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A new transition metal-catalyzed three-component cycloaddition is described. Carbon-substituted alkynes give bicyclo [3.3.0] octenone adducts results from transannular closure of the intermediate eight membered rings.

The study has reported several new organotellurium-based initiators for controlled/living radical polymerization of styrene derivatives that allows accurate molecular weight control with defined end-groups, which can be transformed into a variety of end group modified polystyrenes. Bond dissociation energies and the reactivity of the initiating radicals towards styrene are important factors in controlling the polymerization process.

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]

Research has been conducted on the nanostructured materials. A redox reaction between alkaline selenium solution and cupric complex aqueous solution has been carried out.

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]