Hydrophilic phase

Lipases catalyse reactions at interfaces, and to obtain a high rate of interesterification the reaction systems should have a large area of interface between the water immiscible reactant phase and the more hydrophilic phase which contains the lipase. This can be achieved by supporting the lipase on the surface of macroporous particles. 

Fig. 4 Leachate toxicity effects of whole leachate (a), aqueous/hydrophilic phase (b) and organic/lipophilic phase (c) on HepG2 cells (modified from [17])...

Connectivity of hydrophilic phase at high sulfonic acid content yields membranes with very high water swelling and thus low mechanical properties... 

I was thinking particularly of electrostatic interactions between enzyme residues and substrate molecules. Let us compare the hydrophilic cytoplasmic phase (say, with dielectric constant e = 80) and the hydrophobic regions within membranes (say, with e = 2). Is it possible that protein-substrate interactions may be enhanced in certain membrane-associated enzyme schemes That is, might specific intermolecular forces play a more significant role in influencing the site-to-site migration of intermediate substrates, as compared to the same system in the hydrophilic phase [R. Coleman, Biochim. Biophys. Acta, 300, 1 (1973) P. A. Srere and K. Mosbach, Anti. Rev. Microbiol., 28, 61 (1974) and H. Frohlich, Proc. Nat. Acad. Sci. (U.S.), 72, 4211 (1975).]... 

The stationary phases include hydrophilic phases that are used with aqueous mobile phases (water or salts) and lipophilic phases that are used with organic solvents such as tetrahydrofuran or chloroform. 

For HPLC, polystyrene spheres are available with pore sizes ranging from 5 nm up to hundreds of nanometers. Particles with a 5-p.m diameter yield up to 80 000 plates per meter of column length. Silica (Table 26-4) with controlled pore size provides 10 000-16 000 plates per meter. The silica is coated with a hydrophilic phase that minimizes solute adsorption. A hydroxylated polyether resin with a well-defined pore size can be used over the pH range 2-12, whereas silica phases generally cannot be used above pH 8. Particles with different pore sizes can be mixed to give a wider molecular size separation range. 

The cell membranes are predominantly a lipid matrix or can be considered a lipid barrier with an average width of a membrane being approximately 75 A. The membrane is described as the fluid mosaic model (Figure 6.2) which consist of (1) a bilayer of phospholipids with hydrocarbons oriented inward (hydrophobic phase), (2) hydrophilic heads oriented outward (hydrophilic phase), and (3) associated intra- and extracellular proteins and transverse the membrane. The ratio of lipid to protein varies from 5 1 for the myelin membrane to 1 5 for the inner structure of the mitochondria. However, 100% of the myelin membrane surface is lipid bilayer, whereas the inner membrane of the mitochondria may have only 40% lipid bilayer surface. In this example the proportion of membrane surface that is lipid will clearly influence distribution of toxicants of varying lipophilicity. 

Both polymeric and silica-based columns are in common use.The polymeric columns are heavily used in the analysis of synthetic polymers and plastics where organic solvents are required. Silica-based columns with hydrophilic bonded phases are used to separate aqueous solutions of macromolecules. Finally, polymeric size-separation columns with hydrophilic phases are available for separation of polysaccharides, peptides, and very small proteins. 

The preparation of some (S)-alcohols by ADH from Rhodococcus erythro-polis has been described quite recently. This was the first report of a continuous production process for hydrophobic compounds. An important prerequisite of this method is a membrane which is resistant to organic solvents. It separates the hydrophilic phase, which contains the enzyme and the coenzyme, from the hydrophobic phase with the substrate and the product. Several products were prepared with this enzyme at a multigram scale (Table 16). 

Microemulsions are defined as isotropic, transparent, and thermodynamically stable (in contrast to conventional emulsions) mixtures of a hydrophobic phase (lipid), a hydrophilic phase (often water), a surfactant, and in many cases a co-surfactant. From a lipid formulation perspective, microemulsions are generally regarded as the ultimate extension of the decreased particle size/increased surface area mantra, because emulsion particle sizes are usually less than 50 nm. Microemulsions also have additional pharmaceutical advantages in terms of their solubilizing capacity [54, 55], thermodynamic stability, and capacity for stable, infinite dilution. 

The preferred method of delivery of oral microemulsion formulations is either as a combination of drug, lipid, and surfactant/cosurfactant (generally filled into soft or sealed hard gelatin capsules) that spontaneously microemulsify in the GIT, or as a microemulsion preconcentrate in which the dose form contains a small quantity of hydrophilic phase and is in itself a concentrated O/W or W/O microemulsion, which becomes diluted or phase inverted in the GI fluids. 

As compared with water, ammonia s increased ability to dissolve hydrophobic organic molecules suggests an increased difficulty in using the hydrophobic effect to generate compartmentalization in ammonia, relative to water. This in turn implies that the liposome, a compartment that works in water, generally will not work in liquid ammonia. Hydrophobic phase separation is possible in ammonia, however, albeit at lower temperatures. For example, Brunner reported that liquid ammonia and hydrocarbons form two phases, where the hydrocarbon chain contains from 1 to 36 CH2 units.5 Different hydrocarbons become miscible with ammonia at different temperatures and pressures. Thus, formation of ammonia-phobic and ammonia-philic phases, analogous to the hydrophobic and hydrophilic phases in water, useful for isolation would be conceivable in liquid ammonia at temperatures well below its boiling point at standard pressures. 

If the oil phase is replaced in an oil in water (o/w) emulsion by a hydrophobic monomer, or the water phase in a water in oil (w/o) emulsion by a hydrophilic monomer, an emulsion is obtained that can be employed as a precursor for the preparation of polymer latexes [10, 11]. Similarly, if both phases are replaced, the oil phase by a hydrophobic phase containing a monomer and the water phase by a hydrophilic phase containing a monomer, the generated emulsion could be employed as a precursor in the preparation of polymer composites [12]. However, concentrated emulsions that are generated and stable at room temperature may become unstable at the polymerization temperature. To be suitable for the preparation of polymers and polymer composites, the concentrated emulsion must first form and, subsequently, it must remain stable at the temperature at which polymerization takes place. The scope of the present section is to investigate the factors that influence the formation and stability of concentrated emulsions at the preparation and polymerization temperatures in order to identify the physico-chemical conditions that ensure their stability [9],... 

With present bonding technology, it is not feasible to produce hydrophilic phases which satisfy all these criteria. The strong interactive adsorption of... 

Conducting fraction/gei that includes the conducting gel or hydrophilic phase with ionogenic groups... 

In order to improve the efficiency of the process, the hydrophilic nature of the catalyst was increased by introduction of w-sulfo groups into both diphenylphos-phino groups of the ligand 6. Under the biphasic reaction system which uses a porous hydrophilic support and conventional organic solvents, the novel catalyst bearing the sulfonylated ligand remains in the hydrophilic phase and can be separated easily. Using the so-called supported phase asymmetric catalyst system, the... 

Furthermore, which mechanism prevails is also determined by the membrane microstructure and water/polymer interactions. A pronounced hydropho-bic/hydrophilic phase separation will result in a well-developed porous structure and, thereby promote hydraulic permeation as the relevant mechanism. In random polymer membranes, which exhibit a smaller extent of ion clustering, water fractions will be more dispersed in the... 

S.2.2.10 Membrane Performance Guidelines The key concept used in this chapter on membrane performance in PEFC is the perception of present-day PEMs as phase-separated systems. A hydrophobic phase of polymer backbones that provides mechanical stability and a hydrophilic phase of water-containing pathways for proton and water mobility are distinguished. 

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