Solubilization in AOT−Water Reverse Micelles. Effect of the External Solvent

Abstract

The partition of 1-pyrenemethanol (PyM) between the external medium and AOT/water reverse micelles formed in several organic solvents has been measured and compared with its partition between bulk solvents. The organic solvents employed were n-heptane, cyclohexane, isooctane, dodecane, benzene, chlorobenzene, toluene, and tetrachloroethylene. The partition of PyM in AOT/water/nonpolar solvent reverse micelles is dominated by the free energy of the probe in the external solvent. To evaluate the stability of the probe in micelles dispersed in different solvents, the micellar data were referred to a common (water) solvent. A weakly positive correlation was obtained for the partition of the probe between the different micelles and water. Furthermore, the polarity sensed by PyM is higher in AOT/alkane/water than in AOT/aromatic solvent/water reverse micelles. These results can be explained in terms of two driving forces whose relative importance is determined by the characteristics of the solute and the external solvent. One of them, solvation of the surfactant head by the polar group of PyM, will be disfavored by polar solvents. The second one, interaction of the aromatic part of the micelle associated PyM molecules with the external solvent, would be determined by the solvent/probe affinity, measured by the solvent/ water partition constant.

Kinetics of N-glutaryl-L-phenylalanine p-nitroanilide hydrolysis catalyzed by α-chymotrypsin in aqueous solutions of dodecyltrimethylammonium bromide

“…In this sense, it is tempting to attribute the observed superactivity of the enzyme in the hydrolysis of GPNA to an increase in k 3 associated to conformational changes elicited by the surfactantenzyme interaction. This is confirmed by data obtained for the hydrolysis of 2-NA after reaching the steady-state condition [33].…”

Distribution of amines in water/AOT/n-hexane reverse micelles: influence of the amine chemical structure

“…According to the pseudophase model, the partition constant K can be defined by [6,[18][19][20]30,31] (2)…”

Influence of the Oil on the Properties of Microemulsions as Reaction Media

“…The characteristics of microemulsion aggregates, and hence their ability to incorporate solutes, can be extremely dependent on the particular external solvent. [25][26][27][28][29][30] The most extensive comparative study in this context involved AOT/hydrocarbon/water and AOT/benzene/water microemulsions [31] and showed clustering of benzene molecules around AOT head groups to be seemingly more orderly than in saturated alkanes. [32] However, 1 H NMR studies [33] have shown AOT/benzene microemulsions to contain some free water, even at low W values.…”