Portland State University
Date of Award
Master of Science (M.S.) in Physics
1 online resource (xi, 88 pages)
Membranes (Biology), Biological transport, Pesticides -- Physiological effect
The effect of the following pesticides on DC electrical conductivity of lecithin-cholesterol membranes has been studied: endothall, paraquat, diquat, 2,4-D, 2,4-DB, 2,4,5-T, 2,4-DCP. It has been found that the ions of endothall, paraquat and diquat are essentially membrane impermeable and that they do not bind to the membrane surface. In contrast, 2,4-D, 2,4-DB, 2,4,5-T and 2,4-DCP induce electrical conductivity in lecithincholesterol membranes and in addition they also cause an increase in the nonactin-K+ membrane conductivity.
The compounds 2,4-D, 2,4-DB, 2,4,5-T and 2,4-DCP basically behave as class II uncouplers. The kinetic scheme of charge transfer across the membrane, based on the assumption that the membrane is permeable both to the negatively charged dimers and to the neutral molecules of pesticides, satisfactorily explains the basic features of the experimental results: the concentration dependence of pesticide-induced membrane conductance, effect of proton concentration on membrane conductance, and the effect of pesticide concentration on the voltage dependence of membrane conductance. It fails to predict the effect of proton concentration on the voltage dependence of membrane conductance.
The enhancement of nonactin-K+ membrane conductance by the pesticide is presumably due to the adsorption of the ionized form of the pesticide at the membrane surface. It was found that the Gouy-Chapman diffuse double layer theory was not applicable for the calculation of surface membrane potential due to the adsorbed ions.
Paulis, Malkanthi, "Electrical Conductivity of Thin Lecithin-cholesterol Membranes due to 2,4-D, 2,4-DB, 2,4,5-T and 2,4-DCP" (1976). Dissertations and Theses. Paper 2555.