Properties of lipid vesicles: FT-IR spectroscopy and fluorescence probe studies

The structure, conformation and dynamic properties of lipids in lamellar phases can be studied using FT-IR and optical probe techniques, particularly fluorescence spectroscopy. Recent advances in the analysis of FT-IR spectra of lipids and the use of isotopic labelling techniques have provided new insight into the conformational behaviour of the lipid chains in different lamellar phases and have made it possible to distinguish different hydration sites in the lipid head groups. These techniques have been extended to study lipid mixtures and to help determine whether microdomain formation is possible in liquid-crystalline lamellar systems. Fluorescent probe techniques are ideally suited to study lateral diffusion processes in lipid bilayers using either the fluorescence recovery after photobleaching (FRAP) technique or the excimer fluorescence method, the latter monitoring more local dynamic processes. Rotational dynamics and order of probe molecules can be determined by time-resolved fluorescence anisotropy measurements. Both spectroscopic techniques (FT-IR and fluorescence spectroscopy) are suited to gain information on membrane heterogeneity and have improved our understanding of membrane behaviour.