Molecular Dynamics of POPC Phospholipid Bilayers through the Gel to Fluid Phase Transition: An Incoherent Quasi-Elastic Neutron Scattering Study

Abstract

The microscopic dynamics for the gel and liquid-crystalline phase of highly aligned D 2 O-hydrated bilayers of 1-palmitoyl-oleoylsn-glycero-phosphocholine (POPC) were investigated in the temperature range from 248 to 273 K by using incoherent quasielastic neutrons scattering (QENS). We develop a model for describing the molecular motions of the liquid phase occurring in the 0.3 to 350 ps time range. Accordingly, the complex dynamics of hydrogen are described in terms of simple dynamical processes involving different parts of the phospholipid chain. The analysis of the data evidences the existence of three different motions: the fast motion of hydrogen vibrating around the carbon atoms, the intermediate motion of carbon atoms in the acyl chains, and the slower translational motion of the entire phospholipid molecule. The influence of the temperature on these dynamical processes is investigated. In particular, by going from gel to liquid-crystalline phase, we reveal an increase of the segmental motion mainly affecting the terminal part of the acyl chains and a change of the diffusional dynamics from a localized rattling-like motion to a confined diffusion.

Orientation of lipids in solid supported lipid bilayers studied by polarized ATR-FTIR spectroscopy1

“…Both lipids are expected to be well above their phase transition temperature and in their liquid phase. The phase transition occurs at −2°C [24] for POPC and close to or below 0°C for POPG [17]. Furthermore, we could prove with our measurements that the orientation of the SSLB stays constant over a wide temperature range as long as it stays in the liquid lipid phase.…”

Structural changes introduced by cholesterol and melatonin to the model membranes mimicking preclinical conformational diseases

“…Membrane fluidity is an indicative of the dynamics of membrane components, consisting of rotational and lateral diffusion, and most importantly, the hydrocarbon chain conformational changes (Wanderlingh et al 2017). The less fluid membrane is characteristic of slower diffusion and a high ratio of all-trans chains that have a minimal freedom in conformational changes.…”

Relaxation dynamics of saturated and unsaturated oriented lipid bilayers

“…In the hydrated state, QENS data have shown similar results, in the gel phase acyl chains are likely only relax through chain-kink diffusion. 10 In recent work, Wanderlingh et al 16-17 have carefully characterized the dynamics of D 2 O hydrated bilayers of DMPC and POPC. Their results revealed three motions occurring in three distinct timescales (between 0.3 and 350 ps): a slow diffusion of the whole lipid within a confined cylinder, conformational relaxations of the lipid chains, and fast uniaxial rotations of the protons around their carbon atoms.…”

“…Most QENS studies have been carried out on saturated lipids such as DMPC, DPPC or DMPS, except for the recent studies on POPC. 16-17 The latter mainly concentrated of proposing a very detailed model analysis of motions rather than discussing on the differences between dynamics and lipid structure. To our knowledge only one QENS measurement of DOPC has been performed but in a mixture with DOPS.…”