title: Dynamic properties of bicellar lipid mixtures observed by rheometry and quadrupole echo decay.
abstract: In bicellar dispersions of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-dihexanoyl-sn-glycero-3-phosphocholine (DHPC), the transition from isotropic reorientation to partial orientational order, on warming, is known to coincide with a sharp increase in viscosity. In this work, cone-and-plate rheometry, (2)H NMR spectroscopy, and quadrupole echo decay observations have been used to obtain new insights into the dynamics of phases observed in bicellar DMPC/DHPC mixtures. Samples with 25% of the DMPC component deuterated were used to correlate rheological measurements with phase behavior observed by (2)H NMR spectroscopy. Mixtures containing only normal DMPC (DMPC/DHPC) or only chain perdeuterated DMPC (DMPC-d(54)/DHPC) were used to refine rheology and quadrupole echo decay measurements respectively. The viscosity peaked at 4-9 Pa·s, just above the isotropic-to-nematic transition, and then dropped as samples were warmed through the nematic-to-lamellar transition. Quadrupole echo decay times above the nematic-to-lamellar transition were significantly longer than typically observed in the liquid crystalline phase of saturated lipid multilamellar vesicles. This may indicate a damping of slow bilayer undulations resulting from the coupling of opposite bilayer surfaces by DHPC-lined pores.
authors.affiliation: Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada, A1B 3X7.
authors.forename: Alanna
authors.initials: A
authors.lastname: Flynn
authors.forename: Michael
authors.initials: M
authors.lastname: Ducey
authors.forename: Anand
authors.initials: A
authors.lastname: Yethiraj
authors.forename: Michael R
authors.initials: MR
authors.lastname: Morrow
mesh_terms: D003903:Deuterium; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D010742:Phospholipid Ethers / Q000737:chemistry*; D012212:Rheology; D013499:Surface Properties; D013816:Thermodynamics; D014783:Viscosity
chemical_list: C052298:1,2-dihexadecyl-sn-glycero-3-phosphocholine; D010742:Phospholipid Ethers; D003903:Deuterium; D004134:Dimyristoylphosphatidylcholine