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We have developed an effective chemical-vapor-deposition method to fabricate large-scale cerium hexaboride nanowire arrays on flexible carbon substates. The nanowires show diameters of 80–200 nm and lengths of 5–30 μm. The high resolution transmission electron microcopy (HRTEM) indicates that the nanowire is of high crystalline with the growth orientation of [001]. The field emission of these nanowires shows favorable electron emission properties, including the turn-on fields of 1.76 V μm −1 , threshold fields of 3.60 V μm −1 and high field emission enhancement factors of 2203 ± 27, respectively. The field emission properties depending on the gap between the anode and cathode are also investigated. The results show that the turn-on fields and threshold fields decrease from 1.76 and 3.60 V μm −1 to 1.28 and 2.77 V μm −1 , respectively; whereas the field emission enhancement factors increase from 2203 ± 27 to 4012 ± 66 with the anode-cathode distance increasing from 500 to 700 μm. The excellent field emission performances indicate the promising application prospects of this material in flexible electronics and optoelectronics, such as high light electron sources, flat panel displays and thermal electrical power converters.

Photoelectric responses of ZnO to dry air and formaldehyde under visible light illumination were studied in this work. ZnO film was prepared on Al 2 O 3 substrate by screen printing. Fundamental characteristics of ZnO film were examined through XRD, FE-SEM and PL spectra measurements. Time-dependent photocurrent properties of ZnO were tested in dry air and formaldehyde under the illumination of white light, respectively. The results revealed that, in comparison with dry air, ZnO in formaldehyde exhibited an enhanced photocurrent response. To illustrate it, explanations based on the double Schottky barrier model were proposed. In addition, to demonstrate the authenticity of the proposed mechanism, experiments on the time-dependent photocurrent of ZnO under white light illumination in the light-on and light-off conditions were also carried out.

ZnCo2O4/MnO2 nanocone forests with a mesoporous, hierarchical core-shell structure and a large surface area were hydrothermally grown on 3D nickel foam. The supercapacitor electrodes prepared from the unique structure exhibits exceptional specific capacitances of 2339 and 1526 F g−1 at current densities of 1 and 10 A g−1, respectively, and long-term capacity retention of ~95.9% after 3000 cycles at 2 A g−1 and 94.5% after 8000 cycles at 10 A g−1. These values are proven to be the highest when the capacitances are compared between the current study and similar core/shell-structured metal oxide electrodes taken from the literature. Many synergistic effects are identified to be responsible for the observations: namely, highly conductive 3D Ni foam substrate that totally eliminate binders and conductive additives; high crystalline quality of the ZnCo2O4 core which is directly grown on the conductive current collector, allowing fast electron transport; and the mesoporous MnO2 shell with a huge surface area for fast ion diffusion and intimate electrode/electrolyte contact. In addition, the nanostructured core and shell have redox reactions with anions and cations from the electrolyte, respectively, both of which contribute much to electrochemical charge storage.

Tri-gate transistors offer better performance than planar transistors by exerting additional gate control over a channel from two lateral sides of semiconductor nanowalls (or “fins”). Here we report the bottom-up assembly of aligned CdS nanowalls by a simultaneous combination of horizontal catalytic vapor–liquid–solid growth and vertical facet-selective noncatalytic vapor–solid growth and their parallel integration into tri-gate transistors and photodetectors at wafer scale (cm2) without postgrowth transfer or alignment steps. These tri-gate transistors act as enhancement-mode transistors with an on/off current ratio on the order of 108, 4 orders of magnitude higher than the best results ever reported for planar enhancement-mode CdS transistors. The response time of the photodetector is reduced to the submicrosecond level, 1 order of magnitude shorter than the best results ever reported for photodetectors made of bottom-up semiconductor nanostructures. Guided semiconductor nanowalls open new opportunities...

Binary metal oxides have been regarded as ideal potential anode materials which display electrochemical performances which surpass those of single metal oxides, in terms of reversible capacity, structural stability and electronic conductivity. In this work, hierarchical multi-villous NiCo2O4 nanocyclobenzene arrays (NCAs) on nickel foam have been fabricated by a simple hydrothermal approach combined with a post-annealing treatment. Such unique nanoarchitectures exhibit a remarkable electrochemical performance, with high capacitance and a desirable cycle lifespan at high rates. When evaluated as an electrode material for supercapacitors, the NCAs supported on nickel foam are able to deliver a high specific capacitance of 1545 F g−1 at a current density of 5 A g−1 in 2 M KOH aqueous solution. In addition, the composite electrode shows excellent mechanical behavior and long-term cyclic stability (93.7% capacitance retention after 5000 cycles). All in all, the fabrication strategy presented herein is simple, cost-effective and scalable, which opens new avenues for the large scale application of these novel materials in energy storage.

A series of beta-aminoamides bearing triazolopiperazines has been prepared and evaluated as potent, selective, orally active dipeptidyl peptidase IV (DPP-4) inhibitors. Efforts at optimization of the beta-aminoamide series, which ultimately led to the discovery of JANUVIA (sitagliptin phosphate, compound 1), are described.

ZnCo2O4 nanoflakes, as electrodes for supercapacitors, are grown on a cellular nickel foam using a cost-effective hydrothermal procedure. The mesoporous ZnCo2O4 nanoflakes have large electroactive surface areas with strong adhesion to the Ni foam, allowing fast ion and electron transport. The nanoarchitecture electrodes deliver an excellent specific capacitance of 1220 F g(-1) at a current density of 2 A g(-1) in a 2 M KOH aqueous solution and a long-term cyclic stability of 94.2% capacitance retention after 5000 cycles. The fabrication strategy is facile, cost-effective, and can offer great promise for large-scale supercapacitor applications.

anti-Substituted beta-methylphenylalanine derived amides have been shown to be potent DPP-IV inhibitors exhibiting excellent selectivity over both DPP8 and DPP9. The optimized compound exhibited good pharmacokinetic profiles in three preclinical species.

Modification of in-house screening lead beta-aminoacyl proline 8 gave an equipotent thiazolidide 9. Extensive SAR studies on the phenyl ring of 9 led to the discovery of a novel series of potent and selective DP-IV inhibitors. Introduction of a fluorine at the 2-position proved to be crucial for the potency of this series. The 2,5-difluoro (22q) and 2,4,5-trifluoro (22t) analogues were potent inhibitors of DP-IV (IC(50)=270, 119nM, respectively).

Bandgap engineering of semiconductor nanowires is important in designing nanoscale multifunctional optoelectronic devices. Here, we report a facile thermal evaporation method, and realize the spatial bandgap engineering in single CdS(1-x)Se(x) alloy nanowires. Along the length of these achieved nanowires, the composition can be continuously tuned from x = 0 (CdS) at one end to x = 1 (CdSe) at the other end, resulting in the corresponding bandgap (light emission wavelength) being modulated gradually from 2.44 eV (507 nm, green light) to 1.74 eV (710 nm, red light). In spite of the existing composition (crystal lattice) transition along the length, these multicolor nanowires still possess high-quality crystallization. These bandgap engineered nanowires will have promising applications in such as multicolor display and lighting, high-efficiency solar cells, ultrabroadly spectral detectors, and biotechnology.

The immunosuppressive agent sanglifehrin A has been prepared for the first time by total synthesis. The construction of the macrocyclic unit of the target molecule was achieved through a selective intramolecular Stille coupling, and the spirolactam unit by Paterson-aldol reactions. The final steps involve an intermolecular Stille coupling and the opening of the internal acetal unit. This convergent synthesis opens the way for the synthesis of libraries of novel sanglifehrin analogues for biological screening.

A new class of potential antitumor agents with a taxol-like mechanism of action is presented by the sarcodictyins 1. Modification of the reported syntheses of sarcodictyins permitted the preparation of additional derivatives, the biological properties of which are highly dependent upon the structure.

A retrosynthetic analysis (Scheme 1) of maduropeptin chromophore artifact 1 defined compounds 2 and 3 as required building blocks. The construction of 2 was achieved starting from the 2,5-dimethyl derived aromatic acid 8 and the d -serine derived δ-lactone 12 (Scheme 2), whereas the synthesis of 3 utilized an Evans's aldol condensation reaction between aldehyde 13 and chiral auxiliary 14 (Scheme 3).

The o-bromo-p-methoxyphenyl ether group is introduced as a new protecting/radical translocating (PRT) group. This group protects an alcohol both before and after its use as a translocating group to generate a radical from a C−H bond β to the protected alcohol. All prior PRT groups generate radicals α to the functional group that they protect. The group is introduced by Mitsunobu reaction or Williamson ether synthesis, and removed by oxidation with ceric ammonium nitrate. The efficiency of the radical translocation reaction has been studied by isotopic labeling experiments with tributyltin deuteride. These results were used to design and execute a series of tandem radical translocation/cyclization reactions that illustrate the potential usefulness of the PRT group in synthesis. Secondary radicals are generated with about 50% efficiency due to slow 1,5-hydrogen transfer and competing 1,6-hydrogen transfer. Tertiary radicals are generated with efficiencies of about 80%. Modified PRT groups with added ortho s...

The indirect bandgap of single-crystalline silicon has so far precluded the full integration of silicon microelectronics with photonics-which is expected to allow the realization of low-cost, high-speed optical information processing and communication in the future. Here we report the growth of europium (Eu)-doped Si-SiO2 core-shell nanowires by an oxide-assisted chemical vapor deposition method. The Eu concentration in these nanowires is effectively improved by intentionally increasing the thickness of SiO2 shells. As a result, a strong Si-compatible red emission from Eu(3+) ions was observed under laser illumination. The effect of Eu(3+) concentration on the emission efficiency was comprehensively studied, with the highest efficiency at Eu content about 0.8 at%. The relaxation mechanism of this concentration dependent luminescence was further explored through lifetime measurements. In light of the strong characteristic red emission and nanoscale footprint, these nanowires are promising Si-compatible light emission materials for future integrated nanophotonics.

The first examples of Giese reactions (reductive additions of radicals to electron-poor alkenes) conducted by uni-molecular chain transfer reactions of silicon hydrides are reported.

The first examples of Giese reactions (reductive additions of radicals to electron-poor alkenes) conducted by uni-molecular chain transfer reactions of silicon hydrides are reported.

Most radical reactions are conducted by chain methods that have bimolecular chain transfer steps. It is proposed that unimolecular chain transfer (UMCT) reactions should have advantages for conducting difficult radical transformations. The concepts of the UMCT method are illustrated with allyltributylstannane, and the first examples of UMCT reactions of silicon hydrides are introduced. Examples of bimolecular reactions conducted with silicon hydride UMCT reagents are provided, and the potential of the UMCT method is discussed.

A new class of potential antitumor agents with a taxol-like mechanism of action is presented by the sarcodictyins 1. Modification of the reported syntheses of sarcodictyins permitted the preparation of additional derivatives, the biological properties of which are highly dependent upon the structure.

The synthesis of the macrocyclic core of sanglifehrin A, a newly discovered natural product, is described.

The immunosuppressive agent sanglifehrin A has been prepared for the first time by total synthesis. The construction of the macrocyclic unit of the target molecule was achieved through a selective intramolecular Stille coupling, and the spirolactam unit by Paterson-aldol reactions. The final steps involve an intermolecular Stille coupling and the opening of the internal acetal unit. This convergent synthesis opens the way for the synthesis of libraries of novel sanglifehrin analogues for biological screening.

The synthesis, selectivity, rat pharmacokinetic profile, and drug metabolism profiles of a series of potent fluoroolefin-derived DPP-4 inhibitors (4) are reported. A radiolabeled fluoroolefin 33 was shown to possess a high propensity to form reactive metabolites, thus revealing a potential liability for this class of DPP-4 inhibitors.

A novel series of oxadiazole based amides have been shown to be potent DPP-4 inhibitors. The optimized compound 43 exhibited excellent selectivity over a variety of DPP-4 homologs.

The sarcodictyins A-F and eleutherobin comprise a family of marine-derived diterpenoids with potent cytotoxicities against various tumor cell lines. Investigations have revealed that several of thess compounds exert their cytotoxic effects through tubulin binding in a mechanism analogous to that of the clinical anticancer drug taxol(TM). The biological importance, challenging molecular architecture, and relative scarcity of these natural products have prompted several groups to undertake their total chemical synthesis. In this review, we summarize the current synthetic efforts and examine the preliminary structure-activity relationships which have emerged from early combinatorial libraries.

High-quality dilute tin-doped CdS nanowires with tunable trap-state emissions were grown via simple thermal evaporation with a moving source for studying the influence of trap states on optical waveguiding. Our results demonstrate that the guiding efficiency of these wires is significantly enhanced compared to that of the pure CdS wires. Theoretical simulation based on the fundamental optical absorption principle of semiconductors further reveals that this trap-state enhanced optical waveguiding is attributed to the passive guiding process of the trap-state emissions along these wires. To the best of our knowledge, this study is the first demonstration of using dopants to shift emission away from bandgap absorption for the purpose of optical waveguiding enhancement, which is significant for understanding and optimizing the optical transport ability of semiconductor nanostructures.

The synthesis of the macrocyclic core of sanglifehrin A, a newly discovered natural product, is described.

Most radical reactions are conducted by chain methods that have bimolecular chain transfer steps. It is proposed that unimolecular chain transfer (UMCT) reactions should have advantages for conducting difficult radical transformations. The concepts of the UMCT method are illustrated with allyltributylstannane, and the first examples of UMCT reactions of silicon hydrides are introduced. Examples of bimolecular reactions conducted with silicon hydride UMCT reagents are provided, and the potential of the UMCT method is discussed.