Ionic strength dependence of formation constants, protonation and complexation of phenylalanine with dioxovanadium(V) at different temperatures

The protonation constants of phenylalanine and the stability constants of t he complexes between dioxovanadium(V) ion and phenylalanine have been deter mined spectrophotometrically, in the temperature range 15-35 degrees C and ionic strength ranging from 0.1 to 1.5 mol dm(-3) sodium perchlorate as a b ackground salt, in the pH range 1.5-10.5, with high ligand to metal ratios. The values of enthalpy and entropy changes based on these formation consta nts were calculated. The dependence of protonation and the stability consta nts on ionic strength are described by a Debye-Huckel type equation.