Hydration Dependence of the Head Group Mobility in Phospholipid (DMPC) Membranes

Abstract

The dielectric dispersion in the frequency range 2–800 MHz of the zwitterionic dipolar phosphocholine head group has been measured from −20 to +60°C for DMPC depending on the amount of bound water. It is found that the head group rotation shows a sudden change at the gel‐fluid phase transition, 1. the rotation frequency becomes much higher and 2. the related dielectric response becomes much more pronounced in the fluid phase. Below 15 H2O molecules bound per lipid molecule the head group rotation frequency decreases with decreasing number of bound water. This observation reveals for the first time that there is a correlation between hydration dependence of the chain melting temperature and head group rotation. The thermal activation of the head group rotation in the fluid phase made us conclude that three hydrogen bonds have to be broken in order to rotate the head group.

Percolation models of free and bound water under the influence of nearest neighbour interactions

“…We found that Pc increases with decreasing layer thickness D. In figure 5 pc is plotted versus D. The calculations are in qualitative agreement with the experimental finding, that with decreasing number of water molecules per lecithin molecule the subzero , phase transition temperature decreases, too [7,14,16].…”

“…In this way an enhanced chemical potential of the water molecules between phospholipid bilayers was found with decreasing water contents in the bilayer. This is interpreted as a decreased entropy due to a higher degree of order of hydrogen bonded H20 molecules at the lecithin bilayer surface [5][6][7]. In the present work, correlated site percolation calculations are presented on the ice-like diamond lattice.…”

Two-step impact of Amphotericin B (AmB) on lipid membranes: ESR experiment and computer simulations

“…In order to make the simulation similar to the conditions in which the ESR experiments were carried out, the following parameters were used: T ¼ 295 K -corresponding to the temperature of lecithin in the ESR experiment, 2a ¼ 0.50 nm -approximate dimensions of polar heads of phospholipids (Kubica, 2001;Möhwald, 1990;Stigter et al, 1992), " r ¼ 10approximate value of the dielectric constant for the area of phospholipid head-groups (Kaatze et al, 1984;Nimtz et al, 1985).…”

Theoretical evaluation of the distributed power dissipation in biological cells exposed to electric fields

“…While dielectric relaxation of water molecules and dissolved ions, which are the predominant constituents of cytoplasm and cell exterior, starts only in the GHz region, effects of dielectric relaxation of the membrane already emerge in the range of tens to hundreds of MHz [Nimtz et al, 1985;Klo Èsgen et al, 1996]. The main reason for this is the limited rotational mobility of headgroups of membrane lipids.…”

“…Regrettably, this is not the case for lipid bilayers, where direct measurements remain very scarce. Results have been published on relaxation of colloidal suspensions of lipid vesicles [Pottel et al, 1984], homogenized samples with various water±lipid molecular ratios [Nimtz et al, 1985], and more recently on multilamellar bilayer samples [Klo Èsgen et al, 1996]. An alternative, indirect approach to the determination of relaxation data for lipid bilayers is provided by the P-NMR and 2 H-NMR measurements of headgroup mobility [Dufourc et al, 1992;Ulrich and Watts, 1994].…”