Peroxynitrite-mediated oxidations: nitration and nitrosation

Using a direct ultraviolet second-derivative spectroscopy method, three peroxynitrite preparative methods were investigated for the nitrite and nitrate present either as impurities or produced during peroxynitrite decomposition: (I) ozonation of azide, reaction of hydrogen peroxide with (II) isoamyl nitrite and (III) nitrous acid. The oxidation of morpholine by peroxynitrite in the presence and absence of added carbonate gives N-nitromorpholine and N-nitrosomorpholine. Nitration and nitrosation of morpholine are catalyzed by low levels of CO₂; however, excess CO₂ dramatically reduces the yields of nitrosation but not nitration, and the combined yields of the products are about the same under conditions of high and low concentrations of CO₂. These data indicate that both nitration and nitrosation by peroxynitrite are free radical processes. The morpholine radical, formed from the reactions of carbonate and/or hydroxyl radicals with morpholine, reacts with either ^•NO or ^•NO₂ and serves as a common precursor for both products. The peroxynitrite-mediated oxidation of &#945;-tocopherol and &#947;-tocopherol dispersed in 1,2-dilauroyl-<i>sn</i>-glycero-3-phosphocholine liposomes in the presence and absence of added carbonate gives &#945;-tocopherylquinone and 5-nitro-&#947;-tocopherol, respectively. The formation of the products is consistent with the current understanding of the free radical nature of oxidations of peroxynitrite and its CO₂-adducts; the overall reaction involves a one-electron oxidation of &#945;-tocopherol and &#947;-tocopherol by HO^• or CO₃^•-, followed by the reaction with ^•NO₂. When &#945;-tocopherol and &#947;-tocopherol were present in the same liposome and exposed to peroxynitrite, there was preferential oxidation of &#945;-tocopherol over &#947;-tocopherol. An explanation for the protection of &#947;-tocopherol by &#945;-tocopherol could be that &#947;- and &#945;-tocopheryl radicals, formed from the respective reactions of &#945;-tocopherol and &#947;-tocopherol with HO^• or CO₃^•-, disproportionate to give &#945;-tocopherylquinone and regenerated &#947;-tocopherol. This is consistent with the lack of protection of &#947;-tocopherol by &#945;-tocopherol when &#945;-tocopherol and &#947;-tocopherol dispersed in different liposomes but present in the same incubation mixer are subjected to oxidation by peroxynitrite.

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Chemistry

Grantor

Chemistry

Year dc:date.available

2002

Author dc:creator

• Bolzan, Rachel

• mechanism

Statement dc:rights

• unrestricted
• Release the entire work immediately for access worldwide.

Identifier

etd-0612102-234815
https://repository.lsu.edu/gradschool_dissertations/366

OAI identifier oai:identifier

oai:repository.lsu.edu:gradschool_dissertations-1365