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The optical absorption spectra of Si2-Si33 clusters were systematically studied by a time-dependent density functional theory approach. The calculations revealed that the absorption spectrum becomes significantly broad with increasing cluster size, stretching from ultraviolet to the infrared region. The absorption spectra are closely related to the structural motifs. With increasing cluster size, the absorption intensity of cage structures gradually increases, but the absorption curves of the prolate and the Y-shaped structures are very sensitive to cluster size. If the transition energy reaches -12 eV, it is noted that all the clusters have remarkable absorption in deep ultraviolet region of 100-200 nm, and the maximum absorption intensity is -100 times that in the visible region. Further, the optical responses to doping in the Si clusters were studied. [ABSTRACT FROM AUTHOR]

Colormanipulation of intense multiluminescence from CaZnOS:Mn2+has been realized by adjusting Mn2+concentration.Not only the photoluminescence (PL) of Mn2+emission from 4T1(4G) to 6A1(6S) shows a red shift from yellow to red with increasing Mn2+concentration, which is in contrast to the fixed PL emissionreported by Hintzen et al. (Chem. Mater., 2009), but also mechanoluminescence(ML) and cathodoluminescence (CL) have a similar variation. More attractively,the brightness of multiluminescence is surprisingly intense for allthe CaZnOS:Mn2+with a large-scale Mn2+doping(0.1–10 mol %). Based on the investigation of crystal field,various spectral results, and PL lifetimes, the red-shift mechanismof multiluminescence reported here has been proposed to arise fromthe exchange interaction effect of Mn2+pairs at higherconcentrations. In addition to correcting the previous misunderstandingon the emission of CaZnOS:Mn2+, these findings extend thetunable emission window, opening up new opportunities in multifunctionalapplications of PL, ML, and CL involving multicolor light sources,displays, and stress imaging, especially providing a novel resolutionto design ML colors. [ABSTRACT FROM AUTHOR]

In this article, we present the design and construction of a series of supramolecular poly(benzyl ether) metallodendrimers featuring a well-defined hexagonal metalla-cycle at their cores via coordination-driven self-assembly. It was found that the second generation metallodendrimer 3c was able to hierarchically self-assemble into the regular vesicle-like structures. These nanoscale vesicles were monodisperse in shape and relatively monodisperse in size as detected in SEM, TEM, APM, and DLS experiments. Notably, this kind of hierarchically formed vesicle-like nanostructure adopted a discrete metallacycle as the main skeleton, which is obviously different from many previous reports of nanoscale spherical architectures. Moreover, such supramolecular vesicle-like structures could encapsulate some fluorescent molecules, like BODIPY and SRB, etc. By taking advantage of the dynamic nature of metal-ligand bonds, the disassembly and reassembly of the hexagonal cavity core could be reversibly controlled by the addition and removal of bromide ions, resulting in the transition from the vesicles to micelles. Thus, the controlled release of fluorescence dye was successfully realized by the halide-induced vesicles-micelles transition. These findings not only enrich die library of supramolecular metallodenrimers but also provide a new avenue to the construction of novel "smart" nanomaterials, which have potential application in functional molecules delivery and release. [ABSTRACT FROM AUTHOR]

All-atommolecular dynamics simulations with explicit water solvent were usedto investigate the microstructure and conformational dynamics of celluloseIβ microfibrils as a function of microfibril length and cross-sectionalsize and shape. Cellulose microfibrils quickly develop a right-handedtwist, which then remains stable over the entire 10 ns simulationtime. The helical angle is independent of microfibril length and inverselyproportional to its cross-sectional area, in accord with the expectationsof continuum theory for an intrinsic chiral twist that is opposedby torsional shear. These calculations provideto our knowledgethefirst estimates of the shear modulus of a cellulose microfibril fromMD simulations. The internal strains caused by this helical twist,propagated indefinitely along the microfibril axis, could be relaxedby periodic regions of amorphous structure along the axis of the cellulosemicrofibrils. [ABSTRACT FROM AUTHOR]

Perfluoroalkyl compounds (PFCs) were determined in 22 surface water samples (39-76°N) and three sea ice core and snow samples (77-87°N) collected from North Pacific to the Arctic Ocean during the fourth Chinese Arctic Expedition in 2010. Geographically, the average concentration of ΣPFC in surface water samples were 560 ± 170 pg L-1 for the Northwest Pacific Ocean, 500 ± 170 pg L-1 for the Arctic Ocean, and 340 ± 130 pg L-1 for the Bering Sea, respectively. The perfluoroalkyl carboxylates (PFCAs) were the dominant PFC class in the water samples, however, the spatial pattern of PFCs varied. The C5, C7 and C8 PFCAs (i.e., perfluoropentanoate (PFPA), perfluoroheptanoate (PFHpA), and perfluorooctanoate (PFOA)) were the dominant PFCs in the Northwest Pacific Ocean while in the Bering Sea the PFPA dominated. The changing in the pattern and concentrations in Pacific Ocean indicate that the PFCs in surface water were influenced by sources from the East-Asian (such as Japan and China) and North American coast, and dilution effect during their transport to the Arctic. The presence of PFCs in the snow and ice core samples indicates an atmospheric deposition of PFCs in the Arctic. The elevated PFC concentration in the Arctic Ocean shows that the ice melting had an impact on the PFC levels and distribution. In addition, the C4 and C5 PFCAs (i.e., perfluorobutanoate (PFBA), PFPA) became the dominant PFCs in the Arctic Ocean indicating that PFBA is a marker for sea ice melting as the source of exposure. [ABSTRACT FROM AUTHOR]

By combining rigid 120° dicarboxylate donors substituted with [G-0]–[G-3] Fréchet-type dendrons and complementary 120° ferrocenyl di-Pt(II) acceptors, a new family of neutral dendritic multiferrocenyl hexagons have been successfully prepared under mild conditions in high yields. [ABSTRACT FROM AUTHOR]

We report a novel and straightforward fluorescence recovery assay which enables the detection of protein-DNA interactions and simultaneously determines relative binding affinities of sequence-specific DNA-binding proteins for a variety of DNA sequences in a multiplexed format. The detection of protein-DNA binding is accomplished by monitoring fluorescence recovery during exonuclease digestion of DNA sequences that are modified with fluorophore-quencher pairs. Retardation of fluorescence recovery occurs with binding of the protein to the putative DNA binding element, which arrests exonuclease digestion. The assay detects protein-DNA binding in a homogeneous solution simply, quickly, and reliably without using radioisotopes. Multiplexing is possible by labeling different DNA sequences with spectrally distinct dyes, allowing simultaneous analysis of experimental and control binding reactions in the same mixture. [ABSTRACT FROM AUTHOR]

We performed an unbiased search for low-energy structures of medium-sized neutral Si nand Ge nclusters ( n= 25−33) using a genetic algorithm (GA) coupled with tight-binding interatomic potentials. Structural candidates obtained from our GA search were further optimized by first-principles calculations using density functional theory (DFT). Our approach reproduces well the lowest-energy structures of Si nand Ge nclusters of n= 25−29 compared to previous studies, showing the accuracy and reliability of our approach. In the present study, we pay more attention to determine low-lying isomers of Si nand Ge n( n= 29−33) and study the growth patterns of these clusters. The B3LYP calculations suggest that the growth pattern of Si n( n= 25−33) clusters undergoes a transition from prolate to cage at n= 31, while this transition appears at n= 26 from the PBE-calculated results. In the size range of 25−33, the corresponding Ge nclusters hold the prolate growth pattern. The relative stabilities and different structural motifs of Si nand Ge n( n= 25−33) clusters were studied, and the changes of small cluster structures, when acting as building blocks of large clusters, were also discussed. [ABSTRACT FROM AUTHOR]

Series Al-SBA-16 supports with different crystal sizes were fabricated by adding different inorganic salts to the synthesis system and used as the catalyst support for dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) hydrodesulfurization (HDS). The supports and the corresponding catalysts were well analyzed in depth to investigate their structure-property relationship. NiMo/AS-Mn catalyst with the smallest crystal sizes, the largest BET surface areas, and the highest total acid and Brönsted acid content displayed the highest kHDS of 4,6-DMDBT and DBT. HYD was the preferential route for the DBT HDS over NiMo/AS-Mn, while ISO was the preferential pathway for 4,6-DMDBT HDS. Moreover, the DBT and 4,6-DMDBT HDS reaction networks over NiMo/AS-Mn were proposed. [ABSTRACT FROM AUTHOR]

Al2O3 materials with different crystal forms were synthesized via the hydrothermal synthesis method using the low-cost raw material, and then the corresponding NiMo/Al2O3 catalysts were prepared by using Al2O3 materials with different crystal forms as the supports. The restrictive diffusion effects on the hydrodesulfurization reaction of different reactants with different molecular sizes over the NiMo/Al2O3 catalysts with different crystal forms were investigated systematically for the first time. NiMo/δ-Al2O3 exhibited the highest values of the effective factor (η) and effective diffusion coefficient (De), which could be ascribed to its proper pore diameter and relatively concentrated pore diameter distribution. The hindered magnitudes of diffusion decrease in the order of NiMo/δ-30 (2.23) < NiMo/θ-30 (2.83) < NiMo/γ-30 (3.42), indicating that the restrictive diffusion effect of NiMo/δ-30 catalyst was weaker than those of the other two catalysts. [ABSTRACT FROM AUTHOR]

Fe/Beta@TiO2 core-shell catalysts with nanosize TiO2 thin film as the shell and small-grain Beta supporting Fe oxides as the core were controllably synthesized by a self-assembly method, and their catalytic performances were investigated for selective catalytic reduction of NO x with NH3 (NH3-SCR). It was found that TiO2 shells decrease the acid amount and weaken the acid strength of the catalyst, which could be beneficial to inhibiting the adsorption of acrolein species from covering active sites and then improving the ability of NO oxidation to NO2 during NH3-SCR. Moreover, TiO2 shells not only can prevent the deposition of coke and nitrate species from blocking the active iron sites, but also can serve as an effective barrier to suppress the active metal oxide nanoparticles from aggregating at high temperature. Therefore, Fe/Beta@TiO2 exhibits an improved thermal stability, higher propene, and H2O-tolerance. [ABSTRACT FROM AUTHOR]

The structures, binding energies, and electronic properties for Al7X, Al7X-, Al13X-, Al13X2-, and Al13X12-(X F, Cl, Br) were studied at the B3LYP/6-311G(2d,p) level. Among the systems studied, Al7and Al13clusters in Al7X and Al13X-reveal alkali-like and halogen-like superatom characters, respectively. Al7can bind with one halogen atom to form a salt-like compound as Al7−X-. Al13-can combine with one halogen atom to form a diatomic halogen anion Al13X-. However, when adding more halogens, the superatom structure would be destroyed, resulting in low-symmetry compounds with the center Al atom moving toward the cluster surface. The structures of Al13X1,2,12-(X F, Cl, Br) are similar to those of X I; however, their binding energies and electron structures are much different. In addition, the analyses of the calculated NBO charges show that Cl and Br have similar properties, but much different from F, when interacting with the Al clusters. The Al−Cl and Al−Br bonds have more covalent character in Al7X and Al13X2,12-, in contrast to the corresponding Al−F bond, which has prominent ionic character. [ABSTRACT FROM AUTHOR]

Iron titanate catalysts with variable Nb content was synthesized by the homogeneous precipitation method, and they were applied to the NH3-selective catalytic reduction (SCR). The widest performance temperature window is obtained on the 0.05Nb–0.95Fe–Ti–O catalyst between 200 and 400 °C with a NO conversion higher than 90% at a gas hourly space velocity (GHSV) of 50 000 h–1. The addition of Nb improves the acidity of Fe–Ti–O catalyst while decreasing its reducibility. The excellent performance of 0.05Nb–0.95Fe–Ti–O is attributed to its suitable acidity and reducibility. Both Brønsted and Lewis acid sites over 0.05Nb–0.95Fe–Ti–O catalyst are active in the reaction, and the formation of reactive monodentate nitrate species and cis-N2O22– also promote the performances. [ABSTRACT FROM AUTHOR]

A total of 23 per- and polyfluoroalkyl substances (PFASs) were investigated in the air, dry deposition, and plant leaves at two different landfills and one suburban reference site in Tianjin, China. The potential of landfills as sources of PFASs to the atmosphere and the phase distribution therein were evaluated. The maximum concentrations of ∑PFASs in the two landfills were up to 9.5 ng/m3 in the air, 4.1 μg/g in dry deposition, and 48 μg/g lipid in leaves with trifluoroacetic acid and perfluoropropionic acid being dominant (71%–94%). Spatially, the distribution trend of ionizable and neutral PFASs in all three kinds of media consistently showed the central landfill > the downwind > the upwind > the reference sites, indicating that landfills are important sources to PFASs in the environment. Plant leaves were found effective in uptake of a variety of airborne PFASs including polyfluoroalkyl phosphoric acid diesters, thus capable of acting as a passive air sampling approach for air monitoring. [ABSTRACT FROM AUTHOR]

The enantioselective cross-aldol reaction between o-hydroxyacetophenones and trifluoromethyl ketones catalyzed by chiral thiourea organocatalysts is reported. Gram-scale synthesis of the cross-aldol product was carried out, with no decrease in the yield and enantioselectivity. Furthermore, the cross-aldol products thus prepared were used in the preparation of medicinally interesting 3,5-diaryl-5-trifluoromethyl-2-isoxazoline and β-trifluoromethyl-β-tertiary hydroxy acid ester with high yield and enantiopurity. [ABSTRACT FROM AUTHOR]

The Pd-Ce-Zr solid solution catalysts were in situ synthesized by a sol-evaporation induced self-assembly (SEISA) method. The catalytic performances of the as prepared catalysts for CO oxidation and their physicochemical properties were investigated with various characterization techniques. The catalysts with low doping amount of Pd exhibited unique thermal stability and high activity toward CO oxidation. The CO oxidation activities of the catalysts showed a volcano type relationship with the content of Pd doping in Ce-Zr oxides. Pd-Ce0.8Zr0.2O2 with 1.0% Pd doping gave the highest catalytic activity. Its CO complete conversion temperature was 110 °C with a turnover frequency of 1.52 s-1. Density functional theory (DFT) calculations suggested strong effects of Pd doping on the crystal structure, charge distribution and formation of oxygen vacancy of the Ce-based catalysts. The calculations also suggested that CO oxidation on Pd doped Ce-based catalysts follows Eley- Rideal mechanism, and the direct reaction of CO with a surface oxygen atom appears to be the main pathway of the oxidation. [ABSTRACT FROM AUTHOR]

The use of snow and ice cores as recorders of environmental contamination is particularly relevant for per- and polyfluoroalky substances (PFASs) given their production history, differing source regions and varied mechanisms driving their global distribution. In a unique study perfluoroalkyl acids (PFAAs) were analyzed in dated snow-cores obtained from high mountain glaciers on the Tibetan Plateau (TP). One snow core was obtained from the Mt Muztagata glacier (accumulation period of 1980-1999), located in western Tibet and a second core from Mt. Zuoqiupo (accumulation period: 1996-2007) located in southeastern Tibet, with fresh surface snow collected near Lake Namco in 2010 (southern Tibet). The higher concentrations of ΣPFAAs were observed in the older Mt Muztagata core and dominated by perfluorooctanesulfonic acid (PFOS) (61.4-346 pg/L) and perfluorooctanoic acid (PFOA) (40.8-243 pg/L), whereas in the Mt Zuoqiupu core the concentrations were lower (e.g., PFOA: 37.8-183 pg/L) with PFOS below detection limits. These differences in PFAA concentrations and composition profile likely reflect the upwind sources affecting the respective sites (e.g., European/central Asian sources for Mt Muztagata and India sources for Mt Zuoqiupu). Perfluorobutanoic acid (PFBA) dominated the recent surface snowpack of Lake Namco which is mainly associated with India sources where the shorter chain volatile PFASs precursors predominate. The use of snow cores in different parts of Tibet provides useful recorders to examine the influence of different PFASs source regions and reflect changing PFAS production/use in the Northern Hemisphere. [ABSTRACT FROM AUTHOR]

A new family of 60° dendritic di-Pt(II) acceptor tectons have been successfully designed and synthesized, from which a series of novel "three-component" triangular metallodendrimers were prepared via [3 + 3] coordination-driven self-assembly. The structures of newly designed triangular metallodendrimers are characterized by multinuclear NMR (¹H and 31P), ¹H DOSY NMR, mass spectrometry (CSI-TOF-MS), and elemental analysis. The shape and size of all supramolecular dendritic triangles were investigated with PM6 semiempirical molecular orbital methods. [ABSTRACT FROM AUTHOR]

The structures and stabilities of (Al2O3)~ (n = 1-10 and 30) clusters were studied by means of first principles calculations. The calculated results reveal that the global minima of small (Al2O3)~ (n = 1-5) clusters are cage structures with high symmetries, in which Al and 0 atoms are three- and two-coordinated, respectively, and are linked to neighbors via single bonds. Beyond (A1203)5, we calculated both cage and cage-dimer structures for (Al2O3)~ (n = 6-10), and the results show that, at this size range, cage-dimer structures are more stable than cage structures. Furthermore, an onion-like motif for (A1203)10 was studied, and it is interesting to find that, at this size, the onion structure is more favorable than cage and cage-dimer structures. For large clusters, a shell structure of Al600~ is suggested. Electronic properties and calculations on hydrogen adsorption of these aluminum oxide structures are reported, and we discuss their possible use as hydrogen storage materials. [ABSTRACT FROM AUTHOR]

Two new complex polycyclic alkaloids, macropodumines D (1) and E (2), both possessing unprecedented skeletons, along with four known related alkaloids, were isolated from the leaves and barks of Daphniphyllum macropodumMiq. The structures including the relative stereochemistry of new compounds 1and 2were elucidated on the basis of detailed spectroscopic data analysis. [ABSTRACT FROM AUTHOR]