Coordination properties of 6-aminopenicillanic acid: Binary and ternary complexes involving biorelevant ligands

Formation equilibria of copper(II) complexes of 6-aminopenicillanic acid (APA) and the ternary complexes Cu(APA)B (B = glycine, alanine, valine, isoleucine, phenylalanine, proline, hydroxyproline, serine, threonine, ornithine, histidine, methionine, glycylglycine and inosine) were investigated at 25degreesC and 0.1 M ionic strength. The speciation of the complexes was resolved. Values of Deltalog K, log X and log beta(stat) indicate a large enhancement of the stability of the mixed ligand complexes. The effects of temperature and organic solvent on the dissociation constant of APA and the formation constant of Cu(APA) were studied and thermodynamic parameters were calculated. The solid complex of Cu(APA)CI.2H(2)O was separated and identified by elemental analysis and infrared spectroscopy. In the complex APA is coordinated to copper(II) through the amino group and beta-lactam carbonyl oxygen. Absorption spectra of the binary complexes of copper(II) and APA were also investigated.