Zn[(l)proline]2 in water: A new easily accessible and recyclable catalytic system for the synthesis of pyrazoles

Zn[(l)proline]₂ has been found to be an efficient catalyst for the synthesis of pyrazole derivatives in pure water at room temperature. Reaction afforded moderate to excellent yield within a lesser time. Various pyrazoles which could not be prepared by other methods can be easily prepared by this method efficiently. Catalyst exhibits recyclability up to five runs. Hence our present protocol is economical and clean comprise of green reagent, solvent and catalyst.     

Interatomic exchange in Mn-doped III-V semiconductors

Density-functional calculations are used to determine the electronic structure and magnetic properties of dilute magnetic semiconductors with the composition X_1−xMn_xN (X=Al, Ga, In, x=6.25% and 12.5%). Emphasis is on the interatomic exchange as a function of the Mn-Mn distance. Our superlattice calculations show that the Mn dopants are spin-polarized with a half-metallic band gap and a magnetic moment of 4 μ_B per Mn atom at x=6.25 and 12.5%. The Mn (3d) bands lie in the band gap but partially hybridize with valence band or N 2p electrons, depending on the group-III element and on the spin direction. To calculate the exchange interaction parameters J_ij, we have used a Green-function approach. The interaction between Mn atoms extends over several interatomic interactions and is mediated by nitrogen (2p) electrons. The exchange is always ferromagnetic and largest for the first nearest neighbors, but substantial ferromagnetic interactions persist over Mn-Mn distances up to sixth nearest neighbors in the considered supercell.     

Magnetic nanoparticles catalyzed synthesis of diverse N-Heterocycles

A large library of diversified compounds (pyrano [2,3-d]pyrimidines, pyrido[2,3-d] pyrimidines and a variety of spirooxindoles) were synthesized through a very efficient, economical and environmentally benign process utilizing magnetic nanoparticles. Ease of recovery using an external magnetic field is an additional ecofriendly attribute of this catalytic system. Most of the compounds are new; therefore, could be further explored for their pharmaceutical application. Moreover, column chromatography and recrystallisation of the products is not required as the crude products are already highly pure and hence can be used for target oriented synthesis on a wide scale.     

Numerical investigation of space charge electric field for a sheet electron beam between two conducting planes

Analytical and numerical study of the stability of sheet electron beam in periodically cusped magnetic field (PCM) is made. The beam has been considered as having diffused density profile. The conditions for beam focusing are discussed.     

Semiflexible polymers in a random environment

We present using simple scaling arguments and one step replica symmetry breaking a theory for the localization of semiflexible polymers in a quenched random environment. In contrast to completely flexible polymers, localization of semiflexible polymers depends not only on the details of the disorder but also on the ease with which polymers can bend. The interplay of these two effects can lead to the delocalization of a localized polymer with an increase in either the disorder density or the stiffness. Our theory provides a general criterion for the delocalization of polymers with varying degrees of flexibility and allows us to propose a phase diagram for the highly folded (localized) states of semiflexible polymers as a function of the disorder strength and chain rigidity.     

Dithiomethylether as a ligand in the hydrogenase h-cluster

An X-ray crystallographic refinement of the H-cluster of [FeFe]-hydrogenase from Clostridium pasteurianum has been carried out to close-to atomic resolution and is the highest resolution [FeFe]-hydrogenase presented to date. The 1.39 A, anisotropically refined [FeFe]-hydrogenase structure provides a basis for examining the outstanding issue of the composition of the unique nonprotein dithiolate ligand of the H-cluster. In addition to influencing the electronic structure of the H-cluster, the composition of the ligand has mechanistic implications due to the potential of the bridge-head gamma-group participating in proton transfer during catalysis. In this work, sequential density functional theory optimizations of the dithiolate ligand embedded in a 3.5-3.9 A protein environment provide an unbiased approach to examining the most likely composition of the ligand. Structural, conformational, and energetic considerations indicate a preference for dithiomethylether as an H-cluster ligand and strongly disfavor the dithiomethylammonium as a catalytic base for hydrogen production.     

The structure–activity relationship of some hexacoordinated dimethyltin(IV) complexes of fluorinated β‐diketone/β‐diketones and sterically congested heterocyclic β‐diketones

The study was focused on the structure–activity relationship of some newly synthesized hexacoordinated dimethyltin(IV) complexes of fluorinated β‐diketone/β‐diketones and sterically congested heterocyclic β‐diketones. These complexes were screened for their antibacterial activity against a Gram‐negative bacterium (Pseudomonas aeruginosa) and Gram‐positive bacteria (Streptomyces griseus, Staphylococcus aureus, Bacillus subtilis) and the results were compared with those of a standard antibacterial drug. Some of the complexes were also screened for their antifungal activity against various fungi (Aspergillus niger, A. flavus, Trichoderma viride, Fusarium oxysporum) and were found to be active. These new hexacoordinated complexes of dimethyltin(IV) were generated by reactions of dimethyltin(IV) dichloride and sodium salts of fluorinated β‐diketone/β‐diketones and sterically congested heterocyclic β‐diketones in 1:1:1 molar ratio in refluxing dry benzene. Plausible structures of these complexes were suggested with the aid of physicochemical and spectroscopic studies. ¹¹⁹Sn NMR spectral data revealed the presence of a hexacoordinated tin centre in these dimethyltin(IV) complexes. Copyright © 2015 John Wiley & Sons, Ltd.