Antiradical and antioxidant activity of phenylhydrazones of aromatic aldehydes

Article abstract of DOI:10.1023/A:1012749102609

With the aim of searching for new antioxidants, including those of the biogenic type, the antioxidant properties of phenylhydrazones of some aromatic aldehydes were studied under conditions of ascorbate-dependent peroxide oxidation of oleic acid residues

Full text of DOI:10.1023/A:1012749102609

Russian Journal of Applied Chemistry, Vol. 74, No. 5, 2001, pp. 792 795. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 5,
001, pp. 770 774.
Original Russian Text Copyright
2
2001 by Pleskushkina, Nikolaevskii, Filippenko.
ORGANIC SYNTHESIS
AND INDUSTRIAL ORGANIC CHEMISTRY
Antiradical and Antioxidant Activity of Phenylhydrazones
of Aromatic Aldehydes
E. I. Pleskushkina, A. N. Nikolaevskii, and T. A. Filippenko
Donetsk State University, Donetsk, Ukraine
Received April 29, 2000
Abstract With the aim of searching for new antioxidants, including those of the biogenic type, the antioxi-
dant properties of phenylhydrazones of some aromatic aldehydes were studied under conditions of ascorbate-
dependent peroxide oxidation of oleic acid residues in Tween-80. Also the reactivity of these hydrazones
toward a stable radical, diphenylpicrylhydrazyl, was studied. The correlation between the antioxidant and
antiradical activities of phenylhydrazones was examined.
The reactions of free-radical peroxide oxidation of
lipids (POL) in biomembranes not only play an im-
portant role in the normal cell physiology but also
often act as key units of the mechanisms of various
pathological states, including the radiation sickness,
infection and oncological diseases, etc. [1]. Therefore,
search for physiologically active substances exhibiting
antioxidant and antiradical properties and favoring
normalization of the level of peroxide oxidation of
lipids in biomembranes is an urgent problem. It is
interesting to study in this respect phenylhydrazones,
which exhibit a wide spectrum of physiological activ-
ity. It is known that phenylhydrazones (PHs) of some
ketones exhibit antitubercular and antiviral activity
EXPERIMENTAL
The antiradical activity of phenylhydrazones was
studied relative to a stable radical, diphenylpicryl-
hydrazyl (DPPH), as substrate. The reaction was
monitored photocolorimetrically with a KFK-3 device.
Phenylhydrazones [6] of the formulas
R
N
Ph
N
Ar
R = H, Ar = Ph (1);
_
R = H,
Ar =
(2);
[2, 3]. Salicylaldehyde benzoylhydrazone inhibits
DNA synthesis in cells of radiation-sensitive tissues
and is an effective low-toxic radioprotector [4]. It is
believed that the pharmacological effect of phenylhy-
drazone compounds is associated, directly or indirect-
ly, with their effect on the free-radical processes
occurring in a living body. Data on the antioxidant
activity of phenylhydrazones were obtained only
recently [5]. The quantitative evaluation of the anti-
oxidant and antiradical activity of phenylhydrazones
will give insight into the mechanisms of their biolog-
ical effect, on pathways of their transformations in
radical processes, and on the structure antioxidant
activity relationships.
HO
R = CH2Ph, Ar =
(3);
HO
R = CH Ph, Ar = Ph (4)
2
and DPPH [7]
Ph
O N
2
.
N
N
NO2
Ph
O N
2
In this work we studied the antiradical and anti-
oxidant activity of phenylhydrazones and the correla-
tion of their reactivity in radical reactions with their
composition and molecular structure.
were prepared and purified by standard procedures.
The purity of phenylhydrazones was evaluated by
elemental analysis and IR spectroscopy, and that of
DPPH, by IR, UV, and ESR spectroscopy. Solutions
1
070-4272/01/7405-0792$25.00 2001 MAIK Nauka/Interperiodica

ANTIRADICAL AND ANTIOXIDANT ACTIVITY OF PHENYLHYDRAZONES
793
of DPPH in hexane ( = 1.4 10 l mol mm 1),
3
1
1
3
1
benzene ( = 1.24 10 l mol mm ), and methanol
3
1
1
(
= 1.18 10 l mol mm ) exhibit an absorption
maximum in the visible range (520 nm) and are stable
in storage. Solutions of phenylhydrazones and DPPH
were mixed in an equimolar ratio at 293 K in the
range of reactant concentrations 10 4 10 M, after
which variation of the optical density of the DPPH
solution was monitored in time and the kinetic curves
of DPPH consumption were constructed (DPPH solu-
tions in this concentration range obey the Lambert
Beer law).
5
t, min
Fig. 1. Kinetic curves of the reactions of DPPH with phen-
ylhydrazones of (1) benzaldehyde and (2) salicylaldehyde
in hexane solution at 293 K. (t) Time.
The antioxidant activity of phenylhydrazones was
studied in oxidation of Tween-80 (polyoxyethylene
sorbitan monooleate), which is a model of lipid oxida-
tion. Tween-80 purchased from Laba Chemie Fischa-
mend, Austranal Praparate was used without addi-
tional purification. Oxidation of Tween-80 in dilute
aqueous solutions was performed for 48 50 h at
ln C [M]
2
313 K in the presence of optimal concentrations of
Fe(II) and ascorbic acid. The concentration of malon-
dialdehyde (MDA), which is the peroxidation product,
was determined photocolorimetrically from the ab-
sorption of a pink complex of MDA with thiobarbi-
4
1
1
ln C [M]
turic acid ( = 540 nm, = 1.56 10 l mol mm )
8]. The performance of phenylhydrazones as antioxi-
1
[
Fig. 2. Rate of reaction of DPPH with benzaldehyde phen-
ylhydrazone as a function of the concentrations of (1) phen-
ylhydrazone C1 and (2) DPPH C2.
dants was evaluated from the decrease in the concen-
tration of malondialdehyde as compared to the control
experiment.
as follows:
Figure 1 shows the kinetic curves of consumption
of the DPPH radical in its reaction with phenylhydra-
zones of salicylaldehyde and benzaldehyde in hexane.
Study of the reaction rate as a function of the DPPH
and phenylhydrazone concentrations (Fig. 2) showed
that the reaction is first-order with respect to both
DPPH and phenylhydrazone. Such reaction orders are
preserved in hexane for all the compounds studied.
Thus, the kinetic equation for the reaction rate can be
given as follows:
O2N
H
Ph
.
N
+
N
N
NO2
Ph
N
Ar
Ph
O N
2
O N
2
.
H
N
k
Ph
app
N N
NO + Ph
N
Ar.
2
Ph
W = kapp[DPPH][PH].
O N
2
The constants kapp calculated by this equation from
The final products of this reaction, along with the
reduced form of diphenylpicrylhydrazyl (DPPH H),
are probably recombination products of the phenylhy-
drazone radicals with DPPH and of two phenylhydra-
zone radicals.
the initial rates of DPPH consumption are listed in
Table 1. It is seen that the rate constants of this reac-
tion depend on the composition and structure of phen-
ylhydrazones. Benzaldehyde benzylphenylhydrazone
containing no labile hydrogen atom at nitrogen lacks
antioxidant activity. This fact suggests that in the
reaction with DPPH the reactive center in the phenyl-
Comparison of the rate constants for different
phenylhydrazones in hexane (Table 1) shows that
introduction of the hydroxy group into the aldehyde
hydrazone molecule is the NH group of the hydrazone moiety of the phenylhydrazone (compound 2) signif-
moiety. Thus, the reaction pattern can be represented icantly increases kapp as compared to 1. This fact is
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 74 No. 5 2001

794
PLESKUSHKINA et al.
Table 1. Kinetic parameters of the reactions of aromatic
aldehyde phenylhydrazones with DPPH in various solvents
The decrease in the apparent rate constants, in-
crease in the activation energy, and variation of the
preexponential term in going from hexane to benzene
and methanol show that the reactivity of the hydra-
zones decreases in going from hexane to benzene and
methanol. The logarithm of the preexponential term
linearly correlates with the activation energy (Fig. 3),
which suggests the presence of a compensating effect.
This effect is due to the localized interaction of the
reagent with the solvent. For example, in benzene the
decrease in the reaction rates is due to the well-known
capability of DPPH to form complexes with aromat-
ic hydrocarbons, in which the radical is considerably
less reactive than in the nonsolvated state [9]. In
methanol, the reaction center of phenylhydrazone is
blocked as a result of hydrogen bonding with the
solvent [10]. The decrease in kapp and increase in Ea
are in this case due to a decrease in the concentration
of free, more active phenylhydrazone molecules.
A considerably higher rate constant of the reaction
with 2 in methanol, as compared to 1, is due to active
participation in the reaction of the hydroxy group in
the aldehyde fragment of 2. Owing to the high dielec-
tric permittivity of methanol, the hydroxy group dis-
sociates in this solvent to a greater extent.
(T = 293 K)
kapp, l mol 1 s 1
Compd.
no.*
hexane
benzene
methanol
1
2
3
115 5
201 7
0.10 0.01
11 1
16 20
Weak reaction
6.2 0.6
155 2
3.6 0.5
4
5
No reaction with DPPH
1.5 0.2 0.27 0.01 4.5 0.6
*
Compounds: (1) benzaldehyde phenylhydrazone, (2) salicyl-
aldehyde phenylhydrazone, (3) salicylaldehyde benzylphenyl-
hydrazone, (4) benzaldehyde benzylphenylhydrazone, and
(
5) Ionol.
due to additional contribution of the OH group to the
reaction with DPPH, which occurs with the homolytic
cleavage of the O H bond. This contribution can be
estimated by determining the antiradical activity of
the hydrazone containing the hydroxy group in the
aldehyde moiety but lacking the labile hydrogen atom
at N (compound 3). Table 1 shows that this activity
is low, i.e., the main contribution to the reaction with
DPPH (and hence to the antiradical activity) is made
by the NH group.
The activity of the examined phenylhydrazones in
the reaction with DPPH considerably exceeds that of
the commercial inhibitor Ionol.
Study of the solvent effect on the reaction kinetics
showed that the reaction order is the same in all the
tested solvents but the rate constant kapp strongly
depends on the solvent.
Our data on the antiradical activity of phenylhydra-
zones correlate with data on their antioxidant activity
in oxidation of ethylbenzene [5]. This fact shows that
the antioxidant properties of these compounds are due
to their capability for reacting with radicals and con-
firms the suggested mechanism of the antioxidant
action of these compounds in oxidation of hydrocar-
bons. Study of aromatic aldehyde phenylhydrazones
as antioxidants of the ascorbate-dependent peroxide
oxidation of oleic acid residues in Tween-80 showed,
however, that their activity parameters do not always
correlate with the characteristic of the antiradical
activity (Table 2). This may be due to specific features
of oxidation in this system, and also to possible oper-
ation of alternative mechanisms of the antioxidant
effect of phenylhydrazones. At present, the mechan-
ism of lipid oxidation in the presence of peroxide
oxidation cofactors, Fe(II) and ascorbic acid, is not
fully understood. Along with the radical-chain mech-
anism [1], oxidation by the ionic mechanism [11] is
also probable. As seen from Table 2, the antioxidant
activity of phenylhydrazones increases in the order
The apparent rate constants of the reaction of
DPPH with benzaldehyde phenylhydrazone in various
solvents (kapp, l mol 1 s ) were measured at various
1
temperatures in the range 293 323 K, and the follow-
ing relations were obtained:
3
kapp = 2.29 10 exp[( 6800 380)/RT] (hexane),
7
kapp = 2.27 10 exp[( 36000 1200)/RT] (benzene),
4
kapp = 2.33 10 exp[( 20000 1000)/RT] (methanol).
E , kJ mol 1
a
Fig. 3. Correlation between the preexponential term A and
1
< 2 < 4 < 3. The high antioxidant activity of 3 and
activation energy E of the reaction of DPPH with benzal-
a
dehyde phenylhydrazone in various solvents.
4, with their low antiradical effect, is due to the possi-
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ANTIRADICAL AND ANTIOXIDANT ACTIVITY OF PHENYLHYDRAZONES
795
Table 2. Effect of phenylhydrazones of aromatic alde-
hydes on the rate of accumulation of malondialdehyde
oxidation of oleic acid residues in Tween-80 in aque-
ous solutions. This is due to specific features of oxi-
dation of this system and to possible operation of
alternative mechanisms of antioxidant action.
(MDA) in oxidation of Tween-80
6
MDA concentration C 10 , M Decrease in
Compd.
no.
MDA accumu-
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