DPhPC

Hybrid membranes built from phospholipids and amphiphilic block copolymers seek to capitalize on the benefits of both constituents for constructing biomimetic interfaces with improved performance. However, hybrid membranes have not been formed or studied using the droplet interface bilayer (DIB) method, an approach that offers advantages for revealing nanoscale changes in membrane structure and mechanics and offers a path toward assembling higher-order tissues. We report on hybrid droplet interface bilayers (hDIBs) formed in hexadecane from binary mixtures of synthetic diphytanoyl phosphatidylcholine (DPhPC) lipids and low molecular weight 1,2 polybutadiene-b-polyethylene oxide (PBPEO) amphiphilic block copolymers and use electrophysiology measurements and imaging to assess the effects of PBPEO in the membrane. This work reveals that hDIBs containing up to 15 mol% PBPEO plus DPhPC are homogeneously mixtures of lipids and polymers, remain highly resistive to ion transport, and are stable-including under applied voltage. Moreover, they exhibit hydrophobic thicknesses similar to DPhPC-only bilayers, but also have significantly lower values of membrane tension. These characteristics coincide with reduced energy of adhesion between droplets and the formation of alamethicin ion channels at significantly lower threshold voltages, demonstrating that even moderate amounts of amphiphilic block copolymers in a lipid bilayer provide a route for tuning the physical properties of a biomimetic membrane.

Diphytanoylphosphatidyl choline (DPhPC) is a synthetic ester lipid with methylated tails found in archaeal ether lipids. Because of the stability of DPhPC bilayers and the absence of phase transitions over a broad range of temperatures, the lipid is used as an artificial membrane matrix for the reconstitution of channels, pumps, and membrane-active peptides. We characterized monomolecular films made of DPhPC and its natural ether analog DOPhPC at the air-water interface. We measured compression isotherms and dipole potentials of films made of DPhPC, DPhPE, and DOPhPC. We determined that at 40 mN/m the molecular area of DPhPC is 81.2 Å(2), consistent with X-ray and neutron scattering data obtained in liposomes. This indicates that 40 mN/m is the monolayer-bilayer equivalence pressure for this lipid. At this packing density, the compressibility modulus (Cs(-1 )= 122 ± 7 mN/m) and interfacial dipole potential (V = 355 ± 16 mV) were near their maximums. The molecular dipole moment was estimated to be 0.64 ± 0.02 D. The ether DOPhPC compacted to 70.4 Å(2)/lipid at 40 mN/m displaying a peak compressibility similar to that of DPhPC. The maximal dipole potential of the ether lipid was about half of that for DPhPC at this density, and the elemental dipole moment was about a quarter. The spreading of DPhPC and DOPhPC liposomes reduced the surface tension of the aqueous phase by 46 and 49 mN/m, respectively. This corresponds well to the monolayer collapse pressure. The equilibration time shortened as the temperature increased from 20 to 60 °C, but the surface pressure at equilibrium did not change. The data illustrates the properties of branched chains and the contributions of ester bonds in setting the mechanical and electrostatic parameters of diphytanoyl lipids. These properties determine an environment in which reconstituted voltage- or mechano-activated proteins may function. Electrostatic properties are important in the preparation of asymmetric folded bilayers, whereas lateral compressibility defines the tension in mechanically stimulated droplet interface bilayers.

Cellular membranes employ a variety of strategies for controlling the flow of small molecules into the cytoplasmic space, including incorporation of sterols for modulation of permeability and maintenance of lipid asymmetry to provide both sides of the membrane with differing biophysical properties. The specific case of cholesterol asymmetry, especially, is known to have profound effects in neurological cellular systems. Synthetic membrane models that can readily determine valuable physical parameters, such as water transport rates, for sterol-containing membranes of defined lipid composition remain in demand. We report the use of the droplet interface bilayer (DIB), composed of adherent aqueous droplets surrounded by a lipid monolayer and immersed in a hydrophobic medium, for measurement of water permeability across the membrane, with rapid visualization and ease of experimental setup. We studied droplet bilayer membranes composed of the prototypical synthetic membrane lipid (i.e., the archaeal lipid DPhPC) as well as of symmetric and asymmetric DIBs formed by DPhPC and sodium cholesterol sulfate (S-Chol). The presence of S-Chol in DPhPC in symmetric DIB reduced the passive water permeability rate (P(f)) at all concentrations and increased the activation energy (E(a)) to 17-18 kcal/mol. When only one side of the DIB contains S-Chol (asymmetric DIB), an E(a) of 14-15 kcal/mol was obtained, a value intermediate that of pure lipid and symmetrical DIB containing lipid and S-Chol. Our data are consistent with a capability for regulation of water transport by one leaflet independent of the other. The engineering of our various systems is believed to have implications for garnering detailed knowledge regarding the transport of small moieties across bilayers in a wide variety of lipid systems.

Background:Nicobrevin is a proprietary product marketed as an aid to smoking cessation. It contains quinine, menthyl valerate, camphor and eucalyptus oil.Objectives:The objective of this review was to assess the effects of Nicobrevin on long term smoking cessationSearch strategy:We searched the Cochrane Tobacco Addiction Group trials register.Selection criteria:Randomized trials comparing Nicobrevin to placebo or an alternative therapeutic control, which reported smoking cessation with at least six months follow up.Data collection and analysis:Data were sought on the outcome, method of randomization, and completeness of follow up.Main results:We identified no trials meeting the full inclusion criteria including long-term follow up.Authors' conclusions:There is no evidence available from long-term trials that Nicobrevin can aid smoking cessation.