ELECTRIC DOUBLE-LAYER NEAR SOFT PERMEABLE INTERFACES .1. LOCAL ELECTROSTATICS

We have modeled the soft permeable interface between a dielectric, rep resenting the hydrophobic interior of a membrane or protein, and an aq ueous solution. The intention is to study the electric fields in the a queous solution around a biomembrane or a protein within the framework of the ''local'' electrostatic theory, as a function of four paramete rs: the thickness of the interface; the electric charge and dipole den sities, sigma and nu, at the interface; the Debye length of the aqueou s solution. Our principal result is a plot of the sign of the surface potential as a function of sigma and nu. We show that an electrically neutral surface (sigma = 0) can set up an electric field if nu not-equ al 0. For the general case sigma not-equal 0, nu not-equal 0, we show that we can get various signs of the surface potential depending upon the relative magnitudes of sigma and nu and that changes in the interf ace thickness and Debye length can change the sign of the surface pote ntial. Finally, we relate changes in the interface tension to changes in sigma and nu.