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.

Interaction of the C-Terminal Peptide of Pulmonary Surfactant Protein B (SP-B) with a Bicellar Lipid Mixture Containing Anionic Lipid

“…This likely reflects a further coalescence of particles into larger lamellar structures [47], [48], [51]–[53], possibly due to increased mixing of the long-chain and short-chain lipid components with increasing temperature [49], [50], [78]. The sharpness of the doublets in the lamellar phase spectra of Figure 2a is consistent with previous findings that, at low or zero concentrations of DMPG, echo decay times for the bicellar mixture lamellar phase are longer than is seen in multilamellar dispersion of DMPC- d 54 at corresponding temperatures [54], [55].…”

“…As temperature is raised further, the temperature range over which the magnetically orientable phase persists can vary from a few degrees to more than 10 degrees depending on sample composition. Above this range, there is a transition to a phase which is characteristic of more extended, and more randomly oriented, lamellae [47], [48], [51]–[53] but which also displays some dynamical differences from the multilamellar vesicle phase characteristic of a disaturated phosphatidylcholine dispersion [54], [55]. Bicellar mixture properties have been summarized in more detail elsewhere [55].…”

Rheological characterization of thermal phase behavior of anionic lipid DMPG dispersions

“…Here we should also refer that similar complex temperature dependence of the viscosity has been reported for semidilute bicellar systems in lipid mixtures [22]. They have observed two peaks in the temperature dependence of the viscosity.…”

Reversible phospholipid nanogels for deoxyribonucleic acid fragment size determinations up to 1500 base pairs and integrated sample stacking

“…When the relative amount of long chain lipid increases, the aggregates are transformed from a bilayer disk conformation with a small diameter, to disks with larger diameters and 'ribbons' [19,20]. The temperature also impacts the transformation from nanodisks to nanoribbons and a substantial change in apparent viscosity is observed over a temperature range specific to the preparation [34][35][36]. The morphologies adopted by the matrix were dependent on the ratio of long-to-short chain lipid as well as the temperature of the preparation.…”