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The role of cholesterol (Chol) in promoting lamellar phase formation in mixtures with 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine (Lyso-PPC) in excess water was investigated using multinuclear solid-state NMR and X-ray scattering. It was found that mixtures containing Chol and Lyso-PPC form a liquid-ordered (Lo) lamellar phase over a range of temperatures and concentrations, as previously observed in mixtures of Chol with various diacylphospholipids. The maximum quadrupolar splitting of the 2H-NMR powder patterns for samples containing per-deuterated Lyso-PPC were 40-50 kHz which is strongly indicative of an Lo phase. This evidence was supported by wide angle X-ray scattering data which showed a characteristic diffuse peak centred at 4.2 Å. The Lo phase coexists with an isotropic Lyso-PPC phase at Chol concentrations up to 70 mol% Chol, and with Chol crystals at Chol concentrations above this value. Below 70 mol% Chol, an increase in the concentration of Chol in the system caused a corresponding increase in the proportion of the Lo phase present compared with the amount of isotropic Lyso-PPC. The chemical-shift anisotropy (CSA) of the static 31P-NMR spectra of the Lo phase showed the symmetry of a lamellar phase, but the linewidth, Δσ, was much narrower than CSA powder patterns obtained for diacylphospholipids in similar conditions, being ∼20 ppm as opposed to ∼40 ppm, respectively.

We report a new platform technology to systematically assemble droplet interface bilayer (DIB) networks in user-defined 3D architectures from cell-sized droplets using optical tweezers. Our OptiDIB platform is the first demonstration of optical trapping to precisely construct 3D DIB networks, paving the way for the development of a new generation of modular bio-systems.

Sphingomyelin is the only sphingolipid occurring naturally in mammalian cells and can form up to 50% of the total phospholipid content of the myelin sheath which surrounds nerves. Having predominantly long, saturated acyl chains, it has a relatively high chain melting temperature and has been strongly associated with formation of lipid microdomains. Here, the lyotropic phase behaviour of sphingomyelin from three different natural sources (bovine brain, egg yolk and milk) in excess water is studied as a function of temperature and pressure by small- and wide-angle X-ray scattering, and solid state NMR. The different hydrocarbon chain length distributions of the three lipid extracts results in significant differences in their gel phase structure; both the bovine brain and egg yolk sphingomyelins can form a ripple gel phase but milk sphingomyelin forms an interdigitated gel phase due to the high degree of chain mismatch in its longer hydrocarbon chain components.

Ternary phase diagrams have been shown to be very useful in understanding the phenomena of lipid rafts. Recently a comprehensive ternary phase diagram for DPPC-d62/DOPC/Chol using static 2H-NMR has been reported [S. L. Veatch, O. Soubias, S. L. Keller, and K. Gawrisch Proceedings of the National Academy of Sciences of the United States of America, 2007, 104, 17650–17655]. However, it is often difficult to interpret these ternary phase diagrams as there are many possible ambiguities, in particular, the extent of the gel(so)–Lo–Lα(ld) three phase region and the clear demarcation between the gel(so) and Lo phase. Here we examine the canonical model lipid raft system by a multinuclear approach using 2H static and 13C, 31P Magic Angle Spinning (MAS) NMR. By using deuterated DPPC (DPPC-d62) it is possible to examine changes in the methylene chain order parameters of the saturated lipid whilst changing the ratio of saturated to unsaturated phospholipid. From these data it is possible to propose the existence at low temperatures (

The role of cholesterol (Chol) in promoting lamellar phase formation in mixtures with 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine (Lyso-PPC) in excess water was investigated using multinuclear solid-state NMR and X-ray scattering. It was found that mixtures containing Chol and Lyso-PPC form a liquid-ordered (Lo) lamellar phase over a range of temperatures and concentrations, as previously observed in mixtures of Chol with various diacylphospholipids. The maximum quadrupolar splitting of the 2H-NMR powder patterns for samples containing per-deuterated Lyso-PPC were 40–50 kHz which is strongly indicative of an Lo phase. This evidence was supported by wide angle X-ray scattering data which showed a characteristic diffuse peak centred at 4.2 A. The Lo phase coexists with an isotropic Lyso-PPC phase at Chol concentrations up to 70 mol% Chol, and with Chol crystals at Chol concentrations above this value. Below 70 mol% Chol, an increase in the concentration of Chol in the system caused a corresponding increase in the proportion of the Lo phase present compared with the amount of isotropic Lyso-PPC. The chemical-shift anisotropy (CSA) of the static 31P-NMR spectra of the Lo phase showed the symmetry of a lamellar phase, but the linewidth, Δσ, was much narrower than CSA powder patterns obtained for diacylphospholipids in similar conditions, being ∼20 ppm as opposed to ∼40 ppm, respectively.

A centred-rectangular lyotropic ribbon phase, rarely observed in inverse (type II) systems, has been found in the branched-chain polyoxyethylene surfactant tetradecyloctadecyl-tetraoxyethylene ether (C14C16EO4) in excess water. This phase is stabilised by the application of hydrostatic pressure. The ratio of the 2-D cell parameters, b/a, is observed to be less than √3 (1.732) over the range of temperatures and pressures studied. The constructed pressure–temperature phase diagram shows that, at high temperatures or low pressures, the inverse ribbon phase converts into an inverse micellar cubic phase of spacegroup Fd3m, and at the opposite extreme, a lamellar gel phase was formed. The lattice parameters of the inverse ribbon phase were found to vary with pressure, with the structure becoming increasingly distorted away from 2-D hexagonal symmetry (b/a = √3) with increasing pressure.