Structure and Dynamics of Lipid Model Membranes: FT-IR- and 2H-NMR-Spectroscopic Studies

FT-IR and 2H-NMR-spectroscopy has been used to study structure and dynamics of specifically labeled phospholipids in model membranes. Three examples for the application of these two spectroscopic techniques are given. 1. 2H-NMR-spectroscopy can be used to study the behavior of pure specifically deuterated model compounds of phospholipids with different head groups like phosphatidylcholines (PC**)) and phosphatidylethanolamines (PE). Line shape simulations of powder spectra and of spectra of oriented samples provide information on the mechanism and correlation times of the molecular reorientations. In mixtures of phospholipids with different head groups 2H-NMR-spectroscopy can be used to study the mixing behavior of lipids. Evidence for lipid clustering in the liquid-crystalline phase comes from different splittings observed for the two components. 2. FT-IR-spectroscopy of 13C = O labeled phospholipids gives information on the hydration behavior of the glycerol back bone. Because of the vibrational isotope effect both carbonyl bands of the ester groups of the lipid can be observed separately when one of the C = O groups is labeled with 13C. FT-IR spectra indicate that both ester carbonyl groups of lipids in hydrated membranes are in contact with water. The amount of hydration depends on the phase state and the nature of the lipid head groups. 3. A combination of 2H-NMR and FT-IR-spectroscopy was used to determine structure and dynamics of phospholipids with ω-cyclohexyl fatty acids. Drastic differences in conformational and dynamical behavior between odd- and even-numbered members of this lipid class could be detected.