Fullerenes are one of only 3 types of naturally occurring forms of carbon (the other two being diamond and graphite). They are molecules composed entirely of carbon, taking the form of a hollow sphere, ellipsoid, or tube. Spherical fullerenes are sometimes called buckyballs, while cylindrical fullerenes are called buckytubes or nanotubes.
The molecule was named for Richard Buckminster Fuller, a noted architect who popularized the geodesic dome. Since buckminsterfullerenes have a similar shape to that sort of dome, the name was thought appropriate.
Fullerenes are similar in structure to graphite, which is composed of a sheet of linked hexagonal rings, but they contain pentagonal (or sometimes heptagonal) rings that prevent the sheet from being planar.
The smallest fullerene in which no two pentagons share an edge (which is destabilizing — see pentalene) is C60 (buckminsterfullerene), and as such it is also the most common.
The structure of C60 is that of a truncated icosahedron, which resembles a round soccerball of the type made of hexagons and pentagons, with a carbon atom at the corners of each hexagon and a bond along each edge. A polymerized single-walled nanotubule (P-SWNT) is a substance composed of polymerized fullerenes in which carbon atoms from one buckytube bond with carbons in other buckytubes.
Prediction and discovery
Until the late twentieth century, graphite and diamond were the only known allotropes of carbon. Then, in molecular beam experiments, discrete peaks were observed corresponding to molecules with the exact mass of 60, 70, or greater numbers of carbon atoms. Harold Kroto, from the University of Sussex, James Heath , Sean O'Brien , Robert Curl and Richard Smalley, from Rice University, discovered C60 and the fullerenes. Kroto, Curl, and Smalley were awarded the 1996 Nobel Prize in Chemistry for their roles in the discovery of this class of compounds. C60 and other fullerenes were later noticed occurring outside of a laboratory environment (e.g. in normal candle soot). By 1991 it was relatively easy to produce grams of fullerene powder using the techniques of Donald Huffman and Wolfgang Krätschmer .
As of the early twenty-first century, the chemical and physical properties of fullerenes are still under heavy study, in both pure and applied research labs. In April 2003, fullerenes were under study for potential medicinal use — binding specific antibiotics to the structure to target resistant bacteria and even target certain cancer cells such as melanoma.
Fullerenes are not very reactive due to the stability of the graphite-like bonds, and are also fairly insoluble in many solvents. Researchers have been able to increase the reactivity by attaching active groups to the surfaces of fullerenes. Buckminsterfullerene does not exhibit "superaromaticity". That is, the electrons in the hexagonal rings do not delocalize over the whole molecule.
Other atoms can be trapped inside fullerenes, and indeed recent evidence for a meteor impact at the end of the Permian period was found by analysing noble gases so preserved.
In the field of nanotechnology, heat reistance and Superconductivity are some of the more heavily studied properties.
A common method used to produce fullerenes is to send a large current between two nearby graphite electrodes in an inert atmosphere. The resulting carbon plasma arc between the electrodes cools into sooty residue from which many fullerenes can be isolated.
Although buckyballs have been thought in theory to be relatively inert, a presentation given to the American Chemical Society in March 2004 and described in an article in New Scientist on April 3 2004, suggests the molecule is injurious to organisms. An experiment by Eva Oberdörster at Southern Methodist University which introduced fullerenes into water at concentrations of 0.5 parts per million found that largemouth bass suffered a 17-fold increase in cellular damage in the brain tissue after 48 hours. The damage was of the type lipid peroxidation, which is known to impair the functioning of cell membranes. There were also inflammatory changes in the liver and activation of genes related to the making of repair enzymes. At the time of presentation, the SMU work had not been peer reviewed.
Diffraction of fullerene
In 1999, researchers from the University of Vienna demonstrated that the wave-particle duality applied to macro-molecules such as fullerene.
- Wave-particle duality of C60, M. Arndt , O. Nairz, J. Voss-Andreae, C. Keller, G. van der Zouw, A. Zeilinger, Nature 401, 680-682, 14 October 1999
Fullerenes in mathematics
In mathematics a fullerene is a trivalent
convex polyhedron with pentagonal and hexagonal faces.
Using Euler formula one can easily prove that there are
exactly 12 pentagons in a fullerene. The smallest fullerene is C20, the dodecahedron. There are
no fullerenes with 22 vertices. The number of fullerenes
C2n grows rapidly with increasing n = 12,13, ... For instance, there are 1812 non-isomorphic
fullerenes C60 but only one of them, the buckminsterfullerene, has no pair of adjacent pentagons.