Cardiolipin packing ability studied by grazing incidence X-ray diffraction.

Area of Science:

• Biophysics
• Materials Science
• Surface Chemistry

Background:

• Cardiolipins and phosphatidylcholines are key membrane lipids.
• Understanding lipid monolayer behavior is crucial for membrane biophysics.
• Mixed lipid systems exhibit complex phase behaviors.

Purpose of the Study:

• Investigate the mixing and structural properties of tetramyristoyl cardiolipin (TMCL) and dipalmitoylphosphatidylcholine (DPPC) Langmuir monolayers.
• Determine the influence of surface pressure on the phase behavior of these lipid mixtures.
• Elucidate the role of TMCL in structuring DPPC monolayers.

Main Methods:

• Grazing incidence X-ray diffraction (GIXD) was employed to study pure and mixed monolayers.
• Experiments were conducted at 22°C and two surface pressures: 4 mN/m and 25 mN/m.
• Thermodynamic analysis was used to confirm phase separation.

Main Results:

• At 4 mN/m, TMCL and DPPC were miscible, with TMCL in a liquid-condensed phase and DPPC disordered.
• At 25 mN/m, TMCL adopted a solid phase with perpendicular chains, while DPPC was in the liquid-condensed phase.
• Increasing TMCL in DPPC monolayers at 25 mN/m reduced aliphatic chain tilt angles, achieving close packing at a 1:1 ratio.
• Higher TMCL concentrations at 25 mN/m led to partial phase separation without altering lattice structure or tilt.

Conclusions:

• TMCL induces significant structural changes and ordering in DPPC monolayers, particularly at higher surface pressures.
• The mixing behavior and phase separation are dependent on surface pressure.
• TMCL promotes tight packing of lipid acyl chains, enhancing monolayer order.