Behavior of Hydrated Lipid Bilayers at Cryogenic Temperatures

Area of Science:

• Biophysics
• Materials Science
• Physical Chemistry

Background:

• Phospholipids form multilamellar stacks, crucial for biological membranes.
• Water's behavior within lipid bilayers influences membrane function.
• Cryogenic studies are essential for understanding phase transitions and water dynamics.

Purpose of the Study:

• To investigate the phase behavior of water within 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) multilamellar stacks at cryogenic temperatures.
• To compare water behavior in pure lipid systems with that in natural membranes like purple membrane (PM).
• To characterize the phase transitions of DMPC under cryogenic conditions.

Main Methods:

• Neutron diffraction was employed to analyze water in DMPC multilamellar stacks.
• A flash-cooling protocol was used to achieve cryogenic temperatures.
• Comparative analysis with existing literature data for purple membrane (PM) samples.

Main Results:

• Evidence for a highly viscous water phase between 180 K and 220 K was observed.
• Water was found to leave the intermembrane space at these low temperatures.
• Pure DMPC lipid samples trapped less water and exhibited lower outflow temperatures compared to PM, indicating less hindered water movement.
• The Lβ'-phase of DMPC could be trapped by flash cooling and transformed upon heating to ~260 K.

Conclusions:

• A distinct viscous water phase exists in DMPC multilamellar stacks at cryogenic temperatures.
• The mobility of water in pure DMPC systems is less restricted than in natural membranes.
• Flash cooling can trap specific lipid phases, which undergo further transitions upon warming.