Spectroscopic and photophysical properties of a highly derivatized C60 fullerol

Hydroxylated C-60 molecules, also called fullerols, are a class of water-soluble fullerenes. Here we report the synthesis in acidic conditions of a highly derivatized fullerol (up to 36 carbons per C-60 are oxidized). Spectroscopic investigations (X-ray photoelectron spectroscopy and infrared absorption) highlight the coexistence of both acidic and basic forms for the hydroxyl addends of derivatized C-60. pH titrimetry reveals that, at millimolar concentrations, only ten protons per fullerol molecule are labile. Such a low value, as compared to 36 hydroxyl groups, is explained by the formation of clusters. A UV-vis absorption study performed over a large range of concentrations also points to the aggregation phenomenon. Moreover, this study shows that the clusters of fullerols appear at relatively low (micromolar) concentrations. An electron spin resonance (ESR) study, based on the attack of singlet oxygen ((1)Delta(g)) on 2,2,6,6-tetramethyl-4-piperidinol (TMP-OH), has proved the potential of hydroxylated C-60 for performing efficient generation of singlet oxygen in aqueous solution. ESR measurements, which allow detection and quantification of (1)Delta(g), have also revealed the generation of reactive oxygen species (ROS). The yield of generation of (1)Delta(g), and ROS is strongly correlated to the concentration of fullerol, thus also pointing to the aggregation of fullerol molecules. Exposing glioblastoma cells to oxidative stress in the presence of hydroxylated C-60 and visible light has also been performed. Atomic force microscopy is used to monitor the relevant diminishment of the Young's modulus values for cells exposed to the oxidative stress. These results point to a possible application field of fullerols for performing bio-oxidations.