Solvent Effects on Protonation and Complexation of Glutamic and Aspartic Acids with Molybdenum(VI) in Different Aqueous Solutions of Methanol

Abstract

The formation constants of the species formed in the systems H+ + Mo(VI) + aspartic and glutamic acids and H+ + aspartic and glutamic acids have been determined in different aqueous solutions of methanol [(0 to 40) % v/v] at 25 °C and constant ionic strength (0.1 mol·dm−3 sodium perchlorate), using a combination of spectrophotometric and potentiometric techniques. The composition of the complexes was determined by the continuous variations method. It was shown that molybdenum(VI) forms a mononuclear 1:1 complex with the amino acids of the type MoO3L2− at pH 5.8. The protonation and formation constants in various media were analyzed in terms of Kamlet and Taft’s parameters. Single-parameter correlations of the formation constant, KS, versus α (hydrogen-bond donor acidity), β (hydrogen-bond accepter basicity), and π* (dipolarity/polarizability) are poor in all solutions, but multiparameter correlations represent significant improvements with regard to the single-parameter models. Linear correlation is obser...