Kinetic Effect of Zinc(II) and Cadmium(II) Ions on Configurational Inversion of Δ_LLL-fac(S)-Tris(L-cysteinato-N,S)cobalt(III) Complex

Abstract

It has been confirmed from circular dichroism (CD) spectral changes of aqueous solutions of Δ_LLL-fac(S)-[Co-(L-cys-N,S)₃]^3- that the absolute configurational inversion to the Λ_LLL isomer is remarkably accelerated by zinc(II), while it is retarded by cadmium(II). In the diluted solutions of these metal ions containing excess Δ_LLL-fac(S)-[Co(L-cys-N,S)₃]^3-, the observed inversion rate constant linearly depends on the zinc(II) concentration with an intercept, while it is not affected by the cadmium(II) concentration. The kinetic behavior has been explained by difference between zinc(II)- and cadmium(II)-interactions with lone pairs on sulfur donor atoms of fac(S)-[Co(L-cys-N,S)₃]^3-. It has also been proposed that concentrations of zinc(II) and cadmium(II) can be simultaneously determined by the kinetic measurements.