Regioselective Base-Free Intermolecular Aminohydroxylations of Hindered and Functionalized Alkenes

Regioselective base-free intermolecular aminohydroxylations of functionalized trisubstituted and 1,1-disubstituted alkenes employing benzoyloxycarbamate <b>3a</b> and catalytic OsO₄ are described. In all cases, the more substituted alcohol isomer is favored. Sluggish reactions could be promoted by gentle heating, the use of amine ligands, or increased catalyst loadings. A competitive rearrangement was observed with a secondary allylic alcohol substrate. The adducts serve as useful precursors to dehydroamino acids

Pressure-Induced Emission from All-Inorganic Two-Dimensional Vacancy-Ordered Lead-Free Metal Halide Perovskite Nanocrystals

Although seeking an effective strategy for further improving their optical properties is a great challenge, two-dimensional (2D) halide perovskites have attracted a significant amount of attention because of their performance. In this regard, the pressure-induced emission accompanied by a remarkable pressure-enhanced emission is achieved without a phase transition in 2D vacancy-ordered perovskite Cs3Bi2Cl9 nanocrystals (NCs). Note that the initial Cs3Bi2Cl9 NCs possess extremely strong electron–phonon coupling, leading to the easy annihilation of trapped excitons by the phonon. Upon compression, pressure could effectively suppress phonon-assisted nonradiative decay and give rise to an intriguing emission from “0” to “1”. Both the weakened electron–phonon coupling and the relaxed halide octahedral distortion benefiting from the vacancy-ordered structure contributed to the subsequent enhanced emission. This work not only elucidates the underlying photophysical mechanism but also identifies pressure engineering as a robust means for improving their potential applications in environmentally friendly solid-state lighting at extremes

Pressure-Tailored Band Gap Engineering and Structure Evolution of Cubic Cesium Lead Iodide Perovskite Nanocrystals

Metal halide perovskites (MHPs) have attracted increasing research attention given the ease of solution processability with excellent optical absorption and emission qualities. However, effective strategies for engineering the band gap of MHPs to satisfy the requirements of practical applications are difficult to develop. Cubic cesium lead iodide (α-CsPbI₃), a typical MHP with an ideal band gap of 1.73 eV, is an intriguing optoelectric material owing to the approaching Shockley–Queisser limit. Here, we carried out a combination of in situ photoluminescence, absorption, and angle-dispersive synchrotron X-ray diffraction spectra to investigate the pressure-induced optical and structural changes of α-CsPbI₃ nanocrystals (NCs). The α-CsPbI₃ NCs underwent a phase transition from cubic (α) to orthorhombic phase and subsequent amorphization upon further compression. The structural changes with octahedron distortion to accommodate the Jahn–Teller effect were strongly responsible for the optical variation with the increase of pressure. First-principles calculations reveal that the band-gap engineering is governed by orbital interactions within the inorganic Pb–I frame through the structural modification. Our high-pressure studies not only established structure–property relationships at the atomic scale of α-CsPbI₃ NCs, but also provided significant clues in optimizing photovoltaic performance, thus facilitating the design of novel MHPs with increased stimulus-resistant capability

Selective Access to <i>E</i>- and <i>Z</i>‑ΔIle-Containing Peptides via a Stereospecific E2 Dehydration and an O → N Acyl Transfer

A concise synthesis of peptides that contain <i>E</i>- or <i>Z</i>-dehydroisoleucine (ΔIle) residues is reported. The key reaction is an unusual <i>anti</i> dehydration of β-<i>tert</i>-hydroxy amino acid derivatives that is mediated by the Martin sulfurane. A subsequent tandem Staudinger reduction–O → N acyl transfer process forges an amide bond to the ΔIle residue with minimal <i>E</i>/<i>Z</i> alkene isomerization. Density functional calculations attribute the stereospecific dehydration to a highly asynchronous E2 <i>anti</i> process

Pressure Effects on Structure and Optical Properties in Cesium Lead Bromide Perovskite Nanocrystals

Metal halide perovskites (MHPs) are gaining increasing interest because of their extraordinary performance in optoelectronic devices and solar cells. However, developing an effective strategy for achieving the band-gap engineering of MHPs that will satisfy the practical applications remains a great challenge. In this study, high pressure is introduced to tailor the optical and structural properties of MHP-based cesium lead bromide nanocrystals (CsPbBr₃ NCs), which exhibit excellent thermodynamic stability. Both the pressure-dependent steady-state photoluminescence and absorption spectra experience a stark discontinuity at ∼1.2 GPa, where an isostructural phase transformation regarding the <i>Pbnm</i> space group occurs. The physical origin points to the repulsive force impact due to the overlap between the valence electron charge clouds of neighboring layers. Simultaneous band-gap narrowing and carrier-lifetime prolongation of CsPbBr₃ trihalide perovskite NCs were also achieved as expected, which facilitates the broader solar spectrum absorption for photovoltaic applications. Note that the values of the phase change interval and band-gap red-shift of CsPbBr₃ nanowires are between those for CsPbBr₃ nanocubes and the corresponding bulk counterparts, which results from the unique geometrical morphology effect. First-principles calculations unravel that the band-gap engineering is governed by orbital interactions within the inorganic Pb–Br frame through structural modification. Changes of band structures are attributed to the synergistic effect of pressure-induced modulations of the Br–Pb bond length and Pb–Br–Pb bond angle for the PbBr₆ octahedral framework. Furthermore, the significant distortion of the lead–bromide octahedron to accommodate the Jahn–Teller effect at much higher pressure would eventually lead to a direct to indirect band-gap electronic transition. This study enables high pressure as a robust tool to control the structure and band gap of CsPbBr₃ NCs, thus providing insight into the microscopic physiochemical mechanism of these compressed MHP nanosystems

Bioactive Ceria Nanoenzymes Target Mitochondria in Reperfusion Injury to Treat Ischemic Stroke

Overproduction of reactive oxygen species by damaged mitochondria after ischemia is a key factor in the subsequent cascade of damage. Delivery of therapeutic agents to the mitochondria of damaged neurons in the brain is a potentially promising targeted therapeutic strategy for the treatment of ischemic stroke. In this study, we developed a ceria nanoenzymes synergistic drug-carrying nanosystem targeting mitochondria to address multiple factors of ischemic stroke. Each component of this nanosystem works individually as well as synergistically, resulting in a comprehensive therapy. Alleviation of oxidative stress and modulation of the mitochondrial microenvironment into a favorable state for ischemic tolerance are combined to restore the ischemic microenvironment by bridging mitochondrial and multiple injuries. This work also revealed the detailed mechanisms by which the proposed nanodelivery system protects the brain, which represents a paradigm shift in ischemic stroke treatment