Oxygen radicals photo-induced by ferric nitrilotriacetate complex.

Abstract This study examined the photo-induced generation of reactive oxygen species (ROS) by the carcinogenic iron(III)–NTA complex. Iron(III)–NTA complex (1:1) has three conformations (type (a) in acidic conditions of pH 1−6, type (n) in neutral conditions of pH 3−9, and type (b) in basic conditions of pH 7−10) with two p K a values (p K a1  ≈ 4, p K a2  ≈ 8). The iron(III)–NTA complex was reduced to iron(II) under cool-white fluorescent light without the presence of any reducing agent, and the reduction rates of the three conformations of iron(III)–NTA were in the order type (a) > type (n) > type (b) as reported previously (Akai K. et al., Free Radic. Res. 38, 951–962, 2004). ROS generation was investigated by electron paramagnetic resonance (EPR) spectroscopy with a spin-trapping technique. Apparent EPR signals attributed to PBN/ · 13 CH 3 and PBN/ · OCH 3 spin adducts were observed after incubation of the iron(III)–NTA complex was mixed with α-phenyl- tert -butylnitrone (PBN) and 13 C-DMSO in an aerobic condition. The addition of catalase effectively attenuated the PBN adducts, but superoxide dismutase enhanced them. Taken together, these results indicate that the iron(III)–NTA complex is spontaneously reduced to the iron(II)–NTA complex by light under acidic to neutral pH, and in turn transfers an electron to molecular oxygen to form ROS.