June
Chemistry World Podcast - June 2012
0:54- Binning is best choice for drug disposal
5:30- Silicene seen for the first time
8:05- Henry Snaith on developing dyes to harness solar energy
15:31- Size and shape change Suzuki rates
19:28- Celebratory science with champagne expert Gerard Liger-Belair
26:37- Just hit Ctrl + P for custom glassware
30:08- Enhancing solubility to revive discarded drug candidates
32:59- Trivia: 80 years since the discovery that solved a mass mystery
(Promo)
Brought to you by the Royal Society of Chemistry, this is the Chemistry World Podcast.
(End Promo)
Interviewer - Chris Smith
This month, how best to safely ditch old drugs; solar cells that use dyes rather than silicon and...
Interviewee - Gerard Liger-Belair
(Sound of bottle cork being opened)
The level of the liquid is very important because when bubbles rise towards the champagne surface they continue to absorb CO2. So if you have a high level of liquid you will have big bubbles at the champagne surface.
Interviewer - Chris Smith
Physics of champagne fizz is on the way. Hello I'm Chris Smith and this is the June 2012 edition of Chemistry World podcast.
(Promo)
The Chemistry World podcast is brought to you by the Royal Society of Chemistry. Look us up online at chemistry world dot org.
(End Promo)
(0:54 - Binning is best choice for drug disposal)
Interviewer - Chris Smith
Up first, what should you do with the drugs that you no longer need? Is flushing them down the loo which is the dealer's favoured means of disposal when the police are at the door, the best thing for the environment? Andrew Turley.
Interviewee - Andrew Turley
It's a big problem that a lot of people hang on to their medication often when it is outdated as well and the temptation to use it when it is outdated is a problem. So getting rid of old medication unused medication is important. A lot of people wonder what the best thing to do is and in the US that usually means throwing in the bin.
Interviewer - Chris Smith
So that means landfill?
Interviewee - Andrew Turley
Yeah, so it eventually ends up in landfill and that's not great, because it's getting out into the environment.
Interviewer - Chris Smith
Andrew I think there was a story a year or so ago looking at Tamiflu, they were showing I think several years down the stream of Tamiflu going into landfill, you could detect the molecules coming out in waste water.
Interviewee - Andrew Turley
Right and it's not just the molecules themselves, it's also as they then get broken down in the environment they'll then form other molecules that could be just as dangerous. These are molecules that have been specially designed to interact with biological systems; when they're in the environment that's exactly what they do; but these aren't systems that we want to interact with necessarily.
Interviewer - Chris Smith
Indeed, so what's the alternative, if you don't throw them in the bin?
Interviewee - Andrew Turley
Well, in certain parts of the world, there are long running schemes that encourage people to take them back to the point of purchase and then it's incinerated and dealt with properly in the same way that your batteries might be dealt with or electronic goods are dealt with.
Interviewer - Chris Smith
And especially the advantage of burning something is that it does get around that problem you raise if a biologically focussed agent interacting with a biological system if you burn it, that's it.
Interviewee - Andrew Turley
Exactly, you end up with various innocuous gases.
Interviewer - Chris Smith
So, where is the problem then?
Interviewee - Andrew Turley
Well, innocuous in terms of biological systems in the short term but emissions go up in the longer term and they do a lot of harm.
Interviewer - Chris Smith
So, it's a sort of see-saw here do you want to favour the biology or do you want to favour the environment, so what way do we think the seesaw is tipping at the moment then?
Interviewee - Andrew Turley
Well, with this particular work it's a group there from the University of Michigan led by Steven Skerlos who've looked very closely at the life cycle at these compounds with specific reference to the carbon emissions and they make a strong case that the environmental benefit of actually just binning your unused or out of date medication outweighs the disadvantages.
Interviewer - Chris Smith
Gosh! So, actually they are surrendering or sacrificing biology?
Interviewee - Andrew Turley
Well, exactly and it's a bit of a controversial idea, because how do you place value on one type of harm but these are difficult real work situations that regulated how to deal with and they do have to compare a hormone disrupting well potentially a hormone disrupting chemical in the environment with carbon dioxide released and change in the climate; how do you compare those two things?
Interviewer - Chris Smith
If I go and buy a piece of electronic equipment like my computer monitor, intrinsic to the cost of buying that now is an environmental cost factored into getting the bits that are bad for the environment back recycling and so on. So they do the complete sort of life cycling and the cost. Do pharmaceutical companies have to do that, so that when you buy some penicillin or some meropenem or something and you do or don't use it do they take that into account?
Interviewee - Andrew Turley
Arguably the pharmaceutical companies don't have to look at that quite so closely and if you're to go to the big pharma companies they all have schemes and to look at long term consequences of their chemicals that they produce but it's a very complicated business, I mean even the chemicals that are used are a worry, I mean in the body they may not get consumed at all and the ones that do may come out they may be metabolized into equally disrupting chemicals.
Interviewer - Chris Smith
So, it doesn't really sound like you've got a clear answer from this one than we've got some people who are saying it's better to throw them away but actually there's going to be a cost whichever way you look at it.
Interviewee - Andrew Turley
Well, there is one clear answer which is that whatever you do don't flush them down the loo which is surprisingly common thing to do that absorbs them into the environment very readily but it also increases the emissions, if you put them in the bin then it wraps them up in land fill and a lot of that carbon will then stay within the land and not be released into the environment.
Interviewer - Chris Smith
And the waste dump won't get high blood pressure or whatever was the medication. Andrew thank you very much.
(5:30 - Silicene seen for the first time)
Interviewer - Chris Smith
We're sticking with other kinds of interesting molecules, silicene maybe not such a silly name after all though, Elinor what is silicene?
Interviewee - Elinor Richards
Silicene is the new graphene apparently, so Patrick Vogt of Berlin's Technical University in Germany and Paola De Padova from the Istituto di Struttura della Materia in Italy have grown a one atom thick layer of silicon which they've called silicene for perhaps the first time they say.
Interviewer - Chris Smith
Does it form little hexagonal rings like the carbon equivalent graphene does?
Interviewee - Elinor Richards
Well, it does appear to as you can see by the diagram that they have in the paper; it does look like similar it's not flat but it's corrugated pattern.
Interviewer - Chris Smith
Oh! Why's that?
Interviewee - Elinor Richards
I think it's something to do with the bonding.
Interviewer - Chris Smith
Because they are in the same group of the periodic table so you would sort of expect, it would work the same way graphene does. Have they gone as far as testing it yet?
Interviewee - Elinor Richards
They claim that it might match graphene's electrical properties but they do say that it's difficult to predict how good it would be because they're at the beginning that they are very much at the start of looking at this material really.
Interviewer - Chris Smith
Does the fact that it is silicon based and a lot of electronics is silicon based, does that mean the interfacing the two may be better or easier with this two?
Interviewee - Elinor Richards
That is what they say they claim that it would be easier to integrate them into normal silicon based to stick it and the development of more super miniaturised electronic devices could be accelerated then from that.
Interviewer - Chris Smith
The way that Andre Geim, famous he makes his graphene; he's peeling bits of pencil lead with cello tape. How do they make this?
Interviewee - Elinor Richards
Well, it's a little different and they used vapour deposition techniques to grow this silicon layer on silver crystal surface and then they looked at the chemical structure and the electronics and dimensions of the material and they claimed that they're looking at silicene whereas they say that they have been research groups that have claimed to have made silicene in the past, but the researchers are saying now that you know there was not enough evidence the researchers in the past had used scanning tunnel microscopy, but this alone isn't enough to confirm you know the presence of silicene.
Interviewer - Chris Smith
So how did they image their samples?
Interviewee - Elinor Richards
They looked at the chemical structure, the electronics and dimensions, they looked at bond angles and lengths and they found that these matched density functional theory calculations.
Interviewer - Chris Smith
What do they propose to do next?
Interviewee - Elinor Richards
Yes, they're just going to further investigate the properties and they've also said that it might be worth looking at germanium as well, which would give germanicene.
Interviewer - Chris Smith
Which is available from all good pharmacies by all accounts, oh no sorry that's germolene. Thank you Elinor.
(8:05 - Henry Snaith on developing dyes to harness solar energy)
Interviewer - Chris Smith
Solar technology now and the field of dye-sensitized solar cells, which is light absorbing dyes rather than semiconductor materials like silicon to turn light into electricity. Henry Snaith.
Interviewee - Henry Snaith
So a dye-sensitized solar cell as the name may suggest has dye in it and the dye plays the main function as absorbing sunlight. When light shines on a material that's got colour, the reason why it's got colour is because it absorbs some of the light and in absorbing that light, you promote electronic charge to a higher energy level. So you can imagine the sunlight comes in it, it excites electrons, it promotes electrons to higher energy and that if higher energy they can do work and they can do work in the form of current and do work in an external circuit. The purpose of a solar cell is to basically do as much work as possible from the energy that's been put into electrons to excite them. So in a dye-sensitized solar cell, all that excitation takes place in a dye molecule and then that dye is stuck onto the surface of an electron transporting metal oxide, that metal oxide doesn't absorb light but the electrons will transfer from the dye once they're excited by sunlight they will transfer into the metal oxide, and they'll travel through this metal oxide into an electrical circuit. So, that in essence is one half of the device and the electrons in the circuit go around the circuit, they do work, could be lighting the light bulb, could be powering anything really and then they come back in the other side of the device, we have to complete the circuit, travel through a hole transporter which is then contacted to the rear side of the dye and it goes back into the place, electron returns to where it started in essence. So, you can imagine an electron promoted, it's excited in a dye and leaves the dye, that dye isn't positively charged because it's lost an electron and then it's regenerated by the electron coming back into the solar cell through the electronic circuit.
Interviewer - Chris Smith
So, the actual physics is not grossly different than that which we would see in a standard, what I call a standard photovoltaic , that people put in their roofs at the moment, so what advantage does using a dye rather than the current technology offer?
Interviewee - Henry Snaith
The main advantage is that it's extremely low cost and it's very low embodied energy in making these systems. May be I should just very briefly describe how for instance, a silicon solar cell works, it's the same principle that electrons are excited in the material when it absorbs light, but now the electron transports through the same material that it's absorbed in and also with a hole that's left behind so you can imagine when the electron is excited it leaves positive charge behind, that hole has to migrate through the same materials. Those electrons that are in the semiconductor, in the silicon, can drop back down into the hole at any time, this is called recombination and this is a loss in the solar cell and if they don't move fast enough to get out of the solar cell, they'll drop back into the holes that recombine and the solar cell won't be very efficient. And the only way to get them to move fast enough in a crystalline semiconductor is to have it extremely pure. If there are many impurities in there, the charges don't move fast enough and they recombine.
Interviewer - Chris Smith
And that of course has an embodied cost, because if you're going to grow a high purity crystal, there's going to be a labour and obviously a chemical cost to doing that?
Interviewee - Henry Snaith
Absolutely, and that is the critical challenge for silicon solar cells, as how do you make highly pure crystalline silicon very cheaply. In contrast with the dye-sensitized solar cells, the light is absorbed in the dye and then it's transferred, the electron is transferred into a material which only contains electrons; there's no holes in there. The holes are left on the dye so those electrons can't drop down into holes, which means the electronic properties of the electron transporting metal oxide can be very much inferior to crystalline silicon
Interviewer - Chris Smith
So what is the real rub, why aren't we exploiting it more at the moment, why are we going down the more costly route, which sounds all together worse?
Interviewee - Henry Snaith
There are a few reasons for this. The technical reason is that the most efficient dye-sensitized solar cells to-date use an liquid electrolyte and this is an iodide, triiodide redox couple and its extremely challenging to make square kilometres of solar cells with a liquid sandwich between two sheets of glass for instance, it's extremely challenging to feel it, and it' also slightly corrosive. So there's been a lot of work over the last ten years on developing either jelled electrolyte, solid state electrolytes or replacing the electrolyte entirely with a p-type organic cold conductor and we call these solar cells solid state dye-sensitized solar cells. Once the efficiencies of the solid state cells as good or better than the electrolyte cells, then it really will be a promising technology. The other reason is of course, the solar cell only makes up certain fraction of the overall cost of the whole system for generating and collecting the electricity from solar power. What's turned the balance of systems is for instance is the frame or the inverter of the electrical components to gather the power, turn it into AC electricity and put it into the grid. And this is a cause that sits between the technologies. So at the moment, crystalline silicon solar cell modules are between 16 to 20% efficient and realistically we have to have these lower cost modules have to be above 10% efficient, even if they practically free in comparison to crystalline silicon solar cells, in order to compete. There are a few fundamental aspects or understanding of the fundamental mechanisms that are still perplexing to those researching in the field. We're fully confident that the technology could deliver 20% efficient solar cells, but there are some issues that we need to understand better in order to do that and once that's been achieved, it will be straight forward route to market
Interviewer - Chris Smith
So, if you had to put your money where your mouth is, so it's a tricky one this, but how far away do you think we are? When are we going to see the dye-sensitized solar cell market rivalling what we have at the moment?
Interviewee - Henry Snaith
There's another uniqueness with the dye cells which is advantageous over thin film in silicon technologies is that it does come in a range of colours that can be almost transparent, semi-transparent and that opens up the massive possibility for building integrated photovoltaics. So what we will see is over the next few years, two to five years, we'll see a large uptake in building integrated photovoltaics and this is where the solar cells being used as a cladding for the building instead of using tinted glass for instance you will use a photovoltaic cell which will be a dye-sensitized solar cell. Now the point at which it gets into competition with silicon for utility scale solar cells, I really believe that the efficiency of the modules have to get above 10% on a manufacturing line and probably closer to 15% to really be competitive. And the timing for that I would say within 10 years that I am of course you can have a judgment, might be next year if we have a sort of lot of breakthroughs.
Interviewer - Chris Smith
Oxford University's Henry Snaith.
Interviewer - Chris Smith
You're listening to Chemistry World with me Chris Smith still to come the science of Champagne and the way to give a new lease of life to drugs sidelined by solubility problems.
(15:31 - Size and shape change Suzuki rates)
Interviewer - Chris Smith
But first a way to make the Suzuki reaction run better, Phil Broadwith.
Interviewee - Phillip Broadwith
The Suzuki reaction is a very important reaction in chemistry, that's a way of joining molecules or bits of molecules together by making carbon-carbon bonds. To do that you have one half of a molecule is a boronic acid, so it's a carbon the bit that you want to join attach to a boron which has two OH groups on it to make a boronic acid but those boronic acids are quite unstable in their solid form so they don't have a very good shelf life; they're quite difficult to make, they're not easy to supply for the pharmaceutical industry to make these things. So, people are looking for alternatives, one of the best alternatives is trifluoroboronate salts, so what these trifluoroboronates are, is the carbon that you want to join attached to boron which has three fluorines attached to it.
Interviewer - Chris Smith
And how do those borons with three fluorines attached turn into the boron with the two OH groups that you need?
Interviewee - Phillip Broadwith
Well that's approach is called hydrolysis and it's essentially a reaction with water. So you need some water in the reaction mixture, by reacting with the water you can displace the fluorine from boron which gives you some hydrofluoric acid and you end up with your boronic acid your B(OH)2 with the carbon that you want to join on to it.
Interviewer - Chris Smith
And controlling the conditions to get them to react in the right way must be critical then because otherwise you're going to get all kinds of funny things joining together that shouldn't.
Interviewee - Phillip Broadwith
Yes, well you want to try and limit the amount of hydrofluoric acid that you're producing because that tends to eat glassware, it's not very helpful and if you hydrolyze the trifluoroboronate too quickly you will produce lots of HF but you will also make the boronic acid and it will then start to degrade in your reaction conditions. On the other side if you are not doing the hydrolysis fast enough then your reaction will go very slowly and you risk the catalyst degrading before you've had time to make enough boronic acid to complete the reaction.
Interviewer - Chris Smith
So, what's the solution?
Interviewee - Phillip Broadwith
Well, Chris that's where the work that Guy Lloyd-Jones and his group at Bristol University are doing comes in. What they've done is categorize these trifluoroboronates into three groups. The first group hydrolyzes very quickly but that's not generally a problem, because the boronic acids are very stable under the reaction conditions. There's a second group which hydrolyze very slowly and there's not much you can do about that. The third group which is the really crucial part and that's where by tailoring your reaction conditions you can get the hydrolysis rate just right to deliver just enough boronic acid for the reaction to keep going without it going over the top and having horrible side reactions.
Interviewer - Chris Smith
So, how do you do that tailoring bit?
Interviewee - Phillip Broadwith
The hydrolysis mechanism itself is quite complicated and if you want to go into that you would probably best off to look at the story on the Chemistry World web site but essentially it comes down to how well you stir the reaction mixture.
Interviewer - Chris Smith
Is it all in the wrist?
Interviewee - Phillip Broadwith
Well, generally we use a mechanical or magnetic stirrers but what they are saying is that if you look at the shape of your reaction flask, because the reaction mixtures tend not to be homogeneous, if you have a, for example, a pointy bottomed flask rather than say a round bottom flask, you might have an area that doesn't mix quite so well and therefore the reaction conditions get messed up and you run into all sorts of problems.
Interviewer - Chris Smith
So, shape as well as size is important.
Interviewee - Phillip Broadwith
Yes, absolutely the shape is crucial and it's really about getting the mixture. So the message I think from the story is to just keep stirring that Suzuki reaction.
Interviewer - Chris Smith
Phil Broadwith.
(19:28 - Celebratory science with champagne expert Gerard Liger-Belair)
(Cork of bottle being opened)
Interviewer - Chris Smith
Champagne needs almost no introduction. But behind the problem froth lies a lot of science. In fact Reims University in the heart of the champagne region has its very own fizzy wine physicist in the form of Gerard Liger-Belair who researches what those bubbles do for the drink.
Interviewee - Gerard Liger-Belair
The key thing which makes champagne frothy, bubbly is the very high concentration of dissolved CO2 into the liquid phase, into the champagne and this very high concentration of CO2 is brought with a specific second fermentation in the closed bottle. So the first fermentation which is specific with all wines in the world is the consumption of sugar in the grape juice but during the first fermentation all the CO2 which is produced escapes into the atmosphere because we are in open vats. But during the second fermentation which is specific of champagne elaboration we have enclosed bottles so that the gaseous CO2 which is produced during the fermentation is literally trapped into the bottle and the very high concentration of CO2 remains into the form of dissolved CO2 in to the champagne. So we have a very high volume of about 5 litres of dissolved CO2 in each litre of champagne.
Interviewer - Chris Smith
A lot isn't it? It also explains why those bottles have to be so thick and heavy to avoid exploding.
Interviewee - Gerard Liger-Belair
Absolutely.
Interviewer - Chris Smith
What's the pressure in there?
Interviewee - Gerard Liger-Belair
We have a pressure of about 5 Bars. So, five times the atmospheric pressure.
Interviewer - Chris Smith
Gosh, it is very high, isn't it? So, when one pours out a nice glug of champagne into a glass and you see the bubbles streaming up talk us through the processes actually leading to the elaboration of those bubbles from various points on the glass surface.
Interviewee - Gerard Liger-Belair
Yeah, absolutely.
Interviewer - Chris Smith
And what controls their size and so on?
Interviewee - Gerard Liger-Belair
Okay so when you pour champagne into a glass you can specifically see bubbles rising from specific points of the glass wall. The key point in the nucleation of bubble is that your glass must contain tiny particles stuck on the wall. If you have a glass perfectly clean without any particle without any imperfection, bubbles cannot simply nucleate. So you always have some tiny dust particles stuck on the wall and those tiny dust particles are able to attract the dissolved CO2 to release it into the form of bubbles.
Interviewer - Chris Smith
So, the taller the glass as that bubble makes it way up through the liquid, the bigger the bubble is going to become then. Because the bubble itself is going to encourage more gas to move out of the fluid and into the bubble, so what difference does that make?
Interviewee - Gerard Liger-Belair
The level of the liquid is very important, because when bubbles rise towards the champagne surface they continue to absorb CO2. So they will grew bigger and bigger during their journey to the surface. So if you have a high level of liquid, you will have big bubbles at the champagne surface.
Interviewer - Chris Smith
Because those bubbles containing CO2 will impart a greater amount of acid to the flavour because the CO2 when it goes into the mouth is always an acid anhydride and we're very sensitive to the effects of CO2 orally, so what does champagne manufacturers recommend about serving the drink, should we have those very wide bowl-type glasses or should we go for the taller flute?
Interviewee - Gerard Liger-Belair
Probably the right shape would be quite intermediate between a tall flute and a flute with a very wide aperture, so effectively if you have a tall flute you will have high concentration of gaseous CO2 above the glass and this can be very irritating for the nose of the taster.
Interviewer - Chris Smith
What about some other chemicals that come up with the CO2, because as those bubbles are forming there must be other volatiles and other substances from within the wine substance that will also dissolve in the CO2 and be carried out.
Interviewee - Gerard Liger-Belair
Yes
Interviewer - Chris Smith
So there must be an optimal passage rate for the CO2 or bubble size in order to get just the right amount of flavour coming out to give you the nose and also the right oral experience when you first drink the drink?
Interviewee - Gerard Liger-Belair
Bubbles grow in size because of CO2 diffusion but obviously you have hundreds of chemical compounds in champagne which are volatile and which present aromatic compounds. So those compounds will also be able to be trapped by the bubbles during their rise to the surface and they will be released when the bubbles collapse at the liquid surface. So above a glass of champagne you have a mix of gaseous CO2 and volatile aromatic compounds and there is probably an optimal situation when you have enough aromatic compounds and not too much gaseous CO2 which will be able to mask the perception of aromatic compounds.
Interviewer - Chris Smith
Does it also depend to a certain extent on the year, because certain wines are going to have different levels of volatiles and therefore what works with one glass spec or one size of bubble next year that might not work?
Interviewee - Gerard Liger-Belair
Yes, each champagne are not the same, you can taste young champagne, you can taste much older champagne which have aged in cellars and this is very different for two reasons. During the ageing of champagne there are a lot of biochemical reactions in the liquid phase which release some specific aromas and you will have also during the ageing of champagne significant loss of CO2 through the cork stopper. So when your champagne ages it progressively losses its dissolved CO2 content and it gains these aromas.
Interviewer - Chris Smith
And just as we finish Gerard Liger one myth to rest for everybody, because you see this a lot, people write to me and they say if I put a silver spoon in the neck of my champagne bottle in the fridge will this stop it going flat, what is the gold standard answer?
Interviewee - Gerard Liger-Belair
Unfortunately if you put a spoon in the bottle neck of your opened bottle whatever the metal of the spoon, gold, silver or I don't know what, it will have absolutely no effect on the dissolved CO2 content. The liquid will lose its CO2 with or without your spoon in the bottle neck.
Interviewer - Chris Smith
Right well I shall have to remove that spoon when I get home. That was Reim's Univ
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