COMMUNICATIONS
further stirred for 5 min and directly analyzed by GC. The competitive
hydroxylation of cyclohexane and [D12]cyclohexane was performed with a
mixture of cyclohexane (0.3 mmol) and [D12]cyclohexane (1 mmol).
[11] H. Fujii, Chem. Lett. 1994, 1491 ± 1494.
[12] Solvent and axial ligand effects on the formation of 1 and iron(iii)
porphyrin N-oxide have been observed in the reaction of an electron-
rich iron porphyrin complex, [Fe(tmp)X] (tmp meso-tetramesityl-
porphinato dianion), with m-CPBA in toluene:[5] E. Bill, X.-Q. Ding,
E. L. Bominaar, A. X. Trautwein, H. Winkler, D. Mandon, R. Weiss,
A. Gold, K. Jayaraj, W. E. Hatfield, M. L. Kirk, Eur. J. Biochem. 1990,
188, 665 ± 672.
[13] a) J. H. Dawson, Science 1988, 240, 433 ± 439; b) N. Suzuki, T. Higuchi,
Y. Urano, K. Kikuchi, H. Uekusa, Y. Ohashi, T. Uchida, T. Kitagawa,
T. Nagano, J. Am. Chem. Soc. 1999, 121, 11571 ± 11572, and references
therein; c) T. L. Poulos, J. Biol. Inorg. Chem. 1996, 1, 356 ± 359; d) K.
Yamaguchi, Y. Watanabe, I. Morishima, J. Am. Chem. Soc. 1993, 115,
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[14] a) H.-A. Wagenknecht, W.-D. Woggon, Angew. Chem. 1997, 109, 404 ±
407; Angew. Chem. Int. Ed. Engl. 1997, 36, 390 ± 392; b) Z. Gross, J.
Biol. Inorg. Chem. 1996, 1, 368 ± 371.
[15] a) M. Selke, J. S. Valentine, J. Am. Chem. Soc. 1998, 120, 2652 ± 2653;
b) M. Selke, M. F. Sisemore, J. S. Valentine, J. Am. Chem. Soc. 1996,
118, 2008 ± 2012.
Labeled water (H218O) experiment: H2O2 (0.04 mmol, diluted in CH3CN
(0.5 mL)) was slowly added over a period of 1 h to a stirred solution
containing [Fe(tpfpp)(NO3)] (1 Â 10À3 mmol), substrate (1 mmol), and
H218O (50 mL, 95% 18O enriched) in a solvent mixture (1 mL) of CH3CN
and CH2Cl2 (3:1). The reaction mixture was further stirred for 5 min and
directly analyzed by GC/MS. The 16O and 18O compositions in cyclohexanol
and cyclohexene oxide were determined by the relative abundances of mass
peaks at m/z 57and 59 for cyclohexanol and at m/z 83 and 85 for
cyclohexene oxide. Control reactions, performed by stirring cyclohexanol-
16O or cyclohexene oxide-16O in a solution containing [Fe(tpfpp)(NO3)]
and H218O, showed that the oxygen of the products did not exchange with
labeled water under the reaction conditions.
Electrochemical measurements: All electrochemical experiments were
performed under an N2 atmosphere in a glove box using a BAS 50W
voltammetric analyzer. The cyclic voltammetric measurements were
carried out in a solvent mixture of CH3CN/CH2Cl2 (1:1) containing iron
porphyrin (0.2mm) and tBu4NPF6 (40mm) as a supporting electrolyte in
one compartment. The working electrode was a glassy carbon disk and the
counter electrode was a platinum wire. The potential was measured by
[16] K. Czarnecki, S. Nimri, Z. Gross, L. M. Proniewicz, J. R. Kincaid, J.
Am. Chem. Soc. 1996, 118, 2929 ± 2935.
[17] We reported recently that electron-deficient iron(iii) porphyrin
using a Ag/Ag (0.01m) reference electrode and reported versus a Fc/Fc
À
complexes tend to cleave the O O bond of hydroperoxides hetero-
couple. The cyclic voltammograms were run at a scan rate of 50 mVsÀ1
.
À
lytically in protic solvent systems, whereas O O bond homolysis
predominates in the reactions of electron-rich iron(iii) porphyrins with
the oxidants: W. Nam, H. J. Han, S.-Y. Oh, Y. J. Lee, J.-H. Choi, S.-Y.
Han, C. Kim, S. K. Woo, W. Shin, J. Am. Chem. Soc., in press.
Received: April 26, 2000
Revised: June 19, 2000 [Z15048]
[1] a) J. L. McLain, J. Lee, J. T. Groves in Biomimetic Oxidations
Catalyzed by Transition Metal Complexes (Ed.: B. Meunier), Imperial
College Press, London, 2000, pp. 91 ± 169; b) P. R. Ortiz de Mon-
tellano, Cytochrome P450: Structure, Mechanism, and Biochemistry,
2nd ed., Plenum Press, New York, 1995; c) T. G. Traylor, P. S. Traylor
in Active Oxygen in Biochemistry (Eds.: J. S. Valentine, C. S. Foote, A.
Greenberg, J. F. Liebman), Chapman & Hall, London, 1995, pp. 84 ±
187; d) B. Meunier in Metalloporphyrins Catalyzed Oxidations (Eds.:
F. Montanari, L. Casella), Kluwer, Dordrecht, 1994, pp. 1 ± 47 .
[2] T. G. Traylor, C. Kim, J. L. Richards, F. Xu, C. L. Perrin, J. Am. Chem.
Soc. 1995, 117, 3468 ± 3474, and references therein.
Dynamics of Hole Trapping by G, GG, and
GGG in DNA**
William B. Davis,* Izabela Naydenova,
Reinhard Haselsberger, Alexander Ogrodnik,
Bernd Giese,* and Maria E. Michel-Beyerle*
[3] a) W. Nam, Y. M. Goh, Y. J. Lee, M. H. Lim, C. Kim, Inorg. Chem.
1999, 38, 3238 ± 3240; b) Y. J. Lee, Y. M. Goh, S.-Y. Han, C. Kim, W.
Nam., Chem. Lett. 1998, 837± 838.
[4] J. F. Bartoli, P. Battioni, W. R. De Foor, D. Mansuy, J. Chem. Soc.
Chem. Commun. 1994, 23 ± 24.
[5] J. T. Groves, Y. Watanabe, J. Am. Chem. Soc. 1988, 110, 8443 ± 8452.
[6] R. A. Sheldon, J. K. Kochi, Metal-Catalyzed Oxidations of Organic
Compounds, Academic Press, New York, 1981.
[7] Hydroxylation of alkanes by hydroxyl or alkoxyl radicals by free
radical pathways affords equal amounts of alcohol and ketone
products:[6] P. A. MacFaul, K. U. Ingold, D. D. M. Wayner, L. Que,
Jr., J. Am. Chem. Soc. 1997, 119, 10594 ± 10598.
Oxidative damage to DNA by ionizing radiation, carcino-
genic agents, and photosensitizers occurs predominately at
guanine (G) bases,[1, 2] a result which can be rationalized by
the hierarchy of in vitro oxidation potentials of the isolated
nucleobases (G < A ꢂ C,T).[3] Strand cleavage reactions,
induced, for instance, by piperidine treatment,[4] have shown
consistently that multiple guanine tracts in DNA are more
susceptible to oxidative damage than isolated guanine bases.
[*] Dr. W. B. Davis, Prof. Dr. M. E. Michel-Beyerle, Dr. I. Naydenova,
Dipl.-Phys. R. Haselsberger, Priv.-Doz. Dr. A. Ogrodnik
Institut für Physikalische und Theoretische Chemie
Technische Universität München
[8] a) J. Bernadou, B. Meunier, Chem. Commun. 1998, 2167± 2173;
b) K. A. Lee, W. Nam, J. Am. Chem. Soc. 1997, 119, 1916 ± 1922;
c) J. T. Groves, J. Lee, S. S. Marla, J. Am. Chem. Soc. 1997, 119, 6269 ±
6273.
Lichtenbergstrasse 4, 85748 Garching (Germany)
Fax : (49)89-289-13026
[9] Y. M. Goh, W. Nam, Inorg. Chem. 1999, 38, 914 ± 920.
[10] a) Reaction conditions: m-CPBA (1.5 Â 10À3 mmol and 3 Â 10À3 mmol
for [Fe(tpfpp)Cl] and [Fe(tpfpp)(CF3SO3)] reactions, repectively,
diluted in a solvent mixture (50 mL) of CH3CN and CH2Cl2 (1:1))
was introduced into a 0.1-cm UV cell containing [Fe(tpfpp)X] (5 Â
10À4 mmol and 1 Â 10À3 mmol for [Fe(tpfpp)Cl] and [Fe(tpfpp)-
(CF3SO3)], respectively) in a solvent mixture (0.5 mL) of CH3CN
and CH2Cl2 (1:1) at À608C. Spectral changes were directly monitored
by UV/Vis spectroscopy (Hewlett Packard 8453 spectrophotometer
equipped with Optostat variable-temperature liquid-nitrogen cryostat
(Oxford Instruments)). b) Further evidence that 2 was formed in the
reaction of [Fe(tpfpp)Cl] and m-CPBAwas the silent EPR spectra and
the appearance of a b-pyrrole hydrogen resonance signal at d 4.0 at
À508C.
Prof. Dr. B. Giese
Institut für Organische Chemie der Universität
St.-Johanns-Ring 19, 4056 Basel (Switzerland)
Fax : (41)61-2671105
[**] We thank Joshua Jortner, Notker Rösch, and Alexander Voityuk for
stimulating discussions and critical reading of the manuscript. W.B.D.
greatly appreciates a postdoc fellowship from the Alexander von
Humboldt Foundation. Financial support from the Volkswagenstif-
tung is gratefully acknowledged.
Angew. Chem. Int. Ed. 2000, 39, No. 20
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