Phonon-mediated passive transport in lipid membranes

Through an experiment at the ESRF, scientists from Brookhaven National Laboratory have found evidence for propagating in-plane transverse phonon modes in a DPPC lipid membrane. These transverse phonon modes 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.