Reactive Oxygen Species Induced By Carbon Nanoparticles:a Density Functional Theory Study

Carbon nanoparticles (CNPs) interact with oxygen and induce reactive oxygen species (ROS). Oxidative stress induced by reactive oxygen species (ROS) is the most acceptable mechanism of CNPs toxicity. Investigations on mechanism of molecule oxygen adsorption and ROS generation play an important role in risk assessment of CNPs.Based on density functional theory (DFT), molecule oxygen adsorption on typical CNPs, including fullerene (C60), carbon nanotubes (CNTs) and graphene, were simulated. The frontier molecule orbitals of CNPs were calculated to analyze reaction paths of ROS generation. Also, the influences of typical functional groups (-OH,-COOH,-NH2) to ROS induced by CNPs were investigated by reactivity indexes. The results show:(1) The most stable adsorption configuration is parallel adsorption in the middle of the hexatomic ring on CNPs surface. The adsorption is a spontaneous and exothermic process (AG< 0, AH< 0). Adsorption energy of CNPs and molecule oxygen is 6.80-9.92 kcal/mol. The interactions between oxygen and CNPs are affected by curvature and surface charge distribution of CNPs, and the strength order of interaction is graphene> C60> carbon nanotubes. The charge distributions show that 0.21e charge transfer from fullerene to molecule oxygen.(2) The HOMO-LUMO gap of C6o and CNTs are wide enough (Egap> 0.97 eV) to photoinduce 1O2, while The HOMO-LUMO gap of graphene is too narrow to photoinduce 1O2. C60, CNTs and graphene all form the e--h+ pairs under irradiation and their ELUMO>-4.3 eV (generating potential of O2-), which indicates that they induce O2- via photoinduced electron transfer process. In addition, singly occupied molecular orbital energy (Egomo) of CNPs indicates that fullerene, graphene and (8,0) semi-conductive CNTs cannot absorb electrons from electron-donor NADH and induce O2·- and OH in electron-rich environment like intracellular respiration and (9,0), (6,6) metallic CNTs can induce ·OH as electron transfer media.(3) Functional groups (-OH,-COOH,-NH2) grafting on the CNPs surface change the frontier molecule orbitals of CNPs, but no significant influences on photoinducing 1O2 and O2-. Reactivity indexes hardness are calculated to represent reactivity of charge transfer progress to induce O2-. The results demonstrated that functional groups increase the electron transfer reactivity of C60 and decrease the electron transfer reactivity of graphene and (6,6) CNTs. No significant variation on metallic CNTs. The signifigant change of omo indicates that functional groups grafting on the CNPs surface increase the possibility of electron transfer reaction path to induce O2·- and ·OH when NADH as an electron-donor. The reason is that surface functionalizations increase the electrophilicity of CNPs and make them more stable when obtained electrons.