Potentiometric studies on some cephalosporin complexes

The interaction of Ca(II), Cu(II), Zn(II), Pb(II), and La(III) ions with th e antibiotics cephalexin, cefadroxil, cephaloridine, and cefoperazone as se condary ligands was investigated potentiometrically. The formation constant s were determined for a ligand-to-metal ratio of 1:1 at 25 degreesC and I = 0.1 mol . dm(-3) KNO3. The protonation constants of the complexes were eva luated for the system M : cephalosporin: glycine = 1:1:1. The order of stab ility of the binary and ternary complexes were examined. It was found that glycine adds preferably [M(II)-cephalosporin] rather than to the aqueous co mplexes of M(II). In all cases 1:1:1 complexes were formed.