Chemistry World podcast - February 2013


Audio Files

0:53 Ancient medicines found in a shipwreck reveal their secrets – 'Digging up ancient drug formulations'

4:10 Lanthanide compounds can be used to tag and identify gunshot residues at crime scenes – 'Making criminals leave chemical fingerprints'

7:45 Graham Richards discusses how he used crowdsourcing to generate potential drug candidates – 'People power'

14:17 A superomniphobic material that can even repel non-Newtonian fluids, like custard, has been made – 'Superomniphobic surface sees off non-Newtonian fluids'

17:53 A smartphone app can identify food allergens – 'Worried about food allergens? There's an app for that'

20:53 Eric Wolff tells us about his work using compounds in ice cores to reconstruct past climate – 'Chemical climate proxies'

28:02 A greener way to oxidise alcohols to carboxylic acids – 'Greener route to carboxylic acids'

31:14 Does the kilogram need a New Year diet? 'Kilogram ready to slim down for the new year'

35:25  - Trivia: What is the only material to which a gecko's foot cannot stick?

(Promo)

Brought to you by the Royal Society of Chemistry, this is the Chemistry World Podcast.

(End Promo)

Interviewer - Chris Smith

This month, what did scientists discover inside a 2000-year old medicine chest, found intact on an ancient shipwreck and how do you find out if you're allergic to the food that's being served up in a restaurant. Luckily there's a phone app that can diagnose if your dinner is safe or not.  Find out how it works.

(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)

(0:53 - Ancient medicines found in a shipwreck reveal their secrets)

Interviewer - Chris Smith

Hello, I'm Chris Smith and with us for this the February 2013 edition of Chemistry World are Bibiana Campos-Seijo, Neil Withers and Laura Howes. Laura.

Interviewee - Laura Howes

We all think of pharmacy and medicine as fairly, you know, new and cutting edge. It turns out that if you look at a shipwreck from 2000 years ago, you can find out all about ancient pharmacy.

Interviewer - Chris Smith 

Go on.

Interviewee - Laura Howes

So, this is looking at a ship wreck called the Pozzino shipwreck, which was found off the coast of Tuscany in Italy, near in the Etruscan Harbour from about 200 BC and it was found in 1974, and excavated in the late '80s, but there's quite a lot of finds. They've only just sort of been really going through and evaluating everything that was there. One of the things what they found is what they think is a doctor's chest with lots of medicines and equipment.

Interviewer - Chris Smith

Still intact?

Interviewee - Laura Howes

Pretty much still intact. There were still cups and vessels and there were also quite a lot of vials and some of these vials were made of metal and pretty much medically sealed, not only did you have the equipment, but you had some of the medicines that this doctor was presumably taking with him to use.

Interviewer - Chris Smith 

Uncontaminated?

Interviewee - Laura Howes

Uncontaminated. This is the important thing. There was no seawater in it all. It was exactly as it was.

Interviewer - Chris Smith

How did they then examine those medicines?

Interviewee - Laura Howes

So, first of all, they actually just did an x-ray of the tin to see what they had and they found these sorts of 4cm x 1 cm thick tablets. So, they are not for swallowing

Interviewer - Chris Smith

I would not swallow that would you?

Interviewee - Laura Howes

Yeah, they were not for swallowing. I think actually what I think these were I mean historical reasons why you think these were, that they were dried medicines that would then be made into paste with water or wine or oil or something like that and then what they were doing was doing quite a lot of interesting analytical analysis to look at the inorganic compounds that were within these tablets and what they found was that the majority of the tablets was a couple of zinc minerals, so smithsonite which is a zinc carbonate and also a zinc hydroxycarbonate and obviously just because it's the majority of the tablets doesn't mean that they are active ingredient, but we also know that zinc compounds were used in historical medicine. There's the Pliny the Elder and people like that actually talk about these things compounds being used

Interviewer - Chris Smith

Zinc does have an antibacterial effect, doesn't it?

Interviewee - Laura Howes

Which is why I was going to say, even today zinc oxide and zinc minerals are used for, example, in bandages.

Interviewer - Chris Smith

I suppose what it does is corroborate written records doesn't it?; because the ancient Greeks were quite good at writing things down, but actually corroborating what they said they were using with what the actual stuff is, this is the chemical proof as to what they were playing with.

Interviewee - Laura Howes 

Absolutely, and also when they were writing things down, they weren't necessarily writing things down as we might do today by so and so micrograms of this, so and so milligrams of that.  In fact, when I was talking to someone about this story, they sent me one of the recent, I say recently discovered recipes, written down on a papyrus from Egypt and instead of writing down how much you want off, you know weight wise, they use monetary values. So it's so and so drachmas of this, so and so drachmas of that, so not only is it a corroboration that what they were saying, they were using actually but it makes sense my guess is it was a better idea of the amounts they were using because we just had no idea.

(4:10 - Lanthanide compounds can be used to tag and identify gunshot residues at crime scenes)

Interviewer - Chris Smith 

Thanks Laura. Well something completely useful for a much more modern day, Bibi  and when we're talking about some shipwrecks and things, may be the ship got sunk by someone with nefarious intent using weapons but where this technology that you're going to talk about in existence, maybe we could find out who done it. Tell us more.

Interviewee - Bibiana Campos-Seijo

Yes Yes. We're going to be talking about visual identification of gunshot residue in crime scene investigation actually.  So this is a research that has been carried out by a group of researchers at the Universidad de Brasília in Brazil and basically it's about gunshot residue and how to analyze it.  The current technique is scanning electron microscopy coupled with energy dispersive spectroscopy. It is very time consuming. You also need to have an adequate amount of sample to be able to carry out the analysis.

Interviewer - Chris Smith

So, how would you do this, you would go to a crime scene and swab some skin or the floor or something, looking for products that are emitted when the actual propellant in gun bullets goes off.

Interviewee - Bibiana Campos-Seijo 

Yes. Exactly and then you would have to take it to the lab and actually put your sample into the instrument and you have the potential for false positives because you have the risk of environmental and occupational contamination and that's not the only problem. The other problem at all is that lead-free ammunition is now coming into use and with that, obviously because you don't have lead in your sample and your techniques are but based around the determination of lead, you run into trouble there. So, what this group of researchers have proposed is the use of lanthanide tags. So they have mixed lanthanide compounds into zinc aluminates and they have used that as a luminescent marker that they mix with the ammunition and basically all you have to do is once the gun has been fired, you shine ultraviolet radiation on the surface, whether it is the hands of the shooter, or any other surface, you know, the firearm for example and you actually see the colours developing there.

Interviewer - Chris Smith

I wonder if James Bond would make it, but why is that better than the current technique?  Because surely this is equally capable of being contaminated from the environment isn't it? Or are these things so vanishingly rare, these lanthanides they would normally be in the environment and therefore you wouldn't see fluorescence like this.

Interviewee - Bibiana Campos-Seijo 

 I haven't seen fluorescence used like this.  I think this is quite a specific type of marker that you're adding to your ammunition.  You also can do the analysis in CT as well, you only need to prepare samples and then obviously these markers as well, they have, they're luminescent for 90 days or at least 90 days. So during that period, you can still carry out your experiments and you would get the positive there.

Interviewer - Chris Smith

Given those that the lanthanides are a reasonable group of chemicals, does this mean that you could use a number of them or put a unique cocktail together, so that if I'm a manufacturer of product x, I could put that unique combo into my ammunition?. So then at a crime scene you'd know what ammunition had been used.

Interviewee - Bibiana Campos-Seijo 

Yes.  You can actually produce different mixtures depending on who the manufacturer is, or the use, so whether it is for civilian use or military or anything like that. So actually you've got a lot of information there in terms of ammunition traceability and origin.

(7:45 - Graham Richards discusses how he used crowdsourcing to generate potential drug candidates)

Interviewer - Chris Smith

Or ammunition for legal case, I suppose you might say. Thanks Bibi. And now to a growing online trend, which is the concept of crowdsourcing. This is where you harness the collective power of the online community to solve difficult problems or raise money. One of the early pioneers in this area, producing a web based tool that generated huge numbers of candidate drug molecules was Oxford's Graham Richards.

Interviewee - Graham Richards

I'm quite good at pinching other people's ideas and the first thing in this area was a project called SETI which is the acronym for Search for Extraterrestrial Intelligence, which was set up by some very bright guys at Berkeley and the problem they tried to solve was that on the earth, we are constantly bombarded from all directions by radio signals from outer space and these can be recorded and looked at to see if they're just noise or in fact an intelligent signal , the ET that's somewhere in space sending a signal.  The problem that they have is there are millions and millions of these signals all the time and probably they mean nothing.  They hit on the idea of recording these, sending them out over the internet and getting a piece of software in the screen saver to analyze them. It's a very clever computing idea, but in fact it hasn't ever produced a result because ET is yet to ring in, but tens of millions of people have done this over the years. I rather stole that idea to do something which would produce results. We had protein targets that were likely to be drug targets and we sent out molecules over the internet and the software to analyze whether each individual little molecule bound to the protein was calculated on each individual PCs and the big difference between my project and the SETI project is that every compound we sent out produced results which had to come back so that a lot more data handling to go with it.

Interviewer - Chris Smith

Did you get any positive hits from the analysis of this?

Interviewee - Graham Richards

Yes we did.

Interviewer - Chris Smith

Of molecules.

Interviewee - Graham Richards

Yes, we did and it was in some ways almost an embarrassment.  It was so much more successful than we ever dreamed possible.  So, we got far more results than we could handle and indeed far more even than a pharmaceutical company could handle.

Interviewer - Chris Smith

But you haven't got a drug yet?

Interviewee - Graham Richards

No we haven't yet.  That would take a long time. And it's also true to say rather sadly the early stage drug discovery business is not in a very good shape at the moment.  The pharmaceutical industry is in a bit of trouble, it has to be said, and so they're concentrating their efforts on the later stages

Interviewer - Chris Smith

Now you got started in the relatively early days of this, problem is lots of people are now jumping on this bandwagon. So does this mean that the successes you've had that SETI had this, IBM get with their grid, people are going to get sort of crowdfunding fatigue if you like and they're going to lose the enthusiasm for it and this means that projects that are very valuable that may come along and exploit this as a vehicle in the future won't be able to.

Interviewee - Graham Richards

I think it is going to get harder.  It's going to be split down into lot more smaller projects, but the sheer power of computers means that is less of a problem than it used to be. Many of the things that we did involving as I said millions of computers, you could now do on the crowd, much more easily, so the computer power goes up, so even if you've got less people involved, you can get more done.

Interviewer - Chris Smith

One thing I do want to ask you about was another aspect of this, which is that increasingly we're seeing crowd sourcing type projects where people pitch their ideas at the online community and the online community vote with their mouse button and open their wallet and say, we will all get behind this to the tune of 10 pounds or whatever for that, in fact we had David Braben on an edition of the naked scientists before Christmas, he is seeking to produce the next blockbuster computer program in exactly this way.  There's no risk to him in the sense if he's already raised all the funding to write it, he knows he's met his costs. So his research, likely to go down the same sort of pathway.

Interviewee - Graham Richards

The answer is yes.  If you have a good idea, the internet is a wonderful way of getting this looked at by people.  I think the medical research charities for instance find this quite an attractive field in which to expand their interests.

Interviewer - Chris Smith

It is dangerous though, isn't it? Because in the sense that if you have something that tugs at people's heartstrings you're going to find it much easier to separate people from their money than if you say, I'm a chemist who is very interested in this particular class of molecules and academically this is a very valid project.  It may have future spinoffs and translations but not acutely, you're going to lose out to the person who says, my project got both health and wealth and heart attached to it and so people will go for that one.

Interviewee - Graham Richards

Yeah, once again, I agree entirely with the screensaver project, although it was passive, I did get many thousands of e-mails from people saying my mother has just been diagnosed with breast cancer, I think your project is the most wonderful thing because I think I'm doing something positive and not just giving money.  And it was quite clear, that the cancer aspect of it is what brought people in and if I was just trying to produce a novel packaging which might do the environment a lot of good, it would be much harder to attract people to join.

Interviewer - Chris Smith

So, finish us off here by telling us what we should do to do this better next time.  If you could do this all over again, what would you do next time, where do you think next generation of these things lie?

Interviewee - Graham Richards

In my game of trying to develop novel drug leads, it would have to be adapted somehow to produce enough income to get chemists to synthesize the molecule, look good and to get them screened before they could be on license and in fact we're thinking about something along these lines at this very moment.

(14:17 - A superomniphobic material that can even repel non-Newtonian fluids, like custard, has been made)

Interviewer - Chris Smith

Graham Richards. You're listening to the Chemistry World with me Chris Smith.  Still to come how scientists reconstruct what the climate was doing thousands of years ago and why the kilo is gaining weight, but before that, Neil please tell us what is a Superomniphobic material.

Interviewee - Neil W?ithers

A Superomniphobic surface is able to repel oil and water, you'd have probably seen in the last 10 or 15 years a lot of super-hydrophobic materials that can repel water incredibly well.

Interviewer - Chris Smith

So, how do they work and what is the difference between them and the omniphobic or the superomniphobic?

Interviewee - Neil Withers

So, most of those work, you kind of either have chemical ones or the physical ones. The physical ones are all about the structure.  So that's your lotus leaf kind of things where you have tiny microscopic hairs on the surface and they keep the water away from the actual surface itself, or chemical wands, you have a chemical that doesn't interact well with water.  So, superomniphobic surfaces repel both oil and water and those are just made of surfaces that are super repellent, it again is a really complicated shape and is made of chemicals that are repellent to both or in some cases even I think I've seen where they have a structure with something that repels one and then the liquid layer kind of in between that repels the other one.

Interviewer - Chris Smith

So what is the story?

Interviewee - Neil Withers

So the surface that I'm talking about now is being developed by the scientists at the University of Michigan doesn't just repel water and oil but it also repels non-Newtonian fluids, things like custard, gravy and ketchup.

Interviewer - Chris Smith

The corn flour.

Interviewee - Neil Withers

The corn flour, the classic corn flour, which are all these things that those things I regularly spill on my clothes, my ties and things like that and I would be happy to use these kinds of things. So what Anish Tuteja and his colleagues at the University of Michigan have done is create a superomniphobic surface that as well as repelling of water and oil like the other ones do. It also repels non-Newtonian fluids like custards, ketchup, gravy, the classic corn flour mix that we've all seen jumping around on that on speakers and those are very difficult to repel normally, because they have those strange properties where as they move, they get deformed, their properties change. So if you can imagine that droplet that I was talking about before, if that starts to have, the physical property starts to change, as that gets moved about, then it suddenly becomes very difficult to repel.

Interviewer - Chris Smith

Oh I see, because they behave as a liquid to start with but as soon as the surface tries to push the liquid away, it then stiffens up.

Interviewee - Neil Withers

Yes, exactly.

Interviewer - Chris Smith

So, how does their one do it then?  How they get around that?

Interviewee - Neil Withers

So, their one is a, it's not hugely different to the others, it's again a combination of things.  So it's a, the material is actually a kind of a lattice of stainless steel wires very very fine and then it's coated with two different types of polymers, one a polydimethylsiloxane which is a fairly well used one and a fluorinated version of that as well.  What's interesting about how the polymer is actually coated on the wires, it's coated in beads itself. You can imagine, these beads are highly rounded, so there's again a very small contact area and the layer of air that it traps as well also contributes to this effect.

Interviewer - Chris Smith

So, why does that particular configuration mean that it can move custard off of your tie?

Interviewee - Neil Withers

It's the tiny pockets of air that seem to do that job, because they prevent the acid and bases in the things in the liquid from actually reacting with the surface itself.

Interviewer - Chris Smith

Could we actually use this practically because you're saying that it is stainless steel and stuff like that, so could you coat things in this practically?

Interviewee - Neil Withers

I guess, you wouldn't necessarily coat them in the stainless steel, I think you would make the whole material out of stainless steel. So I think the particular applications that are more important than your tie are for clinical operations in hospitals, where you really don't want to get anything contaminated with materials.

(17:53 - A smartphone app can identify food allergens)

Interviewer - Chris Smith

Well, thanks for that Neil.  Well, still in the health sphere, but something slightly different.  You're out having dinner, and you're not sure if you're going to throw up, if you were to eat the lunch, because you might be allergic to, but Bibi you may have the answer to this one.

Interviewee - Bibiana Campos-Seijo

Yes.  We've talked about research carried out by this group before because they had designed a mobile phone app to detect bacteria like Escherichia Coli and they have now actually adapted this technology to detect allergens in foods.

Interviewer - Chris Smith

First of all, remind us who's done this.

Interviewee - Bibiana Campos-Seijo

The device has been developed by Aydogan Ozcan from the University of California in Los Angeles to design what they call the iTube and basically it is a compact light weight, it's about 40 grams only attachment that goes on the camera unit of your mobile phone. You use this to image a tubes containing food sample and your control.  You have a couple of light emitting diodes there and basically what you're doing ,you're running a calorimetric assay, that looks at the intensity of absorption of light, and we all know how that works.  So, basically you have an app running on your phone as well, which basically connects to the camera and you get a positive or negative answer.

Interviewer - Chris Smith

So, you take a spoonful of food, you put it in this tube and it extracts whatever the allergen it has been chosen to look for out of the food, if it's there, shines light through it and if a certain wavelength comes up on the phone's own built-in camera, it can flash up a thing saying don't you eat this, gluten in there or something.

Interviewee - Bibiana Campos-Seijo 

Yes absolutely.  Not only it tells you that there is gluten there, but it tells you how much as well.

Interviewer - Chris Smith

Well, consider going down very well at a dinner party.  Don't eat anything everybody, just run in my iTube to see if the food is going to make me ill.

Interviewee - Bibiana Campos-Seijo

Yes.  Yes unfortunately, you would have to wait for a little bit, but then once you've done your sample preparation and you've got your tubes in, the detection is very quick.  It should take just a matter of seconds and then obviously personal health and safety is the most important thing, so.

Interviewer - Chris Smith

Since it's also on a mobile, does this mean, it's sort of linked up to Facebook, or I mean, social networking, can you sort of tether it to GPS so it can sort of tag up?.  You know, I ate here, and I got loads of gluten or, you know, got loads of egg protein in my food here.  So, you can either remember yourself or share it with your friends, so they have equivalent allergies, so, you know, people know where to go, where not to go.

Interviewee - Bibiana Campos-Seijo

You actually have the option of pulling all that data onto servers that allow you to draw allergen maps, so whether it is for your own personal use or to actual put on the web, all that information will be available there and you will be able to see how you got poisoned and where, so, you know, if that is the case.

(20:53 - Eric Wolff tells us about his work using compounds in ice cores to reconstruct past climate)

Interviewer - Chris Smith

And the name for that device?  Well its' got to be called the app-etite of course, thanks Bibi.  When climate scientists talk about reconstructing the conditions on earth, thousands, tens of thousands, hundreds of thousands or even millions of years ago, how do they do it? One way is to look at the ice which has been laid down in Antarctica.

Interviewee - Eric Wolff

I'm professor, Eric Wolff from the British-Antarctic Survey, and I work on studying ice cores.  Well, the aim of the work is to understand how climate has changed over hundreds of thousands of years as we've got in and out of ice age cycles and natural causes have changed the climate, so that we could learn more about how climate might change in the future and we do that by measuring thing, in my case, in ice cores that tell us about the climate, but they don't tell us very directly about the climate, so the biggest problem is to understand how to translate what we measure in an ice core into something really useful about the climate.

Interviewer - Chris Smith

What sorts of measures can you use to try and work out what the weather was like and what the climate was like millions of years ago?

Interviewee - Eric Wolff

Well, there are one or two things that are really simple.  So, the first one is measuring gases in the air bubbles that get trapped in the ice and there we actually are essentially opening a bubble of ancient air and measuring the concentrations in it.  So that's really nice and direct, it's not easy to do but it's nice and direct, but the thing we'd really like to know about of course is the temperature, and it's correct but nothing actually record directly the temperature of the earth even as a single spot let alone the global temperature, which is what we'd like to know.  In ice cores what we have is the isotopic ratio of the water molecules in the ice and they do tell us about the temperature but in a slightly indirect way, so we really have to tease out the information from that.

Interviewer - Chris Smith

So what you're actually doing with the ice core in order to try to work out what the temperature was, where that ice was laid down and then more broadly across the rest of the world?

Interviewee - Eric Wolff

So from measuring the temperature from an ice core what we do is to measure the, what we call, the oxygen isotope ratio or the hydrogen isotope ratio, either will do of the water molecule.  So, this is really the water molecules that make up the snow that turns into ice and most of that water is H2O16  so that's oxygen with an atomic mass of 16 but a small proportion of it is H2O18 that's slightly heavier water and that ratio changes according to the way that the water evaporates and condenses as it travels from the ocean towards our ice core site, and it turns out that in the very simplest situation you control analytically that the temperature at the ice core site is reflected in the oxygen isotope ratio rather directly.  The difficulty is that in real life, you don't get a single air mass travelling from the tropics towards the polar regions, you get many many air masses, some hundreds, you know, some hundreds and thousands and so on, and so the end result is that even mean annual temperature at the site is a much more complex relationship with the oxygen isotopes than we would like and you can only really guess at the combination of analytical understanding and global circulation modelling.

Interviewer - Chris Smith

Yes, I was going to say how do you know or how do you validate the data you get from the ice cores and say we know that this maps onto a temperature in location X at the same sort of time or with the certain lag or latency, so that you actually can validate the model.

Interviewee - Eric Wolff

The way that it used to be done was not very satisfactory.  What we used to do was to do a spatial survey of a part of Antarctica which had a wide range of temperature and you can measure the oxygen isotope values in surface snow across this area, compare it with the temperature which you could measure at the time and you did find a good relationship and that's fine.  The only problem with that is that doesn't tell you that it has the whole systems changes with time, you'll get the same relationship.  There are various ways that you can calibrate this but none of them are ideal.  One is to just calibrate and that you got may be 50 years of a temperature record from a particular site and you can compare your isotope ratios with that.  That's not very good, because the year to year temperature variations tend to be a bit stochastic; it's really not a very good relationship on a year to year level, and that's not what you're actually trying to understand.  So there are other ways, one of which is to do with the modelling and the other one to do with measuring things, other things in this ice core or bore hole that tell you about the temperature but not of the same high resolution.

Interviewer - Chris Smith

How far back can you go using ice?

Interviewee - Eric Wolff

We can go back in Antarctica 800,000 years so far.  We think we should be able to go back a little bit further and there's a project underway to work out where we could get back beyond a million years.  In Greenland so far, we've gone back a 128,000 years and that's probably about the limit.  The difficulty is not that there wasn't ice before that, there was.  The difficulty is that in the places where the ice is thickest, and therefore you would think oldest, it tends to be melting at the bottom, so the oldest layer there being melted off.

Interviewer - Chris Smith

Many people would say that the earth is much older than, measured in millions of years, the earth's age is measured in billions of years.  So, is there anything we can do to go back further?

Interviewee - Eric Wolff

Yes.  I mean, we'd very much like to go back further.  Ice cores unfortunately won't take us back much further.  I'd very surprised if we could get beyond one and a half million years.  So to go back further, you have to use other properties and as an example, measuring carbon dioxide in ice cores is very direct.  You could measure it in the air bubbles and that gives us a beautiful record of CO2over the last 800,000 years.  Beyond that, you can use marine sediments with various properties, one of which is boron isotopes, and by comparing those boron isotopes in marine sediments over the last 800,000 years with the ice core data, we can check that. We do actually know what we're doing with the marine sediments and then take them back further.

Interviewer - Chris Smith

So, what is all this revealing to you?

Interviewee - Eric Wolff

Well, ice cores are giving us the best stories that we have of what's happened to the atmosphere over time periods where natural climate processes have made quite significant changes to our climate.  Ice ages have come and gone several times in 800,000 years and you can see the interplay between the greenhouse gases which are revealed by measuring carbon dioxide and methane in the ice, things like volcanism which you can see from sulphate in the ice and the climate.  Of course, it's only the climate in the Polar Regions, where you're measuring it, so you need the data from marine sediments, slate sediments, corals and so on to complete the picture of what's happening to global climate. So, we are now starting to have not just a very vague conceptual model of how ice ages come and go which is what I was told, when I was a student, but we're now starting to really understand the process that occur, what the feedbacks are and of course the critical point about that is that those are the feedback that are going to determine whether putting carbon dioxide into the atmosphere in this century is going to cause a small climate change or a disastrous one.

(28:02 - A greener way to oxidise alcohols to carboxylic acids)

Interviewer - Chris Smith

Eric Wolff and now to a more environmentally friendly way to turn alcohols into acids, Neil.

Interviewee - Neil Withers

So, many of us learned from school and may be early university, the way to make carboxylic acids from alcohols is you have to use a pretty strong oxidizing agent like.

Interviewer - Chris Smith

Dichromate?

Interviewee - Neil Withers

Like dichromate, yeah.

Interviewer - Chris Smith

Calcium dichromate, I love that stuff.

Interviewee - Neil Withers

Potassium dicolour, yeah, well that's there on permanganate which are both very colourful.

Interviewer - Chris Smith

And they're very nice, where they have a big cross on the bottle.

Interviewee - Neil Withers

Yeah, they're both very strong oxidizing agents.

Interviewer - Chris Smith

Probably abandoned in school now.

Interviewee - Neil Withers

I don't know, I think they might not be as long as you're careful.

Interviewer - Chris Smith

Yeah, so harsh conditions to oxidize alcohols, so the C-OH group becomes COOH, that's carboxylic acid.

Interviewee - Neil Withers

Yep, you got to get that extra oxygen in there somewhere and so where that extra oxygen comes from in the case of what you learn at school is from the chromate and the permanganate, you remember those formulae with MnO3 and all that oxygen in there.

Interviewer - Chris Smith

So they're literally the donors.  So it's very,very consumptive because there you're consuming one of those for every oxygen you're adding to the molecule.

Interviewee - Neil Withers

Absolutely, that's why you  call it stoichiometry in action.  It takes one of those chromate or permanganates to make one alcohol into one acid.  It's not catalytic.  So what David Milstein and his colleagues at the Weizmann Institute in Israel have done is, they've produced a catalyst, a ruthenium catalyst, which uses the oxygen from water as the oxygen source to make the carboxylic acid.

Interviewer - Chris Smith

Still pretty energy intensive I would think, isn't it? Because you've got to break the bonds in the water molecule to get the oxygen off.  So is it still not require quite nasty conditions?

Interviewee - Neil Wither

It requires basic conditions and some heat.  So it's not room temperature, but compared to previous ones, it is pretty mild, because you're not using the harsh oxidizing environment.

Interviewer - Chris Smith

So what's the ruthenium doing?

Interviewee - Neil Withers

So the ruthenium is in the form of a pincer complex, so it's got a two pyridine ligands, kind of pinching it, if you can imagine in between your finger and thumb which holds on to the ruthenium and this kind of grabs onto the alcohol, grabs onto the oxygen from the base, sticks them together and out comes not quite the carboxylic acid but a carboxylic acid salt. So it's got the, you know, cation attached to it and you just change that into the acid later down the line.

Interviewer - Chris Smith

Ruthenium is not cheap though, isn't it?

Interviewee - Neil Withers

It is a precious metal, but it's one of the cheaper ones of that classes, not as expensive as platinum or palladium.  And of course the crucial thing is it's a catalyst, so it isn't used up in the interaction, it's only used at the 0.2 moles percent, so it produces many, many more moles of carboxylic acid than it has of itself.

Interviewer - Chris Smith

Will it produce any kind of carboxylic acid that you want or is this reaction restricted to certain molecules of certain sizes or certain type?

Interviewee - Neil Withers

Well, that is often a problem with these kind of newly reported reactions that they don't work on so many things, but this works on a whole range of primary alcohols.  So it works on quite a large substrate range and another interesting thing is, it is also one of the sort of a side products it produces is pure hydrogen. So you can imagine that if you're in a large chemical plant, then you can separate the stream of hydrogen gas that comes off, you can use that in other reactions or you can just burn it for fuel to heat the reaction itself.

(31:14 - Does the kilogram need a new year diet?)

Interviewer - Chris Smith

Terrific.  Well, we're talking about some sort of saving, white saving energy and things like that, the kilo Laura has been gaining weight over the years.

Interviewee - Laura Howes

Yes, like us all here, as the years

Interviewer - Chris Smith

Well, I don't like to say.

Interviewee - Laura Howes

Oh let me too.

Interviewer - Chris Smith

I'm too polite for that.  So go on.  Why is the kilo getting heavier?

Interviewee - Laura Howes

We've been harking back to school lessons.  We'll hark back again.  I remember learning in I think it was physics rather than chemistry all about the standard weights and measures that were put in a vault in Paris in France.  So once the kilogram was decided upon, this is the kilogram to be all kilograms. They made an international prototype kilogram which is a large cylinder of, well actually not that large, a cylinder of platinum and iridium and it's been stored in a vault in Paris and it's been sitting there being the standard kilogram that all other kilograms are based on.

Interviewer - Chris Smith

They made some copies of it didn't they?, which were then distributed around the world for individual countries to use as their kilo, so they had a reference.

Interviewee - Laura Howes

Absolutely and actually this is where our story starts to take a little turn.  About 40 equivalents were made and sent around the country.  So, the one in Paris could stay standard and these 40 replicas were then referred back to that one and obviously every so often you want to check that nothing has gone wrong and no one's, you know, chipped a bit off the corner of one.  So, you bring them back together and you weigh them to make sure they all weigh the same and that's the point where they realized that all the weights and measures, all the weights were slightly slightly different.

Interviewer - Chris Smith

And this wasn't an artefact of the way they were made to start with?  This is a new trait, isn't it?

Interviewee - Laura Howes

This is a new trait.  This could be of variety of reasons.  For some of them where they got lighter, may be they got polished a bit, may be they had some gas absorbed in them and that's been let off.  The one's that have gained weight, that's through absorbing some other molecules from the air, so things like mercury contamination, and also any kind of organics in the air.  If you think about the metals that are being used, they can start to form nice sort of carbonaceous layers on the top.

Interviewer - Chris Smith

So, it's the skin which is making them heavy.  Is it making them heavier by very much?  It doesn't sound like it could.

Interviewee - Laura Howes

Oh it's tiny tiny amounts.  I mean, they're all less than about a 100 micrograms.

Interviewer - Chris Smith

So what's the solution then, to fix it or can we not fix it?

Interviewee - Laura Howes

Well, Peter Cumpson, who's at Newcastle University has been thinking about this and obviously also thinking about high value metals which as we've been talking about platinum, then actually if you're losing bits through having to scrub off the layer and then you remove some of the metal as well, then obviously that's the problem.  You need a way of cleaning the metal without losing any of the metal ions.  So, what he's been looking at is a, basically it's a bit like a chemical peel.  He's washed it with methanol and some water, so now when I say he's really washed it, at the moment, he's been working on model systems.  He hasn't touched the prototype kilogram yet, we should make that clear. He's been making metal foils dirty and then washing them with some methanol and some water to remove the large bouts and then he's put ozone in there, so that's a lot of O3 and UV light. That creates lots and lots of free radicals that can then start to remove all of this sort of carbon layer and things.

Interviewer - Chris Smith

What to do with the mercury you mentioned there, will it?

Interviewee - Laura Howes

No, it won't do with the mercury.  There are still some issues to this, but this might all become academic in a while anyway.  They're looking at redefining the kilogram.  If you think about all the other standard units that we have, things like the meter, that used to be also a meter long piece of metal in a vault in France and then they decided that actually it'd be better if they defined the meter to a constant, and in that case it's the speed of light.  So the meter is now the time that the distance a photon travels in a very small amount of time.  So, the idea is that instead of defining your kilogram by a large number of metal, you'll actually define it by the Planck constant which is another constant, therefore that's the one thing that we haven't felt like comfortable

(35:25 - Trivia: What is the only material to which a gecko's foot cannot stick?)

Interviewer - Chris Smith

Talking of trivial things, what have you got for us this month? Neil?

Interviewee - Neil Withers

Okay, so my question for you this month is, what is the only material to which a gecko's foot cannot stick?

Interviewer - Chris Smith

Hm..I'm torn between two possible answers.  One itself, the other Tony Blair, he's pretty slippery. 

Interviewee - Neil Withers

He, well I couldn't possibly comment.  But the actual answer is Teflon.  So Teflon is so non-stick that a gecko can't stick to it.

Interviewer - Chris Smith

Has someone done the experiment?  Have they put a gecko on a frying pan and seen if it jumps out?

Interviewee - Neil Withers

It depends on how hot the frying pan is, I guess, if it jumps out, but you can imagine they experiment it at different angles of frying pan and how the gecko gets on.

Interviewer - Chris Smith

And on that slippery note, we must bid you farewell for this month.  Thank you to our Chemistry World team Neil Withers, Laura Howes and Bibiana Campos-Seijo and our guests, Eric Wolff and Graham Richards.  The production this month was by Meera Senthilingam and I'm Chris Smith from thenakedscientists dot com.  We're back reacting to more cutting edge chemistry next month, but until then good bye.

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