Electrocatalytic Oxidation of Amines by Ni(1,4,8,11-tetraazacyclotetradecane)2+ Entrapped in Sol-Gel Electrodes

Article abstract of DOI:10.1002/ejic.201500985

NiL²⁺ (L = 1,4,8,11-tetraazacyclotetradecane) was entrapped in sol-gel matrices in the presence of graphite. The matrices thus prepared serve as electrocatalysts for the oxidation of amines. The results point out that: (1) It is easy to prepare electrocatalytic electrodes by using this approach. (2) The properties of the electrodes thus prepared depend on the nature of the precursors used to prepare the matrices. (3) The mechanism of the electrocatalytic process differs from that observed in homogeneous solutions and depends on the nature of the electrode. (4) The matrix protects NiL²⁺ against the oxidation of the ligand.

Full text of DOI:10.1002/ejic.201500985

DOI: 10.1002/ejic.201500985
Full Paper
Electrocatalysis
Electrocatalytic Oxidation of Amines by Ni(1,4,8,11-
tetraazacyclotetradecane)2+ Entrapped in Sol–Gel Electrodes
Ariela Burg,*[a] Dror Shamir,[b] Lina Apelbaum,[c] Yael Albo,[d] Eric Maimon,[b,e] and
Dan Meyerstein[e,f]
Abstract: NiL2+ (L = 1,4,8,11-tetraazacyclotetradecane) was en- nature of the precursors used to prepare the matrices. (3) The
trapped in sol–gel matrices in the presence of graphite. The
matrices thus prepared serve as electrocatalysts for the oxid-
ation of amines. The results point out that: (1) It is easy to
prepare electrocatalytic electrodes by using this approach. (2)
The properties of the electrodes thus prepared depend on the
mechanism of the electrocatalytic process differs from that ob-
served in homogeneous solutions and depends on the nature
of the electrode. (4) The matrix protects NiL2+ against the oxid-
ation of the ligand.
Introduction
fore, the main applications of such electrodes are for analytical
purposes and as sensors.[16]
The simplicity and versatility of preparation of SiO2 matrices by
the sol–gel method, as well as the relative inertness and stabil-
ity of the matrices, have promoted their use in a wide range of
applications.[1] A variety of active species can be incorporated
into these matrices, including organic[1b] and inorganic com-
pounds,[2] metals and metal oxide nanoparticles,[3] bacteria,[4]
yeasts,[5] and enzymes.[1a,4,6] The matrices thus prepared can,
among other things, act as catalysts,[7] photocatalysts,[8] electro-
catalysts,[9] slow-release agents,[10] ion-exchange columns,[11]
and electron-exchange columns.[2]
The advantages of electrodes consisting of an electrocatalyst
entrapped in a sol–gel matrix coating a good conductor are:
(1) The electrocatalyst can be recycled many times.[12] (2) The
electrode can operate in a medium in which the electrocatalyst
is insoluble and/or unstable.[2,12b]
It seemed of interest to check whether the incorporation of
a redox catalyst into a sol–gel matrix synthesized in the pres-
ence of graphite powder, introduced to improve conductivity,
transforms it into an electrocatalyst. NiL2+ (L = 1,4,8,11-tetraaza-
cyclotetradecane) was chosen as the potential electrocatalyst
for the oxidation of amines, as it acts as an electrocatalyst for
this process in homogeneous solutions[12b] and when it is ad-
sorbed onto active carbon.[13] The following questions were
asked:
(1) Does the nature of the precursors used to prepare the sol–
gel matrix affect the electrocatalytic properties of the elec-
trode?
(2) Does the entrapment of NiL2+ protect it from oxidative de-
composition? In homogeneous solutions, NiL3+ decomposes by
a second-order process[17] oxidizing the ligand. This reaction is
base-catalyzed,[17a] that is, the life time of NiIIIL in neutral and
alkaline solutions is very short.[17a] It was shown that NiIIIL en-
trapped in a sol–gel matrix is stable even at pH 10.[3] This obser-
vation was attributed to the inhibition of the reaction between
two NiIIIL complexes in the matrix. However, in electrochemical
experiments the electrode can, in principle, replace the second
NiIIIL and thus decompose the catalyst.
The applications of these matrices in electrocatalysis are lim-
ited, because the matrices are insulators[13] and therefore the
plausible current densities are low.[14] Furthermore, the diffu-
sion of the substrate to the electrocatalyst is slow.[13,15] There-
[a] Chemical Engineering Department,
SCE – Shamoon College of Engineering,
Beer-Sheva, Israel
E-mail: arielab@sce.ac.il
In the present study, we decided to check whether elec-
trodes consisting of a mixture of graphite, as the conducting
component, and a sol–gel matrix containing NiL2+ can be used
for the oxidation of (CH3)nNH3–n. This choice is based on the
following arguments:
[b] Nuclear Research Centre Negev,
P.O.B. 9001, Beer-Sheva, Israel
[c] R & D, Makhteshim Chemical Works, Ltd.,
Beer Sheva, Israel
[d] Chemical Engineering Department, Ariel University,
Ariel, Israel
[e] Chemistry Department, Ben-Gurion University of the Negev,
Beer-Sheva, Israel
[f] Biological Chemistry Department, Ariel University,
Ariel, Israel
(1) NiL2+ is a known electrocatalyst for the oxidation of amines
in aqueous solutions[18] and in heterogeneous systems.[19]
(2) These amines are formed in a variety of industrial processes
as byproducts,[20] that is, as pollutants, and therefore their oxid-
ation is of environmental interest.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/ejic.201500985.
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Results and Discussion
The sol–gel electrodes were prepared by modifying the proce-
dure reported in the literature.[9d] A-1 and A-2 electrodes con-
sist only of graphite and the corresponding precursor of the
sol–gel matrix. A-1 electrodes were prepared with trimethoxy-
methylsilane (MTMOS) as the precursor, and A-2 electrodes
were prepared with trimethoxyphenylsilane (TMOP) as the pre-
cursor. The Ni electrodes are identical to the A-i electrodes but
contain NiL(PF6)2. The composition of the electrodes is summed
up in Table S1 in the Supporting Information.
Figure 1. Voltammograms of methylamine on different electrodes (50 mV/s;
solution containing 3.0
M CH3NH2, 0.10 M NaClO4 at pH 10.0; black: glassy
carbon electrode, red: A-1 and green: A-2 sol–gel electrodes).
Leakage Study
The cyclic voltammograms of Ni-i electrodes in NaClO4 solu-
tions at pH 10.0 (insets in Figures 2 and 3) point out that the
entrapped NiL2+ is pseudo-reversibly oxidized at about 0.8 and
0.9 V in the Ni-1 and Ni-2 electrodes, respectively. These oxid-
ation potentials are similar to the potential at which NiL2+ is
oxidized in homogeneous solutions,[21] 0.78 V vs. Ag/AgCl at pH
2.2. It is important to note that these cyclic voltammograms are
not affected by many repetitions of the cycles or by using the
electrodes in the presence of amines and then, after washing,
in the absence of amines. This result indicates that the ligand
in NiL2+ is not oxidized in the process, as the matrix protects it.
One of the major disadvantages of sol–gel matrices is the plau-
sible leakage of the active species from the matrix. The leakage
of NiIII/IIL from the electrodes was studied. Details of the leakage
study are given in the Supporting Information (Part S2). The
results indicate that the leakage is negligible (less than 1 %) for
both kinds of electrodes. This is lower than that reported for
NiIII/IIL entrapped in sol–gel matrices.[2] The source of this differ-
ence is probably the presence of graphite that affects the na-
ture of the matrices either by adsorption of NiIII/IIL on the graph-
ite and/or by affecting the structure of the matrices.
Oxidation of Amines
The electrochemical oxidation of three amines, methylamine,
dimethylamine, and trimethylamine, was studied by using sol–
gel electrodes without entrapped NiL2+ [glassy carbon (GC), A-
1, and A-2 electrodes]. Figure 1 depicts the electrochemical
oxidation of methylamine on glassy carbon, A-1, and A-2 elec-
trodes. At lower pH values, the catalytic currents are small. As
the sol–gel electrodes have a large surface area, the double-
layer-charging current interferes with the exact measurement
of the catalytic current at pH < 10. Therefore, a pH value of 10
was chosen. The results point out that the three amines studied
are oxidized above 0.90 V vs. Ag/AgCl, when NiL2+ is not en-
trapped in the electrode.
Figure 2. Voltammograms on sol–gel electrodes (50 mV/s; solution containing
3.0
M
(CH3)2NH, 0.10
M
NaClO4 at pH 10.0; red: Ni-1 and black: Ni-2 sol–gel
electrodes; inset: 0.10
electrodes).
M NaClO4 at pH 10.0; red: Ni-1 and black: Ni-2 sol–gel
In the presence of amines (Figures 2 and 3), considerable
oxidation currents are observed at values greater than 0.6 V vs.
Figure 3. Voltammograms on a Ni-2 sol–gel electrode (50 mV/s; all solutions contained 0.10
NH2CH3; inset: 0.10 NaClO4 at pH 10.0).
M NaClO4 at pH 10.0 and 3.0 M each of N(CH3)3, NH(CH3)2, and
M
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Ag/AgCl. The results are similar to the electro-oxidation of these is nearly independent on [NH(CH3)2], that is, that diffusion is
amines on glassy carbon electrodes in the presence of NiL2+ in not the rate-determining step in the process. Even for the Ni-1
solution.[18] Thus, the results demonstrate that NiL2+ acts as an electrodes, the results suggest that at high concentrations of
electrocatalyst also when it is immobilized in sol–gel matrices.
It is of interest to note that the results (Figure 3) point out
that N(CH3)3 is oxidized through an electrocatalyzed process by
the Ni-2 electrodes though this does not happen in the pres-
ence of NiL2+ in homogeneous solutions.[12b] This result sug-
gests that the mechanism of oxidation in homogeneous solu-
tions differs from that in the sol–gel electrodes.
the substrate the dependence of the current on the concentra-
tion is no longer linear and approaches an asymptotic value,
that is, also for these electrodes at high scan rates and high
concentrations, the electrocatalytic process is not diffusion-con-
trolled.
The current was studied as a function of the scan rate with
and without dimethylamine in the solution, Figure 4 describes
the results.
The linear dependence of the current on (scan rate)1/2 sug-
gests that the observed electrochemical oxidations are gov-
erned by diffusion-controlled mechanisms. In the absence of
the amines, it is the oxidation of the NiL2+ complex, in the pres-
ence of amines it is the oxidation of the amines. However, the
intercepts in Figure 4 and the plateau observed for the catalytic
oxidation of NH(CH3)2 on Ni-2 at the high scan rates (Figure 4)
indicate that the mechanism is not simply diffusion-controlled.
Similar results were reported for the oxidation of NiL2+ cova-
lently bound to a sol–gel matrix embedded in a Nafion mem-
brane adsorbed onto a glassy carbon electrode.[22] These results
are not surprising, as the entrapped NiL2+ species clearly do not
Figure 5. Current as a function of [(CH3)2NH]. All solutions containing 0.10
NaClO4 at pH 10.0, 200 mV/s. Red squares: Ni-1 sol–gel electrode; black cir-
cles: Ni-2 sol–gel electrode.
M
The results point out that the composition of the electrodes,
diffuse freely in the matrix. The observation that the depend- that is, the nature of the precursors used to prepare the matri-
ence of the current on (scan rate)1/2, for the electrocatalytic ces, affects the efficiency of the electrocatalytic process consid-
oxidation of amines on Ni-2 electrodes, changes from linear to erably (Figure 4). This result is in accord with previously re-
independent at higher scan rates suggests a change in the rate- ported results.[13,23] The decrease in the current in the Ni-2 elec-
determining step, which implies a change in mechanism from trodes relative to that in the Ni-1 electrodes is attributed to the
diffusion-controlled to electron-transfer-controlled. To check steric hindrance caused by the phenyl groups in the pores and
this possibility, the dependence of the current on the concen- to the increased hydrophobicity of the electrodes. Furthermore,
tration of NH(CH3)2 at the high scan rate was studied (Figure 5). the double-layer-charging current of Ni-1 is larger than that of
The results clearly point out that for Ni-2 electrodes, the current Ni-2, which indicates that the surface area of Ni-1 is considera-
Figure 4. Current as a function of (scan rate)1/2. All solutions at pH 10.0. Red squares: Ni-1 sol–gel electrode; solution containing 3.0
NaClO4; 1.1 V. Blue diamonds: Ni-1 sol–gel electrode; solution containing 0.10 NaClO4; 1.0 V. Blue circles: Ni-2 sol–gel electrode; solution containing 3.0
(CH3)2NH, 0.10 NaClO4; 1.0 V. Green triangles: Ni-2 sol–gel electrode; solution containing 0.10
absence of (CH3)2NH. The original voltammograms are presented in Figures S4–S7.
M
(CH3)2NH, 0.10
M
M
M
M
M
NaClO4; 0.96 V. Inset: magnification of the results in the
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formed with a Metrohm Autolab potentiostat, Multi-channel, which
is connected to Autolab hardware GPES software. All potentials are
vs. Ag°/AgCl. In all the experiments, the counter electrode was Pt.
The sol–gel electrodes were connected to the electrochemical cell
by a Pt wire.
bly larger than that of Ni-2; this might clearly also contribute
significantly to the differences in the observed catalytic current.
(We thank one of the reviewers for pointing this out.)
Formaldehyde,
a known product of the oxidation of
NHn(CH3)3–n, n = 1–3, was identified as a product of the electro-
catalytic processes studied, by applying a literature proce-
dure.[24] The yield of the process, about 30 %, was calculated
from the spectrophotometric results. The source of the rela-
tively low yield might be the electrocatalytic oxidation of the
CH2O formed in the pores near the electrocatalyst. The analyti-
cal method is outlined in the Supporting Information (Part S3).
Preparation of the Electrodes
Sol–gel electrodes were prepared by modifying the procedure re-
ported in the literature[9a,9d] in order to optimize the electrodes for
our applications. The amounts of the graphite, precursors (MTMOS/
TMOP), and NiIIL(PF6)2 components were studied. The optimal con-
ditions were chosen on the basis of the quality of the cyclic voltam-
mograms and the leaching of the active species, NiIIL2+. The precur-
sor effect on the drying time of the electrodes indicates that the
drying process takes several days longer when TMOP is used rela-
tive to the process with use of MTMOS. Table S1 sums up the com-
position of each type of electrode. The nominal surface area of the
electrodes is (7 1) mm2; however, as a result of the porous nature
of the electrodes, it is actually significantly larger, and the capacity
of the double layer is large and inhibits observations of small Fara-
daic currents. As the exact surface area of each electrode differs
somewhat from those of other electrodes, the points for each type
of electrode in one plot were all measured with the same electrode.
Figure S1 describes a sol–gel electrode.
Concluding Remarks
The results presented herein point out that:
(1) The sol–gel electrodes prepared by this simple method are
efficient electrocatalysts; reactive electrocatalysts can be en-
trapped by this technique.
(2) The ligand of the electrocatalyst, NiIIL2+, is not oxidized dur-
ing the catalytic oxidation of the substrates, although it is oxi-
dized at pH 10 in homogeneous solutions. It should be noted
that the pH in the pores of the matrices might be lower than
that in the homogeneous solution because of the (Si–O)3–SiOH
groups.
After each set of cyclic voltammetric measurements with a given
Ni-i sol–gel electrode as a working electrode, the electrode was
checked in a NaClO4 solution. The results pointed out that the cyclic
voltammograms were similar to those shown in the inset of Fig-
ure 2. These experiments point out that the entrapped NiIIL2+ re-
mained intact during the experiments and the ligand was not oxi-
dized, as was reported for NiIIL2+ electrolyzed in alkaline homogene-
ous solutions by using solid working electrodes.[26]
(3) The mechanism of the electrocatalytic process clearly differs
from that in homogeneous solutions. Thus, (CH3)3N is catalyti-
cally oxidized on the sol–gel electrodes, although it is not oxi-
dized on glassy carbon electrodes.[12b]
(4) The mechanism of oxidation of the substrate depends on
the concentration and the nature of the electrode, moving from
a diffusion-controlled to an electron-transfer-controlled proc-
esses with an increase in the scan rate and with an increase in
the concentration of the substrate.
(5) The choice of the precursors used to prepare the sol–gel
matrices has a major impact on the performance of the elec-
trode in electrocatalytic processes. Clearly this has to be opti-
mized.
Acknowledgments
This study was supported in part by a grant from the Pazi
Foundation. A. B. would like to thank Dani Shahar from DS Bio-
analytics, Ltd. and the companies Ivium Technologies BV and
Palmsens BV for their support.
Keywords: Electrochemistry · Sol–gel processes · Oxidation ·
Nickel · Amines
Experimental Section
Materials and Methods
[1] a) D. Avnir, S. Braun, O. Lev, M. Ottolenghi, Chem. Mater. 1994, 6, 1605–
1614; b) D. Avnir, Acc. Chem. Res. 1995, 28, 328–334.
[2] Y. Lavi, A. Burg, E. Maimon, D. Meyerstein, Chem. Eur. J. 2011, 17, 5188–
5192.
[3] a) E. Della Gaspera, M. Guglielmi, A. Martucci, L. Giancaterini, C. Cantalini,
Sensors Actuators B 2012, 164, 54–63; b) E. Della Gaspera, V. Bello, G.
Mattei, A. Martucci, Mater. Chem. Phys. 2011, 131, 313–319.
[4] D. Avnir, T. Coradin, O. Lev, J. Livage, J. Mater. Chem. 2006, 16, 1013–
1030.
A.R. grade sodium perchlorate, perchloric acid, trimethoxyphenyl-
silane (TMOP), trimethoxymethylsilane (MTMOS), methylamine,
graphite, dimethylamine, and trimethylamine were purchased from
Aldrich. The ligand, L = 1,4,8,11-tetraazacyclotetradecane, and the
complex, NiIIL(Cl2)2, were synthesized by a previously reported
method.[25] This complex was transformed into NiIIL(PF6)2 by adding
an equivalent amount of AgPF6 and recrystallizing.
[5] A. Mellati, H. Attar, M. F. Farahani, Asian J. Biotechnol. 2010, 2, 127–132.
[6] a) H. Frenkel-Mullerad, D. Avnir, J. Am. Chem. Soc. 2005, 127, 8077–8081;
b) R. B. Bhatia, C. J. Brinker, A. K. Gupta, A. K. Singh, Chem. Mater. 2000,
12, 2434–2441; c) V. V. Vinogradov, D. Avnir, RSC Adv. 2015, 5, 10862–
10868.
All the solutions were prepared in deionized water that was further
purified by passing through a Milli Q Millipore setup to obtain a
final resistivity greater than 10 MΩ/cm. Ar from Maxima was used
to deaerate the solutions for at least 5 min.
[7] a) O. A. Kholdeeva, N. V. Maksimchuk, G. M. Maksimov, Catal. Today 2010,
157, 107–113; b) R. Abu-Reziq, H. Alper, Appl. Sci. 2012, 2, 260–276; c) E.
Kemnitz, S. Wuttke, S. M. Coman, Eur. J. Inorg. Chem. 2011, 4773–4794;
d) D. P. Debecker, K. Bouchmella, M. Stoyanova, U. Rodemerck, E. M.
Gaigneaux, P. H. Mutin, Catal. Sci. Technol. 2012, 2, 1157–1164; e) D. P.
Debecker, V. Hulea, P. H. Mutin, Appl. Catal. A 2013, 451, 192–206.
All the experiments were performed in solutions with an ionic
strength of 0.10
NaClO4.
M, which was maintained by the addition of
Spectra were measured with a UV/Vis Agilent 8453 Diode Array
spectrophotometer. The electrochemical experiments were per-
Eur. J. Inorg. Chem. 2016, 459–463
www.eurjic.org
462
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
[8] a) U. G. Akpan, B. H. Hameed, Appl. Catal. A 2010, 375, 1–11; b) T. K.
Tseng, Y. S. Lin, Y. J. Chen, H. Chu, Int. J. Mol. Sci. 2010, 11, 2336–2361.
[9] a) O. Lev, Z. Wu, S. Bharathi, V. Glezer, A. Modestov, J. Gun, L. Rabinovich,
S. Sampath, Chem. Mater. 1997, 9, 2354–2375; b) J. A. Cox, J. Solid State
Electrochem. 2011, 15, 1495–1507; c) I. Bilecka, M. Niederberger, Electro-
chim. Acta 2010, 55, 7717–7725; d) O. Lev, S. Sampath, Electroanal. Chem.
2010, 23, 211–304.
[10] a) R. Chen, H. Qu, A. Agrawal, S. Guo, P. Ducheyne, J. Mater. Sci. Mater.
Med. 2013, 24, 137–146; b) K. Li, Q. Su, W. Yuan, B. Tian, B. Shen, Y. Li,
W. Feng, F. Li, ACS Appl. Mater. Interfaces 2015, 7, 12278–12286.
[11] A. Mohammad, S. Hussain, Polymer Composites 2015, Ahead of Print.
[12] a) C. Delacote, J.-P. Bouillon, A. Walcarius, Electrochim. Acta 2006, 51,
6373–6383; b) R. Ciriminna, G. Palmisano, M. Pagliaro, ChemCatChem
2015, 7, 552–558.
[17] a) E. Zeigerson, G. Ginzburg, L. J. Kirschenbaum, D. Meyerstein, J. Electro-
anal. Chem. Interfacial. Electrochem. 1981, 127, 113–126; b) E. Zeigerson,
G. Ginzburg, D. Meyerstein, L. J. Kirschenbaum, J. Chem. Soc., Dalton
Trans. 1980, 7, 1243–1247.
[18] D. Shamir, I. Zilbermann, E. Maimon, D. Meyerstein, Eur. J. Inorg. Chem.
2004, 20, 4002–4005.
[19] G. Subramanian, P. Nalawade, S. J. Hinder, S. C. Pillai, H. Prakash, RSC Adv.
2015, 5, 31716–31724.
[20] a) S.-K. Mourya, D. Bose, A. Durgbanshi, J. Esteve-Romero, S. Carda-Broch,
Anal. Methods 2011, 3, 2032–2040; b) A. E. Poste, M. Grung, R. F. Wright,
Sci. Total Environ. 2014, 481, 274–279, cf. Sacher, S. Lenz, H.-J. Brauch, J.
Chromatogr. A 1997, 764, 85–93.
[21] I. Zilbermann, A. Meshulam, H. Cohen, D. Meyerstein, Inorg. Chim. Acta
1993, 206, 127–130.
[22] S. Attia, A. Shames, I. Zilbermann, G. Goobes, E. Maimon, D. Meyerstein,
Dalton Trans. 2014, 43, 103–110.
[23] Neelam, Y. Albo, D. Shamir, A. Burg, G. Goobes, D. Meyer-
stein, 2015, submitted for publication..
[24] T. Nash, Nature 1952, 170, 976.
[13] M. Pagliaro, R. Ciriminna, M. W. C. Man, S. Campestrini, J. Phys. Chem. B
2006, 110, 1976–1988.
[14] R. Ciriminna, A. Fidalgo, V. Pandarus, F. Beland, L. M. Ilharco, M. Pagliaro,
Chem. Rev. 2013, 113, 6592–6620.
[15] a) M. Kanungo, M. M. Collinson, Langmuir 2005, 21, 827–829; b) B.
Le Ouay., T. Coradin, C. Laberty-Robert, J. Phys. Chem. C 2013, 117,
15918–15923.
[25] E. K. Barefield, F. Wagner, A. W. Herlinger, A. R. Dahl, Inorg. Synth. 1976,
16, 220–225.
[16] a) A. Walcarius, D. Mandler, J. A. Cox, M. Collinson, O. Lev, J. Mater. Chem.
2005, 15, 3663–3689; b) S. Goubert-Renaudin, M. Moreau, C. Despas, M.
Meyer, F. Denat, B. Lebeau, A. Walcarius, Electroanalysis 2009, 21, 1731–
1742; c) O. Nadzhafova, M. Etienne, A. Walcarius, Electrochem. Commun.
2007, 9, 1189–1195; d) R. Pauliukaite, M. Schoenleber, P. Vadgama,
C. M. A. Brett, Anal. Bioanal. Chem. 2008, 390, 1121–1131.
[26] D. A. Issahary, G. Ginzburg, M. Polak, D. Meyerstein, J. Chem. Soc., Chem.
Commun. 1982, 8.
Received: August 29, 2015
Published Online: November 25, 2015
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