New Family of Fluorescent Probes for Characterizing Depth-Dependent Static and Dynamic Properties of Lipid/Water Interfaces

The important biological processes that help communicate between intra- and extracellular environments take place at cell membrane/water interface. However, molecular interactions at these interfaces are strongly affected by the depth-dependent hydration and local environmental polarity across the lipid/water interface and also the lipid ordering. A new family of membrane probes based on 4-aminophthalimide (4AP-Cn) have been synthesized, which are of particular interest here because of their extreme sensitivity towards sensing depth-dependent polarity, hydration and energy transfer dynamics at model lipid/water interfaces in sub-nanometre length scale. We envisage that these new probes will be extremely useful for characterizing the static and dynamic properties of naturally occurring membrane/water interfaces as well. This chapter presents the protocol for 4AP-Cn synthesis, as well as detailed experimental and MD simulation methods for measuring depth-dependent polarity, hydration and multi-molecular energy transfer dynamics at lipid/water interfaces of gel and fluid phases of lipid bilayer.