Enantiomeric resolution of quinolones on crown ether CSP: Thermodynamics, chiral discrimination mechanism and application in biological samples.

The enantiomers of quinolone racemates were resolved using chiral crown ether within 8 min. Thermodynamics data and modeling results were used to determine chiral recognition mechanism. The column used was (+)-Crownpack column (250 mm × 4.6 mm, 5 µm) with three mobile phases I: ACN:Water (80:20) + 10 mM H2SO4 and 10 mM CH3COONH4, II: ACN:Water (80:20) + 20 mM perchloric acid and III: EtOH:Water (80:20) + 20 mM perchloric acid. The flow rate of the mobile phases was 1.0 mL/min with UV detection at different wavelengths. The ranges of retention (k), separation (α), and resolution (Rs) factors were 1.00-5.40, 1.37-2.00 and 1.50-3.30. The tailing factor was 1.o for all peaks with 900-2325 as the number of theoretical plates were 8.0-10.0 and 32.4-22.1 µg. The difference in enthalpy, entropy and free energy varied in the range of -0.350 to -0.024, 18.74 × 10-4 to 3.94 × 10-4 and -0.918 to -0.143, respectively. The thermodynamic and docking results showed chiral discrimination due to physical forces of amnio group cations penetration into the chiral cavity of the chiral selector following hydrogen bindings. The binding energy of S-enantiomers was higher than R-enantiomers; confirming stronger binding of S-enantiomers with CSP than R-enantiomers. The described chiral-HPLC method was used for the analysis of the quinolone enantiomers in urine samples and the results were quite satisfactory. Therefore, the reported method may be used for the enantiomeric separation of quinolone enantiomers in urine samples.

Cobalt doping of titanium oxide nanoparticles for atenolol photodegradation in water.

Cobalt-doped TiO2 nanoparticles were prepared and characterized by FT-IR, TEM, SEM, and XRD. The surface morphology was sphere-shaped with ~ 26.46 nm of the size of the nanoparticles. Ninety percent atenolol photodegradation was obtained with 15 mg/L concentration, 40 min stirring time, 2 pH, 2.0 g/L dosage of nanoparticles, 200.0 nm irradiation UV wavelength, and hydrogen peroxide amount 2.0 mL/L at 30 °C temp. Atenolol photodegradation conformed the first-order kinetics with a mechanism comprising atenolol sorption on the doped TiO2 nanoparticles and its degradation in UV irradiation. Hole (h+) and electron (e-) pairs are produced by doped TiO2 nanoparticles, creating hydroxyl free radicals and superoxide oxygen anions. These species break down atenolol.

Multi-Walled Carbon Nanotubes Solid-Phase Extraction and Capillary Electrophoresis Methods for the Analysis of 4-Cyanophenol and 3-Nitrophenol in Water.

Analysis of 4-cyanophenol and 3-nitrophenol was carried out using multi-walled carbon nanotubes-based solid-phase extraction (SPE) and capillary electrophoresis (CE) methods. Capillary electrophoresis was carried out with 18 kV voltage, 214 nm detection, and phosphate buffer (pH 7.0, 15 mM) as background electrolyte at 25 ± 1 °C temperature with 15.05 and 16.5 min migration times of 4-cyanophenol and 3-nitrophenol. The separation and resolution factors were 1.10 and 2.90. The optimized experimental conditions were 40 mg/L concentration, 1.0 g multi-walled carbon nanotubes (MWCNTs) per SPE cartridge, 5.0 mL/min flow rate of water, 0.1 mL flow rate of eluting solvent. The maximum recoveries were 91% and 98% at 0.1 mL/min flow rate of 4-cyanophenol and 3-nitrophenol. These methods were applied successfully for extraction and estimation of 4-cyanophenol and 3-nitrophenol in the municipal wastewater. The reported methods are reproducible, efficient, and practical for the estimation of these phenols in water.

Copper carboxymethyl cellulose nanoparticles for efficient removal of tetracycline antibiotics in water.

Copper carboxymethyl cellulose nanoparticles were prepared and characterized by FT-IR, XRD, SEM, TEM, and EDX techniques. Removal of tetracycline was obtained at 90% with optimized parameters of 500 µg/L concentration, 40 min contact time, 7.5 pH, 1.5 g/L dose, and 298 K temp. The adsorption followed Freundlich model very well in comparison to Langmuir. Tempkin model described good interactions between tetracycline and nanoparticles. Dubinin-Radushkevich isotherm confirmed the chemical nature of adsorption. The adsorption was pseudo-second order with a liquid film diffusion kinetics mechanism. The adsorption was endothermic and spontaneous as suggested by thermodynamics results. The supramolecular mechanism was developed for the process. Interestingly, the process was suitable at 7.5 pH with low contact time. These features of the adsorption made this process applicable at natural water conditions, making the process eco-friendly and feasible. Therefore, it may be an excellent method for the removal of tetracycline in any water system.

Synthesis of chitosan composite iron nanoparticles for removal of diclofenac sodium drug residue in water.

Iron composite nanoparticles were prepared (90% yield) using macromolecule chitosan and characterized by spectroscopic techniques (FT-IR, XRD, SEM, TEM & EDX). These were utilized to remove diclofenac sodium in water. The adjusted parameters were 400 µg/ L, 50.0 min., 5.0, 2.0 g/ L and 25.0 °C as concentration, contact time, pH, adsorbent amount and temperature for the elimination of diclofenac sodium in water with maximum 85% elimination. The sorption was spontaneous with exothermic. Data followed Langmuir, Temkin and Dubinin-Radushkevich models. Thermodynamic parameter ΔG° values were -12.19, -13.74 and -15.67 kJ/mol at 20, 25 and 30 °C temperatures. The values of ΔH° and ΔS° were 8.58 and 20.84 kJ/mol. Pseudo-first-order and liquid film diffusion mechanisms were proposed for the adsorption. This adsorption method is fast, effective eco-friendly and low-cost as it may be used in natural circumstances of water resources. The sorption method may be applied for the elimination of diclofenac sodium in any water body at a huge and financial scale.

Nanoporous Iron Oxide/Carbon Composites through In-Situ Deposition of Prussian Blue Nanoparticles on Graphene Oxide Nanosheets and Subsequent Thermal Treatment for Supercapacitor Applications.

This work reports the successful preparation of nanoporous iron oxide/carbon composites through the in-situ growth of Prussian blue (PB) nanoparticles on the surface of graphene oxide (GO) nanosheets. The applied thermal treatment allows the conversion of PB nanoparticles into iron oxide (Fe2O3) nanoparticles. The resulting iron oxide/carbon composite exhibits higher specific capacitance at all scan rates than pure GO and Fe2O3 electrodes due to the synergistic contribution of electric double-layer capacitance from GO and pseudocapacitance from Fe2O3. Notably, even at a high current density of 20 A g-1, the iron oxide/carbon composite still shows a high capacitance retention of 51%, indicating that the hybrid structure provides a highly accessible path for diffusion of electrolyte ions.

Mesoporous PtCu Alloy Nanoparticles with Tunable Compositions and Particles Sizes Using Diblock Copolymer Micelle Templates.

A simple, scalable route for the generation of mesoporous Rh particles by chemical reduction on self-assembled block-copolymer micelle templates was reported recently (Nat. Commun. 2017, 8, 15581). Here, this concept is extended to generate mesoporous PtCu alloy nanoparticles through the same approach. The PtCu alloy particles possess high-surface-area nanoporous architectures and good chemical stability for applications in catalysis. Both the composition and diameter of the bimetallic PtCu nanoparticles can be controlled by adjusting the amount of precursor in the reaction, which affects the electrochemical properties of the material. The combination of the mesoporous structure with the synergistic bimetallic electronic effects of PtCu gives rise to enhanced activity for the catalytic oxidation of methanol compared with commercial Pt black.

Cyano-Bridged Cu-Ni Coordination Polymer Nanoflakes and Their Thermal Conversion to Mixed Cu-Ni Oxides.

Herein, we demonstrate the bottom-up synthesis of 2D cyano-bridged Cu-Ni coordination polymer (CP) nanoflakes through a controlled crystallization process and their conversion to Cu-Ni mixed oxides via a thermal treatment in air. The chelating effect of citrate anions effectively prevents the rapid coordination reaction between Cu2+ and K2[Ni(CN)4], resulting in the deceleration of the crystallization process of CPs. Specifically, with addition of trisodium citrate dehydrate, the number of nuclei formed at the early stage of the reaction is decreased. Less nuclei undergo a crystal growth by interacting with [Ni(CN)4]2-, leading to the formation of larger Cu-Ni CP nanoflakes. Following heat treatment in air, the -CN- groups present within the CP nanoflakes are removed and nanoporous Cu-Ni mixed oxide nanoflakes are generated. When tested as an electrode material for supercapacitors using a three-electrode system, the optimum Cu-Ni mixed oxide sample shows a maximum specific capacitance of 158 F g-1 at a current density of 1 A g-1. It is expected that the proposed method will be useful for the preparation of other types of 2D and 3D CPs as precursors for the creation of various nanoporous metal oxides.

Kinetics, Thermodynamics, and Modeling of Amido Black Dye Photodegradation in Water Using Co/TiO2 Nanoparticles.

Titanium oxide nanoparticles were doped with copper and characterized by XRD, FT-IR, TEM, and SEM. The surface morphology was spherical with 15-26 nm as particle size. The doped titanium oxide (Co/TiO2 ) nanomaterial was used for photodegradation of amido black dye in water. The maximum photodegradation of amido black obtained was 90%. The values of free energy and enthalpy were negative, indicating spontaneous photodegradation of amido black dye. The photodegradation of amido black dye obeyed first-order kinetic model. The photodegradation mechanism of amido black involved adsorption of the dye on the surface of cobalt doped titanium oxide and its degradation under UV radiation. The electron (e- ) and hole (h+ ) pairs were generated by Co/TiO2 , which consequently generated superoxide oxygen anion and hydroxyl free radical. These species degraded amido black dye. The reported method was fast, effective, and economic, which may be utilized to remove amido black in water. The doped TiO2 catalyst was quite stable and can be used up to 5 cycles.

Enantiomeric resolution and modeling of DL-alanine-DL-tryptophan dipeptide on amylose stationary phase.

The enantiomeric resolution of DL-alanine-DL-tryptophan dipeptide is described on amylose stationary phase. The eluent used was CH3 OH─CH3 COONH4 (10mM)─CH3 CN (50: 40, 10) at 0.8-mL/min flow, 230-nm detection, 25-minute run time, and 25°C ± 1°C temperature. The chiral phase was amylose [AmyCoat RP (15 cm × 0.46 cm × 5 micron)]. The magnitudes of the retention factors (k) were 2.71, 3.52, 5.11, and 7.75. The magnitudes of separation factor (α) were 1.19, 1.57, and 1.51 while the resolution factors (Rs) were 3.25, 14.84, and 15.76. The limits of detection and quantitation were of 2.5 to 5.4 and 12.8 to 27.5 µg/mL. The enantiomeric resolution is controlled by hydrogen, hydrophobic, π-π, steric, etc interactions. The elution order of the enantiomer was supported by the modeling data. The described method is fast, reproducible, precise, and selective, which can be used successfully for evaluating the enantiomers of the reported dipeptide.