Effects of a Monofluorinated Phospholipid on the Phase Behavior of Different Chain Length Phosphatidylcholines
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In aqueous media, the monofluorinated phospholipid 1-palmitoyl-2-[16-fluoropalmitoyl]sn-glycero-3-phosphocholine (F-DPPC) is known to alter the phase transition behavior of phospholipid bilayers. Most notably, it does so by replacing the rippled gel phase (P'β) with the interdigitated phase (LβI). Given that chemicals such as alcohols and anesthetics have been found to induce bilayer interdigitation, the mechanism underlying the induction of the LβI phase merits investigation. The present study used differential scanning calorimetry (DSC) to examine the capacity of F-DPPC to induce interdigitation in bilayers composed of two naturally occurring phosphatidylcholines: 1,2-distearoyl- sn -glycero-3-phosphocholine (DSPC) and 1,2-dimyristoyl- sn -glycero-3-phosphocholine (DMPC). At elevated F-DPPC concentrations, the pretransition peaks ( T p) disappeared and the main transition ( T m) hysteresis increased. Such findings suggest the onset of bilayer interdigitation in the presence of F-DPPC. To further elucidate phase behaviors of DMPC and DSPC bilayers in the presence of F-DPPC, fluorescence spectroscopy was performed using the probe 1,6-diphenyl-1,3,5-hexatriene (DPH). The fluorescence studies yielded an overall inverse relationship between F-DPPC molarity and fluorescence intensity. This relationship corroborates the trend in T m hysteresis and suggests that F-DPPC encourages interdigitation in fully saturated phosphatidylcholine bilayers.