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Featured researches published by Dong-Qiang Lin.


Fluid Phase Equilibria | 1998

Thermodynamics of aqueous two-phase systems—the effect of polymer molecular weight on liquid–liquid equilibrium phase diagrams by the modified NRTL model

You-Ting Wu; Dong-Qiang Lin; Zi-Qiang Zhu

Abstract The modified NRTL (nonrandom two-liquid) model for binary polymer solutions, proposed in the previous paper, is further extended to calculate the liquid–liquid equilibrium of polyethylene glycol (PEG)–dextran (DEX) aqueous two-phase systems (ATPS) and PEG–salt ATPS. The model has six binary adjustable model parameters, and in the calculation the model parameters between PEG and water, DEX and water, and salt and water are correlated with the vapor–liquid equilibrium of the corresponding binary systems, while those between PEG and DEX or PEG and salt are correlated with two tie-line data of one ATPS. The results show that the model can accurately predict a series of the liquid–liquid equilibrium phase diagrams of ATPS at different polymer molecular weights. The effect that the PEG or DEX molecular weights have on the phase diagrams of ATPS, and the influences that the polydispersity of the polymer molecular weight and the correlation between the model parameters have on the model parameters between PEG and DEX or PEG and salt are also discussed in this paper.


Bioseparation | 2001

Minimising biomass/adsorbent interactions in expanded bed adsorption processes: a methodological design approach

Dong-Qiang Lin; Hector Marcelo Fernández-Lahore; Maria-Regina Kula; Jörg Thömmes

Expanded bed adsorption (EBA) is an integrated technology for the primary recovery of proteins from crude feedstock. Interactions between solid matter in the feed suspension and fluidised adsorbent particles influence bed stability and therefore have a significant impact on protein adsorption in expanded beds. In order to design efficient and reliable EBA processes a strategy is needed, which allows to find operating conditions, where these adverse events do not take place. In this paper a methodological approach is presented, which allows systematic characterisation and minimisation of cell/adsorbent interactions with as little experimental effort as possible. Adsorption of BSA to the anion exchanger Streamline Q XL from a suspension containing S. cerevisiae cells was chosen as a model system with a strong affinity of the biomass towards the stationary phase. Finite bath biomass adsorption experiments were developed as an initial screening method to estimate a potential interference. The adhesiveness of S. cerevisiae to the anion exchanger could be reduced significantly by increasing the conductivity of the feedstock. A biomass pulse response method was used to find optimal operation conditions showing no cell/adsorbent interactions. A good correlation was found between the finite bath test and the pulse experiment for a variety of suspensions (intact yeast cells, E. coli homogenate and hybridoma cells) and adsorbents (Streamline Q XL, DEAE and SP), which allows to predict cell/adsorbent interactions in expanded beds just from finite bath adsorption tests. Under the optimised operating conditions obtained using the prior methods, the stability of the expanded bed was investigated during fluidisation in biomass containing feedstock (up to 15% yeast on wet weight basis) employing residence time distribution analysis and evaluation by an advanced model. Based on these studies threshold values were defined for the individual experiments, which have to be achieved in order to obtain an efficient EBA process. Breakthrough experiments were conducted to characterise the efficiency of BSA adsorption from S. cerevisiae suspensions in EBA mode under varying operating conditions. This allowed to correlate the stability of the expanded bed with its sorption efficiency and therefore could be used to verify the threshold values defined. The approach presented in this work provides a fast and simple way to minimise cell/adsorbent interactions and to define a window of operation for protein purification using EBA.


Chinese Journal of Chemical Engineering | 2007

Purification and Characterization of Glutamate Decarboxylase of Lactobacillus brevis CGMCC 1306 Isolated from Fresh Milk

Jun Huang; Lehe Mei; Qing Sheng; Shan-Jing Yao; Dong-Qiang Lin

Abstract A Lactobacillus brevis CGMCC 1306 isolated from fresh milk without pasteurization was found to have higher glutamate decarboxylase (GAD) activity. An effective isolation and purification procedure of GAD from a cell-free extract of Lactobacillus brevis was developed, and the procedure included four steps: 30%—90% saturation (NH 4 ) 2 SO 4 fractional precipitation, Q sepharose FF anion-exchange chromatography, sephacryl S-200 gel filtration, and resource Q anion-exchange chromatography. Using this protocol, the purified GAD was demonstrated to possess electrophoretic homogeneity via SDS-PAGE. The purification fold and activity recovery of GAD were 43.78 and 16.95%, respectively. The molecular weight of the purified GAD was estimated to be approximately 62 kDa via SDS-PAGE. The optimum pH and temperature of the purified GAD were 4.4 and 37°C, respectively. The purified GAD had a half-life of 50min at 45°C and the K m value of the enzyme from Lineweaver-Burk plot was found to be 8.22. 5′-pyridoxal phosphate (PLP) had little effect on the regulation of its activity.


Journal of Physical Chemistry B | 2012

Molecular insight into the ligand-IgG interactions for 4-mercaptoethyl-pyridine based hydrophobic charge-induction chromatography.

Dong-Qiang Lin; Hong-Fei Tong; Hong-Yin Wang; Shan-Jing Yao

Hydrophobic charge-induction chromatography (HCIC) with 4-mercaptoethyl-pyridine (MEP) as the ligand is a novel technology for antibody purification. In the present work, the molecular simulation methods were used to investigate the interactions between MEP ligand and Fc fragment of IgG (Fc-A). Six ligands with different structures of spacer arm were studied with molecular docking and dynamics simulation at neutral and acidic pH. The binding modes and the interaction energies were analyzed. The results indicated that all ligands tested could bind into the selected pocket on the C(H2) domain of Fc-A at neutral pH. The pyridine ring on the top of MEP ligands acts as a major role to provide the hydrophobic association and hydrogen bond for the ligand-IgG binding; meanwhile, the sulfone group on the spacer arm might form the additional hydrogen bond and enhance the binding of ligand onto the surface of IgG. The replacements of thioether sulfur atom on the spacer arm with either nitrogen or oxygen atom seem to have little influence on the binding. The influences of pH on the ligand-IgG interactions were also studied with the molecular dynamics simulation. It was found that MEP ligands would departed from the surface of Fc-A at low pH due to the electrostatic repulsion. The ligands with a sulfone group on the spacer arm would weaken the electrostatic repulsion and need more acidic conditions for the departing of ligand. The molecular simulation results were in agreement with some experimental observations, which would be useful to elucidate the molecular mechanism of HCIC and design a novel ligand to improve the efficiency of antibody separation.


Journal of Chromatography A | 2012

Enhancing IgG purification from serum albumin containing feedstock with hydrophobic charge-induction chromatography.

Hong-Fei Tong; Dong-Qiang Lin; Xiao-Ming Yuan; Shan-Jing Yao

Hydrophobic charge-induction chromatography (HCIC) with 4-mercaptoethyl-pyridine (MEP) as the ligand is a novel technology for antibody purification, however, the separation selectivity still needs to be improved for the applications, especially for the impurity of serum albumin. In this study, with bovine serum immunoglobulin G (IgG) as the model, the purification of IgG from the serum albumin containing feedstock was developed with the commercial HCIC resin MEP HyperCel, focusing on the optimization of operation pH and salt addition. The adsorption isotherms of IgG and bovine serum albumin (BSA) were investigated at different pHs, and the binding and elution behaviors of two proteins in the column were also studied at varying pHs. In addition, the protein-ligand interactions were investigated with some additives in the buffer. It was found that the conditions of pH 6 with 0.1 M NaCl or pH 8 could be used to effectively remove BSA from the MEP resin without the influence on IgG adsorption. Two modes with control of loading or washing buffer were tested to enhance the purification of IgG from BSA containing feedstock, and the purity of IgG was improved to about 95% compared with 62.9% for the control. The results demonstrated that the control of loading pH or the addition of NaCl in the buffer might be an effective method to improve the purification of antibody with the HCIC process.


Chemical Engineering Science | 2003

Modeling the protein partitioning in aqueous polymer two-phase systems: influence of polymer concentration and molecular weight

Dong-Qiang Lin; You-Ting Wu; Lehe Mei; Zi-Qiang Zhu; Shan-Jing Yao

Aqueous polymer two-phase system provides a powerful method for separation and purification of biomaterials. Among various factors, polymer concentration and polymer molecular weight are essential and have strong impact on the protein partitioning in these systems. Based on the modified Pitzers model, a simple expression has been obtained for correlating protein partitioning in aqueous polymer two-phase systems with varying polymer concentration and different polymer molecular weights. Using only one group of parameters for each target protein, the partition coefficients of five proteins (lysozyme, chymotrypsinogen-A, bovine serum albumin, transferrin and catalase) in 16 sets of polyethylene glycol (PEG)/dextran systems were correlated. In addition, partition behavior of lactate dehydrogenase in PEG/hydroxypropyl starch systems were measured, correlated and partially predicted. A comparison of calculated and experimental data indicated that the model provides good correlation and prediction abilities on the protein partitioning in aqueous polymer two-phase systems with a wide range of polymer concentration and molecular weight.


Journal of Chromatography A | 2013

Evaluation of immunoglobulin adsorption on the hydrophobic charge-induction resins with different ligand densities and pore sizes

Hui-Li Lu; Dong-Qiang Lin; Dong Gao; Shan-Jing Yao

Hydrophobic charge-induction chromatography (HCIC) is a novel technology for antibody purification. The ligand densities and pore properties of HCIC resins have significant effects on the separation behavior of protein, however, the understandings are quite limited. In the present work, new HCIC ligand, 2-mercapto-1-methylimidazole (MMI) was coupled to three agarose matrices with different pore sizes. A series of MMI resins with different ligand density and pore size was prepared by the control of ligand coupling. The adsorption isotherms and kinetics on the series of MMI resins were investigated with bovine serum immunoglobulin as the model IgG, and the effects of salt addition were studied. The Langmuir equation and pore diffusion model were used to fit the experimental data, and the influences of ligand density, pore size and salt addition on the saturated adsorption capacity, the dissociation constant and the effective diffusivity were discussed. It was found that the adsorption capacities and the effective pore diffusion coefficient increased with the increase of ligand density and pore size. The effects of salt addition on the adsorption behaviors were dependent on the ligand density. For low ligand density the IgG adsorption was salt-promoted, while the resins with high ligand density showed a salt-independent property. The results indicated that for a given protein the ligand density and pore size of HCIC resins should be optimized for improving the protein adsorption.


Journal of Chromatography A | 2008

Chromatographic performance of macroporous cellulose-tungsten carbide composite beads as anion-exchanger for expanded bed adsorption at high fluid velocity.

Hai-Feng Xia; Dong-Qiang Lin; Shan-Jing Yao

Macroporous cellulose-tungsten carbide composite beads was designed and prepared as an anion-exchanger for expanded bed adsorption (EBA). The wet density of composite beads was adjusted at the range of 1.2-2.4 g/ml with the control of tungsten carbide addition, and optimized for EBA at high fluid velocity. The results indicated that the wet density of composite beads could increase linearly with the increase of tungsten carbide addition, meanwhile other physical properties, such as size, porosity, specific surface area, mean pore diameter, etc., were hardly or slightly influenced. The composite beads were coupled with diethylaminoethyl (DEAE) as an anion-exchanger for EBA. The expansion characteristics in expanded bed were investigated and sensitively changed as the wet density of composite beads, corresponding to tungsten carbide addition in the preparation. The relation among the operation fluid velocity, the ratio of tungsten carbide to cellulose viscose in the preparation and the expansion factor was found, which could be used to predict the operation velocity of composite beads with varying tungsten carbide addition. The liquid mixing in expanded bed was also tested and showed good bed stability for EBA processes. With the adsorption equilibrium experiments, the saturated adsorption capacity of bovine serum albumin could reach 68.7 mg/g adsorbents (equal to 97.1 mg/ml adsorbents). The ratio of Q(10%) (the dynamic adsorption at 10% breakthrough) in expanded bed to packed bed could reach more than 90% for the fluid velocity of 500 cm/h, even 77.1% for the fluid velocity as high as 900 cm/h. The chromatographic results demonstrated that the composite beads prepared are suitable for EBA applications at high fluid velocity.


Journal of Chromatography A | 2012

Molecular mechanism of hydrophobic charge-induction chromatography: Interactions between the immobilized 4-mercaptoethyl-pyridine ligand and IgG

Dong-Qiang Lin; Hong-Fei Tong; Hong-Yin Wang; Shuang Shao; Shan-Jing Yao

Hydrophobic charge-induction chromatography (HCIC) is a novel bioseparation technology, especially for antibody purification. In order to better understand the molecular mechanism of HCIC, the typical ligand of 4-mercaptoethyl-pyridine (MEP) was coupled onto the cellulose matrix, and the binding and departing of IgG were studied with the molecular dynamics simulation. Based on the previous work with free MEP ligand (J. Phys. Chem. B, 116 (4) (2012) 1393-1400), the pocket around TYR319 and LEU309 on the CH2 domain of IgG was selected as the potential binding site for the Fc fragment of IgG (Fc-A), and the complex of matrix-ligand-Fc-A was formed for the molecular simulation. Both single ligand and ligand net were investigated in the present work. It was found that the MEP ligand immobilized on the cellulose matrix could capture the Fc-A at neutral pH during the simulation, and the Fc-A would depart quickly when pH was changed to 4.0. The hydrophobic interactions and hydrogen bonds controlled the binding of Fc-A on the immobilized ligands at neutral pH and the electrostatic repulsion caused the departing of Fc-A at acid condition. For the ligand net, multipoint binding was found, while one ligand dominated the binding of Fc-A and other ligands might enhance the adsorption of protein. In addition, the adsorption isotherm and the isothermal titration calorimetry (ITC) were used to evaluate the molecular interactions. The experimental results indicated that the hydrophobic interaction is the major driving force for the adsorption of IgG on the MEP resin, which was in good agreement with those findings of molecular simulation. The molecular simulation and thermodynamic results verified strongly the molecular mechanism of HCIC--the hydrophobic interactions for binding and the charge-induction repulsion for elution. Better understanding on the molecular interactions would be beneficial to design new HCIC ligands for improving the efficiency of antibody separation.


Journal of Chromatography A | 2013

Caprylate as the albumin-selective modifier to improve IgG purification with hydrophobic charge-induction chromatography.

Hong-Fei Tong; Dong-Qiang Lin; Dong Gao; Xiao-Ming Yuan; Shan-Jing Yao

Hydrophobic charge-induction chromatography (HCIC) is a novel downstream bioprocessing technology for antibody purification and it has several advantages over traditional purification processes. However, its separation selectivity still needs to be improved. In this work, sodium caprylate (NaCA) was used as the selective modifier to improve IgG purification from serum albumin containing feedstock with a typical HCIC resin, MEP HyperCel. The effects of NaCA on the adsorption equilibrium of bovine serum immunoglobulin G (IgG) and bovine serum albumin (BSA), as well as the dynamic binding and displacement behaviors were investigated. The binding and elution behaviors of these two proteins in the column were studied. It was found that adding 50-75 mM NaCA in the liquid phase could effectively reduce the adsorption of BSA on the MEP resin, but the same treatment has little influence on the adsorption of IgG. Moreover, the mechanism of the competitive binding between caprylate and MEP ligands on the surface of BSA is discussed. It was found that by controlling NaCA addition in the loading or washing buffer, the process efficiency of IgG purification from BSA containing feedstock can be improved, and the purity of IgG could reach to over 98%. The results indicated that caprylate could be a promising albumin-selective modifier to improve the separation efficiency of antibodies with the HCIC process.

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Junxian Yun

Zhejiang University of Technology

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Kejian Yao

Zhejiang University of Technology

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Dongsheng Xue

Hubei University of Technology

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