Temperature and pressure dependence of quercetin-3-O-palmitate interaction with a model phospholipid membrane: film balance and scanning probe microscopy study

The molecular interaction of quercetin-3-O-palmitate (QP) with dimyristoylphosphatidylcholine (DMPC) has been studied. Film balancemeasurements of the average molecular area vs QP molar fraction in DMPC/QP mixed monolayers showed that relevant positive deviationsfrom ideality, i.e., a less dense monolayer packing, occurred for a temperature of 10◦C, below the critical melting transition temperature ofDMPC monolayers (Tcm≈20◦C), while ideal behavior was observed at 37◦C, above this phase transition temperature. The positive deviationobserved at low temperatures in the average molecular area increased with the surface pressure. Scanning probe microscopy measurementsperformed on mixed monolayers transferred on mica showed that the deviations from ideality were connected to the formation of nanometric-scale QP-rich domains. However, the formation of aggregates was observed only for relatively high-QP molar fractionsXQP0.25 at 10◦C,while it was not observed at 37◦C, i.e., when the ideal mixing was found at the air/water interface. The observed effects are explained in termsof a temperature- and surface pressure-dependent phase-separation process based on the predominance at low temperature and low molecularmobility of QP–QP and DMPC–DMPC aggregation forces, prompting the formation of QP-rich domains embedded in a DMPC-rich matrix.High temperature prompts the QP/DMPC ideal mixing.