REDOX ELECTROCATALYSIS BY TETRACYANOQUINODIMETHANE IN PHOSPHOLIPID MONOLAYERS ABSORBED AT A LIQUID-LIQUID INTERFACE

Electron-transfer reactions at the water/1,2-dichloroethane interface with an adsorbed phospholipid monolayer have been studied for three or ganic redox couples: TCNQ, Ru(TPP)(py)2 and Lu(PC)2. The presence of a monolayer at the immiscible interface inhibited electron-transfer rea ctions to increasing extents on going from TCNQ to Ru(TPP)(py)2 to Lu( PC)2. This effect is attributed to the different Gibbs energies of tra nsport across the monolayer of each species resulting from size effect s, which prevent the approach of the redox centres present in the adjo ining phase. Electron transfer mediated by TCNQ in a redox electrocata lytic cycle has been observed between the ruthenium(II) porphyrin comp lex, Ru(TPP)(py)2, and aqueous Fe(CN)63-/4-. The differences in rates of electron transfer for the three compounds are discussed in terms of their structures and of the distances of closest approach between red ox centres present in the different phases.