The chameleon effect in zwitterionic micelles: Binding of anions and cations and use as nanoparticle stabilizing agents

Zwitterionic surfactants are relatively overlooked and some of their properties resemble those of ionic and non-ionic surfactants, but others are unique. There is unimpeachable evidence that aqueous solutions of zwitterionic micelles interact specifically with anions, forming “anionoid” micelles, which concentrate cations in the surfaces. Thus, unlike ionic micelles, both the cation and anion of the electrolyte solution can be concentrated at zwitterionic interfaces. This unique effect, known as the “Chameleon Effect”, can be used to catalyze a variety of simple reactions, as the attraction of ions to the micelle brings the reactants together. Furthermore, zwitterionic surfactants stabilize metallic nanoparticles and the magnetically stirred two-phase system could be reused 3 more times in the hydrogenation of cyclohexene (Pd:cyclohexene ratio of 1:18300), with very little loss in activity, and an average turn-over frequency of 1000 h− 1.

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► Interactions of zwitterionic micelles with anions were found to be ion specific.
► Added salts control micellar catalysis in zwitterionic micelles.
► The anion-modified zwitterionic micelles attract cations to the micellar surface.
► Zwitterionic surfactants are successful as palladium nanoparticle stabilizers.
► Zwitterionic micelle stabilized nanoparticles as efficient hydrogenation catalysts.