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A bioinspired synthesis of spirochensilide A from commercially available lanosterol is reported. The synthesis features a directed C-H oxidation, a Wagner-Meerwein-type double methyl migration, a Meinwald rearrangement, and a double-bond isomerization/spiroketal formation cascade. The proposed biosynthetic speculation was modified by this synthetic sequence, which also served as a platform for the synthesis of other lanostanes with migrating methyl groups.

Developing bifunctional efficient and durable non-noble electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is highly desirable and challenging for overall water splitting. Herein, Co–Mn carbonate hydroxide (CoMnCH) nanosheet arrays with controllable morphology and composition were developed on nickel foam (NF) as such a bifunctional electrocatalyst. It is discovered that Mn doping in CoCH can simultaneously modulate the nanosheet morphology to significantly increase the electrochemical active surface area for exposing more accessible active sites and tune the electronic structure of Co center to effectively boost its intrinsic activity. As a result, the optimized Co1Mn1CH/NF electrode exhibits unprecedented OER activity with an ultralow overpotential of 294 mV at 30 mA cm–2, compared with all reported metal carbonate hydroxides. Benefited from 3D open nanosheet array topographic structure with tight contact between nanosheets and NF, it is able to deliver a high and...

Active centers in Cu/SSZ-13 selective catalytic reduction (SCR) catalysts have been recently identified as isolated Cu2+ and [CuII(OH)]+ ions. A redox reaction mechanism has also been established, where Cu ions cycle between CuI and CuII oxidation states during SCR reaction. While the mechanism for the reduction half-cycle (CuII → CuI) is reasonably well-understood, that for the oxidation half-cycle (CuI → CuII) remains an unsettled debate. Herein we report detailed reaction kinetics on low-temperature standard NH3-SCR, supplemented by DFT calculations, as strong evidence that the low-temperature oxidation half-cycle occurs with the participation of two isolated CuI ions via formation of a transient [CuI(NH3)2]+–O2–[CuI(NH3)2]+ intermediate. The feasibility of this reaction mechanism is confirmed from DFT calculations, and the simulated energy barrier and rate constants are consistent with experimental findings. Significantly, the low-temperature standard SCR mechanism proposed here provides full consiste...

Although significant improvements have been achieved for organic photovoltaic cells (OPVs), the top-performing devices still show power conversion efficiencies far behind those of commercialized solar cells. One of the main reasons is the large driving force required for separating electron-hole pairs. Here, we demonstrate an efficiency of 14.7% in the single-junction OPV by using a new polymer donor PTO2 and a nonfullerene acceptor IT-4F. The device possesses an efficient charge generation at a low driving force. Ultrafast transient absorption measurements probe the formation of loosely bound charge pairs with extended lifetime that impedes the recombination of charge carriers in the blend. The theoretical studies reveal that the molecular electrostatic potential (ESP) between PTO2 and IT-4F is large, and the induced intermolecular electric field may assist the charge generation. The results suggest OPVs have the potential for further improvement by judicious modulation of ESP.

An important challenge for reaction-based fluorescent probes is that they generally require analyte consumption for fluorescence signal generation, thus creating potential perturbation of native analyte homeostasis or change of local concentrations. Herein, we reported two formaldehyde (FA) regeneration fluorescent probes, NAP-FAP-1 and NAP-FAP-2. An unprecedented regiospecific FA-induced intramolecularity strategy is implemented in the probe design, which adopts 3-(benzylamino)-succinimide as the FA-selective reaction group. The probes are able to capture the analyte molecule, induce regiospecific imide bond cleavage, and then release the captured FA molecule with simultaneous fluorescence turn-on response via a unique dual PeT/ICT quenching mechanism. The probes have shown potentials in detection, comparison, and imaging of FA levels intracellularly and inside lysosomes. These features make them useful for the study of FA homeostasis and functions in biological systems with minimal perturbation.

Metal-catalyzed carbon-carbon bond-forming reactions are a mainstay in the synthesis of pharmaceutical agents. A long-standing problem plaguing the field of transition metal catalyzed C-H functionalization chemistry is control of selectivity among inequivalent C-H bonds in organic reactants. Herein we advance an approach to direct site selectivity in the arylation of 2-benzylfurans founded on the idea that modulation of cooperativity in bimetallic catalysts can enable navigation of selectivity. The bimetallic catalysts introduced herein exert a high degree of control, leading to divergent site-selective arylation reactions of both sp(2) and sp(3) C-H bonds of 2-benzylfurans. It is proposed that the selectivity is governed by cation-π interactions, which can be modulated by choice of base and accompanying additives [MN(SiMe3)2, M = K or Li·12-crown-4].

A new tetracyclic lactam building block for polymer semiconductors is reported that was designed to combine the many favorable properties that larger fused and/or amide-containing building blocks can induce, including improved solid-state packing, high charge carrier mobility, and improved charge separation. Copolymerization with thiophene resulted in a semicrystalline conjugated polymer, PTNT, with a broad bandgap of 2.2 eV. Grazing incidence wide-angle X-ray scattering of PTNT thin films revealed a strong tendency for face-on π- stacking of the polymer backbone, which was retained in PTNT:fullerene blends. Corresponding solar cells featured a high open-circuit voltage of 0.9 V, a fill factor around 0.6, and a power conversion efficiency as high as 5% for >200 nm thick active layers, regardless of variations in blend stoichiometry and nanostructure. Moreover, efficiencies of >4% could be retained when thick active layers of ∼400 nm were employed. Overall, these values are the highest reported for a conjugated polymer with such a broad bandgap and are unprecedented in materials for tandem and particularly ternary blend photovoltaics. Hence, the newly developed tetracyclic lactam unit has significant potential as a conjugated building block in future organic electronic materials. Refereed/Peer-reviewed

We examine the possibility of nitrogen-doped C60 fullerene (N-C60) as a cathode catalyst for hydrogen fuel cells. We use first-principles spin-polarized density functional theory calculations to simulate the electrocatalytic reactions on N-C60. The first-principles results show that an O2 molecule can be adsorbed and partially reduced on the N-C complex sites (Pauling sites) of N-C60 without any activation barrier. Through a direct pathway, the partially reduced O2 can further react with H(+) and additional electrons and complete the water formation reaction (WFR) with no activation energy barrier. In the indirect pathway, reduced O2 reacts with H(+) and additional electrons to form H2O molecules through a transition state (TS) with a small activation barrier (0.22-0.37 eV). From an intermediate state to a TS, H(+) can obtain a kinetic energy of ∼0.95-3.68 eV, due to the Coulomb electric interaction, and easily overcome the activation energy barrier during the WFR. The full catalytic reaction cycles can be completed energetically, and N-C60 fullerene recovers to its original structure for the next catalytic reaction cycle. N-C60 fullerene is a potential cathode catalyst for hydrogen fuel cells.

A new zwitterionic conjugated polyelectrolyte without free counterions has been used as an electron injection material in polymer light-emitting diodes. Both the efficiency and maximum brightness were considerably improved in comparison with standard Ca cathode devices. The devices showed very fast response times, indicating that the improved performance is, in addition to hole blocking, due to dipoles at the cathode interface, which facilitate electron injection.

We report the design and synthesis of nanosized Zn(x)Zr(y)O(z) mixed oxides for direct and high-yield conversion of bio-ethanol to isobutene (~83%). ZnO is addded to ZrO(2) to selectively passivate zirconia's strong Lewis acidic sites and weaken Brönsted acidic sites, while simultaneously introducing basicity. As a result, the undesired reactions of bio-ethanol dehydration and acetone polymerization/coking are suppressed. Instead, a surface basic site-catalyzed ethanol dehydrogenation to acetaldehyde, acetaldehyde to acetone conversion via a complex pathway including aldol-condensation/dehydrogenation, and a Brönsted acidic site-catalyzed acetone-to-isobutene reaction pathway dominates on the nanosized Zn(x)Zr(y)O(z) mixed oxide catalyst, leading to a highly selective process for direct conversion of bio-ethanol to isobutene.

A series of molecular pentads, each consisting of a porphyrin dyad (P-P) covalently linked to a carotenoid polyene (C) and a diquinone moiety (Q[sub A]-Q[sub B]), have been prepared, and the photochemical properties of these molecules have been studied using steady-state and transient absorption and emission spectroscopies. Each of the pentads undergoes photoinduced electron transfer from the C-P-[sup 1]P-Q[sub A]-Q[sub B] singlet state to yield the charge-separated state C-P-P[sup [sm bullet]+]-Q[sub A][sup [sm bullet][minus]]-Q[sub B]. Competing with charge recombination of this species are additional electron-transfer reactions operating in series and in parallel which converge on a final C[sup [sm bullet]+]-P-P-Q[sub A]-Q[sub B][sup [sm bullet][minus]] state. The electron-transfer rate constants and the quantum yields of the various charge-separated species are sensitive functions of the state energies and the electronic coupling between the porphyrin and diquinone moieties. One of the pentads undergoes photoinduced electron transfer to produce the final C[sup [sm bullet]+]-P-P-Q[sub A]-Q[sub B][sup [sm bullet][minus]] state with a quantum yield of 0.83 and a lifetime of 55 [mu]s. This example of an artificial photosynthetic reaction center preserves about half of the initial excited singlet state energy as chemical potential. Other pentads have charge-separation lifetimes of several hundred microseconds. 28 refs., 10more » figs., 1 tab.« less

A variety of molecular triads and dyads consisting of covalently linked carotenoid (C) andor porphyrin (P) moieties have been prepared and studied with transient absorption and time-resolved fluorescence techniques. Diporphyrins of the type P A -P B and C-P A -P B triads demonstrate interporphyrin singlet-singlet energy transfer with rate constants ranging from 8.1×10 8 to 2.3×10 10 s −1 . Interporphyrin photoinitiated electron transfer is observed in molecules possessing sufficient thermodynamic driving force to produce P A •+ -P B •− and C-P A •+ -P B •− charge-separated states. The electron-transfer rate constant increases with increasing reaction free energy change for the molecules studied, and rate constants up to 3.5×10 9 s −1 and quantum yields up to 0.68 were measured. The carotenodiporphyrin triad systems undergo a subsequent electron-transfer step to give final C •+ -P A -P B •− states

The enantioselective chemisorption of R- and S-propylene oxide has been measured either on clean Pd(111) that has been exposed to S-2-butanol at various temperatures to vary the proportion of 2-butanol and 2-butoxide species or by adsorbing S-2-butanol on oxygen-covered Pd(111) to form exclusively 2-butoxide. The results reveal that enantioselective chemisorption is only found when 2-butanol is present on the surface. This is ascribed to enantiospecific hydrogen-bonding interactions between 2-butanol and propylene oxide. Measurements of the variation in enantiospecificity with 2-butanol exposure suggest that propylene oxide can interact either with a single adsorbed 2-butanol molecule or, at higher coverages, with two adsorbed 2-butanol species to form enantioselective sites.

The development of new organic semiconductors with improved electrical performance and enhanced environmental stability is the focus of considerable research activity. This paper presents the design, synthesis, optical and electrochemical characterization, crystal packing, modeling and thin film morphology, and organic thin film field effect transistor (OTFT) device data analysis for a novel 2,6-bis[2-(4-pentylphenyl)vinyl]anthracene (DPPVAnt) organic semiconductor. We observed a hole mobility of up to 1.28 cm2/V.s and on/off current ratios greater than 107 for OTFTs fabricated using DPPVAnt as an active semiconductor layer. The mobility value is comparable to that of the current best p-type semiconductor pentacene-based device performance. In addition, we found a very interesting relationship between the charge mobility and molecule crystal packing in addition to the thin film orientation and morphology of the semiconductor as determined from single-crystal molecule packing study, thin film X-ray diffraction, and AFM measurements. The high performance of the semiconductor ranks among the best performing p-type organic semiconductors reported so far and will be a very good candidate for applications in organic electronic devices.

The epidermal growth factor receptor (EGFR) tyrosine kinase was one of the first receptor tyrosine kinases to be targeted for drug development by the pharmaceutical industry due to its ubiquitous overexpression in a variety of tumors. Despite the validation of several quinazoline-based scaffolds in the clinic, there is a dearth of alternative chemical structure classes that are capable of inhibiting EGFR kinase activity selectively. Here we describe the discovery of potent and highly selective 4,6-disubstituted pyrimidine inhibitors of enzymatic and cellular EGFR activity and provide an explanation for their exceptional degree of kinase selectivity.

A one-step nanocasting route has been demonstrated to prepare highly ordered single-crystal indium oxide nanowire (IONW) arrays with mesostructured frameworks. Unlike the reported multistep nanocasting process (synthesis of mesoporous materials, and then incorporation of precursors and formation of inorganic frameworks), a highly ordered mesostructured surfactant-silica monolith with low external surface serves as both the template and the reducing agent and makes the formation of single-crystal IONWs in its channels easily in one step by using normal In(NO(3))(3) as an inorganic precursor. After silica is removed, highly ordered uniform single-crystal IONW arrays with hexagonal (p6mm) or cubic (Ia3d) mesostructures are derived. These new materials are studied by XRD, SEM, TEM, N(2) adsoption, and UV spectrum. Furthermore, this one-step nanocasting synthesis route is a generalized method and can be used to synthesized a highly ordered mesoporous silica monolith with metal oxide nanocrystals in its channels. To the best of our knowledge, this is the first report of a single crystalline mesostructured In(2)O(3) framework.

We have developed a hybrid chemical solution method for preparing nanocomposite thin films composed of a ferroelectric Bi(3.6)Eu(0.4)Ti(3)O(12) (BEuT) matrix and highly c-axis-oriented ZnO nanorods on Si substrates. First, a seed-layer solution growth approach was used to prepare the highly c-axis-oriented ZnO nanorods, and then a chemical solution deposition method was employed to fabricate the BEuT matrix by coating the ZnO nanorods using a spin-coating technique. The nanocomposite thin films obtained exhibited significantly enhanced red photoluminescence (PL) properties. The PL enhancement can be attributed to very efficient radiation energy transfer from the ZnO nanorods to Eu(3+) ions in the BEuT matrix due to two spectral overlaps between the emission spectra of the ZnO nanorods and the excitation bands of Eu(3+) ions in the BEuT matrix: the spectral overlap between the sharp UV emission of ZnO centered at 380 nm and the excitation spectrum of the (7)F(0) --> (5)L(6) transition of Eu(3+) ions at 395 nm and that between the defect-related deep-level green emission band of ZnO centered at 525 nm and the excitation spectrum of the (7)F(0) --> (5)D(2) transition of Eu(3+) ions at 465 nm. Our study opens possibility of realizing highly efficient photoluminescent ferroelectric multifunctional integrated thin-film devices. In addition, the hybrid chemical solution method also provides a useful route for the synthesis of some new nanocomposite thin films consisting of other inorganic matrix and c-axis-oriented ZnO nanorods.

A new and highly efficient Cu(I)/TF-BiphamPhos catalytic system exhibited excellent reactivity, enantio-/diastereoselectivity, and structural scope in asymmetric 1,3-dipolar cycloaddition of azomethine ylides with 0.1-3 mol % of catalyst loading. The present methodology is the best result for asymmetric cycloaddition of azomethine ylides, especially derived from amino esters other than glycinate in terms of reactivity and enantioselectivity.

The development of new organic semiconductors with improved electrical performance and enhanced environmental stability is the focus of considerable research activity. This paper presents the design, synthesis, optical and electrochemical characterization, crystal packing, modeling and thin film morphology, and organic thin film field effect transistor (OTFT) device data analysis for a novel 2,6-bis[2-(4-pentylphenyl)vinyl]anthracene (DPPVAnt) organic semiconductor. We observed a hole mobility of up to 1.28 cm2/V.s and on/off current ratios greater than 107 for OTFTs fabricated using DPPVAnt as an active semiconductor layer. The mobility value is comparable to that of the current best p-type semiconductor pentacene-based device performance. In addition, we found a very interesting relationship between the charge mobility and molecule crystal packing in addition to the thin film orientation and morphology of the semiconductor as determined from single-crystal molecule packing study, thin film X-ray diffraction, and AFM measurements. The high performance of the semiconductor ranks among the best performing p-type organic semiconductors reported so far and will be a very good candidate for applications in organic electronic devices.

The growth of ordered nanorods of mesoporous SBA-15 inside a porous alumina membrane has been achieved for the first time by a simple sol-gel method. The obtained SBA-15 nanorods themselves have ordered hexagonal mesochannels with a size of about 6 nm and have been arranged to form hexagonal arrays by the limitation of pores of the alumina membrane. The synthesized alumina membrane with mesoporous SBA-15 inside combines the advantages of porous alumina membranes and mesoporous SBA-15 and provides fine and vertical mesochannels, which may serve as a new and efficient mold and lead to extensive applications in nanodevice fabrication, biomacromolecule separations, etc.

A biomolecule-assisted simple technique has been developed for the spontaneous ordering of the Bi2S3 nanorods into snowflakelike superstructures in high yield under microwave-hydrothermal conditions. In this method, glutathione (GSH) is used as both an assembling agent and a sulfur source. By controlling the molar ratio between bismuth nitrate and glutathione as well as the synthetic temperature, several kinds of Bi2S3 one-dimensional nanomaterials such as snowflakelike structures, nanowires constructed of particles, short nanorods, and fine and long nanowires have been controllably synthesized.

A four-component molecular device, which consists of two covalently linked porphyrins, one bearing a carotenoid polyene and the other a napthoquinone electron-acceptor, has been prepared to attempt to explain the electron-transfer strategy of photosynthesis. This tetrad was found to demonstrate singlet and triplet energy transfer behavior, which mimics photosynthetic antenna function by chlorophylls and carotenoids and carotenoid photoprotection from singlet oxygen damage. 27 refs., 1 fig.