Trialkylantimony(V) o-amidophenolates: Electrochemical transformations and antiradical activity

Article abstract of DOI:10.1134/S107032841405011X

The electrochemical transformations and antiradical activity of trialkylantimony(V) o-amidophenolate derivatives, (AP)SbR₃ (AP = 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)-o-amidophenolate); R = CH ₃ (I), C₂H₅

Full text of DOI:10.1134/S107032841405011X

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2014, Vol. 40, No. 5, pp. 273–279. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © S.A. Smolyaninova, A.I. Poddel’sky, I.V. Smolyaninov, N.T. Berberova, 2014, published in Koordinatsionnaya Khimiya, 2014, Vol. 40, No. 5, pp. 274–
280.
Trialkylantimony(V) oꢀAmidophenolates: Electrochemical
Transformations and Antiradical Activity
S. A. Smolyaninovaa, *, A. I. Poddel’skyb, I. V. Smolyaninovc, and N. T. Berberovaa
a Astrakhan State Technical University, ul. Tatishcheva 16, Astrakhan, 414025 Russia
b Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences,
ul. Tropinina 49, Nizhnii Novgorod, 603600 Russia
c Southern Research Center, Russian Academy of Sciences, Astrakhan, Russia
*eꢀmail: thiophen@mail.ru
Received August 12, 2013
Abstract—The electrochemical transformations and antiradical activity of trialkylantimony(V)
dophenolate derivatives, (AP)SbR3 (AP = 4,6ꢀdiꢀtertꢀbutylꢀ ꢀ(2,6ꢀdiisopropylphenyl)ꢀ ꢀamidophenolate);
R = CH3 ( ), C2H5 (II), and C6H11 III), are studied. The electrochemical oxidation of compounds III
oꢀamiꢀ
N
o
I
(
I–
proceeds successively to form monoꢀ and dicationic forms of the complexes. The presence of the donor
hydrocarbon groups at the antimony(V) atom shifts the oxidation potentials to the cathodic range and
decreases the stability of the monocationic complexes formed in electrochemical oxidation. The second
anodic process is irreversible and accompanied by
of compounds III is studied in the reaction with the diphenylpicrylhydrazyl radical and oleic acid autooxꢀ
idation. The values obtained for indices EC50 and IC50 indicate the antiradical activity of the studied comꢀ
pounds. Complexes I–III were found to be the efficient inhibitors of oleic acid oxidation and act as efficient
oꢀiminoquinone decoordination. The antiradical activity
I–
destructors of hydroperoxides.
DOI: 10.1134/S107032841405011X
INTRODUCTION
istry is the complex formation of pharmacologically
active organic substrates with organometallic derivaꢀ
tives of transition metals [9, 10]. The result of such a
symbiosis is the manifestation of a new type of activity
or the modulation of the known one [11]. Organic
ligands can be centers of redox reactions in addition to
the metal center. Examples of this type of ligands are
sterically hindered phenol derivatives, catecholates,
aminophenols, polyphenols, and flavonoids.
The redox properties and antiradical activity of the triꢀ
A new approach based on the modification of
structures of compounds by the introduction of metal
atoms is being developed in the antioxidant chemistry
[1]. Syntheses of lowꢀmolecularꢀweight metalꢀconꢀ
taining antioxidants and studies of their biological
activity in vitro and in vivo is caused by their antiꢀ
inflammatory and neuroprotective action and antiradꢀ
ical activity; and these objects can be considered as
promising chemopreventive agents [2–4]. A search for
biologically active substances in a series of organomeꢀ
tallic derivatives of nontransition metals is related to
their ability to manifest both antiꢀ and prooxidant
properties, depending on the method of introduction
and the place and time of their application. The orgaꢀ
nometallic antimony(V) derivatives attract attention
due to a variety of coordination modes and promising
biological properties [5–7].
alkylantimony(V)
oꢀamidophenolate derivatives
(Scheme 1) were studied in the present work.
But
[AP]SbR3
O
R = CH3 (
R = C2H5 (II);
R = C6H11 III
I);
SbR3
But
N
(
)
Pri
Pri
Toxicity and physiological response of organomeꢀ
tallic compounds depend on the oxidation states of
both the metal and organic ligands to which the metal
is bound. The variation of the ligand environment
affects significantly the properties of the formed comꢀ
Scheme 1.
Several centers can be distinguished in the strucꢀ
pounds [8]. The variation of the ligand nature and the ture of the studied molecules: the redoxꢀactive organic
redox state of the metal center is a possibility to conꢀ fragment, antimony(V) atom, and hydrophobic
trol the thermodynamic and kinetic characteristics organic groups. Sterically hindered oꢀ and pꢀamiꢀ
and the biological activity of the complexes. One of nophenols are redoxꢀactive molecules and can maniꢀ
the currently developed trends in bioinorganic chemꢀ fest either proꢀ or antioxidant activity, depending on
273

274
SMOLYANINOVA et al.
1
conditions [12]. Hydroxyanthranilic acid is a natural 544 w, 528 s, 511 s, 481 m, 450 w, 431 w. H NMR
prototype of ꢀaminophenols and one of physiologiꢀ (200 MHz, CDCl3 20 ), , ppm: 1.06 (s, 9H, ꢀBu),
cally active compounds capable of acting as the second 1.11 (d, 3JHH = 6.9 Hz, 6H, 2 CH(CH3)2), 1.12 (s, 9H,
line of antioxidant protection after ascorbate and
ꢀBu), 1.19 (d, 3JHH = 6.9 Hz, 6H, 2 CH(CH3)2), 1.44
o
,
°
C
δ
t
t
3
ubiquinone that provide the protection of lowꢀdensity (s, 9H, SbMe3), 3.15 (sept, JHH = 6.9 Hz, 2H,
lipoproteins from both radical and nonradical oxiꢀ 2 CH(CH3)2), 5.83 (d, 4JHH = 2.3 Hz, 1H, C6H2), 6.58
4
dants [13]. The introduction of the sterically hindered (d, JHH = 2.3 Hz, 1H, C6H2); 7.14–7.37 (m, 3H,
oꢀaminophenolate fragment into the structures of the C6H3).
studied objects can considerably increase the reductive
activity of the compounds.
For C29H46NOSb
The study of the electrochemical behavior of orgaꢀ
nometallic compounds makes it possible to model
reactions with oxidants and to monitor products
formed due to the interaction. As shown earlier for a
series of the triphenylantimony(V) complexes with the
redoxꢀactive ligands, the variation of substituents in
the carbon aromatic ring or the replacement of the
heteroatom in the metallocycle allow to control
anal. calcd., %: C, 63.74; H, 8.48; N, 2.56; Sb, 22.28.
Found, %:
C, 64.01; H, 8.53; N, 2.29; Sb, 22.15.
Compounds II and III were synthesized using
described procedures [16, 17].
1H and 13C NMR spectra were recorded on a
Bruker AVANCE DPXꢀ200 spectrometer using tetꢀ
ramethylsilane as an internal standard and CDCl3 as a
solvent. IR spectra were measured on an FSM 1201
FTꢀIR spectrometer in Nujol. Experiments on synꢀ
theses of the complexes were carried out in evacuated
ampules without oxygen. Absorption spectra were
recorded on an SFꢀ103 spectrophotometer in a range
of 220–1100 nm at room temperature. EPR spectra
were detected on a Bruker EMX spectrometer at a
working frequency of ~9.5 GHz. Hyperfine coupling
constants were determined using the simulation of
theoretical spectra by the Simfonia program (Bruker).
The solvents used were purified and degassed using
standard procedures [18].
the potential of the catecholate(oꢀamidophenoꢀ
late)/ ꢀsemiquinone( ꢀiminosemiquinone) transiꢀ
o
o
tion, thus facilitating or impeding oxidation [14, 15].
In this work, we are intending to evaluate the influence
of the hydrocarbon groups at the antimony atom on
the redox transformations of the (AP)SbR3 complexes
(AP = 4,6ꢀdiꢀtertꢀbutylꢀ
ꢀamidophenolate; R = CH3 (
III)) and their antiradical activity in the reactions
N
ꢀ(2,6ꢀdiisopropylphenyl)ꢀ
o
(
I), C2H5 (II), and C6H11
with the diphenylpicrylhydrazyl radical and in the
inhibition of oleic (cisꢀ9ꢀoctadecenoic) acid oxidaꢀ
tion.
The existence of several redox forms of the ligand
(oꢀamidophenolate/oꢀiminosemiquinolate/oꢀiminobenꢀ
Commercial reagents (2,2ꢀdiphenylꢀ1ꢀpicrylhyꢀ
drazyl (DPPH) radical (Aldrich), [(C5H5)2Fe]BF4
(Aldrich), and oleic (cisꢀ9ꢀoctadecenoic) acid (97%,
Acros Organics)) were used without additional purifiꢀ
cation.
zoquinone) and the presence of donor hydrocarbon
groups at the antimony(V) atom and labile Sb–C bonds
provides a dual anti/prooxidant behavior of similar comꢀ
pounds.
The electrochemical potentials of the studied comꢀ
pounds were measured by cyclic voltammetry (CV) in a
threeꢀelectrode cell using an IPCꢀpro potentiostat in
dichloromethane under argon. The stationary glassyꢀ
carbon (GC) electrode with a diameter of 2 mm was used
EXPERIMENTAL
Synthesis of trimethylantimony(V) (
N
ꢀ(2,6ꢀ
diisopropylphenyl)ꢀ4,6ꢀdiꢀtertꢀbutylꢀ
oꢀamidopheꢀ
nolate) (AP)SbMe3 (I). A portion of a 1 M solution
as a working electrode, and a platinum wire (S
= 18 mm2)
of Me3Sb in toluene was added dropwise with stirꢀ
ring to a solution of
Nꢀ(2,6ꢀdiisopropylphenyl)ꢀ
served as an auxiliary electrode. The reference electrode
(Ag/AgCl/KCl) was equipped with a waterꢀimpervious
membrane. The concentration of compounds I–III was
0.003 mol/L. The number of electrons transferred in the
electrode process was estimated versus ferrocene as a
standard. The potential scan rate was 0.2 V/s. The supꢀ
porting electrolyte was 0.1 M Bu4NClO4 (99%, Acros).
The microelectrolysis of complex II was carried out using
a PIꢀ50ꢀ1.1 potentiostat on stationary platinum elecꢀ
trodes (plates with a surface area of 30 mm2) in an undiꢀ
vided threeꢀelectrode cell (2 mL) at a potential of 0.6 V
4,6ꢀdiꢀtertꢀbutylꢀ ꢀiminobenzoquinone (0.250 g,
o
0.66 mmol) in toluene (15–20 mL) until the cherry
color of the solution turned yellow completely.
Toluene was evaporated in vacuo, and the residue
was heated at 50
in pentane (20 mL). The obtained solution was
cooled to –12 and stored at this temperature for
24 h, a finely crystalline pale yellow powder of
°С for 20 min and then dissolved
°
C
complex
(82%).
I was obtained. The yield was 0.295 g
IR (ν
, cm–1): 1567 m, 1442 s, 1419 s, 1365 m, (electrolysis time 3 h, conversion of the complex 84%).
1334 m, 1320 m, 1288 s, 1245 s, 1222 w, 1200 m, The Ag/AgCl/KCl electrode with an electroconducting
1176 w, 1122 w, 1101 w, 1051 m, 1040 w, 1025 m, 995 s, waterꢀimpervious membrane was used as a reference
926 m, 904 m, 861 m, 851 s, 823 s, 803 s, 771 m, electrode. Complex II
(c = 0.003 mol/L) was added to a
762 m, 712 m, 679 w, 652 m, 606 w, 585 w, 555 m, predeaerated electrochemical cell containing a solution
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TRIALKYLANTIMONY(V)
o
ꢀAMIDOPHENOLATES
275
of the supporting electrolyte (0.1 mol/L
dichloromethane.
n
ꢀBu4NClO4) in initial level for 5 h of oleic acid autooxidation. To
determine IC50, the concentration of complexes I–III
was varied from 0.01 to 1 mmol/L. Therefore, the
lower the IC50 index, the higher the antiradical activity
of the complexes. The results are presented as average
values of three independent experiments.
The antiradical activity of complexes I–III in the
reactions with the DPPH radical in dichloromethane
was determined using a described procedure [4]. Oleic
acid was oxidized in the presence of compounds I–III
in a temperatureꢀcontrolled cell (60°C) at an air flow
rate of 2–4 mL/min for 5 h. Since oleic acid oxidation
proceeds as autooxidation, preliminary air bubbling
was carried out for 2 h before the compounds were
introduced. The concentration of the additives was
1 mmol/L. The activity of the studied compounds
during oleic acid oxidation was estimated by a stanꢀ
dard method from the amount of formed isomeric
hydroperoxides (LOOH) [19].
RESULTS AND DISCUSSION
The electrochemical properties of the antimony(V)
compounds were studied by the CV method (Table 1).
Complexes I–III are oxidized at the GC electrode in
dichloromethane in two successive stages. The first redox
transition for the studied complexes is the quasiꢀreversꢀ
ible oneꢀelectron process. The cyclic voltammogram for
The index of inhibition efficiency (IE) for oleic the oxidation of the triethylantimony 4,6ꢀdiꢀtert
acid autooxidation was determined by the formula ꢀ(2,6ꢀdiisopropylphenyl)ꢀ ꢀamidophenolate
IE = [(1 – сi с0 100%], where сi is the concentration plex (II) is shown in Fig. 1. For compounds I–III, the
of hydroperoxides in the presence of an additive of the first anodic process corresponds to the change in the
complexes (1 mmol/L), and с0 is the content of LOOH redox state of the coordinated ligand: the ꢀamidopheꢀ
formed in the control sample for 5 h. The IC50 index is nolate (AP)– ꢀiminobenzosemiquinone (ISQ) transiꢀ
ꢀ
butylꢀ
comꢀ
N
o
/
) ×
o
o
the inhibitor concentration necessary for decreasing tion occurs to generate monocationic complexes
the concentration of hydroperoxides by 50% of the [(ISQ)SbR3]+ in the nearꢀelectrode region (Scheme 2).
+
++
But
But
But
O
O
N
O
N
SbR3
Pri
SbR3
Pri
•
SbR3
Pri
–e
+e
–e
But
But
N
But
iPr
iPr
iPr
[AP]SbR3
[(ISQ)SbR3]+
[(IBQ)SbR3]+
+
2+
H
–[SbR ]
3
But
iPr
But
But
O•
OH
O
N
2
+
But
But
But
NH
NH
Pri
Pri
iPr
Pri
iPr
ISQH
APH2
IBQ
Scheme 2.
Unlike the earlier studied triphenylantimony comꢀ the voltammogram (–0.82 V) corresponding to the
product of the destruction of complexes, which is
formed after the first anodic stage.
plex (AP)SbPh3 (IV), compounds I–III are characterꢀ
ized by a decrease in the reversibility coefficient (Iс Iа
/
)
(Table 1), indicating a decrease in the stability of the
monocationic forms of the complexes formed in the
electrochemical reaction. The chemical stage followꢀ
ing the electron transfer occurs in the nearꢀelectrode
region (Scheme 2). This conclusion is confirmed by
the irreversible cathodic peak in the reverse branch of
Unlike complexes I–III, this peak for compound IV
appeared only after the second redox process that
characterizes the formation of the dicationic complex.
The detected cathodic process corresponds to the
reduction of decoordinated
oꢀiminobenzoquinone
(
IBQ) (Fig. 1) formed due to the disproportionation of
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276
SMOLYANINOVA et al.
Table 1. Oxidation potentials of the antimony(V) complexꢀ
structure (Fig. 2). The spectrum detected at a lowered
temperature (203–243 K) is a superposition of signals
from two paramagnetic species: the cationic complex
es according to the CV method*
2
E11 2
Compound
Ic/
Ia
n
V
n
[(ISQ)SbMe3][BF4] and
o
ꢀaminophenoxyl radical
Ep,
V
,
(ISQH) [21]. Compound
I
is oxidized with the
decomposition of the monocationic complex accomꢀ
panied by the decoordination and protonation of the
(AP)SbMe3 (
I
)
0.41 0.63 1.0 0.97
0.41 0.71 1.0 0.98
0.35 0.78 1.0 1.17
n
n
n
< 1
< 1
< 1
(AP)SbEt3 (II
)
oꢀiminobenzosemiquinone radical anion. The temꢀ
perature increase results in the disappearance of the
signal from [(ISQ)SbMe3][BF4] and an increase in the
intensity of the signal from ISQH radical.
(AP)Sb(C6H11)3(III
)
(AP)SbPh3 (IV) [15] 0.50 0.94 1.0 1.27
1.0
The electrochemical oxidation of compounds
I
* GC electrode, CH Cl ,
V
= 0.2 V/s, 0.1 M NBu ClO ,
c
= 3
10 mol/L, Ar, vs. Ag/AgCl/KCl (sat.); E1 2 is the halfꢀwave
potential of the first anodic process, is the ratio of currents
×
2
2
4
4
and II at the first stage is accompanied by ꢀiminobenꢀ
o
1
–3
zoquinone decoordination and also by the evolution of
gaseous products at the auxiliary electrode. Similar
phenomena were earlier detected for the triethylantiꢀ
mony(V) complexes with the redoxꢀactive ligands [22,
23]. Evidently, the electron transfer results in the
cleavage of the labile Sb–C bond [24] leading to the
liberation of active methyl and ethyl radicals that
undergo further reactions: recombination on the surꢀ
face of the auxiliary electrode or interaction with the
solvent.
I /I
c a
of the reverse cathodic and direct anodic peaks, n is the number
of electrons transferred during the redox process relatively to
ferrocene as a standard, and Ep2 is the potential of the oxidation
peak of the second anodic process.
the oꢀaminophenoxyl radical (ISQH). The microꢀ
electrolysis of complex II at the controlled potential
(0.6 V) is accompanied by the colorization of the soluꢀ
tion. A new band corresponding to the formation of
The extension of the potential scan range to the
anodic region results in the detection of the second
oxidation stage (Fig. 1). This redox transition for comꢀ
plexes I–III is irreversible and corresponds to the
sterically hindered oꢀiminobenzoquinone appears in
the visible range (λmax = 390 nm) in the absorption
spectrum [20].
transformation of the
oꢀiminobenzosemiquinone
The reaction of compound I with ferrocenium tetꢀ
rafluoroborate ([Fc][BF4]) as a oneꢀelectron oxidant
was carried out at reduced temperature to confirm the
oxidation mechanism of the complexes. The oxidation
of compound
the EPR spectrum (gi = 2.0023) with a weakly resolved
I is accompanied by the appearance of
263 K
I
, mA
0.05
0.04
0.03
0.02
0.01
0
1
2
243 K
223 K
–0.01
–0.02
203 K
–0.95
–0.45
0.05
0.55
1.05
, V
E
3360 3380 3400 3420 3440 3460 3480 3500 3520
, Oe
Fig. 1. Cyclic voltammogram of the oxidation of
complex II at the potential scan ( ) from –0.20 to 1.20 V
and ( ) from –0.92 to 0.60 V (CH Cl , GC anode,
Ag/AgCl/KCl, 0.1 M NBu ClO ,
H
1
2
2
= 3
2
×
–3
c
10 mol/L,
Fig. 2. EPR spectrum of the (AP)SbMe –[Fc][BF ] sysꢀ
3 4
tem (THF, temperature increase from 203 to 263 K).
4
4
argon).
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TRIALKYLANTIMONY(V)
o
ꢀAMIDOPHENOLATES
277
Table 2. Antiradical activity of compounds
with the DPPH radical (CH2Cl2, 298 K) and in the autooxꢀ
idation of oleic acid*
I
–
IV in a test
form of the ligand (ISQ) into the oꢀiminobenzoꢀ
quinone form (IBQ) to produce the corresponding
dicationic complexes [(IBQ)SbR3]++ unstable in the
time scale of CV experiment. The number of transꢀ
ferred electrons is less than one, which is caused by
chemical transformations of intermediates formed in
the first redox stage. The obtained results indicate the
overall decrease in the stability of the oxidized forms of
complexes I–III compared to the triphenylantiꢀ
IC50,
Compound
EC50,
µmol
EI, %
µmol
(AP)SbMe3 (
I
)
18.9 1.2
13.7 0.8
17.6 0.6
9.0 1.3
21.0 0.9
19.5 1.2
21.2 0.7
92.7
94.4
(AP)SbEt3 (II
)
(AP)Sb(C6H11)3 (III
(AP)SbPh3 (IV) [4]
)
97.8
mony(V) derivatives containing the
late ligand.
oꢀamidophenoꢀ
97.5
* EC is the index of antiradical activity of complexes
I
–
IV in the
The value of the oxidation potential of the comꢀ
plexes is affected by the nature of groups at the antiꢀ
mony atom: electronꢀdonor alkyl substituents shift the
1
50
reaction with the DPPH radical, IC is the minimum concenꢀ
50
tration of the antimony(V) complexes resulting in a decrease in
the hydroperoxide content by 50% of the initial level, and IE is the
index of inhibition efficiency for the autooxidation of oleic acid.
parameter to the cathodic region, and the maxiꢀ
E1 2
mum effect is observed for the cyclohexyl group (the
potential shift compared to that of complex IV is
0.15 V). The oxidation potentials remain unchanged
oleic (cisꢀ9ꢀoctadecenoic) acid at 60°С. The peroxide
oxidation of a substrate was controlled by the change
in the concentration of hydroperoxides (LOOH), the
major products of the primary stage of oxidation. The
introduction of additives of compounds I–III
decreases the initial level of hydroperoxides (Fig. 3,
curves 1–3). Then the LOOH concentration remains
almost unchanged during the experiment and
increases regularly in the control experiment (Fig. 3,
on going from methylꢀsubstituted complex
plex II
I to comꢀ
.
The CV method makes it possible to study redox
transformations of organometallic compounds and
also to predict their antiradical activity in vitro
.
The easier the oxidation, the higher the reducing
properties and the probability of interaction with
active species. Therefore, most easily oxidizable comꢀ
plexes I–III should be more efficient radical scavenꢀ
curve 4).
gers than a similar triphenylantimony(V)
oꢀamiꢀ
The addition of complexes I–III exerts an inhibiꢀ
tion effect on the development of the radical chain
process compared to the control experiment. In the
presence of the studied complexes, the amount of
LOOH does not increase but, vice versa, they decomꢀ
pose. The comparative data on the efficiency of the
inhibition effect of complexes I–III are presented
in Table 2. All complexes exhibit high inhibition activꢀ
dophenolate complex. However, the possibility of the
homolytic cleavage of the Sb–C bond in the course of
oxidation of the studied compounds and, hence, the
generation of active alkyl radicals can result in the
prooxidant effect.
It has earlier been shown that the triphenylantiꢀ
mony(V) complexes with the catecholate and oꢀamiꢀ
dophenolate ligands manifest the antiradical activity
[4]. Experiments with the DPPH radical were carried
out to establish the influence of substituents at the
antimony atom on the antiradical activity of the studꢀ
ied compounds and its ability to exhibit the dual
anti/prooxidant properties and the activity of comꢀ
plexes I–III in the inhibition of oleic acid oxidation
was estimated.
c
LOOH, mmol/L
120
100
80
4
The reactions of the DPPH radical with comꢀ
pounds I–III were carried out in a deaerated solution
of CH2Cl2 at 298 K. The introduction of complexes I–
III into a solution containing the DPPH radical
decreases the intensity of the absorption maximum at
527 nm, indicating that the reaction occurs (Table 1).
The possibility of occurrence of the reaction between
the complexes and DPPH radical assumes their ability
to act as efficient radical interceptors, which is conꢀ
firmed by the obtained values of EC50 (Table 2). The
60
40
1
2
3
20
0
2
4
6
8
10 12 14 16 18
τ × 10–3, s
minimum value of EC50 was obtained for complex II
The indices of antiradical activity of complexes I–III
are close to the data for ꢀalkylaminophenols [25].
.
Fig. 3. Kinetic curves of LOOH accumulation in the oxiꢀ
dation of oleic acid at 60°C in the presence of additives
(1 mmol/L) of (1) (AP)SbMe , (2) (AP)SbEt , and
(3) (AP)Sb(C H ) and (4) without additives.
6 11 3
p
The study of the antiradical activity of the studied
compounds was continued for the autooxidation of
3 3
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SMOLYANINOVA et al.
ity. Nearly identical values were detected for comꢀ the hydrocarbon groups at the antimony atom. For
pounds III and IV containing cyclohexyl and phenyl complexes I–III the introduction of donor
groups.
,
groups shifts the oxidation potentials to the cathodic
region, and the stability of the oxidized forms of the
complexes decreases considerably. The lability of the
Sb–C bond assumes that active intermediates capable
of intensifying the development of radical chain oxiꢀ
dation are generated in the oxidation process.
However, the obtained values of EC50 and IC50 indiꢀ
cate the manifestation of the antiradical activity of
complexes I–III. Evidently, the presence of the redoxꢀ
The activity of complexes I–III during LOOH
decomposition is clearly demonstrated by the IC50
index determined in the experiment with oleic acid
preliminarily subjected to autooxidation (60°С, 5 h)
with a high initial concentration of hydroperoxides.
The variation of concentrations of compounds I–III
made it possible to establish the minimum values at
which the LOOH concentration decreased by 50%.
For complexes I–III, the IC50 indices are observed in
the micromolar concentration range and are close. All
complexes demonstrate high activity in the inhibition
of oleic acid oxidation. The studied trialkylantiꢀ
active oꢀamidophenolate ligand plays the key role in
the inhibition effect of these compounds, and the
nature of the hydrocarbon groups at the antimony
atom exerts a minor effect on the total antiradical
activity.
mony(V) oꢀamidophenolates can be considered as
inhibitors of the radical chain process and also as effiꢀ
cient destructors of hydroperoxides.
ACKNOWLEDGMENTS
The organometallic derivatives of antimony
Ph3Sb, Ph3SbHal2) and tin (R2SnHal2, R3SnHal,
This work was supported by the Russian Foundaꢀ
tion for Basic Research (projects nos. 12ꢀ03ꢀ31026
and 13ꢀ03ꢀ00487) and the President of the Russian
Federation (grants nos. MKꢀ445.2014.3, NShꢀ
271.2014.3).
(
RnSnL4–n) are known as promoters of the peroxidation
of unsaturated fatty acids and lipids [4, 26–29].
The such behavior is caused by the easy cleavage of the
σꢀM–R bond upon the interaction with the LOO radꢀ
icals. The indirectly detected products of the partial
(CH3i , C2H5i )
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Translated by E. Yablonskaya
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
No. 5
2014