Ab initio study of [001] GaN nanowires

We present the results of a study of structural, electronic, and optical properties of the unpassivated and H-passivated GaN nanowires having diameters in the range of 3.29 to 18.33 Å grown along [001] direction by employing the first-principles pseudopotential method within density functional theory in the local density approximation. Two types of nanowires having hexagonal and triangular cross-sections have been investigated. The binding energy increases with the diameter of the nanowire because of a decrease in the relative number of the unsaturated surface bonds. The binding energies of the triangular cross-sectional nanowires are somewhat smaller than those of the hexagonal cross-sectional nanowires in accordance with the Wulff’s rule except the smallest diameter triangular cross-sectional nanowire, where the binding energy is comparable with the corresponding hexagonal cross-sectional nanowires. The band gap varies rapidly with the diameter of the nanowire in the case of the smaller diameter nanowires, and quite slowly for the larger diameter nanowires. After atomic relaxation, appreciable distortion occurs in the nanowires, where the chains of Ga- and N-atoms are curved in different directions. These distortions are reduced with the diameters of the nanowires. The optical absorption in the GaN nanowires is quite strong in the ultra-violet region but an appreciable absorption is also present in the visible region for the larger diameter nanowires. The present results indicate the possibility of engineering the properties of nanowires by manipulating their diameter and surface structure. The presently predicted smaller diameter GaN nanowire possessing the triangular cross-section should be observable in the experiments.     

Synthesis and characterization of terbium doped TiO2 nanoparticles and their use as recyclable and reusable heterogeneous catalyst for efficient and environmentally sustainable synthesis of spiroannulated indolo[3,2-c]quinolines- mimetic scaffolds of isocryptolepine

An efficient and environmentally sustainable domino protocol has been presented for the synthesis of structurally diverse spiroannulated indolo[3,2-c]quinolines involving three component sequential reaction of phenylhydrazine, o-aminoacetophenone and cyclic ketones using nanostructured terbium doped TiO₂ as recyclable and reusable heterogeneous catalyst. The nanostructured catalyst was synthesized successfully and characterized by X-ray Diffraction (XRD), transmission electron microscopy (TEM), EDX and Fourier transform infra-red spectroscopy (FTIR). The substitution of Ti⁺⁴ with Tb⁺³ and the formation of Ti-O-Tb bonds as a result of doping of Terbium with TiO₂ NPs increases the catalytic efficiency and facilitates the reaction to provide the products in excellent yields. The present protocol with special features; operational simplicity, atom-economy, mild reaction conditions, environmental sustainability and high synthetic efficiency with recyclability and reusability of catalyst has been reported for the first time to synthesize spiroannulated indoloquinolines and expecting to provide the library of promising new leads in drug discovery research.     

Heat transfer and exergy analysis of solar air heater tube with helical corrugation and perforated circular disc inserts

Journal of Thermal Analysis and Calorimetry - The effects of perforated circular disc swirl generator on heat transfer (HT) and flow fields in a solar air heater helical corrugated tube have been...     

Carbonylative Suzuki coupling reactions catalyzed by ONO pincer–type Pd(II) complexes using chloroform as a carbon monoxide surrogate

Benzoylhydrazone Schiff base–ligated three new ONO pincer–type palladium(II) complexes, [(PdL¹(PPh₃)] ( 1 ), [(PdL²(PPh₃)] ( 2 ), and [(PdL³(PPh₃)] ( 3 ), were synthesized by the reaction of the respective ligand, N-(2-hydroxybenzylidene)benzohydrazide (HL¹), N-(2-hydroxy-3-methoxybenzylidene)benzohydrazide (HL²), or N-(5-bromo-2-hydroxybenzylidene) benzohydrazide (HL³), with Pd(OAc)₂ and PPh₃ in methanol and isolated as air-stable reddish-orange crystalline solids in high yields (78%–83%). All three complexes were fully characterized by elemental analysis, Fourier-transform infrared spectroscopy, UV–Visible, ¹H nuclear magnetic resonance (NMR), ¹³C{¹H} NMR, and ³¹P{¹H} NMR spectroscopic studies. The molecular structure of all three complexes was established unambiguously by single-crystal X-ray diffraction studies which revealed a distorted square planar geometry of all three complexes. The ONO pincer–type ligands occupied three coordination sites at the palladium, while the fourth site is occupied by the monodentate triphenylphosphine ligand. The catalytic potential of all three complexes was explored in the carbonylative Suzuki coupling of aryl bromides and iodides with arylboronic acids to yield biaryl ketones, using CHCl₃ as the source of carbonyl. The reported protocol is convenient and safe as it obviates the use of carbon monoxide (CO) balloons or pressured CO reactors which are otherwise needed for the carbonylation reactions. The methodology has been successfully applied to the synthesis of two antineoplastic drugs, namely, phenstatin and naphthylphenstatin, in good yields (81% and 85%, respectively). Under the optimized reaction conditions, complex 2 exhibited the best catalytic activity in the carbonylative Suzuki couplings. The reported catalysts have wide reaction scope with good functional group tolerance. All catalysts could be retrieved from the reaction after completion and recycled up to three times with insignificant loss in the catalytic activity.     

Synthesis of anomerically pure vinyl sulfone-modified pent-2-enofuranosides and hex-2-enopyranosides: a group of highly reactive Michael acceptors for accessing carbohydrate based synthons

Syntheses of the benzyl or the trityl protected α- and β-anomers of vinyl sulfone-modified pent-2-enofuranosides have been initiated by the ring opening of the suitably masked methyl α-lyxofuranosyl-epoxide or methyl β-ribofuranosyl-epoxide or by the nucleophilic displacement of the leaving groups in benzyl protected 3-O-tosyl xylofuranoside and 3-O-mesyl ribofuranoside by p-thiocresol. In case of the latter set of starting materials, α- and β-methyl glycosides formed in almost equal ratio only from the derivatives of d-xylose. For the synthesis of α- and β-anomers of vinyl sulfone-modified hex-2-enopyranosides, a d-glucose derivative was selected over a d-allose derivative as the starting material because the former almost exclusively produced the required methyl pyranosides whereas the latter produced a mixture. All sulfides were converted to vinyl sulfone-modified carbohydrates by the sequential application of oxidation, mesylation and base induced elimination reactions.     

Self-energy of a charge near a metal surface

A quantum mechanical expression for the self-energy of a charged particle near a metal surface has been derived. The expression incorporates the interaction of the charge with the surface and bulk plasmons including their dispersions in the hydrodynamic model. It is found that the inclusion of the plasmons dispersions gives result for the saturated value of the image potential for copper closer to experiment.     

Synthesis,microstructure, and copolymerization studies of 2-chloroethyl α-chloroacrylate

Poly(2-chloroethyl α-chloroacrylate) was synthesized by radical initiation, and its microstructure was evaluated using carbon-13 NMR. Methyl methacrylate (M₁) and 2-chloroethyl α-chloroacrylate (M₂) were copolymerized in toluene at 55°C using azobisisobutyronitrile as initiator. The reactivity ratios are 0.37 ± 0.28 and 1.21 ± 2.26, The thermal properties of these copolymers have also been reported.