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

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 1 O2 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 1 O2 and NO ؊ in high yields was observed. The 1 O2 generated was trapped as the transannular peroxide (DPAO2) 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 Ϸ2 whereas the yield of trapping of NO ؊ by methemoglobin remained unaffected. Because NO3 ؊ 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 ؊ .nitrosylhemoglobin ͉ diphenylanthracene endoperoxide P eroxynitrite is a potent oxidant formed by the near diffusioncontrolled reaction of nitric oxide (NO ⅐ ) and superoxide ion (O 2 Ϫ ) (1). Both nitric oxide and superoxide are produced by activated macrophages (2, 3), neutrophils (4), and endothelial cells (5, 6). There is evidence that peroxynitrite is formed in significant concentrations in vivo (7-9) and may contribute to an increased risk for cancer (10), artherosclerosis (11), stroke (12), and other diseases (13). Peroxynitrite is a stable anion in alkaline solution (pKa of 6.8); however, once protonated, it decomposes rapidly with a half-life of less than 1 s at physiological pH at 37°C (14), generating reactive species that readily react with biomolecules such as lipids (15), amino acids (16), and DNA (17). Central to the question of the biochemistry of peroxynitrite is the mechanism of decomposition and the identity of the reactive species, a subject of intense research and controversy (18-21). Speculations about the decomposition mechanisms are largely based on kinetic and thermodynamic considerations (22). It has been shown that bicarbonate ion enhances the rate of disappearance of peroxynitrite, leading to the proposal of a nitrosoperoxycarbonate anion adduct, with a distinctly different chemistry from that of OONO Ϫ (19).We reported previously that the mere acidification of an aqueous peroxynitrite solution resulted in chemiluminescence at 1,270 nm characteristic of the deactivation of singlet oxygen (23). By comparing the intensity of this emission to that of 1 O 2 generated by the reaction of hydrogen peroxide (H 2 O 2 ) with hypochlorite anion (OCl Ϫ ), which is known to be stoichiometric (24), it was...

Chemical Effects of Air Plasma Species on Aqueous Solutes in Direct and Delayed Exposure Modes: Discharge, Post-discharge and Plasma Activated Water

“…The same authors [54] also report that the decomposition of peroxynitrous acid is affected by both temperature and local acidity (pH) and produces nitrites, nitrous acid and oxygen. The decomposition of peroxynitrite to nitroxyl anion NO -and singlet oxygen O 2 ( 1 D g ) was also proposed [54] but debated by Koppenol et al [55].…”

“…The same authors [54] also report that the decomposition of peroxynitrous acid is affected by both temperature and local acidity (pH) and produces nitrites, nitrous acid and oxygen. The decomposition of peroxynitrite to nitroxyl anion NO -and singlet oxygen O 2 ( 1 D g ) was also proposed [54] but debated by Koppenol et al [55]. An argument reintroduced by Hugues [56] might be helpful to progress: the singlet ground state of nitroxyl does not react with dioxygen while the reaction with the excited triplet state of NO -takes place.…”

Quantum dots and nanoparticles for photodynamic and radiation therapies of cancer

“…Dihydrorhodamine 123 was rapidly oxidized to a green fluorescent product rhodamine 123 within few minutes of the red light exposure [68]. It is firmly established in the literature that peroxynitrite does not yield singlet oxygen [131–133]. Bandgap of quantum dots is also potentially enough to reduce oxygen to superoxide ( ${\text{O}}_2^{•-}$) or oxidize water or hydroxide ions to hydroxyl radical ( • OH) [134].…”

The Association Between Neuronal Nitric Oxide Synthase and Neuronal Sensitivity in the Brain After Brain Injury

“…Therefore, it can diffuse into the nuclei and into cells other than that in which it is formed. Peroxynitrite undergoes a cleavage reaction to form a hydroxyl radical or singlet oxygen,23 both of which are highly reactive and can cause damage to all cellular components. Modified RNA and DNA can change their coding properties and block chain elongation during transcription and replication.…”