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

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 (L2-) [HL- and L2- = 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.