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A Huisgen 1,3-dipolar cycloaddition 'click chemistry' was employed to immobilize azido sugars (mannose, lactose, [alpha]-Gal) to fabricate carbohydrate self-assembled monolayers (SAMs) on gold. This fabrication was based on preformed SAM templates incorporated with alkyne terminal groups, which could further anchor the azido sugars to form well-packed, stable, and rigid sugar SAMs. The clicked mannose, lactose, and [alpha]-Gal trisaccharide SAMs were used in the analysis of specific carbohydrate-protein interactions (i.e., mannose--Con A; ECL--lactose, ([alpha]-Gal--anti-Gal). The apparent affinity constant of Con A binding to mannose was (8.7 [+ or -] 2.8) x [10.sup.5] and (3.9 [+ or -] 0.2) x [10.sup.6] [M.sup.-1] measured by QCM and SPR, respectively. The apparent affinity constants of lactose binding with ECL and (x-Gal binding with polyclonal anti-Gal antibody were determined to be (4.6 [+ or -] 2.4) x [10.sup.6] and (6.7 [+ or -] 3.3) x [10.sup.6] [M.sup.-1], respectively by QCM. SPR, QCM, AFM, and electrochemistry studies confirmed that the carbohydrate SAM sensors maintained the specificity to their corresponding lectins and nonspecific adsorption on the clicked carbohydrate surface was negligible. This study showed that the clicked carbohydrate SAMs in concert with nonlabel QCM or SPR offered a potent platform for high-throughput characterization of carbohydrate-protein interactions. Such a combination should complement other methods such as ITC and ELISA in a favorable manner and provide insightful knowledge for the corresponding complex glycobiological processes.

Electromagnetic components are important for ultraviolet (UV) applications. However, due to the limitation in the materials' intrinsic responses, there are fewer electromagnetic components in high-frequency regimes than in low-frequency ones. Conventional UV components manipulate the wavefront via geometric phase accumulation; thus, they are significantly bulky and inefficient. In this study, we demonstrate all-dielectric Huygens' metasurface (ADHMS) at a near-ultraviolet (NUV) regime. The NUV-ADHMS is comprised of resonant titanium dioxide (TiO2) nanodisks, with the ultrathin thickness of the fifth wavelength. In addition, by modulating the diameter of the resonant TiO2 nanodisks, we can simultaneously excite and control both electric and magnetic dipoles, achieving a powerful wavefront engineering of the near-unity transmittance and a full range of the 2π phase coverage. Finally, we employed the NUV-ADHMS to bend a normal incident beam, demonstrating a deflection angle of 11° at a wavelength of 405 nm. [ABSTRACT FROM AUTHOR]

A synthetic study demonstrates the utility of dibenzyltriazones (DBT) as a protecting group. The long series of reactions leading to the synthesis of hypusines and other polyamines show that DBT may be generated and cleaved under mild conditions in the presence of other functional groups yet survives redox and homologation reactions. DBT allows solvolytic and analytic operations even on polar intermediates and bestows stability on alpha-amino esters and amino aldehydes. It complements rather than hinder other amino protecting groups.

A simple method was used to prepare a 'switchable' electrode surface by using self-assembled monolayers of dodecanethiol on a gold electrode. The dodecane-modified electrode was electrochemically inactive until the monolayer was soaked in solution of 1,10 phenanthroline or 2,2'-bipyridine.

Electromagnetic metasurfaces with strong nonlinear responses and angular selectivity could offer many new avenues for designing ultrathin optics components. We investigated the optical second harmonic generation from plasmonic metasurfaces composed of aligned gold nanopillars with a pronounced out-of-plane tilt using a flexible nonlinear Fourier microscope. The experimental and computational results demonstrate that these samples function as wavevector-selective nonlinear metasurfaces, that is, the coherent second harmonic signal does not only depend on the polarization and wavelength of the excitation beam, but also of its direction of incidence, in spite of the subwavelength thickness of the active layer. Specifically, we observe that the nonlinear response can vary by almost two orders-of-magnitude when the incidence angle is changed from positive to negative values compared to the surface normal. Further, it is demonstrated that these metasurfaces act as a directional nonlinear mirrors, paving the way for new design of directional meta-mirrors in the nonlinear regime. [ABSTRACT FROM AUTHOR]

Cu2ZnSnS4 (CZTS) is an environmentally friendly photovoltaic material with promising applications in thin-film solar cells. Although CZTS's efficiency is currently too low, stoichiometry/defect engineering presents a strategy for further improvement. As-grown CZTS is typically disordered and therefore prone to form secondary phases, making the final product stoichiometry difficult to determine and even harder to control. We use first-principles quantum mechanics in combination with Monte Carlo simulations to determine CZTS stoichiometry under various experimental conditions. We develop an approach to predicting the optimal CZTS stoichiometry, explaining the physical origin of Zn-enrichment observed in experiments. We further propose practical ways to introduce more free carriers into CZTS in order to screen observed local potential fluctuations, increase conductivity, and ultimately improve the efficiency of CZTS. [ABSTRACT FROM AUTHOR]

Although a promising photovoltaic material that is inexpensive and easy to manufacture, Cu2ZnSnS4 (CZTS) suffers from a low open circuit voltage thought to be due to local potential fluctuations caused by a disordered Cu/Zn sublattice. The disordered character of CZTS is difficult to study experimentally and has been universally neglected in computational studies. Here, we develop a cluster expansion model that enables simulation of the order-disorder phase transition in CZTS for the first time. With a proper atomic structure of the disordered phase in hand, we investigate the temperature-dependent voltage loss in CZTS, illustrating intrinsic limitations of existing synthesis methods and suggesting an optimal annealing temperature. We offer one explanation why Cu-poor CZTS is optimally efficient, as Cu vacancies increase the band gap via interactions between free carriers and the disordered nature of as-grown CZTS. Accordingly, increasing carrier concentrations may be an effective strategy to flatten the fluctuating potentials. [ABSTRACT FROM AUTHOR]

Cu2ZnSnS4-xSex (CZTS) is an important semiconductor with significant potential for applications in the next generation of solar cells. CZTS has an optimal band gap (∼1.5 eV) and contains no expensive or toxic elements. However, CZTS-based solar cells suffer from low efficiency because of poor crystal quality, which is partly caused by secondary phase formation during synthesis. We use density functional theory+U calculations to systematically investigate the stabilities of three CZTS phases: kesterite, stannite, and wurtzite. In agreement with previous experiment and theory, we confirm that these three phases have very similar formation energies. This finding is consistent with the known difficulties in synthesizing pure kesterite CZTS, the phase that is desirable for photovoltaic applications. To overcome this problem, we characterize surfaces and interfaces of CZTS and are able to identify certain "beneficial surfaces" that could be exploited to potentially provide extra stability for the kesterite phase. We propose the zinc blende ZnS (001) surface as a substrate to induce formation of these beneficial surfaces and to stabilize the kesterite phase, thereby serving as an effective crystallization template for the fabrication of high-performance CZTS solar cells. [ABSTRACT FROM AUTHOR]

Holograms, the optical devices toreconstruct predesigned images,show many applications in our daily life. However, applications ofhologram are still limited by the constituent materials and thereforetheir working range is trapped at a particular electromagnetic region.In recent years, the metasurfaces, an array of subwavelength antennawith varying sizes, show the abilities to manipulate the phase ofincident electromagnetic wave from visible to microwave frequencies.Here, we present a reflective-type and high-efficiency meta-hologramfabricated by metasurface for visible wavelength. Using gold crossnanoantennas as building blocks to construct our meta-hologram deviceswith thickness ∼ λ/4, the reconstructed images of meta-hologramshow polarization-controlled dual images with high contrast, functioningfor both coherent and incoherent light sources within a broad spectralrange and under a wide range of incidence angles. The flexibilitydemonstrated here for our meta-hologram paves the road to a wide rangeof applications related to holographic images at arbitrary electromagneticwave region. [ABSTRACT FROM AUTHOR]

In this report, the effects of conductive polymer oxidation states and structures on the design and development of ionic liquid (IL)/conductive polymer (CP) composite films for gas sensing are systematically characterized. Four different polyvinyl ferrocene (PVF) films synthesized by varying the conditioning potential (0.7 vs 0.0 V) and the electrolyte are tested for their gas-sensing properties (e.g., sensitivity, selectivity, response time, linearity, and dynamic range against various gas analytes such as dichloromethane, ethanol, natural gas, methane, formaldehyde (37%), and benzene) utilizing the quartz crystal microbalance (QCM) and ATR-FT-IR. The best available film is further studied as a substrate for the immobilization of various ILs that enhanced both the sensitivity and selectivity. Finally, two arrays, each comprising four sensors with the following scheme are developed and characterized for their ability to classify the four target analytes by using linear discriminant analysis: (1) the highest sensitivity PVF film immobilized with four different ILs and (2) the highest sensitivity IL immobilized in four different PVF films. Array 2 is proven to be much better than array 1 in discriminating the analytes, which is very significant in establishing the fact that a diverse set of PVF redox states allow the rational development of a PVF/IL composite-based sensor array in order to analyze complex mixtures utilizing structural differences and the extent of intermolecular interactions. [ABSTRACT FROM AUTHOR]

A Huisgen 1,3-dipolar cycloaddition ‘click chemistry’ was employed to immobilize azido sugars (mannose, lactose, α-Gal) to fabricate carbohydrate self-assembled monolayers (SAMs) on gold. This fabrication was based on preformed SAM templates incorporated with alkyne terminal groups, which could further anchor the azido sugars to form well-packed, stable, and rigid sugar SAMs. The clicked mannose, lactose, and α-Gal trisaccharide SAMs were used in the analysis of specific carbohydrate-protein interactions (i.e., mannose-Con A; ECL-lactose, α-Gal-anti-Gal). The apparent affinity constant of Con A binding to mannose was (8.7 ± 2.8) ⊗ 105 and (3.9 ± 0.2) ⊗ 106 M-1 measured by QCM and SPR, respectively. The apparent affinity constants of lactose binding with ECL and α-Gal binding with polyclonal anti-Gal antibody were determined to be (4.6 ± 2.4) ⊗ 106 and (6.7 ± 3.3) ⊗ 106 M-1, respectively by QCM. SPR, QCM, AFM, and electrochemistry studies confirmed that the carbohydrate SAM sensors maintained the specificity to their corresponding lectins and nonspecific adsorption on the clicked carbohydrate surface was negligible. This study showed that the clicked carbohydrate SAMs in concert with nonlabel QCM or SPR offered a potent platform for high-throughput characterization of carbohydrate-protein interactions. Such a combination should complement other methods such as ITC and ELISA in a favorable manner and provide insightful knowledge for the corresponding complex glycobiological processes. [ABSTRACT FROM AUTHOR]

Soot particles, coming from the incomplete combustion of fossil or biomass fuels, feature a core-shell structure with inner elemental carbon (EC) and outer organic carbon (OC). Both EC and OC are known to be photoactive under solar radiation. However, research on their coupling effect during photochemical aging remains limited. This study examines how the optical properties and oxidative potential (OP) of wood, coal, and diesel soot particles with varying EC and OC levels are affected by exposure to visible light. Wood soot, which has the highest OC content, showed the most significant changes in both optical properties and OP, indicating its highest sensitivity to visible light aging. Molecular composition analysis revealed that the reduction of polycyclic aromatic hydrocarbons (PAHs) and methyl-PAHs primarily affects the optical properties, while oxygenated PAHs play a major role in OP. Combined with the results from reactive oxygen species detection, it is suggested that EC initiates photoreactions by generating superoxide anions, while OC undergoes compositional changes that result in subsequent atmospheric effects. These findings enhance our understanding of the photochemical aging process of soot particles and their implications for climate and health.

The knowledge of the chemical composition of brown carbon (BrC) is limited to the categories of components or parts of specific organic components. In this paper, the light-absorbing properties and molecular compositions of lipid-soluble organic components in fine particulate matter of Beijing from 2016 to 2018, characterized by an ultraviolet-visible spectrometer and gas chromatography coupled with time-of-flight mass spectrometry, respectively, were combined to untargetedly screen the key BrC molecules by a partial least squares regression model for the first time. A total of 421 molecules were obtained, where 61 molecules were identified qualitatively and 22 molecules quantitatively. To the best of our knowledge, 11 molecules were newly identified BrC species. These qualitative molecules included polycyclic aromatic hydrocarbons with higher ambient concentrations and mass absorbing efficiencies (MAEs), as well as oxygen- and nitrogen-containing aromatic components with relatively lower concentrations and MAEs. The absorption contribution at 365 nm of quantified BrC species to lipid-soluble BrC during heating seasons was 39.1 ± 17.0%, which was about 5 times as high as previous studies. These results help establish a complete BrC molecular database and provide data support for better evaluating the climate effect of atmospheric carbonaceous aerosols and formulating air pollution control strategies.

In life science, rapid mutation detection in oligonucleotides is in a great demand for genomic and medical screening. To satisfy this demand, surface-enhanced resonance Raman spectroscopy (SERRS) in the deep-UV (DUV) regime offers a promising solution due to its merits of label-free nature, strong electromagnetic confinement, and charge transfer effect. Here, we demonstrate an epitaxial aluminum (Al) DUV-SERRS substrate that resonates effectively with the incident Raman laser and the ss-DNA at 266 nm, yielding significant SERRS signals of the detected analytes. For the first time, to the best of our knowledge, we obtaine SERRS spectra for all bases of oligonucleotides, not only revealing maximum characteristic Raman peaks but also recording the highest enhancement factor of up to 10 6 for a 1 nm thick adenine monomer. Moreover, our epitaxial Al DUV-SERRS substrate is able to enhance the Raman signal of all four bases of 12-mer ss-DNA and to further linearly quantify the single-base mutation in the 12-mer ss-DNA.

It is well understood that tetrahydrofuran (THF) molecules are able to stabilize the large cages (5 12 6 4 ) of structure II to form the THF hydrate with empty small cages even at atmospheric pressure. This leaves the small cages to store gas molecules at relatively lower pressures and higher temperatures. The dissociation enthalpy and temperature strongly depend on the size of gas molecules enclathrated in the small cages of structure II THF hydrate. A high-pressure microdifferential scanning calorimeter was applied to measure the dissociation enthalpies and temperatures of THF hydrates pressurized by helium and methane under a constant pressure ranging from 0.10 to 35.00 MPa and a wide THF concentration ranging from 0.25 to 8.11 mol %. The dissociation temperature of binary He + THF and methane + THF hydrates increases along with an increase in the THF concentration in the liquid phase at a fixed pressure (e.g., 30 MPa), reaching a maximum value of 280.8 and 312.8 K, respectively, at stoichiometric concentration (5.56 mol % THF), and then remains nearly constant for even higher THF concentrations (>5.56 mol %). The effect of gas occupancy in the small cages on the dissociation enthalpy of He + THF and methane + THF mixed hydrates was further examined by using molecular dynamics (MD) simulations. The dissociation enthalpy of the He-THF mixed hydrates is independent of pressure with an average of 5.68 kJ/mol H 2 O over the pressure ranging from 0.10 to 30.0 MPa, consistent with the MD results of the He-THF mixed hydrates with low single occupancy (<23%) of helium molecules in the small cages. Consequently, the heat of adsorption of helium molecules in the small cages of the He-THF mixed hydrates is rather too weak to be identified. On the other hand, the dissociation enthalpy of the methane-THF hydrates increases from 9.11 to 10.01 kJ/mol H 2 O along with an increase in methane pressure over the pressure ranging from 5.0 to 30.0 MPa, consistent with the MD results of the methane-THF mixed hydrates with full occupancy of methane molecules in the small cages. These findings provide important information for the design of a potential medium of gas storage and transportation.

Graphene oxide (GO) is commonly used in photocatalytic reactions but mainly as a cocatalyst. Limited information is available on the intrinsic ability of GO to photocatalytically reduce CO 2 as a sole photocatalyst and the activation of light irradiation. In this study, simulated sunlight (SS) and UV-irradiated GO (GO SS and GO UV , respectively) showed enhanced efficiency of photocatalytic reduction of CO 2 compared to pristine GO, with a CO yield (4 h) ratio of GO SS /GO UV /GO of 2.7:2.1:1. Here, irradiation plays two important roles: (1) irradiating GO to eliminate CO released under photolysis from photocatalytic reactions and (2) activating GO to create defects and restore the large π-conjugated network, obtaining photolysis-saturated and photoactivated GO for photocatalytic reduction of CO 2 . The increasing defect density and π conjugation of irradiated GO, as supported by X-ray photoelectron and Raman spectroscopy, improve the yield of photoelectrons and prolong the lifetime of photogenerated charge carriers, as supported by electron spin resonance and transient absorption spectroscopy. This results in an enhanced photocatalytic efficiency of irradiated GO. The higher CO yield of GO SS compared to GO UV indicates that simulated sunlight irradiation is more favorable for GO activation. Our results show that activating GO under irradiation enhances the photocatalytic reduction of CO 2 .

Electromagnetic metasurfaces with strong nonlinear responses and angular selectivity could offer many new avenues for designing ultrathin optics components. We investigated the optical second harmonic generation from plasmonic metasurfaces composed of aligned gold nanopillars with a pronounced out-of-plane tilt using a flexible nonlinear Fourier microscope. The experimental and computational results demonstrate that these samples function as wavevector-selective nonlinear metasurfaces, that is, the coherent second harmonic signal does not only depend on the polarization and wavelength of the excitation beam, but also of its direction of incidence, in spite of the subwavelength thickness of the active layer. Specifically, we observe that the nonlinear response can vary by almost two orders-of-magnitude when the incidence angle is changed from positive to negative values compared to the surface normal. Further, it is demonstrated that these metasurfaces act as a directional nonlinear mirrors, paving the way for new design of directional meta-mirrors in the nonlinear regime.

Novel oxazaborolidines activated by the strong acid triflimide or AlBr 3 form cationic chiral catalysts. These are effective catalysts for highly regio- and enantioselective Diels-Alder reactions using substituted (E)-4-oxopent-2-enoates as dienophiles.

Asymmetric total synthesis of structurally intriguing and highly oxygenated lancifodilactone G acetate (7) has been achieved for the first time in 28 steps from a cheap commodity chemical, 2-(triisopropylsiloxy)-1,3-butadiene.

We combine theory and experiment to demonstrate that a carefully designed gradient meta-surface supports high-efficiency anomalous reflections for near-infrared light following the generalized Snell's law, and the reflected wave becomes a bounded surface wave as the incident angle exceeds a critical value. Compared to previously fabricated gradient meta-surfaces in infrared regime, our samples work in a shorter wavelength regime with a broad bandwidth (750-900 nm), exhibit a much higher conversion efficiency (∼80%) to the anomalous reflection mode at normal incidence, and keep light polarization unchanged after the anomalous reflection. Finite-difference-time-domain (FDTD) simulations are in excellent agreement with experiments. Our findings may lead to many interesting applications, such as antireflection coating, polarization and spectral beam splitters, high-efficiency light absorbers, and surface plasmon couplers.

Growth inhibition and apoptotic/necrotic phenotype was observed in nanogold particle (AuNP)-treated human chronic myelogenous leukemia cells. To elucidate the underlying cellular mechanisms, proteomic techniques including two-dimensional electrophoresis/mass spectrometry and protein microarrays were utilized to study the differentially expressed proteome and phosphoproteome, respectively. Systems biology analysis of the proteomic data revealed that unfolded protein-associated endoplasmic reticulum (ER) stress response was the predominant event. Concomitant with transcriptomic analysis using mRNA expression, microarrays show ER stress response in the AuNP-treated cells. The ER stress protein markers' expression assay unveiled AuNPs as an efficient cellular ER stress elicitor. Upon ER stress, cellular responses, including reactive oxygen species increase, mitochondrial cytochrome c release, and mitochondria damage, chronologically occurred in the AuNP-treated cells. Conclusively, this study demonstrates that AuNPs cause cell death through induction of unmanageable ER stress.

In this report, the effects of conductive polymer oxidation states and structures on the design and development of ionic liquid (IL)/conductive polymer (CP) composite films for gas sensing are systematically characterized. Four different polyvinyl ferrocene (PVF) films synthesized by varying the conditioning potential (0.7 vs 0.0 V) and the electrolyte are tested for their gas-sensing properties (e.g., sensitivity, selectivity, response time, linearity, and dynamic range against various gas analytes such as dichloromethane, ethanol, natural gas, methane, formaldehyde (37%), and benzene) utilizing the quartz crystal microbalance (QCM) and ATR-FT-IR. The best available film is further studied as a substrate for the immobilization of various ILs that enhanced both the sensitivity and selectivity. Finally, two arrays, each comprising four sensors with the following scheme are developed and characterized for their ability to classify the four target analytes by using linear discriminant analysis: (1) the highest sensitivity PVF film immobilized with four different ILs and (2) the highest sensitivity IL immobilized in four different PVF films. Array 2 is proven to be much better than array 1 in discriminating the analytes, which is very significant in establishing the fact that a diverse set of PVF redox states allow the rational development of a PVF/IL composite-based sensor array in order to analyze complex mixtures utilizing structural differences and the extent of intermolecular interactions., (© 2011 American Chemical Society)

Altered choline (Cho) metabolism in cancerous cells can be used as a basis for molecular imaging with PET using radiolabeled Cho. In this study, the metabolism of tracer Cho was investigated in a woodchuck hepatocellular carcinoma (HCC) cell line (WCH17) and in freshly derived rat hepatocytes. The transporter responsible for [(11)C]-Cho uptake in HCC was also characterized in WCH17 cells. The study helped to define the specific mechanisms responsible for radio-Cho uptake seen on the PET images of primary liver cancer such as HCC. Cells were pulsed with [(14)C]-Cho for 5 min and chased for varying durations in cold media to simulate the rapid circulation and clearance of [(11)C]-Cho. Radioactive metabolites were extracted and analyzed by radio-HPLC and radio-TLC. The Cho transporter (ChoT) was characterized in WCH17 cells. WCH17 cells showed higher (14)C uptake than rat primary hepatocytes. [(14)C]-Phosphocholine (PC) was the major metabolite in WCH17. In contrast, the intracellular Cho in primary hepatocytes was found to be oxidized to betaine (partially released into media) and, to a lesser degree, phosphorylated to PC. [(14)C]-Cho uptake by WCH17 cells was found to have both facilitative transport and nonfacilitative diffusion components. The facilitative transport was characterized by Na(+) dependence and low affinity (K(m) = 28.59 ± 6.75 μM) with partial energy dependence. In contrast, ChoT in primary hepatocytes is Na(+) independent and low affinity. Our data suggest that transport and phosphorylation of Cho are responsible for the tracer accumulation during [(11)C]-Cho PET imaging of HCC. WCH17 cells incorporate [(14)C]-Cho preferentially into PC. Conversion of [(14)C]-PC into phosphatidylcholine occurred slowly in vitro. Basal oxidation and phosphorylation activities in surrounding hepatic tissue contribute to the background seen in [(11)C]-Cho PET images.

The inhibition of dihydrofolate reductase (DHFR) by antifolates is a common practice both in cell culture and in chemotherapy. Surprisingly, antifolate resistance was also observed in cultured murine myeloma cells (SP2/0) in the presence of human plasma (HP); thus, we used a proteomic approach to identify novel plasma biomarker(s) for this condition. In contrast to the in vitro antifolate response, metabolic enzymes and translation machinery proteins were found to be up-regulated in the presence of HP. The antifolate resistance inherent in HP may be explained by a simultaneous promotion of cell proliferation and the maintenance of DNA integrity. Furthermore, the factor(s) was found to be extrinsic, heat stable and very small in size. Adenine, a supplemented additive in erythrocyte preservation, was subsequently identified as the contributing factor and exogenous addition in cultures reversed the cytotoxicity induced by antifolates. Importantly, adenine-containing blood components, which may provide enhanced survival to otherwise sensitive antifolate-targeted cells, showed a dose-dependent adverse effect in transfusion recipients receiving antifolate (methotrexate) medications. These findings not only highlight a previously unnoticed role of adenine, but also emphasize a novel mechanistic link between transfusion and subsequently reduced survival in patients taking methotrexate.

A simple method was used to prepare a "switchable" electrode surface by using self-assembled monolayers of dodecanethiol on a gold electrode. The dodecane-modified electrode was electrochemically inactive until the monolayer was soaked in solutions of 1,10-phenanthroline or 2,2'-bipyridine. The electroactive form of the electrode could be reverted back to the nonelectroactive form by rinsing the electrode. Surface IR results showed that both dodecanethiol and 1,10-phenanthroline exist in the mixed monolayer.