Thermodynamic stereoselectivity and tridentate co-ordination in the formation of the complexes [Ni(D/L-Methionine) 2

Abstract

A small, but reproducible, stereoselective effect has been observed in both the free energy and enthalpy changes associated with the formation of the bis complexes [Ni(D/L-methionine) 2], obtained from independent potentiometric and calorimetric measurements. The meso-complex, [Ni(D-Met)(L-Met)], is more stable in ΔH than the optically active bis-complexes by 1.0(±0.1) kJ mol −1. This stereoselectivity is attributed to tridentate binding of the methionine and so supports the existence of weak co-ordination between Ni 2+ and the thioether sulphur atom.