water binding; hydrogen bond; lipids; infrared spectra; high pressure
The sites of water binding in L-1,2-diacylphosphatidylcholines (l-DPPC) were investigated by infrared spectroscopic methods. Evidence is provided that water molecules in fully hydrated samples, and the crystallation water in solid samples, are hydrogen-bonded to the phosphate oxygen atoms of the PO₂⁻ group in the head moiety, as well as to the ester C=O group of the sn-2 acyl chain in the interfacial region. The results indicate that no hydrogen-bonding occurs between water molecules and the ester C=O group of the sn-1 acyl chain of L-1,2-dipalmitoylphosphatidylethanolamine (L-DPPE), L-DPPC and L-1,2-dimyristoyl-phosphatidylcholine (L-DMPC). Although there is no hydrogen-bonding between water and the choline moiety, water molecules are attached to the (CH₃)₃N⁺ group by polar interactions.
Chemistry and Physics of Lipids46, no. 3: 213–224.