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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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Hemoglobin

維基百科， http://en.wikipedia.org/wiki/Hemoglobin

O2 O2

Hemoglobin

Hemoglobin

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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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Structures and formal oxidation states of iron-dioxygen complexes

Chem. Rev. 1994, 94, 659-698

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Fe(III)-peroxo-porphyrin complexes

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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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X-ray crystal structure of [FeⅢ(Porph)Cl]

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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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Conclusion 1

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Time-resolved spectra of the reaction of [FeⅢ(Porph)(DMSO)2]+ and KOH

KOH

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Spectral changes during the reaction of [FeⅢ

(Porph)(DMSO)OH] and KO2

KO2

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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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Conclusion 2

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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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Kinetics and Thermodynamics

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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.