Dielectric spectroscopy ofl-α-lysolecithin-packaged gramicidin A

The complex permittivities of l-α-lysolecithin in the absence and presence of the gramicidin A ion channel were measured over the temperature range 0-60°C and over the frequency range 1-1000 MHz. One dielectric relaxation/loss has been observed. It is located at 103.3 MHz (1.54 ns) for a micellar 0.4 M l-α-lysolecithin solution at 20°C, whereas it is shifted to 71.7 MHz (2.22 ns) for a lamellar l-α-lysolecithin-gramicidin A aqueous solution (0.4 M l-α-lysolecithin, 0.0308 M gramicidin A) at 20°C. The dielectric relaxation decreases and the relaxation time increases when gramicidin A is incorporated into l-α-lysolecithin. These dielectric changes are related, in part, to the micellar-to-lamellar lipid phase transition induced by the incorporation of gramicidin A into lysolecithin. We suggest that the diffuse rotational motion of the polar head group Of l-α-lysolecithin contributes to the dielectric relaxation/loss at around 100 MHz.