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The Redox Thermodynamics for Dioxygen Species (O2, O2-·, HOO·, HOOH, and HOO-) and Monooxygen Species (O, O, ·OH, and -OH) in Water and Aprotic Solvents

  • Donald T. Sawyer
Part of the Basic Life Sciences book series (BLSC, volume 49)

Abstract

Biological systems activate dioxygen (O2) by reduction via electron transfer and H-atom transfer to give intermediates that may be further activated by transition metals in proteins and metabolic co-factors. The reaction thermodynamics for these processes are influenced by the solution matrix and its acidity. Thus, the redox thermodynamics of O2 are directly dependent upon proton activity, O2 + 4H+ + 4e- → 2 H2O E°’ (1) which in turn depends upon the reaction matrix. Table 1 summarizes the pKa’ values for a series of Br0nsted acids in several aprotic solvents and water.1 In acetonitrile the activity values for pKa’ range from -8.8 for (H3O)ClO4 to 30.4 for H2O. This means that the formal potential (E°’) for reaction 1 in acetonitrile (MeCN) is +1.75 V vs. NHE in the presence of 1M(H3O)ClO4 and -0.56 V in the presence of IM (Bu4N)OH.

Keywords

Methyl Viologen Aprotic Solvent Anhydrous Acetonitrile Aprotic Medium Allylic Hydrogen 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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References

  1. 1.
    W.C. Barrette, Jr., H.W. Johnson, Jr., and D.T. Sawyer, Voltam- metric evaluation of the effective acidities (pKa’) for Brønsted acids in aprotic solvents, Anal. Chem. 56:1890 (1984).PubMedCrossRefGoogle Scholar
  2. 2.
    D.T. Sawyer, G. Chiericato, Jr., C.T. Angelis, E.J. Nanni, Jr., and T. Tsuchiya, Effects of media and electrode materials on the electrochemical reduction of dioxygen, Anal. Chem. 54:1720(1982).CrossRefGoogle Scholar
  3. 3.
    R. Parsons, “Handbook of Electrochemical Constants,” Butterworths Scientific Publications, London (1959).Google Scholar
  4. 4.
    H.A. Schwarz and R.W. Dodson, Equilibrium between hydroxyl radicals and thallium(II) and the oxidation potential of OH-(aq), J. Phys. Chem. 88:3643 (1984).CrossRefGoogle Scholar
  5. 5.
    J. Wilshire and D.T. Sawyer, Redox chemistry of dioxygen species, Acc. Chem. Res. 12:105 (1979).CrossRefGoogle Scholar
  6. 6.
    P. Cofré and D.T. Sawyer, Electrochemical reduction of dioxygen to perhydroxyl (HO2·) in aprotic solvents that contain Brønsted acids, Anal. Chem. 58:1057 (1986).PubMedCrossRefGoogle Scholar
  7. 7.
    P. Cofré and D.T. Sawyer, Redox chemistry of hydrogen peroxide in anhydrous acetonitrile, Inorg. Chem. 25:2089 (1986).CrossRefGoogle Scholar
  8. 8.
    D.T. Sawyer, J.L. Roberts, Jr., T. Tsuchiya, and G.S. Srivatsa, Generation of activated oxygen species by electron-transfer reduction of dioxygen in the presence of protons, chlorinated hydrocarbons, methyl viologen, and transition metal ions, in: “Oxygen Radicals in Chemistry and Biology,” W. Bors, M. Saran and D. Tait, eds., Walter de Gruyter and Co., Berlin, (1984).Google Scholar
  9. 9.
    J.L. Roberts, Jr., M.M. Morrison, and D.T. Sawyer, Base-induced generation of superoxide ion and hydroxyl radical from hydrogen peroxide, J. Am. Chem. Soc. 100:329 (1978).CrossRefGoogle Scholar
  10. 10.
    J.L. Roberts, Jr. and D.T. Sawyer, Activation of superoxide ion by reactions with protons. Electrophiles, secondary amines, radicals, and reduced metal ions, Israel J. Chem. 23:430 (1983)Google Scholar
  11. 11.
    D.-H. Chin, G. Chiericato, Jr., E.J. Nanni, Jr., and D.T. Sawyer, Proton-induced disproportionation of superoxide ion in aprotic media, J. Am. Chem. Soc. 104:1296 (1982).CrossRefGoogle Scholar
  12. 12.
    M.J. Gibian, D.T. Sawyer, T. Ungerman, R. Tangpoonpholvivat, and M.M. Morrison, “Reactivity of superoxide ion with carbonyl compounds in aprotic solvents,” J. Am. Chem. Soc. 101:640 (1979).CrossRefGoogle Scholar
  13. 13.
    I. Fridovich, “The Biology of Superoxide and of Superoxide Dismutases—In Brief,” in: “Oxygen and Oxy Radicals,” M.A.J. Rodgers and E.L. Powers, eds., Academic Press, New York, (1981).Google Scholar
  14. 14.
    J.A. Fee, “Is Superoxide Toxic and are Superoxide Dismutases Essential for Aerobic Life?,” in: “Oxygen and Oxy Radicals,” M.A.J. Rodgers and E.L. Powers, eds., Academic Press, New York, (1981).Google Scholar
  15. 15.
    P.K.S. Tsang, P. Cofré, and D.T. Sawyer, Electrochemical oxidation of hydroxide ion in acetonitrile and its facilitation by transition-metal complexes, Inorg. Chem. 26:3604 (1987).CrossRefGoogle Scholar
  16. 16.
    J.L. Roberts, Jr. and D.T. Sawyer, Facile degradation by superoxide ion of carbon tetrachloride, chloroform, methylene chloride, and p,p’-DDT in aprotic media, J. Am. Chem. Soc. 103:712 (1981).CrossRefGoogle Scholar
  17. 17.
    J.L. Roberts, Jr., T.S. Calderwood, and D.T. Sawyer, Oxygenation by superoxide ion of CCl4, FCCl3, HCCl3, p,p’-DDT, and related trichloromethyl substrates (RCCl3) in aprotic solvents, J. Am. Chem. Soc. 105:7691 (1983).CrossRefGoogle Scholar

Copyright information

© Plenum Press, New York 1988

Authors and Affiliations

  • Donald T. Sawyer
    • 1
  1. 1.Department of ChemistryTexas A&M UniversityCollege StationTexasUSA

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