Preparation and characterisation of a quinone-functionalised polythiophene film on a modified electrode. Application to the potentiometric determination of glutathione and cysteine concentrations

Article abstract of DOI:10.1016/j.tet.2008.07.041

The new compound 3-((2,5-dimethoxyphenyl)ethynyl)thiophene has been synthesised by Sonogashira coupling. A modified electrode coated with a polythiophene film bearing a quinone moiety was obtained by electropolymerisation of the thienyl group followed by anodic oxidation of para-dimethoxyphenyl group. The cyclovoltammetric response resulting from the reaction of glutathione with the benzoquinone moiety was investigated. The responses of the modified electrode as a new potentiometric sensor of reduced thiols are proposed.

Full text of DOI:10.1016/j.tet.2008.07.041

Tetrahedron 64 (2008) 9619–9624
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Preparation and characterisation of a quinone-functionalised polythiophene
film on a modified electrode. Application to the potentiometric determination
of glutathione and cysteine concentrations
a
,
, ,
,
,
d
, ,
z
Stephanie Etienne y, Muriel Matt b, Thierry Oster c z, Mohammad Samadi a b, Marc Beley b
*
*
´
´
a LIMBP, IPEM, Universite´ Paul Verlaine-Metz, 1 Boulevard Arago, 57070 Metz, France
b LCME, Universite´ Paul Verlaine-Metz, 1 Boulevard Arago, 57070 Metz, France
c
´
`
Laboratoire Lipidomix ENSAIA-INPL, Nancy-Universite, 15 rue de la Champelle, 54500 Vandœuvre-les-Nancy, France
d
`
´
´
´
`
Synthese Organique et Reactivite, UMR CNRS/UHP7565, Nancy-Universite, Boulevard des Aiguillettes, 54506 Vandœuvre-les-Nancy, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 1 May 2008
Received in revised form 10 July 2008
Accepted 13 July 2008
Available online 17 July 2008
The new compound 3-((2,5-dimethoxyphenyl)ethynyl)thiophene has been synthesised by Sonogashira
coupling. A modified electrode coated with a polythiophene film bearing a quinone moiety was obtained
by electropolymerisation of the thienyl group followed by anodic oxidation of para-dimethoxyphenyl
group. The cyclovoltammetric response resulting from the reaction of glutathione with the benzoqui-
none moiety was investigated. The responses of the modified electrode as a new potentiometric sensor of
reduced thiols are proposed.
Keywords:
Quinone-functionalised polythiophene
Modified electrode
Ó 2008 Elsevier Ltd. All rights reserved.
Glutathione/cysteine electrochemical
sensor
1. Introduction
sulfide produced shows a characteristic yellow colour. However,
this test and more generally spectrophotometric methods require
Reduced thiols are essential in biological systems, on account of
their crucial role in the maintenance of redox homeostasis. Their
concentration and bioavailability are of major importance to
balance the accumulation of reactive oxygen and nitrogen species
and to prevent subsequent deleterious oxidative stress associated
with the pathogenesis of cancer, cardiovascular diseases, athero-
sclerosis, hypertension, ischemia/reperfusion injury, diabetes mel-
litus, neurodegenerative diseases, rheumatoid arthritis and ageing.1
Over the past three decades, intensive studies have been de-
voted to the detection of biological thiols as cysteine, homocysteine
and more particularly glutathione.2 Ellman’s test is the classical
method used for quantification of thiols based on a spectrophoto-
metric method laying an exchange reaction between the thiol and
the disulfide DTNB (5,50-dithiobis-(2-nitrobenzoic acid)).3 The
a pre-treatment when thiols have to be assayed in coloured
samples and their results may be influenced by variable levels of
specific enzyme activities such as glutathione S-transferase or
g-glutamyltransferase.
High-performance liquid chromatography and capillary
electrophoresis are used as separative techniques to determine
glutathione and congeners in several bio-matrices.4 Besides, fluo-
rescence methods have been recently developed for the measure-
ments of glutathione in yeast.5
In contrast with most of these techniques, the electrochemical
methods provide the possibility of being used with coloured sam-
ples, such as blood, without tedious pre-treatment. Two types of
electrochemical sensors for the determination of thiol concentra-
tions are commonly studied.
- With an amperometric sensor, the thiol detection is generally
based on chemically-modified electrodes that induce an elec-
trocatalytic oxidation of another thiol obtained after an ex-
change reaction as in the Ellman’s test.6–9 Another
amperometric approach is the use of organic redox cofactors
like pyrroloquinoline quinone, glutathione peroxidase or in-
organic redox mediators as transition metal complexes
immobilised in a matrix.10–13 In these systems, intermediate
* Corresponding authors. Tel.: þ33 3383678211 (T.O); þ33 3383684783 (M.B).
E-mail addresses: thierry.oster@mtm.nancy.inserm.fr (T. Oster), marc.beley@
sor.uhp-nancy.fr (M. Beley).
y
Present address: Centre de Recherche Public Henri Tudor, Laboratoire de
´
´
Technologies Industrielles, Unite des Materiaux, 66, Rue de Luxembourg, BP 144,
L-4002 Esch-sur-Alzette, Luxembourg.
z
T.O. and M.B. are Associate Professor and Professor, respectively, at the
University Paul Verlaine-Metz.
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.07.041

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S. Etienne et al. / Tetrahedron 64 (2008) 9619–9624
9620
in triethylamine at 80 ꢀC after refluxing for one night, compound II,
2-methyl-4-(2,5-dimethoxyphenyl)-3-butyn-2-ol, was isolated
with a yield of 40%. By a retro-Favorskii reaction, the protective
group R1 was removed by heating compound II in a solution of
sodium hydroxide in toluene.17 The expected product A was pre-
pared by a second coupling between III and 3-bromothiophene. To
try to improve the yield in this last step, we also used the conditions
described by Thorand and Krause,18 but the efficiency was no better
than 38%. The quinonic product corresponding to the chemical
oxidation of A by cerium(IV) ammonium nitrate (CAN) appeared to
be very unstable. Consequently, we attempted to obtain the qui-
none group after electropolymerisation of monomer A.
steps are necessary because the direct oxidation of thiols is
slow at conventional electrodes and consequently require an
important overpotential due to electrode passivation.
- In potentiometric methods, the sensors are usually based on
the reaction between thiols and quinone indicators, as de-
scribed by Davis et al.14Among the electrochemical methods,
the potentiometric method can be implemented very easily.
Lau et al. have shown that the reaction of 1,4 benzoquinone (BQ)
with the reduced form of glutathione (GSH) results in the formation
of adducts that exhibit increasing degrees of glutathione sub-
stitution.15 Moreover, as preliminary studies, the interaction of GSH
with BQ by cyclic voltammetry on a vitreous carbon electrode was
investigated (data not shown). The cyclic voltammogram of BQ was
significantly modified when this compound was added to a solu-
tion of GSH. The principal changes consisted in the oxidation pro-
cess that became irreversible and in the significant decrease in
intensity of the oxidation peak. The latter modification charac-
terised the diffusion of a bigger species than BQ. Consequently, in
agreement with Lau’s work, we postulated that the modification of
the electrochemical behaviour of the couple BQ/BHQ (BHQ¼1,4
hydroquinone) was due to the formation of adducts between GSH
and BQ.
2.2. Electrochemical preparation of a polythiophene film
bearing a quinone moiety
The electrodeposition of the polythiophene film was performed
by successive scans in the positive potential part (0.5–1.5 V). The
coverage of deposited polymer can be adjusted by varying the
number of cyclical potential scans. Typically, after 20 scans corre-
sponding to the exchange of 34 mC, the thickness of the dark green
polymeric film was estimated at 0.2 m
m.19
By chronoamperometry at 1.6 V/SCE for 5 min, the methoxy
groups were oxidised to the corresponding quinonic forms. The
presence of the quinone moiety was confirmed by the cyclic vol-
tammetry experiments performed in the monomer-free buffer
electrolyte (pH 7), the resulting yellow-brown film being washed
with the solvent and water before this experiment. The voltam-
mogram of the corresponding coated electrode (Fig. 1A) indeed
In this work, we describe a new potentiometric sensor for the
detection of glutathione (GSH) and cysteine (CSH). This system is
based on the reaction between the BQ moiety borne by a polymeric
film and the thiol.
2. Results and discussion
clearly shows a reversible peak at 0.0 V/SCE (
D
Ep¼40 mV) corre-
The indicating modified electrode was obtained by anodic
electropolymerisation (Scheme 1) of the thiophene group of
sponding to the BQ/BHQ couple immobilised at the modified
electrode. Moreover, the formation of the quinone after electro-
chemical oxidation of the methoxy group was confirmed by FTIR in
diffuse reflectance mode (DRIFT). The DRIFT analysis of the film
after oxidation shows a strong band at 1659 cmꢁ1 corresponding to
the presence of the quinone group. The efficiency of the electro-
chemical oxidation is confirmed by a large decrease of the
1221 cmꢁ1 band attributed to the methoxy function observed on
the film before the oxidation step.
3-((2,5-dimethoxyphenyl)ethynyl)thiophene
A where the 1,4-
dimethoxyphenyl moiety is the precursor of quinone B.
MeO
electropolymerisation
and electrochemical
deprotection
A
B
O
n
S
S
OMe
O
Scheme 1. Electropolymerisation of 1-(3-(1,4-dimethoxyphenyl)-2-(3-thienyl))ethyne
and deprotection of methoxy groups.
2.3. Cyclic voltammetric response in the presence of
glutathione
2.1. Synthesis of 3-((2,5-dimethoxyphenyl)ethynyl)thiophene
monomer A
The voltammograms of the modified electrode bearing the
quinone moiety are modified in presence of GSH in pH 7 buffer.
Indeed, with 1 mM of GSH, the intensity of the current peak cor-
responding to the BQ/BHQ couple is time-dependent (Fig. 1B, C and
D) and decreases over time. The signal corresponding to the redox
couple completely disappeared after about 1 h. There are two
possible different pathways through which quinone moieties could
After different attempts, the more efficient route to obtain A is
described below (Scheme 2).
By bromination of para-dimethoxybenzene with N-bromo-
succinimide in acetonitrile, 2-bromo-1,4-dimethoxybenzene (I)
was obtained with a yield of 90%. Two routes were tested (step 1,
Scheme 2). In the first one, we used a water/acetonitrile mixture
(1:10) as solvent, room temperature, without copper(I) in presence
of a quaternary ammonium salt to improve the efficiency.16 How-
ever, the yield was no better than 34%. In the second route, with CuI
interact with GSH. In the first one, in agreement with the apparent
0
redox potential (E0
¼ꢁ0.47 V/SCE at pH 7), the quinone
GSSG/GSH
form could oxidise GSH to its corresponding disulfide form (GSSG)
and be reduced in hydroquinone.20 In the second pathway, the
modification of the electrochemical behaviour could be due to
II
III
I
A
OMe
MeO
MeO
MeO
Sonogashira
coupling
Sonogashira
coupling
deprotection
+
R1
R1
Br
S
Br
OMe
OMe
OMe
OMe
S
R1= C(CH3)2OH
Scheme 2. Synthesis of 1-(3-(1,4-dimethoxyphenyl)-2-(3-thienyl))ethyne.

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S. Etienne et al. / Tetrahedron 64 (2008) 9619–9624
9621
Figure 1. Cyclic voltammetric responses without or with glutathione. A: phosphate buffer pH¼7; B, C and D: in presence of GSH (1 mM in phosphate buffer) after 7 min, 14 min and
60 min of reaction time, respectively. Magnetic stirring (100 rpm) between each measurement.
a nucleophilic addition as a reductive 1,4-Michael addition of GSH
to BQ to form a reduced adduct.14a,15 The second pathway is pre-
dominant as the peak corresponding to the redox couple BQ/BHQ
disappeared after 1 h of reaction between GSH and the quinone.
This hypothesis agrees with our preliminary results and the work of
Lau et al.15 A redox mechanism corresponding to the oxidation
of GSH to GSSG by BQ should induce the formation of BHQ that
can be reoxidised in quinone and consequently detected by
cyclovoltammetry.
a value dictated by the relative surface concentrations of oxidised
and reduced forms, which can be quinone, hydroquinone and ad-
ducts also in their oxidised and reduced forms because the mea-
surements were performed with O2 present in the solution, which
can oxidise the adducts. The potential was recorded 4 min after
addition of an aliquot of thiol in order to obtain a steady state
3 µmole GSH
360
These results allowed us to consider the assay of two bio-
logically significant reduced thiols, GSH and cysteine (CSH), by
potentiometry, using this new modified electrode as an indicating
sensor.
3 µmole GSSG
355
350
345
340
335
330
15 µmole GSH
3 µmole GSSG
30 µmole GSH
2.4. Potentiometric measurements of GSH and CSH in a pH 7
buffer solution
30 µmole H2SO4
The potentiometric response of the modified electrode in pH 7
buffer is shown in Figure 2. Upon adding aliquots of GSH to the
solution (3 to 30 mmol), the electrode potential decreases signifi-
cantly. This fact is attributed to the reductive 1,4-Michael addition
of GSH to the quinone moiety borne by the polythiophene film to
form reduced adducts. With a higher concentration of thiol, the
amount of adducts formed increases, hence, the surface concen-
tration in the quinonic moiety decreases and the electrode poten-
tial is modified. The modified electrode potential stabilised at
0
5
10
15
20
Time (min)
25
30
35
40
Figure 2. Response of the modified electrode after addition of several quantities of
GSH, GSSG and H2SO4.

´
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0.400
S. Etienne et al. / Tetrahedron 64 (2008) 9619–9624
0.34
0.32
0.3
0.300
0.200
0.100
0.28
0.26
0.24
0.22
-3.8
-3.6
-3.4
log [GSH]
-3.2
-3
Glutathione
Cysteine
Figure 5. Comparison of electrode response of GSH in pH 7 buffer in the presence (6)
and absence (-) of bovine serum albumin (10 g/L).
0.0E+00
4.0E-04
8.0E-04
1.2E-03
Thiol (M)
Therefore for the same concentration and the same electrode sur-
face, the amount of adducts is more significant with CSH than with
GSH.
Figure 3. Effect of addition of thiol (GSH ,, CSH B) on potential electrode response in
pH 7 buffer.
between the concentration of the quinone at the electrode surface
and the concentration of the thiol in the solution.
2.5. Potentiometric measurements of GSH and CSH in
complex media
It should be pointed out (Fig. 2) that the potential remains
constant after the addition aliquot of GSSG. Likewise, adding acid
(H2SO4, 0.6 mM) does not change the potential. The addition of GSH
has also no effect on the potential of a polythiophene electrode
prepared without quinone moiety. These experiments show clearly
that the decrease of the potential is due to a reaction between GSH
and the quinone on the polythiophene film. To confirm this, we
studied the response of the modified electrode with the addition of
CSH.
The modified electrode was also evaluated in complex media
as culture media in order to determine thiol concentration in
biological samples. Because oxidative stress is increasingly in-
volved in more and more pathological situations, it is necessary to
assess the advantage of the electrode in the clinical measure-
ments of thiols, especially with respect to the possible influence
of albumin and other proteins abundant in most biological
fluids.
Figure 3 shows the potential responses increasing concentra-
tions of GSH and CSH. A plateau appears, giving a maximal de-
tection of 0.8 mM for GSH and 1 mM for CSH, respectively. This
plateau is attributed to the saturation of the surface by the thiol. It
appears that the modified electrode gives a highest response factor
in the case of CSH than for GSH. Figure 4 shows the logarithmic
dependence where a linear response is obtained with a good
The presence of serum albumin (10 g/L) in the potassium buffer
(Fig. 5) does not affect the sensitivity with GSH concentrations up to
1 mM, where the value of potential is decreased. Then, the con-
centration can be estimated with respect to the log equation of
a standard curve established with 0.2–1 mM GSH standards in the
biological medium of interest, yielding a linear response (re-
gression coefficient of at least 0.98) with pretty good repeatability
(variation coefficient lower than 2.5%) and reproducibility (varia-
tion coefficient lower than 7%).
correlation,
the
slope
being
ꢁ0.100 V logꢁ1[CSH]
and
ꢁ0.045 V logꢁ1[GSH]. This behaviour can be explained by the steric
hindrance of the analytes, CSH being far less bulky than GSH.
We compared the levels of reduced thiols (mainly GSH and
CSH) in a standard 5%-foetal calf serum-completed Dulbecco’s
Modified Eagle Medium (DMEM), used for in vitro cell cultures of
numerous mammalian cell types. As expected from previously
reported data obtained after HPLC and fluorometric detection of
GSH adducts,21 the potential response measured by our modified
electrode was roughly 50% lower in the medium in which the
cells grew for 4 days compared with a fresh medium (data not
shown). In addition, the potentials differ proportionally in suc-
cessive dilutions of human and mouse serum samples in the
potassium buffer. The data are in agreement with thiol uptake by
the cells along culture and also suggest that our modified elec-
trode could be a valuable tool in the control of cell culture me-
dium in various biotechnology processes.
0.35
y = -0.045x + 0.125
R2 = 0.9781
0.3
0.25
0.2
3. Conclusions
0.15
y = -0.102x - 0.143
The electropolymerisation of the thienyl group of the new
compound 1-(3-(1,4-dimethoxyphenyl)-2-(3-thienyl))ethyne al-
lows us to obtain a modified electrode bearing quinone and
hydroquinone moieties. The reactivity of the quinone group with
thiols shows that this electrode appears to be a promising po-
tentiometric sensor for thiols’ analysis in biological media. It is
worth emphasising that the method presented here also offers
Glutathione
R2 = 0.9956
Cysteine
0.1
-4.0
-3.5
log [Thiol]
-3.0
Figure 4. Calibration curve for GSH and CSH in pH 7 buffer.

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S. Etienne et al. / Tetrahedron 64 (2008) 9619–9624
9623
many substantial advantages that could make it very helpful for
assaying GSH and thiols as redox status markers. First, this
method can be applied directly to biological sample solutions,
since it does not request complicated pre-analytical steps that
are susceptible to inappropriately modify the balance between
the reduced and oxidised forms of the thiols,22 which also
means that the data could be expected within a few minutes.
Besides, this technique could easily fit in most research and
clinical chemistry laboratories since it does require neither high
technical experience nor expensive equipment and reagents to
acquire. This could lead to further investigations aimed at
establishing the significance of oxidative stress in the clinical
status of many diseases and that could be measured as a follow-
up marker of therapeutic efficiency. Additional experiments are
now required with the view to improve the use of our modified
electrode and to conciliate the whole technique with the re-
quests of these laboratories and the restrained sample volumes
usually available.
mixture was heated at reflux under argon for 4 h. After returning to
room temperature, the mixture was hydrolysed in 15 mL of water
and extracted with diethylether. The organic layer was dried with
sulfate magnesium, filtered and concentrated under vacuum giving
brown oil. Yield was 90%.
1H NMR (250 MHz, CDCl3):
d
¼7.0 (d, J¼2.9 Hz, 1H), 6.91–6.88
(m, 2H), 3.85 (s, 3H), 3.76 (s, 3H), 3.30 (s, 1H).
4.2.4. Synthesis of 3-((2,5-dimethoxyphenyl)ethynyl)thiophene
To
a solution of triphenylphosphine (189 mg, 0.72 mmol,
4 mol %) in 20 mL of anhydrous THF, palladium(II) chloride (64 mg,
0.36 mmol, 2 mol %) was added under argon. Then, copper(I) iodide
(137 mg, 0.72 mmol, 4 mol %), 3-bromothiophene (2.9 g, 18 mmol,
1 equiv) and triethylamine (3.6 mL, 27 mmol, 1.5 equiv) were in-
corporated. A solution of alkyne (2.5 g, 15.4 mmol, 0.86 equiv)
dissolved in 5 mL of anhydrous THF was added over a 1 h period.
The reaction mixture was stirred overnight at room temperature.
Triethylamine bromohydrate then formed was filtered and rinsed
several times with diethylether. The filtrate was concentrated un-
der vacuum and the coupling product purified by column chro-
matography on silica gel using chloroform as eluent. Brown oil.
Yield was 40%.
4. Experimental
4.1. Reagents
1H NMR (250 MHz, CDCl3):
2H), 7.0 (m, 1H), 6.86–6.84 (m, 1H), 3.9 (s, 3H), 3.8 (s, 3H). 13C NMR
(62.5 MHz, CDCl3):
d¼7.57–7.54 (m, 1H), 7.24–7.33 (m,
All chemicals from commercial sources were of analytical grade.
All aqueous solutions were prepared daily using deionised water
d
¼154.5, 153.3, 131.6, 128.2, 123.4, 118.1, 115.8,
with a resistivity superior to 18 M
U
.
113.0, 112.2, 112.1, 85.7, 85.1, 56.5, 55.8.
4.2. Syntheses
4.2.1. Synthesis of 2-bromo-1,4-dimethoxybenzene
4.3. Electrochemical experiments
para-Dimethoxybenzene (5.0 g, 36.2 mmol, 1 equiv) in acetoni-
trile (150 mL) was stirred at room temperature until complete
dissolution. N-Bromosuccinimide (6.44 g, 36.2 mmol, 1 equiv) was
added and the reaction mixture was stirred at room temperature
for 6 h. The mixture was concentrated under vacuum. The residue
was washed with water (50 mL) and extracted with diethylether
(3ꢂ30 mL). The organic layer was dried and concentrated under
vacuum. The residue was purified by distillation (100 ꢀC,
4ꢂ10ꢁ2 mbar) giving an orange oil. Yield was 90%.
All cyclic voltammograms were carried out in a conventional
three-electrode electrochemical cell under argon with a PGP 201
Radiometer potentiostat.
All potentials in the text were quoted versus a saturated calomel
electrode (SCE). The working electrode was a 10 mm Pt wire
(0.1 cm2) and the counter-electrode was a 1 cm2 vitreous carbon
rod.
1H NMR: (250 MHz, CDCl3):
d
¼7.13 (d, J¼2.2 Hz, 1H), 6.84–6.82
(m, 2H), 3.84 (s, 3H), 3.77 (s, 3H). 13C NMR (62.5 MHz, CDCl3):
¼153.9, 150.1, 118.9, 112.8, 111.8, 56.8, 55.6.
4.3.1. Formation of film by electropolymerisation
The electropolymerisation of A in CH3CN with 0.1 M LiClO4 as
supported electrolyte was performed by repeatedly scanning the
potential region from 0.5 to 1.5 V at a scan rate of 100 mV/s. The
thickness of the polythiophene film was controlled by monitoring
the amount of charge passed during the polymerisation.
d
4.2.2. Synthesis of 2-methyl-4-(2,5-dimethoxyphenyl)-
3-butyne-2-ol
Palladium(II) acetate (25 mg, 2 mol %) was added under argon to
a solution of triphenylphosphine (73 mg, 5 mol %) in 25 mL of
triethylamine. 2-Bromo-1,4-dimethoxybenzene (1.23 g, 5.6 mmol,
1 equiv) was incorporated and then copper(I) iodide (32 mg,
3 mol %). 2-Methyl-3-butyn-2-ol (0.7 mL, 6.7 mmol, 1.2 equiv) dis-
solved in 20 mL of triethylamine was then added and the reaction
mixture heated overnight at 80 ꢀC. After returning to room tem-
perature, the triethylamine bromohydrate was filtered and rinsed
several times with diethylether. The filtrate was concentrated un-
der vacuum and the coupling product purified by column chro-
matography on silica gel using chloroform as eluent. Orange oil.
Yield was 40%.
4.3.2. Electrochemical preparation of the quinone active form
The electrochemical deprotection of the methoxy groups to
obtain the quinone active form was obtained by holding the po-
tential at 1.6 V/SCE for about 5 min until the current was constant
and near zero. The formation of a surface-bound quinone was
evidenced by cyclic voltammetry.
4.3.3. Potentiometric measurements
Measurements were carried out at room temperature (21ꢃ2 ꢀC)
in a cell volume of 50 mL using a PHM 210 Radiometer voltammeter
operating under zero current. Without other specification, the
thiols and biological samples were added at appropriate concen-
trations in 50 mL of potassium phosphate buffer (0.05 M pH 7).
Measurements in biological media were performed using bovine
serum albumin (10 g/L) in pH 7 buffer or in a standard 5%-foetal calf
serum-completed DMEM.
1H NMR (250 MHz, CDCl3):
(m, 2H), 3.83 (s, 3H), 3.76 (s, 3H), 1.64 (s, 6H). 13C NMR (62.5 MHz,
CDCl3):
d¼6.92 (d, J¼3.0 Hz, 1H), 6.82–6.80
d
¼154.1, 152.9, 115.8, 112.4, 112.1, 111.8, 83.9, 77.9, 65.2, 56.3,
55.5, 31.0, 30.8.
4.2.3. Synthesis of (2,5-dimethoxyphenyl)ethyne
Both modified electrode and reference electrode were im-
mersed in solutions stirred magnetically. The potentials were
recorded 4 min after thiol addition, i.e., when the electrode re-
sponse was stable.
Sodium hydroxide powder (80 mg, 2 mmol, 0.85 equiv) was
added to
a solution of 2-methyl-4-(2,5-dimethoxyphenyl)-3-
butyne-2-ol (514 mg, 2.34 mmol) in 9 mL of toluene. The reaction

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9. Sehlotho, N.; Nyokong, T.; Zagal, J. H.; Bedioui, F. Electrochim. Acta 2006, 51,
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by adding 100 scans from 4000 to 400 cmꢁ1 with 2 cmꢁ1 resolution
using anhydrous KBr as background.
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Acknowledgements
The authors wish to thank the Paul Verlaine University of Metz
for most of the equipment employed and more particularly Prof.
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