Hydrophobic carrier

A) anodic alumina membrane (pore diameter (E) inclusion of the hydrophobic carriers 5 or 6. 

Intracellular Receptors These receptors are in the cytoplasm or nucleus. Drugs or endogenous ligand molecules have to pass through the cell membrane (a lipid bUayer) to interact with these receptors. The molecules must be hydrophobic or coupled to a hydrophobic carrier to cross the cell membrane. 

The characteristics of a support material are of great importance to the measured enzyme activity [79, 101]. Hydrophobic carriers have a low ability to attract water, thus leaving more available for the enzyme, hence Wehtje et al. [102, 103] have shown that celite is a suitable carrier for the PaHnl to yield an immobilized form of the enzyme. In contrast, controlled pore glass (CPG) and Sephadex G25 were found to be less well suited to enzyme support as, using these systems, cyanohydrin synthesis was significantly reduced (over 30%). Sephadex also promoted the spontaneous addition of HCN to benzaldehyde [102]. A series of batch experiments showed that if the solvent (diisopropyl ether) surrounding the immobilised PaHnl contained insufficient water (i. e. less than 2 %), it would be extracted from the enzyme preparation and consequently enzyme activity was lost [102]. These results were the basis for the production... 

Fig. 6 Schematic representation of the synthetic route to obtain constitutional silica mesoporous membranes is (a) filled with mesostructured silica-CTAB, (b) then calcinated, (c) reacted with hydrophobic ODS and finally filled with the hydrophobic carriers. Generation of directional ion-conduction pathways which can be morphologically tuned by alkali salts templating within dynamic hybrid materials by the hydrophobic confinement of ureido-macrocyclic receptors within silica mesopores [130]...

Figure 2.1 Most lipases are interfacially activated. When immobilized on hydrophobic carriers they are assumed to be in their active conformation.

Table 2.2 Recycling of Novozym 435 (CALB immobilized on a hydrophobic carrier) in the kinetic resolution of 1c in toluene at 60°C.

One might intuitively say that, when immobilized on a hydrophobic carrier, this enzyme should be inactive, since the active site might be inaccessible. It seems that the enzyme instead orients itself in such a way that the active site is stiU readily approachable. 

The carboxylesterases involved in the esterification of geraniol and butyric acid have been partially purified they are tightly membrane bound and only the use of a surfactant such as 3-[(3-cholamidopropyl)dimethylammonium]-l-propanesulfo-nate (CHAPS) allowed their removal from cellular membranes. From a biocatalytic point of view, this situation can be seen as if the enzymes were immobilized into a hydrophobic carrier. 

The electron carriers in the respiratory assembly of the inner mitochondrial membrane are quinones, flavins, iron-sulfur complexes, heme groups of cytochromes, and copper ions. Electrons from NADH are transferred to the FMN prosthetic group of NADH-Q oxidoreductase (Complex I), the first of four complexes. This oxidoreductase also contains Fe-S centers. The electrons emerge in QH2, the reduced form of ubiquinone (Q). The citric acid cycle enzyme succinate dehydrogenase is a component of the succinate-Q reductase complex (Complex II), which donates electrons from FADH2 to Q to form QH2.This highly mobile hydrophobic carrier transfers its electrons to Q-cytochrome c oxidoreductase (Complex III), a complex that contains cytochromes h and c j and an Fe-S center. This complex reduces cytochrome c, a water-soluble peripheral membrane protein. Cytochrome c, like Q, is a mobile carrier of electrons, which it then transfers to cytochrome c oxidase (Complex IV). This complex contains cytochromes a and a 3 and three copper ions. A heme iron ion and a copper ion in this oxidase transfer electrons to O2, the ultimate acceptor, to form H2O. 

The advantage of the LMs is integrating extraction and back-extraction of the desired analyte(s) into one step. Using protonation and deprotonation reactions, selected hydrophobic carriers with carboxyl groups have been shown effective in the separation of amino acids, if the carboxyl functionality was ionized [123]. Optimum values of the stability constants of the complexes between particular amino acids and carrier(s) can be found to increase extraction efficiencies. However, the kinetics of mass transfer often has a more pronounced impact on the efficiency of extraction [118]. 

Lipases act in nature on oil-water interfaces and often have hydrophobic domains on their surface. Hence, immobilization by adsorption to a hydrophobic carrier is often a simple and effective way to immobilize Upases. A wide range of different hydrophobic support materials is commercially available, including synthetic acrylic, divinylbenzene-styrene or polypropylene polymers. An example of the latter is Accurel MP 1000, which is available from Membrana. Novozym 435 is immobilized on Lewatit VP OC 1600, a divinylbenzene-cross-linked poly(methyl methacrylate) resin produced by Lanxess (previously Bayer). 

A series of dihydroxamic acid chelators have been designed as hydrophobic carriers of vanadyl. In an assay of lipogenic stimulation in rat adipocytes, RL-252 was maximally effective at molar ratios of 10 1 vanadyl sulfate chelator, suggesting a shuttle mechanism of action. These compounds were electrically neutral, lipid-soluble, and optically chiral they released the bound metal ion when treated with aqueous glutathione solutions. 

Batchelor FR, Doyle FP, Nayler JHC et al. (1959) Synthesis of penicillin 6-amino penicUlanic acid in penicillin fermentations. Nature 183 257-258 Bmggink A (2001) Synthesis of 3-lactam antibiotics. Kluwer Acad Publ, Dordrecht, 335 pp Bmggink A, Roos EC, de Vroom E (1998) Penicillin acylase in the industrial production of P-lactam antibiotics. Org Proc Res Develop 2 128-133 Bryjak J, Trochimczuk AW (2006) Immobilization of lipase and penicillin acylase on hydrophobic carriers. Enzyme Microb Technol 39 573-578... 

The 08- and 09-specific lipopolysaccharides of Escherichia coli lose their serological activity upon mild acid treatment to liberate their polysaccharide (mannan) moieties.Restoration of the activity was achieved by substitution of one or two stearoyl groups per polysaccharide chain. The D-mannans obtained by in vitro biosynthesis were serologically active only when bound to the membrane-associated hydrophobic carrier. 

Strictly aerobic conditions usually reduce the degree of freedom of an ISPR set-up. The oxygen demand of the cells in an external loop for instance can cause problems. Other Hmitations in an aerobic system can arise through vigorous stirring. This causes difficulties in the application of an organic phase (formation of stable emulsions) or hydrophobic carriers (abrasion) in the reactor vessel. 

Figure 7.2 Representation of BLM structure configured to operate in electro-analytical operation. Ion transport processes are hydrophobic carriers (1), pores (2) and passive electrodiffusion via polar binding sites (3), (Reprinted by kind permission of Elsevier Science Publishers, B.V., Amsterdam).

It has been observed that not all porons snpports are suitable for immobilization, owing to the limitations of pore size, which shonld be at least the same as that of the lipase. By studying the adsorption of Rhizomucor miehei lipase on a porous inorganic support, it was found that the activity depended on a pore size in the range of 100 nm. Beyond this value, the activity is independent suggesting that the internal diffusion restriction is insignificant (Bosley and Clayton, 1994). Similar observations have also been noted with the immobilization of Candida rugosa lipase on different hydrophobic carriers of various pore sizes (Al-Duri et al., 1995). 

Ion transport through liquid organic membranes from one aqueous solution into another is a process which has a sequence of at least three steps, i.e. extraction from an aqueous sourse solution into the organic membrane, diffiision through the membrane due to a concentration gr ent, and reextraction into a receiving aqueous solution. In the case of inorganic ion transport facilitated by a low molecular weight carrier, the total process is complicated by reversible chemical interactions of the hydrophilic ion and usually much more hydrophobic carrier. As a result a... 

---