Enzyme-catalyzed emulsion

It appears from a survey of the literature that the essential properties of micelles in nonpolar solvents are understood, namely their stability and variations of size, the dissociation behavior, and their solubilizing capacities. Reverse micelles can dissolve relatively large amounts of water (1-10% w/v depending on emulsion formula) as well as polar solutes and, of course, water-soluble compounds. Consequently, they can be used as media for a number of reactions, including enzyme-catalyzed reactions. Very few attempts to investigate such reverse micelles at subzero temperatures are known, in spite of the fact that hydrocarbon solutions present very low freezing points. 

Vitamin A in foods is present in its ester form and, after enzyme-catalyzed hydrolysis, it is absorbed into the gastrointestinal tract. After forming an emulsion in the presence of bile salts and pancreatic juices, it is incorporated into molecules of chylomicrons (Olson, 1996). Other forms of carotenoids are oxidatively converted to retinal in the intestinal mucosa. Then, via lymphatic vessels, it is transported from the bloodstream to the liver (Cortner et al., 1987). Vitamin A is primarily stored in the liver, and is also found in ester form in lipocytes. Transport from the liver depends on the level of retinol binding proteins (RBP) (Wolf and Phil, 1991). Vitamin A is well absorbed... 

The use of enzymes to lyse cells, hydrolyze fat emulsions, solubilize proteinaceous colloids, liquify or saccharify starch gels and granules, and degrade various components of celluloslc substrates indicates that many substrates are present in a particulate form. Kinetic forms for such enzyme catalyzed reaction rates are here noted, and will be revisited in the subsequent discussion of immobilized enzyme kinetics. 

A recent study with biotechnology applications relates to amino acid extraction. Schugerl and co-workers (71 ) used a quaternary ammonium carrier in an emulsion liquid membrane system for enzyme catalyzed preparation of L-amino acids. Frankenfield et al. (72) discuss a wide variety of biomedical ELM applications including enzyme encapsulation, blood oxygenation, and treatment of chronic uremia. 

There are many unique polymerization processes which share a conunon heritage with emulsion polymerization, but which often are unrecognized as such. It is the purpose of this review to describe some of these emulsion polymerization-like processes and their products. Some further definition is in order unconventional emulsion polymerizations can be described as those processes whereby the product is a polymer latex that physically resembles latex from emulsion polymerization and cannot be grouped into any other recognized form of heterogeneous polymerization. In many cases the reasons why a process is not recognized as an emulsion polymerization is that the polymerization is not via a free-radical process. This review (hscusses four distinct types of polymerization processes, all of which have examples that produce latex particles and in many ways can be described as unconventional emulsion polymerizations. These are free-radical polymerization, ionic polymerization, transition metal catalyzed polymerization and enzyme-catalyzed polymerization. The precise systems discussed in this review are described in Table 23.1. 

From the environmental viewpoint, the solvent used for coating or film-forming materials is important. The macromonomer technique was therefore applied to form a miniemulsion system of PLA-graft copolymers, as a typical example of the use of water as a green solvent. Four MMm macromonomers (m = 4, 6, 8, and 12 Scheme 1) were prepared and used as comonomer. In the copolymerization, BMA or BA was employed as the vinyl monomer (reaction 2, Scheme 1) [41]. Sodium dodecyl sulfate (SDS) and sodium dioctyl sulfosuccinate (PEREX), both anionic, were found to be appropriate surfactants. To form a stable emulsion system, ultrasound sonication was applied to the mixture of comonomers and surfactant in water before the copolymerization. Then, radical copolymerization was carried out (Table 3) [41, 42]. Relevant to the use of water as reaction solvent. Sect. 4 describes the use of green solvents in enzyme-catalyzed polymerizations. 

Deposition on fibers or fabrics Vapor phase deposition Deposition in nanoscale matrices Photochemically initiated polymerization Enzyme-catalyzed polymerization Polymerization using electron acceptors Miscellaneous polymerization methods Routes to more processible polyanilines Emulsion polymerization Colloidal polyaniline dispersions Substituted polyanilines... 

Lipases (E.C. 3.1.1.3.) catalyze the hydrolysis of lipids at an oil/water interface. In a membrane reactor, the enzymes were immobilized both on the side of the water phase of a hydrophobic membrane as well as on the side of the organic phase of a hydrophilic membrane. In both cases, no other means for stabilization of the emulsion at the membrane were required. The synthesis reaction to n-butyl oleate was achieved with lipase from Mucor miehei, which had been immobilized at the wall of a hollow fiber module. The degree of conversion reached 88%, but the substrate butanol decomposed the membrane before the enzyme was deactivated. 

In a lipase-catalyzed reaction of a water-insoluble oily substrate, the enzyme reversibly adsorbs at the substrate-water interface, and the enzymatic reaction takes place at that interface. The interfacial area strongly depends upon some physical parameters of emulsion, such as the size of the emulsion droplets as well as the amount of the substrate present. However, the importance of the... 

Membrane reactors using biological catalysts can be used in enantioselective processes. Methodologies for the preparation of emulsions (sub-micron) of oil in water have been developed and such emulsions have been used for kinetic resolutions in heterogeneous reactions catalyzed by enantioselective enzyme (Figure 43.4). A catalytic reactor containing membrane immobilized lipase has been realized. In this reactor, the substrate has been fed as emulsion [18]. The distribution of the water organic interface at the level of the immobUized enzyme has remarkably improved the property of transport, kinetic, and selectivity of the immobilized biocatalyst. 

Another example of the presence of a surface altering the course of a reaction is provided by the studies of Wasteneys and Borsook (08). It has already been mentioned (Section VI) that the presence and nature of an oil-water interface modified considerably the acid- and basecombining properties of the complex derivatives whose formation from peptides and an enzyme was catalyzed by an emulsion of oil. 

Shin and Kim developed various methods aimed at increasing the product concentrations of transaminase catalyzed amine resolutions, through the contin uous removal of product ketone from the reactions (Figure 14.21). The application of an aqueous/organic two phase system to the co transaminase catalyzed resolution of racemic ( methylbenzylamine 1 was found to be superior to an aqueous only system in product concentration obtained [26, 27]. A drawback of the biphasic system was an increased enzyme deactivation rate compared to the aqueous only system due to the aqueous/organic emulsion. Another disadvantage was the... 

Li N, and Sakaki K, Performance of an emulsion enzyme membrane reactor combined with premix membrane emulsification for lipase-catalyzed resolution of enantiomers, J. Mem. Sci. 2008 314 183-192. 

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