A sacrificial reductant-free copper-catalyzed benzylic C–H alkoxylation with N-Fluorobenzenesulfonimide (NFSI) was reported. Mechanistic studies suggested a novel pathway for the generation of active CuI species from Cu(OAc)2, NFSI and MeOH. A proper loading amount of copper catalyst was found to balance the reaction rates of benzylic C–H alkoxylation and overoxidation of benzyl ether to exhibit the best performance.
Self-assembly films have demonstrated an efficient method to functionalize the surfaces of variously different materials. In this work, we preliminarily explored the modification effect of 10,12-pentacosadiynoic acid (PCDA) on the optical properties of monolayer molybdenum disulfide (MoS2) grown on a rutile titanium dioxide (r-TiO2) (110) single crystal surface. Atomic force microscopy (AFM) characterizations directly revealed that the PCDA molecules self-assemble into the same lamella structure as on pure MoS2, which can be further polymerized into conductive polydiacetylene (PDA) chains under ultraviolet light (UV) irradiation. Detailed photoluminescence (PL) measurements observed clearly increased luminescence of negative trions (A−) yet decreased total intensities for MoS2 upon adding the PCDA assembly, which is further enhanced after stimulating its polymerization. These results indicate that the PCDA assembly and its polymerization have different electron donability to MoS2, which hence provides a deepened understanding of the interfacial interactions within a multicomponent system. Our work also demonstrates the self-assembly of films as a versatile strategy to tune the electronic/optical properties of hybridized two-dimensional materials.
ATP-binding cassette (ABC) exporters are a class of molecular machines that transport substrates out of biological membranes by gating movements leading to transitions between outward-facing (OF) and inward-facing (IF) conformational states. Despite significant advances in structural and functional studies, the molecular mechanism underlying conformational gating in ABC exporters is not completely understood. A complete elucidation of the state transitions during the transport cycle is beyond the capability of the all-atom molecular dynamics (MD) method because of the limited time scale of MD. In the present work, a coarse-grained molecular dynamics (CG-MD) method with an improved sampling strategy is performed for the bacterial ABC exporter MsbA. The resultant potential of the mean force (PMF) along the center-of-mass (COM) distances, d1 and d2, between the two opposing subunits of the internal and external gates, respectively, are obtained, delicately showing the details of the
Chemical exchange saturation transfer (CEST) magnetic resonance imaging (MRI) is an advanced imaging method that probes the chemical exchange between bulk water protons and exchangeable solute protons. This chemical exchange decreases the MR signal of water and reveals the distribution and concentration of certain endogenous biomolecules or extrogenous contrast agents in organisms with high sensitivity and spatial resolution. The CEST signal depends not only on the concentration of the CEST contrast agent and external magnetic field but also on the surrounding environments of the contrast agent, such as pH and temperature, thus enabling CEST MRI to monitor pH, temperature, metabolic level, and enzyme activity in vivo. In this review, we discuss the principle of CEST MRI and mainly summarize the recent progress of diamagnetic CEST (diaCEST) contrast agents on tumor imaging, diagnosis, and therapy effect evaluation.
Although graphitic carbons, as a support for the cathode catalyst in proton exchange membrane fuel cells, have significant advantages in enhancing the corrosion resistance of the catalyst, the preparation of small-sized Pt particles on the graphitic carbon support often faces challenges due to its low porosity and lack of defect structures. Here, we report a mercaptopropane-assisted impregnation method to achieve size control of Pt nanoparticles on graphitic carbon. We show that mercaptopropane can coordinate with Pt during the impregnation process and transform into sulfur-doped carbon coatings through the subsequent thermal reduction process, which ensures the formation of small-sized Pt nanoparticles on graphitic carbon. Due to effective size control, the prepared cathode catalyst exhibited enhanced fuel cell performance compared to the catalyst prepared by the traditional impregnation method. We performed the accelerated stress test on the synthesized catalyst using the durability protocol recommended by the U.S. Department of Energy (DOE). After 5000 voltage cycles in the range of 1.0–1.5 V, the catalyst showed a negligible voltage loss of only 10 mV at a current density of 1.5 A·cm−2, meeting the DOE support durability target (30 mV).
The development of new magnetic fluorescent materials is of great significance for identification and criminal investigation. Since the photosensitive elements used in conventional cameras have exhibited the highest quantum efficiency in the range of 500–700 nm, lanthanide-based upconversion nanoparticles (UCNPs) with main emission peaks at 507–533 nm, 533–568 nm and 637–683 nm are suitable for constructing magnetic fluorescent materials. In this work, we demonstrate a type of magnetic upconversion nanoparticle (MUCNP) of NaGdF4:Yb,Er-Fe3O4 by a ligand-linked method. After optimizing the reaction parameters, the composite particles possess remarkable magnetic properties and upconversion fluorescence intensity and achieve high contrast for latent fingerprint recognition on various substrates. The combination of upconversion luminescence and magnetism contributes to good fingerprint recognition sensitivity and universality.
The use of intercalation-type metal oxides as anode materials in rechargeable lithium-ion batteries is appealing due to their reduced risk of Li plating at low voltages. However, their implementation for fast-charging applications is limited by their lower energy and power density, as well as cycling instability. Herein, we present an amorphous TiO2 nanosheet that exhibits exceptional cycling stability with a high capacity of 231 mA · h · g−1 after 200 cycles at 500 mA · g−1 and 156.7 mA · h · g−1 after 1000 cycles at a high current density of 6 A · g−1. We attribute the enhanced rate performance to the amorphous nature with high isotropy, which facilitates low energy migration paths and ion availability and can accommodate large changes in volume. This work suggests that amorphization represents a promising strategy for developing unconventional metal oxide electrode materials with high-rate performance.
With the development of algorithms and theoretical chemistry, quantum chemical calculations have been used to explain and predict various chemical experiments. The hydroalkylation of conjugated olefins catalyzed by nickel is an important type of organic chemical reaction, and its mechanism has always been the focus of organic chemists. In this paper, a hydroalkylation reaction developed by the Mazet research group was studied in detail by means of density functional theory (DFT), and a possible mechanism model of the reaction was obtained. In this context, the attractive regioselectivity of the reaction was explored and rationally explained.
To make small molecular photosensitizer-based nanoparticles photostable, we polymerized such photosensitizers via emulsion polymerization, and the resulting nanoparticles exhibited sustained absorption of the excitation wavelength in the near-infrared region, generated stable photothermal and photodynamic effects upon repeated irradiation with an near-infrared laser, and efficiently eradicated cancerous cells even after prior irradiation exposure.
Investigations of strongly correlated quantum impurity systems (QIS), which exhibit diversified novel and intriguing quantum phenomena, have become a highly concerning subject in recent years. The hierarchical equations of motion (HEOM) method is one of the most popular numerical methods to characterize QIS linearly coupled to the environment. This review provides a comprehensive account of a formally rigorous and numerical convergent HEOM method, including a modeling description of the QIS and an overview of the fermionic HEOM formalism. Moreover, a variety of spectrum decomposition schemes and hierarchal terminators have been proposed and developed, which significantly improve the accuracy and efficiency of the HEOM method, especially in cryogenic temperature regimes. The practicality and usefulness of the HEOM method to tackle strongly correlated issues are exemplified by numerical simulations for the characterization of nonequilibrium quantum transport and strongly correlated Kondo states as well as the investigation of nonequilibrium quantum thermodynamics.