Biomedical subjects

Jiwei Hu

Publications and source records attributed to Jiwei Hu.

11 recordsLinked to original sources

PubMed2006

Enantioseparation of tetrahydropalmatine and Tröger's base by molecularly imprinted monolith in capillary electrochromatography.

Two chiral compounds, Tröger's base and tetrahydropalmatine, were enantioseparated on the (5S, 11S)-(-)-Tröger's base and l-tetrahydropalmatine imprinted monolithic capillary columns with CEC, respectively. The monoliths were prepared by in situ thermal-initiated copolymerization of methacrylic acid (MAA) and ethylene dimethacrylate (EDMA). After optimizing the ratio of porogens (toluene and dodecanol), the obtained monolithic capillary columns show good flow-through property and enantioselectivity. The influences of CEC parameters such as pH of the buffer, organic solvent and salt concentration on the electroosmotic flow (EOF) and recognition selectivity were systematically investigated. Under the optimal conditions, baseline resolutions of two chiral compounds were achieved. In addition, the fast separation was obtained within 4 min by applying higher voltage and assisting pressure of 6 bar.

Acetonitriles↗

PubMed2006

Large-pore mesoporous SBA-15 silica particles with submicrometer size as stationary phases for high-speed CEC separation.

A new mesoporous sphere-like SBA-15 silica was synthesized and evaluated in terms of its suitability as stationary phases for CEC. The unique and attractive properties of the silica particle are its submicrometer particle size of 400 nm and highly ordered cylindrical mesopores with uniform pore size of 12 nm running along the same direction. The bare silica particles with submicrometer size have been successfully employed for the normal-phase electrochromatographic separation of polar compounds with high efficiency (e.g., 210,000 for thiourea), which is matched well with its submicrometer particle size. The Van Deemeter plot showed the hindrance to mass transfer because of the existence of pore structure. The lowest plate height of 2.0 microm was obtained at the linear velocity of 1.1 mm/s. On the other hand, because of the relatively high linear velocity (e.g., 4.0 mm/s) can be generated, high-speed separation of neutral compounds, anilines, and basic pharmaceuticals in CEC with C18-modified SBA-15 silica as stationary phases was achieved within 36, 60, and 34 s, respectively.

Chromatography↗

PubMed2006

Hybrid silica monolithic column for capillary electrochromatography with enhanced cathodic electroosmotic flow.

A hybrid silica monolithic stationary phase for RP CEC was prepared by in situ co-condensation of (3-mercaptopropyl)-trimethoxysilane (MPTMS), phenyltriethoxysilane (PTES), and tetraethoxysilane (TEOS) via a sol-gel process. The thiol groups on the surface of the stationary phase were oxidized to sulfonic acids by peroxytrifluoroacetic acid. The introduced sulfonic acid moieties on the monoliths were characterized by a strong and relatively stable EOF in a broad pH range from 2.35 to 7.0 in CEC. Aromatic acids and neutral compounds can be simultaneously separated in this column under cathodic EOF. The CEC column exhibited a typical RP chromatographic mechanism for neutral compounds due to the introduced phenyl groups.

Amino Acids, Aromatic↗

PubMed2005

Molecular orbital studies on brominated diphenyl ethers. Part I--conformational properties.

Polybrominated diphenyl ethers (PBDEs) are widely used as additive flame retardants and quantities in the environment are on the rise. Because they are structurally related to polychlorinated biphenyls and also to thyroid hormones, there is serious concern that PBDEs may pose a danger to human health. Knowledge of their conformational properties is key to assessing their environmental fate and risk. The conformational properties of PBDEs were investigated by quantum chemical methods including semiempirical self-consistent field molecular orbital (SCF-MO), ab initio SCF-MO and density functional theory (DFT). Conformational analyses of model congeners 2,2',4,6'-tetrabromodiphenyl ether and 2,3,4,4',5,6-hexabromodiphenyl ether, based on energy maps calculated by semiempirical AM1 method, may indicate that all PBDE congeners except those with the tetra-ortho-bromination are conformationally flexible (or soft) due to low energy barriers for interconversion of stable conformers. The results of the conformational analyses are in conformity with recently published X-ray crystallographic data. For comparison with the results of the semiempirical method, higher level ab initio and DFT models were applied as well. The optimized geometries all lie well inside low energy regions on the maps and thus also ascertain the semiempirical calculations. According to computed geometric parameters and net atomic charges, the model B3LYP/3-21G* seemed to give better results than B3LYP/6-31G* and HF/6-31G*.

Chemistry Techniques, Analytical↗

PubMed2005

Molecular orbital studies on brominated diphenyl ethers. Part II--reactivity and quantitative structure-activity (property) relationships.

Polybrominated diphenyl ethers (PBDEs) are widely used as flame retardants and are increasingly turning up in the environment. Their structural similarities to polychlorinated biphenyls and thyroid hormones suggest they may be a risk to human health. The present study examines the reactivity of brominated diphenyl ethers (BDEs) on the basis of the electronic structures as calculated by semiempirical AM1 self-consistent field molecular orbital (SCF-MO) method. Frontier orbital energies were used to elucidate the reactivity of BDEs in electrophilic, nucleophilic and photolytic reactions. From an examination of the frontier electron densities, the regioselectivity, or orientation, of metabolic reactions of BDEs was predicted. Furthermore, satisfactory quantitative structure-activity (property) relationship (QSAR and QSPR) models were derived to calculate gas chromatographic and ultraviolet spectral properties and luciferase induction activities from the AM1-computed electronic parameters.

Chemistry Techniques, Analytical↗

PubMed2005

Electrochromatographic evaluation of a silica monolith capillary column for separation of basic pharmaceuticals.

A silica-based monolithic capillary column was prepared via a sol-gel process. The continuous skeleton and large through-pore structure were characterized by scanning electron microscopy (SEM). The native silica monolith has been successfully employed in the electrochromatographic separation of beta-blockers and alkaloids extracted from traditional Chinese medicines (TCMs). Column efficiencies greater than 250 000 plates/m for capillary electrochromatography (CEC) separation of basic compounds were obtained. It was observed that retention of basic pharmaceuticals on the silica monolith was mainly contributed by a cation-exchange mechanism. Other retention mechanisms including reversed-phase and normal-phase mechanisms and electrophoresis of basic compounds also played a role in separation. A comparison of the differences between CEC and capillary zone electrophoresis (CZE) separation was also discussed.

Adrenergic beta-Antagonists↗

PubMed2005

Capillary electrochromatography with a neutral monolithic column for classification of analytes and determination of basic drugs in human serum.

Capillary electrochromatography (CEC) using a neutral hydrophobic polymer-based monolithic column has been developed for classification of analytes based on their acidity and charges of group. The monolithic columns were prepared by in situ copolymerization of lauryl methacrylate and ethylene dimethacrylate without any charged monomers in the reaction mixture. The ionic analytes will only be driven by their electrophoretic mobilities and were separated on the basis of their differences in electrophoretic mobility and in hydrophobic interaction with the stationary phase. Only negatively or positively charged analyte (acid or basic) migrated toward detection window in a single run by applying negative or positive voltage. The CEC system was also applied for the analysis of basic drugs in human serum by internal standard method using acidic running buffer. The sample of human serum spiked with basic drugs was directly injected after a simple sample pretreatment. The calibration curves with regression coefficients (0.9995-0.9997) in the range of 0.318-80 microg/mL were obtained with the limits of detection being below 0.15 microg/mL. The intra- and inter-day precisions, determined as relative standard deviations, were less than 4.21%.

Atenolol↗

PubMed2005

Preparation of monolithic silica column with strong cation-exchange stationary phase for capillary electrochromatography.

A monolithic silica based strong cation-exchange stationary phase was successfully prepared for capillary electrochromatography. The monolithic silica matrix from a sol-gel process was chemically modified by treatment with 3-mercaptopropyltrimethoxysilane followed by a chemical oxidation procedure to produce the desired function. The strong cation-exchange stationary phase was characterized by its substantial and stable electroosmotic flow (EOF), and it was observed that the EOF value of the prepared column remained almost unchanged at different buffer pH values and slowly decreased with increasing phosphate concentration in the mobile phase. The monolithic silica column with strong cation-exchange stationary phase has been successfully employed in the electrochromatographic separation of beta-blockers and alkaloids extracted from traditional Chinese medicines (TCMs). The column efficiencies for the tested beta-blockers varied from 210,000 to 340,000 plates/m. A peak compression effect was observed for atenolol with the mobile phase having a low phosphate concentration.

Journal Article↗

PubMed2004

Di-p-bromophenyl ether, a redetermined crystal structure derived from low-quality diffraction data.

We show that the lack of good quality data, normally essential to successful crystal structure analysis, can in part be compensated for by measuring data from several crystals and merging the resulting data sets. The crystal structure of the flame retardant di-p-bromophenyl ether, C12H8Br2O, a twofold axially symmetric molecule, has been redetermined and refined from such a merged multi-crystal diffraction data set to an acceptable conventional R factor (R1 = 0.06), a result which could not have been obtained from any one of our single-crystal diffraction data sets used alone in the normal manner.

Journal Article↗

PubMed2004

Monolithic columns with mixed modes of reversed-phase and anion-exchange stationary phase for capillary electrochromatography.

A capillary electrochromatography (CEC) monolithic column with mixed modes of reversed-phase and anion-exchange stationary phases was prepared by in situ polymerization of 2-(methacryloxy)ethyltrimethylammonium methyl sulfate (MEAMS) and ethylene dimethacrylate (EDMA) in a binary porogenic solvent consisting 1-propanol and 1,4-butanediol. The ammonium groups on the surface of the stationary phase generate an electroosmotic flow (EOF) from cathode to anode, and serve as a strong anion-exchange stationary phase at the same time. The EOF of the stationary phase can be determined by the amount of MEAMS monomer in reaction mixtures during the polymerization. The monolithic stationary phases exhibited reversed-phase chromatographic behavior toward neutral solutes. For charged solutes, hydrophobic as well as electrostatic interaction/repulsion with the monoliths was observed. Separations of aromatic compounds and basic compounds on the prepared column were performed under the mode of CEC. Peak tailing of basic compounds was avoided and the efficient separation of aromatic acids was achieved using neutral mobile phase due to the same direction of EOF and electrophorestic mobility of negatively charged solutes.

Anion Exchange Resins↗

PubMed2004

Polar stationary phases for capillary electrochromatography.

This review article summarizes the variety of polar stationary phases that have been employed for capillary electrochromatographic separations. Compared with reversed-phase stationary phases, the polar alternatives provide a completely different retention selectivity towards polar and charged analytes. Different types of polar stationary phases are reviewed, including the possible retention mechanisms. Electrochromatographic separations of polar solutes, peptides, and basic pharmaceuticals on polar stationary phases are presented.

Chromatography, Liquid↗