Properties of Mixed Monofluorinated and Unsaturated Phospholipid Bilayers
Connor Smith
Project Advisor: Phoebe Dea

     This study examines the interaction between the monofluorinated phospholipid 1-palmitoyl-2-[16-fluoropalmitoyl]sn-glycero-3-phosphocholine (F-DPPC) and the unsaturated lipid 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). F-DPPC is a unique phospholipid which interdigitates without the use of inducing agents.  Increasing concentrations of DOPC were added to F-DPPC in an effort to determine if F-DPPC remains interdigitated.  Differential scanning calorimetry (DSC) was used to analyze the thermotropic phase behavior of these lipid mixtures.  Introducing DOPC decreases the main transition temperature (T_m), reduces the main transition enthalpy, and increases the T_m hysteresis.  The high T_m hysteresis implies that the membrane remains interdigitated even at high amounts of DOPC. In addition, fluorescence measurements were taken with two fluorescent probes, 1,6-diphenyl-1,3,5-hexatriene (DPH) and the DPH-labeled analogue of DPPC, 2-(3-(diphenylhexatrienyl) propanoyl)-1-hexadecanoyl-sn-glycero-3-phosphocholine (β-DPH HPC).  In contrast to our DSC results, the increase in fluorescence intensity suggests that as more DOPC is added, less of the F-DPPC/DOPC system is interdigitated.  Our fluorescence polarization results reveal that DOPC increases the fluidity of F-DPPC membranes below the T_m.  From these results, it is not definitive if DOPC impedes the interdigitation of F-DPPC, although the presence of the two cis double bonds in the hydrocarbon tail of DOPC clearly disrupts the lipid packing of F-DPPC bilayers.

Support provided by: Norris Science Research Endowment