T. B. Emelina

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.

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.

Electronic structure and absorption spectra of yttrium quinaldinates with an island and polymer structure

The electronic absorption spectra and electronic structure of yttrium quinaldinates with an island and polymer structure were studied. A comparative analysis of the energies of the singlet and triplet excited states, the total energies of complex compounds in the ground state, and Mulliken’s bond overlap populations was performed by the TD-DFT method with the B3LYP density functional. For yttrium quinaldinate with a polymer structure, the distance between the highest occupied and lowest unoccupied orbitals was found to be longer than for the compound with an island structure. The transition energies were shifted to the blue region, which accounts for the higher stability of the polymer 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

Polymorphism and Intramolecular Proton Transfer in Fluoroquinolone Compounds

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 S1*-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.

Electron structure and spectroscopic properties of yttrium compounds with cinnamic and quinaldic acids

The analysis of electron structure of yttrium(III) complexes with cinnamic and quinaldic acids was carried out. Electron transitions were assigned, and influence of the nature of frontier orbitals on the position of absorption bands in the electron spectra was revealed. The TD-DFT calculation has shown that different ratios of intensities of π–π* and n–π* bands in the electron absorption spectra of the compounds are caused by different natures of frontier orbitals of the complexes. It was found that dipole moments of both complexes increase upon photoexcitation, greater changes being observed in Y(III) quinaldate. The reason of the greater Stokes shift of Y(III) quinaldate was established.

Photolysis and quantum-chemical calculations of the nalidixic acid radical states

The nalidixic acid transient spectra were analyzed and the scheme of photo-conversion of the acid was suggested. At a large delay of laser pulses the transient absorption spectra contain the bands due to the dissociation of the products of the cation- and anion-radical photodecomposition in the micro- and millisecond range. By quantum-chemical calculations we revealed that at the transition to the ion-radical state a proton migration occurs subsequent to the movement of the center of gravity of the negative charge. The phototransformation of nalidixic was found to proceed with a TICT-effect.

Intramolecular charge transfer and electronic absorption and luminescence spectra of fluoroquinolinones

TD-DFT study on the effect of donor and acceptor substituents on molecular orbital localization and charge distribution in fluoroquinolinone molecules showed that their photoexcitation is accompanied by electron density redistribution over particular fragments. Depending on the protolytic form, frontier molecular orbitals are localized on different fragments, whereas variation of substituents weakly affects localization of these orbitals.

The role of water molecules in the interfragmental charge transfer of the protolytic forms of fluoroquinolones in the ground and excited states

Quantum-chemical analysis (TD-DFT/B3LYP/6-31G) of the influence of H-bonding in the donor-acceptor fluoroquinolone compounds with the water molecules on the interfragmentary charge transfer was carried out. The values of charge transfer between the molecular fragments in the transition from the ground into the singlet excited state were calculated. It was found that, depending on the protolytic form of a compound, the frontier molecular orbitals are localized on different fragments, which leads to the specificity of the formation of the electron density transfer channel. The influence of individual substituents in the quinolones on the localization of particular MOs is relatively insignificant.