Mixed-ligand complex formation equilibria of copper(II), salicylic acid and some amino acids

Abstract

In this work, the formation of binary and ternary complexes between copper(II), salicylic acid (H2Sal), and between copper(II), salicylic acid (H2Sal) and the amino acids: glycine (HGly), proline (HPro), α-alanine (Hα-Ala), β-Alanine (Hβ-Ala), aspartic acid (H2Asp), glutamic acid (H2Glu) and Histidine (HHis) were studied in aqueous solution at 25°C using 1.0mol·dm−3 KNO3 as the ionic medium. The analysis of the potentiometric data using the least squares computational program LETAGROP indicates the formation of the species Cu(Sal), [Cu(Sal)(OH)]−, [Cu(Sal)2]2−, and [Cu(Sal)2(OH)]3− in the binary Cu(II)-H2Sal system. In the ternary Cu(II)-H2Sal-L where H2L=H2Asp, H2Glu the complexes [Cu(Sal)(HL)]−, [Cu(Sal)(L)]2− and [Cu(Sal)(L)(OH)]3− were observed. For the case of the Cu(II)-H2Sal-HHis system the complexes Cu(Sal)(HL), [Cu(Sal)(L)]− and [Cu(Sal)(L)(OH)]2− were detected. Finally, in the Cu(II)-H2Sal-HL where H2L=glycine (HGly), proline (HPro), α-alanine (Hα-Ala), or β-Alanine (Hβ-Ala) the complexes [Cu(Sal)(L)]− and [Cu(Sal)(L)(OH)]2− were observed.