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Through high-resolution electron microscopy, the surface structure of barium titanate and strontium titanate nanoparticles are found to be terminated by a TiO2 double layer. These results confirm prior observations of TiO2-rich surface reconstructions on strontium titanate nanoparticles made hydrothermally at high pH and single crystals prepared with wet chemical etching. Of all the reconstructions observed on single crystals for these two materials, we report for first time the √13 x √13R33.7° structure on the {001} facets of hydrothermally prepared barium titanate and strontium titanate nanocrystals. The aqueous environment common to the two preparation methods preferentially leaves strontium and barium depleted from the A-sites near the surface and leads to TiO2-terminated surfaces for both materials. Analysis indicates that the observed structures are the thermodynamic lowest energy structures in aqueous conditions. [ABSTRACT FROM AUTHOR]

A visible-light photocatalytic decarboxylative alkyl radical addition cascade reaction of acrylamide-tethered styrenes for the synthesis of benzazepine derivatives is described. This protocol features broad substrate scope, excellent functional group tolerance, and mild reaction conditions, affording the seven-membered rings in good yields. This method was also applied for efficient grafting of the benzazepine scaffold into the pharmaceutically active ursolic acid scaffold. [ABSTRACT FROM AUTHOR]

A general and efficient visible light photocatalytic α-amino carbon radical-based cascade reaction of aroylhydrazones has been described. This protocol tolerates a wide array of α-silylamines and aroylhydrazones to afford the corresponding diversely functionalized hydrazide-containing chroman-2-ones and dihydroquinolin-2-ones in generally good yields with excellent diastereoselectivities. [ABSTRACT FROM AUTHOR]

Conspectus: Visible-light photocatalysis has recently received increasing attention from chemists because of its wide application in organic synthesis and its significance for sustainable chemistry. This catalytic strategy enables the generation of various reactive species, frequently without stoichiometric activation reagents under mild reaction conditions. Manipulation of these reactive intermediates can result in numerous synthetically useful bond formations in a controllable manner. In this Account, we describe our recent advances in the rational design and strategic application of photocatalysis in the synthesis of various synthetically and biologically important heterocycles. Our main research efforts toward this goal can be classified into four categories: formal cycloaddition and cyclization reactions, radical-mediated olefin functionalization/cyclization cascades, photocatalytic generation and cyclization of N-centered radicals, and photocatalytic functionalization of heterocycles by visible-light-induced dual catalysis. Inspired by the wide application of tertiary amines as reductive additives in photoredox catalysis, we exploited a series of readily accessible or rationally designed tertiary amines with reactive sites in a range of photocatalytic formal cycloaddition and cyclization reactions, providing efficient access to diverse nitrogen heterocycles. Employing various photogenerated radical species, we further developed a series of radical-mediated olefin functionalization/cyclization cascade reactions to successfully assemble various five- and six-membered heterocycles. We have also achieved for the first time the direct catalytic conversion of recalcitrant N-H bonds into neutral N-centered radicals through a visible-light-photocatalytic oxidative deprotonation electron transfer. Using this generic strategy, we have devised several types of radical cyclizations of unsaturated hydrazones, leading to the construction of diversely functionalized pyrazoline and pyridazine derivatives in good yields and selectivity. Moreover, we have demonstrated that this photocatalysis can serve as a mild and highly selective tool for direct functionalization of heterocycles because of its powerful capability to controllably generate diverse reactive intermediates under mild reaction conditions. Guided by the fundamental principles of photocatalysis and the redox properties of the photocatalysts, we successfully developed an array of dual-catalyst systems by combining the photocatalysts with palladium, nickel, or amine, enabling efficient and selective coupling reactions. An intriguing phototandem catalytic system using a single photocatalyst was also identified for the development of cascade reactions. Notably, some of the newly developed methodologies have also been successfully utilized for late-stage modification of biologically active natural compounds and complex molecules and as key steps for formal synthesis of natural products. This Account presents a panoramic view and the logic of our recent contributions to the design, development, and application of photocatalytic systems and reactions that provide not only methods for the efficient synthesis of heterocycles but also useful insights into the exploration of new photochemical reactions. [ABSTRACT FROM AUTHOR]

Conventional photocatalytic ozonation usually suffers from the mass transport issue associated with low specific surface area and gas/liquid interface and liquid film. To address this issue, a new membrane microreactor based on optofluidics was developed for wastewater treatment by the photocatalytic ozonation in this work. The key component of the photocatalytic membrane was prepared by coating TiO2 onto carbon paper followed by the hydrophobic treatment with polytetrafluoroethylene. Such design offered several advantages such as large surface-area-to-volume ratio, enhanced mass transport, intense and uniform light irradiation, efficient separation of the liquid/gas phases, and good gas permeability. The performance of the developed microreactor was evaluated by methylene blue degradation, and the products were analyzed by the ion chromatography. Experimental results showed that because of these advantages, the optofluidic membrane microreactor not only yielded better performance but also showed more complete oxidation as compared to photocatalysis and ozonation. Parametric studies indicated that increasing the residence time and decreasing the methylene blue concentration could improve the degradation efficiency. High light intensity benefited photocatalytic ozonation. The obtained results demonstrate that the developed optofluidic membrane microreactor is feasible for wastewater treatment by photocatalytic ozonation. Besides, this new type of microreactor can also be applied to other photocatalytic systems. [ABSTRACT FROM AUTHOR]

The photothermal effect induced phase change is an important phenomenon in optofluidics. In this work, therefore, the characteristics of the phase change in microchannels with different depths induced by a 1550 nm infrared laser under both low and high laser powers was visually studied. It was revealed that at low laser power, the liquid body could be always advanced as a result of the induced evaporation-condensation-coalescence process regardless of the microchannel depth, which can function as a micro pump. The μ-PIV testing results further demonstrated the coalescence was a dominant mechanism in the interface advancement. Interestingly, although large depth increased the absorption length of the laser and thus improved the temperature and enhanced the evaporation, the advancing effect became weak due to the increase of both the flow resistance and liquid water content to be driven. At high laser power, for small depth microchannel, the liquid body was advanced at the beginning. Once a liquid slug along with a sealed gas slug was formed, the liquid body started to move backward, which can function as chemical separation. However, as the microchannel depth increased, despite that the evaporation was enhanced, such phenomena hardly happen because enhanced evaporation allowed large droplets to be generated. Air bubbles instead of a gas slug were easily entrapped in the liquid body during the coalescence process. These air bubbles quickly grew up due to high temperature, which could be an obstacle to the advancing movement of the liquid body or even block the laser heating. Therefore, it can be concluded that the microchannel depth plays an important role in the photothermally induced phase change process. The obtained results are helpful for the design and operation of the photothermal effect based optofluidic microdevices. [ABSTRACT FROM AUTHOR]

A general visible light induced photoredox-catalyzedradical trifluoromethylation/cyclizationcascade of β-aryl-β,γ-unsaturated hydrazones andoximes is described. The protocol enables an efficient access to variousdensely functionalized and biologically important CF3-containingdihydropyrazoles and isoxazolines with generally high yields. [ABSTRACT FROM AUTHOR]

The article discusses the impact of annulation reactions in the synthesis of carbocyclic and heterocyclic systems. It focuses on the application of cyclization and cycloaddition reactions in the modern synthetic organic community. It notes the importance of carbon monoxide (CO) in the transition metal catalysis of carbonylative cycloadditions.

Many drug molecules inhibit the conduction of several families of cation channels by binding to a small cavity just below the selectivity filter of the channel protein. The exact mechanisms governing drug–channel binding and the subsequent inhibition o f conduction are not well understood. Here the inhibition of two K+ channel isoforms, Kv1.2 and KCa3.1, by two drug molecules, lidocaine and TRAM-34, is examined in atomic detail using molecular dynamics simulations. A conserved valinealanine- valine motif in the inner cavity is found to be crucial for drug binding in both channels, consistent with previous studies of similar systems. Potential of mean force calculations show that lidocaine in its charged form creates an energy barrier of ~6 kT for a permeating K+ ion when the ion is crossing over the drug, while the neutral form of lidocaine has no significant effect on the energetics of ion permeation. On the other hand, TRAM-34 in the neutral form is able to create a large energy barrier of ~10 kT by causing the permeating ion to dehydrate. Our results suggest that TRAM-34 analogues that remain neutral and permeable to membranes under acidic conditions common to inflammation may act as possible drug scaffolds for combating local anesthetic failure in inflammation. [ABSTRACT FROM AUTHOR]

A Ag-mediated C–H/P–H functionalization reaction of arylphosphine oxides with internal alkynes was described for the direct preparation of benzo[b]phosphole oxides with a high yield. An unusual aryl migration on the P-atom derived from a C–P bond cleavage and a new C–P bond formation was also observed and demonstrated to proceed via the radical process. [ABSTRACT FROM AUTHOR]

The N-type voltage-gated Ca2+ channel CaV2.2 is one of the important targets for pain management. ω-Conotoxins isolated from venoms of cone snails, which specifically inhibit CaV2.2, are promising scaffolds for novel analgesics. The inhibitory action of ω-conotoxins on CaV2.2 has been examined experimentally, but the modes of binding of the toxins to this and other related subfamilies of Ca2+ channels are not understood in detail. Here molecular dynamics simulations are used to construct models of ω-conotoxin GVIA in complex with a homology model of the pore domain of CaV2.2. Three different binding modes in which the side chain of Lys2, Arg17, or Lys24 from the toxin protrudes into the selectivity filter of CaV2.2 are considered. In all the modes, the toxin forms a salt bridge with an aspartate residue of subunit II just above the EEEE ring of the selectivity filter. Using the umbrella sampling technique and potential of mean force calculations, the half-maximal inhibitory concentration (IC50) values are calculated to be 1.5 and 0.7 nM for the modes in which Lys2 and Arg17 occlude the ion conduction pathway, respectively. Both IC50 values compare favorably with the values of 0.04-1.0 nM determined experimentally. The similar IC50 values calculated for the different binding modes demonstrate that GVIA can inhibit CaV2.2 with alternative binding modes. Such a multiple-binding mode mechanism may be common for ω-conotoxins. [ABSTRACT FROM AUTHOR]

Scorpion α-toxins bind to the voltage-sensing domains of voltage-gated sodium (NaV) channels and interfere with the inactivation mechanisms. The functional surface of α-toxins has been shown to contain an NC-domain consisting of the five-residue turn (positions 8-12) and the C-terminus (positions 56-64) and a core-domain centered on the residue 18. The NC- and core-domains are interconnected by the linker-domain (positions 8-18). Here with atomistic molecular dynamics simulations, we examine the binding modes between two α-toxins, the anti-mammalian AahII and the anti-insect LqhαIT, and the voltage-sensing domain of rat NaV1.2, a subtype of NaV channels expressed in nerve cells. Both toxins are docked to the extracellular side of the voltage-sensing domain of NaV1.2 using molecular dynamics simulations, with the linker-domain assumed to wedge into the binding pocket. Several salt bridges and hydrophobic clusters are observed to form between the NC- and core-domains of the toxins and NaV1.2 and stabilize the toxin-channel complexes. The binding modes predicted are consistent with available mutagenesis data and can readily explain the relative affinities of AahII and LqhαIT for NaV1.2. The dissociation constants for the two toxin-channel complexes are derived, which compare favorably with experiment. Our models demonstrate that the functional surface of anti-mammalian scorpion α-toxins is centered on the linker-domain, similar to that of β-toxins. [ABSTRACT FROM AUTHOR]

An unprecedented strategy to access highly enantioenriched dihydropyrazoles is described. It involves formal [4+1] cycloadditions of in situ-derived azoalkenes and sulfur ylides catalyzed by a chiral copper/Tol-BINAP complex. A variety of synthetically and biologically important dihydropyrazoles have been obtained with high enantioselectivities (up to 97:3 er) in good yields (83-97%). [ABSTRACT FROM AUTHOR]

A polypeptide toxin extracted from scorpion venom, OSK1, is modified such that its potency is drastically enhanced in blocking one class of voltage-gated potassium channels, Kv1.3, which is a pharmacological target for immunosuppressive therapy. The bound complex of Kv1.3 and OSK1 reveals that one lysine residue of the toxin is in the proximity of another lysine residue on the external vestibule of the channel, just outside of the selectivity filter. This unfavorable electrostatic interaction is eliminated by interchanging the positions of two amino acids in the toxin. The potentials of mean force of the wild-type and mutant OSK1 bound to Kv1.1-Kv1.3 channels are constructed using molecular dynamics, and the half-maximal inhibitory concentration (IC50) of each toxin-channel complex is computed. We show that the IC50 values predicted for three toxins and three channels match closely with experiment. Kv1.3 is half-blocked by 0.2 pM mutant OSK1; it is >10000-fold more specific for this channel than for Kv1.1 and Kv1.2. [ABSTRACT FROM AUTHOR]

The strong light–matter interaction within a semiconductor high-Q microcavity has been used to produce half-matter/half-light quasiparticles, exciton-polaritons. The exciton-polaritons have very small effective mass and controllable energy-momentum dispersion relation. These unique properties of polaritons provide the possibility to investigate the fundamental physics including solid-state cavity quantum electrodynamics, and dynamical Bose–Einstein condensates (BECs). Thus far the polariton BEC has been demonstrated using optical excitation. However, from a practical viewpoint, the current injection polariton devices operating at room temperature would be most desirable. Here we report the first realization of a current injection microcavity GaN exciton-polariton light emitting diode (LED) operating under room temperature. The exciton-polariton emission from the LED at photon energy 3.02 eV under strong coupling condition is confirmed through temperature-dependent and angle-resolved electroluminescence spectra. [ABSTRACT FROM AUTHOR]

We carried out molecular dynamics (MD) simulations with the quantum-corrected Sutton−Chen (Q-SC) potential to compute the thermal equation of state (EOS), the solid−liquid interfacial energy, and melting properties of nickel. We simulate the melting with two methods, the hysteresis (one-phase) approach and the solid−liquid coexistence (two-phase) approach. These methods strongly reduced the overheating, and their results are in the close proximity over a large range of pressure. The melting temperature at ambient pressure is in accordance with the diamond anvil cell (DAC) experiment values. With a superheating and undercooling method, solid−liquid interfacial energy as a function of pressure is exhibited. Moreover, the thermal EOS has been investigated, and the linear thermal expansivity as a function of temperature has also been obtained successfully. [ABSTRACT FROM AUTHOR]

A practical protocol for the preparation of parallel solution-phase libraries of the quaternary carbon-containing oxazatricycles and spiropyrans is reported. Target compounds were obtained in moderate to excellent yields by an Et3N-mediated multicomponent reaction from various N-methylisoquinolium or flavylium salts and 4-hydroxycoumarins or dimedone in acetone. Purification of the final products by recrystallization in ethyl acetate/methylene chloride or by column chromatography allowed easy isolation of nine compounds of each array. Preliminary studies indicated that some of the prepared compounds exhibit redox switching, photochromic, and thermochromic properties. [ABSTRACT FROM AUTHOR]

A new type of acylated carboxymethyl amphiphilic chitosan (ACC) with the use of acyl chain of varying lengths, from C2to C12, and various degrees of acyl substitution was successfully synthesized and has been characterized in terms of its self-assembly behavior, structural stability, and drug encapsulation. The resulting nanostructure of the ACC nanoaggregates can be well manipulated through a control of hydrophobicity. Structural evolution of the self-assembled nanoaggregates is extensively characterized via 1H NMR, FTIR, DSC, and TEM. A critical value of the hydrophobic effect, (XDH× XCn), i.e., a product of “degree of acyl substitution” and “carbon number of acyl chain”, can be employed as an indicator for structural variation of the nanoaggregates: when (XDH× XCn) exceeded 1.5, the architecture of the nanoaggregates underwent a structural transformation from solid nanoparticle to hollow nanocapsules. The nanoaggregates exhibited an excellent colloidal and structural stability in aqueous medium. An improved affinity toward drug encapsulation, i.e., doxorubicin, can be technically designed according to the amphiphilic nature of the resulting nanoaggregates for drug delivery. [ABSTRACT FROM AUTHOR]

The synthesis of narrow distribution model macrocyclic polystyrenes initiated with 1,4-dipotassio-bis-1,4-(9′,9′-dimethyl-2′-fluorenyl)butane (DMFB) containing 12 to 55 styrene units and coupled to a single 9,10-anthracenylidene (AN) unit (PS-DMFB-AN) is reported. The initiator is formed via electron transfer/coupling from potassium naphthalenide to give nearly pure DMFB, followed by the addition of styrene and protonation or intramolecular end-to-end coupling with 9,10-bis(chloromethyl)anthracene to give the linear and cyclic polymers, respectively. Förster transfer from the 9,9-dimethyl-2-fluorenyl (DMF) group donors to the AN groups, surprisingly, only slightly increased with lower degrees of polymerization of the PS segments. Extensive simulations indicate the presence of highly asymmetrical polymers in which the two arms of the polymer dianion significantly differ in the degree of polymerization. This appears to be partially due to chain statistics but also to slow initiation relative to polymerization. [ABSTRACT FROM AUTHOR]

An o-hydroxyphenyl-containing spiropyran thermochromic colorant was designed and synthesized. The prepared compound is sensitive to temperature and has a reversible color change with temperature variation. X-ray diffraction analysis and variable-temperature NMR studies suggest that the thermochromism of the compound presumably involved a ring-opening C−O bond cleavage of the spiropyran moiety followed by an intramolecular hydrogen transfer. [ABSTRACT FROM AUTHOR]

Two coumarin-based spiropyran derivatives were synthesized and characterized in two steps to explore their photochromic properties. Both prepared compounds are sensitive to UV light and change colors upon irradiation. The resulting photogenerated zwitterions revert to the original compounds while being heated. A new family of organic photochromic colorants is introduced. [ABSTRACT FROM AUTHOR]

A new class of organocatalysts has been designed by rational combination of proline with cinchona alkaloids. The chiral amine 3a, prepared from L-proline and cinchonidine, has been found to be an efficient catalyst for the direct aldol reactions of acetone or 2-butanone with a wide range of aldehydes (up to 98% ee). The cinchonidine backbone is essential to the reaction efficiency and enantioselectivity. [ABSTRACT FROM AUTHOR]

Sterically and electronically tunable and bifunctional organocatalysts have been developed and evaluated in the direct aldol reaction of heterocyclic ketones. Catalysts with different substituents showed variable catalytic efficiency for analogous substrates, indicating the importance of fine-tuning the strength of the hydrogen bonding in the two NH groups. The reactions all proceeded in good to high yield and with excellent enantioselectivities ranging from 90% to >99% ee. In most cases, high diastereoselectivities ranging from 96/4 to 99/1 were obtained for the anti aldol adduct. [ABSTRACT FROM AUTHOR]

In our effort to systematically investigate the influences of ligand spacers and terminal groups on the Ag/I inorganic framework with large organic cation SDAs (structure-directing agents) (Et3N(CH2)4NEt32, Et3N(CH2)6NEt32, and Me3N(CH2)6NMe32), three silver(I) coordination polymers, Et3N(CH2)4NEt3Ag4I6n (1) Et3N(CH2)6NEt3Ag5I7n (2), and Me3N(CH2)6NMe3Ag4I6n (3), have been synthesized in polar organic solvent. 1−3all consist of one-dimensional polymers that could be described as edge-sharing AgI4tetrahedrons. Electrostatic interactions between organic countercations and inorganic moieties are presented and contribute to the crystal packing. The structural differences among 1−3show the influences of the spacers and substituents of SDAs on the linkage modes of AgI4tetrahedrons. All compounds were further characterized with IR spectra, elemental analysis, thermal measurements, fluorescence analysis, and optical limiting measurements. [ABSTRACT FROM AUTHOR]

The first example of a Pd(OAc)2-catalyzed ring-forming alkene aminoaroylation of unsaturated hydrazones and sulfonamides is described. This protocol features the use of diaryliodonium salts as both oxidants and aryl sources, thus enabling mild reaction conditions, good chemoselectivity, a broad substrate scope, and high functional group tolerance. A wide range of synthetically and biologically important functionalized dihydropyrazoles and isoxazolidines have been obtained in good yields. [ABSTRACT FROM AUTHOR]

It was demonstrated that 3-olefinic oxindoles could generate zwitterionic enolate species with tertiary phosphines and undergo C–C bond formation with various electrophiles in an interrupted Morita–Baylis–Hillman-type reaction manner, followed by a dephosphoration process. Although the in situ formation of phosphorus-ylide intermediates was observed, no Wittig reaction was detected, even in the presence of excess formaldehyde. Moreover, excellent enantioselectivity for the construction of quaternary stereogenic centers was induced with chiral phosphines. Deuterium experiments and density functional theory calculations were conducted to elucidate the reaction mechanism. [ABSTRACT FROM AUTHOR]

A surface metal-organic complex, (-AlOx)Pd(acac) (acac = acetylacetonate), is prepared by chemically grafting the precursor Pd(acac)2 onto γ-Al2O3 in toluene at 25 °C. The resulting surface complex is characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and dynamic nuclear polarization surface-enhanced solid-state nuclear magnetic resonance spectroscopy (DNP SENS). This surface complex is a precursor in the direct synthesis of size-controlled Pd nanoparticles under mild reductive conditions and in the absence of additional stabilizers or pretreatments. Indeed, upon exposure to gaseous ethylene or liquid 1-octene at 25 °C, the Pd2+ species is reduced to form Pd0 nanoparticles with a mean diameter of 4.3 ± 0.6 nm, as determined by scanning transmission electron microscopy (STEM). These nanoparticles are catalytically relevant using the aerobic 1-phenylethanol oxidation as a probe reaction, with rates comparable to a conventional Pd/Al2O3 catalyst but without an induction period. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature-programmed reaction mass spectrometry (TPR-MS) reveal that the surface complex reduction with ethylene coproduces H2, acetylene, and 1,3-butadiene. This process reasonably proceeds via an olefin activation/coordination/insertion pathway, followed by β-hydride elimination to generate free Pd0. The well-defined nature of the single-site supported Pd2+ precursor provides direct mechanistic insights into this unusual and likely general reductive process. [ABSTRACT FROM AUTHOR]

A generaland efficient Pd/sulfoxide-phosphine complex-catalyzeddirect asymmetric N-allylic alkylation of indoleshas been developed to allow for the preparation of various N-allylated indoles in generally good yields with excellentenantioselectivities. This catalytic system could also be extendedto other N-containing heterocycles with good results. [ABSTRACT FROM AUTHOR]

An asymmetric nucleophilic addition/protonation reaction of 3-substituted oxindoles and ethyl 2-phthalimidoacrylate has been described. This strategy can give direct access to Cγ-tetrasubstituted α-amino acid derivatives bearing 1,3-nonadjacent stereocenters with up to 98% yield, 94:6 dr, and >99% ee. Dual activation is proposed in the transition state, and the opposite enantiomers can be obtained simply by changing cinchonidine-derived catalyst to the cinchonine analogue. [ABSTRACT FROM AUTHOR]

The phase transitions and mechanical properties of the energetic material octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) in three pure polymorphs crystals, α-, β-, and δ-phases, have been studied theoretically. Isothermal−isobaric molecular dynamics (MD) simulations were performed in the temperature range of (5 to 555) K at 0 GPa and the pressure range of (0 to 40) GPa at 298 K. The lattice parameters and volumes show nonlinear dependence on the temperature and pressure. In the high-temperature regime, there exist two phase transitions, that is, from β- to α-HMX at 360 K and from α- to δ-HMX at 440 K. Under high pressure, the β-HMX transition to δ-HMX is shown at 27 GPa and 298 K. Within the range of temperature and pressure studies, it can be deduced that the β-HMX at lower temperatures and higher pressures, the α-HMX at higher pressures, and the δ-HMX at lower temperatures have better malleability. [ABSTRACT FROM AUTHOR]

A first-principles plane-wave method with an ultrasoft pseudopotential scheme in the framework of the generalized gradient approximation (GGA) was used to calculate the lattice parameters, bulk modulus and its pressure derivative, energy band structures, density of states, phonon density of states, thermodynamic properties, and absorption spectra of solid β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (β-HMX). The current study is focused on the thermodynamics and electronic properties that were not reported previously. The bulk modulus and its pressure derivative are also consistent with experimental data and other theoretical results. From the results for the band gaps and density of states, it was found that β-HMX has the tendency to become a semiconductor with increasing pressure. As the temperature increases, the heat capacity, enthalpy, product of temperature and entropy, and Debye temperature all increase, whereas the free energy decreases. The optical absorption coefficients shift to higher frequencies/energies with increasing pressure. The present study leads to a better understanding of how energetic materials respond to compression. [ABSTRACT FROM AUTHOR]

The sequential replacement of a bpy ligand (bpy=2,2'-bipyiidine) by a dpb ligand (dpb=2,3-bis(2-pyndyl) benzoquinoxaline) in the seiles [Ru(bpy)3-n(dpb)n]2+ (n = 1-3) leads to a remarkable increase of the excited state lifetime, the ¹O2 quantum yield, and the binding affinity toward dsDNA, rendering both [Ru(bpy)(dpb)2]2+ and [Ru(dpb)3]2+ efficient DNA photodeavage activities upon red light irradiation (⩾600 nm). [ABSTRACT FROM AUTHOR]

By taking advantage of the spectral properties of metal carbonyls, we have designed a surface-enhanced Raman spectroscopy (SERS) ratiometric assay for measuring cellfree circulating DNA (cfDNA) from Epstein-Barr virus in blood for nasopharyngeal carcinoma (NPC). This assay consists of a rhenium carbonyl (Re-CO) to serve as a DNA probe, an osmium carbonyl (Os-CO) embedded within the SERS-active substrate as an internal reference, and a streptavidin layer on the surface of the substrate. Hybridization of cfDNA with biotinylated-capture sequence leads to immobilization of cfDNA on the substrate. The binding of Re-CO via daunorubicin (DNR) to cfDNA is accompanied by an appearance of a strong symmetry stretching vibrations peak at 2113 cm-1, which has spectral overlap with Os-CO (2025 cm-1). This results in an increase in the I2113/I2025 ratio and quantitatively correlates with cfDNA. This SERS assay can be readily used to detect cfDNA in blood samples from patients due to the intensity ratio of I2113/I2025 lying in a silent region (1780-2200 cm-1) in the SERS spectrum of the biomolecules. [ABSTRACT FROM AUTHOR]

A general and efficient Pd/phosphoramidite thioether complex-catalyzed asymmetric N-allylic alkylation of hydrazones with allylic acetates has been developed for the first time. The reaction allows for the preparation of various valuable N-substituted hydrazones with generally good yields and excellent enantioselectivities. Minor structural modification of the ligand resulted in opposite enantiomers, enabling enantiodivergent synthesis of products by the same catalytic system. [ABSTRACT FROM AUTHOR]

A dual visible light photoredox and nickel-catalyzed cross-coupling reaction of 2-arylaziridines and potassium benzyltrifluoroborates is described for the first time. This strategy features high functional group tolerance, exclusive regioselectivity for reaction at the more hindered C-N bond, easily accessible substrates, and mild redox-neutral reaction conditions. A variety of diversely substituted ß-substituted amines are obtained in generally good yields. [ABSTRACT FROM AUTHOR]

A ligand-free, palladium-catalyzed aminoarylation reaction of the unactivated alkenes in β,γ-unsaturated hydrazones is described. This protocol enables efficient and simultaneous formation of C(sp³)--N and C(sp³)--C(sp²) bonds under mild conditions, providing a practical and general approach to various diversely substituted dihydropyrazoles in generally good yields, without the use of any stoichiometric external oxidant. [ABSTRACT FROM AUTHOR]

The Wittig reaction, which produces alkenes from phosphorus ylides (P-ylides) and carbonyls, is one of the most powerful tools in chemical synthesis. This Nobel Prize-winning reaction is widely used in natural product synthesis, fine chemical production (i.e., medicines and agricultural agents), and polymer functionalization. Despite these great achievements, the potential of the Wittig reaction, particularly regarding the access of chiral alkene building blocks, has not been fully exploited. The main area that requires additional exploration is the development of general and practical methods to efficiently prepare chiral P-ylides. Here, we show that highly functionalized chiral P-ylides can be easily synthesized through a copper-catalyzed asymmetric propargylic alkylation reaction from phosphonium salts and racemic propargylic esters. The subsequent Wittig reactions enable the synthesis of versatile alkene building blocks, chiral α-propargylic acrylates, and α-propargylic allenoates, with a wide substrate scope and satisfactory functional group compatibility. This transformation features inexpensive transition-metal catalysts, user-friendly conditions, easily available feedstock, and high-valued products. [ABSTRACT FROM AUTHOR]

A novel photocatalytic hydrazonyl radical-mediated radical cyclization/allylation cascade reaction of β,γ-unsaturated hydrazones is developed using allyl sulfones and Morita-Baylis-Hillman adduct as allyl sources, which provides an efficient and practical access to various diversely functionalized dihydropyrazoles and tetrahydropyridazines. The reaction is enabled by controllable generation of hydrazonyl radicals via an oxidative deprotonation electron transfer strategy and selective trapping of the resultant C-centered radicals under visible light irradiation. [ABSTRACT FROM AUTHOR]

In this work, hierarchical nanostructures Fe(III)-modified BiOBr were successfully prepared via a facile one-step route at room temperature. Compared with pure BiOBr, Fe(III)-modified BiOBr samples possess enhanced photocatalytic abilities for benzyl alcohol oxidation and organic dye degradation in the presence of H2O2 upon light illumination. The improved photocatalytic oxidation and degradation ability of Fe(III)-modified BiOBr is ascribed to the enhanced photogenerated carriers separation efficiency and promoted production of ·OH due to the generation of Fe2+ ions via interfacial charge transfer from Fe3+ ions. This work provides a facial approach to improve photocatalytic efficiency for organic synthesis and environmental remediation. [ABSTRACT FROM AUTHOR]

A novel visible-light-responsive chiral ligand has been developed by grafting a triplet state photosensitizer to chiral bisoxazoline ligands. Complexation of this ligand with Ni(acac)2 results in a powerful catalyst for the asymmetric oxidation reaction of β-ketoesters, which uses oxygen or air as the green oxidant and visible light or sunlight as the ideal driving force. Using this protocol, products containing the α-hydroxy-β-dicarbonyl motif are produced in high yields and with excellent enantiopurities. [ABSTRACT FROM AUTHOR]

The structures of cationic water clusters (H2O)8+ have been globally explored by the particle swarm optimization method in combination with quantum chemical calculations. Geometry optimization and vibrational analysis for the 15 most interesting clusters were computed at the MP2/aug-cc-pVDZ level and infrared spectrum calculation at MPW1K/6-311++G** level. Special attention was paid to the relationships between their configurations and energies. Both MP2 and B3LYP-D3 calculations revealed that the cage-like structure is the most stable, which is different from a five-membered ring lowest energy structure but agrees well with a cage-like structure in the literature. Furthermore, our obtained cage-like structure is more stable by 0.87 and 1.23 kcal/mol than the previously reported structures at MP2 and B3LYP-D3 levels, respectively. Interestingly, on the basis of their relative Gibbs free energies and the temperature dependence of populations, the cage-like structure predominates only at very low temperatures, and the most dominating species transforms into a newfound four-membered ring structure from 100 to 400 K, which can contribute greatly to the experimental infrared spectrum. By topological analysis and reduced density gradient analysis, we also investigated the structural characteristics and bonding strengths of these water cluster radical cations. [ABSTRACT FROM AUTHOR]

Cl-incorporated BiOI nanostructures with different Cl/I molar ratios have been successfully fabricated via a facile room-temperature method in H2O/EG mixture solvent. Combined with FT-IR, Raman spectrum, XRD Rietveld refinements, and DFT calculation, the incorporated Cl ions are found mainly occupied on I sites, resulting in a hybrid valence band consisting of I 5p, O 2p, and Cl 3p orbitals, which deepens the valence band location of the materials and induces photogenerated holes with higher oxidation power. The incorporated Cl ions into the lattice also change the evolution of photogenerated electrons and holes, inducing the broadening of the bandgap but efficient production of photogenerated carriers. The enhanced oxidation power of Cl-incorporated BiOI products was evaluated by photocatalysis degradation of methylene blue, an organic dye for which pure BiOI shows negligible direct oxidation efficiency. Ascribed to the relatively low valence band maximum (VBM) and efficient generation of photoinduced electrons and holes, the incorporated products show distinct enhancement photocatalytic activities. [ABSTRACT FROM AUTHOR]

The main challenges to the commercial viability of polymer electrolyte membrane fuel cells are (i) the high cost associated with using large amounts of Pt in fuel cell cathodes to compensate for the sluggish kinetics of the oxygen reduction reaction, (ii) catalyst degradation, and (iii) carbon-support corrosion. To address these obstacles, our group has focused on robust, carbon-free transition metal nitride materials with low Pt content that exhibit tunable physical and catalytic properties. Here, we report on the high performance of a novel catalyst with low Pt content, prepared by placing several layers of Pt atoms on nanoparticles of titanium nickel binary nitride. For the ORR, the catalyst exhibited a more than 400% and 200% increase in mass activity and specific activity, respectively, compared with the commercial Pt/C catalyst. It also showed excellent stability/durability, experiencing only a slight performance loss after 10?000 potential cycles, while TEM results showed its structure had remained intact. The catalyst's outstanding performance may have resulted from the ultrahigh dispersion of Pt (several atomic layers coated on the nitride nanoparticles), and the excellent stability/durability may have been due to the good stability of nitride and synergetic effects between ultrathin Pt layer and the robust TiNiN support. [ABSTRACT FROM AUTHOR]

The superionic conductor Cu2−δSe has beenshown to be a promising thermoelectric at higher temperatures becauseof very low lattice thermal conductivities, attributed to the liquid-likemobility of copper ions in the superionic phase. In this work, wepresent the potential of copper selenide to achieve a high figureof merit at room temperature, if the intrinsically high hole carrierconcentration can be reduced. Using bromine as a dopant, we show thatreducing the charge carrier concentration in Cu2−δSe is in fact possible. Furthermore, we provide profound insightinto the complex defect chemistry of bromine doped Cu2−δSe via various analytical methods and investigate the consequentialinfluences on the thermoelectric transport properties. Here, we show,for the first time, the effect of copper vacancy formation as compensatingdefects when moving the Fermi level closer to the valence band edge.These compensating defects provide an explanation for the often seendoping inefficiencies in thermoelectrics via defect chemistry andguide further progress in the development of new thermoelectric materials. [ABSTRACT FROM AUTHOR]

Theenergy transfer mechanism between Ho3橷 Er3誉 has been investigated in germanosilicate glass excitedby 980 nm laser diode. A rate equation model was developed to demonstratethe energy transfer from Er3 Ho3誉,quantitatively. Energy transfer efficiency from the Er3:4I13/2to the Ho3:5I7level can reach as high as 75%. Such a high efficiencywas attributed to the excellent matching of the host phonon energywith the energy gap between Er3:4I13/2and Ho3:5I7levels. In addition,the energy transfer microparameter (CDA) from Er3:4I13/2to Ho3:5I7level was estimated to (4.16 ± 0.03)× 10–40cm6·s–1via the host-assisted spectral overlap function, coinciding withthe CDA(2,88 ± 0.04) × 10–40cm6·s–1from decay analysis ofthe Er3:4I13/2level which alsoindicated hopping migration-assisted energy transfer. Furthermore,the concentration quenching of Ho3:5I7→ 5I8transition was the dipole–dipoleinteraction in the diffusion-limited regime, and the quenching concentrationof Ho3귦鲅 4.13 × 1020cm–3. [ABSTRACT FROM AUTHOR]

Here, we describe a novel "switch-on" biosensor based on quinonyl glycosides functionalized quantum dots (QDs) for the specific targeting and imaging of transmembrane glycoprotein receptors on the surface of cancer cells. The design of the quinonyl glycosides lies in that the quinone moiety serves as a quencher of QDs and the glycoside moiety as a biospecific ligand for targeting a receptor. We observed that the quenched photoluminescence of the quinone glycosides functionalized QDs could be significantly recovered by a specific lectin that selectively binds to the glycosides clustering the QDs but was not affected by a panel of nonspecific lectins. Moreover, we determined that quinonyl galactoside functionalized QDs could optically image the asialoglycoprotein receptors of a hepatoma cell line in a target-specific manner. This system might provide new insights into the fabrication of photoluminogenic biosensors for the analysis of the universal ligand-receptor recognitions in nature. [ABSTRACT FROM AUTHOR]

Transition metal-free cascade reactions of alkynols with imines have been achieved using potassium tert-butoxide as catalyst Switching the reaction solvent gives two kinds of products in good yield: isoquinolin-1(2H)-one derivatives and dihydroisobenzofuran derivatives. This approach was used to generate the natural product 8-oxypseudopalrnatine in a two-step procedure from commercially available starting materials. Additionally, multicomponent reactions of alkynols, aldehydes, and amines were also successfully achieved to afford isoquinolin-1(2H)-one derivatives. [ABSTRACT FROM AUTHOR]

An asymmetric synthesis of epoxyoxindoles from isatins has been developed by employing chiral sulfur ylides generated in situ from camphor-derived sulfonium salts. This reaction allows an efficient access to enantioenriched spiro-epoxyoxindoles under mild reaction conditions, featuring high yields and excellent enantio- and diastereoselectivities. [ABSTRACT FROM AUTHOR]

A new simple fiber-optic evanescent wave sensor was created to accurately monitor the growth and hydrogen production performance of biofilms. The proposed sensor consists of two probes (i.e., a sensor and reference probe), using the etched fibers with an appropriate surface roughness to improve its sensitivity. The sensor probe measures the biofilm growth and change of liquid-phase concentration inside the biofilm. The reference probe is coated with a hydrophilic polytetrafluoroethylene membrane to separate the liquids from photosynthetic bacteria Rhodopseudomonas palustris CQK 01 and to measure the liquid concentration. We also developed a model to demonstrate the accuracy of the measurement. The biofilm measurement was calibrated using an Olympus microscope. A linear relationship was obtained for the biofilm thickness range from 0 to 120 μm with a synthetic medium under continuous supply to the bioreactor. The highest level of hydrogen production rate occurred at a thickness of 115 μm. [ABSTRACT FROM AUTHOR]

A [3 + 2] cycloaddition/ring contraction sequence of ylideneoxindoles with in situ-generated 2,2,2-trifluorodiazoethane without the use of any transition-metal catalyst has been developed. The reaction provides efficient access to biologically important and synthetically useful CF3-containing 3,3'-cyclopropyl spirooxindoles in high yield (74-99%) with high diastereoselectivity (>95:5 d.r.). [ABSTRACT FROM AUTHOR]