Page 416 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

Toxicological Impacts of Nanomaterials 399

dermal fibroblasts (a connective tissue cell). Fullerenes that had been
+
derivatized through carboxylation, C ,Na 2–3 [C O 7–9 (OH) 12–15 ], or
60
3
hydroxylation, C (OH) 24, (likely present as colloidal aggregates) showed
60
much less toxicity compared to a variety of colloidal aggregates of C ,
60
nC thought to be derivatized to a much lesser extent (Sayes et al.,
60
2004). However, interpretation of these results is complicated by the fact
that aggregate size was not controlled in these experiments and the
nC 60 aggregate composition varied with respect to not only functional
groups on the fullerene, but also residual solvent.
Fullerene derivatives have been shown to affect protein configura-
tions, a factor that could play a role in dermatotoxic effects. A series of
fullerene-substituted phenylalanine derivatives was prepared to com-
pare their behavior to related functionalized fullerenes. The presence
of the C 60 substituent alters the conformation of the native peptide
(e.g., from a random coil to a β-sheet), making the conditions under
which conversion to an alpha helix occurs important. These studies
showed no apparent toxicity to cells; however, early studies did not
confirm that the peptide was incorporated into the cells (Yang and
Barron, 2004). When human epidermal keratinocytes were exposed to
agglomerates of a fullerene-based amino acid at concentrations of
0.4 mg/ml, clusters of C 60 were observed within large cytoplasmic
vacuoles (Figure 11.1). Also, agglomerates of the fullerene-based
amino acid at 0.4 mg/ml has also been shown to accumulate along the

Figure 11.1 Transmission electron micrograph of a human epidermal keratinocyte
that was exposed to 0.4 mg/ml of a functionalized fullerene for 48 hours. Arrows
depict fullerene agglomerates within cytoplasmic vacuoles.