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The use of achiral surfactant assemblies as a reaction platform for an alkylation reaction resulted in a high enantiomeric excess. Dilauryldimethylammonium bromide (DDAB) vesicles were modified with cholesterol to promote alkylation of N-(diphenylmethylene)glycine tert-butyl ester (DMGBE) with benzyl bromide, resulting in high conversion (∼90%) and high enantioselectivity (up to 80%). The R-enantiomer was formed on using the DDAB vesicles, whereas the use of phospholipid liposomes prepared from 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) produced an excess of the S-enantiomer. Considering the chemical structures of the reaction substrates and amphiphiles as well as the membrane structures and properties of DDAB vesicles and DOPC liposomes, it is suggested that the enantiomeric excesses result from the location of the quaternary amine of the amphiphiles and the DMGBE at the outer surface of the membrane. We show that the enantioselective reaction at the surface of the self-assembly could be regulated by adjusting the chemical structures and resulting membrane properties of the self-assembly.

Artificial vesicles formed from sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in aqueous solution are used successfully as additives for enzymatic oligomerizations or polymerizations of aniline or the aniline dimer p-aminodiphenylamine (PADPA) under slightly acidic conditions (e.g., pH 4.3 with horseradish peroxidase and hydrogen peroxide as oxidants). In these systems, the reactions occur membrane surface-confined. Therefore, (i) the physicochemical properties of the vesicle membrane and (ii) the interaction of aniline or PADPA with the AOT membrane play crucial roles in the progress and final outcome of the reactions. For this reason, the properties of AOT vesicles with and without added aniline or PADPA were investigated by using two fluorescent membrane probes: 1,6-diphenyl-1,3,5-hexatriene (DPH) and 6-lauroyl-2-dimethylaminonaphthalene (Laurdan). DPH and Laurdan were used as "sensors" of the membrane fluidity, surface polarity, and membrane phase state. Moreover, the effect of hexanol, alone or in combination with aniline or PADPA, as a possible modifier of the AOT membrane, was also studied with the aim of evaluating whether the membrane fluidity and surface polarity is altered significantly by hexanol, which, in turn, may have an influence on the mentioned types of reactions. The data obtained indicate that the AOT vesicle membrane at room temperature and pH 4.3 (0.1 M NaH

The micro-polarity and micro-viscosity of liposome membranes were evaluated to develop a platform for the localization of hydrophobic substrates in aqueous solution. The distribution ratios of benzaldoxime (BO) onto the zwitterionic 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposome and onto the cationic 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) liposome were almost the same, while those of benzonitrile oxide (BNO) onto DOTAP liposomes were higher than those of BO. Through the analysis of a polarity-sensitive 6-lauroyl-2-dimethylaminonaphthalene, the membrane surface of the DOTAP liposome was found to be dehydrated in the presence of substrates. Using a fluorescent probe 1,6-diphenyl-1,3,5-hexatriene, we found that the micro-viscosity of the DOTAP liposome membrane increased with BNO. These results indicate that the interaction of hydrophobic substrates induce variations in the microscopic membrane environment.

The hydrophobic interior of a liposome membrane was used as a platform for the organic synthesis of hydrophobic compounds in water. The 1,3-dipolar cycloaddition of benzonitrile oxide (BNO) and N-ethylmaleimide (EMI) in liposome suspensions was carried out, and an increase in the reaction rate constant was observed depending on the liposome characteristics. While the reaction rate constant in 1,4-dioxane was 1.5 times higher than that in water, the reaction rate constant in an aqueous solution of cationic 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) liposome was 3 times higher than in water. The amount of substrate, BNO, accumulated in the DOTAP liposome was higher than that in 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP), indicating that BNO prefers to be distributed in the liposome membrane in the liquid-disordered phase. The membrane polarity, GP340, as monitored by Laurdan, varied with the presence of BNO, while EMI slightly affected the membrane properties of the liposomes. These results suggest that the pseudo-interphase afforded by the liposome membrane can promote the 1,3-dipolar cycloaddition between BNO and EMI in water.