Correlation and dynamics of acyl-chain isomerization rotation in di-myristoyl-phosphatidylcholine bilayers

The dielectric behavior of hydrated di-myristoyl-phosphatitylcholine (DMPO) bilayers was investigated as a function of temperature at frequencies from 4 to 12 GHz. A steplike increase of the dielectric constant occurs at the chain melting phase transition. It is related to a dielectric dispersion due to the onset of the acyl-chain isomerization rotation. The measured dielectric response, with its unexpectedly high values, is interpreted as a cooperative rotational motion within larger chain clusters. A lower limit for the cluster size of at least 250 ${\mathrm{CH}}_2$—${\mathrm{CH}}_2$ bonds with correlated rotation is deduced.