Toward a high added value compound 3, 4-dihydroxyphenylacetic acid by electrochemical conversion of phenylacetic acid

Article abstract of DOI:10.1016/j.electacta.2015.05.074

Abstract The development of the effective procedure to recover the potentially high-added-value phenolic compound, 3,4-dihydroxyphenylacetic acid (3,4-DHPAA) was investigated using electrochemical conversion of phenylacetic acid (PAA). The proposed mechanism is based on the hypothesis of two-electron oxidation of PAA molecule leading to 3-hydroxyphenyl acetic acid. The latter underwent a second bi-electronic transfer by means of a radical cation, thus leading to the formation of the 2,5 dihydroxyphenylacetic (2,5-DHPAA) acid and 3,4-DHPAA as major products. The 3,4-DHPAA was synthesized by anodic oxidation of PAA at lead dioxide electrode and identified by cyclic voltammetry and spectrophotometry UV-visible. It was also confirmed by mass spectrophotometry using LC-MS/MS apparatus. According to their voltammetric behavior during electrolysis, the oxidation potential of 3,4-DHPAA was lower than that of PAA. The antioxidant activity was measured by DPPH assay, showing that the strongest antiradical activity was detected when the 3,4-DHPAA concentration was higher during electrolysis experiments.

Full text of DOI:10.1016/j.electacta.2015.05.074

Electrochimica Acta 173 (2015) 370–376
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Toward a high added value compound 3, 4-dihydroxyphenylacetic acid
by electrochemical conversion of phenylacetic acid
Souhel Kallel Trabelsi, Olfa Dridi Gargouri, Boutheina Gargouri, Ridha Abdelhèdi,
*
Mohamed Bouaziz
Laboratoire d'Electrochimie et Environnement, Ecole Nationale d’Ingénieur de Sfax, BP 1173, 3038 Sfax. Université de Sfax. Tunisia
A R T I C L E I N F O
A B S T R A C T
Article history:
The development of the effective procedure to recover the potentially high-added-value phenolic
compound, 3,4-dihydroxyphenylacetic acid (3,4-DHPAA) was investigated using electrochemical
conversion of phenylacetic acid (PAA). The proposed mechanism is based on the hypothesis of two-
electron oxidation of PAA molecule leading to 3-hydroxyphenyl acetic acid. The latter underwent a
second bi-electronic transfer by means of a radical cation, thus leading to the formation of the
2,5 dihydroxyphenylacetic (2,5-DHPAA) acid and 3,4-DHPAA as major products. The 3,4-DHPAA was
synthesized by anodic oxidation of PAA at lead dioxide electrode and identified by cyclic voltammetry
and spectrophotometry UV-visible. It was also confirmed by mass spectrophotometry using LC-MS/MS
apparatus. According to their voltammetric behavior during electrolysis, the oxidation potential of 3,4-
DHPAA was lower than that of PAA. The antioxidant activity was measured by DPPH assay, showing that
the strongest antiradical activity was detected when the 3,4-DHPAA concentration was higher during
electrolysis experiments.
Received 12 February 2015
Received in revised form 28 April 2015
Accepted 13 May 2015
Available online 16 May 2015
Keywords:
Phenylacetic acid
3,4-dihydroxyphenylacetic acid
anodic oxidation
lead dioxide
cyclic voltammetry
antioxidant activity
ã2015 Elsevier Ltd. All rights reserved.
1. Introduction
In this context, several methods have been developed to
produce 3,4-DHPAA which has the highest antioxidant power. In
Olive oil is a rich source of mono-unsaturated fatty acids and
phenolic compounds from simple to very complex structures [1].
Water-soluble simple phenols of lower molecular weight, includ-
ing 3,4-dihydroxyphenylacetic acid (3,4-DHPAA), are lost during
the production of oils. They pass into the water phase which is
called “Olive Mill Waste Water” (OMWW) [1–3]. Such water
contains a great amount of phenolic compounds, especially
hydroxytyrosol, tyrosol, 3,4-DHPAA, caffeic, p-coumaric, ferrulic,
gallic acids.... Among these compounds, the orto-dihydroxylated
aromatic products exhibit higher antioxidant activity [2,4–6].
Hydroxytyrosol and 3,4-DHPAA are shown to have the highest
radical-scavenging effect on DPPH (2,2-diphenyl-1-picrylhydrazyl
free radical), especially 3,4-DHPAA which has the highest
protective effect against oil oxidation. This compound may
potentially be used as an alternative to butylated hydroxyanisol
(BHA) and butylated hydroxytoluene (BHT), which are natural
antioxidants, to stabilize edible oils. At the same time it can
appease a major concern of consumers over the use of synthetic
antioxidants in food products [2].
fact, it is produced by biological method [7,8] and by chemical
reaction [9].
Different attempts have been used to evaluate the antioxidant
activity of different compounds [10,11] using an accelerated test
[12,13], radical species such as ABTS+ (2,2 azinobis (3-ethyl-
benzthiazoline-6-sulfonic acid) [14], DPPHꢀ [15] and ESR (electron
spin resonance) spin trapping technique [16]. However, all these
procedures have some drawbacks since they require the use of
specific reagents and tedious and time consuming sample
preparation.
Recently, electrochemical measurements have been established
for the determination of antioxidant activity [17], such as their use
as a rapid proof of the antioxidant capacity of a lot of organic
materials. The oxidation potentials measured by cyclic voltam-
metry have been used to compare the antioxidant strength of
compounds such as phenolic acids, flavonoids, cinnamic acids,...
[17–21]. Low oxidation potentials are associated with a greater
facility or strength of a given molecule for the electrodonation, and
thus acting as antioxidant. Cyclic voltammetry has been success-
fully applied to analyze antioxidants present in wine [22], plant
extracts [21], phenolic standards [17,23,24], and even human
plasma [25].
* Corresponding author. Tel : +21698667581.
E-mail address: mohamed.bouaziz@fsg.rnu.tn (M. Bouaziz).
http://dx.doi.org/10.1016/j.electacta.2015.05.074
0013-4686/ã 2015 Elsevier Ltd. All rights reserved.

S.K. Trabelsi et al. / Electrochimica Acta 173 (2015) 370–376
371
Cyclic voltammetry at platinum oxide is used to follow the
degree of antioxidant activity during the electrochemical conver-
sion of PAA. Platinum is often regarded as the ideal solid electrode
for fundamental electrochemical investigation due to its chemical
and electro-catalytic properties in the oxidation reaction by
electronic transfer between the reagent and the anode [26,27].
The electro-catalytic properties of Pt oxides electrode was
characterized by the charge Q corresponding to the electrochemi-
cal formation of the Pt oxides. Besides, we showed in a previous
works that the charge Q allows control of electro-catalytic
properties of the Pt oxides electrode [28].
In this work, we developed the galvanostatic electrolysis
method using an electrode material characterized by a high
oxygen over-potential such as lead dioxide (PbO2), in order to
convert PAA into 3,4-DHPAA as a product with important biological
activities. On the other hand, the antiradical ability of PAA and its
oxidation products was assessed by DPPH assay. The structure of
the converted products was confirmed using Liquid
Chromatography–Mass Spectrometry (LC-MS) analysis.
2. Experimental
Fig. 1. Cyclic voltamograms of PAA at platinum disk in 0.5 mol Lꢂ1 H2SO4 at Ta/PbO2
anode. Potential scan rate 50 mV sꢂ1; Q = 0.6 mC; T = 20 ꢁC. PAA concentration: (1) 0;
2.1. Reagents and chemicals
(2) 8 g Lꢂ1
.
Sodium molybdate dehydrate and organic solvents were
purchased from Merck (Darmstadt, Germany). PAA, 3,4-DHPAA,
DPPH, and all other chemicals were purchased from Sigma–Aldrich
(St. Louis, MO). All used reagents and chemicals were of analytical
grade.
formation and a cathodic peak at 43 mV relative to the Pt oxides
reduction can be noted. In the present research work, the Pt/Pt
oxides electrode was characterized by the amount of electricity (Q)
corresponding to the electrochemical reduction of the formed Pt
oxides. The Q value was measured during a potential scan between
+843 and ꢂ585 mV at a potential scan rate of 50 mV sꢂ1. The
amount of electricity (Q) was considered as the unique parameter
that characterizes the surface state of the Pt/Pt oxides electrode. It
is worthy to note that the amount of electricity (Q) is a global
parameter that does not take into account the heterogeneity of the
electrode surface.
2.2. Appratus
A potentiostat type PJT Tacussel was used for electrochemical
measurements and the data was recorded using a GSTP4 Tacussel
X-Y recorder. The amount of electricity was measured using an
IG6-N Tacussel integrator. In this investigation, all the potentials
refer to Hg/Hg2SO4/K2SO4 electrode (Eꢁ = +0.61 vs SHE/V).
The electronic absorption spectra of PAA solutions under
investigation and their treated solutions by anodic oxidation were
recorded within the wavelength range of 200-400 nm, using a
Shimadzu model UV-1650 PC spectrophotometer.
2.5. Liquid Chromatography–Mass Spectrometry analysis
The liquid chromatography–mass spectrometry (LC–MS) of the
PAA after 16 hours of electrolysis was performed on an Agilent
1100 series LC-MSD. The compounds were separated with a Zorbax
300 Aꢁ Extend-C-18 column (2.1 ꢃ150 mm, particle size 5
mm,
2.3. Electrolysis
Agilent Technology, INC, Wilmingtom, DE, USA). The mobile phase
was a mixture of two solvents: (A: formic acid 1% in water) and (B:
89.5% methanol, 9.5% acetonitrile and 1% formic acid). The analysis
conditions were as described earlier by Bouaziz et al. [30]. The
percentage by volume of (B) varied linearly with time as follows:
from 10 to 30% for the first 5 minutes, then from 30 to 40% up to
25minutes after isocratic during 5 minutes, from 40 to 50% up
to40 minutesandfrom50to100%upto50 minutes,afterthatbackto
10% up to 55minutes and finally isocratic up to 65 minutes. The
column outlet was coupled with an Agilent MSD ion trap XCT mass
spectrometer(Santa Clara, CA, USA)equippedwithanESI ionsource.
The electrolysis of PAA solutions were carried out in an
isothermal reactor using a thermoregulated single compartment
cell (V = 200 cm3). The cathode was a cylindrical mesh made up of
platinum. The initially electrolytic solution contained 8 g Lꢂ1 PAA
in 0.5 mol Lꢂ1 H2SO4. The Ta/PbO2 anode was placed in a coaxial of
the cathode. The total surface area of the working electrode was
6 cm2. The experimental details for the preparation of Ta/PbO2
were described in our previous research work [29]. The solutions of
PAA were electrolyzed at 30 ꢁC, with magnetic stirring and under
different applied current densities 10, 30 and 50 mA cmꢂ2
.
2.6. Ortho-diphenolic determinations
2.4. Treatment of the platinum electrodes
Ortho-diphenolic content was determined following the
previously modified method described by Cert et al. [31]. This
method is based on the formation of a yellow complex between
ortho-diphenols and molybdate ions. Briefly, 2 mL of the sample
was added to 0.5 mL of the sodium molybdate dihydrate solution
0.5 g Lꢂ1 in a mixture of ethanol-water (50% ethanol, 50% water).
The mixture was shaken and after 15 min, the absorbance was
measured at 370 nm at room temperature. Standards of gallic acid
were similarly prepared.
The layer of Pt oxides was prepared by cyclic voltammetry
between ꢂ600 mV and +890 mV at a potential scan rate of
300 V minꢂ1 using a Pt disc (
’= 1 mm), previously polished with
0.3 mm Al2O3 then washed several times with distilled water in
0.5 mol Lꢂ1 sulfuric acid solution. The Pt electrode, initially shining,
was progressively covered with a grey and adherent layer of Pt
oxides. Fig. 1 (curve 1) shows the electrochemical response of the
Pt/Pt oxides electrode in 0.5 mol Lꢂ1 sulfuric acid aqueous solution.
From 143 mV, an anodic wave corresponding to the Pt oxides

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1
2
2HOꢀ
!
O2 þ H2O
(3)
2.7. Determination of DPPH radical-scavenging activity
ads
The DPPH radical scavenging effect was evaluated following the
Therefore, to have a short-time conversion, the best chosen
current density of the subsequent analysis was at 30 mA mꢂ2
procedure described in a previous study [30]. The Aliquots (50
mL)
.
of various concentrations (5, 10, 15, 20 and 25 g/mL) of the test
m
The electrochemical oxidation of PAA at PbO2 anode under
30 mA cmꢂ2 was followed by cyclic voltammetry at the treated
platinum electrode. Fig. 3(a) exhibits the cyclic voltammograms at
different electrolysis time intervals of 8 g Lꢂ1 PAA. The initial
voltammogram for the untreated solution (Fig.1 curve 2 or Fig. 3(a)
curve 1) shows only the oxidation peak I1 of PAA at Epa1 = 643 mV.
The voltammograms (Fig. 3(a) curve 2, 3, 4, 5 and 6) reveal two
peaks I2 and I3 at Epa2 = 100 mV and Epa3 = 185 mV, respectively,
which are related to the more stable oxidation products of PAA.
Peak I2 is ascribed to the oxidation of 3,4-DHPAA by comparison
with its authentic voltammogram recorded under identical
experimental conditions. This peak reached its maximum about
0.2 mA after 16 hours of oxidation, and then decreased (Fig. 3(b)).
However, the peak I1 intensity decreased until zero after 34 hours.
extracts in methanol were added to 5 mL of methanolic solution
containing DPPH radicals (6 10ꢂ6 mol Lꢂ1). After 30 min incubation
period at room temperature and in the dark, the absorbance was
read against control at 517 nm. The inhibition percentage of free
radical DPPH (%RSA) was calculated using Eq (1):
%RSA ¼ ½ðAblank ꢂ AsampleÞ=Ablankꢄ ꢃ 100
(1)
where %RSA is the percentage radical-scavenging activity, Ablank is
the absorbance of the control reaction (containing all reagents
except the test extract), and Asample is the absorbance of the test
extract. The concentration of the test extract providing 50%
inhibition (IC50, expressed in mg Lꢂ1) was calculated from the
graph plotted with inhibition percentage against the extract
concentration. The synthetic antioxidant reagent BHT was used as
positive control and all tests were carried out in triplicate.
3.2. UV-Visible analysis
3. Results and discussion
Fig. 4 presents typical scanning kinetic graphs taken at different
time intervals during the electrochemical oxidation of PAA at
30 mA cmꢂ2. As can be seen from Fig. 4, two new bands appeared at
3.1. Effect of current density in the electrochemical conversion of PAA
at PbO2 anode
The electrochemical conversion of PAA was investigated by
anodic oxidation under three different current densities (japp) 10,
30, and 50 mA cmꢂ2. In anodic oxidation, organic compounds are
directly oxidized by the reaction with hydroxyl radical (HOꢀ)
formed at the anode surface from water decomposition (Eq. (2)).
H2O ! HOꢀads + H+ + 1eꢂ
(2)
Fig. 2 shows a typical profile of variation of orthodiphenols
concentration during the electrolysis essays of 8 g Lꢂ1 PAA at 10,
30 and 50 mA cmꢂ2. As can be seen in this figure, the orthodi-
phenolic concentration was weakly influenced by applied current
density. When the applied current density increases from 10 to
50 mA cmꢂ2, the maximum of orthodiphenolic concentration
passed from 466 to 394 mg Lꢂ1. However, the time necessary for
the electrochemical conversion was very much influenced by the
current density. It was clearly shown that the electrochemical
conversion of PAA at 30 mA cmꢂ2 was more rapid than at
50 mA cmꢂ2
. This behavior could be attributed to the high
reactivity of greater amounts of HOꢀ, which can be lost by the
secondary reaction (Eq. (3)).
500
400
300
200
100
0
0
20
40
60
80
100
Fig. 3. (a) Cyclic voltamograms of 8 g Lꢂ1 PAA at Platinum disk in sulfuric acid
aqueous solution at potential scan rate of 50 mV sꢂ1 as a function of time electrolysis
of PAA at PbO2. japp = 30 mA cmꢂ2, T = 30 ꢁC. Electrolysis time/ h: (1) 0; (2) 6; (3) 13;
(4) 16; (5) 25; (6) 34. (b) Variation of current of the peaks (I1) and (I2) during anodic
oxidation of PAA.
Time/ h
Fig. 2. Effect of current density on the variation of orthodiphenols concentration
with electrolysis time of 8 g Lꢂ1 PAA solutions in 0.5 mol Lꢂ1 H2SO4 at Ta/PbO2
anode. V = 200 cmꢂ3; T = 30 ꢁC; japp/ mA cmꢂ2: (^) 10, (
D) 30 and (~) 50.

S.K. Trabelsi et al. / Electrochimica Acta 173 (2015) 370–376
373
As regards compound 1 (tR, 11.75 min;
l
max, 279 nm), it was
identified as PAA by the comparison of its absorbance spectrum
and retention time with those of an authentic standard. This was
confirmed by the MS-MS, which yielded an [M-H]- at m/z 135.
Concerning compound 2 (tR, 7.97 min;
lmax, 270 nm), it was
identified as 3-hydroxyphenylacetic acid (Fig. 5) on the basis of co-
chromatography with an authentic standard and a mass spectrum
with an [M-H]ꢂ at 151 and prominent MS2 fragments at m/z 151,
133. The ion m/z 133 was obtained by the loss (ꢂ18) of a water
molecule, providing an anion of [M–H–H2O]ꢂ.
With respect to compound 3, it was identified as 3,4-DHPAA
retained at 5.22 minutes (lmax, 280 nm) (Fig. 5). The MS1 spectrum
exhibited a molecular ion at m/z 167 [M-H]ꢂ. The MS2 spectrum
obtained by the fragmentation of the ion m/z 197 presents the
following m/z values: 167, 150 and 149. The fragmentation of the
Pseudomolecular ion [M-H]ꢂ at m/z 167 yielded a fragment at m/z
149 by the loss of 18 mass units of [M–H2O–H]ꢂ (Fig. 6). The
structure of this compound is confirmed by that of an authentic
standard.
Fig. 4. (a) UV–Visible absorption spectra obtained during the electrolysis of 8 g Lꢂ1
of PAA solutions in 0.5 mol Lꢂ1 H2SO4 at Ta/PbO2 anode. Electrolysis time/h: (1) 0;
(2) 6; (3) 13; (4) 16; (5) 25; (6) 34.
As for compound 4 (tR, 5.62 min;
lmax, 325 nm), it was
cochromatographed with 3,4-DHPAA (Fig. 5). It also had the same
absorbance and mass spectra [M-H]ꢂ at m/z 167 and two major
MS2 fragments at m/z 149 and 137 as 3,4-DHPAA [8], which was
previously detected in olive mill wastewater [2]. This compound
was identified as 2,5-DHPAA, which is in good agreement with the
results obtained by the oxidation mechanism proposed using
cyclic voltammetry (Fig. 7). The two isomers can, therefore, be
distinguished chromatographically as well as by MS. This is
because the predominant MS2 ion was derived from 2,5-
dihydroxyphenyl acetic acid at m/z 137, while the corresponding
fragment from 3,4-DHPAA at m/z 149.
280 and 321 nm, indicating that intermediate products were
formed during the electrochemical oxidation of PAA. The first
absorption band which appeared at 280 nm is ascribed to the 3,4-
DHPAA by comparison with its authentic absorption spectrum
recorded under identical experimental conditions.
After reaching its maximum intensity at 16 hours, the new
bands began to decrease until it disappeared, thus demonstrating
that the intermediates can be completely electrochemically
oxidized.
3.3. Liquid Chromatography–Mass Spectrometry analysis
3.4. Oxidation mechanism of the PAA
To elucidate the structures of phenolic compounds present in
the electrochemical treatment solution of 3,4-DHPAA, the obtained
sample after 16 hours was monitored by liquid chromatography
with electrospray mass spectrometry in the negative mode. The
structure assignment of phenolic compounds was based on the UV
absorbance spectra with a systematic search for molecular ions,
using extracted ion mass chromatograms and comparing the MS/
MS spectra with those in the literature [32].
The results presented above suggest that PAA molecules
undergo a bi-electronic transfer followed by hydrolysis, producing
3-hydroxyphenylacetic acid (Fig. 7). The latter undergwent a
second bi-electronic transfer producing phenoxonium carbocation
existing under three mesomeric forms A–C. Taking into account
the electronic effects of the oxo and carboxymethyl groups, the
radical B was found to be the least stable. Then, the hydrolysis of
2
7.97
0.00
450000
400000
350000
300000
4.03
0.00
1
250000
4.22
0.00
0.00
200000
3
150000
100000
50000
0
5.22
0.00
1.72
0.00
7.45
0.00
4
6.68
0.00
3.18
0.00
2.42
0.00
5.62
0.00
8.45
0.00
8.80 9.62
0.00 0.00
18.12
0.00
1.30
0.00
9.77
0.00
6.35
0.00
17.78
0.00
13.32
0.00
4.92
0.00
16.82
15.97
0.00
0.60
0.00
12.17
0.00
15.17
0.00
13.65
0.00
0.00
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
Time (min)
Fig. 5. HPLC chromatogram after 16 hours of PAA anodic oxidation at PbO2,1: PAA; 2: 3-hydroxyphenylacetic acid; 3: 3,4-DHPAA; 4: 2,5-DHPAA.

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S.K. Trabelsi et al. / Electrochimica Acta 173 (2015) 370–376
Fig. 6. LC-MS/MS spectrum (MS1 and MS2) after 16 hours of PAA anodic oxidation at PbO2, japp = 30 mAcmꢂ2; T = 30 ꢁC.
the carbocation A and C led to the formation of 3,4-DHPAA and 2,5-
DHPAA, respectively.
orthodiphenols content in the PAA electrolysis solution suggest
that the radical scavenging effect in the solution can be attributed
to hydroxylated phenolic compounds, particularly the number of
hydroxyl substituents in the aromatic ring and the nature of the
substituents at the para or ortho position [33]. These compounds
react with free radicals formed during autoxidation and generate a
new radical that is stabilized by the resonance effect of the
aromatic nucleus [35]. It was found that 3,4-DHPAA exhibits
antioxidant activity (IC50 = 6 mg Lꢂ1) at a similar level to that of BHT
(IC50 = 8.32 mg Lꢂ1).
Cyclic voltammetry has been applied to characterize the
reducing ability of natural phenolics [17,36] and good correlations
have been observed between redox potentials and antioxidant
properties [37,38]. In accordance with the global mechanism
proposed for PAA oxidation, the hydroxyl groups are oxidized via
two electrons transfer, leading to the generation of a corresponding
quinone after the liberation of 2H+. These results indicate that the
higher number of hydroxyl substituents on the aromatic ring,
corresponds to the lower electrochemical potential. Indeed, it was
reported that an ortho hydroxyl group at position 30 appears to be
3.5. Antioxidant Activity
The DPPH radical-scavenging activities of PAA solution treated
by anodic oxidation at PbO2 were investigated during the
electrolysis of 8 g Lꢂ1 PAA at 30 mA cmꢂ2 (Fig. 8). The low IC50
values designate the potent radical-scavenging effects as low
concentrations are adequate to inhibit the DPPH radicals [33,34].
All samples were proven to exhibit antioxidant activity, which
shows correlation between the orthodiphenols content and DPPH
radical-scavenging activity over all PAA anodic oxidations. The PAA
with no hydroxyl groups had IC50 = 57 mg Lꢂ1, which presents
limited antioxidant activity. On the other hand, the lower IC50
values (6 mg Lꢂ1), which indicate higher antioxidant potential,
were observed for the samples taken at 16 hours of electrolysis.
This is probably due to the significant radical inhibition caused by a
high concentration of orthodiphenols caused by the presence of
3,4-DHPAA. The antioxidant activity and the level of the

S.K. Trabelsi et al. / Electrochimica Acta 173 (2015) 370–376
375
1
COOH
phenylacetic acid
+
-2e-
-H
COOH
+
-H H2O
HO
2
COOH
3-hydroxyphenylacetic acid
- H+
- 2e-
O
- 2e-
- H+
O
- H+
O
- 2e-
+
+
COOH
COOH
COOH
+
C
B
A
H2O / H+
H2O / H+
H2O / H+
HO
HO
HO
OH
4
3
HO
COOH
3,4-dihydroxyphenylacetic acid
COOH
COOH
2,3-dihydroxyphenylacetic acid
OH
2,5-dihydroxyphenylacetic acid
+ 2H+
+ 2H+
2e-
+
2e-
+ 2H+
2e-
+
+
O
O
O
O
O
COOH
O
COOH
COOH
Fig. 7. Oxidation pathways of PAA in aqueous sulfuric acid medium at treated Platinum.
desirable to obtain an anti-oxidative response [33]. Therefore, the
3,4-DHPAA which is easily oxidized (Epa2 = 100 mV) than 2,5-
dihyroxyphenylacetic acid (Epa3 = 185 mV), has a higher antioxi-
dant activity.
Consequently, according to our previous work [24], this study
confirmed again that the application of electrochemical methods
using anode material with a high over-potential for oxygen
evolution and a low cost, is a novel easy clean and solvent free
route for conversion of toxic compound into product with
important biological activities.
500
400
300
200
100
0
60
50
40
30
20
10
0
4. Conclusion
0
10
20
30
40
The results obtained in this study have revealed that the
electrochemical oxidation using PbO2 anode is a rapid, simple and
efficient tool for the conversion of PAA into high-added-value
products such as 3,4-DHPAA. Using LC/MS analysis, it was possible
to determine the structure of majors phenolic intermediates (3,4-
Time/ h
Fig. 8. Free radical scavenging activity and ortho-diphenols tests during anodic
oxidation of PAA at PbO2. japp = 30 mA cmꢂ2; T = 30 ꢁC.

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S.K. Trabelsi et al. / Electrochimica Acta 173 (2015) 370–376
DHPAA and 2,5-DHPAA) produced during the electrochemical
treatment of PAA.
[16] H.L. Madsen, B.R. Nielsen, G. Bertelsen, L.H. Skibsted, Screening of
antioxidative activity of spices, Food Chem. 57 (1996) 331.
[17] P.A. Kilmartin, H. Zou, H. Waterhouse, A cyclic voltammetry method suitable to
characterizing antioxidant properties of wine and wine phenolics, J. Agric.
Food Chem. 49 (2001) 1957.
[18] R. Bortolomeazzi, N. Sebastianutto, R. Toniolo, A. Pizzariello, Comparative
evaluation of the antioxidant capacity of smoke flavouring phenols by crocin
bleaching inhibition DPPH radical scavenging and oxidation potential, Food
Chem. 100 (2007) 1481.
[19] M.A. Samra, V.S. Chedea, A. Economou, A. Calokerinos, P. Kefalas, Antioxidant/
prooxidant properties of model phenolic compounds: Part I. studies on
equimolar mixtures by chemiluminescence and cyclic voltammetry, Food
Chem. 125 (2011) 622.
[20] N.S. Jha, S. Mishra, S.K. Jha, A. Surolia, Antioxidant activity and electrochemical
elucidation of the enigmatic redox behavior of curcumin and its structurally
modified analogues, Electrochim Acta. 151 (2015) 574.
It has reported that oxidation potential measured by cyclic
votammetry was closely related to the compounds structures. The
phenolic structure also influences antioxidant activity. Besides, the
ortho-diphenol compound (3,4-DHPAA) has lower anodic peak
potential and higher antioxidant ability than para-diphenol
compound (2,5-DHPAA).
Finally, the electrochemical conversion of PAA could be used as
a tool to produce a high added value compound, such as 3,4-
DHPAA, which could make significant contributions to the health
benefits associated with the consumption of various food
ingredients.
[21] A. Masek, E. Chrzescijanska, M. Zaborski, Characteristics of curcumin using
cyclic voltammetry UV–VIS, fluorescence and thermogravimetric analysis,
Electrochim Acta. 107 (2013) 441.
References
[22] P.A. Kilmartin, Z. Honglei, A.L. Waterhouse, Correlation of wine phenolic
composition versus cyclic voltammetry response, J. Enol. Viticult. 53 (2012)
294.
[23] A. Simié, D. Manojlovic, D. Segan, M. Todorovic, Electrochemical behavior and
antioxidant and prooxidant activity of natural phenolics, Molecules 12 (2007)
2327.
[24] O. Dridi Gargouri, B. Gargouri, S. Kallel Trabelsi, M. Bouaziz, R. Abdelhèdi,
Synthesis of 3-O-methylgallic acid a powerful antioxidant by electrochemical
conversion of syringic acid, Biochim. Biophys. Acta 1830 (2013) 3643.
[25] S. Chevion, M.A. Roberts, M. Chevion, The Use of Cyclic Voltammetry for the
Evaluation of Antioxidant Capacity, Free Rad. Biol. Med. 28 (2000) 860.
[26] S. Trasatti, in: J. Lipkowski, P.N. Ross (Eds.), Transition Metal Oxides: Versatiles
materials for electrocatalysis, in the Electrochemistry of Novel Materials, VCH
Publishers, New York, 1994, pp. 207.
[27] L.D. Burke, M.B.C. Roche, W.A. O’Leary, The role of hydrous oxide in the
electrochemical behaviour of platinum, J. Appl. Electrochem. 18 (1988) 781.
[28] R. Abdelhedi, M.L. Bouguerra, Passivation d’Electrodes de Platine et d’Or lors de
l’Oxydation Electrochimique Indirecte du Xylène, Electrochim. Acta. 35 (1990)
273.
[29] S. Kallel Trabelsi, N. Belhadj Tahar, B. Trabelsi, R. Abdelhèdi, Electrochemical
oxidation of ferulic acid in aqueous solutions at gold oxide and lead dioxide
electrodes, J. Appl. Electrochem. 35 (2005) 967.
[30] M. Bouaziz, H. Jemai, W. Khabou, S. Sayadi, Oil content, phenolic profiling and
antioxidant potential of Tunisian olive drupes, J. Sci. Food Agric. 90 (2010)
1750.
[31] R. Cert, S. Arranz, J. Pérez-Jiménez, A. Cert, F. Saura-Calixto, Comparison
between free radical scavenging capacity and oxidative stability of nut oils,
Food Chem. 110 (2008) 985.
[32] J. Gruz, O. Novák, M. Strnad, Rapid analysis of phenolic acids in beverages by
UPLC–MS/MS, Food Chem. 111 (2008) 789–794.
[33] M. Bouaziz, R.J. Grayer, M.S.J. Simmonds, M. Damak, S. Sayadi, Identification
and Antioxidant Potential of Flavonoids and Low Molecular Weight Phenols in
Olive Cultivar Chemlali Growing in Tunisia, J. Agric. Food Chem. 53 (2005) 236.
[34] M. Bouaziz, M. Chamkha, S. Sayadi, Comparative Study on Phenolic Content
and Antioxidant Activity during Maturation of the Olive Cultivar Chemlali
from Tunisia, J. Agric. Food Chem. 52 (2004) 5476.
[35] M.E. Cuvelier, H. Richard, C. Berset, Comparison of the antioxidative activity of
some acid phenols: structure-activity relation ship, Biosci. Biotechnol.
Biochem. 56 (1992) 324.
[36] P. Hapiot, A. Neudeck, J. Pinson, H. Fulcrand, P. Neta, C. Rolando, Oxidation of
caffeic acid and related hydroxycinnamic acids, J. Electroanal. Chem. 405
(1996) 169.
[37] D. Galato, K. Ckless, F.M. Susin, C. Giacomelli, M.R. Robeiro-do-Valle, A. Spinelli,
Antioxidant capacity of phenolics and related compounds: correlation among
electrochemical, visible spectroscopy methods and structure-antioxidant
activity, Redox Report 6 (2001) 243.
[1] F. Visioli, A. Poli, C. Galli, Antioxidant and other biological activities of phenols
from olives and olive oil, Med. Res. Rev. 22 (2002) 65.
[2] I. Feki, N. Allouche, S. Sayadi, The use of polyphenolic extract, purified
hydroxytyrosol and 3,4-dihydroxyphenylacetic acid from olive mill waste
water for the stabilization of refined oils: a potential alternative to synthetic
antioxidants, Food Chem. 93 (2005) 197.
[3] K. Papadopoulos, T. Triantis, E. Yannakopoulou, A. Nikokavoura, D. Dimotikali,
Comparative studies on the antioxidant activity of aqueous extracts of olive
oils and seed oils using chemiluminescence, Anal. Chim. Acta. 494 (2003) 41.
[4] C.A. Rice-Evans, N.J. Miller, G. Paganga, Structure-antioxidant activity
relationships of flavonoids and phenolic acids, Free Radic. Biol. Med. 20
(1996) 933.
[5] D. Kim, Y. Ch. Lee, Comprehensive study on vitamin C equivalent antioxidant
Capacity (VCEAC) of various polyphenolics in scavenging a free radical and its
structural relationship, Crit. Rev. Food Sci. Nutr. (2004) 253.
ꢀ
ꢀ
[6] A.C. Pancorbo, L. Cerretani, A. Bendini, A.S. Carretero, M.D. Carlo, T.G. Toschi, G.
Lercker, D. Compagnone, A.F. Gutierrez, Evaluation of the antioxidant capacity
of individual phenolic compounds in virgin olive oil, J. Agric. Food Chem. 53
(2005) 8918.
[7] E. Kevin, O. Connor, P. Niall, O. Leary, J.R. Marchesi, A.D.W. Dobson, W. Duetz,
Isolation and characterization of
a diverse group of phenylacetic acid
degrading microorganisms from pristine soil, Chemosphere 61 (2005) 965.
[8] K. Syslová, L. Rambousek, M. Kuzma, V. Najmanova, V. Valesova, R. Slamberova,
P. Kacer, Monitoring of dopamine and its metabolites in brain microdialysates:
Method combining freeze-drying with liquid chromatography–tandem mass
spectrometry, J. Chromatogr. A 1218 (2011) 3382.
[9] I.N. Meffort, L. Kincel, K.H. Dykstra, J.T. Simpson, S.P. Markey, S. Dietz, R.M.
Wightman, Facile oxidative decarboxylation of 3,4-dihydroxyphenylacetic
acid catalyzed by copper and manganese ions, Biochim. Biophys. Acta. 1290
(1996) 224.
[10] E.N. Frankel, J.W. Finley, How to Standardize the Multiplicity of Methods to
Evaluate Natural Antioxidants, J. Agric. Food Chem. 56 (2008) 490.
[11] J.K. Moon, T. Shibamoto, Antioxidant Assays for Plant and Food Components, J.
Agric. Food Chem. 57 (2009) 1655.
[12] A. Bendini, T.G. Toschi, G. Lercher, Determination of the antioxidant activity of
vegetable extracts by Oxidative Stability Instrument (OSI), Ind. Aliment. 403
(2001) 525.
[13] R. Chirinos, R. Pedreschi, H. Rogez, Y. Larondelle, D. Campos, Phenolic
compound contents and antioxidant activity in plants with nutritional and/or
medicinal properties from the Peruvian Andean region, Industrial Crops and
Products 47 (2013) 145.
[14] J.P. Dzoyem, J.N. Eloff, Anti-inflammatory, anticholinesterase and antioxidant
activity of leaf extracts of twelve plants used traditionally to alleviate pain and
inflammation in South Africa, J. Ethnopharmacol. 160 (2015) 194.
[38] O. Firuzi, A. Lacanna, R. Petrucci, G. Marrosu, L. Saso, Evaluation of the
antioxidant activity of flavonoids by ferric reducing antioxidant power assay
and cyclic voltammetry, Biochim. Biophys. Acta. 1721 (2005) 174.
ꢀ
[15] S. Milardovic, D. Ivekovié, B.S. Grabarié, A novel amperometric method for
antioxidant activity determination using DPPH free radical, Bioelectrochem.
175 (2006) 68.