Watching Nanoparticles Form: An In Situ (Small‐/Wide‐Angle X‐ray Scattering/Total Scattering) Study of the Growth of Yttria‐Stabilised Zirconia in Supercritical Fluids

Understanding nanoparticle‐formation reactions requires multi‐technique in situ characterisation, since no single characterisation technique provides adequate information. Here, the first combined small‐angle X‐ray scattering (SAXS)/wide‐angle X‐ray scattering (WAXS)/total‐scattering study of nanoparticle formation is presented. We report on the formation and growth of yttria‐stabilised zirconia (YSZ) under the extreme conditions of supercritical methanol for particles with Y₂O₃ equivalent molar fractions of 0, 4, 8, 12 and 25 %. Simultaneous in situ SAXS and WAXS reveals a quick formation (seconds) of sub‐nanometre amorphous material forming larger agglomerates with subsequent slow crystallisation (minutes) into nanocrystallites. The amount of yttria dopant is shown to strongly affect the crystallite size and unit‐cell dimensions. At yttria‐doping levels larger than 8 %, which is known to be the stoichiometry with maximum ionic conductivity, the strain on the crystal lattice is significantly increased. Time‐resolved nanoparticle size distributions are calculated based on whole‐powder‐pattern modelling of the WAXS data, which reveals that concurrent with increasing average particle sizes, a broadening of the particle‐size distributions occur. In situ total scattering provides structural insight into the sub‐nanometre amorphous phase prior to crystallite growth, and the data reveal an atomic rearrangement from six‐coordinated zirconium atoms in the initial amorphous clusters to eight‐coordinated zirconia atoms in stable crystallites. Representative samples prepared ex situ and investigated by transmission electron microscopy confirm a transformation from an amorphous material to crystalline nanoparticles upon increased synthesis duration.     

Significant Structural Differences between Transient Amyloid‐β Oligomers and Less‐Toxic Fibrils in Regions Known To Harbor Familial Alzheimer′s Mutations

Small oligomers of the amyloid β (Aβ) peptide, rather than the monomers or the fibrils, are suspected to initiate Alzheimer′s disease (AD). However, their low concentration and transient nature under physiological conditions have made structural investigations difficult. A method for addressing such problems has been developed by combining rapid fluorescence techniques with slower two‐dimensional solid‐state NMR methods. The smallest Aβ₄₀ oligomers that demonstrate a potential sign of toxicity, namely, an enhanced affinity for cell membranes, were thus probed. The two hydrophobic regions (residues 10–21 and 30–40) have already attained the conformation that is observed in the fibrils. However, the turn region (residues 22–29) and the N‐terminal tail (residues 1–9) are strikingly different. Notably, ten of eleven known Aβ mutants that are linked to familial AD map to these two regions. Our results provide potential structural cues for AD therapeutics and also suggest a general method for determining transient protein structures.     

Probing the Structural Stability of and Enhanced CO2 Storage in MOF MIL‐68(In) under High Pressures by FTIR Spectroscopy

The unique structural topology of metal–organic framework (MOF) MIL‐68, featuring two types of channels with distinct pore sizes, makes it a promising candidate for application in gas storage and separation. In this study, the behavior of as‐made and activated MIL‐68(In) was investigated in a diamond‐anvil cell under high pressure by in situ IR spectroscopy. The framework exhibits high stability under compression up to 9 GPa, whereas the bridging OH groups appear to be very sensitive to compression. Pressure‐induced structural modifications were found to be completely reversible for as‐made MIL‐68(In) but irreversible for the activated framework. Moreover, the addition of Nujol as pressure‐transmitting medium makes the framework more resilient to pressure. Finally, when loaded with CO₂, the framework exhibited interesting differential binding affinities with CO₂ in the hexagonal and triangular pores at different pressures. The pressure‐enhanced CO₂ storage behavior and the guest–host interaction mechanism between CO₂ and the MOF framework were explored with the aid of Monte Carlo simulations. These studies demonstrated great potential for MIL‐68(In) in gas‐storage applications that require extreme loading pressures.