The role of the counteranion in the cation-pi interaction

Chemical double mutant cycles have been used to quantify cation-pi interactions in chloroform as a function of the nature of the counteranion. The cation-pi interaction is -2.5 +/- 0.4 kJ mol(-1) and independent of the anion, even though the overall stability of the complexes varies by an order of magnitude due to competition of the anion for alternative binding sites.     

Multivalent recognition of bis- and tris-Zn-porphyrins by N-methylimidazole functionalized gold nanoparticles

N-Methylimidazole-functionalized gold nanoparticles behave as multivalent ligands for porphyrin arrays with an increase in binding strength of up to three order of magnitude with respect to a monovalent system.     

Synthesis of 2-Acetoxy-2-Methoxy-4-Acetoxymethyl-3,5-Cyclohexadien-1-One by Lead Tetraacetate Oxidation of Homovanillic Acid

An efficient synthesis of the title compound is achieved when homovanillic acid is reacted with lead tetraacetate.     

A modified Gaussian quadrature rule for integrals involving poles of any order

By applying the theory of completely symmetric functions we derive a Gaussian quadrature rule which generalizes that due to McNamee. A feature of this generalization is the inclusion of an explicit correction term taking account of the presence of poles (of any order) of the integrand close to the integration-interval. A numerical example is provided to illustrate the formulae.     

Iridium catalyzed alkylation of 2′-hydroxyacetophenone with alcohols under thermal or microwave conditions

2′-Hydroxyacetophenone was alkylated with a range of substituted benzyl and heteroaryl alcohols to afford the corresponding C-alkylated products in good yields under microwave irradiation. The C-alkylated products were reacted with bromoacetonitrile to afford 2-amino-3-benzyl 1,4-naphthoquinone derivatives in moderate yields.     

Coordination networks from Cu cations and tetrakis(methylthio)benzenedicarboxylic acid: tunable bonding patterns and selective sensing for NH(3) gas

This paper aims to illustrate the rich potential of the thioether-carboxyl combination in generating coordination networks with tunable and interesting structural features. By simply varying the ratio between Cu(NO(3))(2) and the bifunctional ligand tetrakis(methylthio)benzenedicarboxylic acid (TMBD) as the reactants, three coordination networks can be hydrothermally synthesized in substantial yields, which present a distinct evolution with regard to metal-ligand interactions. Specifically, Cu(TMBD)(0.5)(H(2)TMBD)(0.5)·H(2)TMBD (1) was obtained with a relatively small (1:1) Cu(NO(3))(2)/TMBD ratio, and crystallizes as an one-dimensional (1D) coordination assembly based on Cu(I)-thioether interactions, which is integrated by hydrogen-bonding to additional H(2)TMBD molecules to form a three-dimensional (3D) composite network with all the carboxylic acid and carboxylate groups remaining uncoordinated to the metal ions. A medium (1.25:1) Cu(NO(3))(2)/TMBD ratio leads to compound Cu(2)TMBD, in which Cu(I) ions simultaneously bond to the carboxylate and thioether groups, while an even higher (2.4:1) Cu(NO(3))(2)/TMBD ratio produced a mixed-cation compound Cu(II)(2)OHCu(I)(TMBD)(2)·2H(2)O (2), in which the carboxylic groups are bonded to (cupric) Cu(II) ions, and the thioether groups to Cu(I). Despite the lack of open channels in 2, crystallites of this compound exhibit a distinct and selective absorption of NH(3), with a concomitant color change from green to blue, indicating substantial network flexibility and dynamics with regards to gas transport.     

Evolution of near‐surface deformed layers during hot rolling of AA3104 aluminium alloy

In the present study, controlled reheating and breakdown rolling experiments have been carried out and the thickness, structure and uniformity of the resultant near‐surface deformed layer have been characterised by scanning and transmission electron microscopy. High aspect ratio rolling, coupled with an increased rolling speed and rough and worn roll surfaces results in a high degree of interaction between the work roll and work pieces. This generates a shingled surface appearance with a high population of transverse surface cracks and a relatively thick near‐surface deformed layer. In contrast, relatively low aspect ratio rolling, coupled with a reduced rolling speed and freshly ground work roll surfaces generates a relatively thin near‐surface deformed layer. The thickness of the near‐surface deformed layer varies across the alloy surface and is directly related to the shingles, the surface cracks and the distribution of coarse intermetallics. Copyright © 2009 John Wiley & Sons, Ltd.     

Highly efficient on-DNA amide couplings promoted by micelle forming surfactants for the synthesis of DNA encoded libraries

DNA encoded libraries (DELs) represent powerful new technology for finding small molecule ligands for proteins and are increasingly being applied to hit finding in medicinal chemistry. Crucial to the synthesis of high quality DELs is the identification of chemical reactions for their assembly that proceed with very high conversion across a range of different substrates, under conditions compatible with DNA-tagged substrates. Many current chemistries used in DEL synthesis do not meet this requirement, resulting in libraries of low fidelity. Amide couplings are the most commonly used reaction in synthesis of screening libraries and also in DELs. The ability to carry out highly efficient, widely applicable amide couplings in DEL synthesis would therefore be highly desirable. We report a method for amide coupling using micelle forming surfactants, promoted by a modified linker, that is broadly applicable across a wide range of substrates. Most significantly, this works exceptionally well for coupling of DNA-conjugated carboxylic acids (N-to-C) with amines in solution, a procedure that is currently very inefficient. The optimisation of separate procedures for coupling of DNA-conjugated acids and amines by reagent screening and statistically driven optimisation is described. The generality of the method is illustrated by the application to a wide range of examples with unprecedented levels of conversion. The utility of the (N-to-C) coupling of DNA-conjugated acids in DEL synthesis is illustrated by the three cycle synthesis of a fully DNA-encoded compound by two cycles of coupling of an aminoester, with intermediate ester hydrolysis, followed by capping with an amine. This methodology will be of great utility in the synthesis of high fidelity DELs.

Highly efficient forward and reverse on-DNA amide couplings were developed exploiting hydrophobic linkers in combination with the micelle forming surfactant TPGS-750M. The method is highly effective for a wide range of substrates in the synthesis of DNA-encoded libraries.     

The numerical evaluation of the error term in a quadrature formula of Clenshaw-Curtis type for the Gegenbauer weight function

A method is derived for the numerical evaluation of the error term arising in a quadrature formula of Clenshaw-Curtis type for functions of the form (1-x²)^{l- \frac12}f(x)(1-x^{2})^{\lambda - \frac{1}{2}}f(x) over the interval [−1,1]. The method is illustrated by an example.     

Non-interactive geometric probing: Reconstructing non-convex polygons

We address the problem of characterizing polygonal shapes that can be reconstructed from a class of scanners that have asymmetric resolution. We approach this problem using the methodology of non-interactive probing.

Laser raster scanners provide very high precision along the direction of a scan, but it is not practical to place scans very close to each other. A system capable of generating an omni-directional scan pattern can make a series of directional measurements sufficient to permit the reconstruction of a scanned polygon based on the position of edge crossings and the path of the scanning beam between edge crossings. We provide a procedure to reconstruct a polygon from such a data set, as well as a characterization of the shapes that can be reconstructed given a particular scan density. Our system applies to both concave and convex polygons, as well as to polygons containing holes.