Myeloperoxidase-induced degradation of N-doped carbon nanotubes: Revealing possible atomistic mechanisms underlying hypochlorite-driven damage of nanotube walls Article uri icon


  • We present a combined experimental and theoretical study dedicated to analyze the human myeloperoxidase (h-MPO)-catalyzed degradation of oxidized nitrogen-doped multi-walled carbon nanotubes (NMWCNTs-Ox) in vitro at 27 °C. NMWCNTs are synthesized by the aerosol assisted chemical vapor deposition (AACVD) technique and are characterized by employing transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), as well as Raman and X-ray photoelectron spectroscopies. H-MPO degradation, involving hypochlorous acid and hypochlorite species, leads to complete removal of CNTs with diameters smaller than 75 nm from the samples. Simultaneously, for larger sizes, it produces the formation of highly deformed NMWCNTs decorated with NaCl nanoparticles, which exhibit reduced cytotoxicity in exposed monocytes studies compared with the initial nanotube samples. Density functional theory (DFT) calculations performed on model nitrogen-doped CNTs are also presented to explore, at an atomistic level, the fundamental aspects underlying degradation. Our DFT results reveal that reactivity of carbon walls is significantly affected around N-doped pyridinic, pyrrolic, and substitutional sites, leading to the existence of HClO molecules physisorbed close to those defects and high local concentrations of chemisorbed ClO species on C atoms adjacent to the N-rich regions. The formation of these hypochlorite molecular islands on the nanotube surface facilitates ClO dissociation producing strongly bound O species and Cl atoms that can be carbon bonded or released into the environment. The previous surface reaction results in the cleavage of the underlying C–C bonds, creating holey regions on the graphitic walls. The continuation of this process would lead to the formation of larger holes on the nanotube surface, allowing, on the one hand, the permeation of ClO molecules to the internal layers and, on the other hand, producing a reduction of the NMWCNTs diameter as observed from our experimental data. © 2021

publication date

  • 2021-01-01

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