Copper‐Catalyzed Amidation of Aryl Iodides in the Presence of Various Chelating Ligands

N,N′‐Dibenzylethylenediamine is presented as a new, efficient, and versatile bidentate ligand suitable for the copper catalyzed formation of the C‐N bond. This bidentate ligand has been demonstrated to facilitate the copper catalyzed cross‐coupling reactions of aryl iodides with amides to afford the desired products in good to excellent yields.     

Novel silica-supported molybdic acid (SSMA): an efficient catalyst for the synthesis of new azo dyes

Research on Chemical Intermediates - Silica-supported molybdic acid (SSMA) as a novel and highly efficient catalyst was prepared and characterized by X-ray fluorescence, X-ray diffraction, and...     

CoFe2O4/TMU‐17‐NH2 as a hybrid magnetic nanocomposite catalyst for multicomponent synthesis of dihydropyrimidines

A new magnetic metal–organic framework nanocomposite (CoFe₂O₄/TMU‐17‐NH₂) was prepared via an embedding approach by synthesis of the metal–organic framework crystals in the presence of magnetic cobalt ferrite nanoparticles. We demonstrated that the resulting magnetic nanocomposite can serve as a recyclable nanocatalyst for one‐pot synthesis of bis‐3,4‐dihydropyrimidin‐2(1H)‐one and 3,4‐dihydropyrimidin‐2(1H)‐one derivatives via three‐component reaction of 1,3‐diketone, urea or thiourea and aromatic aldehyde under solvent‐free conditions. CoFe₂O₄/TMU‐17‐NH₂ was characterized using various techniques. The recovery of the nanocomposite was achieved by a simple magnetic decantation and it was reused at least seven times without significant degradation in catalytic activity.     

Mesoporous silica SBA‐15 functionalized with acidic deep eutectic solvent: A highly active heterogeneous N‐formylation catalyst under solvent‐free conditions

Mesoporous silica SBA‐15 functionalized with N‐methylpyrrolidonium‐zinc chloride based deep eutectic solvent (DES) is found to be a more efficient and reusable catalyst for a convenient N‐formylation of a variety of amines at room temperature. N‐Formylation of primary, secondary as well as heterocyclic amines have been carried out in good to excellent yields by treatment with formic acid in low loading of DES/SBA‐15 an environmentally benign catalyst for the first time. The DES/SBA‐15 catalyst, which possesses both Brønsted and Lewis acidities as well as an active SBA‐15 support, makes this procedure quite simple, reusable, more convenient and practical. This catalyst was tolerant of a wide range of functional groups, and it can be reused for four runs without obvious deactivation.     

Aggregation-enhanced emissions of intramolecular excimers in disubstituted polyacetylenes

Whereas chain aggregation commonly quenches light emission of conjugated polymers, we here report a phenomenon of aggregation-induced emission enhancement (AIEE): luminescence of polyacetylenes is dramatically boosted by aggregate formation. Upon photoexcitation, poly(1-phenyl-1-alkyne)s and poly(diphenylacetylene)s emit blue and green lights, respectively, in dilute THF solutions. The polymers become more emissive when their chains are induced to aggregate by adding water into their THF solutions. The polymer emissions are also enhanced by increasing concentration and decreasing temperature. Lifetime measurements reveal that the excited species of the polymers become longer-lived in the aggregates. Conformational simulations suggest that the polymer chains contain n=3 repeat units that facilitate the formation of intramolecular excimers. The AIEE effects of the polymers are rationalized to be caused by the restrictions of their intramolecular rotations by the aggregate formation.     

Synthesis, structure, aggregation-induced emission, self-assembly, and electron mobility of 2,5-bis(triphenylsilylethynyl)-3,4-diphenylsiloles

2,5-Bis(triphenylsilylethynyl)-3,4-diphenylsiloles with different 1,1-substituents [XYSi(CPh)(2) (C-C≡C-SiPh(3))(2)] (Ph=phenyl) were synthesized in high yields by the Sonogashira coupling of 2,5-dibromo-3,4-diphenylsiloles with triphenylsilylacetylene, and two of these were characterized crystallographically. Crystal structures and theoretical calculations showed that the new silole molecules had higher conjugation than 2,5-diarylsiloles. They possessed low HOMO and LUMO energy levels due to the electron-withdrawing effect of the triphenylsilylethynyl groups. Cyclic voltammetry analysis revealed low electron affinities, which were comparable to those of perfluoroarylsiloles. B3LYP/6-31* calculations demonstrated that the new siloles possessed large reorganization energies for electron and hole transfers and high electron mobilities. A mobility of up to 1.2×10(-5) cm(2) V(-1) s(-1) was obtained by the transient electroluminescence method, which was about fivefold higher than that of tris(8-hydroxyquinolinato)aluminum, a widely used electron-transport material, under the same conditions. All of the silole molecules possessed high thermal stability. Although, their solutions were weakly emissive, their nanoparticle suspensions and thin films emitted intense blue-green light upon photoexcitation, demonstrating a novel feature of aggregation-induced emission (AIE). Polarized emissions were observed in the silole crystals. The addition of solvents, which did not dissolve the silole molecules, into silole-containing solutions caused self-assembly of the molecules, which produced macroscopic fibrils with strong light emissions.     

Heterologous Expression and Engineering of the Nitrogenase Cofactor Biosynthesis Scaffold NifEN

NifEN plays a crucial role in the biosynthesis of nitrogenase, catalyzing the final step of cofactor maturation prior to delivering the cofactor to NifDK, the catalytic component of nitrogenase. The difficulty in expressing NifEN, a complex, heteromultimeric metalloprotein sharing structural/functional homology with NifDK, is a major challenge in the heterologous expression of nitrogenase. Herein, we report the expression and engineering of Azotobacter vinelandii NifEN in Escherichia coli. Biochemical and spectroscopic analyses demonstrate the integrity of the heterologously expressed NifEN in composition and functionality and, additionally, the ability of an engineered NifEN variant to mimic NifDK in retaining the matured cofactor at an analogous cofactor‐binding site. This is an important step toward piecing together a viable pathway for the heterologous expression of nitrogenase and identifying variants for the mechanistic investigation of this enzyme.     

A cubic time algorithm for finding the principal solution to Sylvester matrix equations over (max, +)

We propose an algorithm for finding the so-called principal solution of the Sylvester matrix equation over max-plus algebra. The derivation of our algorithm is based on the concept of tropical tensor product introduced by Butkovi? and Fiedler. Our algorithm reduces the computational cost of finding the principal solution from quartic to cubic. It also reduces the space complexity from quartic to quadratic. Since matrix–matrix multiplication is the most important ingredient of our proposed technique, we show how to use column-oriented matrix multiplications in order to speed-up MATLAB implementation of our algorithm. Finally, we illustrate our results and discuss the connection with the residuation theory.     

Fluorine-hydrocarbon separation and microdomain formation in N-(2,3,5,6-Tetrafluoropyridin-4-yl)benzene-diamines

Compounds with both aromatic and perfluoro aromatic moieties often assemble in the form of π-stacks with alternating arene perfluoroarene arrangements. The 1,4 and 1,3-diamines of N-(2,3,5,6-tetrafluoropyridin-4-yl)benzene (1) and (2), C₁₁H₇F₄N₃, however, show a behavior more commonly observed for diblock perfluoro alkyl derivatives: the fluorinated and the hydrocarbon moieties of the molecules segregate from each other and form fluoro and hydrocarbon microdomains with parallel layers of π-stacked tetrafluoropyridine rings and diamino-phenyl moieties. The structural features of the two derivatives are, despite the different substitution patterns and cell settings, strikingly similar. The main feature in the non-fluorinated domains of 1 and 2 is a set of N–H···H and N–H···π interactions that connect the amino groups of four molecules with each other, which are augmented by some weaker C–H···π and C–H···F interactions, but no π–π stacking is observed. The fluoro microdomains in both 1 and 2 are characterized by extremely short interplanar distances between the tetrafluoropyridine rings of only about 3 Å. The molecules in the layers are shifted sideways against each other by half a pyridyl ring thus bringing the fluorine atoms to atop of the aromatic carbon atoms and vice versa.     

Sterol-containing tetraphenylethenes: synthesis,aggregation-induced emission,and organogel formation

Cholesterol- and stigmasterol-containing tetraphenylethenes (TPEs) (TPE-Chol and TPE-Stig) are facilely synthesized in satisfactory yields by Cu (I)-catalyzed click reaction of 1,2-bis(4-azidomethylphenyl)-1,2-diphenylethene and cholesteryl-4-ethylbenoate and sigmasteryl 11-(4-ethynylphenoxy)undecanoate, respectively. Whereas they are nonluminescent in solution, they become highly emissive when aggregated in the condensed phase. The molecules of TPE-Stig can self-assemble in methanol solution, generating organogels with gelation-induced emission characteristics.