Lifetime, reduction potential and base-induced fragmentation of the veratryl alcohol radical cation in aqueous solution. Pulse radiolysis studies on a ligninase "Mediator"

Journal of Physical Chemistry A

Volumn 102, Issue 38, 1998, Pages 7337-7342

  Bietti, Massimo ^a   Baciocchi, Enrico ^b   Steenken, Steen ^c  

^a UNIVERSITY OF ROME TOR VERGATA   (Italy)

^b SAPIENZA UNIVERSITY OF ROME   (Italy)

^c MAX PLANCK INSTITUTE FOR CHEMICAL ENERGY CONVERSION   (Germany)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 11744380034     PISSN: 10895639     EISSN: None     Source Type: Journal    
DOI: 10.1021/jp9812482     Document Type: Article

References (65)

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25. -1.
26. Baciocchi, E.; Bietti, M.; Steenken, S. J. Am. Chem. Soc. 1997, 119, 4078.
27. Ioele, M.; Steenken, S.; Baciocchi, E. J. Phys. Chem. A 1997, 101, 2979.
28. •+ and 3-(2-methoxyphenoxyl)-1,2-propanediol, for which the potential was reported to be 1.40 V/NHE (a) Jonsson, M.; Lind, J.; Merenyi, G.; Eriksen, T. E. J. Chem. Soc., Perkin Trans. 2, 1995, 67.
29. For details on this technique, see the following. Wardman, P. J. Phys. Chem. Ref. Data 1989, 18, 1637. Steenken, S.; Neta, P. J. Phys. Chem. 1982, 86, 3661. Reference 23a. Typically, the K from the absorbances is more reliable than that from the rates.
30. For details on this technique, see the following. Wardman, P. J. Phys. Chem. Ref. Data 1989, 18, 1637. Steenken, S.; Neta, P. J. Phys. Chem. 1982, 86, 3661. Reference 23a. Typically, the K from the absorbances is more reliable than that from the rates.
31. •+ (see text).
32. Kersten, P. J.; Kalyanaraman, B.; Hammel, K. E.; Reinhammar, B.; Kirk, T. K. Biochem. J. 1990. 268, 475.
33. A similar value was found for manganese peroxidase (see: Popp, J. L.; Kirk, T. K. Arch. Biochem. Biophys. 1991, 288, 145).
34. •+, the spectrum of the 3,4-dimethoxy-α-hydroxybenzyl radical cannot be seen at pH ≤ 7. However, by speeding up the deprotonation reaction with base (see Scheme 2, steps a-c, and e), the spectrum (which turns out to be the same as that from eq 9; see Figure 2) can be easily measured.
35. Baciocchi, E.; Bietti, M.; Steenken, S. Unpublished results.
36. Steenken, S. In Free Radicals: Chemistry, Pathology and Medicine; Rice-Evans, C., Dormandy, T., Eds.; Richelieu Press: London, 1988, p 51.
37. O'Neill, P.; Steenken, S.; Schulte-Frohlinde, D. J. Phys. Chem. 1975, 79, 2773.
38. •- from the side chain is not important.
39. •- from the side chain is not important.
40. Reaction of a radical with the radical cation could proceed via dimerization to yield a (delocalized) cyclohexadienyl-type carbocation or via (electron transfer) disproportionation giving, again, a carbocation.
41. 2.
42. •+.
43. Value obtained by the conductance technique in the dose range 0.5-2 Gy/pulse.
44. On the basis of the redox potentials (see: Wayner, D. D. M.; Sim, B. A.; Dannenberg, J. J. J. Org. Chem. 1991, 56, 4835. Wayner, D. D. M.; McPhee, D. J.; Griller, D. J. Am. Chem. Soc. 1988.) of the pertinent fragments, the conceivable inverse C-C fragmentation, that is, that leading to the tert-butyl cation, is thermodynamically much less favorable. Also, with the 4-methoxy analogue (see: Baciocchi, E.; Bietti, M.; Putignani, L.; Steenken, S. J. Am. Chem. Soc. 1996, 118, 5952), the tert-butyl radical was actually detected by product analysis.
45. On the basis of the redox potentials (see: Wayner, D. D. M.; Sim, B. A.; Dannenberg, J. J. J. Org. Chem. 1991, 56, 4835. Wayner, D. D. M.; McPhee, D. J.; Griller, D. J. Am. Chem. Soc. 1988.) of the pertinent fragments, the conceivable inverse C-C fragmentation, that is, that leading to the tert-butyl cation, is thermodynamically much less favorable. Also, with the 4-methoxy analogue (see: Baciocchi, E.; Bietti, M.; Putignani, L.; Steenken, S. J. Am. Chem. Soc. 1996, 118, 5952), the tert-butyl radical was actually detected by product analysis.
46. On the basis of the redox potentials (see: Wayner, D. D. M.; Sim, B. A.; Dannenberg, J. J. J. Org. Chem. 1991, 56, 4835. Wayner, D. D. M.; McPhee, D. J.; Griller, D. J. Am. Chem. Soc. 1988.) of the pertinent fragments, the conceivable inverse C-C fragmentation, that is, that leading to the tert-butyl cation, is thermodynamically much less favorable. Also, with the 4-methoxy analogue (see: Baciocchi, E.; Bietti, M.; Putignani, L.; Steenken, S. J. Am. Chem. Soc. 1996, 118, 5952), the tert-butyl radical was actually detected by product analysis.
47. 5- (see: Baciocchi, E.; Bietti, M.; Steenken, S. J. Chem. Soc., Perkin Trans. 2 1996, 1261 and references therein) was used for the oxidation of this substrate at 25 °C. In this case, the only observed product was veratrylaldehyde; no ketone was detected.
48. •- which continues the chain.
49. 19 in which it is stated that the lifetime of the radical cation is independent of pH.
50. -1.
51. - addition at the ring.
52. The mechanistic implications of these findings are presently under investigation: Baciocchi, E.; Bietti, M.; Steenken, S. To be published.
53. Eigen, M. Angew. Chem. 1963, 75, 489; Angew. Chem., Int. Ed. Engl. 1964, 3, 1.
54. Eigen, M. Angew. Chem. 1963, 75, 489; Angew. Chem., Int. Ed. Engl. 1964, 3, 1.
55. -1).
56. -1).
57. -1 (this value relates to both VA and VAtBu).
58. Gilbert, B. C.; Laue, H. A. H.; Norman, R. O. C.; Sealy, R. C. J. Chem. Soc., Perkin Trans. 2 1976, 1040. Dobbs, A. J.; Gilbert, B. C.; Laue, H. A. H.; Norman, R. O. C. J. Chem. Sac., Perkin Trans. 2 1976, 1044. Gilbert, B. C.; Holmes, R. G. G.; Laue, H. A. H.; Norman, R. O. C. J. Chem. Soc., Perkin Trans. 2 1976, 1047. Gilbert, B. C.; Warren, C. J. Res. Chem. Interned. 1989, 11, 1. The 1,2-H shift also takes place in alcoholic solvents. See: Elford, P. E.; Roberts, B. P. J. Chem. Soc., Perkin Trans. 2 1996, 2247.
59. Gilbert, B. C.; Laue, H. A. H.; Norman, R. O. C.; Sealy, R. C. J. Chem. Soc., Perkin Trans. 2 1976, 1040. Dobbs, A. J.; Gilbert, B. C.; Laue, H. A. H.; Norman, R. O. C. J. Chem. Sac., Perkin Trans. 2 1976, 1044. Gilbert, B. C.; Holmes, R. G. G.; Laue, H. A. H.; Norman, R. O. C. J. Chem. Soc., Perkin Trans. 2 1976, 1047. Gilbert, B. C.; Warren, C. J. Res. Chem. Interned. 1989, 11, 1. The 1,2-H shift also takes place in alcoholic solvents. See: Elford, P. E.; Roberts, B. P. J. Chem. Soc., Perkin Trans. 2 1996, 2247.
60. Gilbert, B. C.; Laue, H. A. H.; Norman, R. O. C.; Sealy, R. C. J. Chem. Soc., Perkin Trans. 2 1976, 1040. Dobbs, A. J.; Gilbert, B. C.; Laue, H. A. H.; Norman, R. O. C. J. Chem. Sac., Perkin Trans. 2 1976, 1044. Gilbert, B. C.; Holmes, R. G. G.; Laue, H. A. H.; Norman, R. O. C. J. Chem. Soc., Perkin Trans. 2 1976, 1047. Gilbert, B. C.; Warren, C. J. Res. Chem. Interned. 1989, 11, 1. The 1,2-H shift also takes place in alcoholic solvents. See: Elford, P. E.; Roberts, B. P. J. Chem. Soc., Perkin Trans. 2 1996, 2247.
61. Gilbert, B. C.; Laue, H. A. H.; Norman, R. O. C.; Sealy, R. C. J. Chem. Soc., Perkin Trans. 2 1976, 1040. Dobbs, A. J.; Gilbert, B. C.; Laue, H. A. H.; Norman, R. O. C. J. Chem. Sac., Perkin Trans. 2 1976, 1044. Gilbert, B. C.; Holmes, R. G. G.; Laue, H. A. H.; Norman, R. O. C. J. Chem. Soc., Perkin Trans. 2 1976, 1047. Gilbert, B. C.; Warren, C. J. Res. Chem. Interned. 1989, 11, 1. The 1,2-H shift also takes place in alcoholic solvents. See: Elford, P. E.; Roberts, B. P. J. Chem. Soc., Perkin Trans. 2 1996, 2247.
62. Gilbert, B. C.; Laue, H. A. H.; Norman, R. O. C.; Sealy, R. C. J. Chem. Soc., Perkin Trans. 2 1976, 1040. Dobbs, A. J.; Gilbert, B. C.; Laue, H. A. H.; Norman, R. O. C. J. Chem. Sac., Perkin Trans. 2 1976, 1044. Gilbert, B. C.; Holmes, R. G. G.; Laue, H. A. H.; Norman, R. O. C. J. Chem. Soc., Perkin Trans. 2 1976, 1047. Gilbert, B. C.; Warren, C. J. Res. Chem. Interned. 1989, 11, 1. The 1,2-H shift also takes place in alcoholic solvents. See: Elford, P. E.; Roberts, B. P. J. Chem. Soc., Perkin Trans. 2 1996, 2247.
63. - with the radical cation.
64. 2 (see ref 4).
65. We have recently obtained evidence that this mechanism is not restricted to the alcohol function at the α-position.