Further insight into the coordination of 2,5-dicarbothioamidopyrroles: the case of Cu and Co complexes

The coordination chemistry of 2,5-dicarbothioamidopyrrole ligands, namely N2,N5-dibutyl-3,4-diphenyl-1H-pyrrole-2,5-bis(carbothioamide) and N2,N5,3,4-tetraphenyl-1H-pyrrole-2,5-bis(carbothioamide), has been investigated with Cu(II) metal centres by means of X-ray crystallography. This resulted in the formation of the expected planar S,N,S' coordinated complex for the former ligand and unexpected ring-closure reactions, with formation of benzothiazole sidearms, for the latter. Both Cu(II) and Cu(I), used in large excess, were found to favour the ring-closure reaction, although the structural characterisation of the resulting complexes contained only Cu(II) cations, with varying coordination geometries ranging from square planar and square-based pyramidal to tetrahedral. By repeating the reaction using a slight excess of Cu(II) (2?:?1) two more different structures were obtained where the metal was coordinated to the original ligand, N2,N5,3,4-tetraphenyl-1H-pyrrole-2,5-bis(carbothioamide), or to the mixed ligand where only one of the thioamide substituents had converted to a benzothiazole. The essential role of Cu for the ring closure reaction was also established by comparing its complex with structural features of the analogous Co(II) complex, the latter revealing no ring closure to give benzothiazole substituents and co-crystallisation of a mixed Co(II)/Co(III) complex. Finally, the structure and photophysical properties of the corresponding 3,4-diphenyl-2,5-bis(benzothiozol-5-yl)-pyrrole ligand, obtained via treatment of the thioamide with K(3)[Fe(CN)(6)], were also investigated revealing a blue-centered emission.     

Optical and morphological properties of N-doped TiO2 thin films

Nitrogen doped titanium dioxide (TiO₂) thin films were deposited by RF magnetron sputtering onto various substrates. The films were prepared in plasma of argon, oxygen, and nitrogen, with varying the nitrogen content, from 0% up to 70%. The resulting TiOx–Ny films were found to consist of cubic TiN osbornite and tetragonal TiO₂ rutile phases. Using optical spectroscopy with large spectral range from 350 to 1000 nm, the band gap width was determined and a narrowing of the optical gap from 2.76 to 2.32 eV was observed as a function of the N-content. It was found that the optical properties of the TiOx–Ny layers are influenced by the surface morphology, roughness, surface energy and phase content. The chemical composition, the crystalline structure, the surface morphology and the surface energy were thoroughly studied by the Rutherford backscattering spectrometry (RBS), grazing-angle XRD, atomic force microscopy (AFM) and contact angle measurements (wettability), respectively.     

Chemical Investigation of Coloured Minerals in Natural Stones of Commercial Interest

The economic interest in natural stones provides an interesting input to the study of coloured rock-forming minerals. Generally, the colour of a mineral is attributed either to the presence of intrinsically-coloured constituents or of trace elements substituting major elements in the crystallographic sites, or to physical factors such as crystal lattice defects. We have analysed the blue and blue-green silicate minerals dumortierite and amazonite, coming from Mozambique quartzites, and from Malawi and Brazil granitoids, respectively. This study was performed by a multiple analytical approach including (a) a comparison of different signals (optical light-polarized images, backscattered electron images and X-ray multielemental maps); and (b) a collection of quantitative data obtained by WDS systems for major elements, and by WDS and/or micro-PIXE facility for trace elements. A good correlation between Ti concentration zoning and pleochroism variations was observed in dumortierite. In addition, the blue dumortierite of Mozambique, with its unusual significant amounts of antimony (about 5 wt.% Sb₂O₃), represents a mineral with an intermediate composition between dumortierite and holtite. In amazonite the aquamarine colour seems to be related to the Pb content on the order of some hundreds of ppm.     

Templated assembly of a mu6-CO3 2- dodecanuclear lanthanum dibenzoylmethanide hydroxido cluster with concomitant formation of phenylglyoxylate

Reaction of LaCl(3) and dibenzoylmethane (Ph(2)acacH) in methanol with an excess of triethylamine resulted in the unexpected formation of a dodecanuclear hydroxo-bridged La cluster templated by CO(3)(2-) and phenylglyoxylate (Phgly), as determined by X-ray crystallography.     

Synthesis and structural characterisation of cationic, neutral and hydroxo-bridged lanthanoid (La, Gd, Ho, Yb, Y) bis 5-(2-pyridyl)tetrazolate complexes

Reaction of an excess of hydrated LnCl₃ (Ln = La, Gd, Ho, Yb, Y) with sodium 5-(2-pyridyl)tetrazolate (Napytz) in water led to the formation of either cationic disubstituted complexes (La, Gd, Ho) or neutral μ-hydroxo-bridged dimers (Y, Yb). Interestingly, there is a lack of propensity for these disubstituted complexes to redistribute forming trisubstituted ones, which is a common behaviour in lanthanoid chemistry. Also, compared to their corresponding lanthanoid carboxylates, all these products are discrete molecular entities forming an extensive hydrogen-bonded and/or π stacking network rather than hybrid polymeric frameworks.     

Mass spectrometric characterization of metal triflates and triflimides (Lewis superacid catalysts) by electrospray ionization and tandem mass spectrometry

Trifluoromethylsulfonate (triflate) and bis(trifluoromethylsulfonyl)imide (triflimide) salts, well‐known Lewis acid catalysts, present some difficulty in their characterization. By using nitromethane as the solvent, useful electrospray mass spectra in positive and negative ion mode were obtained for salts of metals in oxidation states +2 and +3. In positive mode, addition of a strong Lewis base (triphenylphosphine oxide, TPPO), capable of displacing a triflate (TfO^?) or a triflimide (Tf₂N^?) anion, is necessary for obtaining useful spectra. Under these conditions of solvent and added ligand, the most abundant ions were [M²⁺(A^?)(TPPO)₂]⁺ or [M³⁺(A^?)₂(TPPO)₂]⁺ with A^? = TfO^? or Tf₂N^?. The MS/MS spectra of these diagnostic ions provide additional analytical information. The breakdown curves, in the form of % dissociated as a function of the ion activation energy, offer a mean for investigating the bonding in these ions. Copyright © 2010 John Wiley & Sons, Ltd.     

An insight into the radical thiol/yne coupling: the emergence of arylalkyne-tagged sugars for the direct photoinduced glycosylation of cysteine-containing peptides

An explorative study of the Thiol-Yne Coupling (TYC) reaction has been carried out using an aliphatic (1-octyne) and an aromatic alkyne (phenylacetylene) and two alkanethiols (methyl thioglycolate and N-acetyl-L-cysteine methyl ester). The outcomes of the TYC reactions strongly depend on the experimental conditions (e.g., temperature, solvent, and alkyne/thiol ratio), but these can be properly adjusted to achieve selective production of either mono- or bis-coupling products. With respect to 1-octyne, phenylacetylene undergoes notably easier radical hydrothiolation, further showing a notably higher aptitude for monohydrothiolation exclusive of bis-hydrothiolation. The overall findings were exploited in glycosylation of cysteine derivatives as well as of cysteine-containing peptides. A sugar featuring an arylacetylene moiety gave rise to a true click-reaction, that is, glycosylation of the tripeptide glutathione in its native form, by means of virtually equimolar amounts of reagents. This reaction was successfully applied, under physiological conditions, to a cysteine-containing nonapeptide with marked advantages over the analogous Thiol-Ene Coupling (TEC) derivatization. A TYC/TEC sequence affording bis-armed cysteine derivatives through dual functionalization of an alkynyl sugar was additionally devised.     

Temperature dependence of NMR order parameters and protein dynamics

The helical subdomain, HP36, of the F-actin-binding headpiece domain of chicken villin, is the smallest naturally occurring polypeptide that folds to a thermostable compact structure. Unconstrained molecular dynamics simulations and constrained molecular dynamics simulations using umbrella sampling are used to study the temperature dependence of internal motions of the backbone amide moieties of HP36. The potential of mean force (PMF) for the N-H bond vector, determined from the constrained simulations, is found to be temperature dependent. A simple analytical expression is derived that describes the temperature dependence of the PMF. The parameters of this model are obtained from the PMF, from the unconstrained molecular dynamics simulations, or from experimental values of the generalized order parameter. The results provide a linkage between experimental and theoretical measures of the temperature dependence of protein motions.