THE STRUCTURE OF BUTADIENE DIMERS PRODUCED BY A FREE-RADICAL CHAIN-TRANSFER MECHANISM

Butadiene was dimerized by using acetyl peroxide as source of free radicals and chloroform as solvent and chain-transfer agent. The dimers were identified and their structures were determined by means of ozonolysis and oxidative hydrolysis. It was established that two dimers were produced in nearly equal amount. One dimer was formed only by 1,4-additions, the other only by 1,2-additions. This result implies that polybutadienes may be mixtures of two varieties: one variety resulting from 1,4-additions, the other from 1,2-additions.

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Cyclodextrins in Polymer Synthesis: Free-Radical Polymerization of Methylated β-Cyclodextrin Complexes of Methyl Methacrylate and Styrene Controlled byN-Acetyl-l-cysteine as a Chain-Transfer Agent in Aqueous Medium

Macromolecules ◽

10.1021/ma992012e ◽

2000 ◽

Vol 33 (11) ◽

pp. 4288-4290 ◽

Cited By ~ 27

Author(s):

Patrick Glöckner ◽

Nadine Metz ◽

Helmut Ritter

Keyword(s):

Free Radical ◽

Methyl Methacrylate ◽

Aqueous Medium ◽

Radical Polymerization ◽

Chain Transfer ◽

Free Radical Polymerization ◽

Polymer Synthesis ◽

Chain Transfer Agent ◽

Cyclodextrin Complexes ◽

A Chain

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Glutathione Peroxidase-Like Activity of Simple Selenium Compounds. Peroxides and the Heterocyclic N-Oxide Resazurin Acting as O-Atom Donors

Zeitschrift für Naturforschung C ◽

10.1515/znc-1995-3-409 ◽

1995 ◽

Vol 50 (3-4) ◽

pp. 209-219 ◽

Cited By ~ 3

Author(s):

Walter A. Prtitz

Keyword(s):

Free Radicals ◽

Free Radical ◽

Glutathione Peroxidase ◽

Crystal Violet ◽

The Other ◽

Atom Transfer ◽

Selenium Compounds ◽

Radical Intermediates ◽

Leuco Crystal Violet ◽

Acid Pathway

Selenite and selenocystamine [(CyaSe)2] efficiently activate the decomposition of H2O2 y GSH and by other thiols, as demonstrated using a leuco crystal violet POD-based H2O2 assay which is applicable (unlike other assays) also in presence of thiols. The GPx-like activities were estimated to be 3.6 and 2.7 μmol H2O2/min per μmol SeO32- and (CyaSe)2, respectively. Both selenium compounds also activate reduction of the heterocyclic N-oxide resazurin (RN→O) to resorufin (RN) by GSH; H2O2 competes with reduction of this dye. GSSeH and CyaSeH, formed by interaction of GSH with SeO32- and (CyaSe)2, respectively, are likely to be the active reductants. CyaSeH, generated γ-radiolytically from (CyaSe)2, exhibits an absorption peak at 243 nm and is removed by H2O2 with a rate constant of 9.7x102 ᴍ-1 s-1, and slightly slower by hydroperoxides. We have no evidence for one-electron interactions between GSSeH or CyaSeH and H2O2, with formation of free radical intermediates, as previously proposed in the case of selenium-activated reduction of cytochrome c by GSH (Levander et al., Biochemistry 23, 4591-4595 (1973)). Our results can be explained by O-atom transfer from the substrate to the active selenol group. RSeH + H2O2 (RN→O)→RSeOH + H2O (RN), and recycling of RSeOH to RSeH (+ H2O) by GSH, analogous to the selenenic acid pathway of GPx. The substrate specificity appears to be different, however, in that GPx is unable to catalyse RN→O reduction, and GSSeH hardly catalyses the decomposition of cumene- or t-butyl-hydroperoxide; CyaSeH, on the other hand, is active also with the hydroperoxides. RN→O is reduced to RN also by certain oxidizing free radicals, e.g. by the thiyl CyaS·; O -atom transfer may in this case lead to the generation of reactive oxyl radicals.

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