Performance comparison of low-pressure ion-exchange chromatography media for protein separation

Recent Advances in Structure Separation of Single-Wall Carbon Nanotubes and Their Application in Optics, Electronics, and Optoelectronics

Structural control of single-wall carbon nanotubes (SWCNTs) with uniform properties is critical not only for their property modulation and functional design but also for applications in electronics, optics, and optoelectronics. To achieve this goal, various separation techniques have been developed in the past 20 years through which separation of high-purity semiconducting/metallic SWCNTs, single-chirality species, and even their enantiomers have been achieved. This progress has promoted the property modulation of SWCNTs and the development of SWCNT-based optoelectronic devices. Here, the recent advances in the structure separation of SWCNTs are reviewed, from metallic/semiconducting SWCNTs, to single-chirality species, and to enantiomers by several typical separation techniques and the application of the corresponding sorted SWCNTs. Based on the separation procedure, efficiency, and scalability, as well as, the separable SWCNT species, purity, and quantity, the advantages and disadvantages of various separation techniques are compared. Combined with the requirements of SWCNT application, the challenges, prospects, and development direction of structure separation are further discussed.

Recent progress on the structure separation of single-wall carbon nanotubes

The mass production of single-structure, single-wall carbon nanotubes (SWCNTs) with identical properties is critical for their basic research and technical applications in the fields of electronics, optics and optoelectronics. Great efforts have been made to control the structures of SWCNTs since their discovery. Recently, the structure separation of SWCNTs has been making great progress. Various solution-sorting methods have been developed to achieve not only the separation of metallic and semiconducting species, but also the sorting of distinct (n, m) single-chirality species and even their enantiomers. This progress would dramatically accelerate the application of SWCNTs in the next-generation electronic devices. Here, we review the recent progress in the structure sorting of SWCNTs and outline the challenges and prospects of the structure separation of SWCNTs.

Protein adsorption and transport in polymer-functionalized ion-exchangers

A wide variety of stationary phases is available for use in preparative chromatography of proteins, covering different base matrices, pore structures and modes of chromatography. There has recently been significant growth in the number of such materials in which the base matrix is derivatized to add a covalently attached or grafted polymer layer or, in some cases, a hydrogel that fills the pore space. This review summarizes the main structural and functional features of ion exchangers of this kind, which represent the largest class of such materials. Although the adsorption and transport properties may generally be used operationally and modeled phenomenologically using the same methods as are used for proteins in conventional media, there are noteworthy mechanistic differences in protein behavior in these adsorbents. A fundamental difference in protein retention is that it may be portrayed as partitioning into a three-dimensional polymer phase rather than adsorption at an extended two-dimensional surface, as applies in more conventional media. Beyond this partitioning behavior, however, the polymer-functionalized media often display rapid intraparticle transport that, while qualitatively comparable to that in conventional media, is sufficiently rapid quantitatively under certain conditions that it can lead to clear benefits in key measures of performance such as the dynamic binding capacity. Although possible mechanistic bases for the retention and transport properties are discussed, appreciable areas of uncertainty make detailed mechanistic modeling very challenging, and more detailed experimental characterization is likely to be more productive.

Separation of peptides by HPLC using a surface-confined ionic liquid stationary phase

A butylimidazolium bromide surface-confined ionic liquid stationary phase was synthesized in-house. The synthesized phase was investigated for the separation of five peptides (Gly-Tyr, Val-Tyr-Val, leucine enkephalin, methionine enkephalin, and angiotensin-II). The peptides were successfully separated in less than 5 min. The effect of trifluoroacetic acid (TFA) on the separation of peptides was evaluated with results confirming that TFA was not acting as ion-pairing agent in separation of peptides on this phase.

Fast purification process optimization using mixed-mode chromatography sorbents in pre-packed mini-columns

Pre-packed MediaScout MiniChrom columns of 2.5, 5 and 10 mL were investigated for screening three mixed-mode chromatography sorbents (HEA, PPA and MEP HyperCel). Packing performance was of good quality and the three sorbents displayed higher capacity than traditional HIC sorbents in physiological-like conditions. Each sorbent offered a unique selectivity. Bovine beta-lactoglobulin was partially purified after loading milk whey directly on HEA HyperCel sorbent. The combination of small pre-packed columns and SELDI-MS appeared to be a valuable strategy for high-throughput screening of chromatography sorbents and for enabling rapid process development and optimization.

Comparison of strong anion-exchangers for the purification of a PEGylated protein

We have studied the effect of protein PEGylation on ion-exchange adsorption using bovine serum albumin as a model system. The free sulfhydryl group of BSA, located on cysteine 34, was PEGylated using the maleimido-PEG chemistry. Several different BSA preparations were screened for extent of reaction using a 30 kDa PEG reagent. The highest yielding BSA preparation was PEGylated using linear 12 kDa and 30 kDa PEG reagents at the 1 liter scale. The PEGylated reaction mixture was purified by anion-exchange gradient elution chromatography to remove native protein and aggregates. Purity following anion-exchange chromatography was >90% as determined by analytical size exclusion chromatography. The elution salt concentration decreased with increasing PEG chain length. Breakthrough studies on six commercially available anion-exchange stationary phases with purified PEG-BSA conjugates confirm a very large decrease in dynamic binding capacity compared to the native protein. The decrease in dynamic binding capacity is likely due to modulation of electrostatic interactions caused by the neutral PEG chain and increased mass transfer resistance associated with the large size of the molecule. Of the stationary phases evaluated, the open porous structure of the agarose based ion-exchangers resulted in the highest dynamic binding capacities for the PEG-BSA conjugates. Frontal analysis experiments demonstrate use of this technique for purification of PEGylated proteins. A stationary phase that tended to exclude the large PEG-BSA conjugate was very efficient in removing native protein from a crude reaction mixture by frontal analysis.

Utility of cleavable isotope-coded affinity-tagged reagents for quantification of low-copy proteins induced by methylprednisolone using liquid chromatography/tandem mass spectrometry

Gene expression changes underlie important biological and pharmacological responses. Although mRNA expression profiling is routine, quantification of low-abundance proteins, which typically represent key effectors of responses, remains challenging. A novel strategy was developed for sensitive and accurate quantification of low-abundance proteins in highly complex biological matrixes. First, the cysteine specificity of cleavable isotope-coded affinity tags (cICAT) was employed to reduce the complexity of the digested proteome of tissue homogenates and to improve the quantification of low-abundance proteins. Second, cICAT-treated tissue samples were analyzed on a capillary LC coupled to an ion trap MS to screen for the subset of cICAT-peptides, derived from target proteins of interest, that was successfully labeled and retrieved. Third, putatively identified peptides derived from target proteins were synthesized, cICAT-labeled, and used both to optimize multiple reactions monitoring (MRM) analysis and to confirm chromatographic retention time and fragmentation pattern. Finally, batch quantification of target peptides was performed using MRM on a LC/triple-quad MS/MS using (12)C- (control) and (13)C (experimental)-cICAT-labeled tissue mixtures. The utility of this method was demonstrated by elucidating the time-course of tyrosine aminotransferase induction in the liver of rats following treatment with the corticosteroid methylprednisolone (MPL). This approach significantly improved quantitative sensitivity, and the linear range was 10-fold greater than published previously. An additional advantage is that archived samples may be reinterrogated to investigate the regulation of additional targets that become of interest. Stored samples were sucessfully reinterrogated to monitor the induction of ornithine decarboxylase, which is also an MPL-induced protein. To our knowledge, this is the first report of an ICAT-based method that is capable of quantifying low-abundance proteins in highly complex samples, such as tissue homogenates. The approach enables simultaneous quantification of multiple effector proteins induced by biological or pharmacological stimuli, and the processed samples can be interrogated repeatedly as additional targets of interest arise.

Comparison of chromatographic ion-exchange resins

Strong and weak cation-exchangers were compared for a number of chromatographic parameters, i.e. pH dependence, efficiency, binding strength, particle size distribution, static and dynamic capacity, and scanning electron microscopy (SEM) pictures. Chromatographic resins investigated were Fractogel EMD SO3- (M), Fractogel EMD SE Hicap (M), Fractogel EMD COO- (M), MacroPrep 25S, MacroPrep High S, MacroPrep CM, CM HyperZ, and Matrex Cellufine C-500. Testing was done with three proteins: Anti-FVII Mab (IgG), aprotinin, and lysozyme. For lysozyme and aprotinin with pI above experimental pH, dependence of pH on retention was generally low, though some pronounced decrease of retention with increasing pH was observed for CM HyperZ. For Anti-FVII Mab with pI<7.5, binding was observed on several resins at pH 7.5. Efficiency results present the expected trend of increasing dependence of plate height as a function of increasing flow rate, and the highest flow dependence was observed for Fractogel EMD COO-. Particle size distribution was determined by two independent methods, coulter counting and SEM pictures, with fair agreement. Binding strength data of cation-exchange resins as a function of ionic strength depends on the protein, but binding and elution at high salt concentration may in general be performed with MacroPrep resins. Comparison of dynamic capacity data at 10% break-through and static capacity measurements shows that a very diverse utilization of approximately 25-90% of the total available capacity is employed during chromatographic operation. The effect of competitive binding from yeast fermentation components on dynamic binding capacity of aprotinin was studied showing a significant decrease in binding capacity. Sepharose FF, Toyopearl 650 M, and Ceramic HyperD F strong and weak cation-exchange resins were included in this study. Resins with good pure aprotinin capacity also performed well for aprotinin in fermentation broth, but the highest relative capacity was obtained with MacroPrep High S having a fairly low pure component dynamic capacity. Results of this paper may be used in the selection of resins for further testing in biopharmaceutical protein purification process development.

Construction by Molecular Dynamics Modeling and Simulations of the Porous Structures Formed by Dextran Polymer Chains Attached on the Surface of the Pores of a Base Matrix: Characterization of Porous Structures

Significant increases in the separation of bioactive molecules by using ion-exchange chromatography are realized by utilizing porous adsorbent particles in which the affinity group/ligand is linked to the base matrix of the porous particle via a polymeric extender. To study and understand the behavior of such systems, the M3B model is modified and used in molecular dynamics (MD) simulation studies to construct porous dextran layers on the surface of a base matrix, where the dextran polymer chains and the surface are covered by water. Two different porous polymer layers having 25 and 40 monomers per main polymer chain of dextran, respectively, are constructed, and their three-dimensional (3D) porous structures are characterized with respect to porosity, pore size distribution, and number of conducting pathways along the direction of net transport. It is found that the more desirable practical implications with respect to structural properties exhibited by the porous polymer layer having 40 monomers per main polymer chain, are mainly due to the higher flexibility of the polymer chains of this system, especially in the upper region of the porous structure. The characterization and analysis of the porous structures have suggested a useful definition for the physical meaning and implications of the pore connectivity of a real porous medium that is significantly different than the artificial physical meaning associated with the pore connectivity parameter employed in pore network models and whose physical limitations are discussed; furthermore, the methodology developed for the characterization of the three-dimensional structures of real porous media could be used to analyze the experimental data obtained from high-resolution noninvasive three-dimensional methods like high-resolution optical microscopy. The MD modeling and simulations methodology presented here could be used, considering that the type and size of affinity group/ligand as well as the size of the biomolecule to be adsorbed onto the affinity group/ligand are known, to construct different porous dextran layers by varying the length of the polymeric chain of dextran, the number of attachment points to the base matrix, the degree of side branching, and the number of main polymeric chains immobilized per unit surface area of base matrix. After the characterization of the porous structures of the different porous dextran layers is performed, then only a few promising structures would be selected for studying the immobilization of adsorption sites on the pore surfaces and the subsequent adsorption of the bioactive molecules onto the immobilized affinity groups/ligands.

Generic method for systematic phase selection and method development of biochromatographic processes

Even if the first protein therapeutics are now for more than 20 years on the market the selection of suitable adsorbents for the preparative downstream processing (DSP) of these biomolecules as well as the method development towards process conditions are still based mainly on 'trial and error'. Therefore, theses processes are not perfectly efficient, but indeed very time consuming and laborious. In this study a novel systematic method is introduced to find a suitable adsorbent (not necessarily the best one) with appropriate separation parameters for a specific separation with reduced effort. Following this strategy, the adsorbents must first be packed into columns under preparative conditions and then characterized completely with regard to, e.g. pressure drop, k'-values, plate heights (HETP curves), selectivity and capacity by using test substances, which are similar in their characteristics (molecular mass, size, charge distribution, hydrophobicity) to the target proteins. With the database once determined, a preselection of most suitable adsorbents including separation parameters is made regarding chromatographic and also economical properties. After this, preparative experiments must be conducted with a reduced number of adsorbents to figure out the individual influence of side components. This approach is demonstrated for the separation of an exemplary industrial protein mixture using cation-exchange chromatography (CEX). Characterization of different weak CEX-adsorbents is illustrated. After comparing these phases with each other, a first preselection and a prediction of suitable adsorbents is made. In the following preparative separation conditions (load, velocity, gradient) are determined for the preparative separations using the database and results of some additional experiments. The final comparison of separation performance in preparative scale confirms this selection and so the applicability of the new method.

Comparison of chromatographic ion-exchange resins

A comparative study was performed on heparin resins and strong and weak cation exchangers to investigate the pH dependence, efficiency, binding strength, particle size distribution, static and dynamic capacity, and scanning electron microscopy pictures of chromatographic resins. The resins tested include: Heparin Sepharose FF, SP Sepharose FF, CM Sepharose FF, Heparin Toyopearl 650 m, SP Toyopearl 650 m, CM Toyopearl 650 m, Ceramic Heparin HyperD M, Ceramic S HyperD 20, and Ceramic CM HyperD F. Testing was performed with four different proteins: anti-FVII Mab (IgG), aprotinin, lysozyme, and myoglobin. Dependence of pH on retention was generally very low for proteins with high isoelectric point (pI), though some decrease of retention with increasing pH was observed for CM Ceramic HyperD F and S Ceramic HyperD 20. Binding of anti-FVII Mab with pI < 7.5 was observed on several resins at pH 7.5. Efficiency results show the expected trend of increasing dependence of the plate height with increasing flow rate of Ceramic HyperD resins followed by Toyopearl 650 m resins and the highest flow dependence of the Sepharose FF resins corresponding to their pressure resistance. Determination of particle size distribution by two independent methods, coulter counting and SEM, was in good agreement. Binding strength of cation-exchange resins as a function of ionic strength varies depending on the protein. Binding and elution at high salt concentration may be performed with Ceramic HyperD resins, while binding and elution at low salt concentration may be performed with model proteins on heparin resins. Employing proteins with specific affinity for heparin, a much stronger binding is observed, however, some cation exchangers may still be good substitutions for heparin resins. Dynamic capacity at 10% breakthrough compared to static capacity measurements and dynamic capacity displays that approximately 40-80% of the total available capacity is utilized during chromatographic operation depending on flow rate. A general good agreement was obtained between results of this study and data obtained by others. Results of this study may be used in the selection of resins for testing during protein purification process development.

Effects of ionic strength on lysozyme uptake rates in cation exchangers. I: Uptake in SP Sepharose FF

Fluorescence scanning confocal microscopy was used in parallel with batch uptake and breakthrough measurements of transport rates to study the effect of ionic strength on the uptake of lysozyme into SP Sepharose FF. In all cases the adsorption isotherms were near-rectangular. As described previously, the intraparticle profiles changed from slow-moving self-sharpening fronts at low salt concentration, to fast-moving diffuse profiles at high salt concentration, and batch uptake rates correspondingly increased with increasing salt concentration. Shrinking core and homogeneous diffusion frameworks were used successfully to obtain effective diffusivities for the low salt and high salt conditions, respectively. The prediction of column breakthrough was generally good using these frameworks, except for low-salt uptake results. In those cases, the compressibility of the stationary phase coupled with the shrinking core behavior appears to reduce the mass transfer rates at particle-particle contacts, leading to shallower breakthrough curves. In contrast, the fast uptake rates at high ionic strength appear to reduce the importance of mass transfer limitations at the particle contacts, but the confocal results do show a flow rate dependence on the uptake profiles, suggesting that external mass transfer becomes more limiting at high ionic strength. These results show that the complexity of behavior observable at the microscopic scale is directly manifested at the column scale and provides a phenomenological basis to interpret and predict column breakthrough. In addition, the results provide heuristics for the optimization of chromatographic conditions.

Comparison of chromatographic ion-exchange resins

A comparative study was performed on strong cation-exchangers to investigate the pH dependence, efficiency, binding strength, particle size distribution, static and dynamic capacity, and SEM pictures of chromatographic resins. The resins tested included: SP Sepharose XL, Poros 50 HS, Toyopearl SP 550c, SP Sepharose BB, Source 30S, TSKGel SP-5PW-HR20, and Toyopearl SP 650c. Testing was performed with four different proteins: anti-FVII Mab (IgG), aprotinin, lysozyme, and myoglobin. Dependence of pH on retention was generally very low for proteins with high pI. An unexpected binding at pH 7.5 of anti-FVII Mab with pI < 7.5 was observed on several resins. Efficiency results show the expected trend of higher dependence of the plate height with increasing flow rate of soft resins compared to resins for medium and high-pressure operation. Determination of particle size distribution by two independent methods, Coulter counting and SEM, was in very good agreement. The mono-dispersed nature of Source 30S was confirmed. Binding to cation-exchange resins as a function of ionic strength varies depending on the specific protein. Generally, binding and elution at high salt concentration may be performed with Toyopearl SP 550c and Poros 50 HS, while binding and elution at low salt concentration may be performed with Toyopearl SP 650c. A very high binding capacity was obtained with SP Sepharose XL. Comparison of static capacity and dynamic capacity at 10% break-through shows in general approximately 50-80% utilisation of the total available capacity during chromatographic operation. A general good agreement was obtained between this study and data obtained by others. The results of this study may be used for selection of resins for testing in process development. The validity of experiments and results with model proteins were tested using human insulin precursor in pure state and in real feed-stock on Toyopearl SP 550c, SP Sepharose BB, and Toyopearl SP 650c. Results showed good agreement with experiments with model proteins.

Chemical characterisation of different separation media based on agarose by static time-of-flight secondary ion mass spectrometry

In this paper, the novel application of time-of-flight secondary ion mass spectrometry (TOF-SIMS) for qualitative and semi-quantitative investigation of the surface chemistry of separation media based on beaded agarose is reported. Five different media were studied: DEAE Sepharose Fast Flow, Q Sepharose Fast Flow, SP Sepharose Fast Flow, Phenyl Sepharose Fast Flow at ligand densities between 7 and 33% (w/w) and the base matrix Sepharose 6 Fast Flow. The obtained TOF-SIMS spectra reveal significant chemical information regarding the ligands (DEAE, Q, SP and Phenyl) which are covalently attached to the agarose-based matrix Sepharose 6 Fast Flow. For the anion-exchange media (DEAE and Q Sepharose Fast Flow), the positive TOF-SIMS spectra yielded several strong characteristic fragment peaks from the amine ligands. Structural information was obtained, e.g. from the peak at m/z 173.20, originating from the ion structure [(C2H5)2NCH2CH2NH(C2H5)2l+, which shows that the ligand in DEAE Sepharose Fast Flow is composed of both tertiary and quaternary amines. The positive spectrum of Phenyl Sepharose Fast Flow contained major fragments both from the base matrix and the ligand. The cation-exchanger (SP Sepharose Fast Flow) gave rise to a positive spectrum resembling that of the base matrix (Sepharose 6 Fast Flow) but with a different intensity pattern of the matrix fragments. In addition, peaks with low intensity at m/z 109.94, 125.94 and 139.95 corresponding to Na2SO2+, Na2SO3+ and Na2SO3CH2+, respectively, were observed. The positive TOF-SIMS spectrum of Sepharose 6 Fast Flow contains a large number of fragments in the mass range up to m/z 200 identified as CxHyOz and CxHy structures. The results clearly show that positive TOF-SIMS spectra of different media based on Sepharose 6 Fast Flow are strongly influenced by the ligand coupled to the matrix. The negative TOF-SIMS spectra contained several ligand-specific, characteristic peaks for the cation-exchanger, having sulphonate as the ion-exchange group. Negative fragments such as S-, SO-, SO2-, SO3-, C2H3SO3-, C3H5SO3- and OC3H5SO3- were observed. Phenyl Sepharose Fast Flow, which has an uncharged group (Phenyl) coupled to the agarose matrix yielded one ligand-related peak corresponding to the C6H5O- fragment. DEAE and Q ligands could only be identified by the appearance of the fragments CN- and CNO- in the negative spectrum. However, a strong peak corresponding to the counter ion (Cl-) was observed. TOF-SIMS analysis can also be used for the investigation of residues from the coupling procedure that bonds the ligands to the matrix. One example is the observation of bromine peaks in the negative spectrum of Q Sepharose Fast Flow. Furthermore, it has also been shown that different ligand concentrations of Phenyl Sepharose Fast Flow can easily be detected by TOF-SIMS analysis. Information regarding the difference between the ligand density on the surface of the beads and in the bulk can also be obtained. However, spectra registered on the outermost surface and on the pore surface (crushed beads) of DEAE Sepharose Fast Flow clearly show that the agarose and the DEAE groups are homogeneously distributed in the beads.

Preparation and characterization of prototypes for multi-modal separation aimed for capture of positively charged biomolecules at high-salt conditions

Several prototypes of aromatic (Ar) and non-aromatic (NoAr) cation-exchange ligands suitable for capture of proteins from high conductivity (ca. 30 mS/cm) mobile phases were coupled to Sepharose 6 Fast Flow. These new prototypes of multi-modal cation-exchangers were found by screening a diverse library of multi-modal ligands and selecting cation-exchangers resulting in elution of test proteins at high ionic-strength. Candidates were then tested with respect to breakthrough capacity of bovine serum albumin (BSA), human IgG and lysozyme in buffers adjusted to a high conductivity. By applying a salt-step or a pH-step the recoveries were also tested. We have found that aromatic multi-modal cation-exchanger ligands based on carboxylic acids seem to be optimal for the capture of proteins at high-salt conditions. Experimental evidence on the importance of the relative position of the aromatic group in order to improve the breakthrough capacity at high-salt conditions has been found. It was also found that an amide group on the alpha-carbon was essential for capture of proteins at high-salt conditions. Compared to a strong cation-exchanger such as SP Sepharose Fast Flow the best new multi-modal weak cation-exchangers have breakthrough capacities of BSA, human IgG and lysozyme that are 10-30 times higher at high-salt conditions. The new multi-modal cation-exchangers can also be used at normal cation-exchange conditions and with either a salt-step or a pH-step (to pH-values where the proteins are negatively charged) to accomplish elution of proteins. In addition, the functional performance of the new cation-exchangers was found to be intact after treatment in 1.0 M sodium hydroxide solution for 10 days. For BSA it was also possible to design cation-exchangers based on non-aromatic carboxyl acid ligands with high capacities at high-salt conditions. A common feature of these ligands is that they contain hydrogen acceptor groups close to the carboxylic group. Furthermore, it was also possible to obtain high breakthrough capacities for lysozyme and BSA of a strong cation-exchanger (SP Sepharose Fast Flow) if phenyl groups were attached to the beads. Varying the ligand ratio (SP/Phenyl) could be used for optimizing the function of mixed-ligand ion-exchange media.

Preparation and characterization of prototypes for multi-modal separation media aimed for capture of negatively charged biomolecules at high salt conditions

Several prototypes of multi-modal ligands suitable for the capture of negatively charged proteins from high conductivity (28 mS/cm) mobile phases were coupled to Sepharose 6 Fast Flow. These new prototypes of multi-modal anion-exchangers were found by screening a diverse library of multi-modal ligands and selecting anion-exchangers resulting in elution of test proteins at high ionic strength. Candidates were then tested with respect to breakthrough capacity of BSA in a buffer adjusted to a high conductivity (20 mM Piperazine and 0.25 M NaCl, pH 6.0). The recovery of BSA was also tested with a salt step (from 0.25 to 2.0 M NaCl using 20 mM Piperazine as buffer, pH 6.0) or with a pH-step to pH 4.0. We have found that non-aromatic multi-modal anion-exchange ligands based on primary or secondary amines (or both) are optimal for the capture of proteins at high salt conditions. Furthermore, these new multi-modal anion-exchange ligands have been designed to take advantage not only of electrostatic but also hydrogen bond interactions. This has been accomplished through modification of the ligands by the introduction of hydroxyl groups in the proximity of the ionic group. Experimental evidence on the importance of the relative position of the hydroxyl groups on the ligand in order to improve the breakthrough capacity of BSA has been found. Compared to strong anion-exchangers such as Q Sepharose Fast Flow the new multi-modal weak anion-exchangers have breakthrough capacities of BSA at mobile phases of 28 mS/cm and pH 6.0 that are 20-30 times higher. The new multi-modal anion-exchangers can also be used at normal anion-exchange conditions and with either a salt step or a pH-step to acidic pH can accomplish the elution of proteins. In addition, the functional performance of the new anion-exchangers was found to be intact after treatment in 1.0 M sodium hydroxide solution for 1 week. A number of multi-modal anion-exchange ligands based on aromatic amines exhibiting high breakthrough capacity of BSA have been found. With these ligands recovery was often found to be low due to strong non-electrostatic interactions. However, for phenol derived anion-exchange media the recovery can be improved by desorption at high pH.

Development of rigid bidisperse porous microspheres for high-speed protein chromatography

Development of a high-performance stationary phase is an essential demand for high-speed separation of proteins by liquid chromatography. Based on a novel porogenic mode, that is, using superfine granules of calcium carbonate as solid porogen and a mixture of cyclohexanol and dodecanol as liquid porogen, a rigid spherical biporous poly(glycidyl methacrylate-co-ethylene dimethacrylate) matrix has been prepared by radical suspension-polymerization. The epoxide groups of the matrix were modified with diethylamine to afford the ionizable weak base 1-N,N-diethylamino-2-hydeoxypropy functionalities that are required for ion exchange chromatography. Results from scanning electron microscopy and mercury intrusion porosimetry measurements revealed that the matrix contained two families of pores, that is, micropores (10-90 nm) and macropores (180-4000 nm). Furthermore, the biporous medium possesses specific surface area as high as 91.3 m(2)/g. Because of the presence of the macropores that provided convective flow channels for the mobile phase, the dynamic adsorption capacity was found to be as high as 54.6 mg/g wet bead at 300 cm/h, approximately 63.2% of its static capacity. In addition, the column efficiency and dynamic binding capacity decreased only slightly with mobile-phase flow rate in the range of 300-3000 cm/h. These properties made the packed bed with the bidisperse porous matrix suitable for high-speed protein chromatography.

Collection of Trace Amounts of DNA/mRNA Molecules Using Genomagnetic Nanocapturers

The collection and then the separation of rare DNA/mRNA targets with single-base mismatches in a complex matrix is critically important in human disease diagnostics, gene expression studies, and gene profiling. The major result of this work is the development and application of a novel genomagnetic nanocapturer (GMNC) for the collection, separation, and detection of trace amounts of DNA/RNA molecules with one single-base difference. The GMNC is constructed by bioconjugating molecular beacon DNA probes onto magnetic nanoparticle surfaces. We have successfully applied the GMNC in artificial buffer solution samples and in cancer cell samples, both containing different proteins and random DNA sequences. Our method has three distinctly useful features: highly efficient collection of trace amount of DNA/mRNA samples down to femtomolar (10(-15) M) concentrations; excellent ability to differentiate single-base-mismatched DNA/mRNA samples by combining the exceptional specificity of molecular beacons and the separation power of magnetic nanoparticles; and real-time monitoring and confirmation of the collected gene products. The newly developed genomagnetic nanocapturers will be highly useful for the collection of trace amounts of DNA/mRNA targets in a variety of sample sources in forensic, medical, and biotechnological fields.

Ion-exchange separation of proteins by polyallylamine-grafted cellulose gel

A cellulose-based anion exchanger bearing water-soluble polycation was tested for separation of proteins. The exchanger was obtained by partial oxidation of cellulose gel by aq. NaIO4 followed by Schiff base formation with polyallylamine (PAA, molecular mass 5000). The retention behavior of proteins for three grades of PAA-cellulose gels, with amino group contents of 0.35, 0.59 and 0.96 mmol/g cellulose, was examined at several pH values and compared with that for conventional DEAE-cellulose gel with amino group content of 1.07 mmol/g cellulose. The retention of proteins by PAA-cellulose gels was remarkably greater than that for the DEAE-cellulose gel. Pairs of proteins having close isoelectric points and molecular masses (human and bovine serum albumins; beta-lactoglobulin A and B) could be separated by the PAA-cellulose gel columns. Such efficiency can be ascribed to high local density of grafted polyallylamine, in contrast to the random and sparse charge distribution in DEAE-cellulose.

Effects of bovine serum albumin heterogeneity on frontal analysis with anion-exchange media

The presence of dimers in commercial bovine serum albumin (BSA) samples of nominal high purity is investigated along with their effects on the frontal analysis behavior of preparative anion-exchange media. Size-exclusion and analytical anion-exchange chromatography are used to determine the relative amounts of monomer and dimer for two samples of BSA. While the amount of dimer was generally low, its impact on adsorptive behavior is significant. Equilibrium experiments demonstrate that the anion-exchange media binds the dimer more strongly, leading to an unequal distribution of the monomer and dimer between the two phases. Analysis of the breakthrough behavior of BSA reveals that the monomer breaks through prior to the dimer. This leads to the characteristic tailing breakthrough curve often seen with BSA. Breakthrough experiments carried out using dimer-free BSA confirm that the extreme tailing observed with the commercial samples is curtailed by removing the dimer.

Direct isolation of monoclonal antibodies from tissue culture supernatant using the cation-exchange cellulose Express-Ion S

The chromatography of the murine hybridoma cell C595/102 culture supernatant expressing the therapeutic monoclonal antibody C595, on the cation-exchange cellulose Whatman Express-Ion Exchanger S has been investigated. Initial method scouting studies using purified C595 in 1-ml mini columns demonstrated that binding capacity and binding efficiency were dependent not only on decreasing pH but also on the buffer salts used to prepare the mobile phase. Under optimised conditions of 0.1 M sodium acetate buffer, pH 5.0, we were able to separate purified C595 from BSA, the major contaminant in tissue culture fluid. Under these conditions immunoreactive C595 could be isolated directly from tissue culture supernatant. A scale-down study was carried out using a 25-ml column operated at a flow-rate of 150 cm/h which also yielded purified immunoreactive antibody. This procedure should now be suitable for scale-up.

New approaches to the isolation of DNA by ion-exchange chromatography

The performance of different anion-exchange media have been compared for the isolation of plasmid DNA and genomic DNA from bacterial cells and human whole blood. Whatman DEAE-Magarose, based on an agarose bead containing a paramagnetic component, has been compared with prepacked gravity-flow columns containing a derivatised silica matrix. In each case the DNA isolation at various scales of operation was similar both in terms of yield and quality. The magnetic susceptibility of DEAE-Magarose is very high, facilitating the use of this separation technique for rapid flexible batch chromatographic processes, a limitation of the prepacked column techniques.

Recent developments of magnetic beads for use in nucleic acid purification

The performance of Magarose, an agarose-based bead containing a paramagnetic component has been evaluated. The anion exchanger DEAE-Magarose is effective at binding DNA from a crude cell lysate. The plasmid pBluescript was isolated from 1.5 ml Escherichia coli JM109 cell culture, following alkaline lysis yielding 8.2 micrograms high-quality DNA. Under similar binding conditions 21 micrograms of salmon sperm DNA bound to the ion exchangers. The affinity medium oligo-dT Magarose was demonstrated to bind 75 mumol of an oligo-dA probe/g of medium by hybridization. Under similar conditions mRNA could be isolated from a preparation of baby hamster cell total RNA. The magnetic susceptibility of Magarose is very high, facilitating the use of this separation technique for rapid batch chromatographic processes.

Comparison of diffusion and diffusion-convection matrices for use in ion-exchange separations of proteins

A comprehensive study has been undertaken to characterise a range of chromatographic properties for a series of modified polystyrene-divinylbenzene (PS-DVB) chromatography matrices. The matrices studied included diffusion matrices and matrices that allowed convective mass transfer of liquid into the particles at high flow-rates, so-called "perfusion" matrices. The matrices tested included the following: CG1000sd 20-50 microns (TosoHaas), PLRP4000s 15-25 microns, 50-70 microns (Polymer Labs.), Source 15RPC and 30RPC, 15S, 30S, (Pharmacia Biotech), POROS 20SP type 1 matrix and OH activated POROS 20 type 2 matrix (PerSeptive Biosystems) and SP Sepharose Fast Flow (Pharmacia Biotech). A Van Deemter equation was used to determine bead tortuosities and split ratios. Frontal analysis, resolution studies, ionic capacities and isotherms were measured. It was found that diffusion-convection chromatographic particles had smaller plate heights to comparable diffusion particles. The smallest diffusion bead, Source 15, had the lowest plate heights at low superficial velocities, but the small particle size resulted in a high back pressure at high flow-rates. The equilibrium binding capacities for lysozyme and IgG on the diffusion-convection matrices were substantially lower than the equilibrium binding capacities on the diffusion matrices. The dynamic capacities for these proteins were also lower on the diffusion-convection particles, compared to the diffusion particles, over the tested flow-rates. At high protein loading, resolution between proteins was higher on diffusion particles than on diffusion-convection particles. Diffusion-convection particles showed low or no resolution at high protein loading. At analytical level loadings, the diffusion-convection particles achieved a high resolution over the whole flow-rate range tested and were more suitable for this application than diffusion particles.

Purification of a recombinant protein expressed in yeast: optimization of analytical and preparative chromatography

The industrial production of recombinant proteins requires control of both fermentation and purification steps. For the serodiagnosis of toxoplasmosis, the main antigen is a membrane protein of 30 kDa (P30). The P30 gene was cloned and expressed in Schizosaccharomyces pombe at 0.7 microg/ml in culture medium. Batch fermentation was optimized by the specific choice of peptones, which enabled optimum growth and protein expression without reducing the efficacy of the purification step. Analytical purification was then carried out using cation-exchange chromatography. For larger volumes, scaling up was performed on expanded mode by using a Streamline system (Pharmacia). This purification step allowed us to obtain a 67.5% recovery with a purification factor greater than 27-fold. Expanded bed adsorption technology is a convenient and effective technique for protein capture directly from feedstock, and the eluted fraction is ready for a second affinity chromatography step. This second step is performed with a yield of 40% and provides a final purification factor of 2000-fold.