Thermodynamic and spectroscopic studies on the protonation and Cu2+ complex formation of a synthetic amino diacid: (3-aminopropyl)malonic acid

Abstract

The basicity constants of (3-aminopropyl)malonate have been determined in 0.1 mol dm^–3 NaCl at 25 °C. The structures of the different protonated forms were investigated by Fourier-transform i.r. techniques in aqueous solution and molecular mechanics. The presence of an intramolecular hydrogen bond in the diprotonated form is suggested. On the basis of the structures proposed, the heats and entropies of the protonation are discussed. Three complexes are found with Cu²⁺, of formulae [CuHL]⁺, [CuH₂L₂], and [Cu(HL₂)]^–[H₂L =(3-aminopropyl)malonic acid]. Their structures have been hypothesized on the basis of the thermodynamic and spectroscopic parameters. In all the complexes investigated the co-ordination of both CO₂^– groups is achieved.