Search

A typical type of core-shell polyoxometalates can be obtained through the Keggin-type polyoxometalate-templated growth of a layer of spherical shell structure of {Mo72Fe30}. Small-angle X-ray scattering is used to study the structural features and stability of the core-shell structures in aqueous solutions. Time-resolved small-angle X-ray scattering is applied to monitor the synthetic reactions, and a three-stage formation mechanism is proposed to describe the synthesis of the core-shell polyoxometalates based on the monitoring results. New protocols have been developed by fitting the X-ray data with custom physical models, which provide more convincing, objective, and completed data interpretation. Quasi-elastic and inelastic neutron scattering are used to probe the dynamics of water molecules in the core-shell structures, and two different types of water molecules, the confined and structured water, are observed. These water molecules play an important role in bridging core and shell structures and stabilizing the cluster structures. [ABSTRACT FROM AUTHOR]

Increasing the complexity of hollow structures, in terms of chemical composition and shell architecture, is highly desirable for both fundamental studies and realization of various functionalities. Starting with metal–organic frameworks (MOFs), we demonstrate a general approach toward the large-scale and facile synthesis of complex hollow microboxes via manipulation of the template-engaged reactions between the Prussian blue (PB) template and different alkaline substances. The reaction between PB microcubes with NaOH solution leads to the formation of Fe(OH)3 microboxes with controllable multishelled structure. In addition, PB microcubes will react with the conjugate bases of metal oxide based weak acids, generating multicompositional microboxes (Fe2O3/SnO2, Fe2O3/SiO2, Fe2O3/GeO2, Fe2O3/Al2O3, and Fe2O3/B2O3), which consist of uniformly dispersed oxides/hydroxides of iron and another designed element. Such complex hollow structures and atomically integrated multiple compositions might bring the usual physiochemical properties. As an example, we demonstrate that these complex hollow microboxes, especially the Fe2O3/SnO2 composite microboxes, exhibit remarkable electrochemical performance as anode materials for lithium ion batteries. [ABSTRACT FROM AUTHOR]

Ultrathin one-dimensional (1D) nanostructures such as nanowires and nanorods have drawn considerable attention due to their promising applications in various fields. Despite the numerous reports on 1D nanostructures of noble metals, one-pot solution synthesis of Pt 1D nanostructures still remains a great challenge, probably because of the intrinsic isotropic crystal growth behavior of Pt. Herein, we demonstrate the facile solvothermal synthesis of nanowire assemblies composed of ultrathin (ca. 3 nm) and ultralong (up to 10 μm) Pt nanowires without involving any template. The oriented attachment mechanism is found to be partially responsible for the formation of such ultrathin Pt nanowires. The amine molecules generated during the reaction might assist the formation of nanowire assemblies. Importantly, the present system can be extended to synthesize Pt-based alloy nanowire assemblies such as Pt-Au and Pt-Pd. These Pt nanowires can be easily cast into a free-standing membrane, which exhibits excellent electrocatalytic activity and very high stability for formic acid and methanol oxidation and the oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

An anisotropic etching mode is commonly known for perfect crystalline materials, generally leading to simple Euclidean geometric patterns. This principle has also proved to apply to the etching of the thinnest crystalline material, graphene, resulting in hexagonal holes with zigzag edge structures. Here we demonstrate for the first time that the graphene etching mode can deviate significantly from simple anisotropic etching. Using an as-grown graphene film on a liquid copper surface as a model system, we show that the etched graphene pattern can be modulated from a simple hexagonal pattern to complex fractal geometric patterns with sixfold symmetry by varying the Ar/H2 flow rate ratio. The etched fractal patterns are formed by the repeated construction of a basic identical motif, and the physical origin of the pattern formation is consistent with a diffusion-controlled process. The fractal etching mode of graphene presents an intriguing case for the fundamental study of material etching. [ABSTRACT FROM AUTHOR]

Atomistic molecular dynamics (MD) simulations were carried out to investigate the local dynamics of polyelectrolyte dendrimers dissolved in deuterium oxide (D2O) and its dependence on molecular charge. Enhanced segmental dynamics upon increase in molecular charge is observed, consistent with quasielastic neutron scattering (QENS) measurements. A strong coupling between the intradendrimer local hydration level and segmental dynamics is also revealed. Compelling evidence shows these findings originate from the electrostatic interaction between the hydrocarbon components of a dendrimer and the invasive water. This combined study provides fundamental insight into the dynamics of charged polyelectrolytes and the solvating water molecules. [ABSTRACT FROM AUTHOR]

Fe2O3 microboxes with hierarchically structured shells have been synthesized simply by annealing Prussian blue (PB) microcubes. By utilizing simultaneous oxidative decomposition of PB microcubes and crystal growth of iron oxide shells, we have demonstrated a scalable synthesis of anisotropic hollow structures with various shell architectures. When evaluated as an anode material for lithium ion batteries, the Fe2O3 microboxes with a well-defined hollow structure and hierarchical shell manifested high specific capacity (~950 mA h g-1 at 200 mA g-1) and excellent cycling performance. [ABSTRACT FROM AUTHOR]

Noble metals such as platinum (Pt) are widely used as catalysts in fuel cells and other heterogeneous catalytic processes. However, there is an urgent need to develop substitutes for pure Pt catalysts to reduce the overall use of precious Pt and at the same time to enhance poisoning resistance. A promising strategy is to design Pt based bi- or trimetallic nanostructures because their unique structures and compositions would enhance their catalytic performance. In this study, we report the synthesis, characterization, and electrochemical evaluation of cubic intermetallic PtCu3 nanocages. The influential effects of several important experimental parameters on the final products have been explored through systematic studies on the growth of PtCu3 nanocages. Relative to the current commercial Pt electrocatalyst, these PtCu3 nanocages possess a more accessible surface area and a unique hollow structure, which contribute to improved electrocatalytic activity in the methanol oxidation reaction. [ABSTRACT FROM AUTHOR]

The ability to dope graphene is highly important for modulating electrical properties of graphene. However, the current route for the synthesis of N-doped graphene by chemical vapor deposition (CVD) method mainly involves high growth temperature using ammonia gas or solid reagent melamine as nitrogen sources, leading to graphene with low doping level, polycrystalline nature, high defect density and low carrier mobility. Here, we demonstrate a self-assembly approach that allows the synthesis of single-layer, single crystal and highly nitrogen-doped graphene domain arrays by self-organization of pyridine molecules on Cu surface at temperature as low as 300 °C. These N-doped graphene domains have a dominated geometric structure of tetragonal-shape, reflecting the single crystal nature confirmed by electron-diffraction measurements. The electrical measurements of these graphene domains showed their high carrier mobility, high doping level, and reliable N-doped behavior in both air and vacuum. [ABSTRACT FROM AUTHOR]

The Ala1—Gly28 glycopeptide fragment (28) of EPO was prepared by chemical synthesis as a single glycoform. Key steps in the synthesis include attachment of a complex dodecasaccharide (7) to a seven amino acid peptide via Lansbury aspartylation, native chemical ligation to join peptide 19 with the glycopeptide domain 18, and a selective desulfurization at the ligation site to reveal the natural Ala19. This glycopeptide fragment (28) contains both the requisite N-linked dodecasaccharide and a C-terminal αthioester handle, the latter feature permitting direct coupling with a glycopeptide fragment bearing N-terminal Cys29 without further functionalization. [ABSTRACT FROM AUTHOR]

α-Fe2O3 hollow spheres with sheet-like subunits are synthesized by a facile quasiemulsion-templated method. Glycerol is dispersed in water to form oil-in-water quasiemulsion microdroplets, which serve as soft templates for the deposition of the α-Fe2O3 shell. When tested as anode materials for lithium-ion batteries, these α-Fe2O3 hollow spheres manifest greatly enhanced Li storage properties. [ABSTRACT FROM AUTHOR]

Breaking and forming peptidyl bonds are fundamental biochemical reactions in protein chemistry. Unlike proteases that are abundantly available, fast-acting ligases are rare. OaAEP1 is an enzyme isolated from the cyclotide-producing plant oldenlandia affinis that displayed weak peptide cyclase activity, despite having a similar structural fold with other asparaginyl endopeptidases (AEP). Here we report the first atomic structure of OaAEP1, at a resolution of 2.56 Å, in its preactivation form. Our structure and biochemical analysis of this enzyme reveals its activation mechanism as well as structural features important for its ligation activity. Importantly, through structure-based mutagenesis of OaAEP1, we obtained an ultrafast variant having hundreds of times faster catalytic kinetics, capable of ligating well-folded protein substrates using only a submicromolar concentration of enzyme. In contrast, the protein-protein ligation activity in the original wild-type OaAEP1 enzyme described previously is extremely weak. Thus, the structure-based engineering of OaAEP1 described here provides a unique and novel recombinant tool that can now be used to conduct various protein labeling and modifications that were extremely challenging before. [ABSTRACT FROM AUTHOR]

We report the synthesis of a family of multifluorine substituted oligomers and the corresponding polymer that have the same backbones but different conjugation lengths and amounts of fluorine atoms on the backbone. The physical properties and photovoltaic performances of these materials were systematically investigated using optical absorption, charge mobility, atomic force microscopy, transmission electron microscopy, grazing incidence X-ray diffraction, resonant soft X-ray scattering methods, and photovoltaic devices. The power conversion efficiencies (PCEs) based on oligomers were much higher than that in the polymer. Moreover, the devices based on BIT6F and BIT10F, which have an axisymmetric electron-deficient difluorobenzothiadiazole as the central unit, gave slightly higher PCEs than those with centrosymmetric electron-rich indacenodithiophene (IDT) as the central unit (BIT4F or BIT8F). Using proper solvent vapor annealing (SVA), particularly using thermal annealing (TA) followed by SVA, the device performance could be significantly improved. Notably, the best PCE of 9.1% with a very high FF of 0.76 was achieved using the medium-sized oligomer BIT6F with the optimized film morphology. This efficiency is the highest value reported for organic solar cells from small-molecules without rhodanine terminal group. More excitingly, devices from the shortest oligomer BIT4F showed an impressively high FF of 0.77 (the highest FF value reported for solution-processed small-molecule organic solar cells). These results indicate that photovoltaic performances of oligomers can be modulated through successive change in chain-length and fluorine atoms, alternating spatial symmetric core, and combined post-treatments. [ABSTRACT FROM AUTHOR]

Ivorenolide A (1), a novel 18-membered macrolide featuring conjugated acetylenic bonds and five chiral centers, was isolated from Khaya ivorensis. The structure of 1 was fully determined by spectroscopic analysis, single-crystal X-ray diffraction, and bioinspired total synthesis. Both compound 1 and its synthetic enantiomer 2 showed potent and selective immunosuppressive activity. [ABSTRACT FROM AUTHOR]

Controllable and scalable production is of great importance for the application of graphene; however, to date, it is still a great challenge and a major obstacle which hampers its practical applications. Here, we develop a template chemical vapor deposition method for scalable synthesis of few-layer graphene ribbons (FLGRs) with controlled morphologies. The FLGRs have a good conductivity and are ideal for use in nanoelectromechanics (NEM). As an application, we fabricate a reversible NEM switch and a logic gate by using the FLGRs. This work realizes both controllable and scalable synthesis of graphene, provides an application of graphene in NEM switches, and would be valuable for both the scientific studies and the practical applications of graphene. [ABSTRACT FROM AUTHOR]

The article focuses on the study of the relative thermodynamic stability of C-terminal peptidyl esters of O-hydroxy Thiophenol. Researchers have been studying methods for assembling polypeptides bearing complex oligosaccharide domains. Mechanistic basis in the previously described ligation strategy was determined through the unanticipated result that ligation progresses through quantitative O → S acyl transfer of the N-terminal coupling partner.