Bromine−AOT Charge-Transfer Complexes and Hydrogen-Bond Donor Ability of Water in AOT−isooctane−H₂O Reverse Micelles and Water-in-Oil Microemulsions

Abstract

Changes, induced by aerosol-OT (sodium bis(2-ethylhexyl) sulfosuccinate, AOT), in the absorption spectrum of bromine, are shown to markedly depend on the nature and the hydration of the AOT-aggregates. A chargetransfer complex (CTC) between bromine and monomeric AOT (λ max ) 270 nm, 315 ) 1.4 × 10 3 cm -1 M -1 , and K ) 4 × 10 3 M -1 ) is observed in isooctane, in agreement with a very strong electron donor ability of AOT, attributed to its sulfonate headgroup. In "dry" reverse micelles ([AOT] > cmc), the constant for the CTC formation K ) 1.3 M -1 is markedly smaller. In aqueous reverse micelles, the observed decrease ( 315) is consistent with a competition between water and bromine in the stabilization of the AOT-head groups. Finally, in water-in-oil (w/o) microemulsions (W > 12), the complex disappears. The bromine-tribromide ion equilibrium is also investigated in AOT-w/o microemulsions in the presence of bromide ions. The marked dependence of the equilibrium constant for Br 3formation on the microemulsion composition (W) 12, K ) 178 M -1 ; W g 20, K ) 60 M -1 ; bulk water, K ) 16 M -1 ) is attributed to a change in the transfer free energy of bromide ion from bulk water to the aqueous pseudophase of the microdroplets (δ∆G tr (Br -) ) -2.6 and -1.3 kcal mol -1 for W ) 12 and 20, respectively). The results are discussed in terms of changes in the hydrogen-bond donor ability and polarity of water in AOT-w/o microemulsions.

Control of spontaneous spiral formation in a zwitterionic micellar medium

“…The behavior of iodine, for example, is similar to that of bromine with respect to its ability of forming CTC with amines 44 and anionic surfactants. 42 Moreover, the investigation can also be extended to other self-assembling molecules, like the more biologically relevant phospholipid compounds, in order to find behaviors similar to C 14 DMAO by acting on intermediates with different chemical properties (ionic species, radicals, etc. ).…”

“…At the equilibrium, the concentrations of the complex and of the free reactants are unknown, therefore is impossible to calculate the equilibrium constant (K) for the reaction A1 by means of the classic mass action law and a procedure derived from ref. 42 and 45 and adapted to our purpose was used. The detailed description of the method can be found in the supporting material of the present paper.…”

New features in the dynamics of a ferroin-catalyzed Belousov–Zhabotinsky reaction induced by a zwitterionic surfactant

“…we chose the constants for reaction (4) in order to get a ratio between the forward and the reverse constant roughly equal to 2000. A similar value was calculated for the interaction of bromine with the surfactant sodium bis(2-ethylexhyl)sulfosuccinate (AOT) [33]. All constants were taken from the literature (Ref.…”

Alkaline Fading of Triarylmethyl Carbocations in Self-Assembly Microheterogeneous Media

“…A further point is the drastic changes of water properties with changes in microemulsion composition, altering the hydrogen-bond-donor capacity [189,190].…”