Adsorption affinity

Polymers typically exhibit a high-affinity adsorption isotherm as shown in Fig. XI-5 here the adsorbed amount increases very rapidly with bulk concentration and then becomes practically independent of concentration. 

Alpha-1-proteinase inhibitor and antithrombin III are used to treat people with hereditary deficiencies of these proteins. Both can be recovered from Cohn Fraction IV (Table 7) using ion-exchange chromatography (52) and affinity chromatography (197), respectively. Some manufacturers recover antithrombin III directiy from the plasma stream by affinity adsorption (56,198,199). 

Reaction kinetics at phase houndaiies. Rates of adsorption and desorption in porous adsorbents are generally controlled by mass transfer within the pore network rather than by the kinetics of sorption at the surface. Exceptions are the cases of chemisorption and affinity-adsorption systems used for biological separations, where the kinetics of bond formation can be exceedingly slow. 

Porath, J., and Olin, B. (1983) Immobilized metal ion affinity adsorption and immobilized metal ion affinity chromatography of biomaterials. Serum protein affinities for gel-immobilized iron and nickel ions. Biochemistry 22, 1621-1630. 

FIGURE 16.2 Typical adsorption isotherms, relations between amount of adsorbate attached to the surface of adsorbent and its concentration in supernatant. It shows the high-affinity adsorption isotherm, which is typical for many polymers in contact with an active adsorbent in a weak solvent. Up to a certain extent of the surface saturation, the saturation threshold, all macromolecules are attached to the adsorbent surface. 

Once transfectomas have been generated, they must be screened for the production of the desired fusion. The binding site provided by the expression of the VNP heavy chain in J558L cells and association of the heavy chain with the resident light chain means that the protein fusion can be captured on a solid phase by NP or NIP, and detected using commercially available antibody to mouse X chain and an appropriate enzyme conjugate, in a simple ELISA screening procedure. Similarly, purification can be achieved by affinity adsorption of the fusion onto an NP matrix. An immunoblot method is described here for characterization of selected transfectomas, which allows the mol-wt of the fusion product to be estimated. 

Adsorption can be classified into three categories conventional adsorption, ion exchange, and affinity adsorption. 

Fig. 10.7 Principle of affinity adsorption. The specific ligand (L), such as enzyme inhibitor and antigen, is immobilized on a water-insoluble carrier (C). A solute (S) can react selectively with the affinity ligand.

Affinity Adsorption Affinity adsorption is based on the chemical interaction between a solute and a ligand which is attached to the surface of the carrier particle by covalent or ionic bonds. The principle is illustrated in Figure 10.7. 

Affinity adsorption offers high selectivity in many bioseparations. However, the high cost of the resin is a major disadvantage and limits its industrial use. 

Type G is a high-affinity adsorption isotherm. The molecules bind so strongly that no rest can be detected in the solution or gas phase. The difference to the Langmuir type is quantitative not qualitative. It is often observed for polymer or proteins adsorbing from solution. 

Immunoadsorption, an advanced therapeutic modality, focuses on detoxification of patient blood rich in high-molecular-weight pathogenic substances, mostly abnormal autoantibodies such as rheumatoid factors in rheumatoid arthritis (RA) and anti-DNA autoantibodies in systemic lupus erythematosus (SLE). Detoxification of these pathogens will be accomplished through extracorporeal perfusion of the patient plasma or whole blood over an affinity column made of immunoadsorbents. These adsorbents perform their function through the same mechanism as conventional affinity adsorption, where proteins in the liquid phase are adsorbed on the specific ligands immobilized onto an insoluble support. 

L-type describes high-affinity adsorption between the adsorbate and adsorbent and usually indicates chemisorption (e.g., phosphate-soil interactions)... 

Figure 7-11. Purification ot staphylococcal nuclease by affinity adsorption chromatography on a nuclease-specific agarose column (0.8 x 5 cm). The column was equilibrated with 50mM borate buffer, pH 8.0, containing lOmAf CaClj. Approximately 50 mg of partially purified material containing about 8 mg nuclease was applied in 3.2 ml of the same buffer. After 50 ml of buffer had passed through the column, O.IM acetic acid was added to elute the enzyme. 8.2 mg nuclease and all the original activity was recovered. The flow rate was about 70 ml/hour. [From P. Cuatrecasas, M. Wilchek, and C. B. Anfinsen, Proc. Natl. Acad. Sci. US, 61 636 (1968).]...

Klein E, Yeager DH, Seshadir R, and Baurmiester U. Affinity adsorption devices prepared from microporous poly(amide) hoUow fibers and sheet membranes. J. Membr. Sci. 1997 129 31-46. 

Flygare et al. (1990) demonstrated ET monitoring of an affinity-adsorption procedure. Lactate dehydrogenase (LDH) was recovered from a crude solution by affinity binding to a N6-(6-aminohexyl)-AMP-sepharose gel. The LDH activity signal from the ET was used in a PID controller to regulate the addition of... 

Not always do the adsorption isotherms reported for polymers belong to the high affinity type. Low affinity adsorption isotherms are obtained when the molecular weight of the polymer is not too high, or for polyelectrolytes at unfavorable electrostatic conditions. Negligibly low and even negative adsorption of polymers has been also reported. 

The pattern of the curves of quaternary deposition corresponds to a high-affinity adsorption. For many authors, who link the surface affinity for softeners to the ion exchange capacity, such a pattern reinforces the electrostatic attraction mechanism [23,24,30],... 

Figure 1. Breakthrough curve for affinity adsorption. If feed is stopped at effluent concentration CbT, a portion of the column capacity has not been used. A small amount of solute is lost in the effluent.

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