Adsorption characteristics of an immobilized metal affinity membrane

Preparation of Polyacrylonitrile-Based Immobilized Copper-Ion Affinity Membranes for Protein Adsorption

A polyacrylonitrile (PAN)-based immobilized metal-ion affinity membrane (IMAM) was prepared with a high capacity for protein adsorption. PAN was selected as the substrate due to its excellent thermal and chemical stability. The cyano groups on the PAN membrane were substituted with carboxyl groups, followed by reactions with ethylenediamine (EDA) and ethylene glycol diglycidyl ether (EGDGE) to produce the terminal epoxy groups. The chelating agent iminodiacetic acid (IDA) was then bound to the modified PAN membrane and further chelated with copper ions. The immobilized copper ion amount of membrane was analyzed to obtain the optimal reaction conditions, which were 60 °C/3 h for EDA coupling and 60 °C/4 h for EGDGE grafting. Furthermore, under the use of minor IDA and copper ion concentrations, the immobilized copper ion capacity of the IMAM was 4.8 μmol/cm² (253.4 µmol/mL, or 1.47 μmol/mg). At a neutral pH, the cationic lysozyme exhibited a large adsorption capacity with the IMAM (1.96 μmol/mL), which was most likely multilayer binding, whereas the adsorption capacity for bovine serum albumin (BSA) and histidine-tagged green fluorescent protein (GFP-His₆) was 0.053 μmol/mL and 0.135 μmol/mL, respectively, with a monolayer adsorption arrangement. The protein desorption efficiency was greater than 95%, implying that the prepared IMAM could be reused for protein adsorption.

Functional Microfiber Nonwoven Fabric with Copper Ion-Immobilized Polymer Brush for Detection and Adsorption of Acetone Gas

The detection and removal of volatile organic compounds (VOCs) are emerging as an important problem in modern society. In this study, we attempted to develop a new material capable of detecting or adsorbing VOCs by introducing a new functional group and immobilizing metal ions into a microfiber nonwoven fabric (MNWF) made through radiation-induced graft polymerization. The suitable metal complex was selected according to the data in “Cambridge Crystallographic Data Center (CCDC)”. 4-picolylamine (4-AMP), designated as a ligand through the metal complex data of CCDC, was introduced at an average mole conversion rate of 63%, and copper ions were immobilized at 0.51 mmol/g to the maximum. It was confirmed that degree of grafting (dg) 170% 4-AMP-Cu MNWF, where copper ions are immobilized, can adsorb up to 50% of acetone gas at about 50 ppm, 0.04 mmol/g- 4-AMP-Cu-MNWF, at room temperature and at a ratio of copper ion to adsorbed acetone of 1:10.

Development of a Simplified Radiation-Induced Emulsion Graft Polymerization Method and Its Application to the Fabrication of a Heavy Metal Adsorbent

A simplified radiation-induced emulsion graft polymerization (SREG) method is proposed. This method involves a convenient and easy degassing process of a monomer solution using a commercially available sealed glass jar. A loaded weight on the lid of the jar was used to control the jar's internal pressure as the degassing of the monomer solution took place using a vacuum pump. The degassing method was highly reproducible, resulting from no bumping of the monomer solution. The initial grafting velocity was proportional to the absorbed doses of pre-irradiation between 5 and 20 kGy. This result indicates that dissolved oxygen was sufficiently eliminated from the monomer solution at such a level where the remaining oxygen had little effect on the grafting reaction at a dose of 5 kGy. The method was then applied to the fabrication of a heavy metal adsorbent that possessed a sufficient adsorption capacity of Co(II) ions. The SREG method is applicable to the fabrication of a wide variety of functional graft polymers because high-dose-rate gamma-ray radiation and expensive experimental equipment are not necessary.

Immobilization of copper ions on chitosan/cellulose acetate blend hollow fiber membrane for protein adsorption

The prepared IMAM (CS/CA-Cu) achieved a high adsorption capacity of 69 mg-BSA per g-membrane.

Effects of porogen and cross-linking agents on improved properties of silica-supported macroporous chitosan membranes for enzyme immobilization

A series of silica-supported macroporous chitosan membranes (CM15, CM20, and CM25) was prepared by varying the ratio of 70-230-μm-sized silica particles. These synthesized membranes were further cross-linked using different cross-linking agents for covalent immobilization of biological macromolecules especially enzymes and in this study, Bovine serum albumin and laccase. Effects of silica particle and cross-linking agents on their flow rates, surface properties, and chemical and biological properties were explored. Pore size of as-synthesized membranes was 0.1192, 0.1268, and 0.1623 μm, respectively, for CM15, CM20, and CM25. The effect of various parameters such as temperature and pH on the relative activity of both free and immobilized enzymes was studied in details. The relative enzyme activity upon immobilization was greatly enhanced several folds of its original activity. The stability of enzymes over a range of temperature and pH was significantly improved by immobilization. The optimum temperature and pH were determined to be 50 °C and pH 3, respectively, for both the free and the immobilized enzymes. The immobilized enzyme possessed good operational stability and reusability properties that support its potentiality for practical applications. Among three membranes, CM25 is confirmed to be efficient candidate due to its improved characteristics.

Development of silica gel-supported modified macroporous chitosan membranes for enzyme immobilization and their characterization analyses

The present work was aimed at developing stability enhanced silica gel-supported macroporous chitosan membrane for immobilization of enzymes. The membrane was surface modified using various cross-linking agents for covalent immobilization of enzyme Bovine serum albumin. The results of FT-IR, UV-vis, and SEM analyses revealed the effect of cross-linking agents and confirmed the formation of modified membranes. The presence of silica gel as a support could provide a large surface area, and therefore, the enzyme could be immobilized only on the surface, and thus minimized the diffusion limitation problem. The resultant enzyme immobilized membranes were also characterized based on their activity retention, immobilization efficiency, and stability aspects. The immobilization process increased the activity of immobilized enzyme even higher than that of total (actual) activity of native enzyme. Thus, the obtained macroporous chitosan membranes in this study could act as a versatile host for various guest molecules.

Para-aminobenzamidine linked regenerated cellulose membranes for plasminogen activator purification: effect of spacer arm length and ligand density

Despite membrane-based separations offering superior alternative to packed bed chromatographic processes, there has been a substantial lacuna in their actual application to separation processes. One of the major reasons behind this is the lack of availability of appropriately modified or end-group modifiable membranes. In this paper, an affinity membrane was developed using a commercially available serine protease inhibitor, para-aminobenzamidine (pABA). The membrane modification was optimized for protein binding capacity by varying: (i) the length of the spacer arm (SA; 5-atoms, 7-atoms, and 14-atoms) linking the ligand to membrane surface; (ii) the affinity ligand (pABA) density on membrane surface (5-25nmol/cm(2)). Resulting membranes were tested for their ability to bind plasminogen activators (PAs) from mono- and multi-component systems in batch mode. The membrane containing pABA linked through 7-atoms SA but similar ligand density as in the case of 5- or 14-atoms long SA was found to bind up to 1.6-times higher amounts of PA per nmoles of immobilized ligand from conditioned HeLa cell culture media. However, membranes with similar ligand densities but different lengths of SA, showed comparable binding capacities in mono-component system. In addition, the length of SA did not affect the selectivity of the ligand for PA. A clear inverse linear correlation was observed between ligand density and binding capacity until the point of PA binding optima was reached (11±1.0nmol/cm(2)) in mono- and multi-component systems for 7- as well as 14-atoms SA. Up to 200-fold purification was achieved in a single step separation of PA from HeLa conditioned media using these affinity membranes. The issues of ligand leaching and reuse of the membranes were also investigated. An extensive regeneration procedure allowed the preservation of approximately 95% of the PA binding capacity of the membranes even after five cycles of use.

Cr(VI) adsorption from electroplating plating wastewater by chemically modified coir pith

Coir pith samples were chemically modified by grafting with acrylic acid for the removal of Cr(VI) from electroplating wastewater. The presence of acrylic acid on the coir pith surface was verified by a scanning electron microscope with an electron dispersive x-ray spectrometer (SEM/EDX), Fourier transform infrared spectroscopy (FTIR) and thermogravimetry (TG). The carbonyl groups (C==O) from the carboxylic acids (COOH) increased on the coir pith surface after grafting with acrylic acid. In addition, the thermal stability of the acrylic acid-grafted coir pith also improved. The optimum conditions for grafting the acrylic acid on the coir pith consisted of 2 M acrylic acid and 0.00125 M ceric ammonium nitrate (CAN, as an initiator). The maximum Cr(VI) removal (99.99 ± 0.07%) was obtained with the following conditions: a 1.3% (w/v) dosage of acrylic acid-grafted coir pith, a system pH of 2, a contact time of 22 h, a temperature of 30 °C, a particle size of <150 μm and an initial Cr(VI) of 1,171 mg l(-1). At system pH of 2, Cr(VI) in the HCrO(4)(-) form can be adsorbed with acrylic acid-grafted coir pith via an electrostatic attraction. The adsorption isotherm of 2 M acrylic acid-grafted coir pith exhibited a good fit with the Langmuir isotherm. The maximum Cr(VI) adsorption capacity of the 2 M acrylic acid-grafted coir pith was 196.00 mg Cr(VI) g(-1) adsorbent, whereas for coir pith without grafting, the maximum Cr(VI) removal was 165.00 mg Cr(VI) g(-1) adsorbent. The adsorption capacity of the acrylic acid-grafted coir pith for Cr(VI) was higher compared to the original coir pith. This result was due to the enhancement of the carbonyl groups on the coir pith surface that may have involved the mechanism of chromium adsorption. The X-ray absorption near edged structure (XANES) and desorption studies suggested that most of the Cr(III) that presented on the acrylic acid-grafted coir pith was due to the Cr(VI) being reduced to Cr(III) on the adsorbent surface. FTIR confirmed the involvement of the carbonyl groups (C==O) and the methoxy groups (OCH3) in the mechanism of chromium adsorption. Thermodynamic study, such as enthalpy (ΔH), free energy (ΔG) and entropy change (ΔS) indicated that the overall adsorption process was endothermic, spontaneous and randomness. In addition, the adsorption process was favored at high temperatures.

Production of novel polymer monolithic columns, with stationary phase gradients, using cyclic olefin co-polymer (COC) optical filters

Polymer monolithic columns with controlled surface ligand density, providing stationary phase gradients within monolithic capillary columns, have been developed using photo-grafting through optical filters. Utilising commercially available cyclic olefin co-polymer (COC) films, the production of an optical filter capable of attenuating UV irradiation, in a tailored manner, was investigated. This novel optical filter was successfully applied to the surface modification of poly(BuMA-co-EDMA) monolithic columns in a multi-step grafting procedure. Fabricated columns were subjected to scanning capacitively coupled contactless conductivity (sC(4)D), to determine the distribution of the grafted functional groups, axially along the column. Further modification to produce a chelating stationary phase gradient of iminodiacetic acid (IDA) was demonstrated. To demonstrate the distribution of the IDA sites, a metal cation (Cu(2+)) was complexed to the IDA forming a chelate. Upon the formation of a complex of IDA with Cu(2+), an overall drop in conductive response was observed. The COC optical filter was also used in the fabrication of a grafted gradient of strong cation exchanger (SCX), sulphopropyl methacrylate (SPM) upon a polymer monolith, demonstrating the broader applicability of such a filter.

Preparation and characterization of polyethyleneimine modified ion-exchanger based on poly(methacrylate-co-ethylene dimethacrylate) monolith

A polyethyleneimine (PEI) modified ion-exchanger was prepared based on poly(methacrylate-co-ethylene dimethacrylate) monolith cast in 100 mm x 4.6 mm I.D. stainless steel tube with heptane as the porogenic solvent at 65 degrees C for 12 h. The pores larger than 500 nm presented 85% of total pore volume of PEI monolith and provided the better permeability for separation. Bovine serum albumin (BSA) binding capacity on the column was enhanced with increasing the molecular weight of PEI, indicated that the brush ligand emanated from the surface and captured more protein by multiple binding sites. Titration experiment as well as BSA retention versus the pH of mobile phase showed that the monolith exhibited weak ion-exchange property, and recovered BSA on the monolith reached 97% when NaCl content in mobile phase was higher than 0.5 M. Frontal analysis and gradient elution of BSA indicated that PEI monolith provided the rapid mass transfer in chromatographic procedure, which made the dynamic binding capacities as well as column efficiency keep as constants at high operating flow rate. Fast separation of three mode proteins mixture (lysozyme, hemoglobin and BSA) on the monolith was achieved within 3 min at velocity of 1445 cm/h. This demonstrated the potential of PEI monolith for the rapid analysis and separation of proteins.

Membrane adsorbers as purification tools for monoclonal antibody purification

Downstream purification processes for monoclonal antibody production typically involve multiple steps; some of them are conventionally performed by bead-based column chromatography. Affinity chromatography with Protein A is the most selective method for protein purification and is conventionally used for the initial capturing step to facilitate rapid volume reduction as well as separation of the antibody. However, conventional affinity chromatography has some limitations that are inherent with the method, it exhibits slow intraparticle diffusion and high pressure drop within the column. Membrane-based separation processes can be used in order to overcome these mass transfer limitations. The ligand is immobilized in the membrane pores and the convective flow brings the solute molecules very close to the ligand and hence minimizes the diffusional limitations associated with the beads. Nonetheless, the adoption of this technology has been slow because membrane chromatography has been limited by a lower binding capacity than that of conventional columns, even though the high flux advantages provided by membrane adsorbers would lead to higher productivity. This review considers the use of membrane adsorbers as an alternative technology for capture and polishing steps for the purification of monoclonal antibodies. Promising industrial applications as well as new trends in research will be addressed.

Enhanced Protein Delivery from Photopolymerized Hydrogels Using a Pseudospecific Metal Chelating Ligand

PURPOSE

This study was conducted to investigate the cause of incomplete protein release from photopolymerized poly(ethylene glycol) (PEG) hydrogels and verify the protein-protection mechanism provided by iminodiacetic acid (IDA).

METHODS

The in vitro release of bovine serum albumin (BSA) from PEG hydrogels prepared under different conditions was studied. Photoinitiator and initial protein concentrations were varied as well as the addition of IDA and metal ions. Protein immobilization within the nondegradable networks via free-radical reaction was demonstrated by gel electrophoresis.

RESULTS

Protein release efficiency was shown to be dependent on photoinitiator and initial protein concentration. Gel electrophoresis results revealed immobilization of protein to the polymer network and further indicated the detrimental role of free radicals in lowering protein-release efficiency. Adding IDA to the prepolymer solution enhanced total protein release from the subsequently photopolymerized network in a dose-dependent manner. The addition of metal ions including Cu2+, Zn2+, and Ni2+ further increased BSA release efficiency. Agreement between the protein release data and theoretical model predictions accounting for reversible protein-IDA binding further validated the protection effect provided by IDA and IDA-transition metal complexes.

CONCLUSIONS

The protection effect described in this study offers a novel strategy for increasing the delivery efficiencies of many therapeutically valuable proteins.

Adsorption of Co(II) by a carboxylate-functionalized polyacrylamide grafted lignocellulosics

A new adsorbent (PGBS-COOH) having carboxylate functional group at the chain end was synthesized by graft copolymerization of acrylamide onto banana stalk, BS (Musa Paradisiaca) using ferrous ammonium sulphate/H2O2 redox initiator system. The efficiency of the adsorbent in the removal of cobalt [Co(II)] from water was investigated using batch adsorption technique. The adsorbent exhibits very high adsorption potential for Co(II) and under optimum conditions more than 99% removal was achieved. The maximum adsorption capacity was observed at the pH range 6.5-9.0. The equilibrium isotherm data were analysed using three isotherm models, Langmuir, Freundlich and Scatchard, to determine the best fit equation for the sorption of Co(II) on the PGBS-COOH. A comparative study with a commercial cation exchanger, Ceralite IRC-50, having carboxylate functional group showed that PGBS-COOH is 2.8 times more effective compared to Ceralite IRC-50 at 30 degrees C. Synthetic nuclear power plant coolant water samples were also treated by the adsorbent to demonstrate its efficiency in removing Co(II) from water in the presence of other metal ions. Acid regeneration was tried for several cycles to recover the adsorbed metal ions and also to restore the sorbent to its original state.