Electrochemical determination of antioxidant properties of a series of tetraphenylporphyrin derivatives and their zinc complexes

Article abstract of DOI:10.1142/S1088424615500765

Zinc complexes of a series of substituted tetraphenylporphyrins containing OH-groups in the phenyl rings were synthesized. Their antioxidant capacity was estimated in reaction of the porphyrins with 2,2′-diphenyl-1-picrylhydrazyl (DPPH) by cyclic voltamme

Full text of DOI:10.1142/S1088424615500765

Journal of Porphyrins and Phthalocyanines
J. Porphyrins Phthalocyanines 2015; 19: 1–7
DOI: 10.1142/S1088424615500765
Published at http://www.worldscinet.com/jpp/
Electrochemical determination of antioxidant properties
of a series of tetraphenylporphyrin derivatives and their
zinc complexes
a
b
a◊
Mariya V.Tesakova* , Aleksandr S. Semeikin and Vladimir I. Parfenyuk
a
G.A. Krestov Institute of Solution Chemistry of RAS, Akademicheskaya St. 1, Ivanovo 153045, Russia
Ivanovo State University of Chemistry and Technology, Sheremetevsky Avenue 7, Ivanovo 153000, Russia
b
Received 1 April 2015
Accepted 9 June 2015
ABSTRACT: Zinc complexes of a series of substituted tetraphenylporphyrins containing OH-groups in
the phenyl rings were synthesized. Their antioxidant capacity was estimated in reaction of the porphyrins
with 2,2′-diphenyl-1-picrylhydrazyl (DPPH) by cyclic voltammetry. The electron absorption spectra of
the all synthesized compounds before and after the reaction with 2,2′-diphenyl-1-picrylhydrazyl were
recorded. The effect of structure of the porphyrins and zinc complexes on their antioxidant capacity was
discussed.
KEYWORDS: porphyrins, metalloporphyrins, free radicals, antioxidant capacity, oxidation potential,
cyclic voltammetry.
at which the intensity of absorption band of 2,2′-diphenyl-
-picrylhydrazyl (517 nm) is decreased by 50%. This
method can not be used at high concentrations of
reacting substances and to study antioxidant properties of
chromophores absorbed in the same spectral region with
INTRODUCTION
1
Lipid peroxidation and formation of active oxygen
forms and free radicals in cells lead to membrane damage
and ageing. Search of new antioxidants which are able
“quench” free radicals to prevent oxidative stress is a
2,2′-diphenyl-1-picrylhydrazyl.
very important task. The study of antioxidant properties
of porphyrins is of particular interest.
There are four bands assigned to electronic-vibrational
transitions in the visible range of the electron absorption
spectra of porphyrins. At complex formation with
metal ions and formation of anions, highly symmetrical
particles are formed resulting in two-fold degeneracy of
the electron levels and disappearance of two “visible”
bands [8]. Therefore, the antioxidant properties of the
synthesized porphyrins in the reaction with 2,2′-diphenyl-
A key role of natural porphyrins in metabolism of living
organisms is well-known, for example, Fe-containing
porphyrin of heme (hemoglobin) or Mg-containing
porphyrin (chlorine) in chloroplasts [1, 2]. In the present
work, tetraphenylporphyrin derivatives and their zinc
complexes were synthesized and their antioxidant capacity
wasstudiedinreactionwith2,2′-diphenyl-1-picrylhydrazyl
1
-picrylhydrazyl were estimated by highly sensitive
(DPPH). 2,2′-diphenyl-1-picrylhydrazyl is widely used to
electrochemical method which allows to analyze the
properties in both aqueous and nonaqueous media [9]
Redoxpotentialsareveryimportantcharacteristicsofanti-
oxidantcapacityofpotentialantioxidants[10,11].Thelower
valueofoxidationpotentialofasubstance, themoreefficient
its antioxidant properties. The present work is devoted to
determination of redox potentials of tetraphenylporphyrin,
study antioxidant capacity of different objects. In many
works [3–7] the kinetics of 2,2′-diphenyl-1-picrylhydrazyl
radical reaction is studied by spectrophotometry method.
One of parameters of antioxidant capacity is “efficient
concentration” of antioxidant EC50, i.e. the concentration
◊
SPP full member in good standing
5
5
,10,15,20-tetrakis(4′-hydroxyphenyl)porphyrin,
,10,15,20-tetrakis(3′-hydroxyphenyl)porphyrin,
*
Correspondence to: Mariya V. Tesakova, email: mvt@isc-ras.
ru, tel: +7 (4932)33-6264 (227)
5,10,15,20-tetrakis(4′-hydroxy3′5′-di-tret-butylphenyl)
Copyright © 2015 World Scientific Publishing Company

2
M.V. TESAKOVA ET AL.
porphyrin, Zn(II)5,10,15,20-tetrakis(4′-hydroxyphenyl)
porphyrin, Zn(II)5,10,15,20-tetrakis(3′-hydroxyphenyl)
porphyrin, Zn(II)5,10,15,20-tetrakis(4′-hydroxy3′5′-di-
tret-butylphenyl)porphyrin by electrochemical method
and study of interaction of the porphyrins with 2,2′-
diphenyl-1-picrylhydrazyl.
The main objective of this work is to compare the anti-
oxidant behavior of the porphyrins and their zinc complexes
with different location of hydroxyl groups in order to
elucidate their structure-activity relationships and to explain
why some of these structural features are important.
4:1) (silufol). UV-vis: lmax, nm (log e) 654 (3.97); 597
(3.82); 562 (4.20); 524 (4.24); 427 (5.72) (chloroform).
-1
1
IR (CCl ): n, cm 3633 (nOH). H NMR (ext. Art. TMS):
4
d, ppm 8.95s (8H, b-H); 8.06s (8H, 2,6-H-Ar); 5.56s
(4H, OH); 1.64s (72H, t-Bu); -2.67s (2H, NH) (CDCl3).
Hydrolysis tetra(methoxyphenyl)porphyrin was performed
with boron tribromide by a modified method [13].
To a solution of 1.0 g (1.36 mmol) 5,10,15,20-tetrakis-
(4′-methoxyphenyl)porphyrin in 200 mL of dried
methylene chloride, a solution of 0.5 mL of BBr3
(5.29 mmol) in 10 mL of methylene chloride was added
at stirring and cooling. The mixture was stirred for 2 h at
room temperature. Then 5 mL of methanol was added.
The mixture was neutralized by aqueous ammonium up
to color transition from green to dark cherry, washed
with water, dried over sodium sulfate and evaporated to
dryness. The obtained solid product was dissolved in ethyl
acetate and chromatographed on a column of silica gel
using ethyl acetate as eluent. The column effluent having
dark cherry color was evaporated, and the porphyrin was
precipitated by petroleum ether.
EXPERIMENTAL
Synthesis of porphyrins
Initial tetraarilporfiriny obtained by Adler modified
method in xylene-chloroacetic acid mixture [12].
The compound was prepared by addition of 1.7 mL
(
(
24.6 mmol) of pyrrole to boiling solution of 5.6 g
23.9 mmol) of substituted benzaldehyde and 2.7 g of
5,10,15,20-Tetrakis(4′-hydroxyphenyl)porphyrin
(H T(4-OHPh)P). Yield of the product is 98%. R = 0.33
chloroacetic acid in 100 mL of isomeric xylenes mixture
during 20 min. The obtained mixture was boiled for 1 h
by passing air through the solution. Then the xylenes were
distiled with water vapor, the precipitate was filtered,
washed with water and dried in air atmosphere at 50°C.
The porphyrin dissolved in benzene was chromatographed
on a column of aluminum oxide using benzene as eluent.
The first red zone was collected. The eluent was removed
by evaporation. The porphyrin was precipitated by
methanol, filtered and dried at room temperature.
2
f
(ether) (silufol). UV-vis: lmax, nm (log e) 650 (3.72); 595
(3.71); 556 (3.90); 519 (4.06); 423 (5.43) (chloroform).
-1
IR (KBr): n, cm 3300 (nOH); 1349 (dOH).
5,10,15,20-Tetrakis(3′-hydroxyphenyl)porphyrin
(H T(3-OHPh)P). Yield of the product is 98%. R =
2
f
0.88 (ethyl acetate) (silufol). UV-vis: lmax, nm (log e)
645 (3.71); 588 (3.88); 550 (3.92); 514 (4.31); 419 (5.62)
(chloroform). Zinc complexes of porphyrins were prepared
by refluxing with zinc acetate in DMF at Adler [14].
A mixture of 0.1 g (0.15 mmol) of porphyrin and 0.1 g
(0.46 mmol) of zinc acetate (dihydrate) in 10 mL of DMF
was boiled for 1 h. Then the mixture was poured into
water. The precipitate was filtered and washed with water
and dried at 70°C. The resulting product was dissolved
in ethyl acetate and chromatographed on a column of
silica gel using ethyl acetate as eluent. The eluate was
evaporated and the complex was precipitate by petroleum
ether. The resulting complex was washed and dried in the
air at room temperature.
Tetraphenylporphyrin(H TPhP). Yieldoftheproduct
2
is 35%. R = 0.63 (benzene-hexane; 2:1) (silufol). UV-vis:
f
lmax, nm (log e) 646 (3.71), 590 (3.71), 548 (3.96), 514
1
(
4.27), 420 (5.73) (chloroform). H NMR (ext. Art. TMS):
d, ppm 8.90s (8H, b-H); 8.24–8.29 m (8H, o-H-Ph); 7.76–
.84 m (12H, m,n-H-Ph); -2.72 bs (2H, NH) (CDCl3).
,10,15,20-Tetrakis(4′-methoxyphenyl)porphyrin
H T(4-MeOPh)P). Yield of the product is 38%. R =
7
5
(
2
f
0
.71 (chloroform-hexane; 5:1) (silufol). UV-vis: lmax, nm
(
(
8
log e) 652 (3.77), 595 (3.78), 557 (4.07), 520 (4.25), 423
1
5.69) (chloroform). H NMR (ext. Art. TMS): d, ppm
Zn(II)5,10,15,20-Tetrakis(4′-hydroxyphenyl)
porphyrin (ZnT(4-OHPh)P). Yield of the product
.88s (8H, b-H); 8.13d (8H, J = 8.5 Hz, 2,6-H-Ar); 7.31d
(
8H, J = 8.5 Hz, 3,5-H-Ar); -2.75 bs (2H, NH) (CDCl3).
,10,15,20-Tetrakis(3′-methoxyphenyl)porphyrin
H T(3-MeOPh)P). Yield of the product is 27%. R =
is 81%. R = 0.13 (benzene-methanol; 10:1) (silufol).
f
-3
5
UV-vis: lmax, nm (e × 10 ) 600 (12.4); 559 (19.1); 424
(590.6) (methanol).
(
0
2
f
.45 (chloroform-hexane; 1:1) (silufol). UV-vis: lmax, nm
Zn(II)5,10,15,20-Tetrakis(3′-hydroxyphenyl)
porphyrin (ZnT(3-OHPh)P). Yield of the product
(
(
8
log e) 648 (3.72), 590 (3.83), 550 (3.89), 516 (4.31), 420
1
5.70) (chloroform). H NMR (ext. Art. TMS): d, ppm
is 54%. R = 0.19 (benzene-methanol; 10:1) (silufol).
f
-3
.91s (8H, b-H); 7.83d (4H, J = 7.8 Hz, 6-H-Ar); 7.81s
UV-vis: lmax, nm (e × 10 ) 595 (7.1); 556 (16.2); 422
(425.7) (methanol).
(
(
4H, 2-H-Ar); 7.66t (4H, J = 7.8 Hz, 5-H-Ar); 7.36dd
1
4H, J = 7.8 Hz, J = 2.4 Hz, 4-H-Ar); 4.01s (12H,
Zn(II)5,10,15,20-Tetrakis(4′-hydroxy3′5′-di-tret-
butylphenyl)porphyrin (ZnT(4-OH-3,5-di-t-BuPh)P).
OCH ); -2.78bs (2H, NH) (CDCl ).
3
3
5
,10,15,20-Tetrakis(4′-hydroxy3′5′-di-tret-
Yield of the product is 73%. R = 0.81 (benzene-hexane;
f
-3
butylphenyl)porphyrin (H T(4-OH-3,5-di-t-BuPh)P.
Yield of the product is 37%. R = 0.70 (benzene-heptane,
10:1) (silufol). UV-vis: lmax, nm (e × 10 ) 603 (10.7); 555
2
f
(17.7); 429 (455.3) (chloroform).
Copyright © 2015 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2015; 19: 2–7

ELECTROCHEMICAL DETERMINATION OF ANTIOXIDANT PROPERTIES OF A SERIES
3
Electrochemical measurements
For an electrochemically irreversible reaction the
oxidation potential, E , characterizing antioxidant
capacity depends on scan rate (V). Therefore, the Eox
values for the studied porphyrins were obtained by
ox
Three-electrode system was employed with saturated
calomel electrode as the reference electrode and a platinum
wire as a counter electrode. The a glassy carbon electrode
extrapolation of E = f(V) to V = 0 taking into account
ox
(Siggradur, Germany), 4 mm in diameter, and fluoroplastic
nonfaraday current of double electrical layer charging.
The value of the current of double electrical layer charging
was determined as linear extension of initial part of the
insulation of side surface serves as working electrode. The
three-electrode electrochemical cell [16] was connected
with potentiostat P-30SM (Elin, Chernogolovka, Russia).
All electrochemical measurements were carried out in
argon atmosphere by passing argon for 30–40 min through
the solution before each measurement [16]. Freshly
prepared solutions of the porphyrins in dichloromethane
CVA. The extrapolation of E = f(V) to V = 0 allows to
ox
obtain the potential of oxidation peak of the porphyrins
in irreversible process. For reversible process the Eox/red
value was determined as a half-sum of the oxidation and
reduction (E and E ) potentials. In this case the E
ox
red
ox/red
(
Sigma-Aldrich, Inc.) or dried ethanol (water content was
not greater than 0.7% wt) with addition of base electrolyte
0.02 M tetrabutyl ammonium perchlorate (TBAP)) were
value is independent on the scan rate.
(
Electronic absorption spectra
used. The choice of solvents were determined by the
porphyrin solubility. The porphyrin concentration was
The reactions of the porphyrins with DPPH were
studied at 298 K using a spectrophotometer Agilent 8453
UV-vis.
-
3
1
× 10 M. The 2,2′-diphenyl-1-picrylhydrazyl concen-
-3
tration was 1 × 10 M. To study the reaction of the
porphyrins with 2,2′-diphenyl-1-picrylhydrazyl, different
volumes of the porphyrin solution were added to the
RESULTS AND DISCUSSION
2
,2′-diphenyl-1-picrylhydrazyl solution. The measurements
were performed at room temperature.
Figure 1 shows the structural formulas of the studied
porphyrins. The presence of phenolic fragments
with mobile hydrogen atom supposes antioxidant
capacity of the macrocyclic compounds, similarly to
phenolic antioxidants [19]. Because one of expected
mechanisms of antioxidant action of the porphyrins
is transfer of hydrogen to free radicals, the antioxidant
capacity of the porphyrins was estimated in reaction
with stable 2,2′-diphenyl-1-picrylhydrazyl free radical.
The interaction of the tetraphenylporphyrin derivatives
and their metallocomplexes with 2,2′-diphenyl-1-
picrylhydrazyl was studied by spectrophotometric and
electrochemical methods.
The cyclic voltammogram (CVA) of 2,2′-diphenyl-
-picrylhydrazyl in the potential range from -0.1 to
1
+
1.4 V exhibits four one-electron reversible waves
corresponding to reversible reduction and oxidation of
DPPH radical [17]. The CVA scan was recorded from
the potential of working electrode in 2,2′-diphenyl-
1
-picrylhydrazyl solution (~0.45 V) initially towards
the negative potentials and then towards the positive
potentials. The peaks observed on the cathodic branch of
the CVA correspond to the reduction of DPPH radical to
anion (the first peak) and to the reduction of DPPH cation
to the radical (the second peak). The peaks on anodic
branch of CVA correspond to the oxidation process of
the DPPH anion to the radical and the radical to the
cation. DPPH radical in molecular form exists in the
range of positive potentials from ~0.4 to ~0.7 V relative
to saturated calomel electrode [17]. From the Randles–
Shevcik equation [18]:
For this purpose the electron absorption spectra of the
porphyrin solutions and their mixtures with 2,2′-diphenyl-
1
-picrylhydrazyl solution (v/v) were recorded. However
R
R
5
3/2
1/2 1/2
0
i
I = 2.69 × 10 × z SD v C
(1)
n
it is followed that at given electrode surface and scan
rate, the ratio of peak currents of 2,2′-diphenyl-1-
picrylhydrazyl reduction (oxidation) is equal to the ratio
of 2,2′-diphenyl-1-picrylhydrazyl concentrations:
N
HN
N
N
N
N
N
R
R
R
Zn
R
NH
I/I = C/C ,
(2)
R
0
0
R
where I is the peak current at given 2,2′-diphenyl-1-
picrylhydrazyl concentration C, I is the peak current at
C(CH3)3
OH
OH
0
initial 2,2′-diphenyl-1-picrylhydrazyl concentration, C0.
Therefore, the change of peak current of the redox process
is determined by the change of DPPH concentration and
can serve for estimation of antioxidant capacity of the
substance reacting with 2,2′-diphenyl-1-picrylhydrazyl.
R =
OH
,
H
,
,
C(CH3)3
Fig. 1. Structural formulas of porphyrins
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4
M.V. TESAKOVA ET AL.
Fig. 2. Electronic absorption spectra: (a) H T(4-OH-3,5-di-t-BuPh)P in ethanol (1), after addition of DPPH solution (2); (b) ZnT(3-
2
OHPh)P in ethanol (1), after addition of DPPH solution (2)
O
O
(
H3C)3C
C(CH3)3
(H3C)3C
C(CH3)3
(
H3C)3C
OH
C(CH3)3
(H C) C
C(CH3)3
3
3
N
HN
N
N
HN
N
OH
HO
OH
NH
NH
C(CH3)3
C(CH3)3
(
H3C)3C
(H3C)3C
(
H3C)3C
CH(CH3)3
(H3C)3C
C(CH3)3
O
O
Scheme 1.
changes in 2,2′-diphenyl-1-picrylhydrazyl spectrum were
not fixed because the porphyrins absorb more intensively
than 2,2′-diphenyl-1-picrylhydrazyl in the same region.
The porphyrins have four-lane spectrum with intensive
Sore band (Fig. 2a), whereas their metallocomplexes
exhibit two bands with the pronounced Sore band in
boundary UV-vis region (Fig. 2b).
In contrast to the porphyrin-ligand, the spectrum
of ZnT(4-OH-3,5-di-t-BuPh)P is maintained after the
reaction with DPPH. This testifies about maintenance of
the chromophore structure.
The results of electrochemical DPPH-test showed that
all the studied porphyrins exhibit antiradical capacity,
except H TPP (Table 1). As has been mentioned above,
2
No changes are observed in the spectra of the porphy-
rins after reaction with 2,2′-diphenyl-1-picrylhydrazyl
probable mechanism of the porphyrin antioxidant action
is detachment of hydrogen from the macroheterocyclic
compounds and its interaction with free 2,2′-diphenyl-1-
picrylhydrazyl radical. Several variants of the detachment
are possible.
Introduction of zinc in the porphyrin structure and
studies of antioxidant properties of the zinc complexes
allow to exclude a possibility of hydrogen detachment
inside the macrocycle. The absence of antiradical
properties of the tetraphenylporphyrin in relation to
2,2′-diphenyl-1-picrylhydrazyl excludes breakdown
C–H bond. For the tetraphenylporphyrin derivatives
(
Fig. 2b), except H T(4-OH-3,5-di-t-BuPh)P. The reaction
2
of H T(4-OH-3,5-di-t-BuPh)P with 2,2′-diphenyl-1-picryl-
2
hydrazyl leads to significant spectral changes, notably
transition from the porphyrin four-lane spectrum with
intensive Sore band (423 nm) to the broadened two-
lane spectrum with disappearance of the Sore band
(Fig. 2a). It is likely that the spectral changes may be
associatedwithreorganizationoftheporphyrinchromophore
after detachment of hydrogen and recombination of
biradicals with formation of dipyrrine structures [20].
Copyright © 2015 World Scientific Publishing Company
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ELECTROCHEMICAL DETERMINATION OF ANTIOXIDANT PROPERTIES OF A SERIES
5
Table 1. Oxidation potentials (E ), oxidation-reduction potentials (Eox/red), indexes of efficiency of antioxidant action
ox
(
A A ), and efficient concentration (CI50) for reaction of porphyrins with 2,2′-diphenyl-1-picrylhydrazyl in solution
1
2
Porphyrin
In C H OH
In CH Cl
2
5
2
2
E , V
A1
—
A2
CI , mmol/l
Eox/red, V
A1
A2
ox
50
H TPhP
2
—
—
—
1.02
0.92
0.34
0.67
0
H T(4-OH-3,5-di-t-BuPh)P
2
1.19
0.57
0.66
0.76
0.55
0.79
0.85
0.07
0.41
0.75
0.47
0.78
0.80
0.42
0.42
0.42
0.42
0.33
0.13
0.37
H T(3-OHPh)P
2
1.03
ZnT(4-OH-3,5-di-t-BuPh)P
ZnT(3-OHPh)P
0.90 (ox/red)
0.75
0.80
—
0.56
—
0.60
—
ZnT(4-OHPh)P
0.65
—
—
H T(4-OHPh)P
0.57
—
—
2
porphyrin, possessing four OH-groups in para-position
O H
of its phenyl rings, exhibits a highest antioxidant capacity
(
Table 1). For H T(4-OHPh)P in ethanol the efficient
2
H
concentration of the antioxidant, CI , required for
50
decreasing first reduction peak of DPPH solution with a
—
-3
concentration of 1 × 10 M by 50%, is found to be 1.3 ×
N
H N
N
-4
1
0 M. H T(4-OH-3,5-di-t-BuPh)P, ZnT(4-OH-3,5-di-t-
2
HO
OH
BuPh)P, H T(3-OHPh)P, ZnT(3-OHPh)P, ZnT(4-OHPh)P
2
NH
antioxidant properties are similar (Table 1). At addition of
the porphyrin solutions to 2,2′-diphenyl-1-picrylhydrazyl
solution a decrease of the peak current of the first and the
second oxidation waves and the conjugated reduction
waves is observed on the CVA (Fig. 3). This testifies
about antioxidant properties of all the studied compounds.
The Zn introduction in the macroheterocycles does not
significantly influence the antioxidant capacity of the
porphyrins. For ZnT(3-OHPh)P and ZnT(4-OH-3,5-di-t-
BuPh)P the parameters of antioxidant capacity are higher
than for corresponding ligands whereas the antioxidant
capacity of ZnT(4-OHPh)P is lower in comparison with
OH
Scheme 2.
O
H
H T(4-OHPh)P. The alteration OH-group location in the
2
phenyl ring from para- to meta-also results in the decrease
of antioxidant properties of tetrakis-(hydroxyphenyl)
porphyrin (Table 1).
P
To estimate the antioxidant capacity of the studied
compounds quantitatively, the CVA of 2,2′-diphenyl-1-
picrylhydrazyl solution was recorded in the presence of
the efficient concentration of the porphyrins at a scan rate
of 200 mV/s for 10 min (Fig. 4). The value of A, index
of efficiency of antioxidant action, was calculated from
the 2,2′-diphenyl-1-picrylhydrazyl peak current values at
initial time (I ) and final time (I ) (after 10 min from the
Scheme 3.
containing OH-group single possible variant of hydrogen
detachment exists. It is breakdown of the O–H bond.
Analogous mechanism of antioxidant action,
homolytical detachment of hydrogen from hydroxyl
group of phenol, has been established earlier for phenol
compounds [21, 22].
The structural alterations of the hydroxyl substituted
tetraphenylporphyrin due to introduction of tret-butyl
substitutes and formation of spatially hindered phenolic
fragment insignificantly decreases antioxidant activity of
thestudiedporphyrins(Table1).Theelectrochemicalstudy
demonstrated that 5,10,15,20-tetrakis(4′-hydroxyphenyl)
0
fin
reaction start) [9]:
I0 − I
fin
A =
(3)
I0
The values of A for the reduction peaks (I) and A
1
2
for the oxidation peaks are presented in Table 1. As can
be seen from the obtained data H T(4-OHPh)P has the
2
highest antioxidant capacity (A = 0.85; A = 0.80).
1
2
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J. Porphyrins Phthalocyanines 2015; 19: 5–7

6
M.V. TESAKOVA ET AL.
Fig. 3. Cyclic voltammograms for 2,2′-diphenyl-1-picrylhydrazyl solution at addition of porphyrins: (a) DPPH + H TPhP in
2
dichloromethane; (b) DPPH + H T(3-OHPh)P in ethanol; (c) DPPH + ZnT(3-OHPh)P in ethanol; (d) DPPH + ZnT(4-OHPh)P in
2
ethanol; (e) DPPH + ZnT(4-OH-3,5-di-t-BuPh)P in ethanol
The values of oxidation potentials, E , of the studied
ox
porphyrins in organic solvents are presented in Table 1.
The value of oxidation potential also shows that among
the studied compounds the most efficient antioxidant is
H T(4-OHPh)P. This porphyrin has the lowest oxidation
2
potential 0.57 V.
CONCLUSION
Synthesis and antioxidant properties of a series of
tetraphenylporphyrinderivativeswithdifferentsubstitutes
in the phenyl rings and their Zn(II) complexes are
presented in this work. The obtained results showed that
all the studied porphyrins exhibit antioxidant properties,
except the unsubstituted tetraphenylporphyrin which
Fig. 4. Cyclic voltammograms for 2,2′-diphenyl-1-picryl-
hydrazyl at addition of efficient concentration of H T(3-OHPh)
2
P in ethanol during 10 min at scan rate of 200 mV/s
does not interact with free 2,2′-diphenyl-1-picrylhydrazyl
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ELECTROCHEMICAL DETERMINATION OF ANTIOXIDANT PROPERTIES OF A SERIES
7
radical. The antioxidant capacity of the porphyrins
increase in the following order:
5. Molyneux P. Songklanakarin. J. Sci. Technol. 2004;
26: 211–219.
H TPhP < H T(4-OH-3,5-di-t-BuPh)P < H T(3-OHPh)
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2
2
2
P < ZnT(3-OHPh)P < ZnT(4-OH-3,5-di-t-BuPh)P < ZnT
(
4-OHPh)P < H T(4-OHPh)P.
2
It has been found that 5,10,15,20-tetrakis(4′-
hydroxyphenyl)porphyrin exhibits the highest antioxidant
activity with respect to 2,2′-diphenyl-1-picrylhydrazyl.
The porphyrin has the lowest anodic potential of
oxidation. This agrees with the fact that the redox
potentials are often correlated with antioxidant ability
of different compounds. Probable mechanism of the
porphyrins antioxidant action is hemolytic detachment of
hydrogen from OH-group of their phenyl rings.
10. Tesakova MV, Popov IA, Sheinin VB, Semeikin
AS, Parfenyuk VI and Koifman OI. Macrohetero-
cycles 2013; 6: 152–157.
The alterations of 5,10,15,20-tetrakis(4′-hydroxy-
phenyl)porphyrin structure due to changes in OH-group
location or introduction of two tret-butyl substitutes lead
to decreasing antioxidant capacity. The introduction of
Zn(II) into the macroheterocycles results in insignificant
decrease of ZnT(4-OHPh)P antioxidant capacity in
11. Popov IA, Kuzmin SM, Chulovskaya SA, Semeikin
AS and Parfenyuk VI. Macroheterocycles 2012; 5:
131–135.
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1999; 35: 1236–1239.
comparison with the ligand H T(4-OHPh)P and leads
2
to increasing antioxidant properties of ZnT(3-OHPh)
P and ZnT(4-OH-3,5-di-t-BuPh)P in comparison with
corresponding ligands.
14. AdlerAD, Longo FR, Kampas F and Kim J. J. Inorg.
Nucl. Chem. 1970; 32: 2443–2445.
15. Tesakova MV, Popov IA and Parfenyuk VI. Russ.
J. Electrochem. 2014; 50: 517–522.
1
6. Tesakova MV, Noskov AV, Parfenyuk VI, Bazanov
Acknowledgements
MI and Berezina NM. Russ. J. Phys. Chem. A 2012;
8
This investigation was supported by the Russian
Fundation for Basic Research (grant no. 13-03-00087)
with financial aid.
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1
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