Role of the central manganese(III) ion in the hydrogen peroxide oxidation mechanism of (2,3,7,8,12,13,17,18-Octaalkyl5(5,10)(5,15)-phenyl(diphenyl) porphinato)chloromanganese(III)

Article abstract of DOI:10.1134/S0036023611120424

Complete kinetic description and spectral manifestation of the hydrogen peroxide oxidation of (2,3,7,8,12,13,17,18-octamethyland (2,3,7,8,12,13,17,18- octaethyl-5-phenylporphinato)chloromanganese(III), (2,3,7,8,12,13,17,18- octaethyl-5,10-diphenyland (2,3

Full text of DOI:10.1134/S0036023611120424

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2011, Vol. 56, No. 12, pp. 2001–2008. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © E.N. Ovchenkova, T.N. Lomova, M.E. Klyueva, 2011, published in Zhurnal Neorganicheskoi Khimii, 2011, Vol. 56, No. 12, pp. 2090–2097.
PHYSICAL CHEMISTRY
OF SOLUTIONS
Role of the Central Manganese(III) Ion in the Hydrogen Peroxide
Oxidation Mechanism of (2,3,7,8,12,13,17,18ꢀOctaalkylꢀ
5(5,10)(5,15)ꢀphenyl(diphenyl)porphinato)chloromanganese(III)
E. N. Ovchenkovaa, T. N. Lomovaa, and M. E. Klyuevab
a Institute of Solution Chemistry, Russian Academy of Sciences, Akademicheskaya 1, Ivanovo, 153045 Russia
b Ivanovo State University of Chemical Technology, Ivanovo, Russia
Received March 30, 2010
Abstract—Complete kinetic description and spectral manifestation of the hydrogen peroxide oxidation of
(2,3,7,8,12,13,17,18ꢀoctamethylꢀ and (2,3,7,8,12,13,17,18ꢀoctaethylꢀ5ꢀphenylporphinato)chloromangaꢀ
nese(III), (2,3,7,8,12,13,17,18ꢀoctaethylꢀ5,10ꢀdiphenylꢀ and (2,3,7,8,12,13,17,18ꢀoctaethylꢀ5,15ꢀdipheꢀ
nylporphinato)chloromanganese(III) complexes in water–organic solutions are presented. Two H2O2 conꢀ
centration ranges with different reaction mechanisms and products were distinguished. The ion–molecular
oxidation mechanism was substantiated and the key role of coordination of various hydrogen peroxide speꢀ
cies, their activation, oxidation and reduction was demonstrated. Multiple substitution in the coordinated
macrocycle was found to change the electronic state of the coordination site and quantitative characteristics
of the oxidation; this can be used to develop the synthetic models of natural oxide reductases.
DOI: 10.1134/S0036023611120424
It is known [1] that the action of hemeꢀcontaining rin ring, are implemented on the central metal atom as
catalases that decompose hydrogen peroxide in living
cells is retarded by the presence of low concentrations
of azide and cyanide ions. However, since 1960, it has
been known that nonꢀheme catalases are indifferent to
the presence of these ions [2, 3]. The purified mangaꢀ
neseꢀcontaining catalases, which were first isolated in
1983 from Lactobacillus plantarum [4], are currently
partially characterized [5–8]. They form a new class of
biological items and are of considerable interest for
bioinorganic chemistry for the modeling of an imporꢀ
tant biological reaction. Some complexes with large
molecules approach natural enzymes as regards the
catalytic activity and selectivity and can serve as their
models operating at ambient temperatures and presꢀ
sures. A special place among these compounds is
occupied by metal porphyrins (MPs). The catalytic
properties of MPs, although determined by the highly
the reaction site of the catalyzed reaction.
During the last two decades, a number of original
works dealing with catalytic decomposition of hydroꢀ
gen peroxide have been published [9–12]; in these
works, the kinetic laws of the process and the compoꢀ
sition and the stability of the catalytically active comꢀ
plex were determined and the mechanism was subꢀ
stantiated. However, the causes and the mechanism of
partial degradation of the proper MP catalyst have not
been studied. This issue is of prime importance for
increasing the efficiency of the catalytic process.
Therefore, this communication presents quantitative
kinetic data on the state of some manganese(III) comꢀ
plexes with porphyrins of related structures (I–IV) in
dimethylformamide (DMF) in the presence of aqueꢀ
ous hydrogen peroxide over a broad range of H2O2
polarizable electronꢀexcessive structure of the porphyꢀ concentrations.
R1
Cl
R1
R1
R2
R1
N
R1
R4
R1
N
Mn
R1 = C2H5, R2 = C6H5, R = R4 = H (Cl)MnMPOEP (I)
3
N
R1 = C2H5, R2 = R3 = C6H5, R4 = H (Cl)Mn5.10DPOEP (II
R1 = C2H5, R2 = R4 = C6H5, R3 = H (Cl)Mn5.15DPOEP (III
)
N
)
R1
R3
R1 = CH3, R2 = C6H5, R3 = R = H (Cl)MnMPOMP (IV
)
4
R1
2001

2002
OVCHENKOVA et al.
Table 1. UV/Vis spectra of manganese(III) porphyrin complexes in chloroform
Complex
λ
max, nm (logε)
362 (4.51), 428 (3.75), 476 (4.37), 565 (3.70), 594 (shoulder
370 (4.41), 430 (shoulder), 481 (4.36), 571 (3.55), 606 (shoulder
I
II
)
)
III
IV
365 (4.80), 428 (4.10), 478 (4.72), 569 (4.02), 614 (shoulder
356 (5.30), 420 (4.21), 476 (4.54), 566 (4.01), 596 (shoulder
)
)
EXPERIMENTAL
≠
ΔS
'
= 19.1 logkTeff
+
+
E
'
/
T
– 19.1 log – 205, (1)
T
Metal porphyrins I–IV were prepared by the reacꢀ
tion of the corresponding porphyrin with pure for
analysis grade manganese(II) chloride, MnCl2 4H2O
= 19.1 logkT
E/
T
– 19.1 logT – 205. (2)
≠
ΔS
⋅
,
The equilibrium constant for the reaction of comꢀ
plex III with hydrogen peroxide was calculated from
Eq. (3) and optimized by the leastꢀsquares method.
using the Adler method [13]. To this end, 0.03 to 0.05 g of
porphyrin was dissolved in 15 to 20 mL of DMF, and
then a fivefold molar excess of the salt was added with conꢀ
stant stirring. The reaction mixture was brought to boiling
and refluxed. The time of synthesis was 20 to 30 min. The
complexes were isolated by adding chloroform and
water to the cooled reaction mixture until the chloroꢀ
form layer separated. The chloroform solution of the
complex was washed with water to remove excess salt
and DMF, partly concentrated, and chromatographed
twice on a column filled by Al2O3 (Brockmann activity
II) using CHCl3 as the eluent. The purity of the comꢀ
plexes was confirmed by the invariability of the
UV/Vis spectra during the subsequent purification
stages (Table 1). Porphyrins were synthesized, puriꢀ
fied, and identified by Semeikin [14].
A − A
A − A
∞ 0
(
)
)
(
eq
0
K =
1 − A − A
A − A
∞ 0
(
)
)
(
eq
0
(3)
1
×
,
1 2
c0 − c0X MnP ⋅ A − A
A − A
)
0
(
)
)
(
(
H2O2
eq
0
∞
(
)
where A0, A , and Aeq are the absorbances of solutions
of the starting MP, its axial complex with H2O2, and
their equilibrium mixture at the operating wavelength.
∞
RESULTS AND DISCUSSION
The reactions of complexes I–IV with Н2О2 are
The kinetics of reactions of complexes I–IV with
H2O2 in Н2O–DMF was studied by spectrophotomeꢀ
try using the excess concentrations technique in the
accompanied by changes in the UV/Vis spectra of the
starting complexes (Fig. 1): the intensities of the
absorption bands at 370–380 and 460–471 nm
decrease, and those of the bands at 672–679 and 730–
731 nm increase. The presence of isosbestic points at
570–615 nm in the series of curves attests to interconꢀ
version of two colored compounds. According to pubꢀ
lished data [15–17], the spectra of the final products
temperature range of 288–318 K. The current conꢀ
centration of the complexes was monitored by meaꢀ
suring the absorbance of solutions during the reaction
at an operating wavelength of 460–471 nm. The
UV/Vis spectra of porphyrin solutions were recorded on
Agilent 8453 and SFꢀ26 spectrophometers. Reagent
grade DMF was distilled in vacuum prior to use. The iniꢀ
tial concentration of H2O2 in water [(15.4 0.1) mol/L]
was determined by iodometric titration. The 3ꢀmL
working solutions were prepared by adding 2 mL of an
aqueous hydrogen peroxide (15.4 mol/L) in DMF of
the appropriate concentration to 1 mL of a solution of
formed from complexes
I–IV (Fig. 1) correspond to
the ꢀradical cation form of manganese(III) porphyꢀ
π
rin. The pattern of spectral changes shown in Fig. 1 is
typical of the whole range of Н2О2 concentrations
studied, which unites the complexes in question with
(Cl)MnOEP (OEP is the 2,3,7,8,12,13,17,18ꢀoctaꢀ
ethylporphin dianion) [18]. Unlike the mentioned
complexes, (Cl)MnTPP (TPP is the 5,10,15,20ꢀtetꢀ
raphenylporphin dianion) reacts with hydrogen perꢀ
oxide to give different final products [19], i.e., comꢀ
plexes oxidized at either the macrocycle or the central
the complex in DMF (
The effective rate constants (
tionꢀindependent rate constants (
the reaction ( ) were optimized by the leastꢀsquares
processing of the ln(с0 )– and logkeff
2
×
10–5 mol/L).
eff), the concentraꢀ
), and the orders of
k
k
n
manganese atom, at different .
cH O
2 2
/с
τ
–
lg c
τ
H2O2
dependences, respectively. The effective and true actiꢀ
vation energies of the reaction ( ' and ) were deterꢀ order with respect to the MP concentration (Fig. 2,
Table 2), while the order with respect to changes
The reactions of all of the complexes have the first
E
E
c
H2O2
mined from the slopes of the log eff –1/T and logk –
k
on going from one concentration range to another. For
each complex, three ranges were distinguished in
which the logarithms of keff were linearly correlated
1/ lines, respectively, and the activation entropy
T
≠
≠
(
Δ
S
' and
Δ
S ) was determined from the principal
equation of the transition state theory transformed to
forms (1) and (2).
with
and the reaction order was 1/2, 0, and –1/2
,
cH O
2
2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 12 2011

ROLE OF THE CENTRAL MANGANESE(III) ION
2003
A
1.0
A
371
471
(а)
(b)
379
462
1.0
547
560
685
730
679
400 500 600 700
374
400 500 600 700
A
1.0
A
(c)
(d)
371
465
1.0
461
553
549
673
672
731
400 500 600 700
, nm
400 500 600 700
, nm
λ
λ
5.10
Fig. 1. UV/Vis absorption spectra of manganese(III) porphyrin complexes: (a) (Cl)MnMPOEP, (b) (Cl)Mn DPOEP, (c)
5.15
(Cl)Mn DPOEP, (d) (Cl)MnMPOMP in water–DMF media during the reaction with Н О at 298 K.
= 0.03 mol/L (I–
c
2
2
H2O2
III);
= 0.19 mol/L (IV).
c
H2O2
(Figs. 3, 4; Table 3, the second range of peroxide conꢀ
centrations is shown in italic).
ln(c0/c )
τ
These results make it possible to write down the
experimentally derived full kinetic equations for the
first, second, and third reacting series, respectively.
1
2
1.0
0.8
0.6
0.4
0.2
The equations coincide for complexes
I–IV generally
designated by (Cl)MnIIIP
:
3
4
1 2
−dc Cl MnIII dτ = k1c Cl MnIII
c
Н2О2
P
,
(4)
(5)
P
(
)
(
)
−dc Cl MnIII dτ = k2c Cl MnIII
,
5
P
P
(
)
(
)
−1 2
c
Н2О2
−dc Cl MnIII dτ = k3c Cl MnIII
.
(6)
P
P
(
)
(
)
6
7
The numerical values of the rate constants k1 and k3
and the activation parameters of the reactions are
summarized in Table 3.
8
0
500
1000
1500
τ
, s
Experimentally derived Eq. (4) for the first H2O2
concentration range coincides with the theoretical
equation derived below for the transformation that
includes reactions (7)–(9). The reaction scheme takes
into account the spectral data (Fig. 1) according to
which the manganese(III) porphyrin complexes
Fig. 2. ln(
с
/
с
)–
τ
versus
τ
for the reaction of mangaꢀ
0
τ
(Cl)MnIIIP and the singleꢀelectronꢀoxidized species
5.15
nese(III) porphyrin complexes (
,
(Cl)Mn DPOEP with H O .
1, 2) (Cl)Mn DPOEP,
+i
O=MnIII(
)
are the initial and final species, respecꢀ
(
3
4
) (Cl)MnMPOMP, (5, 8) (Cl)MnMPOEP, (6, 7)
P
5.15
–5
= 2
×
10 mol/L,
) 0.43, (
) 0.19, ( ) 0.028
) 308, ( ) 298. R =
1,
cMP
tively.
2
2
2
(
III);
3
3
T
,
4
(
IV);
) 1.85, (
, K: (
5
,
8
(I
);
) 0.08, (
) 318, (
6,
7
(II).
=
(1
2)
c
H2O2
K1
←⎯⎯⎯
−
O2,
+
⎯⎯⎯→
H2O2
Н + Н
(7)
0.27, (
mol/L.
0.99.
4
,
5,
7
) 0.88, (
6
8
2
1
3
2
,
4
,
5,
7
6,
8
K2
−
−
(Cl)MnIIIP + Н
(Cl)(Н )MnIIIP, (8)
⎯⎯⎯→
O2 ←⎯⎯⎯
O2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 12 2011

2004
OVCHENKOVA et al.
Table 2. Effective rate constants for the reaction of manganese(III) porphyrin complexes with H2O2 in DMF–H2O
keff
×
104, s–1
303 K
≠
E
',
Δ
S
',
Complex
mol/L
,
cH O
2
2
kJ/mol
J/(mol K)
298 K
308 K
0.03
0.08
0.20
0.34
0.51
0.62
0.88
1.31
1.75
2.19
2.63
3.07
0.63 0.01
1.42 0.02
1.99 0.04
2.65 0.04
3.02 0.12
3.05 0.04
3.09 0.12
2.91 0.13
2.60 0.14
2.22 0.14
1.97 0.15
1.81 0.06
1.62 0.03
3.23 0.06
5.25 0.15
6.13 0.21
7.66 0.51
7.58 0.28
7.71 0.11
6.98 0.24
6.39 0.07
5.60 0.11
5.07 0.21
4.58 0.21
3.63 0.07
6.89 0.27
10.67 0.29
14.01 0.33
14.95 0.21
14.81 0.24
14.85 0.19
14.44 0.34
12.81 0.54
11.78 0.41
10.48 0.33
9.45 0.29
69
62
66
66
63
62
62
63
63
66
66
65
2
1
4
1
4
4
4
2
3
3
4
3
–101
–118
–101 13
–99
–108 13
–111 13
–111 13
7
3
3
I
–108
7
–109 10
–100 10
–102 13
–106 10
0.013
0.027
0.08
0.134
0.187
0.267
0.321
0.427
0.67
1.33 0.04
2.12 0.04
3.26 0.04
3.36 0.02
3.29 0.02
3.34 0.02
2.61 0.04
2.24 0.05
2.11 0.08
1.38 0.02
1.03 0.02
3.11 0.09
4.77 0.14
6.98 0.29
7.03 0.32
7.05 0.21
7.02 0.24
6.13 0.22
5.21 0.16
4.68 0.05
3.68 0.07
2.60 0.04
9.40 0.71
59
4
–124 13
II
1.156
2.312
0.013
0.027
0.08
5.49 0.09
9.13 0.32
16.57 0.14
19.87 0.28
20.54 0.19
20.63 0.19
20.33 0.16
18.22 0.46
15.53 0.26
9.51 0.19
7.47 0.15
6.68 0.08
5.78 0.06
11.03 0.14
19.53 0.64
33.73 1.46
39.54 1.82
39.25 2.24
39.36 3.22
39.99 3.59
34.72 2.30
29.91 1.52
18.61 0.52
14.64 0.37
12.72 0.43
11.56 0.37
24.11 1.72
41.59 2.94
67.65 6.07
80.50 6.42
79.91 5.27
77.56 7.27
79.93 7.17
70.49 5.63
60.44 4.28
38.65 3.08
33.10 2.59
26.75 2.19
23.17 1.77
58
60
55
55
53
52
54
53
53
55
59
55
55
3
1
1
1
2
2
1
2
2
2
4
3
1
–120 10
–109
–121
–119
–126
–129
–122
–127
–128
–125
3
3
3
7
7
3
7
7
7
0.134
0.187
0.267
0.321
0.427
0.657
1.314
1.753
2.191
2.629
III
–114 13
–128 10
–129
3
0.03
0.08
0.20
0.34
0.51
0.62
0.88
1.31
1.75
2.19
2.63
3.07
0.63 0.01
1.42 0.02
1.99 0.04
2.65 0.04
3.02 0.12
3.05 0.04
3.09 0.12
2.91 0.13
2.60 0.14
2.22 0.14
1.97 0.15
1.81 0.06
1.62 0.03
3.23 0.06
5.25 0.15
6.13 0.21
7.66 0.51
7.58 0.28
7.71 0.11
6.98 0.24
6.39 0.07
5.60 0.11
5.07 0.21
4.58 0.21
3.63 0.07
6.89 0.27
10.67 0.29
14.01 0.33
14.95 0.21
14.81 0.24
14.85 0.19
14.44 0.34
12.81 0.54
11.78 0.41
10.48 0.33
9.45 0.29
69
62
66
66
63
62
62
63
63
66
66
65
2
1
4
1
4
4
4
2
3
3
4
3
–101
–118
–101 13
–99
–108 13
–111 13
–111 13
7
3
3
IV
–108
7
–109 10
–100 10
–102 13
–106 10
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 12 2011

ROLE OF THE CENTRAL MANGANESE(III) ION
2005
–logkTeff
–logkTeff
1
1
4.0
3.5
3.0
2
2
3.9
3
4
3.5
3
4
3.1
2.7
0.8
1.3
–logcH2O
2
–0.5
0
0.5logcH2O
2
Fig. 3. logkTэф versus logcH O for the reaction of (
1)
Fig. 4. logkTэф versus logcH O for the reaction of (
1
)
2
2
2
2
5.10
5.10
(Cl)MnMPOEP, (
MPOMP, (
H O concentration range at 298 K.
2
)
(Cl)Mn DPOEP, (
3
) (Cl)Mn
(Cl)Mn DPOEP, (
2
) (Cl)MnMPOMP, (
3
) (Cl)Mn
5.15
5.15
4)
(Cl)Mn DPOEP with H O in the first
MPOMP, (
4
)
(Cl)Mn DPOEP with H O in the second
2
2
2
2
2
2
R
= 0.98 (
1
,
2,
4)
H O concentration range at 298 K.
R
= (
1
) 0.97, (2, 3, 4)
2
2
2 2
0.98, (3) 0.99.
0.99.
k3'
−
2
III
III
mophoreꢀcoordinated macrocycle. No transition to
the isoelectronic O=MnIVP species takes place (unlike
that in O=MnIVTPP), as in this case the change in the
UV/Vis spectrum would be the opposite to that
described in the beginning of the section [19]. Due to
Cl HO Mn P ⎯⎯⎯→O = Mn P+i
(
)
(
)
(
)
(9)
+ OH− + Cl− slowly .
(
)
The perhydroxyl anion present in the system in
equilibrium concentrations according to equilibrium
(7) adds reversibly to a coordinatively unsaturated Mn
atom according to reaction (8) to give the donorꢀ
the low concentration of
Н
−, the resulting complex
O2
+i
species O=MnIII(
) does not react with the second
P
acceptor –O–
→
Mn bonds. Hydrogen peroxide is
peroxide molecule, as occurs in all catalytic Н2О2 disꢀ
proportionation processes.
The rate equation for the rateꢀlimiting step has the
form
coordinated not as the H2O2 molecule, as it is in the
(X)MnTPP complexes (X is singleꢀcharged anionic
ligand) considered previously [19], but as a stronger
HO2−.
decrease in the effective positive charge
atom on going from (X)MnTPP to complexes
due to the electronꢀdonating action of eight
nucleophile
This is apparently due to the
'
− dc Cl
dτ = k3c Cl HO− MnIII .
(10)
HO− MnIII
P
P
(
)
(
)
(
(
2
)
2
)
δ
+
on the Mn
IV
ꢀalkyl
I
–
In view of equilibria (7) and (8), the rate equation
is transformed to
β
substituents and by the partial removal of the electronꢀ
withdrawing effect of the mesoꢀphenyl groups. The
−dc Cl
dτ= −dc Cl MnIII dτ =
HO− MnIII
P
P
(
)
(
)
(
2
)
− (reaction (8)) apparently targets
(11)
coordination of
HO2
1 2
c
H2O2
P
K11 2
.
'
= k3K2c Cl MnIII
at the sixth coordination position, the anionic ligand
Cl– remaining in the coordination sphere. This was
confirmed in relation to (X)MnTPP [19] where the
oxidation rate was found to considerably depend on
the nature of X.
(
)
A comparison of Eqs. (4) and (11) shows that they
are identical and the following equality holds:
k1 = k3K11 2K 2,
'
(12)
10–12 at 298 K [20].
The perhydroxyl anion activated by the coordinaꢀ
tion to Mn is reduced by one ꢀelectron of the macroꢀ
cycle and gives off an oxygen atom to metal porphyrin
with elimination of ОН– and displacement of Cl– in
slow intramolecular redox reaction (9).
where
K
1 = 2.4
×
π
For determining the numerical value of K2, specꢀ
trophotometric titration of a DMF solution of
(Cl)Mn5.15DPОЕP with a 0.01–0.14 M aqueous soluꢀ
tion of hydrogen peroxide was carried out (Fig. 5). The
The manganese complex remains in the electrically
titration curve has one step; a complex III
is 1 : 1/2 (Fig. 5b). The numerical value of
106 mol–3/2 L3/2 was calculated using the equilibꢀ
:
K
Н2О2 ratio
2 = (10.8
+i
neutral molecular form, O=MnIII(
), which is
P
readily identified based on the presence of absorption 0.8)
×
at 672–685 nm in the UV/Vis spectra (Fig. 1) resulting rium constant for the coordination of molecular perꢀ
from the singleꢀelectronꢀoxidized state of the chroꢀ oxide calculated from Eq. (3) and taking into account
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 12 2011

2006
OVCHENKOVA et al.
≠
Table 3. Rate constants k, activation energy E, and activation entropy ΔS of the reaction of manganese(III) porphyrin comꢀ
plexes with H2O2 in DMF
≠
S , J/(mol K)
Complex
cH2O2 range, mol/L
T
, K
k
×
103
,
s–1 mol–1 L–1
E
,
kJ/mol
Δ
298
308
318
0.47 0.03
1.12 0.06
2.33 0.15
0.03–0.34
63
64
2
3
–107
7
I
298
308
318
0.33 0.01
0.82 0.02
1.67 0.03
1.31–3.07
–104 10
298
308
1.20 0.07
2.49 0.02
0.01–0.08
0.32–2.31
56
69
1
1
–120
–94
3
3
II
298
308
0.15 0.01
0.37 0.02
298
308
318
5.4 0.4
11.1 1.0
23.1 1.8
0.01–0.13
0.43–2.63
0.01–0.08
0.69–1.85
57
56
51
56
1
3
3
2
–104
3
III
298
308
318
1.01 0.06
1.95 0.12
4.2 0.3
–121 10
–128 10
298
308
318
3.5 0.2
6.4 0.4
12.7 0.9
IV
298
308
318
0.67 0.02
1.32 0.05
2.75 0.05
–124
7
equilibria (7) and (8). The rate constant for elemenꢀ
For the third range of Н2О2 concentrations, the
theoretical reaction scheme consistent with experiꢀ
mentally derived rate equation (6) is more complex:
k3 = k1 K 1 2K 2
'
tary step (9) at 298 K is
= (3.35
)
(
1
0.13)
×
10–4 s–1.
K1
−
O2,
+
⎯⎯⎯→
←⎯⎯⎯
H2O2
Н + Н
(13)
−
2
Cl MnIIIP + HO ⎯⎯⎯→ Cl HO−
k
'
2
(
)
(
)
log
I
(
)
2
(14)
A
× MnIII
P
fast ,
0.8
0.6
0.4
b
(
)
0.45
0.40
0.35
K3
−
III
⎯⎯⎯→
←⎯⎯⎯
Cl HO Mn P
Cl O
(
)
(
)
(
)
2
logcH2O
а
(15)
2
0
–1.7 –1.2
+i
−
= MnIV
P
+ OH ,
)
(
K4
←⎯⎯⎯
ОН– + Н2О2
Н
− + Н2О,
(16)
(17)
⎯⎯⎯→
O2
+i
−
III
2 Cl O = MnIV
P
+ HO ⎯⎯⎯→2O = Mn
0.05
0.10
cH2O , mol/L
0.15
k
'
5
(
)
(
)
2
2
+i
−
× P + HCl + O + Cl
slow .
(
)
(
)
2
Note that due to the relatively low concentration of
−, no gas evolution is observed in the experiment;
the О2 formed exists apparently in the dissolved state.
At higher H2O2 concentrations (in the third range),
Fig. 5.
(
a
) Titration curve and (b) the logarithms of the
H
O2
indicator ratio (log
I
) and hydrogen peroxide concentraꢀ
2
tion in water–organic medium ( logcH O ) (
R = 0.99) for
2
2
5.15
the titration of (Cl)Mn DPOEP in DMF with aqueous
hydrogen peroxide.
the coordination of hydrogen peroxide (as
Н
−) to the
O2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 12 2011

ROLE OF THE CENTRAL MANGANESE(III) ION
2007
sixth coordination position of manganese (reaction
The substitution of the expressions for concentraꢀ
(14)) is fast and irreversible. The transfer of two elecꢀ tions (21) and (22) into rate equation (18) produces
trons from the easily polarizable porphyrin macrocyꢀ Eq. (23), which is in line with the experimentally
cle and the metal cation to the coordinated peroxide erived rate equation (6):
molecule is accompanied by its decomposition
−dc
dτ
+i
( )
according to reversible reaction (15). The equilibrium
Cl O=MnIV
P
(
)
may be established due to the lower stability of the
−1
= −dc
dτ = k5K 3K 4c
c
(23)
Cl MnIII
P
HO2
−
+i
Cl HO MnIII
−
P
(
)
O=MnIII(
)
π
ꢀradical as compared with
2
(
)
(
)
P
Cl)O=MnIV( +i ) (Eq. (9)) and the presence of higher
= k5K 3K 4K11 2
c
c
−1 2
.
H2O2
P
Cl MnIII
P
(
)
−
O2
concentrations of the
Н
and ОН– negative ions,
Thus,
where
which prevent ionization of the Cl– ligand. The latter
remains in the ꢀradical coordination sphere
(Scheme 1). Finally, the reaction with second Н2О2
π
1 2
'
(24)
k3 = k5K3K 4K1
,
K
1 = 2.4 ×
10–12 at 298 K. The coincidence of
(as
Н
−) becomes possible. This reaction is slower
O2
than reaction (14) and is rate limiting. The reduction
of the ꢀradical of the manganese(IV) complex does
the theoretical and experimentally found rate equaꢀ
tions verifies the validity of the proposed reaction
schemes, which account for the variable fractional
order with respect to the peroxide concentration.
π
not proceed to completion, i.e., does not arrive at relꢀ
atively stable O=MnIVP; rather, it stops when the sinꢀ
The oxidation of MP with hydrogen peroxide
proved to be fairly sensitive to the nature of the macroꢀ
+i
gleꢀelectron reduced O=MnIII(
) has been formed.
P
cyclic ligand. The (Cl)Mn5.15DPOEP complex (III
)
This distinguishes the octaalkylporphyrin complexes
from (Cl)MnIIITPP. For the (Cl)MnIIITPP–Н2О2 sysꢀ
tem [19], the twoꢀelectron reduced species is the final
product.
reacts with hydrogen peroxide 13 times faster than
(Cl)MnMPOEP at low (298 K) and 3 times faster
c
H2O2
than (Cl)MnMPOEP at high
The reaction rate
.
cH O
constant k
is an order of magnitud2e higher in the case
2
C2H5
of (Cl)Mn5.15DPOEP over the whole H2O2 concentraꢀ
tion range. In the case of monophenylꢀsubstituted
complexes, the oxidation is faster with (Cl)MnMꢀ
POMP than with (Cl)MnMPOEP. Thus, the comꢀ
O
C2H5
C2H5
C2H5
NIVMn
N
+
•
plexes can be arranged in the order of increasing k298
:
N
N
C2H5
(Cl)MnMPOEP
< (Cl)MnMPOMP < (Cl)Mn5.15DPOEP
(Cl)MnOEP [18] < (Cl)MnTPP [19].
≈
(Cl)Mn5.10DPOEP
C2H5
C2H5
C2H5
Cl
Scheme 1. Suggested structure of the manganese
(25)
≈
IV
+
complex (Cl)O=Mn (P •) with the coordinated
ꢀradical cation macrocycle in relation
to (Cl)MnMPOEP
Analysis of the activation parameters shows a parꢀ
allel variation of the rate constants for oxidation and
the activation energy in the third Н2О2 concentration
range (series (25), Table 3). For the first range, no such
a trend is observed. Obviously, this is related to the
nature of the rateꢀlimiting steps (reactions (9) and (17)
for the first and third ranges, respectively). Although in
both cases, one deals with the reduction of coordiꢀ
nated hydrogen peroxide, this is the second coordiꢀ
π
.
The rate equation for the rateꢀlimiting step (17) is
'
−dc Cl O=MnIV
dτ = k5c Cl O=MnIV cHO
.
(18)
+i
+i
−
P
P
)
(
)
(
)
(
)
(
2
c
By successively expressing
(relations
+i
Cl O=MnIV
P
)
(
)
(
(19) and (20)) from the equations reflecting the prinꢀ nated species in the third concentration range and the
ciple of detailed equilibrium with constants K3 and K4
,
first coordinated species in the first concentration
range. The coordinative saturation of the heptacoordiꢀ
nate complex (Eq. (17)) decreases the role of the
entropy factor and the mentioned parallel variation of
and expressing
with the constant K1 gives relations
c
НО2−
(21) and (22) respectively
E
and k298
.
−1
,
−
ОН
c Cl O=MnIV
= K3c Сl HO MnIII
c
(19)
+i
−
P
P
(
)
(
)
(
(
)
2
)
It can be seen that simultaneous ꢀoctaalkyl and
β
cОН− = cH2 O−K4−1,
mesoꢀphenyl substitution retards the oxidation of MP
with hydrogen peroxide (series (25)). Since despite the
differences in reactions (7) and (19), reduction of the
coordinated hydrogen peroxide in a particular form is
the rateꢀlimiting step of MP oxidation at different
(20)
(21)
2
c Cl O=MnIV
= K3c Сl HO MnIII K4c−2
,
HO2
+i
−
−
P
P
(
)
(
)
(
(
)
2
)
1/2
.
H2O2
(22)
C
= K11/2 ⋅ C
HO2−
, the ratio of the reaction rates in series (25) can
c
H2O2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 12 2011

2008
OVCHENKOVA et al.
3. M. A. Johnston and E. A. Delwiche, J. Bacteriol. 90
,
be attributed to the transfer of the electronꢀwithdrawꢀ
352 (1965).
ing effect of the mesoꢀphenyl groups and the positive
4. Y. Kono and I. Fridovich, J. Biol. Chem. 258, 6015
electron effect of the ꢀalkyl substituents to the coorꢀ
β
(1983).
dination site and the mutual effect of the aromatic
macrocycle and the anionic ligand. Note that the reacꢀ
tion kinetics and mechanism do not change on going
from (Cl)MnOEP to its monoꢀ and diphenyl derivaꢀ
+i
5. G. S. Allgood and J. J. Perry, J. Bacteriol. 168, 563
(1986).
6. K. Phucharoen, Y. Takenaka, and T. Shinozawa, DNA
Sequence 12, 413 (2001).
7. V. RobbeꢀSaule, C. Coynault, M. IbanezꢀRuiz, et al.,
tives and the O=MnIII(
) radicals are always formed
P
as the final reaction product. Upon extraction into
chloroform after the reaction with Н2О2 and the
removal of excess Н2О2, these radicals are converted to
the MnIV complex, O=MnIVP. In the case of
Mol. Microbiol. 39, 15335 (2001).
8. T. Amo, H. Atomi, and T. Imanaka, J. Bacteriol. 184
,
3305 (2002).
9. J. T. Groves, J. Lee, and S. S. Marla, J. Am. Chem. Soc.
119, 6269 (1997).
10. S. Banfi, M. Cavazzini, G. Pozzi, et al., J. Chem. Soc.,
Perkin Trans. II 5, 871 (2000).
11. R. D. Arasasingham, G.ꢀX. He, and T. C. Bruce, J. Am.
Chem. Soc. 115, 7985 (1993).
12. P. N. Balasubramanian, E. S. Schmidt, and T. C. Bruce,
(Cl)MnTPP, the
low Н2О2 concentrations, while at
π
ꢀradical species is formed only at
> 0.1 mol/L,
c
H2O2
the species oxidized at Mn, manganese(IV)tetrapheꢀ
nylporphin, is formed as the final product [19].
Hence, it follows that by varying the electronic strucꢀ
ture of the macrocycle and the Mn–N bonds, one can
attain the optimal parameters for the coordination of
−
J. Am. Chem. Soc. 109, 7865 (1987).
13. E. M. Kuvshinova, D. L. Kuz’min, S. G. Pukhovskaya,
H2O2 molecules and
H
O2
ions at different steps of
et al., Zh. Obshch. Khim. 73, 691 (2003).
reaction with the peroxide and then use these results to
develop synthetic catalases.
14. M. E. Klyueva, T. N. Lomova, B. D. Berezin, and
A. S. Semeikin, Russ. J. Inorg. Chem. 48 (8), 1238
(2003).
ACKNOWLEDGMENTS
15. H. Volz and W. Muller, Chem. Ber. Rec. 130 (5), 1099
(1997).
This work was partially supported by the Fundaꢀ
mental Research Program no. 7 of the Presidium of
the Russian Academy of Sciences (2010), the Russian
Foundation for Basic Research (project no. 09ꢀ03ꢀ
97556ꢀrꢀtsentrꢀa), and the Ministry of Science and
Education Program “Development of the Scientific
Potential of Higher School” (no. 2.2.1.1/2820).
16. L. Kaustov, M. E. Tal, A. I. Shames, and Z. Gross,
Inorg. Chem. 36 (16), 3503 (1997).
17. N. Carnieri, A. Harriman, G. Porter, and K. Kalyanaꢀ
sundaram, J. Chem.. Soc., Dalton Trans, No. 7, 1231
(1982).
18. E. N. Kiseleva, T. N. Lomova, and M. E. Klyueva,
Zh. Obshch. Khim. 77 (4), 687 (2007).
19. T. N. Lomova, M. V. Klyuev, M. E. Klyueva, et al.,
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RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 12 2011