Local Hydrogen Vibrational Modes in GaAs doped with Chalcogenides

Infrared absorption on GaAs doped with Chalcogenides under hydrogen plasma treatment has shown the presence of two new localised modes, namely stretching and wagging modes. We present a simple nine atom molecular model to compute these defect modes by assuming the hydrogen to be bound in the antibonding position of the nearest Ga atom, resulting in a defect complex of C_3V symmetry. Group theoretical methods are employed to obtain the frequencies of the normal modes enabling precise identification of localised modes.     

Kinetics and Thermodynamics of Formation and Electron‐Transfer Reactions of Surfactant Cobalt(III) Complexes Containing Polypyridyl Ligands with Fe(CN)64− in Microheterogeneous Environment

The electron‐transfer reaction of some surfactant cobalt(III) complexes, cis‐[Co(ip)₂(C₁₂H₂₅NH₂)₂]³⁺ 1 , cis‐[Co(dpq)₂(C₁₂H₂₅NH₂)₂]³⁺ 2 , and cis‐[Co(dpqc)₂(C₁₂H₂₅NH₂)₂]³⁺ 3 (ip = imidazo[4,5‐f][1,10]phenanthroline, dpq = dipyrido[3,2‐d:2′‐3′‐f]quinoxaline, dpqc = dipyrido[3,2‐a:2′,4′‐c](6,7,8,9‐tetrahydro)phenazine, C₁₂H₂₅NH₂ = dodecylamine) with the Fe(CN)₆^4? ion has been investigated in microheterogeneous media (micelles, β‐cyclodextrin) at different temperatures by the spectrophotometric method under pseudo‐first‐order conditions using an excess of the reductant. Experimentally, the reaction was found to be second order and the electron transfer postulated as an outer sphere. The rate constant for the electron‐transfer reaction in micelles was found to increase with an increase in the initial concentration of the surfactant–cobalt(III) complex. This peculiar behavior of dependence of the second‐order rate constant on the initial concentration of one of the reactants has been attributed to the presence of various concentrations of micelles under different initial concentrations of the surfactant–cobalt(III) complex in the reaction medium. Inclusion of the long aliphatic chain of the surfactant complex ion into β‐cyclodextrin leads to decrease in the rate constant. Kinetic data and activation parameters are interpreted in terms of an outer‐sphere electron‐transfer mechanism. All these results have been interpreted in terms of the hydrophobic effect and the reactants with the opposite charge.     

An efficient synthesis of the opioid analgesic (R)-phenampromide via an aziridinium ion

A simple and efficient synthesis of the opioid analgesic agent (R)-phenampromide with high enantiopurity (>99% ee) via the formation of an aziridinium ion as a key step using commercially available starting material is described.     

Sequential change in one-pot,three-component protocol: A stepping stone in heterocyclic synthesis

Two different heterocycles, thiazole-2-imines and imidazole-2-thiones, have been conveniently synthesized by just altering the sequential order (1 + 2 + 3 or 1 + 3 + 2) when combining the same components [aryl amine (1), aryl isothiocyanate (2), and phenacyl bromide (3)] in one-pot, three-component protocols. The third possible sequential order of combination (2 + 3 + 1) chemoselectively affords thiazole-2-imine. The finding is a stepping stone in the synthetic applicability of sequential one-pot, three-component protocols.     

Solvent-free protocol for amide bond formation via trapping of nascent phosphazenes with carboxylic acids

A solvent-free synthesis of amides via the coupling of phosphazenes with carboxylic acids is reported. Increasing the rate of heating either by microwave irradiation or conventional heating results in multifold increase in the rate of amide bond formation. Synthesis of a library of amides including a potent antitumour candidate has been accomplished.     

A Facile Method for the Synthesis of Aroyl Pyrazoles from Functionalized Ketene Dithioacetals

On treating with ammonium acetate in DMSO aroyl formyl ketene dithioacetals were transformed into valuable intermediates 3‐amino‐2‐aroyl‐3‐(methylsulfanyl)‐2‐propenals, which could be explored for the synthesis of aroyl aminopyrazoles.     

Octadecylamine cobalt(III) dimethyl glyoximato complexes: synthesis,thermodynamics of micellization,steady-state photolysis and biological activities

A new class of surfactant–cobalt(III) complexes of the type trans-[Co(DH)₂(OA)X], where DH = dimethylglyoxime, OA = octadecylamine, X = Cl^?, Br^?, I^?, N₃ ^?, NO₂ ^?, SCN^? or OA, were synthesized and characterized by physicochemical and spectroscopic methods. The critical micelle concentration (CMC) values of these surfactant–cobalt(III) complexes in ethanol solution were obtained by measuring absorption at ~250 nm. Specific conductivity data (at 303–313 K) served for the evaluation of the temperature-dependent CMC and the thermodynamics of micellization (ΔG _m ⁰ , ΔH _m ⁰ and ΔS _m ⁰ ). Steady-state photolysis and cyclic voltammetry of the complexes were studied. The surfactant–cobalt(III) complexes were screened for their antibacterial and antifungal activities against various microorganisms.     

Three-dimensional flow field measurements using LDV in the exit region of a radial inflow turbine

Detailed flow investigation in the downstream region of a radial inflow turbine was performed using a three component Laser Doppler Velocimeter. The flow velocities are measured in the exit region of the turbine at an off-design operating condition. The measured parameters are correlated to the rotor blade rotation to observe any periodic nature of the flow. The measurements reveal a complex flow pattern near the tip region at the rotor exit due to the interaction of the tip clearance flow. The effect of the rotor on the exit flow field is observed in the proximity of the rotor exit.List of symbols IGV inlet guide vane - LDV Laser Doppler Velocimeter - N data sample size - r radial direction - t tangential direction - U velocity components - mean value of velocity component - U _bl rotor blade velocity - V ₀ total velocity - V _R reference total velocity used for normalizing (time and passage averaged) - W on-axis velocity component - z axial direction - absolute flow angle - standard deviation in a velocity data sample - U measurement uncertainty of velocity component U - coupling angle between the purple optical axis and the blue-green optical axis - angle between the resultant velocity and the blue component velocity - mv mean value - b blue component - g green component - i measurement point - j rotor blade position - m mean value - p purple component - r radial component - rz radial-axial plane - rt radial-tangential plane - t tangential component - z axial component - zt axial-tangential plane This research was supported by NSF Contract No. CTS-9012309 during 1990–1993.A version of this paper was presented at the International Gas Turbine and Aeroengine Congress and Exposition, The Hague, Netherlands, June 13–16, 1994.