Fabrication of bisferrocenyl derivative grafted HTPB with high iron content and its application in dopamine detection

Article abstract of DOI:10.1016/j.jorganchem.2021.121789

In this work, we employed an efficient strategy to increase the graft percentage of ferrocene in hydroxyl terminated polybutadiene (HTPB) polymer framework. For this purpose, we use 5-chloro-2-pentanone to attach the two alkylferrocene derivatives to each other. In order to incorporate the obtained bis-alkylferrocene derivatives to the polymer backbone, the chlorine atom at the end of the coupling agent alkyl chain was converted to a silane group using the Grignard reaction. Finally, hydrosilylation reaction of as-synthesized silane derivatives and HTPB in the presence of Speier's catalyst (H₂PtCl₆) resulted in novel bis-ferrocene modified HTPBs with a variety of iron contents. The iron percentage, viscosity, and glass transition temperature of the novel bis-ferrocene modified HTPBs as essential parameters of polymer characterization were investigated. Obtained polymers are electro-active due to the presence of ferrocenyl groups. Additionally, unlike the virgin polymer (HTPB) they show optical properties. The final polymer was immobilized onto the bare glassy carbon electrode (GCE) surface using the cross-linking effect of terephthaldehyde (TFA) and fresh egg white (FEW). Electrochemical impedance spectroscopy (EIS) confirmed the successful immobilization of the polymer. The ability of the fabricated electrode to mediate dopamine (DA) oxidation was evaluated, and the results show the acceptable detection limits as well as linear ranges for the determination of dopamine using GC/BEFcHTPB/(TFA+FEW).

Full text of DOI:10.1016/j.jorganchem.2021.121789

Journal of Organometallic Chemistry 940 (2021) 121789
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Fabrication of bisferrocenyl derivative grafted HTPB with high iron
content and its application in dopamine detection
Alireza Aghaiepour, Shabnam Rahimpour, Elmira Payami, Reza Mohammadi,
∗
Reza Teimuri-Mofrad
Department of Organic and Biochemistry, Faculty of Chemistry, University of Tabriz, 51664 Tabriz, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
In this work, we employed an efficient strategy to increase the graft percentage of ferrocene in hydroxyl
terminated polybutadiene (HTPB) polymer framework. For this purpose, we use 5-chloro-2-pentanone
to attach the two alkylferrocene derivatives to each other. In order to incorporate the obtained bis-
alkylferrocene derivatives to the polymer backbone, the chlorine atom at the end of the coupling agent
alkyl chain was converted to a silane group using the Grignard reaction. Finally, hydrosilylation reac-
tion of as-synthesized silane derivatives and HTPB in the presence of Speier’s catalyst (H2PtCl6) resulted
in novel bis-ferrocene modified HTPBs with a variety of iron contents. The iron percentage, viscosity,
and glass transition temperature of the novel bis-ferrocene modified HTPBs as essential parameters of
polymer characterization were investigated. Obtained polymers are electro-active due to the presence of
ferrocenyl groups. Additionally, unlike the virgin polymer (HTPB) they show optical properties. The final
polymer was immobilized onto the bare glassy carbon electrode (GCE) surface using the cross-linking ef-
fect of terephthaldehyde (TFA) and fresh egg white (FEW). Electrochemical impedance spectroscopy (EIS)
confirmed the successful immobilization of the polymer. The ability of the fabricated electrode to medi-
ate dopamine (DA) oxidation was evaluated, and the results show the acceptable detection limits as well
as linear ranges for the determination of dopamine using GC/BEFcHTPB/(TFA+FEW).
Received 27 December 2020
Revised 4 March 2021
Accepted 20 March 2021
Available online 22 March 2021
Keywords:
Bis-nuclear ferrocene
Alkylferrocene
Hydrosilylation reaction
Modified polymer
Dopamine detection
©
2021 Elsevier B.V. All rights reserved.
1. Introduction
niques to detect electroactive neurotransmitters, including uric
acid, dopamine, ascorbic acid and etc [13].
Dopamine (DA) is a vital substance in the life of Mammals,
which roles as a catecholamine neurotransmitter in the central
nervous system (CNS) also a hormone in the blood [1–3]. Recently,
abnormal DA concentrations have been shown to cause neuro-
logical disorders such as cases Alzheimer’s disease, Schizophre-
nia, Parkinson’s disease, pheochromocytoma, and attention deficit
hyperactivity disorder [4–6]. Dopamine is an essential drug used
to treat heart failure diseases, especially for premature infants
Recently, direct electrochemical methods (redox on the modi-
fied electrode surface) have received much attention for dopamine
detection due to their simplicity, high-speed response, and high
sensitivity, as well as their wide linear relationship [14–16]. On
the other hand, other electroactive substances, such as ascorbic
acid (AA) interfere with the detection of dopamine [17]. There-
fore, to solve this problem, simple electrodes (glassy carbon [18],
graphene oxide [19], carbon nano-tubes (CNTs) [20], Au electrode
and etc [21].) have been modified and examined via cellulose mi-
crofiber (CMF) [22,23], chitosan [6], cyclic oligosaccharides such as
β-cyclodextrin [3], CuS nanoplates [24], inorganic dye [25], copper
(II) complex [26], and organometallic compounds [27,28]. Some of
the recent development of advanced dopamine sensors were sum-
marized in Table 1.
[
7]. In recent years, much energy has been devoted to the de-
tection of dopamine. Conventional methods utilized for the de-
tection of dopamine are performed using analytical techniques
such as chemiluminescence [8], capillary electrophoresis [9], liq-
uid chromatography [10], mass spectrometry [11], optical or elec-
trochemical detection [12]. However, the most economical, fast
and affordable method is the use of electrochemical sensing tech-
There is more interest in recent decades on ferrocene deriva-
tives specially alkylferrocenes. The use of ferrocenyl compounds
in electrochemical devices [33], optical systems [34], asymmetric
organometallic catalysis [35], chiral cancer drugs and other fields
[36], is because of their unique planar chirality properties, ther-
mal, optical, and redox behaviors. In addition, alkylferrocene with
∗
Corresponding author.
E-mail address: teymouri@tabrizu.ac.ir (R. Teimuri-Mofrad).
https://doi.org/10.1016/j.jorganchem.2021.121789
0
022-328X/© 2021 Elsevier B.V. All rights reserved.

A. Aghaiepour, S. Rahimpour, E. Payami et al.
Journal of Organometallic Chemistry 940 (2021) 121789
Table 1
Some of the recent advanced modified electrodes for dopamine sensors.
Entry
Prepared electrode
Some of the advantages
Ref
1
determination of dopamine in citric acid/KOH buffer
sensitivity: 340.3 nA/μM
[29]
LOD: 10 nM
2
Selective detection dopamine in the presence of ascorbic acid
and uric acid (UA).
[30]
Linear response ranges: 1 μM to 100 μM
LOD: 0.1 μM
3
Selective detection of DA in the presence of some electroactive
compounds.
[22]
Linear response ranges: up to 196.3 μM
LOD: nano molar
4
determination of dopamine in 0.1 M PBS (pH 7.0)
Selective determination of DA in the presence of AA and UA.
Linear response ranges: 0.02 μM to 130 μM
LOD: 0.007 μM
[31]
2

A. Aghaiepour, S. Rahimpour, E. Payami et al.
Journal of Organometallic Chemistry 940 (2021) 121789
Table 1
(
Continued).
Entry
Prepared electrode
Some of the advantages
Ref
5
Selectivity for DA in the presence of 50 folds additions of
potentially active interfering compounds.
Linear response ranges: up to 150.76 μM
LOD: 4 nM
[32]
9
9.2% Recovery of DA in the rat brain
the capability to form an aqueous micellar pseudo phase can be
used as a biosensor. For example, the electrochemical properties
of ferrocene in coupling with some biomolecules such as glucose
oxidase can be used as a biosensor for the determination of the
glucose in aqueous solution [37]. At first, alkylferrocenes were syn-
thesized directly from alkyl cyclopentadienes [38], but now many
routes are used for the synthesis of corresponding alkylferrocenes
from ferrocene as a primary substance. Generally, alkylferrocene
derivatives are prepared via a two-step route include Friedel-Crafts
acylation of ferrocene followed by the reduction of the acylated
ferrocene [39].
trode showed an excellent electrocatalytic effect on the oxidation
of dopamine to quinone dopamine. The morphology studies, cyclic
voltammetry (CV), differential pulse voltammetry (DPV), effect of
pH, selective determination of DA in the presence of AA and elec-
trochemical properties of DA on the GC/BEFcHTPB/(TFA/FEW) elec-
trode were also investigated.
2. Experimental
2
.1. Materials and instrumentation
Nowadays, grafting of ferrocene and its derivatives onto poly-
mers backbone has attracted a lot of attention because it of-
fers unique properties to the obtained modified polymer. Redox-
switchable behavior for electrochemical-induced drug delivery sys-
tems in aqueous medium [40], role playing electroactive groups
on supercapacitor composites [41], Hyperbranched Polymer films
containing organometallic groups [42], burning rate accelerator
catalyst for airbags and other safety devices [43,44], as well as,
ferrocene grafted hydroxyl terminated polybutadiene (HTPB) as a
burning rate accelerator are the examples of such applications [45].
Although, HTPB is not a very famous polymer, it has ideal phys-
ical properties include high loading capacity, storage capacity, low
viscosity, ability to decrease the vulnerability of explosives, high
mechanical-thermal stability and sub-ambient glass transition tem-
perature [46].
All commercial compounds were purchased from Sigma-Aldrich
and used without any purification. 1H-NMR spectra were obtained
with Bruker FT-400 spectrometer in CDCl , the FT-IR spectra were
3
reported with Bruker-Tensor 270 spectrometer on KBr disk. The
mass spectra were obtained with 70 eV by Agilent (5975C VL) in-
strument, the most important peaks were reported in m/z units
+
with M as the molecular ion. The Elemental analyses were car-
ried out with an Elementor Vario EL. III instrument. The Ana-
lytikjene (novaa 400) atomic absorption spectrophotometer was
used for iron analysis. The Brook field RVT viscometer was used
for viscosity measurement. The SPECORD 250 analytik jena UV/Vis
spectrophotometer was used for recording the electronic absorp-
tion spectra. The Field Emission Scanning Electron Microscopy FE-
SEM (MIRA3 TESCAN) was used for surface morphology stud-
ies. Cyclic voltammetry measurements were performed on synthe-
sized polymers in dichloromethane using 0.100 M tetrabutylam-
monium tetrafluoroborate as supporting electrolytes, by potentio-
stat/galvanostat Autolab (PGASTAT 30) equipped with a standard
three-electrode cell. A 2-mm-diameter GC was performed as the
working electrode, a silver/silver chloride (Ag/AgCl) electrode as
reference electrode and a platinum electrode was used as counter
electrodes. electrochemical impedance spectroscopy (EIS) was per-
Herein, to continue our previous attempts on ferrocene-
based compounds and their successful grafting on some poly-
mers [41,47–49], we describe the synthesis of bis-alkylferrocenyl
silane compounds via condensation reaction of as-prepared alkyl-
ferrocenes by appropriate ketone compound. Silylation of ob-
tained bis-alkylferrocene allows the ferrocenyl group to be in-
troduced to HTPB backbone via hydrosilylation reaction. Opti-
cal and electrochemical properties of the novel modified poly-
mer and other important parameters such as iron percent-
age, viscosity and glass transition temperature were investi-
gated. In continue, the modified electrode was prepared via [4,4-
Bis(ethylferrocenyl)pentyl]dimethylsilane grafted HTPB containing
formed in 5.0 mM K [Fe(CN) ]/ K [Fe(CN) ] solution. An AC volt-
3
6
4
6
age was applied with 5 mV amplitude in the frequency range of
.01 Hz - 100 kHz. The thermogravi-metric analysis (TGA) was per-
0
formed by Perkin Elmer thermogravimetric analyzer at a heating
ꢀ
ꢀ
1
5.98% of Fe (4a , BEFcHTPB) as the representative of final fer-
rocenyl polymers, terephthaldehyde (TFA), and fresh egg white
FEW). The success of the electrode modification was confirmed by
electrochemical impedance spectroscopy (EIS). The prepared elec-
−1
rate of 10 °C min
from 25 °C to 700 °C under Ar atmosphere.
DMTA analysis was performed using Mk IV DMTA instrument, Data
were obtained at 10 hz, from -100 to 100 °C and the heating rate
was 2 °C/min.
(
3

A. Aghaiepour, S. Rahimpour, E. Payami et al.
Journal of Organometallic Chemistry 940 (2021) 121789
2
.2. General procedure for the synthesis of
4.08-3.90 (m, 16H, Fc), 2.35-2.26 (m, 4H, -CH -Fc), 1.83-1.81 (m,
2
5
-chloro-2,2-bis(alkylferrocenyl)pentane derivatives (2a, b)
2H, -CH CH Si(Me) H), 1.62-1.55 (m, 5H, CH and CH ), 1.15 (t,
2 2 2 3 2
6
H, CH CH -Fc), 0.53 (t, 2H, -CH Si(Me) H), 0.049-0.043 (m, 6H,
3 2 2 2
2
a and 2b were prepared according to the procedure described
Si(CH ) H); IR (KBr): ν = 3020 (w; C–H, Aromatic), 2926 (s; C–H,
3
2
in our previous report [50]. Briefly, a 25 ml two-necked round bot-
tomed flask was equipped with an Ar inlet adapter and a magnetic
stirrer. Dry methanol (3 ml), sulfuric acid (3 ml), alkylferrocene
Aliphatic), 2107 (w; Si–H), 1636 (m; C=C), 1255 (s; Si–C), 485 (w;
−
1
+
Fe–Cp) cm ; HRMS (ESI) m/z: 554 [M] ; calcd for C
H Fe Si: C
42 2
31
67.16%, H 7.63%, Fe 20.15%; Found: C 67.11%, H 7.59%, Fe 20.13%.
(
16 mmol) (synthesized according to the procedure reported pre-
viously [51]) and 5-chloro-2-pentanone (8 mmol, 0.92 ml) were
mixed and stirred at 65 °C under argon gas. After 30 h, the re-
action mixture was cooled to ambient temperature and after neu-
tralization with sodium carbonate. The mixture was extracted with
dichloromethane (3 × 20 ml). Then the solvent was removed
by rotary evaporator and 5-chloro-2,2-bis(alkylferrocenyl)pentane
derivatives were purified by column chromatography using hexane
as eluent.
2.3.2. [4,4-Bis(propylferrocenyl)pentyl]dimethylsilane (3b)
From 1.67 g of 2b, 1.63 g (2.64 mmol) of the light brown oil
was obtained; yield 88%; 1H NMR (400 MHz, CDCl , δ): 3.99-
3
3.77 (m, 16H, Fc), 2.22-2.12 (m, 4H, -CH -Fc), 1.79-1.69 (m, 2H,
2
-CH CH Si(Me) H), 1.56-1.36 (m, 9H, CH , CH and -CH CH -Fc),
2
2
2
3
2
2
2
0.85 (t, 6H, CH -propyl), 0.75 (t, 2H, -CH Si(Me) H), 0.14-0.01(m,
3
2
2
6H, Si(CH ) H); IR (KBr): ν = 3022 (w; C–H, Aromatic), 2928 (s;
3
2
C–H, Aliphatic), 2112 (w; Si–H), 1635 (m; C=C), 1258 (s; Si–C),
−1
+
4
89 (w; Fe–Cp) cm ; HRMS (ESI) m/z: 582 [M] ; calcd for
2
.2.1. 5-Chloro-2,2-bis(ethylferrocenyl)pentane (2a)
C33H46Fe Si: C 68.05%, H 7.96%, Fe 19.17%; Found: C 68.09%, H
2
From 3.42 g of 1a, 2.54 g (4.8 mmol) of the viscous orange
7.91%, Fe 19.15%.
oil was obtained with 60% yield; 1H NMR (400 MHz, CDCl , δ):
3
4
.01-3.91 (m, 16H, Fc), 3.45 (t, 2H, -CH Cl), 2.35-2.26 (m, 4H, -
2
2.4. General procedure for the synthesis of
[4,4-bis(alkylferrocenyl)pentyl]dimethylsilane grafted HTPB
derivatives (4)
CH -Fc), 1.99-1.95 (m, 2H, -CH CH Cl), 1.67-1.55 (m, 5H, CH and
2
2
2
3
CH ), 1.16 (t, 6H, CH CH -Fc); IR (KBr): ν = 3090 (w; C-H, Aro-
2
3
2
matic), 2971 (s; C–H, Aliphatic), 1638 (m; C=C), 645 (m; C-Cl), 485
−
1
+
+
(
w; Fe–Cp) cm ; HRMS (ESI) m/z: 532 [M+2] , 530 [M] ; calcd
for C29H35ClFe : C 65.63%, H 6.64%, Fe 21.04%; found: C 65.67%, H
A
100 ml round bottomed flask was equipped with
2
an argon inlet adapter and magnetic stirrer. A mix-
6
.61%, Fe 21.03%.
ture of the required amounts (Weight %) of [4,4-
bis(alkylferrocenyl)pentyl]dimethylsilane (3a, b), and hydroxyl
terminated poly butadiene (HTPB), was dissolved in hexane
2
.2.2. 5-Chloro-2,2-bis(propylferrocenyl)pentane (2b)
From 3.65 g of 1b, 2.59 g (4.64 mmol) of the high viscosity or-
(
50 ml) and hexachloroplatinic acid (H PtCl ) was added as
2 6
ange oil was obtained; yield 58%; 1H NMR (400 MHz, CDCl , δ):
4
3
catalyst (0.05 ml of 0.01 M in 2-propanol). The reaction mix-
.00-3.76 (m, 16H, Fc), 3.38 (t, 2H, -CH Cl), 2.24-2.10 (m, 4H, -
2
ture was refluxed until the Si–H peak in the IR spectrum (near
CH -Fc), 1.94-1.82 (m, 2H, -CH CH Cl), 1.60-1.35 (m, 9H, CH , CH
2
2
2
3
2
−1
2
110 cm ) was eliminated. After completion of the reaction,
and -CH CH -Fc), 0.84 (t, 6H, CH -propyl); IR (KBr): ν = 3084 (w;
2
2
3
the mixture was cooled to room temperature, filtered to remove
the Pt-catalyst and solvent was removed by a rotary evapora-
tor. The residue was placed on 3–5 cm silicagel and washed
with hexane to remove the unreacted reactants. Finally, by
washing the silicagel using EtOAc, viscous dark brown oil of [4,4-
bis(alkylferrocenyl)pentyl]dimethylsilane grafted HTPB derivatives
was obtained.
C–H, Aromatic), 2975 (s; C–H, Aliphatic), 1630 (m; C=C), 647 (m;
−
1
+
C–Cl), 483 (w; Fe–Cp) cm ; HRMS (ESI) m/z: 560 [M+2] , 558
+
[
M] ; calcd for C31H39ClFe : C 66.63%, H 7.03%, Fe 19.99%; Found:
2
C 66.59%, H 6.99%, Fe 19.94%.
2
.3. General procedure for the synthesis of
[
4,4-bis(alkylferrocenyl)pentyl]dimethylsilane derivatives (3a, b)
2
.4.1. [4,4-Bis(ethylferrocenyl)pentyl]dimethylsilane grafted HTPB
3a and 3b were prepared according to the procedure described
containing 8.59% of Fe (4a)
by our team [51]. Briefly, a 25 ml round bottomed flask was
equipped with an argon inlet adapter and magnetic stirrer. 5-
chloro-2,2-bis(alkylferrocenyl)pentane (2a, b) (3 mmol) dissolved
in dry THF (8 ml). Then 2 ml of the mentioned solution was added
to 1 mL dry THF containing magnesium turnings (0.072 g, 3 mmol)
and a large Iodine crystal, then this mixture was stirred at room
temperature until the initial reaction was commenced (approxi-
mately 5 min). After that, the remaining of THF solution containing
Using 0.20 g (0.36 mmol) of 3a and 0.26 g of HTPB, 4a was
obtained as viscous dark brown oil.
2
.4.2. [4,4-Bis(ethylferrocenyl)pentyl]dimethylsilane grafted HTPB
ꢀ
containing 11.82% of Fe (4a )
ꢀ
Using 0.20 g (0.36 mmol) of 3a and 0.14 g of HTPB, 4a was
obtained as viscous dark brown oil.
5
-chloro-2,2-bis(alkylferrocenyl)pentane (2a, b) was added slowly
2
.4.3. [4,4-Bis(ethylferrocenyl)pentyl]dimethylsilane grafted HTPB
to the reaction mixture via a dropping funnel for 5 min. The mix-
ture was refluxed under argon gas until all the magnesium turn-
ings dissolved. After completion of the dissolution, the reaction
mixture was cooled to room temperature and was added dropwise
to the solution of chlorodimethylsilane (0.28 g, 3 mmol) in dry THF
ꢀ
ꢀ
containing 15.98% of Fe (4a )
ꢀ
ꢀ
Using 0.20 g (0.36 mmol) of 3a and 0.05 g of HTPB, 4a was
obtained as viscous dark brown oil; 1H NMR (400 MHz, CDCl3,
δ): 5.57-4.91 (m, -C=CH, -C=CH of HTPB), 4.15-3.90 (m, 16H, Fc),
2
2
.31-2.29 (m, 4H, -CH -Fc), 2.07-2.02 (m, -CH , Aliphatic of HTPB),
2 2
???(4 ml) via a dropping funnel in the period of 30 min. The reac-
1
.67-1.57 (m, 5H, CH3 and CH ), 1.19 (t, 6H, CH CH -Fc), 0.91-0.85
tion mixture was refluxed under argon gas for 5 h. After comple-
tion of the reaction, the solvent was removed and light brown oil
of [4,4-bis(alkylferrocenyl)pentyl]dimethylsilane derivatives (3a, b)
were obtained with column chromatography using hexane as elu-
ent.
2 3 2
(
(
(
t, 2H, CH -Si), 0.09-0.05 (d, 6H, -Si(CH ) -); IR (KBr): ν = 3410
2
3 2
br; -OH), 3073 (s; C–H, Aromatic), 2919 (s; C–H, Aliphatic), 1642
m; C=C), 1257 (s; Si–C), 474 (w; Fe–Cp) cm−1.
2
.4.4. [4,4-Bis(propylferrocenyl)pentyl]dimethylsilane grafted HTPB
2
.3.1. [4,4-Bis(ethylferrocenyl)pentyl]dimethylsilane (3a)
containing 8.12% of Fe (4b)
From 1.59 g of 2a, 1.44 g ???(2.73 mmol) of the light brown
Using 0.21 g (0.36 mmol) of 3b and 0.28 g of HTPB, 4b was
obtained as viscous dark brown oil.
oil was obtained; yield 91%; 1H NMR (400 MHz, CDCl , δ):
3
4

A. Aghaiepour, S. Rahimpour, E. Payami et al.
Journal of Organometallic Chemistry 940 (2021) 121789
2
.4.5. [4,4-Bis(propylferrocenyl)pentyl]dimethylsilane grafted HTPB
face, the GC/BEFcHTPB/(TFA+FEW) was prepared as the modified
ꢀ
containing 11.23% of Fe (4b )
electrode.
ꢀ
Using 0.21 g (0.36 mmol) of 3b and 0.14 mg of HTPB, 4b was
obtained as viscous dark brown oil.
3. Results and discussion
2
.4.6. [4,4-Bis(propylferrocenyl)pentyl]dimethylsilane grafted HTPB
ꢀ
ꢀ
containing 15.01% of Fe (4b )
3
.1. Design and preparation of modified polymers
ꢀ
ꢀ
Using 0.21 g (0.36 mmol) of 3b and 0.05 g of HTPB, 4b was
obtained as viscous dark brown oil; 1H NMR (400 MHz, CDCl3,
Scheme
1
illustrated
the
synthesis
of
[4,4-
δ): 5.58-4.84 (m, -C=CH, -C=CH of HTPB), 4.02-3.82 (m, 16H,
2
bis(alkylferrocenyl)pentyl]dimethylsilane derivatives Grafted HTPB
via the facile method and acceptable yields. As the starting point,
alkylferrocene derivatives (Ethyl and Propyl) were prepared via
Friedel-Crafts acylation followed by reduction of the acylated fer-
rocenes to alkyl derivatives [51]. Then the obtained alkylferrocenes
Fc), 2.30-2.28 (m, 4H, -CH -Fc), 2.00-1.96 (m, -CH , Aliphatic of
2
2
HTPB), 1.56-1.36 (m, 9H, CH , CH and -CH CH -Fc), 0.85-0.75
3
2
2
2
(
m, 8H, CH -Si and CH -propyl), 0.07-0.01 (d, 6H, -Si(CH ) -); IR
2 3 3 2
(
KBr): ν = 3564 (br; -OH), 3012 (w; C–H, Aromatic), 2921 (s; C–H,
−1
Aliphatic), 1645 (m; C=C), 1262 (s; Si–C), 483 (w; Fe–Cp) cm
.
(
1a, b) reacted with 5-chloro-2-pentanone according to the con-
densation reaction method described in our previous report [50] in
order to attain 5-chloro-2,2-bis(alkylferrocenyl)pentane derivatives
2
.5. Preparation of modified electrode
Initially, the GC electrode was polished using alumina, soni-
(
2a, b). Since 5-chloro-2,2-bis(alkylferrocenyl)pentane lacks a
suitable functional group for the HTPB polymer framework graft-
ing, the conversion of the chlorine to dimethylhydrosilyl group
was done through Grignard reaction. For this purpose, Grignard
reagent was prepared in situ by adding bis-alkylferrocene contain-
ing chloropentane derivatives (2a, b) to magnesium turnings in dry
THF. The Obtained mixture was reacted with chlorodimethylsilane
and resulted in the formation of ethyl and propyl substituted
[4,4-bis(alkylferrocenyl)pentyl]dimethylsilane derivatives (3a, b)
with 91 and 88% yields, respectively. Finally, hydrosilylation re-
action of bis-alkylferrocenesilane and HTPB in the presence of
cated in H SO4 (2N), and distilled water, sequentially. When the
2
well-defined stable cyclic voltammogram was obtained for scan-
ning of GCE treatment in H SO (2N) at the range of -1 to 1 V,
2
4
the electrode became ready for surface modification. For this pur-
pose, the 10% CH Cl2 solution of terephthaldehyde (TFA) and 10%
2
CH Cl solution of fresh egg white (FEW) was added to 5 mg of as-
2
2
synthesized ferrocene containing polymer (BEFcHTPB) which was
dissolved in CH Cl . The Obtained suspension was sonicated for
2
2
1
0 min to form the homogenous BEFcHTPB/(TFA+FEW) complex.
Finally, with drop-coating of obtained complex (5 μl) on GCE sur-
hexachloroplatinic acid (H PtCl ) as catalyst and hexane as solvent
2
6
Scheme 1. Synthesis of [4,4-bis(alkylferrocenyl)pentyl]dimethylsilane modified derivatives of Grafted HTPBs.
5

A. Aghaiepour, S. Rahimpour, E. Payami et al.
Journal of Organometallic Chemistry 940 (2021) 121789
Fig. 1. FT-IR spectra of HTPB, silane derivative (3a) and final polymer (4a).
finished with the synthesise of the modified electroactive HTPB
persity of polymer, gel permeation chromatography (GPC) was not
a suitable method for the characterization of this type of poly-
mers. The atomic absorption spectroscopy was used for the de-
termination of iron percentage in final polymers. HTPB polymer is
a macromolecule composed of many repeated subunits with C=C
bond. The molecular weight of these repeated units is 54 amu.
Meanwhile the molecular weights of alkylferrocenylsilanes are 554
and 582 amu for ethyl (3a) and propyl (3b) derivatives, respec-
tively. Therefore, the HTPB polymer is capable of ferrocenylsilane
loading. The variation of Fe content in the grafted polymer is ob-
tained by simply making changes in the mole ratio of the HTPB
and the ferrocene derivatives. The catalyst content is constant for
all experiments, since the amount of starting material used in this
study is not very variable (0.05-0.26 g) because it requires a change
in the catalyst value. The used amount of catalyst is surplus. The
mole ratio of C=C bond and Si–H units used in HTPB and ferro-
cenyl derivatives in each reaction were assembled in Table 2.
The comparison of pristine HTPB and ferrocenylsilane FT-IR
spectra with final polymer indicates the introducing of ferrocenyl
units to polymer backbones. As can be seen in comparative Table 3,
in the final polymer the distinct peaks of HTPB are visible as
polymers 4 with high Iron percent (Fe %).
3
.2. Spectroscopy studies
FT-IR spectroscopy was used to monitor the elimination of the
−
1
Si–H absorption peak at approximately 2110 cm
(Fig. 1), which
confirms that the silane compounds were grafted to HTPB back-
bone successfully. On average, it takes 24 h to complete the reac-
tion. Fig. 2 depicts the thin layer chromatography (TLC) plate which
was developed in hexane:EtOAC (8:2) as eluent, then the plate was
dried and sprayed with a 50% v/v aqueous solution of sulfuric acid
in a fume hood in order to manifest the pristine HTPB. As can be
seen the final polymer with Rf = 0.5 was completely separated
from the ferrocenylsilane (R = 0.83) and pristine HTPB (R = 0.16).
f
f
On the other hand; in primary plate A the pristine HTPB was not
detectable, while the final polymer was perfectly visible with the
naked eye due to the attachment of the chromophore groups (fer-
rocene).
Because of the grafting of ferrocenyl nucleus to polymer skele-
ton which cannot apply a perceptible effect on the size and dis-
6

A. Aghaiepour, S. Rahimpour, E. Payami et al.
Journal of Organometallic Chemistry 940 (2021) 121789
Fig. 2. TLC plate for pristine HTPB, 3a and 4a, A) primary plate, B) after spraying with sulfuric acid.
Table 2
Comparison between the mol ratio of C=C bond and Si-H units.
Molar ratio
mol C=C in HTPB
mol Si−H 3a or 3b
0
0
0
0
0
0
.20 g (0.36 mmol) of 3a is equal to 0.36 mmol Si–H bond
.20 g (0.36 mmol) of 3a is equal to 0.36 mmol Si–H bond
.20 g (0.36 mmol) of 3a is equal to 0.36 mmol Si–H bond
.21 g (0.36 mmol) of 3b is equal to 0.36 mmol Si–H bond
.21 g (0.36 mmol) of 3b is equal to 0.36 mmol Si–H bond
.21 g (0.36 mmol) of 3b is equal to 0.36 mmol Si–H bond
0.26 g of HTPB is equal to 4.78 mmol C=C bond
13.27
7.14
2.55
14.30
7.14
2.55
0.14 g of HTPB is equal to 2.57 mmol C=C bond
0.05 g of HTPB is equal to 0.92 mmol C=C bond
0.28 g of HTPB is equal to 5.15 mmol C=C bond
0.14 g of HTPB is equal to 2.57 mmol C=C bond
0.05 g of HTPB is equal to 0.92 mmol C=C bond
Table 3
introduction of these pecks to 1H-NMR spectra of the final poly-
mers, confirms the ferrocene functionalization of HTPB.
IR peak signature of pristine HTPB, 3a and 4a compounds.
HTPB
3a
4a
3
-
345 (-OH)
-
3342 (-OH)
3
.3. Physical properties of synthesized polymers
3022 (-CH aromatic)
2928 (-CH aliphatic)
1258 (C-Si)
3032 (-CH aromatic)
2925 (-CH aliphatic)
1262 (C–Si)
2
9
1
-
917 (-CH aliphatic)
69-1310 (-CH)
In continue, we investigated the physical properties such as iron
440-1643 (C=C)
481 (C-Fe)
481 (C–Fe)
percentage, hydroxyl value, viscosity and glass transition temper-
ature for modified polymers, and compared them with alkylbu-
tacenes which reported in our previous work [47,48]. Results are
summarized in Table 4.
2112 (Si-H)
Disappeared
The iron percentage of the modified polymers was measured
using atomic absorption spectrophotometer in the range of 8-16
wt%. These values are significant compared to that of alkylbu-
tacenes, since in this research bis-nuclear ferrocenyl derivatives
were used as modifying agents. Obviously, with increasing the
grafting of ferrocene moiety, the iron content of final polymer
showed increases as well.
well as ferrocenylsilane peaks. Additionally, 1H-NMR spectra can
also be used for this purpose. In the 1H NMR spectra of fi-
nal polymer, the -CH2 and the peaks for unreacted vinyl groups
of HTPB can be seen along with the indicative ferrocene peaks,
which confirms the modification of pristine HTPB with ferrocenyl-
silane. Bis alkylferrocene-grafted hydroxyl terminated polybutadi-
ene [(alkylFc) -HTPB)], exhibits two sharp resonances for the two
Studies showed that the viscosity of such polymers is affected
by two different factors: 1) Viscosity increased with increasing iron
content, 2) viscosity decreased with increasing the length of alkyl
2
sets of cyclopentadienyl protons at 3.90-4.15 ppm and the proton
resonance from (CH ) Si- is visible at 0.05-0.09 ppm (Fig. 3). The
3
2
7

A. Aghaiepour, S. Rahimpour, E. Payami et al.
Journal of Organometallic Chemistry 940 (2021) 121789
Fig. 3. 1H NMR spectra of 2a, 3a and 4a as representative of synthesized compounds.
Table 4
Iron percentage, viscosity, glass transition temperature and hydroxyl value for HTPB and alkyl Fc-HTPB derivatives.
Glass transition
Hydroxy Value
(mmol OH/g)
Entry
Compound
Iron content (%)
Viscosity (Pa.s)
temperature (°C)
1
2
3
4
5
6
7
8
HTPB a
-
3.4
-73.2
-70.8
-68.4
-64.3
-67.9
-64.4
-61.5
-72.4
0.8
Ethyl Fc-HTPB a
Ethyl Fc-HTPB a
Ethyl Fc-HTPB a
4a
3.16
8.2
3.92
4.48
5.13
4.68
5.43
6.23
3.62
-
-
9.2
-
8.59
11.82
15.98
5.9
0.46
0.33
0.16
-
ꢀ
4a
ꢀ
ꢀ
4a
Propyl Fc-HTPB
a
9
Propyl Fc-HTPB
a
8.2
4.26
4.98
-71.5
-70.1
-
-
1
0
Propyl Fc-HTPB
10.27
a
1
1
1
1
2
3
4b
8.12
4.37
5.14
5.83
-67.1
-63.8
-60.7
0.48
0.34
0.17
ꢀ
ꢀ
4b
11.23
15.01
ꢀ
4b
a
Reference [47].
branch on the ferrocene core. According to the mentioned points,
these polymers have a relatively higher viscosity compared with
similar alkylbutacenes which accounts for a high iron content. On
the other hand, greater extent of side branching substituents in
these polymers caused a decrease in viscosity values in comparison
to polymers of the same iron percentage. As can be seen in Table 4,
the viscosity value in [4,4-bis(ethylferrocenyl)pentyl]dimethylsilane
grafted HTPB derivatives is higher than that of propyl derivatives.
Although this difference is very small, it is recognizable.
Fig. 4(a) shows the plot of iron content versus viscosity for syn-
thesized polymers, this figure obviously shows increasing of the
iron content and decreasing in the length of side chain result in
the viscosity increasing. We report results of glass transition tem-
peratures (Tg) measurements for modified polymers ranging from
about -67.9 °C to about -60.7°C. Fig. 4(b) clearly shows the propor-
tion between the glass transition temperature and iron content of
modified polymers. The Tg values are directly related to the iron
percentage of polymer which reflects the number of grafting fer-
rocenes. In contrast, the glass transition temperature tangibly starts
to decrease with an increasing in the number of carbons in the
substituted groups.
The hydroxyl content of HTPB and all modified polymers were
determined by acetylation with excess acetic anhydride followed
by back-titration with standard alcoholic KOH [45]. Obtained re-
sults were listed in Table 4. Hydroxyl values decreased with in-
creasing of iron content in the modified polymers. Obviously, OH
groups are constant, while a large number of alkylferrocenylsilane
molecules are linked per unit of the polymer. Hydroxyl terminated
groups of pristine HTPB remained intact in the modified HTPB af-
ter hydrosilylation reaction.
3
.4. Thermal properties
The dynamic mechanical thermal analysis (DMTA) was used for
measuring glass transition temperature of prepared polymers, the
tan δ as a function of temperature for all of the final ferrocenyl
8

A. Aghaiepour, S. Rahimpour, E. Payami et al.
Journal of Organometallic Chemistry 940 (2021) 121789
Fig. 4. Plot of (a) the iron content versus the viscosity and (b) the iron content versus glass transition temperature for modified polymers.
Fig. 5. The DMTA plot for (A) ethylferrocene and (B) propylferrocene derivatives grafted HTPB.
Table 5
modified polymers is shown in Fig. 5. In synthetic polymers the
Selected electrochemical data for the synthesized polymers in
position of the tan δ peak was considered as glass transition tem-
perature. As previously stated, the glass transition temperature and
iron content of modified polymers have a direct relationship. On
the other hand, the increase in the number of carbons (ethyl to
propyl) led to a slight decrease in glass transition temperature.
The TGA thermograms of final polymers, are illustrated in Fig. 6.
The thermal degradation profile for all of the ferrocenyl modified
polymers in this work contain the three-stage weight loss process.
At first, the little weight loss (6-7%) can be related to the water re-
moval of samples. In continue, thermal decomposition of polymers
is detectable with significant weight loss in ≤500 °C. Finally, after
heating the polymer samples up to 700 °C, Fe residual as a per-
centage of the sample total weigh was remained, which is in good
agreement with atomic absorption data for iron percentage.
DCM/0.100 M (Bu)4N.BF4 at 25.0 °C.
Entry
compound
Epa
Epc
ꢀE
Ic/Ia
1
2
3
4
5
6
4a
0.6738
0.6787
0.6790
0.7666
0.7715
0.7764
0.4150
0.4196
0.4004
0.4248
0.4346
0.4395
0.2588
0.2591
0.2786
0.3418
0.3369
0.3369
0.5219
0.6187
0.5897
0.5843
0.4484
0.3791
ꢀ
ꢀ
4a
ꢀ
4a
4b
4b
4b
ꢀ
ꢀꢀ
3
.6. Electrochemical properties of modified polymers
In order to investigate the electrochemical properties of
synthesized polymers, cyclic voltammetry was performed in
dichloromethane with 0.1 M tetrabutylammonium tetrafluorobo-
rate as supporting electrolyte. Electrochemical data summarized in
Table 5 and Fig. 8 depicts the CV curves for all polymers, an ob-
3
.5. Optical properties
+
vious redox peak is assigned to the Fc/Fc system. As can be seen
Ferrocenyl compounds display unique optical properties, fer-
in Fig. 8a and 8e by increasing the iron content, peak currents in-
crease. Obtained results are in agreement with the atomic absorp-
tion data and higher peak currents indicate higher ferrocenyl graft-
ing since ferrocene is the electroactive group in final polymers.
Fig. 8d and 8h compare the CV diagrams of mono and bis-nuclear
ferrocene grafting polymers, and the obtained results are in line
with other data and corroborating the increase in ferrocene link-
age to the HTPB framework. Furthermore, the effect of scan rate
on peak current was studied in the same condition in the range of
rocene units in the main chain of polymer create optical proper-
ties in the modified HTPB. Fig. 7 shows the UV-vis spectra of the
prepared ferrocenyl modified polymers. As shown in Fig. 7 there
are two characteristic transitions (λmax), the overall value of lower
∗
wavelengths is approximately 320 nm which is assigned to π-π
transition of ferrocenyl cyclopentadienyl ring and the second one is
located in 440 to 460 nm, this absorption is due to metal-to-ligand
charge transfer (MLCT). As expected, the absorption intensity is in-
fluenced by the sample iron percentage, which means the intensity
of absorption increases with an increase in the ferrocenyl grafting
to HTPB polymer.
25–200 mVs 1 (Fig. 8b and 8f), the linear relationship with 0.99
regression coefficient was obtained via plotting of anodic and ca-
thodic currents versus the square root of scan rates (Fig. 8c and
−
9

A. Aghaiepour, S. Rahimpour, E. Payami et al.
Journal of Organometallic Chemistry 940 (2021) 121789
Fig. 6. TGA thermograms of (A) ethylferrocene and (B) propylferrocene derivatives grafted HTPB.
8
g). This behavior suggests a diffusion-limited characteristic for the
pose, [4,4-Bis(ethylferrocenyl)pentyl]dimethylsilane grafted HTPB
ꢀ
ꢀ
redox process.
containing 15.98% of Fe (4a ) was chosen as representative of the
final ferrocenyl polymers and abbreviated as BEFcHTPB. Since the
appearance of all synthesized ferrocenyl polymers was viscous oil,
it was impossible to dry them on the GCE surface to do elec-
trochemical evaluations. Therefore, terephthaldehyde (TFA): a two
3
.7. Preparation of the modified electrode (GC/BEFcHTPB/(TFA+FEW))
In continue, the electrochemical behavior of the synthesized
polymers was evaluated on the surface of GCE. For this pur-
10

A. Aghaiepour, S. Rahimpour, E. Payami et al.
Journal of Organometallic Chemistry 940 (2021) 121789
Fig. 7. UV-vis spectra of bis-ferrocenyl modified HTPB.
+
functional aldehyde and fresh egg white (FEW): a known and low
cast protein as the cross-linking agent were used [52,53]. At first,
oxidation and reduction peaks of Fc/Fc couple is quite obvious.
Aiming to evaluate the modified electrode capability for dopamine
determination, the fabricated electrode was scanned in the phos-
phate buffer solution (PBS) which spiked with 1mM dopamine un-
der the same condition (Fig. 11a, blue line). As can be seen, the in-
crease in peak current approves the sensitivity of fabricated elec-
trode to dopamine. As mentioned in the literature dopamine can
be oxidized through a two-electron and two-proton change pro-
cess [55], and ferrocene can mediate the oxidation of dopamine.
Fig. 12 shows the electrocatalytic dopamine oxidation process in
the surface of GC/BEFcHTPB/(TFA+FEW) modified electrode. Differ-
ential pulse voltammetry (DPV) is another effective electrochemi-
cal method that has been extensively used for dopamine detection,
DPV studies can provide improved selectivity compared to CV. The
DVP voltammogram of GC/BEFcHTPB/(TFA+FEW) electrode in ab-
the GC electrode was polished using alumina, sonicated in H SO
2
4
(
2N), and distilled water, and scanned at the range of -1 to 1 V
in H SO4 (2N) until the well-defined stable cyclic voltammogram
2
was observed. In continue, the 10% CH Cl solution of TFA and
2
2
1
0% CH Cl2 solution of FEW were added to 5 mg of BEFcHTPB
2
which dissolved in dichloromethane. The final suspension was son-
icated for 10 min and the homogenous BEFcHTPB/(TFA+FEW) com-
plex was obtained. The GC/BEFcHTPB/(TFA+FEW) modified elec-
trode was fabricated by drop-coating of the obtained complex on
the GCE surface.
3
.8. Morphology study of the modified electrode
−1
sence and presence of dopamine (1 mM) at scan rate of 50 mV s
For morphology studies of GCE and GC/BEFcHTPB/(TFA+FEW)
depicted in Fig. 11b. The sensitivity of GC/BEFcHTPB/(TFA+FEW)
modified electrode to dopamine is marked by an increase in peak
intensity.
modified electrode, the Field Emission Scanning Electron Mi-
croscopy (FE-SEM) technique was used. Fig. 9 depicts the related
images at 2 μm magnification, the wrinkled surface of GCE af-
ter drop-coating with BEFcHTPB/(TFA+FEW) complex in compari-
son with the uniform structure of the bare GCE demonstrated the
successful modification of GCE.
3
.11. Effect of solution pH in dopamine detection
The effect of solution pH on the peak current of the DPV
voltammogram has been studied at five constant pH levels be-
3
.9. Interface properties of GC/BEFcHTPB/(TFA+FEW)
tween 4.0 and 8.0 using GC/BEFcHTPB/(TFA+FEW) modified elec-
−1
trode in 0.1 M PBS at a scan rate of 50 mV s . The maximum
value of DPV peak current was obtained in pH = 7 (Fig. 13). Ad-
ditionally, the potential of DA oxidation was plotted versus pH. As
can be seen in Fig. 13c, the positive and negative shift of DA po-
tential was observed with changing in pH values. The result is im-
plying that the modified electrode surface is suitable for actively
electrons transformation in the electrochemical redox reaction of
DA.
Fig. 10 illustrated the Nyquist plots of bare GC and
GC/BEFcHTPB/(TFA+FEW) modified electrode measured in 5 mM
K [Fe(CN) ]/ K [Fe(CN) ] solution, to study the interface proper-
3
6
4
6
ties. The faradaic electron-transfer was reflected in a semicircle
at high frequencies as well as diffusional processes which can be
shown a with linear line at low frequencies [54]. The successful
immobilization of the BEFcHTPB/(TFA+FEW) complex on the
bare GCE surface was demonstrated by a larger diameter of the
semicircle in the Nyquist plot of GC/BEFcHTPB/(TFA+FEW) mod-
ified electrode comparison to bare GC electrode. The semicircle
diameter is related to charge transfer resistance (Rct); with immo-
bilization of BEFcHTPB/(TFA+FEW) complex on the GCE surface,
the decrease in electrode conductivity led to increasing in charge
transfer resistance.
3
.12. Linear range of modified electrode in dopamine detection
After the confirmation of the electrochemical response of the
GC/BEFcHTPB/(TFA+FEW) modified electrode to dopamine, the re-
lationship between dopamine concentration and the oxidation
peak current was evaluated using CV technique in PBS 0.1 M at
pH 7.0. As can be seen in Fig. 14 with increasing the dopamine
concentration at the range of 3 to 125 μM, the oxidation peak cur-
rent increased linearly. According to the calibrate curve, the lin-
3
.10. DPV study of the prepared electrode for the capability of
dopamine detection
FcHTPB/(TFA+FEW) complex, the fabricated electrode was
ear regression equation is: Ipa(μA) = 0.1567C (μM)+1.5613, and
DA
scanned in the phosphate buffer solution (PBS) using a scan rate
the correlation coefficient is 0.9968. The detection limit (3σ/m)
and quantitation limit (10σ/m), was obtained as 0.048 μM and
of 50 mV s 1 at the range of 0 to 1 V (Fig. 11a, red line), the
−
11

A. Aghaiepour, S. Rahimpour, E. Payami et al.
Journal of Organometallic Chemistry 940 (2021) 121789
Fig. 8. Cyclic voltammetry plots for modified polymers (a) CV for ethyl derivatives with a variety of iron content, (b) CV curves of the 4a in different scan rates, (c) Linear
relationship between the peak current and the square root of scan rates for 4a, (d) Comparison between CV curves of 4a and ethyl Fc-HTPB [48], (e) CV curves for propyl
derivatives with variety of iron content, (f) CV curves of the 4b in different scan rates, (g) Linear relationship between the peak current and the square root of scan rates for
4b, (h) Comparison between CV curves of 4b and ethyl Fc-HTPB [48].
12

A. Aghaiepour, S. Rahimpour, E. Payami et al.
Journal of Organometallic Chemistry 940 (2021) 121789
Fig. 9. SEM image of A: Bare GCE, and B: GC/BEFcHTPB/(TFA+FEW).
Fig. 10. The Nyquist curves of Bare GCE, and GC/BEFcHTPB/(TFA+FEW) modified electrode.
Fig. 11. (a) CV curves and (b) DPV voltammograms of GC/BEFcHTPB/(TFA+FEW) electrode in absence and presence of Dopamine. Scan rate: 50 mV s−1
.
13

A. Aghaiepour, S. Rahimpour, E. Payami et al.
Journal of Organometallic Chemistry 940 (2021) 121789
Fig. 12. The electrocatalytic dopamine oxidation process in the surface of GC/BEFcHTPB/(TFA+FEW) modified electrode.
Fig. 13. (a) The effects of solution pH on the DPV peak current. (b) The relationship between DPV peak current and pH.
0.16 μM, where σ and m were the blank standard deviation and
3.13. The interference study in the detection of dopamine
the calibration plot slope, respectively. Also, the sensitivity of the
sensor was calculated (slope of the calibration plot/active surface
In continue, the interference study was performed using fabri-
cated GC/BEFcHTPB/(TFA+FEW) electrode in PBS 0.1 M at pH 7.0
spiked with 1 mM dopamine along with 1 mM ascorbic acid. The
oxidation potential of ascorbic acid is very close to dopamine;
since, the preparation of modified electrodes which is able to
2
−1
−2
area (0.101 cm ) of the modified electrode) as 1.55 μAμM cm .
Table 6 shows the comparison between the results of the present
with other ferrocene-based research for dopamine determination;
it is obvious that our fabricated electrode can compete in this field.
14

A. Aghaiepour, S. Rahimpour, E. Payami et al.
Journal of Organometallic Chemistry 940 (2021) 121789
Fig. 14. (a) The relationship between peak current and dopamine concentration. (b) The calibration plot.
Fig. 15. DPV response GC/BEFcHTPB/(TFA+FEW) electrode for dopamine in the presence of ascorbic acid.
separate the oxidation peaks of dopamine and ascorbic acid is
3.14. Dopamine oxidation mechanism
very attractive for scientists. Fig. 15 shows the oxidation poten-
tial 0.33 and 0.13 V for dopamine and ascorbic acid, respectively.
The 0.20 V peak separations are large enough which allowing the
determination of dopamine without interfering with the ascorbic
acid.
The DA oxidation mechanism in pH = 7 is a two-electron and
two-proton change process. As can be seen in Scheme 2, DA was
oxidized and converted to dopamine-o-quinone.
Scheme 2. DA oxidation mechanism in pH = 7.
15

A. Aghaiepour, S. Rahimpour, E. Payami et al.
Journal of Organometallic Chemistry 940 (2021) 121789
Table 6
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0.21
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In summary, we synthesized the bis-alkylferrocenyl silane
grafted HTPB, via hydrosilylation reaction of bis-alkylferrocene
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based silane derivatives with HTPB in the presence of H PtCl
2
6
catalyst. Viscosity, iron content, and glass transition temperature
of these new ferrocene grafted polymers were investigated. The
predicted structures of the novel synthesized polymers were con-
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analysis. The electrochemical behavior of synthesized compounds
was studied by cyclic voltammetry, and the relationship between
the square root of scan rate and peak currents, showed that the
redox process is diffusion-limited. On the other hand, presence of
ferrocene caused the production of optical properties in the final
polymer. We studied these properties using the UV-vis technique.
Finally, the prepared polymer was drop-coated on the GCE sur-
face, while cross-linking agents were FEW and TFA. The electro-
chemical behavior of the fabricated electrode was studied via EIS,
CV, and DPV. The fabricated GC/BEFcHTPB/(TFA+FEW) electrode
showed enhanced sensitivity in comparison to GCE for determina-
tion of dopamine in PBS. Additionally, based on interference study
results, ascorbic acid did not have any interference with the de-
termination of dopamine using GC/BEFcHTPB/(TFA+FEW) modified
electrode. The most important limitations contain: can be affected
by environmental changes and contamination, possibility of peel-
ing the immobilized polymer from the electrode surface, and short
shelf-life (maximum one month) of fabricated sensor.
[
[
[
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(2019) 179–192, doi:10.1007/978-981-32-9057-0_7.
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This project is supported by a research grant of the University
of Tabriz (number SAD/796-970305).
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