Adsorption ionic binding

Membrane bioreactors have been reviewed previously in every detail [3,4,7,8,18], There are two main types of membrane bioreactors (i) the system consists of a traditional stirred-tank reactor combined with a membrane separation unit (Figure 14.1) (ii) the membrane contains the immobilized biocatalysts such as enzymes, micro-organisms and antibodies and thus, acts as a support and a separation unit (Figure 14.2). The biocatalyst can be immobilized in or on the membrane by entrapment, gelification, physical adsorption, ionic binding, covalent binding or crosslinking [3, 7, 18]. Our attention will be primarily focused on the second case where the membrane acts as a support for biocatalyst and as a separation unit, in this study. The momentum and mass-transport process, in principle, are the same in both cases, namely when there is... 

Characteristic Physical adsorption Ionic binding Chelation Covalent bonding Cross-linking Physical entrapment Membrane entrapment Whole cells... 

It is possible to study step-by-step hydration of biomolecules as was first done by Gluckauf. The hydration is localized and connected to ionic binding. Thus, Gregor et al. found that the order of adsorption onto polystyrene was IT > Li" " > Na > K . 

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

Both chemical and physical methods may be used to immobilize biocatalysts while retaining or modifying their activity, selectivity, or stability. Among the techniques used for immobilization of enzymes are physical adsorption, covalent bonding, ionic binding, chelation, cross-linking, physical entrapment, microencapsulation, and retention in permselective membrane reactors. The mode of immobilization employed for a particular application depends not only on the specific choice of enzyme and support, but also on the constraints imposed by the microenvironment associated with the application. 

Adsorption Covalent binding Ionic binding Crosslinking in gel lattice in microcapsule in film... 

Surfactants play a crucial role in emulsification and emulsion stability. A first step in any quantitative study on emulsions should be to determine the equilibrium and dynamic properties of the oil-water interface, such as interfacial tension, Gibbs elasticity, sinfactant adsorption, counterion binding, siuface electric potential, adsorption relaxation time, etc. Useful theoretical concepts and expressions, which are applicable to ionic, nonionic, and micellar surfac-... 

Carrier binding methods Covalent binding Ionic binding Adsorptive binding... 

At very high electrolyte concentrations, where a large fraction of the solvent is expected to be bound to the ions in their solvation shells, a different approach applies, namely one that considers the solvent to be adsorbed on the ionic sites of the electrolyte, according to the BET method. This was suggested by Stokes and Robinson [14] and recently taken up by Marcus [19] as applying to molten salt hydrates. The terms adsorption and binding sites, taken over from the BET method for sorption of neutral small molecules on solid surfaces, should not be taken too literally. The operative expression is ... 

The simplest immobilization method is nonspecific adsorption, which is mainly based on physical adsorption or ionic binding. 

Other immobilization methods are based on chemical and physical binding to soHd supports, eg, polysaccharides, polymers, glass, and other chemically and physically stable materials, which are usually modified with functional groups such as amine, carboxy, epoxy, phenyl, or alkane to enable covalent coupling to amino acid side chains on the enzyme surface. These supports may be macroporous, with pore diameters in the range 30—300 nm, to facihtate accommodation of enzyme within a support particle. Ionic and nonionic adsorption to macroporous supports is a gentle, simple, and often efficient method. Use of powdered enzyme, or enzyme precipitated on inert supports, may be adequate for use in nonaqueous media. Entrapment in polysaccharide/polymer gels is used for both cells and isolated enzymes. 

The previous sections of this chapter have established that NEMCA, or Electrochemical Promotion, is caused by the electrochemically controlled backspillover of ionic species onto the catalyst surface and by the concomitant change on catalyst work function and adsorption binding energies. Although the latter may be considered as a consequence of the former, experiment has shown some surprisingly simple relationships between change AO in catalyst... 

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