Thermodynamics and kinetic investigation of electron transfer reactions of surfactant cobalt(iii) complexes containing diimine ligands with iron(ii) in the presence of liposome vesicles and amphiphilic salt media

Abstract

The kinetics of reductions of surfactant cobalt(III) complexes, cis-[Co(L)₂(C₁₂H₂₅NH₂)₂](ClO₄)₃ (L = imidazo[4,5-f][1,10]phenanthroline, dipyrido[3,2-d:2′,3′-f]quinoxaline and dipyrido[3,2-a:2′,4′-c](6,7,8,9-tetrahydro)phenazine, C₁₂H₂₅NH₂ = dodecylamine) by iron(II) in liposome vesicles (DPPC) and amphiphilic salt ((BMIM)Br) were studied at different temperatures by UV-Vis absorption spectroscopy method under pseudo first order conditions using an excess of the reductant. The reactions were found to be second order and the electron transfer is postulated as outer-sphere. Below the phase transition temperature of DPPC, the rate decreased with increasing concentration of DPPC, while above the phase transition temperature the rate increased with increasing concentration of DPPC. It is concluded that below the phase transition temperature, there is an accumulation of surfactant cobalt(III) complexes at the interior of the vesicle membrane through hydrophobic effects, and above the phase transition temperature the surfactant cobalt(III) complexes are released from the interior to the exterior surface of the vesicle. The effects of amphiphilicity of the long aliphatic double chains of these surfactant complex ions into ionic liquids on these reactions have also been studied. The second order rate constant for the electron transfer reactions were found to increase with increasing concentrations of amphiphilic salts. The results have been interpreted in terms of the hydrophobic effect.