Molecularly imprinted monolithic stationary phases for liquid chromatographic separation of enantiomers and diastereomers

The method for preparation of molecularly imprinted monolithic stationary phase has been improved to achieve liquid chromatographic separation of enantiomers and diastereomers. By adopting low polar porogenic solvents of toluene and dodecanol and optimal polymerization conditions, the molecularly imprinted monolithic stationary phases with good flow-through properties and high resolution were prepared. Enantiomers of amino acid derivatives and diastereomers of cinchona alkaloids were completely resolved using the monolithic stationary phases. The influence of porogenic composition, monomer-template ratio and polymerization conditions on the chromatographic performance was investigated. Some chromatographic conditions such as the composition of the mobile phase and the temperature were characterized. Scanning electron microscopy showed that the molecularly imprinted monolithic stationary phase has a large through-pore structure to allow the mobile phase to flow through the column at very low backpressure. Accelerated separations of enantiomers and diastereomers were therefore achieved at elevated flow rates. Finally, the chiral recognition performance of the prepared stationary phase in aqueous media was investigated. Hydrophobic interaction, and ionic and/or hydrogen bonding interactions were proposed to be responsible for the recognition mechanism. (C) 2002 Elsevier Science B.V. All rights reserved.

Capillary electrochromatography for separation of peptides driven with electrophoretic mobility on monolithic column

A mode of capillary electrochromatography for separation of ionic compounds driven by electrophoretic mobility on a neutrally hydrophobic monolithic column was developed. The monolithic column was prepared from the in situ copolymerization of lauryl methacrylate and ethylene dimethacrylate to form a C-12 hydrophobic stationary phase. It was found that EOF in this hydrophobic monolithic column was very poor, even the pH value of mobile phase at 8.0. The peptides at acidic buffer were separated on the basis of their differences in electrophoretic mobility and hydrophobic interaction with the stationary phase; therefore, different separation selectivity can be obtained in CEC from that in capillary zone electrophoresis (CZE). Separation of peptides has been realized with high column efficiency (up to 150 000 plates/meter) and good reproducibility (migration time with RSD < 0.5%), and all of the peptides, including some basic peptides, showed good peak symmetry. Effects of the mobile phase compositions on the retention of peptides at low pH have been investigated in a hydrophobic capillary monolithic column. The significant difference in selectivity of peptides in CZE and CEC has been observed. Some peptide isomers that cannot be separated by CZE have been successfully separated on the capillary monolithic column in this mode with the same buffer used.

Protein A immobilized monolithic capillary column for affinity chromatography

Monolithic capillary columns for affinity chromatography were prepared by an in situ polymerization procedure using glycidyl methacrylate (GMA) as a monomer and trimethylolpropane trimethacrylate (TRIM) and ethylene dimethacrylate (EDMA) as cross-linkers, respectively. Scanning electron microscopy was applied to characterize the morphology of the end of monolithic capillary and mercury intrusion porosimetry to characterize the polymer rod prepared within the confines of a stainless steel column with 50 mm x 4.6 mm i.d. under the same polymerization condition. Obvious differences in the porous properties between the TRIM- and EDMA-based monoliths could be observed. Moreover, the mechanical stability of these two monolithic capillary columns was compared by testing the reproducibility of the column performance. The rod prepared with GMA and TRIM proved to be mechanically more stable than that prepared with GMA and EDMA. Protein A was immobilized on the monolithic rod for affinity chromatography and the experiments were performed on a capillary electrophoresis instrument, using its pressure system as the driving force. Non-specific adsorption was not observed on the TRIM-based affinity column, as proved with bovine serum albumin (BSA) as a test protein. The affinity column prepared with GMA and TRIM was then applied to determine the hIgG concentration in human serum. The correlative coefficient of the calibration curve reached 0.9942. The amount of adsorbed hIgG was unaffected by the flow rate of the loading buffer, which makes this method suitable for fast determination of biomacromolecules in microliter samples. (C) 2002 Elsevier Science B.V All rights reserved.

Crystallization Behaviors of n-Octadecane in Confined Space: Crossover of Rotator Phase from Transient to Metastable Induced by Surface Freezing

In this paper, the confined crystallization and phase transition behaviors of n-octadecane in microcapsules with a diameter of about 3 Pm were studied with the combination of differential scanning calorimetry (DSC), temperature dependent Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD).

Template-free fabrication of hexagonal ZnO microprism with an interior space

Well-faceted hexagonal ZnO microprisms with regular interior space have been successfully prepared by a template-free hydrothermal synthetic route. The morphologies of the products depend on the experimental conditions such as the solvent, the concentration of ammonia aqueous solution, and the reaction temperature. Through manipulation of the aging time, the as-prepared ZnO can be controlled as a monodispersed hexagonal twinning solid or as hollow microprisms. Moreover, the evolution process of the hollow ZnO nanoarchitecture after reaction for 2, 6, 12, and 24 h has been investigated by field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). A possible growth mechanism has also been proposed and discussed. Furthermore, the photoluminescence (PL) measurement exhibits the unique emitting characteristic of hollow ZnO nanostructures.

Peripheries of molecular projection in three-dimensional space and studies of quantitative structure-activity relationships

A new index, i.e., the periphery representation of the projection of a molecule from 3D space to a 2D plane is described. The results, correlation with toxicity of substituted nitrobenzenes, obtained by using periphery descriptors are much better than that obtained by using the areas (i.e., shadows) of projections of the compounds. Even better results were achieved by using the combination of periphery descriptors and the projections areas as well as the indicated variable K reflecting the action of group NO position on the benzene ring.

Crystallization behaviors of n-nonadecane in confined space: Observation of metastable phase induced by surface freezing

Crystallization and phase transition behaviors of n-nonadecane in microcapsules with a diameter of about 5 mu m were studied with the combination of differential scanning calorimetry ( DSC) and synchrotron radiation X-ray diffraction ( XRD). As evident from the DSC measurement, a surface freezing monolayer, which is formed in the microcapsules before the bulk crystallization, induces a novel metastable rotator phase ( RII), which has not been reported anywhere else. We argue that the existence of the surface freezing monolayer decreases the nucleating potential barrier of the RII phase and induces its appearance, while the lower free energy in the confined geometry turns the transient RII phase to a " long- lived" metastable phase.

Atom space distance and computing of molecular similarity

A mathematical model on computation of molecular similarity was suggested, The algorithmic techniques for measuring the degree of similarity between pairs of three-dimensional chemical molecules was represented by modified interatomic distance matrices. Current work was carried out on Indigo 2 work station with Sybyl software. Four groups of molecules were used to compute the molecules similarity to testing the mathematical model with satisfactory results.