Complexes of nickel(II) withS-carboxyalkyl-L-cysteines in aqueous medium. Determination of enthalpies by thermometric titrimetry

Abstract

Molar heats for the reaction of nickel(II) with sulphur-containing amino acids,S-carboxymethyl-L-cysteine andS-carboxyethyl-L-cysteine, have been determined by thermometric titrimetry. The data refer to aqueous solutions at 25°C andI=2.0m. From these enthalpies and equilibrium constants, the corresponding entropies have been calculated. The present thermodynamic data are complementary to previous spectrophotometric data in explaining the structures of the complexes. In particular, the importance of solute-solvent external factors in determining different stabilities for successive steps of complex-formation is stressed.