Chiral pyridin-3-ones and pyridines: syntheses of enantiopure 2,4-disubstituted 6-hydroxy-1,6-dihydro-2H-pyridin-3-ones, 2,3-disubstituted 4-iodopyridines, and enantiopure 2,3-disubstituted 4-pyridinemethanols

The development of an innovative method to access enantiopure 2,4-disubstituted 6-hydroxy-1,6-dihydro-2H-pyridin-3-ones starting from D-glucal via the aza-Achmatowicz transformation has been described. These highly functionalized pyridin-3-ones have been utilized for the synthesis of contiguously substituted pyridines through a rapid and efficient Et(3)N/Ac(2)O promoted cyclo-elimination, aromatization cascade, allowing the facile assembly of important pyridine-based building blocks like 2-substituted 3-acetoxy-4-iodopyridines and enantiopure 2-substituted 3-acetoxy-4-pyridinemethanols possessing benzylic stereogenic centers, whose synthesis otherwise would be tedious. The utilization of commercially available sugars as starting materials, mild reaction conditions, catalytic transfer hydrogen (CTH) of α-furfuryl azide derivatives, transfer of chiral aryl/alkyl methanols from enulosides to pyridin-3-ones and pyridines, high yields, and short reaction times are key features of this method. The utility of the method has been further exemplified by demonstrating the usage of the 2-substituted 3-acetoxy-4-iodopyridine for the construction of biologically significant molecules like 2,7-disubstituted furo[2,3-c]pyridines and 7,7'-disubstituted 2,2'-bifuro[2,3-c]pyridines.     

Structural characterisation and thermo-physical properties of glasses in the Li<Subscript>2</Subscript>O–SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–K<Subscript>2</Subscript>O system

This article aims to shed some light on the structure and thermo-physical properties of lithium disilicate glasses in the system Li₂O–SiO₂–Al₂O₃–K₂O. A glass with nominal composition 23Li₂O–77SiO₂ (mol%) (labelled as L₂₃S₇₇) and glasses containing Al₂O₃ and K₂O with SiO₂/Li₂O molar ratios (3.13–4.88) were produced by conventional melt-quenching technique in bulk and frit forms. The glass-ceramics (GCs) were obtained from nucleation and crystallisation of monolithic bulk glasses as well as via sintering and crystallisation of glass powder compacts. The structure of glasses as investigated by magic angle spinning-nuclear magnetic resonance (MAS-NMR) depict the role of Al₂O₃ as glass network former with four-fold coordination, i.e., Al(IV) species while silicon exists predominantly as a mixture of Q ³ and Q ⁴ (Si) structural units. The qualitative as well as quantitative crystalline phase evolution in glasses was followed by differential thermal analysis (DTA), X-ray diffraction (XRD) adjoined with Rietveld-reference intensity ratio (R.I.R.) method, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The possible correlation amongst structural features of glasses, phase composition and thermo-physical properties of GCs has been discussed.     

Synthesis and characterization of Eu doped SrY2O4 phosphor

The present paper reports that TL glow curve and kinetic parameter of Eu³⁺ doped SrY₂O₄ phosphor irradiated by beta source. Sample was prepared by solid state preparation method. Sample was characterized by XRD analysis and particle size was calculated by Debye–Scherrer formula. The sample was irradiated with Sr-90 beta source giving a dose of 10 Gy and the heating rate used for TL measurements are 6.7 °C/s. The samples display good TL peaks at 106 °C, 225 °C and 382 °C. The corresponding kinetic parameters are calculated. The photoluminescence excitation spectrum at 247 and 364 nm monitored with 400 nm excitation and the corresponding emission peaks at 590, 612 and 624 nm are reported.     

Mesoscopic spin-dependent reflection experiments on InSb- and InAs-based heterostructures

Spin–orbit interaction in two-dimensional electron systems can lead to a spin-dependent reflection of carriers off a lithographic barrier. Scattering of a spin-unpolarized beam from the barrier leads to the creation of two fully spin-polarized side beams in addition to an unpolarized specularly reflected beam. We experimentally demonstrate a method to create spin-polarized beams of ballistic electrons in mesoscopic samples fabricated on InSb/InAlSb and InAs/AlGaSb heterostructures. We describe two geometries, one open and one closed, in which the spin-dependent reflection and spin-dependent semiclassical trajectories were observed.     

Measurement of the transverse kinetic energies of argon recoil ions produced in 120 MeV -Ar collisions

Measurements were carried out to deduce the transverse kinetic energies of highly charged argon recoil ions produced in single collisions of 120 MeV ions with argon atoms in which the post collision charge states of the projectiles were not determined. A time of flight spectrometer was designed and fabricated to detect the charge states of recoils. Experimental procedures for optimizing the spectrometer for extraction, transmission and detection of recoils are described. A simple approach for determining the transverse kinetic energy of the recoil ions from FWHM of the peaks is reported. This method is shown to be independent of the choice of collision partners and requires only the knowledge of the physical values of “optimized parameters” of time-of-flight spectrometer used in the experiment. The transverse kinetic energy of the recoil ions determined from the present approach is found to vary from 0.03 eV for to 4.02 eV for Ar¹⁰⁺. These values are compared with the results reported by earlier workers and are shown to follow a q²-behaviour up to a charge state q =8+ of the recoil ions. Received: 5 February 1998 / Revised: 8 June 1998 / Accepted: 11 June 1998     

Radiation grafting of acrylonitrile on ethylene-propylene diene terpolymer rubber: Optimization of grafting parameters and oil resistance properties

Radiation induced grafting of acrylonitrile (ACN) on ethylene-propene diene terpolymer (EPDM) rubber film was investigated by mutual radiation grafting technique. Effect of experimental variables viz. radiation dose, dose rate, type of solvent and monomer content on extent of grafting was studied. From the kinetic studies a mathematical relation R _g α[M]^0.7 D ^0.68 showing non-linear relationship for rate of grafting with monomer concentration and dose was deduced. The grafted samples showed increased hardness and oil resistance.     

X-ray fine structure study and bonding in some ferrites

Extended X-ray absorption fine structure (EXAFS) of the iron K edges in copper, cobalt, zinc and manganese ferrites is studied and the EXAFS parameter α of the Lytle, Sayers and Stern's theory is shown to be a measure of fractional covalency. The linear relationship between metal to oxygen (iron to oxygen) distance and the parameter α leads us to conclude that the copper ferrite is the most covalent among the four ferrites studied in the present investigation.     

Electroproduction of π+ mesons in the resonance region

Results on the reaction ep→e′nπ⁺ are presented in the mass range 1.355 ?W ?1.775 GeV at q₂=1GeV² and in the range 1.415 ? W ? 1.595 GeV at q²=0.6 GeV². From the angular distribution of the π⁺ meson the polarization terms σ_u + ?σ_L, σ_p and σ_I have been determined in the range of production angles 0 <θ_π⁺ ?63°