DETERMINATION OF ENANTIOMERIZATION BARRIERS BY COMPUTER-SIMULATION OF INTERCONVERSION PROFILES - ENANTIOMERIZATION OF DIAZIRIDINES DURING CHIRAL INCLUSION GAS-CHROMATOGRAPHY

A new general computer program has been developed for the simulation of chromatograms featuring dynamic phenomena in chromatography. It has been applied to the determination of enantiomerization barriers by simulation of experimentally observed elution profiles of enantiomers interconverting during their separation on a chiral stationary phase in a chromatographic column. For two diaziridines interconversion profiles could be observed in inclusion gas chromatography using permethylated beta-cyclodextrin dissolved in OV-1701 as stationary phase. The simulation obtained at different temperatures and pressures yielded DELTA-G++s, in the stationary phase 1-4 kJ/mol lower than DELTA-G++m in the mobile phase. From the temperature dependence of DELTA-G++s, the quantities DELTA-H++s and DELTA-S++s in the stationary phase have been determined. Furthermore, the concept of the retention increase R' (caused by the addition of the cyclodextrin to the achiral polysiloxane OV-1701) allowed a separation of the contributions of enantiomerization in the physically dissolved state on the one hand and in the complexed state of the enantiomers on the other hand to the overall enantiomerization barrier in the stationary phase, DELTA-G++s.