| Abstract: | Chiral discrimination in the energetics of formation of diastereomeric pairs between iron (III)-complex ions bound to poly(L -glutamate) or poly (D -glutamate) and L -catecholamines was measured by differential microcalorimetry at 25°C. When the association of substrates by Fe–polypeptide systems was virtually complete, diastereomeric discrimination energies of a few hundred calories per mol were observed, while diastereomeric discrimination entropies were found to be negligibly small. These results are consistent with the finding that the overall stereoselectivity in the electron transfer reaction between the optically active catecholamines and enantiomeric iron(III) materials—corresponding to Δ(ΔG≠) values around 900 cal/mol—is largely controlled by transition state effects in the kinetics. |
