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

Antagonistic Mixing in Micelles of Amphiphilic Polyoxometalates and Hexaethylene Glycol Monododecyl Ether

International audienceHypothesis: Polyoxometalates (POMs) are metal oxygen clusters with a range of interesting magnetic and catalytic properties. POMs with attached hydrocarbon chains show amphiphilic behaviour so we hypothesised that mixtures of a nonionic surfactant and anionic surfactants with a polyoxometalate cluster as headgroup would form mixed micelles, giving control of the POM density in the micelle, and which would differ in size and shape from micelles formed by the individual surfactants. Due to the high charge and large size of the POM, we suggested that these would be nonideal mixtures due to the complex interactions between the two types of surfactants. The nonideality and the micellar composition may be quantified using regular solution theory. With supplementary information provided by small-angle neutron scattering (SANS), an understanding of this unusual binary surfactant system can be established.Experiments: A systematic study was performed on mixed surfactant systems containing polyoxometalate-headed amphiphiles (K10[P2W17O61OSi2(CnH(2n+1))2], abbreviated as P2W17-2Cn, where n = 12, 14 or 16) and hexaethylene glycol monododecyl ether (C12EO6). Critical micelle concentrations (CMCs) of these mixtures were measured and used to calculate the interaction parameters based on regular solution theory, enabling prediction of micellar composition. Predictions were compared to micelle structures obtained from SANS. A phase diagram was also established.Findings: The CMCs of these mixtures suggest unusual unfavourable interactions between the two species despite formation of mixed micelles. Micellar compositions obtained from SANS concurred with those calculated using the averaged interaction parameters for P2W17-2Cn/C12EO6 (n = 12 and 14). We attribute the unfavourable interactions to a combination of different phenomena: counterion-mediated interactions between P2W17 units and the unfolding of the ethylene oxide headgroups of the nonionic surfactant, yet micelles still form in these systems due to the hydrophobic interactions between surfactant tails

Dataset supporting "In situ X-ray reflectivity and GISAXS study of mesoporous silica films grown from sodium silicate solution precursors"

This dataset includes data relating to mesoporous silica films grown from sodium silicate solution precursors: dynamic light scattering (DLS) data for solutions containing cetrimonium bromide and sodium nitrate; small angle X-ray scattering (SAXS) data for films contain cetyltrimethylammonium bromide (CTAB), silica and polyethylenimine (PEI), and silica film; thermogravimetric analysis (TGA) data recording the decomposition of CTAB–PEI–silica in air with temperature; in-situ X-ray reflectivity (XRR) data, surface pressure data, and grazing incidence X-ray scattering (GISAXS) data for the interface between the solution (sodium silicate, CTAB, PEI) and air; and nitrogen sorption data.Full details of the methodology can be found in the Experimental section of the associated paper.The XRR data were normalised.All the data are plotted in Igor Pro software, https://www.wavemetrics.com/.SAXS data has three columns: Q (x axis), scattering intensity (y axis) and error for scattering intensity. GISAXS data are images. XRR data has three columns: Q as x axis, reflectivity (y axis) and error in y axis. Surface pressure data contains two columns: time and surface pressure

Data sets for "Structural Investigation of Sulfobetaines and Phospholipid Monolayers at the air-water interface"

Normalized neutron and X-ray reflectivity data for Langmuir monolayers composed of mixtures of dimyristoylphosphatidylcholine, DMPC and a single 18-carbon tailed sulfobetaine, SB3-18 on pure water at room temperature and at surface pressures of 15 mN/m and 35 mN/m. Neutron measurements are carried out on D2O and air contrast matched water. Measurements were carried out with deuterated and hydrogenated lipids.Neutron reflectivity measurements were carried out on Inter at the ISIS Pulsed Neutron and Muon source at room temperature. Mixtures of DMPC and SB3-18 were investigates on D2O and air contrast matched water, ACMW. Deuterated phospholipid and sulfobetaine were used along with hydrogenated samples. X-Ray reflectivity measurements were carried out on I07 at The Diamond Light Source. As above mixtures of DMPC and SB3-18 were carried out on a water subphase at room temperature under a helium atmosphere. For both data sets are carried out at two surface pressures, the surface pressure in both cases is controlled by a Nima Langmuir trough.Neutron reflectivity data was stitched together and normalised using Mantid software. X-Ray reflectivity data was also normalised to the critical edge and by the incident flux at the Diamond light source.Reflectivity data, here given as .dat files, can be fitted and plotted using a range of programs, the Motofit package for Igor Pro, the Motofit GUI or RASCAL are some examples

Small-angle neutron scattering from mixtures of long- and short-chain 3-alkyl-1-methyl imidazolium bistriflimides

The preparation of mixtures of ionic liquids (ILs) represents an attractive strategy to tune their properties, an important aspect of which is to understand how the structure of the bulk varies with composition. In this study, small-angle neutron scattering (SANS) was used to probe mixtures of methylimidazolium-based ionic liquids [Cnmim][Tf2N] with [C2mim][Tf2N]) (n = 4, 6, 8 and 10) and of [Cmmim][Tf2N] with [C12mim][Tf2N] (m = 2, 4, 6 and 8). Mixtures were prepared in both contrasts, which is to say that one component would be fully hydrogenated while the other was fully deuterated, and vice versa. Data were fitted using a range of appropriate models, of which the Teubner-Strey model provided most useful information and the pure materials showed a nascent Polar Non-polar Peak (PNPP) for n = 6, which became more evident as n increased. In the mixtures [Cnmim]x[C2mim]1−x[Tf2N], the PNPP was evident for n = 10 and 8, nascent for n = 6 and absent for n = 4, with percolation showing a very strong dependence on the chain length of the added IL, [Cnmim][Tf2N]. In contrast, while the ability of [C12mim][Tf2N] to form percolated structures was damped when mixed with [Cmmim][Tf2N], as m increased from 2 to 6, this effect was less strong. However, data obtained for mixtures of [C12mim][Tf2N] and [C8mim][Tf2N], both of which percolate as pure materials, did not fit easily in any of the models applied to the previous systems and gave results that depended on the contrast used. Complementary small-angle X-ray scattering (SAXS) data, however, showed the expected evolution and behaviour of the PNPP, COP and CP, revealing that the unexpected observations were due to an adventitious matching out of isotopic contrasts. As well as revealing details of the structures of these IL mixtures, the results also point to complementary strategies for generating bulk percolated structures as a function of cation chain length

Dataset for "Antagonistic Mixing in Micelles of Amphiphilic Polyoxometalates and Hexaethylene Glycol Monododecyl Ether"

The dataset contains ASCII files for the following: - Small-angle neutron scattering (SANS) curves and fits for mixtures (mole ratios: 3:1, 1:1 and 1:3) containing polyoxometalate-headed surfactant(P2W17-2Cn, n= 12, 14, 16 and 18) and hydrogenated hexaethylene glycol monododecyl ether (C12EO6) as a function of surfactant total concentrations. Solutions are prepared in two different solvents: deuterium dioxide, 7:3 deuterium dioxide and H2O mixture. - SANS curves and fits for mixtures containing P2W17-2Cn surfactant (n = 12 and 14) and tail-deuterated C12EO6 (mole ratios: 3:1, 1:1 and 1:3) as a function of surfactant total concentrations. Solutions are prepared in deuterium dioxide. The dataset also contains Igor files for the following: - The plot of determination of critical micelle concentrations (CMC) of the mixed P2W17-2Cn/C12EO6 H2O system through surface tension measurements and conductivity measurements.SANS experiments were performed on the LOQ and LARMOR instruments in Target Station I and II, respectively at the ISIS Neutron and Muon Spallation Source, Oxfordshire, UK. The samples were measured in 1 cm wide, 1 mm path-length optical quartz cells at 25 degree C, using a thermostat-controlled circulating bath. Samples were measured for 40 μA (D2O) and 80 μA (70 mol% D2O) of neutron current on the LOQ instrument. For experiments on LARMOR, mixtures containing P2W17-2Cn with d-C12EO6 in D2O were measured for 20 μA. The raw data were corrected for sample transmission and backgrounds from the solvent, the sample cell and other instrumental background using standard workflows in the Mantid software package. Scattering data were normalised against the scattering from a partially-deuterated polystyrene blend of known molecular weight, converting it to the differential scattering cross section d/d(q) (in an absolute scale of cm-1). The output data are hence given in absolute scattered intensity, I(q) in cm-1, versus the momentum transfer, q in Å-1. The CMC of the C12EO6 in water was measured using a Du Noüy Ring (Attension Sigma 701 Tensiometer). The CMCs of the binary systems were measured by either conductivity using a METTLER TOLEDO conductivity meter or by a pendant-drop method using a Kruss DSA100 at Diamond Light Source. For P2W17-2Cn-rich mixtures, electrical conductivity measurements give CMC values with more accuracy, whereas surface tension measurements provide more accurate results for the C12EO6-rich mixtures

Superthermal Al Atoms as a Reactive-Atom Probe of Fluorinated Surfaces

We demonstrate a proof-of-concept of a new analytical technique to measure relative F atom exposure at the surfaces of fluorinated materials. The method is based on reactive-atom scattering (RAS) of Al atoms, produced by pulsed laser ablation of solid Al at 532 nm. The properties of the incident ground-state Al were characterized by laser-induced fluorescence (LIF); at typical ablation fluences, the speed distribution is approximately Maxwellian at ∼45000 K, with a most-probable kinetic energy of 187 kJ mol-1 and a mean of 560 kJ mol-1 When these Al atoms impact the surfaces of perfluorinated solids (poly(tetrafluorethylene), PTFE) or liquids (perfluoropolyether, PFPE), gas-phase AlF products are clearly detectable by LIF on the AlF A-X band. Quantitative AlF yields were compared for a small representative set of a widely studied family of ionic liquids based on the common 1-alkyl-3-methylimidazolium ([Cnmim]+) cation. Yields of (1.9 ± 0.2):1 were found from [C2mim][Tf2N] and [C8mim][Tf2N], containing the common fluorinated bis(trifluoromethylsulfonyl)imide anion ([Tf2N]−). This is in quantitative agreement with previous independent low-energy ion scattering (LEIS) measurements and consistent with other independent results indicating that the longer cationic alkyl chains cover a larger fraction of the liquid surface and hence reduce anion exposure. The expected null result was obtained for the ionic liquid [C2mim][EtSO4] which contains no fluorine. These results open the way for further characterization and the potential application of this new variant of the RAS-LIF method

Surface Structure of Alkyl/Fluoroalkylimidazolium Ionic–Liquid Mixtures

The gas-liquid interface of ionic liquids (ILs) is critically important in many applications, for example, in supported IL phase (SILP) catalysis. Methods to investigate the interfacial structure in these systems will allow their performance to be improved in a rational way. In this study, reactive-atom scattering (RAS), surface tension measurements, and molecular dynamics (MD) simulations were used to study the vacuum interface of mixtures of partially fluorinated and normal alkyl ILs. The underlying aim was to understand whether fluorinated IL ions could be used as additives to modify the surface structure of one of the most widely used families of alkyl ILs. The series of ILs 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Cnmim][Tf2N]) with n = 4-12 were mixed with a fixed-length, semiperfluorinated analogue (1H,1H,2H,2H-perfluorooctyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C8mimF13][Tf2N]), forming [Cnmim](1-x)[C8mimF13]x[Tf2N] mixtures, where x is the bulk mole fraction of the fluorinated component. The RAS-LIF method combined O-atom projectiles with laser-induced fluorescence (LIF) detection of the product OH as a measure of surface exposure of the alkyl chains. For [C8mim](1-x)[C8mimF13]x[Tf2N] mixtures, RAS-LIF OH yields are below those expected from stoichiometry. There are quantitatively consistent negative deviations from linearity of the surface tension. Both results imply that the lower-surface-tension fluoroalkyl material dominates the surface. A similar deficit is found for alkyl chain lengths n = 4, 6, 8, and 12 and for all (nonzero) x investigated by RAS-LIF. Accessible-surface-area (ASA) analyses of the MD simulations for [Cnmim](1-x)[C8mimF13]x[Tf2N] mixtures qualitatively reproduce the same primary effect of fluoro-chain predominance of the surface over most of the range of n. However, there are significant quantitative discrepancies between MD ASA predictions and experiment relating to the strength of any n-dependence of the relative alkyl coverage at fixed x, and on the x-dependence at fixed n. These discrepancies are discussed in the context of detailed examinations of the surface structures predicted in the MD simulations. Potential explanations, beyond experimental artifacts, include inadequacies in the classical force fields used in the MD simulations or the inability of simple ASA algorithms to capture dynamical factors that influence RAS-LIF yields