Photo-responsive retention behavior of azobenzene-modified cyclodextrin stationary phase in micro-HPLC

An azobenzene-modified gamma-cyclodextrin stationary phase (Az gamma-CDSP) was prepared and its photo- and temperature-responses for the retention of perylene and pentacene were investigated using a mixture of methanol and water as the mobile phase in micro-HPLC. The retention of perylene slightly increased, whereas that of pentacene significantly decreased by UV light irradiation to Az gamma-CDSP. These retentions recovered upon irradiation with visible light. Both retentions decreased upon an increase in the column temperature. It was presumed that the trans-azobenzene moiety acts as a preventive cap for perylene and a spacing for pentacene in filling the CD cavity. An azobenzene-modified stationary phase changed its retention behavior with the column temperature and the light irradiation. An improvement in the micro-HPLC system and the optimization of the molecular structure of the photo-responsive stationary phase would provide selective retention control by the irradiation of light in micro-separation systems.

Temperature effect on chiral recognition of some amino acids with molecularly imprinted polymer filled capillary electrochromatography

L-Aromatic amino acid imprinted polymers were prepared using azobisnitriles as either photoinitiators or thermal initiators at temperature ranging from 4 to 60 degrees C. Methacrylic acid (MAA) was used as functional monomer and ethylene glycol dimethacrylate (EDMA) was used as cross-linker. The result polymers were ground and sieved to particles < or = 10 microns, filled into the capillary columns and used for enantiomeric separations in capillary electrochromatographic (CEC) mode. The polymer particles < or = 25 were packed into high performance liquid chromatographic (HPLC) columns and used for enantioseparations in the HPLC mode. The mobility and chiral separation of some amino acids were studied on CEC and HPLC columns at different temperature. The relationships of separation factor and column temperatures and demonstrated in linear between logarithm of the separation factor (in alpha) and the inverse of absolute temperature (1/T). Some thermodynamic parameters, such as the apparent change of enthalpy (delta H zero) and the apparent change of entropy (delta S zero), were obtained using van't Hoff plots. The information obtained from the thermodynamic study is discussed in developing strategies for chiral recognitions of amino acids by molecular imprinting technique.

Capillary electrochromatographic separation of amino acid enantiomers using on-column prepared molecularly imprinted polymer

The use of molecularly imprinted polymer polymerized in capillary for the separation of amino acid enantiomers by electrochromatography is described. The substrate-selective polymers were prepared by using L-phenylalanine anilide as print molecule and methacrylic acid and/or 2-vinylpyridine as the functional monomers, which is believed to interact both ionically and through hydrogen bonding with the print molecule. Several aspects of the polymer preparation were investigated, including the treatment of the inside surface of the capillary, the composition of the polymers and the running conditions of the capillary electrochromatography. Such separation was highly specific and depended on the presence of both the print molecule and the functional monomer in the polymerization mixture. This preliminary report demonstrates a novel and simple method for the development of the capillary electrochromatographic separation of amino acid enantiomers using molecularly imprinted polymer.

Separation and determination of some stereoisomers by capillary gel electrophoresis with cyclodextrin incorporated in polyacrylamide gel

Capillary gel electrophoresis (CGE) was successfully applied to the separation of optically active isomers and position isomers by incorporating a suitable cyclodextrin chiral selector in polyacrylamide gel. A commercially available ss-cyclodextrin (ss-CD) was used for enantioselectivity towards o-, m- and p-nitrobenzoic acid, o-, m- and p-hydroxybenzoic acid, o-, m- and p-toluic acid and the optical isomers of dansyl-D,L-leucine and R,S-1,1'-binaphthyl-2,2-dihydrogenphosphate. Especially the effect of organic solvents, such as acetonitrile, methanol, dimethylsulphoxide and others were examined in detail. The resolution varied to some extent with the addition of the organic solvent to the polyacrylamide gel and the running buffer solution. The possible mechanism has also been discussed. In addition, quantitative aspects of the separation of stereoisomers using CGE have been studied, showing that both the resolution and accuracy of the determinations were affected by the ratio of the enantiomers.