Differences in Interactions of Benzoic Acid and Benzoate with Interfaces.

The interaction of benzoic acid and benzoate with model membrane systems was characterized to understand the molecular interactions of the two forms of a simple aromatic acid with the components of the membrane. The microemulsion system based on bis(2-ethylhexyl)sulfosuccinate (AOT) allowed determination of the molecular positioning using 1D NMR and 2D NMR spectroscopic methods. Benzoic acid and benzoate were both found to penetrate the membrane/water interfaces; however, the benzoic acid was able to penetrate much deeper and thus is more readily able to traverse a membrane. The Langmuir monolayer model system, using dipalmitoylphosphatidylcholine, was used as a generic membrane lipid for a cell. Compression isotherms of monolayers demonstrated a pH dependent interaction with a lipid monolayer and confirming the pH dependent observations shown in the reverse micellar model system. These studies provide an explanation for the antimicrobial activity of benzoic acid while benzoate is inactive. Furthermore, these studies form the framework upon which we are investigating the mode of bacterial uptake of pyrazinoic acid, the active form of pyrazinamide, a front line drug used to combat tuberculosis.