Interaction of benzene with bilayers. Thermal and structural studies

Area of Science:

• Physical Chemistry
• Biophysics
• Materials Science

Background:

• Liposomes, particularly saturated phosphatidylcholines like DSPC, are model systems for cell membranes.
• Understanding how small molecules interact with lipid bilayers is crucial for drug delivery and membrane biophysics.
• Benzene's effect on lipid thermal and structural properties is not fully elucidated.

Purpose of the Study:

• To investigate the impact of benzene on the thermal and structural characteristics of saturated phosphatidylcholine liposomes.
• To determine how benzene influences liposome swelling, vesicle formation, and bilayer phase transitions.
• To analyze the changes in heat capacity and enthalpy associated with benzene-lipid interactions.

Main Methods:

• Differential Scanning Calorimetry (DSC) was used to measure thermal transitions (ΔHm, ΔHf, Cp).
• Liposome structural changes (swelling, dispersion, rippling) were observed upon benzene addition.
• Varying mole ratios of DSPC-benzene were studied to map phase behavior.

Main Results:

• Benzene induces liposome swelling and dispersion into multilamellar vesicles with rippled bilayers at 20°C.
• Major thermal changes observed at DSPC:benzene mole ratios of 2:1 and 1:1.
• Increased molar heat capacity (Cp) in the gel phase (0.12 < x < 0.50) attributed to increased defects; decreased transition temperatures and multiple transitions observed at higher benzene fractions (0.50 ≤ x ≤ 0.90).

Conclusions:

• Benzene incorporation into DSPC liposomes increases bilayer disorder and defects, altering thermal properties.
• Benzene appears to 'uncouple' liquid-crystalline acyl chains, evidenced by enthalpy changes.
• Boundary lipids interacting with benzene exhibit higher heat capacity, suggesting localized disruption.