Search results for "IRRADIATION"
showing 10 items of 1012 documents
Microwave-assisted synthesis of novel cyclodextrin–cucurbituril complexes
2011
Microwave irradiation was successfully used in order to obtain stable supramolecular aggregates between cyclodextrins and cucurbiturils, without the participation of any long-chain common ‘molecular thread’ guest. These aggregates were characterised by means of various different techniques, namely NMR, thermogravimetry, polarimetry and ESI-MS. Cross-analysis of experimental data allowed us to obtain insights on the stoichiometries of the composites and their thermal stabilities. The possible structures of the composites are briefly discussed, as well as the actual nature of their intrinsic stability.
Enhancing Selectivity In Photocatalytic Formation Of P-Anisaldehyde In Aqueous Suspension Under Solar Light Irradiation Via Tio2 N-Doping
2012
The photocatalytic partial oxidation of 4-methoxybenzyl alcohol to the corresponding aldehyde (p-anisaldehyde) was performed under simulated solar irradiation by using home prepared N-doped TiO2 catalysts. The photocatalysts were prepared by a sol–gel method, using TiCl4 as TiO2 precursor and NH4Cl, urea or NH4OH as N-doping sources. A commercial TiO2 (Degussa P25) was also used for comparison aims. The prepared catalysts were characterized by BET specific surface area, XRD, ESEM and UV-vis spectroscopy. The reactivity results show that (i) the doped catalysts are predominantly amorphous, and they show selectivity values far higher than those of the corresponding undoped ones and of well cr…
Fluoro heterocycles. A photochemical methodology for the synthesis of 3-amino- and 3-(N-alkylamino)-5-perfluoroalkyl-1,2,4-oxadiazoles
2000
Abstract A photochemical methodology for the synthesis of perfluoroalkyl-1,2,4-oxadiazoles has been described. 3-Amino- and 3-( N -alkylamino)-5-perfluoroalkyl-1,2,4-oxadiazoles have been prepared by irradiation of 3-perfluoroalkanoylamino-4-phenyl-1,2,5-oxadiazoles (furazans) at λ =313 nm in methanol and in the presence of ammonia or primary aliphatic amines.
Effect of N-substitution in multinuclear complexes allows interplay between magnetic states and multistability investigated by Mössbauer spectroscopy
2006
A series of pentadentate ligands N-X-5LH2 (X=H, Methyl, Benzyl)=N-X-saldptn (4-X-N,N′-bis(l-hydroxy-2-benzylidene)-1,7-diamino-4-azaheptane) has been prepared by a Schiff base condensation between 1,7-diamino-4-X-azaheptane and salicylaldehyde. Complexation with Fe(III) yields a series of high-spin (S=5/2) complexes of [FeIII(N-X-5L)Cl]. Such precursors were combined with [Mo(CN)8]4− and a series of blue nonanuclear cluster compounds [MoIV(CN)FeIII(N-X-5L)8]Cl4 resulted. Such star-shaped nonanuclear compounds are high-spin systems at room temperature. On cooling to 10K some of the iron(III) centers switched to the low-spin state as proven by Mossbauer spectra, i.e. multiple electronic trans…
Microwave-Assisted Synthesis of Polysubstituted 4-Quinolones from Deprotonated α-Aminonitriles
2010
The α-alkylation of deprotonated N-aryl-α-aminonitriles with α-bromoesters furnishes intermediates that can be cyclized to 4-quinolones upon microwave irradiation. Alternatively, base-induced dehydrocyanation of the alkylation products furnishes enaminoesters, which can, for example, be converted into quinoline-3-carboxylates.
ChemInform Abstract: Cyclocondensation of α-Aminonitriles and Enones: A Short Access to 3,4-Dihydro-2H-pyrrole 2-Carbonitriles and 2,3,5-Trisubstitut…
2010
The reaction of α,β-unsaturated carbonyl compounds with aminoacetonitrile hydrochloride furnishes 3,5-disubstituted 3,4-dihydro-2H-pyrrole-2-carbonitriles in a one-pot reaction sequence. While these products can serve as starting materials for the preparation of polysubstituted pyrrolizidines, they are kinetically stable against the base-induced elimination of HCN. In contrast, their 2-substituted analogues obtained from α-substituted α-aminonitriles can be readily converted to the corresponding 2,3,5-trisubstituted pyrroles under microwave irradiation. The key step presumably involves the thermal electrocyclization of a stabilized 2-azapentadienyl anion formed by condensation of the reacta…
Optical properties of lithium niobate single crystals
2005
Studies of thermal and γ-irradiation effects on the optical properties in congruous lithium niobate single crystals containing Y, Mg, Gd, B, and Zn dopants including samples with double dopants Y, Mg and Gd, Mg are reported. Formation of defects at irradiation and thermal treatment of the samples is explored by electron absorption spectra. Considerable increase of absorption with the dose of γ-radiation is observed at 500 nm. The changes of absorption examined under different conditions are explained by creation and destruction of Nb 4 + defects.
The Effects of Admixtures on Resistance to Radiation of Lithium Niobate Crystals
2015
The studies of optical absorption and transmission of crystalline lithium niobate compounds modified by rare-earth and alkali-earth elements: LiNbO3: Y (0.46 wt %), LiNbO3: Y (0.32 wt %), Mg (0.24 wt %), LiNbO3: Mg (0.27 wt %), LiNbO3: Gd (0.004, 0.04, 0.26, and 0.43 wt %), and ostensibly pure LiNbO3 is reported. The features of absorption and transmission are examined with respect to the dosage of γ-irradiation, the annealing temperature, and the type and concentration of modifying admixtures. The features revealed in different ways of bleaching γ-irradiated and annealed in vacuum ostensibly pure lithium niobate crystals are used to refine the mechanisms of developing electron and point de…
Light Induced Modifications of Langmuir-Blodgett-Multilayer Assemblies Containing Amphotropic Azocopolymer
1994
Abstract Photochromic LB-multilayers of amphotropic copolymers having rod-like azobenzene moieties as side groups which exhibit thermotropic liquid crystalline behaviour in the bulk have been characterized by UV-VIS spectroscopy as well as by angular dependent and energy dispersive SAXS. Upon irradiation with UV-light the initial optical in-plane anisotropy and the vertical layered structure of LB-films can be destroyed. A new layered structure can be rebuilt on irradiation with visible light or by annealing. Using linearly polarized light for the irradiation an optical anisotropy (POA) has been induced or reversibly modified by a photoselection process.
ChemInform Abstract: Green Conditions for the Suzuki Reaction Using Microwave Irradiation and a New HNT-Supported Ionic Liquid-Like Phase (HNT-SILLP)…
2014
Aryl iodides are coupled with conversions comparable to aryl bromides whereas conversions of aryl chlorides are significantly lower.