Hydrocarbon trans-gauche isomerization in phospholipid bilayer gel assemblies

Area of Science:

• Biophysics
• Materials Science
• Spectroscopy

Background:

• Phospholipid bilayers are fundamental to cell membranes.
• Understanding lipid chain dynamics is crucial for membrane function.
• Trans-gauche isomerization influences membrane fluidity and phase behavior.

Purpose of the Study:

• To investigate lipid hydrocarbon chain trans-gauche isomerization dynamics in DMPC, DPPC, and DSPC water bilayers.
• To characterize the energetic differences between trans and gauche conformers.
• To correlate isomerization with lipid chain length and bilayer structure.

Main Methods:

• Vibrational Raman spectroscopy was employed to analyze lipid-water systems.
• Analysis focused on spectral features associated with trans and gauche conformers.
• Peak intensity measurements were used to estimate enthalpy differences (ΔH).

Main Results:

• A new spectral feature at ~1122 cm-1 indicated gauche bond rotation of terminal methyl groups.
• Enthalpy differences (ΔH) were determined for DMPC-H2O (2.9±0.6 kcal/mol), DPPC-H2O (3.4±0.5 kcal/mol), and DSPC-H2O (9.9±1.2 kcal/mol).
• Results suggest approximately two gauche bonds per lipid for DMPC/DPPC and six for DSPC.

Conclusions:

• Raman spectroscopy effectively probes lipid isomerization dynamics in model membranes.
• Lipid chain length significantly impacts the extent of gauche isomerization and associated enthalpy.
• These findings provide quantitative insights into the molecular basis of lipid phase transitions and membrane properties.