DONOR-ACCEPTOR COMPLEXES AND SEMICONDUCTIVITY OF LIPIDS

The 1:1 electron donor-acceptor complexes of 2,4-dinitrophenol with lipids such as egg lecithin, synthetic lecithin and oxidized cholesterol have been studied spectrophoto-metrically in carbon tetrachloride solution. The charge-transfer absorption band has been found in the near ultraviolet for each complex. The equilibrium constants of these complexes have been estimated from their charge transfer bands and are in the order egg lecithin > synthetic lecithin > oxidized cholesterol. The electrical conductivity of bimolecular lipid membranes increases in the presence of iodine, picric acid, 2,4-dinitrophenol and trinitrobenzene. With increasing temperature, the electrical conductivity of bimolecular lipid membranes of oxidized cholesterol has been found to increase exponentially and the activation energies have been measured for membranes in bathing solutions of iodine, picric acid, 2,4-dinitrophenol, trinitrobenzene and water. The increase of electrical conductivity with decreasing activation energy of oxidized cholesterol bimolecular lipid membranes in the presence of different acceptors supports the suggestion of donor-acceptor complex formation. The strength of the acceptors are in the order iodine > picric acid > 2,4-dinitrophenol > trinitrobenzene. In the solid state, the activation energies of fully hydrated oxidized cholesterol crystals and also in the presence of iodine and 2,4-dinitrophenol have been measured. The values are in good agreement with those obtained for the bimolecular lipid membranes and suggest that the same mechanism of semiconduction appears in both cases. © 1969.