Potentiometric Studies on Some α-Amino Acid-Schiff Bases and Their Manganese(III) Complexes in Dimethyl Sulfoxide–Water Mixtures at 25°C

Abstract

In this study the stoichiometric protonation constants were determined for some α-amino acids (glycine, L-alanine, L-methionine, L-phenylalanine, and L-threonine), the Schiff bases derived from them and 2-hydroxy-1-naphthaldehyde, along with the stoichiometric stability constants of Schiff base–Mn(III) complexes. These equilibrium constants were determined potentiometrically using a combined pH electrode system calibrated in concentration units of the hydrogen ion at 25°C, and at an ionic strength of 0.10 mol-dm−3 NaCl in 30 and 50% dimethyl sulfoxide–water mixtures. The calculations of these constants were carried out using the PKAS and the BEST computer programs. In addition, the effects of solvent composition and structures on the protonation and the complex formation constants were investigated. The mole ratio of Mn(III) to amino acid-Schiff bases was also determined and it was found that the complexes were of the MnL2 type.