Effect of C-5 position on the photochemical properties and phototoxicity of antofloxacin and levofloxacin: A stable and transient study

The photochemistry of two structure-related fluoroquinolones (FQs), antofloxacin (ANT) and levofloxacin (LEV), was studied in aqueous solution using stable and transient methods. The properties for energy transfer and electron transfer of these two FQs were also studied. The transient absorption spectra of FQs were observed, and transient species were assigned. The LEV triplet state ((LEV)-L-3*) spectra (lambda(max) = 610 nm) were determined, whereas the transient absorption of ANT could not be observed. The decay rate constant of (LEV)-L-3* via unimolecular attenuation, self-quenching, and quenching by oxygen was 32 x 10(5) s(-1), 6.72 x 10(8) M-1 s(-1), and 1.01 x 10(9) M-1 s(-1), respectively. A reasonable diagram showing the decay of (1)FQs* consisting of various substituents at the C-5 position was proposed. The phototoxicity of LEV and ANT was investigated and compared. Insertion of an amino group at the C-5 position made ANT relatively photostable and non-phototoxic compared with LEV. (C) 2015 Elsevier B.V. All rights reserved.