Beaded polymer supports and gels

Nucleotide Isolation by Boronic Acid Functionalized Hydrogel Beads

Aminophenyl boronic acid (APBA) modified hydrogel beads were prepared as a new sorbent for nucleotide isolation. Spherical hydrogel beads, obtained by suspension copolymerization, were the base material for the sorbent. The carboxyl groups on the gel bead surface were activated with a water soluble carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). APBA was then covalently attached to the activated structure via the amine groups. The maximum APBA attached to the gel was 34mg/g. The reversible adsorption-desorption behavior of β-nicotinamide adenine dinucleotide (β-NAD) was investigated by using 3.5 and 34mg/g of APBA on the hydrogel beads. The equilibrium -NAD adsorption capacities for these beads were determined as approximately 25 and 100mg/g, respectively. The -NAD absorption capacity of these APBA beads is significantly greater than similar supports.

Effect of monomer dosing rate in the preparation of mesoporous polystyrene nanoparticles by semicontinuous heterophase polymerization

The semicontinuous heterophase polymerization of styrene in the presence of cross-linking and porogen agents was carried out. Latexes with close to 20% solid content, which contained mesoporous nanoparticles with 28 nm in average diameters, up to 0.5 cm3/g in porosity and 6-8 nm in pore diameters were obtained. By varying the monomer dosing rate over the micellar solution, an unexpected direct dependence of instantaneous conversion on the monomer dosing rate was found. This was ascribed to the higher average number of radicals per particle attained in the polymerization at the higher dosing rate, which in turn would arise from the higher gel percentage in the polymer. It is believed that the cross-linked chains prevent encounters between radicals, delaying the bimolecular termination reactions and allowing the existence of more than one radical inside the particles, which in turn increases the propagation rate.

Probing fundamental film parameters of immobilized enzymes--towards enhanced biosensor performance. Part II-Electroanalytical estimation of immobilized enzyme performance

The method of immobilization of a protein has a great influence on the overall conformation, and hence, functioning of the protein. Thus, a greater understanding of the events undergone by the protein during immobilization is key to manipulating the immobilization method to produce a strategy that influences the advantages of immobilization while minimizing their disadvantages in biosensor design. In this, the second paper of a two-part series, we have assessed the kinetic parameters of thin-film laccase monolayers, covalently attached to SAMs differing in spacer-arm length and lateral density of spacer arms. This was achieved using chronoamperometry and an electroactive product (p-benzoquinone), which was modeled in a non-linear regressional fashion to extract the relevant parameters. Finally, comparisons between the kinetic parameters presented in this paper and the rheological parameters of laccase monolayers immobilized in the same manner (Part I of this two paper series) were performed. Improvements in the maximal enzyme-catalysed current, i(max), the apparent Michaelis-Menten constant, K(m) and the apparent biosensor sensitivity were noted for most of the surfaces with increasing linker length. Decreasing the lateral density of the spacer-arms brought about a general improvement in these parameters, which is attributed to the decrease in multiple points of immobilization undergone by functional proteins. Finally, comparisons between rheological data and kinetics data showed that the degree of viscosity exhibited by protein films has a negative influence on attached protein layers, while enhanced protein hydration levels (assessed piezoelectrically from data obtained in Paper 1) has a positive effect on those surfaces comprising rigidly bound protein layers.

Methacrylate-based chromatographic media

This review summarizes the preparation and application of chromatographic separation media based on methacrylate monomers with a major focus on highly crosslinked macroporous beads prepared from 2-hydroxyethyl methacrylate and glycidyl methacrylate, respectively. The effects of process variables such as composition of the polymerization mixture that includes monomers, porogenic solvents, and free radical initiator, suspension stabilizer, reaction temperature, and stirring are detailed for both classical and templated suspension polymerization. In addition, specific features of the preparation of monodisperse beads are also discussed. The performance of methacrylate-based separation media is demonstrated on numerous separations in a variety of chromatographic modes.

Part II. Chromatography using ultra-stable metal oxide-based stationary phases for HPLC

In this part of the review authors discuss methods used for modification of metal oxide surfaces. On the basis of literature data it is shown, that silanization of the surfaces do not form stable supports for chromatography. On the other hand, the success of polymer modified surfaces such as polybutadiene (PBD) and polystyrene (PS) is emphasized. Permanent modification of metal oxide surfaces with Lewis bases is also widely discussed. Chromatographic properties of polymer modified surfaces of zirconia are discussed in details. The perspectives of carbon-coated metal oxide surfaces in HPLC and high temperature separations are described.

Production and characterization of liquid-core capsules made from cross-linked acrylamide copolymers for biotechnological applications

A novel chemistry has been developed for the production of capsules composed of a hydrophobic liquid core surrounded by a cross-linked polyacrylamide/alginate membrane. These liquid-core capsules may be used in capsular perstraction for the removal of inhibitory products from bioprocesses and bioconversions. They have the advantage of having a high surface area to promote rapid mass transfer, while separation of the organic core phase from the aqueous environment by the capsule membrane prevents the formation of stable emulsions and potential problems associated with toxicity of the organic phase for microbial cells or enzymes. Monodisperse spherical liquid-core capsules of between 800 microm and 1.6 mm diameter, with high mechanical resistance, have been prepared by co-extrusion, using the jet break-up technique. Capsules produced from a solution of MBA/total monomer (5%) were found to be more elastic and have a higher burst force when exposed to chelating agents such as phosphate or citrate. The mechanical resistance was unaffected by buffer solutions in the pH range 4-9 and after sterilization at 121 degrees C for 20 min. Capsules having membranes composed of a copolymer of acrylamide and N-hydroxymethylacrylamide exhibited even higher mechanical stability toward chelating agents.

Cellulose beads: a new versatile solid support for microwave- assisted synthesis. Preparation of pyrazole and isoxazole libraries

The synthesis of libraries of substituted pyrazoles and isoxazoles has been developed via in situ generation of polymer-bound enaminones. The synthetic protocol makes use of commercially available aniline cellulose, a low-cost and versatile biopolymer, under very mild conditions. This new support allowed us to carry out reactions in polar solvents under both conventional heating and MW irradiation without degradation of the polymer. The reaction between cellulose-bound enaminone and hydroxylamine or hydrazines to afford the target heterocycles in high yields directly in solution is the key step. The support can be conveniently recycled.

Stationary phase effects on the dynamic affinity of low-molecular-mass displacers

In this paper, the selectivity of a variety of cation-exchange stationary phases was investigated using a homologous series of displacer molecules based on pentaerythritol. These displacers were derived from pentaerythritol and contained either four trimethyl ammonium groups [pentaerythrityl-(trimethylammonium chloride)4, PE(TMA)4], benzene rings [pentaerythrityl-(benzyl dimethylammonium chloride)4, PE(DMABzCl)4], heptyl groups [pentaerythrityl-(heptyl dimethylammonium iodide)4, PE(DMAHepI)4] or cyclohexyl groups [pentaerythrityl-(cyclohexyl dimethylammonium iodide)4, PE(DMACyI)4]. This series enabled us to probe the secondary interactions that can play a role in the affinity of low-molecular-mass displacers for different stationary phases. The relative affinities of these displacers were examined using a displacer ranking plot based on the steric mass action (SMA) isotherm model. While hydrophobicity and aromaticity played important roles in generating the affinity to the hydrophilized polystyrene-divinylbenzene (Source 15S) and polymethacrylate-based (Toyopearl 650M) resins, these secondary interactions had a minimal impact on the selectivity in agarose resins coated with dextran (SP Sepharose XL), "gel in a shell" (S Ceramic HyperD F), and monolithic (Bio-Rad Uno S6) cation-exchange materials. Further, the results with a tentacular stationary phase (Fractogel EMD) suggest that the alkyl chains on PE(DMAHepI)4 play an important role in increasing the affinity, possibly because of strong interactions between the alkyl moiety and the polymer matrix as well as between the charged groups and the polyelectrolyte tentacles. The results of this study provide insight into the design of high affinity, low-molecular-mass displacers for different cation-exchange stationary phase materials.

Hydrophilic polymer supports for solid-phase synthesis: preparation of poly(ethylene glycol) methacrylate polymer beads using "classical" suspension polymerization in aqueous medium and their application in the solid-phase synthesis of hydantoins

Lightly cross-linked hydrophilic polymer beads representing new types of supports for solid-phase synthesis have been prepared from commercial oligoethylene glycol monomethacrylates using an aqueous suspension polymerization process and specifically designed polymerization mixtures. These beads swell extensively in solvents with a wide range of polarities from dichloromethane, tetrahydrofuran, and water to dimethylformamide, and they enable high functional loadings of 1.2-1.8 mmol g(-1). Their ability to serve as supports was demonstrated in the model solid-phase synthesis of a small library of hydantoins. This four-step synthesis using primary amines readily affords yields of over 70%.

New synthetic ways for the preparation of high-performance liquid chromatography supports

The latest developments and in particular important synthetic aspects for the preparation of modern HPLC supports are reviewed. In this context, the chemistry of inorganic supports based on silica, zirconia, titania or aluminum oxide as well as of organic supports based on poly(styrene-divinylbenzene), acrylates, methacrylates and other, more specialized polymers is covered. Special consideration is given to modern approaches such as sol-gel technology, molecular imprinting, perfusion chromatography, the preparation of monolithic separation media as well as to organic HPLC supports prepared by new polymer technologies such as ring-opening metathesis polymerization. Synthetic particularities relevant for the corresponding applications are outlined.

Structural characteristics of low-molecular-mass displacers for cation-exchange chromatography. II. Role of the stationary phase

The relative efficacy of a variety of low-molecular-mass displacers was examined on three different stationary phase materials. Several homologous series of displacer molecules were evaluated on these ion-exchange resins using a displacer ranking plot based on the steric mass action model. The results demonstrate that while aromaticity and hydrophobicity can play a significant role in the affinity of displacer molecules on polymethacrylate based and hydrophilized polystyrene-divinylbenzene based materials, this effect is much less pronounced on an agarose based resin. The work presented in this paper demonstrates that different structural features of low-molecular-mass displacers can dominate their affinity on various stationary phase materials employed and provides rules of thumb for the design of high affinity, low-molecular-mass displacers for a variety of commercial cation-exchange materials.

Properties of solid supports

Many supports including composite materials and functionalized surfaces are available for solid-phase synthesis. In the process of selecting the proper support it is important to consider the optimal performance during solid-phase synthesis. For most purposes the mechanically stable beaded gel resins are preferred. These resins are homogeneous, and the loading and physical and chemical properties can easily be varied. Optimal properties have been obtained by radical polymerization of end group acryloylated long-chain polyethylene glycols. However, polystyrene resins or amide bond free PEG-based resins may be more suited for general organic synthesis where reactivity of radicals, carbenes, carbanions, carbenium ions, or strong Lewis acids have to be considered. Loading of the resins can have a dramatic effect on the outcome of a synthesis and has to be considered separately for each synthesis. Synthesis of long peptides with 50-100 amino acids imposes completely different requirements on the performance, swelling, and loading than a large-scale synthesis of, for example, the pentapeptide enkephalin. Automated multiple synthesizers constructed for columns of beaded gel or composite supports are available from many suppliers. It is therefore expected that the optimization of support properties will continue in order to meet new synthetic challenges. In the synthesis for solid-phase screening of binding of biomolecules to ligands directly on the resin beads, it is an advantage if the resin is not permeable to the biomolecule so unbound molecules can easily be removed by washing. This is the case with polystyrene-based resins, but they do, however, often show nonspecific adhesion of proteins owing to the hydrophobic character of the polystyrene. Modification of the functional groups of polystyrene with polyethylene glycol as spacers for synthesis of the binding ligands can increase the available ligand concentration on the bead surface and eliminate most of the nonspecific adhesion. In contrast to binding studies, solid-phase assays of enzymes require beads that are permeable to the enzyme, as the progress of reaction can be followed and the product of reaction analyzed. The available amount on the surface of the polystyrene-based beads (approximately 0.3%) is not enough for product analysis. Therefore, in the case of enzyme assays, highly swelling permeable PEG-based gel resins or functionalized surfaces of a polar and porous matrix are preferred.

New packing materials for protein chromatography

This review describes new packing materials designed for protein chromatography, covering advances in base supports and stationary phases. Base supports are classified according to their chemical composition. Since most separation media are bead shaped, typical procedures used for their preparation are also presented. In order to provide matrices combining improved chemical stability and chromatographic performances, composite materials continue to be developed, including bonded stationary phases, pore composites and mixed carriers. The different approaches to their preparation are described and characteristics that play a major role in the chromatographic process are discussed. Recently introduced materials and some of their applications under non-denaturing conditions in the different chromatographic modes are also presented.

Improved manufacture and application of an agarose magnetizable solid-phase support

A simple, semiautomated, nonhazardous procedure for the production of a magnetizable solid-phase support (MSPS) has been developed based on the extrusion of molten agarose-iron oxide mixtures, which enables manufacture of a range of differently sized spherical agarose-iron oxide beads. This system has enabled scale-up of an original manufacture procedure and reproducible preparation of kg quantities of MSPS suitable for biomolecular purifications. An improved protocol for the isolation of plasmid DNA directly from cell lysates using this MSPS, derivatized with diethylaminoethyl (DEAE) groups, is reported. This involves a modified alkaline lysis, followed by adsorption to and elution from the support, yielding plasmid DNA of a purity comparable with, or better than, other methods of plasmid isolation. Using the same procedure, plasmid DNA can be isolated from bacterial cell culture volumes of 1.5 mL and 100 mL with equal efficiency and purity.

Preparation and characterization of high-surface-area polymer substrates for microcalorimetry

The preparation and characterization of high-surface-area polymeric substrates suitable for the microcalorimetry of protein adsorption are described. High-surface-area polystyrene, poly(styrene-co-butyl methacrylate) and poly(styrene-co-allyl alcohol) were prepared by adsorbing polymer from solution onto fumed silica. Verification of adsorption of polystyrene by silica was determined by noting peak shifts of the surface silanol group in the infrared. The amount of polymer adsorbed was determined from adsorption isotherms. The minimum thickness of polystyrene required to mask silicon oxide properties was found to be that thickness at which contact angles became constant, about 35 A. Polymer densities were measured. Water contact angles on each polymer surface indicate that poly(styrene-co-allyl alcohol) has the surface most wettable by water. Polymer-water interfacial energies were estimated from pendant drop results and a harmonic mean equation along with contact angles. Two methods were used to estimate the polar and dispersion components of the three polymers. Both methods predicted polystyrene to have the highest interfacial energy against water, and one method predicted poly(styrene-co-allyl alcohol) to have the lowest. A Wilhelmy plate study verified the change in interfacial properties as a function of contact time with water. A study of the heats of adsorption of lysozyme by each substrate using a modified Tien-Calvet microcalorimeter demonstrated the suitability of the substrates for microcalorimetry.

High-performance anion exchange of small anions with polyethyleneimine-coated porous zirconia

The preparation and chromatographic characterization of an ion-exchange high-performance liquid chromatographic support by deposition and crosslinking of polyethyleneimine (PEI) on the surface of porous zirconia is described. Adsorption and evaporation methods were used for coating PEI onto the zirconia particles. These two stationary phases were compared by elemental analysis, ion-exchange capacity and by chromatography. High efficiency and good selectivity were observed for inorganic and organic anions. The addition of a strong, hard Lewis base to the mobile phase dramatically improved the peak shape and efficiency of para benzoic acid derivatives. PEI-coated zirconia showed a distinct elution sequence for organic anions when compared to bare zirconia or silica-based phases. The polyamine coated zirconia was stable over a pH range from 2.75 to 9. Flow studies, using nitrite as a probe solute, showed that both coating procedures produced packed columns with good mass-transfer properties.

The affinity technology in downstream processing

The quality criteria imposed on several biochemicals are stringent, thus, high-separation purification technology is important to downstream processing. Affinity-based purification technologies are regarded as the finest available, and each one differs in its purifying ability, economy, processing speed and capacity. The most widely used affinity technology is classical affinity chromatography, however, other chromatography-based approaches have also been developed, for example, perfusion affinity chromatography, hyperdiffusion affinity chromatography, high-performance affinity chromatography, centrifugal affinity chromatography, affinity repulsion chromatography, heterobifunctional ligand affinity chromatography and the various chromatographic applications of 'affinity tails'. On the other hand, non-chromatographic affinity technologies aim at high throughput and seek to circumvent problems associated with diffusion limitations experienced with most chromatographic packings. Continuous affinity recycle extraction, aqueous two-phase affinity partitioning, membrane affinity filtration, affinity cross-flow ultrafiltration, reversible soluble affinity polymer separation and affinity precipitation are all non-chromatographic technologies. Several types of affinity ligands are used to different extents; antibodies and their fragments, receptors and their binding substances, avidin/biotin systems, textile and biomimetic dyes, (oligo)peptides, antisense peptides, chelated metal cations, lectins and phenylboronates, protein A and G, calmodulin, DNA, sequence-specific DNA, (oligo)nucleotides and heparin. Likewise, there are several support types developed and used; natural, synthetic, inorganic and composite materials.

Microspheres for biomedical applications: preparation of reactive and labelled microspheres

This review describes the synthesis and physico-chemical properties of reactive and labelled microspheres useful for biomedical applications. Preparation of microspheres with specific functional groups, fluorescent species, radionuclides and magnetite particles (Fe2O3) are discussed. Physico-chemical properties of microspheres, including surface charge and hydrophilicity/hydrophobicity, are also briefly covered.