Interactions of a Monofluorinated Phospholipid with Saturated Phosphatidylcholines of Different Chain Lengths

Abstract

This study uses differential scanning calorimetry (DSC) and fluorescence spectroscopy to study the thermodynamic and kinetic effects of the monofluorinated phospholipid 1-palmitoyl-2-[16-fluoropalmitoyl]-phosphatidylcholine (F-DPPC) on bilayers composed of the fully saturated phosphatidylcholines 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC). In both bilayer systems, DSC thermograms indicate a disappearance of pretransition peaks (Tp) along with a rise in main transition (Tm) hysteresis at elevated F-DPPC mol%. Fluorescence intensity measurements reveal an inverse relationship between F-DPPC mol% and the emission intensity of the environment-sensitive probe 1,6-diphenyl-1,3,5-hexatriene (DPH) below the main transitions of the respective lipids. These trends suggest a growth in interdigitated domains with the incorporation of additional F-DPPC into the bilayer. Significant drops in intensity values were observed at lower F-DPPC mole percentages in the DSPC system than the DMPC system, indicating that the latter lipid has a higher threshold for F-DPPC-induced interdigitation. Our results support that F-DPPC encourages the interdigitated phase (LβI) in saturated bilayers and highlight the stabilizing effect that long acyl chains have on this phase.