Hydrophilic reactants

The importance of the material exchange process can hardly be overemphasized since it is the mechanism whereby the equUibrium miceUar size and polydispersity are reached and maintained, the reversed micelles of ionic surfactants become charged, polar and amphiphilic solubilizates are transported, and hydrophilic reactants can come in... 

Different enzymes - particularly lipases - immobilized in membrane reactors have been studied in the presence of two-liquid phases (Table 5). Organic and aqueous phases containing respectively hydrophobic and hydrophilic reactants are separated by a solid mem-... 

Overcoming solubility limitations of hydrophobic and hydrophilic reactants... 

The solubility characteristics of the substrates are important. The hydrophilic reactant must have negligible solubility in the non-polar domain and vice versa. If the lipophilic substrate is soluble in water to an appreciable extent, a bulk reaction in the water domain will accompany the reaction at the interface. This aspect has been investigated in some detail for another substitution reaction, reaction between potassium iodide and four different benzyl bromides using an oil-in-water microemulsion based on D2O, decane and Ci2E5 as reaction medium [ 16]. The lipophilic components were unsubstituted benzyl bromide, 4-methylbenzyl bromide, 4-isopropylbenzyl bromide and 4-fert-butylbenzyl bromide. As... 

The influence of the framework Si/Al ratio of Beta zeolites on the glucosidation of 1-butanol has also been studied [51]. The framework Si/Al ratio is a very important property which determines the activity and selectivity of zeolites used as catalysts. The Si/Al ratio not only defines the number of potential protons, and therefore the number and strength of acid sites, but it also determines the hydrophilic-hydrophobic character of the surface, in other words, the adsorption properties of the zeolite. In the formation of alkyl glucosides one must take into account that a highly hydrophilic reactant (the monosaccharide) and a mueh more hydro-phobic reactant (the alcohol) must diffuse through the pores and become adsorbed... 

X = H, CH2CH2N(CH3)3, etc.] form bilayers at the cmc which may rearrange to spherical shells enclosing water-filled cavities. These vesicles are highly interesting objects because they provide a means to separate hydrophilic reactants. 

Consider the reaction between a hydrophobic reactant A in phase 1, the organic phase, and a hydrophilic reactant B in phase 2, the aqueous phase ... 

Structures of W/O microemulsions are similar to water pool reverse micelles, and ionic and hydrophilic reactants, which are excluded from the bulk solvent, are highly concentrated in the small microdroplets of water [6,19,20,37], As a result, many reactions of water-soluble reactions are very rapid in these reverse micelles or W/O microemulsions. Much of the work on reactivity and acid-base equilibria has been reviewed [6,112], especially as regards effects of the size of the water pool. ... 

The next question is which of the above-discussed scenarios is most Kkely to be found at the catalyst/hydrated membrane interface. It is generally accepted that the proton conductivity of the membrane depends on the characteristics of ionic clusters formed surrounding the polymer hydrophilic sites, both within the bulk polymeric structure and at the interface with the catalyst [79]. The ionic clusters located at the membrane/catalyst interface are the ones that close the circuit of this electrochemical system. That is, these ionic clusters act as bridges through which protons and other hydrophilic reactants and products may pass from the membrane to the catalyst surface and vice versa during fuel cell operation. To get some insights into the possible formation of ionic clusters, we have analyzed the conformation of a hydrated model nation membrane over Pt nanoparticles deposited on a carbon substrate via classical MD simulations [80] at various degrees of hydration. 

Microemnlsion formation with carbon dioxide in supercritical state instead of a hydrocarbon as nonaqueous solvent is a way to take advantage of the low interfacial tension between H2O and CO2 that conld facilitate reaction between organic snbstrates and hydrophilic reactants at the interface. The next point of... 

Biocatalysis has been used for synthesis of surfactants with different hydrophilic groups that are linked to the hydrophobic fatty chain via ester, amide or glycosidic bonds. Among the most crucial parameters to be considered for enzymatic synthesis are the different solubility characteristics of the hydrophobic and hydrophilic reactants. The use of hydrophilic solvents for increasing the solubility of hydrophilic components increases the toxicity of the medium and affects enzyme activity. An alternative would be to modify the hydrophilic moiety in order to increase its solubility in the hydrophobic component. Solubility may also be improved by increasing the temperature, for which the use of thermostable enzymes would be beneficial. Various groups of surfactanfs for which enzymafic synthesis has been applied are described below. 

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