Influence of pyrene on the structure and dynamics of DPPC bilayer

 

J. Čurdová 1, P. Čapková 1and J. Plášek2

 

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

 

We have employed 20 ns molecular dynamics simulation to study the influence of pyrene probe on structure and dynamics of dipalmitoylphosphatidylcholine (DPPC) bilayer. Pyrene is an important fluorescent probe used for monitoring excimer fluorescence. Our simulated system contains 128 molecules of DPPC, 3655 water molecules and various concentrations of pyrene. The simulations were performed using the Gromacs package [1].

Concentrations of pyrene in lipid membrane ware 0:128 and 3:128 at different temperatures. We have chosen two temperatures below the main phase transition of DPPC (314,15 K) and two above.

From our analysis of the trajectory we have obtained information about structural changes caused by presence of pyrene probe in the membrane. Molecular dynamic simulation has shown that the pyrene probe is located in the acyl chains region of DPPC. The major influence of the probe on the lipid membrane is in the nearest surroundings of pyrene. On the other hand the influence of pyrene in the membrane-water interface is negligible.

We have found out decreases thickness of the DPPC membrane with increasing temperature. The membrane with pyrene probes is thicker than in the case without pyrene. The thickness of DPPC membrane without pyrene has decreased noticeably between the temperature of 310 K and 325 K which corresponds to main phase transition of DPPC. In the case of membrane with pyrene we have observed similar decrease of thickness already between 293 K and 310 K. These results probably indicate the decrease of temperature of the main phase transition due to the presence of pyrene in the membrane.