Direct comparison of elastic incoherent neutron scattering experiments with molecular dynamics simulations of DMPC phase transitions.
Neutron scattering techniques have been employed to investigate 1,2-dimyristoyl-sn -glycero-3-phosphocholine (DMPC) membranes in the form of multilamellar vesicles (MLVs) and deposited, stacked multilamellar-bilayers (MLBs), covering transitions from the gel to the liquid phase. Neutron diffraction was used to characterise the samples in terms of transition temperatures, whereas elastic incoherent neutron scattering (EINS) demonstrates that the dynamics on the sub-macromolecular length-scale and pico- to nano-second time-scale are correlated with the structural transitions through a discontinuity in the observed elastic intensities and the derived mean square displacements. Molecular dynamics simulations have been performed in parallel focussing on the length-, time- and temperature-scales of the neutron experiments. They correctly reproduce the structural features of the main gel-liquid phase transition. Particular emphasis is placed on the dynamical amplitudes derived from experiment and simulations. Two methods are used to analyse the experimental data and mean square displacements. They agree within a factor of 2 irrespective of the probed time-scale, i.e. the instrument utilized. Mean square displacements computed from simulations show a comparable level of agreement with the experimental values, albeit, the best match with the two methods varies for the two instruments. Consequently, experiments and simulations together give a consistent picture of the structural and dynamical aspects of the main lipid transition and provide a basis for future, theoretical modelling of dynamics and phase behaviour in membranes. The need for more detailed analytical models is pointed out by the remaining variation of the dynamical amplitudes derived in two different ways from experiments on the one hand and simulations on the other.
Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, 38042, Grenoble Cedex 9, France.
Bachir
B
Aoun
Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, 38042, Grenoble Cedex 9, France.
Eric
E
Pellegrini
Angewandte Physikalische Chemie, Universität Heidelberg, Im Neuenheimer Feld 253, 69120, Heidelberg, Germany.|Helmholtz-Zentrum Berlin für Materialien und Energie, Lise-Meitner Campus, Hahn-Meitner-Platz 1, 14109, Berlin, Germany.
Marcus
M
Trapp
Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, 38042, Grenoble Cedex 9, France.|CNR-IOM-OGG, c/o Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, 38042, Grenoble Cedex 9, France.
Francesca
F
Natali
University of Milan, via F. lli Cervi 93, 20090, Segrate, Italy.
Laura
L
Cantù
University of Milan, via F. lli Cervi 93, 20090, Segrate, Italy.
Paola
P
Brocca
Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, 38042, Grenoble Cedex 9, France.
Yuri
Y
Gerelli
Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, 38042, Grenoble Cedex 9, France.
Bruno
B
Demé
Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, 38042, Grenoble Cedex 9, France.
Michael
M
Marek Koza
Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, 38042, Grenoble Cedex 9, France.
Mark
M
Johnson
Institut Laue-Langevin, 71 avenue des Martyrs, CS 20156, 38042, Grenoble Cedex 9, France. peters@ill.fr.|LiPhy, UFR PhITEM, Univ. Grenoble Alpes, 71 avenue des Martyrs, CS 10090, 38044, Grenoble, France. peters@ill.fr.
Judith
J
Peters
D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D004548:Elasticity; D008051:Lipid Bilayers / Q000737:chemistry; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D033363:Neutron Diffraction; D044367:Phase Transition
D008051:Lipid Bilayers; D004134:Dimyristoylphosphatidylcholine
Living systems: Biological Matter