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1.
FEBS Lett ; 253(1-2): 235-8, 1989 Aug 14.
Article in English | MEDLINE | ID: mdl-2547658

ABSTRACT

The reaction between the phenoxyl radical of Trolox C, a water-soluble vitamin E analogue, and superoxide anion radical was examined by using the pulse radiolysis technique. The results indicate that the Trolox C phenoxyl radical may undergo a rapid one-electron transfer from superoxide radical [k = (4.5 +/- 0.5) x 10(8) M-1.S-1] to its reduced form. This finding indicates that superoxide radical might play a role in the repair of vitamin e phenoxyl radical.


Subject(s)
Benzopyrans , Chromans , Superoxides , Antioxidants , Free Radicals , In Vitro Techniques , Kinetics , Oxidation-Reduction , Pulse Radiolysis , Spectrum Analysis , Vitamin E/analogs & derivatives
3.
Chem Res Toxicol ; 10(11): 1216-20, 1997 Nov.
Article in English | MEDLINE | ID: mdl-9403172

ABSTRACT

The equilibrium constant, K3, of aqueous homolysis of peroxynitrous acid into hydroxyl and nitrogen dioxide free radicals was estimated to be 5 x 10(-10) M. This value was derived from a thermodynamic cycle by use of the experimentally known delta fH degree(ONOO-,aq) = -10.8 kcal/mol and the enthalpy of ionic dissociation of ONOOH(aq), delta H degree 1 = 0 kcal/mol, as well as of the entropy of gaseous ONOOH, S degree(ONOOH,g) = 72 eu. Furthermore we assumed the entropy of hydration of ONOOH, delta S degree 2, to be -25 eu, a value closely bracketed by the hydration entropies of analogous substances. The rate constant of radical recombination of OH. with NO2. to yield ONOOH, k-3, was resimulated from experimental data and found to be ca. 5 x 10(9) M-1 s-1. Together with the estimated K3, this yields the homolysis rate constant k3 = 2.5 s-1. This value is close to 0.5 s-1, the rate constant of formation of a reactive intermediate during the isomerization of peroxynitrous acid to nitrate. Our thermodynamic estimate is therefore consistent with substantial amounts of OH. and NO2. free radicals being formed in this process. The thermodynamic implications for the carbon dioxide/peroxynitrite system are also discussed.


Subject(s)
Carbon Dioxide/chemistry , Nitrates/chemistry , Oxidants/chemistry , Entropy , Free Radicals , Hydroxyl Radical , Nitrogen Dioxide/chemistry , Oxidation-Reduction , Thermodynamics
4.
Chem Res Toxicol ; 11(4): 243-6, 1998 Apr.
Article in English | MEDLINE | ID: mdl-9548793

ABSTRACT

The rate constant of homolysis of peroxynitrite, ONOO-, into O2- and NO was determined to be 0.017 s-1 at 20 degrees C. In combination with other experimental data taken from the literature, this value yields the Gibbs free energy of formation of ONOO-, delta f G o(ONOO-) = 16.6 kcal/mol. On the basis of this result, we conclude that peroxynitrous acid homolyzes to yield nitrogen dioxide (NO2) and hydroxyl (OH) free radicals and derive delta f G o(ONOOH) = 7.7 kcal/mol. The rate constant of the reaction between NO and ONOO- was found to be 5 x 10(-)2 M-1 s-1 at most. The implications of the two homolysis reactions are discussed.


Subject(s)
Nitrates/chemistry , Nitrous Acid/chemistry , Oxidants/chemistry , Free Radicals , Peroxynitrous Acid
5.
Article in Hungarian | MEDLINE | ID: mdl-7833990

ABSTRACT

Good fixation, ability for full weight-bearing in most of the cases, closed surgical technique-these are the advantages of lately developed intramedular osteosynthesis for instabil pertrochanteric and subtrochanteric fractures, called gamma nailing. These advantages do make the general and local complications less and do help the fast rehabilitation. Authors give report on 28 patients, were operated on with gamma nailing within the last 1.5 year. Local complication, infection, loosening, breakage, pseudoarthrosis was not observed. The healing was complete in all evaluated cases. 2/3 of the patients had full weight-bearing following surgery. According to the authors the results are very good in the cases of instabil subtrochanteric and pertrochanteric fractures, therefore the method is highly recommended in similar cases.


Subject(s)
Bone Nails , Femoral Fractures/surgery , Femoral Neck Fractures/surgery , Fracture Fixation, Intramedullary/methods , Adult , Aged , Aged, 80 and over , Female , Femoral Fractures/diagnostic imaging , Femoral Fractures/rehabilitation , Femoral Neck Fractures/diagnostic imaging , Femoral Neck Fractures/rehabilitation , Follow-Up Studies , Fracture Fixation, Intramedullary/instrumentation , Humans , Male , Middle Aged , Radiography , Wound Healing
6.
J Biolumin Chemilumin ; 5(1): 53-6, 1990.
Article in English | MEDLINE | ID: mdl-2156408

ABSTRACT

The mechanism of luminol chemiluminescence is a special case of nucleophilic addition to carbonyl compounds. The breakdown of the key intermediate, an alpha hydroxy hydroperoxide, produces a peracid ortho to an acyl diazene group. After intramolecular addition of the peracid, the energy from nitrogen expulsion is utilized in the formation of an anti-aromatic endoperoxide. Rupture along the O,O bond leaves a substantial part of the ensuing phthalate in its excited state. The emitter is shown to be a mono-protonated phthalate unaccessible by photoexcitation. The dark reaction is a concerted decomposition of the alpha hydroxy hydroperoxidixe to yield ground-state phthalate.


Subject(s)
Luminescent Measurements , Luminol , Pyridazines , Chemical Phenomena , Chemistry , Electrons , Hydroxides , Hydroxyl Radical , Oxidation-Reduction , Superoxides
7.
Chem Res Toxicol ; 14(9): 1273-6, 2001 Sep.
Article in English | MEDLINE | ID: mdl-11559043

ABSTRACT

The reaction of ONOO(-) with CO(2) at alkaline pH was recently reported to form a transient absorption with a maximum at 640 nm and a half-life of ca. 4 ms at 10 degrees C [Meli et al. (1999) Helv. Chim. Acta 82, 722-725]. This transient absorption was hardly affected by the presence of *NO, and therefore was attributed to the adduct ONOOC(O)O(-). This conclusion contradicts all current experimental results as it suggests that the decomposition of this adduct via homolysis of the O-O bond into CO(3)(*)(-) and *NO(2) is a minor pathway. In the present work the observations of Meli et al. will be shown to be artifacts resulting from light coming from the UV region. When these experiments are carried out in the presence of appropriate cutoff filters, the only observable intermediate formed in the reaction of ONOO(-) with CO(2) at alkaline pH is the carbonate radical ion with a maximum at 600 nm. This transient absorption is not observed in the presence of *NO or ferrocyanide. In the latter case ferricyanide is formed, and its yield was determined to be 66 +/- 2% of the initial concentration of peroxynitrite. The reaction of ONOO(-) with 16 mM CO(2) with and without ferrocyanide was also studied at pH 5.6-7.7 in the presence of 0.1 M phosphate, where both the initial pH and [CO(2)] remain constant. Under these conditions the rate constant of the decay of peroxynitrite was found to be identical to that of the formation of ferricyanide, indicating that ONOOC(O)(-) does not accumulate. These results confirm our earlier observations, i.e., the reaction of peroxynitrite with excess CO(2) takes place via the formation of about 33% CO(3)(*)(-) and *NO(2) radicals in the bulk of the solution.


Subject(s)
Carbon Dioxide/chemistry , Carbonates/chemistry , Peroxynitrous Acid/chemistry , Absorption , Ferricyanides/chemistry , Ferrocyanides/chemistry , Free Radicals/chemistry , Half-Life , Hydrogen-Ion Concentration
8.
Chem Res Toxicol ; 14(6): 657-60, 2001 Jun.
Article in English | MEDLINE | ID: mdl-11409935

ABSTRACT

In a recent publication [Nauser et al. (2001) Chem. Res. Toxicol. 14, 248-350], the authors estimated a value of 14 +/- 3 kcal/mol for the standard Gibbs energy of formation of ONOO(-) and argued that the experimental value of 16.6 kcal/mol [Merényi, G., and Lind, J. (1998) Chem. Res. Toxicol. 11, 243-246] is in error. The lower value would suggest that the yield of free radicals during decomposition of ONOOH into nitrate is negligibly low, i.e., less than 0.5%, though within the large error limit given, the radical yield might vary between 0.003% and ca. 80%. The experimental value of 16.6 +/- 0.4 kcal/mol was based on the determination of the rate constant of the forward reaction in the equilibrium ONOO(-) <==> (*)NO and O2(*-) by use of C(NO2)4, an efficient scavenger of O2(*-) which yields C(NO2)3(-). Nauser et al. reported that addition of (*)NO has no significant effect on the rate of formation of C(NO2)3(-), and therefore the formation of C(NO2)3(-) is due to a process other then reduction of C(NO2)4 by O2(*-). In addition, they argued that Cu(II) nitrilotriacetate enhances the rate of peroxynitrite decomposition at pH 9.3 without reduction of Cu(II). In the present paper, we show that the formation of C(NO2)3(-) due to the presence peroxynitrite is completely blocked upon addition of (*)NO. Furthermore, the acceleration of the rate of peroxynitrite decomposition at pH 9 in the presence of catalytic concentrations of SOD ([ONOO(-)]/[SOD] > 30) results in the same rate constant as that obtained in the presence of C(NO(2))(4). These results can only be rationalized by assuming that ONOO(-) homolyses into (*)NO and O2(*-) with k = 0.02 s(-1) at 25 degrees C. Thus, the critical experiments suggested by Nauser et al. fully support the currently accepted thermodynamics as well as the mode of decomposition of the ONOOH/ONOO(-) system.


Subject(s)
Nitrates/chemistry , Oxidants/chemistry , Kinetics , Nitric Oxide/chemistry , Nitrogen Dioxide/chemistry , Thermodynamics
9.
Proc Natl Acad Sci U S A ; 97(15): 8216-8, 2000 Jul 18.
Article in English | MEDLINE | ID: mdl-10880577

ABSTRACT

In a recent article [Khan, A. U., Kovacic, D., Kolbanovsky, A., Desai, M., Frenkel, K. & Geacintov, N. E. (2000) Proc. Natl. Acad. Sci. USA 97, 2984-2989], the authors claimed that ONOO(-), after protonation to ONOOH, decomposes into (1)HNO and (1)O(2) according to a spin-conserved unimolecular mechanism. This claim was based partially on their observation that nitrosylhemoglobin is formed via the reaction of peroxynitrite with methemoglobin at neutral pH. However, thermochemical considerations show that the yields of (1)O(2) and (1)HNO are about 23 orders of magnitude lower than those of ( small middle dot)NO(2) and ( small middle dot)OH, which are formed via the homolysis of ONOOH. We also show that methemoglobin does not form with peroxynitrite any spectrally detectable product, but with contaminations of nitrite and H(2)O(2) present in the peroxynitrite sample. Thus, there is no need to modify the present view of the mechanism of ONOOH decomposition, according to which initial homolysis into a radical pair, [ONO( small middle dot) ( small middle dot)OH](cage), is followed by the diffusion of about 30% of the radicals out of the cage, while the rest recombines to nitric acid in the solvent cage.


Subject(s)
Methemoglobin/chemistry , Nitrates/chemistry , Nitrogen Oxides/chemistry , Oxygen/chemistry , Animals , Anions , Cattle , Free Radicals , Hydrogen Peroxide/chemistry , Nitrites/chemistry , Nitrogen Dioxide/chemistry , Singlet Oxygen , Spectrophotometry, Ultraviolet
10.
J Biol Chem ; 275(5): 3031-6, 2000 Feb 04.
Article in English | MEDLINE | ID: mdl-10652282

ABSTRACT

Radiation chemical experiments demonstrate that the reaction of tyrosyl radical (TyrO(.)) with (.)NO(2) yields 45 +/- 3% 3-nitrotyrosine and that a major product of the reaction of TyrO(.) with (.)NO is 3,3'-dityrosine. Radiolysis was used to generate (.)NO and O-(2) in the presence of tyrosine and bicarbonate at pH 7.5 +/- 0.1. The nitration yield was found to be dose rate-dependent, and the yield per radical produced by pulse radiolysis was identical to that obtained with authentic peroxynitrite. The proposed mechanism that accounts for the data is as follows: (i) In the presence of CO(2) the reaction of (.)NO with O-(2) yields 33% (.)NO(2) and CO-(3), where the latter reacts rapidly with tyrosine to form TyrO(.); (ii) The formation of 3-nitrotyrosine takes place via the reaction of (.)NO(2) with TyrO(.), which is the main process at high dose rates; and (iii) Under continuous generation of (.)NO and O-(2), the formation of 3-nitrotyrosine is strongly suppressed because of efficient scavenging of (.)NO(2) by tyrosine. The proposed model shows that the highest nitration yield is obtained for similar fluxes of (.)NO and O-(2) and is completely inhibited upon excess production of O-(2) because of efficient scavenging of TyrO(.) by O-(2). The biological implications of these findings are discussed.


Subject(s)
Free Radicals/chemistry , Nitrates/chemistry , Tyrosine/chemistry , Animals , Humans
11.
Chem Res Toxicol ; 12(2): 132-6, 1999 Feb.
Article in English | MEDLINE | ID: mdl-10027789

ABSTRACT

Nitric oxide reacts slowly with ONOO- (k < 1.3 x 10(-)3 M-1 s-1), and therefore does not affect the stability of peroxynitrite at pH >12. A chain consumption of peroxynitrite by *NO takes place at pH <12 through the reaction of N2O3 with ONOO-, where the former is formed through two initiation steps: (i) autoxidation of *NO, which is the main process in alkaline solutions, and (ii) spontaneous decomposition of peroxynitrite. The effect of *NO on the decomposition of peroxynitrite depends on the rate of the reaction of ONOO- with N2O3 (propagation step) relative to that of the hydrolysis of N2O3 (termination step). Therefore, rapid consumption of peroxynitrite occurs upon increasing the peroxynitrite concentration, decreasing the phosphate concentration, and lowering the pH, as the hydrolysis of N2O3 is base-catalyzed. The rate constant of the reaction of ONOO- with N2O3 has been determined in alkaline solutions to be (3.1 +/- 0.3) x 10(8) M-1 s-1. The decomposition of ONOOH in acidic solutions is hardly affected by *NO, as N2O3 does not react with ONOOH. Under physiological conditions, the reaction of *NO with peroxynitrite cannot give rise to a chain consumption of peroxynitrite as the reaction of N2O3 with the relatively low concentrations of peroxynitrite cannot compete with the hydrolysis of N2O3.


Subject(s)
Hydroxyl Radical/chemistry , Nitrates/chemistry , Nitric Oxide/chemistry , Nitrous Acid/chemistry , Oxidants/chemistry , Hydrogen-Ion Concentration , Kinetics , Oxidation-Reduction , Peroxynitrous Acid , Spectrophotometry , Superoxides/chemistry
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