The decomposition of peroxynitrite to nitroxyl anion (NO -) and singlet oxygen in aqueous solution

Ahsan Ullah Khan, Dianne Kovacic, Alexander Kolbanovskiy, Mehul Desai, Krystyna Frenkel, Nicholas Geacintov

Research output: Contribution to journalArticle

Abstract

The mechanism of decomposition of peroxynitrite (OONO -) in aqueous sodium phosphate buffer solution at neutral pH was investigated. The OONO - was synthesized by directly reacting nitric oxide with superoxide anion at pH 13. The hypothesis was explored that OONO -, after protonation at pH 7.0 to HOONO, decomposes into 1O 2 and HNO according to a spin-conserved unimolecular mechanism. Small aliquots of the concentrated alkaline OONO - solution were added to a buffer solution (final pH 7.0-7.2), and the formation of 1O 2 and NO - in high yields was observed. The 1O 2 generated was trapped as the transannular peroxide (DPAO 2) of 9,10-diphenylanthracene (DPA) dissolved in carbon tetrachloride. The nitroxyl anion (NO -) formed from HNO (pKa 4.5) was trapped as nitrosylhemoglobin (HbNO) in an aqueous methemoglobin (MetHb) solution. In the presence of 25 mM sodium bicarbonate, which is known to accelerate the rate of decomposition of OONO -, the amount of singlet oxygen trapped was reduced by a factor of ≃2 whereas the yield of trapping of NO - by methemoglobin remained unaffected. Because NO 3/ - is known to be the ultimate decomposition product of OONO -, these results suggest that the nitrate anion is not formed by a direct isomerization of OONO -, but by an indirect route originating from NO -.

Original languageEnglish (US)
Pages (from-to)2984-2989
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume97
Issue number7
DOIs
StatePublished - Mar 28 2000

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Singlet Oxygen
Peroxynitrous Acid
Anions
Methemoglobin
Buffers
Sodium Bicarbonate
Carbon Tetrachloride
Peroxides
Superoxides
Nitrates
Nitric Oxide
nitroxyl

Keywords

  • Diphenylanthracene
  • Endoperoxide
  • Nitrosylhemoglobin

ASJC Scopus subject areas

  • Genetics
  • General

Cite this

The decomposition of peroxynitrite to nitroxyl anion (NO -) and singlet oxygen in aqueous solution. / Khan, Ahsan Ullah; Kovacic, Dianne; Kolbanovskiy, Alexander; Desai, Mehul; Frenkel, Krystyna; Geacintov, Nicholas.

In: Proceedings of the National Academy of Sciences of the United States of America, Vol. 97, No. 7, 28.03.2000, p. 2984-2989.

Research output: Contribution to journalArticle

Khan, Ahsan Ullah ; Kovacic, Dianne ; Kolbanovskiy, Alexander ; Desai, Mehul ; Frenkel, Krystyna ; Geacintov, Nicholas. / The decomposition of peroxynitrite to nitroxyl anion (NO -) and singlet oxygen in aqueous solution. In: Proceedings of the National Academy of Sciences of the United States of America. 2000 ; Vol. 97, No. 7. pp. 2984-2989.
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N2 - The mechanism of decomposition of peroxynitrite (OONO -) in aqueous sodium phosphate buffer solution at neutral pH was investigated. The OONO - was synthesized by directly reacting nitric oxide with superoxide anion at pH 13. The hypothesis was explored that OONO -, after protonation at pH 7.0 to HOONO, decomposes into 1O 2 and HNO according to a spin-conserved unimolecular mechanism. Small aliquots of the concentrated alkaline OONO - solution were added to a buffer solution (final pH 7.0-7.2), and the formation of 1O 2 and NO - in high yields was observed. The 1O 2 generated was trapped as the transannular peroxide (DPAO 2) of 9,10-diphenylanthracene (DPA) dissolved in carbon tetrachloride. The nitroxyl anion (NO -) formed from HNO (pKa 4.5) was trapped as nitrosylhemoglobin (HbNO) in an aqueous methemoglobin (MetHb) solution. In the presence of 25 mM sodium bicarbonate, which is known to accelerate the rate of decomposition of OONO -, the amount of singlet oxygen trapped was reduced by a factor of ≃2 whereas the yield of trapping of NO - by methemoglobin remained unaffected. Because NO 3/ - is known to be the ultimate decomposition product of OONO -, these results suggest that the nitrate anion is not formed by a direct isomerization of OONO -, but by an indirect route originating from NO -.

AB - The mechanism of decomposition of peroxynitrite (OONO -) in aqueous sodium phosphate buffer solution at neutral pH was investigated. The OONO - was synthesized by directly reacting nitric oxide with superoxide anion at pH 13. The hypothesis was explored that OONO -, after protonation at pH 7.0 to HOONO, decomposes into 1O 2 and HNO according to a spin-conserved unimolecular mechanism. Small aliquots of the concentrated alkaline OONO - solution were added to a buffer solution (final pH 7.0-7.2), and the formation of 1O 2 and NO - in high yields was observed. The 1O 2 generated was trapped as the transannular peroxide (DPAO 2) of 9,10-diphenylanthracene (DPA) dissolved in carbon tetrachloride. The nitroxyl anion (NO -) formed from HNO (pKa 4.5) was trapped as nitrosylhemoglobin (HbNO) in an aqueous methemoglobin (MetHb) solution. In the presence of 25 mM sodium bicarbonate, which is known to accelerate the rate of decomposition of OONO -, the amount of singlet oxygen trapped was reduced by a factor of ≃2 whereas the yield of trapping of NO - by methemoglobin remained unaffected. Because NO 3/ - is known to be the ultimate decomposition product of OONO -, these results suggest that the nitrate anion is not formed by a direct isomerization of OONO -, but by an indirect route originating from NO -.

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