Interdigitated hydrocarbon chain packing causes the biphasic transition behavior in lipid/alcohol suspensions

Area of Science:

• Biochemistry
• Biophysics
• Materials Science

Background:

• Ethanol exhibits a biphasic effect on the transition temperature (Tm) of phosphatidylcholine bilayers.
• This effect involves reducing Tm at low concentrations and increasing it at high concentrations.

Purpose of the Study:

• To elucidate the structural basis for the biphasic effect of ethanol on phosphatidylcholine bilayer Tm.
• To investigate the induction of an unusual gel phase by ethanol.

Main Methods:

• X-ray diffraction was employed to analyze the structure of phosphatidylcholine bilayers.
• Data were correlated with spectroscopic and calorimetric findings for various lipid-drug systems.

Main Results:

• X-ray diffraction confirmed the induction of an interdigitated gel phase at high ethanol concentrations.
• This interdigitated phase explains the reversal of Tm, lipid chain length dependence, and narrow transition width.
• The findings are consistent across various alcohols and chlorpromazine.

Conclusions:

• The interdigitated gel phase is the key structural change responsible for ethanol's biphasic effect on bilayer Tm.
• This model provides a unified explanation for diverse experimental observations in lipid-drug interactions.