Sarah E. Rogers

Shape of tropoelastin, the highly extensible protein that controls human tissue elasticity

Elastin enables the reversible deformation of elastic tissues and can withstand decades of repetitive forces. Tropoelastin is the soluble precursor to elastin, the main elastic protein found in mammals. Little is known of the shape and mechanism of assembly of tropoelastin as its unique composition and propensity to self-associate has hampered structural studies. In this study, we solve the nanostructure of full-length and corresponding overlapping fragments of tropoelastin using small angle X-ray and neutron scattering, allowing us to identify discrete regions of the molecule. Tropoelastin is an asymmetric coil, with a protruding foot that encompasses the C-terminal cell interaction motif. We show that individual tropoelastin molecules are highly extensible yet elastic without hysteresis to perform as highly efficient molecular nanosprings. Our findings shed light on how biology uses this single protein to build durable elastic structures that allow for cell attachment to an appended foot. We present a unique model for head-to-tail assembly which allows for the propagation of the molecule’s asymmetric coil through a stacked spring design.

Anionic Surfactants and Surfactant Ionic Liquids with Quaternary Ammonium Counterions

Small-angle neutron scattering and surface tension have been used to characterize a class of surfactants (SURFs), including surfactant ionic liquids (SAILs). These SURFs and SAILs are based on organic surfactant anions (single-tail dodecyl sulfate, DS, double-chain aerosol-OT, AOT, and the trichain, TC) with substituted quaternary ammonium cations. This class of surfactants can be obtained by straightforward chemistry, being cheaper and more environmentally benign than standard cationic SAILs. A surprising aspect of the results is that, broadly speaking, the physicochemical properties of these SURFs and SAILs are dominated by the nature of the surfactant anion and that the chemical structure of the added cation plays only a secondary role.

Small Angle Neutron Scattering Using Sans2d

The Loq small angle neutron scattering (SANS) instrument at ISIS target station one (TS1) has proved an extremely popular and immensely productive SANS facility over the last 20 years. Loq is routinely operated with a 25 Hz disc chopper removing alternate neutron pulses from the 50 Hz source to provide a usable wavelength range of 2.2 to 10 Å. Scattered neutrons are recorded on a 0.64 m square 3He multiwire proportional counter (Ordela 2661N) fixed at ∼ 4 m from the sample, with a total flight path of 15 m from the decoupled liquid hydrogen moderator [1].

Universal Surfactant for Water, Oils, and CO2

A trichain anionic surfactant sodium 1,4-bis(neopentyloxy)-3-(neopentyloxycarbonyl)-1,4-dioxobutane-2-sulfonate (TC14) is shown to aggregate in three different types of solvent: water, heptane, and liquid CO(2). Small-angle neutron scattering (SANS) has been used to characterize the surfactant aggregates in water, heptane, and dense CO(2). Surface tension measurements, and analyses, show that the addition of a third branched chain to the surfactant structural template is critical for sufficiently lowering the surface energy, tipping the balance between a CO(2)-incompatible surfactant (AOT) and CO(2)-philic compounds that will aggregate to form micelles in dense CO(2) (TC14). These results highlight TC14 as one of the most adaptable and useful surfactants discovered to date, being compatible with a wide range of solvent types from high dielectric polar solvent water to alkanes with low dielectrics and even being active in the uncooperative and challenging solvent environment of liquid CO(2).

Tri‐Chain Hydrocarbon Surfactants as Designed Micellar Modifiers for Supercritical CO2

Getting their feet wet: Low-cost hydrocarbon surfactants act as fluid modifiers for supercritical carbon dioxide (scCO(2)). Increased terminal branching of the surfactant chains aids micelle formation (see middle picture: CO(2) green), and more chains allows water to be incorporated (right, blue).

Nanoparticles decorated with proteolytic enzymes, a promising strategy to overcome the mucus barrier.

The intestinal mucus gel layer represents a stumbling block for drug adsorption. This study is aimed to formulate a nanoparticulate system able to overcome this barrier by cleaving locally the glycoprotein substructures of the mucus. Mucolytic enzymes such as papain (PAP) and bromelain (BRO) were covalently conjugated to poly(acrylic acid) (PAA). Nanoparticles (NPs) were then formulated via ionic gelation method and characterized by particle size, zeta potential, enzyme content and enzymatic activity. The NPs permeation quantified by rotating tube studies was correlated with changes in the mucus gel layer structure determined by pulsed-gradient-spin-echo NMR (PGSE-NMR), small-angle neutron scattering (SANS) and spin-echo SANS (SESANS). PAP and BRO functionalized NPs had an average size in the range of 250 and 285 nm and a zeta potential that ranged between -6 and -5 mV. The enzyme content was 242 μg enzyme/mg for PAP modified NPs and 253 μg enzyme/mg for BRO modified NPs. The maintained enzymatic activity was 43% for PAP decorated NPs and 76% for BRO decorated NPs. The rotating tube technique revealed a better performance of BRO decorated NPs compared to PAA decorated NPs, with a 4.8-fold higher concentration of NPs in the inner slice of mucus. Addition of 0.5 wt% of enzyme functionalized NPs to 5 wt% intestinal mucin led to c.a. 2-fold increase in the mobility of the mucin as measured by PGSE-NMR indicative of a significant break-up of the structure of the mucin. SANS and SESANS measurements further revealed a change in structure of the intestinal mucus induced by the incorporation of the functionalized NPs mostly occurring at a length scale longer than 0.5 μm. Accordingly, BRO decorated NPs show higher potential than PAP functionalized NPs as mucus permeating drug delivery systems.

Rod-like micelles thicken CO2

A new approach to thicken dense liquid CO(2) is described using the principles of self-assembly of custom-made CO(2) compatible fluorinated dichain surfactants. Solutions of surfactants in CO(2) have been investigated by high-pressure phase behavior, small-angle neutron scattering (HP-SANS) and falling cylinder viscosity experiments. The results show that it is possible to control surfactant aggregation to generate long, thin reversed micellar rods in dense CO(2), which at 10 wt % can lead to viscosity enhancements of up to 90% compared to pure CO(2). This represents the first example of CO(2) viscosity modifiers based on anisotropic reversed micelles.

Super-Efficient Surfactant for Stabilizing Water-in-Carbon Dioxide Microemulsions

The fluorinated double-tailed glutarate anionic surfactant, sodium 1,5-bis[(1H,1H,2H,2H-perfluorodecyl)oxy]-1,5-dioxopentane-2-sulfonate (8FG(EO)(2)), was found to stabilize water-in-supercritical CO(2) microemulsions with high water-to-surfactant molar ratios (W(0)). Studies were carried out here to obtain detailed information on the phase stability and nanostructure of the microemulsions by using a high-pressure UV-vis dye probe and small-angle neutron scattering (SANS) measurements. The UV-vis spectra, with methyl orange as a reporter dye, indicated a maximum attainable W(0) of 60 at 45 and 75 °C, and SANS profiles indicated regular droplet swelling with a linear relationship between the water core nanodroplet radius and W(0). This represents the highest water solubilization reported to date for any water-in-CO(2) microemulsion. Further analysis of the SANS data indicated critical packing parameters for 8FG(EO)(2) at the microemulsion interface >1.34, representing approximately 1.1 times the value for common aerosol-OT in water-in-heptane microemulsions under equivalent conditions.

On the Role of Specific Interactions in the Diffusion of Nanoparticles in Aqueous Polymer Solutions

Understanding nanoparticle diffusion within non-Newtonian biological and synthetic fluids is essential in designing novel formulations (e.g., nanomedicines for drug delivery, shampoos, lotions, coatings, paints, etc.), but is presently poorly defined. This study reports the diffusion of thiolated and PEGylated silica nanoparticles, characterized by small-angle neutron scattering, in solutions of various water-soluble polymers such as poly(acrylic acid) (PAA), poly(N-vinylpyrrolidone) (PVP), poly(ethylene oxide) (PEO), and hydroxyethylcellulose (HEC) probed using NanoSight nanoparticle tracking analysis. Results show that the diffusivity of nanoparticles is affected by their dimensions, medium viscosity, and, in particular, the specific interactions between nanoparticles and the macromolecules in solution; strong attractive interactions such as hydrogen bonding hamper diffusion. The water-soluble polymers retarded the diffusion of thiolated particles in the order PEO > PVP > PAA > HEC whereas for PEGylated silica particles retardation followed the order PAA > PVP = HEC > PEO. In the absence of specific interactions with the medium, PEGylated nanoparticles exhibit enhanced mobility compared to their thiolated counterparts despite some increase in their dimensions.

Hybrid CO2-philic surfactants with low fluorine content.

The relationships between molecular architecture, aggregation, and interfacial activity of a new class of CO(2)-philic hybrid surfactants are investigated. The new hybrid surfactant CF2/AOT4 [sodium (4H,4H,5H,5H,5H-pentafluoropentyl-3,5,5-trimethyl-1-hexyl)-2-sulfosuccinate] was synthesized, having one hydrocarbon chain and one separate fluorocarbon chain. This hybrid H-F chain structure strikes a fine balance of properties, on one hand minimizing the fluorine content, while on the other maintaining a sufficient level of CO(2)-philicity. The surfactant has been investigated by a range of techniques including high-pressure phase behavior, UV-visible spectroscopy, small-angle neutron scattering (SANS), and air-water (a/w) surface tension measurements. The results advance the understanding of structure-function relationships for generating CO(2)-philic surfactants and are therefore beneficial for expanding applications of CO(2) to realize its potential using the most economic and efficient surfactants.