Determination of fluoroquinolone antibiotics in surface waters from Mondego River by high performance liquid chromatography using a monolithic column

A novel LC-fluorescence detection method based on the use of a monolithic column for the determination of norfloxacin, ciprofloxacin, and enrofloxacin antibiotic residues in environmental waters was developed. Fluoroquinolones (FQs) were isocratically eluted using a mobile phase consisting of 0.025 M phosphoric acid solution at pH 3.0 with tetrabutylammonium and methanol (960:40, v/v) through a Chromolith Performance RP-18e column (100x4.6 mm) at a flow rate of 2.5 mL/min and detected at excitation and emission wavelengths of 278 and 450 nm, respectively. After acidification and addition of EDTA, water samples were extracted using an Oasis HLB cartridge. Linearity was evaluated in the range of 0.05 to 1 microg/mL and correlation coefficients of 0.9945 for norfloxacin, 0.9974 for ciprofloxacin, and 0.9982 for enrofloxacin were found. The limit of quantification was 25 ng/L for the three FQs. The recovery of FQs spiked into river water samples at 25, 50, and 100 ng/L fortification levels ranged from 76.5 to 91.0% for norfloxacin, 78.5 to 97.2% for ciprofloxacin, and 79.4 to 93.6% for enrofloxacin. This method was successfully applied to the analysis of water samples from the Mondego River, and ciprofloxacin and enrofloxacin residues were detected in eight water samples.     

Water Interaction with Iron Oxides

We present a mechanistic study on the interaction of water with a well‐defined model Fe₃O₄(111) surface that was investigated by a combination of direct calorimetric measurements of adsorption energies, infrared vibrational spectroscopy, and calculations bases on density functional theory (DFT). We show that the adsorption energy of water (101 kJ mol⁻¹) is considerably higher than all previously reported values obtained by indirect desorption‐based methods. By employing ¹⁸O‐labeled water molecules and an Fe₃O₄ substrate, we proved that the generally accepted simple model of water dissociation to form two individual OH groups per water molecule is not correct. DFT calculations suggest formation of a dimer, which consists of one water molecule dissociated into two OH groups and another non‐dissociated water molecule creating a thermodynamically very stable dimer‐like complex.     

Origin‐independent sum over states simulations of magnetic and electronic circular dichroism spectra via the localized orbital/local origin method

Although electronic and magnetic circular dichroism (ECD, MCD) spectra reveal valuable details about molecular geometry and electronic structure, quantum‐chemical simulations significantly facilitate their interpretation. However, the simulated results may depend on the choice of coordinate origin. Previously (?těpánek and Bou?, J. Comput. Chem. 2013, 34, 1531), the sum‐over‐states (SOS) methodology was found useful for efficient MCD computations. Approximate wave functions were “resolved” using time‐dependent density functional theory, and the origin‐dependence was avoided by placing the origin to the center of mass of the investigated molecule. In this study, a more elegant way is proposed, based on the localized orbital/local origin (LORG) formalism, and a similar approach is also applied to generate ECD intensities. The LORG‐like approach yields fully origin‐independent ECD and MCD spectra. The results thus indicate that the computationally relatively cheap SOS simulations open a new way of modeling molecular properties, including those involving the origin‐dependent magnetic dipole moment operator. © 2015 Wiley Periodicals, Inc.     

Hydrogenation of coumarin to octahydrocoumarin over a Ru/C catalyst

The production of octahydrocoumarin, which can serve as a replacement for toxic coumarin, was investigated using 5% Ru on active carbon (Ru/C) as the catalyst for the hydrogenation of couma-rin. The hydrogenation was studied by optimizing the reaction conditions (pressure, solvent and coumarin concentration). The activity and selectivity of the Ru/C catalyst were compared for dif-ferent solvents. The mechanism of coumarin hydrogenation was deduced. The formation of side products was explained. The optimal hydrogenation reaction conditions were: 130 °C, 10 MPa, 60 wt% coumarin in methanol, and 0.5 wt% (based on coumarin) of Ru/C catalyst. At the complete conversion of coumarin, the selectivity to the desired product was 90%.     

Detection of hydrogen peroxide and glucose by enzyme product precipitation on sensor surface

Biocatalysed precipitation of an insoluble product accumulated on the enzyme-modified electrode surface was applied as the amplification path for low concentration sensing of hydrogen peroxide and glucose. Sensitive electrochemical and quartz-crystal microbalance (QCM) biosensors based on biocatalytic precipitation were developed. A horseradish peroxidase (HRP) monolayer-modified electrode was used to sense H₂O₂ via the oxidation of 4-chloro-1-naphthol (4CN) forming insoluble benzo-4-chlorocyclohexadienone. Additionally, the bienzyme system employed glucose oxidase (GOx) linked to HRP/4CN. The amount of the precipitate assembled on the sensing surface corresponded to the concentration of analytes and to the length of the incubation interval. The precipitated deposits were followed as a change of impedance using cyclic voltammetry (CV), mass change was determined continuously using a microgravimetric quartz-crystal microbalance, and optical microscopy enabled the visualisation of the precipitate. Regeneration of the enzyme-modified electrode was performed using cathodic reduction of the insoluble product. Thus, a simple biosensor for multiple analyses with low detection limits and of low cost can be developed.     

Phenol‐Substituted Tetrapyrazinoporphyrazines: pH‐Dependent Fluorescence in Basic Media

Tetrapyrazinoporphyrazines (TPyzPzs) bearing one, two, four or eight 3,5‐di(tert‐butyl)‐4‐hydroxyphenol moieties were synthesized as zinc(II) complexes and metal‐free derivatives. The deprotonation of the phenol using tetrabutylammonium hydroxide induced the formation of a strong donor for intramolecular charge transfer that switched OFF the red fluorescence (λ_F～660 nm) of the parent zinc TPyzPzs. The changes were fully reversible for TPyzPzs with one to four phenolic moieties, and an irreversible modification was observed for TPyzPzs substituted with eight phenols. The sensors were anchored to lipophilic particles in water, and a pK_a approximately 12.5–12.7 was determined for the phenolic hydroxyl based on fluorescence changes in different buffers. In addition, a novel concept for fluorescence OFF‐ON‐OFF switching in metal‐free TPyzPzs bearing phenolic moieties upon addition of specific amounts of base was demonstrated.     

Effect of Layering Pattern on the Mechanical Properties of Bark Cloth (Ficus natalensis) Epoxy Composites

The quest for sustainable materials as a consequence of a global drive to mitigate climate change has led to a focus on natural fiber–reinforced composite materials. In this study, skillful ply angle arrangement of bark cloth–reinforced laminar epoxy composites was carried out for the first time using vacuum-assisted resin transfer molding, and the composites fabricated were characterized for the effect of the layering pattern on their static and dynamic mechanical properties. Tensile strength and flexural strength were shown to be dependent on the ply angle arrangement. Dynamic mechanical analysis of the composites showed a glass transition temperature of 70°C, and the storage modulus and mechanical damping properties showed that the developed composites can withstand considerable loads and have excellent fiber-to-matrix adhesion.     

The extraction of europium and americium by the nitrobenzene solution of dicarbollylcobaltate in the presence of some commercially available dioxadiamides

Journal of Radioanalytical and Nuclear Chemistry - We investigated the extraction of microamounts of Eu3+ and Am3+ from aqueous nitric acid solutions using nitrobenzene solutions of hydrogen...