Diffraction techniques for nonlamellar phases of phospholipids.

Area of Science:

• Membrane Biophysics
• Neutron Scattering
• Structural Biology

Background:

• Substrate-supported lipid membranes are crucial models for biological systems.
• Nonlamellar lipid phases present unique structural challenges for analysis.
• Neutron diffraction offers advantages for studying lipid phases due to its sensitivity to hydrogen.

Purpose of the Study:

• To describe and validate a neutron diffraction method for nonlamellar lipid phases on substrates.
• To determine intensity and phase information for lipid phases, specifically the hexagonal phase of diphytanoyl phosphatidylcholine (DPhPC).
• To elucidate the molecular packing within the DPhPC hexagonal phase.

Main Methods:

• Utilized neutron diffraction on flat substrate-supported lipid membranes.
• Employed layered symmetry of nonlamellar phases for structure determination.
• Varied D2O/H2O ratio in relative humidity to solve the phase problem.
• Constructed and analyzed neutron scattering length density distribution.

Main Results:

• Successfully applied neutron diffraction to determine the structure of the hexagonal phase of DPhPC.
• Verified data reduction procedures using hexagonal symmetry.
• Elucidated the packing of DPhPC molecules in the hexagonal phase.
• Found limited incorporation of tetradecane into the DPhPC hexagonal phase.

Conclusions:

• The developed neutron diffraction method is effective for analyzing nonlamellar lipid phases on substrates.
• The structural insights into DPhPC hexagonal phase are relevant for understanding its rhombohedral phase stalk structure.
• Lipid-phase behavior, such as tetradecane incorporation, can be effectively studied using this method.