Reactions in vesicles

Vesicles form when the hydrophobic interactions are increased relative to the ionic or dipolar repulsions, as happens when the second hydrophobic residue is present. 

A discussion of the structure of vesicles is beyond the scope of this article, but vesicles can have large effects upon both thermal and photochemical reactions [159]. 

The reaction of OH with 5,5 -dithiobis(2-nitrobenzoic acid) is effectively catalyzed by vesicles of dioctadecyldimethylammonium chloride, as well as by micelles 

Vesicles differ considerably from micelles in several ways. Micelles are very dynamic species, so that both monomeric surfactant and solubilized materials are constantly exchanging between the aqueous and micellar pseudophases. However, vesicles are relatively long-lived species, and can be separated from other materials by techniques such as gel-permeation chromatography, and they can be isolated and the structures determined by electron microscopy (159, 160]. In addition the bilayer has an inside and an outside surface, so that the transport of solutes across the bilayer is of considerable interest. 

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Reactions in vesicles 268 Reactions in microemulsions 271 Submicellar self-assembly aggregates 273... 

Mechanistic studies of organic reactivities in vesicles have focused on two questions the first is the application of the pseudophase model to reactions in vesicles and the second that of reaction at the inner and outer vesicular surfaces. 

This limited amount of kinetic evidence suggests that the kinetic models developed for reactivity in aqueous micelles are directly applicable to reactions in vesicles, and that the rate enchancements have similar origins. There is uncertainty as to the appropriate volume element of reaction, especially if the vesicular wall is sufficiently permeable for reaction to occur on both the inner and outer surfaces, because these surfaces will have different radii of curvature and one will be concave and the other convex. Thus binding, exchange and rate constants may be different at the two surfaces. 

We are approaching the final part of the book, concerned with cellular models based on vesicles. The main keywords are now compartment and (if this word exists) compartmentation. The biological potential of these aggregates is closely related to their physical properties, and for this reason some of these basic characteristics will first be briefly considered. Also, to give a proper background to these properties, it may be useful to compare various kinds of compartments, such as micelles, reverse micelles, cubic phases, and vesicles. This will be useful to understand better biochemical reactions in vesicles, which will be dealt with in the next chapter. 

The road map to the minimal cell. 1 Complex biochemical reactions in vesicles... 

Blocher, M., Walde, R, and Dunn, I. J. (1999). Modeling of enzymatic reactions in vesicles the case of alpha-chymotrypsin. / Biotechnol Bioeng., 62, 36 3. 

The effects of the addition of sugars, long-tailed n-alkyl pyranosides, n-alkyl glycerol ethers and n-alcohols on the properties of di-n-hexadccyldi methyl ammonium bromide (DHAB) vesicles have been studied.54 Upon addition of most additives, an inhibiting effect on the decarboxylation reaction of 6-nitrobenzisoxazole-3-carboxylate anion has been observed relative to the reaction in vesicles without any additive. The largest inhibition was observed in the case of cholesterol. 

The pseudophase kinetic models for speeded or inhibited bimolecular, second-order, reactions are more complex. Here the focus is on reaction between a neutral organic substrate and a reactive counterion in micellar solutions in the absence of oil (d>o = 0, Scheme 4). Micellar effects on reactions of substrates with reactive counterions are important because they illustrate the general differences of micellar effects on spontaneous and bimolecular reactions and also how specific counterion effects influence the results. Pseudophase models also work for bimolecular reactions between two uncharged organic substrates and third-order reactions, reactions in vesicles and microemulsions, which may include partitioning into and reaction in the oil region, reactions of substrates with an ionizable (e.g., deprotonatable) second reactant, and the effect of association colloids on indicator equilibria. ... 

Oxidation reactions in vesicles were also the subjects of intense investigations in order to mimic the active center of cytochrome P450. For instance, the... 

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