Micelles as Media for Photochemical Reactions

1 Models of MiceOar Solutions Influencing the Reactivity of the Solubilizates 

A wide range of chemical reactions in micellar systems depend mainly upon the difference of properties of the micellar phase and the bulk phase. One should only distinguish the solubilized and non-solubilized reactant molecules, the micelles altogether being considered as a pseudophase. For second-order reactions, the intermicellar distribution of reactant molecules should be taken into consideration as discussed above. 

Both models fail to precisely locate the solubilizate molecules within the micelles which can evidently influence the rate constant of the reactions and interfacial exchange of the solubilizates. 

Muckerjee et al. [63-65] proposed a so-called three-phase model of the micellar solutions which considers the molecules adsorbed at the micelle surfaces as a separate phase. This model was applied to allow a comprehensive analysis of the distribution of several organic nitroxides between dodecane and water, their surface activity at this system and the solubilization constants of these nitroxides by SDS and other micelles. The high values of the binding constants of nitroxides by micelles can be explained not by their solubility in the hydrophobic nuclei of the micelles, but by their adsorption at the interface of the micelles and the aqueous phase. 

The existence of ion pairs of hydroxy aromatic anions with polar groups of cationic micelles was proposed by Zaitsev et al. [66] to explain the effective charge of anions close to zero, observed in acid-base photoreactions of hydroxyaromatics in CTAB solutions. Such a value for the effective charge was found by simulation of the values of the diffusion rate constants of hydrogen ions to excited anions of hydroxyaromatics to make the calculated diffusion-controlled protonation reaction of the excited anions rate constants close to experimentally observed ones. In aqueous solution, the excited anions are protonated with diffusional values of the rate constant with some nonsignificant steric factor [67,68]. The three-phase model can help to interpret the reactivity of polar and charged substances in micellar solutions. 

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