Photochemical Properties and Reactions with Biomolecules of 4'-N-Acetyl Derivative of Norfloxacin

Abstract

The photochemical properties of 4'-N-acetyl derivative of norfloxacin (ANFX) were investigated in different solutions. Both UV-Vis absorption and the quantum yields of excited states are pH-dependent, and pK_a value of ground state for the protonation of 3-carboxylic group was determined to be 6.5 ± 0.2. Pulse radiolysis and laser flash photolysis experiments were carried out to characterize transient species of ANFX and to investigate reactions with tryptophan (TrpH) and 2'-seoxyguanosine-5'-monophosphoric acid disodium salt (dGMP). The ANFX undergoes the photoejection of electron by a mixed mechanism of one-photon and two-photon processes. Under moderate laser energy conditions, two-photon process is predominantly. The ANFX radical dianion (ANFX(–H)^·2−) formed in reaction with e_aq⁻ is characterized by the absorption around 370 nm, and the rate constant was determined to be 1.2 × 10¹⁰ dm³ mol⁻¹ s⁻¹. The ³ANFX(–H)^−∗ is able to oxidize TrpH and dGMP with bimolecular rate constants of 5.4 × 10⁸ and 9.5 × 10⁶ dm³ mol⁻¹ s⁻¹, respectively. The ANFX(–H)^·2− and the oxidized radicals of TrpH and dGMP were observed directly. Under aerobic conditions, the photo-oxidations involve both type I and type II mechanisms.