Formation studies of binary and ternary complexes of copper(II) with an oxazol derivative of nicotinic acid and some amino acids

Binary and ternary complexes of copper(II) with the 2-(benzo[d]oxazol-2-yl)nicotinic acid (Ligand HL) and the amino acids Glycine (HGly, HB), Proline (HPro, HB), alpha-Alanine (H alpha-Ala, HB), beta-Alanine (H beta-Ala, HB) were studied in aqueous solution at 25 degrees C, using 1.0 mol . dm(-3) KNO3 as the ionic medium. The types of complexes formed and their overall stability constants were established on the basis of the computer analysis of the potentiometric data, using a version of the program LETAGROP. It was inferred that the aromatic oxazol Ligand L-1 acts as a primary ligand in the ternary complexes, while the oxygen and nitrogen donor-containing amino acids are the secondary ligands. The analysis showed the formation of five complexes: [Cu(L)(HB)](+), Cu(L)(B), [Cu(L)(B) (OH)(-), [Cu(L)(2)(B)](-) and [Cu(L)(B)(2)](-) in the Cu(II)-L--Gly and Cu(II)-L--beta Ala systems, for the Cu(II)-L--Pro system, the complexes [Cu(L)(HB)](+), Cu(L)(B), [Cu(L)(B)(OH)(-) and [Cu(L)(B)(2)](-) were detected and, finally, in the Cu(II)- L- - alpha Ala system, only the complexes [Cu(L)(HB)](+), Cu(L)(B) and [Cu(L)(B)(OH)(-) were observed. The concentration distributions of various species formed in aqueous solution were also evaluated as a function of pH. (C) 2016 Elsevier B.V. All rights reserved.