Dielectric Relaxation Study of Dynamic Properties of Hydrated Phospholipid Bilayers

The dynamical properties of hydrated di‐myristoyl‐phosphatidylcholin were studied at microwave frequencies. The relaxation frequency and the energy of bound water were determined: the properties of bound water vary quasi‐continuously with the amount of bound water. Water is stronger bound in the fluidlike than in the gel phase. For the first time we could measure directly the trans‐gauche isomerization rotation of the alcyl chains. It was observed that two mechanisms are separately operating at the phase transition of the hydrated bilayers: 1. a change of hydration coupled with a change of headgroup conformation and 2. the chain melting. The binding or release of water is preceding the chain melting or freezing by 1 K. It was found that hysteresis effects of the phase transition depend strongly on the rate of hydration.