PHOTO INDUCED OXIDATION OF Fe(N4Py) AND RELATED COMPLEXES

The complex [Fe(N4Py)(CH₃CN)](ClO₄)₂¹ (1) is one of the most active Fe based oxidation-catalysts reported and has been used in DNA cleavage² and oxidation catalysis.³ The activity towards DNA cleavage by 1 was found to be enhanced under UV/Vis irradiation.⁴ This activity increase is dependent on the structure of the complex and the wavelength and power of irradiation. In order to understand the origin of the photo-enhanced DNA cleavage, a study of the photochemistry of this complex itself is necessary. Here we report on the photochemistry of 1 and its alkylated analogue [Fe(MeN4Py)(CH₃CN)](ClO₄)₂ (2).⁵ Irradiation of aqueous, dichloromethane or methanolic solutions of 1 and 2 leads to formation of Fe^III species. Addition of ascorbic acid to the photo product recovers the UV/Vis spectrum of 1 and 2, fully indicating electron transfer oxidation. Oxygen was found to be the terminal oxidant. Recently we demonstrated that in the aqueous solutions of complexes 1 and 2, there are equilibria between two different species and spin states.⁵ The equilibrium between spin states in solution is proposed to be the origin of the effectiveness of 1 in cleaving DNA in water with ³O₂ as terminal oxidant and of the photochemical enhancement of this process.