Synthesis of six-coordination proximal base conjugation iron (III) porphyrin complexes and evaluation as a superoxide sensor

Reactive oxygen species (ROS) such as the superoxide anion radical (O₂^-•) play an essential role on normal cellular growth and homeostasis. However, excess ROS generated by perturbing O₂^-• homeostasis under various conditions of oxidative stress induce high radical toxicity, resulting in many diseases such as a cancer, brain and mitocondrial infarction, and inflammation. Therefore, quantitative measurement of O₂ ¹• in vivo is important for clarifying their relationship under various conditions. However, in most cases, the biological significance and mechanism of the O₂ ¹• generation are not well understood yet. We have developed a O₂¹• sensor composed of a thin film of N-methylimidazole-coordinated iron meso-tetra (3-thienyl) porphyrin ((Im)₂FeT3ThP) for the electrochemical detection of O₂^-•. The microsensor displayed high selectivity and activity for the oxidation of O₂ ^-• and showed a linear relationship between electric current and O₂^-• concentration. In this study, we have designed and synthesized a novel hexa-coordinated iron (III) porphyrin compound, which is more stable than the meso-tetra (3-thienyl) porphyrin coordinating imidazoles. This compound was electropolymerized onto the electrode and used as a O₂ ^-• sensor. The redox potential of the electrode suggests that the molecular structure in the electropolymerized film is maintained. This novel modified electrode displayed a high activity for the oxidation of O₂^-• even in the presence of H₂O₂ and showed a linear relationship between the electric current and O₂^-• concentration.