13C NMR of indazoles

The carbon-13 chemical shifts and some selected coupling constants of 183 indazoles are reported. The main conclusions of the original references are briefly summarized.Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1159–1179, September, 1995.     

Theoretical study on interaction of different coordination modes of BH4 ligand with transition metal in [TM(BH4)(CO)4] (TM = Cr, Mo)

Density functional calculations were performed on bonding and structural features of [(ηⁿ-BH₄)TM(CO)₄]⁻ (n = 1, 2, 3; TM = Cr, Mo) complexes. Calculations show that the ground state is bidentate which is in good agreement with experimental results. It has been found that the bridge and terminal hydrogen atoms will interchange by two pathways: (i) twist of BH₄ about one of the bridge B-H and (ii) twist of BH₄ about one of the terminal B-H. The molecular orbital calculations and natural bond orbital methodologies for different isomers of these complexes have been evaluated. The final results indicate that case (i) is more preferable relative to another case.     

Honeycomb nets with interpenetrating frameworks involving iminodiacetato-copper(II) blocks and bipyridine spacers: syntheses, characterization, and magnetic studies

Three coordination polymers of copper(II), viz. ([Cu(ida)(4,4'-bipyH)]ClO(4))( proportional, variant ) (1), ([Cu(2)(ida)(2)(micro-4,4'-bipy)].2H(2)O)( proportional, variant ) (2), and [Cu(2)(ida)(2)(bpa)]( proportional, variant ) (3) have been synthesized by the process of self-assembly using Cu(ida) [ida = iminodiacetate(2-)] as the building block and 4,4'-bipyridyl and 1,2-bis(4-pyridyl)ethane (bpa) as linkers. Crystals of 1 are orthorhombic, of space group Pna2(1), with a = 13.8956(12) A, b = 16.3362(16) A, c = 7.3340(12), and Z = 4. Both compounds 2 and 3 crystallize in monoclinic space group P2(1)/a with a = 10.1887(8) A (9.6779(10) A for 3), b = 8.0008(11) A (9.1718(10) A), c = 11.6684(9) A (12.9144(12) A), beta = 98.307(11) degrees (102.796(18) degrees ), and Z = 2 (2). Compound 1 has a zigzag chain structure with an extensive hydrogen-bonded network while compounds 2 and 3 are honeycomb (6,3) nets with interpenetrating structures. Variable temperature (2-300 K) magnetic study indicates the presence of weak antiferromagnetic interactions (J = 0.82 +/- 0.01 cm(-)(1)) in 1 and ferromagnetic in 2 (J = -0.45 +/- 0.05 cm(-)(1)) and 3 (J = -0.21 +/- 0.02 cm(-)(1)). The extent of planarity of the bridging "Cu-O-C-O-Cu" moiety, acting as the super-exchange pathway between the neighboring copper centers, probably controls the sign of the magnetic exchange coupling in these compounds.     

Solid phase extraction of nitrate and nitrite anions using naturally and available sorbent

Radioactive waste contains nitrate and nitrite as well as radioactive fission products. Nitrate and nitrite anions are two of the major components of nuclear waste streams and contribute to environmental release hazards. The removal of nitrate and nitrite is a necessary step for the further treatment low-level radioactive wastes. The focus of the research is to evaluate the adsorption potential of solid phase derived from rice straw for nitrate and nitrite anions in single- and binary-component systems due to the fact that the rice straw is a very abundant and by-product material. The removal was accomplished under the optimize conditions of temperature, concentration, pH, contact time and quantity of adsorbent as these parameters are some of the main factors influencing the uptake of two solutes at the solid–solution interface. Batch-mode kinetic and equilibrium studies have been carried out. The experimental data was analyzed using equilibrium isotherm and kinetic models. The thermodynamic parameters (?G°, ?H°, and ?S°) were also determined using the equilibrium constant value obtained at different temperatures. Results show that this adsorbent is effective and much better or even superior than many sorbents for removal of nitrate and nitrite. The prepared sorbent as solid-phase extractant was successfully applied for the extraction of nitrate from actual water samples.     

An efficient one-pot multi-component synthesis of 3,4,5-substituted furan-2(5H)-ones catalyzed by tetra-n-butylammonium bisulfate

A facile one-pot synthesis of 3,4,5-substituted furan-2(5H)-one derivatives from a three-component reaction of aniline derivatives, dialkylacetylenedicarboxylates and aromatic aldehydes under mild conditions using tetra-n-butylammonium bisulfate as a catalyst has been developed.     

Catalytic behaviors of Co-Mn/TiO2 catalysts for Fischer-Tropsch synthesis

The 15%(Co-Mn)/TiO₂,(Co/Mn=1/6) catalyst was prepared using fusion procedure and studied for the conversion of synthesis gas to C_2~4 olefins. The effects of calcination conditions and operation conditions such as the H₂/CO molar feed ratio at different temperatures, gas hourly space velocity (GHSV) and total reaction pressure on the catalytic performance of catalyst were investigated. The stability of the catalyst during 150 h at optimal operation conditions (t=250 ℃ H₂/CO=2/1, GHSV=1 500 h^-1 and p=0.3 MPa) has been investigated. It is found that this catalyst is high stable for production C_2~4 olefins. Characterizations of both precursors and calcined catalysts by powder X-ray diffraction, scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) specific surface area measurement and thermal analysis methods such as thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) show that the different preparation method influences the catalyst precursor structure and morphology.     

Intramolecular hydrogen bonding in chemoselective synthesized 2-substituted pyrrole stable phosphorus ylide: GIAO, AIM, and NBO approaches

The chemoselectivity of geometrically ylide compounds is often hard to assign from experimental techniques, particular system with intramolecular hydrogen bonding (IHB) are even more challenging. Herein, theoretical calculations were performed to investigate whether theoretical results would provide consistent evidence for the existence of IHB to confirm experimental data and to evaluate strength of the N–H···O IHB from geometrical synthesized 2-substituted pyrrole stable phosphorus ylide (dimethyl 2-(1H-pyrrol-2-yl)-3-(triphenylphosphoranylidene) butanedioate in a single chemoselective compound. Topological parameters at the bond critical points (BCP) of intramolecular hydrogen bonds from Bader’s atoms in molecules (AIM) theory and Winhold’s natural bond orbital (NBO) calculations were analyzed at the B3LYP/6-311++g** level in details. A series of gage-including atomic orbital chemical shift (GIAO c.s.) calculations at the HF and DFT levels of theory were carried out to assign the ¹H NMR chemical shifts. The best prediction of the experimental ¹H NMR values was obtained at the mPW1PW91 levels using the 6-31G** basis set. Theoretical results, in agreement with the experimental data, were confirmed the N–H···O IHB was caused the deshielding of the proton to lower field. The barriers in double bond and single bond rotation were theoretically estimated in detailed and the AIM and NPA approaches were confirmed the loss of charge of the hydrogen atom involving in intramolecular N–H···O hydrogen bonding. The geometrical and topological parameters from AIM and NBO analyses were indicated the medium N–H···O IHB.     

In Silico and Experimental Characterization of Chimeric Bacillus thermocatenulatus Lipase with the Complete Conserved Pentapeptide of Candida rugosa Lipase

Lipases are one of the highest value commercial enzymes as they have broad applications in detergent, food, pharmaceutical, and dairy industries. To provide chimeric Bacillus thermocatenulatus lipase (BTL2), the completely conserved pentapeptide (¹¹²Ala-His-Ser-Gln-Gly¹¹⁶) was replaced with similar sequences (²⁰⁷Gly-Glu-Ser-Ala-Gly²¹¹) of Candida rugosa lipase (CLR) at the nucleophilic elbow region. For this purpose, three mutations including A112G, H113E, and Q115A were inserted in the conserved pentapeptide sequence of btl2 gene. Based on the crystal structures of 2W22, the best structure of opened form of the chimeric lipases were garnered using the MODELLER v9.10 software. The native and chimeric lipases were docked to a set of ligands, and a trial version of Molegro Virtual Docker (MVD) software was used to obtain the energy values. Docking results confirmed chimeric lipase to be better than the native lipase. Following the in silico study, cloning experiments were conducted and expression of native and chimeric btl2 gene in Pichia pastoris was performed. The native and chimeric lipases were purified, and the effect of these mutations on characteristics of chimeric lipase studied and then compared with those of native lipase. Chimeric lipase exhibited 1.6-fold higher activity than the native lipase at 55 °C. The highest percentage of both lipases activity was observed at 60 °C and pH of 8.0. The ion Ca²⁺ slightly inhibited the activity of both lipases, whereas the organic solvent enhanced the lipase stability of chimeric lipase as compared with the native lipase. According to the results, the presence of two glycine residues at the conserved pentapeptide region of this chimeric lipase (¹¹² Gly-Glu-Ser-Ala-Gly ¹¹⁶) may increase the flexibility of the nucleophilic elbow region and affect the enzyme activity level.     

One-pot five-component synthesis of highly functionalized piperidines using oxalic acid dihydrate as a homogenous catalyst

An efficient green protocol is described for the preparation of highly functionalized piperidines via a one-pot five-component reaction between aromatic aldehydes,anilines andβ-ketoesters in the presence of oxalic acid dihydrate as catalyst in ethanol at ambient temperature.The structure as well as the relative stereochemistry of these compounds was confirmed by single X-ray crystallographic analysis.     

Determination of traces of nitrite and nitrate in water by solid phase spectrophotometry

A simple and sensitive method for the determination of nitrite and nitrate in water using solid phase spectrophotometry is described. The method utilizes the quantitative and rapid sorption of the dye formed from nitrite, using the Griess reaction, into a thin layer of polyurethane foam (PUF) where a preconcentration factor of >140 has been achieved. Nitrate is pre-reduced using a cadmium reductor before applying the Griess reaction. The direct spectrophotometric measurement of the dye enriched in the solid foam phase has allowed the detection of as little as 5 and 40 ng ml⁻¹ nitrite and nitrate, respectively. Optimization of the parameters affecting the quantitative formation and sorption of the dye into PUF has been considered. Analysis of natural water samples has been performed.