Solid supports hydrophobic

The concept of zeolite action was tested in a particular reaction where the enzyme is exposed from the beginning to an acidic environment the esterification of geraniol with acetic acid catalyzed by Candida antarctica lipase B immobilized on zeolite NaA [219]. Lipases have been used for the hydrolysis of triglycerides and due to their ambivalent hydrophobic/hydrophilic properties they are effective biocatalysts for the hydrolysis of hydrophobic substrates [220]. When water-soluble lipases are used in organic media they have to be immobilized on solid supports in order to exhibit significant catalytic activity. 

The liquid liquid partition chromatography (LLPQ method involves a stationary liquid phase that is more or less immobilized on a solid support, and a mobile liquid phase. The analyte is therefore distributed between the two liquid phases. In conventional LLPC systems, the stationary liquid phase is usually a polar solvent and the mobile liquid phase is an essentially water-immiscible organic solvent. On the other hand, in reversed-phase chromatography (RPQ, the stationary liquid is usually a hydrophobic... 

The selection of solvents for LLPC is similar to the selection of solvents in liquid-liquid extraction systems. The solid support has little effect upon the selection of the solvent pair, except for the obvious fact that a hydrophilic support for a polar stationary phase requires a hydrophobic... 

Solid supports for RP-HPLC are, in most cases, silica gel derivatized with cyano, C4, C8, Q8, or diphenyl groups and, therefore, have limited stability at pH values <2.0 or >8.0. Less commonly used supports are polymer based that will withstand high pH. Besides their carbon load, silica gel particles can be of different sizes, shapes, and with pore sizes ranging from 80 to 500 A. Literally hundreds of different columns are available.147 48 A commonly used particle is spherical, 5 pm in diameter, and with 300-A pore size. Whereas C4 and C8 columns are preferred for proteins or very hydrophobic peptides, C18 is most commonly used for a wide variety of peptides. 

A peptide of some 150 residues of GroEL (e.g., residues 191-345) folds stably into a monomer that is functionally active as a chaperone in vitro 97 Further, it can be covalently attached to agarose and other solid supports where the monodispersed fragment is extremely active as a chaperone.98 Crystal structures of recombinant minichaperones reveal that the active site is a flexible hydrophobic patch.99 It fits best to extended /3 strands. The basic function of GroEL is to provide a surface for binding exposed hydrophobic patches of denatured... 

Example 12.5. The stabilizing effect of powders was impressively demonstrated by making liquid marbles in air [549], Liquid marbles (Fig. 12.11) are obtained by making a small amount of water (typically 1 mm3) roll on a very hydrophobic powder. The powder particles go into the interface and completely coat it so that, after spontaneous formation of the spherical drop, only the solid caps of powder particles come into contact with the solid support. 

The CSPs based on chiral crown ethers were prepared by immobilizing them on some suitable solid supports. Blasius et al. [33-35] synthesized a variety of achiral crown ethers based on ion exchangers by condensation, substitution, and polymerization reactions and were used in achiral liquid chromatography. Later, crown ethers were adsorbed on silica gel and were used to separate cations and anions [36-39]. Shinbo et al. [40] adsorbed hydrophobic CCE on silica gel and the developed CSP was used for the chiral resolution of amino acids. Kimura et al. [41-43] immobilized poly- and bis-CCEs on silica gel. Later, Iwachido et al. [44] allowed benzo-15-crown-5, benzo-18-crown-6 and benzo-21-crown-7 CCEs to react on silica gel. Of course, these types of CCE-based phases were used in liquid chromatography, but the column efficiency was very poor due to the limited choice of mobile phases. Therefore, an improvement in immobilization was realized and new methods of immobilization were developed. In this direction, CCEs were immobilized to silica gel by covalent bonds. 

Reversed phase HPLC methods have many supporters who insist that careful application of this technique can deliver log Poct values very reliably (Klein, 1988). When the stationary support is octanol-saturated silica, the process most nearly imitates the completely solvated distribution between phases (Mirrlees, 1976), but great care must be taken to avoid "channeling" in the solid support, especially for hydrophobic solutes where column length is short. 

The use of "generator columns," in which water is flowed slowly through a tube packed with a solid support coated with the chemical, reduces this risk (Wasik et al., 1993). Hydrophobic substances tend to sorb appreciably to solid surfaces such as... 

The two liquids thus formed are immiscible, but in thermodynamic equilibrium. Therefore, we may speak of a dynamic system of two immiscible phases. Figure 3.10 shows an example of a practical system applied to create a dynamic LLC phase system. A practical phase system can be created by pumping a mobile phase through a column, the composition of which corrresponds to a ternary mixture that is in dynamic equilibrium with another mixture (the two mixtures can be connected by a nodal line). If the mobile phase is the more polar one of the two ternary mixtures in equilibrium, then a non-polar (hydrophobic) solid support must be used and a reversed phase system can be generated. If the mobile phase is the less polar of the two mixtures in equilibrium, a polar support is required. 

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