Chemistry at the Synchrotron

Meera – An exciting area emerging from research at Diamond is the synthesis of new, specialist molecules, known as supramolecular chemistry and the scientist pioneering this field is Harry Anderson from the University of Oxford.

Harry – I’m interested in organic molecules with strongly coupled electrons and controlling their properties often using non-covalent, weak, reversible interactions.

Meera – And what kinds of molecules are these?

Harry – Well they tend to be coloured compounds, a bit like dyes, a lot of the molecules we work with are made from porphyrins, which are naturally occurring pigments. But the ones we work with are not naturally occurring, I mean we make them ourselves from scratch but they’re related to the compounds that make blood red and grass green.

Meera – So are you essentially building molecules and then working with them from there?

Harry – Yes, we do synthesis from very simple starting components and we make compounds and design the compounds. So we are making compounds that have never existed anywhere ever before and so we’re interested in learning about their properties and relating the properties to the molecular structure.

Meera – The actual molecules you’re making are quite big, so how do you actually set about constructing these from scratch?

Harry – It’s a classical, organic synthesis except we also use templates quite a lot. So a template is a molecule around which you can build another molecule which determines the shape of the components in the right places as you link them together and then you can remove the template afterwards. So we’ve developed new ways of using templates to make bigger molecules.

Meera – And is it then hoped that they can have some new applications as well?

Harry – Yeah, of course. So the sort of molecules we work with have strongly coupled electrons which means they are often semiconductors. Organic semiconductors have one important area of application in devices like, well, display devices, electroluminescent displays, but also their interaction with light. They are often fluorescent and have unusual ways of interacting with light that can be used in optical switching devices. And some of the materials which we work with generate singlet oxygen which can be useful in medical applications.

Meera – and could you give an example of a particular molecule that you’ve worked on recently? So how you’d set about making it, why you wanted to make it and maybe some of the uses that it could now have?

Harry – One of the sorts of molecules that we’re excited about are molecular wires that are in rings rather than being straight. So we’ve worked on, what we call, molecular wires which are straight molecules down which you can transfer electrons, but recently we’ve realised that it’s possible to make rings of these molecules. So part of the challenge is just to make a molecular wire into a ring and then look at the charge mobility around the ring but for this particular class of molecules, then it’s not that easy to identify applications here, but we think that it may have unusual properties, maybe magnetic properties, than can get them to behave like little loops of magnetic wire. So we’re just investigating them to see how they behave.

Meera – What are the applications of the first set of molecular wires that were created, the linear ones?

Harry – Yes, potentially in molecular electronics, that means molecular scale electronics, transistors or electronic devices on the molecular scale, the ultimate in miniaturisation as integration circuits get smaller and smaller. So a lot of people are working in that area but it’s still a very long way from being useful. On the other hand in devices made on a larger scale, using larger amounts of material, like solar cells and maybe also organic transistors, it’s useful to have materials which can transfer charge efficiently. The molecular wires might be components in a material, perhaps in a solar cell.

Meera – So would the circular forms have different applications? So you’ve mentioned that they could perhaps alter magnetic fields and so on. So changing the shape of them could give them different properties and other uses?

Harry – Yes, just like a bit of wire, if it’s in a solenoid shape it behaves quite differently to if it’s in a straight shape. That’s one of the amazing things about molecules that just changing the shape, thinking about the shape, often relates to the properties.

Meera – And how do you use Diamond in all of this? How do you use synchrotron radiation to perhaps aid this process?

Harry - For structurally characterising the compounds that we make, proving that they are actually the compounds which we think they are, and for getting information on the shapes. So there are two techniques that we use at Diamond; small angle x-ray scattering of solutions, is very useful for getting low resolution information on the shapes of the molecules. It hasn’t been used much before for synthetic molecules, it has been used a lot for proteins, and it’s useful because you don’t have to grow crystals, you can take a compound and take a dilute solution and just from the small angle x-ray scattering you can get information on the 3-dimensional shape of the molecule. And the other thing that we use at Diamond is x-ray crystallography, and it gives much higher resolution information than the solution phase scattering.

Meera – Is there a particular molecule that has perhaps been your most successful to date in terms of how far you’ve managed to go with it?

Harry – Well, I suppose we’ve worked most on porphyrin-based molecular wires. Perhaps they’ve been most successful because they’re so versatile. That a similar group of molecules can have potential applications in medicine and photodynamic therapy and also in molecular electronics and there are lots of other potential applications too, they have such a rich range of properties.

Meera - Harry Anderson, Professor of Chemistry from the University of Oxford.

Tony – So I study the structure of polymers, plastics and colloid suspensions. So one example might be the structure of molecules that make up a shampoo bottle and also the structure of the molecules that make up the shampoo.

Meera – and how do you set about looking into this?

Tony – Well we do various things in the labs, we synthesise special molecules, we synthesise molecules that we can label so we know where they are and then we use the synchrotron as a source of high-intensity x-ray beams that allows us either to penetrate deep into a sample, or to look at a sample on its surface as it is doing its stuff and we can work out where the atoms are and how the whole molecules are organised.

Meera – And so what’s your real aim here, so what are you actually trying to find out about the molecules?

Tony – So, if we take the example of a shampoo bottle, then we are wanting to know when the material was processed, how the stretching of the molecules affected the way they crystallised. So when you make a bottle, you take a liquid and essentially you blow a bubble in the liquid to a special shape, that’s the shape of the bottle, and the stretching and the cooling causes the polymer molecules to organise themselves so that they crystallise and we study the stretching and the cooling and the crystallisation by following what the molecules do, in real time, by x-ray scattering.

Meera – and what have been, perhaps, some of your key findings having monitored the molecules in this way?

Tony – Well we’ve just had a paper published that compares the crystallisation of synthetic polymers like polyethylene, with the crystallisation of silk, from a silk worm. By using the synchrotron and by using other techniques in the lab at home, we’ve been able to estimate the energy needed to do the processing and we find out that the silk worm uses about 10% of the energy that we use to process polyethylene to make a fibre. So silk worms are much better a making fibres than people.

Meera – So is the aim then to really find out a bit more about how the silk worm does this to reduce our energy needs, or usages?

Tony – So what we can do from what we’ve learned about how silk worms go about processing silk, we’ve learned that it’s a different mechanism to the mechanism that’s used in making fibres of synthetic polymers. So what we can do is look to mimic the silk worms’ method in engineering materials. What the synchrotron has allowed us to do is compare the energetic of the 2 processes; learn that one process is much less energy intensive than the other and now we understand both how and why it’s less energy intensive to try and replicate that methodology in synthetic materials. So it actually means going back to the molecular drawing board and doing synthetic chemistry again.

Meera – Could you perhaps give a bit of insight into an even wider range of areas of chemistry that the synchrotron can be used for and that benefits other scientists?

Tony – So my colleagues in the chemistry field use the synchrotron for many, many reasons. So they do spectroscopy that they can’t do anywhere else to see what the local environment of individual atoms are, how catalysts work, like the catalytic converter in your car, other colleagues use it to study the crystallisation of drugs. So you can separate polymorphs, different forms of drugs because drugs crystallise in different ways and if you have the wrong sort of crystals in a tablet, they don’t work. But they can even work out how proteins interact with each other, so how proteins interact with drugs using a different set of scattering techniques called macromolecular crystallography. So there’s a whole variety of different techniques, imaging techniques, spectroscopy techniques that chemists use to study many, many different aspects of science. Whether it be; how rain clouds form or how drugs are taken into the marketplace.

Meera – And I guess with the opening of the new beamlines, which you must know about as well being on the Board of Directors and so on, this just must increase as well as each beamline opens as well?

Tony – The new beamline proposals open new areas of science, so for example, parts of what we do in terms of molecular engineering have been transformed by the availability of microbeams. So you can look in very fine detail in large parts. You only need very small crystals to be able to solve the structure. So all the time the techniques ands the technology at the synchrotron are pushing the envelope of what we can do and that generates new scientific opportunities with it.

Meera – What will you be looking into next then? What will be your next use for the synchrotron for your own work?

Tony – Well I’m really interested in how we use catalysts to clean up the environment so I’ve been working with and artist on making catalytic clothes and so what we want to do is to stick tiny catalyst particles to peoples clothes so they can walk around and take out environmental pollution - to use people and their clothing as catalyst supports. But to do that we need to understand how the catalyst particles stick to fibres and so my next project at the synchrotron will be to understand this process of depositing nanoparticles on to fibres. And we’ll use both imaging and scattering techniques to do that.

Meera – That’s a really interesting idea and so if you can just get a certain percentage of the population to wear that, that could make quite a big difference.

Tony – Yes, it would actually have to be quite a large proportion of the population. Each person could take out about 3 grams of nitric oxide a day, which doesn’t sound like very much but once you have a million people doing it then they take out 3 tonnes of pollution a day and once you start to get those sorts of numbers of people involved then you can have a significant impact on the urban environment.

Meera – So how can people get involved with this and find out more?

Tony – So there’s a great website called www.catalytic-clothing.org and there’s been lots of social media activity around this. At some point we’re going to be doing a pop-up laundry and we may even run a pop-up laundry at Diamond.

Meera – Tony Ryan from the University of Sheffield.