Photophysics and photochemistry of nalidixic acid

Primary photophysical and photochemical processes for cerium ammonium nitrate (CAN) in acetonitrile

Cerium ammonium nitrate (CAN) is an important photolytic source of NO3• radicals in aqueous nitric acid solutions and in acetonitrile. In this work we performed the study of primary photochemical processes for CAN in acetonitrile by means of ultrafast TA spectroscopy and quantum chemical calculations. Photoexcitation of CAN is followed by ultrafast (< 100 fs) intersystem crossing; the vibrationally cooled triplet state decays to pentacoordinated Ce(III) intermediate and NO3• radical with the characteristic time of ca. 40 ps. Quantum chemical (QM) calculations satisfactorily describe the UV-vis spectrum of the triplet state. An important feature of CAN photochemistry in CH3CN is the partial stabilization of the radical complex (RC) [(NH4)2CeIII(NO3)5…NO3•], which lifetime is ca. 2 μs. The possibility of the RC stabilization is supported by the QM calculations.

Comparative Study of the Removal Efficiency of Nalidixic Acid by Poly[(4-vinylbenzyl)trimethylammonium Chloride] and N-Alkylated Chitosan through the Ultrafiltration Technique and Its Approximation through Theoretical Calculations

Emerging antibiotic contaminants in water is a global problem because bacterial strains resistant to these antibiotics arise, risking human health. This study describes the use of poly[(4-vinylbenzyl) trimethylammonium chloride] and N-alkylated chitosan, two cationic polymers with different natures and structures to remove nalidixic acid. Both contain ammonium salt as a functional group. One of them is a synthetic polymer, and the other is a modified artificial polymer. The removal of the antibiotic was investigated under various experimental conditions (pH, ionic strength, and antibiotic concentration) using the technique of liquid-phase polymer-based retention (LPR). In addition, a stochastic algorithm provided by Fukui's functions is used. It was shown that alkylated N-chitosan presents 65.0% removal at pH 7, while poly[(4-vinylbenzyl)trimethylammonium chloride] removes 75.0% at pH 9. The interaction mechanisms that predominate the removal processes are electrostatic interactions, π-π interactions, and hydrogen bonding. The polymers reached maximum retention capacities of 1605 mg g-1 for poly[(4-vinylbenzyl) trimethylammonium chloride] and 561 mg g-1 of antibiotic per gram for alkylated poly(N-chitosan). In conclusion, the presence of aromatic groups improves the capacity and polymer-antibiotic interactions.

Synthesis, Spectral Characterization and Potential Fluorescent Properties of Three Lanthanide(III) Ions Complexes with Nalidixic Acid

Three new solid lanthanide complexes with nalidixic acid (HNal) with the stoichiometry [Ln(Nal)₃]·5·.5H₂O (Ln = Tb, Dy and Ho) were synthesized applying the green synthesis method from the aqueous solutions without the organic solvent addition and fully characterized by the elemental analysis, XRF, complexometric titration, gravimetric analysis, molar conductivity and solubility measurements, powder X-Ray diffraction, UV-Vis and infrared (FT-IR) spectroscopies. Moreover, the luminescent properties of the Tb(III), Dy(III), and Ho(III) complexes in the solid state and in the solutions were investigated. On the basis of the detailed spectral analysis, it was concluded that the nalidixate ligands bind to the lanthanide ions by the bidentate carboxylate and carbonyl groups while water molecules belong to the outer coordination sphere. At the excitation of UV light, the complexes exhibited characteristic emission of central lanthanide ions, the intensity of which depends significantly on the excitation wavelength and/or the solvent. Thus, the application of nalidixic acid (apart from biological activity) for the synthesis of luminescent lanthanide complexes was confirmed which can find potential applications in the field of photonic devices and/or bioimaging agents.

Direct UV photodegradation of nalidixic acid in aqueous solutions: A mechanistic study

Mechanism of direct UV photolysis of nalidixic acid (NA), a model quinolone antibiotic, was revealed using a combination of steady-state photolysis coupled with high resolution LC-MS and DFT quantum-chemical calculations. Both quantum yields of photodegradation and detailed identification of final products were performed for the first time for two main forms of NA: neutral and anionic. The quantum yield of NA photodegradation is 0.024 and 0.0032 for the neutral and anionic forms in the presence of dissolved oxygen and 0.016/0.0032 in deoxygenated solutions, respectively. The main process is photoionization with the formation of a cation radical, which undergoes transformation into three different neutral radicals and further into final photoproducts. It is shown that the triplet state does not play a role in the photolysis of this compound. The main products of photolysis are the products of the loss of carboxyl, methyl and ethyl groups in the NA molecule, as well as the dehydrogenation of the ethyl group. The results obtained may be important for understanding the fate of pyridine herbicides in the processes of disinfection by UV and in natural waters under the action of sunlight.

Effects of Magnesium, Calcium, and Aluminum Chelation on Fluoroquinolone Absorption Rate and Bioavailability: A Computational Study

Fluoroquinolones (FQs) are a widespread class of broad-spectrum antibiotics prescribed as a first line of defense, and, in some cases, as the only treatment against bacterial infection. However, when administered orally, reduced absorption and bioavailability can occur due to chelation in the gastrointestinal tract (GIT) with multivalent metal cations acquired from diet, coadministered compounds (sucralfate, didanosine), or drug formulation. Predicting the extent to which this interaction reduces in vivo antibiotic absorption and systemic exposure remains desirable yet challenging. In this study, we focus on quinolone interactions with magnesium, calcium and aluminum as found in dietary supplements, antacids (Maalox) orally administered therapies (sucralfate, didanosine). The effect of FQ-metal complexation on absorption rate was investigated through a combined molecular and pharmacokinetic (PK) modeling study. Quantum mechanical calculations elucidated FQ-metal binding energies, which were leveraged to predict the magnitude of reduced bioavailability via a quantitative structure-property relationship (QSPR). This work will help inform clinical FQ formulation design, alert to possible dietary effects, and shed light on drug-drug interactions resulting from coadministration at an earlier stage in the drug development pipeline.

Oxidative degradation of nalidixic acid by nano-magnetite via Fe2+/O2-mediated reactions

Organic pollution has become a critical issue worldwide due to the increasing input and persistence of organic compounds in the environment. Iron minerals are potentially able to degrade efficiently organic pollutants sorbed to their surfaces via oxidative or reductive transformation processes. Here, we explored the oxidative capacity of nano-magnetite (Fe3O4) having ∼ 12 nm particle size, to promote heterogeneous Fenton-like reactions for the removal of nalidixic acid (NAL), a recalcitrant quinolone antibacterial agent. Results show that NAL was adsorbed at the surface of magnetite and was efficiently degraded under oxic conditions. Nearly 60% of this organic contaminant was eliminated after 30 min exposure to air bubbling in solution in the presence of an excess of nano-magnetite. X-ray diffraction (XRD) and Fe K-edge X-ray absorption spectroscopy (XANES and EXAFS) showed a partial oxidation of magnetite to maghemite during the reaction, and four byproducts of NAL were identified by liquid chromatography-mass spectroscopy (UHPLC-MS/MS). We also provide evidence that hydroxyl radicals (HO(•)) were involved in the oxidative degradation of NAL, as indicated by the quenching of the degradation reaction in the presence of ethanol. This study points out the promising potentialities of mixed valence iron oxides for the treatment of soils and wastewater contaminated by organic pollutants.

Photochemical Properties and Reactions with Biomolecules of 4'-N-Acetyl Derivative of Norfloxacin

The photochemical properties of 4'-N-acetyl derivative of norfloxacin (ANFX) were investigated in different solutions. Both UV-Vis absorption and the quantum yields of excited states are pH-dependent, and pK a value of ground state for the protonation of 3-carboxylic group was determined to be 6.5 ± 0.2. Pulse radiolysis and laser flash photolysis experiments were carried out to characterize transient species of ANFX and to investigate reactions with tryptophan (TrpH) and 2'-seoxyguanosine-5'-monophosphoric acid disodium salt (dGMP). The ANFX undergoes the photoejection of electron by a mixed mechanism of one-photon and two-photon processes. Under moderate laser energy conditions, two-photon process is predominantly. The ANFX radical dianion (ANFX(–H)·2−) formed in reaction with eaq − is characterized by the absorption around 370 nm, and the rate constant was determined to be 1.2 × 1010 dm3 mol−1 s−1. The 3ANFX(–H)−∗ is able to oxidize TrpH and dGMP with bimolecular rate constants of 5.4 × 108 and 9.5 × 106 dm3 mol−1 s−1, respectively. The ANFX(–H)·2− and the oxidized radicals of TrpH and dGMP were observed directly. Under aerobic conditions, the photo-oxidations involve both type I and type II mechanisms.

Structure and Medium Effects on the Photochemical Behavior of Nonfluorinated Quinolone Antibiotics†

The photophysical behavior of the quinolone antibiotics, oxolinic (OX), cinoxacin (CNX) and pipemidic (PM) acids was studied as a function of pH and solvent properties. The ground state of these compounds exhibits different protonated forms, which also exist in the first excited states. Theoretical calculations of the Fukui indexes allowed to assigning the different protonation equilibria. The pK values indicate that the acidity of the 3-carboxylic and 4-carbonyl groups increases with the N-atom at position 2 in CNX. It has been found that fluorescence properties are strongly affected by pH, the more fluorescent species is that with protonated carboxylic acid, protonated species at the carbonyl group and the totally deprotonated form present very low fluorescence. The fluorescence behavior also depends on the chemical structure of the quinolone and on the solvent properties. The analysis of the solvent effect on the maximum and the width of the fluorescence band of OX, using the linear solvent-energy relation solvatochromic equation, indicates that the polarizability and hydrogen bond donor ability are the parameters that condition the spectral changes. The hydrogen bond acceptor ability of the solvents also contributes to the spectral shifts of CNX. The compound bearing the piperazinyl group at the position 7, PM only is fluorescent in high protic solvents. These results are discussed in terms of the competition between the intra- and intermolecular hydrogen bonds. The irradiation of OX, CNX and PM using 300 nm UV light led to a very low photodecomposition rate. Under the same conditions the nalidixic acid (NA), a structurally related quinolone, photodecomposes two orders of magnitude faster.

Photophysics and Photochemical Studies of 1,4-Dihydropyridine Derivatives

The absorption and fluorescence properties of nifedipine (NPDHP), felodipine (CPDHP) and a series of structurally related 1,4-dihydropyridines were studied in aqueous solution and organic solvents of different properties. The absorption and fluorescence spectra were found to depend on the chemical nature of the substituents at the position 4 of the 1,4-dihydropyridine ring (DHP) and on solvent properties. In aqueous solution, the fluorescence spectra of 4-phenyl substituted compounds are blue-shifted with respect to the alkyl substituted compounds. The more fluorescent compound is CPDHP. Nifedipine is not fluorescent. All compounds, with the exception of CPDHP, present monoexponential fluorescence decay with very short lifetime (0.2-0.4 ns). CPDHP showed a biexponential emission decay with a long-lived component of 1.7 ns; this behavior is explained in terms of different conformers because of the hindered rotation of the phenyl group by the ortho-substitution. Analysis of the solvent effect on the maximum of the absorption spectrum by using the linear solvent-energy relation solvato-chromic equation indicates the redshifts are influenced by the polarizability, hydrogen bonding ability and the hydrogen bond acceptance of the solvent. Whereas, the fluorescence characteristics (spectra, quantum yields and lifetimes) are sensitive to the polarizabilty and hydrogen bond ability of the solvents. Photo-decomposition of nifedipine is dependent on the solvent properties. Faster decomposition rates were obtained in nonprotic solvents. The 4-carboxylic derivative goes to decarboxylation. Under similar conditions, the other DHP compounds did not show appreciable photodecomposition.