Active Oxygen Species Generated from Photoexcited Fullerene (C₆₀) as Potential Medicines:  O₂^-•versus¹O₂

Abstract

To characterize fullerenes (C(60) and C(70)) as photosensitizers in biological systems, the generation of active oxygen species, through energy transfer (singlet oxygen (1)O(2)) and electron transfer (reduced active oxygen radicals such as superoxide anion radical O(2)(-)* and hydroxyl radical *OH), was studied by a combination of methods, including biochemical (DNA-cleavage assay in the presence of various scavengers of active oxygen species), physicochemical (EPR radical trapping and near-infrared spectrometry), and chemical methods (nitro blue tetrazolium (NBT) method). Whereas (1)O(2) was generated effectively by photoexcited C(60) in nonpolar solvents such as benzene and benzonitrile, we found that O(2)(-)* and *OH were produced instead of (1)O(2) in polar solvents such as water, especially in the presence of a physiological concentration of reductants including NADH. The above results, together with those of a DNA cleavage assay in the presence of various scavengers of specific active oxygen species, indicate that the active oxygen species primarily responsible for photoinduced DNA cleavage by C(60) under physiological conditions are reduced species such as O(2)(-)* and *OH.

Photodynamic therapy with fullerenes

“…32 In a similar fashion to the tetrapyrrole PS used for photodynamic therapy, 33,34 illumination of fullerenes dissolved in organic solvents in the presence of oxygen leads to the efficient generation of highly reactive singlet oxygen via energy transfer from the excited triplet state of the fullerene.35 However, some recent reports have shown that in polar solvents, especially those containing reducing agents (such as NADH at concentrations found in cells), illumination of various fullerenes will generate different reactive oxygen derivatives, such as superoxide anion. 36 These two pathways (singlet oxygen and superoxide anion) are analogous to the Type II and Type I photochemical mechanisms frequently discussed in PDT with tetrapyrroles. 37 , 38 Fullerenes with their triply degenerate, low lying LUMO are excellent electron acceptors capable of accepting as many as six electrons.…”

“…Yamakoshi et al 36 carried out a photochemical study comparing energy transfer processes (singlet oxygen 1 O 2 ) and electron transfer (reduced active oxygen radicals such as superoxide anion radical O 2 −• ), using various scavengers of ROS, physicochemical (electron paramagnetic resonance (EPR) radical trapping and near-infrared spectrometry), and chemical methods (nitro blue tetrazolium reaction with superoxide). Whereas 1 O 2 was generated effectively by photoexcited C 60 in nonpolar solvents such as benzene and benzonitrile, they found that O 2 −• and OH • were produced instead of 1 Highly water-soluble hexa(sulfobutyl)fullerenes (FC4S) were synthesized by the treatment of C 60 in dimethoxyethane with sodium naphthalide followed by reacting the resulting hexaanionic fullerene intermediates with an excess of 1,4-butanesulfone.…”

Study on the generation mechanism of reactive oxygen species on calcium peroxide by chemiluminescence and UV‐visible spectra

“…The CL signals were not evidently changed, even when scavengers at a high concentration (0.05 mol/L DABCO or tryptophan) were added to the system of MCLA on CaO 2 (Fig. 3) (31,32). This method was also chosen for these experiements.…”

Phototoxicity and cytotoxicity of fullerol in human lens epithelial cells

“…Photoexcitation of fullerene derivatives efficiently produces an excited triplet state (Arbogast et al, 1991;Guldi and Prato, 2000) and through energy and electron transfer to molecular oxygen produce both singlet molecular oxygen (Prat et al, 1999) and superoxide (Yamakoshi et al, 2003). Although the carboxylated water-soluble fullerene derivatives were not found to be phototoxic to B lymphocytes (Irie et al, 1996), the malonic acid derivatives of fullerenes were found to be cytotoxic and phototoxic to both HeLa (Yang et al, 2002) and Jurkat cells (Rancan et al, 2002).…”