Arbutin blocks defects in the ripple phase of DMPC bilayers by changing carbonyl organization

The effect of arbutin, a 4-hydroxyphenyl-β-glucopyranoside, on dimyristoylphosphatidylcholine (DMPC) bilayers was studied by turbidimetry, EPR and FTIR spectroscopies. The disruption of DMPC multilamellar vesicles (MLV's) with monomyristoylphosphatidylcholine (lysoPC), a product of hydrolysis of phospholipase A2 (PLA2), is more efficient at 18 °C, where DMPC MLV's are known to be in the ripple Pβ′ phase, than at 10 °C (Lβ′ flat gel phase). Disruption at 18 °C was inhibited by increasing concentrations of arbutin in the solution. This inhibition was correlated with the disappearance of the ripple phase in MLV's when arbutin is present. Shifts in FTIR carbonyl bands caused by arbutin or by temperature changes allow us to propose a model. It is interpreted that the changes in the water–hydrocarbon interface caused by arbutin, forcing a reaccommodation of the carbonyl groups, eliminate the topological defects in the lattice due to mismatches among regions with different area per lipid where lysoPC can insert.