Dynamical correlation between hydration water and head group of phospholipids at different hydration levels by QENS, complemented by SANS, SAXS and light scattering and absorption methods

 

Topic  57
Main supervisor Aurel Radulescu (a.radulescu@fz-juelich.de)
MLZ institution FZJ
Local supervisor 1
Toshikuni Nagaya
Institution
TEKHNECorporation
Local supervisor 2 Aristeidis Papagiannopoulos
Institution National Hellenic Research Foundation
Local supervisor 3 –
Institution –
Local supervisor 4 –
Institution –
Title
Dynamical correlation between hydration water and head group of phospholipids at different hydration levels by QENS, complemented by SANS, SAXS and light scattering and absorption methods
Description
Biomembranes that work as a wall of the cells consist of phospholipid bilayers, proteins, small amounts of carbohydrates, etc. Within the bilayers, phospholipids exhibit translational/rotational dynamics, thereby allowing waste and nutrients to pass from the inside to the outside of the cell, and vice versa. The water in phospholipid membranes named hydration water (HW) behaves differently than bulk water. Recently, Rahman et al. (Struct. Dyn. 10, 044701, 2023) investigated 1,2-dimyristoyl-sn-glycero-3-phosphoethanoloamine (DMPE) and water mixture by the quasi-elastic neutron scattering (QENS) and molecular dynamics simulation. They observed three different types of DMPE headgroup dynamics and three different types of HW dynamics classified as slow, medium speed, and fast. The slow and medium speed of the both DMPE headgroup dynamics and HW dynamics are translational dynamics while the fast dynamics of the both DMPE headgroup and HW are rotational dynamics. These findings may suggest that the phospholipid headgroup dynamics and HW in the biomembranes are correlated to show similar types of dynamics. Yamada et al. (J. Phys. Chem. B 121, 8322, 2017) observed three different HW dynamics in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayers, namely free HW (similar to bulk water), loosely bound HW (10 times slower than bulk water), and tightly bound HW (100 times slower than bulk water). It is known that the existence of a sufficient amount of loosely bound HW is important for biocompatibility. The real biomembrane consists of a high percentage of zwitterionic (neutral) phospholipids, but it contains some charged phospholipids such as phosphatidylserine (PS), phosphatidylglycerol (PG), phosphatidylinositol (PI), cardiolipin (CL), phosphatidylacid (PA), etc. It is already established that for the small change of the headgroup structure between two phospholipids, the HW dynamics between them could be significantly changed (Seto & Yamada, Appl. Phys. Lett. 116, 133701, 2020).
However, the correlation between the HW and phospholipid headgroup dynamics for the mixture of different phospholipids is still not clarified.
In this project, headgroup and water dynamics in different mixtures of phospholipids in hydrated state will be investigated as multilamellar vesicle (MLV) samples by using incoherent QENS complemented by small-angle neutron and X-ray scattering (SANS, SAXS), FTIR and DLS. The MLV formation of the samples will be identified by SANS and SAXS, while the conformation of the lipid molecules and the correlation between headgroup dynamics and HW dynamics in mixed phospholipid samples will be investigated by FTIR. State-of-the-art light scattering facilities are available for sample preparation. With a powerful and versatile humidity generator coupled to the QENS and SANS/SAXS sample chambers, the hydration conditions of the membranes can be varied in a controlled manner so that the degree of hydration and neutron contrast can be rapidly changed in-situ by playing with hydration under H2O, D2O or a mixed atmosphere.

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