Jean-Marie Lehn


Interview, December 2001

Interview with Professor Jean-Marie Lehn by Joanna Rose, science writer, 8 December 2001.

Professor Lehn talks about how the Nobel Prize changed his life; the development of supermolecular chemistry (3:52); his pathway from philosophy via neurochemistry to chemistry (9:25); and about storing information in supermolecules (16:00).

Interview transcript

Welcome to the Nobel interview, Professor Jean-Marie Lehn. You are one of a few French Nobel Prize winners I would say. How did the prize change your life or academic work?

Jean-Marie Lehn: It didn’t change my work because when you are a scientist you have your own way of looking at things and the prize doesn’t change that so much. It may make you think about starting to change fields. That is possible. On the other hand, it changed life quite a bit. First of all one has more to speak about science and chemistry because of this resonance the Nobel Prize now has in the society, in newspapers, in media. You are supposed to be interpreter of science in some ways. To speak in more public occasions which we must do. One may or may not like it but one must do it because it’s a way to talk about your field. To talk about your colleagues. To talk about what’s going on in the area. Maybe more generally even to talk about what science is doing in society. And this is the most important I would say. I like to talk about what chemistry has been doing, which often is underestimated and very much neglected. But more generally I think just trying to tell people that science is part of culture. Not only literature and arts. Science is also part of our culture. It penetrates our life in practical terms even more than any other forms of human culture.

Science in general and chemistry in particular.

Jean-Marie Lehn: Yes, chemistry is so insidious I would say that you often don’t notice it. We are sitting here, and I think probably most of what we are wearing is chemistry. Most of the way in which … when we are sick what do we do? We use pharmaceuticals. What is pharmaceuticals? Molecules. Chemistry. So we meet chemistry all the time, all day long. It’s hidden. You don’t see it, in most cases. That’s one of the problems. Chemistry is not in the forefront. But it’s always there. People should realise that.

That’s what you are doing in France. You talk with the public.

Quote… a rational approach to society problems would be very good for people …

Jean-Marie Lehn: In my laboratory I do research, but I try when I have an occasion which is worthwhile to illustrate. I wouldn’t say defend. I don’t think science can be defended but a defensive attitude. It’s more to illustrate and say what’s going on. Also in present society having more of what I would call a scientific, maybe a rational approach to society problems would be very good for people.

After the Nobel Prize, did you consider changing fields?

Jean-Marie Lehn: Yes, you consider it but you know, on the other hand I’m of the type where I like to deduce things from one another. So the field has evolved enormously. And in fact, what we are doing now has absolutely nothing to do with what I got the Nobel Prize for. But it is deduced from it. It came out rationally by expanding it and by going to other areas. It’s a total change in subject in the type of the things we are doing in the laboratory. But it is not a change in the direction. It’s an evolution which when you look back at it looks quite logical.

Super molecular chemistry this is your field. You mean that the field has developed so fast and …

Jean-Marie Lehn: Yes, what happens it is an area which some people say a bit diffused which is true because it’s very wide. It has the interface with physics on one hand, material science. With biology, medicine, on the other hand. And of course at the core is chemistry. So because of this very large and wide interest the field makes many developments in many areas so that it may look very, very different. The general idea in this area is the following. It’s that molecules are single entities, but in the real world they are never alone. These molecules are always among other molecules. And the properties of collectivities of molecules are not the same as single ones. That’s what we’re interested in. What happens to the real world molecules which are always together with others. They interact. They do things together. And I sometimes call it molecule sociology. It happens in a society of molecules.

Let me give you an example which I think also for people who will be looking at this interview may be telling them what is the real essence of it.  Water, which I have in this glass, is a very simple molecule. It’s three atoms. One H bound to an oxygen, hydrogen oxygen hydrogen. A triangle.  An isolated water molecule can be studied but it has no melting point, no freezing point, no evaporation. And so if a glass of water – this can freeze. A single molecule cannot freeze. So obviously this is concerned with super molecular chemistry. What does the collection of water molecules do? These are many, many, many water molecules. They’re liquid. A single molecule is a gas.  What are the properties of this? And this is what we are trying to understand. What happens when molecules are together? What are the properties? And this new property of being able to freeze is something which does not exist for the single molecule.

What is the relation between the properties? For example the society of molecules and their structure. Can you digest properties from the structure.

Jean-Marie Lehn: That’s exactly the point. You see there is this big question which is a philosophical one. Can one reduce everything to atoms and particles? I would say although I am convinced there is an explanation in everything, I don’t believe one should do the reduction. I call it a deduction. In other words, you cannot reduce the melting or the freezing of water to the single molecule. But you can deduce it from the properties of the single molecule which interacts with other single molecules. In other words reduce it I don’t think this is correct because you cannot reduce it but you can’t deduce the property of the collectivity from the properties of the single.

Quote… you cannot reduce the thinking to atoms. Atoms don’t think …

So for me the matris is getting more and more complex. Starting from atoms, molecules, super molecular entities, and so on. And each level new properties appear which do not exist at the level below but can be deduced from the level below. So you cannot reduce to it but deduce from. For instance we think OK. You cannot say thinking can be reduced to atoms. But it can be deduced from atoms. We are thinking with the brain which is made from atoms, molecules and all that. So obviously there is a deductive relationship between the atoms which form our brains and eventual thinking. But you cannot reduce the thinking to atoms. Atoms don’t think. So this is my view of things that you can deduce more and more comparatively higher and higher levels of complexity from the ones below. But you cannot reduce it.

There is this physicist Philip Anderson, also another prize winner, who said ‘More is different’.

Jean-Marie Lehn: Yes, in some ways. You can … this is a very condensed way of saying it. For instance more water molecules is different but it’s still water.

More water molecules is different from the one.

Jean-Marie Lehn: From the single one, yes. But when you know exactly the cup of one water you can deduce the properties of the liquid water from the single molecule but you have to take into account everything that happens in the collection. So more is different. More water makes liquid water. One single water is not liquid water. More is different. I woul’d subscribe to that too.

What kind of molecules do you study? All super molecules?

Jean-Marie Lehn: Life is short. And the day is only 24 hours. That is the problem. We would like to have days with many many more hours and life’s much longer. So you have to select things. So we started with trying to understand simple processes. The idea is the following. The way I started is sort of an inductive way. It starts from something small and you see it’s wider than you initially thought. And then you go ahead with it.

When did you start?

Jean-Marie Lehn: 1967. 66/67. But it started in what you might call an awkward way. It didn’t lead to that. I didn’t call it super molecular chemistry at the start because you don’t realise when field is very broad you get the broad ideas only when you see what you are doing is more general than what you thought it was. So I was in fact interested in neuro chemistry which seems to have nothing to do with it. In fact I was interested in philosophy first. I wanted to study philosophy first.

Philosophy of science or philosophy?

Jean-Marie Lehn: Philosophy in general. Philosophy of knowledge. That’s what I was interested in. I was extremely interested when I was a youngster in the way we think. What is in there? Of course a fantastic problem. But you soon realise that I don’t think we have an answer to that. So let’s be more modest and study something where progressively we build up this area. At least approach it. And so I thought neuro chemistry, neuro system, has something to do with thinking so why not start there?

And then if you are a chemist you realise that the neuro system is extremely complicated and you cannot approach it like that. And one simple way of approaching it is to try to see if there is a process inter neural system which is simple and which one might have access to and might study. This is the following which I became interested in. In the nerve membrane the propagation of the electric influx, the neural influx occurs by pumping or by exchanging across the membrane of the nerves of two types of ions. Entities called ions. Potassium and sodium. That’s exactly how our nerves function. These run along like this.


Jean-Marie Lehn: Bionic but it’s an electric charge. A positive charge not a negative one. And so I thought these nerve membranes must possess molecules which are able to make the difference between a sodium and a potassium. What’s the difference? Both of these entities are small spheres. And have one positive charge. But one is a little bit larger than the other one. The potassium is a little bit larger, 30% larger, than the sodium. How do the molecules make the difference? If they don’t make it we have a short circuit. We are dead. So they must make the difference. And so we tried to understand how you can distinguish a given sphere from a little bit larger one.

And you build molecules which have cavities where you can adjust the cavities. We call that crypts. Kryptons. And you can adjust the cavities so they are smaller or larger and indeed it works. When they’re smaller sodium goes in and the larger potassium goes in and so on, so you can play with this That was the start. Then you realise what have you done? You have done something. You are able to build molecular entities which are able to make the difference between smaller spheres, larger and larger and larger. In other words they recognise a given sphere.

Quote… all the processes which occur in our organism are molecules sitting together and recognising each other …

This is molecular recognition. Molecules that recognise each other. Then you say if you can recognise spheres you can recognise more complicated objects. And obviously in biology all the processes which occur in our organism are molecules sitting together and recognising each other. When we have an antibody against a given sickness our molecules recognise the antigen and they sit on it and do something with it. They hinder it and inhibit it. When a virus penetrates into our body it goes into a cell by recognising molecules on that cell. Or when in our organism killer cells, which defend our organisms against abnormal cancer cells, when they do their job they find the cancer cell. Recognise that this is a cancer cell and not a normal cell and then destroy the cancer cell. That’s what they are supposed to do.

Now these are very complicated molecules. So we thought, as often in science we have to simplify things to understand them better. So the general idea was let’s develop the area of molecular recognition. How do molecules recognise each other and develop the basic principles of that which then of course operate in all complicated molecules or biology also. Starting small. That’s where it started. Studying molecular recognition. And then if I may add one thing once you realise that molecular recognition is something you’re understanding which is a very widely important subject in biology and everywhere when molecules get together. Then you ask yourself what’s the basis of molecular recognition? The basis of molecular recognition is interaction between molecules. What happens between molecules? Not inside the molecules.

Exchange of information.

Jean-Marie Lehn: Yes exchange of information and sitting together. Just attaching to one another. Like water binds to another water. And then you realise that there is a chemistry one should develop which is not the chemistry of molecules and for the general public, let me say the chemistry of molecules deals with the way in which you construct molecules. Molecules are like houses made from bricks which are the atoms. So you connect the atoms and you build nice houses.  Molecules. But in a village of many houses and people interact with each of these houses, they make a village.

This is the sociology part.

Jean-Marie Lehn: That is the area and then you get into super molecular chemistry and you consider not just the single houses, the single molecules, but the general organisation of all those when they interact with one another and so on. Sometimes I also say atoms are letter. Molecules are the words.  And super molecular entities are the sentences and the chapters and of course – science is the book.

This is really a fascinating subject. My last question, when you talk about communication, language is communication, you also talk about storing information in super molecules.

Jean-Marie Lehn: Yes and this is one of my dada as one says in French.

Which means?

Jean-Marie Lehn: Which means … what I like to express and attach to this aspect. Not so much because it needs it becausein society information is such a big word. And what I usually start with, and conclude with in many of my lectures especially for public or young students and undergraduates and so on, is that chemistry of course deals with matter. Definition of chemistry can be given to science of matter.

Molecules are matter.

Quote… molecules have information and it is stored in the structure …

Jean-Marie Lehn: And its transformation. What is matter? How to transform matter? Problem. Chemists also know how to take one thing and make something else out of it. That’s one thing. Matter and energy obviously. But it also deals with information. And you immediately realise that. I told you a moment ago molecules recognise each other. How can I recognise you? I met you yesterday OK. This morning I recognised you because I had information about you. How do molecules recognise another molecule? Because they have information. So there must be information even if it is not expressed. You cannot catalogue it or quantitate it the way information theory define information. Nevertheless molecules have information and it is stored in the structure. That’s molecular. But then the way they interact, the way they get together, this is the reading of this information and that is super molecular.

So I consider chemical systems and in fact that’s one of our major interests now to study programming of molecular systems. Meaning we make molecules that store given information by their structure. You can see the structure. And then you let them interact. This is reading the information. And by this interaction there is something coming out of it. The output which is a given architecture which give some functions. And so of course obviously the basic question, I told you I was interested in philosophy. If you think about all these problems and make it even more general then you realise one thing which is quite evident but it makes you think, when you start with the big bang when the universe started. It started many many many years ago. At present, what we think is the highest evolution of the universe is the human being. Course it doesn’t end here. Things which come afterwards. That is something which is also an interesting question.

But in the meantime, starting with the beginning where there was only energy and then it cooled down and then it make particles and then it make atoms and then molecules. How come the complexification of matter has led to life and to a thinking organism? So as chemists we are dealing with what starts when it’s cold enough in the universe to make atoms and molecules. And then life started later. But from then on the moment it was cold enough to make atoms and molecules chemistry starts. So I think it’s a fantastic problem to try and understand why – what made matter become complex. I have one idea which of course is so broad that you can’t …it’s a philosophical idea. But it’s a scientific also. I think in some ways one could say it’s under the pressure of information. Because matter has become more and more complex, more and more instructed.

They had to do it.

Jean-Marie Lehn: In some ways yes that’s the problem. I don’t like this thing where it looks like a dogma. It had to do it. But in some ways at least without saying that it is the explanation there is a parallelism between the age of the universe, the evolution of the universe and the increase in complexity in some entities in that universe. One of them being the human being. On other planets there may be even more complicated organisms than we are, or whatever, something more complicated. We know the human being. We cannot go beyond that, at least not for the moment, maybe some day we’ll be able to go beyond it. And so I think very small tiny part of that we hope to contribute to understanding how the universe has led to this very complex state and preparing the next complex state.

I really hope we’ll get the answer.

Jean-Marie Lehn: My impression is we’ll not get it so quickly. We’d like to be around when we get it.

And the time is short. Thank you very much for taking the time. Thank you.

Jean-Marie Lehn: Very kind. And thanks to Mr Nobel because it brings people together also.

Interview, December 2001

Interview with Professor Jean-Marie Lehn by Joanna Rose, science writer, 8 December 2001.

Professor Lehn talks about how the Nobel Prize changed his life; the development of supermolecular chemistry (3:52); his pathway from philosophy via neurochemistry to chemistry (9:25); and about storing information in supermolecules (16:00).

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