Overview of Common Spectroscopic Methods to Determine the Orientation/Alignment of Membrane Probes and Drugs in Lipidic Bilayers

The in-depth location and orientation of membrane probes and drugs inserted in lipidic bilayers are regarded important key-properties that cannot be overlooked during molecular design and synthesis. Several spectroscopic phenomena (e.g. excitonic interaction) and molecular recognition (e.g. ligand-receptor interaction) depend on these properties. However, molecular orientation in lipidic membranes is scarcely addressed. This paper overviews some of the most important techniques and methodologies used to study orientation of molecules relative to the surrounding lipidic matrix, namely: FTIR linear dichroism, UV-Vis linear dichroism, Time-resolved fluorescence anisotropy, NMR, and Surface Plasmon Resonance.