Photo-response assisted enantiomer separations on an azobenzene-modified gamma-cyclodextrin stationary phase in micro-HPLC.
The photo-responses of the retention and enantioseparation of several optical isomers were evaluated using an azobenzene-modified gamma-cyclodextrin stationary phase (Az gamma-CDSP) in micro-HPLC. UV light irradiation induced a decrease in the retention and the chiral selectivity for N-(3,5-dinitrobenzoyl)-1-phenylethylamine (DNBPEA) and N-(3,5-dinitrobenzoyl)-1-(1-naphtylethyl)amine (DNBNEA), while an increase was induced for dansylphenylalanine (DnsPhe) using a mixture of methanol and aqueous phosphate buffer as the mobile phase. No changes in the retention and the enantiomer separation of benzoin were observed with UV light irradiation. The retention behaviors were recovered by visible-light irradiation. It was speculated that the main factor of the change in the retention behavior was a change in the pi-pi interaction due to the azobenzene moiety of the stationary phase with photo-irradiation. Comparing the retention behavior before and after UV light irradiation, a suitable condition for obtaining a better resolution and enantiomer separation would be chosen using Az gamma-CDSP.
Control of the elution order of enantiomers by light irradiation using azobenzene-modified chiral stationary phases in micro liquid chromatography
In micro liquid chromatography, a method for the reversible control of the elution order of enantiomers by light irradiation was developed. Two photo-responsive chiral stationary phases (CSP(1) and CSP(2)) with an azobenzene moiety were prepared using D- and L-valine, respectively. The prepared stationary phases were continuously packed into a UV-permeable polymer-coated fused-silica capillary tubing (100 μm, i.d.) with 20 cm of length, respectively, and used as a micro column. When 3,5-dinitrobenzoyl-D,L-leucine isopropyl ester and 3,5-dinitrobenzoyl-D,L- alanine methyl ester were used as test samples, the samples were eluted in the order D-form and L-form, after UV light was irradiated to only the part of CSP(1) in the column. Continuously, when UV light was irradiated to the part of CSP(2) after visible light was irradiated to the CSP(1), the elution order became L-form and D-form. It could be seen that a reversible change in the retention order was caused by the reduction of the enantio-selectivity of the stationary phase by UV light irradiation.
Cyclodextrin Bonded Phases For the Liquid Chromatographic Separation of Optical, Geometrical, and Structural Isomers
Application a des separations non realisables auparavant; aminoacides dansyliques, barbiturates, benzopyrenes, etc. Amelioration des separations realisees en chromatographie inverse classique