Pulse radiolysis study on gatifloxacin — A fluoroquinolone antibiotic

Abstract

The reactions between gatifloxacin (GFX) and various one-electron oxidants, such as ^·OH, N₃ ^·, Br₂ ^·−, and SO₄ ^·−, have been studied by pulse radiolysis techniques. The GFX radical anion formed in the reaction of GFX with e_aq ⁻ could either be protonated or deprotonated, and the absorption of GFX radical anion was located at 390 nm. The transient species produced by the reaction of GFX with ^·OH radical shows a broad band in the 380–600 nm region with a shoulder, while the oxidation by N₃ ^·, SO₄ ^·−, and Br₂ ^·− results in an absorption band with λ _max = 370 nm. At neutral condition (pH 7), the rate constants of GFX reacting with ^·OH, N₃ ^·, Br₂ ^·−, SO₄ ^·− and e_aq ⁻ are estimated to be 1.0 × 10¹⁰, 3.1 × 10⁹, 2.8 × 10⁹, 3.0 × 10⁹, and 1.8 × 10¹⁰ dm³ mol⁻¹ s⁻¹, respectively. From the pH dependence on the formation of electron adducts and on the rate constant of GFX with e_aq ⁻, the pK_a of GFX radical anion is estimated to be 5.5 and 9.3.