Photoredox Reactions in Liposome Systems and its Application to the Conversion of Light Energy into Chemical Energy

Abstract

For designing a system which might effect the conversion of light energy into chemical energy through a coupling of photoredox reactions across membrane, we prepared a dispersion of phosphatidylcholine bilayer liposomes containing chlorophyll a.
The concentration change of Cu²⁺, [Fe(CN)₆]^3- or O₂ in the solution of outer compartment was measured during illumination with the light absorbable by chlorophyll a by the use of ESR, ion selective electrode or oxygen electrode.
The enhancement of the photoreduction of Cu²⁺ by a reductant such as potassium ascorbate localized in a solution of the opposite side of the membrane suggested that photoredox reactions at both the membrane-solution interfaces of a liposome were coupled through the bilayer. Kinetic analysis of the reactions based on a possible reaction scheme was carried out and some of kinetic parameters were determined.
The photo-induced consumption of [Fe(CN)₆]^3- or O₂ in a solution of outer compartment was observed without addition of a particular reductant to the system. The reaction rate was strongly affected by the addition of carbonyl cyanide m-chlorophenylhydrazone (CCCP) to the dispersion. The O₂ consumption was supressed by the existence of [Fe(CN)₆]^3- in a solution of the inner compartment. These facts suggest that the photoredox reactions at both the membrane-solution interfaces will be coupled in this case, through electron transport facilitated by the addition of CCCP across the bilayer membrane.