Catalytic and non-catalytic growth of amorphous silica nanowires and their photoluminescence properties

A simple method based on the thermal oxidation of Si wafers in presence of a mixture of MgO and graphite powder was developed for large-scale synthesis of very long amorphous silica nanowires. The synthesis was done with and without gold as the catalyst. Almost aligned uniform nanowires with diameters within 60-90 nm and length up to few hundred micrometers were obtained using gold as the catalyst while bicycle chain like nanowires were obtained in absence of the catalyst. The growth sequence of the nanowires was observed through scanning electron microscope. Both forms of the nanowires emitted blue lights at 414 nm (3 eV) under excitation at 250 nm.     

Clan structure in high energypn,pp andp\bar p interactions

We have analysed ourpn data at 400 GeV (corresponding to a centre-of-mass energy \(\sqrt s = 27.5\) GeV) together with otherpp and \(p\bar p\) data in the centre of mass energy range 11.5–900 GeV. The fits of all these distributions to a negative binomial distribution are performed. The variations in the fitted average multiplicity and in the inverse of the fitted parameterk are obtained with respect to the centre of mass energy. An assessment of the single diffractive component in the multiplicity distribution is made and its variation with the centre of mass energy discussed. The average number of clans and the average charged multiplicity per clan are determined and the centre of mass energy dependences shown.     

Simple Organic Salts Having a Naphthalenediimide (NDI) Core Display Multifunctional Properties: Gelation,Anticancer and Semiconducting Properties

Following a supramolecular synthon rationale, a dicarboxylic acid derivative having a naphthalenediimide (NDI) core, namely, bis‐N‐carboxymethyl naphthalenediimide ( NDI‐G ), was reacted with n‐alkyl amines with varying alkyl chain lengths to generate a new series of primary ammonium dicarboxylate (PAD) salts. The majority of the salts (≈85 %) were found to gel various polar solvents. The gels were characterized by dynamic rheology and high‐resolution electron microscopy. Single‐crystal and powder X‐ray diffraction analyses were used to study the supramolecular synthon present in one of the gelator salts (i.e., S8 ). Charge‐transfer (CT)‐induced gelation with donor molecules such as anthracene methanol ( Ant ) and pyrene ( Py ) was also possible with S8 . The CT complex ( S8.Ant ) displayed anticancer activity as probed by cell migration assay on the highly aggresive breast cancer cell line MDA‐MB‐231 . The DMSO gel of S8.Ant also displayed semiconducting behavior. To the best of our knowledge, simple organic salts with an NDI core that display such mulitifunctional properties are hitherto unknown.     

Time-resolved fluorescence of tryptophans in yeast hexokinase-PI: effect of subunit dimerization and ligand binding

Time-resolved and steady-state fluorescence measurements have been performed on monomeric and dimeric forms of yeast hexokinase-PI. Observation of similar emission spectra and fluorescence decay parameters for both the forms of the enzyme suggests that tryptophan residue(s) are not likely to be present at the subunit-subunit interface and the process of dimerization does not perturb the local environment of tryptophan(s). The fluorescence decay of tryptophans in enzyme could be fitted to a bi-exponential function with two lifetime components, tau1 approximately 2.2 ns and tau2 approximately 3.9 ns. Binding of glucose, which is known to convert the 'open' conformation of the enzyme to a 'closed' active conformation, results in approximately 30% reduction in emission intensity and a selective decrease in tau1 from approximately 2.2 to approximately 1.1 ns. These effects can be reversed by the addition of trehalose 6-phosphate (an inhibitor of yeast hexokinase), suggesting that the trehalose 6-phosphate inhibits the enzyme by binding to its 'open' inactive conformation rather than competing with glucose to bind to the 'closed' active conformation. Binding of nucleotide ligands (ATP, ADP and adenyl-(beta,gamma-methylene)-diphosphate (AMPPCP)) to the monomeric or dimeric form of enzyme quenched the steady-state fluorescence by approximately 4-8%, but had no measurable effect on the distribution of lifetimes or on their magnitudes. Addition of nucleotides to the enzyme-glucose complex also did not produce any further change in fluorescence decay parameters. These results indicate that it is highly unlikely that the formation of a ternary enzyme-glucose-nucleotide complex from the binary enzyme-glucose complex is accompanied by a large conformational change in the enzyme, as has been surmised in some earlier studies.     

Lanthanum(III) and praseodymium(III) complexes with isatin thiosemicarbazones

Ten new lanthanum(III) and praseodymium(III) complexes of the general formula Na[La(L)2H2O] (Ln=La(III) or Pr(III); LH2=thiosemicarbazones) derived from the condensation of isatin with 4-phenyl thiosemicarbazide, 4-(4-chlorophenyl) thiosemicarbazide, 4-(2-nitrophenyl) thiosemicarbazide, 4-(2-bromophenyl) thiosemicarbazide and 4-(2-methylphenyl) thiosemicarbazide, have been synthesized in methanol in presence of sodium hydroxide. The XRD spectra of the complexes were monitored to verify complex formation. The complexes have also been characterized by elemental analysis, molar conductance, electronic absorption and fluorescence, infrared, far infrared, 1H and 13C NMR spectral studies. Thermal studies of these complexes have been carried out in the temperature range 25-800 degrees C using TG, DTG and DTA techniques. All these complexes decompose gradually with the formation of Ln2O3 as the end product. The Judd-ofelt intensity parameter, oscillator strength, transition probability, stimulated emission cross section for different transitions of Pr3+ for 4-phenyl thiosemicarbazones have been calculated.     

Reaction of benzyl chloride with ammonium sulfide under liquid–liquid phase transfer catalysis: Reaction mechanism and kinetics

The reaction between benzyl chloride and aqueous ammonium sulfide was carried out in an organic solvent – toluene, using tetrabutylammonium bromide (TBAB) as phase transfer catalyst (PTC). Two products, namely dibenzyl sulfide (DBS) and benzyl mercaptan (BM), were identified in the reaction mixture. The selectivity of DBS was maximised by changing various parameters such as NH₃/H₂S mole ratio, stirring speed, catalyst loading, concentration of benzyl chloride, volume of aqueous phase, and temperature. The highest selectivity of DBS obtained was about 90% after 445 min of reaction with excess benzyl chloride at 60 °C. Complete conversion of benzyl chloride could be achieved at the cost of very low selectivity of DBS and very high selectivity of BM. The apparent activation energy for the kinetically controlled reaction was found to be 12.3 kcal/mol. From the detailed study of the effects of various parameters on the reaction, a suitable mechanism was established which could explain the course of the reaction.     

On the usefulness of generalised quantum chemical valence parameters in monitoring the course of a chemical reaction: A case study of the photochemical decomposition of HNO in excited states

A variant of the orthogonal gradient method of orbital optimization in the INDO-MCSCF framework has been used to study the photochemical decomposition of the HNO molecule into H + NO in the lowest^1.3A″ states. A complete geometry optimization has been carried out at all points of the reaction path which appears to be almost barrierless. The one-electron density matrix extracted from the optimized wavefunction at each point has been used to generate the relevant sets of quantum chemical valence parameters. A sharp transition is noted in the N-H bond order and hydrogen free valence index when plotted as functions of r_NH. This enables us to locate the transition region easily.     

One electron oxidation induced dimerization of 5-hydroxytryptophol: role of 5-hydroxy substitution

Reaction of one-electron oxidant (Br(2)(*-)) with tryptophol (TP) and 5-hydroxytryptophol (HTP) have been studied in aqueous solution in the pH range from 3 to 10, employing nanosecond pulse radiolysis technique and the transients detected by kinetic spectrophotometry. One-electron oxidation of TP has produced an indolyl radical that absorbs in the 300-600 nm region with radical pK(a) = 4.9 +/- 0.2, while the reaction with HTP has produced an indoloxyl radical with lambda(max) at 420 nm and radical pK(a) < 3. Hydroxyl radicals ((*)OH) react with these two compounds producing (*)OH radical adducts that undergo water elimination to give one-electron-oxidized indolyl and indoloxyl radical species, respectively. The indoloxyl radicals react with the parent compound to form dimer radicals with an average association constant of (6.7 +/- 0.4) x 10(4) M(-1). No such dimerization is observed with indolyl radical, indicating that the presence of the 5-hydroxy group markedly alters its ability to form a dimer. A possible explanation behind such a difference in reactivity has been supported with ab initio quantum chemical calculations.     

Radiometric analysis of silver in galena

A radiometric procedure for quantitative analysis of traces of silver in galena has been demonstrated. The mineral sample was dissolved in HNO₃ (31) and silver present in the solution was precipitated as insoluble AgI by adding an excess amount of¹³¹I-labeled KI solution and was coprecipitated with zirconium hydrogen phosphate, Zr(HPO₄)₂, in 0.5N H₂SO₄ medium. The method of radiometric analysis of silver which was estimated from the knowledge of the loss of¹³¹I activity in solution, was found to be effective in determination of the element even below ppb level. Applicability of the radiometric procedure in routine analysis or preconcentration of traces of silver in galena has been stressed.