Polyacrylamide derivatives to the service of bioseparations

Comparison between mass transfer properties of weak-anion-exchange resins with graft-functionalized polymer layers and traditional ungrafted resins

Glycidylmethacrylate was grafted to Toyopearl HW-65M and subsequently modified with diethylamine to obtain a weak anion exchanger. The degree of grafting was varied from 11 to 50%. The binding capacity for bovine serum albumin was 11 mg/ml for the lowest degree of grafting and 97 mg/ml for the highest degree of grafting. The maximum binding capacity was observed at 27% degree of grafting. The mass transfer properties of the grafted resins and an ungrafted resin(Toyopearl DEAE 650M) were investigated assuming rectangular isotherms. Simple models for reaction kinetics, pore- and surface diffusion and film diffusion were used to describe the concentration-time data in batch mode. The data were best fitted by a pore diffusion model. The estimated pore diffusion coefficients (D(P)) for bovine serum albumin were fitted by a polynome to the degree of grafting with an maximum value at 27% of D(P) = 1.95-10(-11) m2/s. Compared to published data of other ungrafted resins and to the molecular diffusion coefficient of bovine serum albumin in free solution of D(P) = 5.6 10(-11) m2/s, the diffusion in grafted layers seems to be accelerated. The breakthrough curves for columns packed with various resins showed a decrease in sharpness with increasing degree of grafting which could not be described by a simple pore diffusion model using the calculated transport coefficients from batch mode. The shape of the breakthrough curves could be well described by a combined film and pore diffusion model. For the ungrafted Toyopearl DEAE 650M resin the breakthrough curve is more favorable and the influence of film diffusion to the mass transfer is reduced. It can be concluded that grafting will increase the capacity and the pore diffusion in batch mode but in column operation the grafting layer has a film resistance which plays an important role in the overall mass transfer.

Cross-linked poly(N-acetylethylenimine) as an isoelectric focusing matrix

Agarose and polyacrylamide are the gels used for most analytical and micropreparative electrophoresis of biopolymers. In an alternative approach that offers different physico-chemical properties from these standard gels, nonionic hydrogels and amphigels composed of poly(N-acetylethylenimine) (PAEI) and a variety of cross-linkers were prepared and used as anticonvective matrices for isoelectric focusing. PAEI was prepared from the ring opening, ionic polymerization of 2-methyl-2-oxazoline. The N-acetyl side chains were hydrolyzed with aqueous sodium hydroxide to produce secondary amine sites which were used for the attachment of cross-linkers. Several cross-linkers were tested for their suitability for electrophoresis, and the cross-linker system based on the Diels-Alder reaction between a furan and maleimide tethered to PAEI gave a moldable gel that can be reversibly converted to a sol at 80 degrees C. This gel was used for isoelectric focusing under both denaturing and nondenaturing conditions. Several protein standards were resolved as well as was achieved with polyacrylamide.

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.

Manufacture of recombinant proteins with safe and validated chromatographic sorbents

Purification of recombinant proteins to achieve homogeneity, purity, consistency and potency as required for therapeutic proteins and in vivo diagnostics is performed under stringent and validated conditions. As liquid chromatography is one of the major technologies used for this purpose, it has to be carried out according to special regulatory guidelines. One of the reported aspects is the long-term consistency of a chromatographic process and validation of its operation; other aspects described are more sorbent oriented. In-place cleaning and sterilization are also very important aspects, the efficiency of which is dependent on the chosen working conditions and the chemical nature of the sorbents. Drastic cleaning may deteriorate the chromatographic matrices, releasing chemicals that may contaminate the biologicals of interest, which modifying the behaviour of the chromatographic columns. Moreover, leachable compounds, when present, could have adverse effects in case of high toxicity. Determination of leaching levels and toxicity tests are part of the validation steps to turn chromatographic separations into consistent, effective and safe production processes for biologicals.

Molecular modeling of acrylamide derivatives: the case of N-acryloylaminoethoxyethanol versus acrylamide and trisacryl

Molecular mechanics (for evaluation of total energies of individual structures of monomers and oligomers) and molecular dynamics (for evaluating dynamic dependencies of structural features) were used for obtaining information on some unique chemical behavior of a novel N-substituted acrylamide (N-acryloylaminoethoxyethanol; AAEE) vs. conventional acrylamide and trisacryl (N-acryloyl-2-amino-2-hydroxymethyl-1,3-propane diol, an extremely hydrophilic derivative; Tris-A). As free monomers, Tris-A degrades with zero-order and acrylamide with first-order kinetics, whereas AAEE is highly resistant to hydrolysis. It is found that Tris-A (and its dideoxy derivative) is constantly forming hydrogen bonds between the -OH groups and the carbonyl of the amido group (bond distances of 1.64 to 1.70 A); this activates a mechanism of "N-O acyl transfer" which leads to quick degradation of the amido bond even under mildly alkaline conditions. Conversely, AAEE (which also contains an omega-OH group increasing its hydrophilicity) has no tendency to form H-bonds with the amido carbonyl, thus being resistant to the above degradation mechanism. In fact, the oxygen in the ethoxy moiety of the N-substituent chain acts as a preferential partner for H-bond formation with the omega-OH group. In the oligomeric state, it is found that Tris-A (tetrameric and dodecameric structures were simulated) tends to form inter-residue H-bonds (approximately parallel to the growing chain) competing with the intra-residue H-bonds (folding onto the amido carbonyl and approximately perpendicular to the oligomer chain), thus greatly increasing its stability.(ABSTRACT TRUNCATED AT 250 WORDS)

DNA shape and separation efficiency in polymer media: a computerized method based on electrophoretic mobility data

The computer program ELPHOFIT for evaluation of the nonlinear plots of log-(mobility) vs. polymer concentration (Ferguson plots) in terms of molecular and polymer properties has been extended to yield a measure of the molecular sieving capacity of the polymer medium. The usefulness of the extended program, version 2.2, was exemplified by the evaluation of DNA shape and separation efficiency in solutions and gels of agarose and polyacrylamide, using previous reports in the literature as a data base. That application of the extended program yields the following results:(i) The size of migrating DNA can be compared with an equivalent sphere having the same free mobility for a particular set of experimental conditions. The decrease in size of the equivalent sphere with polymer concentration previously demonstrated for agarose solutions applies to all of these polymer media; it reveals a steep, hyperbolic decline of that radius in uncrosslinked polyacrylamide solutions in contrast to the shallow decline in the other three media. (ii) The separation efficiency of polyacrylamide gels exceeds that of uncrosslinked polyacrylamide solutions; the separation efficiency of agarose solutions for DNA smaller than 1 kb in length is higher than that of polyacrylamide solutions. Program ELPHOFIT 2.2 is available on request from the first author.

Polyhydroxy and polyethyleneglycol (meth)acrylate polymers: physical properties and general studies for their use as electrophoresis matrices

A new series of materials have been tested for their suitability as electrophoresis matrices. The mechanical and optical properties of gels composed of polyethyleneglycol (meth)acrylate esters or polyhydroxy (meth)acrylate esters in water and in various concentrations of organic solvents are described. Several crosslinkers including polyethyleneglycol and polyhydroxy di(meth)acrylates, piperazine diacrylate, and bisacrylamide were used in these studies. Electrophoretic migration and separation of a series of protein standards through polyethyleneglycol methacrylate (PEGM) 200, PEGM 400, and glyceryl methacrylate is demonstrated. Further, copolymerization of all of the monomers with acrylamide was performed and the distribution of monomer incorporation into the polymer network calculated. All monomers and copolymers that were examined by IR spectroscopy showed greater than 99% polymerization. These results justify their further study for biomolecule separations.

Structural and functional investigations of cholinesterases by means of affinity electrophoresis

1. After a brief survey of the basic affinity electrophoresis concepts, the usual ways for preparing affinity electrophoresis ligands are examined. 2. Then results obtained on cholinesterases are reviewed. This section includes (a) structural and functional investigations on anionic sites, i.e., study of ligand-induced conformational change, organophosphate-induced "aging," genetic variants, and active-site topology; and (b) characterization of cholinesterase conjugates (hybrid proteins) and glycoinositol phospholipid-anchored cholinesterases. 3. The future prospects of affinity electrophoresis, e.g., investigations on the esteratic site and exploration of the carbohydrate moiety, are emphasized in the concluding section.

Recent developments in electrophoretic methods

13. Given the recent extended review by Vesterberg [J. Chromatogr., 480 (1989) 3-19] of electrokinetic methods, this survey has been restricted to the last decade, which has seen tremendous progress in several fields. DNA electrophoresis has experienced strong developments, both in the sequencing strategies (which have been largely automated with the use of fluorescent probes) and in pulsed field analysis of mega-DNA fragments, which has seen such developments as inverse-field, contour-clamped and rotating gel platforms, all allowing for straight band migration in each lane. Chromosome size mapping has now become a reality. Two-dimensional (2D) maps have also shown a dramatic improvement in performance, largely through the development of immobilized pH gradients, giving highly reproducible protein spots in the 2D plane and allowing the exploration of very narrow pH regions. Blotting techniques, combined with 2D mapping, allow sequence analysis and fingerprinting of a single polypeptide spot in a complex sample without resorting to lengthy chromatographic purification steps. Chromatophoresis generates a novel type of 2D mapping, based on hydrophobicity vs. size, rather than on charge vs. size, by direct coupling of a reversed-phase high-performance liquid chromatographic (HPLC) eluate to sodium dodecyl sulphate electrophoresis. The new rising star, capillary zone electrophoresis, offers speed, a large number of theoretical plates, selectivity and small sample requirements in a highly automated equipment.

Of matrices and men

Matrices used in modern electrokinetic techniques are surveyed. They are essentially three: cellulose acetate, agarose and polyacrylamide gels. The use of cellulose acetate is confined mostly to analyses in clinical chemistry labs. The properties of agarose are discussed, in particular its capacity of forming large-pore structures via supercoiling, i.e. formation of suprafibers with average radii of approximately 20-25 nm. Several modified agaroses are reviewed, in particular the SeaPlaque, SeaPrep, NuSieve, NuFix, Seakem and Isogel brands and a composite agarose-polyacrylamide matrix, quite popular in the seventies for DNA and RNA separations. The field of polyacrylamide gels seems to be bursting, with the large number of crosslinkers described, imparting special properties to such matrices. The properties of new, modified acrylamide monomers, little known in the field of electrophoresis, are evaluated; in particular: trisacryl gels, hydroxyalkyl methacrylate gels and acryloylmorpholine-bisacrylylpiperazine gels, the latter formed by amphiphilic monomers, highly resistant to alkaline hydrolysis. The properties and formulas of a host of acidic and basic acrylamido derivatives (11 of them) used as buffers and titrants for isoelectric focusing in immobilized pH gradients are reviewed here for the first time. The review culminates with a glimpse at a new generation of amphiphatic matrices, such as HydroLink and 'shielded hydrophobic phase' gels, which appear to be the latest developments in the fields of electrophoresis and chromatography, respectively.