The impact of high hydrostatic pressure on structure and dynamics of ß-lactoglobulin.

METHODS: Combining small-angle X-ray and neutron scattering measurements with inelastic neutron scattering experiments, we investigated the impact of high hydrostatic pressure on the structure and dynamics of ß-lactoglobulin (ßLG) in aqueous solution. BACKGROUND: ßLG is a relatively small protein, which is predominantly dimeric in physiological conditions, but dissociates to monomer below about pH3. RESULTS: High-pressure structural results show that the dimer-monomer equilibrium, as well as the protein-protein interactions, are only slightly perturbed by pressure, and ßLG unfolding is observed above a threshold value of 3000bar. In the same range of pressure, dynamical results put in evidence a slowing down of the protein dynamics in the picosecond timescale and a loss of rigidity of the ßLG structure. This dynamical behavior can be related to the onset of unfolding processes, probably promoted from water penetration in the hydrophobic cavity. GENERAL SIGNIFICANCE: Results suggest that density and compressibility of water molecules in contact with the protein are key parameters to regulate the protein flexibility.

Diatom-inspired self-assembly for silica thin sheets of perpendicular nanochannels.

HYPOTHESIS: Multistage silicate self-organization into light-weight, high-strength, hierarchically patterned diatom frustules carries hints for innovative silica-based nanomaterials. With sodium silicate in a biomimetic sol-gel system templated by a tri-surfactant system of hexadecyltrimethylammonium bromide, sodium dodecylsulfate, and poly(oxyethylene-b-oxypropylene-b-oxyethylene) (P123), mesoporous silica nanochannel plates with perpendicular channel orientation are synthesized. The formation process, analogous to that of diatom frustules, is postulated to be directed by an oriented self-assembly of the block copolymer micelles shelled with charged catanionic surfactants upon silication. EXPERIMENTS: The postulated formation process for the oriented silica nanochannel plates was investigated using time-resolved small-angle X-ray and neutron scattering (SAXS/SANS) and freeze fracture replication transmission electron microscopy (FFR-TEM). FINDINGS: With fine-tuned molar ratios of the anionic, cationic, and nonionic surfactants, the catanionic combination and the nonionic copolymer form charged, prolate ternary micelles in aqueous solutions, which further develop into prototype monolayered micellar plates. The prolate shape and maximized surfactant adsorption of the complex micelles, revealed from combined SAXS/SANS analysis, are of critical importance in the subsequent micellar self-assembly upon silicate deposition. Time-resolved SAXS and FFR-TEM indicate that the silicate complex micelles coalesce laterally into the prototype micellar nanoplates, which further fuse with one another into large sheets of monolayered silicate micelles of in-plane lamellar packing. Upon silica polymerization, the in-plane lamellar packing of the micelles further transforms to 2D hexagonal packing of vertically oriented silicate channels. The unveiled structural features and their evolution not only elucidate the previously unresolved self-assembly process of through-thickness silica nanochannels but also open a new line of research mimicking free-standing frustules of diatoms.

Direct Evidence of Confined Water in Room-Temperature Ionic Liquids by Complementary Use of Small-Angle X-ray and Neutron Scattering.

The direct evidence of confined water ("water pocket") inside hydrophilic room-temperature ionic liquids (RTILs) was obtained by complementary use of small-angle X-ray scattering and small-angle neutron scattering (SAXS and SANS). A large contrast in X-ray and neutron scattering cross-section of deuterons was used to distinguish the water pocket from the RTIL. In addition to nanoheterogeneity of pure RTILs, the water pocket formed in the water-rich region. Both water concentration and temperature dependence of the peaks in SANS profiles confirmed the existence of the hidden water pocket. The size of the water pocket was estimated to be ∼3 nm, and D2O aggregations were well-simulated on the basis of the observed SANS data.