Binding of some alkyl-substituted ferrocenes to vesicular aggregates studied by a kinetic method

Abstract

Binding of ferrocene and its 1,1′-dimethyl and butyl derivatives to surfactant vesicles of didodecyldimethylammonium (DDAB), ditetradecyldimethylammonium (DTDAB) and dioctadecyldimethylammonium (DODAB) bromides and to phospholipid vesicles of dipalmitoylphosphatidylcholine (DPPC), has been studied at 20.0°C in aqueous acidic solutions by examining the inhibiting effects of the vesicular aggregates upon the rates of the electron-transfer reactions of iron(III) ions with these substrates. With a given vesicle, the rate inhibition increases with increasing hydrophobicity of the reducing substrates. The binding constants of the ferrocenes show that solubilization in the vesicles depends on both the hydrophobic nature of the reductants and the hydrophobicity and the fluidity of the hydrocarbon vesicular bilayer. Both the binding constants and the incremental Gibbs energy of transfer of a methylene group of the substrates from water to the vesicular phase, provide evidence for the penetration of the ferrocene solubilizates into the hydrocarbon bilayer of the vesicles. The present data are compared with those obtained previously in the presence of non-ionic and cationic single-chain surfactant micelles.