Probing and repairing damaged surfaces with nanoparticle-containing microcapsules.

Nanoparticles have useful properties, but it is often important that they only start working after they are placed in a desired location. The encapsulation of nanoparticles allows their function to be preserved until they are released at a specific time or location, and this has been exploited in the development of self-healing materials and in applications such as drug delivery. Encapsulation has also been used to stabilize and control the release of substances, including flavours, fragrances and pesticides.

Using nanoparticle-filled microcapsules for site-specific healing of damaged Substrates: creating a "repair-and-go" system.

Using a hybrid computational approach, we simulate the behavior of nanoparticle-filled microcapsules that are propelled by an imposed shear to move over a substrate, which encompasses a microscopic crack. When the microcapsules become localized in the crack, the nanoparticles can penetrate the capsule's shell to bind to and fill the damaged region. Initially focusing on a simple shear flow, we isolate conditions where the microcapsules become arrested in the cracks and those where the capsules enter the cracks for a finite time but are driven to leave this region by the imposed flow.

Sizing nanoparticle-covered droplets by extrusion through track-etch membranes.

Interfacial segregation of nanoparticles on droplets, such as water droplets in oil, is achieved by mixing or shaking organic solutions of the nanoparticles with water. This typically results in the formation of droplets with a large distribution of sizes, ranging from 10 microm to greater than 200 microm in diameter. Here we describe the application of track-etch membranes to control the size of these nanoparticle-coated droplets.

Pressure perturbation calorimetric studies of the solvation properties and the thermal unfolding of proteins in solution--experiments and theoretical interpretation.

We used pressure perturbation calorimetry (PPC), a relatively new and efficient technique, to study the solvation and volumetric properties of amino acids and peptides as well as of proteins in their native and unfolded state. In PPC, the coefficient of thermal expansion of the partial volume of the protein is deduced from the heat consumed or produced after small isothermal pressure jumps, which strongly depends on the interaction of the protein with the solvent or cosolvent at the protein-solvent interface. Furthermore, the effects of various chaotropic and kosmotropic cosolvents on the volume and expansivity changes of proteins were measured over a wide concentration range with high precision.

Pressure perturbation and differential scanning calorimetric studies of bipolar tetraether liposomes derived from the thermoacidophilic archaeon Sulfolobus acidocaldarius.

Differential scanning calorimetry (DSC) and pressure perturbation calorimetry (PPC) were used to characterize thermal phase transitions, membrane packing, and volumetric properties in multilamellar vesicles (MLVs) composed of the polar lipid fraction E (PLFE) isolated from the thermoacidophilic archaeon Sulfolobus acidocaldarius grown at different temperatures. For PLFE MLVs derived from cells grown at 78 degrees C, the first DSC heating scan exhibits an endothermic transition at 46.7 degrees C, a small hump near 60 degrees C, and a broad exothermic transition at 78.

Ethanol-perturbed amyloidogenic self-assembly of insulin: looking for origins of amyloid strains.

A model cosolvent, ethanol, has profound and diversified effects on the amyloidogenic self-assembly of insulin, yielding spectroscopically and morphologically distinguishable forms of beta-aggregates. The alcohol reduces hydrodynamic radii of insulin molecules, decreases enthalpic costs associated with aggregation-prone intermediate states, and accelerates the aggregation itself. Increasing the concentration of the cosolvent promotes curved, amorphous, and finally donut-shaped forms.

Protein encapsulation in mesoporous silicate: the effects of confinement on protein stability, hydration, and volumetric properties.

On the basis of the predictions of statistical-thermodynamic models, it is postulated that excluded volume effects may play a significant role in the stability, interaction, and function of proteins. We studied the effects of confinement on protein un/refolding and stability. Our approach was to encapsulate a model protein, RNase A, in a mesoporous silica, MCM-48, with glasslike wall structure and with well-defined pores to create a crowded microenvironment.

Hydration and packing effects on prion folding and beta-sheet conversion. High pressure spectroscopy and pressure perturbation calorimetry studies.

The main hypothesis for prion diseases proposes that the cellular protein (PrP(C)) can be altered into a misfolded, beta-sheet-rich isoform (PrP(Sc)), which undergoes aggregation and triggers the onset of transmissible spongiform encephalopathies. Here, we compare the stability against pressure and the thermomechanical properties of the alpha-helical and beta-sheet conformations of recombinant murine prion protein, designated as alpha-rPrP and beta-rPrP, respectively. High temperature induces aggregates and a large gain in intermolecular antiparallel beta-sheet (beta-rPrP), a conformation that shares structural similarity with PrP(Sc).

Folding and unfolding of an elastinlike oligopeptide: "inverse temperature transition," reentrance, and hydrogen-bond dynamics.

The temperature-dependent behavior of a solvated oligopeptide, GVG(VPGVG), is investigated. Spectroscopic measurements, thermodynamic measurements, and molecular dynamics simulations find that this elastinlike octapeptide behaves as a two-state system that undergoes an "inverse temperature" folding transition and reentrant unfolding close to the boiling point of water. A molecular picture of these processes is presented, emphasizing changes in the dynamics of hydrogen bonding at the protein/water interface and peptide backbone librational entropy.

The diastereomeric assembly of polylysine is the low-volume pathway for preferential formation of beta-sheet aggregates.

The interaction of left- and right-handed polylysine chains (poly(D-lysine) and poly(L-lysine)) results in a dramatic increase in the propensity to form aggregated beta-sheet structure (and amyloid-like fibrils), which is reflected by an approximately 15 degrees C decrease of temperature of the alpha-helix-to-beta-sheet transition. While a relative volume expansion of 13-19 mL x mol(-1) accompanies the alpha-to-beta-transition in a single enantiomer, this does not hold true for the mixture, which, along with substantially more negative heat capacity changes, points to a lower solvent-entropy cost of the transition as the possible thermodynamic driving force of the diastereomeric aggregation. The underlying solvational mechanism may be one of the decisive factors responsible for the spontaneous protein aggregation in vivo and, as such, may shed new light on the molecular basis of amyloid-associated diseases.

Aggregation of bovine insulin probed by DSC/PPC calorimetry and FTIR spectroscopy.

Pressure perturbation calorimetry (PPC), differential scanning calorimetry (DSC), and time-resolved Fourier transform infrared spectroscopy (FTIR) have been employed to investigate aggregation of bovine insulin at pH 1.9. The aggregation process exhibits two distinguished phases.

On the temperature--pressure free-energy landscape of proteins.

We studied the thermodynamic stability of a small monomeric protein, staphylococcal nuclease (Snase), as a function of both temperature and pressure, and expressed it as a 3D free-energy surface on the p,T-plane using a second-order Taylor expansion of the Gibbs free-energy change delta G upon unfolding. We took advantage of a series of different techniques (small-angle X-ray scattering, Fourier-transform infrared spectroscopy, differential thermal analysis, pressure perturbation calorimetry and densitometry) in the evaluation of the conformation of the protein and in evaluating the changes in the thermodynamic parameters upon unfolding, such as the heat capacity, enthalpy, entropy, volume, isothermal compressibility and expansivity. The calculated results of the free-energy landscape of the protein are in good agreement with experimental data of the p,T-stability diagram of the protein over a temperature range from 200 to 400 K and at pressures from ambient pressure to 4000 bar.