ESR Detection of Free Radical and Active Oxygen Species Generated during Photolysis of Fluoroquinolones

Abstract

The photolysis of six fluoroquinolone agents was investigated in neutral aqueous solution by means of ESR spectroscopy. Lomefloxacin (LFLX), sparfloxacin (SPFX), ciprofloxacin (CPFX), enoxacin (ENX) and sitafloxacin (STFX) generated free radicals in the process of photochemical degradation, while levofloxacin (LVFX) did not.The free radicals and active oxygen species observed were presumed to be carbon-centered radical (·C), hydroxyl radical (·OH) and singlet oxygen (¹O₂). No superoxide anion radical (O^·-₂) was detected by the 5, 5-dimethyl-pyrrolineN-oxide (DMPO) spin trapping method in our system. 8-Fluorine-substituted fluoroquinolones (LFLX, SPFX) produced ·C, and generated a high degree of ¹O₂. On the other hand, the fluoroquinolones which have hydrogen, oxygen or chlorine at the 8-position (CPFX, LVFX, STFX) did not produce ·C, and generated a low degree of ¹O₂. ENX produced ·C, and generated a low degree of ¹O₂. These results suggest that the nature of the substituent at the 8-position of the fluoroquinolone ring plays an important role in the formation of free radicals and active oxygen species during photoirradiation.