2H-NMR study and molecular dynamics simulation of the location, alignment and mobility of pyrene in POPC bilayers
Barbara Hoff 1, Erik Strandberg 1, Anne S. Ulrich 1, D. Peter Tieleman 2 and Clemens Posten 1*
1 University of Karlsruhe
2 University of Calgary
* To whom correspondence should be addressed. E-mail: clemens.posten{at}mvm.uka.de.
Submitted on September 8, 2004
Revised on October 14, 2004
Accepted on 29 November 2004
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Abstract |
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The alignment of pyrene in a POPC bilayer was investigated using two different approaches, namely solid-state 2H-NMR spectroscopy and molecular dynamics (MD) simulations. Quadrupolar splittings from 2H-NMR spectra of deuterated pyrene-d10 in an oriented lipid bilayer give information about the orientation of C-D bonds with respect to the membrane normal. From MD simulations geometric information is accessible via trajectories. By defining molecular and bond order parameters, the data from MD trajectories and NMR spectra can be compared straightforwardly. To ensure that the results from both methods are comparable, parameters of the experimental and the simulation set-up were chosen to be as similar as possible. From simulations we saw that pyrene prefers a position inside the lipid membrane near the head groups and has no tendency to diffuse from one monolayer of the membrane to the other. The results from simulation and NMR show that the normal of the molecular plane is aligned nearly perpendicular to the bilayer normal. The long axis of pyrene lies preferentially parallel to the bilayer normal within a range of +/- 30°. The results from the two different methods are remarkably consistent. The good agreement can be explained by the fact that the different kind of motions of a pyrene molecule are already averaged within a few nanoseconds, which is the time-scale covered by the MD simulation.
Key Words:
Computer simulation, Lipid membranes, Model membranes, Order parameters, Polycyclic aromatic hydrocarbons, Solid-state 2H-NMR
