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Electric Field-Induced Changes in Lipids Investigated by Modulated Excitation FTIR Spectroscopy

Michael Schwarzott ^*, Peter Lasch , Dieter Baurecht ^*, Dieter Naumann  and Urs Peter Fringeli ^*

^* Institute of Physical Chemistry, University of Vienna, A-1090 Vienna, Austria; and Robert Koch-Institut, 13533 Berlin, Germany

Correspondence: Address reprint requests to Urs Peter Fringeli, Institute of Physical Chemistry, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria. Tel.: +43-1-4277-525-30; Fax: +43-1-4277-9525; E-mail: urs.peter.fringeli{at}univie.ac.at.

The effect of electric fields on dry oriented multibilayers of dimyristoylphosphatidylcholine (DMPC) was investigated by transmission Fourier transform infrared electric field modulated excitation (E-ME) spectroscopy. A periodic rectangular electric potential (0–150 V, 1.25 Hz, 28.4°C ± 0.2°C) was applied across the sample. To discriminate electric field-induced effects from possible temperature-induced effects resulting from a current flow (<1 pA) across the sample, corresponding temperature-modulated excitation (T-ME) measurements within the temperature uncertainty limits of ±0.2°C at 28.4°C were performed. T-ME induced reversible gauche defects in the hydrocarbon chains, whereas E-ME resulted in reversible compression of dry DMPC bilayers. Periodic variation of the tilt angle of the hydrocarbon chains is suggested. The degree of absorbance modulation in the CH-stretching region was found to be in the order of 1:700, corresponding to a variation of the bilayer thickness of z = 0.0054 nm. Using a series connection of capacitors as equivalent circuit of the cell resulted in E = (1.2 ± 0.7) x 10⁷ V/m for the electric field in DMPC. Young's elasticity modulus of DMPC could be calculated to be E = 2.2 x 10⁶ Pa ± 1.8 x 10⁶ Pa, which is in good agreement with published data obtained by electric field-dependent capacitance measurements.