Open vessel mode microwave-assisted synthesis of 2-oxazolines from carboxylic acids

Microwave-assisted synthesis of 2-oxazolines from carboxylic acids using the open vessel technique is described. This efficient method involves direct condensation of carboxylic acids with excess 2-amino-2-methyl-1-propanol at 170 °C to give the corresponding 2-oxazolines in moderate to excellent yields.     

A new approach to explain concentration-dependent changes of isotropic Raman line width in the associated binary mixtures

We report on a new empirical relationship to explain the concentration-dependent isotropic Raman line width changes of a vibrational mode in uniform binary mixtures. The factors contributing to the intrinsic line width and several other broadening mechanisms are, in general, concentration-dependent. Concentration fluctuation in a microscopic volume and microviscosity are the two factors that are known to cause a concentration-dependent line width variation. These two factors combined in a specific manner successfully explain the variation of the line width with concentration strongly associated with binary systems. A readily usable empirical relationship for line width is suggested. It has been demonstrated that it can successfully explain the line width variation with concentration in a given class of hydrogen-bonded systems taking some representative binary mixtures.     

Viscous corrections for the viscous potential flow analysis of magnetohydrodynamic Kelvin-Helmholtz instability with heat and mass transfer

A ??E-E telescope exploiting a single silicon chip for both ??E measurement and scintillation light collection has been tested. It is a Si - CsI (Tl) telescope tailored for mass identification of light charged particles and intermediate mass fragments. A procedure based on two different shaping filters allows for extraction of the ??E-E information from the single silicon signal. The quality of the obtained fragment identification is expressed in terms of a figure of merit and compared to that of a standard ??E-E telescope. The presented configuration could be a good candidate for the basic cell of a large solid angle array of ??E-E telescopes, given the reduction in complexity and cost of the front-end electronics.     

Theoretical investigations on structural, elastic and electronic properties of thallium halides

Theoretical investigations on structural, elastic and electronic properties, viz. ground state lattice parameter, elastic moduli and density of states, of thallium halides (viz. TlCl and TlBr) have been made using the full potential linearized augmented plane wave method within the generalized gradient approximation (GGA). The ground state lattice parameter and bulk modulus and its pressure derivative have been obtained using optimization method. Young's modulus, shear modulus, Poisson ratio, sound velocities for longitudinal and shear waves, Debye average velocity, Debye temperature and Grüneisen parameter have also been calculated for these compounds. Calculated structural, elastic and other parameters are in good agreement with the available data.     

Amperometric determination of thorium as selenite

Summary Amperometric titration of thorium as selenite in a base electrolyte consisting of 0.9 M ammonium acetate in 60–70 per cent alcohol (ph 6.2–6.4) has been described. The titration is carried out at –1.0 V vs. S.C.E. A reversed L-type of curve is obtained and the formation of a normal selenite is suggested. The accuracy of the procedure is comparable with that obtained with other classical methods.

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Zusammenfassung Es wird ein Verfahren zur amperometrischen Titration von Thorium mit Selenitlösung beschrieben. Die Titration wird bei –1,0 V (gegen die ges. Kalomelelektrode) ausgeführt, bei Gegenwart von 0,9 m Ammoniumacetat und 60–70% Alkohol (pH 6,2–6,4). Man erhält eine Titrationskurve, die etwa die Form eines umgekehrten L hat. Die Genauigkeit des Verfahrens ist vergleichbar mit der anderer klassischer Methoden. Es wird angenommen, daß die Reaktion zur Bildung eines normalen Selenits führt.

     

Rapid,clean and efficient one-pot synthesis of thiopyrano[2,3-b]quinolines via domino Michael addition/cyclization reactions

Rapid and efficient one-pot synthesis of thiopyrano[2,3-b]quinolines is described from the reaction of 3-formyl-quinoline-2-thiones with acrylonitrile using economical organic base Et₃N at room temperature. The reaction proceeded smoothly via domino Michael addition/cyclization reactions and did not require dry solvent, inert atmosphere and column chromatography purifications.     

Densely functionalized 1,2-dihydrobenzo[b][1,6]naphthyridines: one-pot synthesis via sequential Ugi and Heck reactions

A facile one-pot synthesis of functionalized 1,2-dihydrobenzo[b][1,6]naphthyridines is described via sequential Ugi four components using 2-chloroquinoline-3-carboxaldehydes, allyl amine, acetic acid, isocyanides and ligand free Heck reactions in good yields.     

A reaction based chromofluorogenic turn-on probe for specific detection of fluoride over sulfide/thiols

A new reaction based probe fluorescein nosylate (R1) has been designed and synthesized for selective recognition of F⁻ in acetonitrile (CH₃CN) by exploiting both its nucleophilic and basic character. Probe R1 consists of fluorescein dye as a signalling unit while 4-nitrobenzenesulfonyl chloride as the masking unit. The F⁻ plays the role of de-masking agent to set free the fluorescein moiety in its open form from R1 leading to significant changes in its absorption/emission profile. The detection of F⁻ amidst of sulfide/thiols through receptors undergoing nucleophilic scission is a tedious job due to similarity in their extent of basicity/nucleophilicity. Here, we present a convenient solution for the same in the form of R1 which detects F⁻ selectively over sulfide/thiols in CH₃CN with a high detection limit of 4.6 × 10⁻⁷ M and 2.75 × 10⁻⁸ M determined through UV–visible and fluorescence titration data, respectively.     

Tightening of active site interactions en route to the transition state revealed by single-atom substitution in the guanosine-binding site of the Tetrahymena group I ribozyme

Protein enzymes establish intricate networks of interactions to bind and position substrates and catalytic groups within active sites, enabling stabilization of the chemical transition state. Crystal structures of several RNA enzymes also suggest extensive interaction networks, despite RNA's structural limitations, but there is little information on the functional and the energetic properties of these inferred networks. We used double mutant cycles and presteady-state kinetic analyses to probe the putative interaction between the exocyclic amino group of the guanosine nucleophile and the N7 atom of residue G264 of the Tetrahymena group I ribozyme. As expected, the results supported the presence of this interaction, but remarkably, the energetic penalty for introducing a CH group at the 7-position of residue G264 accumulates as the reaction proceeds toward the chemical transition state to a total of 6.2 kcal/mol. Functional tests of neighboring interactions revealed that the presence of the CH group compromises multiple contacts within the interaction network that encompass the reactive elements, apparently forcing the nucleophile to bind and attack from an altered, suboptimal orientation. The energetic consequences of this indirect disruption of neighboring interactions as the reaction proceeds demonstrate that linkage between binding interactions and catalysis hinges critically on the precise structural integrity of a network of interacting groups.     

Photomagnetism of a sym-cis-dithiocyanato iron(II) complex with a tetradentate N,N'-bis(2-pyridylmethyl)1,2-ethanediamine ligand

A comprehensive study of the magnetic and photomagnetic behaviors of cis-[Fe(picen)(NCS)(2) ] (picen = N,N'-bis(2-pyridylmethyl)1,2-ethanediamine) was carried out. The spin-equilibration was extremely slow in the vicinity of the thermal spin-transition. When the cooling speed was slower than 0.1?K min(-1), this complex was characterized by an abrupt thermal spin-transition at about 70?K. Measurement of the kinetics in the range 60-70?K was performed to approach the quasi-static hysteresis loop. At low temperatures, the metastable HS state was quenched by a rapid freezing process and the critical T(TIESST) temperature, which was associated with the thermally induced excited spin-state-trapping (TIESST) effect, was measured. At 10?K, this complex also exhibited the well-known light-induced excited spin-state-trapping (LIESST) effect and the T(LIESST) temperature was determined. The kinetics of the metastable HS states, which were generated from the freezing effect and from the light-induced excitation, was studied. Single-crystal X-ray diffraction as a function of speed-cooling and light conditions at 30?K revealed the mechanism of the spin-crossover in this complex as well as some direct relationships between its structural properties and its spin state. This spin-crossover (SCO) material represents a fascinating example in which the metastability of the HS state is in close vicinity to the thermal spin-transition region. Moreover, it is a beautiful example of a complex in which the metastable HS states can be generated, and then compared, either by the freezing effect or by the LIESST effect.