GRAZING-INCIDENCE X-RAY-DIFFRACTION STUDY OF DIMYRISTOYLPHOSPHATIDIC ACID MONOLAYERS ON AQUEOUS SUBPHASES IN THE PRESENCE OF CALCIUM OR MAGNESIUM-IONS

Focusing on the difference in the isotherms of dimyristoylphosphatidic acid (DMPA) monolayers on aqueous subphases in the presence of calciu m and magnesium ions, the structures of the DMPA monolayer on the aque ous subphases were investigated by grazing incidence X-ray diffraction . We observed the reflections from the lattice of hydrocarbon chain pa cking of DMPA monolayers. It was found that the lattice spacings obser ved by X-ray diffraction in the presence of calcium ions are shorter t han those in the presence of magnesium ions at every surface pressure measured. We discussed this result in terms of the hydration of these ions.