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Iron(III) Complex of a Crown Ether-Porphyrin Conjugate and
Reversible Binding of Superoxide to Its Iron(II) Form
Katharina Dürr, Brendan P. Macpherson, Ralf Warratz, Frank Hampel, Felix Tuczek, Matthias Helmreich, Norbert Jux,*, and Ivana Ivanović-Burmazović,*
J. Am. Chem. Soc. 2007, 129, 4217 - 4228
Speaker :鍾柏源
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Superoxide dismutase (SOD)
The SOD-catalysed dismutation of Superoxide may be written with the following half-reactions :
where M = Cu (n=1) ; Mn (n=2) ; Fe (n=2) ; Ni (n=2)
Journal of Inorganic Biochemistry, 2002, 91, 349–355
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Electron-withdrawing group
J. Am. Chem. Soc. 1996, 118, 2008-2012
The effect of electron-withdrawing groups on the stability
No reaction
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An interaction between the potassium ion and the coordinated peroxo ligand
Infrared spectra of the oxygen-oxygen stretching region for
(A) [K][Fe(OEP)O2] (B) [Me4N][Fe(OEP)O2]
=> (A) is more stable than (B).
J. Am. Chem. SOC. 1988, 110, 1382-1388
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Switching on the Nucleophilic Reactivity of a Ferric Porphyrin Peroxo Complex
J. Am. Chem. SOC. 1987, 109, 1425-1434
J. Am. Chem. Soc. 1998, 120, 2652-2653
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Synthesis of Crown Ether-Porphyrin
Reflux 24hr
H2Porph / CHCl3 FeCl2 / EtOH+Reflux 24hr
Fe¢» (Porph)Cl
N2,6-lutidine
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Synthesis
H2Porph
[FeⅢ(Porph)Cl] : FeCl2
[(FeⅢ(Porph))2O] : 2 M NaOH
K[FeⅢ(Porph)(CN)2] : KCN
[FeⅢ(Porph)(DMSO)2]+ : DMSO[FeⅢ(Porph)OH] : water or NaOH[FeⅡ(Porph)] : by chemical reduction
K[FeⅢ(Porph)(O22-)] : KO2
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To study the influence of the potassium ion
Inorg. Chem. 2002, 41, 2761-2768
KCN β-pyrrolic protons : -3 and -5 ppm
Bu4N+CN-
β-pyrrolic protons : -8 to -10 ppm
Authors interpret this to mean that the bulky Bu4N+ cation cannot be coordinated by the crown ether.
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UV/vis absorption spectra
[FeⅢ(Porph)(DMSO)2]+ [FeⅢ(Porph)OH] [(FeⅢ(Porph))2O]
[FeⅡ(Porph)(DMSO)2] K[FeⅢ(Porph)(O22-)]
420 nm 429 nm
414 nm
430 nm 440 nm
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UV/vis spectra for the reaction of [FeⅢPorph(DMSO)2]+ and KO2
Na+Na+
S
O
O-
S
O
-O
sodium dithionite
KO2 ordithionite
Before(λmax= 420 nm)
After(λmax= 430 nm)
Reduction bydithionite
[FeⅢPorph(DMSO)2]+ = 5 x 10-6 M KO2 = 5 x 10-5 M
At 25 in DMSO℃
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Time-resolved spectra for the reaction of K[F
eⅢ(Porph)(DMSO)(O22-)] and 5 x 10-5 M HOTf
HOTf S OO
OH
F
F
F
trifluoromethanesulfonic acid
K[FeⅢ(Porph)(O22-)] = 1 x 10-5 M
[HOTf] = 5 x 10-5 M
After(λmax= 430 nm)
Before(λmax= 440 nm)
At 25 in DMSO℃
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UV/vis spectra for the reaction of K[FeⅢPorph(DMSO)(O2
2-)] and 0.1 M HOTf
K[FeⅢ(Porph)(O22-)] + 0.1 M HOTf
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Spectral changes upon mixing mCPBA with TBPH and [FeⅢ(Porph)Cl]
J. Am. Chem. SOC. 1984, 106, 755-764
m-chloroperbenzoic acid (mCPBA)
2,4,6-tri-(tert-butyl)phenol (TBPH)
TBPH forms an oxygen-centered radical, which results inan increase of absorbance at 380, 400, and 630 nm.
mCPBA = 10-3 M TBPH = 10-1 M[FeⅢ(Porph)Cl] = 1.3 x 10-5 M
BeforeAfter mixing
At r.t in KCl-saturated DMSO/CH3CN
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Cyclic voltammograms of [FeⅢ(Porph)Cl] and [ZnⅡ(Porph)]
b) Redox couples for [ZnⅡ(Porph)] under nitrogen
a) Redox couples for [FeⅢ(Porph)]+ under nitrogen-1.54V
-1.06V0.225V
-1.47V-0.983V0.313V
-1.23V
-1.63V
-1.56V-1.16V
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Mössbauer spectra of reduced 57Fe-enriched [FeⅢ(Porph)Cl] and K[FeⅢ(Porph)(O2
2-)]
[FeⅢ(Porph)Cl] [FeⅢ(Porph)Cl] + KO2Mössbauer Parameters of the Studied Complexes inFrozen DMSO at 80 K
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Time-resolved spectra for the reaction between [FeⅡ(Porph)] and KO2
[FeⅡ(Porph)] = 5 x 10-6 M [KO2] = 5 x 10-4 M
At 25 in DMSO℃
KO2
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Plots of kobs versus [O2-] for the second step of the reaction of 5 x 10-6 M complex and KO2
■:starting from the Fe(II) complex and using different mixing volume ratios○:starting from the Fe(II) complex and preparing a new solution for each [O2]△:starting from the Fe(III) complex and preparing a new solution for each [O2-]
=>From the slope of the plot the second-order rate constant kon was determined to be 36500 500 M-1 s-1
kobs / [O2-] = kon
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Time-resolved spectra for the reaction of K[FeⅢ(Porph)(O2
2-)] and 5 x 10-5 M HOTf
K[FeⅢ(Porph)(O22-)] = 1 x 10-5 M
[HOTf] = 5 x 10-5 M
After(λmax= 430 nm)
Before(λmax= 440 nm)
At 25 in DMSO℃
First-orderkobs = koff
koff = 0.21 0.001 s-1
KO2- = kon / koff
= (1.7 0.2) x 105 M-1
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Changes in absorbance upon addition of O2- to a solution of [FeⅡ(Porph)(DMSO)2]
[FeⅡ(Porph)(DMSO)2] = 5 x 10-6 M
With electrolyteKO2
- = (0.9 0.1) x 105 M-1
Without electrolyteKO2
- = (1.4 0.1) x 104 M-1
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Time-resolved spectra for the reaction between [FeⅢ(Porph)Cl] and KO2
[FeⅢ(Porph)Cl] = 5X10-6 M [KO2] = 2.5X10-5 M
Mixture of DMSO/CH3CN
25℃
- 40℃
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Eyring plot for the second reaction step
[[FeⅢ(Porph)Cl]] = 5 x 10-6 M [KO2] = 1 mM
In the DMSO/CH3CN mixture (30% DMSO)
Eyring Equation
kB = Boltzmann's constant [1.381·10-23 J · K-1] T = absolute temperature in degrees Kelvin (K) h = Plank constant [6.626·10-34 J · s]
ΔH‡ = 61.2 ± 0.9 kJ mol-1 ΔS‡ = +48 ± 3 J K-1 mol-1
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Kinetic and Thermodynamic Parameters
Kinetic and Thermodynamic Parameters for Binding of Superoxide to FeⅡ(Porph) at 25 °C (Second Reaction Step)
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Dissociative mechanism
=> kobs = kon[O2-] + koff
kon = k1k2/k-1
koff = k-2
Second-order
First-order
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Conclusions
Authors have synthesized and characterized the new Fe(III)-porphyrin complex [FeⅢ(Porph)Cl], which carries a covalently bound aza-crown ether in close proximity to the iron center.
The second reaction step, binding of superoxide to the Fe(II) species and formation of the Fe(III)-peroxo complex, could be studied in detail. To our knowledge, this is the first time that superoxide concentration and temperature-dependent kinetic studies of reactions with superoxide.
Moreover, authors have observed for the first time that the superoxide anion can bind reversibly to a metal center.
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