Biomedical subjects

Zhen Liu

Publications and source records attributed to Zhen Liu.

62 records · Page 4Linked to original sources

PubMed2002

Modeling of retention behavior in capillary electrochromatography from chromatographic and electrophoretic data.

A phenomenological approach was presented to describe the retention behaviors of solutes in capillary electrochromatography (CEC). Equations for calculation of the retention time and actual chromatographic retention factor for ionic solutes, weak monoprotic acid and weak monoprotic base were derived, which can be described by two general expressions regardless the charge status of the solute. The general expressions enable calculation of the retention time and retention factor in CEC from chromatographic and electrophoretic data, which were experimentally verified with a variety of compounds and a variety of CEC modes. Based on this approach, the chromatographic retention and the electrophoretic migration in the CEC systems studied were found to be two independent processes. The validity of this approach was also discussed.

Chromatography, Micellar Electrokinetic Capillary↗

PubMed2002

Study of competitive binding of enantiomers to protein by affinity capillary electrochromatography.

Affinity capillary electrochromatography (CEC) with zonal elution method was used to probe the competitive interactions of enantiomers with protein. In this approach, a known concentration of a competing agent is continuously applied to a CEC column with bovine serum albumin (BSA) physically adsorbed on SAX packing while injections of a small amount of analyte are made. The binding sites of solutes on the BSA molecule were determined by the changes in the retention factors of the solutes resulted from the addition of competitive agent. By using D- or L-tryptophan as competitive agents and D-, L-tryptophan and benzoin enantiomers as injected analytes showed that BSA molecule has a primary site to strongly bind L-tryptophan, but D-tryptophan dose not bind at this site; D- and L-tryptophan share a weak binding site on the BSA molecule. Benzoin enantiomers do not share any binding sites with either D- or L-tryptophan. Non-chiral compounds of trichloroacetic acid and n-hexanoic acid were applied as the competitive agents to study the binding of warfarin enantiomers to BSA, it was observed that trichloroacetic acid and n-hexanoic acid had a same binding site for warfarin enantiomers binding to BSA molecule.

Binding, Competitive↗

PubMed2002

Physically adsorbed chiral stationary phase of avidin on monolithic silica column for capillary electrochromatography and capillary liquid chromatography.

The physical adsorption method proposed previously has been successfully applied to a monolithic silica column. By virtue of the physical adsorption, a chiral stationary phase of avidin was prepared onto the silica monolith. The phase ratio of resulting stationary phase was evaluated with frontal analysis. The method proved to be comparable in phase ratio to the chemical bonding methods used in high-performance liquid chromatography (HPLC). Enantiomer separations were carried out in capillary electrochromatography (CEC) and capillary liquid chromatography (CLC) modes. Due to its larger phase ratio, the resulting column showed more powerful separation capability as compared to open-tubular CEC (OTCEC). Twelve chiral compounds were baseline-resolved. The resulting column showed high separation efficiency, with average theoretical plate numbers of 66 000/m for CLC and 122 000/m for CEC. Good reproducibility was observed, with RSD value less than 1.3% for retention time, retention factor and separation factor, and less than 6.6% for plate counts and resolution (n = 40). Fast separations were achieved with a short column. The test enantiomers were baseline-resolved within 4 min under CLC and CEC modes. In addition, field-enhanced sample injection (FESI) was coupled to CLC as well as CEC to improve the detection sensitivity.

Adsorption↗

PubMed2002

Recent progress in adsorbed stationary phases for capillary electrochromatography.

This review surveys the recent progress in the adsorbed stationary phases for capillary electrochromatography (CEC). Adsorption-based methods for preparation of stationary phase are novel approaches in CEC, which allow rapid and facile preparing stationary phases with desirable selectivity onto an open-tubular fused-silica capillary, a bare-silica or ion-exchange packed column or a monolithic silica or polymer column. A variety of adsorbing agents have been developed as adsorbed stationary phases, including ionic long-chain surfactant, protein, peptide, amino acid, charged cyclodextrin (CD), basic compound, aliphatic ionene, and ion-exchange latex particle. The adsorbed stationary phases have been applied to separation of neutral, basic and acidic organic compounds, inorganic anions and enantiomers. They have also been applied to on-line sample concentration, fast separation and study of the competitive binding of enantiomers with protein.

Adsorption↗

PubMed2002

High-throughput screening for ion channel modulators.

Ion channels present a group of targets for major clinical indications, which have been difficult to address due to the lack of suitable rapid but biologically significant methodologies. To address the need for increased throughput in primary screening, the authors have set up a Beckman/Sagian core system to fully automate functional fluorescence-based assays that measure ion channel function. They apply voltage-sensitive fluorescent probes, and the activity of channels is monitored using Aurora's Voltage/Ion Probe Reader (VIPR). The system provides a platform for fully automated high-throughput screening as well as pharmacological characterization of ion channel modulators. The application of voltage-sensitive fluorescence dyes coupled with fluorescence resonance energy transfer is the basis of robust assays, which can be adapted to the study of a variety of ion channels to screen for both inhibitors and activators of voltage-gated and other ion channels.

Automation↗

PubMed2002

Cloning and high-level expression of scorpion toxin BmKITa1 in Escherichia coli and insect cells.

BmK ITa1 cDNA was cloned and highly expressed in E. coli and insect cell. SDS-PAGE and western blot analysis revealed that subunit molecular weight of expression products is about 40 kDa and 10 kDa respectively. The expression product purified by a Ni(2+)-IDA-sepharose 6B column was toxic for insect, which indicated that it was biologically activity. Furthermore, Quantitative estimation show that the biological activity of recombinant BmK ITa1 from Tn cells was more powerful than from E. coli.

Amino Acid Sequence↗

PubMed2002

Data, network, and application: technical description of the Utah RODS Winter Olympic Biosurveillance System.

Given the post September 11th climate of possible bioterrorist attacks and the high profile 2002 Winter Olympics in the Salt Lake City, Utah, we challenged ourselves to deploy a computer-based real-time automated biosurveillance system for Utah, the Utah Real-time Outbreak and Disease Surveillance system (Utah RODS), in six weeks using our existing Real-time Outbreak and Disease Surveillance (RODS) architecture. During the Olympics, Utah RODS received real-time HL-7 admission messages from 10 emergency departments and 20 walk-in clinics. It collected free-text chief complaints, categorized them into one of seven prodromes classes using natural language processing, and provided a web interface for real-time display of time series graphs, geographic information system output, outbreak algorithm alerts, and details of the cases. The system detected two possible outbreaks that were dismissed as the natural result of increasing rates of Influenza. Utah RODS allowed us to further understand the complexities underlying the rapid deployment of a RODS-like system.

Algorithms↗

PubMedDate not supplied

Capillary isoelectric focusing with laser-induced fluorescence whole column imaging detection as a tool to monitor reactions of proteins.

Capillary isoelectric focusing (CIEF) with laser-induced fluorescence (LIF) whole column imaging detection (WCID) has the characteristics of high resolution, high speed and high sensitivity for separation of amphoteric biomolecules. These features enable a CIEF-LIF-WCID system to monitor the dynamic process of a protein reaction. The reaction can be a physical change or a chemical reaction, provided that the kinetics of the reaction is slower than the focusing speed or that the intermediates involved have long enough life-span compared to the analysis time. The processes of denaturation (a physical reaction), reduction and carbamylation (both chemical reactions) were dynamically monitored. The CIEF profiles at successive reaction times clearly displayed the formation of different products at different stages. At incomplete denaturation, intermediates with higher apparent pI values relative to the products at complete denaturation were detected. Carbamylation products of a protein were detected when the protein reacted with a urea solution that had prepared three months earlier, exhibiting gradually decreased pI values. Mechanisms involved in these reactions were rationalized. A combined mechanism of denaturation and reduction was suggested to explain the denaturing process under high concentrations of urea. Potential applications and critical factors to manipulate these reactions were also discussed.

Animals↗