Fullerene carbon: Implications and applications of reactive oxygen species generation under irradiated and non-irradiated conditions
Understanding the ramifications of nanomaterials in natural systems presents a major challenge to environmental engineers. Utilizing fullerenes, a quintessential type of nanomaterial, three central questions regarding the interaction of nanomaterials with the environment were explored in this dissertation. First, generation of reactive oxygen species (ROS) by fullerene in the dark has been pointed out as a possible culprit in the toxicity of these materials towards human cells and bacteria. What role does ROS actually play in this effect? Second, the fundamental properties of fullerene molecules make them photochemically active. To what degree does aggregation in aqueous systems affect ROS production under illumination and can this effect be modeled? Third, fullerenes have been demonstrated to interact with microorganisms deleteriously. What is the source of these negative effects and can they be exploited to detect ROS generation levels from fullerenes?
Determining the possibility of dark ROS generation by fullerene varieties was predominately done via two methods: XXT a chemical assay that measures superoxide by its reduction and the oxidation of NADH both of which were monitored spectrophotometrically. In the presence of XTT no significant superoxide generation occurs above background levels when three major varieties of suspended fullerene aggregates (aqu/nC60, THF/nC60, and fullerol) were present with the cellular reductant NADH. However, aqu/nC60 reacted with superoxide in suspension indicating an antioxidant effect. Oxidation rates of NADH in the presence of three aggregate types matched control values indicating negligible potential ROS formation via redox cycling.
Experimental detection of ROS via fullerene photosensitization was accomplished by electron paramagnetic resonance (EPR), spectrofluorimetry, or XTT assays. These results indicate that fullerol is the only significant singlet oxygen producer amongst the three aggregate types. Fullerene ROS production modeling confirms that: loose fullerol and dense aqu/nC60 aggregate structure could explain experimental results.
Bacteriophage inactivation enumeration was employed to determine the effect of fullerene on viruses and as a biological assay for ROS detection. Photosensitized ROS generation and subsequent virus inactivation demonstrates that fullerol is the most effective inactivating aggregate under illuminated conditions. Mechanistic pathways to inactivation involve the reaction of singlet oxygen with phage capsids and DNA.