Organozinc hydroxylamides: on the bulk-dependent interplay of nuclearity, structure and dynamics

The reactions of zinc dialkyls, R(2)Zn (1a-d; R = Me (a), Et (b), iPr (c) and tBu (d)), with N,N-dialkylhydroxylamines, HO-NR'(2) (2a-c; R' = Me (a), Et (b) and iPr (c)), afford organozinc hydroxylamides under alkane extrusion. Species of different nuclearity are observed, depending on the hydroxylamine 2 employed. The smaller 2a and 2b give pentanuclear complexes of the general formula Zn(RZn)(4)O-NR'(2))(6) (R = Me, Et, iPr and tBu; R' = Me and Et), whereas the derivatives of 2c are tetramers of the general formula (RZn)(4)(O-NR'(2))(4) (R = Me, Et and iPr; R' = iPr) as governed by bulk issues about the N-donor. Due to the ability of the double-donor unit O-NR(2) to change its bridging mode, two coordination isomers exist for both types of compounds. The pentanuclear species crystallise either in a heterofenestrane or an octahedroid motif. For these species, the central Zn atom exhibits either coordination number 4 or 6; in solution, a rapid change between coordination isomers is observed. Due to the absence of a central Zn atom in the tetranuclear species, these aggregate in heterocubane geometries or such derived thereof. They display the O-N units in either κ(3)O or κ(2)O;κ(1)N mode. The tetranuclear species are also yielded with the less sterically encumbered precursors under thermodynamic conditions (i.e. reflux), as exemplified by the reaction of Me(2)Zn (1a) with HO-NEt(2) (2b). They are non-dynamic in solution, showing that a central cation is mandatory for the fluxional behaviour observed for the pentanuclear derivatives. DFT studies on the O-NMe(2) series reveal that the relative energies of the pentazinc isomers become more similar with increasing RZn group size; possible conversions of these to their tetrazinc counterparts were also scrutinised. Two κ(3)O-bridged degradation products of hydroxylamide complexes could be structurally characterised. They were formed either by partial product hydrolysis, or by in situ oxygenation of the starting zinc dialkyl.     

Iron catalyzed highly regioselective dimerization of terminal aryl alkynes

Iron can catalyze head-to-head dimerization of terminal aryl alkynes to give the corresponding (E) selective conjugated enynes in high yields. A variety of substituted aryl acetylenes underwent smooth dimerization using catalytic FeCl(3) and DMEDA in the presence of KO(t)Bu.     

Direct determination of uranium in sintered deeply depleted uranium oxide pellets by wavelength dispersive X-ray fluorescence spectrometry

This paper presents studies on direct non-destructive determination of uranium in sintered deeply depleted (DD) uranium oxide (UO₂) pellets by wavelength dispersive X-ray fluorescence (WDXRF) spectrometry. A special collet was designed and fabricated for holding the sintered DDUO₂ pellets for direct analysis, thus avoiding the sample preparation steps. The samples were analyzed using a calibration plot obtained from WDXRF spectra of matrix matched calibration standards. The WDXRF determined uranium values were found to be in very close agreement with titrimetric values and has reproducibility better than 0.05% (RSD, 1 s, n = 10) for the sintered DDUO₂ pellets having U: 86.81–88.04 wt%.

     

Interaction Between Tachyon and Hessence (or Hantom) Dark Energies

In this work, we have considered that the universe is filled with tachyon and hessence (or hantom) dark energies. Subsequently we have investigated the interactions between tachyon and hessence (hantom) dark energies and calculated the potentials considering the power law form of the scale factor. It has been revealed that the tachyonic potential always decreases and hessence (or hantom) potential increases with corresponding fields. Furthermore, we have considered a correspondence between the hessence (or hantom) dark energy density and variable modified Chaplygin gas energy density. From this, we have found the expressions of the arbitrary positive constants B ₀ and C of variable modified Chaplygin gas.     

Concise synthesis of a pentasaccharide repeating unit corresponding to the O-antigen of Escherichia coli O102

An efficient synthetic strategy has been developed for the synthesis of a pentasaccharide repeating unit of the O-antigen of Escherichia coli O102 strain. The target pentasaccharide 1 has been synthesized using a [2+3] block glycosylation strategy. All glycosylation steps are highly stereoselective and high yielding. Concept of armed-disarmed and orthogonal glycosylation strategies has been applied during the synthesis. The target compound has been synthesized using the minimum number of steps.     

Expedient synthesis of a tetrasaccharide and a pentasaccharide corresponding to the cell wall O-antigen of Escherichia coli O77 and Escherichia coli O17

A concise chemical synthetic strategy has been developed for the synthesis of a tetrasaccharide and a pentasaccharide corresponding to the O-antigen of Escherichia coli O77 and E. coli O17 strains, respectively using [2+2] and [3+2] block glycosylation approaches from suitably functionalized common monosaccharide intermediates. All of the intermediate steps are high yielding while the glycosylation steps are highly stereoselective. A number of recently developed methodologies have been used in the synthesis.     

The quasi-equilibrium phase of nonlinear chains

We show that time evolution initiated via kinetic energy perturbations in conservative, discrete, spring-mass chains with purely nonlinear, non-integrable, algebraic potentials of the formV(x _i − x _i +1) ∼ (x _i − x _i+1 ) ²ⁿ ,n ≥ 2 and an integer, occurs via discrete solitary waves (DSWs) and discrete antisolitary waves (DASWs). Presence of reflecting and periodic boundaries in the system leads to collisions between the DSWs and DASWs. Such collisions lead to the breakage and subsequent reformation of (different) DSWs and DASWs. Our calculations show that the system eventually reaches a stable ‘quasi-equilibrium’ phase that appears to be independent of initial conditions, possesses Gaussian velocity distribution, and has a higher mean kinetic energy and larger range of kinetic energy fluctuations as compared to the pure harmonic system withn = 1; the latter indicates possible violation of equipartition.