Electrochemical oxidation of caffeic and ferulic acid derivatives in aprotic medium

Article abstract of DOI:10.1590/S0103-50532011000400012

We studied the electrochemical behaviour as a function of the structure of a series of caffeic and ferulic acids derivatives as well as their corresponding redox moieties catechol and guaiacol by cyclic voltammetry. Results revealed that the medium is key

Full text of DOI:10.1590/S0103-50532011000400012

J. Braz. Chem. Soc., Vol. 22, No. 4, 693-701, 2011.
Printed in Brazil - ©2011 Sociedade Brasileira de Química
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Article
A
Electrochemical Oxidation of Caffeic and Ferulic Acid Derivatives in Aprotic Medium
Magali Salas-Reyes,*,a Javier Hernández,a Zaira Domínguez,a Felipe J. González,b
Pablo D. Astudillo,b Rosa Elena Navarro,c Evelin Martínez-Benavidez,d,a
Carlos Velázquez-Contrerase and Samuel Cruz-Sáncheza
aUnidad de Servicios de Apoyo en Resolución Analítica, Universidad Veracruzana,
Apdo. Postal 575, Xalapa, Ver., México
bDepartamento de Química del Centro de Investigación y Estudios Avanzados, Av. Instituto
Politécnico Nacional 2508, 07360, Apdo. Postal 14-740, México, D. F., México
cDepartamento de Investigación en Polímeros y Materiales, Hermosillo, Son., México
dInstituto de Ciencias Básicas, Universidad Veracruzana, Apdo. Postal 525, Xalapa, Ver., México
eDepartamento de Ciencias Químico Biológicas, Universidad de Sonora, 83000, Hermosillo, Son., México
O comportamento eletroquímico em função da estrutura de uma série de derivados dos ácidos
cafeico e ferúlico, assim como de seus precursores catecol e guaiacol, eletroquimicamente ativos, foi
avaliado por voltametria cíclica. Os resultados revelaram que as condições experimentais são a chave
para as mudanças no mecanismo de oxidação do guaiacol e ácido ferúlico.A oxidação eletroquímica
dos derivados amida do ácido ferúlico revelou que o átomo de nitrogênio desempenha um papel
importante na derivatização da superfície do eletrodo. Além disso, a atividade sequestradora de
radicais dos compostos, avaliada através da porcentagem de inibição do radical 2,2’-difenil-1-
picril-hidrazila, mostrou uma boa correlação com os potenciais de oxidação.
We studied the electrochemical behaviour as a function of the structure of a series of caffeic
and ferulic acids derivatives as well as their corresponding redox moieties catechol and guaiacol
by cyclic voltammetry. Results revealed that the medium is key for changes in the oxidation
mechanism of guaiacol and ferulic acid. Electrochemical oxidation of the ferulic acid amide
derivatives revealed that the nitrogen atom plays an important role in the derivatization of the
electrode surface. In addition, radical scavenging activity of the compounds evaluated through the
percentage of inhibition of the 2,2’-diphenyl-1-picrylhidrazyl radical showed a good relationship
with the oxidation potentials.
Keywords: cyclic voltammetry, hydroxycinnamic acids, caffeic acid phenethyl ester,
antioxidant activity, DPPH radical
Introduction
It has been demonstrated that CAPE is an efficient free
radical scavenger and an inhibitor of some enzymes as
cyclooxygenase,17 lipoxygenase, and the HIV-1 integrase.5,18
Additionally, it possesses antiinflammatory and antitumor
activities.14-16 Particularly, the antitumor activity of CAPE
has been related to its capacity to induce apoptosis and also
to modulate the cellular redox states.19,20
Since the biological activity of CA and FA is related to
the electron transfer processes, several mechanistic studies
on the electrochemical oxidation of these acids have been
documented in the literature.21-25 However, to the best of
our knowledge, no study has been focused to understand
the electrochemical behavior of its corresponding esters
Caffeic (CA) and ferulic (FA) acids and their
corresponding esters are widely distributed in plants and
also in propolis from diverse geographic zones of the
world.1,2 During the last years, these compounds have
received the attention of numerous research groups since
it has been suggested that some of them have important
biological properties.3-18 Special interest has received
caffeic acid phenethyl ester (CAPE), which is one of the
most active components isolated from honeybee propolis.
*e-mail: magasalas@uv.mx

694
Electrochemical Oxidation of Caffeic and Ferulic Acid Derivatives in Aprotic Medium
J. Braz. Chem. Soc.
or amides, nevertheless some compounds such as CAPE
and caffeic acid phenethyl amide (CAPEA) have shown
even higher in vitro antioxidant activity respect to that of
CA.9,10,26
ferulic acid (FA) (99%), dihydrocaffeic acid (DHCA)
(99%), caffeic acid (CA) (99%), and 2,2´-diphenyl-1-
picrylhidrazyl radical (DPPH) were purchased from
Sigma-Aldrich.Acetonitrile (AN) (content of H2O < 0.1%),
dimethylsulfoxide (DMSO) (content of H2O < 0.1%)
spectra grade (Merck Uvasol) and ethanol chromasolv®
were used as solvents. Caffeic acid phenethyl ester
(CAPE) was prepared according to the procedure reported
by Grunberger.27 All of the amides were synthesized
from the free acid and the corresponding amine using
(benzotriazol-1-yloxy)tris(dimethylamino)phosphonium
hexafluorophosphate (BOP) as coupling reagent, as has
been described before.9
In the present work the anodic oxidation of a series of
caffeic and ferulic acids derivatives (Figure 1) in aprotic
medium is reported, as well as for their corresponding redox
moieties catechol (C) and guaiacol (G). Some mechanistic
details of the redox behavior of the complete series were
investigated and are also discussed here, since they may be
related to the known antioxidant properties of this kind of
compounds in biological systems. The radical scavenging
activity of the ten compounds was also evaluated using the
DPPH assay, in order to analyze if there is a relationship
between this property and the corresponding potential
oxidation value.
Free radical scavenging activity (DPPH assay)
The free radical scavenging activity (FRS) was
measured according to the following procedure: 500 mL
of a 2,2´-diphenyl-1-picrylhidrazyl radical (DPPH)
ethanolic solution (300 mmol L-1) was mixed with the same
volume of the test compound solution (17.5 mmol L-1).
The reaction mixtures were vigorously vortexed for
10 s. Absorbance of the resulting solutions was read at
Experimental
Chemicals
Tetrabutylammonium hexafluorophosphate 98%
(n-Bu4NPF6), catechol (C) (99%), guaiacol (G) (> 98%),
O
HO
HO
G
HO
C
O
O
O
HO
HO
HO
HO
O
OH
OH
OH
HO
DHCA
FA
CA
O
O
HO
HO
N
O
H
HO
HO
CAPE
CAPEA
O
HO
HO
N
H
CABzA
O
O
O
O
N
N
H
H
HO
HO
FAPEA
FABzA
Figure 1. Compounds studied in the present work.

Vol. 22, No. 4, 2011
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695
517 nm in a spectrophotometer (Varian, CARY 100), after
30 min of incubation at room temperature in darkness.
The scavenging activity was determined by comparing
the absorbance with that of the blank containing only
2,2´-diphenyl-1-picrylhidrazyl radical (DPPH) and ethanol.
Results were expressed as inhibition percentage.3
Instrumentation and electrodes
Cyclic voltammetry and coulometry experiments were
performed in a radiometer potentiostat 1MT102-DEA332
with positive feedback resistance compensation. A three-
electrode cell was used in the electrochemical experiments.
The working electrode was a 3 mm diameter glassy carbon
disk (Sigradur G from HTW, Germany). This electrode
was polished with 1 mm alumina powder and rinsed in
ultrasound bath with distilled water and ethanol before
each run. Platinum mesh was used as counter electrode
and saturated calomel electrode (SCE) as reference. The
reference electrode was connected to the cell through a
salt bridge containing the same supporting electrolyte
concentration as the working solution.All electrochemical
experiments were performed at 25 °C under an argon
atmosphere. Coulometry was carried out with a glassy
carbon rotating rod electrode under constant rotation
(1000 rpm) and controlled potential.
Figure 2. Cyclic voltammetry in acetonitrile + 0.2 mol L-1 n-Bu4NPF6,
on glassy carbon electrode (3 mm f) at 2 mmol L-1 and 0.1 V s-1 of
a) CAPE and b) FA.
The electrochemical responses of CA, DHCA, and
CAPE under these experimental conditions are similar to
that found for catechol, and are in good agreement with the
anodic oxidation of hydroquinone (an isomer of catechol)
reported before,28-32 which follows an ECE mechanism that
involves the lost of one electron in the system, followed
by a fast deprotonation reaction and, finally, the lost of a
second electron. Scheme 1 shows the complete mechanism,
which is the starting point for the following discussion. A
further deprotonation reaction is also included as the last
step, since additional spectroscopic studies have suggested
that the o-quinone (Q) is obtained as the final product.28
In Figure 2b, it can also be observed that the
voltammogram of FA did not show significant differences
with respect to the electrochemical responses of catechol
and caffeic acid derivatives, such as CAPE (Figure 2a).
Consequently, a two-electron mechanism is also involved
in the oxidation of G and FA in acetonitrile. Despite the
fact that the electrochemical oxidation of both compounds
is still unclear, it is known that the mechanism involves
the o-quinone form, which has been identified as the main
product obtained during the oxidation of FA.25,28
Results and Discussion
Electrochemical study of the oxidation process of C, G, CA,
DHCA, CAPE and FA
The electrochemical behaviour in acetonitrile of caffeic
acid (CA), dihydrocaffeic acid (DHCA), caffeic acid
phenethyl ester (CAPE), guaiacol (G), and ferulic acid (FA)
showed a typical chemically irreversible oxidation wave
(I) and the corresponding broadened reduction wave (II)
in the reverse scan. The voltammogram of CAPE is shown
in Figure 2a as a representative example of this behaviour.
The bielectronic nature of the oxidative process of CAPE
was confirmed by coulometry (napp = 2.02). Since the current
peak intensity (ip) for the rest of the systems was similar to
the current peak intensity recorded for CAPE at the same
scan rate and concentration, it was deduced that the electron
stoichiometry was also two in all the cases.
When the scan rate is increased in the case of CA,
FA, and CAPE, the peak potential I is anodically shifted,
HO
HO
HO
O
HO
O
–e–
–e–
–H+
–H+
HO
O
HO
O
.
+
.
QH +
Q
QH2
QH2
QH
Scheme 1.

696
Electrochemical Oxidation of Caffeic and Ferulic Acid Derivatives in Aprotic Medium
J. Braz. Chem. Soc.
showing a linear variation with the logarithm of the scan
rate of 31, 30, and 42 mV dec-1, respectively (Table 1).
The analysis of a transition of the mechanism controlled
by the follow-up chemical reaction to a mechanism where
the electron transfer is rate determining, has been well
characterized.33 Thus, at 25 °C, this transition involves
a variation of ∂Ep/∂log v from 29.6 to 59.2 mV dec-1.
The results presented here suggest that in the case of CA
and FA the initial electron and proton transfer reactions
are consecutive, and they occur under a pure kinetic
control of the radical cation deprotonation. In contrast,
the substitution of the acidic proton of the caffeic acid by
the phenethyl group induces an increase in the rate of the
deprotonation chemical reaction in the case of CAPE and,
as a consequence, the global kinetic occurs under mixed
control.
catechol and guiacol moieties due to the presence of the
conjugated double bond (Scheme 2).
On the other hand, Astudillo et al.32 reported that
hydrogen bonding acceptor solvents play an important role
on the anodic oxidation of hydroquinone. They proposed
that DMSO interacts with hydroquinone through hydrogen
bonding associations, causing the shift of the oxidation
peaks toward less positive potentials. Taking into account
the structural similarity between hydroquinone and the
catechol moiety in C, CA, DHCA, and CAPE, we also
analyzed the electrochemical behavior of these compounds
in DMSO (Figure 3).
Table 1.Variation of oxidation potentials vs. the logarithm of the scan rate
Compound
C
∂Ep/∂log v
38
31
39
42
40
30
CA
DHCA
CAPE
G
FA
On the other hand, ∂Ep/∂log v was analyzed for C,
DHCAandG (Table 1), in order to know the effect that the
conjugation between the aromatic ring and the double bond
exerts on the global kinetic oxidation mechanisms of CA
and FA systems. The variation of ∂Ep/∂log v was 38, 39,
and 40 mV dec-1 for C, DHCA, and G, respectively. This
observation suggests that the oxidation mechanism for
these compounds proceeds under mixed kinetic control.33
In addition, we found that the difference between
the oxidation wave I and the reduction wave II for the
conjugated systems CA, CAPE, and FA is smaller (326,
355, and 447 mV, respectively) than in the case of the non-
conjugated compounds C, DHCA, and G (530, 552, and
677 mV, respectively), since there is a higher stabilization
of the radical cations coming from the oxidation of the
Figure 3. Cyclic voltammetry in DMSO + 0.2 mol L-1 n-Bu4NPF6, on
glassy carbon electrode (3 mm f) at 2 mmol L-1 and 0.1 V s-1 of a) C,
b) CA, c) DHCA and d) CAPE.
As in the case of hydroquinone, the peak potentials of C,
CA,DHCA,andCAPEpresentedadisplacementof>250mV
towards less anodic potentials in DMSO, in comparison
with the measurements obtained in AN (Table 2).
The behaviour suggests that under these conditions the
interaction between the catechol moiety (QH2, scheme 1)
of the four compounds with DMSO decreases the
dissociation energy of the O–H bonds, making the proton
R1
O
O
R1
O
O
R1
O
O
OR2
OR2
OR2
HO
HO
HO
R1 = H, OMe; R2 = H,
1 = H; R2 = CH=CHCOOCH2CH2Ph (CAPE)
R
Scheme 2.

Vol. 22, No. 4, 2011
Salas-Reyes et al.
697
Table 2. Oxidation potentials of C, CA, DHCA, and CAPE in AN and
DMSOa
Compound
C
Ep (AN) / V vs. SCE
Ep (DMSO) / V vs. SCE
1.11
1.08
1.07
1.01
0.86
0.78
0.79
0.73
CA
DHCA
CAPE
aAll oxidation potentials were obtained at 2 mmol L-1 and at 0.1 V s-1.
transfer reaction more favorable in the second step of the
oxidation mechanism (reactions 1-3). This observation can
be explained considering the fact that the proton affinity is
higher in DMSO than inAN, and that the proton transfer in
pure DMSO is carried out into a hydrogen bonding complex
formed between the hydroxyl groups of catechol and the
DMSO molecules.32,34
Figure 4. Cyclic voltammetry in DMSO + 0.2 mol L-1 n-Bu4NPF6, on
glassy carbon electrode (3 mm f) at 2 mmol L-1 and 0.1 V s-1 of a) G
and b) FA.
(1)
(2)
(3)
were labeled as III and II´ respectively in the Figure 4b. In
addition, the reduction wave (II) intensity of G was smaller
than the recorded for FA.
Additionally, the variation of Ep vs. log v for all the
compounds (38.4-41.9 mV dec-1) indicates a mixed kinetic
control of steps 1 and 2 on the global reaction, which
is not affected by the structural differences among the
four compounds (C, CA, CAPE, and DHCA). This is a
consequence of the competition between deprotonation
and radical cation delocalization, where the most favored
process is the first one.
Since hydrogen bonding acceptor solvents play an
important role on the oxidation mechanisms of catechol
and caffeic acid derivatives, we also carried out the cyclic
voltammetry of G and FA in DMSO (Figure 4). A two-
electron chemically irreversible oxidation wave I was
observed in both cases, however the voltammogram of FA
shows additional oxidation and reduction waves, which
On the other hand, the analysis of the variation of
Ep vs. log v on the wave I from the voltammogram of FA
showed a slope of 23 mV dec-1. This value is consistent
with a radical-radical dimerization mechanism, since it
has been previously reported that dimeric species can
be formed during the chemical and electrochemical
oxidation of neutral and dianionic hydroxycinnamic acid,
respectively.28,33,35 Taking into account this result, it was
proposed the dimerization mechanism of FA in DMSO as
follow (Scheme 3).
Thus, the wave III observed in the cyclic voltammetry
of FA corresponds to the oxidation of the guaiacol moieties
present in the resulting dimer (Scheme 3). The absence of
a second oxidation wave in the voltammogram of G and
a slope of 36 mV dec-1 calculated from the Ep vs. log v
O
O
O
O
O
O
O
OH
OH
OH
O
O
OH
O
COOH
O
O
O
O
OH
COOH
HO
Scheme 3.

698
Electrochemical Oxidation of Caffeic and Ferulic Acid Derivatives in Aprotic Medium
J. Braz. Chem. Soc.
variation from the corresponding wave I confirm this
proposal. In addition, the reduction waves II observed in
the voltammograms of both G and FA in DMSO (Figure 4),
showed lower intensities respect to the data obtained in
AN, which suggest that o-quinone is obtained in small
quantities during their oxidation processes under these
experimental conditions. However, the potential scan of
the electrochemical responses of G and FA from -2 to
1.5 V (Figures 5 and 6 respectively), showed an additional
reduction wave (IV) in -1.75 V for G and two waves more
(V and VI) for FA. It should be mentioned, however that
the wave VI is also observed in the cyclic voltammetry of
FA in AN.
From these results, it can be inferred that the products
obtained during the oxidation processes of both compounds
in DMSO, correspond to o-quinone or p-quinone
derivatives, which are substituted with the methoxy group,
and emerge from a nucleophilic attack between the water
traces present in DMSO and a phenoxy cation generated in
a second oxidation step (favored by the electron-releasing
power of the methoxy group).
The presence of a methoxy group on the quinone type
products is in agreement with the fact that the reduction
waves found for G and FA (IV andV, respectively) are more
negative than the wave II.36
Electrochemical behaviour of caffeic and ferulic acids
amide derivatives in acetonitrile
The electrochemical behaviours of the caffeic (CABzA
and CAPEA) and ferulic acid (FABzA and FAPEA)
amide derivatives, in AN, are shown in Figures 7 and 8,
respectively. In all the cases, it was observed the bielectronic
oxidation peak I and its corresponding reduction peak II.
Additionally, a small reduction wave (III) to less positive
potential values is also observed for all the amides, and an
oxidation wave I´ is recorded only in the voltammograms
of FABzA and FAPEA.
Figure 5. Cyclic voltammetry of G at 2 mmol L-1 in DMSO + 0.2 mol L-1
n-Bu4NPF6, on glassy carbon electrode (3 mm f). Scan from 1.5 to
-2.0 V. a) anodic direction and b) cathodic direction.
Figure 7. Cyclic voltammetry in acetonitrile + 0.2 mol L-1 n-Bu4NPF6,
on glassy carbon electrode (3 mm f) at 2 mmol L-1 and 0.1 V s-1 of
a) CABzA and b) CAPEA.
Figure 6. Cyclic voltammetry of FA 2 mmol L-1 in DMSO + 0.2 mol L-1
n-Bu4NPF6, on glassy carbon electrode (3 mm f). Scan from 1.5 to
-2.0 V. a) anodic direction and b) cathodic direction.

Vol. 22, No. 4, 2011
Salas-Reyes et al.
699
Figure 9. Cyclic voltammetry in DMSO + 0.2 mol L-1 n-Bu4NPF6, on
glassy carbon electrode (3 mm f) of CABzA at 2 mmol L-1 and different
scan rate.
Figure 8. Cyclic voltammetry in acetonitrile + 0.2 mol L-1 n-Bu4NPF6,
on glassy carbon electrode (3 mm f) at 2 mmol L-1 and 0.1 V s-1 of
a) FABzA and b) FAPEA.
In the case of CABzA, when the scan rate is increased
a new peak (I´) appears toward more positive potentials
respect to the wave I (Figure 9), which indicates that two
oxidative processes must be occurring on this compound.
On the other hand, the peak II and the post wave observed in
both, CABzA and CAPEA, become a new broad reduction
wave at high scan rates.
In addition, the corresponding anodic peak of
FABzA and FAPEA decrease steadily with the number
of cycles until they disappears completely (see
supplementary information).
This behaviour could be related to the derivatization of
the electrode surface phenomenon, since the voltammetric
behaviour of FABzA is recovered if the electrode surface is
polished. From these results, it is evident that the reactivity
of the nitrogen atom must be considered also as a part of
the global oxidation mechanism of both compounds37,38 as
follow (Scheme 4).
Oxidation potentials vs radical scavenging activity
The electrochemical parameters such as the redox
potential, the number of electrons, and the electron transfer
rate have been used to evaluate the oxidant capabilities of
polyphenols.39-42 The redox potential could be a key factor
that governs the antioxidant activity of this type of systems.
Therefore, the oxidation potentials of polyphenols are often
measured and compared to their antioxidant activities,
including the radical scavenging activity. The DPPH assay
has been extensively used to evaluate this property of the
phenolic compounds, hydroxycinnamic acids and related
systems.8-13,43,44 In order to see if the electrochemical
O
O
O
O
O
O
O
-e-, -H+
NR
NR
NR
H
H
H
HO
O
O
O
O
O
O
O
O
O
O
GCE
NR
GCE
N
R
NR
H
H
H
GCE = Glassy Carbon Electrode
R = CH2Ph, or CH2CH2Ph
Scheme 4.

700
Electrochemical Oxidation of Caffeic and Ferulic Acid Derivatives in Aprotic Medium
J. Braz. Chem. Soc.
oxidation capability of all the compounds is linked in some
way with their free radical scavenging activity, we carried
out DPPH assays of the complete series.
The oxidation potential of the ten compounds reported
in this work is shown in Table 3. As it can be observed,
the highest values correspond to the guaiacol and ferulic
systems, from 1.20 to 1.16V vs. SCE, whereas the catechol
and caffeic acid derivatives exhibit oxidation potentials
between 1.11 and 0.98 V vs. SCE.
mechanism. The analyses of the oxidation peak variation
with the scan rate of the six compounds, demonstrated that in
the case of CA and FA, the initial electron and proton transfer
reactionsareconsecutive andtheyoccurunderkineticcontrol
of the deprotonation chemical reaction, since the conjugation
of the aromatic ring with the double bond exerts a major
stabilization of the radical cation QH2•+ generated from the
twocompounds. In contrast, the oxidations of C, DHCA, G,
and CAPE occur under kinetic mixed control. In addition,
the substitution of the acidic proton of the caffeic acid by the
phenethyl group in the case of CAPE, induces an increase
in the rate of the chemical deprotonation.
Table 3. Oxidation potential of C, G, CA and FA derivatives and their
corresponding inhibition percentage of 2,2’-diphenyl-1-picrylhidrazyl
radical (DPPH)
On the other hand, the formation of hydrogen bond
association complexes between DMSO and the catechol
moiety of caffeic acid derivatives induce a displacement
of the oxidation peaks toward less anodic values respect to
the oxidation potentials obtained inAN. In addition, several
methoxy quinone type compounds must be generated
during the oxidation of G and FA. In the case of anodic
oxidation of FA, the analysis of variation of Ep vs. scan rate
revealed the establishment of a radical-radical dimerization
mechanism in DMSO.
The voltammograms of the four amides analyzed here
showed additional waves in AN, respect to the rest of the
series.Adsorption processes were even observed during the
oxidation of FABzA and FAPEA, which suggests that in
addition to the catechol and guaiacol moieties, the nitrogen
atom plays also an important role in the global oxidation
mechanism of this type of compounds.
Compound
C
Ep / V vs. SCEa
1.11
Inhibition / (%) ( SD) DPPHb
31.77 1.06
CA
1.08
30.56 1.52
DHCA
CAPE
CABzA
CAPEA
G
1.07
40.52 0.45
1.01
43.48 0.54
0.98
50.38 0.49
1.07
36.86 1.49
1.18
10.86 0.50
FA
1.16
19.33 2.05
FABzA
FAPEA
1.20
8.03 1.58
1.19
10.81 0.47
aOxidation potential of caffeic and ferulic acid derivatives were obtained
at 2 mmol L-1 and at 0.1 V s-1 in acetonitrile. bThe values represent means
S.D. from three experiments and indicate the percentage of inhibition
at 17 mmol L-1 of C, G, CA and FA derivatives.
In agreement with the electrochemical results, the
catechol and caffeic systems showed a major inhibition
percentage of the 2,2’-diphenyl-1-picrylhydrazyl radical
(DPPH) between 30 to 50%, whereas the guaiacol and
ferulic acid derivatives showed a lower inhibition percentage
between 10 and 20% (Table 3). In addition, the lower
oxidation potentials values of the series corresponded to
caffeic acid phenethyl ester (CAPE) and one of the caffeic
acid amides (CABzA) (1.01 and 0.98V, respectively). Both
compounds exhibited also the higher scavenging radical
activity (43.48 and 50.38% of inihibition respectively). A
linear regression of the Ep for the ten compounds against their
inhibition percentage of a 2,2’-diphenyl-1-picrylhydrazyl
radical (DPPH) showed a good agreement between the two
sets of data (correlation coefficient of 0.978).
Finally, the analysis of the oxidation potential of the ten
compounds in AN demostrated that catechol and caffeic
acid derivatives have a major oxidation capacity respect
to the guaiacol and ferulic analogues. This is in agreement
with the radical scavenging activity evaluated through a
DPPH assay. The results showed that CAPE and CABzA
exhibited the lower oxidation potentials, as well as the
highest reactivity with 2,2’-diphenyl-1-picrylhydrazyl
radical. These results corroborate the observation made by
other authors, since the reducing power of an antioxidant
could be a key factor that governs its antioxidant activity.39,42
Supplementary Information
Supplementary data are available free of charge at
http://jbcs.sbq.org.br, as PDF file.
Conclusions
Acknowledgments
The electrochemical oxidation of the compounds studied
in this work, catechol (C), guaiacol (G), caffeic acid (CA),
dihydrocaffeic acid (DHCA), ferulic acid (FA), and caffeic
acid phenethyl ester (CAPE), in acetonitrile follows an ECE
M. S. R thanks CONACyT-México for the financial
support given to this work through project 52064. J. H.
thanks CONACyT México and COVECyT México for

Vol. 22, No. 4, 2011
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701
FOMIX VER-2009-C03-127523. We are very grateful
to Dr. Myrna H. Matus and Dr. Gabriel Merino for
their comments. E. Martinez-Benavidez thanks also to
CONACyT-México for a Master scholarship.
21. Giacomelli, C.; Ckless, K.; Galato, D.; Miranda, F. S.; Spinelli,
A.; J. Braz. Chem. Soc. 2002, 13, 332.
22. Hotta, H.; Ueda, M.; Nagano, S.; Tsujino, Y.; Koyama, J.;
Osakai, T.; Anal. Biochem. 2002, 303, 66.
23. Trabelsi, A. K.; Tahar, N. B.; Abdelhedi, R.; Electrochim. Acta
2004, 49, 1647.
References
24. Arakawa, R.; Yamaguchi, M.; Hotta, H.; Osakai, T.; Kimoto,
T.; J. Am. Soc. Mass Spectrom. 2004, 15, 1228.
25. Hapiot, P.; Neudeck, A.; Pinson, J.; Fulcrand, H.; Neta, P.;
Rolando, C.; J. Electroanal. Chem. 1996, 405, 169.
26. Rapta, P.; Vladimir, M.; Stasko, A.; Vrábel, I.; Free Radical
Biol. Med. 1995, 18, 901.
1. Herrmann, K.; Crit. Rev. Food Sci. Nutr. 1989, 28, 315.
2. Burdock, G. A.; Food Chem. Toxicol. 1998, 36, 347.
3. Velazquez, C.; Navarro, M.; Acosta, A.; Angulo, A.;
Domínguez, Z.; Robles, R.; Robles R.; Lugo, E.; Goycoolea,
F. M.; Velázquez, E. F.; Astiazaran, H.; Hernández, J.; J. Appl.
Microbiol. 2007, 103,1747.
27. Grunberger, D.; Banerjee, R.; Eisinger, K.; Oltz, E. M.; Efros,
L.; Caldwell, M.; Estevez,V.; Nakanishi, K.; Experientia 1988,
44, 230.
4. Beck, J. J.; Kim, J. H.; Campbell, B. C.; Chou, S-C.; J. Nat.
Prod. 2007, 70, 779.
5. Burke, T. R. Jr.; Fesen, M.; Mazumder, A.; Yung, J.; Wang, J.;
Carothers, A. M.; Grunberger D.; Driscoll, J.; Pommier, Y.;
Kohn, K.; J. Med. Chem. 1995, 38, 4171.
28. Petrucci, R.;Astolfi, P.; Greci, L.; Firuzi, O.; Saso, L.; Marrosu,
G.; Electrochim. Acta 2007, 52, 2461.
29. Parker, V. D.; Chem. Commun. 1969, 716.
30. Parker, V. D.; Eberson, L.; Chem. Commun. 1970, 1289.
31. Parker, V. D.; Electrochim. Acta 1973, 18, 519.
32. Astudillo D. P.; Tiburcio, J.; González, F. J.; J. Electroanal.
Chem. 2007, 604, 57.
6. Hernandez, J.; Goycoolea, F. M.; Quintero, J.; Acosta, A.;
Castañeda, M.; Domínguez, Z.; Robles, R.; Vázquez-Moreno,
L.; Velázquez, E. F.; Astiazaran, H.; Lugo, E.; Velázquez, C.;
Planta Med. 2007, 73,1469.
7. Nagaoka, T.; Banskota, A. H.; Tezuka,Y.; Saiki, I.; Kadota, S.;
Bioorg. Med. Chem. 2002, 10, 3351.
33. L. Nadjo, L.; Savéant, J. M.; J. Electroanal. Chem. 1973, 48,
113.
8. Chen, J. H.; Ho, J. C-T.; J. Agric. Food Chem. 1997, 45, 2374.
9. Rajan, P.; Vedernikova, I.; Cos, P.; Berghe, V. D.; Ausgustyns,
K.; Haemers, A.; Bioorg. Med. Chem. Lett. 2001, 11, 215.
10. Son, S.; Lewis, B. A.; J. Agric. Food Chem. 2002, 50, 468.
11. Kikuzaki, H.; Hisamoto, M.; Hirose, K.; Akiyama, K.;
Taniguchi, H.; J. Agric. Food Chem. 2002, 50, 2161.
12. Nenadis, N.; Zhang, H.-Y.; Tsimidou, M. Z.; J. Agric. Food
Chem. 2003, 51, 1874.
34. Foti, M. C.; Ross, L.; Barclay, C.; Ingold, K. U.; J. Am. Chem.
Soc. 2002, 124, 12881.
35. Savéant, J. M.; Elements of Molecular and Biomolecular
Electrochemistry: An Electrochemical Approach to Electron
Transfer Chemistry, Wiley-Interscience: New Jersey, 2006.
36. Bautista-Martínez, J. A.; González, I.; Aguilar-Martínez, M.;
J. Electroanal. Chem. 2004, 573, 289.
37. Weinberg, N. L.; Weinberg, H. R.; Chem. Rev. 1968, 68, 449.
38. Garrido, E.M.; Lima, J. L. F. C.; Delerue-Matos, C.; Borges, F.;
Silva, Oliveira A. M. S.; Brett, A. M.; Anal. Chim. Acta 2001,
434, 35.
13. Ordoudi, S. A.; Tsimidou, M. Z.; Vafiadis, A. P.; Bakalbassis,
E. G.; J. Agric. Food Chem. 2006, 54, 5763.
14. Borreli, F.; Maffia, P.; Pinto, L.; Ianaro,A.; Russo,A.; Capasso,
F.; Ialenti, A.; Fitoterapia 2002, 73, S53.
39. Born, M.; Carrupt, P-A; Zini, R.; Brée, F.; Tillement, J-P.;
Hostettmann, K.; Testa, B.; Helv. Chim. Acta 1996, 79, 1147.
40. Peyrat-Maillard, M. N.; Bonnely, S.; Berset, C.; Talanta 2000,
51, 709.
15. Chen, J-H; Shao,Y.; Huang, M-T.; Chin, C-K.; Ho, C-T.; Cancer
Lett. 1996, 108, 211.
16. Lee, Y-J.;.Liao, P-H; Chen, W-K.; Yang, C-C.; Cancer Lett.
2000, 153, 51.
41. Yang, B.; Kotani, K.; Arai, K.; Kusu, F.; Anal. Sci. 2001, 17,
599.
17. Michaluart, P.; Masferrer, J. L.; Carothers,A. M.; Subbaramaiar,
K.; Zweifel, B. S.; Koboldt, C.; Mestre, J. R.; Grunberger, D.;
Sacks, P. G.; Tanabe, T.; Dannenberg, A. J.; Cancer Res. 1999,
59, 2347.
42. Hotta, H.; Nagano, S.; Ueda, M.; Tsujino, Y.; Koyama, J.;
Osakai, T.; Biochim. Biophys. Acta 2002, 1572, 123.
43. Huang, D.; Ou, B.; Priori, R. L; J. Agric. Food Chem. 2005, 53,
1841.
18. Sud´ina, G. F.; Mirzoeva, O. K.; Pushkareva, M.A.; Korshunova,
G. A.; Sumbatyan, N. V.; Varfolomeev, S. D.; FEBS J. 1993,
329, 21.
44. Foti, M. C.; Daquino, C.; Geraci; C., J. Org. Chem. 2004, 69,
2309.
19. Nomura, M.; Kaji, A.; Ma, W.; Miyamoto, K.; Dong, Z.; Mol.
Carcinog. 2001, 31, 83.
Submitted: May 7, 2010
20. Chiao, C.; Carothers, A. M.; Grunberger, D.; Solomon, G.;
Preston, G. A.; Barrett, J. C.; Cancer Res. 1995, 55, 3576.
Published online: December 21, 2010

J. Braz. Chem. Soc., Vol. 22, No. 4, S1, 2011.
Printed in Brazil - ©2011 Sociedade Brasileira de Química
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Supplementary Information
SI
Electrochemical Oxidation of Caffeic and Ferulic Acid Derivatives in Aprotic Medium
Magali Salas-Reyes,*,a Javier Hernández,a Zaira Domínguez,a Felipe J. González,b
Pablo D. Astudillo,b Rosa Elena Navarro,c Evelin Martínez-Benavidez,d,a
Carlos Velázquez-Contrerase and Samuel Cruz-Sáncheza
aUnidad de Servicios de Apoyo en Resolución Analítica, Universidad Veracruzana,
Apdo. Postal 575, Xalapa, Ver., México
bDepartamento de Química del Centro de Investigación y Estudios Avanzados, Av. Instituto
Politécnico Nacional 2508, 07360, Apdo. Postal 14-740, México, D. F., México
cDepartamento de Investigación en Polímeros y Materiales, Hermosillo, Son., México
dInstituto de Ciencias Básicas, Universidad Veracruzana, Apdo. Postal 525, Xalapa, Ver., México
eDepartamento de Ciencias Químico Biológicas, Universidad de Sonora, 83000, Hermosillo, Son., México
Figure S1. Cyclic voltammetries of FABzA in acetonitrile + 0.2 mol L-1 n-Bu4NPF6, on glassy carbon electrode (3 mm f) at 0.1 V s-1 and 2 mmol L-1.
A) During eleven continuous cycles and B) (a) Cyclic voltammetry of FABzA on 11th cycle; (b) after polishing electrode surface.
*e-mail: magasalas@uv.mx