Gravimetric determination of tungsten(vi) with n-benzoyl-n-phenylhydroxylamine

Tungsten can be quantitatively precipitated with N-benzoylphenyl-N-hydroxylamine in presence of hydrochloric acid (0.5–1 N). The precipitate can be weighted as WO₂(C₁₃H₁₀O₂N)₂ or WO₃. Molybdenum, vanadium, titanium, and iron can be separated by prior precipitation of these mutais with the above reagent in presence of tartrate ions; tungsten is then determined in tlie filtrate. L'ranium does not interfere, but chromium (VI), fluoride and phosphate do.     

Synthesis, characterization and catecholase-like activity of [Mn2L2(μ1,5-dca)2(dca)2]·H2O [L?=?N,N′-ethylenebis(2-benzoylpyridineimine), dca?=?dicyanamide]

A dinuclear Mn^II complex, namely [Mn₂L₂(μ_1,5-dca)₂(dca)₂]·H₂O [L = N,N′-ethylenebis(2-benzoylpyridineimine), dca = dicyanamide], has been synthesized and structurally characterized in order to study its catecholase-like activity. Single-crystal X-ray analysis revealed that the molecule possesses a center of inversion at the midpoint of the line bisecting the adjacent metal centers of the dimers. The coordination number of each Mn^II center is seven, and the coordination geometry is approximately distorted pentagonal bipyramid. The complex is an efficient catalyst for the oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylbenzoquinone under air in methanol solution but is inactive in acetonitrile solution. A kinetic study of the catalysis was treated on the basis of the Michaelis–Menten model and reveals high turnover numbers (k _cat = 4.5 × 10² h⁻¹) in methanol.     

Family of double-cubane Mn4Ln2 (Ln = Gd, Tb, Dy, Ho) and Mn4Y2 complexes: a new Mn4Tb2 single-molecule magnet

The synthesis and characterization of a family of Mn(2)(III)Mn(2)(II)Ln(III)(2) complexes (Ln = Gd (1), Tb (2), Dy (3), and Ho (4)) of formula [Mn(4)Ln(2)O(2)(O(2)CBu(t))(6)(edteH(2))(2)(NO(3))(2)] are reported, where edteH(4) is N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine. The analogous Mn(4)Y(2) (5) complex has also been prepared. They were obtained from reaction of Ln(NO(3))(3) or Y(NO(3))(3) with Mn(O(2)CBu(t))(2), edteH(4), and NEt(3) in a 2:3:1:2 molar ratio. The crystal structures of representative 1 and 2 were obtained, and their core consists of a face-fused double-cubane [Mn(4)Ln(2)(μ(4)-O(2-))(2)(μ(3)-OR)(4)] unit. Such double-cubane units are extremely rare in 3d metal chemistry and unprecedented in 3d-4f chemistry. Variable-temperature, solid-state dc and ac magnetic susceptibility studies on 1-5 were carried out. Fitting of dc χ(M)T vs T data for 5 gave J(bb) (Mn(III)···Mn(III)) = -32.6(9) cm(-1), J(wb) (Mn(II)···Mn(III)) = +0.5(2) cm(-1), and g = 1.96(1), indicating a |n, 0, n> (n = 0-5) 6-fold-degenerate ground state. The data for 1 indicate an S = 12 ground state, confirmed by fitting of magnetization data, which gave S = 12, D = 0.00(1) cm(-1), and g = 1.93(1) (D is the axial zero-field splitting parameter). This ground state identifies the Mn(II)···Gd(III) interactions to be ferromagnetic. The ac susceptibility data independently confirmed the conclusions about 1 and 5 and revealed that 2 displays slow relaxation of the magnetization vector for the Mn(4)Tb(2) analogue 2. The latter was confirmed as a single-molecule magnet by observation of hysteresis below 0.9 K in magnetization vs dc field scans on a single crystal of 2·MeCN on a micro-SQUID apparatus. The hysteresis loops also displayed well-resolved quantum tunneling of magnetization steps, only the second 3d-4f SMM to do so.     

Nonclassicality generated by propagation of atoms through a cavity field

We successively pass two V-type three-level atoms through a single-mode cavity field. Considering the field to be initially in a classical state, we evaluate various statistical properties such as the quasiprobability Q function, Wigner distribution, Mandel?s Q parameter and normal squeezing of the resulted field. We notice that the sequential crossing of atoms induces nonclassicality into the character of a pure classical state (coherent field). The initial thermal field shows sub-Poissonian as well as squeezing property after interacting with the V atoms.     

Fluorescent Carbon Quantum Dots Functionalized by Poly L-Lysine: Efficient Material for Antibacterial,Bioimaging and Antiangiogenesis Applications

Journal of Fluorescence - This study illustrates the synthesis of functionalized carbon quantum dots (CQDs) by the one-pot pyrolysis method. The functionalization agent used in CQD synthesis was...     

On rheology,cure kinetics and chemorheology of gum rubbers

The paper presents an experimentally supported modeling approach, which describes the rheology, detailed cure kinetics, and chemorheology of a gum elastomer in course of sulfur accelerated vulcanization. Changes in the rheology during cure reaction are correlated with degree of cross-linking, described by vulcanization kinetics. Oil extended SBR exemplifies the approach.     

Coupled tapered/uptapered optical beams

For the first time we propose the phenomenon of coupled tapering and uptapering in two mutually incoherent beams coaxially co-propagating in a nonlinear medium with small gain or loss. During tapering or uptapering, the widths and powers of the beams evolve in such a manner that they always satisfy the condition of soliton pairing. It is shown that under certain condition one beam can taper/uptaper, while, other uptaper/taper during coupled tapering/uptapering which is quite counterintuitive.     

Hump structure below Tc in the thermal conductivity of MgB2 superconductor

A reasonable cause of absence of hump structure in thermal conductivity of MgB₂ below the superconducting transition temperature (T_c) lies in the appearance of multigap structure. The gaps of lower magnitude can be suppressed by defects so that this system becomes effectively a single-gap superconductor. When such a situation is created, it is hoped that thermal conductivity (κ) will show hump below T_c. Proceeding along these lines, a sample of MgB₂ with a relatively higher residual resistivity ρ_o = 33.8 μΩ cm has been found to show a hump structure below T_c. The actual electronic thermal conductivity κ_el of this sample is less than that expected from the Wiedeman–Franz law by more than a factor of 2.6 in the considered temperature range.Modifying the Wiedeman–Franz law for the electronic contribution by replacing the Lorenz number L₀ = 2.45 × 10^?8 W Ω K^?2 by an effective Lorenz number L_eff (<L₀) we have obtained two sets of κ_el, namely those with L_eff = 0.1L₀ and 0.2L₀. Corresponding to these two sets of κ_el, two sets of the phonon thermal conductivity κ_ph are obtained. κ_ph has been analyzed in terms of an extended Bardeen–Rickayzen–Tewordt theory. The main result of this analysis is that the hump structure corresponds to a gap ratio of 3.5, and that large electron-point defect scattering is the main source of drastic reduction of the electronic thermal conductivity from that given by the usual Wiedeman–Franz law.