13C cross-polarization magic angle spinning NMR study on the chain packing in anhydrous and hydrated DL- and L-dipalmitoylphosphatidylcholine

With I3C cross-polarization magic angle spinning (CP-MAS) NMR it is demonstrated that the anhydrous forms of DL- and L-DPPC show pronounced packing differences in both the headgroup region and the hydrocarbon part of the bilayer. In DL-DPPC the acyl chains and more specifically their end groups are more closely packed than in the L modification. The anhydrous L- and DL-DPPC structures show a completely different behavior toward the addition of 1 equiv of water. DL-DPPC is far less hygroscopic and forms small domains of dihydrated and anhydrous DPPC as was concluded from the combined results of the NMR and a DSC study. The dihydrated form of DL-DPPC is arranged according to a similar structure as is observed for anhydrous L-DPPC. On the other hand, L-DPPC did not show any packing changes in the acyl chains on going from the anhydrous state to the hydrated forms. These results reveal that stereospecific interactions can be responsible for different lipid packing modes and hence in their behavior toward the uptake of water.