A dual-catalysis approach to the asymmetric Steglich rearrangement and catalytic enantioselective addition of O-acylated azlactones to isoquinolines

A dual-catalysis approach, namely the combination of an achiral nucleophilic catalyst and a chiral anion-binding catalyst, was applied to the Steglich rearrangement to provide α,α-disubstituted amino acid derivatives in a highly enantioselective fashion. Replacement of the nucleophilic co-catalyst for isoquinoline resulted in a divergent reaction pathway and an unprecedented transformation of O-acylated azlactones. This strategy provided highly substituted α,β-diamino acid derivatives with excellent levels of stereocontrol.     

Photo-neutron cross-section of 100Mo

The ¹⁰⁰Mo(γ, n) reaction cross-section was experimentally determined at end point bremsstrahlung energy of 10 and 12.5 MeV using off-line γ-ray spectrometric technique. It was also found that ¹⁰⁰Mo(γ, n) reaction cross-section increases sharply from the end point bremsstrahlung energy of 10 MeV to 12.5 MeV, which may be because of GDR around the energy region of 12–16 MeV. The ¹⁰⁰Mo(γ, n) reaction cross-section as a function of photon energy was calculated theoretically using TALYS 1.2 computer code. The flux-weighted average values of ¹⁰⁰Mo(γ, n) reaction cross-section for bremsstrahlung having end point energy of 10 and 12.5 MeV were also calculated using the experimental and theoretical data of mono-energetic photon. The present experimental ¹⁰⁰Mo(γ, n) reaction cross-sections were compared with the bremsstrahlung flux-weighted average values of experimental and theoretical data and found to be in the lower side for 10 MeV and in the higher side for 12.5 MeV.     

Band head spin assignment of superdeformed bands in Hg isotopes through power index formula

The power index formula has been used to obtain the band head spin(I_0) of all the superdeformed(SD) bands in Hg isotopes. A least squares fitting approach is used. The root mean square deviations between the determined and the observed transition energies are calculated by extracting the model parameters using the power index formula. Whenever definite spins are available, the determined and the observed transition energies are in accordance with each other. The computed values of dynamic moment of inertia J~((2)) obtained by using the power index formula and its deviation with the rotational frequency is also studied. Excellent agreement is shown between the calculated and the experimental results for J~((2)) versus the rotational frequency. Hence, the power index formula works very well for all the SD bands in Hg isotopes expect for ~(195)Hg(2, 3, 4).     

Significance of the HO2 + CO reaction during the combustion of CO + H2 mixtures at high pressures

This paper constitutes an experimental and numerical study, using uncertainty analysis of the most important parameters, to evaluate the mechanism for the combustion of CO + H₂ mixtures at high pressures in the range 15-50 bar and temperatures from 950 to 1100 K. Experiments were performed in a rapid compression machine. Autoignition delays were measured for stoichiometric compositions of CO + H₂ containing between 0 and 80% CO in the total fuel mixture. The experimental results showed an unequivocal monotonic increase as the proportion of CO in the mixture was raised. Comparisons were made also with the measured ignition delays in mixtures of H₂ with increasing dilution by N₂, corresponding to the proportions of CO present. These times also increased monotonically, albeit with a greater sensitivity to the extent of dilution than those measured in the CO + H₂ mixtures. By contrast, numerical simulations for the same mixtures, based on a kinetic model derived by Davis et al. displayed a qualitative discrepancy as there was virtually no sensitivity of the ignition delay to the changing ratio of CO + H₂, certainly up to 80% replacement. No exceptions to this trend were found, despite tests being made using seven other kinetic models for CO + H₂ combustion. Global uncertainty analyses were then applied to the Davis et al. model in order to trace the origins of this discrepancy. The analyses took into account the uncertainties in all rate parameters in the model, which is a pre-requisite for evaluation against ignition delay data. It is shown that the reaction rate constant recommended by Baulch et al. for the HO₂ + CO reaction, at T ∼ 1000 K, could be up to a factor of 10 too high and that lowering this rate corrected the qualitative anomaly between experiment and numerical prediction.     

Separation and preconcentration of metal ions and their estimation in vitamin, steel and milk samples using o-vanillin-immobilized silica gel

o-Vanillin-immobilized silica gel has been used for the adsorption and estimation of copper, cobalt, iron and zinc by both batch and column techniques. Metal ions were quantitatively retained on the column packed with immobilized silica gel in the pH range 4.0-6.0 for Cu, 5.0-6.0 for Co, 4.5-6.0 for Fe and 6.0-8.0 for Zn. The distribution coefficient D determined for each metal was as follows (ml g(-1)): Fe, 5.4x10(2); Cu, 4.9x10(2); Zn, 4.4x10(2); Co, 3.8x10(2). Methods have been developed to estimate zinc, copper and cobalt in milk, steel and vitamin samples, respectively.     

Remote control of the reversible assembly/disassembly of supramolecular aggregates

ABSTRACT

A multi-component system is presented in which the actuation of a copper-loaded nanoswitch by zinc(II) ions as an external trigger and the thereby prompted release of copper(I) ions allows self-assembly of 11 parts resulting in the formation of a three-component supramolecular prism. Using the same protocol, a three-component rectangle was made from eight parts. Disassembly of the aggregates was accomplished by selective removal of zinc(II) ions using hexacyclen. In sum, the reversible assembly and disassembly of supramolecular aggregates was controlled in a multi-component mixture through intermolecular communication using a second messenger.     

High CEC generation and surface modification in mica and vermiculite minerals

Montmorillonite layered silicate has been commonly used to reinforce polymer matrices. Due to its swelling in water, organic modification of the mineral surface is easily achieved which makes the surface compatible with polymers. Other minerals like mica and vermiculite though can also lead to high aspect ratio platelets in nanocomposites, but they do not swell in water owing to much stronger electrostatic forces of attraction holding their platelets together (layer charge density >0.5?eq?·?mol^?1 in comparison with 0.25–0.5?eq?·?mol^?1 for montmorillonite). In current study, milling, delamination and cation exchange processing of mica and vermiculite minerals has been reported to explore their potential as reinforcement materials. Wet grinding and subsequent sieving of the coarse minerals led to fine-sized particles suitable to perform chemical delamination in water. The delamination process resulted in Li-mica and Na-vermiculite with enhanced access to the interlayer cations, thus, higher CEC. Successful surface modification of the delaminated minerals with alkyl ammonium ions could be achieved which resulted in significant enhancements in their basal plane spacing. Peak degradation temperatures of 260°C were measured for C18 and 2C18 modified vermiculite, whereas 300°C and 275°C were observed respectively for C18 and 2C18 modified mica minerals which make them suitable for compounding with polymers at high temperature.     

3,5-Difluorobenzonitrile: ab initio calculations,FTIR and Raman spectra

Geometry, vibrational wavenumbers and several thermodynamic parameters were calculated using ab initio quantum chemical methods for the 3,5-difluorobenzonitrile molecule. The results were compared with the experimental values. With the help of three specific scaling procedures, the observed vibrational wavenumbers in FTIR and Raman spectra were analysed and assigned to different normal modes of the molecule. Most of the modes have wavenumbers in the expected range and the error obtained was in general very low. Using PEDs the contributions were determined for the different modes to each wavenumber. From the PED, it is apparent that the frequency corresponding to C[triple bond]N stretching contains 87% contribution from the C[triple bond]N stretching force constant and it mixes with the C-CN stretching mode 13 to the extent of 12%. Other general conclusions were also deduced.     

Synthesis of temperature responsive polymer brushes from polystyrene latex particles functionalized with ATRP initiator

Thermally responsive poly(N-isopropylacrylamide) (PNIPAAM) brushes were grafted from polystyrene particles synthesized with surfactant free emulsion polymerization and functionalized with a thin shell of ATRP initiator on the surface. The ATRP initiator was present in the shell either alone or along with copolymerized styrene and also a crosslinker. The grafted brushes were characterized with transmission electron microscopy before and after negative staining with uranyl acetate. Cryo-scanning electron microscopy confirmed the growth of extremely long PNIPAAM layers from the surface, which otherwise looked shrunken in the transmission electron microscope owing to dehydration and possibly the effect of staining agent. The amount of grafted polymer also increases proportionally to the increase of the monomer concentration in the initial reaction system. The change in character from hydrophilic to hydrophobic with temperature and salt was found to be reversible and fast. The adsorption of protein complexes (tobacco mosaic virus) could be readily achieved at higher temperatures indicating the potential of the grafted particles to be used as stationary phases in temperature regulated chromatographic separations.     

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.