No abstract

The proton ionization constants (pK 011 and pK 012 ) of phenylglycine were determined in aqueous solution using Bjerrum's potentiometric technique. The measurements were carried out at three ionic strengths [(µ ) 0.05, 0.10, and 0.15) M KNO 3 ] and three temperatures [(25, 35, and 45) °C]. From the data obtained, the thermodynamic ionization constants (pK°0 11 and pK°0 12 ) and the isoelectric points (pI s ) for phenylglycine were calculated. The interactions between phenylglycine and some transition metal ions (Mn 2+ , Ni 2+ , Cu 2+ , Zn 2+ , and Cd 2+ ) were studied at the same conditions of the ionic strengths and temperatures in aqueous media by using the same technique. The stoichiometric and thermodynamic stability constants as well as the degree of formation (n ˜) for all studied systems were determined and discussed. The standard thermodynamic parameters (∆pK°and ∆ log K°) and the thermodynamic parameter differences (∆G°, ∆∆G°, ∆H°, ∆∆H°, ∆S°, and ∆∆S°) were calculated for all possible reactions. Advanced discussions of these functions as well as the factors that may control the ionization and complexation processes from the thermodynamic point of view have been reported.

The refractive indices (n) and the densities (ρ) of: (1) protic‐protic solvent mixtures (methanol‐ethanol, methanol‐porpanol, methanol‐butanol and ethanol‐water), (2) aprotic‐aprotic solvent mixtures (acetonitrile‐dimethylformamide, acetonitrile‐dimethylsulphoxide, and acetonitrile‐1,4‐dioxane) and (3) aprotic‐protic solvent mixtures (dimethylformamide, acetonitrile with water and some aliphatic alcohols) were measured experimentally at different temperatures (25, 30 and 35 °C). From the values of the measured refractive indices and densities, the excess refractive indices (nE), molar refractions (R), atomic polarization (PA), molar volumes (V), solvated radii (r) and polarizabilities (α) of the mixed solvents were calculated. The results show that the solvent‐solvent interaction reaches maximum value at a definite mole fraction (x) of each solvent depending on its nature. Also, the excess refractive indices, densities and atomic polarizations are found to decrease as the temperature increases. On the other hand, the molar volumes, solvated radii, molar refractions and polarizabilities are found to increase as the temperature increases.