MEKC with bile salt micelles for the enantiomeric separation of bis(8-((pyridine-2-methylene)amino)quinoline)iron(II) hexafluorophosphate: Kinetics and mechanism of the racemization

Abstract

Unsymmetrical tridentate ligands can form meridional optical isomers in octahedral complexes. Micellar electrokinetic chromatography with sodium taurochenodeoxycholate or glycochenodeoxycholate micelles is used to separate the enantiomers of bis(8-((pyridine-2-methylene)amino)quinoline)iron(II) hexafluorophosphate, Fe(PMAQ)₂(PF₆)₂, and it is used to follow the temperature dependence of the racemization of the isolated enantiomers. The racemization is studied over a 20° temperature range (60–80°C), and at four different pH values (3.0, 4.45, 7.0, 9.0). Energies and entropies of activation are reported. There is no significant change in the energy of activation as a function of pH. Simple capillary electrophoretic instrumentation with manual, electrokinetic injection, and ambient run temperature conditions provides reliable kinetic data. Half-lives range from 28 to 640 min. A mechanism involving a trigonal prism transition state is proposed for this racemization process. © 2000 John Wiley & Sons, Inc. J Micro Sep 12: 391–397, 2000