Photochemical Reactions of Microcrystalline Thymidine

Nucleoside/nucleotide/oligonucleotide photoreactions usually result in a number of products simultaneously due to a wide range of conformers existing at a given time. Such a complicated reaction pattern makes it difficult for one to focus on a single DNA photoproduct and elucidate the requirements for its formation. A rare example of thymidine photoreaction in microcrystals is reported, where 5-thyminyl-5,6-dihydrothymine, e.g., the spore photoproduct (SP), is produced as the dominant species in ∼85% yield. This unprecedented high yield clears the major obstacle for future SP photochemistry studies in detail

A Comparative Study on Dinuclear and Mononuclear Aluminum Methyl Complexes Bearing Piperidyl–Phenolato Ligands in ROP of Epoxides

Dinuclear aluminum methyl complexes stabilized by piperidyl–phenolato ligands were prepared and characterized. The ring-opening polymerizations of cyclohexene oxide (CHO) and propylene oxide (PO) initiated by dinuclear complexes and mononuclear analogues were investigated and compared. Enhanced activity of dinuclear complexes compared to that of mononuclear analogues in both the ring-opening polymerization of CHO and PO proves the synergistic interaction of two Al centers in the former. End-group analysis of oligomers by MALDI-TOF mass spectrometry confirms the role of methyl groups as initiating groups. A bimetallic mechanism is proposed, in which the cooperation of two Al centers are involved in polymerization processes

Synthesis and Characterization of Dinuclear Salan Rare-Earth Metal Complexes and Their Application in the Homo- and Copolymerization of Cyclic Esters

Four rare-earth-metal aryloxo complexes stabilized by a tetradentate Salan ligand were prepared, and their catalytic properties for the (co)­polymerization of lactides and ε-caprolactone were elucidated. The proton-exchange reactions of (C₅H₅)₃Ln­(THF) with the Salan ligand <i>N</i>,<i>N</i>′-(CH₂Ph)₂-<i>N</i>,<i>N</i>′-[CH₂(2-OH-C₆H₂-Me₂-3,5)]₂ (LH₂) in a 1:1 molar ratio, and subsequently with 1 equiv of <i>p</i>-methylphenol, gave the rare-earth-metal aryloxides [LLn­(OC₆H₄-4-CH₃)­(THF)_<i>n</i>]₂ [<i>n</i> = 0 and Ln = Y (<b>1</b>), Sm (<b>2</b>), and Nd (<b>3</b>); <i>n</i> = 1 and Ln = La (<b>4</b>)] in good isolated yields. These complexes were fully characterized by elemental analysis, IR, and NMR spectroscopy (for complexes <b>1</b> and <b>4</b>). Solid-state structures of complexes <b>1</b>–<b>4</b> were confirmed by single-crystal X-ray diffraction analysis. Complexes <b>1</b>–<b>4</b> have dinuclear solid-state structures, with a Ln₂O₂ core bridging the Salan ligands. The coordination geometry around each of the metals is a slightly distorted octahedron in complexes <b>1</b>–<b>3</b>, whereas it is a capped trigonal prism in complex <b>4</b>. It was found that complexes <b>1</b>–<b>4</b> can initiate efficiently the homopolymerization of l-lactide (l-LA) and <i>rac</i>-lactide (<i>rac</i>-LA) at 30 °C in tetrahydrofuran. The increasing activity of these complexes is in agreement with increasing ionic radii. A kinetic study revealed that seven-coordinated lanthanum complex <b>4</b> is more active for <i>rac</i>-LA polymerization compared with l-LA. A further study revealed that complex <b>4</b> was also an efficient initiator for the random copolymerization of l-LA and ε-caprolactone with the simultaneous addition of these two monomers, and the <i>T</i>_g values of the copolymers obtained increase linearly from −30.2 to +38.3 °C with an increase of the percentage of LA units. A mechanism study revealed that transesterification plays a crucial role in the formation of a random copolymer

A Comparative Study on Dinuclear and Mononuclear Aluminum Methyl Complexes Bearing Piperidyl–Phenolato Ligands in ROP of Epoxides

Dinuclear aluminum methyl complexes stabilized by piperidyl–phenolato ligands were prepared and characterized. The ring-opening polymerizations of cyclohexene oxide (CHO) and propylene oxide (PO) initiated by dinuclear complexes and mononuclear analogues were investigated and compared. Enhanced activity of dinuclear complexes compared to that of mononuclear analogues in both the ring-opening polymerization of CHO and PO proves the synergistic interaction of two Al centers in the former. End-group analysis of oligomers by MALDI-TOF mass spectrometry confirms the role of methyl groups as initiating groups. A bimetallic mechanism is proposed, in which the cooperation of two Al centers are involved in polymerization processes

Integrated Design for Regulating the Interface of a Solid-State Lithium–Oxygen Battery with an Improved Electrochemical Performance

A composite solid-state electrolyte (SSE) with acceptable safety and durability is considered as a potential candidate for high-performance lithium–oxygen (Li–O2) batteries. Herein, to address the safety issues and improve the electrochemical performance of Li–O2 batteries, a solvent-free composite SSE is prepared based on the thermal initiation of poly(ethylene glycol) diacrylate radical polymerization, and an integrated battery is achieved by injecting an electrolyte precursor between electrodes during the assembly process through a simple heat treatment. The Li-metal symmetric cells based on this composite SSE achieve a critical current density of 0.8 mA cm–2 and a stable cycle life of over 900 h at a current density of 0.2 mA cm–2. This composite SSE effectively inhibits the erosion of O2 on the Li metal anode, optimizes the interface between the electrolyte and cathode, and provides abundant reaction sites for the electrochemical reactions during cycling. The integrated solid-state Li–O2 battery prepared in this work achieves stable long cycling (118 cycles) at a current density of 500 mA g–1 at room temperature, showing the promising future application prospects

Direct Synthesis and Practical Bandgap Estimation of Multilayer Arsenene Nanoribbons

Direct Synthesis and Practical Bandgap Estimation of Multilayer Arsenene Nanoribbon

Sequential Cation Exchange Generated Superlattice Nanowires Forming Multiple p–n Heterojunctions

Fabrication of superlattice nanowires (NWs) with precisely controlled segments normally requires sequential introduction of reagents to the growing wires at elevated temperatures and low pressure. Here we demonstrate the fabrication of superlattice NWs possessing multiple p–n heterojunctions by converting the initially formed CdS to Cu₂S NWs first and then to segmented Cu₂S–Ag₂S NWs through sequential cation exchange at low temperatures. In the formation of Cu₂S NWs, twin boundaries generated along the NWs act as the preferred sites to initiate the nucleation and growth of Ag₂S segments. Varying the immersion time of Cu₂S NWs in a AgNO₃ solution controls the Ag₂S segment length. Adjacent Cu₂S and Ag₂S segments in a NW were found to display the typical electrical behavior of a p–n junction

Plasma-Assisted Synthesis of High-Mobility Atomically Layered Violet Phosphorus

Two-dimensional layered materials such as graphene, transition metal dichalcogenides, and black phosphorus have demonstrated outstanding properties due to electron confinement as the thickness is reduced to atomic scale. Among the phosphorus allotropes, black phosphorus, and violet phosphorus possess layer structure with the potential to be scaled down to atomically thin film. For the first time, the plasma-assisted synthesis of atomically layered violet phosphorus has been achieved. Material characterization supports the formation of violet phosphorus/InN over InP substrate where the layer structure of violet phosphorus is clearly observed. The identification of the crystal structure and lattice constant ratifies the formation of violet phosphorus indeed. The critical concept of this synthesis method is the selective reaction induced by different variations of Gibbs free energy (Δ<i>G</i>) of reactions. Besides, the Hall mobility of the violet phosphorus on the InP substrate greatly increases over the theoretical values of InP bulk material without much reduction in the carrier concentration, suggesting that the mobility enhancement results from the violet phosphorus layers. Furthermore, this study demonstrates a low-cost technique with high compatibility to synthesize the high-mobility atomically layered violet phosphorus and open the space for the study of the fundamental properties of this intriguing material as a new member of the fast growing family of 2D crystals

Oligo[2]catenane That Is Robust at Both the Microscopic and Macroscopic Scales

Polycatenanes are extremely attractive topological architectures on account of their high degrees of conformational freedom and multiple motion patterns of the mechanically interlocked macrocycles. However, exploitation of these peculiar structural and dynamic characteristics to develop robust catenane materials is still a challenging goal. Herein, we synthesize an oligo[2]catenane that showcases mechanically robust properties at both the microscopic and macroscopic scales. The key feature of the structural design is controlling the force-bearing points on the metal-coordinated core of the [2]catenane moiety that is able to maximize the energy dissipation of the oligo[2]catenane via dissociation of metal-coordination bonds and then activation of sequential intramolecular motions of circumrotation, translation, and elongation under an external force. As such, at the microscopic level, the single-molecule force spectroscopy measurement exhibits that the force to rupture dynamic bonds in the oligo[2]catenane reaches a record high of 588 ± 233 pN. At the macroscopic level, our oligo[2]catenane manifests itself as the toughest catenane material ever reported (15.2 vs 2.43 MJ/m3). These fundamental findings not only deepen the understanding of the structure-property relationship of poly[2]catenanes with a full set of dynamic features but also provide a guiding principle to fabricate high-performance mechanically interlocked catenane materials