Influence of DPH on the Structure and Dynamics of a DPPC bilayer

¹ Department of Chemical Physics and Optics, Charles University, Prague, Czech Republic
² Department of Ophthalmology, University of Helsinki, Finland
³ Department of Physics and Physical Oceanography, Memorial University of Newfoundland, Canada
⁴ Laboratory of Physics and Helsinki Institute of Physics, Helsinki University of Technology, Finland

^* To whom correspondence should be addressed. E-mail: ilpo.vattulainen{at}csc.fi.

Submitted on November 1, 2004
Revised on November 24, 2004
Accepted on 2 February 2005

	Abstract

We have conducted extensive molecular dynamics (MD) simulations together with differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) experiments to quantify the influence of free 1,6-diphenyl-1,3,5-hexatriene (DPH) fluorescent probes on the structure and dynamics of a dipalmitoylphosphatidylcholine (DPPC) bilayer. Atomistic MD simulations show that in the membrane-water interface the influence of DPH is minor, while in the acyl chain region DPH gives rise to major perturbations. In the latter case, DPH is found to influence a wide range of membrane properties, such as the packing and ordering of hydrocarbon tails and the lateral diffusion of lipid molecules. The effects are prominent but of local nature, i.e., the changes observed in the properties of lipid molecules are significant in the vicinity of DPH, but reduce rapidly as the distance from the probe increases. Long-range perturbations due to DPH are hence not expected. Detailed DSC and 2H NMR measurements support this view. DSC shows only subtle perturbation to the co-operative behavior of the membrane system in the presence of DPH, and 2H NMR shows that DPH gives rise to a slight increase in the lipid chain order, in agreement with MD simulations. Potential effects of other probes such as pyrene are briefly discussed.

Key Words: DSC, Molecular dynamics simulation, NMR, fluorescent probe, lipid bilayer, lipid membrane

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