Effect of externally applied electric field on lipid monolayers at the air-water interfase

N. WILKE, BRUNO MAGGIO1, SERGIO A. DASSIE, EZEQUIEL P. M. LEIVA

La Cumbre

Taller; Primera Escuela Argentina de Matemática y Biología; 2005

BioMat

Lipid and protein molecules anisotropically oriented at a hydrocarbon-aqueous interface configure a dynamic array of selforganizedmolecular dipoles. Electrostatic fields applied to lipid monolayers have been shown to induce in-plane migration ofdomains or phase separation in a homogeneous system. In this work, we have investigated the effect of externally applied electrostaticfields on the distribution of the condensed ceramide-enriched domains in mixed monolayers with sphingomyelin. Inthese monolayers, the lipid segregates in different phases at all pressures. This allows analyzing by epifluorescence microscopythe effect of the electrostatic field at all lateral pressures since dark domains are always present. Our observations indicate thata positive potential applied to an electrode placed over the monolayer induces lateral displacements of the dark-condenseddomains from the electrode perturbed region. The effect is rather insensitive to the film composition, depends inversely on thelateral pressure and exhibits threshold dependence on the in-plane elasticity. The experimental results were modeled consideringthe repulsive force created by the electrostatic field on the dipole clusters and an opposing force generated by the dipolarrepulsion between the domains. The electric force was calculated assuming a cylindrical rode homogeneously charged (electrode)at a given distance of the ground (electrolyte solution). Once a steady state of displacement is reached, the electrode andthe dipolar forces are compensated for two exclusion zone sizes values.