salts into the solution and this causes phase separation and then actually the spider removes the water with epithelial cells, so the water is actively pumped off and this is what we can do also technically. So, we just sort out the proteins and we removed the water. Second part is then, you have to align the molecules and this is done by the spider in a way that the spider always pulls at the end of the fibre using the hind legs or using gravity, if it just drops and we can also do that mechanically by pulling out the molecules out of the spinning duct, so to say. This actually works technically, so we can sort out the molecules, remove the water and simultaneously align the molecules in one machine and on the laboratory scale this already works. So, I am pretty confident that within the next two or three years we might have a stable spinning process that allows us to make silk fibres that look like or even better than the natural ones.
Interviewer - Chris Smith
Will these fibres mechanically scaled, it's one thing for a spider to make a very small thread which when you measure it mechanically has a behaviour equivalent to steel in terms of its tensile strength and things. What about if we made a big rope that could sustain and support a human, would those properties be conserved and preserved or are we going to have to rethink this?
Interviewee - Thomas Scheibel
I think a very important issue is how to process the individual fibres. So, these monofilaments and this is also technically quite complicated because if you talk to textile producers they cannot handle such fibres and the reason is the diameters of a silk fibre is too thin. So, what we actually think about is making not a single filament but develop spinning processes that allows us to make multi-filaments that actually can be further well made into yarns and these yarns can then be used for making textiles, or ropes or whatsoever. The question then is if we can maintain the superior mechanical properties of the individual thread or if we lose some of the properties. The other issue could be that we gain new properties that probably are not very good in the single filament so far. One of this is supercontraction. So, if a fibre gets wet actually it shrinks and it grows in diameter and of course it changes its mechanical properties. This is something you are not going to have in the technical fibre and maybe you can out rule that by making really thicker fibres, ropes, may be also in combination with other materials.
Interviewer - Chris Smith
Thomas Scheibel talking to me from Bayreuth University in Germany.
Jingle
End jingle
Interviewer - Chris Smith
You're listening to the Chemistry World podcast with Phil, Akshat Rathi, Mike Brown and me Chris Smith. Still to come, the chemistry of cocktail making and how big is father Christmas' liver. But first to what've been dubbed nano hazards. Where do those tiny particles in airborne pollution end up in your body? Akshat
(16:18- Inhaled nanoparticles, from there to where?)
Interviewee - Akshat Rathi
Yeah, Chris. So this is work done at the Harvard School of Public Health in Massachusetts, USA. Akira Tsuda and researchers have looked at how nanoparticles when inhaled travel through our body and accumulate in different parts of the body.
Interviewer - Chris Smith
Because this has been a longstanding question, isn't it? People have known for donkeys' years actually that when there's a bad pollution day, there's a surge in the number of people having heart attacks and strokes, the number of cases who have asthma attacks goes up. So we know these particles that are in pollution for example and in the air get into our bodies but actually how far they get in is unknown isn't it?
Interviewee - Akshat Rathi
Yeah, what these researchers have looked at is what size of nano particles actually get in the body, so they found out that that if nano particles are greater than 34 nanometres in size they would stay in the lung and not be as harmful. If the nano particles are smaller than 6 nanometres then they're cleared by the kidneys.
Interviewer - Chris Smith
So this is really useful, because now it puts the sorts of limits on the sorts of sizes that might be biologically relevant, doesn't it? So that presumably means that will inform engine manufacture exhaust scavenging systems so that we can design better systems so exhausts outflow this stuff.
Interviewee - Akshat Rathi
Yes you are right exactly Chris, because it's this range between 34 nanometres and 6 nanometres which is potentially harmful to human beings.
Interviewer - Chris Smith
How do you actually do this study though, because you are playing around with something which is the size of a virus? Isn't it, 30 nanometres and smaller means it is the very smallest of viruses, individual viruses and how did they do this?
Interviewee - Akshat Rathi
So, these researchers they synthesize these nanoparticles which were fluorescent in nature and they made rats inhale these. After a certain time, they dissected the rat and looked at which parts in the body were fluorescing and because these nano particles were of different sizes, they could figure out which size nano particles travel to where inside the body.
Interviewer - Chris Smith
So by following the fluorescence. How do they know that these particles are representative of what really goes on out there in the polluted London streets or you know around Cambridge in the rush hour?
Interviewee - Akshat Rathi
They are not very sure but they reckon that most of the nano particles are greater than 34 nanometres but there would be this difficult range of 34 to 6 which could be harmful and they recommend that there should be chemistry which should be looked at so that this range of nanoparticles is avoided.
Interviewer - Chris Smith
What about the actual chemistry of the particles themselves, presumably they didn't change the nature of the particles by making them fluorescent but did they test all kinds of chemical characteristics of the particles. Some particles maybe just very carbon rich uncharged molecules, others maybe acidic, others might be basic. Do they test that?
Interviewee - Akshat Rathi
They do not talk about the acidity or the basicity of the molecules but they did look at the different charges these molecules can have and they found that if they are non-cationics that mean they are either zwitterionic so they have both positive and negative charge on them or if they are anionic then these are the particles which travel inside the body.
Interviewer - Chris Smith
So that puts the limit on, as we have said. We know that if they're smaller than 6 nanometres they get into the bloodstream and they make it through the kidneys. So that they are therefore seen pretty much every tissue in the body and that could be significant. If they are bigger than 34 nanometres, they stay in your lungs that could be significant. But what fraction of exhaust coming out of the car or a power station whatever actually is these particular sized particles or are they of significant fraction?
Interviewee - Akshat Rathi
Researchers are sure that most of them, are bigger than 34 nanometres, but there's always the possibility of the small ones. Donaldson at Edinburgh says that this study is just the beginning of looking at what nano particles will do inside the body.
(20:15- World's smallest chromatography column)
Interviewer - Chris Smith
Okay thank you very much Akshat. Now Mike staying with the very small again, chromatography now under the spotlight, tell us about this one.
Interviewee - Mike Brown
Okay, yes so we're talking about arguably the world's smallest column chromatography. Researchers at Northwestern University in Illinois have taken a 3 mm molecular organic framework crystal also known as a morph and they're using it to separate mixtures of fluorescent dyes like you would in chromatography.
Interviewer - Chris Smith
What sorts of scale are we talking about, because you said the world's smallest, but how small is this then?
Interviewee - Mike Brown
What the team have done is separate fluorescent dyes on a micrometre scale using these crystals. So what they do is they put the 3-mm crystal on top of a gel which contains the fluorescent dye mixture and over time the fluorescent dyes diffuse up the crystal and then separate. The team then used fluorescence confocal microscopy to analyze what's happening inside the crystal and they've found that there's definite separation between the fluorescent dyes.
Interviewer - Chris Smith
So in other words it's an it's an incredibly tiny trick and the amazing feat to pull this off to actually do this on this sort of scale but why is this useful, how do they propose we could use these tiny crystals in this way?
Interviewee - Mike Brown
What they're hoping is they can take their crystals and actually put them on chips, so they can put them on microchips and actually separate different fractions of compounds on these microchips which obviously will be useful in microfluidics. They also say that in the future they're hoping to do continuous flow chromatography with these crystals as well. So instead of putting them on a gel, you're actually flowing liquids through the top of the crystal all the way through to the bottom and collecting fractions.
Interviewer - Chris Smith
Because most people will think of chromatography you know back in school days as separating the dyes that are in chlorophyll or something but presumably you can use it not just for coloured things, you can do any kind of molecule and look at any colour separation. So it would be really good as you say for microfluidics to interrogate a set of samples to see if certain things are there, because they're going to move to certain distance under those certain conditions on that.
Interviewee - Mike Brown
Yeah that's right. So one of the things that the team is really looking into is well it's separating DNA strands so they're hoping that in the future, they'll be able to use instead of fluorescent dyes they'll be able to separate DNA in these kind of systems. Another thing was also instead of separating things in these crystals, they can actually put two reactants in at separate ends and then watch the reaction happening using different spectroscopies because the crystals are transparent.
Interviewer - Chris Smith
Incredible Mike, thank you.
(23:00 - University of Western Ontario's Darcy O'Neil explains the chemistry behind making the perfect cocktail)
Interviewer - Chris Smith
I love cocktails but what is going on chemically speaking inside that shaker. To find out I got together with University of Western Ontario chemistry and cocktail connoisseur Darcy O'Neil.
Interviewee - Darcy O'Neil
Early on I studied chemistry and then I ended up working in a refinery for six years and then I decided to move onto a different city and didn't find anything that was really working for me career wise, so I decided to do some bartending and then ended up back at the University of West Ontario and then I decided to take the science and applied to the drinks that I was making.
Interviewer - Chris Smith
Was it relatively easy to start to dig in to the chemistry of cocktails? Did you actually find that it was pretty easy to, from a chemist point of view understand what was going on or it is still just a black art to cocktail making and that shake and not stirred is very much it on the lips of the consumer but there's much science behind it.
Interviewee - Darcy O'Neil
Early on I was lucky - I was probably one of the first dozen people actually look at science in cocktails. So there's a lot of you know well hanging fruit to work with. So we even just talk about ice you know why things cool down and how they cool down, talking about how certain things mix. I mean I was pretty simple early on, now it's actually getting more difficult because you always are going to find a new material or new interesting facts that people want to hear.
Interviewer - Chris Smith
Give us some examples.
Interviewee - Darcy O'Neil
Well, see right now, we are doing essential oils, there's been this perception that they're artificial flavours which they're not, they're just distilled oils so much like ethanol. We distil off the ethanol but if you're to continue distilling grape brandy for let's say you would end up with cognac oil which comes off at about 110 Celsius. So, it's not artificial but it's a very, very potent flavour compound that you can make a champagne flavoured non-alcoholic beverage.
Interviewer - Chris Smith
But the interesting thing is that we're now in a position where someone like you who has a lot of chemistry knowledge behind you can take your knowledge and explain what we are already doing, but could we turn the equation round and start saying right based on what we know about chemistry we could start doing something very unusual to make a whole new type of drink or cocktail or combination or I guess sort of gustatory experience.
Interviewee - Darcy O'Neil
Yeah, that's actually starting to happen. It's following after molecular gastronomy which is the science of food, and what they've called it now is molecular mixology and it's taking science and doing something with cocktail to create something completely unique. The most interesting ones are early ones that really got a lot of media attention was Caviar and that's not really fish eggs but they look like fish eggs. So what it was is to take sodium alginate and calcium chloride and then making calcium chloride bath, add a flavour to mix with the alginate and then drop it into the calcium chloride bath and form these little spheres. So, one of the things you can do with these little spheres is to put them in a glass of champagne
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