ABSTRACT In this research work, a potentiometric technic was used to measure the acidic dissociate constants (pKa,s) for glycyl aspartic acid (GLY-ASP) at temperatures (298.15, 303.15, 313.15, and 318.15) K and in 0.1 mol/l ionic strength of chloride sodium. Using this data, we calculated the thermodynamic properties (changes of enthalpy, ΔH, changes of entropy, ΔS, and changes of Gibbs free energy, ΔG) for acidic dissociation reaction of GLY-ASP. All analyses of data were studied in pH = 1.5-11 and in the aqueous solution. In addition, the value of the acid dissociation constants (pKa1, pKa2, and pKa3), the optimized structure, and the thermodynamic properties of GLY-ASP were calculated in aqueous solution at various temperatures by ab initio and DFT methods. Density function theory (DFT) has been used based on the B3LYP/6-31+G(d) theory to explain the obtained acid dissociation constants of GLY-ASP as well as interactions between solvent and solvated cation, anion, and neutral species of GLY-ASP. Thomasi's method was used to analyze the formation of intermolecular hydrogen bonding between the water molecule and various species of GLY-ASP. In addition, the energy gap of anionic, cationic, and neutral species of GLY-ASP were obtained for dissociation reactions of GLY-ASP. Finally, for GLY-ASP, the theoretically calculated and experimentally determined pKa,s were compared together and a good agreement was observed between them in the first, second, and third ionization constant of GLY-ASP.

Abstract. The protonation constants of the betanin (pKa1, pKa2, and pKa3) were determined in mixed solvent of water and methanol containing 0, 10, 20, 30, 40, 50, 60, 70, and 80 % (v/v) methanol, using a combination of the spectrophotometric and potentiometric methods at T = 25 ºC and constant ionic strength (0.1 mol.dm-3 NaClO4). The obtained protonation constants were analyzed using Kamlet, Abboud, and Taft parameters. KAT parameters are α (hydrogen-bond donor acidity), β (hydrogen-bond acceptor basicity), and π* (dipolarity/polarizability). In this study, a good linear relationship was obtained between protonation constants (on the logarithmic scale) and dielectric constant (ɛ) of the water-methanol mixed solvents. It was found that the dual-parameter correlation between log10K,s and π*, β give us the best result in various volume fractions of methanol for water-methanol mixed solvent. Finally, the results are discussed in terms of the effect of the solvent on the protonation constants.

Resumen. Las constantes de protonación de la betanina (pKa1, pKa2 y pKa3) se determinaron en un disolvente mixto de agua y metanol que contenía metanol al 0, 10, 20, 30, 40, 50, 60, 70 y 80% (v / v), utilizando una combinación de los métodos espectrofotométricos y potenciométricos a T = 25 ºC y fuerza iónica constante (0,1 mol.dm-3 NaClO4). Las constantes de protonación obtenidas se analizaron utilizando los parámetros de Kamlet, Abboud y Taft. Los parámetros KAT son α (acidez del donante de enlaces de hidrógeno), β (basicidad del aceptor de enlaces de hidrógeno) y π* (dipolaridad / polarizabilidad). En este estudio, se obtuvo una buena relación lineal entre las constantes de protonación (en la escala logarítmica) y la constante dieléctrica (ɛ) de los disolventes mixtos agua-metanol. Se encontró que la correlación de doble parámetro entre log10K, s y π*, β nos da el mejor resultado en varias fracciones de volumen de metanol para el disolvente mixto agua-metanol. Finalmente, los resultados se discuten en términos del efecto del solvente en las constantes de protonación.

Abstract. The glycerol, D-glucose monohydrate (DGMH), sucrose, and sodium chloride are used in food industries and the measurement of properties for these components and their aqueous solutions can be important. In this research work, the refractive indices for binary solutions of (methanol + glycerol), (ethanol + glycerol), ternary solutions of (water + glycerol + DGMH), (water + glycerol + sucrose), (water + sucrose + DGMH), (water + sucrose + ethanol), (water + ethanol + DGMH), (water + NaCl + DGMH), (water + methanol + NaCl), (water + ethanol + NaCl), (water + NaCl + glycerol), (water + sucrose + NaCl), and quaternary solutions of (water + ethanol + sucrose + DGMH), (water + ethanol + sucrose + glycerol), (water + NaCl + sucrose + glycerol) were measured in wide range of mole fractions at T = 293.15 K and atmospheric pressure. For binary solutions of this study, the changes of refractive index on mixing, ∆n D, were calculated in each mole fraction at T = 293.15 K. Also, the refractive index of binary solutions was fitted by a semi-empirical equation. The constant of this equation, Kr, was introduced and suggested by Koohyar in 2018. This constant can be used to investigate strength of interactions between solute and solvent molecules. For ternary and quaternary solutions of this study, a semi-empirical equation was used to determine refractive indices at given temperature. The comparison between calculated and experimental refractive indices shows that there is a good agreement between them especially in lower molal concentrations (diluted solution). In other words, linear behavior of the refractive index occurs only in the diluted solutions.

Resumen. El glicerol, D-glucosa monohidrato (DGMH), sacarosa y cloruro de sodio se utilizan en las industrias alimentarias y la medición de las propiedades de estos componentes y sus soluciones acuosas puede ser importante. En este trabajo de investigación, los índices de refracción para soluciones binarias de (metanol + glicerol), (etanol + glicerol), soluciones ternarias de (agua + glicerol + DGMH), (agua + glicerol + sacarosa), (agua + sacarosa + DGMH) , (agua + sacarosa + etanol), (agua + etanol + DGMH), (agua + NaCl + DGMH), (agua + metanol + NaCl), (agua + etanol + NaCl), (agua + NaCl + glicerol), ( agua + sacarosa + NaCl) y soluciones cuaternarias de (agua + etanol + sacarosa + DGMH), (agua + etanol + sacarosa + glicerol), (agua + NaCl + sacarosa + glicerol) se midieron en un amplio rango de fracciones molares en T = 293.15 K y presión atmosférica. Para las soluciones binarias de este estudio, los cambios del índice de refracción en la mezcla, nD, se calcularon en cada fracción molar a T = 293.15 K. Además, el índice de refracción de las soluciones binarias se ajustó mediante una ecuación semi-empírica. La constante de esta ecuación, Kr, fue representada por Koohyar et al. en 2011. Esta constante se puede usar para investigar la fuerza de las interacciones entre las moléculas de soluto y solvente. Para las soluciones ternarias y cuaternarias de este estudio, se utilizó una ecuación semi-empírica para determinar los índices de refracción a una temperatura dada. La comparación entre los índices de refracción calculados y experimentales muestra que existe una buena concordancia entre ellos, especialmente en concentraciones más bajas de molal (solución diluida). En otras palabras, el comportamiento lineal del índice de refracción ocurre solo en las soluciones diluidas

Abstract. The acid-ionization constant (pKa) is an important physico-chemical property of molecules. In this research work, the ab initio and density functional theory (DFT) methods, in combination with the polarized continuum model (PCM), were used to calculate the acid-ionization constant of sulfamethazine (SMZ) and sulfamerazine (SMR) solved in water. For these molecules, the calculated pKa value is in relatively good agreement with the experimental one. Also, in these calculations some structural properties such as dihedral angle between the indicated atoms: D, bond lengths between the indicated atoms: d, Bohr radius: a˳, intermolecular hydrogen bond: IHB, and total atomic charge: au have been determined. These data can be used in nano drug modeling of sulfamethazine and sulfamerazine.

Resumen. La constante de disociación ácida (pKa ) es una propiedad fisicoquímica importante de las moléculas. In este trabajo de investigación se usaron métodos de la teoría de funcionales de la densidad (TFD), en combinación con el modelo continuo polarizado (MCP), para calcular las constantes de ionización de sulfametazina (SMZ) y sulfamerazina (SMR) solvatadas en agua. Para estas moléculas, el valor calculado de pKa es en relativo buen acuerdo con el experimental. Además, en estos cálculos se determinaron algunas propiedades estructurales tales como ángulos diedro (D), longitud de enlace (d), radio de Bohr (a0), enlace de hidrógeno intermolecular (EHI) y carga atómica total (au). Estos datos se pueden usar en el modelado de nano medicamentos de sulfametazina y sulfamerazina.

This work aimed to develop an ab initio procedure for accurately calculating pKa values and applied it to study the acidity of asparagine and glycyl-asparagine. DFT methods with B3LYP composed by 6-31+G(d) basis set were applied for calculating the acidic dissociation constant of asparagine and glycyl-asparagine. The formation of intermolecular hydrogen bonds between the available species and water was analyzed using Tomasi,s method. Results showed that in alkaline solutions, the cation, anion and neutral species of asparagine and glycyl-asparagine were solvated with one, two, three and four molecules of water, respectively. There was an excellent similarity between the experimentally attained pKavalues and the theoretically ones in this work.

No presente trabalho, calculou-se a constante de dissociação do ácido (pKa) dos derivados de muscimol, utilizando-se o método da teoria do funcional de densidade (DFT). Com esse objetivo, calcularam-se os valores das espécies neutra, protonada e desprotonada do muscimol em água em base B3LYP/6-31G(d). A formação da ligação de hidrogênio de todas as espécies foi analisada utilizando o método de Tomasi. Demonstrou-se que os valores de pKa calculados teoricamente estavam em boa concordância com os valores experimentais disponíveis, determinados por eletroforese capilar, titulação potenciométrica e medidas por espectrofotometria UV-visível.

In the present work, acid dissociation constant (pKa) values of muscimol derivatives were calculated using the Density Functional Theory (DFT) method. In this regard, free energy values of neutral, protonated and deprotonated species of muscimol were calculated in water at the B3LYP/6-31G(d) basis sets. The hydrogen bond formation of all species had been analyzed using the Tomasi's method. It was revealed that the theoretically calculated pKa values were in a good agreement with the existing experimental pKa values, which were determined from capillary electrophoresis, potentiometric titration and UV-visible spectrophotometric measurements.

A potentiometric Nickel sensor was prepared using 2-hydroxy-1-naphthylidene-N-cyanoacetohydrazone as electro-active material and epoxy resin as a binding material. A membrane composed of 40% Schiff's base and 60% epoxy resin exhibited the best performance. The membrane showed excellent response in the concentration range of 0.15 ppm to 0.1 mol L- 1 Ni+2 ions with non-Nernstian slope of 22.0 mV/decade, had a rapid response time (less than 10 s), and can be used for three months without any considerable loss of potential. The sensor was useful within the pH range of 1.3 to 9.6, and was able to discriminate between Ni2+ and a large number of alkaline earth and transition metal ions. The practical utility of the sensor has been demonstrated by using it successfully as an indicator electrode in the potentiometric titration of Ni2+ with EDTA and oxalic acid.