RESUMEN

The effect of intermolecular proton transfer on the spectral properties of levofloxacin in the ground and excited electronic states was studied. The preferred direction of possible protolytic reactions induced by UV irradiation in this compound was studied. It was found that the proton transfer processes have a considerable effect on the capability of the compound to emit light and occur on the nanosecond timescale. The photochemical reactions of the tree forms of levofloxacin (pH: 4.0, 7.0, 10.0) were studied by laser flash photolysis and product studies. Irradiation at pH 4 yielded a pulse and transient (λmax  = 395, 515, 575 nm) assigned to the protonated triplet. Irradiation at pH 7 yielded a transient species (λmax  = 525, 610 nm) assigned to the neutral form. Protonation of the anionic singlet excited state was also observed (λmax  = 440, 570, 680 nm).

RESUMEN

Electronic absorption, luminescence, IR and Raman spectra of polymorphous forms of fluoroquinolones were investigated. Assignment of the band maxima due to π→π* and n→π* electronic transitions were done. The structural changes are responsible for the absorption band modifications. One-electron transitions in the long wavelength region, excitation wavelengths, oscillator strengths and involved molecular orbitals for the zwitter-ionic and cationic protonated forms for different fluoroquinolones were calculated with quantum-chemical and molecular dynamic methods. The electron density redistributions on the FQs separate fragments during the photoexcitation to the S(1)*-state were carry out by Mulliken calculations. It was shown that the degree of neutral and zwitter-ion FQs penetration through the bacterium membrane is different.

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RESUMEN

Electronic absorption and luminescent spectra of nonfluorinated nalidixic (nlqH) and pipemidic acid (pifqH), monofluoroquinolones - norfloxacin (nfqH) and pefloxacin (pfqH) as well as of their difluorinated analogs 1-ethyl-6,8-difluoro-1,4-dihydro-7-(1-(4-methylpiperazinyl) - 4-oxo-3-quinolinecarboxylic (mdfqH) acid and 1-ethyl-6,8-difluoro-1,4-dihydro-7-(1-piperazinyl) - 4-oxo-3-quinolinecarboxylic acid (dfqH) - were investigated. Quantum yields, lifetimes of excited states and rate constants of radiative and nonradiative transitions of the compounds were measured. The Mulliken charges of atoms from these compounds were calculated by quantum-chemical complex GAMESS. Differences in the electronic structures of these compounds and their spectral-luminescent characteristics were compared with the data of the phototoxicity degree of fluoroquinolones. Analysis of the Mulliken charges of the difluoroquinolones points to the changes of the redistribution of the electron density along π-conjugated system, and on the oxygen atoms of the carbonyl and carboxyl groups. The analysis of the molecular orbitals involved in the electronic transitions of the compounds revealed that both defluorination and piperazine photolysis are photodecomposition mechanisms which may take place in the excited states of these compounds. The relationship between the location order of the π-π* excited levels of the FQs and the degree of their phototoxicity has been determined.

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