Metal ion interactions with antibiotic drugs: Part III-Complex formation of copper(II) with ampicillin

Abstract

Combined <i>p</i>H-metric and spectrophotometric study on the complex formation of Cu²⁺ with ampicillin, <i>α-d</i>-( - )aminobenzylpenicilln, ampH^±, at 37°C in aqueous medium at a fixed ionic strength, <i>l</i>= 0.1 <i>M </i>NaNO₃, indicates formation of complexes of the types: Cu(amp)⁺, Cu(amp)₂ Cu(H_-1 amp), Cu(H_-1 amp)(amp)^- and Cu(H_-1 amp)<img src='http://www.niscair.res.in/jinfo/twobytwo.gif' border=0>. Proton-ligand and metal-ligand constants are found to be: <i>pK</i><img src='http://www.niscair.res.in/jinfo/equation72.gif' border=0> 2.50; <i>pK</i><img src='http://www.niscair.res.in/jinfo/equation73.gif' border=0>, 7.05; <i>pK</i><img src='http://www.niscair.res.in/jinfo/equation74.gif' border=0>(calc.), 13.37; log K<img src='http://www.niscair.res.in/jinfo/equation75.gif' border=0>_(amp), 4.79; log K<img src='http://www.niscair.res.in/jinfo/equation75.gif' border=0>_(amp)₂, 7.70; <i>pK</i><img src='http://www.niscair.res.in/jinfo/equation76.gif' border=0>_(amp), 8.50; <i>pK</i><img src='http://www.niscair.res.in/jinfo/equation76.gif' border=0>_(amp)₂, 9.81; <i>pK</i><img src='http://www.niscair.res.in/jinfo/equation76.gif' border=0><sub>(amp)_{(H_-1,amp)(amp)} 10.31; log <i>β</i><img src='http://www.niscair.res.in/jinfo/equation75.gif' border=0>_{(H_-1,amp)}, -3.71; log <i>β</i><img src='http://www.niscair.res.in/jinfo/equation75.gif' border=0>_{(H_-1,amp)(amp)}, - 2.11; log <i>β</i>_{(H_-1,amp)₂}, -12.42 and log <i>K</i><img src='http://www.niscair.res.in/jinfo/equation76.gif' border=0>_{(H_-1,amp)+(amp)}, - 22.08 ± 0.05. Ambidentate nature of the ligand and its possible modes of coordination with the Cu^{2 +} at different <i>p</i>H values have been elucidated on the basis of electronic spectral measurements.