Synthesis of functionalized 1H-indenes via copper-catalyzed arylative cyclization of arylalkynes with aromatic sulfonyl chlorides

A variety of polysubstituted 1H-indenes can be prepared through the copper-catalyzed arylative cyclization of simple arylalkynes with commercially available aromatic sulfonyl chlorides that function as an aryl group donor. The reaction tolerates a broad range of functional groups, including bromide and iodide, nitrile, ketone, and nitro groups. The reaction allowed the synthesis of polycyclic aromatic hydrocarbons, such as a bis(indene), indacene, and fused polyarene derivatives, some of them showing strong fluorescence in solution and the solid state.     

Tuning the transport properties of a (C60)2 bridge with electron and hole dopings

The tuning effects of substitutional B and N dopings on the electron transport properties of a C(60) dimer bridge [(C(60))(2)] are investigated by nonequilibrium Green's functions in combination with density functional theory. It is found that, unlike C(60), the equilibrium conductance of (C(60))(2) is very small. However, it can be controlled by electron (N) doping or hole (B) doping, which shifts the molecular energy levels so that the LUMOs or HOMOs align well with the Fermi level and results in LUMO-mediated transport or HOMO-mediated transport. The conductance increases accordingly with a certain number of N or B atoms doped in the C(60)s. Interestingly, when one C(60) is doped with N atoms and the other is doped with B atoms, new transport behaviors arise and rectification is achieved due to the special alignment of the energy levels of the individual C(60)s with the Fermi level. It suggests that cluster or molecule assembling can often realize specific functions which are not available by single molecules and should be taken into consideration in the design of molecular devices.     

A low dielectric constant polyimide/polyoxometalate composite

A silane‐modified mono‐lacunary Keggin‐type polyoxometalate (POM), (Bu₄N)₄[SiW₁₁O₃₉{(CH₂?CH? Si)₂O}] (SiW₁₁? CH?CH₂), was obtained by reaction of vinyltrimethoxysilane with K₈(SiW₁₁O₃₉) in acidic MeCN/H₂O mixed solutions. Then, the modified polyoxometalate was physically blended with the pyromellitic dianhydride (PMDA)‐4,4′‐oxydianiline (ODA) poly(amic acid) and the blends were thermally imidized to form polyimide/ polyoxometalate composites. The X‐ray diffraction (XRD) analysis indicates that the polyoxometalate clusters cannot form crystalline structures in the composite, suggesting that the blending leads to improved compatibility between the polymer matrix and the modified polyoxometalate. The EDS (W‐mapping) studies on the composite films reveal that the polyoxometalate clusters are well dispersed in the polyimide matrix. The physical incorporation of modified POM into polyimide remarkably reduced the dielectric constant of the latter from 3.29 to 2.05 when 20 wt% of SiW₁₁? CH?CH₂ was used. Besides, the addition of the modified POM into polyimide increased the storage modulus of polyimide without severely affecting its thermal properties. Copyright © 2009 John Wiley & Sons, Ltd.     

Species-specific and inhibitor-dependent conformations of LpxC: implications for antibiotic design

LpxC is an essential enzyme in the lipid A biosynthetic pathway in gram-negative bacteria. Several promising antimicrobial lead compounds targeting LpxC have been reported, though they typically display a large variation in potency against different gram-negative pathogens. We report that inhibitors with a diacetylene scaffold effectively overcome the resistance caused by sequence variation in the LpxC substrate-binding passage. Compound binding is captured in complex with representative LpxC orthologs, and structural analysis reveals large conformational differences that mostly reflect inherent molecular features of distinct LpxC orthologs, whereas ligand-induced structural adaptations occur at a smaller scale. These observations highlight the need for a molecular understanding of inherent structural features and conformational plasticity of LpxC enzymes for optimizing LpxC inhibitors as broad-spectrum antibiotics against gram-negative infections.     

Anion induced diversification from heptanuclear to tetranuclear clusters: syntheses, structures and magnetic properties

Three new polynuclear complexes, [Co(7)(bm)(12)]·(ClO(4))(2)·13H(2)O (1), [Co(4)(bm)(4)Cl(4)(C(3)H(7)OH)(4)] (2), and [Co(4)(bm)(4)(μ-HCO(2))(2)(μ(2)-HCO(2))(2)(C(3)H(7)OH)(2)] (3) (Hbm = (1H-Benzimidazol)-methanol), have been synthesized and characterized by elemental analysis, IR, powder X-ray diffraction and X-ray single-crystal diffraction. Compound 1 features a centrosymmetric wheel-like heptanuclear Co(II) cluster. Compound 2 having a I4(1)/a space group exhibits a tetranuclear Co(II) cluster with a cubane topology in which the central Co(II) ion and oxygen atoms from bm occupy the alternate vertices of the cube. However, compound 3 has a tetranuclear Co(II) cluster with a C2/c space group different from that of compound 2. These results show that the geometries and sizes of the corresponding anions as well as their coordinating and hydrogen-bonding properties are essential in determining the final structures of the assemblies. Magnetic properties of 1-3 in the 2-300 K have also been discussed. The {Co(7)} (1) and {Co(4)} (2) cores display dominant ferromagnetic interactions while the {Co(4)} (3) core displays dominant anti-ferromagnetic interactions.     

Interplay of olefin metathesis and multiple hydrogen bonding interactions: covalently cross-linked zippers

Hydrogen-bonded zippers bearing terminal alkene groups were treated with Grubbs' catalyst, leading to covalently cross-linked zippers without violating H-bonding sequence specificity. The yield of a cross-linked zipper depended on the stability of its H-bonded precursor, with a weakly associating pair giving reasonable yields only at high concentrations while strongly associating pairs showed nearly quantitative yields. The integration of thermodynamic (H-bonding) and kinetic (irreversible C═C bond formation) processes suggests the possibility of developing many different covalent association units for constructing molecular structures based on a self-assembling way.     

Fe3O4 nanoparticle-supported copper(I) pybox catalyst: magnetically recoverable catalyst for enantioselective direct-addition of terminal alkynes to imines

An Fe(3)O(4) nanoparticle-supported copper(I) pybox catalyst, which exhibits excellent reactivity and yields products with good enantioselectivity, was developed. As a proof of concept, six optically active propargyl amines were obtained in excellent yields. The catalyst can be magnetically removed and recycled easily six times without a decrease in activity or enantioselectivity.     

Folding-promoted TBACl-mediated chemo- and regioselective demethylations of methoxybenzene-based macrocyclic pentamers

Tetrabutylammonium chloride (TBACl) salt alone has not been shown previously to be capable of removing methoxy groups. It is demonstrated here that the use of TBACl achieves efficient folding-promoted chemo- and regioselective demethylations, eliminating up to two out of five methyl groups situated in similar macrocyclic chemical microenvironments.     

Bilayer matrix composed of polycation/DNA complex and sodium alginate gel as a tumor cell catcher

A bilayer matrix consisting of TABP-SS/DNA complexes and sodium alginate gel is formed via electrostatic interaction. In vitro cell adhesion, proliferation and transfection of the bilayer matrix are investigated in HepG2, HeLa and COS7 cells. Results show that this matrix can only promote tumor cell attachment and growth. Compared with normal cells, the bilayer matrix exhibits significantly higher transfection efficacy in tumor cells. Cell co-culture competitive transfection assay shows that the cell uptake of TABP-SS/DNA complexes is significantly enhanced in tumor cells rather than normal cells under the co-culture competitive condition, which confirms that TABP-SS/DNA complexes have strong tumor cell selectivity and tumor targeting transfection ability.     

A link-free method for testing the significance of predictors

One important step in regression analysis is to identify significant predictors from a pool of candidates so that a parsimonious model can be obtained using these significant predictors only. However, most of the existing methods assume linear relationships between response and predictors, which may be inappropriate in some applications. In this article, we discuss a link-free method that avoids specifying how the response depends on the predictors. Therefore, this method has no problem of model misspecification, and it is suitable for selecting significant predictors at the preliminary stage of data analysis. A test statistic is suggested and its asymptotic distribution is derived. Examples are used to demonstrate the proposed method.