Ultrafast Energy Migration Pathways in Self-Assembled Phospholipids Interacting with Confined Water

Phospholipids self-assembled into reverse micelles in benzene are introduced as a new model system to study elementary processes relevant for energy transport in hydrated biological membranes. Femtosecond vibrational spectroscopy gives insight into the dynamics of the antisymmetric phosphate stretching vibration νAS(PO2)−, a sensitive probe of local phosphate–water interactions and energy transport. The decay of the νAS(PO2)− mode with a 300-fs lifetime transfers excess energy to a subgroup of phospholipid low-frequency modes, followed by redistribution among phospholipid vibrations within a few picoseconds. The latter relaxation is accelerated by adding a confined water pool, an efficient heat sink in which the excess energy induces weakening or breaking of water–water and water–phospholipid hydrogen bonds. In parallel to vibrational relaxation, resonant energy transfer between νAS(PO2)− oscillators delocalizes the initial excitation.