reaction of Fe(II) → Fe(III). The high oxidation potentials for these
complexes reveal the extraordinary stabilization of the ferrous
complex, which support that the ligand ctb is good for stabilizing
ferrous complexes, and also implies that ferric complexes 2 and 3
are strong oxidants.
lipoxygenase activity, while ferric alkoxide complexes 2 and 3
can catalyze the peroxidation of linoleic acid and oxidation of
1,4-cyclohexadiene and 9,10-dihydroanthracene via the hydrogen
atom abstraction reaction mechanism.
UV-vis spectra of the three compounds were performed in
methanol solution (Fig. S3 in ESI†). Complex 1 exhibits no
obvious absorptions above 300 nm, while complexes 2 and 3
Acknowledgements
D. L. gratefully acknowledges the financial support from the Youth
Chen-Guang Project of Wuhan (No. 200850731361), Specialized
Research Fund for the Doctoral Program of Higher Education
(No. 200805111004) and the Scientific Research Foundation
for the Returned Overseas Chinese Scholars, State Education
Ministry of China.
all show a broad and intense absorption around 368 nm (e ~
M
1
-1
4
800 L mol- cm ), which can be attributed to the ligand-to-metal
charge-transfer (LMCT) transition from the alkyloxyl-to-Fe(III)
center by comparison the spectra of complexes 1 and 2/3. This is
consistent with the active LO which exhibits a yellow chromophore
(
l
max = 350 nm) arising from a hydroxo-to-iron(III) charge-transfer
16
transition.
Notes and references
Apreliminarystudy onthe activities ofthe complexes to catalyze
the peroxidation of linoleic acid was performed by the classic
1
(a) L. Que, Jr. and R. Y. N. Ho, Chem. Rev., 1996, 96, 2607; (b) M.
Costas, M. P. Mehn, M. P. Jensen and L. Que, Jr., Chem. Rev., 2004,
17-19
thiobabituric acid (TBA) test.
The UV-vis spectra for complex
1
04, 939.
2 M. Noordermeer, G. Veldink and J. Vliegenthatr, ChemBioChem, 2001,
, 494.
3
4
1
and LA treated with TBA did not show any change during the
2
test for 10 h, while those for complexes 2 and 3 changed with
time. The catalysis data demonstrate a pseudo-first-order rate for
complexes 2/3 in the presence of a large excess of LA. Fitting the
G. Spiteller, Chem. Phys. Lipids, 1998, 95, 105.
W. Minor, J. Steczko, J. Bolin, Z. Otwinowski and B. Axelrod,
Biochemistry, 1993, 32, 6320.
-
2
5
6
S. A. Gillmor, A. Villasenor, R. Fletterichk, E. Sigal and M. Browner,
Nat. Struct. Biol., 1997, 4, 1003.
E. Skrzypczak-Jankun, R. A. Bross, R. T. Carroll, W. R. Dunham and
M. O. Funk, Jr., J. Am. Chem. Soc., 2001, 123, 10814.
data gave the second-order rate constant k2corr = 4.2 ± 0.2 ¥ 10
and 1.0 ± 0.1 ¥ 10 L mol at 333 K for 2 and 3, respectively
Fig. S4 and Table S2 in ESI†). It is obvious that ferric complexes
and 3 show LO-like activity, while ferrous complex 1 does not.
-
2
-1 -1
s
(
2
7 J. Boyington, B. Gaffney and B. Amzel, Science, 1993, 260, 1482.
8
9
K. W. Rickert and J. P. Klinman, Biochemistry, 1999, 38, 12218.
D. R. Tomchick, P. Phan, M. Cymborowski, W. Minor and T. R.
Holman, Biochemistry, 2001, 40, 7509.
This indicates that the ferrous form complex 1 is inactive and
must be oxidized to the ferric state to exhibit the catalytic activity,
which is the same as that of the lipoxygenases. The catalysis
10 (a) S. Ogo, S. Wada, Y. Watanabe, M. Iwase, A. Wada, M. Harata, K.
Jitsukawa, H. Masuda and H. Einaga, Angew. Chem., Int. Ed., 1998,
13
mechanism can be proposed according to Stack’s results: the
3
7, 2102; (b) S. Ogo, R. Yamahara, M. Roach, T. Suenobu, M. Aki, T.
alkoxyl groups in 2/3 abstract a hydrogen atom from LA to give a
Ogura, T. Kitagawa, H. Masuda, S. Fukuzumi and Y. Watanabe, Inorg.
Chem., 2002, 41, 5513.
∑
LA radical, which binds dioxygen to form peroxyl–LA (LA–OO ).
Then, the hydroperoxides are oxidatively cleaved into alkanals and
alkenals, which react with TBA to generate stable yellow, orange
and pink chromophores with the maximal absorbance at 455,
11 C. E. MacBeth, R. Gupta, K. R. Mitchell-Koch, V. G. Young, Jr., G. H.
Lushington, W. H. Thompson, M. P. Hendrich and A. S. Borovik,
J. Am. Chem. Soc., 2004, 126, 2556.
1
2 J. Kim, Y. Zang, M. Costas, R. G. Harrison, E. C. Wilkinson and L.
19
4
95 and 532 nm. To confirm the hydrogen atom abstraction
Que, Jr., JBIC, J. Biol. Inorg. Chem., 2001, 6, 275.
13 (a) R. T. Jonas and T. D. P. Stack, J. Am. Chem. Soc., 1997, 119, 8566;
reactions for complexes 2 and 3, we measured the reduction of
complexes 2 and/or 3 in the presence of 1,4-cyclohexadiene (CHD)
and 9,10-dihydroanthracene (DHAn). The compounds exhibited
(
2
b) C. R. Goldsmith, R. T. Jonas and T. D. P. Stack, J. Am. Chem. Soc.,
002, 124, 83.
1
4 (a) B. J. O’Keefe, L. E. Breyfogle, M. A. Hillmyer and W. B. Tolman,
J. Am. Chem. Soc., 2002, 124, 4384; (b) G. Roelfes, M. Lubben, K.
Chen, R. Y. N. Ho, A. Meetsma, S. Genseberger, R. M. Hermant, R.
Hage, S. K. Mandal, V. G. Young, Jr., Y. Zang, H. Kooijman, A. L.
Spek, L. Que, Jr. and B. L. Feringa, Inorg. Chem., 1999, 38, 1929; (c) S.
Taktak, S. V. Kryatov and E. V. Rybak-Akimova, Inorg. Chem., 2004,
43, 7196.
III
2+
the same behavior as [Fe (PY5)(OMe)] (PY5 = 2,6-bis(bis(2-
13
pyridyl)methoxymethane)pyridine), showing the ability to ab-
stract hydrogen atoms from the substrates (see Fig. S5 and Table
S2 in ESI†). In addition, the deuterated analogue of DHAn (d
4
-
DHAn) was also examined for 2 in MeOH to assess the kinetic
1
1
5 R. C. Scarrow, M. G. Trimitsis, C. P. Buck, G. N. Grove, R. A. Cowling
and M. J. Nelson, Biochemistry, 1994, 33, 15023.
6 Y. Zhang, M. S. Gebhard and E. I. Solomon, J. Am. Chem. Soc., 1991,
113, 5162.
isotope effect. The ratio of the rate constants (kDHAn/k 4
confirmed the hydrogen atom abstraction reactions for the ferric
complexes.
d
-DHAn = 5.1)
In conclusion, we have reported two novel non-heme ferric
17 V. Nair and G. A. Turner, Lipids, 1984, 19, 804.
III
18 Y. Nishisa and K. Yamada, J. Chem. Soc., Dalton Trans., 1990, 3639.
ethoxide/methoxide complexes, [Fe (OEt)(Hctb)](ClO
4
)
3
·EtOH
O (3), as models
of active lipoxygenases. Ferrous complex 1 does not show any
1
9 (a) A. de las Heras, A. Schoch, M. Gibis and A. Fischer, Eur. Food Res.
Technol., 2003, 217, 180; (b) Q. Sun, C. Faustman, A. Senecal, A. L.
Wilkinson and H. Furr, Meat Sci., 2001, 57, 55.
III
(
2) and [Fe (OMe)(Hctb)](ClO
4
)
3
·3MeOH·4.5H
2
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Dalton Trans., 2010, 39, 4267–4269 | 4269