Complexes of aminophosphonates. Part 3. Copper(II) complexes of several monophosphono and diphosphono dipeptides

Abstract

The stoicheiometries and stability constants of the proton and copper(II) complexes of several monophosphono dipeptides (where the C-terminal carboxylate group is replaced by a phosphonate moiety) and diphosphono dipeptides (where both the C-terminal carboxylate and the N-terminal amino groups are replaced by phosphonate moieties) have been determined pH-metrically at 25°C and at an ionic strength of 0.2 mol dm^–3(KCI). From the stability data and spectral parameters of the complexes, it has been established that the PO₃^2–/CO₂^– and PO₃^2–/NH₂ substitutions do not significantly change the basic bonding modes of the simple dipeptides. However, the copper(II)-induced deprotonation and co-ordination of the peptide-amide group becomes less favoured, although, similarly to the NH₂ group, the terminal PO₃^2– group can act as an anchor to bind the metal ion and thus induce deprotonation of amide NH.