Interactions and reactions in restricted polar media. Binding of cyanide ion to hemin in surfactant-solubilized methanol in benzene

Abstract

One molecule of monomeric hemin is solubilized by 2100 ± 400 molecules of uncharged surfactant lgepal CO-530 in benzene containing 0·2%(v/v) methanol. The substrate–surfactant binding constant in this system is (3·5 ± 0·5)× 104 l mol–1. The environment of hemin in this restricted methanol pool is less polar than in bulk methanol. The interaction of cyanide ion with hemin, localized in the polar cavity of surfactant aggregates in benzene, has been treated in terms of a two-step process. Rate (k1, k–1, k2, k–2) and equilibrium (K) constants have been determined. Values for K, k–2, K2/k–1 and k1 in 0·70M lgepal CO-530 in benzene, containing 1·0%(v/v) methanol are 960-times greater, 200-fold smaller, 10-fold greater, and identical, respectively, to those in bulk methanol. The significance of these results are discussed and compared to those available in aqueous surfactant systems.