Identification and releasing characteristics of β-cyclodextrin–phenylethanoid glycosides inclusion complex

β-Cyclodextrin–phenylethanoid glycosides inclusion complex was prepared and its releasing characteristic was investigated in this study. The results, obtained from Fourier-transform infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction, indicated that phenylethanoid glycosides (PG) were able to form an inclusion complex with β-cyclodextrin (β-CD). This complex exhibited different spectroscopic features, thermal stability and crystalline structure from PG. Molecular simulation results showed the benzene rings of PG incorporating into the hydrophobic cavity of β-CD during the complex formation. Furthermore, the releasing rate of the included PG in the inclusion complex was positively correlated with temperature and it was slightly higher in 0.5 % HCl solution than in water. These results suggested that the complexation technique using β-CD was a promising strategy for increasing the applications of PG in food and healthcare industries.     

手性助剂诱导催化不对称Strecker反应研究进展

亚胺的不对称Strecker反应是合成α-氨基酸化合物的重要途径之一,一般在手性助剂的诱导下进行.近年来,用于诱导不对称Strecker反应的各类手性助剂的研究受到广泛关注.本文综述了α-苯乙胺、α-氨基酸、α-氨基酸衍生的酰胺、α-苯甘氨醇、亚磺酰基亚胺、糖胺、肼等七类化合物作为手性助剂在不对称Strecker反应中的应用研究现状,就该研究领域存在的问题进行了分析,并对其前景进行了展望.     

A Pressure-Induced Inverse Order–Disorder Transition in Double Perovskites

Given the consensus that pressure improves cation ordering in most of known materials, a discovery of pressure-induced disordering could require recognition of an order–disorder transition in solid-state physics/chemistry and geophysics. Double perovskites Y₂CoIrO₆ and Y₂CoRuO₆ polymorphs synthesized at 0, 6, and 15 GPa show B-site ordering, partial ordering, and disordering, respectively, accompanied by lattice compression and crystal structure alteration from monoclinic to orthorhombic symmetry. Correspondingly, the long-range ferrimagnetic ordering in the B-site ordered samples are gradually overwhelmed by B-site disorder. Theoretical calculations suggest that unusual unit-cell compressions under external pressures unexpectedly stabilize the disordered phases of Y₂CoIrO₆ and Y₂CoRuO₆.     

Growth of Single-Walled Carbon Nanotubes with Controlled Structure: Floating Carbide Solid Catalysts

Single-walled carbon nanotube (SWNT) horizontal arrays with specific chirality can be enriched using solid carbide catalysts on substrates. However, scale-up production by continuous loading of the solid catalysts onto the substrates is challenging. Described here is the preparation of a floating carbide solid catalyst (FSC) for the controlled growth of SWNTs. The FSC, titanium carbide (TiC) nanoparticle, was directly obtained in the carrier gas phase by decomposition and carbonization of the titanocene dichloride precursor at high temperature. By using the TiC nanoparticle FSC, both SWNT horizontal arrays and randomly distributed networks can be obtained. The chirality of the as-grown SWNTs were thermodynamically controlled to have fourfold symmetry. Further optimization of growth condition resulted in an abundance of (16,8) tubes with about a 74 % content. This FSC chemical vapor deposition (FSCCVD) method has potential for realizing mass growth of SWNTs with controlled structures.     

Pressure-Suppressed Carrier Trapping Leads to Enhanced Emission in Two-Dimensional Perovskite (HA)2(GA)Pb2I7

A remarkable PL enhancement by 12 fold is achieved using pressure to modulate the structure of a recently developed 2D perovskite (HA)₂(GA)Pb₂I₇ (HA=n-hexylammonium, GA=guanidinium). This structure features a previously unattainable, extremely large cage. In situ structural, spectroscopic, and theoretical analyses reveal that lattice compression under a mild pressure within 1.6 GPa considerably suppresses the carrier trapping, leading to significantly enhanced emission. Further pressurization induces a non-luminescent amorphous yellow phase, which is retained and exhibits a continuously increasing band gap during decompression. When the pressure is released to 1.5 GPa, emission can be triggered by above-band gap laser irradiation, accompanied by a color change from yellow to orange. The obtained orange phase could be retained at ambient conditions and exhibits two-fold higher PL emission compared with the pristine (HA)₂(GA)Pb₂I₇.     

Dysprosiacarboranes as Organometallic Single-Molecule Magnets

The dicarbollide ion, nido-C₂B₉H₁₁²⁻ is isoelectronic with cyclopentadienyl. Herein, we make dysprosiacarboranes, namely [(C₂B₉H₁₁)₂Ln(THF)₂][Na(THF)₅] (Ln=Dy, 1Dy ) and [(THF)₃(μ-H)₃Li]₂[{η⁵-C₆H₄(CH₂)₂C₂B₉H₉}Dy{η²:η⁵-C₆H₄(CH₂)₂C₂B₉H₉}₂Li] 3Dy and show that dicarbollide ligands impose strong magnetic axiality on the central Dy^III ion. The effective energy barrier (U_eff) for the loss of magnetization can be varied by the substitution pattern on the dicarbollide. This finding is demonstrated by comparing complexes of nido-C₂B₉H₁₁²⁻ and nido-[o-xylylene-C₂B₉H₉]²⁻, which show a U_eff of 430(5) K and 804(7) K, respectively. The blocking temperature defined by the open hysteresis temperature of 3Dy reaches 6.8 K. Moreover, the linear complex [Dy(C₂B₉H₁₁)₂]⁻ is predicted to have comparable properties with the linear [Dy(Cp^Me3)₂]⁺ complex. As such, carboranyl ligands and their derivatives may provide a new type of organometallic ligand for high-performance single-molecule magnets.     

Machine-Driven Chemoenzymatic Synthesis of Glycopeptide

Historically, researchers have put considerable effort into developing automation systems to prepare natural biopolymers such as peptides and oligonucleotides. The availability of such mature systems has significantly advanced the development of natural science. Over the past twenty years, breakthroughs in automated synthesis of oligosaccharides have also been achieved. A machine-driven platform for glycopeptide synthesis by a reconstructed peptide synthesizer is described. The designed platform is based on the use of an amine-functionalized silica resin to facilitate the chemical synthesis of peptides in organic solvent as well as the enzymatic synthesis of glycan epitopes in the aqueous phase in a single reaction vessel. Both syntheses were performed by a peptide synthesizer in a semiautomated manner.     

Porous Tantalum Nitride Single Crystal at Two-Centimeter Scale with Enhanced Photoelectrochemical Performance

Porous tantalum nitride (Ta₃N₅) single crystals, combining structural coherence and porous microstructure, would substantially improve the photoelectrochemical performance. The structural coherence would reduce the recombination of charge carriers and maintain excellent transport properties while the porous microstructure would not only reduce photon scattering but also facilitate surface reactions. Here, we grow bulk-porous Ta₃N₅ single crystals on a two-centimeter scale with (002), (023), and (041) facets, respectively, and show significantly enhanced photoelectrochemical performance. We show the preferential facet growth of porous crystals in a lattice reconstruction strategy in relation to lattice match and lattice channel. We present the facet engineering to enhance light absorption, exciton lifetime and transport properties. The porous Ta₃N₅ single crystal boosts photoelectrochemical oxidation of alcohols with the (002) facet showing the highest performance of >99 % alcohol conversion and >99 % aldehyde/ketone selectivity.     

Electrochemical Phase Evolution of Metal-Based Pre-Catalysts for High-Rate Polysulfide Conversion

In situ evolution of electrocatalysts is of paramount importance in defining catalytic reactions. Catalysts for aprotic electrochemistry such as lithium–sulfur (Li-S) batteries are the cornerstone to enhance intrinsically sluggish reaction kinetics but the true active phases are often controversial. Herein, we reveal the electrochemical phase evolution of metal-based pre-catalysts (Co₄N) in working Li-S batteries that renders highly active electrocatalysts (CoS_x). Electrochemical cycling induces the transformation from single-crystalline Co₄N to polycrystalline CoS_x that are rich in active sites. This transformation propels all-phase polysulfide-involving reactions. Consequently, Co₄N enables stable operation of high-rate (10 C, 16.7 mA cm⁻²) and electrolyte-starved (4.7 μL mg_S⁻¹) Li-S batteries. The general concept of electrochemically induced sulfurization is verified by thermodynamic energetics for most of low-valence metal compounds.     

DMSO-Enabled Selective Radical O−H Activation of 1,3(4)-Diols

Control of selectivity is one of the central topics in organic chemistry. Although unprecedented alkoxyl-radical-induced transformations have drawn a lot of attention, compared to selective C−H activation, selective radical O−H activation remains less explored. Herein, we report a novel selective radical O−H activation strategy of diols by combining spatial effects with proton-coupled electron transfer (PCET). It was found that DMSO is an essential reagent that enables the regioselective transformation of diols. Mechanistic studies indicated the existence of the alkoxyl radical and the selective interaction between DMSO and hydroxyl groups. Moreover, the distal C−C cleavage was realized by this selective alkoxyl-radical-initiation protocol.