Ab-initio study of electronic and elastic properties of B2-type ductile YM (M=Cu, Zn and Ag) intermetallics

A theoretical study of structural, electronic, elastic, thermal and mechanical properties of nonmagnetic intermetallics YM (M=Cu, Zn and Ag), which crystallize in CsCl-type structure, is performed using first principles density functional theory based on full potential linearized augmented plane wave (FP-LAPW) method. The calculations are carried out within the generalized gradient approximation (GGA) for the exchange correlation potential. The calculated ground state properties such as lattice constants, bulk modulus and elastic constants agree well with the experiment. From energy dispersion curves, it is found that these compounds are metallic in nature. The ductility of these intermetallics is determined by calculating the bulk to shear ratio B/G_H. The calculated results indicate that YAg is the most ductile amongst the present YM compounds. The results obtained are compared with the available experimental and theoretical results. The mechanical and thermal properties are predicted from the calculated values of elastic constants.     

CuAAC macrocyclization: high intramolecular selectivity through the use of copper-tris(triazole) ligand complexes

A range of multivalent heteroaryl ligands, copper sources, and solvent systems have been investigated for use in CuAAC-mediated macrocyclization reactions. These studies have revealed the key factors governing selectivity for macrocyclization versus dimerization and identified a simple but specific set of reaction conditions capable of efficiently generating a diverse series of drug-like macrocycles at modest dilution in up to 95% yield.     

Meson production in p + d reactions

Total and differential cross sections for the reactions p + d → ³He + m ⁰ with m=π, η and p + d → ³H+π⁺ were measured with the GEM detector at COSY for beam momenta between threshold and the maximum of the corresponding baryon resonance. For both reactions a strong forward-backward asymmetry was found. The data were compared with model calculations. The aspect of isospin symmetry breaking is studied. Representing the GEM Collaboration     

The onset of coulomb explosions in polyatomic molecules

With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd.     

Ab?initio study of the phonon spectrum, entropy and lattice heat capacity of disordered Re-W alloys

The Re(1-x)W(x) alloy is formed by continuous neutron bombardment of W, the core material making up the shield in fusion devices. Here, we present an ab?initio study of the lattice dynamical properties of this commercially important alloy. The dynamical (force constant) matrix was obtained through a first-principles, density functional perturbation theory. Various vibrational properties, such as fuzzy phonon dispersion relations, density of states (DOS), scattering life-times, vibrational entropy and specific heat are studied. The effects of short-range ordering is shown to be important in the 50-50 alloy.     

A task-specific ionic liquid [bmim]SCN for the conversion of alkyl halides to alkyl thiocyanates at room temperature

A new “task-specific” ionic liquid (TSIL), 1-n-butyl-3-methylimidazolium thiocyanate ([bmim]SCN), has been prepared and used for the first time as the medium as well as reactant for the synthesis of alkyl thiocyanates from the corresponding alkyl halides by thiocyanate-halide exchange at room temperature. The alkyl thiocyanate products can be easily isolated from the reaction mixture by simple extraction and the ionic liquid 1-n-butyl-3-methylimidazolium halide may be reused for the synthesis of the ionic liquid [bmim]SCN and recycled for further use.     

Quinine as an organocatalytic dual activator for the diastereoselective synthesis of spiro-epoxyoxindoles

A highly efficient organocatalytic approach has been developed for the diastereoselective epoxidation of (E)-3-ylidene-indolin-2-one derivatives using readily available natural product quinine and urea-hydrogen peroxide (UHP) in DCM at 10 °C to afford trans spiro-epoxyoxindoles which were further utilized to obtain β-hydroxy-α-amino esters by water mediated regioselective ring opening from the less hindered end with aniline derivatives, under sonication.