Impact on Photophysical and Photochemical Properties ofFluoroquinolones by Interaction with Lysozyme in Aqueous Solutions

HUGO A. PÉREZ; FAUSTINO E. MORÁN VIEYRA ; CLAUDIO D. BORSARELLI

Cordoba

Congreso; 16th International Congress on Photobiology; 2014

Fluoroquinolones (FQs) are broad-spectrum antibiotics that have been used in the treatment ofvarious infections [1]. They are capable of absorbing UV-VIS radiation generating excitedstates that can react with molecular oxygen or biomolecules such as proteins [2].In this work we studied the interaction between lysozyme (Lyz) and the FQs: ciprofloxacin(Cpx), norfloxacin (Nor) and levofloxacin (Lev) at different pH conditions, using steady-stateand dynamic absorption and emission spectroscopies. UV-Vis and fluorescence spectra of theFQs were dependent on pH, indicating the formation of cationic, zwitterionic, and anionicspecies at pH 5, 7 and 10, respectively. At pH 5 and 7, a moderated fluorescence quenching ofFQs by Lyz is observed (Fig. 1), with KSV=104M-1. Fluorescence lifetime measurements of FQsconfirmed a static quenching mechanism, indicating the formation of an antibiotic-enzymeadduct with Ka=104M-1. Conversely, at pH 10, the addition of Lys increases the FQsfluorescence intensity, suggesting that a different binding site is occupied. The Langmuirisotherm yielded Ka=106M-1, two-order of magnitude larger than at lower pH, indicating the roleof electrostatic attractive interactions between the anionic form of FQs and the positivelycharged enzyme (pI=11.5).The photodegradation of FQs depends on O2 concentration. An efficient quenching existsbetween FQs triplet states and O2 with a kQ=2-3x109M-1s-1. However, quantum yields of 1O2 for Nor and Cpx are lower than 6%. The presence of Lyz decreases the photodegradation rate of the FQs through an efficient quenching of the FQs triplet states, kQ=7-10x109M-1s-1, evidencing a photoprotective effect of Lyz.[1] W. Domagala, K. Weber and M. Osborn, Acta Cytol, 1986, 30, 225.[2] N. Wagai and K. Tawara, Arch. Toxicol, 1992, 66, 392.