Absolute configuration of C2-symmetric spiroselenurane: 3,3,3',3'-tetramethyl-1,1'-spirobi[3 H,2,1]benzoxaselenole

The enantiomers of 3,3,3',3'-tetramethyl-1,1'-spirobi[3 H,2,1]benzoxaselenole have been separated on a chiral preparative chromatographic column. The experimental vibrational circular dichroism (VCD) spectra have been obtained for both enantiomers in CH(2)Cl(2). The theoretical VCD spectra have been obtained by means of density functional theoretical calculations with the B3 LYP density functional. From a comparison of experimental and theoretical VCD spectra, the absolute configuration of an enantiomer with positive specific rotation in CH(2)Cl(2) at 589 nm is determined to be R. This conclusion has been verified by comparing results of experimental optical rotatory dispersion (ORD) and electronic circular dichroism (ECD) to predictions of the same properties using the B3 LYP functional for the title compound.     

Protein crystal nucleation: is the pair interaction potential the primary determinant of kinetics?

Fundamental understanding of protein crystal nucleation facilitates crystallization of biological macromolecules for structure determination and control of crystal size distribution. In the studies presented here, nucleation kinetics of hen egg-white lysozyme crystals were measured at solution conditions that exhibited equal solubility by adjusting pH, temperature, or sodium chloride concentration. It was observed that solution conditions that lead to equal solubility resulted in equal nucleation rates and hence kinetic parameters. Since the solubility of globular proteins correlates with the osmotic second virial coefficient, B(22), an integral measure of the protein pair interaction potential, this observation indicates that the protein pair interaction plays a key role in determining nucleation kinetic parameters.     

Phase equilibria for binary systems of octane boosters with 2,2,4-trimethylpentane

Isobaric vapor–liquid equilibrium data at 95.96 kPa for the three binary systems of 2,2,4-trimethylpentane with methyl tert-butyl ether, di-isopropyl ether and dimethoxymethane are determined. A Swietoslawski type ebulliometer is used for the measurements. The experimental T–x data are used to estimate Wilson parameters and the parameters, in turn, are used to calculate vapor phase compositions and activity coefficients. All the systems studied here do not exhibit azeotropes and behave like non-ideal solutions.     

Electro-oxidation and electro-reduction of some iron (II), cobalt(II) and nickel(II) polypyridyl complexes in acetonitrile

Cyclic voltammetry and controlled potential coulometry studies of 2,2′-bipyridyl, 4,4′-dimethyl-2,2′-bipyridyl and 2,2′, 2″-terpyridyl complexes of Fe(II), Co(II) and Ni(II) in acetonitrile are described. E_1/2 values for M(III)/M(II) and M(II)/M)I) couples are compared and crystal field effects discussed. A series of M(I) and M(III) polypyridyl complexes have been prepared by controlled potential electrolysis; these include a number of 3+ and 1+ oxidation state complexes of nickel which have not previously been isolated — [Ni(bipy)₃]-(ClO₄)₃, [Ni(dimbipy)₃](ClO₄)₃, [Ni(terpy)₂](ClO₄)₃ and [Ni(bipy)₂]ClO₄.     

Sol-gel-derived micron scale optical fibers for chemical sensing

We report for the first time on the preparation of organically-doped room temperature processed sol-gel-derived micron scale optical fibers as platforms for chemical- and bio-sensors. Micron scale optical fibers are drawn from fluorescent dye-doped tetraethoxysilane (TEOS)-derived sol-gel solution processed under ambient conditions. Such a simple methodology to entrap organic and even bioactive species within the optical fiber offers many advantages over more conventional ways of immobilizing organic probes for the development of optical sensors. Specifically, we report on the photophysical properties of fluorescein (a pH sensitive fluorescent dye) and rhodamine 6G (R6G; laser dye) entrapped within sol-gel-derived optical fibers. We present the preliminary results on the viability of such doped optical fibers for chemical sensing. Our results demonstrate that a fluorescein-doped sol-gel-derived optical fiber responds to ammonia and acid vapors with a response time of 1–2 seconds.     

Thermal decomposition of 2,3,5-triphenyl tetrazolium halochromate complexes

Thermal decomposition studies of 2,3,5-triphenyl tetrazolium halochromates have been carried out upto 1000°C at a linear heating rate of 10 deg·min^?1. The complexes undergo two stage decomposition. First one corresponds to the redox decomposition of the complex along with the loss of a phenyl halide molecule and 3/2 mol of oxygen. While, the second step corresponds to the oxidation of the formazan type structure formed in the first step. The first step decomposition follows diffusion controlled reaction mechanism in a sphere governed by the equationg(α)=[1?(1?α)^1/3]². Activation energy and pre-exponential factors have been determined by Coats-Redfern model and Dixit-Ray model. Activation energy decreases as the electronegativity of the halide ion decreases.     

Study of geometrical parameters in N-H...N type of hydrogen bonds

Geometrical parameters associated with N-H ... N types of hydrogen bonds have been analysed using crystal structure data on nucleic acids, amino acids and related compounds. Histograms depicting the frequency distribution of N-H ... N length (l) and H-N ... N angle (θ) have been drawn and conclusions on the favoured geometry of such bonds have been arrived at. The distribution ofl shows a pronounced maximum in the range between 2.9? and 3.0? with an overall average of 2.98 ?. The θ distribution shows a pronounced maximum for the hydrogen bond angle in the range 0°-10°, with a rapid fall-off in frequency for nonlinear hydrogen bonds. The frequency shows a cos⁶θ dependence as compared to cos²θ dependence term used earlier to predict the angular dependence of hydrogen bond potential energy in proteins and polypeptides.     

Determination of H2 and D2 content in metals and alloys using hot vacuum extraction

A hot vacuum extraction technique for the determination of hydrogen in metal and alloy samples has been standardised. After measuring the total pressure of the evolved gases, individual hydrogen and deuterium intensities are measured using an on-line quadrupole mass spectrometer. Synthetic mixtures of H₂ and D₂, in known concentrations, have been analysed by QMS and an analytical expression correlating the measured [D₂]/[HD] intensity ratio with the mole fraction of deuterium in the synthetic mixture has been arrived at. The precision and accuracy in the measurement of hydrogen is about 10% at 50 ppmw level.     

Syntheses of substituted pyrazolo[3,4-b]quinolines, 3,4-dihydro-4-oxopyrimido[4′,5′:4,5]theino[2,3-b]quinoline and pyrido[1′,2′:1,2]pyrimido[4,5-b]quinoline

Syntheses of substituted pyrazolo[3,4-b]quinolines, 3,4-dihydro-4-oxopyriraido[4′,5′:4,5]theino[2,3-b]quinoline and 12-phenylpyrido[1′,2′:1,2[pyrimido[4,5-b]quinoline are described.     

Asymmetric synthesis of beta-amino carbonyl compounds with N-sulfinyl beta-amino Weinreb amides

[reaction: see text] Diverse organometallic reagents readily add to enantiopure N-sulfinyl beta-amino Weinreb amides providing the corresponding, stable, N-sulfinyl beta-amino carbonyl compounds in good to excellent yields. This new methodology represents a general solution to the problem of beta-amino carbonyl syntheses, which are important chiral building blocks and constituents of natural products. N-Sulfinyl beta-amino Weinreb amides are prepared by reaction of the potassium enolate of N-methoxy N-methylacetamide with sulfinimines (N-sulfinyl imines) or lithium N,O-dimethylhydroxylamine with N-sulfinyl beta-amino esters.