Search

Noble-metal nanocrystals with well-controlled shapes or morphologies are of great interest for a variety of applications. To utilize these nanomaterials in consumer products, one has to produce the colloidal nanocrystals in large quantities while maintaining good control over their physical parameters and properties. Droplet reactors have shown great potential for the continuous and scalable production of colloidal nanocrystals with controlled shapes. However, the efficiencies of most previously reported systems are still limited because of the complex post-treatment procedures. For example, the mixture of silicone oil and an aqueous suspension of solid products has to be separated by leveraging their miscibility and difference in density, while the solid products often need to be purified and concentrated by centrifugation. Herein, we report the design and construction of a droplet-reactor system that include new features such as a homemade unit for the automatic separation of silicone oil from the aqueous phase as well as a cross-flow filtration unit for the effective purification and concentration of the nanocrystals. Using various types of Pd nanocrystals as examples, we have demonstrated the feasibility of using this system to automatically produce and collect samples with uniform sizes and well-controlled shapes. [ABSTRACT FROM AUTHOR]

Modern society needs various chemical products for its survival. The chemical products are classified in terms of single species products, multiple species products, and devices. Multiple species products such as mixtures and blends are one of the most widely used chemical products. However, the common design methods for this kind of product are still mostly by trial and error or by rule-based approaches. A computer-aided methodology integrated with experimental verification is presented in this article. In the first step of this methodology, model-based computer-aided techniques are employed to the design of mixtures and blends. In the second step, the properties of the most promising product candidates are verified through experiments and/or rigorous models. The starting point is to analyze the product needs and translate them into target property constraints. A list of molecules that serve as ingredient-chemicals for addition to the blended product together with their pure compound properties are generated using a well-known computer-aided design molecular design technique. A mixed integer nonlinear programming (MINLP) model is established for the selection of the ingredient-chemicals and their compositions in the blended product. The solution methods for the MINLP model are presented. For the first time, phase equilibrium based properties (such as liquid solution activity coefficients) are modeled and solved simultaneously in the MINLP model through the use of UNIFAC model. Finally, the optimization results are verified through experiments and rigorous models. Two application examples highlighting tailor-made surrogate fuel designs of a gasoline blend and a jet-fuel blend are presented. [ABSTRACT FROM AUTHOR]

Alzheimer’s disease (AD) is characterized by accumulation of β-amyloid (Aβ) plaques and neurofibrillary tau tangles in the brain. β-Site amyloid precursor protein cleaving enzyme 1 (BACE1) plays a key role in the generation of Aβ fragments via extracellular cleavage of the amyloid precursor protein (APP). We became interested in developing a BACE1 PET ligand to facilitate clinical assessment of BACE1 inhibitors and explore its potential in the profiling and selection of patients for AD trials. Using a set of PET ligand design parameters, compound 3 (PF-06684511) was rapidly identified as a lead with favorable in vitro attributes and structural handles for PET radiolabeling. Further evaluation in an LC-MS/MS “cold tracer” study in rodents revealed high specific binding to BACE1 in brain. Upon radiolabeling, [18F]3 demonstrated favorable brain uptake and high in vivo specificity in nonhuman primate (NHP), suggesting its potential for imaging BACE1 in humans. [ABSTRACT FROM AUTHOR]

We describe here an operationally simple and straightforward synthesis method for a series of diverse 4,5-disubstituted 1,2,3-thiadiazoles via the nucleophilic addition of α-diazo carbonyl compounds to carbon disulfide. This method features using abundant and inexpensive carbon disulfide under mild reaction conditions. [ABSTRACT FROM AUTHOR]

An anodic oxidation/cyclization of 2-arylbenzoic acids for the synthesis of dibenzopyranones has been developed. The reaction proceeds at room temperature with no oxidant or electrolyte required and exhibits a high atom economy with H2 being the only byproduct. A series of dibenzopyranones was obtained in good to excellent yields. Urolithins A, B, and C are formally synthesized by adopting this method as a key step to demonstrate its synthetic utility. [ABSTRACT FROM AUTHOR]

The reaction mechanisms of Pd(OAc)2-catalyzed dehydrogenative alkylation of 2-phenylpyridine with oxirane were investigated using DFT calculations. The most plausible reaction pathway was confirmed as a PdII/IV/II catalytic cycle consisting of four processes: C-H activation, ring-opening oxidative addition of oxirane, reductive elimination, and recovery of the catalyst. According to the B2PLYP/DGDZVP computational data, the oxidative addition of oxirane for converting PdII to PdIVwas assigned to be the rate-determining step with a free-energy barrier of 28.1 kcal•mol-1. For comparison, we also studied the alternative PdII-only pathway without a change of oxidation state and found that it was hindered kinetically by a high free-energy barrier of 75.1 kcal•mol-1 occurring for the ring-opening migratory insertion of oxirane. In addition, the small-ring strain of oxirane should be responsible for the feasible C-O bond-cleavage and subsequent PdII → PdIVconversion, because the designed four-, five-, and six-membered-ring reagents did not display such an oxidative addition reactivity. Lastly, an extended reactivity order among oxirane, PhI, PhBr, and PhCl toward oxidative addition onto PdII to form PdIV was proposed in this article based on the computed kinetic parameters. [ABSTRACT FROM AUTHOR]

Mixed-mode chromatography (MMC) is a promising technology for protein separation with high adsorption capacity, good selectivity, salt-tolerance, and facile elution. Expanded bed adsorption (EBA) can capture target proteins directly from bioparticle containing crude feedstock without solid-liquid separation. In this study, MMC and EBA were combined to develop a mixed-mode EBA technique for human serum albumin (HSA) separation. Two mixed-mode EBA resins (using quartz-densified agarose beads and tungsten carbide/agarose composite beads, respectively) with tryptamine as the ligand were prepared (TA-S and TA-T). Static and dynamic adsorption behaviors of HSA were determined under varying conditions and typical adsorption properties of pH dependence and salt-tolerance were found. The performance of the resins in expanded bed was studied, and the dynamic binding capacities at 10% breakthrough (Q10%) of TA-S and TA-T at bed expansion of 1.8 were 27.54 and 18.04 mg/mL settled resin, respectively. Moreover, these two resins were used to separate recombinant HSA (rHSA) from Pichia pastoris culture broth. TA-S showed better separation performance and the purity of rHSA monomer reached to 83.3% with the recovery of 91.6% through a two-step elution process. Total content of rHSA monomer and degraded fragment was 99.8%. The results demonstrate that the combination of MMC and EBA would be a potential platform for protein capture with fewer pretreatments and high process efficiency. [ABSTRACT FROM AUTHOR]

A series of ceria based dual composite oxides were prepared via a co-precipitation method, and we focus on studying the relationships between the catalytic activity and physicochemical properties of ceria based catalysts. It is found that catalytic activity followed the order of CeTi > CeSi > CeAl > pure CeO2; X-ray diffraction indicates that all the ceria based dual composite oxides were the cubic fluorite-type phase of CeO2; the NH3 adsorption-desorption results reveal that the NH3 adsorption stability and amount of CeO2 were improved by modification with TiO2, SiO2, or Al2O3; and the order of surface acidity was in agreement with the order of catalytic activity. Combined with other characterizations, we suppose that surface acidity is a decisive factor in influencing the catalytic activity of ceria based catalysts in the NH3-SCR reaction. [ABSTRACT FROM AUTHOR]

Palladium-catalyzed dehydrogenative homocoupling of two arenes provides a powerful and straightforward method for the synthesis of biaryls. In contrast to the Heck reaction for efficient cross-coupling of arene with alkene, dehydrogenative homocoupling of two arenes is not readily accessible through traditional PdII/0/II catalytic cycles, which limits its application to the construction of desired C-C bonds. Herein, we performed DFT studies to explore the detailed mechanisms of the PdII-catalyzed homocoupling of benzophenones in the presence of the strong oxidant K2S2O8. Calculation results demonstrated that the favorable reaction pathway is a PdII/IV/IIcatalytic cycle, including four sequential processes: C-H activation at the PdII center, oxidation of PdII to PdIV, C-H activation at the PdIV center, and reductive elimination. It was found that C-H activation at the PdIV center is the rate-determining process, with a free energy barrier of 26.0 kcal mol-1. The oxidant K2S2O8 plays an important role in converting PdII to PdIV and facilitating the second C-H activation step. In contrast, the alternative PdII/0/II pathway has been characterized as an inaccessible reaction channel from our calculations, because the second C-H activation is hindered by a free energy barrier of 38.9 kcal mol-1. In addition, the electronic effect of the spectator ligand on C-H activation has been investigated in terms of molecular orbital theory, which disclosed the origin of the critical role of PdIV intermediates in promoting the biaryl synthesis. [ABSTRACT FROM AUTHOR]

A previous report demonstrated that EuDO3A could be used as an NMR shift reagent for imaging extracellular lactate produced by cancer cells using CEST imaging. In this work, a series of heptadentate macrocyclic YbDO3A-trisamide complexes with δ-chiral carbons in the three pendant side-arms were examined as shift reagents for lactate detection. High resolution ¹H NMR spectra and DFT calculations provided evidence for the formation of stereoselective lactate·YbDO3Atrisamide complexes each with a different CEST signature. This stereoselectivity allowed discrimination of D- versus L-lactate by both high-resolution NMR and CEST. This work demonstrates that lanthanide-based paramagnetic shift reagents can be designed to detect important metabolites by CEST MRI selectively. [ABSTRACT FROM AUTHOR]

Sensitivity and reproducibility are two major concerns to improve the performance and extend the range of practical applications of surface-enhanced Raman scattering (SERS). A theoretical report reveals that hot spots formed by gold nanoparticles with a tip-to-tip configuration would generate the maximum electric field enhancement because of the lightning rod effect. In our present study, we constructed a giant vesicle consisting of anchored tiny gold nanowires to provide a high density of sharp tip-to-tip nanogaps for SERS application. The tiny gold nanowires were directly grown and anchored onto the surfaces of polystyrene (PS) microspheres by a seed-mediated method. Then, the removal of PS microspheres by tetrahydrofuran led to the formation of the giant gold vesicles with hierarchical cage structures, providing the sharp tips and high density of hot spots for improving SERS performance. Compared with the nonwire structure (island and inhibited nanoparticle), giant gold vesicles with tiny wires showed a higher SERS enhancement factor (9.90 × 107) and quantitative SERS analysis in the range of 10-4 to 10-7 M. In addition, the large-scale giant gold vesicle array on the silica substrate resulted in a high reproducibility of SERS signals with the variation of intensities less than 7.6%. [ABSTRACT FROM AUTHOR]

Proteome-wide quantitative analysis of protein ubiquiti- nation is important to gain insight into its various cellular functions. However, it is still challenging to monitor how ubiquitination at each individual lysine residue is independently regulated, especially the whereabouts of peptides containing more than one ubiquitination site. In recent years, isobaric peptide termini labeling has been considered a promising strategy in quantitative proteomics, benefiting from its high accuracy by quantifying with a series of b, y fragment ion pairs. Herein, we extended the concept of isobaric peptide termini labeling to large- scale quantitative analysis of protein ubiquitination. A novel MS2 fragment ion based quantitative approach was developed, allowing the quantification of ubiquitination at site level via isobaric K-ε-GG peptide labeling, which combined metabolic labeling, K-ε-GG immunoaffinity enrichment, and site-selective N-terminus dimethylation. The feasibility of this proposed strategy was demonstrated through the ubiquitin proteome analysis of differently labeled MCF-7 cell digests. As a result, 2970 unique K-ε-GG peptides of 1383 proteins containing 2874 ubiquitinated sites were confidently quantified with high accuracy and sensitivity. In addition, we demonstrated that quantification on MS2 fragment ion level makes it possible to precisely quantify each individual ubiquitinated lysine residue in 39 K-ε-GG peptides bearing two ubiquitination sites by the use of specific ubiquitinated b, y ion pairs. It is expected that this proposed approach will serve as a powerful tool to quantify ubiquitination at the site level, especially for those multiubiquitinated peptides. [ABSTRACT FROM AUTHOR]

As part of our effort in identifying phosphodiesterase (PDE) 4B-preferring inhibitors for the treatment of central nervous system (CNS) disorders, we sought to identify a positron emission tomography (PET) ligand to enable target occupancy measurement in vivo. Through a systematic and cost-effective PET discovery process, involving expression level (Bmax) and biodistribution determination, a PET-specific structure-activity relationship (SAR) effort, and specific binding assessment using a LC-MS/MS "cold tracer" method, we have identified 8 (PF-06445974) as a promising PET lead. Compound 8 has exquisite potency at PDE4B, good selectivity over PDE4D, excellent brain permeability, and a high level of specific binding in the "cold tracer" study. In subsequent non-human primate (NHP) PET imaging studies, [18F]8 showed rapid brain uptake and high target specificity, indicating that [18F]8 is a promising PDE4B-preferring radioligand for clinical PET imaging. [ABSTRACT FROM AUTHOR]

The use of biomimetic approaches toward the production of nonsolid yet functional architectures holds potential for the emergence of novel device concepts. Gels, in particular those obtained via self-assembly of π-conjugated molecules, are dynamic materials possessing unique (opto)-electronic properties. Their adaptive nature imparts unprecedented responsivity to various stimuli. Hitherto, a viable device platform to electrically probe in situ a sol--gel transition is still lacking. Here we describe the fabrication of a sub-micrometer electrodic cavity, which enables low-voltage electrical operation of π-gels. Thanks to the in situ supramolecular self-assembly of the π-gelator occurring within the cavity, we conceived a novel gelbased memristor whose sol--gel transition is reversible and can be controlled via heating and dc bias. This work opens perspectives toward the fabrication of a novel generation of nonsolid multiresponsive devices. [ABSTRACT FROM AUTHOR]

Water vapor generation through sunlight harvesting and heat localization by carbon-based porous thin film materials holds great promise for sustainable, energy-efficient desalination and water treatment. However, the applicability of such materials in a high-salinity environment emphasizing zero-liquid-discharge brine disposal has not been studied. This paper reports the characterization and evaporation performance of a nature-inspired synthetic leaf made of graphene oxide (GO) thin film material, which exhibited broadband light absorption and excellent stability in high-salinity water. Under 0.82-sun illumination (825 W/m²), a GO leaf floating on water generated steam at a rate of 1.1 L per m² per hour (LMH) with a light-to-vapor energy conversion efficiency of 54%, while a GO leaf lifted above water in a tree-like configuration generated steam at a rate of 2.0 LMH with an energy efficiency of 78%. The evaporation rate increased with increasing light intensity and decreased with increasing salinity. During a long-term evaporation experiment with a 15 wt % NaCl solution, the GO leaf demonstrated stable performance despite gradual and eventually severe accumulation of salt crystals on the leaf surface. Furthermore, the GO leaf can be easily restored to its pristine condition by simply scraping off salt crystals from its surface and rinsing with water. Therefore, the robust high performance and relatively low fabrication cost of the synthetic GO leaf could potentially unlock a new generation of desalination technology that can be entirely solar-powered and achieve zero liquid discharge. [ABSTRACT FROM AUTHOR]

A measurement of nonlinearity (MoN) method is proposed for single-input-single-output (SISO) Hammerstein systems based on the included angle, which is helpful for both analysis and control synthesis of Hammerstein systems. Based on the MoN method, a systematic multimodel decomposition method is put forward to get a set of local models to approximate the considered Hammerstein system. Then linear model predictive controllers (MPCs) are designed based on the local models. Finally, an included angle based weighting method is initiated to combine the MPCs into a global multimodel MPC controller (MMPC), which can be employed for set-point tracking and disturbance rejection control. Two SISO Hammerstein systems are investigated to illustrate the effectiveness of the proposed methods. Simulations prove that the proposed method is superior to the common nonlinearity inversion method. [ABSTRACT FROM AUTHOR]

Alkylated graphene (AGN) with an excellent oil dispersion property was synthesized using an in situ alkylation reaction. The structure and morphology of AGN were characterized by Fourier transform-infrared spectroscopy, X-ray powder diffraction, Thermogravimetric analysis, and transmission electron microscopy and the results indicate that long alkyl chains was successfully grafted on the surfaces of graphene sheets. Tribology properties of AGN as friction-reduction and wear-resistance additive in hydroisomerization dewax base oil (VHVI8) were evaluated using a four-ball machine. The results show that the friction coefficient (COF) and wear scar diameter (WSD) were reduced by 10.9% and 23.0% compared with bare VHVI8 base oil. The friction-reduction and wear-resistance properties are attributed to the stable dispersion, nanobearing mechanism, and ultimate strength of AGN. [ABSTRACT FROM AUTHOR]

Alkylated graphene (AGN) with an excellent oil dispersion property was synthesized using an in situ alkylation reaction. The structure and morphology of AGN were characterized by Fourier transform-infrared spectroscopy, X-ray powder diffraction, Thermogravimetric analysis, and transmission electron microscopy and the results indicate that long alkyl chains was successfully grafted on the surfaces of graphene sheets. Tribology properties of AGN as friction-reduction and wear-resistance additive in hydroisomerization dewax base oil (VHVI8) were evaluated using a four-ball machine. The results show that the friction coefficient (COF) and wear scar diameter (WSD) were reduced by 10.9% and 23.0% compared with bare VHVI8 base oil. The friction-reduction and wear-resistance properties are attributed to the stable dispersion, nanobearing mechanism, and ultimate strength of AGN. [ABSTRACT FROM AUTHOR]

Novel oxazaborolidines activated by the strong acid triflimide or AlBr3 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. [ABSTRACT FROM AUTHOR]

Sialic acids play many important roles in several physiological and pathological processes, including cancers, infection, and blood diseases. Sialic acids are fragile and prone to fragmentation under electrospray ionization and matrix-assisted laser desorption/ionization. It is crucial to modify sialic acids for qualitative and quantitative identification of their change in abundance in complex biological samples. Permethylation is a method of choice for sialic acid stabilization, but the harsh conditions during permethylation may lead to the decomposition of O-acetyl groups. Esterification or amidation in solution effectively protects sialic acids, yet it is not trivial to purify glycans from their reagents. Quantitative analysis of glycans can be achieved by labeling their reducing end using fluorescent tags. Loss of sialic acids during labeling is a major concern. In this study, we demonstrated the utility of sialic acids modification for the analysis of sialyl oligosaccharides and glycopeptides. Without modification, sialic acids are partially or completely lost during sample preparation, leading to the presence of false glycans or glycopeptides in the sample. The stabilized sialic acids not only result in accurate identification of sialylated glycans but also improve the characterization of intact glycopeptides. The modification of sialic acids on the solid support facilitates analysis of glycans and their intact glycoproteins. [ABSTRACT FROM AUTHOR]

A PPh3 mediated reductive annulation reaction between isatins and 4,4-dicyano-2-methylenebut-3-enoates was developed. The reaction provided an alternative method for constructing five- and three-membered all-carbon spirooxindole compounds. Lithium chloride as a Lewis acid played a key role in the synthesis of spirocyclopentenyl oxindole compounds. [ABSTRACT FROM AUTHOR]

Relative energies and binding energies are crucial quantities that determine various molecular properties of ice and water. We developed a new effective method to compute those energies of bulk ice-liquid water systems. In this work, ten ice-liquid 144-mers and ten periodic ice-liquid (H2O)64 systems are taken from the molecular dynamics simulations in the melting process of ice-Ih crystals. They are investigated at the levels of density functional theory (DFT), explicitly correlated second-order Møller-Plesset perturbation theory (MP2-F12), and coupled-cluster singles and doubles with noniterative triples corrections [CCSD(T)-F12b] in the framework of generalized energy-based fragmentation approach. Our results show that the changing of noncovalent interactions significantly influences the performances of DFT and electron correlation methods for those systems in the melting process of ice. Various DFT methods predict quite different results for ice and mixed ice-liquid structures but give similar results for pure liquid ones. It also explains why many DFT-based simulations lead to inaccurate densities of ice and liquid water. The CCSD(T)-F12b results suggest that the MP2-F12 method provides satisfactory results and is expected to be employed to simulate the phase transitions of ice crystal. [ABSTRACT FROM AUTHOR]

Addition of potassium graphite (KC8) to a solution of (η5-C5Me5)2UCl2 (1) and 2,2'-bipyridine (bipy) gives the uranium bipyridyl metallocene (η5-C5Me5)2U(bipy) (2) in good yield. In complex 2 a bipy radical anion is coordinated to a U(III) atom, and it is therefore an ideal starting material for small-molecule activation: e.g., it serves as a synthetic equivalent for the (η5-C5Me5)2UII fragment on treatment with conjugated alkynes and a variety of heterounsaturated molecules such as imines, carbodiimide, organic azides, hydrazine, and azo derivatives. Alternatively, it may also react with aldehydes, ketones, nitriles, and α,β-unsaturated reagents such as p-ClPhCHO, (CH2)5CO, PhCN, and methyl methacrylate (MMA), forming the C-C bond coupling products (η5-C5Me5)2U[(bipy)(p-ClPhCHO)] (10), (η5-C5Me5)2U[(bipy){(CH2)5CO}] (11), (η5-C5Me5)2U[(bipy)(PhCN)] (12), (η5-C5Me5)2U[(bipy){CH2C(Me)CO(OMe)] (13a), and [(η5-C5Me5)2U{OC(OMe)C(Me)CH2-3-bipy}]2 (13b), respectively, in quantitative conversion. Furthermore, addition of CuI to complex 2 induces a single-electron-transfer process to form the uranium(III) iodide complex (η5-C5Me5)2U(I)(bipy) (14) [ABSTRACT FROM AUTHOR]

Hyper-cross-linked polynaphthalene nanoparticles (PNNs) capable of catalyzing the degradation of organic pollutants upon exposure to visible light have been developed. The nascent and metal-free PNNs with a porous structure, high specific surface area, and narrow bandgap are chemically and thermally stable in the catalytic system, which make it promising as a kind of excellent photocatalytic material compared to conventional photocatalysts. The photocatalytic activity of the as-obtained PNNs exhibits remarkable photocatalytic performance for the degradation of rhodamine B (RhB) and methyl blue (MB) under the irradiation of visible light. The easy preparation, high catalytic activity, and recyclability of the PNNs open new opportunities in the visible-light-promoted degradation of organic pollutants. [ABSTRACT FROM AUTHOR]

The synthesis, electronic structure, and reactivity of a uranium metallacyclocumulene were studied. Reduction of [(η5-C5Me5)2UCl2] (1) with potassium graphite (KC8) in the presence of 1,4-bis(trimethylsilyl)butadiyne (Me3SiCC-CCSiMe3) forms the uranium metallacyclocumulene [(η5-C5Me5)2U{η4-C4(SiMe3)2}] (2) in good yield. Magnetic susceptibility data confirm that 2 behaves as a U(IV) complex, and density functional theory (DFT) studies indicate a substantial 5f orbital contribution to the bonding of the metallacyclopentatriene U(η4-CCCC) moiety, leading to more covalent bonds between the [(η5-C5Me5)2U]2+ and [η4-C4(SiMe3)2]2- fragments than those found in the related Th(IV) compound. Consequently, very different reactivity patterns emerge; e.g., 2 can act as a synthetic equivalent for the (η5-C5Me5)2U(II) fragment when reacted with conjugated species such as butadiyne, bipy, and diazabutadiene derivatives. Alternatively, the [(η4-Me3SiCCCCSiMe3)]2- moiety in 2 may react as a nucleophile when exposed to a variety of simple heterounsaturated molecules such as aldehydes, ketones, nitriles, isothiocyanates, carbodiimides, pyridines, and organic azides. DFT studies are included to complement the experimental observations. [ABSTRACT FROM AUTHOR]

A general and efficient method for accessing enantiomerically pure arylpyrroles by utilizing the catalytic asymmetric Paal-Knorr reaction has been developed for the first time. A wide range of axially chiral arylpyrroles were obtained in high yields with good to excellent enantioselectivities. The key to success is the use of the combined-acid catalytic system involving a Lewis acid and a chiral phosphoric acid for achieving effective enantiocontrol. Noteworthy is that an unexpected solvent-dependent inversion of the enantioselectivity was observed in the above-mentioned asymmetric reaction. [ABSTRACT FROM AUTHOR]

We demonstrate a new method to reverse the polarity and charge transport behavior of naphthalenediimide (NDI)-based copolymers by inserting a vinylene linker between the donor and acceptor units. The vinylene linkers minimize the intrinsic steric congestion between the NDI and thiophene moieties to prompt backbone planarity. The polymers with vinylene linkers exhibit electron n-channel transport characteristics under vacuum, similar to the benchmark polymer, P(NDI2OD-T2). To our surprise, when the polymers are measured in air, the dominant carrier type switches from n- to p-type and yield hole mobilities up to 0.45 cm² V-1 s-1 with hole to electron mobility ratio of three (μh/μe, ∼3), which indicates that the hole density in the active layer can be significantly increased by exposure to air. This increase is consistent with the intrinsic more delocalized nature of the highest occupied molecular orbital of the charged vinylene polymer, as estimated by density functional theory (DFT) calculations, which facilitates hole transport within the polymer chains. This is the first demonstration of an efficient NDI-based hole semiconducting polymer, which will enable new developments in all-polymer solar cells, complementary circuits, and dopable polymers for use in thermoelectrics. [ABSTRACT FROM AUTHOR]

The first-principles method is challenged by accurate prediction of van der Waals interactions, which are ubiquitous in nature and crucial for determining the structure of molecules and condensed matter. We have contributed to this by constructing a set of pseudopotentials and pseudoatomic orbital basis specialized for molecular systems consisting of C/H/N/O elements. The reliability of the present method is verified from the interaction energies of 45 kinds of complexes (comparing with CCSD(T)) and the crystalline structures of 23 kinds of typical explosive solids (comparing with experiments). Using this method, we have studied the phase transition of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) under static compression up to 50 GPa. Kinetically, intramolecular deformation has priority in the competition with intermolecular packing deformation by ∼87%. A possible γ → β phase transition is found at around 2.10 GPa, and the migration of H2O has an effect of kinetically pushing this process. We make it clear that no β → δ/ε → δ phase transition occurs at 27 GPa, which has long been a hot debate in experiments. In addition, the P-V relation, bulk modulus, and acoustic velocity are also predicted for α-, δ-, and γ-HMX, which are experimentally unavailable. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) calculations with the B3LYP functionals elucidated the reactivity, selectivity, and mechanisms of a rhodium-catalyzed intermolecular [2 + 2] cycloaddition of terminal alkynes with electron-deficient alkenes. The most plausible reaction pathway was discussed as three distinct processes in full catalytic cycles, including (1) substrate exchange, (2) nucleophilic addition and cyclization, and (3) separation of product and recycling of catalyst; the formal [2 + 2] cycloaddition indeed proceeded through a rate-determining and stepwise addition-cyclization process. We then compared the outer-sphere and inner-sphere mechanisms for the formation of cyclobutene intermediates and reported that the former pathway is more accessible kinetically and thus more competitive, being contrary to the proposed mechanism for some nickel-catalyzed cycloaddition reactions in the literature. Furthermore, the substituent effect has been investigated using various alkenes CH2CHR (R = COOMe, CN, H, CH3) as reaction partners, which disclosed that the reaction pathway for electron-deficient alkenes was mediated by a zwitterion intermediate, whereas that for electron-neutral alkenes was characterized as a diradical-like mechanism with an inaccessible free-energy barrier of more than 46 kcal mol-1. In addition, the effects of ligand and base have been discussed in detail from the perspective of Houk's distortion/interaction model, providing a valuable case study for understanding the roles played by different phosphine ligands and additives. [ABSTRACT FROM AUTHOR]

A comprehensive DFT investigation has been performed for a series of the Pd(OAc)2-catalyzed C-H activations, updating and extending the understanding of directing group effect. In the beginning, the directed and undirected C-H activation mechanisms, based on 10 model reactions, have been discussed comparatively, which disclosed that directing group can exert a thermodynamic driving force, not necessarily a kinetic promotion, on the C-H activation process. Formation of the open palladation species via the undirected pathway is thermodynamically unspontaneous (ΔG = 4-9 kcal/mol), in sharp contrast to that of the cyclopalladation species via the directed pathway (ΔG < 0). Further calculations revealed that the free-energy barriers of proton-transfer are in fact not so high on the undirected pathway (17-24 kcal/mol), while mediation of some O-center groups in the directed pathway would increase the free-energy barriers of proton-transfer. For pyridine N-oxide systems, the undirected mechanism was estimated to be more plausible than the 4-member-directed one both thermodynamically and kinetically. In addition, the uncommon 7-membered cyclopalladation has been tentatively explored using two current examples, predicting that electron-rich directing groups can help to stabilize the 7-membered palladacycles formed. [ABSTRACT FROM AUTHOR]

Mesoporous zeolite ZSM-5 (ZSM-5-M) was synthesized and used as support for the preparation of highly efficient nickel phosphide catalyst (Ni2P/ZSM-5-M) in the deep hydrogenation of phenanthrene and in the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (4,6-DM-DBT). Compared with Ni2P catalysts supported silica and high surface area hexagonal mesoporous silica (HMS) (Ni2P/SiO2 and Ni2P/HMS), Ni2P/ZSM-5-M exhibits higher hydrogenation and HDS activity. The phenanthrene conversion and deep hydrogenation products selectivity over Ni2P/ZSM-5-M (95% and 83%) are much higher than those over Ni2P/SiO2 (61% and 73%) and Ni2P/HMS (69% and 45%) under mild conditions. The 4,6-DM-DBT conversion over Ni2P/ZSM-5-M (93%) was higher than that over Ni2P/SiO2 (62%). This feature is attributed to the difference in surface properties of support. A large amount of acidic hydroxyl groups on the zeolites can interact strongly with catalyst precursor, resulting in the formation of highly dispersed Ni2P particles with small sizes, which provide abundant hydrogenation active sites. [ABSTRACT FROM AUTHOR]

We report a 3.6 nm Ti52--oxo cluster with precise atomic structure, which presents a largest size record in the family of titanium--oxo clusters (TOCs). The crystal growth of such large Ti52 is based on a stepwise interlayer assembly approach from Ti6 substructures. The possible growth mechanism of Ti52 could be deduced from crystal structures of two substructures, Ti6 and Ti17, which were also synthesized under similar conditions as Ti52. Moreover, these TOCs show cluster-size-dependent photocatalytic hydrogen evolution activities with Ti52 giving a H2 production rate up to 398 μmol/h/g, which is also the highest record in the family of TOCs. This work not only represents a milestone in constructing large TOCs with comparable sizes as TiO2 nanoparticles but also brings significant advances in improving photocatalytic behaviors of TOCs. [ABSTRACT FROM AUTHOR]

A facile method for preparing nickel hydroxyl nanoparticles loaded graphene aerogels has been established. The prepared aerogels were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and Raman spectroscopy. Their applications as absorbents or electrode materials for supercapacitors were investigated. They showed excellent performance on the absorption of different dyes. The absorption capacities ranged from 202 to 513 mg g-1. They also displayed high absorption capacities toward oils and organic solvents. The aerogels demonstrated high capacitance and stability as electrode materials of supercapacitors. The specific capacitance reached 702 F g-1 at current densities of 1 A g-1. [ABSTRACT FROM AUTHOR]

Harnessing surface plasmon of metal nanostructures to promote catalytic organic synthesis holds great promise in solar-to-chemical energy conversion. High conversion efficiency relies not only on broadening the absorption spectrum but on coupling the harvested energy into chemical reactions. Such coupling undergoes hot-electron transfer and photothermal conversion during the decay of surface plasmon; however, the two plasmonic effects are unfortunately entangled, making their individual roles still under debate. Here, we report that in a model system of bimetallic Au-Pd core-shell nanostructures the two effects can be disentangled through tailoring the shell thickness at atomic-level precision. As demonstrated by our ultrafast absorption spectroscopy characterizations, the achieved tunability of the two effects in a model reaction of Pd-catalyzed organic hydrogenation offers a knob for enhancing energy coupling. In addition, the two intrinsic plasmonic modes at 400-700 and 700-1000 nm in the bar-shaped nanostructures allow for utilizing photons to a large extent in full solar spectrum. This work establishes a paradigmatic guidance toward designing plasmonic-catalytic nanomaterials for enhanced solar-to-chemical energy conversion. [ABSTRACT FROM AUTHOR]

Nanozymes, the nanostructures with enzymatic activities, have attracted considerable attention because, in comparison with natural enzymes, they offer the possibility of lowered cost, improved stability, and excellent recyclability. However, the specificity and catalytic activity of current nanozymes are still far lower than that of their natural counterparts, which in turn has limited their use such as in bioanalysis. To address these challenges, herein we report the design and development of integrated nanozymes (INAzymes) by simultaneously embedding two cascade catalysts (i.e., a molecular catalyst hemin and a natural enzyme glucose oxidase, GOx) inside zeolitic imidazolate framework (ZIF-8) nanostructures. Such integrated design endowed the INAzymes with major advantage in improved catalytic efficiency as the first enzymatic reaction occurred in close (nanoscale) proximity to the second enzyme, so products of the first reaction can be used immediately as substrates for the second reaction, thus overcoming the problems of diffusion-limited kinetics and product instability. The considerable high catalytic activity and stability enabled the INAzymes to efficiently draw a colorimetric detection of glucose with good sensitivity and selectivity. When facilitated with in vivo microdialysis, the INAzyme was successfully used for facile colorimetric visualization of cerebral glucose in the brain of living rats. Moreover, when further combined with microfluidic technology, an integrative INAzyme-based online in vivo analytical platform was constructed. The promising application of the platform was successfully illustrated by continuously monitoring the dynamic changes of striatum glucose in living rats' brain following ischemia/reperfusion. This study developed a useful approach to not only functional nanomaterial design but also advanced platforms developments for diverse targets monitoring. [ABSTRACT FROM AUTHOR]

The synthesis, structure, and reactivity of a uranium metallacyclopropene were comprehensively studied. Reduction of (η5-C5Me5)2UCl2 (1) with potassium graphite (KC8) in the presence of bis(trimethylsilyl)acetylene (Me3SiC≡CSiMe3) allows the first stable uranium metallacyclopropene (η5-C5Me5)2U[η2-C2(SiMe3)2] (2) to be isolated. Magnetic susceptibility data confirm that 2 is a U(IV) complex, and density functional theory (DFT) studies indicate substantial 5f orbital contributions to the bonding of the metallacyclopropene U-(η2-C=C) moiety, leading to more covalent bonds between the (η5-C5Me5)2U2+ and [η2-C2(SiMe3)2]2- fragments than those in the related Th(IV) compound. Consequently, very different reactivity patterns emerge, e.g., 2 can act as a source for the (η5-C5Me5)2U(II) fragment when reacted with alkynes and a variety of heterounsaturated molecules such as imines, bipy, carbodiimide, organic azides, hydrazine, and azo derivatives. [ABSTRACT FROM AUTHOR]

The cell membrane is a major barrier for drug transport. Given that many cancer drugs must passively cross the cell membrane, understanding drug-membrane interactions is crucial. We used fluorescence-activated cell sorting to investigate how cholesterol influences the transport of the cancer drugs ellipticine and pirarubicin across cell membranes. We showed that cholesterol depletion helped pirarubicin cross the membranes of nonsmall cell lung carcinoma and Chinese hamster ovary cells. In contrast, the uptake of ellipticine was not strongly influenced by cholesterol depletion. To study the microscopic origins of these observations, atomistic molecular dynamics simulations were performed. Doxorubicin (similar in structure to pirarubicin) and ellipticine were simulated in model membranes of POPC and POPC with 40 mol % cholesterol. Atomistic free energy calculations for the translocation of a single ellipticine and doxorubicin across the lipid bilayers qualitatively matched the experiment results. The free energy barrier for doxorubicin crossing the bilayer was strongly increased when cholesterol was present, while for ellipticine the barrier remained similar with and without cholesterol. Molecular dynamics simulations showed that the different hydrogen-bonding propensities of the two drugs are likely the major factor for the different behaviors. The qualitative agreement between cell experiments and atomistic computer simulations illustrates the potential to link observed biological phenomena and single molecule mechanisms of actions. Our results suggest that the traditional understanding of drug permeation and the influence of cholesterol on the small molecule transport is naïve and needs to be re-examined. [ABSTRACT FROM AUTHOR]

The pyrolysis treatment with biomass is a promising technology for the remediation of chromitc-ore-processing residue (COPR). However, the mechanism of this process is still unclear. In this study, the behavior of pyrolysis reduction of Cr(VI) by cellulose, the main component of biomass, was elucidated. The results showed that the volatile fraction (VI:) of cellulose, ie. gas and tar, was responsible for Cr(Vl) reduction. All organic compounds, as well as CO and H2 in VF, potentially reduced Cr(Vl). X-ray absorption near-edge structure (XANES) spectroscopy and extended X-ray absorption fine-structure (EXAFS) spectroscopy confirmed the reduction or Cr(VI) to Cr(lll) and the formation of amorphous Cr2O3. The remnant Cr(VT) content in COPR can be reduced below the detection limit (2 mg/kg) by the reduction of COPR particle and extension of reaction time between VF and COPR. This study provided a deep insight on the co-pyrolysis of cellulose with Cr(Vl) in COPR and an ideal approach by which to characterize and optimize the pyrolysis treatment for COPR by other organics. [ABSTRACT FROM AUTHOR]

The interaction between a water-soluble anionic Ga(III) corrole [Ga(tpfc)(SO3Na)2] and calf thymus DNA (ct-DNA) has been investigated by using femtosecond transient absorption spectroscopy. A significant broadening from 570 to 585 nm of positive absorption band of the blend of Ga(tpfc)(SO3Na)2 and ct-DNA (Ga(tpfc)(SO3Na)2-ctDNA) has been observed from 0.15 to 0.50 ps after photoexcitation of Ga(tpfc)(SO3Na)2 into the Soret band. The control experiment has been performed on the model DNA ([poly(dG-dC)]2) rich in guanine bases, which exhibits a similar spectral broadening, whereas it is absent for [poly(dA-dT)]2 without guanine bases. The molecular orbital calculation shows that HOMO of Ga(tpfc)(SO3Na)2 is lower than that of guanine bases. The results of the electrochemical experiment show the reversible electron transfer (ET) between Ga(tpfc)(SO3Na)2 and guanine bases of ct-DNA is thermodynamically favorable. The dynamical analysis of the transient absorption spectra reveals that an ultrafast forward ET from the guanine bases to Ga(tpfc)(SO3Na)2 occurs within the pulse duration (156 fs), leading to the formation of an intermediate state. The following back ET to the ground state of Ga(tpfc)(SO3Na)2 may be accomplished in 520 fs. [ABSTRACT FROM AUTHOR]

Mixed-mode chromatography (MMC) has been developed as a cost-effective new technique for antibody purification. Nuvia cPrime (NP) is a novel MMC resin with p-aminohippuric acid as the functional ligand. The adsorption of human immunoglobulin G (IgG) and bovine serum albumin (BSA) on NP was measured, including single component adsorption at different pH and binary coadsorption at various pH values and IgG/BSA mass ratios. Typical pH-dependent adsorption behavior was found in the single component adsorption which can be described by a two-parameter equation that offered a convenient way to analyze pH effects. Moreover, a competitive and preferential adsorption of IgG to BSA was investigated in binary coadsorption. Extended Langmuir (EL) and Extended Langmuir-Freundlich (ELF) models with parameters obtained from single-component isotherms were used to describe the coadsorption behaviors of IgG and BSA at various mass ratios. The results indicated the ELF model was more suitable for IgG adsorption, while the EL model was better for describing the weak binding of BSA at pH 7.0 and 8.0. [ABSTRACT FROM AUTHOR]

Two 46-membered [2 + 2] Schiff-base macrocyclic dinuclear Zn(II) complexes (1a and 1b) were investigated deeply by the postmodification strategy, and two types of supramolecular processes (ring-contraction and self-assembly) have been achieved after the addition of specific anions as stimulus for the equilibrium of Schiff-base macrocyclic complexes. Namely, in the presence of linear three-atom SCN-, 1a was degraded into two 23-membered [1 + 1] Schiff-base macrocyclic complexes simultaneously (mononuclear Zn(II) complex 2 and dinuclear Zn(II) complex 3). In contrast, 1b was only transformed into the macrocyclic mononuclear complex 5. More interestingly, in the case of pseudolinear five-atom N(CN)2-, supramolecular self-assembly took place instead of the above-mentioned ring-contraction. Finally, 1a was assembled into a unique molecular box 4 with two 46-membered [2 + 2] Schiff-base macrocyclic heteronuclear Zn4Na4 substrates and double μ2-N(CN)2- bridges, while no similar assembly process was observed for 1b. The geometry of anions and pH values slightly adjusted by the pendant arms on the macrocyclic skeletons are believed to be the critical factors for the different supramolecular processes originating from the dynamic covalent chemistry of Schiff-base imine bonds. [ABSTRACT FROM AUTHOR]

The selective preparation of 1,1,1-tris-(boronates) from vinylarenes and bis(pinacolato)diboron is described. The reactions occur at ambient temperature with excellent selectivity, high yields, and good functional group tolerance. Mechanistic studies suggest that Co(l)-catalyzed double dehydrogenative borylations generate a 1,1-diborylalkene intermediate, which undergoes hydroboration with pinacolborane formed in situ to yield 1,1,1-tris(boronate). [ABSTRACT FROM AUTHOR]

Reduction of (η5-C5Me5)2ThCl2 (1) with potassium graphite (KC8) in the presence of 1,4-diphenylbutadiyne (PhC≡CC≡CPh) yields the first actinide metallacyclocumulene, the thorium metallacyclopentatriene (η5-C5Me5)2Th(η4-C4Ph2) (2). The structure and reactivity of 2 were investigated in detail; structural parameters and density functional theory (DFT) studies confirm the presence of a metallacyclopentatriene unit in 2. Furthermore, DFT computations also indicate a notable contribution of the 5f orbitals to the bonding of the metallacyclopentatriene Th-(η4-C=C=C=C) moiety. While complex 2 shows no reactivity toward alkynes, it reacts with a variety of heterounsaturated molecules such as isothiocyanates, carbodiimides, aldehydes, ketones, nitriles, pyridines, and diazoalkane derivatives. DFT studies complement the experimental observations and provide additional insights. Furthermore, in comparison to group 4 metals, the thorium metallacyclopentatriene 2 exhibits distinctively different reactivity patterns. [ABSTRACT FROM AUTHOR]

PolycycloiridalsA–D, four novel iridals with an unprecedentedα-terpineol moiety resulting from cyclization of the homofarnesylsidechain, were isolated from the ethanol extract of rhizomes of Iris tectorum. Their structures were elucidated on the basisof comprehensive spectroscopic analysis. The absolute configurationof 1was determined by the modified Mosher’s methodand comparison of experimental and calculated electronic circulardichroism (ECD) spectrum. A possible biosynthetic pathway was postulated. [ABSTRACT FROM AUTHOR]

In classical transition state theory, a transition state is connected to its reactant(s) and product(s). Recently, chemists found that reaction pathways may bifurcate after a transition state, leading to two or more sets of products. The product distribution for such a reaction containing a bifurcating potential energy surface (bPES) is usually determined by the shape of the bPES and dynamic factors. However, if the bPES leads to two intermediates (other than two products), which then undergo further transformations to give different final products, what factors control the selectivity is still not fully examined. This missing link in transition state theory is founded in the present study. Aiming to develop new methods for the synthesis of azocinoindole derivatives, we found that 2-propargyl-β-tetrahydrocarbolines can undergo ring expansion and spirocyclization under gold catalysis. DFT study revealed that the reaction starts with the intramolecular cyclization of the gold-activated 2-propargyl-β-tetrahydrocarboline with a bPES. The cyclization intermediates can not only interconvert into each other via a [1,5]-alkenyl shift, but also undergo ring expansion (through fragmentation/protodeauration mechanism) or spirocyclization (through deprotonation/protodeauration mechanism). Detailed analysis of the complex PESs for substrates with different substituents indicated that the reaction selectivity is under dynamic control if the interconversion of the intermediates is slower than the ring expansion and spirocyclization processes. Otherwise, the chemical outcome is under typical kinetic control and determined by the relative preference of ring expansion versus spirocyclization pathways. The present study may enrich chemist's understanding of the determinants for selectivities on bPESs. [ABSTRACT FROM AUTHOR]

A magnesium oxide nanosheet assembly(NS-MgO) with high surfacearea (255 m2/g) and nanopore volume (0.30 cm3/g) was prepared by a pressure-assisted carbonation method at largescale. After loading of cobalt and molybdenum (CoMo) species and followedby sulfidation, the NS-MgO supported CoMo catalyst (Co-MoS2/NS-MgO) exhibits high activity (94.2%) and good nitrogen tolerancein the hydrodesulfurization (HDS) of dibenzothiophene (DBT), comparedwith a conventional γ-alumina-supported CoMo catalyst (64.1%).These results are attributed to the difference in the basicity ofthe NS-MgO and γ-Al2O3supports. The largeamount of the middle strong basic sites on NS-MgO can avoid the polymerizationof Mo species and form small Mo oxide clusters. After sulfidation,the small MoS2clusters with shorter lengths and less stackingformed on the NS-MgO contribute to an increase in the sites availablefor Co promotion, resulting in the Co-MoS2/NS-MgO catalystwith high HDS activity. [ABSTRACT FROM AUTHOR]

Identical 34-membered [2 + 2] pendent-armed Schiff-base macrocyclic ligands (H4La and H4Lb) can be constructed via the condensation reactions between rigid o-phenylenediamine and extended dialdehydes (H2hpdd/H2pdd) in the presence of either LnIII or ZnII template with remarkable distinction on the ion radii and charge. X-ray single-crystal diffraction analyses reveal the formation of mononuclear LnIII complexes (1-4 and 7) and dinuclear ZnII complexes (5 and 6). It is noted that LnIII macrocyclic complexes have eight-coordinate sandwich-like mononuclear structures fully surrounded by flexible and large-sized macrocyclic ligands. Photophysical studies have demonstrated that both H4La and H4Lb can serve as effective sensitizers for the YbIII ion (2 and 7) exhibiting near-infrared emission at 974 nm with high quantum yields in solution (C2H5OH and CH3OH, ~1%). Moreover, the quantum yields of two YbIII complexes 2 and 7 could be increased ~15% in CH3OH under weak alkaline condition (pH = 8-9), while no significant changes are observed in C2H5OH by contrast. We think the unique sandwich-like macrocyclic structures of YbIII complexes 2 and 7 play important roles in simultaneously guaranteeing the effective match of the energy levels of YbIII centers as well as shielding from the solvent molecules and counterions. [ABSTRACT FROM AUTHOR]

Gold nanoparticles (AuNPs) labeled lateral-flow test strip immunoassay (LFTS) has been widely used in biomedical, feed/food, and environmental analysis fields. Conventional ILFS assay usually uses spherical AuNPs as labeled probes and shows low detection sensitivity, which further limits its widespread practical application. Unlike spherical AuNP used as labeled probe in conventional ILFS, in our present study, a hierarchical flowerlike AuNP specific probe was designed for LFTS and further used to detect Escherichia coli O157:H7 (E. coli O157:H7). Three types of hierarchical flowerlike AuNPs, such as tipped flowerlike, popcornlike, and large-sized flowerlike AuNPs were synthesized in a one-step method. Compared with other two kinds of Au particles, tipped flowerlike AuNPs probes for LFTS particularly exhibited highly sensitive detection of E. coli O157:H7. The remarkable improvement of detection sensitivity of tipped flowerlike AuNPs probes can be achieved even as low as 10³ colony-forming units (CFU)/mL by taking advantages of its appropriate size and hierarchical structures, which is superior over the detection performance of conventional LFTS. Using this novel tipped flower AuNPs probes, quantitative detection of E. coli O157:H7 can be obtained partially in a wide concentration range with good repeatability. This hierarchical tipped flower-shaped AuNPs probe for LFTS is promising for the practical applications in widespread analysis fields. [ABSTRACT FROM AUTHOR]

The article explores on the impact of Morita-Baylis-Hillman carbonates with azomethine imines to the enantioselectivity of phosphine. It highlights the importance of nucleophilic phosphine-catalyzed annulation reaction to the synthesis of natural products. It cites the accessibility and stability of azomethine imines in metal-catalyzed and organocatalytic cycloadditions.

Polycyclic aromatic hydrocarbons (PAHs), consisting of laterallyfused benzene rings, are among the most widely studied small-moleculeorganic semiconductors, with potential applications in organic field-effecttransistors (OFETs) and organic photovoltaics (OPVs). Linear acenes,including tetracene, pentacene, and their derivatives, have receivedparticular attention due to the synthetic flexibility in tuning theirchemical structure and properties and to their high device performance.Unfortunately, longer acenes, which could exhibit even better performance,are susceptible to oxidation, photodegradation, and, in solar cellswhich contain fullerenes, Diels–Alder reactions. This Accounthighlights recent advances in the molecular design of two-dimensional(2-D) PAHs that combine device performance with environmental stability. [ABSTRACT FROM AUTHOR]