The Supramolecular world
Nanosciences, nanotechnologies and supramolecular chemistry are today fields of universal scientific interest. Recent proof of this is demonstrated by the 2001 United States budget allocation for nanosciences through the “National Nanotechnology Initiative”. It amounts to some $500 million, which is more than double the amount allocated for the year 2000.
In analogy, a significant number of internationally-recognized research laboratories here in Switzerland are also working in the areas of supramolecular chemistry and/or materials chemistry. Indeed, several research groups are currently well established in these areas, since they began their investigations when this field of science was first introduced. This places Swiss research teams at the forefront of these research domains.
These are materials capable of fulfilling very specific tasks. Supramolecular functional materials are composed of supermolecules and as a consequence belong to the nanoworld.
Invisible to the naked eye, their size scale is in the nanometer range. Nano, from the Greek word nanos meaning dwarf, is a prefix signifying one-billionth (1/1,000,000,000, 10-9). Let us make two comparisons: a chemical bound which links two atoms is generally, on the Angström unit of measurement, or one-tenth of a nanometer, and the diameter of a single strand of human hair is about 100,000 nanometers (0.1 mm).
The field covered by the term nanosciences is very wide, hence it is difficult to give a single starting point. As a consequence, it is perhaps advisable to speak in terms of two separate approaches namely, the nanotechnological and the supramolecular approach.
The nanotechnological approach is based on the individual manipulation of atoms and molecules in order to assemble complex structures with precision. For a many years, this type of approach was thought to be unfeasible. As recently as the 1950s, Erwin Schrödinger – winner of the Nobel prize for physics in 1933 – could not imagine that it would be possible to attempt an experiment on one electron, an atom or even a single molecule. Some years later he was proved wrong by another distinguished scientist, Richard P. Feynman, who was awarded the Nobel physics prize in 1965. Invited by the American Physical Society to its annual meeting on December 29, 1959, Feynman gave a memorable lecture entitled “There’s Plenty of Room at the Bottom”. He said: “The principles of physics, as far as I can see, do not speak against the possibility of manoeuvering things atom by atom.”
The major limitation at that time was a lack of suitable technology. For this problem to be overcome, it was necessary to wait until the early 1980's for the invention of what is effectively scanning tunneling microscopy (STM), and atomic force microscopy (AFM). In 1986, the German Gerd Binning and the Swiss Heinrich Roher were jointly awarded the Nobel prize in physics for the invention of the scanning tunnel microscope.
These instruments were initially conceived for the observation of atomic matter, but have since undergone modifications which have aided their applications in the manipulation and study of atoms. It is perhaps worth pointing out that as an experiment the acronym "IBM" was once written in 35 xenon atoms, carefully laid out over a single surface.
In the supramolecular approach, the conception and realization of nanoscopic systems begins on the molecular scale. The strategies for realizing these systems are in general based on the principle of self-assembly. Molecules are linked together as supermolecules exploiting the non-covalent interactions nature has used for millions of years to assemble large functional biological molecules such as DNA and proteins (enzymes). Equally on speaks in terms of molecular recognition, applying the lock and key analogy to aid the understanding of this process. A receptor molecule (enzyme) can selectively recognize, bind and react with a complementary host (substrate) molecule.
The first scientist to introduce this principle was the research chemist Emil Fischer, at the turn of the 20th century. While studying the reaction of an enzyme with its substrate, Fischer came to the conclusion that in order to recognize and then react, the 'shape' of a substrate molecule needs to be complementary with that of its receptor site. Rather like a key (substrate) with its corresponding lock (receptor). For these findings, he was awarded the Nobel prize in chemistry in 1902.
It was not until nearly 100 years later that the full impact of Fischer's research was fully realized, when the chemist Jean-Marie Lehn began to work in the area he has since named as "supramolecular chemistry". Isolated molecules have properties which result from their molecular structure. However, a molecule is never totally isolated because it finds itself in a chemical environment with wich it is able to interact. From these interactions come new chemical and physical properties. The combination of molecular interactions is the concept on which supramolecular chemistry is based. Lehn received the Nobel chemistry prize in 1987 for his work on the "development and use of molecules with structure-specific interactions of high selectivity".
To obtain supramolecular structures which are “made to measure”, or in other words, functional supramolecular structures, scientists are currently exploiting the possibilities of using molecular building blocks for the controlled self-assembly of larger supermolecules.
The supramolecular and nanotechnological approaches are radically different from the approaches still generally adopted by the industry. The industrial approach is currently referred to as "top-down", or to put it another way, one starts on the largest scale and then reduces the size to develop increasingly smaller devices. In contrast however, the nanotechnological and the supramolecular approaches are referred to as being "bottom-up" - in other words one begins on the smallest (molecular) level and increases the size to move towards larger nanoscale dimensions.
Although different, both approaches have important applications in the field of nanoscience and in the end lend themselves to a common goal namely, the conception and construction of "nanomachines" which will have a considerable impact on new technologies. The adventure is only just beginning, but the wildest dreams are already permissible. To quote Christine L. Peterson, president of the Foresight Institute: "If you're looking ahead long-term, and what you see looks like science fiction, it might be wrong. But if it doesn't look like science fiction, it's definitely wrong."
I envisaged to study philosophy at the University of Strasbourg, but being still undecided, I began with first year courses in physical, chemical and natural sciences (SPCN). During this year 1957/58, I was impressed by the coherent and rigorous structure of organic chemistry. I was particularly receptive to the experimental power of organic chemistry, which was able to convert at will, it seemed, complicated substances into one another following well defined rules and routes. I bought myself compounds and glassware and began performing laboratory practice experiments at my parents home. The seed was sown, so that when, the next year, I followed the stimulating lectures of a newly appointed young professor, Guy Ourisson, it became clear to me that I wanted to do research in organic chemistry.
After having obtained the degree of Licenci?-?s-Sciences (Bachelor), I entered Ourisson's laboratory in October of 1960, as a junior member of the Centre National de la Recherche Scientifique in order to work towards a Ph.D. degree. This was the first decisive stage of my training. My work was concerned with conformational and physico-chemical properties of triterpenes. Being in charge of our first NMR spectrometer, I was led to penetrate more deeply into the arcanes of this very powerful physical method; this was to be of much importance for later studies. My first scientific paper in 1961 reported an additivity rule for substituent induced shifts of proton NMR signals in steroid derivatives.
Having obtained my degree of Docteur ?s Sciences (Ph.D.) in June of 1963, I spent a year in the laboratory of Robert Burns Woodward at Harvard University, where I took part in the immense enterprise of the total synthesis of Vitamin B12. This was the second decisive stage of my life as a researcher. I also followed a course in quantum mechanics and performed my first computations with Roald Hoffmann. I had the chance to witness in 1964 the initial stages of what was to become the Woodward-Hoffmann rules.
After my return to Strasbourg, I began to work in the area of physical organic chemistry, where I could combine the knowledge acquired in organic chemistry, in quantum theory and on physical methods. It was clear that, in order to be able to better analyze physical properties of molecules, a powerful means was to synthesize compounds that would be especially well suited for revealing a given property and its relationships to structure. This orientation characterized the years 1965- 1970 of my activities and of my young laboratory, newly established after my appointment in 1966 as ma?tre de conf?rences (assistant professor) at the Chemistry Department of the Univerity of Strasbourg. Our main research topics were concerned with NMR studies of conformational rate processes, nitrogen inversion, quadrupolar relaxation, molecular motions and liquid structure, as well as ab initio quantum chemical computations of inversion barriers, of electronic structures and later on, of stereoelectronic effects.
While pursuing these projects, my interest for the processes occurring in the nervous system (stemming diffusely from the first year courses in biology as well as from my earlier inclination towards philosophy), led me to wonder how a chemist might contribute to their study. The electrical phenomena in nerve cells depend on sodium and potassium ion distributions across membranes. A possible entry into the field was to try to affect the processes which allow ion transport and gradients to be established. I related this to the then very recent observations that natural antibiotics were able to make membranes permeable to cations. It thus appeared possible to devise chemical substances that would display similar properties. The search for such compounds led to the design of cation cryptates, on which work was started in October 1967. This area of research expanded rapidly, taking up eventually the major part of my group and developing into what I later on termed "supramolecular chemistry". Organic, inorganic and biological aspects of this field were explored and investigations are continuing. In 1976 another line of research was started in the area of artificial photosynthesis and the storage and chemical conversion of solar energy; it was first concerned with the photoly is of water and later with the photoreduction of carbon dioxide.
I was promoted associate professor in early 1970 and full professor in October of the same year. I spent the two spring semesters of 1972 and 1974 as visiting professor at Harvard University giving lectures and directing a research project. This relationship extended on a loose basis to 1980. In 1979, I was elected to the chair of "Chimie des Interactions Mol?culaires" at the Coll?ge de France in Paris. I took over the chemistry laboratory of the Coll?ge de France when Alain Horeau retired in 1980 and thereafter divided my time between the two laboratories in Strasbourg and in Paris, a situation continuing up to the present. New lines of research developed, in particular on combining the recognition, transport and catalytic properties displayed by supramolecular species with the features of organized phases, the long range goal being to design and realize "molecular devices", molecular components that would eventually be able to perform signal and information processing at the molecular level. A major research effort is presently also devoted to supramolecular self-organisation, the design and properties of "programmed" supramolecular systems.
The scientific work, performed over twenty years with about 150 collaborators from over twenty countries, has been described in about 400 publications and review papers. Over the years I was visiting professor at other institutions, the E.T.H. in Z?rich, the Universities of Cambridge, Barcelona, Frankfurt.
In 1965 I married Sylvie Lederer and we have two sons, David (born 1966) and Mathias (born 1969).
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