Syntheses, structures, and characterizations of four new silver(I) sulfonate coordination polymers with neutral ligands

In this paper, four novel silver(I) sulfonate coordination polymers containing neutral ligands, namely, [Ag(2)Ll (biim)(2)]center dot 2H(2)O (1). AgL2(biim) (2), [Ag(HL3)(Pic)(2)]center dot H2O (3), and [Ag-3(L3)(HL3)(4,4'-bipy)(3)(H2O)(2)]center dot 4H(2)O (4), have been synthesized [L1 = 3-carboxy-4-hydroxybenzenesulfonate, L2 = p-aminobenzenesulfonate, H(2)L3 = p-hydroxybenzenesulfonic acid, biim = 1,1'-(1.4-butanediyl)-bis(imidazole), Pic = beta-picoline, 4,4'-bipy = 4,4'-bipyridine]. For compounds 1 and 2, Ag(I) cations are bridged by biim ligands to form a one-dimensional (1D) "zigzag" chain, and L1 and L2 sulfonate ligands are not coordinated to the silver cation. Compound 3 has a dimeric structure in which two silver cations are bridged by two HL3 ligands. For compound 4, L3 ligand coordinates to a silver cation as a monodentate ligand, and Ag(l) cations are bridged by 4,4'-bipy ligands to form a ID chain. Compound 1 contains water dimers, while compound 4 contains water trimers. Compounds 1-3 display room-temperature photoluminescence.

Geometries and electronic properties of Ta-n, TanO and TaOn (n=1-3) clusters

Geometries, vibrational frequencies, electron affinities, ionization potentials and dissociation energies of the title clusters in both neutral and positively and negatively charged states were studied by use of density functional theory. For both neutral and charged species, different initial isomers were studied in order to determine the structure with the lowest energy. Vibrational analysis was also performed in order to characterize these isomers. For Ta-2, Ta-Ta metallic bond is strengthened by adding or removing an electron, i.e. the charged species are much more stable than the neutral counterpart. For Ta-3, equilateral triangle with D-3h symmetry has the lowest energy for both neutral and charged species (near equilateral triangle for cation). TaO and its charged species have much larger dissociation energy compared with other tantalum oxides. For Ta2O and TaO2. structure with C-2v symmetry is much more stable than linear chains. For Ta3O, planar structure with doubly bridging oxygen atoms of C-2v, symmetry is the global minimum for both neutral and charged species. While for TaO3, three-dimensional structures are favored for both neutral (C-1 symmetry) and charged species (C-3v symmetry).

Syntheses and crystalline structures of clusters Co-3(CO)(7)(mu(3)-S)(mu, eta(2)-SCNR2)

Through the reaction of Co-2(CO)(8) with four thiuram [R2NC(S)S](2), four new sulfur-capped trinuclear cobalt carbonyl clusters Co-3 (CO)(7) (mu(3)-S) (mu, eta(2)-S* C* NR2) ( I : R = Me; I : R = Et; II : R = i-Pr; IV : NR= -N [GRAPHICS] were prepared and characterized by elementary analysis, IR,H-1 NMR and MS spectroscopy. The crystal structure of the cluster Co-3(CO)(7)(mu(3)-S)[mu, eta(2)-S*C*N (i-Pr)(2)]( III) was determined by X-ray single crystal diffraction method. The crystal of m is monoclinic, belonging to space group P2(1)/n, and the cell parameters are as follows: a = 1, 145 2(2) nm, b = 1. 502 8(3) nm, c = 1, 214 4(2) nmj alpha = 90 degrees, beta = 92, 15(3)degrees, gamma = 90 degrees; V = 2. 088 5(7) nm(3) , Z = 4, F (000) = 1 096, D-c = 1. 747 mg . m(-3), mu = 2. 588 mm(-1), R=0. 040 7, R-w=0. 062 4, The structural analysis shows that cluster II has a pyrimidal Co3S framework and contains a heterocylic bridging bidentate ligand [mu, eta(2)-S* C* N (i-Pr)(2)] linked to the Co2 and Co3 atoms of the cluster by a cobalt-carbon and a cobalt-sulfur bond respectively.

Controlled growth of uniform silver clusters on HOPG

We have investigated growth of silver clusters on three different, i.e. normally cleaved, thermally oxidized and Ar+ ion sputtered highly oriented pyrolytic graphite (HOPG), surfaces. Scanning tunneling microscopy (STM) observations reveal that uniformly sized and spaced Ag clusters only form on the sputtered surface. Ar+ sputtering introduces relatively uniform surface defects compared to other methods. These defects are found to serve as preferential sites for Ag cluster nucleation, which leads to the formation of uniform clusters. (c) 2005 Elsevier B.V. All rights reserved.

The VLT-FLAMES survey of massive stars: Observations in the Galactic clusters NGC 3293, NGC 4755 and NGC 6611

We introduce a new survey of massive stars in the Galaxy and the Magellanic Clouds using the Fibre Large Array Multi- Element Spectrograph ( FLAMES) instrument at the Very Large Telescope ( VLT). Here we present observations of 269 Galactic stars with the FLAMES- Giraffe Spectrograph ( R similar or equal to 25 000), in fields centered on the open clusters NGC3293, NGC4755 and NGC6611. These data are supplemented by a further 50 targets observed with the Fibre- Fed Extended Range Optical Spectrograph ( FEROS, R = 48 000). Following a description of our scientific motivations and target selection criteria, the data reduction methods are described; of critical importance the FLAMES reduction pipeline is found to yield spectra that are in excellent agreement with less automated methods. Spectral classifications and radial velocity measurements are presented for each star, with particular attention paid to morphological peculiarities and evidence of binarity. These observations represent a significant increase in the known spectral content of NGC3293 and NGC4755, and will serve as standards against which our subsequent FLAMES observations in the Magellanic Clouds will be compared.

Iron abundances of B-type post-asymptotic giant branch stars in globular clusters: Barnard29 in M13 and ROA5701 in ωCen

High-resolution optical and ultraviolet (UV) spectra of two B-type post-asymptotic giant branch (post-AGB) stars in globular clusters, Barnard29 in M13 and ROA5701 in ?Cen, have been analysed using model atmosphere techniques. The optical spectra have been obtained with FEROS on the ESO 2.2-m telescope and the 2d-Coudé spectrograph on the 2.7-m McDonald telescope, while the UV observations are from the Goddard high-resolution spectrograph on the Hubble Space Telescope (HST). Abundances of light elements (C, N, O, Mg, Al and S) plus Fe have been determined from the optical spectra, while the UV data provide additional Fe abundance estimates from FeIII absorption lines in the 1875-1900 Å wavelength region. A general metal underabundance relative to young B-type stars is found for both Barnard29 and ROA5701. These results are consistent with the metallicities of the respective clusters, as well as with previous studies of the objects. The derived abundance patterns suggest that the stars have not undergone a gas-dust separation, contrary to previous suggestions, although they may have evolved from the AGB before the onset of the third dredge-up. However, the Fe abundances derived from the HST spectra are lower than those expected from the metallicities of the respective clusters, by 0.5 dex for Barnard29 and 0.8 dex for ROA5701. A similar systematic underabundance is also found for other B-type stars in environments of known metallicity, such as the Magellanic Clouds. These results indicate that the FeIII UV lines may yield abundance values which are systematically too low by typically 0.6 dex and hence such estimates should be treated with caution.

The death of massive stars - I. Observational constraints on the progenitors of Type II-P supernovae

We present the results of a 10.5-yr, volume-limited (28-Mpc) search for supernova (SN) progenitor stars. In doing so we compile all SNe discovered within this volume (132, of which 27 per cent are Type Ia) and determine the relative rates of each subtype from literature studies. The core-collapse SNe break down into 59 per cent II-P and 29 per cent Ib/c, with the remainder being IIb (5 per cent), IIn (4 per cent) and II-L (3 per cent). There have been 20 II-P SNe with high-quality optical or near-infrared pre-explosion images that allow a meaningful search for the progenitor stars. In five cases they are clearly red supergiants, one case is unconstrained, two fall on compact coeval star clusters and the other twelve have no progenitor detected. We review and update all the available data for the host galaxies and SN environments (distance, metallicity and extinction) and determine masses and upper mass estimates for these 20 progenitor stars using the STARS stellar evolutionary code and a single consistent homogeneous method. A maximum likelihood calculation suggests that the minimum stellar mass for a Type II-P to form is m(min) = 8.5(-1.5)(+1) M-circle dot and the maximum mass for II-P progenitors is m(max) = 16.5 +/- 1.5 M-circle dot, assuming a Salpeter initial mass function holds for the progenitor population (in the range Gamma = -1.35(-0.7)(+0.3)). The minimum mass is consistent with current estimates for the upper limit to white dwarf progenitor masses, but the maximum mass does not appear consistent with massive star populations in Local Group galaxies. Red supergiants in the Local Group have masses up to 25 M-circle dot and the minimum mass to produce a Wolf-Rayet star in single star evolution (between solar and LMC metallicity) is similarly 25-30 M-circle dot. The reason we have not detected any high-mass red supergiant progenitors above 17 M-circle dot is unclear, but we estimate that it is statistically significant at 2.4 sigma confidence. Two simple reasons for this could be that we have systematically underestimated the progenitor masses due to dust extinction or that stars between 17-25 M-circle dot produce other kinds of SNe which are not II-P. We discuss these possibilities and find that neither provides a satisfactory solution. We term this discrepancy the 'red supergiant problem' and speculate that these stars could have core masses high enough to form black holes and SNe which are too faint to have been detected. We compare the Ni-56 masses ejected in the SNe to the progenitor mass estimates and find that low-luminosity SNe with low Ni-56 production are most likely to arise from explosions of low-mass progenitors near the mass threshold that can produce a core-collapse.

Facile in situ synthesis of nanofluids based on ionic liquids and copper oxide clusters and nanoparticles

Two stable nanofluids comprising of mixed valent copper(_I,_II) oxide clusters (<1 nm) suspended in 1-butyl-3-methylimidazolium acetate, [C(₄)mim][OAc], and copper(_II) oxide nanoparticles (<50 nm) suspended in trioctyl(dodecyl) phosphonium acetate, [P-₈₈₈₁₂][OAc], were synthesised in a facile one-pot reaction from solutions of copper(_II) acetate hydrate in the corresponding ionic liquids. Formation of the nanostructures was studied using ¹³C NMR spectroscopy and differential scanning calorimetry (DSC). From a solution of Cu(OAc)₂ in 1-ethyl-3-methylimidazolium acetate, [C₂mim][OAc], crystals were obtained that revealed the structure of [C₂mim][Cu₃(OAc)₅(OH)₂(H₂O)]center dot H₂O, indicating the formation of copper hydroxo-clusters in the course of the reaction. Synthesised nanostructures were studied using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Physical properties of the prepared IL-nanofluids were examined using IR and UV-VIS spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and densitometry. 

Pan-genome analysis of the emerging foodborne pathogen Cronobacter spp. suggests a species-level bidirectional divergence driven by niche adaptation

Background: Members of the genus Cronobacter are causes of rare but severe illness in neonates and preterm infants following the ingestion of contaminated infant formula. Seven species have been described and two of the species genomes were subsequently published. In this study, we performed comparative genomics on eight strains of Cronobacter, including six that we sequenced (representing six of the seven species) and two previously published, closed genomes.

Results: We identified and characterized the features associated with the core and pan genome of the genus Cronobacter in an attempt to understand the evolution of these bacteria and the genetic content of each species. We identified 84 genomic regions that are present in two or more Cronobacter genomes, along with 45 unique genomic regions. Many potentially horizontally transferred genes, such as lysogenic prophages, were also identified. Most notable among these were several type six secretion system gene clusters, transposons that carried tellurium, copper and/or silver resistance genes, and a novel integrative conjugative element.

Conclusions: Cronobacter have diverged into two clusters, one consisting of C. dublinensis and C. muytjensii (Cdub-Cmuy) and the other comprised of C. sakazakii, C. malonaticus, C. universalis, and C. turicensis, (Csak-Cmal-Cuni-Ctur) from the most recent common ancestral species. While several genetic determinants for plant-association and human virulence could be found in the core genome of Cronobacter, the four Cdub-Cmuy clade genomes contained several accessory genomic regions important for survival in a plant-associated environmental niche, while the Csak-Cmal-Cuni-Ctur clade genomes harbored numerous virulence-related genetic traits.

In situ FTIR spectroscopy studies on electrochemical redox processes of high nuclearity osmium carbonyl clusters

The electrochemical redox processes of two high nuclearity osmium carbonyl clusters [(PhP)N[OsC(CO) ]·PPN (1) and Os(CO) (6) have been studied by electrochemical in situ FTIR. The five oxidation states of 1, i.e., [OsC(CO)], have been characterized. There are no significant structural changes for these species. Hence, the ability of this decanuclear cluster to act as an electron reservoir has been demonstrated. The structural rearrangement associated with the two-electron reduction of bicapped tetrahedral 6 to octahedral dianion [Os(CO)] and [Os(CO)] tetraanion has also been investigated. © 1996 American Chemical Society.

Theorizing temporary spatial clusters and institutional boundary-work in industrial markets

To better understand the nature of temporary spatial clusters (TSC’s) in industrial marketing settings, this conceptual paper first provides a theoretical synthesis of spatial understanding from the industrial marketing (IM) and economic geography (EG) fields, focusing particularly on Doreen Massey’s work on relational space. This leads to a conceptual schema for organizing the IM literature in terms of spatiality, and which also helps clarify the ontological nature of TSCs. We then move to introduce the notion of institutional boundary-work, drawing on the work of Thomas Gieryn, and Andrea Brighenti’s examination of territorology, to conceptualize the activities of market actors engaged in the ongoing social accomplishment of TSCs. Such activities, we suggest, involve these actors ‘marching’ boundaries to assume network influence and maintain market order in IM settings. In summary, therefore, our paper addresses two fundamental questions: i) How do we conceptualize the form of TSCs in IM settings? And, ii) what function(s) are TSCs performing (and how is this being undertaken) in IM? The paper closes by providing methodological guidance for how a research agenda on TSCs within IM activity might be developed, followed by a summary of the managerial implications that emerge from our theorizations.

Kaire. 1843. G. [Gami] El Hakem. M [...] [sic] : [i.e. Château Saint-Pierre, Bodrum, Turquie] : [photographie] / [Joseph Philibert Girault de Prangey]

Ancien possesseur : Simony, Charles de (Cte Anne Marie Charles de)

Electron Transfer Involving the Phylloquinone (A1) Cofactor of Photosystem I Examined with Time Resolved Absorbance and Electron Paramagnetic Resonance Spectroscopy

The dependence of the electron transfer (ET) rate on the Photosystem I (PSI) cofactor phylloquinone (A1) is studied by time-resolved absorbance and electron paramagnetic resonance (EPR) spectroscopy. Two active branches (A and B) of electron transfer converge to the FX cofactor from the A1A and A1B quinone. The work described in Chapter 5 investigates the single hydrogen bond from the amino acid residue PsaA-L722 backbone nitrogen to A1A for its effect on the electron transfer rate to FX. Room temperature transient EPR measurements show an increase in the rate for the A1A- to FX for the PsaA-L722T mutant and an increased hyperfine coupling to the 2-methyl group of A1A when compared to wild type. The Arrhenius plot of the A1A- to FX ET in the PsaA-L722T mutant suggests that the increased rate is probably the result of a slight change in the electronic coupling between A1A- and FX. The reasons for the non-Arrhenius behavior are discussed. The work discussed in Chapter 6 investigates the directionality of ET at low temperature by blocking ET to the iron-sulfur clusters FX, FA and FB in the menB deletion mutant strain of Synechocyctis sp. PCC 6803, which is unable to synthesize phylloquinone, by incorporating the high midpoint potential (49 mV vs SHE) 2,3-dichloro-1,4-naphthoquinone (Cl2NQ) into the A1A and A1B binding sites. Various EPR spectroscopic techniques were implemented to differentiate between the spectral features created from A and B- branch electron transfer. The implications of this result for the directionality of electron transfer in PS I are discussed. The work discussed in Chapter 7 was done to study the dependence of the heterogeneous ET at low temperature on A1 midpoint potential. The menB PSI mutant contains plastiquinone-9 in the A1 binding site. The solution midpoint potential of the quinone measures 100 mV more positive then wild-type phylloquinone. The irreversible ET to the terminal acceptors FA and FB at low temperature is not controlled by the forward step from A1 to FX as expected due to the thermodynamic differences of the A1 cofactor in the two active branches A and B. Alternatives for the ET heterogeneity are discussed.

Synthesis, properties and characterization of N-Alkyl substituted b-Diketiminato copper(I) Complexes

Le ligand nacnacxylH (xyl = C6Me2H3) et les ligands dikétimines N-alkyle substitués (nacnacCH(Me)PhH, nacnacBnH and nacnaciPrH) ont été préparés avec de bons rendements à l’exception du nacnaciPrH (23%) en utilisant un protocole en une étape et à l’aide d’un montage Dean-Stark. La réaction du S,S-nacnacCH(Me)PhH et du nacnacBnH avec le nBuLi dans le THF conduit au S,S-nacnacCH(Me)PhLi(THF) et au nacnacBnLi(THF). Les tentatives de bromation de ces composés par le N-bromosuccinimide conduisent plutôt aux ligands S,S-succnacnacCH(Me)PhH et succnacnacBnH (succ = succinimido) substitués par un groupement succinimido sur le carbone  La chloration par le N-chlorosuccinimide conduit au produit désiré, mais avec des impuretés. La réaction de ces ligands avec le CuOtBu (ou bien MesCu, où Mes = C6Me3H2, et une quantité catalytique de CuOtBu) en présence de bases de Lewis donne les (nacnacxylCu)2(-toluène), nacnacxylCuCNC6H3(Me)2, nacnacCH(Me)PhCuL (L = PPh3, PMe3, CNC6H3(Me)2, DMAP, lutidine, Py, MeCN), nacnacBnCuL (L = PPh3, CNC6H3(Me)2, styrène, trans-stilbene, phenylvinylether, acrylonitrile, diphenylacetylène), nacnaciPrCuL (L = PPh3, CNC6H3(Me)2, MeCN) et le succnacnacCH(Me)PhCuL (PPh3, CNC6H3(Me)2, pyridine). Tous ces complexes sont jaunes et sensibles à l’air et à l’humidité. En l’absence de fortes bases de Lewis, on n’observe pas de réaction entre les précurseurs de cuivre et les ligands N-alkyle substitués. Les études RMN des complexes dans le C6D6 ne présentent pas de complexe de toluène mais un mélange à l’équilibre du (nacnacxylCu)2(-C6D6) et nacnacxylCu(C6D6) dans une proportion de 2 pour 1. Alors que l’addition de plus de cinquante équivalents soit de THF, soit de toluène n’induit aucun changement des spectres RMN, l’addition de 2 équivalents de MeCN conduit instantanément au complexe nacnacxylCu(MeCN). De plus, le (nacnacxylylCu)2(-C6D6) ne se coordone ni ne réagit avec le N2O, même après avoir été chauffé à 60°C pendant treize jours. En présence de DPA (diphenylacétylène), la réaction du nacnacBnH avec le CuOtBu conduit au dimère ponté (nacnacBnCu)2(µ-DPA). L’addition d’un excès de DPA (10-12 équivalents) transforme le dimère ponté en complexe lié en position terminale nacnacBnCuDPA. Les nacnacRH (R = CH(Me)Ph et i-Pr) ne forment pas de complexe ni avec les oléfines ni avec le DPA. Une réactivité similaire a été observée avec les complexes de nacnacCH(Me)PhCu(NCMe) et nacnaci-PrCu(NCMe). Tandis que le complexe lié en position terminale par MeCN a été isolé et caractérisé, l’équilibre en solution nous laisse suspecter la formation d’un complexe d’acétonitrile ponté. Des études de réactivité comparatives ont été menées sur quelques complexes de cuivre. La Morpholine ne réagit pas avec le nacnacBnCu(acrylonitrile) contrairement à l’acrylonitrile libre. L’expérience de l’échange d’oléfine montre que l’acrylonitrile (une oléfine électro-attractrice) se lie plus fortement que les autres oléfines, mettant ainsi en évidence l’importance de la rétrodonation  face à la donation La rétrodonation est cependant faible comparée aux autres complexes de styrène structurellement caractérisés. Les complexes nacnacCH(Me)PhCuL (L = PPh3 et MeCN) ont été employés dans la cyclopropanation catalytique du styrène et dans l’addition conjuguée du ZnEt2 sur la 2-cyclohexénone, mais les résultats indiquent que le ligand dikétimine est éliminé avant son entrée dans le cycle catalytique. Par conséquent, il n’y a pas d’induction chirale. Les complexes tétra coordinées de cuivre avec les nacnacRCu(phen) (R = Bn, CH(Me)Ph et Phen = 1,10-phenanthroline, 2-Mes-1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline (dmp) et 2,9-diphenyl-1,10-phenanthroline (dpp)) ont été synthétisés. Ces complexes sont d’une intense couleur bleue et des interactions d’empilement entre l’un des cycles phényle des ligands nacnac et la phénanthroline ont été observées dans les structures à l’état solide. Les mesures en absorption UV-visible ont été effectuées dans le toluène et les bandes MLCT sont déplacées vers le rouge par rapport à celles des complexes de cuivre et bisphénanthroline. Tous ces composés émettent à l’état solide mais les complexes 1,10-phenanthroline et 2-Mes-1,10-phenanthroline n’émettent pas en solution. Pour renforcer les interactions d’empilement , les nouveaux ligands nacnacRH (R = CH2C6H2(OMe)3, CH2C6F5) et leurs complexes de cuivre respectifs ont été préparés avec du dmp et dpp. Afin de permettre la comparaison, le nacnaciBuCu(dmp) a été synthétisé. Alors que les complexes dmp montrent une augmentation des interactions intramoléculaires - avec les substituants phényle du ligand dikétimine et de la phénanthroline, les complexes dpp ne révèlent pas de telles interactions. Les complexes perfluorés montrent, en absorption et en émission, un déplacement significatif vers le bleu, alors que les complexes substitués par un groupements isobutyle présentent des transitions déplacées vers le rouge. Alors que les intensités de luminescence et les durées de vie sont faibles, les déplacements réduits de Stokes et les pics étroits de luminescence comparables indiquent une réduction des distorsions de l’état excité.

Two-dimensional clusters of liquid 4He

The binding energies of two-dimensional clusters (puddles) of¿4He are calculated in the framework of the diffusion Monte Carlo method. The results are well fitted by a mass formula in powers of x=N-1/2, where N is the number of particles. The analysis of the mass formula allows for the extraction of the line tension, which turns out to be 0.121 K/Å. Sizes and density profiles of the puddles are also reported.