E. T. Karaseva

The formation of nalidixic acid dimers and excimers in aqueous solutions

The influence of optical excitation on the formation of nalidixic acid dimers and excimers in aqueous media in the ground and excited states was studied. Quantum-chemical calculations of the total energy of monomers and dimers were performed. The spectral-luminescent characteristics of pairs of nlqH molecules were measured, and changes in charges on atoms in the ground and excited states were estimated.

Crystal structure and spectroscopic properties of ciprofloxacinium pentachloroantimonate(III) monohydrate (C17H19N3O3F)SbCl5 · H2O

Synthesis, X-ray diffraction, IR and luminescence spectroscopic studies of the monohydrate of pentachloroantimonate(III) of doubly protonated ciprofloxacin (C17H19N3O3F)SbCl5 · H2O (I) were performed. The structure of I is formed by SbCl6 octahedra combined into polymeric chains [SbCl5]n2n− through common vertices, ciprofloxacinium cations (CfH3)2+, and water molecules linked by hydrogen bonds. CfH is protonated at the carbonyl oxygen atom and the terminal nitrogen atom of the piperazinyl group. The electronic and geometric aspects determining the luminescence properties of I and of related compounds are discussed.

Synthesis and structure of nalidixium tetrachloroantimonate monohydrate, (C12H13N2O3)SbCl4 · H2O

Nalidixium tetrachloroantimonate monohydrate, (C12H13N2O3)SbCl4 · H2O, has been synthesized and its crystal structure has been determined. The structure is built of the [Sb2Cl8]2− anions, C12H13N2O3+ nalidixium cations, and H2O molecules joint by hydrogen bonds and π-π-and Cl⋯Cl interactions. The [Sb2Cl8]2− anion is a dimer of the SbCl5E distorted octahedra sharing common Cl⋯Cl edge (E is the lone electron pair). The Sb polyhedra contain two short Sb-Cl bonds (2.387 and 2.395 Å), one bond of a medium length (2.508 Å), and two long bridging bonds (2.745 and 3.054 Å).

Photochemical Behavior and Photolysis of Protonated Forms of Levofloxacin

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).

Spectroscopic and Photophysical Properties of Protonated Forms of Some Fluoroquinolones in Solutions

Electronic absorption and fluorescence spectra of ciprofloxacin, norfloxacin, enoxacin, pefloxacin and nalidixic acid in aqueous solutions were investigated. The time-resolved fluorescence spectra were measured and interpreted. The changes of the luminescence spectra and electron structure of the compounds under study are explained by different degrees of the spin-orbital interaction caused by nitrogen heteroatoms lone pairs effect. Possible ways of the protonation process for naphtyridine and quinolone rings with different substitutions are discussed. The photophysical behavior of FQs was studied using density functional theory (DFT) calculations.

Crystal structure and X-ray photoelectron spectroscopy of ciprofloxacinium tetrachloroaurate monohydrate

The complex (CfqH2AuCl4 · H2O ((CfqH2)+ is the ciprofloxacinium cation) was isolated and analyzed by spectral luminescence, X-ray photoelectron spectroscopy, and X-ray diffraction analysis. The central Au(III) atom has no direct interatomic contacts with the 1-cyclopropyl-6-fluoro-4-oxo-(1-piperazinyl)-1,4-dihydro-3-quinolinecarboxylic acid (CfqH) molecule. The structure is formed by the [AuCl4]− anions having a square structure, (CfqH2)+ cations, and water molecules combined by hydrogen bonds. The protonation of CfqH occurs at the terminal nitrogen atom of the piperazinyl group. Core-level X-ray photo-electron spectra of carbon, oxygen, nitrogen, and fluorine were measured. Cleavage of the Su-Cl bond was shown to be the primary step of the photoinduced decomposition of the compound.

Spectral-luminescent properties and molecular orbital treatment of some mono- and difluoroquinolones

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

Photochemical behavior of levofloxacin

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 time scale.

The Photochemical Behavior of Nalidixic Acid

AbstractThe influence of intermolecular proton transfer on the spectral properties of nalidixic acid (nlqH) in the ground and excited electronic states was studied. A scheme of possible protolytic reactions that occurred in this compound under the action of pH and UV radiation in aqueous medium was constructed. The total energies of model nlqH molecules in the monomeric and dimeric states were calculated quantum-chemically. Proton transfer was found to substantially influence the radiation capacity of nlqH related to the protonation and dimerization of molecules.

Structure, spectral and luminescence properties of compounds of europium(III) with nicotinic acid and enrofloxacin

The compounds of Eu(III) with nicotinic acid and enrofloxacin are synthesized. Their composition and structure are proved by the data of elemental analysis, IR and luminescence spectroscopy, powder and single crystal X-ray diffraction. By single crystal X-ray diffraction, the structure of the compound of Eu with nicotinic acid is identified as a centrosymmetric dimer with 4 carboxylate bridges of the composition Eu2(C6H4NO2)6·4H2O. The Stark structure of the 5D0-7Fj transitions in the mixed-ligand compounds of Eu(III) with nicotinic acid and enrofloxacin is determined. The bands of IR spectra are assigned; the conclusion about the bidentate coordination of ligands is made.