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  • 1. Armstrong, David A.
    et al.
    Huie, Robert E.
    Koppenol, Willem H.
    Lymar, Sergei V.
    Merenyi, Gabor
    KTH, Skolan för kemivetenskap (CHE), Kemi, Tillämpad fysikalisk kemi.
    Neta, Pedatsur
    Ruscic, Branko
    Stanbury, David M.
    Steenken, Steen
    Wardman, Peter
    Standard electrode potentials involving radicals in aqueous solution: inorganic radicals (IUPAC Technical Report)2015Ingår i: Pure and Applied Chemistry, ISSN 0033-4545, E-ISSN 1365-3075, Vol. 87, nr 11-12, s. 1139-1150Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recommendations are made for standard potentials involving select inorganic radicals in aqueous solution at 25 degrees C. These recommendations are based on a critical and thorough literature review and also by performing derivations from various literature reports. The recommended data are summarized in tables of standard potentials, Gibbs energies of formation, radical pK(a)'s, and hemicolligation equilibrium constants. In all cases, current best estimates of the uncertainties are provided. An extensive set of Data Sheets is appended that provide original literature references, summarize the experimental results, and describe the decisions and procedures leading to each of the recommendations.

  • 2. Armstronga, D. A.
    et al.
    Huie, R. E.
    Lymar, S.
    Koppenol, W. H.
    Merényi, Gabor
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Tillämpad fysikalisk kemi.
    Neta, P.
    Stanbury, D. M.
    Steenken, S.
    Wardman, P.
    Standard electrode potentials involving radicals in aqueous solution: Inorganic radicals2013Ingår i: BioInorganic Reaction Mechanisms, ISSN 2191-2491, Vol. 9, nr 1-4, s. 59-61Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Inorganic radicals, such as superoxide and hydroxyl, play an important role in biology. Their tendency to oxidize or to reduce other compounds has been studied by pulse radiolysis; electrode potentials can be derived when equilibrium is established with a well-known reference compound. An IUPAC Task Group has evaluated the literature and produced the recommended standard electrode potentials for such couples as (O2/O2 ·-), (HO·, H+/H2O), (O3/O3 ·-), (Cl2/Cl2 ·-), (Br2 ·-/2Br-), (NO2 ·/NO2 -), and (CO3 ·-/CO3 2-). 

  • 3.
    Augusto, Ohara
    et al.
    Univ Sao Paulo, Inst Quim, Dept Bioquim, BR-5508000 Sao Paulo, Brazil..
    Goldstein, Sara
    Hebrew Univ Jerusalem, Chem Inst, IL-91904 Jerusalem, Israel..
    Hurst, James K.
    Oregon State Univ, Dept Biochem & Biophys, Corvallis, OR 97331 USA..
    Lind, Johan
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH).
    Lymar, Sergei, V
    Brookhaven Natl Lab, Dept Chem, Upton, NY 11973 USA..
    Merényi, Gabor
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Kemi, Tillämpad fysikalisk kemi.
    Radi, Rafael
    Univ Republica, Dept Bioquim, Fac Med, Montevideo 11800, Uruguay.;Univ Republica, Ctr Free Rad & Biomed Res, Fac Med, Montevideo 11800, Uruguay..
    Carbon dioxide-catalyzed peroxynitrite reactivity - The resilience of the radical mechanism after two decades of research2019Ingår i: Free Radical Biology & Medicine, ISSN 0891-5849, Vol. 135, s. 210-215Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Peroxynitrite, ONOO-, formed in tissues that are simultaneously generating NO center dot and O-2(center dot-), is widely regarded as a major contributor to oxidative stress. Many of the reactions involved are catalyzed by CO2 via formation of an unstable adduct, ONOOC(O)O-, that undergoes O-O bond homolysis to produce NO2 center dot and CO3 center dot- radicals, whose yields are equal at about 0.33 with respect to the ONOO- reactant. Since its inception two decades ago, this radical-based mechanism has been frequently but unsuccessfully challenged. The most recent among these [Serrano-Luginbuehl et al. Chem. Res. Toxicol. 31: 721-730; 2018] claims that ONOOC(O)O- is stable, predicts a yield of NO2 center dot/CO3 center dot- of less than 0.01 under physiological conditions and, contrary to widely accepted viewpoints, suggests that radical generation is inconsequential to peroxynitrite-induced oxidative damage. Here we review the experimental and theoretical evidence that support the radical model and show this recently proposed alternative mechanism to be incorrect.

  • 4. Bauer, Georg
    et al.
    Chatgilialoglu, Chryssostomos
    Gebicki, Jerzy L.
    Gebicka, Lidia
    Gescheidt, Georg
    Golding, Bernard T.
    Goldstein, Sara
    Kaizer, Jozsef
    Merenyi, Gabor
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Speier, Gabor
    Wardman, Peter
    Biologically relevant small radicals2008Ingår i: Chimia (Basel), ISSN 0009-4293, Vol. 62, nr 9, s. 704-712Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Biologically relevant small radicals are at the focus of the working group 4 (WG4) of the COST Action CM0603 (Free Radicals in Chemical Biology, CHEMBIORADICAL). This article surveys the areas of research being undertaken by the partners in WG4. The character of the radicals is described together with experimental techniques utilized to follow their structure and reactivity. Specifically, C-, S-, N- and O-centered radicals of small size, and their interaction with different biomolecules are described. Processes at the molecular level exemplifying important biological signaling and damaging pathways are introduced.

  • 5.
    Carlsson, Magnus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Lind, Johan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Merényi, Gabor
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    A selectivity study of reaction of the carbonate radical anion with methyl beta- D-cellobioside and methyl beta-D-glucoside in oxygenated aqueous solutions2006Ingår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 60, nr 2, s. 130-136Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the presence of oxygen, radiolytically generated carbonate radical anions, CO3.-, were reacted with methyl beta-D-cellobioside and methyl beta-D-glucoside. From the ensuing product pattern, it was concluded that CO3 center dot- abstracts hydrogen atoms predominantly from glucosidic C1 - H bonds. This high intramolecular selectivity was rationalised mainly in terms of a polar effect on the transition state of the hydrogen abstraction reaction. The present findings are in sharp contrast to the relative inertness of CO3(center dot-) towards glucosidic C1 - H bonds previously observed in cotton linters. The reasons for this discrepancy are discussed in light of a possible future role of CO3 center dot- as a bleaching agent for pulp.

  • 6.
    Carlsson, Magnus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Stenman, David
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Merényi, Gabor
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Reitberger, Torbjörn
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    A comparative study on the degradation of cotton linters induced by carbonate and hydroxyl radicals generated from peroxynitrite2005Ingår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 59, nr 2, s. 132-142Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Carbonate (CO3.(-)) and hydroxyl (HO.) radicals were chemically produced in cotton linter suspensions using peroxynitrite as a radical precursor. Both radicals could degrade cotton linters, as shown by viscosity and GPC-SEC measurements. As evidenced by the viscosity measurements, the presence of oxygen during the cotton linter treatments slightly increased cellulose degradation by both radicals. For the carbonate radical, more than 90% of the viscosity losses could be recovered by reductive NaBH4 treatment before measuring the viscosity, whereas only approximately 40% of the viscosity was recovered after hydroxyl radical degradation and subsequent NaBH4 treatment. This indicates that carbonate radicals mainly abstract H-atoms adjacent to hydroxyl groups, i.e., at C-2, C-3 and C-6. This intramolecular selectivity may reflect a polar effect, whereby hydrogen atom abstractions from these positions are favoured. In addition, abstraction at C-6 would be sterically and statistically favoured.

  • 7.
    Carlsson, Magnus
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Stenman, David
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Merényi, Gabor
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Reitberger, Torbjörn
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    The Carbonate Radical as One-Electron Oxidant of Carbohydrates in Alkaline media2005Ingår i: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 59, nr 2, s. 143-146Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mechanism by which the carbonate radical anion reacts with D-glucose in alkaline aqueous solutions has been studied by means of gamma-radiolysis. From the product analysis it is concluded that the reaction sequence is initiated by a one-electron transfer between the carbonate radical anion and deprotonated D-glucose. In the presence of molecular oxygen, the major, if not only products of this reaction sequence are formic acid, arabinose and gluconic acid and reaction schemes are proposed to account for the observed formation of these products.

  • 8. Eriksson, P.
    et al.
    Engman, L.
    Lind, Johan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Merenyi, Gabor
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Aqueous phase one-electron reduction of sulfonium, selenonium and telluronium salts2005Ingår i: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, nr 4, s. 701-705Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Triorganylsulfonium, -selenonium and -telluronium salts were reduced by carbon dioxide radical anions/solvated electrons produced in aqueous solution by radiolysis. The radical expulsion accompanying reduction occurred with the expected leaving group propensities (benzyl > secondary alkyl > primary alkyl > methyl > phenyl), although greater than expected loss of the phenyl group was often observed. Diorganyl chalcogenides formed in the reductions were conveniently isolated by extraction with an organic solvent. Product yields based on the amount of reducing radicals obtained from the T-source were often higher than stoichiometric (up to 1800 %) in the reduction of selenonium and telluronium compounds; it is likely that this result can be accounted for in terms of a chain reaction with carbon-centred radicals/formate serving as the chain transfer agent. The product distribution was essentially independent of the reducing species for diphenyl alkyl telluronium salts, whereas significant variations were seen for some of the corresponding selenonium salts. This would suggest the intermediacy of telluranyl radicals in the one-electron reduction of telluronium salts. However, pulse radiolysis experiments indicated that the lifetimes of such a species (the triphenyltelluranyl radical) would have to be less than 1 mus.

  • 9. Goldstein, S.
    et al.
    Czapski, G.
    Lind, Johan
    KTH, Tidigare Institutioner                               , Kemi.
    Merenyi, Gabor
    KTH, Tidigare Institutioner                               , Kemi.
    Carbonate radical ion is the only observable intermediate in the reaction of peroxynitrite with CO22001Ingår i: Chemical Research in Toxicology, ISSN 0893-228X, E-ISSN 1520-5010, Vol. 14, nr 9, s. 1273-1276Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The reaction of ONOO- with CO2 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 degreesC [Meli et al. (1999) Helv. Chim. Acta 82, 722-725]. This transient absorption was hardly affected by the presence of (NO)-N-., 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 CO3.- and . NO2 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 CO2 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)-N-. 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 CO2 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 [CO2] 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 CO2 takes place via the formation of about 33% CO3.- and (NO2)-N-. radicals in the bulk of the solution.

  • 10. Goldstein, S.
    et al.
    Czapski, G.
    Lind, Johan
    KTH, Tidigare Institutioner                               , Kemi.
    Merenyi, Gabor
    KTH, Tidigare Institutioner                               , Kemi.
    Gibbs energy of formation of peroxynitrate-order restored2001Ingår i: Chemical Research in Toxicology, ISSN 0893-228X, E-ISSN 1520-5010, Vol. 14, nr 6, s. 657-660Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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 [Merenyi, 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- reversible arrow (NO)-N-. and O-2(.-) by use of C(NO2)(4), an efficient scavenger of O-2(.-) which yields C(NO2)(3)(-). Nauser et al. reported that addition of.NO has no significant effect on the rate of formation of C(N02)3-, and therefore the formation of C(No-2)(3-) is due to a process other then reduction of C(NO2)(4) by O-2 (.-) 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(N02)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(NO2)4. These results can only be rationalized by assuming that ONOO- homolyses into (NO)-N-. and O-2(.-) With k = 0.02 S-1 at 25 degreesC. 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.

  • 11. Goldstein, S.
    et al.
    Czapski, G.
    Lind, Johan
    KTH, Tidigare Institutioner                               , Kemi.
    Merenyi, Gabor
    KTH, Tidigare Institutioner                               , Kemi.
    Tyrosine nitration by simultaneous generation of (NO)-N-center dot and O-2(center dot) under physiological conditions - How the radicals do the job2000Ingår i: Journal of Biological Chemistry, ISSN 0021-9258, E-ISSN 1083-351X, Vol. 275, nr 5, s. 3031-3036Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Radiation chemical experiments demonstrate that the reaction of tyrosyl radical (TyrO(.)) with (NO2)-N-. yields 45 +/- 3% 3-nitrotyrosine and that a major product of the reaction of TyrO(.) with (NO)-N-. is 3,3'-dityrosine. Radiolysis was used to generate (NO)-N-. 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 CO2 the reaction of (NO)-N-. with O-2(-.) yields 33% (NO2)-N-. and CO3-. where the latter reacts rapidly with tyrosine to form TyrO; (ii) The formation of 3-nitrotyrosine takes place via the reaction of (NO2)-N-. with TyrO(.), which is the main process at high dose rates; and (iii) Under continuous generation of (NO)-N-. and O-2(-.) the formation of 3-nitrotyrosine is strongly suppressed because of efficient scavenging of NO2, by tyrosine. The proposed model shows that the highest nitration yield is obtained for similar fluxes of (NO)-N-. 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.

  • 12. Goldstein, S.
    et al.
    Lind, Johan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Merenyi, Gabor
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Chemistry of peroxynitrites as compared to peroxynitrates2005Ingår i: Chemical Reviews, ISSN 0009-2665, E-ISSN 1520-6890, Vol. 105, nr 6, s. 2457-2470Artikel, forskningsöversikt (Refereegranskat)
  • 13. Goldstein, S.
    et al.
    Lind, Johan
    KTH, Tidigare Institutioner, Kemi.
    Merenyi, Gabor
    KTH, Tidigare Institutioner, Kemi.
    Reaction of organic peroxyl radicals with (NO2)-N-center dot and (NO)-N-center dot in aqueous solution: Intermediacy of organic peroxynitrate and peroxynitrite species2004Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 108, nr 10, s. 1719-1725Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work, we studied the reactions of alkyl peroxyl radicals with (NO2)-N-. and (NO)-N-. using the pulse radiolysis technique. The rate constants for the reaction of (NO2)-N-. with (CH3)(2)C(OH)CH2OO., CH3OO. and c-C5H9OO. vary between 7 x 10(8) and 1.5 x 10(9) M-1 s(-1). The reaction produces relatively long-lived alkyl peroxynitrates, which are in equilibrium with the parent radicals and have no appreciable absorption above 270 nm. It is also shown that (NO)-N-. adds rapidly to (CH3)(2)C(OH)CH2OO. and CH3OO. to form alkyl peroxynitrites. The rate constants for these reactions were determined to be 2.8 x 10(9) and 3.5 x 10(9) M-1 s(-1), respectively. However, in contrast to alkyl peroxynitrates, alkyl peroxynitrites do not accumulate. Rather, they decompose rapidly via homolysis along the relatively weak O-O bond, initially forming a geminate pair. Most of this pair collapses in the cage to form an alkyl nitrate, RONO2, and about 14% diffuses out as free alkoxyl and (NO2)-N-. radicals. A thermokinetic analysis predicts the half-life of CH3OONO in water to be less than 1 mus, an estimate that agrees well with previous experimental findings of ours for other alkyl peroxynitrites. A comparison of aqueous and gaseous thermochemistry of alkyl peroxynitrates reveals that alkyl peroxyl radicals and the corresponding alkyl peroxynitrates are similarly solvated by water.

  • 14. Goldstein, S.
    et al.
    Lind, Johan
    KTH, Tidigare Institutioner                               , Kemi.
    Merenyi, Gabor
    KTH, Tidigare Institutioner                               , Kemi.
    The reaction of ONOO- with carbonyls: Estimation of the half-lives of ONOOC(O)O- and O2NOOC(O)O2002Ingår i: Journal of the Chemical Society. Dalton Transactions, ISSN 1472-7773, E-ISSN 1364-5447, nr 5, s. 808-810Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The equilibrium constant for the formation of an adduct between a carbonyl and a hydroperoxide ion varies linearly with the acid dissociation constant of the hydroperoxide. Based on this relationship, the half-life of the adduct formed between ONOO- and CO2, ONOOC(O)O-, is estimated to be shorter than 100 ns. Consequently, this adduct should not play any role whatsoever in chemical or biological systems. O2NOO- and CO2 are believed to be involved in a fast equilibrium reaction forming an adduct, O2NOOC(O)O-. This adduct does not appear to homolyse either along the O-O or the N-O bond. Furthermore, at realistic CO2 concentrations, the equilibrium should be shifted far to the O2NOO- + CO2 side. Therefore, the rate of self-decomposition of O2NOO- into NO2- and O-2 is unaffected by the presence of bicarbonate.

  • 15. Goldstein, S.
    et al.
    Merenyi, Gabor
    KTH, Tidigare Institutioner                               , Kemi.
    Russo, A.
    Samuni, A.
    The role of oxoammonium cation in the SOD-Mimic activity of cyclic nitroxides2003Ingår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 125, nr 3, s. 789-795Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cyclic nitroxides (RNO.) mimic the activity of superoxide dismutase (SOD) and demonstrate antioxidant properties in numerous in vitro and in vivo models. Their broad antioxidant activity may involve the participation of their reduced and oxidized forms, that is, hydroxylamine (RNO-H) and oxoammonium cation (RNO+). To examine this possibility we studied the reactions of RNO+ and RNO+ with HO2./O-2(.-) and with several reductants by pulse radiolysis and rapid-mixing stopped-flow techniques. The oxoammonium cations were generated by electrochemical and radiolytic oxidation of 2,2,6,6-tetramethylpiperidinoxyl (TPO) and 3-carbamoyl-2,2,5,5-tetramethylpyrrolidinoxyl (3-CP). The rate constant for the reaction of RNO. with HO2. to form RNO+ was determined to be (1.2 +/- 0.1) x 10(8) for TPO and (1.3 +/- 0.1) x 10(6) M-1 s(-1) for 3-CP. The kinetics results demonstrate that the reaction of RNO. with HO2. proceeds via an inner-sphere electron-transfer mechanism. The rate constant for the reaction of RNO. with O-2(.-) is lower than 1 x 10(3) M-1 s(-1). The rate constant for the reaction of RNO+ with O-2(.-) was determined to be (3.4 +/- 0.2) x 10(9) for TPO+ and (5.0 +/- 0.2) x 10(9) M-1 s(-1) for 3-CP+. Hence, both nitroxides catalyze the dismutation of superoxide through the RNO./RNO+ redox couple, and the dependence of the catalytic rate constant, k(cat), on pH displayed a bell-shaped curve having a maximum around pH 4. The oxoammonium cation oxidized ferrocyanide and HO2- by a one-electron transfer, whereas the oxidation of methanol, formate, and NADH proceeded through a two-electron-transfer reaction. The redox potential of RNO./RNO+ couple was calculated to be 0.75 and 0.89 V for 3-CP and TPO, respectively. The elucidated mechanism provides a clearer insight into the biological antioxidant properties of cyclic nitroxides that should permit design of even more effective antioxidants.

  • 16. Goldstein, S.
    et al.
    Merenyi, Gabor
    KTH, Tidigare Institutioner, Kemi.
    Samuni, A.
    Kinetics and mechanism of (NO2)-N-. reacting with various oxidation states of myoglobin2004Ingår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 126, nr 48, s. 15694-15701Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nitrogen dioxide ((NO2)-N-.) participates in a variety of biological reactions. Of great interest are the reactions of (NO2)-N-. with oxymyoglobin and oxyhemoglobin, which are the predominant hemeproteins in biological systems. Although these reactions occur rapidly during the nitrite-catalyzed autoxidation of hemeproteins, their roles in systems producing (NO2)-N-. in the presence of these hemeproteins have been greatly underestimated. In the present study, we employed pulse radiolysis to study directly the kinetics and mechanism of the reaction of oxymyoglobin (MbFe(II)O(2)) with (NO2)-N-.. The rate constant of this reaction was determined to be (4.5 +/- 0.3) x 10(7) M(-1)s(-1), and is among the highest rate constants measured for (NO2)-N-. with any biomolecule at pH 7.4. The interconversion among the various oxidation states of myoglobin that is prompted by nitrogen oxide species is remarkable. The reaction of MbFeIIO(2) with (NO2)-N-. forms MbFeIIIOONO(2), which undergoes rapid heterolysis along the O-O bond to yield MbFe(V)=O and NO3-. The perferryl-myoglobin (MbFe(V=)O) transforms rapidly into the ferryl species that has a radical site on the globin ((.)MbFe(IV)=O). The latter oxidizes another oxymyoglobin (10(4) M(-1)s(-1) < k(17) < 10(7) M(-1)s(-1)) and generates equal amounts of ferrylmyoglobin and metmyoglobin. At much longer times, the ferrylmyoglobin disappears through a relatively slow comproportionation with oxymyoglobin (k(18) = 21.3 +/- 5.3 M(-1)s(-1)). Eventually, each (NO2)-N-. radical converts three oxymyoglobin molecules into metmyoglobin. The same intermediate, namely MbFe(III)OONO(2), is also formed via the reaction peroxynitrate (O2NOO-/O2NOOH) with metmyoglobin (k(19) = (4.6 +/- 0.3) x 10(4) M(-1)s(-1)). The reaction of (NO2)-N-. With ferrylmyoglobin (k(20) = (1.2 +/- 0.2) x 10(7) M(-1)s(-1)) yields MbFe(III)ONO(2), which in turn dissociates (k(21) = 190 +/- 20 s(-1)) into metmyoglobin and NO3-. This rate constant was found to be the same as that measured for the decay of the intermediate formed in the reaction of MbFe(II)O(2) with (NO2)-N-. which suggests that MbFe(III)ONO(2) is the intermediate observed in both processes. This conclusion is supported by thermokinetic arguments. The present results suggest that hemeproteins may detoxify (NO2)-N-. and thus preempt deleterious processes, such as nitration of proteins. Such a possibility is substantiated by the observation that the reactions of NO2 with the various oxidation states of myoglobin lead to the formation of metmyoglobin, which, though not functional in the gas transport, is nevertheless nontoxic at physiological pH.

  • 17. Goldstein, S.
    et al.
    Samuni, A.
    Hideg, K.
    Merenyi, Gabor
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Structure-activity relationship of cyclic nitroxides as SOD mimics and scavengers of nitrogen dioxide and carbonate radicals2006Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 110, nr 10, s. 3679-3685Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Synthetic nitroxide antioxidants attenuate oxidative damage in various experimental models. Their protective effect reportedly depends on ring size and ring substituents and is greater for nitroxides having lower oxidation potential. The present study focuses on the kinetics and mechanisms of the reactions of piperidine, pyrrolidine and oxazolidine nitroxides with HO2 center dot/O-2(center dot-), (NO2)-N-center dot and CO3 center dot- radicals, which are key intermediates in many inflammatory and degenerative diseases. It is demonstrated that nitroxides are the most efficient scavengers of (NO2)-N-center dot at physiological pH (k = (3-9) x 10(8) M-1 s(-1)) and among the most effective metal-independent scavengers Of CO3 center dot- radicals (k = (2 - 6) x 10(8) M-1 s(-1)). Their reactivity toward HO2 center dot, though not toward center dot NO2 and CO3 center dot-, depends on the nature of the ring side-chain and particularly on the ring-size. All nitroxide derivatives react slowly with O-2(center dot-) and are relatively inefficient SOD mimics at physiological pH. Even piperidine nitroxides, having the highest SOD-like activity, demonstrate a catalytic activity of about 1000-fold lower than that of native SOD at pH 7.4. The present results do not indicate any correlation between the kinetics of HO2 center dot/O-2(center dot-), (NO2)-N-center dot, and CO3 center dot- removal by nitroxides and their protective activity against biological oxidative stress and emphasize the importance of target-oriented nitroxides, i.e., interaction between the biological target and specific nitroxides.

  • 18. Goldstein, S.
    et al.
    Samuni, A.
    Merenyi, Gabor
    KTH, Tidigare Institutioner, Kemi.
    Reactions of nitric oxide, peroxynitrite, and carbonate radicals with nitroxides and their corresponding oxoammonium cations2004Ingår i: Chemical Research in Toxicology, ISSN 0893-228X, E-ISSN 1520-5010, Vol. 17, nr 2, s. 250-257Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cyclic nitroxides effectively protect biological systems against radical-induced damage. However, the mechanism of the reactions of nitroxides with nitrogen-derived reactive species and carbonate radicals is far from being elucidated. In the present study, the reactions of several representative piperidine- and pyrrolidine-based nitroxides with (NO)-N-., peroxynitrite, and CO3.- were investigated, and the results are as follows: (i) There is no evidence for any direct reaction between the nitroxides and the (NO)-N-.. In the presence of oxygen, the nitroxides are readily oxidized by (NO2)-N-., which is formed as an intermediate during autoxidation of (NO)-N-.. (ii) (NO)-N-. reacts with the oxoammonium cations to form nitrite and the corresponding nitroxides with k(1) = (9.8 +/- 0.2) x 10(3) and (3.7 +/- 0.1) x 10(5) M-1 s(-1) for the oxoammonium cations derived from 2,2,6,6-tetramethylpiperidine-1-oxyl (TPO) and 3-carbamoyl-proxyl (3-CP), respectively. (iii) CO3.- oxidizes all nitroxides tested to their oxoammonium cations with similar rate constants of (4.0 +/- 0.5) x 10(8) M-1 s(-1), which are about 3-4 times higher than those determined for H-abstraction from the corresponding hydroxylamines TPO-H and 4-OH-TPO-H. (iv) Peroxynitrite ion does not react directly with the nitroxides but rather with their oxoammonium cations with k(10) = (6.0 +/- 0.9) x 10(6) and (2.7 +/- 0.9) x 10(6) M-1 s(-1) for TPO+ and 3-CP+, respectively. These results provide a better insight into the complex mechanism of the reaction of peroxynitrite with nitroxides, which has been a controversial subject. The small effect of relatively low concentrations of nitroxides on the decomposition rate of peroxynitrite is attributed to their ability to scavenge efficiently (NO2)-N-. radicals, which are formed during the decomposition of peroxynitrite in the absence and in the presence Of CO2. The oxoammonium cations, thus formed, are readily reduced back to the nitroxides by ONOO-, while forming (NO)-N-. and O-2. Hence, nitroxides act as true catalysts in diverting peroxynitrite decomposition from forming nitrating species to producing nitrosating ones.

  • 19. Goldstein, Sara
    et al.
    Merenyi, Gabor
    KTH, Skolan för kemivetenskap (CHE), Kemi.
    The chemistry of peroxynitrite: Implications for biological activity2008Ingår i: Methods in Enzymology / [ed] Poole, RK, 2008, Vol. 436, s. 49-61Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    In biological systems, nitric oxide (NO) combines rapidly with superoxide (O(2)(-)) to form peroxynitrite ion (ONOO(-)), a substance that has been implicated as a culprit in many diseases. Peroxynitrite ion is essentially stable, but its protonated form (ONOOH, pK(a) = 6.5 to 6.8) decomposes rapidly via homolysis of the O-O bond to form about 28% free NO(2) and OH radicals. At physiological pH and in the presence of large amounts of bicarbonate, ONOO- reacts with CO(2) to produce about 33% NO(2) and carbonate ion radicals (CO(3)(-)) in the bulk of the solution. The quantitative role of OH/CO(3)(-) and NO(2) radicals during the decomposition of peroxynitrite (ONOOH/ONOO(-)) under physiological conditions is described in detail. Specifically, the effect of the peroxynitrite dosage rate on the yield and distribution of the final products is demonstrated. By way of an example, the detailed mechanism of nitration of tyrosine, a vital aromatic amino acid, is delineated, showing the difference in the nitration yield between the addition of authentic peroxynitrite and its continuous generation by NO and O(2)(-) radicals.

  • 20. Goldstein, Sara
    et al.
    Samuni, Amram
    Merenyi, Gabor
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Kinetics of the reaction between nitroxide and thiyl radicals: Nitroxides as antioxidants in the presence of thiols2008Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 112, nr 37, s. 8600-8605Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cyclic nitroxides effectively protect cells, tissues, isolated organs, and laboratory animals from radical-induced damage. The present study focuses on the kinetics and mechanisms of the reactions of piperidine and pyrrolidine nitroxides with thiyl radicals, which are involved in free radical "repair" equilibria, but being strong oxidants can also produce cell damage. Thiyl radicals derived from glutathione, cysteine, and penicillamine were generated in water by pulse radiolysis, and the rate constants of their reactions with 2,2,6,6-tetramethylpiperidine-1-oxyl (TPO), 4-OH-TPO, and 3-carbamoyl-proxyl were determined to be (5-7) x 10(8) M-1 s(-1) at pH 5-7, independent of the structure of the nitroxide and the thiyl radical. It is suggested that the reaction of nitroxide (>NO center dot) with thiyl radical (RS center dot) yields an unstable adduct (>NOSR). The deprotonated form of this adduct decomposes via heterolysis of the N-O bond, yielding the respective amine (>NH) and sulfinic acid (RS(O)OH). The protonated form of the adduct decomposes via homolysis of the N-O bond, forming the aminium radical (>NH center dot+) and sulfinyl radical (RSO center dot), which by subsequent reactions involving thiol and nitroxide produce the respective amine and sulfonic acid (RS(O)(2)OH). Nitroxides that are oxidized to the respective oxoammonium cations (>N+=O) are recovered in the presence of NADH but not in the presence of thiols. This suggests that the reaction of >N+=O with thiols yields the respective amine. Two alternative mechanisms are suggested, where >N+=O reacts with thiolate (RS-) directly generating the adduct >NOSR or indirectly forming >NO center dot and RS center dot, which subsequently together yield the adduct >NOSR. Under physiological conditions the adduct is mainly deprotonated, and therefore nitroxides can detoxify thiyl radicals. The proposed mechanism can account for the protective effect of nitroxides against reactive oxygen- and nitrogen-derived species in the presence of thiols.

  • 21.
    Jonsson, Mats.
    et al.
    KTH, Tidigare Institutioner                               , Kemi.
    Lind, Johan
    KTH, Tidigare Institutioner                               , Kemi.
    Merenyi, Gabor
    KTH, Tidigare Institutioner                               , Kemi.
    Redox and acidity properties of 2,2 '- and 4,4 '-biphenol and the corresponding phenoxyl radicals2002Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 106, nr 18, s. 4758-4762Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The redox and acidity properties of 2,2'- and 4,4'-biphenol and the corresponding phenoxyl radicals have been determined using UV-vis spectrophotometry, pulse radiolysis, and cyclic voltammetry. The pK(a)'s for 4,4'-HO-Ph-Ph-OH, 4,4'-O--Ph-Ph-OH, 4,4'-O-circle-Ph-Ph-OH, 2,2'-HO-Ph-Ph-OH, 2,2'-O--Ph-Ph-OH, and 2,2'-O-circle-Ph-Ph-OH were determined to be ca. 9.7, ca. 9.7, 6.3, 7.6, 13.7, and 10, respectively. At the same time, the one-electron reduction potentials for 4,4'-O--Ph-Ph-O-circle and 2,2'-HO-Ph-Ph-O-circle were determined to be 0.44 and 1.00 V vs NHE, respectively. By using a thermochemical cycle, the experimentally inaccessible one-electron reduction potentials for 4,4'-HO-Ph-Ph-O-circle and 2,2'-O--Ph-Ph-O-circle were calculated to be 0.64 and 0.78 V vs NHE, respectively. From the redox and acidity data we also estimated the O-H bond dissociation enthalpies for 4,4'-HO-Ph-Ph-OH, 4,4'-O--Ph-Ph-OH, 2,2'-HO-Ph-Ph-OH, and 2,2'-O--Ph-Ph-OH to be 349, 330, 372, and 385 W mol(-1), respectively. The results are discussed in light of previously established substituent effects on the thermochemistry of phenols and phenoxyl radicals.

  • 22.
    Jonsson, Mats.
    et al.
    KTH, Tidigare Institutioner                               , Kemi.
    Lind, Johan
    KTH, Tidigare Institutioner                               , Kemi.
    Merenyi, Gabor
    KTH, Tidigare Institutioner                               , Kemi.
    Reply to comment on Redox and acidity properties of 2,2 '- and 4,4 '-biphenols and corresponding phenoxyl radicals2003Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 107, nr 30, s. 5878-5879Artikel i tidskrift (Refereegranskat)
  • 23.
    Lind, Johan
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Merenyi, Gabor
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Kinetic and thermodynamic properties of the aminoxyl (NH2O center dot) radical2006Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 110, nr 1, s. 192-197Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The product of one-electron oxidation of (or H-atom abstraction from) hydroxylamine is the H2NOcenter dot radical. H2NOcenter dot is a weak acid and deprotonates to form HNO-center dot; the pK(a)(H2NOcenter dot) value is 12.6 +/- 0.3. Irrespective of the protonation state, the second-order recombination of the aminoxyl radical yields N-2 as the sole nitrogen-containing product. The following rate constants were determined: k(r)(2H(2)NO(center dot)) = 1.4 x 10(8) M-1 s(-1), k(r)(H2NOcenter dot + HNO-center dot) = 2.5 x 10(9) M-1 s(-1), and k(r)(2HNO(-center dot)) = 4.5 x 10(8) M-1 s(-1). The HNO-center dot radical reacts with 02 in an electron-transfer reaction to yield nitroxyl (HNO) and superoxide (O-2(-center dot)), with a rate constant of k(e)(HNO-center dot + O-2 -> HNO + O-2(-center dot)) = 2.2 x 10(8) M-1 s(-1). Both O-2 and O-2(-center dot) seem to react with deprotonated hydroxylamine (H2NO-) to set up an autoxidative chain reaction. However, closer analysis indicates that these reactions might not occur directly but are probably mediated by transition-metal ions, even in the presence of chelators, such as ethylenediamine tetraacetic acid (EDTA) or diethylenetriamine pentaacetic acid (DTPA). The following standard aqueous reduction potentials were derived: E degrees(H2NO center dot,2H(+)/H3NOH+) = 1.25 +/- 0.01 V; E degrees(H2NOcenter dot,H+/H2NOH) = 0.90 +/- 0.01 V; and E degrees(H2NOcenter dot/H2NO-) = 0.09 +/- 0.01 V. In addition, we estimate the following: E degrees(H2NOH+center dot/H2NOH) = 1.3 +/- 0.1 V, E degrees(HNO, H+/H2NOcenter dot) = 0.52 +/- 0.05 V, and E degrees(HNO/HNO-center dot) = -0.22 +/- 0.05 V. From the data, we also estimate the gaseous O-H and N-H bond dissociation enthalpy (BDE) values in H2NOH, with BDE(H2NO-H) = 75-77 kcal/mol and BDE(H-NHOH) = 81-82 kcal/mol. These values are in good agreement with quantum chemical computations.

  • 24.
    Lind, Johan
    et al.
    KTH, Tidigare Institutioner                               , Kemi.
    Merenyi, Gabor
    KTH, Tidigare Institutioner                               , Kemi.
    Johannson, E.
    Brinck, Tore
    KTH, Tidigare Institutioner                               , Kemi.
    Reaction of peroxyl radicals with ozone in water2003Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 107, nr 5, s. 676-681Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The reactivity of alkylperoxyl radicals and -O3SOO* toward ozone was investigated. The peroxyl radicals were produced by steady-state gamma-radiolysis in the presence Of O-3. The rate constants were extracted from the decay rate of ozone measured during the irradiation. The rate constants vary between 7 x 10(3) and 2 x 10(5) M-1 s(-1) and there is a trend of increasing rate constant with electron-withdrawing substituent. Quantum chemical computations support a mechanism, according to which formation of an alkyl trioxide radical is the rate-determining step. This is followed by rapid expulsion Of O-2 to yield the alkoxyl radical. Conceivably, the alkyl trioxide radical is preceded by an extremely unstable alkyl pentoxide radical in equilibrium with the reactants.

  • 25.
    Merenyi, Gabor
    et al.
    KTH, Tidigare Institutioner                               , Kemi.
    Lind, Johan
    KTH, Tidigare Institutioner                               , Kemi.
    Czapski, G.
    Goldstein, S.
    Direct determination of the Gibbs' energy of formation of peroxynitrous acid2003Ingår i: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 42, nr 12, s. 3796-3800Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The kinetics of decomposition of peroxynitrous acid (ONOOH) was investigated in the presence of 0.1-0.75 M HClO4 and at a constant ionic strength. The decay rate of ONOOH decreased in the presence of H2O2, approaching a limiting value well below 75 mM H2O2. It also decreased in the presence of relatively low [HNO2] but did not approach a lower limiting value, since ONOOH reacts directly with HNO2. The latter reaction corresponds to a HNO2- and H+-catalyzed isomerization of ONOOH to nitrate, and its third-order rate constant was determined to be 520 +/- 30 M-2 s(-1). The mechanism of formation of O2NOOH from ONOOH in the presence of H2O2 was also scrutinized. The results demonstrated that in the presence of 0.1-0.75 M HClO4 and 75 mM H2O2 the formation Of O2NOOH is insignificant. The most important finding in this work is the reversibility of the reaction ONOOH + H2O reversible arrow HNO2 + H2O2, and its equilibrium constant was determined to be (7.5 +/- 0.4) x 10(-4) M. Using this value, the Gibbs' energy of formation of ONOOH was calculated to be 7.1 +/- 0.2 kcal/mol. This figure is in good agreement with the value determined previously from kinetic data using parameters for radicals formed during homolysis of peroxynitrite.

  • 26.
    Merenyi, Gabor
    et al.
    KTH, Tidigare Institutioner                               , Kemi.
    Lind, Johan
    KTH, Tidigare Institutioner                               , Kemi.
    Czapski, G.
    Goldstein, S.
    The decomposition of peroxynitrite does not yield nitroxyl anion and singlet oxygen2000Ingår i: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 97, nr 15, s. 8216-8218Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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 (HNO)-H-1 and O-1(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 O-1(2) and (HNO)-H-1 are about 23 orders of magnitude lower than those of (NO2)-N-. and (OH)-O-., 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 H2O2 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, [(ONOOH)-O-..](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.

  • 27.
    Merenyi, Gabor
    et al.
    KTH, Tidigare Institutioner                               , Kemi.
    Lind, Johan
    KTH, Tidigare Institutioner                               , Kemi.
    Goldstein, S.
    The rate of homolysis of adducts of peroxynitrite to the C=O double bond2002Ingår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 124, nr 1, s. 40-48Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nucleophilic additon of the peroxynitrite anion, ONOO-, to the two prototypical carbonyl compounds, acetalclehyde and acetone, was investigated in the pH interval 7.4-14. The process is initiated by fast equilibration between the reactants and the corresponding tetrahedral adduct anion, the equilibrium being strongly shifted to the reactant side. The adduct anion also undergoes fast protonation by water and added buffers. Consequently, the rate of the bimolecular reaction between ONOO- and the carbonyl is strongly dependent on the pH and on the concentration of the buffer. The pK(a) of the carbonyl-ONOO adduct was estimated to be similar to11.8 and similar to12.3 for acetone and acetaldehyde, respectively. It is shown that both the anionic and the neutral adducts suffer fast homolysis along the weak O-O bond to yield free alkoxyl and nitrogen dioxide radicals. The yield of free radicals was determined to be about 15% with both carbonyl compounds at low and high pH, while the remainder collapses to molecular products in the solvent cage, The rate constants for the homolysis of the adducts vary from ca. 3 x 10(5) to ca. 5 x 10(6) s(-1), suggesting that they cannot act as oxidants in biological systems. This small variation around a mean value of about 10(6) s(-1) suggests that the O-O bond in the adduct is rather insensitive to its protonation state and to the nature of its carbonyl precursor. An overall reaction scheme was proposed, and all the corresponding rate constants were evaluated. Finally, thermokinetic considerations were employed to argue that the formation of dioxirane as an intermediate in the reaction of ONOO- with acetone is an unlikely process.

  • 28.
    Merenyi, Gabor
    et al.
    KTH, Tidigare Institutioner                               , Kemi.
    Lind, Johan
    KTH, Tidigare Institutioner                               , Kemi.
    Goldstein, S.
    Thermochemical properties of alpha-hydroxy-alkoxyl radicals in aqueous solution2002Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 106, nr 46, s. 11127-11129Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experimental kinetic data related to the reaction of carbonyl compounds with peroxynitrite anion, ONOO-, in aqueous solutions was combined with estimated rate constants for the recombination of alkoxyl radicals with nitrogen dioxide. The equilibrium constants for O- transfer from ONOO- and OH transfer from ONOOH to the carbonyls were derived and the Gibbs' energies of formation of the neutral and anionic alpha-hydroxy alkoxyl radicals were calculated. By means of these data the O-H bond strengths in carbonyl hydrates as well as reduction potentials of the alkoxyl radicals were obtained.

  • 29.
    Merenyi, Gabor
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Lind, Johan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Naumov, Sergej
    von Sonntag, Clemens
    Reaction of Ozone with Hydrogen Peroxide (Peroxone Process): A Revision of Current Mechanistic Concepts Based on Thermokinetic and Quantum-Chemical Considerations2010Ingår i: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 44, nr 9, s. 3505-3507Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The reaction of ozone with the anion of H2O2 (peroxone process) gives rise to (OH)-O-center dot radicals (Staehelin, J.; Hoigne, J. Environ. Sci. Technol. 1982, 16, 676-681). Thermokinetic considerations now suggest that the electron transfer originally assumed as the first step has to be replaced by the formation of an adduct, HO2- + O-3 -> HO5- (Delta G degrees = -39.8 kJ mol(-1)). This decomposes into HO2 center dot and O-3(center dot-) (Delta G degrees = 13.2 kJ mol(-1)). HO2 center dot is in equilibrium with O-2(center dot-) + H+ and O-2(center dot-) undergoes electron transfer to O-3 giving rise to further O-3(center dot-). The decay of O-3 into (OH)-O-center dot is now discussed on the basis of the equilibria O-3(center dot-) reversible arrow O-2 + O center dot- and O center dot- + H2O reversible arrow (OH)-O-center dot + OH-, excluding HO3 center dot as the intermediate originally assumed. To account for the observation of the peroxone process being only 50% efficient, the decay of HO5- into 2 O-2 + OH- (Delta G degrees = -197 kJ mol(-1)) is proposed to compete with the decay into HO2 center dot; and O-3(center dot-).

  • 30.
    Merenyi, Gabor
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Lind, Johan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Naumov, Sergej
    von Sonntag, Clemens
    The Reaction of Ozone with the Hydroxide Ion: Mechanistic Considerations Based on Thermokinetic and Quantum Chemical Calculations and the Role of HO4- in Superoxide Dismutation2010Ingår i: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 16, nr 4, s. 1372-1377Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The reaction of OH- with O-3 eventually leads to the formation of center dot OH radicals. In the original mechanistic concept (J. Staehelin, J. Hoigne, Environ. Sci. Technol. 1982, 16, 676-681) it was suggested that the first step occurred by O transfer: OH- + O-3 -> HO2- + O-2 and that center dot OH was generated in the subsequent reaction(s) of HO2- with O-3 (the peroxone process). This mechanistic concept has now been revised on the basis of thermokinetic and quantum chemical calculations. A onestep O transfer such as that mentioned above would require the release of O-2 in its excited singlet state (O-1(2), O-2-((1)Delta(g))); this state lies 95.5 kJ mol(-1) above the triplet ground state ((3)Sigma(-)(g))). The low experimental rate constant of 70m(-1) s(-1) is not incompatible with such a reaction. However, according to our calculations, the reaction of OH- with O-3 to form an adduct (OH- + O-3 -> HO4-; Delta G = 3.5 kJ mol(-1)) is a much better candidate for the rate-determining step as compared with the significantiv more endergonic O transfer (Delta G=26.7 kJ mol(-1)). Hence, we favor this reaction; all the more so as numerous precedents of similar ozone adduct formation are known in the literature. Three potential decay routes of the adduct HO4- have been probed: HO4- -> HO2- + O-1(2) is spin allowed, but markedly endergonic (Delta G=23.2 kJ mol(-1)). HO4- -> HO2- + O-3(2) is spin forbidden (Delta G = -73.3 kJ mol(-1)). The decay into radicals, HO4- -> HO2 center dot + O-2(center dot-), is spin allowed and less endergonic (Delta G=14.8 kJ mol(-1)) than HO4- -> HO2- + O-1(2). It is thus HO4- -> HO2 center dot + O-2(center dot-) by which HO4- decays. It is noted that a large contribution of the reverse of this reaction, HO2 center dot + O-2(center dot-)-> HO4-, followed by HO4- -> HO2- + O-3(2), now explains why the measured rate of the bimolecular decay of HO2 center dot and O-2(center dot-) into HO2- + O-2 (k=1x10(8) m(-1) s(-1)) is below diffusion controlled. Because k for the process HO4- -> HO2 center dot + O-2(center dot-) is much larger than k for the reverse of OH- + O-3 -> HO4-, the forward reaction OH- + O-3 -> HO4- is practically irreversible.

  • 31. Sjodin, Martin
    et al.
    Irebo, Tania
    Utas, Josefin E.
    Lind, Johan
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Merenyi, Gabor
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Akermark, Bjorn
    Hammarstrom, Leif
    Kinetic effects of hydrogen bonds on proton-coupled electron transfer from phenols2006Ingår i: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, nr 40, s. 13076-13083Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The kinetics and mechanism of proton-coupled electron transfer (PCET) from a series of phenols to a laser flash generated [Ru(bpy)(3)](3+) oxidant in aqueous solution was investigated. The reaction followed a concerted electron-proton transfer mechanism (CEP), both for the substituted phenols with an intramolecular hydrogen bond to a carboxylate group and for those where the proton was directly transferred to water. Without internal hydrogen bonds the concerted mechanism gave a characteristic pH-dependent rate for the phenol form that followed a Marcus free energy dependence, first reported for an intramolecular PCET in Sjodin, M. et al. J. Am. Chem. Soc. 2000, 122, 3932-3962 and now demonstrated also for a bimolecular oxidation of unsubstituted phenol. With internal hydrogen bonds instead, the rate was no longer pH-dependent, because the proton was transferred to the carboxylate base. The results suggest that while a concerted reaction has a relatively high reorganization energy (lambda), this may be significantly reduced by the hydrogen bonds, allowing for a lower barrier reaction path. It is further suggested that this is a general mechanism by which proton-coupled electron transfer in radical enzymes and model complexes may be promoted by hydrogen bonding. This is different from, and possibly in addition to, the generally suggested effect of hydrogen bonds on PCET in enhancing the proton vibrational wave function overlap between the reactant and donor states. In addition we demonstrate how the mechanism for phenol oxidation changes from a stepwise electron transfer-proton transfer with a stronger oxidant to a CEP with a weaker oxidant, for the same series of phenols. The hydrogen bonded CEP reaction may thus allow for a low energy barrier path that can operate efficiently at low driving forces, which is ideal for PCET reactions in biological systems.

  • 32. Zhao, R.
    et al.
    Lind, Johan
    KTH, Tidigare Institutioner                               , Kemi.
    Merenyi, Gabor
    KTH, Tidigare Institutioner                               , Kemi.
    Jonsson, Mats
    KTH, Tidigare Institutioner                               , Kemi.
    Eriksen, T. E.
    Reduction potentials and kinetics of beta-fragmentation reactions of 4-substituted benzoylthiyl radicals2000Ingår i: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 104, nr 37, s. 8524-8526Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By means of pulse radiolysis, the one-electron reduction potentials of 4-substituted benzoylthiolates E degrees(4-XPhC(O)S-./4-XPhC(O)S-), where X is CH3, CH3O, CF3, and CN, were measured in aqueous solutions. The kinetics of beta-fragmentation reactions of the 4-XPhC(O)S-. radicals to form the corresponding 4-XPh. radicals and COS (i.e., 4-XPhC(O)S-. --> 4-XPh. + COS) were also determined. The pK(a)s of the corresponding acids (4-XPhC(O)SH) were measured by a spectrophotometric method. Thus, the values of E degrees(4-XPhC(O)S-., H+/ 4-XPhC(O)SH) and the S-H bond strength of the 4-XPhC(O)S-H were calculated. The substituent effects on the redox potential, the pK(a), and the kinetics of their beta-fragmentation reactions were examined.

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