Differences in Interactions of Benzoic Acid and Benzoate with Interfaces

Area of Science:

• Biochemistry
• Membrane Biophysics
• Physical Chemistry

Background:

• Benzoic acid and benzoate are two forms of a simple aromatic acid.
• Understanding their interaction with cell membranes is crucial for explaining biological activity.
• Previous models have not fully elucidated their differential membrane interactions.

Purpose of the Study:

• To characterize the molecular interactions of benzoic acid and benzoate with model membrane systems.
• To determine the molecular positioning and membrane penetration capabilities of benzoic acid and benzoate.
• To provide a mechanistic basis for the antimicrobial activity of benzoic acid.

Main Methods:

• Utilized a bis(2-ethylhexyl)sulfosuccinate (AOT) microemulsion system.
• Employed 1D NMR and 2D NMR spectroscopy for molecular positioning.
• Used Langmuir monolayer model systems with dipalmitoylphosphatidylcholine (DPPC) and compression isotherms.

Main Results:

• Both benzoic acid and benzoate interact with membrane/water interfaces.
• Benzoic acid penetrates significantly deeper into the membrane than benzoate.
• pH-dependent interactions were observed in both microemulsion and monolayer systems, confirming benzoic acid's enhanced membrane traversal.

Conclusions:

• Benzoic acid's deeper membrane penetration explains its antimicrobial efficacy, while benzoate's inactivity.
• These findings establish a framework for investigating the bacterial uptake of pyrazinoic acid, the active form of pyrazinamide.
• The study highlights the importance of molecular form and pH in membrane interactions of weak acids.