Intermolecular hydrogen-bond interactions in dppe and dmpc phospholipid membranes revealed by far-infrared spectroscopy

The vibrational signature in the far-infrared region of two different phospholipids, phos-phatidylcholine (PC) and phosphatidylethanolamine (PE), was investigated as a function of relative humidity from 0 to 75% in order to evaluate the effect of headgroup composition on the formation of intermolecular interactions. The substructures of the frequency region between 50 and 300 cm−1 were identified, and changes in the frequency and intensity of the related vibrations with hydration were analyzed. Interestingly, in PE, two additional vibrational bands with respect to PC were found at 162 and 236 cm−1 and assigned to intermolecular hydrogen bonds between the hydrogen-bond-donating groups, −NH+3, and hydrogen-bond-accepting groups, —P—O− and —COO, of adjacent molecules. The presence of these interactions also affected the penetration of water, severely reducing the hydration capability of PE lipids.