HPLC of biological macromolecules: The first decade

Soy protein recovery in a solvent-free process using continuous liquid-solid circulating fluidized bed ion exchanger

Soy protein concentrates and soy protein isolates act as ingredients in bakery, meat and dairy products, baby formulas, starting materials for spun textured vegetable products, and other nutritional supplements. In this study, the effectiveness of a liquid-solid circulating fluidized bed (LSCFB) ion exchanger is demonstrated for the recovery of soluble soy proteins from full fat and defatted soy flour. Under steady-state operating conditions, about 50% of the proteins could be recovered from the feed streams entering the ion exchanger. The LSCFB was shown to be a promising system for the recovery of soy protein from both defatted and full fat soy flour solutions. As the ion exchange process captures dissolved proteins, the system may offer a less damaging form of processing compared with the acid precipitation process where soy protein aggregates form and functionality is affected. In addition, the LSCFB allows simultaneous adsorption and desorption of the proteins allowing for a continuous operation. No prefiltration of feed containing suspended particles is required as well, because fluidization is used in place of packed bed technology to improve on current ion exchange processes.

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.

Regio-specific adsorption of cytochrome c on negatively charged surfaces

Studies are reported on the identification of the chromatographic contact domain of equine cytochrome c during its interaction with negatively charged sorbents. A negatively charged resin was designed that would simultaneously adsorb the protein electrostatically and covalently bind it through amide bond formation to succinate groups coupled to the support in an ester linkage. Protein immobilization occurred through lysine residues participating in electrostatic adsorbed cytochrome c to the resin surface. After covalent bond formation in the interface between the protein and the sorbent, ester linkages coupling succinate groups to the support were hydrolyzed, and the protein was released. Lysine residues on the protein that had participated in covalent capture were labeled with succinate residues. The tagged protein was then tryptic-mapped and the peptides were examined by matrix-assisted laser desorption ionization mass spectrometry to determine the position of the amino acids that had been tagged. Comparing the tagged sites with the X-ray crystallographic structure of cytochrome c, it was concluded that a single face of the protein dominated the adsorption process and the 3-D structure of the protein remained largely undisturbed during adsorption.

Reversed-phase liquid chromatography of proteins and peptides using multimodal copolymer-encapsulated silica

Multimodal copolymer-encapsulated particles for liquid chromatography were prepared by bonding 1-octadecene and unsaturated carboxylic acids on silica particles (5 microm diameter, 300 A pores) for liquid chromatography of proteins. These multimodal copolymer-encapsulated particles can provide both hydrophobic and hydrogen bonding interactions with polar compounds. The chromatographic performance of these multimodal copolymer-encapsulated particles for peptide and protein separations was evaluated under reversed-phase conditions. Compared with typical C8-bonded silica, polymer-encapsulated particles were more stable in acidic mobile phases and provided better recoveries, especially for large proteins (Mr>0.5 x 10(6)). Totally hydrophobic polymer-encapsulated particles were found to produce broad peaks for proteins, and significant improvements were observed by introducing hydrophilic groups (-COOH) onto the polymer-encapsulated surface to form a multimodal phase. For the reversed-phase liquid chromatography of peptides and proteins, improved selectivity and increased solute retention were found using the multimodal polymer-encapsulated particles. More peaks were resolved for the separation of complex peptide mixtures such as protein digests using the multimodal polymer-encapsulated particles as compared to totally hydrophobic polymer-encapsulated particles.

Protein-protein interactions on weak-cation-exchange sorbent surfaces during chromatographic separations

This paper examines the nature of chromatographic separations on a weak cation-exchange material in which immobilized protein coats 24% or less of the sorbent surface. It was found that columns on which proteins were immobilized still behaved as a cation-exchange chromatography sorbents, but their selectivity was different from the parent weak cation-exchange column. This was interpreted to mean that in addition to the normal electrostatic interactions expected in ion- exchange chromatography, protein analytes interact with immobilized protein on the sorbent surface. Anionic proteins were not adsorbed, indicating that immobilized proteins were acting synergistically with ionic stationary phase groups to enhance retention. It is concluded that these protein-protein interactions occur after proteins are captured by the primary interaction mechanism of the column, in this case, electrostatic interaction. Protein-protein interaction is a secondary, lateral process. These lateral interactions were observed between 4% and 24% surface saturation. The significance of this observation is that in preparative chromatography and the case of "fouled" columns, strongly adsorbed proteins could alter the elution characteristics of sample proteins being target for analysis or purification.

Separation of a triterpenoid saponin mixture from Maesa lanceolata: semipreparative reversed-phase wide pore high performance liquid chromatography with temperature control

A mixture of triterpenoid saponins derived from the dried leaves of Maesa lanceolata was separated, without structure deterioration, in its components. Seven fractions (I-VII) of high molecular weight (1234-1358) saponins were obtained on a semipreparative scale using wide pore reversed-phase high performance liquid chromatography with an acetonitrile trifluoroacetic acid (500:0.3 w/w)-water-trifluoroacetic acid (391:0.3, w/w) gradient from 35 to 56% in 30 min. The mobile phase was cooled in an ice bath (0 degrees C) during chromatography in order to prevent bubble formation and to improve the quality of the separation. Freeze-dried fractions IV, V, VI and VII were further separated using solvent systems developed for each of the fractions. Fourteen pure triterpenoid saponins were isolated in this way and their molar weight determined.

Perfusion chromatography

Perfusion chromatography is a technique based on fluid dynamics for reducing stagnant mobile phase mass transfer in liquid chromatography. This is achieved by using supports with large pores that allow mobile phase to flow through particles.

Evaluation of advanced silica packings for the separation of biopolymers by high-performance liquid chromatography. VI. Design, chromatographic performance and application of non-porous silica-based anion exchangers

The linear solvent strength model of Snyder was applied to describe fast protein separations on 2.1-micron non-porous, silica-based strong anion exchangers. It was demonstrated on short columns packed with these anion exchangers that (i) a substantially higher resolution of proteins and nucleotides was obtained at gradient times of less than 5 min than on porous anion exchangers; (ii) the low external surface area of the non-porous anion exchanger is not a critical parameter in analytical separations and (iii) microgram-amounts of enzymes of high purity and full biological activity were isolated.

Micropreparative high-performance liquid chromatography of proteins and peptides

The use of short microbore reversed phase and ion-exchange HPLC columns in the preparation of low level (submicrogram) quantities of proteins and peptides is discussed. The sequential use of columns of differing selectivity to purify complex mixtures is described. An example is given of the use of microbore columns to purify a murine myeloid leukemia inhibitory factor prior to sequence analysis.