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. The detection of various transients allowed to propose a rationale for the cleavage of the carbon-fluorine bond in these molecules involving different pathways depending on the molecular structure and the characteristics of the medium. The 6,8-difluoroquinolone derivative, the drug lomefloxacin (LOM), underwent heterolytic cleavage of the C8-F bond proceeding from the excited singlet state. With the 6-monofluoroquinolone norfloxacin (NOR) and the corresponding 1,8-naphtyridinone 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 underwent cleavage of the C6-F bond through a solvent mediated process likely proceeding 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 assessed. The correlation between the transients observed and the final photoproducts in the different media was elucidated.
Multifaceted photoreactivity of 6-fluoro-7-aminoquinolones from the lowest excited states in aqueous media: a study by nanosecond and picosecond spectroscopic techniques
Monti S;
2001
Abstract
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. The detection of various transients allowed to propose a rationale for the cleavage of the carbon-fluorine bond in these molecules involving different pathways depending on the molecular structure and the characteristics of the medium. The 6,8-difluoroquinolone derivative, the drug lomefloxacin (LOM), underwent heterolytic cleavage of the C8-F bond proceeding from the excited singlet state. With the 6-monofluoroquinolone norfloxacin (NOR) and the corresponding 1,8-naphtyridinone 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 underwent cleavage of the C6-F bond through a solvent mediated process likely proceeding 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 assessed. The correlation between the transients observed and the final photoproducts in the different media was elucidated.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
