Adiabatic thermokinetics and process safety of pyrotechnic mixtures

Pyrotechnic mixtures are susceptible to explosive decompositions. The aim of this paper is to generate thermal decomposition data under adiabatic conditions for fireworks mixtures containing potassium nitrate, barium nitrate, sulfur, and aluminum which are manufactured on a commercial scale. Differential scanning calorimeter is used for screening tests and accelerating rate calorimeter is used for other studies. The self heat rate data obtained showed onset temperature in the range of 275?C295?°C for the fireworks atom bomb, Chinese cracker and palm leaf cracker. Of the three mixtures studied, atom bomb mixture had an early onset at 275?°C. The mixtures in general showed vigor exothermic decompositions. Palm leaf mixture exhibits multiple exotherm and reached a final temperature of 414?°C. The thermal decomposition contributes to substantial rise in system pressure. The heats of exothermic decomposition and Arrhenius kinetics were computed. The kinetic data are validated by comparing the predicted self heat rates with the experimental data.     

Diffusion of organic dyes in a niosome immobilized on a glass surface using fluorescence correlation spectroscopy

Giant multilameller niosomes containing cholesterol and triton X-100 are studied using fluorescence correlation spectroscopy (FCS). Dynamic light scattering (DLS) data indicates formation of niosomes of broadly two different sizes (diameter)--~150 nm and ~1300 nm. This is confirmed by field emission scanning electron microscopy (FE-SEM) and confocal microscopy. The diffusion coefficient (D(t)) of three organic dyes in the niosome immobilized on a glass surface is studied using fluorescence correlation spectroscopy. On addition of the room temperature ionic liquids (RTIL) (1-methyl-3-pentylimidazolium bromide, [pmim][Br] and 1-methyl- 3-pentylimidazolium tetra-fluoroborate, [pmim][BF(4)]) the size of the niosome particles increases. The D(t) of all the organic dyes (DCM, C343 and C480) increases on addition of RTILs, indicating faster diffusion. The viscosity calculated from the D(t) of the three dyes exhibits weak probe dependence. Unlike lipid or catanionic vesicle, the D(t) values in a niosome exhibit very narrow distribution. This indicates that the niosomes are fairly homogeneous with small variation of viscosity.     

Heterogeneous shear in hard sphere glasses

There is growing evidence that the flow of driven amorphous solids is not homogeneous, even if the macroscopic stress is constant across the system. Via event-driven molecular dynamics simulations of a hard sphere glass, we provide the first direct evidence for a correlation between the fluctuations of the local volume fraction and the fluctuations of the local shear rate. Higher shear rates do preferentially occur at regions of lower density and vice versa. The temporal behavior of fluctuations is governed by a characteristic time scale, which, when measured in units of strain, is independent of shear rate in the investigated range. Interestingly, the correlation volume is also roughly constant for the same range of shear rates. A possible connection between these two observations is discussed.     

Ferric reducing, antiradical and beta-carotene bleaching activities of nicotinic acid and picolinic acid bioconjugates of curcumin

Although curcumin displays several beneficial properties, its medicinal use is limited by its low bioavailability. In the present study we report the antioxidant potentials of two bioconjugates of curcumin with nicotinic acid and picolinic acid: di-O-nicotinoyl curcumin [1,7-bis (4-O nicotinoyl-3-methoxyphenyl)-1,6-heptadiene-3, 5-dione] and di-O-picolinoyl curcumin [1,7-bis (4-O-picolinoyl-3-methoxyphenyl)-1,6-heptadiene-3, 5-dione], in terms of ferric reducing, radical scavenging and beta-carotene bleaching abilities, and comparing the observed activity with that of curcumin. Results demonstrate that both the bioconjugates possess higher antioxidant potentials as evidenced by enhanced ferric reducing, radical scavenging and beta-carotene bleaching abilities, in comparison with curcumin. On the basis of our results we conclude that these bioconjugates of curcumin may be better than curcumin for medicinal and pharmacological applications.     

Isolation of four new CoII/CoIII and NiII complexes with a pentadentate Schiff base ligand: syntheses, structural descriptions and magnetic studies

In this paper we report the temperature and pH dependent syntheses and systematic characterization of four new Co(II)/Co(III) and Ni(II) complexes with a pentadentate Schiff base ligand H(3)L obtained by condensing 1,3,-diaminopropan-2-ol with 2-hydroxyacetophenone in 1:2 molar ratio. The room temperature syntheses involving Co(II) and Ni(II) nitrates and the ligand H(3)L lead to the isolation of the dinuclear species [Co(2)L(2)(H(2)O)] (1), and the mononuclear complex [Ni(LH)] (3), respectively, whereas refluxing at basic pH leads to the tetranuclear complexes, [Co(II)(2)Co(III)(2)L(2)(μ(3)-OMe)(2)(NO(3))(H(2)O)(2)]NO(3)·2(H(2)O) (2), and [Ni(4)L(2)(μ(3)-OMe)(2)(H(2)O)(2)]·2H(2)O (4). 1 is found to be a simple mono alkoxo-bridged Co(III) dinuclear species, whereas 2 and 4 are both rhomb-like tetrameric complexes with double oxo bridges and μ(3)-methoxo bridges, derived from the methanol solvent, in an open dicubane arrangement. Moreover 2 shows six coordinate ordered Co(II) and Co(III) ions and 4 has both six- and five-coordinate Ni(II) centers. Compound 3 is assigned a tentative mononuclear structure based on IR, UV-Vis spectroscopic, (1)H-NMR and ESI mass study results and is supposed to have one Ni(II) center coordinated with a ligand fragment in square planar geometry. The variable temperature magnetic susceptibility study for 2 and 4 is performed which indicate for both 2 and 4 the presence of intracluster dominant ferromagnetic interactions.     

Kinetics and mechanism of the oxidation of hydroxylamine by a {Mn3O4}4+ core in aqueous acidic media

In this work we report the kinetics of oxidation of hydroxylamine by a trinuclear Mn(IV) oxidant, [Mn(3)(μ-O)(4)(phen)(4)(H(2)O)(2)](4+) (1, phen = 1,10-phenanthroline), in aqueous solution over a pH range 2.0-4.0. The trinuclear Mn(IV) species (1) deprotonates in aqueous solution at physiological pH: 1 ? 2 + H(+); pK(1) = 4.00 (± 0.15) at 25.0 °C, I = 1.0 (M) NaNO(3). Both 1 and 2 are reactive oxidants reacting with the conjugate acid of hydroxylamine, viz. NH(3)OH(+) where the deprotonated oxidant 2 reacts faster. This finding is in contrast to a common observation and belief that protonated oxidants react quicker than their deprotonated analogues. Mn(IV)(3) to Mn(II) transition in the present reaction proceeds through the intervention of a spectrally detected mixed-valent Mn(III)Mn(IV) dimer that quickly collapses to Mn(II). The rate of the reaction was found to be lowered in D(2)O-enriched media in comparison to that in pure H(2)O media. An initial one electron one proton transfer to Mn(IV)(3) (electroprotic; 1e, 1H(+)) could be mechanistically conceived as the rate step. We also demonstrate by means of high level DFT studies that, among the two sets of Mn(IV) atoms in the trinuclear oxidant, the unique one that is coordinated with two phen ligands and two oxo-bridges is reduced to Mn(III) at the rate step. This is explained based on energetic and spin density calculations. Moreover, this result agrees with the charge distribution on the Mn atoms of the trinuclear complex.     

Separation behavior of U(VI) and Th(IV) on a cation exchange column using 2,6-pyridine dicarboxylic acid as a complexing agent and its application for the rapid separation and determination of U and Th by ion chromatography

The retention behavior of U and Th as their 2,6-pyridine dicarboxylic acid (PDCA) complexes on a cation exchange column was investigated under low pH conditions. Based on the observed retention characteristics, an ion chromatographic method for the rapid separation of uranium and thorium in isocratic elution mode using 0.08 mM PDCA and 0.24 M KNO(3) in 0.22 M HNO(3) as the eluent was developed. Both uranium and thorium were eluted as their PDCA complexes within 2 min, whereas the transition and lanthanide metal cations were eluted as an unresolved broad peak after thorium. Under the optimized conditions both U and Th have no interference either from alkali and alkaline earth elements up to a concentration ratio of 1:500 or from other elements up to 1:100. The detection limits (LOD) of U and Th were calculated as 0.04 and 0.06 ppm, respectively (S/N=3). The precision in the measurement of peak area of 0.5 ppm of both U and Th was better than 5% and a linear calibration in the concentration range of 0.25-25 ppm of U and Th was obtained. The method was successfully applied to determine U and Th in effluent water samples.     

Total chemical synthesis of biologically active vascular endothelial growth factor

Efficient access: the 204-residue covalent-dimer vascular endothelial growth factor with full mitogenic activity was prepared from three unprotected peptide segments by one-pot native chemical ligations. The covalent structure of the synthetic VEGF was confirmed by precise mass measurement, and the three-dimensional structure of the synthetic protein was determined by high-resolution X-ray crystallography.