Stability constants of the ternary copper(II) complexes with 2-(benzo(d)oxazol-2-yl)nicotinic acid and some amino acids

Abstract

In this work, we present the results from a study of the speciation of the ternary systems formed by copper(II),2-(benzo(d)oxazol-2-yl)nicotinic acid (Oxa, HL) as the main ligand, and the amino acids Serine (Ser, A–), Threonine (Thr, A–), Methionine (Met, A–), Phenylalanine (Phe, A–), Aspartate (Asp, A2–), Glutamate (Glu, A2–), and Histidine (His, A–) as secondary ones. The potentiometric data was analyzed using the computational program LETAGROP for systems in aqueous solution at 25 °C and 1.0 M KNO3 as the ionic medium. The ternary complexes [Cu(L)(HA)]+, [Cu(L)(A)], [Cu(L)2(A)]–, [Cu(L)(A)2]–, [Cu(L)(A)(OH)]– and [Cu(L)(A)(OH)2]2– were detected. The relative stability of the ternary complexes was compared to the binary ones considering the values of ΔlogK and logχ (defined in text of results and analysis). Subsequently using the formation constants, the species distribution diagrams were generated and are briefly discussed. The UV–visible spectra of the ternary complexes show a maximum at 610–654 nm indicating that the Cu2+ is penta-coordinated.