Hydration behaviour of POPC/C12-Bet mixtures investigated by sorption gravimetry, 31P NMR spectroscopy and X-ray diffraction

► Sorption gravimetry, 31P NMR-spectroscopy and X-ray diffraction (SAXD) were used to describe the hydration behaviour of POPC/C12-Bet mixtures. ► Lamellar mixtures of amphiphiles with opposing dipole orientations in their headgroup show reduced hydration. ► We propose inner-salt forming in phospholipid membranes.