Theoretical investigation of adsorption of the gabapentin drug on the heteroborospherene

Structural Chemistry - This is an analysis report on the use of density functional theory (DFT) to investigate the potentials of pristine and amino acid–functionalized C4B32 borospherenes in...     

Selective homogeneous liquid-liquid extraction and preconcentration of copper(II) into a micro droplet using a benzo-substituted macrocyclic diamide, and its determination by electrothermal atomic absorption spectrometry

A fast and reliable method was developed for the selective separation and preconcentration of Cu²⁺ ions using homogeneous liquid-liquid extraction using a novel benzo-substituted macrocyclic diamide, 5,6,7,8,9,10-hexahydro-2H-1,13,4,7,10-benzodioatriazacyclo-pentadecine-3,11(4 H,12 H)-dione, as a selective complexing agent. An aqueous solution of Zonyl FSA (FSA) was used as a phase-separation agent at pH 4.5. Electrothermal atomic absorption spectrometry was used for Cu²⁺ determination after preconcentration. The influences of pH, type and volume of the water-miscible organic solvent, concentration of FSA, concentration of the ligand and the effect of diverse ions were investigated. Factorial design and response surface methods were used for the optimization purposes. Under the optimum experimental conditions, 50 ng of Cu²⁺ in 5 mL aqueous sample could be extracted quantitatively into 76 µL of the sediment phase. The maximum preconcentration factor was 65. The calibration curve was linear in the concentration range 0.2 to 4.0 µg L^?1. The detection limit and relative standard deviation were 4 ng L^?1 and 4.6%, respectively. The method was successfully applied to the extraction and determination of Cu²⁺ in natural water samples.     

Relationship between rheological and electrical percolation in a polymer nanocomposite with semiconductor inclusions

Microstructure, electrical conductivity, and rheological properties of nanocomposites based on isotactic polypropylene (iPP) containing semiconductor nanoparticles of TiO₂ were studied. Compatibilized and uncompatibilized nanocomposites containing a wide range of TiO₂ concentrations (up to 15 vol%) were prepared by melt compounding in a twin-screw extruder via a masterbatch method. An anhydride-modified PP (AMPP) was used as the compatibilizer. Atomic force microscopy (AFM), scanning electron microscopy (SEM), and image analysis techniques were utilized to study the morphology evolution in the samples. Analyzing the results of direct current (DC) electrical conductivity measurements showed a lower percolation threshold for the uncompatibilized samples, compared to the compatibilized ones. In order to estimate the percolation threshold, linear and nonlinear melt-state viscoelastic properties of the samples were studied. Liquid-solid transition and nonterminal behavior of the uncompatibilized samples were observed at relatively lower range of TiO₂ loading, compared to the compatibilized samples. It was an indication of lower rheological percolation threshold in the uncompatibilized nanocomposites which was in agreement with the electrical percolation threshold. Scaling analysis of strain sweep tests above the percolation thresholds of the nanocomposites resulted in a lower fractal dimension for the uncompatibilized samples.     

Experimental and computational study on the aqueous acidity constants of some new aminobenzoic acid compounds

The acidity constants of three new aminobenzoic acid derivatives were determined using potentiometric and spectrophotometric methods in 0.10 M aqueous potassium nitrate solution as supporting electrolyte. The potentiometric data and UV–Vis absorption spectra of solutions were recorded in the course of their pH-metric titration with a standard base solution. The protolytic equilibrium constants, concentration distribution diagrams and number of components involved have been calculated. The relative pK_a values for three acids were also calculated using ab initio quantum mechanical method at the HF/6-31G** level of theory in combination with CPCM continuum solvation method. The influence of substituents on the ionization constants of the studied molecular structures was investigated. The satisfactory agreement between the experimentally derived and theoretically calculated pK_a values provides solid support for the acid–base reactions proposed in this work.