Underpotential surface reduction of mesoporous CeO2 nanoparticle films

The formation of variable-thickness CeO2 nanoparticle mesoporous films from a colloidal nanoparticle solution (approximately 1–3-nm-diameter CeO2) is demonstrated using a layer-by-layer deposition process with small organic binder molecules such as cyclohexanehexacarboxylate and phytate. Film growth is characterised by scanning and transmission electron microscopies, X-ray scattering and quartz crystal microbalance techniques. The surface electrochemistry of CeO2 films before and after calcination at 500 °C in air is investigated. A well-defined Ce(IV/III) redox process confined to the oxide surface is observed. Beyond a threshold potential, a new phosphate phase, presumably CePO4, is formed during electrochemical reduction of CeO2 in aqueous phosphate buffer solution. The voltammetric signal is sensitive to (1) thermal pre-treatment, (2) film thickness, (3) phosphate concentration and (4) pH. The reversible ‘underpotential reduction’ of CeO2 is demonstrated at potentials positive of the threshold. A transition occurs from the reversible ‘underpotential region’ in which no phosphate phase is formed to the irreversible ‘overpotential region’ in which the formation of the cerium(III) phosphate phase is observed. The experimental results are rationalised based on surface reactivity and nucleation effects

Robust Ordered Cubic Mesostructured Polymer/Silica Composite Films Grown at the Air/Water Interface

Polymer/silica composite films, stable to calcination, were produced using catanionic surfactant mixtures (hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS)) and polymers (polyethylenimine (PEI) or polyacrylamide (PAAm)) at the air/water interface. Film formation processes were probed by time-resolved neutron reflectivity measurements. Grazing incidence X-ray diffraction (GID) measurements indicate that the mesophase geometry of the interfacial films could be controlled to give lamellar, 2D hexagonal, and several cubic phases (<i>Pn</i>3̅<i>m</i>, <i>Fm</i>3̅<i>m</i>, and <i>Im</i>3̅<i>m</i>) by varying the polyelectrolyte molecular weight, polyelectrolyte chemical nature, or the cationic:anionic surfactant molar ratio. On the basis of GID results, a phase diagram for the catanionic surfactant/polyelectrolyte/TMOS film system was drawn. These films can be easily removed from the interface and mesoporous silica films which retain the film geometry can be obtained after calcination; moreover, this film preparation method provides a simple way to impart polymer functionality into the mesostructured silica wall, which means these films have potential applications in a variety of fields such as catalysis, molecular separation, and drug delivery

Water-Responsive Internally Structured Polymer–Surfactant Films on Solid Surfaces

Water-insoluble films of oppositely charged polyion–surfactant ion “complex salts” (CS) are readily cast on solid surfaces from ethanolic solutions. The methodology introduces new possibilities to study and utilize more or less hydrated CS. Direct SAXS measurements show that the surface films are water-responsive and change their liquid crystalline structure in response to changes in the water activity of the environment. In addition to the classical micellar cubic and hexagonal phases, a rectangular ribbon phase and a hexagonal close-packed structure have now been detected for CS composed of cationic alkyltrimethylammonium surfactants with polyacrylate counterions. Added cosurfactants, decanol or the nonionic surfactant C₁₂E₅, yield additional lamellar and bicontinuous cubic structures. Images of the surfaces by optical and atomic force microscopy show that the films cover the surfaces well but have a more or less irregular surface topology, including “craters” of sizes ranging from a few to hundreds of micrometers. The results indicate possibilities to create a wealth of water-responsive structured CS films on solid surfaces

Free-Standing High Surface Area Titania Films Grown at the Air–Water Interface

Free-standing titania films were grown at the air–water interface, a novel method to synthesize robust TiO₂ nanowire/nanoparticle composite films. The calcined films contain an anatase crystal phase and have a high surface area with a structure composed of one-dimensional long nanowires and mesoporous nanoparticle branches. These suggest a promising way to manufacture large areas of thick porous titania films for many applications. As one possible application, use of these films in a dye-sensitized solar cell demonstrates the potential of these materials

Surfactant–Solvent Interaction Effects on the Micellization of Cationic Surfactants in a Carboxylic Acid-Based Deep Eutectic Solvent

Deep eutectic solvents have been demonstrated to support amphiphile self-assembly, providing potential alternatives as structure-directing agents in the synthesis of nanostructures, and drug delivery. Here we have expanded on this recent research to investigate the self-assembly of alkyltrimethylammonium bromide surfactants in choline chloride:malonic acid deep eutectic solvent and mixtures of the solvent with water. Surface tension and small-angle neutron scattering were used to determine the behavior of the amphiphiles. Surfactants were found to remain active in the solvent, and surface tension measurements revealed changes in the behavior of the surfactants with different levels of hydration. Small-angle neutron scattering shows that in this solvent the micelle shape depends on the surfactant chain length, varying from globular micelles (aspect ratio ∼2) for short chain surfactants to elongated micelles (aspect ratio ∼14) for long chain surfactants even at low surfactant concentration. We suggest that the formation of elongated micelles can be explained through the interaction of the solvent with the surfactant headgroup, since ion–ion interactions between surfactant headgroups and solvent may modify the morphology of the micelles. The presence of water in the deep eutectic solvents promotes an increase in the charge density at the micelle interface and therefore the formation of less elongated, globular micelles

Influence of Poly(styrene-<i>co</i>-maleic acid) Copolymer Structure on the Properties and Self-Assembly of SMALP Nanodiscs

Polymer stabilized nanodiscs are self-assembled structures composed of a polymer belt that wraps around a segment of lipid bilayer, and as such are capable of encapsulating membrane proteins directly from the cell membrane. To date, most studies on these nanodiscs have used poly­(styrene-<i>co</i>-maleic acid) (SMA) with the term SMA-lipid particles (SMALPs) coined to describe them. In this study, we have determined the physical and thermodynamic properties of such nanodiscs made with two different SMA copolymers. These include a widely used and commercially available statistical poly­(styrene-<i>co</i>-maleic acid) copolymer (coSMA) and a reversible addition–fragmentation chain transfer synthesized copolymer with narrow molecular weight distribution and alternating styrene and maleic acid groups with a polystyrene tail, (altSMA). We define phase diagrams for each polymer, and show that, regardless of polymer topological structure, self-assembly is driven by the free energy change associated with the polymers. We also show that nanodisc size is polymer dependent, but can be modified by varying polymer concentration. The thermal stability of each nanodisc type is similar, and both can effectively solubilize proteins from the <i>E. coli</i> membrane. These data show the potential for the development of different SMA polymers with controllable properties to produce nanodiscs that can be optimized for specific applications and will enable more optimized and widespread use of the SMA-based nanodiscs in membrane protein research

Controlling Interfacial Film Formation in Mixed Polymer–Surfactant Systems by Changing the Vapor Phase

Here we show that transport-generated phase separation at the air–liquid interface in systems containing self-assembling amphiphilic molecules and polymers can be controlled by the relative humidity (RH) of the air. We also show that our observations can be described quantitatively with a theoretical model describing interfacial phase separation in a water gradient that we published previously. These phenomena arises from the fact that the water chemical potential corresponding to the ambient RH will, in general, not match the water chemical potential in the open aqueous solution. This implies nonequilibrium conditions at the air–water interface, which in turn can have consequences on the molecular organization in this layer. The experimental setup is such that we can control the boundary conditions in RH and thereby verify the predictions from the theoretical model. The polymer–surfactant systems studied here are composed of polyethylenimine (PEI) and hexadecyltrimethylammonium bromide (CTAB) or didecyldimethylammonium bromide (DDAB). Grazing-incidence small-angle X-ray scattering results show that interfacial phases with hexagonal or lamellar structure form at the interface of dilute polymer–surfactant micellar solutions. From spectroscopic ellipsometry data we conclude that variations in RH can be used to control the growth of micrometer-thick interfacial films and that reducing RH leads to thicker films. For the CTAB–PEI system, we compare the phase behavior of the interfacial phase to the equilibrium bulk phase behavior. The interfacial film resembles the bulk phases formed at high surfactant to polymer ratio and reduced water contents, and this can be used to predict the composition of interfacial phase. We also show that convection in the vapor phase strongly reduces film formation, likely due to reduction of the unstirred layer, where diffusive transport is dominating

<i>In vitro</i> cytotoxicity and uptake of carboplatin NP.

<p>(A) Carboplatin NP showed increased cytotoxicity over 48 hours. The cytotoxic effect of the carboplatin nanoparticles (Carboplatin NP) were assessed by MTT assay in UPAB and SNB19 human glioblastoma multiforme (GBM) cell lines. For UPAB, 0.18mg/ml and for SNB19, 0.03mg/ml carboplatin was used as these concentrations represent the IC50 after 72 hours. Paired <i>t-test</i> statistical analysis comparing cytotoxicity revealed significant differences for SNB19 at 24hours (p = 0.001) and 48 hours (p = 0.004), indicated by asterix. (B) Uptake of fluorescein-labelled carboplatin NP (green) occurs within 24 hours of dosing. Cells were dosed and fixed after defined periods of culture. Cells were stained with phalloidin (red), to visualise actin cytoskeleton and DAPI (blue) for cell nuclei. Uptake into cells is indicated by white arrows.</p

<i>In vitro</i> neurotoxicity in primary rat hippocampal cultures.

<p>Carboplatin NP are less toxic to neurones compared to the free drug. Primary rat brain hippocampal cultures were dosed with either carboplatin (0.03mg/ml) or carboplatin NP (1mg/ml) and assayed after 72 hours of culture. (A) MTT analysis shows significant increase in cell viability with carboplatin NP (p<0.001). (B) Carboplatin alone causes deregulation of the neurones and loss of the glial cells, whilst carboplatin NP retained neuronal connections and glial cells. Immunofluorescent analysis of the neurones (B3tubulin; green) and glial cells (GFAP; red). Cells were counterstained with DAPI to visualise cell nuclei (blue) (Scale bar; 100μm).</p

Toxicity analysis after CED into the striatum of rat brains.

<p>CED of aCSF (negative control), carboplatin (0.72mg/ml; 5μl volume) (or carboplatin NP (1mg/ml; 5μl volume) was conducted and toxicity in rat striatum assessed. Dual IHC analysis of neurons (NeuN) and Glial cell (GFAP) demonstrated minimal toxicity localised to the needle track. No glial or neuronal cell loss was observed elsewhere. Scale bar: 100μm.</p