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 wa...

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...

The infrared spectra of rare earth metal chloride complexes of 2,2'-bipyridyl and 1,lO-phenanthroline are reported from 650 to 70 cm-'. The position of the V M -N vibration is observed to vary with the properties of the metal and ligand.From the infrared spectra in this region, frequency assignments are suggested for the Y M -N vibrations.A number of 2-carbamoyldimedone and N-phenyl-2-carbamoyldimedone complexes of the first transition metal series have been synthesized. The metal-ligand coordination has been investigated by spectral, magnetic, and proton and electron resonance measurements. The results indicate that the oxygen rather than the nitrogen of the carbamoyl group is coordinated to the metal ion. These findings are compared with the coordinate bonding reported for acetoacetamide and salicylamide complexes. Evidence of intermolecular bonding is presented, and a molecular structure is proposed.

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