A kinetic study of the reactions of sulfate and dihydrogen phosphate radicals with epicatechin, epicatechingallate, and epigalocatechingallate

Article abstract of DOI:10.1002/kin.20492

The bimolecular rate constants for the reactions of sulfate radicals with epicatechin (EC), epicatechingallate (ECG), and epigallocatechingallate (EGCG) were found to be (1.46 ± 0.06) × 10⁹, (1.20 ± 0.08) × 10⁹, and (1.04 ± 0.07) × 109, respectively. The activation energy [E_A = 9 ± 3 kJ mol ^-1] and preexponential factor [A = (4.8 ± 0.6) × 10 ¹⁰] for the reaction of EC with the sulfate radical were measured in the temperature range 288-303 K. The phenoxyl radicals of EC (λ_max = 310 nm) were obtained both by the reaction of this flavonoid with the sulfate radicals and by photoionization. The measured bimolecular rate constants for the reactions of the dihydrogen phosphate radicals with EC, ECG, and EGCG were (7.8 ± 0.9) × 10⁸, (8.5 ± 0.4) × 10⁸, and (6.8 ± 0.4) × 10⁸, respectively.

Full text of DOI:10.1002/kin.20492

A Kinetic Study of the
Reactions of Sulfate and
Dihydrogen Phosphate
Radicals with Epicatechin,
Epicatechingallate, and
Epigalocatechingallate
´
´
LAURA S. VILLATA, MONICA C. GONZALEZ, DANIEL O. MARTIRE
Instituto de Investigaciones Fisicoqu ´ı micas Te o´ ricas y Aplicadas (INIFTA), Universidad Nacional de La Plata, Casilla de
Correo 16, Sucursal 4, 1900 La Plata, Argentina
Received 15 October 2009; revised 4 December 2009; accepted 16 December 2009
DOI 10.1002/kin.20492
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: The bimolecular rate constants for the reactions of sulfate radicals with epicatechin
(
0
[
EC), epicatechingallate (ECG), and epigallocatechingallate (EGCG) were found to be (1.46 ±
9
9
9
.06) × 10 , (1.20 ± 0.08) × 10 , and (1.04 ± 0.07) × 10 , respectively. The activation energy
−
1
1
0
EA = 9 ± 3 kJ mol ] and preexponential factor [A = (4.8 ± 0.6) × 10 ] for the reaction of
EC with the sulfate radical were measured in the temperature range 288–303 K. The phenoxyl
radicals of EC (λmax = 310 nm) were obtained both by the reaction of this flavonoid with
the sulfate radicals and by photoionization. The measured bimolecular rate constants for the
reactions of the dihydrogen phosphate radicals with EC, ECG, and EGCG were (7.8 ± 0.9) ×
8
8
8
1
0 , (8.5 ± 0.4) × 10 , and (6.8 ± 0.4) × 10 , respectively. ꢀC 2010 Wiley Periodicals, Inc. Int J
Chem Kinet 42: 391–396, 2010
INTRODUCTION
production of ROS. Some antioxidants (endogenous)
are produced by living organisms, and others (exoge-
nous) are ingested [1,2].
Low concentrations of antioxidants retard or prevent
the free radical oxidation of biomolecules. The mech-
anism of action of the antioxidants may occur by radi-
cal scavenging, by catalytic effect on reactions involv-
ing the generation of reactive oxygen species (ROS),
or by complexing traces of metals necessary for the
Over the past decade, evidence has been ac-
cumulated that plant polyphenols are an important
class of exogenous antioxidants. These compounds
are widespread virtually in all plant foods, often
at high levels, and include phenols, phenolic acids,
flavonoids, tannins, and lignans. Among the antioxi-
dants, flavonoids represent a large and different group
of phenolic compounds ubiquitous in plants [3]. It is
well known that diets rich in fruits and vegetables are
Correspondence to: Laura S. Villata; e-mail: laura@inifta
.
unlp.edu.ar.
ꢀ
c 2010 Wiley Periodicals, Inc.

3
92
VILLATA, GONZALEZ, AND M A´ RTIRE
EXPERIMENTAL
3
′
2′
4′
Na2S2O8 (Merck p.a.), NaH2PO4·H2O (Aldrich p.a.),
1
8
B
6′
1′
3 4
and H PO (Merck p.a.) were used as received. EC
O
5
′
7
6
(>90%), ECG (>95%), and EGCG (>98%) were pur-
2
3
chased from Sigma-Aldrich (Buenos Aires, Argentina)
and used without further purification. Potassium per-
oxodiphosphate was electrochemically synthesized as
described in the literature [15]. Distilled water (>18
A C
5
4
Scheme 1 Flavonoid structure.
−1
Mꢀ cm , <20 ppb of organic carbon) was obtained
from a Millipore system.
Sulfate and dihydrogen phosphate radicals were
generated by photolysis of unbuffered Na2S2O8 so-
lutions [16] and buffered peroxodiphosphate solutions
protective against cardiovascular disease and certain
forms of cancer [4]. Numerous studies have shown that
the antioxidative effect of flavonoids in vitro is either
due to chelation of transition metals, preventing free
radical formation, or due to electron donation toward
reactive oxygen and nitrogen species, which leads to
the formation of less reactive flavonoid aroxyl radi-
cals. These compounds also deactivate singlet molecu-
lar oxygen by physical and chemical quenching [5–10].
The basic flavonoid structure is the flavan nucleus,
which consists of 15 carbon atoms arranged in three
rings (C6 C3 C6), labeled A, B, and C (Scheme 1).
The various classes of flavonoids differ in the level
of oxidation and substitution pattern of the C ring,
whereas individual compounds within a class differ in
the substitution pattern of the A and B rings.
Epicatechin (EC), epicatechingallate (ECG), and
epigalocatechingallate (EGCG) are well-known
flavonoids that belong to the family of flavan-3-ols and
are present in several natural products such as green tea.
In EGCG, the α-OH group corresponding to carbon
number 3 forms an ester with gallic acid [1]. The cor-
responding substitution patterns are shown in Table I.
Since the reactions of inorganic radicals with or-
ganic molecules important for biological processes are
a relevant domain of research, the reaction of sul-
fate and phosphate radical anions with such molecules
has been investigated in the literature [12–14]. In an
attempt to make a contribution to the free radical
chemistry of EC, ECG, and EGCG, in this study we
investigated the reactions of sulfate and dihydrogen
phosphate radicals with these flavonoids.
(
[
pH = 4.0 ± 0.2, controlled with H3PO4/KH2PO4)
17]. The ionic strength of these solutions was within
the range 0.1–0.2 M.
Flash-photolysis experiments were carried out in
a conventional apparatus (model 720C; Xenon Co.,
Wilmington, MA, USA) with modified optics and elec-
tronics [18]. The flash lamps emit in the wavelength
range from 210 to 600 nm, with an emission maximum
at 400 nm. In experiments performed to investigate the
reactions of inorganic radicals with EC, the emission
of the flash lamps was filtered with saturated aqueous
solutions of this flavonoid to avoid its photolysis. In
this case, the excitation light useful for the generation
of radicals was in the range 240–280 nm. The analy-
sis source was a high-pressure mercury lamp (Osram
HBO-100 W). The optical path length of the cell was
1
0 cm. The temperature was maintained at ± 0.1 K with
a Grant model GD 1200 thermostat (Chelmsford, UK).
To avoid product accumulation, each solution was ir-
radiated only once. Signals arising from single shots
were averaged.
RESULTS AND DISCUSSION
The absorption spectra of aqueous solutions of ECG
of different pH values are shown in Fig. 1. From the
analysis of the ratio of absorbances at 326 nm (ε326 =
−1
−1
−1
−1
827 M cm ) and 276 nm (ε276 = 940 M cm ),
Table I Substitution Patterns for Epicatechin (EC), Epicatechingallate (ECG), and Epigalocatechingallate (EGCG)
ꢁ
ꢁ
ꢁ
5
3
5
7
3
4
pKai
a
EC
ECG
EGCG
α-OH
α-Gallate
α-Gallate
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
H
H
OH
8.64; 9.41; 11.26; 13.4
b
(7.1 ± 0.2)
a,c
7.75; 8.0
a
From ref. [11].
This work.
pKa3 not measured.
b
c
International Journal of Chemical Kinetics DOI 10.1002/kin

KINETICS OF SULFATE AND DIHYDROGEN PHOSPHATE RADICALS WITH FLAVONOIDS
393
0
0
0
0
.6
.4
.2
.0
spectra immediately after the flash of light are in
.
−
agreement with those of SO . The traces taken at
1
0
8
6
4
4
λ = 450 nm showed faster decay kinetics with increas-
ing concentrations of the organic substrates (S) and
could be well fitted to ꢁA = ꢁA0 exp(−kapp × t) + C
(Fig. 2). The very small constant term C (<1% of
A
the maximum absorbance) is associated with the
absorption of a longer lived species, that is, the organic
radicals formed in reaction (1). The bimolecular rate
constants k1, obtained from the slopes of the linear
plots of kapp vs. [S] (see inset of Fig. 2 for EC), are
given in Table II [13].
log [B]/[A].
pH
3
00
350
400
450
.−
SO4 + S → Organic radicals
(1)
λ (nm)
Figure 1 Absorption spectra of 0.45 mM solutions of epi-
catechingallate at different pH values. The path length of the
cell employed is 1 cm. Inset: Plot of pH vs. log [B]/[A].
The value of k1 for EC was measured in the temper-
ature range from 283.2 to 303.2 K. For this purpose,
experiments in the absence and presence of EC were
performed. The decay acceleration observed in exper-
iments without EC is accounted for the activation en-
ergy reported for the pseudo-first-order decay of the
sulfate radicals in [21]. The linear plots of kapp vs.
where the basic (B) and acid (A) forms of ECG mainly
absorb, the linear plot of pH vs. log [B]/[A] is obtained
(Fig. 1, inset). From the intercept of this plot, the value
[EC] are shown in the inset of Fig. 3. The correspond-
of pKa = 7.1 ± 0.2 is obtained (see Table I).
ing Arrhenius plot for EC is shown in Fig. 3. From
−
1
this plot, activation energy EA = 9 ± 3 kJ mol and
10
−1 −1
preexponential factor A = (4.8 ± 0.9) × 10
M s
Sulfate Radical Experiments
are obtained. These parameters are within the range re-
ported by Alfassi et al. [22] for the reactions of several
inorganic radicals with phenols in aqueous solutions
(i.e., 7 ≤ EA ≤ 41 kJ mol and 9.2 ≤ log A ≤ 13.9,
respectively). These authors found that although the
rate constant of these reactions is related to the exother-
micity of the reaction, the temperature dependence of
the rate constant is not.
.−
The reactions of SO4 with EC, ECG, and EGCG
were investigated in solutions of pH 4.2, in which the
substrates are mainly undissociated, by following the
−1
.−
decay rate of SO4 as a function of added substrate
2
−
concentration. Photolysis experiments of S2O in
8
the presence of low concentrations of the substrates
(S) showed traces at λ > 400 nm, whose absorption
0
0
0
0
.06
.04
.02
.00
2
500
2
2
1
1
500
000
500
000
2
2
2
2
1.2
1.1
1.0
0.9
2000
1500
1000
500
k
k
k
0
1 × 10
2 × 10
A
0
.0
4.0e-7
8.0e-7
1.2e-6
[EC] (M)
[EC] (M)
0
.0033
0.0034
0.0035
0.0036
0.000
0.002
0.004
0.006
0.008
T
t (s)
Figure 3 The Arrhenius plot for reaction (1). Inset: Plots
of kapp vs. [EC] obtained at 295 K ( ) and 291 K ( ). The
intercepts are (902 ± 51) and (390 ± 110) s for the ex-
periments at 295 and 291 K, respectively. Abbreviation: EC,
epicatechin.
Figure 2 Decay traces obtained at 450 nm for 5 mM so-
lutions of Na2S2O8 containing different amounts of epicat-
echin (EC): 0 (upper trace); 0.4 μM (middle trace), and
᭹
᭺
−1
1
.2 μM. Inset: Plot of kapp vs. [EC].
International Journal of Chemical Kinetics DOI 10.1002/kin

3
94
VILLATA, GONZALEZ, AND M A´ RTIRE
0
.015
.010
.005
.000
3000
2
2
1
500
000
500
0
0
0
A
k
1000
0.0000
0.0015
t (s)
0.0030
5
00
0
1
×
10
2
×
10
3 × 10
(a)
[
S](M)
0
0
0
0
.09
.06
.03
.00
Figure 5 Plots of kapp vs. [S] for epigalocatechingallate
), epicatechin (
), and epicatechingallate (ꢀ).
(
᭺
A
<10 μM) showed absorption traces at λ > 400 nm,
whose spectra immediately after the flash of light were
.
4
in agreement with that of H PO . The absorption traces
2
showed faster decay kinetics with increasing concen-
trations of the organic substrates and could be well
fitted to a first-order rate law with an apparent rate
constant, kapp. The slopes of the linear plots of kapp vs.
substrate concentration (see Fig. 5) yield the bimolec-
300
350
400
450
500
λ (nm)
(b)
.
4
ular rate constants for the reactions of H2PO with the
Figure 4 (a) Decay traces obtained at 450 nm for 5 mM
solutions of Na2S2O8 containing 0.1 mM of epicatechin. (b)
substrates [15] (Table II).
Absorption spectra obtained at 500 μs (
after the flash of light.
᭹
) and 4.5 ms (
᭺
)
The reactivities of other transient oxidants with the
substrates are included in Table II for comparison. As
can be seen, the rates of oxidation of flavonoids with the
hydroxyl, sulfate, and azidyl radicals are more or less
diffusion controlled, reflecting their favorable electron-
donating properties toward the flavonoids. The rates
of one-electron oxidation of the substrates with dihy-
drogen phosphate, nitrogen dioxide, carbonate, dithio-
cyanate, and formyl radicals are lower, as may be ex-
pected from the relatively lower reduction potentials
of these oxidants [25].
To obtain further information on reaction (1), the
nature of organic radicals formed in the reaction with
EC as the substrate was investigated. For this purpose,
peroxodisulfate solutions containing EC at the concen-
tration of 0.1 mM (pH = 4.2) were employed for the
flash-photolysis experiments. Typical absorption traces
are shown in Fig. 4a.
The absorption spectrum obtained at 500 μs after
the flash of light is in agreement with that reported for
the sulfate radical [23], whereas that obtained at 4.5 ms
is assigned to the phenoxyl radicals of EC (Fig. 4b; see
the following text). Phenoxyl radicals of polyphenols
are obtained by the reaction of one-electron oxidants,
such as the azidyl [14], carbonate [19], and sulfate
radicals [13,24], with these substrates.
Photolysis of EC
Both one-electron oxidation with strong transient ox-
idants and photoionization of phenols yield phenoxyl
radicals [14]. Thus, to investigate the phenoxyl radicals
of EC generated by direct photolysis, flash-photolysis
experiments of EC solutions in the concentration range
1
0–50 μM were performed. The observed intermedi-
ate shows an absorption spectrum with λmax = 310 nm
Fig. 6).
As expected, there is an agreement between the ab-
Dihydrogen Phosphate Radical
Experiments
(
.
4
The reactions of H2PO with polyphenols are conve-
sorption spectra of the phenoxyl radicals of EC ob-
tained by its reaction with sulfate radicals (Fig. 4b)
and those obtained by direct photolysis (Fig. 6).
The decay of the phenoxyl radicals of EC obtained
by photolysis follows a pseudo-first-order rate law.
.
4
niently studied following the decay rate of H2PO as
a function of added substrate concentration. Photol-
ysis experiments of P2O4 solutions of pH = 4.2 in
−
8
the presence of low concentrations of substrates ([S]
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KINETICS OF SULFATE AND DIHYDROGEN PHOSPHATE RADICALS WITH FLAVONOIDS
395
Table II Rate Constants of Oxidation of the Flavonoids with Transient Oxidants and One-Electron Reduction
Potentials of the Phenoxyl Radicals (E7)
a
7
−1 −1
Phenol Derivative (Ar-OH)
Epicatechin
E (V)
Oxidant (X)
k (X + Ar-OH) (M
s
)
.
9b
0.57
OH
6.4 × 10
.
N
3
9c
4.0 × 10
.
−
9d
SO
(1.46 ± 0.06) × 10
4
.
4
8e
H2PO
(7.8 ± 0.9) × 10
.
NO
2
7f,g
9.0 × 10
.
3
−
8f,h
CO
5.6 × 10
.
9b
Epicatechingallate
0.55
0.43
OH
5.8 × 10
.
N
3
9c
4.7 × 10
.
−
9d
9d
SO
(1.20 ± 0.08) × 10
4
.
4
8e
H2PO
(8.5 ± 0.4) × 10
.
9b
Epigalocatechingallate
OH
7.1 × 10
.
N
3
9c
4.8 × 10
.
−
SO
(1.04 ± 0.07) × 10
4
.
8f,g
NO
1.2 × 10
2
.
−
8c
CO
6.6 × 10
3
.
−
8c
(
SCN)
4.2 × 10
2
.
7c
CH2CH2O
4.6 × 10
.
H2PO
4
8e
(6.8 ± 0.4) × 10
a
From ref. [17].
b
Data from ref. [19] (pH = 11).
c
Data from ref. [13] (pH = 7).
d
This work (pH = 4.2) at 295 K.
e
This work (pH = 4.0).
f
From ref. [20].
g
pH = 7.
h
pH = 11.
From the linear plot of the apparent rate constant
for the decay of the first intermediate vs. [EC] (in-
set of Fig. 6), a bimolecular rate constant for reaction
phenoxyl radicals [26].
Phenoxyl radical + EC → Products
(2)
4
−1 −1
s , was obtained.
(
1), k2 = (9.3 ± 0.9) × 10 M
These results are in complete agreement with those ob-
tained by Jovanovic et al. [14], who generated the phe-
noxyl radicals derived from flavonoids by one-electron
oxidation of the substrates with the azidyl radical [14].
In the latter case, the process leads to the formation
of a mixture of A ring-phenoxyl (λmax = 490 and
550 nm at pH 3 and 7, respectively) and B ring-
phenoxyl (λmax = 310 and 340, 420 nm at pH 3 and
The first-order decay was observed for several other
2
2
2
1
1
1
4
2
0
8
6
4
0
0
0
0
0
0
0
0
.28
.24
.20
.16
.12
.08
.04
.00
k
7, respectively) radicals. This finding was confirmed
12
A
0
5e-5
EC] (M)
1e-4
by comparison with the spectra of the phenoxyl rad-
icals of model single-ring compounds. Subsequent to
the one-electron oxidation of flavonoids, the resorci-
nol phenoxyl radical (at the A ring) transforms to the
apparently most stable gallate phenoxyl radical (at the
B ring) via inter- and intramolecular electron transfer
(see Scheme 2 for EC).
[
2
80
300
320
340
360
380
400
λ (nm)
The time resolution of our experiments precluded
observation of the phenoxyl radical (at the A ring).
Thus, only the phenoxyl radical at the ring B is ob-
served both by reaction with the sulfate radicals and
by direct photolysis of EC.
Figure 6 Absorption spectra of the phenoxyl radicals ob-
tained by direct photolysis of epicatechin (EC) solutions
of different concentration: 14.1 μM (
1.1 μM (ꢀ), and 40 μM (ꢁ). Inset: Plot of kapp vs. [EC].
᭹
), 17.6 μM ( ),
᭺
2
International Journal of Chemical Kinetics DOI 10.1002/kin

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VILLATA, GONZALEZ, AND M A´ RTIRE
HO
HO
OH
OH
B
.
.O
B
HO
O
SO4
O
A
C
A
C
OH
OH
HO
HO
EC
HO
O.
B
HO
O
A
C
OH
HO
Scheme 2 Formation of A ring- and B ring-phenoxyl radicals of epicatechin (EC). The phenoxyl radical in ring A may be at
ꢁ
ꢁ
either position 5 or position 7 and that in ring B, at position 3 or 4 .
BIBLIOGRAPHY
13. Caregnato, P.; David Gara, P. M.; Bosio, G. N.; Gonza-
lez, M. C.; Russo, N.; Michelini, M.; M a´ rtire, D. O. J
Phys Chem A 2008, 112, 1188–1194.
1. Gosmann, G.; Schenkel, E. P.; Seligmann, O. J Nat Prod
14. Jovanovic, S. V.; Hara, Y.; Steenken, S.; Simic, M. G. J
Am Chem Soc 1995, 117, 9881–9888.
1989, 52(6), 1367–1370.
2
3
. Pietta, P. J Nat Prod 2000, 63, 1035–1042.
. Larson, R. A. Naturally Occurring Antioxidants; CRC
Press LLC: New York, 1997.
1
5. (a) Rosso, J. A.; Rodr ´ı guez Nieto, F. J.; Gonzalez, M. C.;
M a´ rtire, D. O. J Photochem A: Chem 1998, 116, 21–
2
5; (b) Cencione, S. S.; Gonzalez, M. C.; M a´ rtire,
D. O. J Chem Soc Faraday Trans 1998, 94, 2933–
937.
4. Hollman, P. C.; Katan, M. B. Biomed Pharmacother
1997, 51, 305–310.
2
5
. Korkina, L. G.; Afanas’ev, I. B. Antioxidant and Chelat-
ing Properties of Flavonoids; In Antioxidants in Dis-
ease Mechanisms and Therapy; Sies, H. (Ed.); Academic
Press: New York, 1997; Vol. 38, pp. 151–163.
1
1
1
6. McElroy, W. J.; Waygood, S. J. J Chem Soc Faraday
Trans 1990, 86, 2557–2564.
7. Bors, W.; Michel, C. Free Radic Biol Med 1999, 27(11–
12), 1413–1426.
6
. Pannola, A.; Rice-Evans, C.; Halliwell, B.; Singh, S.
Biochem Biophys Res Commun 1997, 232, 164–168.
8. (a) Alegre, M. L.; Geron e´ s, M.; Rosso, J. A.; Bertolotti,
S. G.; Braun, A. M.; M a´ rtire, D. O.; Gonzalez, M. C.
J Phys Chem A 2000, 104, 3117–3125; (b) M a´ rtire, D.
O.; Rosso, J. A.; Bertolotti, S. G.; Carrillo LeRoux, G.;
Braun, A. M.; Gonzalez, M. C. J Phys Chem A 2001,
´
7. Avila, V.; Bertolotti, S. G.; Criado, S.; Pappano, N.;
Debattista, N.; Garc ´ı a, N. A. Int J Food Sci Technol
2001, 36, 25–33.
8
9
. Monta n˜ a, M. P.; Miskoski, S.; Criado, S.; Gianello, J.
C.; Pappano, N.; Debattista, N.; Garc ´ı a, N. A. Dyes
Pigments 2003, 58, 113–120.
105, 5385–5392.
1
9. Miao, J. L.; Wang, W. F.; Pan, J. X.; Lu, C. Y.; Li,
R. Q.; Yao, S. D. Radiat Phys Chem 2001, 60, 163–
´
. Monta n˜ a, P.; Pappano, N.; Debattista, N.; Avila Posadaz,
168.
A.; Bertolotti, S. G.; Garc ´ı a, N. A. Can J Chem 2003,
2
2
2
2
2
2
2
0. Leopoldini, M.; Marino, T.; Russo, N.; Toscano, M. J
Phys Chem A 2004, 108, 4916–4922.
1. David Gara, P. M.; Bosio, G. N.; Gonzalez, M. C.;
M a´ rtire, D. O. Int J Chem Kinet 2008, 40, 19–24.
2. Alfassi, Z. B.; Huie, R. E.; Neta, P.; Shoute, L. C. T. J
Phys Chem 1990, 94, 8800–8805.
81, 909–914.
1
0. (a) Mor a´ n Vieyra, F. E.; Boggetti, H. J.; Zampini, I. C.;
Ordo n˜ ez, R. M.; Isla, M. I.; Alvarez, R. M. S.; De Rosso,
V.; Mercadante, A. Z.; Borsarelli, C. D. Free Radic
Res 2009, 43(6), 553–564; (b) Tournaire, C.; Croux, S.;
Maurette, M. T.; Beck, I.; Hocquaux, M.; Braun, A. M.;
Oliveros, E. J Photochem Photobiol B 1993, 19(3),
3. Hug, G. L. Nat Stand Ref Data Ser, US Nat Bur Stand
1
981, 69.
4. Tamba, M.; Torreggiani, A. Radiat Phys Chem 2004, 71,
1–25.
5. Wardman, P. J Phys Chem Ref Data 1989, 18, 1637–
755.
6. Neta, P.; Grodkowski, J. J Phys Chem Ref Data 2005,
4(1), 109–199.
205–215.
1
1
1. Jovanovic, S. V.; Steenken, S.; Tosic, M.; Marjanovic,
B.; Simic, M. G. J Am Chem Soc 1994, 116(11), 4846–
2
4851.
1
2. Bosio, G.; Criado, S.; Massad, W.; Gonzalez, M. C.;
Garc ´ı a, N. A.; M a´ rtire, D. O. Photochem Photobiol Sci
3
2005, 4, 840–846.
International Journal of Chemical Kinetics DOI 10.1002/kin