Synthesis of unnatural 3′-phospha-2′-deoxyfuranose nucleoside analogues

This Letter describes the synthesis of racemic analogues of unnatural 2′-deoxy nucleoside with a phosphorus atom replacing the carbon atom in the 3′-position. A seven-step sequence was developed in racemic series to afford unnatural 3′-phospha-2′-deoxyfuranose nucleosides. The phospha nucleoside analogues were tested against HCV, but did not show any antiviral activity at a 10 μM maximum concentration used for the inhibition assays of analogues 2-T, 2-C and 4-Tα.     

Syntheses, structures, and photophysical properties of mono- and dinuclear sulfur-rich gold(I) complexes

The dinuclear gold complexes [{Au(PPh 3)} 2(mu- dmid)] ( 1) ( dmid = 1,3-dithiole-2-one-4,5-dithiolate) and [{Au(PPh 3)} 2(mu- dddt)] ( 2) ( dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate) were synthesized and characterized by X-ray crystallography. Both complexes exhibit intramolecular aurophilic interactions with Au...Au distances of 3.1984(10) A for 1 and 3.1295(11) A for 2. A self-assembly reaction between 4,5-bis(2-hydroxyethylthio)-1,3-dithiole-2-thione ( (HOCH 2 CH 2 ) 2 dmit) and [AuCl(tht)] affords the complex [AuCl{ (HOCH 2 CH 2 ) 2 dmit}] 2 ( 4), which possesses an antiparallel dimeric arrangement resulting from a short aurophilic contact of 3.078(6) A. This motif is extended into two dimensions due to intra- and intermolecular hydrogen bonds via the hydroxyethyl groups, giving rise to a supramolecular network. Three compounds were investigated for their rich photophysical properties at 298 and 77 K in 2-MeTHF and in the solid state; [Au 2(mu- dmid)(PPh 3) 2] ( 1), [Au 2(mu- dddt)(PPh 3) 2] ( 2), and [AuCl{( HOCH 2 CH 2 ) 2 dmit}] ( 4). 1 exhibits relatively long-lived LMCT (ligand-to-metal charge transfer) emissions at 298 K in solution (370 nm; tau e approximately 17 ns, where M is a single gold not interacting with the other gold atom; i.e., the fluxional C-SAuPPh 3 units are away from each other) and in the solid state (410 nm; tau e approximately 70 mus). At 77 K, a new emission band is observed at 685 nm (tau e = 132 mus) and assigned to a LMCT emission where M is representative for two gold atoms interacting together consistent with the presence of Au...Au contacts as found in the crystal structure. In solution at 77 K, the LMCT emission is also red-shifted to 550 nm (tau e approximately 139 mus). It is believed to be associated to a given rotamer. 2 also exhibits LMCT emissions at 380 nm at 298 K in solution and at 470 nm in the solid state. 4 exhibits X/MLCT emission (halide/metal to ligand charge transfer) where M is a dimer in the solid state with obvious Au...Au interactions, resulting in red-shifted emission band, and is a monomer in solution in the 10 (-5) M concentration (i.e., no Au...Au interactions) resulting in blue-shifted luminescence. Both fluorescence and phosphorescence are observed for 4.     

Performance evaluation of Wi‐Fi and WiMAX over OFDM physical layer

Orthogonal frequency division multiplexing (OFDM) is an alternative technology that is constrained to keep up with the increasingly high data transmission rate due to its robustness against selective frequency fading and its resistance to intersymbol interference (ISI). This paper aims to study and optimize its performance, namely, its probability of communication failure and signal‐to‐interference‐plus‐noise ratio (SINR) metrics. The mathematical tool used to perform OFDM evaluation and analysis is the Fourier transform and its properties. The obtained results of those equations led to the demonstration of the probability of communication outage and to notice that the cutoff time occurs after the 10th iteration for values of λ less than or equal to 1. It could also be checked that this period is small if λ exceeds 1 by considering the sensitivity factor. Moreover, for the obtained results, in terms of bit error rate (BER) and SINR, the influence of the modulation on the error vector magnitude (EVM) shows the sensitivity factor Ω presents a key role in the transmission chain.     

Direct laser-driven ramp compression studies of iron: A first step toward the reproduction of planetary core conditions

The study of iron under quasi-isentropic compression using high energy lasers, might allow to understand its thermodynamical properties, in particular its melting line in conditions of pressure and temperature relevant to Earth-like planetary cores (330–1500 GPa, 5000–8000 K). However, the iron alpha-epsilon solid–solid phase transition at 13 GPa favors shock formation during the quasi-isentropic compression process which can depart from the appropriate thermodynamical path. Understanding this shock formation mechanism is a key issue for being able to reproduce Earth-like planetary core conditions in the laboratory by ramp compression. In this article, we will present recent results of direct laser-driven quasi-isentropic compression experiments on iron samples obtained on the LULI 2000 and LIL laser facilities.     

Biomimetic Interaction between FeII and O2: Effect of the Second Coordination Sphere on O2 Binding to FeII Complexes: Evidence of Coordination at the Metal Centre by a Dissociative Mechanism in the Formation of μ‐Oxo Diferric Complexes

We report that the formation of μ‐oxo diferric compounds from O₂ and FeCl₂ complexes within the tris(2‐pyridylmethyl)amine series (N. K. Thallaj et al. Chem. Eur. J., 2008 , 14, 6742–6753) involves coordination of O₂ to the metal centre and that this reaction occurs following initial dissociation of the bound equatorial chloride anion. We also report evidence of the formation of a reduced form of dioxygen by an inner‐sphere mechanism, thus leading to modification of the ligand. The solid‐state structures of [FeCl₂L] complexes (L¹=mono(α‐pivalamidopyridylmethyl)bis(2‐pyridylmethyl)amine, L²=mono(α‐pivalesteropyridylmethyl)bis(2‐pyridylmethyl)amine, L³=bis(α‐pivalamidopyridylmethyl)mono(2‐pyridylmethyl)amine are described, and spectroscopic data support the structural retention in solution. In [FeCl₂L³], the two amide hydrogen atoms stabilise the equatorial chloride anion in such a way that its exchange by a weak ligand is impossible: [FeCl₂L³] is perfectly oxygen‐stable. In [FeCl₂L²], the equatorial chloride anion is completely free to move and coordination of O₂ can take place. The reaction product with [FeCl₂L²] is a μ‐oxo diferric complex in which the ester function has been transformed into a phenol group. This conversion can be seen as a hydrolysis reaction in basic medium, hence supporting the initial formation of a reduced form of dioxygen in the medium. Complex [FeCl₂L¹] exhibits a very weak reactivity with O₂, in line with a semistabilised equatorial chloride counteranion.     

Etablissement du diagramme binaire hydroxy.2 naphtalene-chloro.2 naphtalene par differentes analyses thermiques

The phase diagram of the 2-chloronaphthalene-2-hydroxynaphthalene binary system has been established in three thermal investigations (calorimetric, crystallographic and optical methods). This diagram is fairly complicated. The main feature is the presence of three invariants: a eutectoid atT _e =309 K, a peritectic atT _p =333 K and a metatectic atT _m =364 K.     

Synthesis of indolizines and pyridinium ylids from 4,5-disubstituted α-picolines

New 1,3-diacetylindolizines were obtained from 4-phenyl- and 4-benzyl-2,5-dimethylpyridines; some transformations involving their acetyl groups were realized. The same pyridine bases were used in syntheses of pyridinium ylids. The transformations of the latter to indolizines were studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 506–510, April, 1976.     

Sur la régularité de Castelnuovo–Mumford des idéaux,en dimension 2

We give a bound on the Castelnuovo–Mumford regularity of a homogeneous ideal I, in a polynomial ring A, in terms of the number of variables and the degrees of generators, when the dimension of $A/I$ is at most two. This bound improves the one obtained by Caviglia and Sbarra in [G. Caviglia, E. Sbarra, Characteristic-free bounds for the Castelnuovo–Mumford regularity, Prépublication, math.AC/0310122]. In the continuation of the examples constructed in Chardin and D'Cruz [M. Chardin, C. D'Cruz, Castelnuovo–Mumford regularity: examples of curves and surface, J. Algebra 270 (2003) 347–360], we use families of monomial curves to construct homogeneous ideals showing that these bounds are quite sharp. To cite this article: M. Chardin, A.L. Fall, C. R. Acad. Sci. Paris, Ser. I 341 (2005).