Journal of Physical and Theoretical Chemistry
Volume:9 Issue: 1, Spring 2012

According to the Bronsted definition, any compound which has a hydrogen atom is an acid, since itmay be lost as a proton. A thermodynamical cycle is proposed to calculate absolute pKa values forBronsted acids in aqueous solution. The equilibrium of dissociation of a Bronsted acid depends onthe interaction of the acid and its conjugate base with solvent molecules. There fore the pKa valuedepends on the solvent medium. The polarizable continuum model (PCM) was used to describe thesolvent, and absolute pKa values were computed for different compounds: HCOOH, CH3COOH,C6H5COOH, FCH2COOH and CH3CH2COOH. The model of furnishes pKa values was in goodagreement with the experimental results for some classes of compounds. The quantum Mechanics(QM) calculations were carried out with the GAUSSIAN 98 program based on HF/6-31+G** level.

The IR and NMR spectra were coupled with quantum chemical calculations in DFT approach usingthe hybrid B3LYP exchange-correlation functional to confirm the structure of 2-methoxycarbonyl-7-methyl-1,3-thiazino[3,2-b][1,2,4]triazine-4,8-dione 2d.

Ab initio calculations at the density functional theory (DFT) and the second-order Møller−Plessetperturbation theory levels with 6-31+G(d), 6-31G(d) basis sets for non-metal atoms and LANL2DZfor metal have been performed for the adsorption of dimethyl methylphosphonate (DMMP) on ZnOby Gaussisn 98 program. The calculated rotational constants by B3LYP/6-31G(d) are in moreagreement with the experimental values. The type of interaction between the Zn from ZnO andphosphoryl group from DMMP is estimated by AIM analysis. The molecular adsorption occurs byvan der waals interaction of Zn⋯O=With one Hydrogen bonding, between CH3 groups andoxygen of zinc oxide.

Diamond like carbon (DLC) film was grown by hot filament chemical vapor deposition (HFCVD)technique. In the present work, we investigated the quality of the DLC films groew on the substratesthat were coated with various metal nanocatalysts (Au and Ni). A combination of CH4/Ar/H2 rendersthe growth of carbon nanostructures technique (diamond like carbon). The utilized samples werecharacterized by the scanning electron microscopy (SEM) and Raman spectroscopy techniques.

This study describes a new simple, sensitive and selective catalytic kinetic spectrophotometricmethod for the determination of vanadium (V). The method is based upon the catalytic effect ofvanadium (V) on the oxidation of Carminic acid by bromate in sulfuric acid media. The reaction wasfollowed spectrophotometrically by measuring the decrease in absorbance at 490 nm and thedependence of sensitivity on the effective reaction variables was studied. Under optimumexperimental conditions, the fixed time procedure was used to obtain a calibration curve over therange of 0.05–10.8 μg mL-1of vanadium (V). The calculated detection limit was 0.015 μg mL-1 fortwelve replicate measurement of blank signal. The relative standard deviations (n = 6) were 1.12,0.98% for 2.0, 8.0 μg mL-1 of vanadium (V), respectively. The effect of various species commonlyassociated with vanadium (V) in real samples was also investigated. The proposed method wassuccessfully applied for the determination of vanadium (V) in water and standard alloy samples.

In this paper, the photocatalytic degradation of Lidocaine HCl, an anesthetic was investigated inaqueous solution using CuO/ZnO as a photocatalyst. The degradation was studied under differentconditions including the amount of the photocatalyst, irradiation time, initial concentration of drug,pH of the system, initial concentration, addition of oxidant on the reaction rate and anion presence.The results showed that the photocatalytic degradation of Lidocaine HCl was strongly influenced bythese parameters. The best conditions for the photocatalytic degradation of Lidocaine HCl wereobtained. The optimum amount of the photocatalyst used is 0.48 g/L. The photodegradationefficiency of Lidocaine HCl increases with the increase of the illumination time. It was found that thephotodegradation efficiency decreased with increasing the initial concentration of Lidocaine HCl.The photodegradation efficiency of Lidocaine HCl was accelerated by adding a small amount ofH2O2. The possible roles of the additives on the reactions and the possible mechanisms of effect werealso discussed.

In this study, the ion association phenomenon in the saturated solution of KCl in the mixed solvent(methanol+water) was studied. The solubility of this compound in the mixed solvent (methanol+water by value percent of methanol = 60%), and in the presence of various molarities of NaNO3 wasdetermined by the solvent evaporation method at 25.0°C. The results enable us to estimate the valueof thermodynamic solubility product, Ksp(th), of KCl in the mixed solvent upon the extrapolationmethod (Ksp(th) = 0.1356). Although the model solubility product, Ksp(m), was calculated upon the semitheoretical semi experimental Debey-Huckle theory shows (Ksp(m) = 0.2308 ). Comparing the valuesof Ksp(th) and Ksp(m) with the concentration solubility product, (Ksp(c) = 0.5537), we can see that thedifferences are noticeable.We assume that, part of the differences comes from non-ideality and the other part from ionassociation phenomenon.

The acid-base equilibria of glycine have been studied in different aqueous solutions of 1,4-dioxane(0-50 % by v/v) using potentiometric method. In this study, the macro and micro protonationconstants of the amino acid and its tautomeric constant have been determined at 25 °C and constantionic strength 0.1 mol dm-3 (NaCl). The protonation and the tautomeric constants of glycine indifferent binary mixtures were analyzed in terms of Kamlet, Abboud and Taft (KAT) parameters.Single-parameter correlations of the constants versus α (hydrogen-bond donor acidity), β (hydrogenbondacceptor basicity) and π* (dipolarity/polarizability) are poor in all solutions. Multi-parametercorrelations show better results, but dual-parameter correlations represent significant improvementswith regard to the single- and multi-parameter models. Linear correlation is observed when theexperimental protonation constant values are plotted versus the calculated ones, while the KATparameters are considered. Finally, the results are discussed in terms of the effect of the solvent onprotonation and tautomeric constants.