Mechanism of hydroxyl radical generation from a silica surface: molecular orbital calculations

The interaction of an H(2)O molecule with cluster models of fractured silica surfaces was studied by means of quantum mechanical calculations. Two clusters representing homolytic cleavage (triple bond Si(*) and triple bond SiO(*)) and two representing heterolytic cleavage (triple bond Si(+) and triple bond Si-O(-)) of silica surfaces were modeled. Vibrational frequencies of the reactants and products of these silica surfaces reacting with H(2)O have been calculated and compare favorably with experiment. Comparisons of the Gibbs free and potential energies for the model ionic and radical states were made, and the radical pair of sites was predicted to be more stable by approximately -70 to -85 kJ/mol, depending on the computational methodology. These calculations suggest that when silica is fractured in a vacuum homolytic cleavage is favored. Reaction pathways were investigated for these four model surface sites interacting with H(2)O. The reaction of H(2)O with triple bond SiO(*) was predicted to generate OH(*). Rate constants for these reactions were also calculated and predict a rapid equibrium for the reaction triple bond SiO(*) + H(2)O --> triple bond SiOH + OH(*). Stability of a finite number of triple bond SiO(*) sites at equilibrium in the above reaction with H(2)O was also predicted, which implies a long-term ability of silica surfaces to produce OH(*) radicals if the sites of the broken bonds do not repolymerize to form siloxane groups.     

Generation of extended trains of compressed picosecond pulses with stable energy and time characteristics in a ND:YAG laser with passive negative feedback

A comparative analysis of the parameters of picosecond laser pulses generated under conditions of pure passive mode-locking and passive negative feedback was made. A twofold pulse compression (from 31 to 13.9 ps) was obtained. For the case of generation of extended flattened pulse trains under conditions of passive negative feedback, a considerable decrease in energy (from 24 to 5.7%) and time (from 20 to 3%) instabilities was achieved.     

Optimization of Factors Influencing Microinjection Method for Agrobacterium tumefaciens-Mediated Transformation of Tomato

A simple and efficient protocol for Agrobacterium-mediated genetic transformation of tomato was developed using combination of non-tissue culture and micropropagation systems. Initially, ESAM region of 1-day-old germinated tomato seeds were microinjected for one to five times with Agrobacterium inoculums (OD₆₀₀?=?0.2–1.0). The germinated seeds were cocultivated in the MS medium fortified with (0–200 mM) acetosyringone and minimal concentrations of (0–20 mg?L^?1) kanamycin, and the antibiotic concentration was doubled during the second round of selection. Bacterial concentration of OD₆₀₀?=?0.6 served as an optimal concentration for infection and the transformation efficiency was significantly higher of about 46.28 %. In another set of experiment, an improved and stable regeneration system was adapted for the explants from the selection medium. Four-day-old double cotyledonary nodal explants were excised from the microinjected seedlings and cultured onto the MS medium supplemented with 1.5 mg?L^?1 thidiazuron, 1.5 mg?L^?1 indole-3-butyric acid, 30 mg?L^?1 kanamycin, and 0–1.5 mg?L^?1 adenine sulphate. Maximum of 9 out of 13 micropropagated shoots were shown positive to GUS assay. By this technique, the transformation efficiency was increased from 46.28 to 65.90 %. Thus, this paper reports the successful protocol for the mass production of transformants using microinjection and micropropagation techniques.     

Regiospecific Chlorination of Xylenes Using K-10 Montmorrillonite Clay

Regiospecific chlorination of xylenes has been developed by employing NCS as a reagent and K-10 montmorrillonite clay as a solid support.     

CuCN-Mediated O-Alkylation of N,N,-Dimethylformamide with Alkyl Halides

This article reports the CuCN-mediated O-alkylation of formamide with 2-bromomethylindole. In addition, the formyloxylation products have been successfully exploited in the synthesis of novel indol-2-ylmethyl ether derivatives.     

Effect of aluminum on the hyperfine field and crystallization behaviour of NANOPERM alloy

The effect of Al on the hyperfine fields and crystallization of NANOPERM alloy has been studied by introducing 2% Al for Fe in Fe₈₈Zr₇B₄Cu₁. Al is found to enhance the nucleation rate in these alloys. Mössbauer spectroscopic technique has been used to trace the effect of Al on the hyperfine interactions in the amorphous and nanocrystalline state of these alloys. The hyperfine field clearly shows the presence of Al both in the amorphous and the nanocrystalline phase. Magnetic measurements using VSM and also XRD, TEM and DSC studies have been used to support the conclusions derived using Mössbauer spectroscopy.     

Supramolecular interactions in some organic hydrated 2,4,6-triaminopyrimidinium carboxylate and sulfate salts

Four salts, namely, 2,4,6-triaminopyrimidinium 6-chloronicotinate dihydrate, C₄H₈N₅⁺·C₆H₃ClNO₂⁻·2H₂O, (I), 2,4,6-triaminopyrimidinediium pyridine-2,6-dicarboxylate dihydrate, C₄H₉N₅²⁺·C₇H₃NO₄²⁻·2H₂O, (II), 2,4,6-triaminopyrimidinediium sulfate monohydrate, C₄H₉N₅²⁺·SO₄²⁻·H₂O, (III), and 2,4,6-triaminopyrimidinium 3,5-dinitrobenzoate dihydrate, C₄H₈N₅⁺·C₇H₃N₂O₆⁻·2H₂O, (IV), were synthesized and characterized by X-ray diffraction techniques. Proton transfer from the corresponding acid to the pyrimidine base has occurred in all four crystal structures. Of the four salts, two [(I) and (IV)] exist as monoprotonated bases and two [(II) and (III)] exist as diprotonated bases. In all four crystal structures, the acid interacts with the pyrimidine base through N—H…O hydrogen bonds, generating an R₂²(8) ring motif. The sulfate group mimics the role of the carboxylate anions. The water molecules present in compounds (I)–(IV) form water-mediated large ring motifs. The formation of water-mediated interactions in these crystal structures can be used as a model in the study of the hydration of nucleobases. Water molecules play an important role in building supramolecular structures. In addition to these strong hydrogen-bonding interactions, some of the crystal structures are further enriched by aromatic π–π stacking interactions [(I) and (II)].