Two‐Dimensional CuSe Nanosheets with Microscale Lateral Size: Synthesis and Template‐Assisted Phase Transformation

Semiconducting nanosheets with microscale lateral size are attractive building blocks for the fabrication of electronic and optoelectronic devices. The phase‐controlled chemical synthesis of semiconducting nanosheets is of particular interest, because their intriguing properties are not only related to their size and shape, but also phase‐dependent. Herein, a facile method for the synthesis of phase‐pure, microsized, two‐dimensional (2D) CuSe nanosheets with an average thickness of approximately 5 nm is demonstrated. These hexagonal‐phased CuSe nanosheets were transformed into cubic‐phased Cu_2?xSe nanosheets with the same morphology simply by treatment with heat in the presence of Cu^I cations. The phase transformation, proposed to be a template‐assisted process, can be extended to other systems, such as CuS and Cu_1.97S nanoplates. Our study offers a new method for the phase‐controlled preparation of 2D nanomaterials, which are not readily accessible by conventional wet‐chemical methods.     

Formation of Triple‐Shelled Molybdenum–Polydopamine Hollow Spheres and Their Conversion into MoO2/Carbon Composite Hollow Spheres for Lithium‐Ion Batteries

Unique triple‐shelled Mo‐polydopamine (Mo‐PDA) hollow spheres are synthesized through a facile solvothermal process. A sequential self‐templating mechanism for the multi‐shell formation is proposed, and the number of shells can be adjusted by tuning the size of the Mo‐glycerate templates. These triple‐shelled Mo‐PDA hollow spheres can be converted to triple‐shelled MoO₂/carbon composite hollow spheres by thermal treatment. Owing to the unique multi‐shells and hollow interior, the as‐prepared MoO₂/carbon composite hollow spheres exhibit appealing performance as an anode material for lithium‐ion batteries, delivering a high capacity of ca. 580 mAh g^?1 at 0.5 A g^?1 with good rate capability and long cycle life.     

One‐dimensional Nanomaterial Electrocatalysts for CO2 Fixation

Electroreduction of CO₂ into valuable molecules or fuels is a sustainable pathway for CO₂ reduction as well as energy storage. However, the premature development stage of electrocatalysts with high activity, selectivity, and durability still remains a significant bottleneck that hinders this field. One‐dimensional (1D) nanomaterials, including nanorods, nanotubes, nanoribbons, nanowires, and nanofibers, are generally considered as high‐activity and stable electromaterials, due to their unique uniform structures, orientated electronic and mass transport, and rigid tolerance to stress variation. During the past several years, 1D nanomaterials and nanostructures have been extensively studied due to their potentials in serving as CO₂ electroreduction catalysts. In this minireview, recent studies and advances in 1D nanomaterials for CO₂ eletroreduction are summarized, from the viewpoints of both computational and experimental aspects. Based on the composition, the 1D nanomaterials are studied in four categories, including metals, transition‐metal oxides/nitrides, transition‐metal chalcogenides, and carbon‐based materials. Different parameters in tuning 1D materials are also summarized and discussed, such as the crystal facets, grain boundaries, heteroatoms doping, additives and the electrochemical tuning effects. Finally, the challenges and prospects in this direction will be discussed.     

On the “Tertiary Structure” of Poly‐Carbenes; Self‐Assembly of sp3‐Carbon‐Based Polymers into Liquid‐Crystalline Aggregates

The self‐assembly of poly(ethylidene acetate) (st‐PEA) into van der Waals‐stabilized liquid‐crystalline (LC) aggregates is reported. The LC behavior of these materials is unexpected, and unusual for flexible sp³‐carbon backbone polymers. Although the dense packing of polar ester functionalities along the carbon backbone of st‐PEA could perhaps be expected to lead directly to rigid‐rod behavior, molecular modeling reveals that individual st‐PEA chains are actually highly flexible and should not reveal rigid‐rod induced LC behavior. Nonetheless, st‐PEA clearly reveals LC behavior, both in solution and in the melt over a broad elevated temperature range. A combined set of experimental measurements, supported by MM/MD studies, suggests that the observed LC behavior is due to self‐aggregation of st‐PEA into higher‐order aggregates. According to MM/MD modeling st‐PEA single helices adopt a flexible helical structure with a preferred trans‐gauche syn‐syn‐anti‐anti orientation. Unexpectedly, similar modeling experiments suggest that three of these helices can self‐assemble into triple‐helical aggregates. Higher‐order assemblies were not observed in the MM/MD simulations, suggesting that the triple helix is the most stable aggregate configuration. DLS data confirmed the aggregation of st‐PEA into higher‐order structures, and suggest the formation of rod‐like particles. The dimensions derived from these light‐scattering experiments correspond with st‐PEA triple‐helix formation. Langmuir–Blodgett surface pressure–area isotherms also point to the formation of rod‐like st‐PEA aggregates with similar dimensions as st‐PEA triple helixes. Upon increasing the st‐PEA concentration, the viscosity of the polymer solution increases strongly, and at concentrations above 20 wt % st‐PEA forms an organogel. STM on this gel reveals the formation of helical aggregates on the graphite surface–solution interface with shapes and dimensions matching st‐PEA triple helices, in good agreement with the structures proposed by molecular modeling. X‐ray diffraction, WAXS, SAXS and solid state NMR spectroscopy studies suggest that st‐PEA triple helices are also present in the solid state, up to temperatures well above the melting point of st‐PEA. Formation of higher‐order aggregates explains the observed LC behavior of st‐PEA, emphasizing the importance of the “tertiary structure” of synthetic polymers on their material properties.     

A Stable and Conductive Metallophthalocyanine Framework for Electrocatalytic Carbon Dioxide Reduction in Water

Transformation of carbon dioxide to high value‐added chemicals becomes a significant challenge for clean energy studies. Here a stable and conductive covalent organic framework was developed for electrocatalytic carbon dioxide reduction to carbon monoxide in aqueous solution. The cobalt(II) phthalocyanine catalysts are topologically connected via robust phenazine linkage into a two‐dimensional tetragonal framework that is stable under boiling water, acid, or base conditions. The 2D lattice enables full π conjugation along x and y directions as well as π conduction along the z axis across the π columns. With these structural features, the electrocatalytic framework exhibits a faradaic efficiency of 96 %, an exceptional turnover number up to 320 000, and a long‐term turnover frequency of 11 412 hour^?1, which is a 32‐fold improvement over molecular catalyst. The combination of catalytic activity, selectivity, efficiency, and durability is desirable for clean energy production.     

Self-assembled heterotrimeric collagen triple helices directed through electrostatic interactions

Collagen, a fibrous protein, is an essential structural component of all connective tissues such as cartilage, bones, ligaments, and skin. Type I collagen, the most abundant form, is a heterotrimer assembled from two identical alpha1 chains and one alpha2 chain. However, most synthetic systems have addressed homotrimeric triple helices. In this paper we examine the stability of several heterotrimeric collagen-like triple helices with an emphasis on electrostatic interactions between peptides. We synthesize seven 30 amino acid peptides with net charges ranging from -10 to +10. These peptides were mixed, and their ability to form heterotrimers was assessed. We successfully show the assembly of five different AAB heterotrimers and one ABC heterotrimer. The results from this study indicate that intermolecular electrostatic interactions can be utilized to direct heterotrimer formation. Furthermore, amino acids with poor stability in collagen triple helices can be "rescued" in heterotrimers containing amino acids with known high triple helical stability. This mechanism allows collagen triple helices to have greater chemical diversity than would otherwise be allowed.     

3D aluminum/silver hierarchical nanostructure with large areas of dense hot spots for surface‐enhanced raman scattering

Plasmonic nanomaterials possessing large‐volume, high‐density hot spots with high field enhancement are highly desirable for ultrasensitive surface‐enhanced Raman scattering (SERS) sensing. However, many as‐prepared plasmonic nanomaterials are limited in available dense hot spots and in sample size, which greatly hinder their wide applications in SERS devices. Here, we develop a two‐step physical deposition protocol and successfully fabricate 3D hierarchical nanostructures with highly dense hot spots across a large scale (6 × 6 cm²). The nanopatterned aluminum film was first prepared by thermal evaporation process, which can provide 3D quasi‐periodic cloud‐like nanostructure arrays suitable for noble metal deposition; then a large number of silver nanoparticles with controllable shape and size were decorated onto the alumina layer surfaces by laser molecular beam epitaxy, which can realize large‐area accessible dense hot spots. The optimized 3D‐structured SERS substrate exhibits high‐quality detection performance with excellent reproducibility (13.1 and 17.1%), whose LOD of rhodamine 6G molecules was 10^?9 M. Furthermore, the as‐prepared 3D aluminum/silver SERS substrate was applied in detection of melamine with the concentration down to 10^?7 M and direct detection of melamine in infant formula solution with the concentration as low 10 mg/L. Such method to realize large‐area hierarchical nanostructures can greatly simplify the fabrication procedure for 3D SERS platforms, and should be of technological significance in mass production of SERS‐based sensors.     

Switchable Proline Derivatives: Tuning the Conformational Stability of the Collagen Triple Helix by pH Changes

(4S)‐Aminoproline is introduced as a pH‐sensitive probe for tuning the conformational properties of peptides and proteins. The pH‐triggered flip of the ring puckering and the formation/release of a transannular H bond were used to switch the formation of collagen triple helices on and off reversibly.     

Two‐Dimensional Skyrmion Lattice Formation in a Nematic Liquid Crystal Consisting of Highly Bent Banana Molecules

We synthesized a novel banana‐shaped molecule based on a 1,7‐naphthalene central core that exhibits a distinct mesomorphism of the nematic‐to‐nematic phase transition. Both the X‐ray profile and direct imaging of atomic force microscopy (AFM) investigations clearly indicates the formation of an anomalous nematic phase possessing a two‐dimensional (2D) tetragonal lattice with a large edge (ca. 59 Å) directed perpendicular to the director in the low‐temperature nematic phase. One plausible model is proposed by an analogy of skyrmion lattice in which two types of cylinders formed from left‐ and right‐handed twist‐bend helices stack into a 2D tetragonal lattice, diminishing the inversion domain wall.     

Assembly of Gold Nanoparticles on a Molecular Ultrathin Film: Tuning the Surface Plasmon Resonance

A number of methodologies for immobilizing metal nanoparticles in 2‐dimensional aggregate structures on various substrates, some with concomitant tuning of the surface plasmon resonance (SPR), have been reported. Many of them involve special functionalization of the nanoparticles, multiple fabrication steps or lengthy procedures. The present study demonstrates that monolayer Langmuir–Blodgett (LB) film of a hemicyanine‐based amphiphile with cationic headgroup is an easily fabricated platform for harnessing citrate‐stabilized gold nanoparticles. It is shown that a single immersion step can be used to immobilize the nanoparticles uniformly on large area films and that systematic variation of the immersion time from 10 min to 6 h leads to controlled assembly of the particles and tuning of the SPR band over ～100 nm. A model for the structural reorganization in the LB film that facilitates the assembly of nanoparticles is presented and the advantages of the current methodology over earlier protocols are pointed out. The versatility of LB films in terms of the molecular level control of fabrication it enables and the variety of film structures that can be realized, point to the wide scope for future explorations, expanding upon the present observations.     

Lyotropic Supramolecular Helical Columnar Phases Formed by C3‐Symmetric and Unsymmetric Rigid Molecules

Unlike thermotropic liquid‐crystalline C₃‐symmetric molecules with flexible chains, the herein‐designed fully rigid three‐armed molecules (C₃‐symmetric and unsymmetric) create a fancy architecture for the formation of lyotropic liquid crystals in water. First, hollow columns with triple‐stranded helices, analogous to helical rosette nanotubes, are spontaneously constructed by self‐organization of the rigid three‐armed molecules. Then, the helical nanotubes arrange into hexagonal liquid‐crystalline phases, which show macroscopic chirality as a result of supramolecular chiral symmetry breaking. Interestingly, the helical nanotubes constructed by the fully rigid molecules are robust and stable over a wide concentration range in water. They are hardly affected by ionic defects at the molecular periphery, that is, further decoration of functional groups on the molecular arms can presumably be realized without changing the helical conformation. In addition, the formed columnar phases can be aligned macroscopically by simple shear and show anisotropic ionic conductivity, which suggests promising applications for low‐dimensional ion‐conductive materials.     

Supramolecular Polymerization Promoted and Controlled through Self‐Sorting

A new method in which supramolecular polymerization is promoted and controlled through self‐sorting is reported. The bifunctional monomer containing p‐phenylene and naphthalene moieties was prepared. Supramolecular polymerization is promoted by selective recognition between the p‐phenylene group and cucurbit[7]uril (CB[7]), and 2:1 complexation of the naphthalene groups with cucurbit[8]uril (CB[8]). The process can be controlled by tuning the CB[7] content. This development will enrich the field of supramolecular polymers with important advances towards the realization of molecular‐weight and structural control.     

Selective covalent capture of collagen triple helices with a minimal protecting group strategy

Collagens and their most characteristic structural unit, the triple helix, play many critical roles in living systems which drive interest in preparing mimics of them. However, application of collagen mimetic helices is limited by poor thermal stability, slow rates of folding and poor equilibrium between monomer and trimer. Covalent capture of the self-assembled triple helix can solve these problems while preserving the native three-dimensional structure critical for biological function. Covalent capture takes advantage of strategically placed lysine and glutamate (or aspartate) residues which form stabilizing charge–pair interactions in the supramolecular helix and can subsequently be converted to isopeptide amide bonds under folded, aqueous conditions. While covalent capture is powerful, charge paired residues are frequently found in natural sequences which must be preserved to maintain biological function. Here we describe a minimal protecting group strategy to allow selective covalent capture of specific charge paired residues which leaves other charged residues unaltered. We investigate a series of side chain protecting groups for lysine and glutamate in model peptides for their ability to be deprotected easily and in high yield while maintaining (1) the solubility of the peptides in water, (2) the self-assembly and stability of the triple helix, and (3) the ability to covalently capture unprotected charge pairs. Optimized conditions are then illustrated in peptides derived from Pulmonary Surfactant protein A (SP-A). These covalently captured SP-A triple helices are found to have dramatically improved rates of folding and thermal stability while maintaining unmodified lysine–glutamate pairs in addition to other unmodified chemical functionality. The approach we illustrate allows for the covalent capture of collagen-like triple helices with virtually any sequence, composition or register. This dramatically broadens the utility of the covalent capture approach to the stabilization of biomimetic triple helices and thus also improves the utility of biomimetic collagens generally.

A minimal protecting group strategy is developed to allow selective covalent capture of collagen-like triple helices. This allows stabilization of this critical fold while preserving charge–pair interactions critical for biological applications.     

Theoretical Investigation on the Hydrogen Evolution,Oxygen Evolution,and Oxygen Reduction Reactions Performances of Two-Dimensional Metal-Organic Frameworks Fe3(C2X)12 (X = NH,O, S)

Two-dimensional metal-organic frameworks (2D MOFs) inherently consisting of metal entities and ligands are promising single-atom catalysts (SACs) for electrocatalytic chemical reactions. Three 2D Fe-MOFs with NH, O, and S ligands were designed using density functional theory calculations, and their feasibility as SACs for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) was investigated. The NH, O, and S ligands can be used to control electronic structures and catalysis performance in 2D Fe-MOF monolayers by tuning charge redistribution. The results confirm the Sabatier principle, which states that an ideal catalyst should provide reasonable adsorption energies for all reaction species. The 2D Fe-MOF nanomaterials may render highly-efficient HER, OER, and ORR by tuning the ligands. Therefore, we believe that this study will serve as a guide for developing of 2D MOF-based SACs for water splitting, fuel cells, and metal-air batteries.     

Identification and quantitative analysis of physalin D and its metabolites in rat urine and feces by liquid chromatography with triple quadrupole time‐of‐flight mass spectrometry

Physalin D is known to show extensive bioactivities. However, no excretion study has elucidated the excretion of physalin D and its metabolites. This study investigates the excretion of physalin D and its metabolites in rats. Metabolites in rat urine and feces were separated and identified by liquid chromatography with triple quadrupole time‐of‐flight mass spectrometry. Furthermore, a validated high‐performance liquid chromatography with tandem mass spectrometry method was developed to quantify physalin D, physalin D glucuronide, and physalin D sulfate in rat feces and urine after the intragastric administration of physalin D. The analyte showed good linearity over a wide concentration range (r  > 0.995), and the lower limit of quantification was 0.0532 μg/mL and 0.226 μg/g for urine and feces, respectively. Nine metabolites, including five phase I and four phase II metabolites, were identified and clarified after dosing in vivo. Only 4.0% of the gavaged dose, including physalin D and its phase II metabolites, was excreted in urine, whereas 10.8% was found in feces in the unchanged form. The results indicate that the extensive and rapid metabolism may be the main factors leading to the short half‐life of physalin D. These results can provide a basis for further studies on the structural modification and pharmacology of physalin D.     

A Two‐Dimensional Polymer Synthesized at the Air/Water Interface

A trifunctional, partially fluorinated anthracene‐substituted triptycene monomer was spread at an air/water interface into a monolayer, which was transformed into a long‐range‐ordered 2D polymer by irradiation with a standard UV lamp. The polymer was analyzed by Brewster angle microscopy, scanning tunneling microscopy measurements, and non‐contact atomic force microscopy, which confirmed the generation of a network structure with lattice parameters that are virtually identical to a structural model network based on X‐ray diffractometry of a closely related 2D polymer. The nc‐AFM images highlight the long‐range order over areas of at least 300×300 nm². As required for a 2D polymer, the pore sizes are monodisperse, except for the regions where the network is somewhat stretched because it spans over protrusions. Together with a previous report on the nature of the cross‐links in this network, the structural information provided herein leaves no doubt that a 2D polymer has been synthesized under ambient conditions at an air/water interface.     

Chiral Mesoporous Organosilica Nanospheres: Effect of Pore Structure on the Performance in Asymmetric Catalysis

(R)‐(+)‐1,1′‐Bi‐2‐naphthol ((R)‐(+)‐Binol)‐functionalized (Binol=2,2′‐dihydroxy‐1,1′‐binaphthyl) chiral mesoporous organosilica nanospheres with uniform particle size (100 to 300 nm) have been synthesized by co‐condensation of tetraethoxysilane and (R)‐2,2′‐di(methoxymethyl)oxy‐6,6′‐di(1‐propyl trimethoxysilyl)‐1,1′‐binaphthyl in a basic medium with cetyltrimethylammonium bromide as the template. Nanospheres with a radiative 2D hexagonal channel arrangement exhibit higher enantioselectivity and turnover frequency than those with a penetrating 2D hexagonal channel arrangement (94 versus 88 % and 43 versus 15 h^?1, respectively) in the asymmetric addition of diethylzinc to aldehydes. In addition, under similar conditions, the enantioselectivity of the nanospheres can be greatly improved as the structural order of the framework increases. These results clearly show that the structural order of nanospheres affects enantioselective reactions. The enantioselectivity of the nanospheres synthesized by the co‐condensation method is higher than that of nanospheres prepared by a grafting method and even higher than that of their homogeneous counterpart. These results indicate that the bite angle of (R)‐(+)‐Binol bridging in a more rigid porous network is in a more favorable position for achieving higher enantioselectivity. The efficiency of a co‐condensation method for the synthesis of high‐performance heterogeneous asymmetric catalysts is also reported.     

Spatial transitions between local structures in condensed systems

Scattering data and radial distributions in amorphous matter can be represented accurately in terms of models based on a small set of structural elements which specify local atomic configurations, and on certain spatial random processes specifying the fraction of such elements and the decay of their correlations with distance. The local structural elements, expressed in terms of globally ordered structures, particularly in terms of lattices (L), are subject to radially evolving Markoffian-like processes of relative displacements and of transitions between Ls at different points in space. Including an empty lattice L ₀ in the set (L) leads to a definition of random voids and their spatial correlations, depending on the size of the local domains considered. The models provide representation of a continuous range of amorphous structures from liquids and glasses via nanomaterials to crystalline powders.     

cis‐Verbenol

cis‐Verbenol (alternative name: 4,6,6‐tri­methyl­bi­cyclo­[3.1.1]­hept‐3‐en‐2‐ol), C₁₀H₁₆O, forms an orthorhombic P2₁2₁2₁ crystal that contains three mol­ecules per asymmetric unit. These three mol­ecules form hydrogen‐bonded helices parallel to the shortest axis of the lattice. The O?O distances associated with the hydrogen bonds are 2.760 (3), 2.760 (3) and 2.766 (3) Å.     

Enhanced Charge Transport by Incorporating Formamidinium and Cesium Cations into Two‐Dimensional Perovskite Solar Cells

Organic‐inorganic hybrid two‐dimensional (2D) perovskites (n≤5) have recently attracted significant attention because of their promising stability and optoelectronic properties. Normally, 2D perovskites contain a monocation [e.g., methylammonium (MA⁺) or formamidinium (FA⁺)]. Reported here for the first time is the fabrication of 2D perovskites (n=5) with mixed cations of MA⁺, FA⁺, and cesium (Cs⁺). The use of these triple cations leads to the formation of a smooth, compact surface morphology with larger grain size and fewer grain boundaries compared to the conventional MA‐based counterpart. The resulting perovskite also exhibits longer carrier lifetime and higher conductivity in triple cation 2D perovskite solar cells (PSCs). The power conversion efficiency (PCE) of 2D PSCs with triple cations was enhanced by more than 80 % (from 7.80 to 14.23 %) compared to PSCs fabricated with a monocation. The PCE is also higher than that of PSCs based on binary cation (MA⁺‐FA⁺ or MA⁺‐Cs⁺) 2D structures.