Complexation du cuivre(II) par les phénylsérines thréo et érythro: étude thermodynamique

Abstract

Conductimetric and potentiometric measurements in aqueous solution as a function of temperature show that cupric ions promote the deprotonation of the hydroxy side chain of threo and erythro β-phenylserines. The threo ligand yields at 298 K the formation constants: Cu(L), K1 = 7.99; Cu(L)2, K2 = 6.71; Cu(L2H−1), K3 = −9.51; Cu(L2H−2), K4 = −10.83. The erythro isomer yields the corresponding constants: K1 = 7.70, K2 = 6.70, K3 = −9.82, and K4 = −11.20. Thermodynamic parameters for the first two complexation steps are −ΔH = 21.3 and 44.7 kJ mol−1; ΔS = 82 and 132 J K−1 mol−1, respectively, for the threo form and −ΔH = 20.7 and 44.1, ΔS = 79 and 129 for the erythro form. Deprotonation of the complexes corresponds to an additional enthalpy of −21 kJ mol−1. These results and the structures of the complexes are discussed.