Recoil128I atoms in iodine pentoxide under /n, γ/ process

An attempt js made to study the behaviour of recoil¹²⁸I atoms in neutron irradiated I₂O₅ at ambient temperature. The initial retention is found to be 44±2%. However, a substantial increase /57±2%/ in the value is observed upon heating the sample at 473 K for 1 h prior to irradiation. A kinetic study of post-recoil thermal annealing of neutron irradiated material is also presented. Effect of pre-heat treatment results in a decrease of rate constants and saturation retention values at respective temperatures while the E_act for the overall process remains almost unaltered.     

Extraction of Zr(IV) by TBP-DMSO and TBP-Py from aqueous solutions containing monobasic acids

The distribution ratios for the extraction of Zr(IV) by TBP and its binary mixtures with DMSO or Py in n-dodecane in the presence of HNO₃, and HClO₄ have been determined. Based on stoichiometric and slope analysis methods a possible mechanism for the extraction has been proposed.     

Formation of YAG from coprecipitated yttrium aluminium hydroxides

Thermal decomposition of the amorphous coprecipitate of yttrium and aluminium hydroxides forming yttrium aluminium garnet has been investigated employing thermal analyses, X-ray diffraction and IR spectroscopy. On heating, the coprecipitate progressively loses water forming a stable but highly disordered hydroxy garnet which crystallizes at 1180 K and decomposes to YAG at 1290 K. Nucleation of the crystalline phase appears to begin at 800 K.The authors thank Dr. P. V. Ravindran of the Analytical Chemistry and Shri N. K. Kulkarni of the Fuel Chemistry Divisions of BARC for their assistance in the thermoanalytical experiments.     

One pot,three component 1,3 dipolar cycloaddition: Regio and diastereoselective synthesis of spiropyrrolidinyl indenoquinoxaline derivatives

A competent and highly discriminating one-pot synthesis of highly diversified novel functionalized indenoquinoxalone grafted spiropyrrolidine linked chromene-3-carbonitrile conjugates accumulating three pharmocophoric cores, heterocyclic indenoquinoxalone, pyrrolidines and chromene-3-carbonitrile in a single molecular framework by means of 1,3-dipolar cycloaddition reaction between indenoquinoxalone, proline/benzyl amine and chromene-3-carbonitrile in ethanol under classical and microwave conditions is described. The three component 1,3-dipolar cycloaddition reaction proceeds via in situ generation of azomethine ylides by the decarboxylative condensation of indenoquinoxalone with proline/benzyl amine and their selectivity towards the endo cyclic double bonds of dipolarophile (chromene-3-carbonitrile) leading to the formation of highly functionalised regio- and diastereoselective molecular hybrids. This methodology exemplifies the green chemistry protocol such as mild reaction conditions, high yields, one-pot procedure and operational simplicity.     

Site-selective C–H nitration of N-aryl-7-azaindoles under palladium(II) catalysis

The site-selective C–H nitration reaction of 7-azaindoles with t-butyl nitrite under palladium catalysis is described. This protocol provides an efficient method for the construction of ortho-nitrated N-aryl-7-azaindoles with excellent site-selectivity and functional group compatibility. The formed 7-azaindole derivatives can be readily transformed into 7-azaindoles containing an aniline functional group under palladium-catalyzed hydrogenation conditions.     

Temperature-dependent vibrational spectroscopic studies of pure and gold nanoparticles dispersed 4-n-Hexyloxy-4’-cyanobiphenyls

Raman spectra of pure and 2 wt.% gold nanoparticles (GNPs) dispersed liquid crystalline compound 4-n-Hexyloxy-4?- cyanobiphenyls (6OCB) has been recorded as a function of temperature from room temperature (solid crystal) to 80°C (isotropic liquid) in the spectral region of 500–2500 cm^?1. The variation of Raman spectral parameters (peak positions and line width) with temperature is used to explain the changes in molecular alignment and its effect on inter-/intra-molecular interactions at crystal-Nematic (K-N) transition. To understand the change in molecular structure during phase transition and on account of dispersion of gold nanoparticles in pure liquid crystal more precisely, two spectral regions 1000–1500 cm^?1 and 1500–2400 cm^?1 have been selected separately. From the detailed study, it is concluded that increased orientational/vibrational freedom of the molecules as well as delocalisation of electron clouds results in the spectral anomalies at K-N transition. The geometrical structure of 6OCB was optimised using density functional theory (DFT) and theoretical Raman spectra have been obtained for comparison with experimental spectra. The tentative assignment of vibrational modes observed in our region of study was calculated based on potential energy distribution (PED) using vibrational energy distribution analysis (VEDA) calculation.     

Terminal Hydride Species in [FeFe]‐Hydrogenases Are Vibrationally Coupled to the Active Site Environment

A combination of nuclear resonance vibrational spectroscopy (NRVS), FTIR spectroscopy, and DFT calculations was used to observe and characterize Fe?H/D bending modes in CrHydA1 [FeFe]‐hydrogenase Cys‐to‐Ser variant C169S. Mutagenesis of cysteine to serine at position 169 changes the functional group adjacent to the H‐cluster from a ‐SH to ‐OH, thus altering the proton transfer pathway. The catalytic activity of C169S is significantly reduced compared to that of native CrHydA1, presumably owing to less efficient proton transfer to the H‐cluster. This mutation enabled effective capture of a hydride/deuteride intermediate and facilitated direct detection of the Fe?H/D normal modes. We observed a significant shift to higher frequency in an Fe?H bending mode of the C169S variant, as compared to previous findings with reconstituted native and oxadithiolate (ODT)‐substituted CrHydA1. On the basis of DFT calculations, we propose that this shift is caused by the stronger interaction of the ‐OH group of C169S with the bridgehead ‐NH‐ moiety of the active site, as compared to that of the ‐SH group of C169 in the native enzyme.     

Preparation of Cs2ZrO3 and Cs2ThO3 Through Sol-gel Method and Their Characterization

Cesium zirconate and cesium thorate were prepared by sol-gel method following citrate-nitrate route. The compounds were characterized by X-ray diffraction, chemical analysis and simultaneous TG-DTA. The methods of preparation of Cs₂ZrO₃ and Cs₂ThO₃ reported in literature involve difficult steps and require stringent experimental conditions for obtaining the compounds. In this work we report an easier method for the preparation of these compounds at relatively low temperature. This revised version was published online in July 2006 with corrections to the Cover Date.     

An ab initio study of water clusters in gas phase and bulk aqueous media: (H2O)n,n=1–12

Geometries of several clusters of water molecules including single minimum energy structures of n‐mers (n=1–5), several hexamers and two structures of each of heptamer to decamer derived from hexamer cage and hexamer prism were optimized. One structural form of each of 11‐mer and 12‐mer were also studied. The geometry optimization calculations were performed at the RHF/6‐311G* level for all the cases and at the MP2/6‐311++G** level for some selected cases. The optimized cluster geometries were used to calculate total energies of the clusters in gas phase employing the B3LYP density functional method and the 6‐311G* basis set. Frequency analysis was carried out in all the cases to ensure that the optimized geometries corresponded to total energy minima. Zero‐point and thermal free energy corrections were applied for comparison of energies of certain hexamers. The optimized cluster geometries were used to solvate the clusters in bulk water using the polarized continuum model (PCM) of the self‐consistent reaction field (SCRF) theory, the 6‐311G* basis set, and the B3LYP density functional method. For the cases for which MP2/6‐311++G** geometry optimization was performed, solvation calculations in water were also carried out using the B3LYP density functional method, the 6‐311++G** basis set, and the PCM model of SCRF theory, besides the corresponding gas‐phase calculations. It is found that the cage form of water hexamer cluster is most stable in gas phase among the different hexamers, which is in agreement with the earlier theoretical and experimental results. Further, use of a newly defined relative population index (RPI) in terms of successive total energy differences per water molecule for different cluster sizes suggests that stabilities of trimers, hexamers, and nonamers in gas phase and those of hexamers and nonamers in bulk water would be favored while those of pentamer and decamer in both the phases would be relatively disfavored. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 90–104, 2001     

Growth of Cyanobacteria: Optimization for Increased Carbohydrate Content

Growths of Lyngbya limnetica and Oscillatoria obscura were investigated at varying pH, light intensity, temperature, and trace element concentration with a view to optimize these parameters for obtaining the maximum carbohydrate content. The maximum growth for both strains was obtained at pH 9.0 and temperature 20 ± 3 °C using a light intensity of 68.0 μmol m^?2 s^?1 with continuous shaking. Growth under the nitrogen starvation condition affected the carbohydrate content more compared to the phosphorus starvation, and maximum concentrations were found as 0.660 and 0.621 g/g of dry biomass for L. limnetica and O. obscura, respectively. Under the optimized nitrogen-rich conditions, the specific growth rates for the two strains were found to be 0.187 and 0.215 day^?1, respectively. The two-stage growth studies under nitrogen-rich (stage I) followed by nitrogen starvation (stage II) conditions were performed, and maximum biomass and carbohydrate productivity were found as 0.088 and 0.423 g L^?1 day^?1 for L. limnetica. This is the first ever attempt to evaluate and optimize various parameters affecting the growth of cyanobacterial biomass of L. limnetica and O. obscura as well as their carbohydrate contents.