pH Effects on the Spectroscopic and Photochemical Behavior of Enoxacin: A Steady-State and Time-Resolved Study

Sortino, Salvatore; Guidi, Guido De; Giuffrida, Salvatore; Monti, Sandra; Velardita, A.

doi:10.1562/0031-8655(1998)067<0167:peotsa>2.3.co;2

Cited by 66 publications

(77 citation statements)

References 22 publications

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“…[8] Such a transient band is identical to that detected for the same substrate in sulfite buffer (compare Figure 7 in ref. [8] and Figure 1 in ref. [5] ).…”

Section: Evidence Concerning the Course Of The Reactionsupporting

confidence: 76%

“…[5,8] With naphthryridinone 1b, we also reported that a different transient band was seen in phosphate buffer (a broad band centred at 670 nm). [8] Such a transient band is identical to that detected for the same substrate in sulfite buffer (compare Figure 7 in ref. [8] and Figure 1 in ref.…”

Section: Evidence Concerning the Course Of The Reactionmentioning

confidence: 51%

“…2.8 eV), [8] thus giving E red (1b 3 *) ഠ 1.45 V. The potential of the couple HPO 4 Ϫ· /HPO 4 2Ϫ has not yet been reported, but we estimate it to be significantly lower than 1.9 V vs. NHE. This is in agreement with the weaker oxidative power of HPO 4 Ϫ· as compared to H 2 PO 4 · (the potential of the couple H 2 PO 4…”

Section: ϫ·mentioning

confidence: 70%

“…Products from the photolysis of compounds 1a؊c in water and in bisulfite buffer pect. [8,11] The acidity of the medium thus needs to be controlled during the course of the reaction. The aforementioned product studies [5] were carried out under neutral conditions by adjusting the pH to 7.2 through the addition of small amounts of sodium hydrogen carbonate.…”

Section: Introductionmentioning

confidence: 99%

“…Generally, it has been assumed that such buffers have no other effect on the chemistry that occurs. Some studies on the photostabilities of the aforementioned fluoroquinolones have been carried out in phosphate buffers (from 0.007 to 0.2 ), [7,8] but in a preliminary investigation we found that the addition of phosphate had a more significant effect than buffering the solution, since the photodecomposition quantum yields of compounds 1a,b changed by more than a factor of ten on adjusting the phosphate concentration while the pH was kept constant. [6] Thus, it appeared worthwhile to explore whether the products formed might also change under these conditions.…”

Section: Introductionmentioning

confidence: 99%

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Unexpected Photoreactions of Some 7-Amino-6-fluoroquinolones in Phosphate Buffer

et al. 2001

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The products of irradiation of some 6‐fluoro‐7‐piperazino‐4‐quinolone‐3‐carboxylic acids in phosphate buffer arise from a combination of reductive defluorination of the heteroaryl ring and oxidative fragmentation of the piperazine side chain. This unusual reaction contrasts with the fluorine atom substitution observed in neat water. The results of steady‐state and time‐resolved experiments are consistent with initiation of the process by electron‐transfer quenching of the triplet state of these heterocycles by the phosphate anion. For one of the compounds, a transient band (λmax = 670 nm), previously attributed to the defluorinated cation, must now be reassigned to the radical anion. This intermediate undergoes inefficient reductive defluorination of the ring. In the process, a phosphate radical anion is expected to be formed and to abstract a hydrogen atom from the piperazine group, leading to degradation of the latter.

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“…[8] Such a transient band is identical to that detected for the same substrate in sulfite buffer (compare Figure 7 in ref. [8] and Figure 1 in ref. [5] ).…”

Section: Evidence Concerning the Course Of The Reactionsupporting

confidence: 76%

Section: Evidence Concerning the Course Of The Reactionmentioning

confidence: 51%

Section: ϫ·mentioning

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Unexpected Photoreactions of Some 7-Amino-6-fluoroquinolones in Phosphate Buffer

et al. 2001

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Multifaceted Photoreactivity of 6-Fluoro-7-aminoquinolones from the Lowest Excited States in Aqueous Media: A Study by Nanosecond and Picosecond Spectroscopic Techniques

Monti¹,

et al. 2001

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Nanosecond and picosecond absorption and emission spectroscopic techniques were applied to the investigation of the reactivity from the lowest excited states of some 6-fluoro-7-piperazino-4-quinolone-3-carboxylic acids (FQs) in aqueous media at neutral pH, in the absence and presence of different sodium salts. Following the detection of various transients, we proposed a mechanism for the cleavage of the carbonÀfluorine bond that proceeded through different reaction pathways, dependent on the molecular structure and the characteristics of the medium. The drug lomefloxacin (LOM), a 6,8-difluoroquinolone derivative, underwent heterolytic cleavage of the C8ÀF bond from the excited singlet state. With the 6-monofluoroquinolone norfloxacin (NOR) and the corresponding 1,8-naphthyridinone enoxacin (ENX), the lowest singlet state was not significantly reactive and an important deactivation channel was intersystem crossing (ISC) to the triplet manifold. The lowest triplet state underwent cleavage of the C6ÀF bond through a solvent mediated process possibly via a cyclohexadienyl anionic adduct. In the presence of sulfite or phosphate buffer a novel defluorination mechanism, induced by electron transfer from the inorganic anions to the FQ triplet state, was observed. The correlation between the transients observed and the final photoproducts in the different media was elucidated.

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Enhanced Photostability of Fluoroquinolone Antibacterials Capped on Silver Nanoparticles

Giuffrida

Sortino

2011

Adv Eng Mater

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The photolabile and phototoxic fluoroquinolone (FQ) antibacterial drugs norfloxacin and rufloxacin have been used as capping agents for 25 nm Ag nanoparticles, exploiting the noncovalent interaction between the cationic piperazinyl ring of both FQs and the negatively charged metal surface. The resulting FQ‐protected silver nanoclusters (Ag@FQs), ca. 80 nm in diameter, are dispersible in phosphate buffer at physiological pH and their response to light excitation has been studied by steady‐state and time‐resolved spectroscopic and photochemical techniques. The fluorescence emission of the FQs chromophores is not extensively quenched in the Ag@FQs. In contrast, both Ag@FQs exhibit a photochemical stability more than one order of magnitude larger than that of the free drugs. This is the result of significant and differentiated quenching effects by the Ag surface on the kinetic and population of the excited triplet states of FQs, which are the key intermediate in the drugs photodecomposition. In view of the well‐known antimicrobial properties of the Ag nanoparticles, the Ag@FQs could represent intriguing nanohybrids in the perspective multifunctional nanodrugs.

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pH Effects on the Spectroscopic and Photochemical Behavior of Enoxacin: A Steady-State and Time-Resolved Study

Cited by 66 publications

References 22 publications

Unexpected Photoreactions of Some 7-Amino-6-fluoroquinolones in Phosphate Buffer

Unexpected Photoreactions of Some 7-Amino-6-fluoroquinolones in Phosphate Buffer

Multifaceted Photoreactivity of 6-Fluoro-7-aminoquinolones from the Lowest Excited States in Aqueous Media: A Study by Nanosecond and Picosecond Spectroscopic Techniques

Enhanced Photostability of Fluoroquinolone Antibacterials Capped on Silver Nanoparticles

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