Effect of electric fields on the structure of phosphatidyl choline in a multibilayer system

Polarized attenuated total reflection (ATR)-FTIR measurements were carried out on aligned multibilayers of dipalmitoyl phosphatidyl choline (DPPC) under the influence of high electric fields. The electric fields varied from 0 up to 5.5 x 10(6) V/cm in the hydrocarbon layer and up to 1.1 x 10(6) V/cm in the polar layer of the aligned multibilayer, when the applied potential across the 1-microm-thick multibilayer plus the 0.5-microm-thick air gap reached the value of 1000 V. At relatively low applied potentials of less than 100 V, when the electric fields in the hydrocarbon and in the polar layer were below 5.5 x 10(5) and 1.1 x 10(5) V/cm, respectively, the inhomogeneous field between the two layers is adequate to start driving the polar groups into the hydrocarbon layer, exerting a pressure and penetrating them. This results in distortion of the orientation of the hydrocarbon chains. Only at much higher potentials above 600 and 700 V starts the direct reorientation of the dipoles of the different polar residues by the electric field.