The effect of phloretin on the hydration of egg phosphatidylcholine multilayers

The effect of phloretin on the hydration, structure and interactive properties of supported phospholipid bilayers has been studied by a combination of direct water adsorption measurements and X-ray diffraction. Adsorption isotherms show that over a wide range of relative vapor pressures (from 0 to approximately 1.0) the addition of 20 or 40 mol% phloretin significantly alters the amount of water adsorbed by egg phosphatidylcholine (EPC) multilayers. X-ray diffraction analysis shows that the incorporation of phloretin decreases the width of the EPC bilayer, thereby increasing the area per lipid molecule from approximately 64 A2 for EPC to about 78 A2 for EPC:Ph, 3:2, M:M. Phloretin also decreases the distance between apposing EPC bilayers, most likely because it causes a reduction in repulsive hydration/steric pressure between apposing bilayers. Because phloretin decreases the fluid layer between bilayers by a larger amount than it increases the area per EPC molecule, phloretin has the effect of decreasing the water volume in the multilayers.