44
Koji KANO and Hiroaki KITAGISHI (Doshisha University, Kyoto, Japan) Cyclodextrin Dimers as Simple Myoglobin Models in Aqueous Solution
Koji KANO and Hiroaki KITAGISHI
(Doshisha University, Kyoto, Japan)
Cyclodextrin Dimers as Simple Myoglobin Models in
Aqueous Solution
Cyclodextrin Dimers as Simple Myoglobin Models in
Aqueous Solution
Carrier of Diatomic Molecules
Fe(II)
Fe(II)-O2
O2 CO
Fe(II)-CO
h NOFe(II)-NO
Myoglobin (Mb) is an oxygen-storage hemoprotein.
Oxygen bound to Mb is stabilized by two His residues.
Heme center is surrounded by a hydrophobic wall of the protein.
His 64(distal His)
His 93(proximal His)
A picket-fence Por prepared by Prof. Collman’s groupA picket-fence Por prepared by Prof. Collman’s group
Collman, J. P.; Boulatov, R.; Sunderland, C. J.; Fu. L. Chem. Rev. 2004, 104, 561-588.
Jameson, G. B.; Rodley, G. A.; Robinson, W. T.; Gagne, R. R.; Reed, C. A.; Collman, J. P. Inorg. Chem. 1978, 17, 850-857.
N N
NN
NHO
HNO
FeHN
O
HNO
2MeIm
N N
NN
NHO
HNO
FeHN
O
HNO
2MeIm
Many artificial dioxygen receptors have been prepared.
These model compounds can bind dioxygen only in absolute organic solvents such as toluene.
Dioxygen adducts are easily autoxidized in the presence of a trace amount of water.
Many artificial dioxygen receptors have been prepared.
These model compounds can bind dioxygen only in absolute organic solvents such as toluene.
Dioxygen adducts are easily autoxidized in the presence of a trace amount of water.
N N
NN
X
X
X
X
Fe
X =O
O
O
O
O
O
CH3
CH3
CH3
CH34
Jiang, D.-L.; Aida, T. Chem. Commun. 1996, 1523-1524.
Zingg, A.; Felber, B.; Gramlich, V.; Fu, L.; Collman, J. P.; Diederich, F. Helv. Chim. Acta 2002, 85, 333-351.
Dendrimers as Mb models
Difficulty in preparation of five coordinate Fe(II)Por Difficulty in preparation of five coordinate Fe(II)Por
Why is modeling of the Mb or Hb functions so difficult?Why is modeling of the Mb or Hb functions so difficult?
N N
NNFe
N
N
H N N
NNFe
N N
NNFe
Im
Im
Im
N N
NNFe
N
N
H N N
NNFe
N N
NNFe
Im
Im
Im
Easy oxidative dimerization of O2-Fe(II)Por yielding a -oxo-dimer of Fe(III)Por
Easy oxidative dimerization of O2-Fe(II)Por yielding a -oxo-dimer of Fe(III)Por
Why is modeling of the Mb or Hb functions so difficult?Why is modeling of the Mb or Hb functions so difficult?
Fe(II)Fe(II)
OO
Fe(III)
O
O+
Fe(III)
Fe(IV)
O
Fe(IV)
O
Fe(II)+
Fe(III)
O
Fe(III)
Fe(II)Fe(II)
OO
Fe(III)
O
O+
Fe(III)
Fe(IV)
O
Fe(IV)
O
Fe(II)+
Fe(III)
O
Fe(III)
Direct oxidation of Fe(II)Por to Fe(III)Por with O2 Direct oxidation of Fe(II)Por to Fe(III)Por with O2
Why is modeling of the Mb or Hb functions so difficult?Why is modeling of the Mb or Hb functions so difficult?
N N
NNFeII N N
NNFeIII
O2N N
NNFeII N N
NNFeIII
O2
Water-promoted autoxidation of O2-Fe(II)Por Water-promoted autoxidation of O2-Fe(II)Por
Why is modeling of the Mb or Hb functions so difficult?Why is modeling of the Mb or Hb functions so difficult?
N N
NNFeII N N
NNFeIII
H2O
O2
+
H2O
O2
B B
N N
NNFeII N N
NNFeIII
H2O
O2
+
H2O
O2
B B
FeIII
OH2
FeII
O2
H2O+
+ O2•
The main reason why modeling in aqueous solution is so difficult.The main reason why modeling in aqueous solution is so difficult.
Chem. Lett. 1996, 925-926.
J. Am. Chem. Soc. 2002, 124, 9937-9944.
Chem. Lett. 1996, 925-926.
J. Am. Chem. Soc. 2002, 124, 9937-9944.
H3CO
OCH3
OO
OCH3
7N
HNNNH
SO3-
-O3S
-O3S SO3-
TPPS-O3S
-O3S SO3-
NHNN
NH
SO3-
TMe--CD
2
very stable 2 : 1 inclusion complex
+
pKa 4.8
pKa 0.4
Inorg. Chem. 2006, 45, 4448-4460.
J. Am. Chem. Soc. 2008, 130, 8006-8015.
SO3-
S S
N
NN
NN
SO3--O3S
-O3S
FeII
3 3
SO3-
O O
N
NN
NN
SO3--O3S
-O3S
FeII
2 2
hemoCD1
SS
N
O
O OHH3CO
OCH3
O
O
O
OCH3
H3CO
OCH3
OO
OCH3
OCH3
H3CO O
O
H3CO
OCH3
H3CO
O
O
H3COOCH3
OCH3
O
OH3CO
OCH3
OCH3O
OCH3
H3CO
O
OHO
OCH3
OCH3
O
O
O
H3CO
OCH3
OCH3
O O
H3CO
H3COOCH3O
O
OCH3
H3CO
OCH3
O
O
OCH3
H3CO
OCH3
O
O OCH3
H3CO
OCH3
O
OCH3
OCH3
33
OCH3
O
O OH3CO
OCH3
OO
O OCH3
OCH3
OCH3
OO
OCH3
OCH3
H3CO
O
O
H3CO
OCH3
H3CO
O
O
H3COOCH3
OCH3
OO
H3CO
H3CO OCH3O
OCH3
H3CO
O
OOOCH3
OCH3
O O
OH3CO
OCH3
OCH3
OO
OCH3
H3CO
OCH3
O
O
OCH3
H3CO
OCH3
O
O
OCH3H3CO
OCH3
OO
OCH3
OCH3H3CO
O
H3CO
OCH3N2
2CH3O
Py3CD
Py2CD Fe(II)PCD
OH[HO]7
[OH]13
O[HO]7 O [OH]7
N
[OH]13 [HO]13
2 2 2
-CD
O[MeO]7 O [OMe]7
N
[OMe]13 [MeO]13
2 2
NaOH,
N
CH2BrBrH2C
dry DMSO
NaH, CH3I
dry DMF
16 % 25 %
OH[HO]7
[OH]13
OTs[HO]7
[OH]13
O[HO]7
[OH]12
O[MeO]7
[OMe]12
S[MeO]7 S [OMe]7
N
[OMe]12 [MeO]12
N
HSH2C CH2SH
2 22
3
2
3
2
3 3
NaH, TsCl
0.2 M NaHCO3
NaH, CH3I
0.1 M NaHCO3
-CD
OH HO 2
33%67%
61% 20%
DMF
DMF/ THF
Synthetic route of Py2CD and Py3CD
Py2CD
Py3CD
Experimental procedures for examining O2 and CO binding of Fe(II)PCD in an aqueous solution at pH 7.0.
Experimental procedures for examining O2 and CO binding of Fe(II)PCD in an aqueous solution at pH 7.0.
SO3-
O ON
NN
NN
SO3--O3S
-O3S
FeIII
OCH3
O
O OH3CO
OCH3
OO
O OCH3
OCH3
OCH3
OO
OCH3
OCH3
H3COO
O
H3CO
OCH3
H3CO
O
O
H3COOCH3
OCH3
OO
H3CO
H3CO OCH3O
OCH3
H3CO
O
OOOCH3
OCH3
O O
OH3CO
OCH3
OCH3O
O
OCH3
H3CO
OCH3O
O
OCH3
H3CO
OCH3
O
O
OCH3H3CO
OCH3
OO
OCH3
OCH3H3CO O
H3CO
OCH3N2
2
CH3O
Py2CD
+ FeIIITPPS
SO3-
O ON
NN
NN
SO3--O3S
-O3S
FeII
CO-Fe(II)PCD
CO
Na2S2O4
SO3-
O ON
NN
NN
SO3--O3S
-O3S
FeII
Fe(II)PCD
Air
SO3-
O ON
NN
NN
SO3--O3S
-O3S
FeII
O2-Fe(II)PCD
O2
CO
Fe(III)PCD
300 400 500 600 7000
0.4
0.8
1.2
1.6
Wavelength / nm
CO adductmax = 422 nm
O2 adductmax = 422 nm
deoxymax = 435 nm
x 5
Ab
so
rban
ce
UV-vis spectra of Fe(II)PCD, O2-Fe(II)PCD and CO-Fe(II)PCD in
phosphate buffer at pH 7.0 and 3 oC.
O2 affinity at 25 oC and pH 7.0
P1/2: hemoCD 17 Torr
Fe(II)PCD 176 Torr
P1/2: Mb (sperm whale) 0.29 Torr
Hb (human R) 0.17
Hb (human T) 26
Model systems in organic solvents
0.1 ~ 2150
O2 affinity at 25 oC and pH 7.0
P1/2: hemoCD 17 Torr
Fe(II)PCD 176 Torr
P1/2: Mb (sperm whale) 0.29 Torr
Hb (human R) 0.17
Hb (human T) 26
Model systems in organic solvents
0.1 ~ 2150
CO affinity at 25 oC and pH 7.0
P1/2: hemoCD 1.5 x 10-5 Torr
Fe(II)PCD 0.016 Torr
P1/2: Mb (sperm whale) 0.02 Torr
Hb (human R) 0.013
CO affinity at 25 oC and pH 7.0
P1/2: hemoCD 1.5 x 10-5 Torr
Fe(II)PCD 0.016 Torr
P1/2: Mb (sperm whale) 0.02 Torr
Hb (human R) 0.013
(a) (b)eclipsed staggered
A conformation of Fe(II)PCD is similar to that of Mb or Hb.
A conformation of hemoCD is similar to that of leghemoglobin.
Cage Effects
The Fe center of FeTPPS is
completely capped with the
two CD cavities.
O2 as well as CO released
from the Fe(II) center cannot
slip out of the cleft of CD capsule because of its
hydrophobic nature.
Released O2 or CO rebinds
to the Fe(II) center.
Fe(II)PCD
Picket-fence porphyrin
Oxy-hemoCD
Reductive nitrosylation of Fe(III)PCD and oxidation of (NO)Fe(II)PCD
Reductive nitrosylation of Fe(III)PCD and oxidation of (NO)Fe(II)PCD
SO3-
O O
N
NN
NN
SO3--O3S
-O3S
FeIII
2 2
Fe(III)PCD
NO
SO3-
O O
N
NN
NN
SO3--O3S
-O3S
FeII
2 2
(NO)Fe(II)PCD
NO
O2
SO3-
O O
N
NN
NN
SO3--O3S
-O3S
FeIII
2 2
Fe(III)PCD
NO3-+
Nitric Oxide N ONO is biosynthesized from arginine and dioxygen by nitric oxide synthases (NOS).
NO causes relaxation of smooth muscle to control blood pressure.
NO stimulates the soluble guanylate cyclase leading to subsequent formation of cyclic GMP.
Macrophages generate NO to kill antigen.
etc.
Nitrosylation of Fe(II)PCD
NO
SO3-
O O
N
NN
NN
SO3--O3S
-O3S
FeIII
2 2
Fe(III)PCD
SO3-
O O
N
NN
NN
SO3--O3S
-O3S
FeII
2 2
Fe(II)PCD
e
NO
NO
SO3-
O O
N
NN
NN
SO3--O3S
-O3S
FeII
2 2
(NO)Fe(II)PCD
FeIIINO
FeIII
NOH2O
FeII
N
OHO
-H+ -NO2-, -H+
FeIINO
FeII
NO
max 420 nm
max 401 nm
Reductive nitrosylation of Fe(III)P(TMe--CD)2 complex
NN
NN
SO3--O3S
-O3S
FeIII
Fe(III)TPPS/TMe--CD
NO
SO3-
NN
NN
SO3--O3S
-O3S
FeII
(NO)Fe(II)P(TMe--CD)2
SO3-
NO
NN
NN
SO3--O3S
-O3S
FeIII
Fe(III)TPPS
NO
SO3-
No reductive nitrosylation occurs in the absence of cyclodextrin.
FeIII
NO
FeII
NO
max = 401 nm
max = 420 nm
No reductive nitrosylation
FeIII
Py
NOFeII
Py
NO
FeIII NOFeII
NO
FeII
OO
NOFeII
OO N O
FeIII + NO3-
FeII
NO
+ O2
FeIII
NOO-O
FeII
OO
+ NO
FeIII + NO3-
This mechanism has been well established.
Oxy-Mb regulates NO in biological system.
The mechanism has not been clarified.
NO inhibits the activities of proteins such as cyt P450, cyt c oxidase, nitrile hydrase, and catalase.
3000
0.2
0.4
0.6
0.8
1.0
400 500 600 700
420 nm
Wavelength / nm
404 nm
Ab
sorb
ance Time / h
0 10 20 30 40
0.6
0.8
1.0
kobs = (3.04 ± 0.05) x 10-5 s-1 ( t1/2 = 6.3 h)
Ab
sorb
ance
at
420
nm
(NO)Fe(II)PCD is gradually oxidized to
Fe(III)PCD and NO3- in an aerobic aqueous
solution at pH 7.0,
(NO)Fe(II)P(TMe--CD)2 is not oxidized at all.
300 400 500 600 700Wavelength / nm
0
0.2
0.4
0.6
Ab
so
rban
ce
(a)
0 200 400 600 800 1000 12000.2
0.3
0.4
0.5
0.6
Ab
sorb
ance
at
413
nm
Time / s
(b)
In the case without cyclodextrin
In the absence of CD, reductive nitrosylation cannot be applied.
(NO)Fe(II)TPPS can be prepared from nitrosylation of Fe(II)TPPS in a glove box.
(NO)Fe(II)TPPS is very unstable in an aerobic aqueous solution. Ring-opening reaction of FeTPPS may occur.
FeII
NOO2
FeII
NOO2
t1/2 = 6.3 h
t1/2 = ∞No oxidation occurs.
Decomposition of the porphyrin ring occurs.
FeII
NO
O2FeII
Py
NO
+FeIII
Py
NO3-
FeII
NO
Py
FeIII
NO3-
Py
O2
kmax
FeII
NO
Py
FeIII
NO
Py
COCO
koff
kmax : the maximum reaction rate constant for autoxidation of
(NO)Fe(II)PCD kmax = 5.1 x 10-5 s-1
koff : the reaction rate constant for the dissociation of NO from
(NO)Fe(II)PCD koff = 5.6 x 10-5 s-1
Mechanism for oxidation of (NO)Fe(II)PCD with dioxygen
Mechanism for oxidation of (NO)Fe(II)PCD with dioxygen
N
Fe(II)
OO
NO
O2
N
Fe(II)
OO
NO
O2
N
Fe(II)
OO
O2
N
Fe(III)
OO
NO3-
NO
Rate-determining stepRate-determining step
-14
-15
-16
-17
-183.2 3.3 3.4 3.5
103 / T (K-1)
ln (
k ob
s /
T)
Eyring plot for autoxidation of (NO)Fe(II)PCD.
H‡ = 98.9 kJ mol-1
S‡ = 0.17 J mol-1K-1
A large activation enthalpy change reflects the endothermic dissociation of the NO-Fe(II) bond.
Since activation entropy change is almost zero, no bimolecular reaction participates in the rate-determining step.
The thermodynamic parameters support the reaction mechanism proposed herein.
The thermodynamic parameters support the reaction mechanism proposed herein.
N
Mn(III)
OO
Na2S2O4
N
Mn(II)
OO
NO
N
Mn(II)
OO
NO
N
Mn(II)
OO
NO O2
N
Mn(III)
OO
+ NO3-
Oxidation of (NO)Mn(II)PCD by O2
300 400 500 600 7000
0.2
0.4
0.6
0.8
1.0
1.2428 nm
471 nm
Ab
sorb
ance
Wavelength / nm
0
0.4
0.8
1.2
20 40 60 80 100 1200
428 nm
Time / h
t1/2 ~ 35 h
471 nm
Ab
sorb
ance
s at
428
an
d 4
71 n
m
Autoxidation of (NO)Mn(II)PCD
(NO)Mn(II)
Mn(III)
Zero-order kinetics was
observed for the aut-
oxidation of (NO)Mn(II)PCD.
t1/2 ~ 35 h
N
Mn(II)
OO
NO O2
N
Mn(III)
OO
+ NO3-
Mn(II)
NO
Mn(II)
NOO2
Mn(III)
NOO2
Mn(III) + NO3-
relatively fast
If the equilibrium A B exclusively shifts to A and a ⇌very small amount of B existing in the system
relatively rapidly reacts to yield a final product, such a
reaction obeys zero-order kinetics.
If the equilibrium A B exclusively shifts to A and a ⇌very small amount of B existing in the system
relatively rapidly reacts to yield a final product, such a
reaction obeys zero-order kinetics.
very slow
300 400 500 600 700
Wavelength / nm
0
0.4
0.8
1.2
442 nm
471 nm
Ab
s. 0 10 20 30 400
0.4
0.8
1.2
Time / h
kobs = (3.31 ± 0.09) x 10-5 s-1 (t1/2 = 5.8 h)
Ab
s at
44
2 n
m
Mn(II) O2 Mn(III)+ + O2
The rate of autoxidation of
Mn(II)PCD is much faster
than that of
(NO)Mn(II)PCD.
300 400 500 600 7000
0.4
0.8
1.2
1.6
426 nm
465 nm
(a)
Wavelength / nm
Ab
sorb
an
ce
5 10 15 2000
0.4
0.8
1.2
1.6
Time / h
(b)
465 nm
426 nm
t1/2 ~ 6 h
Ab
so
rban
ce
Autoxidation of (NO)Mn(II)P(TMe--CD)2
(NO)Mn(II)
Mn(III)
Mn(II)
Mn(II)
NO
Mn(II)
NOO2
Mn(III)
NOO2
Mn(III) + NO3-
relatively fast
Mechanism for Oxidation of (NO)Mn(II)PCD with Dioxygen
Mechanism for Oxidation of (NO)Mn(II)PCD with Dioxygen
Mechanism for oxidation of (NO)Fe(II)PCD with dioxygenMechanism for oxidation of (NO)Fe(II)PCD with dioxygen
N
Fe(II)
OO
NO
O2
N
Fe(II)
OO
NO
O2
N
Fe(II)
OO
O2
N
Fe(III)
OO
NO3-
NO
HemoCD and Fe(II)PCD are good carriers of simple diatomic molecules such as O2, CO, and NO in aqueous solution.
HemoCD shows the extremely high CO affinity that might be used for medicinal purposes.
Fe(II)PCD is a good model for studying interactions of NO with hemoproteins.
The mechanism for oxidation of (NO)Fe(II)Por by O2 was clarified in the present study.
HemoCD and Fe(II)PCD are good carriers of simple diatomic molecules such as O2, CO, and NO in aqueous solution.
HemoCD shows the extremely high CO affinity that might be used for medicinal purposes.
Fe(II)PCD is a good model for studying interactions of NO with hemoproteins.
The mechanism for oxidation of (NO)Fe(II)Por by O2 was clarified in the present study.
SummarySummary
