Monolith columns for liquid chromatographic separations of intact proteins: A review of recent advances and applications

Design and fabrication of fluorous monoliths with tunable surface property for capillary liquid chromatography

Hierarchically porous monoliths with satisfactory properties have been employed in diverse fields, especially separation. In this study, pentafluorophenyl acrylate (PFPA), pentaerythritol tetraacrylate (PETA) and trimethylolpropane tris(3-mercaptopropionate) (TTMP) were selected as precursors to fabricate a novel monolithic column by thermally initiated polymerization in the presence of a binary porogenic system containing tetrahydrofuran and 1-propanol. The fabricated poly(PFPA-co-PETA-co-TTMP) monolithic column revealed excellent permeability and mechanical stability. Additionally, baseline separation of the mixture of small molecules can be achieved, involving alkylbenzene and fluorobenzene in chromatographic assessment, and the theoretical plate number is up to 60,500 plates/m for butylbenzene with a linear velocity of 0.14 mm/s. Tryptic digest of HeLa as an analyte was used to investigate the possibility of the poly(PFPA-co-PETA-co-TTMP) monolith in biological separation by cLC-MS/MS. Moreover, benefiting from the existence of pentafluorophenyl groups, the cucurbit[8]uril (CB[8]) could be modified on the prepared poly(PFPA-co-PETA-co-TTMP) monolith through host-guest interaction to obtain poly(PFPA-co-PETA-co-TTMP)-CB[8] monolith. It could be observed that significant changes in retention behavior of analytes appeared after immobilizing CB[8] on the monolith. It offered an innovative approach by utilizing host-guest interaction to fabricate monolithic columns with different chromatographic behaviors.

Influence of the Polymerization Parameters on the Porosity and Thermal Stability of Polymeric Monoliths

Rigid porous polymeric monoliths are robust, highly efficient, versatile stationary phases. They offer simple preparation and convenient modification provided by a whole range of synthesis factors, e.g., starting monomers, cross-linkers, initiators, porogens, polymerization techniques, and temperature. The main aim of this study was to synthesize polymeric monoliths and determine the correlation between polymerization parameters and the porosity and thermal stability of the obtained materials. Polymeric monoliths were synthesized directly in HPLC columns using N-vinyl-2-pyrrolidone (NVP) and 4-vinylpiridine (4VP) as functional monomers, with trimethylolpropane trimethacrylate (TRIM) serving as the cross-linking monomer. During copolymerization a mixture of cyclohexanol/decane-1-ol was used as the pore-forming diluent. Polymerization was carried out at two different temperatures: 55 and 75 °C. As a result, monoliths with highly developed internal structure were synthesized. The value of their specific surface area was in the range of 92 m2/g to 598 m2/g, depending on the monomer composition and polymerization temperature. Thermal properties of the obtained materials were investigated by means of thermogravimetry (TG). Significant differences in thermal behavior were noticed between monoliths synthesized at 55 and 75 °C. Additionally, the poly(NVP-co-TRIM) monolith was successfully applied in GC analyses.

Monolithic stationary phases prepared via cyclic anhydride ring-opening polymerization as tunable platforms for chromatographic applications

Polymer monolithic stationary phases were prepared based on a cyclic anhydride as a reactive and tunable platform via ring-opening post-polymerization using primary amines, octadecylamine and benzylamine. The characterization techniques indicated the insertion of the functional groups into the original monoliths and confirmed the amidation reactions. The post-polymerization modification also improved the monolith's thermal and mechanical stability and induced significant improvement in their surface area. The stationary phases were synthesized inside small dimension stainless-steel columns (2.1 mm i.d. × 50 mm length). The prepared columns before and after modifications have been tested for the separation of the alkylbenzene series and some polycyclic aromatic hydrocarbons (PAHs) as model compounds. In all cases, the chromatographic performance in terms of the height equivalent to a theoretical plate on the functionalized monoliths was remarkably improved when compared with that on the unmodified monolith, which was between 9.59-39.49 μm and 4.08-31.50 μm using monoliths modified with octadecylamine and benzylamine, respectively. Under the same chromatographic conditions, the functionalization of monoliths with octadecylamine provided more hydrophobic interactions and enhanced the retention of alkylbenzenes, while the modification of monoliths with benzyl groups improved the separation and the retention of the PAHs through the strong π-π interactions. However, post-modification polymerization with octadecylamine and benzylamine enhanced the separation efficiency of the prepared columns toward all studied compounds. The repeatability of the injections on the same column and the reproducibility of the prepared columns have been studied for some selected parameters and estimated in terms of percent relative standard deviation (%RSD) for some of the studied compounds. The repeatability of the prepared columns was ≤9.42% (n = 5) based on run-to-run injections and ≤9.48% based on day-to-day injections for five successive days. The reproducibility levels, on the other hand, were ≤20.95% for all studied parameters in all cases. To assess their performance for the analysis of real samples, the applicability of the prepared columns was examined for the separation of the active ingredients extracted from some commercial pharmaceutical formulations and for the separation of tea water extract constituents. The validation data show the suitability of the columns for practical use in the routine analysis of these samples.

Cryogels and Monoliths: Promising Tools for Chromatographic Purification of Nucleic Acids

The increasing demand for highly pure biopharmaceuticals has put significant pressure on the biotechnological industry to innovate in production and purification processes. Nucleic acid purification, crucial for gene therapy and vaccine production, presents challenges due to the unique physical and chemical properties of these molecules. Meeting regulatory standards necessitates large quantities of biotherapeutic agents of high purity. While conventional chromatography offers versatility and efficiency, it suffers from drawbacks like low flow rates and binding capacity, as well as high mass transfer resistance. Recent advancements in continuous beds, including monoliths and cryogel-based systems, have emerged as promising solutions to overcome these limitations. This review explores and evaluates the latest progress in chromatography utilizing monolithic and cryogenic supports for nucleic acid purification.

Fabrication of a biochar-doped monolithic adsorbent and its application for the extraction and determination of coumarins from Angelicae Pubescentis Radix

A monolithic adsorbent was designed aiming to the structure of osthole and columbianadin, and fabricated using diallyl phthalate as the monomer and ethylene dimethacrylate as the crosslinker with the addition of bamboo biochar, via polymerization reaction in a stainless-steel tube. The prepared composite adsorbent packed in the tube was used as a solid-phase extraction column for the extraction and determination of two coumarins (osthole and columbianadin) in Angelicae Pubescentis Radix, combing with a C18 analytical column through an HPLC instrument, which show excellent matrix-removal ability and good selectivity to osthole and columbianadin. Furthermore, the present adsorbent shows good applicability, which was used for the extraction of osthole from Duhuo Jisheng Pill. Compared to the commercial C18 and phenyl adsorbent, the present adsorbent own better selectivity and higher resolution. These results attributed to the enhanced specific surface area (141 m2/g) and enriched interaction sites of the resulting composite adsorbent, due to the doping of bamboo biochar, which can produce hydrogen bond, dipole-dipole, π-π and hydrophobic force interactions with the osthole and columbianadin. The methodology validation indicated that the present method showed good precision and good accuracy, and the composite adsorbent showed good preparative repeatability, which can be reused for no less than 100 times with the relative standard deviation ≤4.6 % (n = 100). The present work provided a simple and efficient method for the extraction and determination osthole and columbianadin from Angelicae Pubescentis Radix.

Recent advances in top-down proteome sample processing ahead of MS analysis

Top-down proteomics is emerging as a preferred approach to investigate biological systems, with objectives ranging from the detailed assessment of a single protein therapeutic, to the complete characterization of every possible protein including their modifications, which define the human proteoform. Given the controlling influence of protein modifications on their biological function, understanding how gene products manifest or respond to disease is most precisely achieved by characterization at the intact protein level. Top-down mass spectrometry (MS) analysis of proteins entails unique challenges associated with processing whole proteins while maintaining their integrity throughout the processes of extraction, enrichment, purification, and fractionation. Recent advances in each of these critical front-end preparation processes, including minimalistic workflows, have greatly expanded the capacity of MS for top-down proteome analysis. Acknowledging the many contributions in MS technology and sample processing, the present review aims to highlight the diverse strategies that have forged a pathway for top-down proteomics. We comprehensively discuss the evolution of front-end workflows that today facilitate optimal characterization of proteoform-driven biology, including a brief description of the clinical applications that have motivated these impactful contributions.

Solid phase extraction as sample pretreatment method for top-down quantitative analysis of low molecular weight proteins from biological samples using liquid chromatography - triple quadrupole mass spectrometry

Targeting and quantifying intact proteins from biological samples is still a very challenging research area. Several crucial steps exist in the analytical workflow, including development of a reliable sample preparation method. Here, we developed and applied for the first time a non-immunoaffinity sample preparation method based on a generally widely available micro-elution solid phase extraction (μSPE) strategy for the extraction of multiple lower molecular weight intact proteins (<30 kDa) from various biological matrices. Omission of a time-consuming drying and reconstitution step after extraction resulted in a more simple and rapid sample preparation procedure. A model set of eleven intact proteins (molecular weights: 5.5-29 kDa; isoelectric points: 4.5-11.3) were analyzed in multiple biological fluids using reversed-phase liquid chromatography with a triple quadrupole mass spectrometer operated in multiple reaction monitoring mode. Various sample pre-treatment reagents, sorbent types, and washing and elution solvents were experimentally tested and optimized to obtain the μSPE clean-up condition for a broad mixture of intact proteins having variable physicochemical properties. 1% trifluoroacetic acid and 0.2% Triton 100-X were selected as suitable sample pre-treatment reagents for releasing protein-protein interactions in human serum/plasma and human urine, respectively. Hydrophilic lipophilic balanced μSPE sorbent was selected as a high performing stationary phase. Addition of 1% trifluoroacetic acid to all washing and elution solutions showed the most beneficial effect for the extraction recovery of the proteins. Under the optimized conditions, reproducible extraction recoveries >65% for all targeted proteins (up to 30 kDa) in human urine and >50% for most of the proteins in serum/plasma were achieved. The selected conditions were applied also for the analysis of clinical serum and urine samples to demonstrate the feasibility of the developed method to target intact proteins directly by more affordable μSPE sample preparation and triple quadrupole mass spectrometry, which could be beneficial in many application fields.

One-step fabrication of three-dimensional macropore copolymer-modified polycarbonate array by photo-crosslinking for protein immunoassay

A photocross-linked copolymer was prepared, and could rapidly form a macropore structure in phosphate buffer solution (PBS) without the addition of porogen. The photo-crosslinking process contained the crosslinking of the copolymer itself and that with the polycarbonate substrate. The three-dimensional (3D) surface was achieved through one-step photo-crosslinking of the macropore structure. The macropore structure can be finely regulated by multiple dimensions, including monomer structure of the copolymer, PBS and copolymer concentration. Compared with the two-dimensional (2D) surface, the 3D surface has a controllable structure, a high loading capacity (59 μg cm^-2) and immobilization efficiency (92%), and the effect of inhibiting the coffee ring for protein immobilization. Immunoassay results show that a 3D surface immobilized by IgG has high sensitivity (LOD value of 5 ng mL^-1) and broader dynamic range (0.005-50 μg mL^-1). This simple and structure-controllable method for preparing 3D surfaces modified by macropore polymer has great potential applications in the fields of biochips and biosensing.

Montmorillonite-based polymethacrylate composite monoliths as stationary phase materials for food and pharmaceutical analysis in capillary liquid and gas chromatography

This work relates to the preparation of novel and promising stationary phases containing inorganic-organic composites for capillary liquid and gas chromatography. A naturally occurring montmorillonite was introduced to polymethacrylate monoliths, then used under different conditions of GC and HPLC at the same time. The performance of the columns was evaluated for the separation of alkane and alkylbenzene series in GC and capillary HPLC, respectively. While the bare monoliths failed to separate the model analytes, montmorillonite-based polymethacrylate allowed a full separation of the mixtures with R_s≥1.42. The columns were applied for the determination of myrcene and limonene isomers in the peel extracts of some fruits using GC, and for the analysis of active ingredients including aspirin, vitamin-C, caffeine, and ibuprofen extracted from common drugs using capillary HPLC. In GC, fast separation was achieved in 1.0 min with R_s of 6.53. The columns exhibited the best efficiency for myrcene with 20,900 plates/m. Using the capillary HPLC columns, the active ingredients were resolved in 10 min with R_s≥5.72. The efficiency values located between 12,800-21,700 plates/m in all cases. The developed methods were found to be linear in the range of 0.10-10.0 and 0.20-180 μg/mL for GC and HPLC, respectively. In comparison with commercial columns, the results in GC methods reveal that, despite their much shorter length, the prepared columns proved a faster separation with higher efficiency and comparable detection limits and chromatographic resolution. The prepared HPLC capillaries exposed lower run times and detection limits with comparable efficiency and resolution, and consume fewer samples and mobile phase solvents. The results demonstrate that the montmorillonite-based polymethacrylate composites are applicable as stationary phases for routine analysis and quality control of important fields such as food and pharmaceutical samples.

Effect of the Structure of Magnetic Nanocomposite Adsorbents on the Lysozyme Separation Efficiency

In this study, we prepared various anionic magnetic adsorbents through the carboxyl functionalization of core/shell-structured Fe₃O₄/SiO₂ (FS) particles by either succinic anhydride (FSC), low-molecular-weight (MW 1800) polyacrylic acid (PAA) (FSP1), or high-molecular-weight (MW 100,000) PAA (FSP2), and then, investigated the effect of the structure of adsorbents and operational parameters on their performance for the lysozyme separation. The type and size of functional molecules have significant effects on the surface concentration of functional carboxyl groups onto the adsorbent particles (increase in the order of FSP2 > FSP1 > FSC), and consequently on the adsorption efficiency (AE) (∼100, 98, and 62%, respectively) and adsorption capacity (AC) (∼1000, 980, and 621 mg·g^-1, respectively) of the adsorbents. However, the loss of the antibacterial activity of separated lysozyme molecules due to the molecular conformational change increased in the order of FSP2 > FSP1 = FSC, as compared to the free lysozyme. The application of basic buffer solutions for the elution of adsorbed enzyme molecules resulted in more adverse effects on the enzyme activity. The obtained results recommend that FSP1 can be used as a suitable anionic adsorbent for the isolation of positively charged proteins, owing to its high adsorption capacity, excellent reusability, and structural stability, as well as the high purity, structural stability, and activity recovery of the isolated proteins.

Chromatographic separation of peptides and proteins for characterization of proteomes

Characterization of proteomes aims to comprehensively characterize proteins in cells or tissues via two main strategies: (1) bottom-up strategy based on the separation and identification of enzymatic peptides; (2) top-down strategy based on the separation and identification of intact proteins. However, it is challenged by the high complexity of proteomes. Consequently, the improvements in peptide and protein separation technologies for simplifying the sample should be critical. In this feature article, separation columns for peptide and protein separation were introduced, and peptide separation technologies for bottom-up proteomic analysis as well as protein separation technologies for top-down proteomic analysis were summarized. The achievement, recent development, limitation and future trends are discussed. Besides, the outlook on challenges and future directions of chromatographic separation in the field of proteomics was also presented.

Preparation of composite monoliths of quaternized chitosan and diatom earth for protein separation

In this study, composite monoliths with porous structures were prepared using quaternized chitosan and diatom earth for protein separation. Quaternized chitosan (N-[(2-hydroxy-3-trimethylammonium)propyl] chitosan chloride) dissolved in water was mixed with diatom earth and crosslinked with glutaraldehyde under low-temperature conditions to form a cryogel. Interconnected porous monoliths were obtained after removing ice crystals from the cryogel. The monoliths adsorbed bovine serum albumin selectively from the solution mixture of bovine serum albumin and bovine ɤ-globulin, and bovine ɤ-globulin was recovered in the flow-through fraction. The adsorption selectivity was enhanced by changing the solution pH from 6.8 to 5.5. The adsorption of bovine serum albumin by the monolith was replicated at least five times following its washing with a buffer containing 400 mM NaCl and subsequent regeneration with a 10 mM acetate buffer. The composited monolith is a promising adsorbent for the removal of acidic proteins, such as serum albumin contamination in neutral proteins, for example, ɤ-globulins, in bioproduction processes.

Naturally Occurring Montmorillonite-Based Polymer Monolith Composites as Stationary Phases for Capillary Liquid and Gas Chromatography

This work is associated with the preparation of capillary chromatographic columns containing inorganic-organic composites comprised of naturally occurring montmorillonite (MMT) clay mineral and polymethacrylate monolithic material. The prepared composites combine the best qualities of both constituents, offering desirable properties for use under the disparate conditions of both GC and HPLC at the same time. The stationary phases were investigated by scanning electron microscopy (SEM), the specific surface area, and thermogravimetric analysis (TGA) and examined in terms of various conditions utilized for GC and HPLC methods. The prepared columns demonstrated an excellent permeability and stability against common chromatographic conditions, such as the eluent type, flow rate, pressure, and temperature. The results confirmed that the addition of small amounts of MMT into the monolith induced significant improvement in the specific surface area, which contributed to the formation of more active sites and enhanced the retention of analytes. The registered column backpressures did not exceed 980 kPa and 16,500 kPa for the prepared GC and HPLC columns, respectively. The prepared columns were subjected to the separation of various interesting compounds possessing different chemistries and polarities, including alkanes, alkylbenzenes, polycyclic aromatic hydrocarbons (PAHs), alcohols, ketones, phenols, some common organic solvents, and isomeric mixtures. Under the optimal conditions, the efficiency of the columns fell between 4900–38,500 plates m−1 for GC and 3400–58,800 plates m−1 for capillary HPLC applications. In all cases, the measured chromatographic resolution was more than 1.38, with excellent an peak symmetry and low tailing factors. In comparison with the most commonly used commercial columns, the polysiloxane open tubular column for GC and silica-based C18 packed column for HPLC, the prepared GC columns demonstrated a faster separation with a higher efficiency, comparable resolution and tailing factors, and lower consumption of carrier gas. Regarding the capillary columns prepared for HPLC, the chromatographic experiments exposed a much lower run time with a comparable efficiency and resolution and drastically lower consumption of mobile phase solvents and samples. The results demonstrate that the MMT-based polymethacrylate monolith composites are applicable as novel and promising separation media for analyzing various mixtures of interest in different fields, such as petrochemical and environmental samples.

Protein Attachment Mechanism for Improved Functionalization of Affinity Monolith Chromatography (AMC)

This work aims at understanding the attachment mechanisms and stability of proteins on a chromatography medium to develop more efficient functionalization methodologies, which can be exploited in affinity chromatography. In particular, the study was focused on the understanding of the attachment mechanisms of bovine serum albumin (BSA), used as a ligand model, and protein G on novel amine-modified alumina monoliths as a stationary phase. Protein G was used to develop a column for antibody purification. The results showed that, at lower protein concentrations (i.e., 0.5 to 1.0 mg·mL⁻¹), protein attachment follows a 1st-order kinetics compatible with the presence of covalent binding between the monolith and the protein. At higher protein concentrations (i.e., up to 10 mg·mL⁻¹), the data preferably fit a 2nd-order kinetics. Such a change reflects a different mechanism in the protein attachment which, at higher concentrations, seems to be governed by physical adsorption resulting in a multilayered protein formation, due to the presence of ligand aggregates. The threshold condition for the prevalence of physical adsorption of BSA was found at a concentration higher than 1.0 mg·mL⁻¹. Based on this result, protein concentrations of 0.7 and 1.0 mg·mL⁻¹ were used for the functionalization of monoliths with protein G, allowing a maximum attachment of 1.43 mg of protein G/g of monolith. This column was then used for IgG binding–elution experiments, which resulted in an antibody attachment of 73.5% and, subsequently, elution of 86%, in acidic conditions. This proved the potential of the amine-functionalized monoliths for application in affinity chromatography.

Matrices and Affinity Ligands for Antibody Purification and Corresponding Applications in Radiotherapy

Antibodies have become an important class of biological products in cancer treatments such as radiotherapy. The growing therapeutic applications have driven a demand for high-purity antibodies. Affinity chromatography with a high affinity and specificity has always been utilized to separate antibodies from complex mixtures. Quality chromatographic components (matrices and affinity ligands) have either been found or generated to increase the purity and yield of antibodies. More importantly, some matrices (mainly particles) and affinity ligands (including design protocols) for antibody purification can act as radiosensitizers or carriers for therapeutic radionuclides (or for radiosensitizers) either directly or indirectly to improve the therapeutic efficiency of radiotherapy. This paper provides a brief overview on the matrices and ligands used in affinity chromatography that are involved in antibody purification and emphasizes their applications in radiotherapy to enrich potential approaches for improving the efficacy of radiotherapy.

Ethane-Bridged Hybrid Monolithic Column with Large Mesopores for Boosting Top-Down Proteomic Analysis

Top-down proteomics is challenged by the high complexity of biological samples. The coelution of intact proteins results in overlapped mass spectra, and hence, an increased peak capacity for protein separation is needed. Herein, ethane-bridged hybrid monoliths with well-defined large mesopores were successfully prepared based on the sol-gel condensation of 1,2-bis(trimethoxysilyl)ethane and tetramethoxysilane, followed by two-step base etching of the Si-O-Si domain while maintaining the Si-C-C-Si domain in the structure. Relatively homogeneous macropores of 1.1 μm and large mesopores of 24 nm were obtained, permitting fast mass transfer of large molecules and efficient diffusion without obstruction. The use of less hydrophobic C1 ligand further sharpened the peak shape and improved peak capacity. A 120 cm-long capillary column was used for top-down proteomic analysis of E. coli lysates under low backpressure with 16 MPa. High peak capacity of 646 was achieved within 240 min gradient. With MS/MS analysis, 959 proteoforms corresponding to 263 proteins could be unambiguously identified from E. coli lysates in a single run. Furthermore, to illustrate the separation performance for large proteoforms, such monoliths were applied to top-down analysis of the SEC fraction of E. coli lysates with Mw ranging from 30 to 70 kDa. With highly effective separation, 347 large proteoforms with Mw higher than 30 kDa were detected in the single 75 min run. These results showed great potential for top-down proteomic analysis in complex samples.

Hydrophobic AEROSIL®R972 Fumed Silica Nanoparticles Incorporated Monolithic Nano-Columns for Small Molecule and Protein Separation by Nano-Liquid Chromatography

A new feature of hydrophobic fumed silica nanoparticles (HFSNPs) when they apply to the preparation of monolithic nano-columns using narrow monolithic fused silica capillary columns (e.g., 50-µm inner diameter) was presented. The monolithic nano-columns were synthesized by an in-situ polymerization using butyl methacrylate (BMA) and ethylene dimethacrylate (EDMA) at various concentrations of AEROSIL^®R972, called HFSNPs. Dimethyl formamide (DMF) and water were used as the porogenic solvents. These columns (referred to as HFSNP monoliths) were successfully characterized by using scanning electron microscopy (SEM) and reversed-phase nano-LC using alkylbenzenes and polyaromatic hydrocarbons as solute probes. The reproducibility values based on run-to-run, column-to-column and batch-to-batch were found as 2.3%, 2.48% and 2.99% (n = 3), respectively. The optimized column also indicated promising hydrophobic interactions under reversed-phase conditions, while the feasibility of the column allowed high efficiency and high throughput nano-LC separations. The potential of the final HFSNP monolith in relation to intact protein separation was successfully demonstrated using six intact proteins, including ribonuclease A, cytochrome C, carbonic anhydrase isozyme II, lysozyme, myoglobin, and α-chymotrypsinogen A in nano-LC. The results showed that HFSNP-based monolithic nanocolumns are promising materials and are powerful tools for sensitive separations.

Monolithic Materials-Based RPLC-MS for Proteoform Separation and Identification

High-performance separation of proteoforms plays an important role in top-down proteomic ananlysis due to high complexity of the proteome. To this end, the functionalized ethylene-bridged hybrid monolithic materials have been developed for reversed-phase liquid chromatographic separation of proteoforms followed by online combination with high-resolution mass spectrometry (MS) for top-down proteomic analysis. Such monoliths have advantages of homogenously distributed functional groups in the framework, good chemical stability, and high permeability and, thus, show high resolution, good reproducibility, and low backpressure for proteoform separation. This chapter describes in detail the preparation of such monoliths and online combination with high-resolution MS for proteoform separation and identification.

Preparation of Affinity Chromatography Monolith in Miniaturized Format and Application for Protein Separation

Affinity chromatography is one of the versatile technique to selectively separate target biomolecules from complex biological sources (plasma, saliva, urine, etc.). Conventional chromatography resins possess technical limitations at mini-analytical scale, which was overcome with the use of alternative material known as monoliths. This chapter discusses on the how to modify the fused silica capillary inner surface, prepare polymer monoliths within the capillary confinements, chelation of metal-ions on monoliths and protein separation from diluted human plasma using metal-ion monolith microcolumn.

Poly(acrylamide-co-N,N'-methylenebisacrylamide) Monoliths for High-Peak-Capacity Hydrophilic-Interaction Chromatography-High-Resolution Mass Spectrometry of Intact Proteins at Low Trifluoroacetic Acid Content

In this study, we optimized a polymerization mixture to synthesize poly(acrylamide-co-N,N′-methylenebisacrylamide) monolithic stationary phases for hydrophilic-interaction chromatography (HILIC) of intact proteins. Thermal polymerization was performed, and the effects of varying the amount of cross-linker and the porogen composition on the separation performance of the resulting columns were studied. The homogeneity of the structure and the different porosities were examined through scanning electron microscopy (SEM). Further characterization of the monolithic structure revealed a permeable (K_f between 2.5 × 10^–15 and 1.40 × 10^–13 m²) and polar stationary phase suitable for HILIC. The HILIC separation performance of the different columns was assessed using gradient separation of a sample containing four intact proteins, with the best performing stationary phase exhibiting a peak capacity of 51 in a gradient of 25 min. Polyacrylamide-based materials were compared with a silica-based particulate amide phase (2.7 μm core–shell particles). The monolith has no residual silanol sites and, therefore, fewer sites for ion-exchange interactions with proteins. Thus, it required lower concentrations of ion-pair reagent in HILIC of intact proteins. When using 0.1% of trifluoroacetic acid (TFA), the peak capacities of the two columns were similar (30 and 34 for the monolithic and packed column, respectively). However, when decreasing the concentration of TFA to 0.005%, the monolithic column maintained similar separation performance and selectivity (peak capacity 23), whereas the packed column showed greatly reduced performance (peak capacity 12), lower selectivity, and inability to elute all four reference proteins. Finally, using a mobile phase containing 0.1% formic acid and 0.005% TFA, the HILIC separation on the monolithic column was successfully hyphenated with high-resolution mass spectrometry. Detection sensitivity for protein and glycoproteins was increased and the amount of adducts formed was decreased in comparison with separations performed at 0.1% TFA.

Preparation of Polystyrene Microsphere-Templated Porous Monolith for Wastewater Filtration

Porous monoliths prepared using templates are highly sought after for filtration applications due to their good mass transport properties and high permeability. Current templates, however, often lead to the formation of dead-end pores and irregular pore distributions, which reduce the efficiency of the substrate flow across the monolith column. This study focused on the preparation of a microsphere-templated porous monolith for wastewater filtration. The optimal template/monomer ratio (50:50, 60:40, 70:30) was determined, and appropriate template removal techniques were assessed for the formation of homogenous pores. The physicochemical characteristics and pore homogeneity of the monoliths were examined. The 60:40 ratio was determined to result in monoliths with homogeneous pore distributions ranging from 1.9 μm to 2.3 μm. SEM and FTIR investigations revealed that solvent treatment was effective for removing templates from the resulting solid monolith. The water quality assessments revealed reductions in the turbidity and the total number of suspended particles in the tested wastewater of up to 96–99%. The findings of this study provide insightful knowledge regarding the fabrication of monoliths with homogenous pores that are beneficial for wastewater treatment.

Chromatography-Free Purification Strategies for Large Biological Macromolecular Complexes Involving Fractionated PEG Precipitation and Density Gradients

A complex interplay between several biological macromolecules maintains cellular homeostasis. Generally, the demanding chemical reactions which sustain life are not performed by individual macromolecules, but rather by several proteins that together form a macromolecular complex. Understanding the functional interactions amongst subunits of these macromolecular machines is fundamental to elucidate mechanisms by which they maintain homeostasis. As the faithful function of macromolecular complexes is essential for cell survival, their mis-function leads to the development of human diseases. Furthermore, detailed mechanistic interrogation of the function of macromolecular machines can be exploited to develop and optimize biotechnological processes. The purification of intact macromolecular complexes is an essential prerequisite for this; however, chromatographic purification schemes can induce the dissociation of subunits or the disintegration of the whole complex. Here, we discuss the development and application of chromatography-free purification strategies based on fractionated PEG precipitation and orthogonal density gradient centrifugation that overcomes existing limitations of established chromatographic purification protocols. The presented case studies illustrate the capabilities of these procedures for the purification of macromolecular complexes.

A review on recent advances in the enrichment of glycopeptides and glycoproteins by liquid chromatographic methods: 2016-Present

Among various protein post-translational modifications (PTMs), glycosylation has received special attention due to its immense role in molecular interactions, cellular signal transduction, immune response, etc. Aberration in glycan moieties of a glycoprotein is associated with cancer, diabetes, and bacterial and viral infections. In biofluids (plasma, saliva, urine, milk, etc.), glycoproteins are low in abundance and are masked by the presence of high abundant proteins. Hence, prior to their identification using mass spectrometry methods, liquid chromatography (LC)-based approaches were widely used. A general enrichment strategy involves a protein digestion step, followed by LC-based enrichment and desorption of glycopeptides, and enzymatic excision of the glycans. The focus of this review article is to highlight the articles published since 2016 that dealt with different LC-based approaches for glycopeptide and glycoprotein enrichment. The preparation of stationary phases, their surface activation, and ligand immobilization strategies have been discussed in detail. Finally, the major developments and future trends in the field have been summarized.

Nano-liquid chromatography with a new nano-structured monolithic nanocolumn for proteomics analysis

Herein, we report the preparation and application of a new nano-structured monolithic nanocolumn based on modified graphene oxide using narrow fused silica capillary column (e.g., 50 μm internal diameter). The nanocolumn was prepared by an in situ polymerization using butyl methacrylate, ethylene dimethacrylate, and methacryloyl graphene oxide nanoparticles. Dimethyl formamide and water were used as the porogenic solvent. After polymerization, the obtained nanocolumn was coated with dimethyloctadecylchlorosilane in order to enhance the hydrophobicity. Both isocratic and gradient nano-liquid chromatographic separations for small molecules (e.g., alkylbenzenes) and macromolecules (e.g., intact proteins) were performed. Theoretical plates number up to 3600 plates/m in isocratic mode for propylbenzene were achieved. It was demonstrated that the feasibility of graphene oxide modified monolithic nanocolumn for high-efficiency and high-throughput nanoscale proteomics analysis. The high resolving power of monolithic nanocolumn yielded sensitive protein separation with narrower peak width while a high-resolution analysis of peptides from trypsin-digested cytochrome C could be obtained. Graphene oxide based monolithic nanocolumns are promising and can allow to powerful tools for trace proteom sample analysis.

Critical Assessment of Purification and Analytical Technologies for Enveloped Viral Vector and Vaccine Processing and Their Current Limitations in Resolving Co-Expressed Extracellular Vesicles

Viral vectors and viral vaccines are invaluable tools in prevention and treatment of diseases. Many infectious diseases are controlled using vaccines designed from subunits or whole viral structures, whereas other genetic diseases and cancers are being treated by viruses used as vehicles for delivering genetic material in gene therapy or as therapeutic agents in virotherapy protocols. Viral vectors and vaccines are produced in different platforms, from traditional embryonated chicken eggs to more advanced cell cultures. All these expression systems, like most cells and cellular tissues, are known to spontaneously release extracellular vesicles (EVs). EVs share similar sizes, biophysical characteristics and even biogenesis pathways with enveloped viruses, which are currently used as key ingredients in a number of viral vectors and licensed vaccine products. Herein, we review distinctive features and similarities between EVs and enveloped viruses as we revisit the downstream processing steps and analytical technologies currently implemented to produce and document viral vector and vaccine products. Within a context of well-established viral vector and vaccine safety profiles, this review provides insights on the likely presence of EVs in the final formulation of enveloped virus products and discusses the potential to further resolve and document these components.

Graphene oxide-octadecylsilane incorporated monolithic nano-columns with 50 μm id and 100 μm id for small molecule and protein separation by nano-liquid chromatography

In this study, graphene oxide-octadecylsilane incorporated monolithic nano-columns were developed for protein analysis by nano liquid chromatography (nano LC). The monolithic column with 100 μm id was first prepared by an in situ polymerization using ethylene dimethacrylate (EDMA), 3-chloro-2-hydroxypropylmethacrylate (HPMA-Cl), and methacryloyl graphene oxide nanoparticles (MGONPs). MGONPs were synthesized by the treatment of 3-(trimethoxysilyl)propylmethacrylate (TMSPM) and GO. Tetrahydrofuran (THF) and dodecanol were used as the porogenic solvent. The resulting column was functionalized by dimethyloctadecylch lorosilane (DODCS) for the enhancement of hydrophobicity. The functionalization greatly improved the baseline separation of hydrophobic compounds such as polyaromatic hydrocarbons (PAHs). The optimized monolith with respect to total polymerization mixture was characterized by using Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) X-ray diffraction (XRD) and chromatographic analyses. The blank monoliths without functionalization exhibited poor separation while a good separation performance of MGONPs functionalized monoliths was achieved. The monolith with 100 μm id was evaluated in protein separation in nano LC using RNase A, Cytochrome C, Lysozyme, Trypsin, and Ca isozyme II as the test proteins. It was shown that protein separation mechanism was based on large π-system of GO and hydrophobicity of the monolithic structure. Theoretical plates number up to 57 600 plates were achieved. The nano-column with 50 μm id was also prepared using the same polymerization mixture under the same chemical conditions. These nano-columns were employed for protein separation by nano LC, and the dependence of both nano-column performance on the internal diameter was also discussed.

Macroporous Polymer Monoliths in Thin Layer Format

Nowadays, macroporous polymer monoliths represent widely used stationary phases for a number of dynamic interphase mass exchange processes such as high-performance liquid chromatography, gas chromatography, electrochromatography, solid-phase extraction, and flow-through solid-state biocatalysis. This review represents the first summary in the field of current achievements on the preparation of macroporous polymer monolithic layers, as well as their application as solid phases for thin-layer chromatography and different kinds of microarray.

Polymeric stationary phases for size exclusion chromatography: A review

Synthetic and natural macromolecules are commonly used in a variety of fields such as plastics, nanomedicine, biotherapeutics, drug delivery and tissue engineering. Characterising macromolecules in terms of their structural parameters (size, molar mass and distribution, architecture) is key to have a better understanding of their structure-property relationships. Size exclusion chromatography (SEC) is a commonly used technique for polymer characterization since it offers access to the determination of the size of a macromolecule, its molar mass and the molar mass distribution. Moreover, detectors that allow the determination of true molar masses, macromolecule's architecture and the composition of copolymers can be coupled to the chromatographic system. Like other chromatographic techniques, the stationary phase is of paramount importance for efficient SEC separations. This review presents the basic principles for the design of stationary phases for SEC as well as synthetic methods currently used in the field. Current status of fully-porous polymeric stationary phases used in SEC is reviewed and their advantages and limitations are also discussed. Finally, the potential of polymer monoliths in SEC is also covered, highlighting the limitations this column technology could address. However, further development in the polymer structure is needed to consider this column technology in the field of macromolecule separation.

[Fabrication of nanomaterials incorporated polymeric monoliths and application in sample pretreatment]

Polymeric monolithic columns are fabricated by in situ polymerization of the corresponding monomer, crosslinkers, porogenic solvents and radical initiators within a mold. Compared with the conventional packed solid phase extraction adsorbents, polymeric monolithic columns with a continuous porous structure process distinctive advantages of rapid mass transfer and excellent permeability, which facilitates the extraction of trace amounts of the target from the matrix even at high flow velocities. Besides, these materials can be easily fabricated in situ within various cartridges, avoiding a further packing step associated with packed particulate adsorbents. Additionally, the abundant monomer availability, flexible porous structure, and wide applicable pH range make monoliths versatile for use in separation science. Thus, polymeric monolithic columns have been increasingly applied as efficient and promising extraction media for sample pretreatment food, pharmaceutical, biological and environmental analyses. However, these materials usually have the difficulty in morphology control and their interconnected porous micro-globular structure, which may result in low porosity, limited specific surface area and poor efficiency. In addition, polymeric monoliths suffer from the swelling in organic solvents, thus decreasing the service life and precision while increasing the cost consumption. Recently, the development of nanomaterial-incorporated polymeric monoliths with an improved ordered structure, enhanced adsorption efficiency and outstanding selectivity has attracted considerable attention. Nanoparticles are considered as particulates within the size range of 1-100 nm in at least one dimension, which endows them with unique optical, electrical and magnetic properties. These materials have a large surface area, excellent thermal and chemical stabilities, remarkable versatility, as well as a wide variety of active functional groups on their surface. With the aim of exploiting these advantages, researchers have shown great interest in applying nanomaterial-incorporated polymeric monoliths to separation science. Accordingly, significant progress has been achieved in this field. Nanomaterials can be entrapped via the direct synthesis of a polymerization solution that contains well dispersed nanomaterials in porogens. In addition, nanoparticles can be incorporated into the monolithic matrix by copolymerization and post-polymerization modification via specific interactions. Therefore, nanomaterial-incorporated polymeric monoliths combined the different shapes, chemical properties, and physical properties of the polymers with those of the nanoparticles. The presence of nanoparticles can improve the structural rigidity as well as the thermal and chemical stabilities of monolithic adsorbents. Besides, nanoparticles are capable of increasing the specific surface area and providing multiple active sites, which leads to enhanced extraction performance and selectivity of polymeric monolithic materials. In recent years, diverse types of nanomaterials, such as carbonaceous nanoparticles, metallic materials and metal oxides, metal-organic frameworks, covalent organic frameworks and inorganic nanoparticles have been extensively explored as hybrid adsorbents in the modes of solid phase extraction, solid phase microextraction, stir bar sorption extraction and on-line solid phase extraction. This review specifically summarizes the fabrication methods for nanomaterial incorporated polymeric monoliths and their application to the field of sample pretreatment. The existing challenges and future possible perspectives in the field are also discussed.

Construction of polymer monolithic columns in polypropylene ink-pen tubes for separation of proteins by cation-exchange chromatography

We describe the synthesis of polymer monoliths inside polypropylene tubes from ink pens. These tubes are cheap, chemically stable, and resistant to pressure. UV-initiated grafting with 5 wt% benzophenone in methanol for 20 min activated the internal surface, thus enabling the covalent binding of ethylene glycol dimethacrylate, also via photografting. The pendant vinyl groups attached a poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) monolith prepared via photopolymerization. These tubes measured 100-110 mm long, with 2 mm of internal diameter. The parent monoliths were functionalized with Na₂ SO₃ or iminodiacetate to produce strong and weak cation exchangers, respectively. The columns exhibited permeabilities varying from 2.7 to 3.3 × 10^-13  m² , which enabled the separation of proteins at 500 µL/min and back pressures <2.8 MPa. Neither structure collapse nor monolith detachment occurred at flow rates as high as 2.0 mL/min, which produced back pressures between 6.9 and 9.0 MPa. The retention times of ovalbumin, ribonuclease A, cytochrome C, and lysozyme in salt gradient at pH 7.0 followed the order of increasing isoelectric points, confirming the cation exchange mechanism. Separation and determination of lysozyme in egg white proved the applicability of the columns to the analysis of complex samples.

Nano-liquid chromatography-mass spectrometry and recent applications in omics investigations

Liquid chromatography coupled to mass spectrometry (LC-MS) is one of the most powerful tools in identifying and quantitating molecular species. Decreasing column diameter from the millimeter to micrometer scale is now a well-developed method which allows for sample limited analysis. Specific fabrication of capillary columns is required for proper implementation and optimization when working in the nanoflow regime. Coupling the capillary column to the mass spectrometer for electrospray ionization (ESI) requires reduction of the subsequent emitter tip. Reduction of column diameter to capillary scale can produce improved chromatographic efficiency and the reduction of emitter tip size increased sensitivity of the electrospray process. This improved sensitivity and ionization efficiency is valuable in analysis of precious biological samples where analytes vary in size, ion affinity, and concentration. In this review we will discuss common approaches and challenges in implementing nLC-MS methods and how the advantages can be leveraged to investigate a wide range of biomolecules.

Separation of saccharides using fullerene-bonded silica monolithic columns via π interactions in liquid chromatography

We report on a potential method to separate sugars by using the specific interaction between fullerenes and saccharides in liquid chromatography (LC). Aromatic rings with high electron density are believed to interact strongly with saccharides due to CH–π and/or OH–π interactions. In this study, the fullerene-bonded columns were used to separate saccharides by LC under aqueous conditions. As a result, 2-aminobenzamide-labeled glucose homopolymer (Glcs) was effectively separated by both C60 and C70 columns in the range of Glc-1 to Glc-20 and high blood glucose level being retained in greater quantity. Furthermore, similar separations were identified by LC–mass spectrometry with non-labeled glucose homopolymers. Theoretical study based on molecular dynamics and DFT calculation demonstrated that a supramolecular complex of saccharide–fullerene was formed through CH–π and/or OH–π interactions, and that the interactions between saccharide and fullerene increase with the increase units of the saccharide. Additionally, the C60 column retained disaccharides containing maltose, trehalose, and sucrose. In this case, it was assumed that the retention rates were determined by the difference of the dipole moment in each saccharide. These results suggest that the dipole-induced dipole interaction was dominant, and that maltose—with the higher dipole moment—was more strongly retained compared to other disaccharides having lower dipole moment.

Binding Kinetics of Ruthenium Pyrithione Chemotherapeutic Candidates to Human Serum Proteins Studied by HPLC-ICP-MS

The development of ruthenium-based complexes for cancer treatment requires a variety of pharmacological studies, one of them being a drug's binding kinetics to serum proteins. In this work, speciation analysis was used to study kinetics of ruthenium-based drug candidates with human serum proteins. Two ruthenium (Ru) complexes, namely [(η⁶-p-cymene)Ru(1-hydroxypyridine-2(1H)-thionato)Cl] (1) and [(η⁶-p-cymene)Ru(1-hydroxypyridine-2(1H)-thionato)pta]PF₆ (2) (where pta = 1,3,5-triaza-7-phosphaadamantane), were selected. Before a kinetics study, their stability in relevant media was confirmed by nuclear magnetic resonance (NMR). Conjoint liquid chromatography (CLC) monolithic column, assembling convective interaction media (CIM) protein G and diethylamino (DEAE) disks, was used for separation of unbound Ru species from those bound to human serum transferrin (Tf), albumin (HSA) and immunoglobulins G (IgG). Eluted proteins were monitored by UV spectrometry (278 nm), while Ru species were quantified by post-column isotope dilution inductively coupled plasma mass spectrometry (ID-ICP-MS). Binding kinetics of chlorido (1) and pta complex (2) to serum proteins was followed from 5 min up to 48 h after incubation with human serum. Both Ru complexes interacted mainly with HSA. Complex (1) exhibited faster and more extensive interaction with HSA than complex (2). The equilibrium concentration for complex (1) was obtained 6 h after incubation, when about 70% of compound was bound to HSA, 5% was associated with IgG, whereas 25% remained unbound. In contrast, the rate of interaction of complex (2) with HSA was much slower and less extensive and the equilibrium concentration was obtained 24 h after incubation, when about 50% of complex (2) was bound to HSA and 50% remained unbound.

Monolithic chromatography on conjoint liquid chromatography columns for speciation of platinum-based chemotherapeutics in serum of cancer patients

BACKGROUND

Monolithic chromatography using convective interaction media (CIM) disks or columns can be used in the separation step of speciation analysis. When different monolithic disks are placed in one housing, forming conjoint liquid chromatography (CLC) monolithic column, two-dimensional separation is achieved in a single chromatographic run.

METHODS

Here, we assembled low-pressure (maximum 50 bar) CLC monolithic column, which consists of two 0.34 mL shallow CIM monolithic disks and high-pressure CLC column (maximum 150 bar) from 0.1 mL analytical high performance short bed CIMac monolithic disks. Both the CLC columns constructed from affinity Protein G and weak anion exchange diethylamine (DEAE) disks, were applied for the speciation of cisplatin, oxaliplatin and carboplatin in spiked standard serum proteins, spiked human serum and serum of cancer patients. The analytical performances of the CLC columns used were evaluated by comparing their robustness, selectivity, repeatability and reproducibility. The separated serum proteins were detected on-line by ultraviolet (UV) and eluted Pt species by inductively coupled plasma mass spectrometry (ICP-MS). For accurate quantification of the separated Pt species (unbound Pt-based chemotherapeutic from species associated to transferrin (Tf), human serum albumin (HSA) and Immunoglobulin G (IgG)), post column isotope dilution (ID)-ICP-MS was used.

RESULTS

The data from analyses showed that both tested CLC monolithic columns gave statistically comparable results, with the low-pressure CLC column exhibiting better resolving power and robustness. It also enables more effective cleaning of monolithic disks and to analyse larger series of serum samples than the high-pressure CLC column. Analyses of serum samples of cancer patients treated with cisplatin or carboplatin showed that Pt-chemotherapeutics were bound preferentially to HSA (around 80%). The portion of unbound Pt in general did not exceed 2%, up to 5% of Pt was associated with Tf and approximately 20% with IgG. Column recoveries, calculated as a ratio between the sum of concentrations of Pt species eluted and concentration of total Pt in serum samples, were close to 100%.

CONCLUSIONS

Low-pressure CLC column exhibited greater potential than high-pressure CLC column, and can be thus recommended for its intended use in speciation analysis of metal-based biomolecules.

Challenges and Advances in the Fabrication of Monolithic Bioseparation Materials and their Applications in Proteomics Research

High-performance liquid chromatography integrated with tandem mass spectrometry (HPLC-MS/MS) has become a powerful technique for proteomics research. Its performance heavily depends on the separation efficiency of HPLC, which in turn depends on the chromatographic material. As the "heart" of the HPLC system, the chromatographic material is required to achieve excellent column efficiency and fast analysis. Monolithic materials, fabricated as continuous supports with interconnected skeletal structure and flow-through pores, are regarded as an alternative to particle-packed columns. Such materials are featured with easy preparation, fast mass transfer, high porosity, low back pressure, and miniaturization, and are next-generation separation materials for high-throughput proteins and peptides analysis. Herein, the recent progress regarding the fabrication of various monolithic materials is reviewed. Special emphasis is placed on studies of the fabrication of monolithic capillary columns and their applications in separation of biomolecules by capillary liquid chromatography (cLC). The applications of monolithic materials in the digestion, enrichment, and separation of phosphopeptides and glycopeptides from biological samples are also considered. Finally, advances in comprehensive 2D HPLC separations using monolithic columns are also shown.