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

. WILKE, B. MAGGIO, SA DASSIE, EPM LEIVA

Actas de la Academia Nacional de Ciencias

Año: 2007 p. 123 - 128

0325-7533

Lipid and protein molecules anisotropically oriented at a hydrocarbon-aqueous interface configure a dynamic array of selforganized molecular dipoles. Electrostatic fields applied to lipid monolayers have been shown to induce in-plane migration of domains or phase separation in a homogeneous system. In this work, we have investigated the effect of externally applied electrostatic fields on the distribution of the condensed ceramide-enriched domains in mixed monolayers with sphingomyelin. In these monolayers, the lipid segregates in different phases at all pressures. This allows analyzing by epifluorescence microscopy the effect of the electrostatic field at all lateral pressures since dark domains are always present. Our  observations indicate that a positive potential applied to an electrode placed over the monolayer induces lateral displacements of the dark-condensed domains from the electrode perturbed region. The effect is rather insensitive to the film composition, depends inversely on the lateral pressure and exhibits threshold dependence on the in-plane elasticity. The experimental results were modeled considering the repulsive force created by the electrostatic field on the dipole clusters and an opposing force generated by the dipolar repulsion 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 and the dipolar forces are compensated for two exclusion zone sizes values.