Triplet Excimers of Fluoroquinolones in Aqueous Media

Abstract

Generation of triplet eximers of 6-fluoro-7-piperazinyl-quinolone-3-carboxylic acids (FQs) have been detected in aqueous media using laser flash photolysis (LFP). These transient species (SS) are generated by self-quenching reactions of FQ triplet excited states such as pefloxacin (PFX), norfloxacin (NFX), the N-acetylated form of NFX (ANFX), and its methyl ester (EANFX) with their ground states. In this context, self-quenching rate constants in the range of (1-7) × 10(8) M(-1) s(-1) were determined. The triplet excimers show transient absorption spectra with λ(max) ca. 710 nm for SS(NFX), 740 nm for SS(PFX), and 620 nm for SS(ANFX) and E(ANFX), which are red-shifted with respect to their predecessors triplet excited states. These excimers can be also observed in the presence of phosphate buffer (PB). Experiments performed with NFX and ANFX at different PB concentrations showed that deprotonation processes are not involved in the generation of SS. The triplet multiplicity of the FQ excimers was confirmed by energy transfer reactions with naproxen. The correlation between fluorescence, intersystem crossing, excimer and photodegradation quantum yields of (A)NFX indicated that FQ self-quenching reactions are mainly a deactivation pathway. On the other hand, generation of FQ radical anions absorbing at λ(max) ca. 620 nm has been observed by an efficient electron transfer reaction from Trp to NFX, PFX, and ANFX (rate constants ca. 1 × 10(9) M(-1) s(-1)).

Assessing physical properties of amphoteric fluoroquinolones using phosphorescence spectroscopy

“…710 nm) was done by analogy to those described for NFX, PFX and related compounds. [8] Thus, it was observed that the PPA excimer shows a transient absorption spectrum with a maximum above 700 nm and it is efficiently quenched by molecular oxygen but not using BPC, which is in agreement with the photophysical properties described in the literature for other triplet excimers. [8,26] Conversely, PRA triplet excited state did not generate any secondary transient species when the anionic form of PRA was studied under the same conditions and concentrations as those used for the amphoteric PPA.…”

“…[3] The occurrence of FQ selfassociations in aqueous media has also been proposed to explain the generation of triplet eximers in water from the reaction of FQ triplet excited states ( 3 FQs) with their ground states at very low concentrations (below 10 -4 M). [8] Thereby, fluoroquinolone triplet excited states ( 3 FQs) have been shown as reporters of FQ self-association using laser flash photolysis technique. In this context, drugbiomolecules interactions including FQs-DNA associations have been also studied analysing the reactivity of the triplet excited state with the surrounding [9][10][11].…”

Impact of Hydrogen Bonding on the Fluorescence of N‐Amidinated Fluoroquinolones

“…To study the differences in fluorescence properties, ciprofloxacin and its derivative CIP-1,w ere compared in solution and in the solid state ( Figure 2). In comparison with the parent ciprofloxacina nd other fluoroquinolones, [9,21] these N-amidinated ciprofloxacin derivatives generally showed distinctd ifferences in fluorescence properties. In the solid state, amidine CIP-1 showed as imilar absorption profile as ciprofloxacin, but displayed red-shifted fluorescencew ith a maximum at 460 nm (ex:3 42 nm) compared to a l max at 416 nm for the parentc ompound (ex: 340 nm).…”

Femtosecond Transient Absorption Spectroscopy Study of the Early Events of Norfloxacin in Aqueous Solutions with Varying pH Values

“…9,16 Bosca and co-workers reported the first clear example of excimer detection in aqueous media and studied electron transfer reactions between NF and naproxen, tryptophan, etc., and photophysical properties of NF. 17 Although numerous studies have attempted to characterize the transient species and photophysical transformations of NF, there are several important issues that remain unaddressed, specifically, (1) there are few clear identifications of the form(s) of the NF molecule actually being excited in neutral aqueous solution and (2) femtosecond time-resolved spectroscopies have not yet been used to elucidate the initial photophysical events for NF in aqueous solutions with varying pH values after photoexcitation. In the present work, resonance Raman spectroscopy and density functional theory (DFT) calculations were used to characterize and determine the form(s) of NF that is/are photoexcited under different conditions.…”