Apparent inhibition of photoredox reactions of magnesium octaethylporphyrin at the lipid bilayer-water interface by neutral quinones.

Neutral quinones rapidly equilibrate across the lipid bilayer, hereby rendering the photoeffects seen in pigmented bilayers sensitive to the redox properties at both interfaces. The lack of photoeffect by quinones themselves and their apparent quenching reactions with aqueous acceptors is thus explained. An aqueous donor is needed on one side to break the symmetry and to allow vectorial electron transfer to be recorded. It is concluded that the neutral quinone accumulates on the polar side of the interface with respect to the hydrophobic pigment. The system may allow the study of kinetics of proton transfer accompanying the redox reactions of the quinones.