Alternative Affinity Approaches

Aqueous two-phase systems have been extensively applied to bimolecular purifications, by attaching affinity ligands to one of a pair of phase-forming polymers, a method known as affinity partitioning. Although a substantial body of research literature is available, few systems appear to have been adopted for commercial purposes. Reactive dyes, with their simple and well-defined coupling chemistries, have generally been favoured as the active ligand. The advantage of affinity partitioning is that the process is less diffusion-controlled, binding capacities are high and the recovery of bound proteins is easier, created by the process operating with fewer theoretical plates than those generated by chromatography columns. This technique has also been combined with affinity precipitation, where a homo-bifunctional ligand composed of two ligand entities connected by a spacer (for example a bis-dye) is used. However, even in combination this approach suffers from considerable nonspecific binding and relatively low purification factors. A review of this combination suggests that it is more suited to large scale, low purity products. In contrast, perfluorocarbon emulsion chemistry utilizing mixer-settlers may offer more promise. By using a series of mixer-settlers connected in a loop a continuous process has been developed. A ligand (usually a reactive dye) is covalently bonded to a high density perfluorocarbon emulsion and contacted with the crude protein solution. After settling in the first tank the emulsion is pumped to a second settler and washed before passing to the third settler for elution. The emulsion is regenerated in the fourth settler. The supernatants from each settler, still containing some unbound target protein, are normally discarded. Although reasonable recoveries and yields are obtained, significant development is needed for this type of system to become competitive with conventional chromatography column methods.

Another favoured research approach to improving efficiency is to use expanded beds. Various techniques have been tried, with the primary objective of eliminating the 'solid bed' effect, where the bed acts as a filter, trapping insolubles and creating significant back-pressure. By partially removing the normal constraints of upper and lower retaining frits, which pack the particles tightly in the bed, the particles can expand, thereby releasing trapped solid impurities. Consequently longer operational cycles and higher flows result. One limitation of the expanded bed system is that adsorption can only be carried out in one stage, resulting in a less efficient process.

Expanded beds are only an intermediate stage towards fluidized beds. Several variations of fluidized bed technology have been adopted to evaluate them for affinity processing. One example is the use of perfluorocarbon emulsions in a countercurrent contactor. The affinity perfluorocarbon emulsion is loaded with crude source material into the base of a column in a similar manner to that of an expanded bed. The adsorbent is then removed from the base of the bed and carried forward through four identical contactors where washing, elution and regeneration are carried out successively. This process is claimed to improve significantly removal of target proteins compared to an expanded bed system.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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