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Polychlorinated biphenyls (PCBs) have been found to be persistent in the environment and possibly harmful. Many buildings are characterized with high PCB concentrations. Knowledge about partitioning between primary sources and building materials is critical for exposure assessment and practical remediation of PCB contamination. This study develops a C-depth method to determine diffusion coefficient (D) and partition coefficient (K), two key parameters governing the partitioning process. For concrete, a primary material studied here, relative standard deviations of results among five data sets are 5%-22% for K and 42-66% for D. Compared with existing methods, C-depth method overcomes the inability to obtain unique estimation for nonlinear regression and does not require assumed correlations for D and K among congeners. Comparison with a more sophisticated two-term approach implies significant uncertainty for D, and smaller uncertainty for K. However, considering uncertainties associated with sampling and chemical analysis, and impact of environmental factors, the results are acceptable for engineering applications. This was supported by good agreement between model prediction and measurement. Sensitivity analysis indicated that effective diffusion distance, contacting time of materials with primary sources, and depth of measured concentrations are critical for determining D, and PCB concentration in primary sources is critical for K. [ABSTRACT FROM AUTHOR]

The activation of C02 and its hydrogenation to methanol are of much interest as a way to utilize captured C02. Here, we investigate the use of sizeselected Cu4 clusters supported on Al203 thin films for C02 reduction in the presence of hydrogen. The catalytic activity was measured under near-atmospheric reaction conditions with a low C02 partial pressure, and the oxidation state of the clusters was investigated by in situ grazing incidence X-ray absorption spectroscopy. The results indicate that size-selected Cu4 clusters are the most active low-pressure catalyst for catalytic C02 conversion to CH3OH. Density functional theory calculations reveal that Cu4 clusters have a low activation barrier for conversion of C02 to CHjOH. This study suggests that small Cu clusters may be excellent and efficient catalysts for the recycling of released C02. [ABSTRACT FROM AUTHOR]

Upgrading furan and small oxygenatesobtained from the decompositionof cellulosic materials via formation of carbon–carbon bondsis critical to effective conversion of biomass to liquid transportationfuels. Simulation-driven molecular level understanding of carbon–carbonbond formation is required to design efficient catalysts and processes.Accurate quantum chemical methods are utilized here to predict thereaction energetics for conversion of furan (C4H4O) to C5–C8ethers and the transformationof furfural (C5H6O2) to C13–C26alkanes. Furan can be coupled with variousC1to C4low molecular weight carbohydratesobtained from the pyrolysis via Diels–Alder type reactionsin the gas phase to produce C5–C8cyclicethers. The computed reaction barriers for these reactions (∼25kcal/mol) are lower than the cellulose activation or decompositionreactions (∼50 kcal/mol). Cycloaddition of C5–C8cyclo ethers with furans can also occur in the gas phase,and the computed activation energy is similar to that of the firstDiels–Alder reaction. Furfural, obtained from biomass, canbe coupled with aldehydes or ketones with α-hydrogen atoms toform longer chain aldol products, and these aldol products can undergovapor phase hydrocycloaddition (activation barrier of ∼20 kcal/mol)to form the precursors of C26cyclic hydrocarbons. Thesethermochemical studies provide the basis for further vapor phase catalyticstudies required for upgrading of furans/furfurals to longer chainhydrocarbons. [ABSTRACT FROM AUTHOR]

The mechanism of the reverse water-gas shift reaction (CO2 + H2 → CO + H2O) was investigated using the 3d transition metal complexes L′M (M = Fe, Mn, and Co, L′ = parent β-diketiminate). The thermodynamics and reaction barriers of the elementary reaction pathways were studied with the B3LYP density functional and two different basis sets: 6-311+G(d) and aug-cc-pVTZ. Plausible reactants, intermediates, transition states, and products were modeled, with different conformers and multiplicities for each identified. Different reaction pathways and side reactions were also considered. Reaction Gibbs free energies and activation energies for all steps were determined for each transition metal. Calculations indicate that the most desirable mechanism involves mostly monometallic complexes. Among the three catalysts modeled, the Mn complex shows the most favorable catalytic properties. Considering the individual reaction barriers, the Fe complex shows the lowest barrier for activation of CO2. [ABSTRACT FROM AUTHOR]

A highly diastereo- and enantioselective asymmetric allylic alkylation reaction with respect to prochiral 3-substituted benzofuran-2(3H)-ones and MBH carbonate by a chiral biscinchona alkaloid catalyst was investigated. The corresponding adducts, containing a quaternary center at the C3-position of the benzofuran-2(3H)-one as well as a vicinal tertiary center, were generally obtained in high yields (up to 97%) with very good diastereo- (up to 98:2 dr) and enantioselectivities (up to 95% ee). [ABSTRACT FROM AUTHOR]

Protein amyloid oligomers have been strongly linked to amyloid diseases and can be intermediates to amyloid fibers. β-Sheets have been identified in amyloid oligomers. However, because of their transient and highly polymorphic properties, the details of their self-association remain elusive. Here we explore oligomer structure using a model system: macrocyclic peptides. Key amyloidogenic sequences from Aβ and tau were incorporated into macrocycles, thereby restraining them to β-strands, but limiting the growth of the oligomers so they may crystallize and cannot fibrillate. We determined the atomic structures for four such oligomers, and all four reveal tetrameric interfaces in which β-sheet dimers pair together by highly complementary, dry interfaces, analogous to steric zippers found in fibers, suggesting a common structure for amyloid oligomers and fibers. In amyloid fibers, the axes of the paired sheets are either parallel or antiparallel, whereas the oligomeric interfaces display a variety of sheet-to-sheet pairing angles, offering a structural explanation for the heterogeneity of amyloid oligomers. [ABSTRACT FROM AUTHOR]

This paper describes studies of a series of macrocyclic β-sheet peptides 1 that inhibit the aggregation of a tau-protein-derived peptide. The macrocyclic β-sheet peptides comprise a pentapeptide "upper" strand, two δ-linked ornithine turn units, and a "lower" strand comprising two additional residues and the β-sheet peptidomimetic template "Hao". The tau-derived peptide Ac-VQIVYK-NH2 (AcPHF6) aggregates in solution through β-sheet interactions to form straight and twisted filaments similar to those formed by tau protein in Alzheimer's neurofibrillary tangles. Macrocycles 1 containing the pentapeptide VQIVY in the "upper" strand delay and suppress the onset of aggregation of the AcPHF6 peptide. Inhibition is particularly pronounced in macrocycles 1a, 1d, and 1f, in which the two residues in the "lower" strand provide a pattern of hydrophobicity and hydrophilicity that matches that of the pentapeptide "upper" strand. Inhibition varies strongly with the concentration of these macrocycles, suggesting that it is cooperative. Macrocycle 1b containing the pentapeptide QIVYK shows little inhibition, suggesting the possibility of a preferred direction of growth of AcPHF6 β-sheets. On the basis of these studies, a model is proposed in which the AcPHF6 amyloid grows as a layered pair of β-sheets and in which growth is blocked by a pair of macrocycles that cap the growing paired hydrogen-bonding edges. This model provides a provocative and appealing target for future inhibitor design. [ABSTRACT FROM AUTHOR]

The reverse water−gas shift reaction CO2+ H2→ H2O + CO has been investigated using a set of homogeneous catalyst models L′MI(L′ = β-diketiminate, C3N2H5−; M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn). The thermodynamics of prototypical reaction pathways were simulated at two levels of theory: B3LYP/6-311+G(d) and B3LYP/aug-cc-pVTZ. The modeled catalytic reaction has been considered in the following steps: coordination of CO2by the catalyst to generate a carbon dioxide complex, L′M(CO2); scission of L′M(CO2) to yield L′M(CO) and L′M(O); L′M(O) hydrogenation to form L′M(H2O). The final products, H2O and CO, were obtained from the dissociation of L′M(H2O) and L′M(CO). All of the reactants, intermediates, and products were modeled, where different possible conformers and multiplicities were identified and considered as potential minima. The reaction enthalpy ΔH, of all steps for each catalyst as a function of transition metal have been determined. The Mn and Fe catalysts show more thermodynamically accessible pathways than the other catalyst models studied. The overall reaction enthalpy has been determined not only by B3LYP/6-311+G(d) and B3LYP/aug-cc-pVTZ but also via a more rigorous ab initio electron-correlation-based approach, the correlation consistent Composite Approach (ccCA). [ABSTRACT FROM AUTHOR]

Treatment of 2-allenyl indole 4with a catalytic 1:2 mixture of (S)-2Au2Cl2(S)-2 (S)-3,5-tBu-4-MeO-MeOBIPHEP and AgBF4in toluene at −10 °C for 17 h led to isolation of tetrahydrocarbazole 5 in 88% yield with 92% ee. The protocol was effective for the cyclization of terminally disubstituted allenes and for the formation of seven-membered rings. [ABSTRACT FROM AUTHOR]

Reaction of benzyl (2,2-diphenyl-4,5-hexadienyl)carbamate (4) with a catalytic 1:1 mixture of Au[P(t-Bu)2(o-biphenyl)]CI (2) and AgOTf (5 mol %) in dioxane at 25 °C for 45 min led to isolation of benzyl 4,4-diphenyl-2-vinylpyrrolidine-l-carboxylate (5) in 95% yield. The Au(I)-catalyzed intramolecular hydroamination of N-allenyl carbamates tolerated substitution at the alkyl and allenyl carbon atoms and was effective for the formation of piperidine derivatives. γ-Hydroxy and δ-hydroxy allenes also underwent Au-catalyzed intramolecular hydroalkoxylation within minutes at room temperature to form the corresponding oxygen heterocycles in good yield with high exo-selectivity. 2-Allenyl indoles underwent Au-catalyzed intramolecular hydroarylation within minutes at room temperature to form 4-vinyl tetrahydrocarbazoles in good yield. Aucatalyzed cyclization of Noallenyl carbamates, allenyl alcohols, and 2-allenyl indoles that possessed an axially chiral allenyl moiety occurred with transfer of chirality from the allenyl moiety to the newly formed stereogenic tetrahedral carbon atom. [ABSTRACT FROM AUTHOR]

The transition metal-catalyzed addition of a carbonyl group to an olefin is a transformation of considerable importance that has been applied to the synthesis of both complex organic molecules and commodity chemicals. Industrial processes, most notably, olefin hydroformylation, typically involve the addition of a hydrogen atom and a carbonyl group across the C = C bond of the olefin. Here this article reports the palladium-catalyzed cyclization/carboalkoxylation of alkenyl indoles, which represents the first effective protocol for the catalytic addition of a carbon nucleophile and a carbonyl group across the C C bond of an olefin.

Fused polycyclic indoles including the carbazoles, carbolines, and their partially saturated counterparts represent a prominent class of heterocyclic compounds with varied and often potent biological activity. As a result, considerable effort has been directed in this article to the development of new and efficient methods for the synthesis of polycyclic indoles. The article finally, develops a mild and effective platinum-catalyzed procedure for the intramolecular alkylation of indoles with unactivated olefins and establishes a mechanism for indole alkylation involving nucleophilic attack on a platinum-complexed olefin.

The chemical and electronic interactions of organometallic species with metal oxide support materials are of fundamental importance for the development of new classes of catalytic materials. Chemisorption of Cp*(PMe3)IrMe2 on sulfated alumina (SA) and sulfated zirconia (SZ) led to an unexpected redox mechanism for deuteration of the ancillary Cp* ligand. Evidence for this oxidative mechanism was provided by studying the analogous homogeneous reactivity of the organo-metallic precursors toward trityl cation ([Ph3C]+), a Lewis acid known to effect formal hydride abstraction by one-electron oxidation followed by hydrogen abstraction. Organometallic deuterium incorporation was found to be correlated with surface sulfate concentration as well as the extent of dehydration under thermal activation conditions of SA and SZ supports. Surface sulfate concentration dependence, in conjunction with a computational study of surface electron affinity, indicates an electron-deficient pyrosulfate species as the redox-active moiety. These results provide further evidence for the ability of sulfated metal oxides to participate in redox chemistry not only toward organometallic complexes but also in the larger context of their application as catalysts for the transformation of light alkanes. [ABSTRACT FROM AUTHOR]

SHP2, a cytoplasmic protein-tyrosine phosphatase encoded by the PTPN11 gene, is involved in multiple cell signaling processes including Ras/MAPK and Hippo/YAP pathways. SHP2 has been shown to contribute to the progression of a number of cancer types including leukemia, gastric, and breast cancers. It also regulates T-cell activation by interacting with inhibitory immune checkpoint receptors such as the programmed cell death 1 (PD-1) and B- and T-lymphocyte attenuator (BTLA). Thus, SHP2 inhibitors have drawn great attention by both inhibiting tumor cell proliferation and activating T cell immune responses toward cancer cells. In this study, we report the identification of an allosteric SHP2 inhibitor 1-(4-(6-bromonaphthalen-2-yl)thiazol-2-yl)-4-methylpiperidin-4-amine (23) that locks SHP2 in a closed conformation by binding to the interface of the N-terminal SH2, C-terminal SH2, and phosphatase domains. Compound 23 suppresses MAPK signaling pathway and YAP transcriptional activity and shows antitumor activity in vivo. The results indicate that allosteric inhibition of SHP2 could be a feasible approach for cancer therapy. [ABSTRACT FROM AUTHOR]

Ozone production efficiency (OPE), a measure of the number of ozone (O3) molecules produced per emitted NOX (NO + NO2) molecule, helps establish the relationship between NOX emissions and O3 formation. We estimate long-term OPE variability across the eastern United States using two novel approaches: an observation-based empirical method and a chemical transport model (CTM) method. The CTM approach explicitly controls for differing O3 and NOX reaction product (NOZ) deposition rates and separately estimates OPEs from on-road mobile and electricity generating unit sources across a broad spatial scale. We find lower OPEs in urban areas and that average July OPE increased over the eastern United States domain between 2001 and 2011 from 11 to 14. CTM and empirical approaches agree at low NOZ concentrations, but CTM OPEs are greater than empirical OPEs at high NOZ. Our results support that NOX emissions reductions become more effective at reducing O3 at lower NOZ concentrations. Electricity generating unit OPEs are higher than mobile OPEs except near emissions locations, meaning further utility NOX emissions reductions will have greater per unit impacts on O3 regionally. [ABSTRACT FROM AUTHOR]

Atomically ordered intermetallic nanoparticles (iNPs) have sparked considerable interest in fuel cell applications by virtue of their exceptional electronic and structural properties. However, the synthesis of small iNPs in a controllable manner remains a formidable challenge because of the high temperature generally required in the formation of intermetallic phases. Here we report a general method for the synthesis of PtZn iNPs (3.2 ± 0.4 nm) on multiwalled carbon nanotubes (MWNT) via a facile and capping agent free strategy using a sacrificial mesoporous silica (mSiO2) shell. The as-prepared PtZn iNPs exhibited ca. 10 times higher mass activity in both acidic and basic solution toward the methanol oxidation reaction (MOR) compared to larger PtZn iNPs synthesized on MWNT without the mSiO2 shell. Density functional theory (DFT) calculations predict that PtZn systems go through a “non-CO” pathway for MOR because of the stabilization of the OH* intermediate by Zn atoms, while a pure Pt system forms highly stable COH* and CO* intermediates, leading to catalyst deactivation. Experimental studies on the origin of the backward oxidation peak of MOR coincide well with DFT predictions. Moreover, the calculations demonstrate that MOR on smaller PtZn iNPs is energetically more favorable than larger iNPs, due to their high density of corner sites and lower-lying energetic pathway. Therefore, smaller PtZn iNPs not only increase the number but also enhance the activity of the active sites in MOR compared with larger ones. This work opens a new avenue for the synthesis of small iNPs with more undercoordinated and enhanced active sites for fuel cell applications. [ABSTRACT FROM AUTHOR]

An iridium-catalyzed asymmetric hydrogenation/oxidative fragmentation of 6-substituted 5H-benzo[d] benzofuro[3,2-b]azepines has been developed, providing an efficient access to optically active 4-substituted 4,5-dihydro-1H-benzo[d]azepin-1-ones with up to 91% ee. A possible reaction pathway includes the asymmetric hydrogenation to furnish chiral cyclic amines and oxidative fragmentation under an air atmosphere. [ABSTRACT FROM AUTHOR]

Graphene quantum dots (GQDs) have been widely used as fluorescence probes to detect metal ions with satisfactory selectivity. However, the diverse chemical structures of GQDs lead to selectivity for multiple metal ions, and this can lead to trouble in die interpretation of selectivity due to the lack of an in depth and systematic analysis. Herein, bare GQDs were synthesized by oxidizing carbon black with nitric acid and used as fluorescent probes to detect metal ions. We found that the specific ability of GQDs to recognize ferric ions relates to the acidity of the medium Specifically, we demonstrated that the coordination between GQDs and Fe3+ is regulated by the pH of the aqueous GQDs solution. Dissociative Fe3+ can coordinate with the hydroxyl groups on die surface of the GQDs to form aggregates (such as iron hydroxide), which induces fluorescence quenching. A satisfactory selectivity for Fe3+ ions was achieved under relatively acidic conditions; this is because of the extremely small of Ksp ferric hydroxide compared to those of other common metal hydroxides. To direcdy survey the key parameter for Fe3+ ion specificity, we performed the detection experiment in an environment free of interference from the buffer solution, noninherent groups, and other complex factors. Thus study will help researchers understand the selectivity mechanisms of GQDs as fluorescence probes for metal ions, which could guide the design of other GQD-based sensor platforms. [ABSTRACT FROM AUTHOR]

A novel fibrous sorbent, amidoxime-grafted activated carbon fibers (ACFs-AO), was prepared using a chemical grafting method and tested for the efficient removal of uranium from aqueous solution. The sorbent was characterized using X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, elemental analysis, thermogravimetric analysis, and Brunauer-Emmett-Teller. The effects of pH, contact time, initial concentration, and temperature on the sorption of U(VI) were investigated. The sorption of U(VI) on ACFs-AO obeyed the pseudo-second-order model and Langmuir isotherm. The sorption capacity of ACFs-AO for U(VI) (about 191.6 mg/g) was much higher than that of activated carbon fibers (ACFs) (about 70.52 mg/g), which was mainly attributed to surface complexation between U(VI) and the amidoxime group on ACFs-AO. Additionally, the thermodynamic parameter results showed that the sorption process of U(VI) was spontaneous, feasible, and endothermic. Moreover, ACFs-AO adsorbed U(VI) selectively in an aqueous solution containing competitive ions, and was regenerated and reused efficiently. The findings of this work indicate that ACFs-AO could be a promising sorbent for the effective removal of U(VI) from aqueous solution. [ABSTRACT FROM AUTHOR]

For the promotion of lithium-oxygen batteries available for practical applications, the development of advanced cathode catalysts with low-cost, high activity, and stable structural properties is demanded. Such development is rooted on certain intelligent catalyst-electrode design that fundamentally facilitates electronic and ionic transport and improves oxygen diffusivity in a porous environment. Here we design a biphasic nitrogen-doped cobalt@graphene multiple-capsule heterostructure, combined with a flexible, stable porous electrode architecture, and apply it as promising cathodes for lithium-oxygen cells. The biphasic nitrogen-doping feature improves the electric conductivity and catalytic activity; the multiple-nanocapsule configuration makes high/uniform electroactive zones possible; furthermore, the colander-like porous electrode facilitates the oxygen diffusion, catalytic reaction, and stable deposition of discharge products. As a result, the electrode exhibits much improved electrocatalytic properties associated with unique morphologies of electrochemically grown lithium peroxides. [ABSTRACT FROM AUTHOR]

Protein microtubule is a significant self-assembled architecture found in nature with crucial biological functions. However, mimicking protein microtubules with precise structure and controllable self-assembly behavior remains highly challenging. In this work, we demonstrate that by using dual supramolecular interactions from a series of well-designed ligands, i.e., protein-sugar interaction and p-p stacking, highly homogeneous protein microtubes were achieved from tetrameric soybean agglutinin without any chemical or biological modification. Using combined cryo-EM single-particle reconstruction and computational modeling, the accurate structure of protein microtube was determined. The helical protein microtube is consisted of three protofilaments, each of which features an array of soybean agglutinin tetramer linked by the designed ligands. Notably, the microtubes resemble the natural microtubules in their structural and dynamic features such as the shape and diameter and the controllable and reversible assembly behavior, among others. Furthermore, the protein microtubes showed an ability to enhance immune response, demonstrating its great potential for biological applications. [ABSTRACT FROM AUTHOR]

While N6-methyladenine (m6A) is a common modification in prokaryotic and lower eukaryotic genomes and has many biological functions, there is no simple and cost-effective way to identify a single N6-methyladenine in a nucleic acid target. Here we introduce a robust, simple, enzyme-free and hybridization-based method using a new silver cluster probe, termed methyladenine-specific NanoCluster Beacon (maNCB), which can detect single m6A in DNA targets based on the fluorescence emission spectra of silver clusters. Not only can maNCB identify m6A at the single-base level but it also can quantify the extent of adenine methylation in heterogeneous samples. Our method is superior to high-resolution melting analysis as we can pinpoint the location of m6A in the target. [ABSTRACT FROM AUTHOR]

Amyloid fibers, once exclusively associated with disease, are acquiring utility as a class of biological nanomaterials. Here we introduce a method that utilizes the atomic structures of amyloid peptides, to design materials with versatile applications. As a model application, we designed amyloid fibers capable of capturing carbon dioxide from flue gas, to address the global problem of excess anthropogenic carbon dioxide. By measuring dynamic separation of carbon dioxide from nitrogen, we show that fibers with designed amino acid sequences double the carbon dioxide binding capacity of the previously reported fiber formed by VQIVYK from Tau protein. In a second application, we designed fibers that facilitate retroviral gene transfer. By measuring lentiviral transduction, we show that designed fibers exceed the efficiency of polybrene, a commonly used enhancer of transduction. The same procedures can be adapted to the design of countless other amyloid materials with a variety of properties and uses. [ABSTRACT FROM AUTHOR]