The slow short-time motions of phospholipid molecules with a focus on the influence of multiple scattering and fitting artifacts

TL;DR

This paper investigates the slow short-time motions of phospholipid molecules using quasielastic neutron scattering, highlighting artifacts that can distort analysis and proposing a framework based on glass physics concepts to explain observed behaviors.

Contribution

It identifies and discusses artifacts affecting neutron scattering analysis of phospholipid motions and introduces a novel interpretation framework using glass physics concepts.

Findings

Long-range molecular motion has a flow-like character on 60 ps timescale

Similar velocities observed above and below phase transition

Artifacts can significantly distort motion analysis results

Abstract

Quasielastic neutron scattering is a powerful tool for the study of non-periodic motions in condensed matter as a detailed line shape analysis can give information about the geometry and rate of the scatterers' displacements. Unfortunately, there are also a number of artifacts which can masquerade as signatures of motions and can therefore lead to erroneous results. Their influence on the evaluation of the motions of the phospholipid dimyristoylphosphatidylcholine (DMPC) is discussed. On a 60 ps time scale, the long-range motion of the molecules has a flow-like character with similar velocities above and below the main phase transition. It is proposed that the concepts of dynamical heterogeneities and "floppy modes" developed in glass physics provide a framework to explain the observed behaviour.