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- W2037604842 abstract "Phenylamine has been oxidized by radiolytically generated hydroxyl and sulfate radicals, the ensuing intermediates and their reactions have been studied by pulse radiolysis and product analysis in the absence and presence of oxidants such as Fe(CN) 6 3- and O 2 . Upon OH radical attack, hydroxycyclohexadienyl-type radicals are mainly formed while Η-abstraction reactions can be neglected. In the presence of Fe(CN) 6 3- these radicals are for the most part oxidized to the corresponding tyrosines (80%), except for the ipso-OH-adduct radicals (≈ 20%). It is concluded that ˙OH-addition is almost random, but with a slight avoidance of the metaposition relative to the ortho-, para- and ipso-positions. Oxygen adds reversibly to the OH-adduct radicals (k f = 1.8 × 10 8 dm 3 mol -1 s -1 , k r = 5.4 × 10 4 s -1 ). In this case, tyrosine formation occurs by HO 2 ˙-elimination. However, due to side reactions, tyrosine formation only reaches 52% of the OH radical yield. The tyrosine yield drops to 10% in the absence of an oxidant. Upon SO 4 ˙⁻-attack, decarboxylation becomes a major process (33% of SO 4 ˙⁻) alongside the production of tyrosines (43%). Here, with Fe(CN) 6 3- as the oxidant the formation of p-Tyr (18.5%) and m-Tyr (16.5%) is preferred over o-Tyr formation (8.5%). It is believed that in analogy to other systems a radical cation is formed immediately upon SO 4 ˙⁻-attack which either reacts with water under the formation of hydroxycyclohexadienyl-type (“OH-adduct”) radicals, or decarboxylates after intramolecular electron transfer. The radical cation can also arise indirectly through H + -catalysed water elimination from the ˙OH-adduct radicals. At pH 2 and a dose rate of 0.0046 Gy s -1 CO 2 formation matches the OH radical yield when ˙OH is the attacking radical. Below pH 2, G(CO 2 ) decreases with falling pH. This indicates the occurrence of another, unimolecular, pathway under these conditions competing effectively with decarboxylation. This appears to be a relatively slow deprotonation reaction of the carboxylprotonated phenylalanine radical cation which gives rise to the benzyl-type radical." @default.
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- W2037604842 date "1993-06-01" @default.
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- W2037604842 title "Phenylalanine: Its ˙OH and SO<sub>4</sub>˙⁻-Induced Oxidation and Decarboxylation. A Pulse Radiolysis and Product Analysis Study" @default.
- W2037604842 doi "https://doi.org/10.1515/znb-1993-0610" @default.
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