Physicochemical Properties of Ampicillin and Amoxicillin as Biologically Active Ligands with Some Alkali Earth, Transition Metal, and Lanthanide Ions in Aqueous and Mixed Solvents at 20, 30, and 40?C

Abstract

The acid-base equilibria of ampicillin and amoxicillin were investigated in pure water and different solvent + water mixtures (solvent = methanol, ethanol, acetone, dimethylformamide, and dimethyl sulfoxide) at a constant ionic strength (I = 0.1 mol-dm−3 KNO3) and organic solvent volume fractions of 10, 20, and 30%. The effect of temperature on these equilibria was studied at 20, 30, and 40∘C. Thermodynamic functions of these ligands were calculated and discussed in terms of ΔG∘, ΔH∘, and ΔS∘. The number of ionizable protons was determined using conductometric titrations. The formation constant of the complexes, which form by reaction of the ligands with Mg(II), Ca(II), Zn(II), Cu(II), Ni(II), Co(II), Ce(III), Pr(III), Eu(III), Gd(III), Ho(III), Er(III), and Yb(III), are determined. The relative stability of the alkali earth, transition, and lanthanide elements are compared with each other and discussed in terms of the ionic radius and the electronic structure of the outer shell of that ion. The results obtained are discussed in terms of macroscopic properties of the mixed solvents and the possible variation in microheterogenity of the solvation shells around the solute.