Interaction of ampicillin with Mn(II), Co(II), and Ni(II) ions

The interaction of ampicillin with the Mn²⁺, Co²⁺, and Ni²⁺ ions in aqueous solution at 20°C (supporting electrolyte 0.1 M KNO₃) was studied pH-metrically and spectrophotometrically. In weakly acidic and neutral media, Ni²⁺ forms with the anionic ampicillin species 1: 1 and 1: 2 complexes, whereas Mn²⁺ and Co²⁺ form only 1: 1 complexes. The stability constants of the complexes were determined, and their possible structures were discussed.