What does lipid hydration tell us? A minireview

The hydration of a variety of phospholipids has been studied, gravimetrically. The water adsorption isotherms obtained have been analyzed by the use of BET methodology. The major findings are as follows: Phospholipids containing choline, as part of their head group and having a glycerol backbone are „strong” water adsorbers; the nature and fluidity of the hydrocarbon chains do not control the „strong” vs „weak” nature of the water binding but do modulate the amount of adsorbed water. The number of methyl groups present on the N+ moiety of the head groups determines both the nature of the water binding as well as the amount of water adsorbed. The electrical charge on the phospholipid head group does not, in itself, determine the nature of the water binding; it does, however affect the amount of water bound. All of the phospholipids studied exhibit a very rapid rise in electrical conductivity as water is adsorbed; this rise reaches a limiting saturation value at or close to fnat for the completion of the first monolayer of water adsorbed. These findings are discussed in terms of the molecular structure of the phospholipids.