title: Properties of phosphatidylcholine in the presence of its monofluorinated analogue.
abstract: In aqueous solution, the monofluorinated phospholipid 1-palmitoyl-2-[16-fluoropalmitoyl]sn-glycero-3-phosphocholine (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) was used to determine the miscibility and thermotropic phase behavior of these binary lipid mixtures. In addition, the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH) and a DPH-labeled analogue of DPPC, 2-(3-(diphenylhexatrienyl) propanoyl)-1-hexadecanoyl-sn-glycero-3-phosphocholine (beta-DPH HPC, aka DPH-PC or DPHpPC), were used to detect interdigitation. In F-DPPC, the fluorescence intensity of both probes decreased a similar amount and to a degree that is consistent with an interdigitated system. We also determined that there are two separate effects of increasing the ratio of F-DPPC in the DPPC/F-DPPC system. With low amounts of F-DPPC, there is little evidence that the system is heavily interdigitated. Instead, we hypothesize that the introduction of F-DPPC provides nucleation sites that alter the kinetics, reversibility, and temperature of the main transition (T(m)). At higher mol% of F-DPPC, we propose that interdigitated F-DPPC-rich domains form to create a phase-segregated system. While DPPC/F-DPPC was highly miscible, the DAPC/F-DPPC system was significantly less miscible. Additionally, we observed that DAPC/F-DPPC samples have reduced solubility in water, which affected the acquisition of fluorescence data. However, our DSC results indicate the existence of DAPC-rich and F-DPPC-rich components. Furthermore, this data support that the mixing was disruptive to lipid packing and that the presence of DAPC hinders the interdigitation of F-DPPC.
authors.affiliation: Department of Chemistry, Occidental College, 1600 Campus Road, Los Angeles, CA 90041, USA.
authors.forename: Eric A
authors.initials: EA
authors.lastname: Smith
authors.forename: Christiaan M
authors.initials: CM
authors.lastname: van Gorkum
authors.forename: Phoebe K
authors.initials: PK
authors.lastname: Dea
mesh_terms: D055592:Biophysical Phenomena; D002152:Calorimetry, Differential Scanning; D008051:Lipid Bilayers / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry*; D012995:Solubility; D013816:Thermodynamics
chemical_list: C115319:1-palmitoyl-2-(16-fluoropalmitoyl)phosphatidylcholine; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; C044819:1,2-diarachidonoyl-glycero-3-phosphocholine