Membrane phase transition during heating and cooling: molecular insight into reversible melting

Abstract

With increasing temperature, lipid bilayers undergo a gel-fluid phase transition, which plays an essential role in many physiological phenomena. In the present work, this first-order phase transition was investigated for variable heating and cooling rates for a dipalmitoylphosphatidylcholine (DPPC) lipid bilayer by means of atomistic molecular dynamics simulations. Alternative methods to track the melting temperature \(T_m\) are compared. The resulting \(T_m\) is shown to be independent of the scan rate for small heating rates (0.05–0.3 K/ns) implying reversible melting, and increases for larger heating (0.3–4 K/ns) or cooling rates (2–0.1 K/ns). The reported dependency of the melting temperature on the heating rate is in perfect agreement with a two-state kinetic rate model as suggested previously. Expansion and shrinkage, as well as the dynamics of melting seeds is described. The simulations further exhibit a relative shift between melting seeds in opposing membrane leaflets as predicted from continuum elastic theory.

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