Fullerenes: An introduction and overview of their biological properties


Ever since their experimental discovery in 1985, fullerenes have attracted considerable attention in different fields of sciences. Investigations of chemical, physical and biological properties of fullerenes have yielded promising information. Their unique carbon cage structure coupled with immense scope for derivatization makes fullerenes a potential therapeutic agent. Henceforth various potential therapeutic applications of fullerenes have been reviewed in the present paper. These include antiHIV- protease activity, photodynamic DNA cleavage, free radical scavenger, antimicrobial action and use of fullerenes as diagnostic agents.

Carbon, the common element in organic compounds, is known to exist in two allotropic forms, viz, diamond and graphite. In 1985, a third form of carbon called fullerenes was discovered [1]. The group of scientists led by Smalley, Kroto and Curl attempted to simulate the conditions under which carbon nucleates in the atmosphere of red giant stars. In the experiment, a surface of solid graphite was vaporized by irradiation with the laser into plasma containing atoms and free ions. The free atoms and ions were chilled down due to the collision with the helium atoms. Through the collision, clusters containing various numbers of carbon atoms were formed. The clusters were examined in a mass spectrometer, and it was found that clusters that had 60 and 70 carbon atoms dominated, and that most clusters had 60 carbon atoms. In the beginning, the scientists had problem in producing sufficient amount of fullerenes. They had succeeded to prepare only less than 10-15 g. But after 5 years, Kratschmer and Huffmann [2], and then Kroto et al [3] developed new high yielding preparative methods for fullerenes.

These scientists named the newly found molecule after the architect Richard Buckminster Fuller, who created the dome in 1967 with the same shape as the carbon cluster. Fullerenes generated so much interest and excitement among research scientists that the three scientists who discovered fullerenes [1] received Nobel Prize in Chemistry in 1996. Fullerenes were later found to exist naturally in interstellar dust as well as in geological formations on Earth, though only in the ppm-range. Some of these places are Shunga/Russia [4], New Zealand [5] and Sudbury/ Canada [6].

Structure and Properties

Fullerenes are large carbon cage molecules (Fig.1) considered to be three-dimensional analogues of benzene. The most abundant form of fullerenes is Buckminster fullerene (C60) with 60 carbon atoms arranged in a spherical structure. The shape of the molecule, known as truncated icosahedron [2], resembles that of a soccer ball, which contains 12 pentagons and 20 hexagons. Fullerenes fulfill the EULER’s theorem, i.e., if a polyeder is to build a closed structure from pentagons and hexagons; it has to contain exact 12 pentagons. Following this rule, the smallest stable fullerene is C60, which has no two pentagons side by side, making it the most stable structure.

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