Local structure of the high-temperature thermoelectric material PbTe using the maximum entropy method (MEM) and pair distribution function (PDF)

The electron density distribution and the local structure of the high temperature thermoelectric material PbTe has been studied. Powder X-ray data set of PbTe is analyzed in terms of cell parameter, thermal vibration parameters, 1D, 2D and 3-dimensional electron density distributions. The bonding between the atoms using the maximum entropy method (MEM) and bond-length distribution using pair distribution function (PDF) have been analyzed. Both the pictorial and the numerical results of electron density and PDF studies show mixed ionic and covalent characters in PbTe.     

The catalytic role of polyaniline salt in coumarins synthesis

Polyaniline‐sulfate salt acts as a simple and powerful polymer‐supported acid catalyst in the condensation of phenolic compounds and β‐keto esters into coumarin derivatives by a thermal heating process. This process is being reported for the first time. The catalytic use of polyaniline salt is quite feasible because of its easy preparation, activity, recovery, recyclability, stability and eco‐friendliness of the catalyst. Copyright © 2004 John Wiley & Sons, Ltd.     

2‐[(E)‐(4‐Chloro­phenyl)­methyl­ene­amino]‐N‐(X‐methyl­phenyl)‐4,5,6,7‐tetra­hydro‐1‐benzo­thio­phene‐3‐carbox­amide,where X = 2 and 3

The title compounds, both C₂₃H₂₁ClN₂OS, are isomeric, with (I) and (II) being the N‐3‐methyl­phenyl and N‐2‐methyl­phenyl derivatives, respectively. The dihedral angle between the 4‐chloro­phenyl group and the thio­phene ring in (II) [38.1 (1)°] is larger than that in (I) [7.1 (1)°], indicating steric repulsion between the chloro­phenyl and o‐toluidine groups in (II). In both compounds, an intramolecular N—H⋯N hydrogen bond forms a pseudo‐six‐membered ring, thus locking the molecular conformation. In the crystal structures, mol­ecules are connected via N—H⋯O hydrogen bonds, forming chains along the b axis in (I) and along the c axis in (II). Intermolecular C—H⋯O/S and π–π interactions are also observed in (II), but not in (I).     

Voltammetric determination of nitroaromatic and nitramine explosives contamination in soil

The contamination of soil by nitroaromatic and nitramine explosives is widespread during the manufacture, testing and disposal of explosives and ammunitions. The analysis for the presence of trace explosive contaminants in soil becomes important in the light of their effect on the growth of different varieties of plants and crops. 2,4,6-Trinitrotoluene (TNT), cyclotrimethylene trinitramine (Research Department explosive, RDX) and cyclotetramethylene tetranitramine (high melting point explosive, HMX), other related explosive compounds and their by-products must be monitored in soil and surrounding waterways since these are mutagenic, toxic and persistent pollutants that can leach from the contaminated soil to accumulate in the food chain. In this study, a voltammetric method has been developed for the determination of explosive such as RDX, HMX and TNT. The electrochemical redox behavior of RDX, HMX and TNT was studied through cyclic voltammetry and quantitative determination was carried out by using square wave voltammetry technique. Calibration curves were drawn and were linear in the range of 63-129 ppm for RDX with a detection limit of 10 ppm, 49-182 ppm for HMX with a detection limit of 1 ppm and 38-139 ppm for TNT with a detection limit of 1 ppm. This method was applied to determine the contaminations in several soil samples that yielded a relative error of 1% in the concentrations.     

Regio- and stereoselective synthesis of methyl 5-methylenetetrahydropyran-3-carboxylates from Baylis-Hillman adducts via allyltributylstannane-mediated radical cyclization

Two types of regioisomeric methyl 5-methylenetetrahydropyran-3-carboxylate derivatives 3a-c and 6a-c were synthesized stereoselectively starting from the Baylis-Hillman adducts via the allyltributylstannane-mediated vinyl radical cyclization as the key step.     

Effect of Varying Dzyaloshinskii-Moriya Interaction on the Bistable Nano-Scale Soliton Switching

The effect of Dzyaloshinskii-Moriya (D-M) interaction on the bistable nano-scale soliton switching offers the possiblity of developing a new innovative approach for data storage technology. The dynamics of Heisenberg ferromagnetic spin system is expressed in terms of generalized inhomogeneous higher order nonlinear Schrödinger (NLS) equation. The bistable soliton switching in the ferromagnetic medium is established by solving the associated coupled evolution equations for amplitude and velocity of the soliton using the fourth order Runge-Kutta method numerically.     

Doping level of Mn in high temperature grown Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O studied through electronic charge distribution,magnetization, and local structure

Mn inclusion in the oxide based diluted magnetic semiconductor Zn_1−x Mn _x O (x = 0.04, 0.06, 0.08, and 0.10) grown by standard high temperature solid state reaction technique has been studied. The local and average structure of Zn_1−x Mn _x O was characterized by the super resolution technique maximum entropy method and pair distribution function analysis using the X-ray powder data. Magnetic studies on this material using a Vibrating Sample Magnetometer were also carried out to ascertain the doping level in Zn_1−x Mn _x O.     

Unraveling the Rationale Behind Organic Solvent Stability of Lipases

Organic solvent-stable lipases have pronounced impact on industrial economy as they are involved in synthesis by esterification, interesterification, and transesterification. However, very few of such natural lipases have been isolated till date. A study of the recent past provided few pillars to rely on for this work. The three-dimensional structure, inclusive of the surface and active site, of 29 organic solvent-stable lipases was analyzed by subfamily classification and protein solvent molecular docking based on fast Fourier transform correlation approach. The observations revealed that organic solvent stability of lipases is their intrinsic property and unique with respect to each lipase. In this paper, factors like surface distribution of charged, hydrophobic, and neutral residues, interaction of solvents with catalytically immutable residues, and residues interacting with essential water molecules required for lipase activity, synergistically and by mutualism contribute to render a stable lipase organic solvent. The propensity of surface charge in relation to stability in organic solvents by establishing repulsive forces to exclude solvent molecules from interacting with the surface and prohibiting the same from gaining entry to the protein core, thus stabilizing the active conformation, is a new finding. It was also interesting to note that lipases having equivalent surface-exposed positive and negative residues were stable in a wide range of organic solvents, irrespective of their LogP values.     

Post-synthesis dispersion of metal nanoparticles by poly(amidoamine) dendrimers: size-selective inclusion, water solubilization, and improved catalytic performance

Intermetallic Pt(3)Ti nanoparticles are solubilized in water by using a generation-five, hydroxyl-terminated, poly(amidoamine) dendrimer, G5OH, as a post-synthesis surfactant. Pt(3)Ti nanoparticles, encapsulated in G5OH and dispersed over the electrode surface, exhibited a superior catalytic activity toward the electro-reduction reaction of oxygen compared to as-prepared, highly agglomerated nanoparticles.     

Synthesis of dypnone by solvent free self condensation of acetophenone over nano-crystalline sulfated zirconia catalyst

Nano-crystalline sulfated zirconia catalyst, prepared by two-step sol–gel method, has been studied for the solvent free self condensation of acetophenone to dypnone. The influence of calcination temperature on the structural, textural and catalytic activity of sulfated zirconia has been analyzed. The surface acidity along with the structural and textural features of the catalyst influenced its activity. The conversion of acetophenone was found to be effected by the variation in the reaction and calcination temperature, however, the dypnone selectivity was not affected much. The catalyst calcined at 650 °C, showed maximum dypnone selectivity of 92% with 68.2% acetophenone conversion at 170 °C after 7 h. The catalyst was reused up to five cycles with marginal decrease in acetophenone conversion, however, without losing its selectivity for dypnone.