Membrane phase transition during heating and cooling: molecular insight into reversible melting
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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.
KeywordsMolecular dynamics DPPC Phase transition Heating/cooling rate Reversible melting Melting seed
This work was supported by the German Science Foundation (DFG) within the Research Training Group 1962—Dynamic Interactions at Biological Membranes, the SFB1027—Physical Modeling of Non-Equilibrium Processes in Biological Systems, and by a scholarship from the China Scholarship Council (CSC, to LS).
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