PHYSICAL STUDIES OF PHOSPHOLIPIDS .12. NUCLEAR MAGNETIC RESONANCE STUDIES OF MOLECULAR MOTION IN SOME PURE LECITHIN-WATER SYSTEMS

Proton magnetic resonance spectra of 1,2-dipalmitoyl-l-phosphatidylcholine and its perdeuterated analogue have been obtained at tempertures between 24 and 150° at various hydrations. The use of a perdeuterated lecithin enables the various lineshapes either to be assigned to the dipolar interactions of group protons, or to the long chain protons in the gel and liquid-crystalline phases. In the gel phase the motion of the head group protons and hydrocarbon chain protons is dominated by the first 4-5 moles of water (2H2O) per mole of lecithin. The range n = 4-10 moles may indicate a weaker secondary hydration shell. The linewidths are not further reduced for n > 10. The decreasing linewidth corresponding to the CH2 protons of the fatty acid residues parallels the reduction of the temperature (Tc) for the gel to liquid-crystalline phase transition. Above the transition temperature a broad line (1.5 gauss) remains. Thus, for all hydrations, some residual anisotropy exists in the lamellar liquid crystalline phase for the head group protons, and this may be connected with some degree of order at the polar/apolar interface, that is, quase-orientation of the glycerol residue. A narrow component (approx. 10-2 gauss) is also observed and corresponds to the unresolved lineshapes due to the anisotropic but rapid molecular motion of the long chain protons and of the N+(CH3)3 protons of the head group. © 1969.