Mutually Beneficial Combination of Molecular Dynamics Computer Simulations and Scattering Experiments.

Nebojša Zec,José Luis Ortega-Roldan,Mario Campana,Robert Barker,Sebastian Busch,Henrich Frielinghaus,Alex C Hendry,Gaetano Mangiapia,Jean-François Moulin,Alexandros Koutsioubas

doi:10.3390/membranes11070507

Abstract

We showcase the combination of experimental neutron scattering data and molecular dynamics (MD) simulations for exemplary phospholipid membrane systems. Neutron and X-ray reflectometry and small-angle scattering measurements are determined by the scattering length density profile in real space, but it is not usually possible to retrieve this profile unambiguously from the data alone. MD simulations predict these density profiles, but they require experimental control. Both issues can be addressed simultaneously by cross-validating scattering data and MD results. The strengths and weaknesses of each technique are discussed in detail with the aim of optimizing the opportunities provided by this combination.

Highlights

Phospholipid-based bilayers are the main components of biological membranes and represent their basic structural elements [1]
The typical membrane length scales are relatively large compared to atomic dimensions, the focus of this work is on scattering by large-scale structures which can be investigated by reflectometry and small-angle scattering methods
The scattering length density (SLD), which describes how strongly a given medium will scatter as a function of its composition, is introduced and used to express the index of refraction, which in turn is used to predict the propagation of neutrons or photons in matter and eventually analyze reflectometry and small-angle experiments

Summary

Introduction

Phospholipid-based bilayers are the main components of biological membranes and represent their basic structural elements [1]. Of special interest in this paper are the scattering methods that give access to the structure and dynamics of the system under investigation. These methods are non-invasive, non-destructive over the duration of the data collection and probe a large sample volume, providing statistically relevant information [15]. The SLD, which describes how strongly a given medium will scatter as a function of its composition, is introduced and used to express the index of refraction, which in turn is used to predict the propagation of neutrons or photons (both considered as waves) in matter and eventually analyze reflectometry and small-angle experiments. Q is a function of the experiment geometry, which we symbolically represent here by θ, and of the wavelength of the radiation used, λ:

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