Liquid chromatography of recombinant proteins and protein drugs

Purification and Activity Evaluation of a Novel Thrombopoietin Mimetic Peptide

The emergence of thrombopoietin mimetic peptides presents a promising therapeutic strategy for addressing thrombocytopenia. This particular study aimed to establish a direct, expeditious, and efficient method for modifying and purifying a novel thrombopoietin mimetic peptide. Precursor proteins were subjected to modification utilizing three distinct fatty acids: C25H42O7N2, C39H66O15N4, and C41H70O15N4. Liquid chromatography analyses demonstrated that C41H70O15N4 yielded the most effective modification results. Mass spectrometry findings validated the correspondence between the theoretical and actual molecular weights of each sample. In vivo experiments conducted on normal mice showcased that the C41H70O15N4 modification group exhibited the highest platelet count, peaking at an impressive 5047 × 109/L. This count was approximately twice that of the peak platelet count observed in the dTMP group and four times higher than the control group. Pharmacokinetic investigations revealed that the C41H70O15N4 modification group displayed the lengthiest half-life among beagles, persisting for 128.5 h. This duration was approximately 28.5 times longer than that of the unmodified dTMP group. These findings underscore the effectiveness of the established C41H70O15N4 modification and purification method in preserving the biological activity of the thrombopoietin mimetic peptide. The novel thrombopoietin mimetic peptide showcased notable attributes of simplicity and cost-effectiveness, while also exhibiting a significant platelet-promoting effect and an extended half-life. Consequently, this novel peptide holds substantial significance for advancing the treatment of thrombocytopenia.

A novel protein purification scheme based on salt inducible self-assembling peptides

BACKGROUND

Protein purification remains a critical need for biosciences and biotechnology. It frequently requires multiple rounds of chromatographic steps that are expensive and time-consuming. Our lab previously reported a cleavable self-aggregating tag (cSAT) scheme for streamlined protein expression and purification. The tag consists of a self-assembling peptide (SAP) and a controllable self-cleaving intein. The SAP drives the target protein into an active aggregate, then by intein-mediated cleavage, the target protein is released. Here we report a novel cSAT scheme in which the self-assembling peptide is replaced with a salt inducible self-assembling peptide. This allows a target protein to be expressed first in the soluble form, and the addition of salt then drives the target protein into the aggregated form, followed by cleavage and release.

RESULTS

In this study, we used MpA (MKQLEDKIEELLSKAAMKQLEDKIEELLSK) as a second class of self-assembling peptide in the cSAT scheme. This scheme utilizes low salt concentration to keep the fusion protein soluble, while eliminating insoluble cellular matters by centrifugation. Salt then triggers MpA-mediated self-aggregation of the fusion, removing soluble background host cell proteins. Finally, intein-mediated cleavage releases the target protein into solution. As a proof-of-concept, we successfully purified four proteins and peptides (human growth hormone, 22.1 kDa; LCB3, 7.7 kDa; SpyCatcherΔN-ELP-SpyCatcherΔN, 26.2 kDa; and xylanase, 45.3 kDa) with yields ranging from 12 to 87 mg/L. This was comparable to the classical His-tag method both in yield and purity (72-97%), but without the His-tag. By using a further two-step column purification process that included ion-exchange chromatography and size-exclusion chromatography, the purity was increased to over 99%.

CONCLUSION

Our results demonstrate that a salt-inducible self-assembling peptide can serve as a controllable aggregating tag, which might be advantageous in applications where soluble expression of the target protein is preferred. This work also demonstrates the potential and advantages of utilizing salt inducible self-assembling peptides for protein separation.

Effect of stereoconfiguration of aromatic ligands on retention and selectivity of terphenyl isomer-bonded stationary phases

The structure of ligands has a significant influence on the separation properties of alkyl and aromatic phases in reversed-phase liquid chromatography. Compared with alkyl phases, the effect of stereoconfiguration of aromatic ligands on the retention and selectivity of stationary phases has rarely been addressed. To illustrate the issue, three terphenyl isomer-bonded stationary phases were prepared via the coupling chemistry of isocyanate with terphenyl amine isomers, 3,4-diphenylaniline, 2,4-diphenylaniline and 4-amino-p-terphenyl, respectively. The retention behaviors of stationary phases were assessed in terms of retention strength, selectivity, hydrophobic and π-π interaction by five kinds of solutes. It is found that the selectivity towards the solutes is slightly larger on the branched m-terphenyl-bonded phase (m-π³) than o-terphenyl-bonded phase (o-π³) but is significantly improved on the chain p-terphenyl-bonded phase (p-π³). The results can be interpreted by the ease self-adjustment of the conformation of the chain p-terphenyl ligand and the smaller steric effect of p-π³ towards the insertion of solutes into the ligand brushes. In addition, the p-π³ yields excellent selective separation towards aromatic solutes. These findings are of significance in the design of aromatic stationary phases.

Non-specificity as the sticky problem in therapeutic antibody development

Antibodies are highly potent therapeutic scaffolds with more than a hundred different products approved on the market. Successful development of antibody-based drugs requires a trade-off between high target specificity and target binding affinity. In order to better understand this problem, we here review non-specific interactions and explore their fundamental physicochemical origins. We discuss the role of surface patches - clusters of surface-exposed amino acid residues with similar physicochemical properties - as inducers of non-specific interactions. These patches collectively drive interactions including dipole-dipole, π-stacking and hydrophobic interactions to complementary moieties. We elucidate links between these supramolecular assembly processes and macroscopic development issues, such as decreased physical stability and poor in vivo half-life. Finally, we highlight challenges and opportunities for optimizing protein binding specificity and minimizing non-specificity for future generations of therapeutics.

Development and evaluation of a hydrogenated rosin (β-acryloxyl ethyl) ester-bonded silica stationary phase for high-performance liquid chromatography separation of paclitaxel from yew bark

Paclitaxel (PTX) is a complex diterpenoid anticancer drug whose separation from yew biomass poses a significant challenge. In this study, a new stationary phase comprising hydrogenated rosin (β-acryloxyl ethyl) ester (HRE)-bonded silica (HRE@SiO₂) is developed to separate and purify PTX from crude yew-bark extract using high-performance liquid chromatography. In HRE@SiO₂, HRE molecules, which are functional ligands, are bonded to the surface of a silica gel matrix using a coupling agent, (3-mercaptopropyl)trimethoxysilane. The proposed HRE@SiO₂ stationary phase was characterized by Fourier-transform infrared spectroscopy, elemental analysis, thermogravimetric analysis, scanning electron microscopy, laser diffraction granulometry, and nitrogen gas adsorption. The HRE@SiO₂ column exhibited excellent chromatographic performance, satisfactory performance reproducibility, and typical reversed-phase chromatographic behavior. An HRE@SiO₂ column was used to separate PTX and its analogs, achieving resolutions exceeding 7.43 for consecutively eluted species. Stoichiometric displacement theory for retention (SDT-R), the van Deemter equation, and van 't Hoff plots were used to analyze the separation mechanism and properties of the HRE@SiO₂ column. The results showed that hydrophobic interactions determine the analyte retention and the separation of PTX and its analogs on an HRE@SiO₂ column is an exothermic process driven by enthalpy. Furthermore, an HRE@SiO₂ column was employed to separate and purify PTX from crude yew-bark extract, increasing PTX purity from 6% to 82%. The findings of this study provide insights for developing rosin-based stationary phases for the separation of natural products.

Expression, purification, and characterization of pneumococcal PsaA-PspA fusion protein

Streptococcus pneumoniae is a gram-positive bacterial pathogen causing invasive pneumonia, meningitis, otitis media, and bacteremia. Owing to the current pitfalls of polysaccharide and polysaccharide-conjugate vaccines, protein vaccines are considered promising candidates against pneumonia. Pneumococcal surface protein A (PspA) and pneumococcal surface adhesin A (PsaA) are virulence proteins showing good immunogenicity and protective effects against S. pneumoniae strains in mice. In this study, we expressed the fusion protein PsaA-PspA, which consists of PsaA and the N-terminal region of PspA family 1 and 2, in Escherichia coli. We describe a novel and effective method to purify PsaA-PspA using hydroxyapatite and two-step chromatography. After determining the optimal induction conditions and a series of purification steps, we obtained PsaA-PspA fusion protein with over 95% purity at a final yield of 22.44% from the starting cell lysate. The molecular weight of PsaA-PspA was approximately 83.6 kDa and its secondary structure was evaluated by circular dichroism. Immunization with the purified protein induced high levels of IgG antibodies in mice. Collectively, these results demonstrate that our purification method can effectively produce high-purity PsaA-PspA fusion protein with biological activity and chemical integrity, which can be widely applied to the purification of other PspA subclass proteins.

Optimized protocol for soluble prokaryotic expression, purification and structural analysis of human placenta specific-1(PLAC1)

Placenta specific -1 (PLAC1) has been recently introduced as a small membrane-associated protein mainly involved in placental development. Expression of PLAC1 transcript has been documented in almost one hundred cancer cell lines standing for fourteen distinct cancer types. The presence of two disulfide bridges makes difficult to produce functional recombinant PLAC1 in soluble form with high yield. This limitation also complicates the structural studies of PLAC1, which is important for prediction of its physiological roles. To address this issue, we employed an expression matrix consisting of two expression vectors, five different E. coli hosts and five solubilization conditions to optimize production of full and truncated forms of human PLAC1. The recombinant proteins were then characterized using an anti-PLAC1-specific antibody in Western blotting (WB) and enzyme linked immunosorbent assay (ELISA). Structure of full length protein was also investigated using circular dichroism (CD). We demonstrated the combination of Origami™ and pCold expression vector to yield substantial amount of soluble truncated PLAC1 without further need for solubilization step. Full length PLAC1, however, expressed mostly as inclusion bodies with higher yield in Origami™ and Rosetta2. Among solubilization buffers examined, buffer containing Urea 2 M, pH 12 was found to be more effective. Recombinant proteins exhibited excellent reactivity as detected by ELISA and WB. The secondary structure of full length PLAC1 was considered by CD spectroscopy. Taken together, we introduced here a simple, affordable and efficient expression system for soluble PLAC1 production.

Mixed-mode reversed phase/positively charged repulsion chromatography for intact protein separation

A mixed-mode reversed phase/positively charged repulsion stationary phase C8PN composed of octyl and amino group has been developed for separation of intact protein. Before the separation of proteins, a set of probe compounds were employed to evaluate the chromatographic properties of C8PN, demonstrating typical reversed phase/positively charged repulsion interaction on this stationary phase as estimated. Then the new C8PN stationary phase was used to separate a standard protein mixture on the reversed phase mode. Compared with a commercial C4 stationary phase, it showed different selectivity for some proteins. In order to better understand the properties of C8PN, the effect of acetonitrile content was investigated based on retention equation. Higher values of the equation parameters on C8PN demonstrated that the protein retentions were more sensitive to the change of acetonitrile content. Besides, the influences of buffer salt additives on the protein retentions were also studied. The retention factors of the proteins got larger with the increase of buffer salt concentration, which confirmed the positively charged repulsion interaction on the column. Finally, the C8PN was further applied to separate oxidized- and reduced- forms of Recombinant Human Growth Hormone. Our study indicated the advantages and application potential of mixed-mode reversed phase/positively charged repulsion stationary phase for intact protein separation.

Purification of single-chain antibody fragments exploiting pH-gradients in simulated moving bed chromatography

This paper deals with the theoretical design and experimental validation of an affinity-based continuous multi-column chromatography process for the purification of single-chain Fragment variable (scFv) antibodies. An open-loop 3-zone pH-gradient simulated moving bed (SMB) process was investigated exploiting the highly specific affinity of metal ions toward histidine-tagged recombinant proteins. The separation problem was simplified by considering the cell culture supernatant as a pseudo-binary mixture. The influence of mobile phase pH on the adsorption isotherm parameters was estimated by the inverse method using recorded pH-gradient batch elution profiles. Suitable operating parameters for the SMB process were identified using an equilibrium stage model and subsequently validated in a lab-scale SMB unit. Finally, the performance of the pH-gradient SMB process was compared against a non-optimized batch process. Biologically active single-chain Fragment variable antibody formats were purified continuously with 9% more recovery, 11 times more productivity (576 mg of purified scFv per day and liter stationary phase in SMB) and enriched by a factor of 2.5 compared to those obtained in the non-optimized batch process.

High-yield reactivation of anionic tobacco peroxidase overexpressed in Escherichia coli

Anionic tobacco peroxidase (TOP) is extremely active in chemiluminescence reaction of luminol oxidation without addition of enhancers and more stable than horseradish peroxidase under antibody conjugation conditions. In addition, recombinant TOP (rTOP) produced in Escherichia coli is known to be a perfect direct electron transfer catalyst on electrodes of various origin. These features make the task of development of a high-yield reactivation protocol for rTOP practically important. Previous attempts to reactivate the enzyme from E. coli inclusion bodies were successful, but the reported reactivation yield was only 14%. In this work, we thoroughly screened the refolding conditions for dilution protocol and compared it with gel-filtration chromatography. The impressive reactivation yield in the dilution protocol (85%) was achieved for 8 μg/mL solubilized rTOP protein and the refolding medium containing 0.3 mM oxidized glutathione, 0.05 mM dithiothreitol, 5 mM CaCl2, 5% glycerol in 50 mM Tris-HCl buffer, pH 9.6, with 1 μM hemin added at the 24th hour of incubation. A practically important discovery was a 30-40% increase in the reactivation yield upon delayed addition of hemin. The reactivation yield achieved is one of the highest reported in the literature on protein refolding by dilution. The final yield of purified active non-glycosylated rTOP was ca. 60 mg per L of E. coli culture, close to the yield reported before for tomato and tobacco plants overexpressing glycosylated TOP (60 mg/kg biomass) and much higher than for the previously reported refolding protocol (2.6 mg per L of E. coli culture).

Fast separation of native proteins using sub-2 μm nonporous silica particles in a chromatographic cake

A novel method for the fast separation of native proteins was investigated using sub-2 μm nonporous silica packing inside a chromatographic cake having a diameter much larger than its thickness. Various silica-based particles ranging from 630 nm to 1.2 μm were synthesized and chemically modified with polyethylene glycol 600. The packing material was laterally packed into a series of chromatographic cakes containing the same diameter (10mm) and different thicknesses, ranging from 2 to 10 mm, and tested by hydrophobic interaction chromatography. The results showed that the sub-2 μm NPS particles in a small chromatographic cake were found to have a high efficiency at a flow rate of 10 mL/min and a backpressure of <20 MPa. The effect of the thickness of the chromatographic cake on the resolution of the proteins was also investigated and it was found that too short a column length could dramatically decrease the protein resolution; the minimum column length was also qualitatively evaluated. The presented method is expected to be useful for routine analysis of native and/or intact proteins in hospitals and as a tool for the fast screening protein drugs and optimization of experimental laboratory conditions.

Separation of mAbs molecular variants by analytical hydrophobic interaction chromatography HPLC: overview and applications

Hydrophobic interaction chromatography-high performance liquid chromatography (HIC-HPLC) is a powerful analytical method used for the separation of molecular variants of therapeutic proteins. The method has been employed for monitoring various post-translational modifications, including proteolytic fragments and domain misfolding in etanercept (Enbrel®); tryptophan oxidation, aspartic acid isomerization, the formation of cyclic imide, and α amidated carboxy terminus in recombinant therapeutic monoclonal antibodies; and carboxy terminal heterogeneity and serine fucosylation in Fc and Fab fragments. HIC-HPLC is also a powerful analytical technique for the analysis of antibody-drug conjugates. Most current analytical columns, methods, and applications are described, and critical method parameters and suitability for operation in regulated environment are discussed, in this review.

Refolding and simultaneous purification of recombinant human proinsulin from inclusion bodies on protein-folding liquid-chromatography columns

Protein-folding liquid chromatography (PFLC) is an effective and scalable method for protein renaturation with simultaneous purification. However, it has been a challenge to fully refold inclusion bodies in a PFLC column. In this work, refolding with simultaneous purification of recombinant human proinsulin (rhPI) from inclusion bodies from Escherichia coli were investigated using the surface of stationary phases in immobilized metal ion affinity chromatography (IMAC) and high-performance size-exclusion chromatography (HPSEC). The results indicated that both the ligand structure on the surface of the stationary phase and the composition of the mobile phase (elution buffer) influenced refolding of rhPI. Under optimized chromatographic conditions, the mass recoveries of IMAC column and HPSEC column were 77.8 and 56.8% with purifies of 97.6 and 93.7%, respectively. These results also indicated that the IMAC column fails to refold rhPI, and the HPSEC column enables efficient refolding of rhPI with a low-urea gradient-elution method. The refolded rhPI was characterized by circular dichroism spectroscopy. The molecular weight of the converted human insulin was further confirmed with SDS-18% PAGE, Matrix-Assisted Laser Desorption/ Ionization Time of Flight Mass Spectrometry (MALDI-TOF-MS) and the biological activity assay by HP-RPLC.

One-step refolding and purification of recombinant human tumor necrosis factor-α (rhTNF-α) using ion-exchange chromatography

Protein refolding is a key step for the production of recombinant proteins, especially at large scales, and usually their yields are very low. Chromatographic-based protein refolding techniques have proven to be superior to conventional dilution refolding methods. High refolding yield can be achieved using these methods compared with dilution refolding of proteins. In this work, recombinant human tumor necrosis factor-α (rhTNF-α) from inclusion bodies expressed in Escherichia coli was renatured with simultaneous purification by ion exchange chromatography with a DEAE Sepharose FF column. Several chromatographic parameters influencing the refolding yield of the denatured/reduced rhTNF-α, such as the urea concentration, pH value and concentration ratio of glutathione/oxidized glutathione in the mobile phase, were investigated in detail. Under optimal conditions, rhTNF-α can be renatured and purified simultaneously within 30 min by one step. Specific bioactivity of 2.18 × 10(8) IU/mg, purity of 95.2% and mass recovery of 76.8% of refolded rhTNF-α were achieved. Compared with the usual dilution method, the ion exchange chromatography method developed here is simple and more effective for rhTNF-α refolding in terms of specific bioactivity and mass recovery.

The ionic liquid isopropylammonium formate as a mobile phase modifier to improve protein stability during reversed phase liquid chromatography

The room temperature ionic liquid isopropylammonium formate (IPAF) is studied as a reversed phase HPLC mobile phase modifier for separation of native proteins using a polymeric column and the protein stability is compared to that using acetonitrile (MeCN) as the standard organic mobile phase modifier. A variety of important proteins with different numbers of subunits are investigated, including non-subunit proteins: albumin, and amyloglucosidase (AMY); a two subunit protein: thyroglobulin (THY); and four subunit proteins: glutamate dehydrogenase (GDH) and lactate dehydrogenase (LDH). A significant enhancement in protein stability is observed in the chromatograms upon using IPAF as a mobile phase modifier. The first sharper peak at about 2min represented protein in primarily the native form and a second broader peak more retained at about 5-6min represented substantially denatured or possibly aggregated protein. The investigated proteins (except LDH) could maintain the native form within up to 50% IPAF, while a mobile phase, with as low as 10% MeCN, induced protein denaturation. The assay for pyruvate using LDH has further shown that enzymatic activity can be maintained up to 30% IPAF in water in contrast to no activity using 30% MeCN.

Metal Species in Biology: Bottom-Up and Top-Down LC Approaches in Applied Toxicological Research

Since the inception of liquid chromatography (LC) more than 100 years ago this separation technique has been developed into a powerful analytical tool that is frequently applied in life science research. To this end, unique insights into the interaction of metal species (throughout this manuscript “metal species” refers to “toxic metals, metalloid compounds, and metal-based drugs” and “toxic metals” to “toxic metals and metalloid compounds”) with endogenous ligands can be obtained by using LC approaches that involve their hyphenation with inductively coupled plasma-based element specific detectors. This review aims to provide a synopsis of the different LC approaches which may be employed to advance our understanding of these interactions either in a “bottom-up” or a “top-down” manner. In the “bottom-up” LC-configuration, endogenous ligands are introduced into a physiologically relevant mobile phase buffer, and the metal species of interest is injected. Subsequent “interrogation” of the on-column formed complex(es) by employing a suitable separation mechanism (e.g., size exclusion chromatography or reversed-phase LC) while changing the ligand concentration(s), the column temperature or the pH can provide valuable insight into the formation of complexes under near physiological conditions. This approach allows to establish the relative stability and hydrophobicity of metal-ligand complexes as well as the dynamic coordination of a metal species (injected) to two ligands (dissolved in the mobile phase). Conversely, the “top-down” analysis of a biological fluid (e.g., blood plasma) by LC (e.g., using size exclusion chromatography) can be used to determine the size distribution of endogenous metalloproteins which are collectively referred to as the “metalloproteome”. This approach can provide unique insight into the metabolism and the plasma protein binding of metal species, and can simultaneously visualize the dose-dependent perturbation of the metalloproteome by a particular metal species. The concerted application of these LC approaches is destined to provide new insight into biochemical processes which represent an important starting point to advance human health in the 21st century.

Role of α-helical structure in organic solvent-activated homodimer of elastase strain K

Recombinant elastase strain K overexpressed from E. coli KRX/pCon2(3) was purified to homogeneity by a combination of hydrophobic interaction chromatography and ion exchange chromatography, with a final yield of 48% and a 25-fold increase in specific activity. The purified protein had exhibited a first ever reported homodimer size of 65 kDa by SDS-PAGE and MALDI-TOF, a size which is totally distinct from that of typically reported 33 kDa monomer from P. aeruginosa. The organic solvent stability experiment had demonstrated a stability pattern which completely opposed the rules laid out in previous reports in which activity stability and enhancement were observed in hydrophilic organic solvents such as DMSO, methanol, ethanol and 1-propanol. The high stability and enhancement of the enzyme in hydrophilic solvents were explained from the view of alteration in secondary structures. Elastinolytic activation and stability were observed in 25 and 50% of methanol, respectively, despite slight reduction in α-helical structure caused upon the addition of the solvent. Further characterization experiments had postulated great stability and enhancement of elastase strain K in broad range of temperatures, pHs, metal ions, surfactants, denaturing agents and substrate specificity, indicating its potential application in detergent formulation.

Recombinant protein purification using gradient-assisted simulated moving bed hydrophobic interaction chromatography. Part I: selection of chromatographic system and estimation of adsorption isotherms

The design of gradient simulated moving bed (SMB) chromatographic processes requires an appropriate selection of the chromatographic system followed by the determination of adsorption isotherm parameters in the relevant range of mobile phase conditions. The determination of these parameters can be quite difficult for recombinant target proteins present in complex protein mixtures. The first part of this work includes the estimation of adsorption isotherm parameters for streptokinase and a lumped impurity fraction present in an Escherichia coli cell lysate for a hydrophobic interaction chromatography (HIC) matrix. Perturbation experiments were carried out using a Butyl Sepharose matrix with purified recombinant protein on buffer equilibrated columns as well as with crude cell lysate saturated columns. The Henry constants estimated for streptokinase were found to exhibit in a wide range a linear dependence on the salt concentration in the mobile phase. These parameters were applied in subsequent investigations to design a simulated moving bed (SMB) process capable to purify in a continuous manner recombinant streptokinase from the E. coli cell lysate.

HIC resolution of an IgG1 with an oxidized Trp in a complementarity determining region

Susceptibility of tryptophan (Trp) in a complementarity-determining region (CDR) to oxidation is a significant issue for recombinant monoclonal antibody (mAb) therapeutics due to the clinical efficacy and stability concerns. Here we present a case study using hydrophobic interaction chromatography (HIC) to separate an oxidized Trp containing population of an IgG1. The best separation was achieved using dual Dionex ProPac HIC-10 columns, and the oxidized Trp population was isolated as a separated pre-peak. Peptide map analysis revealed that the oxidized Trp is located in a heavy chain CDR. In addition, the HIC method was capable of monitoring the oxidation status of the CDR Trp, as the oxidation rate of the CDR Trp measured by HIC directly correlated with the results of the peptide maps. The same method conditions were also capable of separating oxidized methionine (Met) and isomerization/deamidation products, which co-elute as another pre-peak at a different retention time from the oxidized Trp species. These observations indicate that the HIC procedure can be utilized to monitor the oxidative status of the CDR Trp in the IgG1.

Protein folding liquid chromatography

A method for carrying out protein folding with simultaneous separation by protein folding liquid chromatography (PFLC) is described herein. Furthermore, a two-dimensional chromatographic column, termed a 2D column, which can be independently employed for accomplishing PFLC in either weak cation exchange mode or hydrophobic interaction chromatography mode is reported. The content of this chapter describes the most commonly employed methods and operations of PFLC, such as the use of urea or guanidine hydrochloride as a denaturant with the protein in either the reduced or oxidized state and solving problems caused by the formation of the precipitates during protein folding. The PFLC can be performed using conventional chromatographic columns and a new chromatographic cake. A protocol for fast renaturation with simultaneous purification of inclusion body protein of the recombinant human interferon-gamma to obtain purity ≥95% and high specific bioactivity in a single step and in 1 h is introduced.

Monolithic phases for ion chromatography

Monolithic media are continuing to increase in popularity in chromatographic applications, and the ongoing use of commercially available materials in ion chromatography (IC) has made monoliths a viable alternative to packed-bed columns for routine use. We discuss different strategies for the synthesis of polymeric and silica monoliths with ion-exchange functionality, such as direct incorporation of ion-exchange functionality during monolith preparation and different postpolymerization alterations such as grafting and coating. The formulations and strategies presented are focused on materials intended for use in IC. We also discuss strategies for materials characterization, with emphasis on nondestructive techniques for the characterization of monolith surface functionality, especially those with applicability to in situ analysis. Finally, we describe selected IC applications of polymeric and silica monoliths published from 2008 to 2010.