Sequential diethylaminoethyl dextran-grafting and diethylaminoethyl modification improve the adsorption performance of anion exchangers.

Ion exchangers with high adsorption capacity, fast mass transfer, and high salt-tolerance synchronously are highly desired for high-performance protein purification. Here, we propose a sequential diethylaminoethyl dextran-grafting and diethylaminoethyl chloride modification strategy to achieve high-performance anion exchangers. The advantages of the double-modification strategy lie in: (1) the introduction of diethylaminoethyl in the second modification has no diffusion limitation due to the small molecular size, thus a high ionic capacity; (2) the grafting ligands not only provide three-dimensional adsorption space for high adsorption capacitybut alsofacilitate surface diffusion of protein by chain delivery. The maximum adsorption capacity of the obtained anion exchangers for bovine serum albumin reaches 333 mg/mL, the ratio of effective pore diffusivity (De) to free solution diffusivity (D0) reaches 0.69, and the adsorption amount reaches 97 mg/mL even in 100 mmol/L NaCl concentration,. All these results demonstrate the proposed sequential modification strategy are promising for the preparation of high-performance ion exchangers.

Rigid crosslink improves the surface area and porosity of ß-cyclodextrin beads for enhanced adsorption of flavonoids.

Many reported ß-cyclodextrin (ß-CD) polymers have poor flavonoid adsorption performance due to their low surface area and porosity resulting from the compact stack of the ß-CD molecules crosslinked by flexible crosslinkers. Here, we propose a rigid crosslink strategy that uses phytic acid (PA) having rigid cyclic group as crosslinkers, achieving a high-surface-area (61.42-140.23 m2/g) and porous ß-CD beads. The improved surface area and porosity are attributed to the rigid cyclic groups in PA, which expand the network structure of ß-CD polymers. Benefitting from the advantages, the optimized PA-crosslinked ß-CD (PA-ß-CD) beads have an over tenfold increased adsorption amount and an threefold increased diffusivity for rutin compared with traditional non-porous ß-CD beads crosslinked by epichlorohydrin. Moreover, dynamic adsorption experiments reveal that PA-ß-CD beads are able to treat about 1100 mL of rutin solution (0.05 mg/mL), over 5 times higher than that of the non-porous ß-CD beads (200 mL). These results demonstrate the promise of PA-ß-CD beads for rapid and high-capacity adsorption of rutin.

Evaluation of dynamic control of continuous capture with periodic counter-current chromatography under feedstock variations.

Multi-column periodic counter-current chromatography is a promising technology for continuous antibody capture. However, dynamic changes due to disturbances and drifts pose some potential risks for continuous processes during long-term operation. In this study, a model-based approach was used to describe the changes in breakthrough curves with feedstock variations in target proteins and impurities. The performances of continuous capture of three-column periodic counter-current chromatography under ΔUV dynamic control were systematically evaluated with modeling to assess the risks under different feedstock variations. As the concentration of target protein decreased rapidly, the protein might not breakthrough from the first column, resulting in the failure of ΔUV control. Small reductions in the concentrations of target proteins or impurities would cause protein losses, which could be predicted by the modeling. The combination of target protein and impurity variations showed complicated effects on the process performance of continuous capture. A contour map was proposed to describe the comprehensive impacts under different situations, and nonoperation areas could be identified due to control failure or protein loss. With the model-based approach, after the model parameters are estimated from the breakthrough curves, it can rapidly predict the process stability under dynamic control and assess the risks under feedstock variations or UV signal drifts. In conclusion, the model-based approach is a powerful tool for continuous process evaluation under dynamic changes and would be useful for establishing a new real-time dynamic control strategy.

Multi-size optimization of macroporous cellulose beads as protein anion exchangers: Effects of macropore size, protein size, and ligand length.

Multi-size optimization of ion exchangers based on protein characteristics and understanding of underlying mechanism is crucial to achieve maximum separation performance in terms of adsorption capacity and uptake kinetic. Herein, we characterize the effects of three different sizes, macropore size, protein size, and ligand length, on the protein adsorption capacity and uptake kinetic of macroporous cellulose beads, and provide insights into the underlying mechanism. In detail, (1) for smaller bovine serum albumin, macropore size has a negligible effect on the adsorption capacity, while for larger γ-globulin, larger macropores improve the adsorption capacity due to the high accessibility of binding sites; (2) there is a critical pore size (CPZ), at which the adsorption uptake kinetic is minimum. When pore sizes are higher than the CPZ, uptake kinetics are enhanced by pore diffusion. When pore sizes are lower than CPZ, uptake kinetics are enhanced by surface diffusion; (3) increasing ligand length improves the adsorption capacity by three-dimensionally extended polymer chains in pores and enhances uptake kinetic by improved surface diffusion. This study offers an integrated perspective to qualitatively assess the effects of multiple sizes, providing guidance for designing advanced ion exchangers for protein chromatography.

Boronate-immobilized cellulose nanofiber-reinforced cellulose microspheres for pH-dependent adsorption of glycoproteins.

High strength and excellent selectivity are two important aspects of porous cellulose microspheres as adsorbents for protein separation. For this purpose, self-reinforced all-cellulose microspheres (SCMs) with high strength were fabricated using natural cellulose nanofibers (CNFs) as fillers and then immobilized via 3-aminophenylboronic acids as affinity ligands for selective enrichment of glycoproteins. In particular, the inherent stiffness of entrapped CNFs endowed SCMs with more inflexibility, because the stress can be efficiently transferred from the network of SCMs to the stiff CNFs during the separation process. Besides, SCMs, as an all-cellulose material with homogenous surface chemistry and pore structure characteristics, are more suitable as supports for adsorbents. Finally, the SCMs were immobilized with 3-aminophenylboronic acids (BA/EPI-SCMs) and tested their performance in affinity adsorption of glycoproteins. BA/EPI-SCMs showed fast separation, high adsorption amount, and excellent selectivity toward glycoproteins.

Preparation of cellulose-based chromatographic medium for biological separation: A review.

Cellulose is a kind of renewable linear polysaccharide with good safety, hydrophilicity, biocompatibility and biodegradability and has become a commonly used chromatographic medium for biological separation and purification. The purpose of this paper is to describe the recent developments in the applications of cellulose-based absorbents as chromatographic medium. This review also attempts to explain the current situation of cellulose-based chromatographic medium from the aspects of cellulose dissolution, common strategies for generating spherical particles of cellulose and its derivatives (such as titration, emulsification, microfluidic and other synthesis methods) and improvement of adsorption properties. Furthermore, non-spherical cellulose-based chromatographic medium are also described briefly.

Macroporous chitin microspheres prepared by surfactant micelle swelling strategy for rapid capture of lead (II) from wastewater.

Heavy metal pollution of water source continues to be one of the most serious environmental problems which have attracted major global concern. Here, a macroporous chitin microsphere is prepared by surfactant micelle swelling strategy followed by modification with tetraethylenepentamine for Pb2+ removal from wastewater. The resultant adsorbent not only exhibits fast adsorption kinetic (>80% of its equilibrium uptake within 20 min) but also has high adsorption capacity of 218.4 ± 6.59 mg/g and excellent reusability (>75% of its initial adsorption capacity after five adsorption/desorption cycles). More importantly, under the continuous operating mode, the adsorbent can treat about 39,000 kg water/kg adsorbent, and the Pb2+ concentration decreases from 2000 µg/L to smaller than 10 µg/L, meeting the drinking water standard recommended by the World Health Organization (10 µg/L). All results indicate that the tetraethylenepentamine-modified macroporous chitin microspheres have great potential in the treatment of heavy metal contamination.

Proteinaceous porous nanofiber membrane-type adsorbent derived from amyloid lysozyme protofilaments for highly efficient lead(II) biologic scavenging.

To overcome the technical bottleneck of fine amyloid lysozyme fibrils in environmental engineering, a novel co-operative strategy was identified to fabricate free-standing lysozyme complex nanofibers based membrane-type adsorbent (Lys-CNFs membrane) through a combination of vacuum filtration for lead remediation. The composition of the membrane integrated the linear amyloid protofilaments that were obtained by acid-heating fibrillation and polydopamine that adjusted the fibers' diameters and surface chemistry. As expected, the Lys-CNFs membrane not only showed nanofibrous morphology and layer stacking architecture but presented a hierarchical macro-mesoporous structure along with a high surface area of 220.4 m2/g. Besides, the thermal stability up to 200 â„ƒ and wetting nature of below 2 s endowed its further applicability. Adsorption experiments showed that Lys-CNFs membrane can effectively uptake Pb(II) ions with acceptable selectivity, high adsorption capacity of 270.3 mg/g, rapid equilibrium kinetic within only 10 mins, and good reusability that dropped by 14.9% efficiency even after five cycles, indicating that Lys-CNFs membrane can be as an affordable technology for alleviating the lead pollution issues.

Bisphosphonated-immobilized porous cellulose monolith with tentacle grafting by atom transfer radical polymerization for selective adsorption of lysozyme.

Here, a m-xylene bisphosphonate immobilized tentacle-type cellulose monolith (BP-PCM) is prepared by atom transfer radical polymerization for lysozyme purification. In the preparation, the m-xylene bisphosphonate was anchored glycidyl methacrylate and then polymerized to enhance the flexibility of the ligands to improve lysozyme adsorption capacity, and glycerol monomethacrylate serves as spacer to further optimize the layers structure and ligands density of the grafted tentacles for satisfactory adsorption capacity. The maximum static and dynamic adsorption capacity (10% breakthrough) of BP-PCM reach to 169.6 and 102.6 mg mL-1, respectively. Moreover, BP-PCM displays weak nonspecific adsorption and is able to successfully enrich lysozyme from diluted chicken egg white, indicating the excellent selectivity. The results demonstrated that BP-PCM is promising for use as high-capacity protein chromatography.

Tentacle-type poly(hydroxamic acid)-modified macroporous cellulose beads: Synthesis, characterization, and application for heavy metal ions adsorption.

Herein, a facile yet efficient template method to fabricate macroporous cellulose beads (MCBs) is reported. In this method, micro-size CaCO3 is utilized to create macroporous structure for fast mass transfer, and tentacle-type poly(hydroxamic acid) as adsorption ligand is immobilized on the MCBs to improve adsorption capacity. The obtained tentacle-type poly(hydroxamic acid)-modified MCMs (TP-CMCBs) show uniform spherical shape (about 80 µm), bimodal pore system (macropores≈3.0 µm; diffusional pores≈14.5 nm), and high specific surface area (52.7 m2/g). The adsorption performance of TP-CMCBs is evaluated by heavy metal ions adsorption. TP-CMCBs exhibit not only high adsorption capacities (342.5, 261.5 and 243.2 mg/g for Cu2+, Mn2+ and Ni2+, respectively.), but also fast adsorption rate (>70% of its equilibrium uptake within 30 min). Additionally, TP-CMCBs have excellent reusability, as evidenced by that the adsorption capacities have no obvious change even after five-time consecutive adsorption-desorption cycles. All results demonstrate that the proposed TP-CMCBs have great potential in removal of heavy metal ions.

High-strength, blood-compatible, and high-capacity bilirubin adsorbent based on cellulose-assisted high-quality dispersion of carbon nanotubes.

Excess bilirubin can accumulate in body organs and has serious effects on human health. In this work, a simple engineering strategy, based on cellulose-assisted high-quality dispersion of carbon nanotubes (CNTs), is proposed to produce high-performance bilirubin adsorbents. By dispersing cellulose and CNTs in NaOH/thiourea aqueous solution, a homogeneous and stable cellulose/CNTs solution is achieved. The obtained cellulose/CNTs solution is applied for the fabrication of cellulose/CNTs microspheres (CCMs), in which cellulose serves as a base material and guarantees the blood compatibility of the composite material, and CNTs contribute to the improved mechanical strength and high adsorption capacity. To further improve blood compatibility and adsorption capacity, lysine is immobilized on the CCMs. The obtained lysine-modified CCMs (LCCMs) exhibit a large surface area (171.31 m2/g) and hierarchically porous structure. Experimental results demonstrate LCCMs have high bilirubin adsorption capacity (204.12 mg/g) that is significantly higher than most of the reported adsorbents. The combination of high strength, blood compatibility, and high adsorption capacity positions the LCCMs as a promising candidate for bilirubin removal.

Direct preparation of porous cellulose microspheres via a self-growth process on bamboo fibers and their functionalization for specific adsorption of histidine-rich proteins.

The traditional preparation of cellulose microspheres always involves tedious synthetic procedures (e.g., dissolution, emulsification and regeneration) and inevitable organic solvents, which undergoes both high production cost and environmental contamination. To overcome these issues, a feasible and green synthesis strategy is proposed to construct porous cellulose microspheres (PCMs) via one-step spontaneous formation relying on sodium periodate oxidation of pure bamboo fibers. By this strategy, a cluster of robust cellulose microspheres grow up on the surface of bamboo fibers in aqueous phase through amorphous oxidized cellulose self-assembly accumulation and then drop out when their sizes increase to about 15 µm. After being immobilized with Cu(II), the prepared cellulose microspheres serve as metal affinity adsorbent for proteins adsorption, showing high adsorption capacity, good selectivity and excellent reusability for bovine hemoglobin (BHb). Together with green and easy synthesis, the novel cellulose microspheres show a promising alternative to commercially available adsorbent support.

The construction of porous chitosan microspheres with high specific surface area by using agarose as the pore-forming agent and further functionalized application in bioseparation.

Adsorbents with synchronously high protein adsorption performance and a facile synthetic route are highly desired in protein separation. In this study, a facile yet effective strategy to develop porous chitosan microspheres (PCMs) with high specific surface area (SSA) using agarose as the pore-forming agent is reported. Through heat treatment, the agarose chains in the chitosan/agarose composite microspheres (CAM) were removed, leading to the generation of nanopores/nanochannels and the improvement of SSA. The obtained PCMs showed hierarchical porous structure and a maximum SSA of 246.48 m2 g-1. For the application of PCMs as a protein adsorbent, by modification, the resultant immobilized Cu2+ affinity adsorbent (denoted as Cu2+PCM-15) exhibited a high adsorption capacity (301.88 mg g-1), fast adsorption rate (reaching equilibrium in less than 15 min), and excellent adsorption selectivity for BHb. Together with its environmental-friendliness, and abundant biomass chitosan and agarose, the as-prepared affinity adsorbent with high performance has great application potential in the field of bioseparation.