Structural investigation of sulfobetaines and phospholipid monolayers at the air-water interface

Mixtures of sulfobetaine based lipids with phosphocholine phospholipids are of interest in order to study the interactions between zwitterionic surfactants and the phospholipids present in cell membranes. In this study we have investigated the structure of mixed monolayers of sulfobetaines and phosphocholine phospholipids. The sulfobetaine used has a single 18-carbon tail, and is referred to as SB3-18, and the phospholipid used is DMPC. Surface pressure-area isotherms of the samples were used to determine whether any phase transitions were present during the compression of the monolayers. Neutron and X-ray reflectometry were then used to investigate the structure of these monolayers perpendicular to the interface. We found that the average headgroup and tail layer thickness was reasonably consistent across all mixtures, with a variation of less than 3 Å reported in the total thickness of the monolayers at each surface pressure. However, by selective deuteration of the two components of the monolayers, it was found that the two components have different tail layer thicknesses. For the mixture with equal compositions of DMPC and SB3-18 or with a higher composition of DMPC the tail tilts were found to be constant, resulting in a greater tail layer thickness for SB3-18 due to its longer tail. For the mixture higher in SB3-18 this was not the case, the tail tilt angle for the two components was found to be different and DMPC was found to have a greater tail layer thickness than SB3-18 as a result.</p

Magnetically Responsive Materials based on Polymeric Ionic Liquids and Graphene Oxide for Water Clean-up

Hypothesis Owing to attractive interactions between negatively charged graphene oxide (GO) and a paramagnetic cationic polyelectrolyte (polyallydimethylammonium chloride with a FeCl4− counterion (Fe-polyDADMAC) it should be possible to generate magnetic materials. The benefit of using charge-based adsorption is that the need to form covalently linked magnetic materials is offset, which is expected to significantly reduce the time, energy and cost to make such responsive materials. These systems could have a wide use and application in water treatment. Experiments Non-covalent magnetic materials were formed through the mixing of Fe-pDADMAC and GO. A systematic study was conducted by varying polymer concentration at a fixed GO concentration. UV–Vis was used to confirm and quantify polymer adsorption onto GO sheets. The potential uses of the systems for water purification were demonstrated. Findings Fe-polyDADMAC adsorbs to the surface of GO and induces flocculation. Low concentrations of the polymer (20 mmol/L) induce restabilization. Difficult-to-recover gold nanoparticles can be separated from suspensions as well as the pollutant antibiotic tetracycline. Both harmful materials can be magnetically recovered from the dispersions. This system therefore has economical and practical applications in decontamination and water treatment

Langmuir monolayers composed of single and double tail sulfobetaine lipids

AbstractHypothesisOwing to structural similarities between sulfobetaine lipids and phospholipids it should be possible to form stable Langmuir monolayers from long tail sulfobetaines. By modification of the density of lipid tail group (number of carbon chains) it should also be possible to modulate the two-dimensional phase behaviour of these lipids and thereby compare with that of equivalent phospholipids. Potentially this could enable the use of such lipids for the wide array of applications that currently use phospholipids. The benefit of using sulfobetaine lipids is that they can be synthesised by a one-step reaction from cheap and readily available starting materials and will degrade via different pathways than natural lipids. The molecular architecture of the lipid can be easily modified allowing the design of lipids for specific purposes. In addition the reversal of the charge within the sulfobetaine head group relative to the charge orientation in phospholipids may modify behaviour and thereby allow for novel uses of these surfactants.ExperimentsStable Langmuir monolayers were formed composed of single and double tailed sulfobetaine lipids. Surface pressure-area isotherm, Brewster Angle Microscopy and X-ray and neutron reflectometry measurements were conducted to measure the two-dimensional phase behaviour and out-of-plane structure of the monolayers as a function of molecular area.FindingsSulfobetaine lipids are able to form stable Langmuir monolayers with two dimensional phase behaviour analogous to that seen for the well-studied phospholipids. Changing the number of carbon tail groups on the lipid from one to two promotes the existence of a liquid condensed phase due to increased Van der Waals interactions between the tail groups. Thus the structure of the monolayers appears to be defined by the relative sizes of the head and tail groups in a predictable way. However, the presence of sub-phase ions has little effect on the monolayer structure, behaviour that is surprisingly different to that seen for phospholipids

Shape Modification of Water-in-CO₂ Microemulsion Droplets through Mixing of Hydrocarbon and Fluorocarbon Amphiphiles

An oxygen-rich hydrocarbon (HC) amphiphile has been developed as an additive for supercritical CO₂ (scCO₂). The effects of this custom-designed amphiphile have been studied in water-in-CO₂ (w/c) microemulsions stabilized by analogous fluorocarbon (FC) surfactants, nFG­(EO)₂, which are known to form spherical w/c microemulsion droplets. By applying contrast-variation small-angle neutron scattering (CV-SANS), evidence has been obtained for anisotropic structures in the mixed systems. The shape transition is attributed to the hydrocarbon additive, which modifies the curvature of the mixed surfactant films. This can be considered as a potential method to enhance physicochemical properties of scCO₂ through elongation of w/c microemulsion droplets. More importantly, by studying self-assembly in these mixed systems, fundamental understanding can be developed on the packing of HC and FC amphiphiles at water/CO₂ interfaces. This provides guidelines for the design of fluorine-free CO₂ active surfactants, and therefore, practical industrial scale applications of scCO₂ could be achieved

Studies of black diamond as an antibacterial surface for gram negative bacteria: the interplay between chemical and mechanical bactericidal activity

‘Black silicon’ (bSi) samples with surfaces covered in nanoneedles of length ~5 μm were fabricated using a plasma etching process and then coated with a conformal uniform layer of diamond using hot filament chemical vapour deposition to produce ‘black diamond’ (bD) nanostructures. The diamond needles were then chemically terminated with H, O, NH2 or F using plasma treatment, and the hydrophilicity of the resulting surfaces were assessed using water droplet contact-angle measurements, and scaled in the order O > H ≈NH2 >F, with the F-terminated surface being superhydrophobic. The effectiveness of these differently terminated bD needles in killing the Gram-negative bacterium E. coli was semiquantified by Live/Dead staining and fluorescence microscopy, and visualised by environmental scanning electron microscopy. The total number of adhered bacteria was consistent for all the nanostructured bD surfaces at around 50% of the value for the flat diamond control. This, combined with a chemical bactericidal effect of 20–30%, shows that the nanostructured bD surfaces supported significantly fewer viable E. coli than flat surfaces. Moreover, the bD surfaces were particularly effective at preventing the establishment of bacterial aggregates – a precursor to biofilm formation. The percentage of dead bacteria also decreased as a function of hydrophilicity. These results are consistent with a predominantly mechanical mechanism for bacteria death based on the stretching and disruption of the cell membrane, combined with an additional effect from the chemical nature of the surface

Evidence of Lipid Exchange in Styrene Maleic Acid Lipid Particle (SMALP) Nanodisc Systems

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Langmuir, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.langmuir.6b02927Styrene-alt-maleic Acid lipid particles (SMALPs) are self-assembled discoidal structures composed of a polymer belt and a segment of lipid bilayer, which are capable of encapsulating membrane proteins directly from the cell membrane. Here we present evidence of the exchange of lipids between such “nanodiscs” and lipid monolayers adsorbed at either solid-liquid or air-liquid interfaces. This behavior has important implications for the potential uses of nanodiscs, including the potential to control lipid composition within nanodiscs containing membrane protein

Integration of medical service provision and nature conservation worldwide 1980–2022: collaborative evidence mapping of 43 projects across 22 countries

Background Biodiversity protection is fundamental to human wellbeing, and, in turn, serving human health in medically underserved areas can sometimes strengthen conservation. We aimed to collaboratively map the evidence on projects worldwide that are, or have been, providing health services with the intention of producing conservation outcomes in addition to health improvements. Methods Scoping indicated many NGO projects are never published in the academic literature. To avoid missing such interventions we asked conservation staff worldwide to contribute data online or through zoom calls. Advertising to join the collaboration was through formal networks (International Union for Conservation of Nature, Planetary Health Alliance, etc.), professional contacts, funders, and a call in The Lancet Planetary Health. Additionally, data and literature were synthesised from libraries and datasets of collaborators at Population Reference Bureau, Sussex Sustainability Research Programme, and Ecological Levers for Health. Findings Forty-three projects from 22 countries fitted inclusion criteria. Around half had not been published in the collected literature, with data only available through direct submission. Tropical wet forest was by far the most common habitat, followed by tropical dry forest, coral reefs, and tropical grasslands. The most represented region was Sub-Saharan Africa with 27 projects, followed by South-East Asia (five), South Asia (five), Oceania (two), South America (two), Central America (one), Europe (one). Projects ranged from basic health interventions bolted on to pre-existing conservation programmes to generate goodwill (e.g., vaccination rounds bordering national parks) to complex schemes jointly acting on health and biodiversity driven (and funded) by concerns for human welfare as much as conservation. Interpretation Synergistic action on biodiversity conservation and health service provision is very often effective and the approach is more widespread than literature would indicate. However, funding was usually provided on a siloed basis for either health or conservation, and this remains a barrier to wider adoption