Translocation of C60 from Aqueous Stable Colloidal Aggregates into Surfactant Micelles

Abstract

C(60)'s unique property of forming stable aggregates (nC(60)) in water, despite its exceedingly low aqueous solubility, has been linked to the potential for transport in the environment and exposure to biological receptors. The reversibility of aggregate formation could be an equally important parameter in understanding the ultimate fate of C(60), including accumulation in nonaqueous environments such as biological membranes, micellular phases, and the organic fraction of soils. This study suggests that C(60) molecules in nC(60) readily translocate into nonionic surfactant micelles, a commonly used surrogate for biological membranes. Upon contact with surfactant micelles, the restoration of C(60)'s photochemical reactivity was observed; i.e., efficient production of reactive oxygen species (ROS) such as singlet oxygen upon UVA irradiation. Further evidence to support C(60)'s spontaneous translocation from colloidal aggregates into surfactant micelles is provided, including UV-vis spectral change, visual observation via transmission electron microscope, change in the fluorescence of surfactant micelles, and a reduction in the particle size of the parent nC(60). Experiments performed with Escherichia coli also showed that singlet oxygen was produced when E. coli was in contact with nC(60), resulting in peroxidation of lipids. These findings collectively suggest that micelle/lipid systems could be one of the receptors of C(60) in the environment and provide insights into the previous observations of ROS production in biological systems exposed to nC(60).