Content uploaded by Pablo Salgado Mendoza
Author content
All content in this area was uploaded by Pablo Salgado Mendoza on Jun 23, 2014
Content may be subject to copyright.
Note
Chemiluminescence of the Fenton reaction and a dihydroxybenzene-driven
Fenton reaction
David Contreras
a,b,
⇑
, Jaime Rodríguez
b,c
, Pablo Salgado
b
, Cesar Soto-Salazar
a
, Yuhui Qian
d
, Barry Goodell
d
a
Analytical and Inorganic Chemistry Department, Faculty of Chemical Sciences, University of Concepción, Casilla 160-C, Concepcion, Chile
b
Biotechnology Center, University of Concepción, Concepcion, Chile
c
Forest Science Faculty, University of Concepción, Concepcion, Chile
d
Department of Wood Science and Forest Products, College of Natural Resources, Virginia Tech, Blacksburg, VA, USA
article info
Article history:
Available online 5 March 2011
Dedicated to Professor W. Kaim
Keywords:
Chemiluminescence
Fenton reaction
Fenton-like reaction
Dihydroxybenzenes driven Fenton reaction
Fe(IV)
abstract
A dihydroxybenzenes(DHB)-driven Fenton reaction was found to be more efficient than a simple Fenton
reaction based on
OH radical and activated species production. The reason for this enhanced reactivity by
[Fe DHB] complexes is not well understood, but results suggest that it may be explained by the formation
of oxidation species different from those formed during the classic Fenton reactions. In previous work,
greater concentrations, and more sustained production of
OH over time were observed in DHB driven
Fenton reactions versus neat Fenton and Fenton-like reactions. In this work, chemiluminescence (CL)
was monitored, and compared to
OH production kinetics. The CL of the DHB-driven Fenton reaction
was shorter than that for sustained production of
OH. CL appears to have been caused by excited Fe(IV)
species stabilized by the DHB ligands initially formed in the reaction. Formation of this species would
have to have occurred by the reaction between
OH and Fe(III) in a DHB complex.
Ó2011 Elsevier B.V. All rights reserved.
1. Introduction
1,2-Dihydroxybenzenes (DHBs) display antioxidant and/or pro-
oxidant activity in biological systems [1–8] depending on reaction
conditions [6,1] and microenvironment. These compounds are ac-
tively involved in important biochemical processes in plant, ani-
mal, and fungal systems. Among those, wood biodegradation by
brown rot fungi [9], plant defense against pathogens, Parkinson’s
disease [10] and the multiple pathways for toxicity that catechol
(CAT) [7] compounds promote. DHBs have also been used to in-
crease the oxidant proprieties of Fentons reagent in studies involv-
ing the degradation of recalcitrant compounds [8,11,12]. The
prooxidant properties of these compounds are based upon their
ability to reduce Fe(III) and O
2
to Fe(II) and HO
2
, respectively,
which dismutate to H
2
O
2
and in this way drive Fenton reactions
(1).
FeðIIÞþH
2
O
2
!FeðIIIÞþ
OH þOH
ð1Þ
Several pathway shave been proposed to explain the DHB dri-
ven effect which enhances the Fenton reaction, but these do not
completely explain important differences in rates of product in
or capacity for substrate degradation,
OH radical and chemilumi-
nescence (CL) production [13]. In previous work these effects were
attributed to participation of the [Fe DHB] complex in maintaining
OH production [14].
2. Materials and methods
2.1. General procedures
All reagent solutions were prepared in darkness under an argon
atmosphere, and the pH was adjusted to 3.4 with HNO
3
just prior
to the start of the experiments. The reaction conditions were the
same for all reactions in order to compare these systems. In this
work, the same experimental conditions were used as that in pre-
vious work [15] to permit study of the CL-time profile with
OH
radical production.
2.2. Reagents
All reagents were p.a. grade unless otherwise stated and they
were used as received without additional purification. The reagents
were: Catechol (CAT) 99%, 2,3-dihydroxybenzoic acid (2,3-DHBA)
99%, 3,4-dihydroxybenzoic acid(3,4-DHBA) 97%, H
2
O
2
35%, FeCl
3
anhydrous, FeSO
4
6H
2
O(Aldrich, Germany).
0020-1693/$ - see front matter Ó2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.02.082
⇑
Corresponding author at: Analytical and Inorganic Chemistry Department,
Faculty of Chemical Sciences, University of Concepción, Casilla 160-C, Concepcion,
Chile. Fax: +56 41 2245974.
E-mail address: dcontrer@udec.cl (D. Contreras).
Inorganica Chimica Acta 374 (2011) 643–646
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
2.3. Chemiluminescence measurement
A Turner Biosystem 20/20
n
luminometer with an internal injec-
tion device was utilized. The instrument was operated in darkness
at controlled room temperature.
2.4. Determination of kinetic parameters
All CL time profiles were divided into growth and decay phases
and. the data collected for these phases were separately fitted for
analysis. The decay phase curve data were fitted using first order
kinetics with the area under the curve obtained by integration.
Growth phases were characterized using the initial slope of the
curve taken immediately after initiation of CL production.
2.5. Reactions
The final concentrations of reagents were 150
l
M for DHB,
150
l
M for FeCl
3
or FeSO
4
and 2 mM for H
2
O
2
. The reaction was
started by addition of Fe(II) or Fe(III) inside of the luminometer
3. Results and discussion
3.1. CL time profile for Fenton and Fenton like reaction
The Fenton reaction displays a characteristic ‘‘flash’’ CL profile
(Fig. 1A) with CL
max
occurring instantaneously (with the maximum
at the 0.2 s point in Fig. 1A simply because of the registration lag
time for the instrument). The exponential decay phase of the CL
curve ranged from about 1 to 2 min depending on reaction condi-
tions. CL readings for Fenton reactions have been reported by Shen
et al. [16] and later by Rodriguez et al. [13] with the Fe(IV) shown
to be the chemiluminescent species [16]. This species is produced
together with
OH in Fenton reactions [17].
When the Fenton-like reaction (Fe(III)/H
2
O
2
) was monitored, an
induction (I
t
) time of 0.7 s was observed with steady state condi-
tions occurring during the period from 8.4 to 12.6 s. This was fol-
lowed by a first order decay which continued for approximately
8 min. In the anoxic environment used for these experiments,
and in absence of organic compounds, no other species would be
capable of generating luminescence and it is there for possible to
assign the CL under these conditions to an aqueous Fe(IV)–H
2
O ex-
cited complex. CL under these conditions is not attributable to
1
O
2
,
because this species is not chemiluminescent in aqueous environ-
ments [19].
According to Pignatello at al. and references therein [18] the
Fe(IV)–H
2
O excited complex is produced from the reaction of
Fe(III) with
OH. The peak activity for CL of the Fenton-like reaction
occurs after 8 s, (Fig. 1B) differing from the neat Fenton reaction
where maximal CL production begins immediately. This difference
occurs initially because of the lag time for production of
OH by
residual Fe(II) in solution and, in a second step, the reaction time
for that
OH to react with Fe(III) for production of Fe(IV).
3.2. CL time profile for DHB driven Fenton reaction
CL emission occurs in both Fe(II) and Fe(III) CAT driven Fenton
but higher CL values were observed in the Fe(III) containing system
(Fig. 2). The CL for the CAT/Fe(II)/H
2
O
2
system increases exponen-
tially (I
t
= 2 s) during the first 0.6 min, reaching steady state at
0.8 min (Fig. 2A, inset). CL then decreases following a first order
rate of decay. The CL time profile for the CAT/Fe(III)/H
2
O
2
system
is similar to the CAT/Fe(II)/H
2
O
2
system, but steady state was
reached at 0.4–0.6 min with I
t
= 3 s. The area under the curve
determined through integration is proportional to the amount of
activated CL species produced [13]. This value is 7% higher for
the Fe(III) containing system than with the Fe(II) system. In addi-
tion, the initial CL increase for the Fe(III) system is 60% greater than
for the Fe(II) system (68.6 and 113 Ms
1
, respectively). These re-
sults are in agreement with the relative rate of
OH production
by this system reported in previous work [15]. Thus, in this system,
CL is directly proportional to
OH production.
The CL produced by the 3,4-DHBA driven Fenton system dis-
played greater amounts of CL production than by the CAT driven
systems (Fig. 3). Further, the difference was also proportional to
the production of
OH [15]. The CL profile for the 3,4-DHBA sys-
tems, including Fe(II) and Fe(III), is similar to the CAT profiles. I
t
were 2.2 and 7.1 s for the Fe(II) and Fe(III) systems, respectively.
The time to reach steady state ranged from 1.2 to 1.5 min for the
3,4-DHBA/Fe(II)/H
2
O
2
system and ranged from 1.8 to 2.1 min for
the 3,4-DHBA/Fe(III)/H
2
O
2
system. The area under curve was 68%
greater for the Fe(III) system than for Fe(II) system and this differ-
ence therefore reflects the amount of
OH produced by the different
systems [15]. Similarly, the initial rate of CL production for the 3,4-
DHBA/Fe(III)/H
2
O
2
system (35.3 Ms
1
) was three times greater
than for 3,4-DHBA/Fe(II)/H
2
O
2
system (10.5 Ms
1
). The first order
(t
1/2
) decay rates for CL in the 3,4-DHBA/Fe(II)/H
2
O
2
system and
CAT/Fe(II)/H
2
O
2
system were similar suggesting a similar dynamic
occurs in these reactions with regard to the production of activated
species. Fe(III) systems, however, produced a slower first order (t
1/2
decay which presumably is due to prolonged production of
0.0 0.5 1.0 1.5 2.0
0
400
800
1200
1600
2000
CL signal AU
Time (Min)
0.0 0.4 0.8 1.2 1.6 2.0
0
2000
4000
6000
8000
10000
CL signal AU
Time (Min)
0246810
0
2000
4000
6000
8000
10000
CL signal AU
Time (s)
A
B
Fig. 1. CL time profile measured for (A) a Fe(II)/H
2
O
2
system and (B) a Fe(III)/H
2
O
2
system. (Inset plot: initial time scale detail.)
644 D. Contreras et al. / Inorganica Chimica Acta 374 (2011) 643–646
0246810
0
5
10
15
20
25
30
35
CL signal (AU)
Time(min)
A
0.0 0.2 0.4 0.6 0.8 1.0
0
5
10
15
20
25
30
CL signal AU
Time(min)
0246810
0
5
10
15
20
25
30
35
CL signal AU
Time (min)
B
0.0 0.2 0.4 0.6 0.8 1.0
0
5
10
15
20
25
30
CL signal AU
Time (min)
Fig. 2. CL time profile measured for (A) a CAT/Fe(II)/H
2
O
2
system and (B) a CAT/Fe(III)/H
2
O
2
system. (Inset plot: initial time scale detail.)
0246810
0
5
10
15
20
25
30
35
40
45
CL signal (AU)
Time(min)
0246810
0
5
10
15
20
25
30
35
40
45
CL Signal AU
Time (min)
A
0.0 0.4 0.8 1.2 1.6 2.0
0
10
20
30
40
CL signal AU
Time(min)
B
0.0 0.4 0.8 1.2 1.6 2.0
0
10
20
30
40
CL signal AU
Time(min)
Fig. 3. CL time profile measured for (A) a 3,4-DHBA/Fe(II)/H
2
O
2
system and (B) b 3,4-DHBA/Fe(III)/H
2
O
2
system. (Inset plot: initial time scale detail.)
0
5
10
15
20
25
CL signal AU
Time (min)
0.0 0.4 0.8 1.2 1.6 2. 0
0
5
10
15
20
25
CL signal AU
Time (min)
A
0246810 0246810
0
5
10
15
20
25
Time (min)
CL signal AU
B
0.0 0.4 0.8 1.2 1.6 2.0
0
5
10
15
20
25
CL signal AU
Time (min)
Fig. 4. CL time profile measured for (A) the 2,3-DHBA/Fe(II)/H
2
O
2
system (Inset plot: initial time scale detail). (B) the 2,3-DHBA/Fe(III)/H
2
O
2
system. (Inset plot: initial time
scale detail.)
D. Contreras et al. / Inorganica Chimica Acta 374 (2011) 643–646 645
activated species compared to Fe(II) systems. The CL time profile
for 2,3-DHBA driven systems achieves a similar steady state after
1.5–1.8 min (Fig. 4). The areas under curve were similar to that ob-
served with the CAT driven systems and are similarly in accor-
dance with initial area values (proportional to initial
OH
production) [15].
At difference with the other DHB system, the 2,3-DHBA/Fe(II)/
H
2
O
2
shows two overlayed curves at the exponential increased
step (Fig. 4A, inset). This behavior can be related with the role
for the carboxylate group in the Fe(III) reduction mechanism
[20]. A similar behavior was observed for
OH production [15].
The data demonstrate that the CL production time in the 2,3-
DHBA/Fe(II)/H
2
O
2
system is greater than that for the DHB/Fe(II)/
H
2
O
2
systems but this can be explained because of the presence
of two CL reactions occurring simultaneously in the same reaction
system (Fig. 4A, inset).
Interestingly, the CL of the DHB-driven Fenton reaction period is
less than that of the
OH production period previously reported [15].
This suggests therefore that, CL is related the excited species formed
in the early stages of the reaction with other reactions continuing for
longer periods to sustain
OH production, but at reduced levels from
that in the initial reaction. CL could be generated by Fe(IV) species
stabilized by the DHB ligands. We postulate that this ligated species
would need to be formed by reaction of
OH and Fe(III) in a DHB com-
plex (Scheme 1). This postulate is consistent with the larger I
t
in
Fe(II) systems compared to Fe(III) systems in the presence of DHB,
because Fe(II) must be oxidized to Fe(III) before oxidation to Fe(IV)
by
OH can occur (Scheme 1).
Lasovsky et al. [21] studied CL associated with CAT oxidation in
a Co(II) Fenton reaction using CTAB micelles under neutral to alka-
line pH conditions. These authors concluded that the source of CL is
probably the excited triplets and singlet oxygen of hydroxylated
quinones [21]. Belaya et al. [22] postulated that electronically ex-
cited quinones are the source of CL in the polyphenol oxidation
by peroxy radicals. These CL sources cannot be discounted in that
work. However, in the current model presented here, two facts ar-
gue that the pathways we have outlined may have greater merit.
First, we have demonstrated that CL production decreases and ter-
minates more rapidly than does
OH production. Secondly, our
studies have demonstrated that quinones are present in the reac-
tion mixture [23] after CL production has terminated, even as
OH production continues.
4. Conclusion
The CL of DHB-driven Fenton reactions compared to neat Fen-
ton reactions is greater and more prolonged, demonstrating that
substrate oxidation permits greater yields of chemiluminescent-
active radical species. CL measurements permitted a comparison
of the reactivity of different DHB-driven Fenton reactions. CL was
not a direct measurement of
OH production; however, it was pro-
portional to
OH production in early stages of DHB-driven reac-
tions. The CL of both a Fenton, and a Fenton-like reaction, is
postulated to be associated with Fe(IV) species production; how-
ever, direct spectroscopic analyses will be needed to confirm this.
Acknowledgements
The financial support for this work was provided by FONDECYT
iniciacion (Grant No. 11090312) and FONDECYT (Grant No.
1100898).
References
[1] Y. Nakamura, K. Torikai, Y. Ohto, A. Murakami, T. Tanaka, H. Ohigashi,
Carcinogenesis 21 (2000) 1899.
[2] C.A. Gomes, T.G. da Cruz, J.L. Andrade, N. Milhazes, F. Borges, M.P.M. Marques, J.
Med. Chem. 46 (2003) 5395–5401.
[3] K. Ohara, Y. Ichimura, K. Tsukamoto, M. Ogata, S. Nagaoka, K. Mukai, Bull.
Chem. Soc. Jpn. 79 (2006) 1501.
[4] L.Y. Zang, G. Cosma, H. Gardner, V. Castranova, V. Vallyathan, Mol. Cell.
Biochem. 247 (2003) 205.
[5] H. Iwahashi, H. Morishita, T. Ishii, R. Sugata, R. Kido, J. Biochem. 105 (1989)
429.
[6] J.F. Moran, R.V. Klucas, R.J. Grayer, J. Abian, M. Becana, Free Radic. Biol. Med. 22
(1997) 861.
[7] N. Schweigert, A.J.B. Zehnder, R.I.L. Eggen, Environ. Microbiol. 3 (2001) 81.
[8] J. Rodriguez, D. Contreras, C. Oviedo, J. Freer, J. Baeza, Water Sci. Technol. 49
(2004) 81.
[9] B. Goodell, G. Daniel, J. Jellison, Y.H. Qian, Holzforschung 60 (2006) 630.
[10] D.M. Kuhn, R.E. Arthur, D.M. Thomas, L.A. Elferink, J. Neurochem. 73 (1999)
1309.
[11] J. Rodriguez, D. Contreras, C. Parra, J. Freer, J. Baeza, N. Duran, Water Sci.
Technol. 40 (1999) 351.
[12] M.L. Rodriguez, V.I. Timokhin, S. Contreras, E. Chamarro, S. Esplugas, Adv.
Environ. Res. 7 (2003) 583.
[13] J. Rodriguez, C. Parra, J. Freer, J. Baeza, Water Sci. Technol. 44 (2001) 251.
[14] D. Contreras, J. Freer, J. Rodriguez, Int. Biodeterior. Biodegrad. 57 (2006) 63.
[15] D. Contreras, J. Rodriguez, J. Freer, B. Schwederski, W. Kaim, J. Biol. Inorg.
Chem. 12 (2007) 1055.
[16] X. Shen, J.D. Tian, J. Li, X.Y. Li, Y.L. Chen, Free Radic. Biol. Med. 13 (1992) 585.
[17] M.L. Kremer, Phys. Chem. Chem. Phys. 1 (1999) 3595.
[18] J.J. Pignatello, E. Oliveros, A. MacKay, Crit. Rev. Environ. Sci. Technol. 36 (2006)
1.
[19] C. Schweitzer, R. Schmidt, Chem. Rev. 103 (2003) 1685.
[20] J.H. Xu, R.B. Jordan, Inorg. Chem. 27 (1988) 1502.
[21] J. Lasovsky, J. Hrbac, D. Sichertova, P. Bednar, Luminescence 22 (2007) 501.
[22] N.I. Belaya, T.A. Filippenko, A.N. Nikolaevskii, V.A. Pilipenko, O.Y. Ovcharova,
Theor. Exp. Chem. 39 (2003) 166.
[23] Y. Qian. Study of basic wood decay mechanisms and their biotechnological
applications. PhD Thesis. Universityof Maine, Orono, 2008.
Scheme 1.
646 D. Contreras et al. / Inorganica Chimica Acta 374 (2011) 643–646
