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.
Exactly what are supramolecular functional materials?
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
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 Schrцdinger – 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.
Two approaches, one single aim
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."