Differences between coumaric and cinnamic acids in membrane permeation as evidenced by time-dependent calorimetry

Area of Science:

• Biophysics
• Membrane Biophysics
• Physical Chemistry

Background:

• Bioactive plant phenols, cinnamic and p-coumaric acids, are investigated for their membrane interaction.
• Understanding how molecular structure and pH affect membrane permeability is crucial for drug delivery and biological processes.

Purpose of the Study:

• To investigate the differential effects of cinnamic and p-coumaric acids on dimyristoylphosphatidylcholine (DMPC) model membranes.
• To evaluate how pH and molecular substituents influence liposolubility and vesicle permeability.
• To correlate changes in membrane phase transition with altered permeability.

Main Methods:

• Differential scanning calorimetry (DSC) was used to analyze the phase transition of DMPC vesicles.
• The study compared the effects of cinnamic and p-coumaric acids on both unilamellar and multilamellar vesicles.
• Experiments were conducted at two different pH values (4 and 7.4) to assess pH-dependent interactions.

Main Results:

• P-coumaric acid did not significantly alter the thermotropic behavior of the DMPC model membrane.
• Cinnamic acid interacted with lipid vesicles at both tested pH values, with a more pronounced effect at acidic pH (4) compared to neutral pH (7.4).
• The interaction of cinnamic acid with lipid bilayers was hypothesized to be due to the absence of a hydroxyl group, and this interaction was enhanced in its protonated (acidic) form.

Conclusions:

• The presence or absence of a hydroxyl group in phenolic compounds significantly impacts their interaction with lipid bilayers.
• Cinnamic acid's interaction with DMPC vesicles, enhanced at acidic pH, suggests it can modify membrane permeability.
• Structural variations in bioactive molecules can lead to differential effects on membrane properties, influencing their biological activity.