Translocation of C₆₀ from aqueous stable colloidal aggregates into surfactant micelles

C₆₀'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 C₆₀ molecules in nC₆₀ readily translocate into nonionic surfactant micelles, a commonly used surrogate for biological membranes. Upon contact with surfactant micelles, the restoration of C₆₀'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 C₆₀'s spontaneous translocation from colloidal aggregates into surfactant micelles is provided, includingUV-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 nC₆₀. Experiments performed with Escherichia coli also showed that singlet oxygen was produced when E. coli was in contact with nC₆₀, resulting in peroxidation of lipids. These findings collectively suggest that micelle/lipid systems could be one of the receptors of C₆₀ in the environment and provide insights into the previous observations of ROS production in biological systems exposed to nC ₆₀.