JOURNAL OF PHYSICAL AND THEORETICAL CHEMISTRY
Year:2012 | Volume:9 | Issue:1|Papers Count:9

According to the Bronsted definition, any compound which has a hydrogen atom is an acid, since it may be lost as a proton. A thermodynamical cycle is proposed to calculate absolute pKa values for Bronsted acids in aqueous solution. The equilibrium of dissociation of a Bronsted acid depends on the interaction of the acid and its conjugate base with solvent molecules. There fore the pKa value depends on the solvent medium. The polarizable continuum model (PCM) was used to describe the solvent, and absolute pKa values were computed for different compounds: HCOOH, CH3COOH, C6H5COOH, FCH2COOH and CH3CH2COOH. The model of furnishes pKa values was in good agreement 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 using the 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 Moller-Plesset perturbation theory levels with 6-31+G (d), 6-31G (d) basis sets for non-metal atoms and LANL2DZ for metal have been performed for the adsorption of dimethyl methylphosphonate (DMMP) on ZnO by Gaussisn 98 program. The calculated rotational constants by B3LYP/6-31G (d) are in more agreement with the experimental values. The type of interaction between the Zn from ZnO and phosphoryl group from DMMP is estimated by AIM analysis. The molecular adsorption occurs by van der waals interaction of Zn...O=P With one Hydrogen bonding, between CH3 groups and oxygen 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 substrates that were coated with various metal nanocatalysts (Au and Ni). A combination of CH4/Ar/H2 renders the growth of carbon nanostructures technique (diamond like carbon). The utilized samples were characterized by the scanning electron microscopy (SEM) and Raman spectroscopy techniques.

This study describes a new simple, sensitive and selective catalytic kinetic spectrophotometric method for the determination of vanadium (V). The method is based upon the catalytic effect of vanadium (V) on the oxidation of Carminic acid by bromate in sulfuric acid media. The reaction was followed spectrophotometrically by measuring the decrease in absorbance at 490 nm and the dependence of sensitivity on the effective reaction variables was studied. Under optimum experimental conditions, the fixed time procedure was used to obtain a calibration curve over the range of 0.05–10.8 mg mL-1of vanadium (V). The calculated detection limit was 0.015 mg mL-1 for twelve replicate measurement of blank signal. The relative standard deviations (n=6) were 1.12, 0.98% for 2.0, 8.0 mg mL-1 of vanadium (V), respectively. The effect of various species commonly associated with vanadium (V) in real samples was also investigated. The proposed method was successfully 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 in aqueous solution using CuO/ZnO as a photocatalyst. The degradation was studied under different conditions 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 by these parameters. The best conditions for the photocatalytic degradation of Lidocaine HCl were obtained. The optimum amount of the photocatalyst used is 0.48 g/L. The photodegradation efficiency of Lidocaine HCl increases with the increase of the illumination time. It was found that the photodegradation efficiency decreased with increasing the initial concentration of Lidocaine HCl. The photodegradation efficiency of Lidocaine HCl was accelerated by adding a small amount of H2O2. The possible roles of the additives on the reactions and the possible mechanisms of effect were also 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 was determined by the solvent evaporation method at 25.0oC. The results enable us to estimate the value of thermodynamic solubility product, Ksp (th), of KCl in the mixed solvent upon the extrapolation method (Ksp (th)=0.1356). Although the model solubility product, Ksp (m), was calculated upon the semi theoretical semi experimental Debey-Huckle theory shows (Ksp (m)=0.2308). Comparing the values of Ksp (th) and Ksp (m) with the concentration solubility product, (Ksp (c)=0.5537), we can see that the differences are noticeable.We assume that, part of the differences comes from non-ideality and the other part from ion association 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 protonation constants of the amino acid and its tautomeric constant have been determined at 25oC and constant ionic strength 0.1 mol dm-3 (NaCl). The protonation and the tautomeric constants of glycine in different binary mixtures were analyzed in terms of Kamlet, Abboud and Taft (KAT) parameters.Single-parameter correlations of the constants versus a (hydrogen-bond donor acidity), b (hydrogenbond acceptor basicity) and p* (dipolarity/polarizability) are poor in all solutions. Multi-parameter correlations show better results, but dual-parameter correlations represent significant improvements with regard to the single- and multi-parameter models. Linear correlation is observed when the experimental protonation constant values are plotted versus the calculated ones, while the KAT parameters are considered. Finally, the results are discussed in terms of the effect of the solvent on protonation and tautomeric constants.