1,721,344 research outputs found
The influence of solid-state molecular organization on the reaction paths of thiyl radicals
No full textElectron paramagnetic resonance (EPR) spectroscopy has been
employed to investigate the effect of solid-state molecular organization on the reaction of thiyl radicals with thiols. In an irradiated C18H37SH/thiourea clathrate, the conversion of thiyl to perthiyl radicals is substantial, due to the head-to-head arrangement of the reactants within the channels and the suppression of other possible competing reactions due to hindrance by the clathrate walls. The perthiyl radical was identified using EPR analysis of its molecular dynamics within the clathrate channels. Irradiated polyethylene film containing 30% C18H37SH afforded a negligible conversion of thiyl to perthiyl radicals because of the random distribution of reactants. These results suggest that in the absence of favorable structure-control effects, the reaction between RSC and RSH is unimportant with respect to other competing reactions.
Perthiyl radicals are also the major product in the vacuum
solid-state radiolysis of lysozyme. A proposal of the mechanism
involved in all cases is based on the equilibrium RSC+
RSHÐRSSC(H)R, followed by the irreversible conversion of the sulfuranyl radical to the perthiyl radical. As the equilibrium is
strongly shifted to the left, the intermediate sulfuranyl radicals
were not detected, but the lack of other competing reactions for
the thiyl radicals caused the formation of perthiyl radicals to
become the major path in the clathrate and in solid lysozyme radiolysis
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
ESR of free radical reactions in gamma-irradiated ethylene–propylene-based terpolymers. II
No full textThe gamma irradiation at liquid nitrogen temperature of dicyclopentadiene, 2-methylennorbornene, and cyclopentadienyl-5-endo-norbor-2-enyl-methane-based ethylene–propylene terpolymers leads to the formation of macroradicals of the alkyl type by loss of hydrogen atoms from the ethylene–propylene chains. When warmed almost to glass transition temperature these primary alkyl species decay and generate new radicals by the double-bond addition and/or H abstraction from the unsaturations. The nature of the radical products was determined by ESR and MO methods
ESR study of paramagnetic centres in irradiated platinum complexes
No full textPlatinum dichloride complexes with diolefins and phosphines were γ-irradiated at 77K and studied by ESR spectroscopy. Several paramagnetic species were simultaneously produced by electron capture, electron loss and bond homolysis in the pure compounds. An high selectivity in the generation of the reduced species was reached by the irradiation at 77K of the metal complexes in methyltetrahydrofuran solutions. The ESR spectra analysis of the paramagnetic Pt(I) species suggested a SOMO of σ-antibonding character for diolefins complexes and 7π-out-of-plane character for phosphine complexes
EPR study of cation-radicals of cyclic alkenes in chlorofluorocarbon matrices
No full textBy gamma irradiation of cycloheptatriene, bicyclo(3.3.0)octene and dehydrodicyclopentadiene in chlorofluorocarbon matrices at 77 K the radical cations generated by electron loss from the parent molecules have been obtained and their electronic structure analyzed by EPR spectroscopy and by INDO and MNDO-PM3 molecular orbital calculations. On warming above 77 K these species undergo deprotonation to form neutral radicals. In the case of dicyclopentadiene the primary radical-cation is not stable at 77 K but decomposes probably by ring opening giving a bis-allylilic type cation-radical
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