Kevin M. Lewandowski

Chiral electrochromatography with a ‘moulded’ rigid monolithic capillary column

Several monolithic chiral stationary phases for reversed-phase electrochromatography have been prepared within the confines of untreated fused silica capillaries by the direct copolymerization of the chiral monomer 2-hydroxyethyl methacrylate (N-L-valine-3,5- dimethylanilide) carbamate with ethylene dimethacrylate, 2-acrylamido-2-methyl-1-propanesulfonic acid and butyl or glycidyl methacrylate in the presence of a porogenic solvent. The hydrophilicity of the stationary phase, which may be enhanced further by the hydrolysis of the epoxide functionalities of the glycidyl methacrylate moieties within the monolith, was found to have a pronounced effect on the enantioseparation. Using the most hydrophilic monolithic capillary column and optimized elution conditions, a separation of N-(3,5-dinitrobenzoyl)leucine diallylamide enantiomers with an efficiency of 61000 plates m–1 and a resolution of 2.0 was achieved.

Highly selective chiral recognition on polymer supports: preparation of a combinatorial library of dihydropyrimidines and its screening for novel chiral HPLC ligands

A library of more than 140 racemic 4-aryl-1,4-dihydropyrimidines has been synthesized using the single step Biginelli multicomponent condensation; the individual compounds were screened for enantiomer resolution, and the best candidate attached to a solid macroporous polymer support to afford a highly selective separation medium for chiral HPLC.

A Novel Polar Separation Medium for the Size Exclusion Chromatography of Small Molecules: Uniformly Sized, Porous Poly(vinylphenol-co-divinylbenzene) Beads

Abstract A novel separation medium based on uniform size beads of 4-hydroxystyrene-divinylbenzene can be used for both the size exclusion chromatography of small molecules and their separation by reversed-phase chromatography. The new 5 μm material is prepared by the controlled swelling of monodispersed polystyrene particles, that serve both as porogen and shape template, with a polymerization mixture consisting of the monomers and dibutylphthalate, followed by a suspension polymerization. Removal of the acetoxy groups by hydrolysis with aqueous base leads to the final poly(4-vinylphenol-co-divinylbenzene) monodispersed beads. Polymerization conditions that favor the formation of very small pores were developed to optimize the beads for the SEC separation of small molecules. The SEC calibration curve confirms that the optimized beads contain a large volume of pores suitable for the separation of solutes with a molecular weight of up to about 1000. The ability to separate alkylbenzenes according to their h...

COMBINATORIAL 'LIBRARY ON BEAD' APPROACH TO POLYMERIC MATERIALS WITH VASTLY ENHANCED CHIRAL RECOGNITION

A general screening method for enantiomer recognition is introduced for the rapid preparation of novel chiral stationary phases for HPLC in which libraries of mixed chiral selectors are immobilized on polymer beads and the resulting chiral phases tested in the separation of racemic targets followed by deconvolution to afford an optimized separation medium.