Liangmo Zhou

Membrane affinity chromatography of alkaline phosphatase

Abstract A method for the preparation of a microporous cellulose membrane is described. The triazine dyes Cibacron Blue F3GA and Active Red K2BP were immobilized as affinity ligands. Up to 90 mg of Active Red K2BP can be coupled to 1 g of membrane matrix. A membrane cartridge containing red affinity membranes was also prepared. The flux of the cartridge containing 80 sheets of membrane can reach 5.0 ml min with a pressure drop of 0.1 MPa. On this cartridge, the chromatography of alkaline phosphatase was performed with a 60% recovery of activity and a 40-fold purification.

Gas chromatographic enantiomer separation on single and mixed cyclodextrin derivative chiral stationary phases

SummaryCapillary gas chromatographic enantiomer separation of some polar compounds, including α-phenylethylamine, styrene oxide, pyrethroid insecticides and other carboxylates, was investigated on modified cyclodextrin (CD) chiral stationary phases. The chiral stationary phases studied included permethylated β-CD (PMBCD), heptakis (2,6-di-O-butyl-3-O-butyryl)-β-CD (DBBBCD), heptakis (2,6-di-O-nonyl-3-O-trifluoroacetyl)-β-CD (DNTBCD), the mixture of PMBCD and DBBBCD, and the mixture of PMBCD and DNTBCD. On the mixed chiral stationary phases containing the mixtures of derivatized cyclodextrins, enantiomer separation was improved significantly for some compounds as compared to the single cyclodextrin derivative chiral stationary phases, and synergistic effects were observed for some compounds on the mixed cyclodextrin derivative chiral stationary phases.

Removal of Endotoxin from Aqueous Solutions by Affinity Membrane

Endotoxin was removed by affinity membranes with histidine immobilized as affinity ligand. Macropore cellulose membrane was prepared from filter paper by alkaline treatment and chemical crosslinking, and was used as matrix for the immobilization of affinity ligand. The matrix membrane was derived by hexamethylenediamine and activated by glutaraldehyde before histidine was immobilized. Membrane cartridges containing 40 or 80 sheets of affinity membrane were also prepared, which can be used to remove pyrogen from aqueous solutions. Using a cartridge with 40 sheets of affinity membrane, the endotoxin content in solution can be reduced to a minimum of 0.12 EU/mL.

Gas chromatographic enantiomer separation on long-chain alkylated β-cyclodextrin chiral stationary phases

Two new chiral stationary phases, heptakis(2,6-di-O-nonyl-3-O-trifluoroacetyl)-beta-cyclodextrin (DNTBCD) and heptakis(2,6-di-O-dodecyl-3-O-trifluoroacetyl)-beta-cyclodextrin (DDTBCD), were synthesized. The gas chromatographic enantiomeric separation of amines, alcohols, diols, carboxylic acids, amino acids, epoxides, halohydrocarbons and ketones were investigated on DNTBCD, DDTBCD and heptakis(2,w6-di-O-npentyl-3-O-trifluoroacetyl)-beta-cyclodextrin (DPTBCD) stationary phases. It is observed that DNTBCD exhibits the best chiral selectivity among three stationary phases for most racemates investigated. An enthalpy-entropy compensation effect exists within the a-phenylethylamine derivatives separated on DPTBCD and DNTBCD stationary phases

MOLECULE IMPRINTING CHIRAL STATIONARY PHASE

Molecule imprinting polymers (MIPs) with high chiral selectivity for N(alpha)-protected amino acids were synthesized in polar solvent using acrylamide (AM) or combined functional monomer methacrylic acid (MAA) + vinyl pyridine (VP). Factors that influence the chiral selectivity of MIPs and mechanisms of the chiral recognition process were investigated. It was found that the rigid structure and the polar functional group of the print molecule were very important for the chiral selectivity of MIPs. For MIPs made using a combined functional monomer, ionic and hydrophobic interaction may be responsible for the chiral recognition process in aqueous media. The number of binding sites on MIPs and dissociation constants for the complex of enantiomers and MIPs were determined by frontal chromatography analysis.

Direct enantiomeric separation of phenylalanine, DOPA and their intermediates by supercritical fluid chromatography

Abstract Phenylalanine (Phe), 3-(3,4-dihydroxyphenyl)alanine (DOPA) and their corresponding intermediates [N-acyl alkyl esters of Phe, DOPA, 3-(3,4-dimethoxylphenyl)alanine, 3-(3-methoxyl-4-hydroxyphenyl)alanine and 3-(3,4-methylenedioxyphenyl)alanine] were enantiomerically separated by supercritical fluid chromatography with carbon dioxide as the mobile phase in a cross-linked polycyanoethyl vinyl siloxane, l -Val- tert. -butylamide fused-silica capillary column. The effects of substituents in the benzene ring and the acyl and alkyl groups of the intermediates or derivatives of Phe and DOPA on enantioselectivity were investigated. The optical purities of some intermediates of Phe and DOPA were determined.

Investigation of the effect of acylation on the enantiomeric separation of amino acid isopropyl esters by gas chromatography

Abstract The effects of acylation on the enantiomeric separation of isopropyl esters of alanine, valine, allo-isoleucine, isoleucine, leucine and aspartic acid were investigated with a cross-linked polycyanoethyl vinyl siloxane- l -Val- tert -butylamide fused-silica capillary column. The gas chromatographic behaviour of N-formyl, N-acetyl, N-trifluoroacetyl and N-benzoyl derivatives of the amino acid isopropyl esters were studied. The chiral recognition mechanism of the solutes on diamide chiral stationary phases is discussed.

Design and use of a thermal conductivity detector at reduced pressure for temperature-programmed capillary gas chromatography

Abstract Based on a systematic study of the response characteristics of a thermal conductivity detector (TCD) at reduced pressure, a newly designed TCD was constructed and evaluated for use in temperature-programmed capillary gas chromatography. The effective cell volume is as low as 1.3 μl (physical volume 100 μl), and there is no dead corner along the sensing path. Capillary columns of I.D. ⩾0.25 mm can couple directly with the TCD without a make-up gas. The detector response time is less than 0.1 s, the linear dynamic range is about four orders of magnitude and the detection limit is about 10 ppm (v/v) for octadecane. In the split injection mode, a simple configuration of the capillary inlet system offers a constant carrier gas flow-rate through the column with temperature-programmed operation. Practical examples are given that demonstrate the applicability of this detector and the system.

Chiral recognition of enantiomeric amides on a diamide chiral stationary phase by gas chromatography

Abstract Several α-alkyl-, α-cycloalkyl- and α-aromatic-substituted ethylamine enantiomers were separated with a cross-linked polycyanoethyl vinyl siloxane- l -valine otert.-butylamide fused-silica capillary column. Kovats retention indices of cyclohexane, benzene, anisole and the derivatized amines on the chiral stationary phase (CSP) were determined and compared with those on SE-30. By extrapolation of the retention behaviour, the chiral recognition mechanism of enantiomeric amides on diamide CSPs is discussed.

Separation of the enantiomers of 2-phenylcyclopropanecarboxylate esters by capillary gas chromatography on derivatized cyclodextrin stationary phases

SummarySeparation of the enantiomers of 2-phenylcyclopropanecarboxylate esters has been investigated on derivatized cyclodextrin chiral stationary phases (CD CSPs) to enable direct determination of the enantiomeric purity of the products of enantioselective cyclopropanation. Four stereoisomers of these chiral compounds could be resolved to baseline on permethylated β-cyclodextrin CSP. Some unusual phenomena, iso-enthalpy retention behavior and entropically driven chiral separation, were observed for the enantioseparation of 2-phenylcyclo-propanecarboxylates on the CD CSPs. Thermodynamic parameters were evaluated and an enthalpy-entropy compensation effect was observed forn-alkyl esters of 2-phenylcyclopropanecarboxylate separated on CD CSPs.