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.
Beta-cyclodextrin chiral stationary phases for liquid chromatography. Effect of the spacer arm on chiral recognition.
Cyclodextrins (CDs) can be bound on silica to prepare chiral stationary phases (CSPs) for liquid chromatography. The cyclodextrin ring is connected to a spacer previously bonded on the silica surface. Three different CD-CSPs were prepared with three different spacers. (i) A dimethylethoxysilane with a linear 6 carbon chain produced a monomeric layer. The bonded CD units can move and rotate freely. (ii) The corresponding trimethoxysilane produced a polymeric layer. The bonded CD units were not located at the same distance of the silica surface, but they could still move and rotate freely. (iii) The third spacer contained a cyclohexyl ring that may introduce some conformational rigidity in the CD connection to silica. The three CSPs prepared contained a CD surface coverage of about 0.3 micromol/m(2) which is approximately half of the maximum theoretical CD coverage. The first spacer was the most efficient to bond CDs with an average value of 1.7 spacers per CD ring, whereas 5.5 spacers per CD ring were needed with the two other spacers. The chiral recognition capabilities of the three phases were compared using 14 racemic compounds. No pronounced differences were noted, but the CSP prepared with the dimethylethoxysilane monomeric spacer seems to be the most efficient for chiral recognition.
PHOTORESPONSIVE ARTIFICIAL MEMBRANE. REGULATION OF MEMBRANE PERMEABILITY OF LIPOSOMAL MEMBRANE BY PHOTOREVERSIBLE CIS‐TRANS ISOMERIZATION OF AZOBENZENES
Abstract— Photoresponsive artificial membranes have been prepared by embedding amphiphatic alkyl‐ammonium salts containing azobenzene chromophore in dipalmitoylphosphatidylcholine liposomes. The configurational change due to trans→cis photoisomerization of the azobenzene chromophore provided the perturbation of the membrane structure to result in the increase of the water and bromo‐thymol blue permeability of the liposomal membranes.