Ternary copper(II) complexes with 2,2′-bipyridine and N-tosyl-substituted amino acids. Part 1. Polarographic and pH-metric study

Abstract

The solution behaviour of ternary complexes of Cu²⁺ with 2,2′-bipyridine (bipy) and N-tosyl (toluene-4-sulphonyl) derivatives of asparagine and glutamine was investigated by pH-metric and polarographic tools, and compared with the corresponding binary Cu²⁺–N-tosylamino acidate systems. The experimental techniques agree about the type and stability of the complex species, in which the amino acidic ligands co-ordinate through the carboxylate group (HL^–) or act as bidentate ligands through the carboxylic oxygen and the deprotonated sulphonamide nitrogen (L^2–)[HL^– and L^2–=N-tosyl-DL-asparaginate (or -L-glutaminate) monoanion and dianion respectively]. The following prevailing species were detected: [Cu(bipy)(HL)₂], [Cu(bipy)L], and [Cu(bipy)L₂]^2–. Evidence has also been obtained for the presence of the species [Cu(bipy)(HL)]⁺ and [Cu₂(bipy)₂L₂(OH)]^–. The copper(II)-promoted sulphonamide deprotonation of the amino acidic ligands in the ternary systems is observed at lower pH values than that in the corresponding binary systems (pH ≈ 5 vs. pH ≈ 7); this effect was not observed for the peptide-nitrogen deprotonation of the ternary copper(II) complexes of peptides with 2,2′-bipyridine.