Reducing the Toxicity of Carbon Nanotubes and Fullerenes Using Surface Modifi cation Strategy - Management of Natural Resources in a Changing Environment - page 180

Fullerenes

Synthesis, Substitution and Modifi cation

The carbon allotrope C 60 , usually referred to as a 'buckyball', is geometrically
shaped as a truncated dodecahedron with a carbon atom sitting at each corner of the
polyhedron (Sayes et al. 2004 ). Synthesis of fullerenes (Grushko et al. 2007 )
involves the vapourisation of carbon fragments into an inert atmosphere in which
they combine and deposit to form fullerenes and other carbon-based compounds,
including CNTs. Another method involves the production of fullerene-containing
soot deposits through chemical vapour deposition. Fullerenes are known to be
essentially insoluble in water. However, their solubility can be increased (up to
2 mM) through appropriate coatings or by being suspended in colloidal solution.
Functional groups may be added to the fullerene in order to increase its water
solubility (Table 4 ). Hence, it is useful to consider the exposure of biological
molecules, such as DNA, to fullerenes in aqueous solutions.
The cytotoxic and photocytotoxic effects of two water-soluble fullerene deriva-
tives, a dendritic C (60) mono-adduct and the malonic acid C (60) tris-adduct were
tested (Rancan et al. 2002 ) on Jurkat cells. It was proposed that the two fullerene
derivatives may interact with the cell membrane in different ways. Tris-malonic acid
fullerene was found to be more phototoxic than the dendritic derivative.

Toxicology Comparison of Fullerenes With and Without
Substitution/Modifi cation

Pristine C 60 can cause membrane leakage. Qiao et al. ( 2007 ) also found that the
functionalization of C 60 dramatically lowered toxicity with no resultant membrane
leakage. It has been reported that attaching water solubilising groups such as
carboxyl or alcohol groups increase the solubility and reduce the toxicity of fullerene.

Table 4 Functional group addition and surface modifi cation for fullerenes (C60)
Modifi cation/Reagents Product References

Hydroxylation/Reaction with
nitroniumborofl uoride and a carboxylic
acid followed by basic hydrolysis

Hydroxylated fullerene Schneider et al.

( 1994 )

Carboxylation Carboxylated fullerene Sayes et al. ( 2004 )

Adding polymers, macromolecules C60-containing polymers,

fullerodendrimers

Kong et al. 2004 and
Nierengarten ( 2003 )

Hydroxyl, amino or carboxylic acid
functional groups to fullerene followed
by coupling to a protected amino
acid or peptide

Fulleryl amino acid and
peptide derivatives

Burley et al. ( 1999 )

Proline derivatives/1,3-Dipolar
cycloaddition of azomethineylides

Fulleroproline derivatives Bianco et al. ( 1996 )