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 PO32–/CO2– and PO32–/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 PO32– group can act as an anchor to bind the metal ion and thus induce deprotonation of amide NH.