Adsorption biospecific

Concerning label attachment, all types of binding (covalent, adsorption, biospecific interactions, etc.) are included in the labeling techniques used. 

The protein binding capacity of immobilized dye adsorbents is also high and exceeds the binding capacity normally exhibited by natural biospecific adsorption ligands. 

Biospecific adsorption, 6 396-397, 399 Biospecific binding, in microarray fabrication, 16 385 Biospecific elution, in affinity chromatography, 6 398 Biosphere, selenium occurrence in, 22 78. 

Membrane absorbers are continuous chromatographic supports, which circumvent some of the above-mentioned problems of particulate stationary phases. They were originally derived from membrane (filtration) technology. The immobilization of interactive (ionic, hydrophobic, or biospecific) groups on the surface of microfiltration membranes was found to increase the selectivity of certain separation procedure. Ideally such activated membranes, or membrane adsorbers, allow the selective adsorption of certain substances and substance classes, which may subsequently be eluted by means of a stepwise change of the mobile phase (elution buffer). More complete information on the various types of modern membrane technology can be found in some recent reviews [e.g., 31-33]. 

Adsorption is a physical phenomenon in which some components adsorbates) in a fluid (liquid or gas) move to, and accumulate on, the surface of an appropriate solid adsorbent) that is in contact with the fluid. With the use of suitable adsorbents, desired components or contaminants in fluids can be separated. In bioprocesses, the adsorption of a component in a liquid is widely performed by using a variety of adsorbents, including porous charcoal, silica, polysaccharides, and synthetic resins. Such adsorbents of high adsorption capacities usually have very large surface areas per unit volume. The adsorbates in the fluids are adsorbed at the adsorbent surfaces due to van der Waals, electrostatic, biospecific, or other interactions, and thus become separated from the bulk of the fluid. In practice, adsorption can be performed either batchwise in mixing tanks, or continuously in fixed-bed or fluidized-bed adsorbers. In adsorption calculations, both equilibrium relationships and adsorption rates must be considered. 

Figure 8.2 Variants of affinity chromatography, (a) biospecific AC (b) metal chelate chrom. (c) charge transfer adsorption chrom. (d) hydrophobic interaction chrom. and (e) covalent chrom. (chemisorption). Abbreviations E = enzyme, L = amino acid group, me = meted ion, Rw = electron - withdrawing substituent, Rr = electron -donating substituent taken from ref. (47) with permission.

Membranes used in nonseparation applications may have special structural requirements. Examples are membranes that serve as flow-through chemical reactors (q.v.), in which reactants are converted to products by contact with catalysts inside the pores of the membrane, or as a reversible adsorption matrix based on biospecific inter-... 

At low HSA concentrations the model fits well the whole breakthrough curve (Fig. 5). Two parameters are necessary to describe the model, the column capacity Qx and the number of transfer units n. The overall adsorption process is described by an apparent association rate constant that includes the transport to the active sites and the biospecific interaction (Eq. (6)]. 

Table 2 lists the two parameters n and Qx necessary to describe the model as determined with columns differing by the density of immobilized polyclonal antibody. As previously described, from the variation of the column capacity one can evaluate the contribution to the transport to the binding sites (I/nmt = 0.040) and calculate the effective adsorption rate constant ka. The results agree with those obtained from frontal analysis. The value of the apparent adsorption rate constant k is close to the value of Aa for experiments carried out both at high flow rates and with an immunoadsorbent column of low capacity 22). In this case, the rate-controlling step is the biospecific interaction. 

Sophisticated mathematical models based on the numerical simulation of the chromatographic process consider different kinetic and thermodynamic mechanisms [19], The theoretical approaches describe the biospecific adsorption of monovalent and multivalent adsorbates. They also account for the film mass transfer and pore diffusion contributions to the adsorption process and can be applied to analyze various complex experimental situations. Thus, ideally, the appropriate model will have to be selected to describe the actual chromatographic system. 

The main problem in the determination of association rates at the gas-liquid interface is the interplay of the mass transport effects and the biospecific sorption process. The experimental studies show that both effects are involved in the binding of antigen to the antibody attached to a surface. The variations of the value of the apparent adsorption rate constant with various experimental conditions reveal the importance of the nonideal effects in such experiments. To determine the effective rate of interaction, it is important both to minimize the diffusion resistances and to estimate this contribution by increasing the amount of information. Studies with varying flow rates, particle sizes, ligand densities. 

Molecular structure/biospecific adsorption Surface charge/ionic binding Metals complex formation/coordination complex Molecular size and shape/size exclusion Hydrophobicity/hydrophobic complex formation... 

Invertase Biospecific adsorption adsorption on Con A-bead cellulose... 

In an isolation step, where yield and concentration are more important than purity, the adsorption mechanism can be considered an on/off process, and several alternative contacting schemes can be used. Ligands have been bound to magnetized particles (137, 138) for continuous countercurrent adsorption in magnetically stabilized fluidized beds. Ligands attached to liquid perfluorocarbons (143), to dextran and related polymers (144), or incorporated into liposomes (145), or reversed micelles (146) may be used for biospecific liquid-liquid extraction or "affinity partitioning". Ligands have also been attached to surfactants and biopolymers for selective precipitation of dilute protein species (147, 148). 

The use of small affinity adsorbent particles immobilized in hydrogel beads has been investigated for whole broth processing (1). The adsorbent particles can contain biospecific ligands covalently attached to a porous solid support. A mathematical model was developed to study bioproduct adsorption using immobilized affinity adsorbent beads in batch operation. 

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