Properties of Phosphatidylcholine in the Presence of its Monofluorinated Analogue
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In aqueous solution, the monofluorinated phospholipid 1-palmitoyl-2-[16-fluoropalmitoyl]-phosphatidylcholine (F-DPPC) interdigitates without the use of inducing agents. To understand the thermal and physical properties of this unique lipid, F-DPPC was combined with the non-fluorinated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-diarachidoyl-sn-glycero-3-phosphocholine (DAPC). Differential scanning calorimetry (DSC) demonstrated that both DPPC and DAPC mixed with F-DPPC to create lipid bilayers, but with thermal peaks that were broader than the pure lipids by themselves. DPPC was shown to be significantly more miscible with F-DPPC than DAPC. In addition, a fluorescently-labeled analogue of DPPC, 2-(3-(diphenylhexatrienyl) propanoyl)-1-hexadecanoyl-sn-glycero-3-phosphocholine (β-DPH HPC) and the unattached 1,6-diphenyl-1,3,5-hexatriene (DPH) were used as tests for interdigitation. Fluorescence measurements and DSC results indicate that as more F-DPPC is added, more of DPPC/F-DPPC system is interdigitated. However, since F-DPPC and DAPC demonstrate only limited miscibility and solubility in water, there was less evidence of cooperative large-scale interdigitation in the DAPC/F-DPPC system.