A NEW MONOFLUORINATED PHOSPHATIDYLCHOLINE FORMS INTERDIGITATED BILAYERS

16-Fluoropalmitic acid was synthesized from 16-hydroxypalmiticacid usi ng diethylaminosulfur trifluoride. This monofluorinated fatty acid the n was used to make lmitoyl-2-[16-fluoropalmitoyl]-phosphatidylcholine (F-DPPC) as a fluorinated analog of dipalmitoylphosphatidylcholine (DP PC). Surprisingly, We found that the phase transition temperature (T-m ) of F-DPPC occurs near 50 degrees C, similar to 10 degrees C higher t han its nonfluorinated counterpart, DPPC, as judged by both differenti al scanning calorimetry and infrared spectroscopy. The pretransition o bserved for DPPC is absent in F-PPC. A combination of REDOR, (r) under bar otational-(e) under bar cho <(do)under bar>uble-(r) under bar eso nance,an conventional solid-state N-MR experiments demonstrates that F -DPPC forms a fully interdigitated bilayer in the gel phase. Electron paramagnetic resonance experiments show that below T-m, the hydrocarbo n chains of F-DPPC are more motionally restricted than those of DPPC. X-ray scattering experiments confirm that the thickness and packing of gel phase F-DPPC is similar to that of heptanetriol-induced interdigi tated DPPC. F-DPPC is the first phosphoglyceride containing sn-l: and sn-2 ester-linked fatty acyl chains of equal length that spontaneously forms interdigitated bilayers in the gel state in the absence of indu cing agents such as alcohols.