N-ACYLPHOSPHATIDYLETHANOLAMINES - EFFECT OF THE N-ACYL CHAIN-LENGTH ON ITS ORIENTATION

N-Acylphosphatidylethanolamines, or NAPEs, are found in tissues involv ed in degenerating processes, such as dehydrated endosperm of seeds, e rythrocyte membranes, or cell injury, To determine the conformation an d orientation of the acyl chains of these phospholipids, NAPEs with de uterated N-acyl chains of 6 and 16 carbon atoms were synthesized and s tudied by transmission and attenuated total reflectance (ATR) infrared spectroscopy, For N-C16d-DPPE, the ATR measurements show that the N-a cyl chain has the same orientation as the two acyl chains attached to the glycerol moiety, while the N-acyl chain of N-C6d-DPPE is randomly oriented, These results demonstrate that for N-C16d-DPPE, the N-acyl c hain is embedded into the hydrophobic core of the bilayer, while for t he short chain derivative the N-acyl chain remains in the lipid headgr oup region. The analysis of the carbonyl stretching band and of the am ide I band suggests that, for the long N-acyl chain lipid, the ester C =O and the N-H groups are linked by intermolecular hydrogen bonds.