Well-Defined Colloidal 2‑D Layered Transition-Metal Chalcogenide Nanocrystals via Generalized Synthetic Protocols

While interesting and unprecedented material characteristics of two dimensionality (2-D) layered nanomaterials are emerging, their reliable synthetic methodologies are not well developed. In this study we demonstrate general applicability of synthetic protocols to a wide range of colloidal 2-D layered transition-metal chalcogenide (TMC) nanocrystals. As distinctly different from other nanocrystals, we discovered that 2-D layered TMC nanocrystals are unstable in the presence of reactive radicals from elemental chalcogen during the crystal formation. We first introduce the synthesis of titanium sulfide and selenide where well-defined single crystallinity and lateral size controllability are verified, and then such synthetic protocols are extended to all of group IV and V transition-metal sulfide (TiS₂, ZrS₂, HfS₂, VS₂, NbS₂, and TaS₂) and selenide (TiSe₂, ZrSe₃, HfSe₃, VSe₂, NbSe₂, and TaSe₂) nanocrystals. The use of appropriate chalcogen source is found to be critical for the successful synthesis of 2-D layered TMC nanocrystals. CS₂ is an efficient chalcogen precursor for metal sulfide nanocrystals, whereas elemental Se is appropriate for metal selenide nanocrystals. We briefly discuss the effects of reactive radical characteristics of elemental S and Se on the formation of 2-D layered TMC nanocrystals

Magnetic Properties of Annealed Core–Shell CoPt Nanoparticles

A precise control and understanding of the magnetization dynamics of nanostructures is an important topic in applied nanosciences. Herein, we perform such control by annealing crystalline (Co/core)–(Pt/shell) nanoparticles. Using electron tomography, temperature dependent electron microscopy and time-resolved magneto-optics, we establish a clear correlation between the magnetization dynamics and the crystalline structure of the nanoparticles. For a mild laser annealing (370 K) the Co–Pt nanoparticles keep their core–shell structure and remain superparamagnetic with a blocking temperature <i>T</i>_B = 66 K. Their time-resolved reflectivity shows that they are locally organized into a supra-crystalline ordered layer in the region of the laser spot. In contrast, a thermal annealing at higher temperatures (up to 700 K) modifies the structure of the individual nanoparticles into a CoPt crystalline ferromagnetic phase, with <i>T</i>_B,anneal = 347 K. Correspondingly, the magneto-crystalline anisotropy of the annealed CoPt nanoparticles increases and their magnetization dynamics displays a motion of precession, characteristic of ferromagnetic nanostructures and which is absent in the superparamagnetic Co–Pt core–shells

Negatively Charged Metal Oxide Nanoparticles Interact with the 20S Proteasome and Differentially Modulate Its Biologic Functional Effects

The multicatalytic ubiquitin–proteasome system (UPS) carries out proteolysis in a highly orchestrated way and regulates a large number of cellular processes. Deregulation of the UPS in many disorders has been documented. In some cases, such as carcinogenesis, elevated proteasome activity has been implicated in disease development, while the etiology of other diseases, such as neurodegeneration, includes decreased UPS activity. Therefore, agents that alter proteasome activity could suppress as well as enhance a multitude of diseases. Metal oxide nanoparticles, often developed as diagnostic tools, have not previously been tested as modulators of proteasome activity. Here, several types of metal oxide nanoparticles were found to adsorb to the proteasome and show variable preferential binding for particular proteasome subunits with several peptide binding “hotspots” possible. These interactions depend on the size, charge, and concentration of the nanoparticles and affect proteasome activity in a time-dependent manner. Should metal oxide nanoparticles increase proteasome activity in cells, as they do <i>in vitro</i>, unintended effects related to changes in proteasome function can be expected