Cleavage of Ge–S and C–H bonds in the reaction of electron-deficient [Os₃(CO)₈(μ-H)(μ₃-Ph₂PCH₂P(Ph)C₆H₄)] with Ph₃GeSPh: Generation of thiophenol derivatives [Os₃(CO)₈(μ-H)(μ-SPh)(μ-dppm)] and [Os₃(CO)₇(μ-H)(μ-SPh)(μ₃-SC₆H₄)(μ-dppm)]

Heating the electron-deficient [Os₃(CO)₈(μ-H)(μ₃-Ph₂PCH₂P(Ph)C₆H₄)] (1) and Ph₃GeSPh in benzene at 80 °C led to the thiolato bridged compounds, [Os₃(CO)₈(μ-H)(μ-SPh)(μ-dppm)] (2) and [Os₃(CO)₇(μ-H)(μ-SPh)(μ₃-SC₆H₄)(μ-dppm)] (3), formed by cleavage of Ge–S and C–S bonds of the ligand, in 40% and 17% yields, respectively. Both compounds 2 and 3 have been characterized by a combination of elemental analysis, infrared and ¹H NMR spectroscopic data together with single crystal X-ray crystallography. Compound 3 contains an open triangle of osmium atoms bridged by a SPh and SC₆H₄ ligands on opposite sides of the cluster with a dppm ligand bridging one of the Os–Os edges. Compound 2 consists of a closed triangular cluster of osmium atoms with a bridging SPh, and a bridging hydride ligand on the same Os–Os edge, and a dppm ligand bridging one of the remaining Os–Os edges

Ruthenium and osmium carbonyl clusters incorporating stannylene and stannyl ligands

The reaction of [Ru₃ (CO)₁₂] with Ph₃SnSPh in refluxing benzene furnished the bimetallic Ru-Sn compound [Ru₃(CO)₈(μ-SPh)₂(μ3-SnPh₂)(SnPh₃)₂] 1 which consists of a SnPh₂ stannylene bonded to three Ru atoms to give a planar tetra-metal core, with two peripheral SnPh₃ ligands. The stannylene ligand forms a very short bond to one Ru atom [Sn-Ru 2.538(1) Å] and very long bonds to the other two [Sn-Ru 3.074(1) Å]. The germanium compound [Ru₃(CO)₈(μ-SPh)₂(μ₃-GePh₂)(GePh₃)₂] 2 was obtained from the reaction of [Ru₃ (CO)₁₂] with Ph₃GeSPh and has a similar structure to that of 1 as evidenced by spectroscopic data. Treatment of [Os₃(CO)₁₀(MeCN)₂] with Ph₃SnSPh in refluxing benzene yielded the bimetallic Os-Sn compound [Os₃(CO)₉(μ-SPh)(μ₃-SnPh₂)(MeCN)(ƞ¹-C₆H₅)] 3. Cluster 3 has a superficially similar planar metal core, but with a different bonding mode with respect to that of 1. The Ph₂Sn group is bonded most closely to Os(2) and Os(3) [2.7862(3) and 2.7476(3) Å respectively] with a significantly longer bond to Os(1), 2.9981(3) Å indicating a weak back-donation to the Sn. The reaction of the bridging dppm compound [Ru₃(CO)₁₀(μ-dppm)] with Ph₃SnSPh afforded [Ru₃(CO)₆(μ-dppm)(μ₃-S)(μ₃-SPh)(SnPh₃)] 5. Compound 5 contains an open triangle of Ru atoms simultaneously capped by a sulfido and a PhS ligand on opposite sides of the cluster with a dppm ligand bridging one of the Ru-Ru edges and a Ph₃Sn group occupying an axial position on the Ru atom not bridged by the dppm ligand

An electron-deficient triosmium cluster containing the thianthrene ligand: Synthesis, structure and reactivity of [Os₃(CO)₉(μ3-η2-C₁₂H₇S₂)(μ-H)]

Reaction of [Os₃(CO)₁₀(CH₃CN)₂] with thianthrene at 80 °C leads to the nonacarbonyl dihydride compound [Os₃(CO)₉(μ-3,4-η²-C₁₂H₆S₂)(μ-H)₂] (1) and the 46-electron monohydride compound [Os₃(CO)₉(μ₃-η²-C₁₂H₇S₂)(μ-H)] (2). Compound 2 reacts reversibly with CO to give the CO adduct [Os₃(CO)₁₀(μ-η²-C₁₂H₇S₂)(μ-H)] (3) whereas with PPh₃ it gives the addition product [Os₃(CO)₉)(PPh₃)(μ-η²-C₁₂H₇S₂)(μ-H)] (4) as well as the substitution product 1,2-[Os₃(CO)₁₀ ((PPh₃)₂] (5) Compound 2 represents a unique example of an electron-deficient triosmium cluster in which the thianthrene ring is bound to cluster by coordination of the sulfur lone pair and a three-center-two-electron bond with the C(2) carbon which bridges the same edge of the triangle as the hydride. Electrochemical and DFT studies which elucidate the electronic properties of 2 are reported

Automatic Spectroscopic Data Categorization by Clustering Analysis (ASCLAN): A Data-Driven Approach for Distinguishing Discriminatory Metabolites for Phenotypic Subclasses

We propose a novel data-driven approach aiming to reliably distinguish discriminatory metabolites from nondiscriminatory metabolites for a given spectroscopic data set containing two biological phenotypic subclasses. The automatic spectroscopic data categorization by clustering analysis (ASCLAN) algorithm aims to categorize spectral variables within a data set into three clusters corresponding to noise, nondiscriminatory and discriminatory metabolites regions. This is achieved by clustering each spectral variable based on the r(2) value representing the loading weight of each spectral variable as extracted from a orthogonal partial least-squares discriminant (OPLS-DA) model of the data set. The variables are ranked according to r(2) values and a series of principal component analysis (PCA) models are then built for subsets of these spectral data corresponding to ranges of r(2) values. The Q(2)X value for each PCA model is extracted. K-means clustering is then applied to the Q(2)X values to generate two clusters based on minimum Euclidean distance criterion. The cluster consisting of lower Q(2)X values is deemed devoid of metabolic information (noise), while the cluster consists of higher Q(2)X values is then further subclustered into two groups based on the r(2) values. We considered the cluster with high Q(2)X but low r(2) values as nondiscriminatory, while the cluster with high Q(2)X and r(2) values as discriminatory variables. The boundaries between these three clusters of spectral variables, on the basis of the r(2) values were considered as the cut off values for defining the noise, nondiscriminatory and discriminatory variables. We evaluated the ASCLAN algorithm using six simulated (1)H NMR spectroscopic data sets representing small, medium and large data sets (N = 50, 500, and 1000 samples per group, respectively), each with a reduced and full resolution set of variables (0.005 and 0.0005 ppm, respectively). ASCLAN correctly identified all discriminatory metabolites and showed zero false positive (100% specificity and positive predictive value) irrespective of the spectral resolution or the sample size in all six simulated data sets. This error rate was found to be superior to existing methods for ascertaining feature significance: univariate t test by Bonferroni correction (up to 10% false positive rate), Benjamini-Hochberg correction (up to 35% false positive rate) and metabolome wide significance level (MWSL, up to 0.4% false positive rate), as well as by various OPLS-DA parameters: variable importance to projection, (up to 15% false positive rate), loading coefficients (up to 35% false positive rate), and regression coefficients (up to 39% false positive rate). The application of ASCLAN was further exemplified using a widely investigated renal toxin, mercury II chloride (HgCl2) in rat model. ASCLAN successfully identified many of the known metabolites related to renal toxicity such as increased excretion of urinary creatinine, and different amino acids. The ASCLAN algorithm provides a framework for reliably differentiating discriminatory metabolites from nondiscriminatory metabolites in a biological data set without the need to set an arbitrary cut off value as applied to some of the conventional methods. This offers significant advantages over existing methods and the possibility for automation of high-throughput screening in "omics" data

Constraints on small-scale cosmological perturbations from gamma-ray searches for dark matter

Events like inflation or phase transitions can produce large density perturbations on very small scales in the early Universe. Probes of small scales are therefore useful for e.g. discriminating between inflationary models. Until recently, the only such constraint came from non-observation of primordial black holes (PBHs), associated with the largest perturbations. Moderate-amplitude perturbations can collapse shortly after matter-radiation equality to form ultracompact minihalos (UCMHs) of dark matter, in far greater abundance than PBHs. If dark matter self-annihilates, UCMHs become excellent targets for indirect detection. Here we discuss the gamma-ray fluxes expected from UCMHs, the prospects of observing them with gamma-ray telescopes, and limits upon the primordial power spectrum derived from their non-observation by the Fermi Large Area Space Telescope.Comment: 4 pages, 3 figures. To appear in J Phys Conf Series (Proceedings of TAUP 2011, Munich

The rings of Uranus: Results of the 10 April 1978 occultation

Observations of the 10 April 1978 stellar occultation by the rings of Uranus are presented. Nine rings were observed and their radii and widths are calculated. Rings η,y, and δ are found to be most likely circular and coplanar, in agreement with previous analyses; the remaining rings are either noncircular or slightly inclined. The width of the є ring is a linear function of its radius from the center of Uranus, projected onto the satellites' orbital plane; this suggests that it forms one continuous noncircular ring. The optical depth profile of the є ring has not changed significantly since March 1977. A model of this ring which fits all available observations adequately is that of a uniformly precessing Keplerian ellipse coplanar with the satellites' orbits. This model permits predictions of the radius and width of the є ring for future occultations. The precession rate is used to determine J_2 for Uranus, on the assumption that precession is caused solely by the planetary oblateness and not by satellite-ring interactions

An XMM-Newton and Chandra investigation of the nuclear accretion in the Sombrero Galaxy (NGC4594)

We present an analysis of the XMM-Newton and Chandra ACIS-S observations of the LINER nucleus of the Sombrero galaxy and we discuss possible explanations for its very sub-Eddington luminosity by complementing the X-ray results with high angular resolution observations in other bands. The X-ray investigation shows a hard (Gamma=1.89) and moderately absorbed (N_H=1.8 10^21 cm^-2) nuclear source of 1.5 10^40 erg s^-1 in the 2-10 keV band, surrounded by hot gas at a temperature of \sim 0.6 keV. The bolometric nuclear luminosity is at least \sim 200 times lower than expected if mass accreted on the supermassive black hole, that HST shows to reside at the center of this galaxy, at the rate predicted by the spherical and adiabatic Bondi accretion theory and with the high radiative efficiency of a standard accretion disc. The low luminosity, coupled to the observed absence of Fe-K emission in the nuclear spectrum, indicates that such a disc is not present. This nucleus differs from bright unobscured AGNs also for the lack of high flux variability and of prominent broad Halpha emission. However, it is also too faint for the predictions of simple radiatively inefficient accretion taking place at the Bondi rate; it could be too radio bright, instead, for radiatively inefficient accretion that includes strong mass outflows or convection. This discrepancy could be solved by the possible presence of nuclear radio jets. An alternative explanation of the low luminosity, in place of radiative inefficiency, could be unsteady accretion.Comment: 24 pages, including 7 figures; to be published in the Ap

Critical behavior of repulsive linear kk-mers on triangular lattices

Monte Carlo (MC) simulations and finite-size scaling analysis have been carried out to study the critical behavior in a submonolayer two-dimensional gas of repulsive linear $k$-mers on a triangular lattice at coverage $k/(2k+1)$. A low-temperature ordered phase, characterized by a repetition of alternating files of adsorbed $k$-mers separated by $k+1$ adjacent empty sites, is separated from the disordered state by a order-disorder phase transition occurring at a finite critical temperature, $T_c$. The MC technique was combined with the recently reported Free Energy Minimization Criterion Approach (FEMCA), [F. Rom\'a et al., Phys. Rev. B, 68, 205407, (2003)], to predict the dependence of the critical temperature of the order-disorder transformation. The dependence on $k$ of the transition temperature, $T_c(k)$, observed in MC is in qualitative agreement with FEMCA. In addition, an accurate determination of the critical exponents has been obtained for adsorbate sizes ranging between $k=1$ and $k=3$. For $k>1$, the results reveal that the system does not belong to the universality class of the two-dimensional Potts model with $q=3$ ($k=1$, monomers). Based on symmetry concepts, we suggested that the behavior observed for $k=1, 2$ and 3 could be generalized to include larger particle sizes ($k \geq 2$).Comment: 17 pages, 13 figure