Immobilization hosts

Using enantiomeric pure chiral hosts, the separation of racemic substrates hopefully will be possible soon. It seems of great advantage in this context that the guests must not necessarily bear functions, but can be hydrocarbons, heterocycles, and so on. This will also include immobilized hosts bound to resins. Then not only enantiomer separations will be possible, but affinity-type chromatography will allow more specific separations of guests, which can be separated of a mixture of similar substrate molecules. 

The ionic-salt complex includes the groxmd water, which does not participate in the flow and actually is part of the composition of immobile host rocks. This water is positioned in closed porosity, on the interface and within unflushable dead ends of open porosity. 

Wicklein B, Harder M, Aranda P, Ruiz-Hitzky E (2010) Bio-organoclays based on phospholipids as immobilization hosts for biological species. Langmuir 26 5217-5225... 

The attachment of a redox center to a calkarene-substituted PPy has been achieved by the anodic oxidation of pyrrole-substituted trisbipyridylruthenium(II)-Iinked calixarenes [307]. However, only thin films with a low amount of immobilized [Ru(bpy)3] (bpy = 2,2 -bipyridine) were obtained by homopolymerization. Thicker films could be grown from copolymerization with iV-methylpyrrole. Even if the sensory properties of these polymers have not been investigated yet, it can be predicted that the electrochemical and/or luminescent responses of the ruthenium complex could be changed upon the complexation of a guest cation by the immobilized host calixarene. It must be pointed out that such a recognition event had been already observed with a polypyrrole film N-substituted by an aza crown ether-linked bipyridine ruthenimn (II) complex [271]. 

The above two processes employ isolated enzymes - penicillin G acylase and thermolysin, respectively - and the key to their success was an efficient production of the enzyme. In the past this was often an insurmountable obstacle to commercialization, but the advent of recombinant DNA technology has changed this situation dramatically. Using this workhorse of modern biotechnology most enzymes can be expressed in a suitable microbial host, which enables their efficient production. As with chemical catalysts another key to success often is the development of a suitable immobilization method, which allows for efficient recovery and recycling of the biocatalyst. 

Wei, Y., Xu, J., Feng, Q., Lin, M., Dong, H., Zhang, W.-J. and Wang, C. (2001) A novel method for enzyme immobilization direct encapsulation of add phosphatase in nanoporous silica host materials. Journal of Nanoscience and Nanotechnology, 1, 83-93. 

Recent reports describe the use of various porous carbon materials for protein adsorption. For example, Hyeon and coworkers summarized the recent development of porous carbon materials in their review [163], where the successful use of mesoporous carbons as adsorbents for bulky pollutants, as electrodes for supercapacitors and fuel cells, and as hosts for protein immobilization are described. Gogotsi and coworkers synthesized novel mesoporous carbon materials using ternary MAX-phase carbides that can be optimized for efficient adsorption of large inflammatory proteins [164]. The synthesized carbons possess tunable pore size with a large volume of slit-shaped mesopores. They demonstrated that not only micropores (0.4—2 nm) but also mesopores (2-50 nm) can be tuned in a controlled way by extraction of metals from carbides, providing a mechanism for the optimization of adsorption systems for selective adsorption of a large variety of biomolecules. Furthermore, Vinu and coworkers have successfully developed the synthesis of... 

Porous polymer materials, especially in particulate form, are of interest in a diverse range of applications, including controlled drug delivery, enzyme immobilization, molecular separation technology, and as hosts for chemical synthesis [101-104]. MS materials have been used as hosts for the template synthesis of nanoporous polymer replicas through in situ polymerization of monomers in the mesopores [105-108]. 

Clay minerals or phyllosilicates are lamellar natural and synthetic materials with high surface area, cation exchange and swelling properties, exfoliation ability, variable surface charge density and hydrophobic/hydrophilic character [85], They are good host structures for intercalation or adsorption of organic molecules and macromolecules, particularly proteins. On the basis of the natural adsorption of proteins by clay minerals and various clay complexes that occurs in soils, many authors have investigated the use of clay and clay-derived materials as matrices for the immobilization of enzymes, either for environmental chemistry purpose or in the chemical and material industries. 

A series of enzyme and proteins (met-myoglobin, lysozyme, met-hemoglobin, glucose oxidase, a-chymotrypsin) was also immobilized in a-ZrP by Kumar et al. [134]. Binding constant values clearly confirm the high affinity of the various proteins with the host structure (Table 15.4). 

Immobilization of Enzymes in 3-D Inorganic Hosts 15.4.2.1 Immobilization in Si02... 

---