It has been widely accepted that the thermally excited motions of the molecules in a cell membrane is the prerequisite for the cell to carry its biological functions. On the other hand, the detailed mapping of the ultrafast picosecond single-molecule and the collective dynamics in a cell membrane remains rather elusive. In the present work, for the first time, we provide a convincing experimental evidence for propagating in-plane transverse phonon modes in a single component DPPC membrane and optical phononic modes in binary DPPC-Cholesterol systems. These transverse phonon modes in DPPC exhibit phononic gaps upon temperature increase, providing a direct signature of the existence of transient voids caused by short-lived lipid density fluctuations that mediate solute permeation across the membrane. The finding supports the mechanism of passive transport through entropic expulsion of the solute from higher to lower lipid density regions across the membrane. In binary DPPC-Cholesterol systems, the optical phononic branch exhibits energy-momentum gap. The gap evolution as a function of Chol%mol provides insight into the mechanism defining the membrane’s surface tension.

Phonon-mediated biological functions of a cell membrane

255th National Meeting (2018)

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