Sulfur Precursor Reactivity Affecting the Crystal Phase and Morphology of Cu2−xS Nanoparticles

For plasmonic copper-deficient Cu_2−xS nanoparticles (NPs), accurate control of the crystal phase and morphology is highly desirable as both of which are known to determine the localized surface plasmon resonance (LSPR) wavelength and amplitude. Here, how the sulfur precursor reactivity in the synthesis of Cu_2−xS NPs affects the resulting crystal phase and morphology is examined. Djurleite Cu_1.94S, roxbyite Cu_1.8S, digenite Cu_1.8S as well as covellite CuS nanodisks were synthesized by using 1-dodecanethiol, N,N-dibutylthiourea, and crystal sulfur 1-octadecene/oleylamine solutions and their crystal phase dependent LSPR properties were exhaustively discussed. In addition, crystal phase interconversion between covellite CuS and djurleite/roxbyite Cu_2−xS was realized in the presence of the above sulfur precursors. On the other hand, djurleite Cu_1.94S nanorods rather than nanodisks were prepared by replacing 1-dodecanethiol with more reactive tert-dodecanethiol. The structural and morphological Cu_2−xS NPs here holds great promise in the application of photothermal therapy, photocatalysis, surface-enhanced Raman scattering (SERS), and many others.     

The atomic-level structure of bandgap engineered double perovskite alloys Cs2AgIn1−xFexCl6

Although lead-free halide double perovskites are considered as promising alternatives to lead halide perovskites for optoelectronic applications, state-of-the-art double perovskites are limited by their large bandgap. The doping/alloying strategy, key to bandgap engineering in traditional semiconductors, has also been employed to tune the bandgap of halide double perovskites. However, this strategy has yet to generate new double perovskites with suitable bandgaps for practical applications, partially due to the lack of fundamental understanding of how the doping/alloying affects the atomic-level structure. Here, we take the benchmark double perovskite Cs₂AgInCl₆ as an example to reveal the atomic-level structure of double perovskite alloys (DPAs) Cs₂AgIn_1−xFe_xCl₆ (x = 0–1) by employing solid-state nuclear magnetic resonance (ssNMR). The presence of paramagnetic alloying ions (e.g. Fe³⁺ in this case) in double perovskites makes it possible to investigate the nuclear relaxation times, providing a straightforward approach to understand the distribution of paramagnetic alloying ions. Our results indicate that paramagnetic Fe³⁺ replaces diamagnetic In³⁺ in the Cs₂AgInCl₆ lattice with the formation of [FeCl₆]³⁻·[AgCl₆]⁵⁻ domains, which show different sizes and distribution modes in different alloying ratios. This work provides new insights into the atomic-level structure of bandgap engineered DPAs, which is of critical significance in developing efficient optoelectronic/spintronic devices.

Through Fe³⁺-alloying, the bandgap of benchmark double perovskite Cs₂AgInCl₆ can be tuned from 2.8 eV to 1.6 eV. The atomic-level structure of Cs₂AgIn_1−xFe_xCl₆ was revealed by solid-state nuclear magnetic resonance (ssNMR).     

On-surface isostructural transformation from a hydrogen-bonded network to a coordination network for tuning the pore size and guest recognition

Rational manipulation of supramolecular structures on surfaces is of great importance and challenging. We show that imidazole-based hydrogen-bonded networks on a metal surface can transform into an isostructural coordination network for facile tuning of the pore size and guest recognition behaviours. Deposition of triangular-shaped benzotrisimidazole (H₃btim) molecules on Au(111)/Ag(111) surfaces gives honeycomb networks linked by double N–H⋯N hydrogen bonds. While the H₃btim hydrogen-bonded networks on Au(111) evaporate above 453 K, those on Ag(111) transform into isostructural [Ag₃(btim)] coordination networks based on double N–Ag–N bonds at 423 K, by virtue of the unconventional metal–acid replacement reaction (Ag reduces H⁺). The transformation expands the pore diameter of the honeycomb networks from 3.8 Å to 6.9 Å, giving remarkably different host–guest recognition behaviours for fullerene and ferrocene molecules based on the size compatibility mechanism.

A hydrogen-bonded network on a Ag(111) surface can transform into an isostructural Ag(i) coordination network, giving drastically different host–guest recognition behaviours.     

The video-rate imaging of sub-10 nm plasmonic nanoparticles in a cellular medium free of background scattering

Plasmonic nanoparticles (e.g., gold, silver) have attracted much attention for biological sensing and imaging as promising nanoprobes. Practical biomedical applications demand small gold nanoparticles (Au NPs) with a comparable size to quantum dots and fluorescent proteins. Very small nanoparticles with a size below the Rayleigh limit (usually <30–40 nm) are hard to see by light scattering using a dark-field microscope, especially within a cellular medium. A photothermal microscope is able to detect very small nanoparticles, down to a few nanometers, but the imaging speed is usually too slow (minutes to hours) to image living cell processes. Here an absorption modulated scattering microscopy (AMSM) method is presented, which allows for the imaging of sub-10 nm Au NPs within a cellular medium. The unique physical mechanism of AMSM offers the remarkable ability to remove the light scattering background of the cellular component. In addition to having a sensitivity comparable to that of photothermal microscopy, AMSM has a much higher imaging speed, close to the video rate (20 fps), which allows for the dynamic tracking of small nanoparticles in living cells. This AMSM method might be a valuable tool for living cell imaging, using sub-10 nm Au NPs as biological probes, and thereby unlocking many new applications, such as single molecule labeling and the dynamic tracking of molecular interactions.

An absorption modulated scattering microscopy technique that allows for the imaging of sub-10 nm gold nanoparticles within a cellular scattering medium is presented.     

Asymmetric total synthesis of (+)-xestoquinone and (+)-adociaquinones A and B

The asymmetric total synthesis of (+)-xestoquinone and (+)-adociaquinones A and B was achieved in 6–7 steps using an easily accessible meso-cyclohexadienone derivative. The [6,6]-bicyclic decalin B–C ring and the all-carbon quaternary stereocenter at C-6 were prepared via a desymmetric intramolecular Michael reaction with up to 97% ee. The naphthalene diol D–E ring was constructed through a sequence of Ti(Oi-Pr)₄-promoted photoenolization/Diels–Alder, dehydration, and aromatization reactions. This asymmetric strategy provides a scalable route to prepare target molecules and their derivatives for further biological studies.

The asymmetric total synthesis of (+)-xestoquinone and (+)-adociaquinones A and B was achieved in 6–7 steps using an easily accessible meso-cyclohexadienone derivative.

Various halenaquinone-type natural products with promising biological activity have been isolated from marine sponges of the genus Xestospongia¹ from the Pacific Ocean. (+)-Halenaquinone (1),^2,3 (+)-xestoquinone (2), and (+)-adociaquinones A (3) and B (4)^4,5 bearing a naphtha[1,8-bc]furan core (Fig. 1) are the most typical representatives of this family. Naturally occurring (−)-xestosaprol N (5) and O (6)^6,7 have the same structure as 3 and 4 except for a furan ring, while a naphtha[1,8-bc]furan core can also be found in fungus-isolated furanosteroids (−)-viridin (7) and (+)-nodulisporiviridin E (8)^8,9 (Fig. 1). Halenaquinone (1) was first isolated from the tropical marine sponge Xestospongia exigua² and it shows antibiotic activity against Staphylococcus aureus and Bacillus subtilis. Xestoquinone (2) and adociaquinones A (3) and B (4) were firstly isolated, respectively, from the Okinawan marine sponge Xestospongia sp.^4a and the Truk Lagoon sponge Adocia sp.,^4b and they show cardiotonic,^4a,c cytotoxic,^4b,i antifungal,⁴ⁱ antimalarial,^4j and antitumor^4l activities. These compounds inhibit the activity of pp60v-src protein tyrosine kinase,^4d topoisomerases I^4e and II,^4f myosin Ca²⁺ ATPase,^4c,g and phosphatases Cdc25B, MKP-1, and MKP-3.^4h,kOpen in a separate windowFig. 1Structure of halenaquinone-type natural products and viridin-type furanosteroids.Owing to their diverse bioactivities, the synthesis of this family of natural compounds has been extensively studied, with published pathways making use of Diels–Alder,^{3a,d,e,5a–c,e,g} furan ring transfer,^5b Heck,^{3b,c,5f,7,9b,d} palladium-catalyzed polyene cyclization,^5d Pd-catalyzed oxidative cyclization,^3f and hydrogen atom transfer (HAT) radical cyclization^9c reactions. In this study, we report the asymmetric total synthesis of (+)-xestoquinone (2), (−)-xestoquinone (2′), and (+)-adociaquinones A (3) and B (4) (Fig. 1).The construction of the fused tetracyclic B–C–D–E skeleton and the all carbon quaternary stereocenter at C-6 is a major challenge towards the total synthesis of xestoquinone (2) and adociaquinones A (3) and B (4). Based on our retrosynthetic analysis (Scheme 1), the all-carbon quaternary carbon center at C-6 of cis-decalin 12 could first be prepared stereoselectively from the achiral aldehyde 13via an organocatalytic desymmetric intramolecular Michael reaction.^10,11 The tetracyclic framework 10 could then be formed via a Ti(Oi-Pr)₄-promoted photoenolization/Diels–Alder (PEDA) reaction^12–16 of 11 and enone 12. Acid-mediated cyclization of 10 followed by oxidation state adjustment could be subsequently applied to form the furan ring A of xestoquinone (2). Finally, based on the biosynthetic pathway of (+)-xestoquinone (2)^4b,5c and our previous studies,⁷ the heterocyclic ring F of adociaquinones A (3) and B (4) could be prepared from 2via a late-stage cyclization with hypotaurine (9).Open in a separate windowScheme 1Retrosynthetic analysis of (+)-xestoquinone and (+)-adociaquinones A and B.The catalytic enantioselective desymmetrization of meso compounds has been used as a powerful strategy to generate enantioenriched molecules bearing all-carbon quaternary stereocenters.^10,11 For instance, two types of asymmetric intramolecular Michael reactions were developed using a cysteine-derived chiral amine as an organocatalyst by Hayashi and co-workers,^11a,b while a desymmetrizing secondary amine-catalyzed asymmetric intramolecular Michael addition was later reported by Gaunt and co-workers to produce enantioenriched decalin structures.^11c Prompted by these pioneering studies and following the suggested retrosynthetic pathway (Scheme 1), we first screened conditions for organocatalytic desymmetric intramolecular Michael addition of meso-cyclohexadienone 13 (Table 1) in order to form the desired quaternary stereocenter at C-6. Compound 13 was easily prepared on a gram scale via a four-step process (see details in the ESI^†).Attempts of organocatalytic desymmetric intramolecular Michael addition^a

Boosting the synthesis of value-added aromatics directly from syngas via a Cr2O3 and Ga doped zeolite capsule catalyst

Even though the transformation of syngas into aromatics has been realized via a methanol-mediated tandem process, the low product yield is still the bottleneck, limiting the industrial application of this technology. Herein, a tailor-made zeolite capsule catalyst with Ga doping and SiO₂ coating was combined with the methanol synthesis catalyst Cr₂O₃ to boost the synthesis of value-added aromatics, especially para-xylene, from syngas. Multiple characterization studies, control experiments, and density functional theory (DFT) calculation results clarified that Ga doped zeolites with strong CO adsorption capability facilitated the transformation of the reaction intermediate methanol by optimizing the first C–C coupling step under a high-pressure CO atmosphere, thereby driving the reaction forward for aromatics synthesis. This work not only reveals the synergistic catalytic network in the tandem process but also sheds new light on principles for the rational design of a catalyst in terms of oriented conversion of syngas.

The single-pass conversion of syngas into para-xylene was realized using a bifunctional catalyst Cr₂O₃/Ga-ZSM-5@SiO₂. The Ga species facilitates the methanol consumption process by C–C coupling optimization, enhancing the yield of the target aromatics.     

Metal-Organic Frameworks with Novel Catenane-like Interlocking: Metal-Determined Photoresponse and Uranyl Sensing

The assembly of two tripyridinium-tricarboxylate ligands and different metal ions leads to seven isostructural MOFs, which show novel 2D→2D supramolecular entanglement featuring catenane-like interlocking of tricyclic cages. The MOFs show tripyridinium-afforded and metal-modulated photoresponsive properties. The MOFs with d¹⁰ metal centers ( 1-Cd , 1-Zn , 2-Cd , 2-Zn ) show fast and reversible photochromism and concomitant fluorescence quenching, 1-Ni displays slower photochromism but does not fluoresce, and 1-Co and 2-Co are neither photochromic nor fluorescent. It is shown here that the network entanglement dictates donor-acceptor close contacts, which enable fluorescence originated from interligand charge transfer. The contacts also allow photoinduced electron transfer, which underlies photochromism and concomitant fluorescence response. The metal dependence in fluorescence and photochromism can be related to energy transfer through metal-centered d-d transitions. In addition, 1-Cd is demonstrated to be a potential fluorescence sensor for sensitive and selective detection of UO₂²⁺ in water.     

Intermetallic Compounds: Liquid-Phase Synthesis and Electrocatalytic Applications

Characterized by long-range atomic ordering, well-defined stoichiometry, and controlled crystal structure, intermetallics have attracted increasing attention in the area of chemical synthesis and catalytic applications. Liquid-phase synthesis of intermetallics has arisen as the promising methodology due to its precise control over size, shape, and resistance toward sintering compared with the traditional metallurgy. This short review tends to provide perspectives on the liquid-phase synthesis of intermetallics in terms of both thermodynamics and methodology, as well as its applications in various catalytic reactions. Specifically, basic thermodynamics and kinetics in the synthesis of intermetallics will be first discussed, followed by discussing the main factors that will affect the formation of intermetallics during synthesis. The application of intermetallics in electrocatalysis will be demonstrated case by case at last. We conclude the review with perspectives on the future developments with respect to both synthesis and catalytic applications.     

Functional Group Modification and Bonding Characteristics of Ti3C2 MXene-Organic Composites from First-Principles Calculations

The unique physical structure and abundant surface functional groups of MXene make the grafted organic molecules exhibit specific electrical and optical properties. This work reports the results of first-principles calculations to investigate the composite systems formed by different organic molecular monomers, namely acrylic acid (AA), acrylamide (AM), 1-aziridineethanol (1-AD) and glucose, and Ti₃C₂ MXene saturated with different functional groups, namely −OH, −O and −F. The results show that the interaction between organic molecules and the MXene surface depends on the type of functional groups of the organic molecules, while the strength of the interaction is determined by the type of surface functional groups and the number of hydrogen bonds. The bare Ti₃C₂ and Ti₃C₂(OH)₂ can readily form strong chemical and hydrogen bonds with AA and AM molecules, leading to strong adsorption energy and a large amount of charge transfer, while the interaction between organic molecules and MXene saturated by −F or −O groups mainly exhibits physical interactions, accompanied by low adsorption energy and a small amount of charge transfer. This research provides theoretical guidance for the synthesis of high-performance MXene organic composite systems.     

Amorphous Carbon Film with Self-modified Carbon Nanoparticles Synthesized by Low Temperature Carbonization of Phenolic Resin for Simultaneous Sensing of Dopamine and Uric Acid

A self-modified film electrode consisting of homogeneous snowflake-shaped nanoparticles on the amorphous carbon substrate (HNAC) was prepared by low temperature carbonization of phenolic resin. Such a unique structure was beneficial to enhance the electroanalysis signal responds. Simultaneous detection of DA and UA was performed on the HNAC using differential pulse voltammetry (DPV) at pH 8 phosphate buffer. The well-defined oxidation peak potential separation reached 260 mV between DA and UA. Meanwhile, the detection limit of HNAC were 0.401 μM (DA) and 2.800 μM (UA).