Noel Sydney Hush was born in Sydney in 1924. He finished secondary school in 1941 and began university the following year. Hush completed a BSc Hons (1945) and MSc (1948) from the University of Sydney. For the latter part of this time he worked as a research fellow in the Department of Chemistry (1945-49). Hush then accepted an assistant lectureship at the University of Manchester (1950-54). On the basis of his published work, he was awarded the University’s Doctor of Science (D.Sc.) degree in 1959. In 1955, Hush moved to the University of Bristol where he worked firstly as a lecturer and then reader (1955-71) in the Department of Chemistry.
Hush returned to Australia and the University of Sydney in 1971 to found a new department of Theoretical Chemistry, a position he held for nearly two decades (1971-89). Upon his formal retirement, Hush accepted an appointment as emeritus foundation professor of Theoretical Chemistry at the University of Sydney, while continuing his research. In 2002, he also became convenor of the University of Sydney Molecular Electronics Group.
Professor Hush was elected to the fellowship of the Australian Academy of Science in 1977 and served as a member (1978-81, 1984-89) and chairman (1981-82, 1989-92) of the Sectional Committee for Chemistry and as a member on the Science Policy Working Group (1987-97).
Interviewed by Professor Robyn Williams in 2011
Contents
Hello, I’m Robyn Williams. Today it is my pleasure to interview the great chemist Professor Noel Hush from the University of Sydney.
Noel, have you been on television before?
No. It is a new experience.
I see. You have carefully avoided it?
Nobody has asked me before. If they had asked me, I would have probably said no. When you asked me, I could do nothing but say yes.
That is terribly kind.
But my general attitude would be Auden’s ‘private faces in public places are wiser and nicer than public faces in private places’. To be not able to walk into a coffee shop without being recognised would be very boring.
Charge repulsion between mother and child
Noel, may I do something that I have never done on television before? Would you extend your thumb for me please? Why is that a quantum event?
What you are doing there is mimicking a child’s first experience of reality. That is, a child’s first experience of reality is with quantum reality.
How come?
Because I am a child and that is my finger and it is exploring. The first thing that it explores is his mother’s face. Your thumb was the mother’s cheek. When his finger touches her cheek, it doesn’t go through her cheek – it stops, it meets resistance. But why is that? The surface of the child’s finger is just made of electrons, and so is the mother’s cheek. Why don’t they just interpenetrate, like clouds? When two usual clouds meet they mix with each other. But, the electronsare negatively charged and they don’t like to get too close together and they are quantum objects.
If you asked the baby, and he had read a bit, he would say, ‘I realise why mummy’s cheek is resisting me. It is because of exchange quantum repulsion.’ And he would be quite right too.
That explains the other thing that has always puzzled me: atoms are actually empty space, aren’t they.
Yes.
So the fact that we have any resistance at all is amazing.
Well, that is the answer: it is exchange repulsion.
And this has been the basis of your work: understanding exchange repulsion?
It is implicit in it, yes. We are not just talking about a concept. It is the sort of thing that we calculate and put numbers to. We can calculate the repulsion between the baby and the cheek, so to speak.
An almost perfect score from holiday reading
Let us go back to those very early years of you as a baby and then growing up. You have never explained much to me about what those early days were like. Were they unusual? Was it a straightforward childhood?
Just about. I first attended the state schools. I went to a private coeducational school for my secondary education. That is a little bit unusual, I suppose.
For those days. They were the 1930s?
Yes, it would have been the very late thirties. In fact, my only achievement has been in the intermediate examination. Out of eight subjects, I had an almost perfect score. Nothing like that has ever happened again. It was a peak which I have never got up to again.
So you were tremendous.
No, no. The exam result was the one thing of that order. I was a voracious reader – I devour books. It was really in the vacations that I felt that I learned anything. One could get through an enormous amount of stuff in these vacations. A bit like Aldous Huxley, who had his entry in Who’s Who under ‘education’, whilst was on holiday from Eton.
I think Aldous Huxley was being unfair about Eton, because he had a tremendously broad education. Were you similarly omnivorous?
Yes, absolutely so. But I was always looking for very general patterns. At school I made a nuisance of myself. When they were trying to tell me about Ethelred the Unready and all the problems of the Kings of EnglandI would point out Wells’s A Short History of the World. The book began with the world five billion years ago. We didn’t know exactly how the world began, but it went up through the formation of stars and so on. After a while, you began to get to things coming out of the sea, then they got legs, then they started to write books about philosophy, then they discovered atoms and then it started to be interesting. The book showed an unfolding of almost certainly interpretable complexity modulated by contingency, although I didn’t put it like that. Like the weird business about Ethelred, there was no pattern to school history, it was just one after the other. Ambrose Bierce described history as a lot of untruths about powerful people doing foolish things for no reason at all and having other people die for them. That seemed to summarise history as it was being taught.
University studies and a background to quantum physics
What was the standard of Australian science education like way back then?
It was quite good. The more relevant question is what it was like at the universities. When I came up to universitythe war was on. I came up in 1942. I took the preliminary exam at the end of 1941, I was only 16. I then entered when I was 17.The academic staff were pretty depleted in wartime in subjects like physics, mathematics and chemistry. In chemistry, for example, there were a couple of organic chemists, but the physical and inorganic staff was comprised of four people. Only two of whom were research active – not big. It would be difficult to judge
Did you choose general science or was it a straight chemistry degree?
It was chemistry, physics and mathematics – all three of them. But I knew, by the time I began my course, that everything was electronic. I also wanted to look at the world at the level of chemistry. You can be doing things at the level of galaxies or the level of molecules or people, or you can go down to the nuclear level. Now you can look at a sub-nuclear level.
But how did you know that most events were essentially electronic?
Just from general reading. By that time, we knew what atoms were made of. Eddington had written about these things and had scandalised people by saying that a table was just a massive empty space. Also, I had read a bit of the pre-Socratics, who were always concerned with the question of what things are made of. It was very early in my reading when I came across Thales. He was the very first philosopher and the first scientist. We only know what he taught from hearsay. But it seems that he was the man who said that the principle of the world is water. The logical positivists thought it was a very ridiculous statement. But he had latched onto the fact of transformation: one substance being transformed iswater being vaporised and becoming what he called air. Then he saw the water solidify into ice. So he thought that the rocks were probably even more compressed forms of water. The idea was that this one substance transformed itself into many different forms by a difference in density. His mistake was identifying it with a particular substance. There had to be something underlying that. The people who followed him, like Anaximander, did argue it was something more basic. But the elaboration of the idea of a universal substance whose density variation governs everything in the world earned the Nobel Prize for Kohn and Sham. This was for the discovery of density functional theory. In other words, in order to efficiently calculate the properties of something and to solve the Schrodinger equation, you calculate the electron density. Thales would have approved. But the general basic ideas were clear from many good popular science books at the time, such as Eddington’s.
I think it is quite normal to be intensely interested in one particular stratum, as you might say. There was a Cambridge philosopher and mathematician, Frank Ramsay, a marvellous chap, who died at the age of only 28. He was famous for saying, ‘To me, the moon is sixpence and the stars are threepenny bits.’ That is all he needed to know. He claimed he wasn’t further interested. That is an exaggeration. Obviously I am interested in the structure of the galaxyand also in the sub-nuclearrealm, but only in a very general way.I know well people who have been pioneers in these areas. In Bristol I used to walk together with the man down the hill from where I lived to the university. He was the co-originator of particle physics. His name wasCecil Powell andhe discovered the mu-meson. I learned a lot about both on these walks. But I find it difficult to get too excited about the charm and the various subcategories of chromodynamics.
Quarks and so forth.
It is very interesting, but my understanding of the chemical role of acids is not usefully enhanced by the knowledge that a proton consists of two up and one down quark, plus gluons.
When did you first become aware of quantum mechanics?
I read popular works, so I was aware of what had been done in the late twenties. It was really recent, and I was familiar with the idea that something rather weird was going on. That something we had thought to be continuous was no longer continuous but discrete. This was a general idea that was floating around at the time. The idea that you had to have a special sort of physics to deal with that, physics that went beyond the Newtonian. I had no idea of exactly what it was, but I knew that I was going to be coming across something quite different from the ordinary physics that we knew. In my first year, as the general ideas of quantum physics were introduced, I began to realize that solving the Schrodinger equation would probably solve every problem that I needed, at least in principle. That was the dream, that you solve the Schrodinger equation, and that would solve any chemical problem. It is true, of course – stressing the in principle reservation.
Were you ever embarrassed, as Ernest Rutherford was, by the difference between chemistry and physics? He got a Nobel Prize for Chemistry, but he insisted that he was a physicist. Were you torn in the same sort of way?
I am called a theoretical chemist, but I am a chemical physicist because I also do experiments. I do calculations and, if they are fairly out of the ordinary, I like to have some experiments going on by which I can check them.
So you did ‘stinks and bangs’ as well.
Oh, yes. In my honours year, I began an experimental project that was quite interesting.There were a couple of research-active people in that department. One of them had just come back from working with Linus Pauling in California, which was a big thing. In my fourth year I was presented with a number of possible research projects and one of them was to do with a magnetic molecule. Michaelis was a famous biochemist at the Rockefeller Institute in the US. You would think all that he would be interested in would be biochemical molecules, but he had published a paper on some peculiar substances which had been synthesised in the 19th century by a German chemist. The substances were called Wurster’s Red and Wurster’s Blue. Michaelis got on to these Wurster salts because they were analogous in a way to quinones. Quinones and hydroquinones are very important – they are ubiquitous in biological systems. Photosynthesis, for example, deals with the reduction of a quinone. Michaelis saw that there was a parallel with these salts and proposed an explanation of their magnetic properties in terms of Pauling’s ‘resonance’ theory.
It was clear enough to me that Michaelis, an enormously clever man, had not got ‘resonance’ quite right. So I was able to devise a molecule which would be a test for his theory. By making and it and taking magnetic measurements, I showed that it was not correct. The first paper I ever published was in Nature on this work. People would think that was a wonderful thing these days, but the pressure to get published in Nature wasn’t quite the thing then. It was a more normal way to have something published. It was a curious thing – one of these amazing accidents – because that problem embodied something which has been occupying me ever since. That is, the ways in which nuclear and electronic motions become mixed up with each other. This is heavily involved in all kinds of things, like oxidation reduction and electron transfer. Electron transfer is the thing with which I have later been much concerned.
We will come to that in a minute. Linus Pauling: I have always felt that he is the greatest chemist of the 20th Century. Do you agree?
Well, he stopped being productive by 1950 when he had gone to this alternative medicine and Vitamin C stuff. But his great legacy went on and it still does.
There were other people who then took on from there. One person I was very closely associated with was the inorganic chemist Henry Taube at Stanford. We first made contact because I had made a prediction. The prediction was that in certain systems you might find a very lowlying electronic transition which would be indicative of an unusual and important electronic structure relevant to electron transfer mechanisms. This had never been seen and this was part of the reason why Taube set out to synthesise an ion to verify this. He put his graduate student Carol Creutz on to it. Within two years they produced the Creutz-Taube ion. There has been argument about the detailed electronic structure of the Creutz-Taube ion ever since and even now. This has served as a focus for interpretation of the properties of mixed-valence and molecular oxidation-reduction systems and contributed ultimately to Taube’s Nobel Prize. It was in 1967 that I made the prediction, and by 1969 he had made the ion which verified it. Over the intervening years, until he died about five years ago, we talked about that and very many other things. Frequently these discussions led to further fruitful experimental work by him and further theoretical work by me.
Let me ask you about your transition to Manchester. Obviously they didn’t know you. Were you hoping that you could make your application on paper and get it that way?
That is interesting. In the days I am talking about now there was no such thing as a PhD degree. It hadn’t yet come in Australia. It was late coming in England because they thought it was one of those second-rate things. You had to have a DSc or at least an ScD. So everybody was going from England to Germany to work for an ScD and thus they were losing graduate students. So reluctantly they brought in the PhD. There was at the time no PhD degree in Australia.
After I graduated, I spent a couple of years getting an MSc. It was on experimental work on these semiquinones of Wurster and some electrochemistry, but also theoretical work on solvation. Chemistry is concerned with what happens in solution in general and, if you put a charged ion into a solvent, it releases an amount of energy (solvation energy) and the energetics of the reactions depends a lot on that. There was a lot of discussion about how solvation worked. I had written a paper on this. I had made an interesting discovery. Quite a number of people had discussed how all this worked – you put the molecule or ion into water and the water molecules rearrange themselves around it. They all agreed about the same thing – there was no way of measuring this. You could measure the sum of two solvation energies. For example, if you put sodium chloride into the solution, you had a chloride ion and a positive ion from the sodium, and you could measure the sum of the two solvation energies. You would just measure the total. But you couldn’t get the individual ion measurements. I prowled amongst the literature in my usual way of reading around and I found, in the Zeitschrift für Physikalische Chemie, an obscure paper by a German physicist. He was working on contact potentials and Volta potentials. That was the key to the fact that you could get an absolute value.
This, incidentally, turns out to be not merely a matter of theory. We are now dealing with nanoscience and molecular electronics and if you have solutions containing ions from which electrons are transferred to a metal, unless you know that absolute level in the solution, you don’t know anything. Everybody knows that this is so now. But, if you were to ask 99,999 out of 100,000 chemists, ‘What are Volta potentials?’ they would not know. They might know what the absolute potential of the hydrogen electrode is, because we now know what the absolute solvation energies are, but they would not know how they were obtained. That is an example of the disparate way in which we can inhabit almost separate universes.
Anyway, to get back to what you were asking me. I had heard that the University of Manchester was doing a lot of work in relevant areas, although I hadn’t actually read any papers from them. So I wrote to the professor of Physical Chemistry, M. G. Evans, to ask about the possibility of an ICI Fellowship. ICI gave these things to Manchester. That seemed pretty remote. But within about a couple of weeks – this was snail-mail days – I got back an international telegram. It was in the old imperial style, with bits pasted on it, which said, ‘No Fellowships, but would you take an Assistant Lectureship?’, which was pretty amazing. I said, ‘Yes, I certainly would.’ Then, again by telegram, things were arranged. By the end of the month, I was told, ‘There it is. Do you want it?’ and I said, ‘Yes.’ By the end of the year, I was in Manchester.
How did you get to Manchester back in those days?
By boat, the Ormonde. When we were at the Bay of Biscay there were raging torrents. We were heeling over to this side and that side. The captain’s message board was full of little pieces of paper saying ‘SOS’ from the ships all around us. But it was wonderful, although it was slow. I went with my fiancée. We called in all over the world. We went north to Brisbane, which at that time was a very grey city. Then you were suddenly in Penang, Singapore, Colombo and India. Then you had crossed the Indian Ocean and were over in Aden. As soon as I stepped ashore in Bombay I felt a tap on my shoulder. I looked around and it was a leper whose arm had gone. It was the stump of his arm that was begging from me. The squalor that you saw there was like something out of Dante. You wouldn’t believe it. I picked up an infection in my heel. I was wearing sandals, which was foolish enough. This was a long stretch where we were out of range of help. It was an awful infection, a rapidly spreading tropical ulcer. We had the usual ship’s drunken doctor, with no possibility of any help. Luckily, we were just beginning to get antibiotics in. Otherwise I might have been done for. He treated my heel and so I was able to limp off the boat at Aden. We went around to Aden, the Red Sea and the pyramids. Then we made our way out through to Malta, then Sicily, through beautiful Mediterranean countryside with buildings, grapes and peaches and, finally, to England.
And Manchester.
And then to Manchester by train. We had come from Australia in the summer. When we got off the train in Manchester we found that it never really rains but is always drizzling. There is always drizzle. The sky is always overcast and grey. Through the drizzle I could see this poster on the station wall. It was an Arab, pointing at you like Lord Kitchener, saying ‘If you were in my country, you wouldn’t waste water.’ But water was around us all the time then. Anyway, that was Manchester. It was black with soot. Even the hedges were black with soot. It was freezing cold in the winter. There was rationing. Even though it was well after the war, rationing was in full force – two ounces of meat and butter a week.
I suppose your wife, Thea, thanked you for taking her to this marvellous, salubrious place.
You might think this was the end of the world, but we were very resilient. Manchester was the Athens of the north. ‘What Manchester thinks today’ they said, ‘London thinks tomorrow’ and it was indeed intellectually highly stimulating. The Manchester Guardian then was a great newspaper.
Based in Manchester, I assume.
Absolutely. It was the ‘Manchester Guardian’ of the Scott dynasty, who insisted on the complete separation between news and commentary. I got to know the Guardian people, and Wadsworth, the editor. The BBC people were there as well, including the satirist Peter Simple, as he became later and we knew him well. The University had quite a complement of brilliant eccentrics. Manchester was still suffering from bad bomb damage. The wonderful Hallé Orchestra under Barbirolli was now under a huge tent near the Belle Vue Zoo and, in a slow movement of the symphony, a lion would suddenly roar or a hyena would scream. We would now call it a multimedia event. Of course, we had the wonderful fog. You couldn’t see a yard ahead. But it was an exhilarating time. I must admit that we did live on food parcels. We were sent regular food parcels from home, without which we probably wouldn’t have had a very good time.
I managed, by a miracle, to get a rather pleasant little flat close to the university. There was only one purpose built block of flats in Manchester, where Barbirolli lived. When you looked at anything for rent, it was usually something absolutely squalid. What was called the kitchen probably didn’t even have a sink in it. You had to put your own sink in. We were extraordinarily fortunate to get this delightful little part of a house.
What about the work of understanding how electrons move from molecule to molecule? Were you in the right place at the right time?
Absolutely. I wrote to MG Evans. I knew that he was the professor of chemistry there.
A very handsome man.
Yes. His full name was Meredith Gwynne Evans. Meredith is also a man’s name in Welsh. He was the pupil, then the student and then the collaborator and colleague of Michael Polanyi. Polanyi was one of the most amazing people you could possibly hope to meet. He was a polymath. He was Hungarian by origin and he had served in the First World War at a very young age. He had done a medical degree and then physical chemistry at Budapest. During the course of this, Polanyi wrote to Einstein asking scientific advice and Einstein wrote back. Anyway, Polanyi got to Germany and did a physical chemistry PhD there and so on. Soon he was well established at the Kaiser Wilhelm Institute in Berlin and he went from strength to strength. This was at a time when everything was new. He did a bit of X-ray crystallography for the very first time – they were just finding out what it was. He made an important discovery in x-ray crystallography and he became a very famous man. In the end he was head hunted by Manchester University and he finally came in 1933.
When Michael Polanyi came to Manchester he absolutely transformed chemistry. Not only did he develop a general theory of the rate at which reactions happen – the speed at which they happen, the kinetics. For example, to boil an egg, you have to put some energy into the reaction – to boil it – to heat it up. You put some energy in and you get some product. He was able to quantify this pathway quantum mechanically showing that the hill that you climbed was an energy one. You began with the reactants, you ended with products and, in the middle, you had something which was given the name of ‘the transition state’. If you are studying reaction dynamics, what you are trying to do in general is to investigate the nature of the transition state. So I was coming to Manchester, at which that phrase ‘transition state’ had first been articulated. This was the ‘transition state theory’ and sometimes it was called the ‘absolute reaction rate theory’. It is what people use now in an extended form to calculate chemical dynamics.
So you ask whether that was the place to be – it certainly was. You might ask why Polanyi wasn’t there with Evans. It was because Polanyi was a polymath and the vice-chancellor had come to him two years before I arrived and said, ‘We are going to make you an honest man, Polanyi. You are going to be a professor of social science’. Polanyi had also worked in economics in Germany. During the war, he wrote a book called The Logic of Liberty, in which he pointed out, before Popper, this idea of the ‘closed and open society’ but in mathematical terms. At a time when Russia was our ally, he predicted, mathematically and economically, the collapse. He couldn’t tell the year, just that it was going to collapse. He then wrote a succession of books. If you look up the internet, you will find that there are several biographies. He gave the Gifford Lectures and he wrote a book called Personal Knowledge, which is really about the nature of scientific knowledge. He depicted scientists as being free agents interacting, not under any kind of direction at all but like a ‘Hobbesian free market’, in which they all just came together. This is a very famous model.
By the way, is it true that his son is John Polanyi, the winner of the Nobel Prize for Chemistry? He lives in Canada.
Yes. John, when I was at Manchester, was just finishing his PhD and went on to work initially in his father’s area. He became a Canadian citizen and shared the Nobel Prize for highly ingenious experimental work on quantised cascading of energy from the transition to ground state.
Is this the kind of work that Ahmed Zewail in Caltech took up and got the Nobel Prize for?
Closely connected. By its very nature the transition state is not something that you can actually look at. It lasts for only about a femtosecond – that is a millionth of a millionth of a second – not very long. John Polanyi carried on studying the very simplest of reactions, taking a hydrogen atom and slapping it into a hydrogen molecule. You might think that nothing happens, but in fact one atom comes out of the hydrogen molecule and links on to the other. So H + H2 gives you H2 + H. That was first studied theoretically by Polanyi Senior and that was the first reaction whose rate was calculated by quantum methods. That was the start of the reaction rate theory. Anyway, John carried on in gas-phase kinetics. He was trying to look at the transitional state, even though it lasted for such a short time. This was very original but he had limited success. He had little experimental means of doing so, until this very brilliant Egyptian by origin, Ahmed Zewail, provided it. I know the man who achieved picosecond resolution. That is 10 to the minus 12, and that was important. But Ahmed Zewail extended this to femtoseconds in chemistry – a giant step. Ahmed and Polanyi got together and they were able to get the spectroscopy of the transition state. That was a big deal.
Germans, Russians and Kasha – ahead of the rest
What about your role in all of this? What were you doing then in the lab?
Many things, mainly but not exclusively, theoretical. As I have said all of Polanyi’s work had been in the gas phase and Evans’ was in solution so they were the sorts of things that I was interested in: oxidation, reduction and so on. Oxidation is removal of electronsfrom something. For example, when a nail rusts, the metal is losing electrons and becoming ionic.Reduction is the reverse. If you react haemoglobin with oxygen, it takes up electrons. Evans was studying these oxidation-reduction reactions in solution, so that was right up my alley. He had also worked on solvation. One of my first seminars in chemistry in the department was on solvation and how it was possible to get absolute ion energy values. I had in front of me some of the cleverest people in Europe and what was their reaction? They thought it was nonsense.
Why?
‘Volta potentials, interfacial potentials? Who’s heard of interfacial potentials?’ They said. ‘This is some nonsense of some obscure German. Who has heard of Lange? Nobody has heard of Lange.’
Also at Manchester was a graduate student called Michael Kasha from America. He was on a postgraduatefellowship. He had worked with the distinguished chemist Gilbert Lewis in Berkeleyon the electronic spectra of molecules. Sometimes molecules briefly fluoresce. But there is a much longer emission of light called phosphorescence where things glow in the dark, which was not understood. They showed that in phosphorescence there is a lower magnetic excited state from which energy trickles out slowly, and called it the ‘triplet’ state. Lewis unfortunately died, and it was left to Kasha to take the good news to Chicago. He spoke in front of a physics audience, a galaxy of famous physicists, and, again, ‘rubbish’, ‘nonsense’, ‘it couldn’t possibly be’. If you look at that now, you would say, ‘What else could it possibly be?’ But this is the common reception of anything which is a bit unusual: first of all, they don’t believe it at all and then, a few years later, ‘Of course, we always knew that.’ Kasha became the leading U.S. molecular spectroscopist.
Did that blockage annoy you?
No. It amused me. By this time I had become very used to the fact that there were these huge gaps. Another gap was one of language. It turned out that Russian electrochemistry was the most advanced in the world at the time, although we didn’t know this. I didn’t know it, because it was all in Russian, but I soon found out. I soon found out also that what I was talking about was standard electrochemistry in Russia. It had been known for about 10 years. But that was how it went.
Perhaps we can come back to your actual role amongst these four revolutions in Manchester?
I was working, first of all, with Evans. We worked on calculating the energetics of many reactions. In particular those involving hydrogen peroxide and its various breakdown products like HO2, oxygen and the radicals. It was very important at the time. Evans had been working on that during the war. High-test peroxide was a rocket fuel. So the reactions of that were very interesting. But the reactions of these with metal ions were of great importance in many industrial applications. We worked out theoretical interpretations of data for about 80 important reactions. We worked out the details of the energies and entropies of these reactions, which became a standard for next 10 years or so. At the same time I was also looking at electrode processes and the basic theory of them.
As for knowing the energy of those reactions and being able to quantify them, what does that enable you to do that you couldn’t do before?
Our results provided fundamental information on reactions of fleeting unstable radicals which were hard to characterise experimentally. There were people out in industry who would have a radical, like HO2, that would be generated in some way. They would be in the oil industry or in the polymer industry, for example. It would react with a metal ion and induce various types of reaction, such as polymerisation. It was of very great use to have reliable estimates of radical energetics in designing synthetic methods. Also, it was important for biochemistry, where free radicals of this sort have a very important role and little was known about their energetics at the time.The people who followed up this work most immediately werein Israel. They were checking on our numbers, and one got very excited because he found a slight discrepancy with our calculated dissociation constant of the hypothetical radical HO2. The methods that we were using at the time were very ‘ambitious’. We were able to use phrases like ‘this encourages us to interpolate’ – you would never get away with that in a journal these days. But, luckily, we were pretty well right.
Another very important thing at Manchester was the presence of a man who was No. 2 in quantum theory in the country. His name was Christopher Longuet-Higginsand he had studied under Charles Coulson, Waynflete Professor of Mathematics at Oxford. Coulson was the leading British authority on molecular quantum mechanics, and Christopher had been his student and colleague and was now at Manchester. Christopher was very young. Within six months of being there, I was fully acquainted with the theory by which one could actually make calculations. By a strange quirk, the systems on which you could do these calculations most easily were large hydrocarbons like benzene, naphthalene and these sorts of aromatics. I embarked on quantum investigations of properties and of energetics of electron transfer amongst such species. It was ironic that you could do useful calculations for these large molecules whereas you couldn’t for a water molecule. It is very complicated with water for various reasons, including symmetry and electron diversity.
Within six months or so, I was working on papers calculating the energetics of electronic disproportion, ionisation and so on. From then until now, I have been deeply concerned with molecular quantum calculations using theory as it has developed. We began what was called Huckel theory after the German chemist who sometimes turned up in England after the war at Faraday Society Discussions. Physicists now call it the tight-binding theory. It is a parameterised rather than an ab initio approach.
Working with Turing on coupled diffusion and reaction
For computation, I had a little hand calculator which had been captured from the German army. Now we do rather better. Alan Turing was there at the time too. To us, he was just another chap. We knew nothing about his background at Bletchley. We didn’t yet have a computer, although one was approaching completion. He was simply an interesting mathematician in baggy flannels who you talked to over a lunch table. That is untilan arrangement was made by Evans for he and I to talk together seriously. Evans realised that we were doing something similar. This wasan aspect ofTuring’s work that most people don’t know about outside of the biological area.
Just to interrupt: Alan Turing – a legendary name – is world famous for three things. First of all, he helped win the war at Bletchley with Enigma. Then he is one of the master minds behind the invention of modern computing. Also, some of his equations were quite groundbreaking and I would imagine they would have affected your field as well.
There was a common element. This was realized by Evans, who saw that the work I was doing in electrochemical electron rate theory had something in common. Evans knew him quite well so he made an arrangement for Turing and me to talk together seriously because of this. What Turing was investigating was what would now be called ‘morphogenesis’. That is, how living things get their shape and their function.
That is what Darcy Thompson wrote about.
That sort of thing, yes. The simplest possible example would be that you have an animal with a textured skin – a tiger with stripes, for example. The stripes are bands of colour which somehow have to be formed. In a general way, you would think, ‘Well, to get the pattern, something has to move along the skin and get to a point. Then perhaps something else comes to that point, these two react and you get the pattern.’ So the substances moving along would be diffusing and then they would react together. You would have coupled diffusion and reaction. I was studying the theory and also the practice of the basic electrode process. In this process an ion or molecule would diffuse to the surface of an electrode and then transfer an electron to the metal. The question for me was how do you disentangle this motion of the species coming up to the surface from that of the electron getting out from the Fermi level of the metal? This had never before been done and I succeeded in solving it. I was considering elementary reactions and also coupled reversible and irreversible reactions.
What Turing was doing was solving diffusion in two dimensions, which is more complex, and for far more complicated reactions. I was mostly only in one dimension, except when I had, for example, a hemispherical surface. We had a useful discussion about methods of solution, from which I benefitted. On the other hand Turing was a mathematician, at that stage, and not very conversant with magnitudes, the natures of diffusion coefficients and general chemical work in that area. I was able, not only to brief him on that sort of thing, but also to acquaint him with the reaction rate theory. The transition state theory had been applied to diffusion as well, which he didn’t know. So that was useful information for him although it was an extremely modest contribution to his work.
Technically, these diffusion differential equations raise interesting challenges. A PhD student, Keith Oldham, was working with me on them. He became so interested that he has devoted his entire subsequent successful research career to solving such problems for electrochemical systems. He has even resurrected a little-known concept, called ‘fractional calculus’ (as well as the differential d/dx you have d1/2/dx etc.) This concept was played with by Leibnitz and others. It turns out to have very useful applications in this area. Oldham is co-author of the first monograph in that field.
Turing published the results of this research. It remained unnoticed for twenty years or so, but I understand it now forms the generally accepted textbook explanation of morphogenesis and has inspired much research in the area.
Did you know anything then about the tragedy of his life?
Oh, very much so. I left Manchester in 1954 and he had committed suicide two months before that. He got the cyanide from our chemistry department and put it into an apple. According to Hodge’s biography Turing was fascinated by the story of Snow White. But, the suicide was because he was about to come up before a court on what was then regarded as a serious homosexual charge.
In fact, I remember that he had actually called the police because there was a burglary in his place, and the police came in and arrested him for being a homosexual.
A couple of years before, he had been hauled up on a case of accosting or some sort of thing. He had been ‘let off’ from conviction on the grounds that he undertook chemical castration – which he did
Which depressed him terribly.
He lived fairly close to me and I had been talking to him not long before he died. We sometimes sat across the table in the Common Room. It was a very democratic place. The vice-chancellor would eat there as well.
My interaction with Turing had come about owing to my work on extracting rates of elementary oxidation-reduction processes from experimental data. But I was now also starting to work on the basic theory of kinetics (in addition to overall energetics) of such reactions. I was working on how these were linked with the overall energy of the reaction, which soon became an abiding concern for me. My first paper on this dealt with the application of the transition-state theory to the interpretation of rates of coupled hydrogen transfer oxidation-reduction reactions involving semiquinone radicals. The paper also dealt with applying quantum-mechanical methods to calculate the correlation of rate with overall calculated energy. This was applied, with encouraging results when compared with experimental work on such systems by Michael Szwarc. He was also then at Manchester, and was interested in such analyses. Szwarc later moved to the USA. He became one of the most important polymer chemists of the 20th century with his work on ‘living polymers’.
Entanglement in a non-local world
By the way, what is ‘entanglement’?
It is really the basic idea of quantum mechanics. You think of things being separate. There is an apple on the table and there is a glass on the table, and these are two very different things. But the apple will be described, at the basic level, by a wave function. For example, there would be a pigment in the skin of the apple, which is what makes it red. Well, that will be a molecule and I could calculate the structure of that molecule. In other words, that would be a part of the quantum mechanical interpretation and that would hold for the whole thing. A wave function, which characterises the nature of the molecule, has a shape and a density. But it doesn’t stop at the surface. It gradually decays to infinity exponentially. The molecules in the glass on the table also have such functions and the functions of the glass and the apple will interpenetrate and intermingle. So a more correct description of the apple and the glass would be that the wave functions of these two objects are interacting and in that sense entangled. That is a hint of the basic idea of entanglement in terms of electrons only. Technically, it gets more complicated, dealing with issues of coherence and decoherence and leading to the possibility of quantum computing, and teleportation, for example. Every particle in the universe can in principle be entangled with every other and there is, in principle, a wave function of the Universe.
What is that?
We don’t know. It doesn’t matter that we don’t know it. It has to exist. It will probably never be calculated because it is too complicated. So any wave function that we calculate is just a subfunction of that wave function of the universe. But the fact of entanglement is very important. That is what we call ‘non-locality’ and it is the thing that puzzled Einstein for several decades.
It puzzles most of us. Does it puzzle you?
I am marginally less puzzled than I used to be. Let us put it that way. Let us say that I accept it. I live with it, so to speak. I think Richard Feynman thought that, ‘if you try to lie awake at night thinking about things like that, you probably go mad.’ But the issues have become a little clearer. I can go to sleep fairly peacefully, accepting the fact that it is a non-local world.
Yes, it’s a non-local world. I’m going to delocalise you from Manchester way back to 1972 and Australia. What was it like then?
Actually, I delocalized first to Bristol University following the very untimely death of Meredith Evans in my third year in the North. His death resulted in a dispersal of staff and research students who had been working with him. Almost without exception, their subsequent research careers were important, some extremely so.
I began a research collaboration with M.H.L. Pryce, who had left the Chair of Theoretical Physics at Oxford to head the Bristol Department. This was in the quite new area of crystal field theory, which was revolutionizing our understanding of the electronic structure of transition metal ions. This is of paramount importance in electron transfer processes and enabled me to make quantitative predictions. Pryce was incidentally a near-contemporary of Turing, and Hodge’s biography contains an interesting account of their interaction. Another person who influenced me strongly in those early days was David Bohm. He had just put forward the de Broglie-Bohm interpretation of quantum mechanics. There was a very small group who met with him over a period to discuss and try to work out problems associated with it. It was a very deep problem, which we found immensely stimulating.
My further time at Bristol University was spent in a wide variety of quantum theoretical and allied experimental work. A recurring element of the work was the new and challenging field of electron transfer.
I returned to Australia, to the University of Sydney in 1971. I hadn’t intended to return. I was embedded in England as you might say, but the opportunity came up to start a new department. It was the department of Theoretical Chemistry, in Sydney. There wasn’t such a department at all in Australia, and it promised be quite an interesting and exciting venture. By that time I wanted to move. For various reasons the obvious place to go was the States but, for family reasons, that was out.
I have no doubt that your wife was quite keen to come back to Australia.
She was. She wouldn’t have liked to go to America. Let’s put it that way. I didn’t think of coming to Australia as a necessarily permanent move. But, it generally turns out that things are more permanent than you think – which was not a disappointment. So I came back and we did establish this department, and it was the only one in the country. We had a very vigorous undergraduate teaching course which attracted a large number of very talented students. Many of the students went on with highly successful careers in theoretical or experimental research or development of computational methods. Some are running some of the world’s largest supercomputer centres. We also set up summer schools, which helped to spread theoretical advances around the country. It really, as you might say, lit the country up in that way. The research that we were turning out was of a very high quality and volume. It was altogether a very exciting time. The department’s success was due to the fact that a number of highly outstanding scientists quickly joined me. Robert Gilbert, Sture Nordholm, George Bacskay and Pieter Schipper were particular towers of strength.
Now that you are ‘emeritus’, do you keep up with the chemical work?
I have not stopped. ‘Emeritus’ simply meant that I changed my description and I didn›t do any more teaching or administration. Fortunately, I had been supported by the ARC from the moment I arrived, and I still am. I continue to enjoy my collaboration with a very distinguished colleague, Jeffrey Reimers, whose interests strongly overlap with mine. I am also in contact with the condensed matter theoretical physics community which is resulting in fruitful collaboration. Partly as a result of this, I am beginning to see how much the diverse electronic structural and dynamic phenomena with which I have been long concerned are underlain by deeper apparently simple but quite profound quantum insights
Molecular electronics and the ‘special pair’ of photosynthesis
You have been recognised by most of the academies, including the American academy, the Royal Society and others. And you got the Welch prize. Was that a surprise?
Out of the blue, yes. Any recognition I have had has always been out of the blue.
Looking at the impact of your field, it has had tremendous kinds of repercussions in all sorts of areas, electronics and otherwise. But, going back to photosynthesis, which is electronics these little plants are doing all on their own – how does that work quantum mechanically?
The simplest systems are the bacterial photosynthetics. They are a little bit simpler than the green leaf ones. I was saying before, when we were talking about how in order to get reactions going, that you have to put some energy into the systemand this is commonly thermal energy – heat. But you can also use light – visible or near ultraviolet from the sun. Nature discovered that you could make molecules which would absorb the energy from the sun and could store it. This energy from the sun is atomic energy, which people forget about. The absorbed energy could then feed into something in the middle, which could then knock an electron out. That electron would then whip down to the other end and would sit on a quinone, and would reduce it. That is the first step to synthesising carbohydrate. So we have the energy coming in from the sun and it strikes these acceptors of the energy. They are arranged in beautiful geometric patterns – lovely patterns only because that is the most economical of energy. Then they funnel that energy down to what is called the ‘special pair’. The electron is flipped out of the special pair by that energy. In about a picosecond the electron hits the quinone. Then out at the other end flows the carbohydrate: the leaves, the branches and, in our case, our tissues and our bodies. So you have an electron transfer reaction, which is a photochemical electron transfer. Our problem is to find out what it is and its details.
When I began in Manchester, it was possible to do very simple parameterised calculations on molecules – quantum mechanical calculations. At the time I left England, at the beginning of the seventies, it was just possible to do a ‘serious’ calculation (that is, one using only the fundamental physical constants) on a single water molecule. You could do approximate calculations. By the mid-seventies, you could do a serious calculation ona pair of water molecules – a water dimer. There are three water dimers. They differ only by small amounts of energy, which would have been impossible to calculate earlier. The water dimers are very important to living systems, particularly with hydrogen bonding. What was happening was that we were improving our methods of calculation all along the way. But the difficulty of the calculation can go up at to the fourth power of the number of functions – higher for more exact calculations.This makes great demands on computer power.Moore’s Law, which predicts the essentially exponential increase of computing power over time, was helping us along the way. But we also had to improve the efficiency of the calculations. That is where Thales came in. Kohn and Sham brought in the density functional method of calculating, not the wave function directly, but the electron density. That made it much easier. A combination of these advances means that we are now able to consider increasingly more complex systems.
In about the late eighties and nineties with JR Reimers, on the photosynthetic system, calculations here use a bit of a trick – ‘divide and conquer’. The important reaction centre is in the middle and it is surrounded by a great protein network, like a basket, which we treat rather more approximately. The bit in the middle we treat with much more precision. So we have many atoms, of which the middle reaction centre atoms are treated rather carefully. We have to account for the vibrations of this centre. We have four million vibrational states. Right in the middle we have these two molecules, over which, an odd electron is distributed. This electron is going to jump out to start the reduction reaction. These vibrational states give a very detailed understanding of the reaction mechanism. When I say ‘the photosynthetic system’, there are many natural varieties. There areabout 50 different ones and the reaction centre is different in each one.
I have mentioned that electronic transition that got Taube so excited. We predicted that there would also be that sort of transition in the photosynthetic centre, and it has been found. When you look at that transition, you can actually check back on your calculations and this all ties together. So quantum mechanics gives you a pretty good picture of what is going on. Although there is still an enormous amount yet to be done. For example, the electron can choose between two almost identical pathways to travel down to reduce the quinone, but it always obeys European traffic rules and keeps to the left. Why, we don’t yet know.
Nano and molecular electronics
A final technical question on the future of your work and its influence on nanotechnology – those tiny wires and various other aspects. How much do you think that work has influenced the progress in that field?
Very closely. Typically, the sort of thing that Taube would do, would be to take an ion and then link it to a bridging molecule with another ion at the other end – this was his big innovation. So, instead of these two ions whirling round and colliding in solution, you knew exactly where they were. They were connected by this bridge. A lot of our research was on working out how the electron gets from one end to the other through this bridge.
One of these things, that people again did not at first believe, was that, if that bridge were made of a non-conjugated ‘aliphatic’ molecule, like paraffin, you could get electrons to travel through it. You get paraffin in petrol – paraffin wax is an electrical insulator that used to be in telephones. If you attach something with a mobile electron to this ‘dead’ bridging molecule and attach an acceptor at the other end you could actually get transfer at a measureable rate. People found it hard to believe that. But we were able to show that you can. Collaborative theoretical and experimental work, with Australian and Dutch groups, showed that you get transfer at almost picosecond rates at around eight Angstrom separation through such a bridge. I reported on this at the first international Bioinorganic meeting in Florence.
The point is that what goes for a hydrocarbon molecule will also go for a protein molecule. A protein molecule is again a non-conductor. You can’t light up your house by putting protein between the light bulb and a dynamo. It is accepted now that electron transfer through bridges is what is going in your body. For example, there is an enzyme called Cytochrome C, whose catalytic action depends on an electron travelling through its protein network. It travels from the iron atom in a haem group at the centre to a substrate at the periphery. It does it in milliseconds. If it did it any faster, we would just fuse. So that is what nature does. It attunes the electron transfer rates, it attunes the lifetimes with great precision.
Referring back to the previous topic we have, in our group, devised a solar cell which is biomimetic. We asked, ‘What has nature done over the eons?’ It has engineered these photosynthetic molecules to within fractions or hundredths of fractions of an Angstrom. That is why they work. You get 100 per cent efficiency of the light energy being transformed into electronic energy in the reaction centre. What we have here are biological electronic devices working at the nanoscale level. Over 25 years ago, I realised the significance of what Feynman had said much earlier. Do you know of that famous essay of his called ‘There’s plenty of room at the bottom’, which he gave in 1959?
Yes, it’s brilliant.
People say that you can write the Lord’s Prayer on the head of a pin – isn’t that wonderful. But Feynman said, ‘If you think about how small atoms are and you think about a crystal surface and putting things on that surface, you are down in orders and orders of magnitude. And, if you can assemble molecules on a crystal surface in an engineered way you would have a complete new technology.’
Where do you think all this is going to lead, looking at the future and the way our lives might change as a result?
It is very hard to predict. These general ideas of ‘molecular electronics’ began in about the 1970s. There was a visionary physicist named Forrest Carter at a US National Laboratory who made beautiful pictures of circuits made just of molecules. He showed a design for a transistor which was just a molecule, which he thought could be assembled on a surface as part of a nanoscale circuit. Around the same time, Mark Ratner and his student Ari Aviram, also in the US, published a seminal paper in which the fundamental principles underlying molecular switching etc. were enunciated. This gave rise to a brief spurt of great enthusiasm as to what might be done. In fact, I was in at the beginning of the literature of this. A journal called Journal of Molecular Electronics was produced in 1985, initiated by a friend of mine, Robert Munn. He was then at Manchester University and was a former colleague at Bristol University. I was involved in this John Wiley journal as a member of the Editorial Board. We kept it going for about two to three years. The problem was that little was really happening. We had great difficulty in getting articles in the field of ‘molecular electronics’. The issues got smaller and finally Wiley changed the title to Optics and Opto Electronics.
By this time the Scanning Tunnelling Microscope had been invented. With this you could see a single atom – I wouldn’t have believed it, but it can be done. And we now have a laboratory doing just that. As is often the case with innovations, it is much simpler than you think. In fact, an American scientist in one of the National Laboratories had almost done it 20 years before, but they cut his funding. He had got it to the point where it worked but it wobbled too much, and he was not allowed to continue. But these days you can knock this microscope up in an electronics workshop in a couple of days – not a very good one, but it would work.
Everything took off at that point. It is all very well talking about assembling a single molecule on a surface but nobody would really believe it unless they could see it. Nowadays there are highly successful journals like Journal of Nanotechnology Letters or Nanoletters and others. There are so many papers coming in that they could not possible print more than a small fraction. However, even though there are many advances, even though all sorts of experiments have been done, the basic simplest thing to do is synthesise molecular wires. These are molecules, and you have to attach them to a nanoelectrode. The way in which you do this is critical. You may, if you are lucky, form a self-assembled monolayer of these on a surface and you can see it in a Scanning Tunnelling Microscope image. But it is not like looking at a picture of your favourite dog. You have to work out what that image represents, as it is not really a picture but an electron density patterns. For example, in our recent work in collaboration with Jens Ulstrup’s STM group in Denmark, Reimers and I have examined attachment of thiol radicals. These serve as anchors for molecular wires to gold nanosurfaces. We find that instead of simply forming a bond with the surface, the radical acts as a ‘gold miner’, digging out a gold atom from the surface and then sitting on it like a monocycle, ultimately forming a supersurface, is very unexpected. That involves highly complex calculations to work out exactly what you’ve got. Advanced quantum theory and large-scale computing is absolutely essential here.
So we are at the stage where we have all kinds of recipes – it is like having a cook book with all these recipes in it – but with no proper stove and few instructions. But ultimately molecular electronics, the most fundamental form of nanotechnology, must happen. This stage is now a slow one, but we are getting better every day. I wouldn’t like to predict what we will be able to do. I think the possibilities are limitless.
A final question – rather a more personal one – about your son, who has become a musician. We have actually heard his playing work during this video. How did he come to be a musician rather than a theoretical chemist?
That is interesting. It was my daughter Julia who took the academic scientific turn. She began as a plant biophysicist doing very original work on electric field influences on plant cell growth. Whilst on a Fulbright stint in the US with Hepler, she made the first ever measurements of rates of processes going on inside the intact living plant cell. But she has changed direction completely and now works on human problems in medical research, specifically on pain, using many techniques including f-MRI. She is deeply absorbed in this. Like David, her early life was in England.
David was at Clifton College in Bristol, which had a good musical background. However, he didn’t think of music as an actual profession. In fact, they had a tied scholarship to Cambridge in law and that was what he hoped to do. He came out to Australia, finished school and did an arts law degree. I felt guilty that he had not been able to follow the Clifton option up. But it turned out that it was possible for him to go to Cambridge and to move on to law. A College was arranged and it was all fixed up. At the very last minute he said, ‘I don’t want to do it. I want to be a composer.’ So he followed this path.
He did a music degree here in Sydney and then he wrote to Princeton, which was the leading music school in the US, asking about a graduate fellowship. I understand he was the first person ever to get one there from Australia. He was at that time very interested in 20th Century music. It is very mathematical. Milton Babbitt, who was the great guru of 20th Century music, was there. Babbitt was David’s supervisor. So David’s PhD was in that kind of area, which was theory mainly. But he gradually realised that this sort of music, however ingenious, was so complex that the human ear has great difficulty in registering it. It is like having a Bach fugue with literally 12 voices instead of four. You can appreciate it by reading the score, but you can’t easily hear it. Possibly, in the future, we will have human ears which have been improved to that point! So he moved away from that kind of composition. He wants to re-establish links with the great classical tradition. He would call himself a neo-classical composer, if pressed. These are difficult times for composers. His work is played mainly overseas.
Thank you very much
© 2024 Australian Academy of Science
