Laser isotope separation of 13C: A comparative study

IR laser chemistry of (CF₃Br/Cl₂) mixture and neat CF₂HCl are examined in the context of ¹³C enrichment. Decomposition extent, enrichment factor and energy absorbed are measured for both systems at their respective optimum conditions. A direct comparison is obtained by keeping extraneous factors such as laser, its pulse duration, cell, irradiation geometry etc. the same. The halogen scavenged CF₃Br MPD requires lower fluence compared to neat CF₂HCl irradiation. Overall throughput for a product with 60–65% ¹³C content in a single stage is the same for both systems requiring a similar amount of energy. However, at lower enrichment levels, CF₂HCl MPD is better than (CF₃Br/Cl₂) photolysis in terms of both product yield and energy absorption.     

Finline Integrated Trans-receiver at Ka-Band

This paper describes the design and development of Integrated Finline Trans-receiver at Ka-Band. Integrated trans-receiver has been designed for Simplex Voice Communication System. The trans-receiver includes a modulator, duplexer and a mixer integrated together on a single substrate RT Duroid 5880. Two Millimeter Wave Gunn sources, one as transmit source and the other one as Local Oscillator source, in Waveguide are connected externally. The system has been realised and tested with the integrated trans-receiver unit for ASK voice Communication System for a range of 2.5 KM LOS. The system is highly useful for short-range communication systems such as Hand-held Millimeter Wave Radio.     

Flow past a square cylinder at low Reynolds numbers

Results are presented for the flow past a stationary square cylinder at zero incidence for Reynolds number, Re ? 150. A stabilized finite‐element formulation is employed to discretize the equations of incompressible fluid flow in two‐dimensions. For the first time, values of the laminar separation Reynolds number, Re_s, and separation angle, θ_s, at Re_s are predicted. Also, the variation of θ_s with Re is presented. It is found that the steady separation initiates at Re = 1.15. Contrary to the popular belief that separation originates at the rear sharp corners, it is found to originate from the base point, i.e. θ_s=180^° at Re = Re_s. For Re > 5, θ_s approaches the limit of 135 ^°. The length of the separation bubble increases approximately linearly with increasing Re. The drag coefficient varies as Re^?0.66. Flow characteristics at Re ? 40 are also presented for elliptical cylinders of aspect ratios 0.2, 0.5, 0.8 and 1 (circle) having the same characteristic dimension as the square and major axis oriented normal to the free‐stream. Compared with a circular cylinder, the flow separates at a much lower Re from a square cylinder leading to the formation of a bigger wake (larger bubble length and width). Consequently, at a given Re, the drag on a square cylinder is more than the drag of a circular cylinder. This suggests that a cylinder with square section is more bluff than the one with circular section. Among all the cylinder shapes studied, the square cylinder with sharp corners generates the largest amount of drag. Copyright © 2010 John Wiley & Sons, Ltd.     

Reactions of nucleophiles with triarylpropenones and triarylbutenones

From a study of the reactions of nucleophiles with 1,2,3-triaryl-propenones and-butenones in a chemical ionization source it has been found that stronger nucleophiles, such as, MeO^?, EtO^? and MeS^?, attack the α,β-unsaturated system at the β-carbon (Michael addition) or the carbonyl carbon giving rise to tetrahedral adducts, while weaker nucleophiles, such as, Cl^? form the adduct ion by H-bonding with the β-hydrogen. The effect of substituents and source temperature supports the operation of these processes. The triaryl butenone did not give the adduct ion with MeO^? as deprotonation leads to a stable [M ? H]^? ion.     

IR and Raman spectra,density functional computations of vibrational spectrum,molecular geometry,atomic charges,and some molecular properties of 3‐aminobenzonitrile molecule

Geometry, vibrational wavenumbers, and several thermodynamic parameters have been calculated using ab initio quantum chemical methods for the 3‐aminobenzonitrile molecule for the first time. The results were compared with experimental values. With the help of specific scaling procedures, the observed vibrational wavenumbers were analyzed and assigned to different normal modes of the molecule. In general, the error obtained was very low. Using potential energy distribution (PED), the contributions of the different modes to each wavenumber were determined. Other general conclusions were also deduced. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Zusammensetzung und Stabilität des Thallium(I)-Komplexes der β-Mercaptopropionsäure

Zusammenfassung Durch potentiometrische und konduktometrische Titrationen wird die genaue Zusammensetzung des Komplexes untersucht, der sich aus Thallium(I) und -Mercaptopropionsäure in wäßriger 0,1m-KNO₃-Lösung bildet. Es zeigt sich, daß Thallium nur einen einzigen Komplex bildet. Er ist farblos, hat die Molzusammensetzung 11 und liegt besonders im pH-Bereich 9,0–10,5 vor. Durch Anwendung der vonCalvin undMelchior erweiterten Meßmethode vonBjerrum wird für drei verschiedene Temperaturen der Wert der Komplexbildungskonstante bestimmt. Als Werte für logK ergaben sich bei 20° 2,775, bei 30° 2,850 und bei 40° 2,935. Die Werte der thermodynamischen Zustandsfunktionen berechnen sich für die Komplexbildung zu G=–3,95 kcal/Mol, H=–3,34 kcal/Mol und S=+2,01 cal/grad.

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The precise nature of the complex formation between Thallium(I) and -mercaptopropionic acid in aqueous 0.1M-KNO₃ has been investigated by potentiometric and conductometric titration techniques. It was found that Tl(I) forms only one, 11, colourless complex predominating at pH 9.0–10.5. The stability constant of the complex has been determined by applyingCalvin andMelchior's extention ofBjerrum's method at three different temperatures. The logK values were found to be 2.775, 2.850 and 2.935 at 20, 30 and 40° C respectively. The thermodynamic functions of complexation, G, H and S were also evaluated at 30° C and found to be –3.95 K-cal/mole, –3.34 K-cal/mole and +2.01 Cal/deg. respectively.

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Kinetics and mechanism of oxidation of hydrazinium ion with peroxomonophosphoric acid in acid perchlorate solutions and role of trace iodide ions

The reaction of peroxomonophosphoric acid and hydrazinium ion in acid perchlorate solutions occurs as per stoichiometry (i), and the rate law (ii) at large [N₂H₅ ⁺], where K′_d is the first acid dissociation constant of H₃PO₅ and k ₁ and k ₂ are rate constants found to be 2.6 × 10^?4 s^?1 and 5.0 × 10^?2 M^?1 s^?1, respectively, at 35°. The reaction is greatly catalyzed by iodide ions. The mechanism involves a redox cycle I^?/I₂ and the rate is independent of [N₂H₅ ⁺] in the presence of iodide ions. K′_d was found to be 0.55 M^?1 and independent of temperature.     

ON THE NATURE OF CHLOROPHYLL a IN AQUEOUS MICELLAR SYSTEMS

Abstract— Absorption and fluorescence spectra of chlorophyll a in aqueous micellar solutions were studied. Solutions in anionic micelles gave an absorption band at 740 nm, attributable to microcrystal- line chlorophyll a. Solutions in cationic and nonionic micelles do not show this band. The positions of the spectral bands in anionic micelles and the possible structure of microcrystalline form are discussed. A comparison is made of the behaviour of microcrystalline form in hydrocarbon solvents and in micellar solutions.     

Geometrical control of the active site electronic structure of pyranopterin enzymes by metal-dithiolate folding: aldehyde oxidase

Density functional calculations on geometry-optimized oxidized (Mo(VI)) and reduced (Mo(IV)) analogues of the isolated active site of aldehyde oxidase (MOP), a member of the xanthine oxidase family of pyranopterindithiolate enzymes, show that fold angle changes of the dithiolate ligand modulate the relative metal and dithiolate contributions to the frontier redox orbitals. Proton abstraction from the equatorial aqua ligand of the oxidized Mo(VI) site also flattens the metal dithiolate fold angle. It is proposed that static and/or dynamic changes in the structure of the protein surrounding the active site can induce changes in the dithiolate fold angle and thereby provide a mechanism for electronic buffering of the redox orbital, for fine-tuning the nucleophilicity of the equatorial aqua/hydroxide ligand, and for modulating the electron-transfer regeneration of the active sites of molybdenum and tungsten enzymes via a "dithiolate folding effect".     

Kinetic and redox characteristics of semireduced species derived from phenosafranine in homogeneous aqueous and sodium dodecyl sulfate micellar media

One‐electron reduction of phenosafranine (PS⁺ 3,7‐diamino‐5‐phenylphenazinium chloride), a phenazinium dye, has been studied in homogeneous aqueous and sodium dodecyl sulfate (SDS) micellar media, using the pulse radiolysis technique. The various reducing radicals employed for the study in homogeneous aqueous medium were e_aq^?, H^˙, CO_2,^˙?, and isopropyl ketyl radicals (CH₃)₂ ^˙COH. Semireduced species generated by these reactions have been characterized by their absorption spectra, decay kinetics, and pK_a. The one‐electron reduction potential of PS⁺ was determined at pH 7 in homogeneous aqueous solution employing nitrobenzene (NB/NB^˙?) as the standard couple. One‐electron reduction in SDS micellar medium and a detailed spectrophotometric investigation of the parent dye in this surfactant system was carried out in order to understand the dye–surfactant interactions in the micellar and premicellar media.© 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 56–66, 2002