Effects of terpenes on fluidity and lipid extraction in phospholipid membranes

Electron paramagnetic resonance (EPR) spectroscopy was used in a detailed study of the interactions of several terpenes with DPPC membranes. EPR spectra of a spin-label lipid allowed the identification of two well-resolved spectral components at temperatures below and above the main phase transition of the lipid bilayer. Terpenes caused only slight mobility increases in each of these spectral components; however, they substantially increased the population of the more mobile component. In addition, the terpenes reduced the temperature of the main phase transition by more than 8 °C and caused the extraction of the spin-labeled lipid. Nerolidol, which had the highest octanol-water partition coefficient, generated the highest amount of spin label extraction. Acting as spacers, terpenes should cause major reorganization in cell membranes, leading to an increase in the overall molecular dynamics of the membrane. At higher concentrations, terpenes may cause lipid extraction and thus leakage of the cytoplasmic content.