Electron reactions and electron transfer reactions catalyzed by micellar systems

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Abstract
The kinetics of the reaction of hydrated electrons with pyrene, pyrene butyric acid, and pyrene sulfonic acid (PSA) have been investigated in aqueous solutions of cetyltrimethylammonium bromide (CTAB). With all three solubilizates the formation of the electron adduct (P−) occurs very rapidly with rate constants ≳1011M−1⋅sec−1. These abnormally high rate constants are shown to be due to fast trapping of eaq− in the positive potential field of the micelle and subsequent efficient penetration of electrons into the micellar interior. A similar enhancement was observed for electron transfer reactions between CO−2 and solutes solubilized in or on the micelle. For example CO−2 readily transfers an electron to pyrene sulfonic acid on the surface of the micelle. This reaction does not occur in homogeneous solution but is catalyzed by the positive electrostatic surface potential. Addition of electrolyte drastically reduces the rate of eaq− and CO2− with solubilizates. The Debye−Hückel theory of electrolytes was invoked to elucidate the role of the charged micellar interface in facilitating the penetration of the electron into the micelle and promoting the electron transfer reaction on the surface. Ion distributions were calculated via solution of a Poisson−Boltzmann equation, generalized to take into account the probable change of the microscopic dielectric constant in the vicinity of the micellar interface.