Biomimetic transport of simple olive biophenol and analogues through model biological membranes by differential scanning calorimetry

The different interactions of p-hydroxybenzoic acid (1), a simple biophenol (BP) found in olives and their food products, and its substitute analogues, benzoic (2), anisic (3), and toluic (4) acids, with a model membrane represented by dimyristoylphosphatidylcholine (DMPC) multilamellar vesicles (MLV) was studied by differential scanning calorimetry (DSC). The influence of their different lipophilic character on transfer and absorption processes through an aqueous medium into a lipid bilayer was also investigated. DSC experiments allowed monitoring of the interaction of BP with biomembranes by considering the effects exerted on the thermotropic behavior of DMPC multilamellar and unilamellar vesicles at different pHs (4 and 7.4). The examined compounds affect the transition temperature (T-m) of phospholipid vesicles, causing a shift toward lower values, which is modulated by the molecular fraction entering into the lipid bilayer, as well as by their molecular interaction with the lipids. Kinetic calorimetric measurements were performed on suspensions of blank liposomes immediately after being added to fixed weighed amounts of powdered compounds and after increasing incubation periods at 37 degreesC. T-m shifts, due to molecular dissolution and transfer of the compounds into the membrane surface occurring during the incubation time, were compared with those determined by a fixed molar fraction of free compounds directly dispersed in the membrane. The results show that the kinetic process, involved in molecular release, transfer through aqueous medium, and uptake by the model membrane surface, is influenced by lipophilicity as well as by pH, acting on the acid solubility and membrane disorder, allowing us to gather useful information on the BP intake process of olive derived foodstuffs.