Simulation of the lipid membrane with pyrene probe in the gel and liquid crystalline phase

J. Čurdová ¹, P. Čapková ¹, J. Plášek², J. Repáková ³, I. Vattulainen³

¹Department of Chemical Physics and Optics, Charles University, Ke Karlovu 3, 121 16 Prague 2, Czech Republic

²Institute of Physics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague 2, Czech Republic

³Laboratory of Physics and Helsinki Institute of Physics, Helsinki University of Technology, P.O.Box 1100, FI-02015 HUT, Finland

Most of the experimental studies of lipid membrane are based on the fluorescence technique.

Since membrane do not exhibit any fluorescence the fluorescent probes are used. One of the most common is pyrene. The aim of our study was to investigate influence of this pyrene probe to the structure and dynamics of dipalmytoilphosphatidylcholine ( DPPC ) bilayer by means of molecular dynamics simulation. Although, this DPPC bilayer has the main phase tranistion between gel and liquid crystalline phase at 314 K. So we had to make several simulations on different tempretatures and phases.

We have employed 20 ns and 50 ns molecular dynamics simulations of DPPC lipid membrane with different concentrations of pyrene fluorescent probe at temperatures below and above the main phase transition of DPPC. Molecular dynamics simulations shows that the pyrene prefers position in the hydrophobic acyl chains region close to the headgroup region of DPPC molecules, concretely between atoms C4 and C7. The most probable orientation of pyrene is approximately parallel with the bilayer normal but its orientation slightly dependents on the structure of the membrane. Further, pyrene affects ordering of close DPPC molecules. Although this effect with increasing distance from the probe the influence diminishes and at distance larger then 1.5 nm it is negligible. Finally, there was found the decrease of diffusion coefficient at lower temperatures and with additional probes in the DPPC membrane. The summary is that, the presence of pyrene in the membrane do not affect noticeably their properties and it is suitable for study of the lipid membrane.

Fig. 1 A snapshot of the lipid bilayers with pyrene fluorescent probe in a} gel and b) liquid crystalline phase.