Complexes of doubly chelating ligands. Part I. Proton and copper(II) complexes of L-β-(3,4-dihydroxyphenyl)alanine (DOPA)

Abstract

The four acid dissociation constants of the DOPA cation have been determined at 25°± 0·02° and 1·0M ionic strength (KNO₃) by means of a glass–calomel electrode system. The reactions of the ligand with copper(II) ions were also examined by potentiometric methods by use of both glass and copper amalgam electrodes, and the polymerisation of copper–DOPA complexes has been studied. Stability constants (measured at 25°± 0·02° and 1·0M ionic strength) for the copper complexes have been measured for both chelating sites and the dimerization constant obtained. The implications of these results with regard to metal-catalysed oxidations of catechol derivatives are discussed.