We report calculated ab initio energies and barriers to internal rotation
for ONOO-anion and ONOO-radical species at the 6-31G** level. The anion is 48 kJ/mol more stable than the radical in its lowest 2A" (trans) state. The difference between the more stable trans and less stable cis conformations of the ONOO-anion and ONOO-radical is small, amounting to 4.6 and 3.9 kJ/mol, respectively. However, the energy of the 90° skew form is 68 kJ/mol above the trans form in the ONOO-anion, but only 40 kJ/mol in ONOO radical. Several ways to produce the ONOO-anion for FTMS analysis and determination of its thermodynamic properties are presented

Dunja Srzić

Leo Klasinc

Ljiljana Paša-Tolić

Suzana Martinović

English

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CROATICA CHEMICA ACTA CCACAA69 (3) 1007-1011 (1996)ISSN-0011-1643CCA-2358 Original Scientific PaperGas Phase Properties of ONOO-anion andONOO-radicalLeo Klasine, Dunja Srzić, Ljiljana Paša-Tolić, and Suzana MartinovićRuđer Bošković Institute, Bijenička 54, HR-1000l Zagreb, CroatiaReceived March 30, 1996; revised May 6, 1996; accepted June 3, 1996We report calculated ab initio energies and barriers to internal ro-tation for ONOO-anion and ONOO-radical species at the 6-31G**level. The anion is 48 kJ/mol more stable than the radical in itslowest 2A" (trans) state. The difference between the more stabletrans and less stable cis conformations of the ONOO-anion andONOO-radical is small, amounting to 4.6 and 3.9 kJ/mol, respec-tively. However, the energy of the 90° skew form is 68 kJ/mol abovethe trans form in the ONOO-anion, but only 40 kJ/mol in ONOO-radical. Several ways to produce the ONOO-anion for FTMS analy-sis and determination of its thermodynamic properties are pre-sented.Peroxynitrite (ONOO-) is a toxic compound' formed in solution from thereaction of the radical species superoxide and nitric oxide. Both radicals areproduced by activated macrophages and neutrophils. The product is not sta-ble and isomerizes to nitrate. The anion or the protonated form (ONOOH,pKa = 6.8) oxidizes biomolecules through presently poorly understood path-ways. Much effort is recently put in investigating how peroxynitrite or itsprotonated form carry out these deleterious reactions. Only a few thermo-dynamic parameters have been measured: the enthalpy of formation ofONOO-,2the pKa of ONOOH and enthalpy of ionization.š For a better un-derstanding of the reactivity of peroxynitrite and peroxynitrous acid morethermochemical data are essential.The oxoperoxonitrate radical (ONOO') is considered a transient speciesformed in the trimolecular reaction of nitric oxide and oxygen in the gasphase and which could be important for biological systems.1008 L. KLASINC ET AL.Nitric acid and halogennitrates (particularly CION02), which are formedin the stratosphere by radical recombination reactions, play an importantrole in the stratospheric ozone layer chemistry, acting as temporary reser-voirs for radicals. Recently, formatian of ONOOH by radical recombinationupon nitric acid photolysis in solid argon was observed and its spectrum re-ported.v" Such photolysis is not currently considered in the atmosphericmodels, nor any reaction involving ONOOH. McGrath and Rowland? inves-tigated theoretically the confarrnational potential energy surfaces ofONOOH and ONOOCI and found that conformers of ONOOH may well beformed by reactions of OH with N02 in the atmosphere while formatian ofONOOCI from CIO with N02 is thermodynamically unfavourable.Preliminary ab initio calculations at the 6-31G** level yielded the struc-tural parameters described in Ref. 8. At this level, peroxynitrous acid in thecis- configuration is more stable than that in the trans - form by 3.9 kJ/mol,which is nearly identical to the result obtained by McGrath et al.9 of 3.8 kJ/mol,at the RMP2/6-31G* level. A calculation by the same authors at the RMP2/6-311++G** level resulted in a difference of 5.4 kJ/mol.Our ab initio calculations, also at the 6-31G** level for the 90° skewforms of the anion and radical species indicate that this form is 68 kJ/molabove the trans form in ONOO-anion but only 38.9 kJ/mol in ONOO- radical(Table 1). Thus, it is understandable if one observes that this latter energycorresponds to the difference in total energies between the trans - form andthe sum of O2 (-149.532997H) and NO (-129.247883H) energy.The HF/6-31G**level calculations were performed using the GAUSSIANsystem of programs 10 at the Computing Centre of the University of Dussel-dorf, Germany.Gas phase reactions of negative ions with neutral molecules are of greatinterest for several reasons. They enable determination of gas phase acidi-ties, electron affinities and thermochemical data. Gas phase studies of re-actions important in solution yield informatian on solvation effects and in-trinsic reactivity. In particular, reactions of superoxide anions have receivedattention through the ir importance in ionospheric and stratospheric ionchemistry, chemical ionization mass spectrometry and the chemistry of plas-mas. Studying the reactivity of superoxide towards halocarbons, McDonald.and Chowdhury!' found superoxide to be an excellent intrinsic gas phase nu-cleophile. Streit12 used a flowing afterglow apparatus to study the reactionsof 0·- and O2.- with a number of compounds, but the technique did not allowthe ionic products to be assigned particularly to 0- and O2-, Morris+ useda variable temperature selected ion flow tube instrument to determine therate constants and product branching fractions of 0·- and O2'- with halocar-bons. He produced superoxide from a mixture of N20 and O2 in the source,as follows: the 0- produced from electron attachment to N20 reacts with an-other N20 to form NO-, which transfers its electron to O2, Thus, the reactionTABLEIDistancesandbondanglesforONOO-andONOO'ONOO-ONOO'skewClStransClStransA'A"A'A"1.1881.1981.1771.1501.1401.4441.1481.2701.2641.3211.3541.4221.3831.4021.4281.4461.5151.3721.2961.3671.297118.5113.2114.0115.1113.8109.5108.9118.2111.3102.8113.1107.3107.2108.6O=NN-O0-0O=N-ON-O-OE(H)rel.E(kJ/mol)o ;l> en '"0 ~ ~ "''"0 '"0 '"0 "' '">-3 [;J en 0 '" 0 z 0 0 ~skew::: zA"~ 01.1370 z 0 0 :'<I1.467E; (=i1.294~109.7107.34.668.1(5.8)o-278.81051-278.81224-278.78629-278.77126-278.79241-278.769062-278.79386-278.7790938.9(0)o3.8•..... o o co1010 L. KLAS INC ET AL.of NO- with O2 seems to involve only charge transfer without formation ofan (02·NO-) adduct. However, already in 1970 Adams and coworkers-? no-ticed that, among the superoxide clusters with dinitrogen, dioxygen, water,carbon dioxide and nitrogen monoxide, the (02·NO) cluster is the most stableand, when formed in Reaction 1:(1)yields a product which is different from that formed by Reaction 2:(2)because the former reacts with nitrogen monoxide, whereas the latter doesnot. Although the authors explained this by claiming that the reactive N03-is in an electronically excited state, it seems that this N03 - is actually gase-ous peroxynitrite. Therefore, we propose to form peroxynitrite from reactivecollisions of presorted 02·- with ·NO gas in the mass spectrometer. It is pos-sible to remove all but the desired ionic species using special procedures ina Fourier transform mass spectrometer.(with FTMS detection) (3)(with FTMS detection) (4)The first proposed synthesis (Reaction 3) is exothermic and may not besuccessful. In the second synthesis (Reactions 4) there a is inert reactionpartner that can carry away the excess energy. In general, a problem existsif asingle compound is formed by collision of two reactants in the gas phase,because there is no additional product, wall or solvent over which the excessenergy of the reaction could be distributed.If O2.02- is the reaction partner (Reaction 4), it can be formed by flowingan 021He mixture past an electron gun. Dioxygen will capture an electronand, at higher pressure, 02·0i- is the dominant ion. This species can be in-troduced by differential pumping into the Fourier transform mass spec-trometer and, reacting with NO introduced through pulsed valves, yieldONO 0- which can be analysed and measured.Acknowledgement. - This work was financed by the Ministry of Science of Croa-tia and subrnitted for support to the Fogarty International Research CollaborationAward. Helpful and stimulating discussions with Professors J. S. Beckmann (Uni-versity of Alabama, Birmingham), J. V.Knop (University of Dusseldorf), W.H. Kop-penol (ETH, Zurich), M. M. Kreevoy (University of Minnesota, Minneapolis) and W.A. Pryor (LSU, Baton Rouge) are gratefuly acknowledged.GAS PHASE PROPERTIES OF ONOO·ANWN AND ONOO·RADICAL 1011REFERENCES1. (a) J. o. Edwards and R C. Plumb, Prag. Inorg. Chem. 41 (1994) 599; (b) J. S.Beckman, M. Carson, C. D. Smith, and W li. Koppenol, Nature 364 (1993) 484;(c)W A Pryor and G. 1. Squadrito, Am.J. Physiol. (Lung), 268 (1995) L699.2. J. D. Ray, J. Inorg. NucZ. Chem. 24 (1962) 1159.3. W. li. Koppenol, J. J. Moreno, W.A Pryor, li. Ischiropoulos, and J. S. Beckman,Chem. Res. Toxicol. 5 (1992) 834.4. B.-M. Cheng, J.-W Lee, and T. P Lee, J. Phys. Chem. 95 (1991) 2814.5. W-J. Lo and Y P Lee, J. Chem. Phys. 101 (1994) 5494.6. D. S. Bohle, B. Hansert, S. C. Paulson, and B.D. Smith, J. Am. Chem. Soc. 116(1994) 7423.7. M. P McGrath and F. S. Rowland, J. Phys. Chem. 98 (1994) 1061.8. W li. Koppenol and L. Klasinc, Int.J.Quantum Chem. QBS20 (1993) 1.9. M. P McGrath, M. M. Francl, F. S. Rowland, and W J. Hehre, J. Phys. Chem. 92(1988) 5352.10. Gaussian 90 and 92. Pittsburgh, PA: Gaussian, Inc.; 1992.11. R N. McDonald and A K Chowdhury, J. Am. Chem. Soc. 107 (1985) 4123.12. G. E. Streit, J. Phys. Chem. 86 (1982) 2321.13. R AMorris, J. Chem. Phys. 97 (1992) 2372.14. N. G. Adams, D. K Bohme, D. B. Dunkin, F. C. Fehsenfeld, and F. E. Ferguson,J. Chem. Phys. 52 (1970) 3133.SAŽETAKSvojstva ONOO-amona i ONOO-radikala u plinskoj faziLeo Klasinc, Dunja Srzić, Ljiljana Paša-Tolić i Suzana MartinovićOdređene su energije i barijere interne rotacije ONOO-aniona i ONOO-radikala natemelju ab initio 6-31G**računa. Anion je 48 kJ/mol stabilniji no radikal u svom naj-nižem 2A"(trans) stanju. Razlika izmedu stabilnije trans i manje stabilne cis konforma-cije ONOO-aniona i ONOO-radikala je mala i iznosi 4,6 kJ/mol odnosno 3,9 kJ/moL Me-dutim energija konformacije zakrenute za 90° je 68 kJ/mol iznad energije transkonformacije ONOO-aniona, ali samo 40 kJ/mol iznad energije ONOO-radikala. Pri-kazano je nekoliko načina dobivanja ONOO-aniona za FTMS analizu i određivanjanjegovih termodinamičkih svojstava.

Gas Phase Properties of ONOO-anion and ONOO-radical

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