Abstract
The dielectric constant (epsilon) and refractive index (n) of a bilayer lipid membrane is determined from the known values of the polarizabilities of the carbon-carbon and carbon-hydrogen bonds. It is assumed that the hydrocarbon chains are hexagonally arranged in an all-trans conformation perpendicular to the plane of the membrane. The only variable in the calculation is the average separation between the chains and the theory relates epsilon to this separation. The calculation and results differ significantly from those presented in a 1968 publication by Ohki. It is shown that a thin membrane is not homogeneously polarized by the applied field. This effect is analysed and the dependence of epsilon on the membrane thickness is determined. The theoretical results are in good quantitative agreement with experimental measurements on bulk paraffins and on oriented multilayers of saturated fatty acids. The most important conclusion is that the dielectric constant for an applied field perpendicular to the membrane (which is the appropriate value for capacitance measurements) differs by only a few percent from the value for the macroscopic (bulk) liquid hydrocarbon. Thus the dielectric constant of a bilayer membrane can be approximated by the value for the appropriate bulk hydrocarbon.
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Selected References
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- Cherry R. J., Chapman D. Optical determination of the thickness of thin lipid films. J Theor Biol. 1969 Aug;24(2):137–146. doi: 10.1016/s0022-5193(69)80041-x. [DOI] [PubMed] [Google Scholar]
- Cherry R. J., Chapman D. Optical properties of black lecithin films. J Mol Biol. 1969 Feb 28;40(1):19–32. doi: 10.1016/0022-2836(69)90293-9. [DOI] [PubMed] [Google Scholar]
- Ohki S. Properties of lipid bilayer membranes. Determination of membrane thickness. J Theor Biol. 1969 Apr;23(1):158–168. doi: 10.1016/0022-5193(69)90073-3. [DOI] [PubMed] [Google Scholar]
- Ohki S. Properties of lipid bilayer membranes. Membrane thickness. J Theor Biol. 1970 Feb;26(2):277–287. doi: 10.1016/s0022-5193(70)80018-2. [DOI] [PubMed] [Google Scholar]
- Oki S. Dielectric constant and refractive index of lipid bilayers. J Theor Biol. 1968 Apr;19(1):97–115. doi: 10.1016/0022-5193(68)90008-8. [DOI] [PubMed] [Google Scholar]
- den Engelsen D., de Koning B. Ellipsometry of black lipid membranes of egg lecithin and chloroplast extracts. Photochem Photobiol. 1975 Feb;21(2):77–80. doi: 10.1111/j.1751-1097.1975.tb06631.x. [DOI] [PubMed] [Google Scholar]