First Pre‐Functionalised Polymeric Aromatic Framework from Mononitrotetrakis(iodophenyl)methane and its Applications

Starting from mononitrotetrakis(iodophenyl)methane as monomer, we report the preparation of the first pre‐functionalised porous aromatic frameworks (PAFs) and their application as supports for organometallic catalysts. Neutral coordinate imino‐pyridine Schiff base ( PAF‐NPy ) or chiral bis‐amino ( PAF‐NPro ) ligands were obtained by post‐synthetic treatment of PAF‐NH₂ and treated with copper(I) or rhodium(I) to yield the corresponding supported transition‐metal catalysts. The as‐prepared PAF‐NN‐M catalysts exhibited activity and selectivity similar to that of the corresponding homogeneous catalysts and were easily removed from reaction media and recycled without loss of activity or selectivity.     

Ag2CuMnO4: A new silver copper oxide with delafossite structure

The use of hydrothermal methods has allowed the synthesis of a new silver copper mixed oxide, Ag₂CuMnO₄, the first example of a quaternary oxide containing both elements. It crystallizes with the delafossite 3R structure, thus being the first delafossite to contain both Ag and Cu. Synthesis conditions affect the final particle size (30-500 nm). Powder X-ray diffraction Rietveld refinement indicates a trigonal structure and cell parameters and , where Cu and Mn are disordered within the octahedral B positions in the plane and linearly coordinated Ag occupies de A position between layers. X-ray absorption near edge spectroscopy (XANES) for copper and manganese, and XPS for silver evidence +2, +4, and +1 oxidation states. The microstructure consists of layered particles that may form large twins showing 5 nm nanodomains. Finally, magnetic measurements reveal the existence of ferromagnetic coupling yielding in-plane moments that align antiferromagnetically at lower temperatures. The singularity of the new phase resides on the fact that is an example of a bidimensional arrangement of silver and copper in an oxide that also shows clear bidimensionality in its physical properties. That is of special relevance to the field of high T_c superconducting oxides, while the ferromagnetic coupling in a bidimensional system deserves itself special attention.     

A singular perturbation problem with discontinuous data in a cuboid

We analyse the asymptotic behaviour of the solution of a 3Dsingularly perturbed convection–diffusion problem withdiscontinuous Dirichlet boundary data defined in a cuboid. Wewrite the solution in terms of a double series and we obtainan asymptotic approximation of the solution when the singularparameter 0. This approximation is given in terms of a finitecombination of products of error functions and characterizesthe effect of the discontinuities on the small -behaviour ofthe solution in the singular layers.     

The natural constituents of historical textile dyes

The sources and structures of dyes used to colour Western historical textiles are described in this tutorial review. Most blue and purple colours were derived from indigo--obtained either from woad or from the indigo plant--though some other sources (e.g. shellfish and lichens) were used. Reds were often anthraquinone derivatives obtained from plants or insects. Yellows were almost always flavonoid derivatives obtained from a variety of plant species. Most other colours were produced by over-dyeing--e.g. greens were obtained by over-dyeing a blue with a yellow dye. Direct analysis of dyes isolated from artefacts allows comparison with the historical record.     

Comparison of two extraction methods for the determination of selective serotonin reuptake inhibitors in sewage sludge by hollow fiber liquid-phase microextraction

This paper presents two procedures for the determination of four selective serotonin reuptake inhibitors (citalopram, paroxetine, fluoxetine, and sertraline) and one metabolite (norfluoxetine) in sewage sludge utilizing three-phase hollow fiber liquid-phase microextraction (HF-LPME). First, direct HF-LPME was used for extraction, clean-up, and preconcentration. The pharmaceuticals were extracted from slurry samples into an organic phase and then back-extracted into an aqueous phase in the lumen of the hollow fiber. Second, a procedure combining pressurized hot water extraction and HF-LPME for clean-up and preconcentration was developed for the same analytes and matrix. The extracts were subsequently analyzed by liquid chromatography-mass spectrometry. For direct HF-LPME, limits of detection were between 1 and 12 ng g(-1) (dry weight) and the relative standard deviation (RSD) values were 3-12%. For the second method, limits of detection were approximately 6 ng g(-1) for all the compounds and RSD values were 8-12%. The methods were validated by comparison of results for the same samples. Sewage sludge from a Swedish wastewater treatment plant was analyzed by both methods; average concentrations were similar for citalopram, paroxetine, and fluoxetine with values of approximately 530, 40, and 200 ng g(-1) , respectively.     

From red to near infra-red OLEDs: the remarkable effect of changing from X = -Cl to -NCS in a cyclometallated [Pt(N^C^N)X] complex {N^C^N = 5-mesityl-1,3-di-(2-pyridyl)benzene}

[PtL(6)X] {X = Cl or NCS and L(6) = 5-mesityl-1,3-di(2-pyridyl)-benzene} display similar luminescence in solution but, in the solid state, the packing of the molecules is different, with short PtPt interactions for X = NCS, leading to a red-shifted emission band. The effect has been used to generate OLEDs that emit squarely in the NIR region (855 nm).     

Sequential ring-closing metathesis–vinyl halide Heck cyclization reactions: access to the tetracyclic ring system of ervitsine

A chemoselective indole-templated ring-closing metathesis is used to assemble the cyclohepta[b]indole substructure of the indole alkaloid ervitsine. A subsequent intramolecular Heck coupling of the resulting alkene functionality with an amino-tethered vinyl halide accomplishes the closure of the unique 2-azabicyclo[4.3.1]decane framework of the alkaloid with concomitant incorporation of the exocyclic E-ethylidene substituent.     

ESR, electrochemical, molecular modeling and biological evaluation of 4-substituted and 1,4-disubstituted 7-nitroquinoxalin-2-ones as potential anti-Trypanosoma cruzi agents

Electrochemical and ESR studies were carried out in this work with the aim of characterizing the reduction mechanisms of 4-substituted and 1,4-disubstituted 7-nitroquinoxalin-2-ones by means of cyclic voltammetry in DMSO as aprotic solvent. Two reduction mechanisms were found for these compounds: the first, for compounds bearing a labile hydrogen by following a self-protonation mechanism (ECE steps), and the second, for compounds without labile hydrogen, based on a purely electrochemical reduction mechanism (typical of nitroheterocycles). The electrochemical results were corroborated using ESR spectroscopy allowing us to propose the hyperfine splitting pattern of the nitro-radical, which was later corroborated by the ESR simulation spectra. All these compounds were assayed as growth inhibitors against Trypanosoma cruzi: first, on the non-proliferative (and infective) form of the parasite (trypomastigote stage), and then, the ones that displayed activity, were assayed on the non-infective form (epimastigote stage). Thus, we found four new compounds highly active against T. cruzi. Finally, molecular modeling studies suggest the inhibition of the trypanothione reductase like one of the possible mechanisms involved in the trypanocidal action.