On the Photophysicochemical Properties of Selected Fluoroquinolones: Solvatochromic and Fluorescence Spectroscopy Study

The photophysicochemical properties of selected fluoroquinolones in different solvents of various physical properties, including polarity and hydrogen bonding ability, were investigated using steady state fluorescence spectroscopy. The solvent-dependant fluorescence emission spectra of selected fluoroquinolones, namely ciprofloxacin (CIPR) and enrofloxacin (ENRO), were employed to gain insights concerning its photophysicochemical properties of interests. Interestingly, fluorescence spectra of the selected drugs exhibited structured emission spectra in nonpolar solvents such as hexane, whereas unstructured spectra were observed in more polar solvents such as alcohols and water. Also, a notable bathochromic shift in $ \lambda_{{\max }}^{{em}} $ was observed in fluorescence spectra of both drugs with increasing solvent polarity that resulted in biphasic behavior upon applying the Lippert-Mataga correlation that correspond to general and specific solvent effects. Applying the Lippert-Mataga correlation to the fluorescence spectra of CIPR and ENRO in various solvents was employed to estimate the dipole moment difference between the ground and excited states of them, $ \Delta \mu \left( {{\mu_e} - {\mu_g}} \right) $ , where obtained results revealed the values of 9.4 and 16.2 Debye for the LE and ICT states of ENRO, respectively, and 8.0 and 16.2 Debye for the LE and ICT states of CIPR, respectively. Multiple linear regression analysis (MLRA) based on Kamlet-Taft equating was applied against absorption frequency (ν_abs), emission frequency (ν_em), Stokes shift (?ν), and fluorescence quantum yield (Φ_f), where obtained results revealed excellent correlation (R: 0.916–0.966) that are consistent with other results considering the effect of solvent polarizability, hydrogen bonding ability, and viscosity on the photophysicochemical properties of the studied fluoroquinolones.     

Thermal decomposition of haemin chloride and related derivatives

Differential scanning calorimetry was used to study the thermal decomposition of haemin chloride and its derivatives protoporphyrin and bilirubin. Under a static air atmosphere, exothermic transitions due to degradation were recorded for the two former compounds, whereas bilirubin exhibited a higher thermal stability. Thermogravimetry indicated that the weight loss process with these compounds under an oxidizing atmosphere of oxygen was different from that under an inert atmosphere of nitrogen. Infrared spectra of these compounds were also recorded and are briefly discussed.     

Solution equilibria and stability of the complexes of pyridinecarboxylic acids: Complexation reaction of mercury(II) with 2-hydroxynicotinic acid

Summary The solution equilibria of 2-hydroxynicotinic acid (hyna) complexes with mercury(II) have been studied spectrophotometrically in 50% (v/v) ethanol at 20°C and an ionic strength of 0.1mol dm^–3 (NaClO₄). Three mercuric complexes are formed in solution in dependence on the acidity of the medium. The basic characteristics of the different complexes are determined and the analytical aspects of the complexation reaction are demonstrated. A critical investigation has also been presented of the solution equilibria and stability of the mixed complex of mercury(II) withhyna and thiosalicylic acid (tsa). The various complex transitions leading to the formation of the 1 : 1 : 1 Hg(tsa)(hyna) ternary complex in solution are investigated. The non-charged mono-ligand complex Hg(hyna) is used for UV-spectrophotometric determination of mercury atpH 4.5–5 (_max=325nm, =0.8·10⁴lmol^–1cm^–1). The system obeyed Beer's law up to 36.1 µg ml^–1 of Hg(II). The optimum concentration range (Ringbom) is between 6 and 28.5µg ml^–1. Interference caused by a number of ions was masked by the addition of fluoride ions.

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Lösungsgleichgewichte und Stabilitätskonstanten von Komplexen der Pyridincarbonsäuren: Die Komplexierungsreaktion von Quecksilber(II) mit 2-Hydroxynikotinsäure

Zusammenfassung Die Lösungsgleichgewichte von 2-Hydroxynikotinsäure (hyna) mit Hg(II) wurde spektrophotometrisch in 50% (v/v) Ethanol bei 20°C und einer Ionenstärke von 0.1 mol dm^–3 (NaClO₄) untersucht. In Abhängigkeit von der Acidität des Mediums werden drei Quecksilberkomplexe gebildet. Die grundlegenden Charakteristika der Komplexe wurden bestimmt und die analytischen Aspekte aufgezeigt. Die gemischten Komplexe von Hg(II) mithyna und Thiosalicylsäure (tsa), insbesondere die verschiedenen Komplexübergänge zum ternären 1 : 1 : 1 Hg(tsa)(hyna)-Komplex, wurden ebenfalls untersucht. Der ungeladene Monoligandenkomplex Hg(hyna) kann beipH 4.5–5 zur UV-spektroskopischen Quecksilberbestimmung eingesetzt werden (_max=325nm, =0.8·10⁴lmol^–1cm^–1). Das System gehorcht bis zu einer Hg(II)-Konzentration von 36.1µgml^–1 dem Beerschen Gesetz. Der optimale Konzentrationsbereich (Ringbom) liegt zwischen 6 und 28.5µgml^–1. Interferenzen mit einer Reihe anderer Ionen konnten durch Maskierung mit Fluoridionen umgangen werden.

     

Dimethyltin(IV) complexes with zwitterionic buffers (Mes and Mops)

Equilibrium studies in aqueous solution are reported for dimethyltin(IV) complexes of the zwitterionic buffers “Good’s buffer”, such as Mes and Mops (L). Stoichiometry and stability constants for the complexes formed were determined at different temperature and ionic strength 0.1 M NaNO₃. The results showed the best fit of the titration curves were obtained when complexes ML, MLH₋₁, MLH₋₂, and MLH₋₃ were expected beside the hydrolysis products of the dimethyltin(IV) cation. The thermodynamic parameters ΔH°, ΔS° and ΔG° calculated from the temperature dependence of the formation constant of the dimethyltin(IV)-Mes complex was investigated. The effect of dioxane as a solvent on the formation constants of dimethyltin(IV)-Mes complex was discussed. The concentration distribution of the various complex species was evaluated as a function of pH. The bonding sites of the dimethyltin(IV) complexes in solid state with Mes and Mops were characterized by means of elemental analyses and FTIR. The NMR (¹H, ¹³C) spectra of the DMT-Mes complex exhibits the strongly distorted octahedron geometry around tin atom. Also, thermal analyses (TGA and DTA) were discussed. Thermodynamic parameters such as activation energy (E_a), pre-exponential factor (A), entropy of activation (ΔS^∗) and free energy of activation (ΔG^∗) have been calculated for each step, employing integral method Coats and Redfern. The reaction enthalpy (ΔH) is obtained from DTA data.     

Iodine/potassium iodide catalyst for the synthesis of trifluoromethylated quinazolines via intramolecular cyclization of 2,2,2-trifluoro-N-benzyl-N′-arylacetimidamides

Molecular Diversity - An efficient and simple protocol for the synthesis of trifluoromethylated quinazolines has been described by I2-/KI-promoted oxidative C(sp3)–C(sp2) bond under the...     

Analytical Approximate Solution of SchrSdinger Equation in D Dimensions with Quadratic Exponential-Type Potential for Arbitrary/-State

We present the bound state solution of Schr6dinger equation in D dimensions for quadratic exponential-type potential for arbitrary l-state. We use generalized parametric Nikiforov-Uvarov method to obtain the energy levels and the corresponding eigenfunction in dosed form. We also compute the energy eigenvalues numerically.     

All optical self signal processing using chalcogenide nonlinear fiber Bragg grating

In this study, we simulate numerically quasi pulse propagation in a uniform nonlinear fiber Bragg grating (FBG) made of chalcogenide glasses. Because of bistability and nonlinearity behavior of FBG, the shapes of output pulse vary abruptly and strongly according to the input peak intensity. We take Gaussian pulse as input and produce saw-tooth wave and square wave in the output by suitable input amplitude and FBG length also we could reach pulse chopping and pulse compression. These all optical signal processing achieved for a few length, i.e. 6.6 mm and few intensity, i.e. 35 W/m² because of high nonlinearity of chalcogenide glasses.     

Ab‐Initio calculations of the CO adsorption and dissociation on substitutional Fe–Cu surface alloys relevant to Fischer–Tropsch Synthesis: bcc‐(Cu)Fe(100) and fcc‐(Fe)Cu(100)

Direct CO dissociation is seen the main path of the first step in the Fischer–Tropsch Synthesis (FTS) on the reactive iron surfaces. Cu/Fe alloy film is addressed with various applications over face‐centered‐cubic (fcc)‐Cu and body‐centered‐cubic (bcc)‐Fe in the FTS, i.e. preventing iron carbide formation (through direct CO dissociation) by moderating the surface reactivity and facilitating the reduction of iron surfaces, respectively. In this study by density functional theory, the stable configurations of CO molecule on various Cu/Fe alloys over fcc‐Cu(100) and bcc‐Fe(100) surfaces with different CO coverage (25% and 50%) have been evaluated. Our results showed that the ensemble effect plays a fundamental role to CO adsorption energy on the surface alloys over bcc‐Fe(100); on the other hand, the ligand effect determines the CO stability on the fcc‐Cu(100) surface alloys. CO dissociation barrier was also calculated on the surface alloys that showed although the CO dissociation process is thermodynamically possible on the more reactive surface alloys, but according to their high barrier, CO dissociation does not occur directly on these surfaces. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermal and structural studies of zinc zirconate nanoscale composite derived from sol–gel process

In the present investigation, a novel synthetic zinc zirconate nanocomposites were prepared by a sol–gel technique using a very stable sol containing zirconium acetylacetonate, zinc acetate, monoethanolamine, and 1,3-propanediol as chelating agent. Thermal analysis results indicated that the decomposition of zinc zirconate precursors occurred at 225 and 234 °C. The influence of thermal annealing (temperatures and duration) on their structural properties has been studied by means of X-ray diffraction and Fourier transform-infrared spectroscopy techniques. The results indicated that a higher percent of zinc zirconate is formed at 800 °C and reached maximum at 1,000 °C in 120 min. The morphology, composition, and bandgap properties of zinc zirconate nanoparticles were characterized by transmission electron microscope, scanning electron microscope (SEM), Energy-dispersive X-ray spectroscopy, and ultraviolet diffiuse reflectance. The SEM observation showed that average grain size of zinc zirconate nanopowders was 58 nm. The optical results revealed maximum absorbances at 394, 413, and 438 nm for ZnZrO₃ sample annealed at 400, 800, and 900 °C for 30 min, respectively. This is an indication that the nanopowder can absorb lights in the higher wavelength.