Photophysical Properties of Rufloxacin in Neutral Aqueous Solution

Abstract

The photophysical properties of rufloxacin, 9‐fluoro‐2r3‐dihydro‐10‐(4‐methyl‐l‐pyrazinyl)‐7‐oxo‐7‐H‐pyri‐do[l,2,3‐de]‐l,4‐benzothiazin‐6‐carboxylic acid, a fluoroquinolone antibacterial drug exhibiting photosensitizing action toward biological substrates, were studied in aqueous solutions at neutral pH. The lowest excited electronic states of the zwitterion were characterized by both experimental techniques and theoretical methods. Steady‐state and time‐resolved emission, triplet‐state absorption and singlet oxygen production were investigated. The results indicate that the lowest excited singlet is a fluorescent, relatively long‐lived state (φr= 0.075, Tr≅ 4.5 ns) with an efficient intersystem crossing to the triplet manifold (φisc≅ 0‐7)‐ The lowest triplet is a long‐lived state (TT≅ 10 μs at 295 K in 0.01 M phosphate buffer), with properties that make it a good candidate for being the precursor of the photodecarboxylation of the drug. It is quenched by oxygen at a rate of 1.7 times 109M‐1 s‐1 and singlet oxygen is formed with a quantum yield of 0.32 in air‐saturated solutions.

Photochemistry of 1-Cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7- (piperazin-1-yl)quinoline-3-carboxylic Acid (=Ciprofloxacin) in Aqueous Solutions

“…This had undergone reductive decarboxylation, not defluorination. With fluoroquinolinones, decarboxylation has been reported only in the case of the 8-(alkylthio) derivative rufloxacin, for which defluorination was not the main photoproces (`40%) in H 2 O [8] [21]. In the present case, decarboxylated 8 was isolated under conditions in which the triplet of 1 was fully quenched and gave the radical anion.…”

Enhanced Photostability of Fluoroquinolone Antibacterials Capped on Silver Nanoparticles

“…form (see Scheme 1 for clarity) is not fluorescent whereas both the zwitterionic and cationic forms strongly emit with maxima peaked at well-different wavelengths. [21,23,33] As reported in Figure 3, the free NF and RF show intense fluorescence emission arising from their zwitterionic forms with maxima at 430 and 470 nm, respectively, according to literature (spectra a in Figure 3). These emissions were slightly red-shifted in the case of Ag@FQs confirming that the fluorescence observed originates from the zwitterionic FQs bound to the AgNPs.…”

“…In fact, while a type I process (radical mediated) occurs for NF, [32] a type II pathway (singlet oxygen mediated) mainly occurs for RF. [33] Results and Discussion…”

“…[21,23,33] Therefore, fluorescence spectroscopy represents a powerful diagnostic tool to get more insights into binding nature with the metal nanoparticles. In particular, the anionic S. Giuffrida and S. Sortino/Enhanced Photostability of Fluoroquinolone Antibacterials .…”

“…Detailed literature data show that the photodegradation of NF and RF mainly involve their lowest excited triplet state ( 3 FQ Ã ), formed after effective intersystem crossing (isc), as the key reactive intermediate in the drugs photodegradation. [32,33] The triplet states of NF and RF undergo two different deactivation pathways in phosphate buffer solution, which, for sake of clarity, are recalled in Scheme 3. In the case of NF, a photoinduced electron transfer involving the phosphate ions of the buffer leads to the NF radical anion, which initiates the radical-mediated drug photodecomposition.…”