Micron-particulate crystalline hexagonal aluminium nitride: a novel, efficient and versatile heterogeneous catalyst for the synthesis of some heterocyclic compounds

The present work reports the application of micron-particulate crystalline hexagonal aluminium nitride/aluminium as a novel, mild acidic and reusable solid heterogeneous catalyst in organic synthesis. The catalyst was synthesized by thermal plasma technique and characterized using X-ray diffractometer and scanning electron microscopy. It catalyzes efficiently many organic transformations such as the synthesis of heterocyclic compounds 2,4,5-triaryl-substituted imidazoles and 2-aryl benzimidazoles.     

Microwave Induced Bismuth Trichloride Catalysed Beckmann Rearrangement of Oximes

A new and efficient method for the rearrangement of oximes 1 has been achieved by a simple reaction of a ketoximes with bismuth trichloride under microwave irradiation in the solid state.     

Transition metal complexes of pyrazole head 24-membered polyazamacrocyclic bimetal cores: synthesis, characterization, electrochemistry and spectral study

A series of new 24-membered macrocyclic Co^II, Ni^II, Cu^II and Zn^II complexes of the ligands L¹H₂ and L²H₂ were prepared by the non-template and template methods respectively. The ligand L¹H₂ was formed by the condensation of pyrazole-3,5-dicarbohydrazide and glyoxal and all attempts to isolate the ligand L²H₂ were unsuccessful. These, ligand and transition metal complexes were characterized on the basis of elemental analysis, IR, ¹HNMR, UV–Visible, magnetic susceptibility measurements, ESR, conductivity measurements, FAB-mass and thermal analysis. The redox behavior of metal ions in the polyazamacrocyclic ligand field is also studied. Electroreduction of carbon dioxide to carbon monoxide is mainly focused on using polydentate azamacrocyclic ligands with amine and imine functionalities, based on the electrochemical behavior of nickel (II) ion in the macrocyclic territory.     

Triclabendazole: An Intriguing Case of Co‐existence of Conformational and Tautomeric Polymorphism

The crystal polymorphism of the anthelmintic drug, triclabendazole ( TCB ), is described. Two anhydrates (Forms I and II), three solvates, and an amorphous form have been previously mentioned. This study reports the crystal structures of Forms I ( 1 ) and II ( 2 ). These structures illustrate the uncommon phenomenon of tautomeric polymorphism. TCB exists as two tautomers A and B. Form I (Z′=2) is composed of two molecules of tautomer A while Form II (Z′=1) contains a 1:1 mixture of A and B. The polymorphs are also characterized by using other solid‐state techniques (differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), PXRD, FT‐IR, and NMR spectroscopy). Form I is the higher melting form (m.p.: 177 °C, ΔH_f=≈105±4 J g^?1) and is the more stable form at room temperature. Form II is the lower melting polymorph (m.p.: 166 °C, ΔH_f=≈86±3 J g^?1) and shows high kinetic stability on storage in comparison to the amorphous form but it transforms readily into Form I in a solution‐mediated process. Crystal structure analysis of co‐crystals 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 further confirms the existence of tautomeric polymorphism in TCB . In 3 and 11 , tautomer A is present whereas in 4 , 5 , 6 , 7 , 8 , 9 , 10 the TCB molecule exists wholly as tautomer B. The DFT calculations suggest that the optimized tautomers A and B have nearly the same energies. Single point energy calculations reveal that tautomer A (in Form I) exists in two low‐energy conformations, whereas in Form II both tautomers A and B exist in an unfavorable high‐energy conformation, stabilized by a five‐point dimer synthon. The structural and thermodynamic features of 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 are discussed in detail. Triclabendazole is an intriguing case in which tautomeric and conformational variations co‐exist in the polymorphs.     

Removal of Cr(VI) from Aqueous Solution Using Activated Cow Dung Carbon

Removal of hexavalent chromium from aqueous medium by using activated cow dung carbon was studied. Cow dung was carbonized and activated by treating with concentrated H(2)SO(4) followed by heating for 24 h at 120 degrees C. The extent of adsorption was studied as a function of pH, contact time, amount of adsorbent, concentration of adsorbate, and temperature. At lower pH (<3.5), the prepared sorbent was capable of removing approximately 90% Cr(VI) at 5 ppm concentration from aqueous synthetic solution. The dynamics of migration of the sorbate ions from the bulk onto the sorbent surface was studied and the results obtained under various experimental conditions were found to follow standard adsorption isotherms. The reaction kinetics was found to be of first order. Copyright 2000 Academic Press.     

Development of Petri Net-Based Dynamic Model for Improved Production of Farnesyl Pyrophosphate by Integrating Mevalonate and Methylerythritol Phosphate Pathways in Yeast

In this case study, we designed a farnesyl pyrophosphate (FPP) biosynthetic network using hybrid functional Petri net with extension (HFPNe) which is derived from traditional Petri net theory and allows easy modeling with graphical approach of various types of entities in the networks together. Our main objective is to improve the production of FPP in yeast, which is further converted to amorphadiene (AD), a precursor of artemisinin (antimalarial drug). Natively, mevalonate (MEV) pathway is present in yeast. Methyl erythritol phosphate pathways (MEP) are present only in higher plant plastids and eubacteria, but not present in yeast. IPP and DAMP are common isomeric intermediate in these two pathways, which immediately yields FPP. By integrating these two pathways in yeast, we augmented the FPP synthesis approximately two folds higher (431.16 U/pt) than in MEV pathway alone (259.91 U/pt) by using HFPNe technique. Further enhanced FPP levels converted to AD by amorphadiene synthase gene yielding 436.5 U/pt of AD which approximately two folds higher compared to the AD (258.5 U/pt) synthesized by MEV pathway exclusively. Simulation and validation processes performed using these models are reliable with identified biological information and data.     

Proton transfer and N(+)-H...S(-) hydrogen bonds in the crystal structure of 4-aminothiophenol

4-Aminothiophenol exists as 4-ammonio-1-benzenethiolate in the solid and liquid state. The crystal structure is characterised by a tetrahedral beta-As type network which is the driving force for the proton transfer.     

Regio- and stereoselective transfer of p-toluenesulfonamido group from sulfur to carbon: preparation of aminoalcohol derivatives from allylalcohols

A novel methodology for the regio- and stereoselective synthesis of amino alcohol derivatives from allylalcohols/ethers via intramolecular nucleophilic participation by the sulfilimine moiety is disclosed. The sulfilimine moiety is stereospecifically transformed to a sulfinyl moiety with an inverted configuration. The reaction is general and affords highly functionalised products.     

Mixed Ligand Complexes of Am3+, Cm3+ and Eu3+ with HEDTA and HEDTA + NTA—Complexation Thermodynamics and Structural Aspects

The stability constants and the associated thermodynamic parameters of formation for the 1:1 binary complexes of Am³⁺, Cm³⁺ and Eu³⁺ with N-(2-hydroxyethyl) ethylenediaminetriacetate (HEDTA) and their 1:1:1 ternary complexes with HEDTA + NTA (nitrilotriacate) were determined by distribution ratio measurements using solvent extraction in aqueous solutions of I=0.10?mol?L^?1 (NaClO₄) at temperatures of 0?C45?°C. Formation of these complexes is favored by both the enthalpy (exothermic) and the entropy (endothermic) terms. Luminescence lifetime measurements with Cm and Eu were used to study the coordination environment of these complexes over a range of concentrations and pH values. In the binary complexes M(HEDTA), HEDTA is a hexadentate ligand with three waters of hydration, while in the ternary complexes M(HEDTA)(NTA)^3? we propose that the HEDTA retaines hexadentate coordination with NTA binding via three sites, depending on the pH of the solution, with the observation that the complex may contain a single water of hydration.