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Radiolytically induced reductive degradation of halothane in air-saturated aqueous solutions in the presence of methionine

Flyunt R., Makogon O., Schoneich Ch., Asmus K.

Nukleonika

2000

Vol. 45, nr 1

45-50

It was established that peroxyl radicals (CF3CHClOOź) derived from halothane (CF3CHClBr) quantitatively react with methionine (MetS) to the corresponding sulfoxide (MetSO). This reaction was accompanied by the formation of oxyl radicals (CF3CHClOź), which, in a first step, appear to rearrange by 1,2-hydrogen shift to CF3Cź(OH)Cl. The latter may react via one of two pathways: direct addition of oxygen or immediate elimination of hydrochloric acid (HCl) from CF3Cź(OH)Cl. Direct addition of oxygen yields the corresponding peroxyl radical, which, upon H+/O2ź- elimination and subsequent hydrolysis of CF3COCl, could account for the formation of trifluoroacetic acid (TFA), one of the major observed products. An alternative and, based on the combined evidence of our data, probably more favorable route is based on immediate elimination of HCl from CF3Cź(OH)Cl, which generates CF3Cź(OH)2 upon hydrolysis. Subsequent reaction of this radical with O2 yields CF3C(OOź)(OH)2, followed by H+/O2ź- elimination, which also leads to CF3CO2H. This route accounts for approximately 41% of the initial CF3CHClOOź radicals. To accommodate the high yields of fluoride ions and carbon dioxide, which indicate a complete breakdown of the halothane molecule, a competing reaction pathway of the CF3Cź(OH)2 radicals is proposed. In its first step elimination of one fluoride ion to yield źCF2CO2- is envisaged (possibly involving a deprotonated form of CF3Cź(OH)2). The peroxyl radicals źOOCF2CO2-, formed upon oxygen addition to źCF2CO2-, are suggested to react with MetS, yielding MetSO and alkohol radicals (źOCF2CO2-). It is proposed that the latter decompose via carbon-carbon bond cleavage to COF2, and CO2ź-. This pathway, which leads to complete halogen release (as halide ions), accounts for approximately 53% of the initially formed CF3CHClOOź radicals. The observed high MetSO yields, G=(5.6), are explained by oxidation of MetS by CF3CHClOOź and źOOCF2CO2- via 2-electron transfer mechanisms. A detailed reaction scheme and quantitative material balance is provided on the basis of the measured yields of CF3CO2H, Br-, Cl-, F- and CO2 as major components and carbon monoxide (CO) and oxalate as minor components.

Odd-electron bonded sulfur- and selenium-centered radical cations as studied by radiation chemical and complementary methods

Asmus K.

Nukleonika

2000

Vol. 45, nr 1

3-10

A selected survey of the formation and properties of a number of sulfur- and selenium-centered radical ions is presented. The focus is on radical cations in which two heteroatoms are linked by a bond containing a total of three electrons, namely two bonding s-electrons and one antibonding s*-electron. Examples are (R2S\SR2)+ and (R2Se\SeR2)+ derived from simple aliphatic sulfides and selenides, and corresponding species in which the heteroatom coupling occurs intramolecularly. It will be demonstrated how structure and substituents influence the thermodynamic and kinetic stability of such systems. Owing to the strong and distinct optical absorptions in the ultraviolet (UV) and visible all of these species may conveniently be detected by means of time-resolved optical spectroscopy, especially pulse radiolysis. These and complementary data obtained from mass spectrometry and electrochemistry will be presented and discussed.