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Electrocatalytic oxidation of dopamine on the surface of ferrocene grafted hydroxyl terminated polybutadiene modified electrode
Polymer 192 (2020) 122310
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Electrocatalytic oxidation of dopamine on the surface of ferrocene grafted hydroxyl terminated polybutadiene modified electrode Keshvar Rahimpour , Reza Teimuri-Mofrad * Department of Organic and Biochemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords: Hydroxyl terminated polybutadiene Dopamine Electrocatalyst
In this study, 4-(dimethylsilyl)butylferrocene was prepared using 4-chlorobutylferrocene via Grignard reaction in dry THF and the reaction of prepared reagent with chlorodimethylsilane. In continue, obtained ferrocenylsilane derivative was grafted to hydroxyl terminated polybutadiene (HTPB) via hydrosilylation reaction. Ferrocenyl units in polymer backbone gave a couple of reversible peaks of cyclic voltammetry (CV). Additionally, FT-IR, 1H NMR, UV–Vis spectroscopy along with molecular weight and TGA analysis confirmed the polymer modification. The modified polymer was coated onto the surface of glassy carbon electrode (GCE); meanwhile, fresh egg white (FEW) and terephthaldehyde (TFA) were used as cross-linking agents. The successful immobilization of polymer was demonstrated using Electrochemical impedance spectroscopy (EIS). The modified electrode showed an electrocatalytic effect on the oxidation of DA, the Fc/Fcþ couple mediate the oxidation of DA on the surface of GC/Butacene/(TFA þ FEW) electrode. The optimum pH ¼ 7 was obtained for this response. The electrode protected 86% of its initial electrocatalytic after 500 cycles and 90% of its initial current after 30 day storage at 4 � C. The results indicated that GC/Butacene/(TFA þ FEW) electrode possessed satisfactory linear ranges and detection limits for detection of DA.
1. Introduction Dopamine (DA) is a neurotransmitter which plays a key role in the life science [1]. Different methods have been used for DA detection, including Surface-Enhanced Raman Scattering (SERS) [2], fluorescence [3], UV–vis spectrophotometry [4], derivatization [5], colorimetric biosensors [6], and electrochemical sensors [7]. Nowadays, surface modification of common electrodes such as glass carbon (GC), and platinum electrode using physical or chemical methods is a successful strategy for overcoming of analyte detection problems [8]. The low sensitivity, high detection limit, narrow linear range, and longtime response along with the interface effect of other analytes are the most known problems in electrochemical measurements [9–11]. In the last decades, the electrochemical sensors based on modified electrodes were prepared via covalently or physically incor porating of different organic, biomolecules and organometallic com pounds. Using this method, new electrochemical properties can be created in routine electrodes such as glassy carbon or platinum electrode [12–15]. Some of the recent development of advanced electrode mate rials for dopamine detection were summarized in Table 1.
Ferrocene and its derivatives widely used as electrochemical active species. High thermal stability, high redox activity and chemical versatility of these compounds, give the ferrocene a special reputation among other metallocenes. Ferrocene can be easily oxidized and reduced, which is known as redox behavior of Fc/Fcþ couple. Ferrocene is a neutral charge molecule without any functional group and it cannot be adsorbed on the surface of electrode; hence, it is approximately impossible chemically immobilization of ferrocene on the electrode surface. For this reason, in most researches, ferrocenyl compounds were attached to a nanoparticle or polymeric backbones [21–24]. We used hydroxyl terminated polybutadiene (HTPB) as a polymeric framework. HTPB is a liquid rubber containing hydroxyl groups in ter minal carbons of the polymer backbone and many vinyl groups in the chain, which made by traditional radical polymerization of 1,3-buta diene. Nowadays, the living radical polymerization was extensively developed for HTPB preparation [25]. Recently, HTPB was been suc cessfully used for the fabrication of elastic conducting polymer micro-particles with core-shell structure [26]. The ferrocene grafted HTPB was known as Butacene. For the first time, Soci�et�e Nationale de Poudres et Explosifs (SNPE, France) inset Butacene as a new burning rate
* Corresponding author. E-mail address: [email protected] (R. Teimuri-Mofrad). https://doi.org/10.1016/j.polymer.2020.122310 Received 28 November 2019; Received in revised form 31 January 2020; Accepted 19 February 2020 Available online 24 February 2020 0032-3861/© 2020 Published by Elsevier Ltd.
Electrode structure
Table 1 Some of recent development of advanced electrode materials for dopamine detection.
[7]
[20]
[19]
[17]
Ref [18]
Electrode structure
[16]
Ref
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accelerator catalyst. Butacene can be prepared with a various iron per centage, which calculates according to the amount of grafted ferrocene to the backbone of HTPB [27,28]. Additionally, other ferrocenyl de rivatives e.g. ferrocene carboxaldehyde and iodoferrocene were used for terminal functionalization of HTPB, obtained compounds were used as a binder with improved burn rate [29]. Based on our best knowledge, there is no report on using this ferrocenyl grafted polymer in the modification of electrodes. In this study, Butacene with 19.8% by weight of ferrocenyl unit was prepared via hydrosilylation reaction of 4-(dimethylsilyl)butylferrocene with HTPB. Characteristic data including the molecular weight distri bution, FT-IR, 1HNMR, UV–Vis spectroscopy along with electrochemical properties and thermal stability of synthesized polymer were studied. The synthesized polymer was coated on the surface of the GC electrode; the observations show ferrocenyl based polymer increase the oxidation of dopamine in biological media. The catalytic peak current was enhanced in pH ¼ 7. 2. Experimental 2.1. Materials
Scheme 1. Synthesis of ferrocene grafted HTPB with 19.8% ferrocenyl unit. i) Grignard reagent [Mg/THF/(CH3)2HSiCl], ii) Hydrosilylation reaction [H2PtCl6/Hexane].
Commercial grade of compounds [Ferrocene, HTPB, chlor odimethylsilane, H2PtCl6, iodide, magnesium, terephthaldehyde (TFA), LiClO4, potassium dihydrogen phosphate] were used as required chemicals.
ethyl acetate was use as eluent to obtain a brown viscose oil. FT-IR (KBr, cm 1): 3077 (C–H, Aromatic), 2920, 2847 (C–H, Aliphatic), 1641, 1443 – C), 1072 (C–Si), 488 (Fe-Cp); 1HNMR (δ in ppm): 5.60–4.94 (m, (C– – CH, C– – CH2, HTPB), 4.10–4.05 (m, Cp), 2.36–2.32 (t, CpCH2), C– 2.09–2.05 (m, CH2, HTPB), 1.56–1.33 (m, -CH2), 0.63–0.60 (m, CH2–Si), 0.07–0.01 (m, Si(CH3)2). Iron content 6%.
2.2. Equipment The Bruker-Tensor 270 spectrometer was used for recording FT-IR spectra as wave numbers νe (cm 1). The Bruker FT-400 spectrometer was used for recording NMR spectra. The 70 eV by Agilent (5975C VL) instrument, applied for mass spectra operating. The Analytikjene (novaa 400) atomic absorption spectrophotometer was used for iron analysis, and SPECORD 250 analytikjena UV/vis spectrophotometer was used for recording of UV/vis spectra. Brookfield RVT viscometer was used for measurement of viscosity. The viscosity, measured in a Brook field RVT viscometer. The FESEM (MIRA3 TESCAN), was used for analysis of surface morphology.
2.5. Thermal stability studies Thermogravimetric analysis (TGA) was performed between 25 and 700 � C on a TGA PYRIS 1 and Triton Tritec 2000 DMN instruments under N2 at heating rate of 10 � C/min to study of thermal decomposition of modified polymer. 2.6. Preparation of modified electrode
2.3. Synthesis of 4-(dimethylsilyl)butylferrocene
The electrode preparation procedure includes two steps: pretreat ment of the GC electrode, and immobilization of Butacene on the elec trode surface (1) the glassy carbon electrode (GCE), was sequentially polished with alumina powder, and sonicated in 2.0 M sulfuric acid and double-distilled water, respectively. The GC electrode was subjected to cyclic scanning in 0.2 M H2SO4 solution in the potential range from 1 V to 1 V (vs Ag/AgCl) until well-defined cyclic voltammogram was ob tained. Then electrode cleaned with distilled water and dried in air. (2) Butacene/(TFA þ FEW) complex was prepared by dissolving 5 mg Butacene in CH2Cl2 and adding 2 ml of 10% solution of TFA and fresh egg white (FEW) solutions in dichloromethane. 5 μl of obtained blend was coated on the GCE surface and air-dried to obtain the GC/Butacene/ (TFA þ FEW) electrode.
0.072 g (3 mmol) of Magnesium turnings and catalytic amount of iodine crystal were dispersed in 1 ml dry THF under argon atmosphere. 0.83 g (3 mmol) of 4-chlorobutylferrocene [30] was dissolved in 8 ml dry THF and slowly added to the above suspension. The obtained mixture was stirred at reflux temperature until all the magnesium turnings were dissolved. After 24 h, cooling the mixture and THF diluted chlorodimethylsilane (0.28 g, 3 mmol) slowly added to the reaction flask via dropping funnel. The reaction mixture was refluxed under argon gas for 3 h and then cooled to room temperature. After solvent evaporation dark orange oil with 86% yield was obtained with column chromatog raphy, hexane was used as eluent. FT-IR (KBr, cm 1): 3091 (C–H, Aro – C), matic), 2928, 2861 (C–H, Aliphatic), 2110 (Si–H), 1637, 1454 (C– 1050 (C–Si), 490 (Fe-Cp); 1HNMR (δ in ppm): 4.10–4.05 (m, 9H, Cp and 1H, Si–H), 2.35–2.31 (t, 2H, CH2-Cp), 1.58–1.38 (m, 4H, -CH2), 0.65–0.61 (m, 2H, CH2–Si), 0.08 (s, 6H, Si(CH3)2). MS (70 eV): m/z ¼ 300 [M]þ.
2.7. Electrochemical measurements Potentiostat/galvanostat Autolab (PGASTAT 30) were used for electrochemical experiments using a three-electrode cell configuration: Ag/AgCl, GC, and platinum wire as the reference, working and counter electrodes, respectively. CV voltammograms were collected in the 0–0.8 V potential range with respect to the Ag/AgCl. Electrochemical imped ance spectroscopy (EIS) experiments was recorded in 5.0 mM Potassium ferricyanide/Potassium ferrocyanide. An AC voltage was applied with 5 mV amplitude in 0.01 Hz up to 100 kHz frequency range.
2.4. Synthesis of ferrocene grafted HTPB A mixture of 4-(dimethylsilyl)butylferrocene and 0.2 g of HTPB was stirred in 15 ml dry hexane as solvent. 30 μL of hexachloroplatinic acid used as catalyst. After 24 h reflux at 60 � C, the reaction mixture was filtered. After the evaporation of solvent, ferrocene grafted HTPB was obtained using column chromatography. Gradient ratio of hexane and 3
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Fig. 1. FT-IR spectra of HTPB, 4-(dimethylsilyl)butylferrocene (FcSiH) and Butacene. Fig. 3. UV–Vis spectra of HTPB and Butacene. Table 2 Molecular weight distribution parameters and viscosity of HTPB and Butacene. Sample Name
HTPB
Butacene 19.8%
MW Mn Polydispersity Viscosity (Pa.s)
12368 8187 1.511 3.40
15148 10657 1.421 4.35
4-chlorobutylferrocene doesn’t have suitable functional group for grafting to the HTPB polymer framework, therefore Grignard reaction was used for conversion of the chlorine to dimethylhydrosilyl group. The Grignard reagent was prepared in situ by adding 4-chlorobutylferrocene to magnesium turnings in dry THF. Obtained mixture was reacted with chlorodimethylsilane and result in preparation of 4-(dimethylsilyl) butylferrocene with 90% yield. Finally, hydrosilylation reaction was carried out between ferrocenylsilane and HTPB; the hexachloroplatinic acid (H2PtCl6) and hexane were used as catalyst and solvent, respectively. The FT-IR spectroscopy of HTPB, ferrocenylsilane and final polymer was illustrated in Fig. 1. The disappearance of Si–H stretching vibration in 2110 cm 1 and revelation of Fe-Cp stretching vibration in 488 cm 1 is a clear evidence for grafting of ferrocene in the polymer backbone. These observations are in full agreement with the 1H NMR results (Fig. 2). The chemical shifts of 4.08, 2.34, 1.2 and 0.3 ppm in the final polymer spectrum are related to cyclopentadienyl rings (Cp), CH2 in the vicinity of Cp, CH2 of chain, CH2 and CH3 in the vicinity of silicon atom, respectively. After grafting of ferrocene to polymer skeleton, obtained Butacene shows π-π* transition in 324 nm and MLCT (Metal to Ligand) transition in 441 nm in UV–Vis spectra (Fig. 3). The HTPB is a colorless and clear oily liquid. Increasing of viscosity and change in the final polymer color to dark orange are the most obvious reasons for grafting of ferrocenyl derivative on polymer backbone and achievement to final product. Increasing in number average molecular weight (Mn) and weight average molecular weight (Mw) of Butacene 19.8% compared with HTPB indicates the polymer functionalization (Table 2). Polydispersity is defined as Mw/Mn and it was decreased with grafting of ferrocene to HTPB. On the other hand, increasing in the viscosity of final polymer in comparison with pristine HTPB confirmed the attaching of ferrocenyl moieties to polymer backbone. The TGA and dTGA (first derivative curve) thermograms of HTPB, and Butacene, are illustrated in Fig. 4. For HTPB a two-stage weight loss process is visible. The minor weight loss was occurred until 340 � C, can be related to the removal of sample water, the major thermal decom position of HTPB was assigned with weight loss process in the range of 405–495 � C. For Butacene, the TGA results illustrated different thermal degradation profile containing three-stage weight loss process. The
Fig. 2. 1H NMR spectra of HTPB, 4-(dimethylsilyl)butylferrocene (FcSiH) and Butacene.
3. Result and discussion 3.1. Synthesis and characterization of butacene 19.8% (percent by weight of ferrocenyl unit) Over the past years (from 1995) [31], Butacene was prepared with different percentages of iron for using as burning rate catalyst. To the extent of our knowledge, this is the first work that reports electro chemical application of ferrocenyl grafted HTPB. In this work, Butacene with 19.8% grafted ferrocenyl unit was synthesized via hydrosilylation reaction of HTPB with 4-(dimethylsilyl)butylferrocene as a well-known procedure for Butacene preparation (Scheme 1). In summary, 4
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Fig. 4. TGA and dTGA thermograms of HTPB and Butacene 19.8%.
Fig. 5. SEM images of (A)bare glassy carbon electrode, (B) GC/Butacene and (C) GC/Butacene/(TFA þ FEW) electrode.
maximum rate of weight loss at roughly 481 � C ( 77.18% weight loss). By heating the sample up to 700 � C, 6% of the sample total weigh was remained, which is corresponds to Fe residual. In the case of HTPB, sample weight was reached zero at this temperature. 3.2. Electrochemical evaluation of butacene 19.8% Modified GC electrode was fabricated by diluted Butacene in CH2Cl2, for immobilization of Butacene on the GC surface, terephthaldehyde (TFA) and fresh egg white (FEW) were used as a cross-linking agent. Bovine serum albumin (BSA) is a known protein which used in electrode preparation, FEW is also a kind of protein and can be used for this purpose. The result showed that the immobilization with FEW was effective, feasible, more convenient, and inexpensive. The use of this FEW as cross-linking agent has been few reported in literatures [32] so it is relatively new method. 5 mg of Butacene was dissolved in CH2Cl2 and 2 ml of 10% solution of TFA and FEW solutions in dichloromethane was added to the prepared butacene solution under stirring. 5 μl of obtained blend was coated on the GCE surface and air-dried to obtain the GC/Butacene/(TFA þ FEW) electrode. Field Emission Scanning Electron Microscopy (FE-SEM) was employed to characterize the top views of the bare electrode, GC/ Butacene and (C) GC/Butacene/(TFA þ FEW) electrode (Fig. 5). Fig. 5A shows uniform structure of the bare working GC electrode. The pure Butacene film shows a loose and fibrillary structure distributed on to the surface of the GC electrode (Fig. 5B). Fig. 5C shows SEM image of GC/ Butacene/(TFA þ FEW) film reveal the uniform, homogenous dispersion of Butacene/(TFA þ FEW) on the electrode’s surface. The SEM image of modified electrode indicates that modifiers were successfully immobi lized on the glassy carbon electrode’s surface.
Fig. 6. EIS spectra recorded for Bare GC and GC/Butacene/(TFA þ FEW). Inset: A zoom of the impedance results in high and intermediate frequency range.
Electrochemical impedance spectroscopy (EIS) for bare GC and GC/ Butacene/(TFA þ FEW) electrode were measured in 5 mM Potassium ferricyanide/Potassium ferrocyanide solution (Fig. 6). EIS was used for studying the interface properties of surface-modified electrode. Both GC and GC/Butacene/(TFA þ FEW) electrodes showed a semicircle at high frequencies related to faradaic electron-transfer along with a linear line at low frequencies related to diffusional processes [33]. The diameter of semicircle in GC/Butacene/(TFA þ FEW) electrode was relatively larger than bare GC electrode (Inset diagram), which indicated the successful immobilization of Butacene on the electrode surface. It is known that, the diameter of semicircle appearing in the Nyquist plot equals with the charge transfer resistance, Rct, of the electrode [34]. When the 5
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Fig. 7. Cyclic voltammetry of a) GC in 1 mM Butacene and GC/Butacene/(TFA þ FEW) in CH3CN, 1 mM LiClO4, b) Bare GC electrode and GC/Butacene/(TFA þ FEW) in PBS solution, 1 mM NaCl as electrolyte.
Fig. 8. Cyclic voltammetry of GC/Butacene/(TFA þ FEW) electrode a) in different scan rates, b) stability of peak shape after 500 cycles, c) linear relationship between the peak current and the square root of scan rates.
Butacene/(TFA þ FEW) was immobilized on GC electrode the EIS showed a large resistance due to decrease in conductivity of electrode surface. Redox-active polymers are very attractive for scientists because they have outstanding advantages such as applicability in the field of sensors, supercapacitors and etc. HTPB is not electrochemically active, the incorporation of the ferrocenyl groups make it electroactive. The elec troactivity of Butacene was demonstrated by recording of cyclic vol tammetry (CV) measurements in CH3CN solution using LiClO4 as a supporting electrolyte (Fig. 7a, red line). The redox peak at 0.39 V is related to oxidation and reduction of Fc/Fcþ couple. Furthermore, the
CV curve GC/Butacene/(TFA þ FEW) electrode in acetonitrile solution was shown in Fig. 7a, green line. The CV curves of bare GC and GC/ Butacene/(TFA þ FEW) electrodes in phosphate buffer solution (PBS) were illustrated in Fig. 7b. The effect of different scan rates on the CV curves of GC/Butacene/ (TFA þ FEW) electrode was shown in Fig. 8a, the peak current was increased with increasing of scan rate listed in order 250 > 200>150 > 100>50 > 25 mVS 1. The modified electrode displays the 86% cycling stability after recording 500 CVs in 50 mVS 1 (Fig. 8b). The storage stability of the modified electrode was also evaluated by measuring the decrease in the redox peak current during repetitive CV measurements 6
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Fig. 9. a) Cyclic voltammetry and b) DPV voltamogram of GC/Butacene/(TFA þ FEW) electrode in presence of Dopamine. Scan rate: 50 mVS 1.
Fig. 10. Effects of solution pH on the peak current of 1 mM DA in PBS. Scan rate: 50 mVs
1
.
Fig. 11. a) Cyclic voltammograms of dopamine changed with its concentration. Buffer: 0.1 M PBS, pH 7.0. b) The relationship between peak current and con centration of dopamine.
for every week over 1 month, the modified electrode was kept in the refrigerator (4 � C). The GC/Butacene/(TFA þ FEW) electrode protected 90% of its initial current, indicating good stability of electrochemical
response for modified electrode. As can be seen in Fig. 8c, the plot of peak current versus ν1/2 (ν ¼ scan rate) was linear, means that redox processes were diffusion controlled. In continue, the usability of prepared ferrocenyl electrode as medi ator for electrocatalytic oxidation of dopamine (DA) was examined. The electrocatalytic behavior of the GC/Butacene/(TFA þ FEW) electrode in oxidation of DA was studied using CV and differential pulse voltam metry (DPV) methods. Fig. 9 showed the voltammetric response of the GC/Butacene/(TFA þ FEW) electrode in 100 mM PBS spiked with DA (1 mM). In the presence of DA, the anodic peak current (ipa) of GC/Buta cene/(TFA þ FEW) electrode in CV voltammogram was increased as well as increasing in DVP profile. Effect of solution pH on the oxidation peak current (ipa) of DPV voltamogram as electrochemical response of DA on the GC/Butacene/ (TFA þ FEW) electrode was investigated by DPV method in 0.1 M PBS at various pH values ranging from 4.0 to 8.0. According to Fig. 10, the oxidation peak current of DA on the modified electrode surface has the
Table 3 Summary of the linear range and limit of detection for dopamine using different ferrocene-based electrodes. Electrode
Linear response range (μM)
LOD (μM)
Ref
Fc-SWNT/GCE GC/CTP-GNR1(nanocoil) Fc-S-Au/CNC/graphene/ GCE PEDOT/FC1/PEDOT … SDS 3DGH-Fc/GCE GC/Butacene/(TFA þ FEW)
5.0–30 2–20 0.2–2.5
0.050 0.003 0.050
[35] [36] [37]
6–300
0.069
[38]
10–180 5–150
0.042 0.045
[39] This work
7
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voltammetry (DPV). The GC/Butacene/(TFA þ FEW) electrode dis played good sensitivity, stability, repeatability, and reproducibility. In details, sensitivity of GC electrode is enhanced when butacene redox mediators was coated on the surface of electrode. The oxidation of DA enhanced on the surface of GC/Butacene/(TFA þ FEW) electrode, Fc/ Fcþ couple mediated the oxidation of DA in pH ¼ 7. Additionally, the interference study show that AA had nearly no interference for the determination of DA. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. CRediT authorship contribution statement
Fig. 12. Interference study. DPVs response of GC/Butacene/(TFA þ FEW) electrode for DA in the presence of AA.
Keshvar Rahimpour: Investigation, Software, Writing - original draft. Reza Teimuri-Mofrad: Funding acquisition, Project administra tion, Supervision, Writing - review & editing. Acknowledgements This work was supported with the Iran National Science Foundation (INSF).
Fig. 13. Electro-oxidation of DA on the surface of GC/Butacene/(TFA þ FEW) electrode.
References [1] L. Tang, S. Li, F. Han, L. Liu, L. Xu, W. Ma, H. Kuang, A. Li, L. Wang, C. Xu, SERSactive Au@ Ag nanorod dimers for ultrasensitive dopamine detection, Biosens. Bioelectron. 71 (2015) 7–12, https://doi.org/10.1016/j.bios.2015.04.013. [2] X. Yu, X. He, T. Yang, L. Zhao, Q. Chen, S. Zhang, J. Chen, J. Xu, Sensitive determination of dopamine levels via surface-enhanced Raman scattering of Ag nanoparticle dimers, Int. J. Nanomed. 13 (2018) 2337, https://doi.org/10.2147/ IJN.S156932. [3] J. Wang, J. Dai, Y. Xu, X. Dai, Y. Zhang, W. Shi, B. Sellergren, G. Pan, Molecularly imprinted fluorescent test strip for direct, rapid, and visual dopamine detection in tiny amount of biofluid, Small 15 (1) (2019) 1803913, https://doi.org/10.1002/ smll.201803913. [4] X. Hun, S. Wang, S. Wang, J. Zhao, X. Luo, A photoelectrochemical sensor for ultrasensitive dopamine detection based on single-layer NanoMoS2 modified gold electrode, Sensor. Actuator. B Chem. 249 (2017) 83–89, https://doi.org/10.1016/ j.snb.2017.04.065. [5] M. Lan, S. Zhao, X. Wei, K. Zhang, Z. Zhang, S. Wu, P.W. Wang, Zhang, Pyrenederivatized highly fluorescent carbon dots for the sensitive and selective determination of ferric ions and dopamine, Dyes Pigments 170 (2019) 107574, https://doi.org/10.1016/j.dyepig.2019.107574. [6] A.P. Vs, P. Joseph, K.D. SCG, S. Lakshmanan, T. Kinoshita, S. Muthusamy, Colorimetric sensors for rapid detection of various analytes, Mater. Sci. Eng. C 78 (2017) 1231–1245, https://doi.org/10.1016/j.msec.2017.05.018. [7] Q. Yuan, Y. Liu, C. Ye, H. Sun, D. Dai, Q. Wei, G. Lai, T. Wu, A. Yu, L. Fu, K. W. Chee, Highly stable and regenerative graphene–diamond hybrid electrochemical biosensor for fouling target dopamine detection, Biosens. Bioelectron. 111 (2018) 117–123, https://doi.org/10.1016/j.bios.2018.04.006. [8] S. Sharma, N. Singh, V. Tomar, R. Chandra, A review on electrochemical detection of serotonin based on surface modified electrodes, Biosens. Bioelectron. 107 (2018) 76–93, https://doi.org/10.1016/j.bios.2018.02.013. [9] L. Liu, J. Du, S. Li, B. Yuan, H. Han, M. Jing, N. Xia, Amplified voltammetric detection of dopamine using ferrocene-capped gold nanoparticle/streptavidin conjugates, Biosens. Bioelectron. 41 (2013) 730–735, https://doi.org/10.1016/j. bios.2012.09.061. [10] C. Villena, M. Bravo, B. Alonso, C.M. Casado, J. Losada, M.P. Armada, Sizecontrolled gold nanoparticles obtained from electrodeposited amidoferrocenylpoly (propyleneimine) dendrimer-templates for the electrochemical sensing of dopamine, Appl. Surf. Sci. 420 (2017) 651–660, https://doi.org/10.1016/j. apsusc.2017.05.098. [11] M. Liu, L. Wang, J. Deng, Q. Chen, Y. Li, Y. Zhang, H. Li, S. Yao, Highly sensitive and selective dopamine biosensor based on a phenylethynyl ferrocene/graphene nanocomposite modified electrode, Analyst 19 (2012) 4577–4583, https://doi.org/ 10.1039/C2AN35708A. [12] H. Miyaji, H. Komada, K. Goto, J. Fujimoto, N. Kiriyama, J.H. Tucker, Selective recognition and electrochemical sensing of dopamine using a ferrocene-based heteroditopic receptor, Tetrahedron Lett. 43 (2018) 3853–3857, https://doi.org/ 10.1016/j.tetlet.2018.09.026. [13] M. Devendiran, K.K. Kumar, S.S. Narayanan, Fabrication of a novel Ferrocene/ Thionin biomediator modified electrode for the electrochemical determination of
maximum value in pH ¼ 7. The dependence of the oxidation peak currents on the concentrations of DA is presented in Fig. 11a. The oxidation peak current increases linearly with the concentrations of DA ranging from 5 to 150 μM. The calibrate curve for dopamine analyze was shown in Fig. 11b, the linear regression equation is expressed as: Ipa (μA) ¼ 1.38 þ 0.17[DA] (μM) with correlation coefficient of 0.99. The detection limit (3σ/m), where σ is the standard deviation of blank and m is the slope of the calibration plot, was 0.045 μmol L 1. These data were comparable to the values obtained by other research groups (Table 3). For further investigations, the prepared GC/Butacene/(TFA þ FEW) electrode was used to study of interference of AA. The AA can be oxidized at a potential close to that of DA, it is normally difficult to obtain separated voltammetric waves for AA and DA. Fig. 12 show the DPV of DA and AA in a mixture. As can be seen two peaks are separated with potential separation of about 0.19 V, the potentials are 0.39 and 0.20 V for DA and AA, respectively. The potential separation is large enough to allow the determination of DA in the presence of AA. The results showed that prepared GC/Butacene/(TFA þ FEW) elec trode can be catalyzed the electro-oxidation of DA. In the literatures, oxidation of DA was described as a two-proton and two-electron change process [40]. For as-prepared GC/Butacene/(TFA þ FEW) electrode this process could be expressed as Fig. 13. 4. Conclusion In summary, ferrocene grafted hydroxy terminated polybutadiene (Butacene) was prepared with 19.8% ferrocenyl unit. For this purpose, 4-chlorobutylferrocene was converted to 4-(dimethylsilyl)butylferro cene via Grignard reaction and obtained silylferrocene derivative was attached to polymeric backbone using hydrosilylation reaction. The obtained polymer structure was evaluated using FT-IR, 1H NMR, and UV–Vis spectroscopy. Synthesized polymer was drop-coating on the surface of GCE, terephthaldehyde (TFA) and fresh egg white (FEW) were used as a cross-linking agent. The electrochemical performances of modified electrode was evaluated using cyclic voltammetry, electro chemical impedance spectroscopy (EIS), and differential pulse 8
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[14] [15]
[16]
[17] [18]
[19]
[20]
[21] [22]
[23] [24] [25] [26]
Polymer 192 (2020) 122310 [27] K. Rahimpour, R. Teimuri-Mofrad, H. Abbasi, M. Parchehbaf, S. Abedinpour, S. Soleimani, Polym. Plast. Technol. Mater. (2019), https://doi.org/10.1080/ 25740881.2019.1625383. [28] R. Teimuri-Mofrad, K.D. Safa, S. Abedinpour, K. Rahimpour, J. Iran. Chem. Soc. 20 (2013) 5873–5878, https://doi.org/10.1021/om400468p. [29] B.N. Rao, K. Malkappa, N. Kumar, T. Jana, Ferrocene grafted hydroxyl terminated polybutadiene: a binder for propellant with improved burn rate, Polymer 163 (2019) 162–170, https://doi.org/10.1016/j.polymer.2019.01.008. [30] K.D. Safa, H. Abbasi, R. Teimuri-Mofrad, Synthesis of novel ferrocenyl silyl ethers via dehydrocoupling reactions under Karstedt catalyst, J. Organomet. Chem. 740 (2013) 56–60, https://doi.org/10.1016/j.jorganchem.2013.04.027. [31] G. Doriath, Energetic insensitive propellants for solid and ducted rockets, J. Propul. Power 11 (1995) 870–882, https://doi.org/10.2514/3.23912. [32] B. Fang, W. Zhang, X. Kan, H. Tao, X. Deng, M. Li, Fabrication and application of a novel modified electrode based on β-cyclodextrin/ferrocenecarboxylic acid inclusion complex, Sensor. Actuator. B Chem. 117 (2006) 230–235, https://doi. org/10.1016/j.snb.2005.11.027. [33] A.S. Kumar, P. Swetha, K.C. Pillai, Enzyme-less and selective electrochemical sensing of catechol and dopamine using ferrocene bound Nafion membrane modified electrode, Anal. Methods 2 (2010) 1962–1968, https://doi.org/10.1039/ c0ay00430h. [34] N.G. Tsierkezos, U. Ritter, Oxidation of dopamine on multi-walled carbon nanotubes, J. Solid State Electrochem. 6 (2012) 2217–2226, https://doi.org/ 10.1007/s10008-012-1647-1. [35] S. Jiao, M. Li, C. Wang, D. Chen, B. Fang, Fabrication of Fc-SWNTs modified glassy carbon electrode for selective and sensitive determination of dopamine in the presence of AA and UA, Electrochim. Acta 52 (19) (2007) 5939–5944, https://doi. org/10.1016/j.electacta.2007.03.039. _ As¸ık, S. Yavuz, A. Kariper, Z. Üstünda� [36] A. Erkal, I. g, Biosensor application of carbonaceous nanocoil material: preparation, characterization, and determination of dopamine and uric acid in the presence of ascorbic acid, J. Electrochem. Soc. 163 (5) (2016) H269–H277, 0013-4651/2016/163(5)/H269/9/. [37] L. Yang, N. Huang, Q. Lu, M. Liu, H. Li, Y. Zhang, S. Yao, A quadruplet electrochemical platform for ultrasensitive and simultaneous detection of ascorbic acid, dopamine, uric acid and acetaminophen based on a ferrocene derivative functional Au NPs/carbon dots nanocomposite and graphene, Anal. Chim. Acta 903 (2016) 69–80, https://doi.org/10.1016/j.aca.2015.11.021. [38] N.F. Atta, A. Galal, S.M. Ali, S.H. Hassan, Electrochemistry and detection of dopamine at a poly (3, 4-ethylenedioxythiophene) electrode modified with ferrocene and cobaltocene, Ionics 21 (8) (2015) 2371–2382, https://doi.org/ 10.1007/s11581-015-1417-z. [39] Q. Zhu, J. Bao, D. Huo, M. Yang, H. Wu, C. Hou, Y. Zhao, X. Luo, H. Fa, 3DGH-Fc based electrochemical sensor for the simultaneous determination of ascorbic acid, dopamine and uric acid, J. Electroanal. Chem. 799 (2017) 459–467, https://doi. org/10.1016/j.jelechem.2017.07.004. [40] C.R. Raj, T. Ohsaka, Electroanalysis of ascorbate and dopamine at a gold electrode modified with a positively charged self-assembled monolayer, J. Electroanal. Chem. 496 (2001) 44, https://doi.org/10.1016/S0022-0728(00)00335-1.
dopamine and hydrogen peroxide, J. Electroanal. Chem. 802 (2017) 78–88, https://doi.org/10.1016/j.jelechem.2017.08.016. P.C. Pandey, D.S. Chauhan, V. Singh, Effect of processable polyindole and nanostructured domain on the selective sensing of dopamine, Mater. Sci. Eng. C 1 (2012) 1–11, https://doi.org/10.1016/j.msec.2011.08.020. H. Cheng, H. Qiu, Z. Zhu, M. Li, Z. Shi, Investigation of the electrochemical behavior of dopamine at electrodes modified with ferrocene-filled double-walled carbon nanotubes, Electrochim. Acta 63 (2012) 83–88, https://doi.org/10.1016/j. electacta.2011.12.083. M. Sajid, M.K. Nazal, M. Mansha, A. Alsharaa, S.M.S. Jillani, C. Basheer, Chemically modified electrodes for electrochemical detection of dopamine in the presence of uric acid and ascorbic acid, Trends Anal. Chem. 76 (2016) 15–29, https://doi.org/10.1016/j.trac.2015.09.006. M. Sajid, N. Baig, Chemically modified electrodes for electrochemical detection of dopamine: challenges and opportunities, Trends Anal. Chem. 118 (2019) 368–385, https://doi.org/10.1016/j.trac.2019.05.042. L. Xiao, L. Jia, S. Zhao, X. Tang, C. Zhu, H. Huang, J. Jiang, M. Li, Solvent-free synthesis of sheet-like carbon coated MnO with three-dimensional porous structure for simultaneous detection of dopamine and uric acid, J. Electroanal. Chem. (2020) 113823, https://doi.org/10.1016/j.jelechem.2020.113823. A. Thamilselvan, P. Manivel, V. Rajagopal, N. Nesakumar, V. Suryanarayanan, Improved electrocatalytic activity of Au@ Fe3O4 magnetic nanoparticles for sensitive dopamine detection, Colloids Surf., B 180 (2019) 1–8, https://doi.org/ 10.1016/j.colsurfb.2019.04.034. X. Zhang, Y.C. Zhang, L.X. Ma, One-pot facile fabrication of graphene-zinc oxide composite and its enhanced sensitivity for simultaneous electrochemical detection of ascorbic acid, dopamine and uric acid, Sensor. Actuator. B Chem. 227 (2016) 488–496, https://doi.org/10.1016/j.snb.2015.12.073. T. Daeneke, T.H. Kwon, A.B. Holmes, N.W. Duffy, U. Bach, L. Spiccia, Highefficiency dye-sensitized solar cells with ferrocene-based electrolytes, Nat. Chem. 3 (2011) 211, https://doi.org/10.1038/nchem.966. R. Sun, L. Wang, H. Yu, Z.U. Abdin, Y. Chen, J. Huang, R. Tong, Molecular recognition and sensing based on ferrocene derivatives and ferrocene-based polymers, Organometallics 18 (2014) 4560–4573, https://doi.org/10.1021/ om5000453. M. Tropiano, N.L. Kilah, M. Morten, H. Rahman, J.J. Davis, P.D. Beer, S. Faulkner, Reversible luminescence switching of a redox-active ferrocene–europium dyad, J. Am. Chem. Soc. 31 (2011) 11847–11849, https://doi.org/10.1021/ja203069s. J. Elbert, M. Gallei, C. Rüttiger, A. Brunsen, H. Didzoleit, B. Stühn, M. Rehahn, Ferrocene polymers for switchable surface wettability, Organometallics 32 (20) (2013) 5873. J.M. Chen, Z.J. Lu, G.Q. Pan, Y.X. Qi, J.J. Yi, H.J. Bai, Synthesis of hydroxylterminated polybutadiene possessing high content of 1, 4-units via anionic polymerization, Chin. J. Polym. Sci. 28 (5) (2010) 715–720. R.M. Sankar, T.K. Roy, T. Jana, Functionalization of terminal carbon atoms of hydroxyl terminated polybutadiene by polyazido nitrogen rich molecules, Bull. Mater. Sci. 34 (4) (2011) 745.
9
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Electrocatalytic oxidation of dopamine on the surface of ferrocene grafted hydroxyl terminated polybutadiene modified electrode Keshvar Rahimpour , Reza Teimuri-Mofrad * Department of Organic and Biochemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Iran
A R T I C L E I N F O
A B S T R A C T
Keywords: Hydroxyl terminated polybutadiene Dopamine Electrocatalyst
In this study, 4-(dimethylsilyl)butylferrocene was prepared using 4-chlorobutylferrocene via Grignard reaction in dry THF and the reaction of prepared reagent with chlorodimethylsilane. In continue, obtained ferrocenylsilane derivative was grafted to hydroxyl terminated polybutadiene (HTPB) via hydrosilylation reaction. Ferrocenyl units in polymer backbone gave a couple of reversible peaks of cyclic voltammetry (CV). Additionally, FT-IR, 1H NMR, UV–Vis spectroscopy along with molecular weight and TGA analysis confirmed the polymer modification. The modified polymer was coated onto the surface of glassy carbon electrode (GCE); meanwhile, fresh egg white (FEW) and terephthaldehyde (TFA) were used as cross-linking agents. The successful immobilization of polymer was demonstrated using Electrochemical impedance spectroscopy (EIS). The modified electrode showed an electrocatalytic effect on the oxidation of DA, the Fc/Fcþ couple mediate the oxidation of DA on the surface of GC/Butacene/(TFA þ FEW) electrode. The optimum pH ¼ 7 was obtained for this response. The electrode protected 86% of its initial electrocatalytic after 500 cycles and 90% of its initial current after 30 day storage at 4 � C. The results indicated that GC/Butacene/(TFA þ FEW) electrode possessed satisfactory linear ranges and detection limits for detection of DA.
1. Introduction Dopamine (DA) is a neurotransmitter which plays a key role in the life science [1]. Different methods have been used for DA detection, including Surface-Enhanced Raman Scattering (SERS) [2], fluorescence [3], UV–vis spectrophotometry [4], derivatization [5], colorimetric biosensors [6], and electrochemical sensors [7]. Nowadays, surface modification of common electrodes such as glass carbon (GC), and platinum electrode using physical or chemical methods is a successful strategy for overcoming of analyte detection problems [8]. The low sensitivity, high detection limit, narrow linear range, and longtime response along with the interface effect of other analytes are the most known problems in electrochemical measurements [9–11]. In the last decades, the electrochemical sensors based on modified electrodes were prepared via covalently or physically incor porating of different organic, biomolecules and organometallic com pounds. Using this method, new electrochemical properties can be created in routine electrodes such as glassy carbon or platinum electrode [12–15]. Some of the recent development of advanced electrode mate rials for dopamine detection were summarized in Table 1.
Ferrocene and its derivatives widely used as electrochemical active species. High thermal stability, high redox activity and chemical versatility of these compounds, give the ferrocene a special reputation among other metallocenes. Ferrocene can be easily oxidized and reduced, which is known as redox behavior of Fc/Fcþ couple. Ferrocene is a neutral charge molecule without any functional group and it cannot be adsorbed on the surface of electrode; hence, it is approximately impossible chemically immobilization of ferrocene on the electrode surface. For this reason, in most researches, ferrocenyl compounds were attached to a nanoparticle or polymeric backbones [21–24]. We used hydroxyl terminated polybutadiene (HTPB) as a polymeric framework. HTPB is a liquid rubber containing hydroxyl groups in ter minal carbons of the polymer backbone and many vinyl groups in the chain, which made by traditional radical polymerization of 1,3-buta diene. Nowadays, the living radical polymerization was extensively developed for HTPB preparation [25]. Recently, HTPB was been suc cessfully used for the fabrication of elastic conducting polymer micro-particles with core-shell structure [26]. The ferrocene grafted HTPB was known as Butacene. For the first time, Soci�et�e Nationale de Poudres et Explosifs (SNPE, France) inset Butacene as a new burning rate
* Corresponding author. E-mail address: [email protected] (R. Teimuri-Mofrad). https://doi.org/10.1016/j.polymer.2020.122310 Received 28 November 2019; Received in revised form 31 January 2020; Accepted 19 February 2020 Available online 24 February 2020 0032-3861/© 2020 Published by Elsevier Ltd.
Electrode structure
Table 1 Some of recent development of advanced electrode materials for dopamine detection.
[7]
[20]
[19]
[17]
Ref [18]
Electrode structure
[16]
Ref
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2
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accelerator catalyst. Butacene can be prepared with a various iron per centage, which calculates according to the amount of grafted ferrocene to the backbone of HTPB [27,28]. Additionally, other ferrocenyl de rivatives e.g. ferrocene carboxaldehyde and iodoferrocene were used for terminal functionalization of HTPB, obtained compounds were used as a binder with improved burn rate [29]. Based on our best knowledge, there is no report on using this ferrocenyl grafted polymer in the modification of electrodes. In this study, Butacene with 19.8% by weight of ferrocenyl unit was prepared via hydrosilylation reaction of 4-(dimethylsilyl)butylferrocene with HTPB. Characteristic data including the molecular weight distri bution, FT-IR, 1HNMR, UV–Vis spectroscopy along with electrochemical properties and thermal stability of synthesized polymer were studied. The synthesized polymer was coated on the surface of the GC electrode; the observations show ferrocenyl based polymer increase the oxidation of dopamine in biological media. The catalytic peak current was enhanced in pH ¼ 7. 2. Experimental 2.1. Materials
Scheme 1. Synthesis of ferrocene grafted HTPB with 19.8% ferrocenyl unit. i) Grignard reagent [Mg/THF/(CH3)2HSiCl], ii) Hydrosilylation reaction [H2PtCl6/Hexane].
Commercial grade of compounds [Ferrocene, HTPB, chlor odimethylsilane, H2PtCl6, iodide, magnesium, terephthaldehyde (TFA), LiClO4, potassium dihydrogen phosphate] were used as required chemicals.
ethyl acetate was use as eluent to obtain a brown viscose oil. FT-IR (KBr, cm 1): 3077 (C–H, Aromatic), 2920, 2847 (C–H, Aliphatic), 1641, 1443 – C), 1072 (C–Si), 488 (Fe-Cp); 1HNMR (δ in ppm): 5.60–4.94 (m, (C– – CH, C– – CH2, HTPB), 4.10–4.05 (m, Cp), 2.36–2.32 (t, CpCH2), C– 2.09–2.05 (m, CH2, HTPB), 1.56–1.33 (m, -CH2), 0.63–0.60 (m, CH2–Si), 0.07–0.01 (m, Si(CH3)2). Iron content 6%.
2.2. Equipment The Bruker-Tensor 270 spectrometer was used for recording FT-IR spectra as wave numbers νe (cm 1). The Bruker FT-400 spectrometer was used for recording NMR spectra. The 70 eV by Agilent (5975C VL) instrument, applied for mass spectra operating. The Analytikjene (novaa 400) atomic absorption spectrophotometer was used for iron analysis, and SPECORD 250 analytikjena UV/vis spectrophotometer was used for recording of UV/vis spectra. Brookfield RVT viscometer was used for measurement of viscosity. The viscosity, measured in a Brook field RVT viscometer. The FESEM (MIRA3 TESCAN), was used for analysis of surface morphology.
2.5. Thermal stability studies Thermogravimetric analysis (TGA) was performed between 25 and 700 � C on a TGA PYRIS 1 and Triton Tritec 2000 DMN instruments under N2 at heating rate of 10 � C/min to study of thermal decomposition of modified polymer. 2.6. Preparation of modified electrode
2.3. Synthesis of 4-(dimethylsilyl)butylferrocene
The electrode preparation procedure includes two steps: pretreat ment of the GC electrode, and immobilization of Butacene on the elec trode surface (1) the glassy carbon electrode (GCE), was sequentially polished with alumina powder, and sonicated in 2.0 M sulfuric acid and double-distilled water, respectively. The GC electrode was subjected to cyclic scanning in 0.2 M H2SO4 solution in the potential range from 1 V to 1 V (vs Ag/AgCl) until well-defined cyclic voltammogram was ob tained. Then electrode cleaned with distilled water and dried in air. (2) Butacene/(TFA þ FEW) complex was prepared by dissolving 5 mg Butacene in CH2Cl2 and adding 2 ml of 10% solution of TFA and fresh egg white (FEW) solutions in dichloromethane. 5 μl of obtained blend was coated on the GCE surface and air-dried to obtain the GC/Butacene/ (TFA þ FEW) electrode.
0.072 g (3 mmol) of Magnesium turnings and catalytic amount of iodine crystal were dispersed in 1 ml dry THF under argon atmosphere. 0.83 g (3 mmol) of 4-chlorobutylferrocene [30] was dissolved in 8 ml dry THF and slowly added to the above suspension. The obtained mixture was stirred at reflux temperature until all the magnesium turnings were dissolved. After 24 h, cooling the mixture and THF diluted chlorodimethylsilane (0.28 g, 3 mmol) slowly added to the reaction flask via dropping funnel. The reaction mixture was refluxed under argon gas for 3 h and then cooled to room temperature. After solvent evaporation dark orange oil with 86% yield was obtained with column chromatog raphy, hexane was used as eluent. FT-IR (KBr, cm 1): 3091 (C–H, Aro – C), matic), 2928, 2861 (C–H, Aliphatic), 2110 (Si–H), 1637, 1454 (C– 1050 (C–Si), 490 (Fe-Cp); 1HNMR (δ in ppm): 4.10–4.05 (m, 9H, Cp and 1H, Si–H), 2.35–2.31 (t, 2H, CH2-Cp), 1.58–1.38 (m, 4H, -CH2), 0.65–0.61 (m, 2H, CH2–Si), 0.08 (s, 6H, Si(CH3)2). MS (70 eV): m/z ¼ 300 [M]þ.
2.7. Electrochemical measurements Potentiostat/galvanostat Autolab (PGASTAT 30) were used for electrochemical experiments using a three-electrode cell configuration: Ag/AgCl, GC, and platinum wire as the reference, working and counter electrodes, respectively. CV voltammograms were collected in the 0–0.8 V potential range with respect to the Ag/AgCl. Electrochemical imped ance spectroscopy (EIS) experiments was recorded in 5.0 mM Potassium ferricyanide/Potassium ferrocyanide. An AC voltage was applied with 5 mV amplitude in 0.01 Hz up to 100 kHz frequency range.
2.4. Synthesis of ferrocene grafted HTPB A mixture of 4-(dimethylsilyl)butylferrocene and 0.2 g of HTPB was stirred in 15 ml dry hexane as solvent. 30 μL of hexachloroplatinic acid used as catalyst. After 24 h reflux at 60 � C, the reaction mixture was filtered. After the evaporation of solvent, ferrocene grafted HTPB was obtained using column chromatography. Gradient ratio of hexane and 3
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Fig. 1. FT-IR spectra of HTPB, 4-(dimethylsilyl)butylferrocene (FcSiH) and Butacene. Fig. 3. UV–Vis spectra of HTPB and Butacene. Table 2 Molecular weight distribution parameters and viscosity of HTPB and Butacene. Sample Name
HTPB
Butacene 19.8%
MW Mn Polydispersity Viscosity (Pa.s)
12368 8187 1.511 3.40
15148 10657 1.421 4.35
4-chlorobutylferrocene doesn’t have suitable functional group for grafting to the HTPB polymer framework, therefore Grignard reaction was used for conversion of the chlorine to dimethylhydrosilyl group. The Grignard reagent was prepared in situ by adding 4-chlorobutylferrocene to magnesium turnings in dry THF. Obtained mixture was reacted with chlorodimethylsilane and result in preparation of 4-(dimethylsilyl) butylferrocene with 90% yield. Finally, hydrosilylation reaction was carried out between ferrocenylsilane and HTPB; the hexachloroplatinic acid (H2PtCl6) and hexane were used as catalyst and solvent, respectively. The FT-IR spectroscopy of HTPB, ferrocenylsilane and final polymer was illustrated in Fig. 1. The disappearance of Si–H stretching vibration in 2110 cm 1 and revelation of Fe-Cp stretching vibration in 488 cm 1 is a clear evidence for grafting of ferrocene in the polymer backbone. These observations are in full agreement with the 1H NMR results (Fig. 2). The chemical shifts of 4.08, 2.34, 1.2 and 0.3 ppm in the final polymer spectrum are related to cyclopentadienyl rings (Cp), CH2 in the vicinity of Cp, CH2 of chain, CH2 and CH3 in the vicinity of silicon atom, respectively. After grafting of ferrocene to polymer skeleton, obtained Butacene shows π-π* transition in 324 nm and MLCT (Metal to Ligand) transition in 441 nm in UV–Vis spectra (Fig. 3). The HTPB is a colorless and clear oily liquid. Increasing of viscosity and change in the final polymer color to dark orange are the most obvious reasons for grafting of ferrocenyl derivative on polymer backbone and achievement to final product. Increasing in number average molecular weight (Mn) and weight average molecular weight (Mw) of Butacene 19.8% compared with HTPB indicates the polymer functionalization (Table 2). Polydispersity is defined as Mw/Mn and it was decreased with grafting of ferrocene to HTPB. On the other hand, increasing in the viscosity of final polymer in comparison with pristine HTPB confirmed the attaching of ferrocenyl moieties to polymer backbone. The TGA and dTGA (first derivative curve) thermograms of HTPB, and Butacene, are illustrated in Fig. 4. For HTPB a two-stage weight loss process is visible. The minor weight loss was occurred until 340 � C, can be related to the removal of sample water, the major thermal decom position of HTPB was assigned with weight loss process in the range of 405–495 � C. For Butacene, the TGA results illustrated different thermal degradation profile containing three-stage weight loss process. The
Fig. 2. 1H NMR spectra of HTPB, 4-(dimethylsilyl)butylferrocene (FcSiH) and Butacene.
3. Result and discussion 3.1. Synthesis and characterization of butacene 19.8% (percent by weight of ferrocenyl unit) Over the past years (from 1995) [31], Butacene was prepared with different percentages of iron for using as burning rate catalyst. To the extent of our knowledge, this is the first work that reports electro chemical application of ferrocenyl grafted HTPB. In this work, Butacene with 19.8% grafted ferrocenyl unit was synthesized via hydrosilylation reaction of HTPB with 4-(dimethylsilyl)butylferrocene as a well-known procedure for Butacene preparation (Scheme 1). In summary, 4
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Fig. 4. TGA and dTGA thermograms of HTPB and Butacene 19.8%.
Fig. 5. SEM images of (A)bare glassy carbon electrode, (B) GC/Butacene and (C) GC/Butacene/(TFA þ FEW) electrode.
maximum rate of weight loss at roughly 481 � C ( 77.18% weight loss). By heating the sample up to 700 � C, 6% of the sample total weigh was remained, which is corresponds to Fe residual. In the case of HTPB, sample weight was reached zero at this temperature. 3.2. Electrochemical evaluation of butacene 19.8% Modified GC electrode was fabricated by diluted Butacene in CH2Cl2, for immobilization of Butacene on the GC surface, terephthaldehyde (TFA) and fresh egg white (FEW) were used as a cross-linking agent. Bovine serum albumin (BSA) is a known protein which used in electrode preparation, FEW is also a kind of protein and can be used for this purpose. The result showed that the immobilization with FEW was effective, feasible, more convenient, and inexpensive. The use of this FEW as cross-linking agent has been few reported in literatures [32] so it is relatively new method. 5 mg of Butacene was dissolved in CH2Cl2 and 2 ml of 10% solution of TFA and FEW solutions in dichloromethane was added to the prepared butacene solution under stirring. 5 μl of obtained blend was coated on the GCE surface and air-dried to obtain the GC/Butacene/(TFA þ FEW) electrode. Field Emission Scanning Electron Microscopy (FE-SEM) was employed to characterize the top views of the bare electrode, GC/ Butacene and (C) GC/Butacene/(TFA þ FEW) electrode (Fig. 5). Fig. 5A shows uniform structure of the bare working GC electrode. The pure Butacene film shows a loose and fibrillary structure distributed on to the surface of the GC electrode (Fig. 5B). Fig. 5C shows SEM image of GC/ Butacene/(TFA þ FEW) film reveal the uniform, homogenous dispersion of Butacene/(TFA þ FEW) on the electrode’s surface. The SEM image of modified electrode indicates that modifiers were successfully immobi lized on the glassy carbon electrode’s surface.
Fig. 6. EIS spectra recorded for Bare GC and GC/Butacene/(TFA þ FEW). Inset: A zoom of the impedance results in high and intermediate frequency range.
Electrochemical impedance spectroscopy (EIS) for bare GC and GC/ Butacene/(TFA þ FEW) electrode were measured in 5 mM Potassium ferricyanide/Potassium ferrocyanide solution (Fig. 6). EIS was used for studying the interface properties of surface-modified electrode. Both GC and GC/Butacene/(TFA þ FEW) electrodes showed a semicircle at high frequencies related to faradaic electron-transfer along with a linear line at low frequencies related to diffusional processes [33]. The diameter of semicircle in GC/Butacene/(TFA þ FEW) electrode was relatively larger than bare GC electrode (Inset diagram), which indicated the successful immobilization of Butacene on the electrode surface. It is known that, the diameter of semicircle appearing in the Nyquist plot equals with the charge transfer resistance, Rct, of the electrode [34]. When the 5
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Fig. 7. Cyclic voltammetry of a) GC in 1 mM Butacene and GC/Butacene/(TFA þ FEW) in CH3CN, 1 mM LiClO4, b) Bare GC electrode and GC/Butacene/(TFA þ FEW) in PBS solution, 1 mM NaCl as electrolyte.
Fig. 8. Cyclic voltammetry of GC/Butacene/(TFA þ FEW) electrode a) in different scan rates, b) stability of peak shape after 500 cycles, c) linear relationship between the peak current and the square root of scan rates.
Butacene/(TFA þ FEW) was immobilized on GC electrode the EIS showed a large resistance due to decrease in conductivity of electrode surface. Redox-active polymers are very attractive for scientists because they have outstanding advantages such as applicability in the field of sensors, supercapacitors and etc. HTPB is not electrochemically active, the incorporation of the ferrocenyl groups make it electroactive. The elec troactivity of Butacene was demonstrated by recording of cyclic vol tammetry (CV) measurements in CH3CN solution using LiClO4 as a supporting electrolyte (Fig. 7a, red line). The redox peak at 0.39 V is related to oxidation and reduction of Fc/Fcþ couple. Furthermore, the
CV curve GC/Butacene/(TFA þ FEW) electrode in acetonitrile solution was shown in Fig. 7a, green line. The CV curves of bare GC and GC/ Butacene/(TFA þ FEW) electrodes in phosphate buffer solution (PBS) were illustrated in Fig. 7b. The effect of different scan rates on the CV curves of GC/Butacene/ (TFA þ FEW) electrode was shown in Fig. 8a, the peak current was increased with increasing of scan rate listed in order 250 > 200>150 > 100>50 > 25 mVS 1. The modified electrode displays the 86% cycling stability after recording 500 CVs in 50 mVS 1 (Fig. 8b). The storage stability of the modified electrode was also evaluated by measuring the decrease in the redox peak current during repetitive CV measurements 6
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Fig. 9. a) Cyclic voltammetry and b) DPV voltamogram of GC/Butacene/(TFA þ FEW) electrode in presence of Dopamine. Scan rate: 50 mVS 1.
Fig. 10. Effects of solution pH on the peak current of 1 mM DA in PBS. Scan rate: 50 mVs
1
.
Fig. 11. a) Cyclic voltammograms of dopamine changed with its concentration. Buffer: 0.1 M PBS, pH 7.0. b) The relationship between peak current and con centration of dopamine.
for every week over 1 month, the modified electrode was kept in the refrigerator (4 � C). The GC/Butacene/(TFA þ FEW) electrode protected 90% of its initial current, indicating good stability of electrochemical
response for modified electrode. As can be seen in Fig. 8c, the plot of peak current versus ν1/2 (ν ¼ scan rate) was linear, means that redox processes were diffusion controlled. In continue, the usability of prepared ferrocenyl electrode as medi ator for electrocatalytic oxidation of dopamine (DA) was examined. The electrocatalytic behavior of the GC/Butacene/(TFA þ FEW) electrode in oxidation of DA was studied using CV and differential pulse voltam metry (DPV) methods. Fig. 9 showed the voltammetric response of the GC/Butacene/(TFA þ FEW) electrode in 100 mM PBS spiked with DA (1 mM). In the presence of DA, the anodic peak current (ipa) of GC/Buta cene/(TFA þ FEW) electrode in CV voltammogram was increased as well as increasing in DVP profile. Effect of solution pH on the oxidation peak current (ipa) of DPV voltamogram as electrochemical response of DA on the GC/Butacene/ (TFA þ FEW) electrode was investigated by DPV method in 0.1 M PBS at various pH values ranging from 4.0 to 8.0. According to Fig. 10, the oxidation peak current of DA on the modified electrode surface has the
Table 3 Summary of the linear range and limit of detection for dopamine using different ferrocene-based electrodes. Electrode
Linear response range (μM)
LOD (μM)
Ref
Fc-SWNT/GCE GC/CTP-GNR1(nanocoil) Fc-S-Au/CNC/graphene/ GCE PEDOT/FC1/PEDOT … SDS 3DGH-Fc/GCE GC/Butacene/(TFA þ FEW)
5.0–30 2–20 0.2–2.5
0.050 0.003 0.050
[35] [36] [37]
6–300
0.069
[38]
10–180 5–150
0.042 0.045
[39] This work
7
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voltammetry (DPV). The GC/Butacene/(TFA þ FEW) electrode dis played good sensitivity, stability, repeatability, and reproducibility. In details, sensitivity of GC electrode is enhanced when butacene redox mediators was coated on the surface of electrode. The oxidation of DA enhanced on the surface of GC/Butacene/(TFA þ FEW) electrode, Fc/ Fcþ couple mediated the oxidation of DA in pH ¼ 7. Additionally, the interference study show that AA had nearly no interference for the determination of DA. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. CRediT authorship contribution statement
Fig. 12. Interference study. DPVs response of GC/Butacene/(TFA þ FEW) electrode for DA in the presence of AA.
Keshvar Rahimpour: Investigation, Software, Writing - original draft. Reza Teimuri-Mofrad: Funding acquisition, Project administra tion, Supervision, Writing - review & editing. Acknowledgements This work was supported with the Iran National Science Foundation (INSF).
Fig. 13. Electro-oxidation of DA on the surface of GC/Butacene/(TFA þ FEW) electrode.
References [1] L. Tang, S. Li, F. Han, L. Liu, L. Xu, W. Ma, H. Kuang, A. Li, L. Wang, C. Xu, SERSactive Au@ Ag nanorod dimers for ultrasensitive dopamine detection, Biosens. Bioelectron. 71 (2015) 7–12, https://doi.org/10.1016/j.bios.2015.04.013. [2] X. Yu, X. He, T. Yang, L. Zhao, Q. Chen, S. Zhang, J. Chen, J. Xu, Sensitive determination of dopamine levels via surface-enhanced Raman scattering of Ag nanoparticle dimers, Int. J. Nanomed. 13 (2018) 2337, https://doi.org/10.2147/ IJN.S156932. [3] J. Wang, J. Dai, Y. Xu, X. Dai, Y. Zhang, W. Shi, B. Sellergren, G. Pan, Molecularly imprinted fluorescent test strip for direct, rapid, and visual dopamine detection in tiny amount of biofluid, Small 15 (1) (2019) 1803913, https://doi.org/10.1002/ smll.201803913. [4] X. Hun, S. Wang, S. Wang, J. Zhao, X. Luo, A photoelectrochemical sensor for ultrasensitive dopamine detection based on single-layer NanoMoS2 modified gold electrode, Sensor. Actuator. B Chem. 249 (2017) 83–89, https://doi.org/10.1016/ j.snb.2017.04.065. [5] M. Lan, S. Zhao, X. Wei, K. Zhang, Z. Zhang, S. Wu, P.W. Wang, Zhang, Pyrenederivatized highly fluorescent carbon dots for the sensitive and selective determination of ferric ions and dopamine, Dyes Pigments 170 (2019) 107574, https://doi.org/10.1016/j.dyepig.2019.107574. [6] A.P. Vs, P. Joseph, K.D. SCG, S. Lakshmanan, T. Kinoshita, S. Muthusamy, Colorimetric sensors for rapid detection of various analytes, Mater. Sci. Eng. C 78 (2017) 1231–1245, https://doi.org/10.1016/j.msec.2017.05.018. [7] Q. Yuan, Y. Liu, C. Ye, H. Sun, D. Dai, Q. Wei, G. Lai, T. Wu, A. Yu, L. Fu, K. W. Chee, Highly stable and regenerative graphene–diamond hybrid electrochemical biosensor for fouling target dopamine detection, Biosens. Bioelectron. 111 (2018) 117–123, https://doi.org/10.1016/j.bios.2018.04.006. [8] S. Sharma, N. Singh, V. Tomar, R. Chandra, A review on electrochemical detection of serotonin based on surface modified electrodes, Biosens. Bioelectron. 107 (2018) 76–93, https://doi.org/10.1016/j.bios.2018.02.013. [9] L. Liu, J. Du, S. Li, B. Yuan, H. Han, M. Jing, N. Xia, Amplified voltammetric detection of dopamine using ferrocene-capped gold nanoparticle/streptavidin conjugates, Biosens. Bioelectron. 41 (2013) 730–735, https://doi.org/10.1016/j. bios.2012.09.061. [10] C. Villena, M. Bravo, B. Alonso, C.M. Casado, J. Losada, M.P. Armada, Sizecontrolled gold nanoparticles obtained from electrodeposited amidoferrocenylpoly (propyleneimine) dendrimer-templates for the electrochemical sensing of dopamine, Appl. Surf. Sci. 420 (2017) 651–660, https://doi.org/10.1016/j. apsusc.2017.05.098. [11] M. Liu, L. Wang, J. Deng, Q. Chen, Y. Li, Y. Zhang, H. Li, S. Yao, Highly sensitive and selective dopamine biosensor based on a phenylethynyl ferrocene/graphene nanocomposite modified electrode, Analyst 19 (2012) 4577–4583, https://doi.org/ 10.1039/C2AN35708A. [12] H. Miyaji, H. Komada, K. Goto, J. Fujimoto, N. Kiriyama, J.H. Tucker, Selective recognition and electrochemical sensing of dopamine using a ferrocene-based heteroditopic receptor, Tetrahedron Lett. 43 (2018) 3853–3857, https://doi.org/ 10.1016/j.tetlet.2018.09.026. [13] M. Devendiran, K.K. Kumar, S.S. Narayanan, Fabrication of a novel Ferrocene/ Thionin biomediator modified electrode for the electrochemical determination of
maximum value in pH ¼ 7. The dependence of the oxidation peak currents on the concentrations of DA is presented in Fig. 11a. The oxidation peak current increases linearly with the concentrations of DA ranging from 5 to 150 μM. The calibrate curve for dopamine analyze was shown in Fig. 11b, the linear regression equation is expressed as: Ipa (μA) ¼ 1.38 þ 0.17[DA] (μM) with correlation coefficient of 0.99. The detection limit (3σ/m), where σ is the standard deviation of blank and m is the slope of the calibration plot, was 0.045 μmol L 1. These data were comparable to the values obtained by other research groups (Table 3). For further investigations, the prepared GC/Butacene/(TFA þ FEW) electrode was used to study of interference of AA. The AA can be oxidized at a potential close to that of DA, it is normally difficult to obtain separated voltammetric waves for AA and DA. Fig. 12 show the DPV of DA and AA in a mixture. As can be seen two peaks are separated with potential separation of about 0.19 V, the potentials are 0.39 and 0.20 V for DA and AA, respectively. The potential separation is large enough to allow the determination of DA in the presence of AA. The results showed that prepared GC/Butacene/(TFA þ FEW) elec trode can be catalyzed the electro-oxidation of DA. In the literatures, oxidation of DA was described as a two-proton and two-electron change process [40]. For as-prepared GC/Butacene/(TFA þ FEW) electrode this process could be expressed as Fig. 13. 4. Conclusion In summary, ferrocene grafted hydroxy terminated polybutadiene (Butacene) was prepared with 19.8% ferrocenyl unit. For this purpose, 4-chlorobutylferrocene was converted to 4-(dimethylsilyl)butylferro cene via Grignard reaction and obtained silylferrocene derivative was attached to polymeric backbone using hydrosilylation reaction. The obtained polymer structure was evaluated using FT-IR, 1H NMR, and UV–Vis spectroscopy. Synthesized polymer was drop-coating on the surface of GCE, terephthaldehyde (TFA) and fresh egg white (FEW) were used as a cross-linking agent. The electrochemical performances of modified electrode was evaluated using cyclic voltammetry, electro chemical impedance spectroscopy (EIS), and differential pulse 8
K. Rahimpour and R. Teimuri-Mofrad
[14] [15]
[16]
[17] [18]
[19]
[20]
[21] [22]
[23] [24] [25] [26]
Polymer 192 (2020) 122310 [27] K. Rahimpour, R. Teimuri-Mofrad, H. Abbasi, M. Parchehbaf, S. Abedinpour, S. Soleimani, Polym. Plast. Technol. Mater. (2019), https://doi.org/10.1080/ 25740881.2019.1625383. [28] R. Teimuri-Mofrad, K.D. Safa, S. Abedinpour, K. Rahimpour, J. Iran. Chem. Soc. 20 (2013) 5873–5878, https://doi.org/10.1021/om400468p. [29] B.N. Rao, K. Malkappa, N. Kumar, T. Jana, Ferrocene grafted hydroxyl terminated polybutadiene: a binder for propellant with improved burn rate, Polymer 163 (2019) 162–170, https://doi.org/10.1016/j.polymer.2019.01.008. [30] K.D. Safa, H. Abbasi, R. Teimuri-Mofrad, Synthesis of novel ferrocenyl silyl ethers via dehydrocoupling reactions under Karstedt catalyst, J. Organomet. Chem. 740 (2013) 56–60, https://doi.org/10.1016/j.jorganchem.2013.04.027. [31] G. Doriath, Energetic insensitive propellants for solid and ducted rockets, J. Propul. Power 11 (1995) 870–882, https://doi.org/10.2514/3.23912. [32] B. Fang, W. Zhang, X. Kan, H. Tao, X. Deng, M. Li, Fabrication and application of a novel modified electrode based on β-cyclodextrin/ferrocenecarboxylic acid inclusion complex, Sensor. Actuator. B Chem. 117 (2006) 230–235, https://doi. org/10.1016/j.snb.2005.11.027. [33] A.S. Kumar, P. Swetha, K.C. Pillai, Enzyme-less and selective electrochemical sensing of catechol and dopamine using ferrocene bound Nafion membrane modified electrode, Anal. Methods 2 (2010) 1962–1968, https://doi.org/10.1039/ c0ay00430h. [34] N.G. Tsierkezos, U. Ritter, Oxidation of dopamine on multi-walled carbon nanotubes, J. Solid State Electrochem. 6 (2012) 2217–2226, https://doi.org/ 10.1007/s10008-012-1647-1. [35] S. Jiao, M. Li, C. Wang, D. Chen, B. Fang, Fabrication of Fc-SWNTs modified glassy carbon electrode for selective and sensitive determination of dopamine in the presence of AA and UA, Electrochim. Acta 52 (19) (2007) 5939–5944, https://doi. org/10.1016/j.electacta.2007.03.039. _ As¸ık, S. Yavuz, A. Kariper, Z. Üstünda� [36] A. Erkal, I. g, Biosensor application of carbonaceous nanocoil material: preparation, characterization, and determination of dopamine and uric acid in the presence of ascorbic acid, J. Electrochem. Soc. 163 (5) (2016) H269–H277, 0013-4651/2016/163(5)/H269/9/. [37] L. Yang, N. Huang, Q. Lu, M. Liu, H. Li, Y. Zhang, S. Yao, A quadruplet electrochemical platform for ultrasensitive and simultaneous detection of ascorbic acid, dopamine, uric acid and acetaminophen based on a ferrocene derivative functional Au NPs/carbon dots nanocomposite and graphene, Anal. Chim. Acta 903 (2016) 69–80, https://doi.org/10.1016/j.aca.2015.11.021. [38] N.F. Atta, A. Galal, S.M. Ali, S.H. Hassan, Electrochemistry and detection of dopamine at a poly (3, 4-ethylenedioxythiophene) electrode modified with ferrocene and cobaltocene, Ionics 21 (8) (2015) 2371–2382, https://doi.org/ 10.1007/s11581-015-1417-z. [39] Q. Zhu, J. Bao, D. Huo, M. Yang, H. Wu, C. Hou, Y. Zhao, X. Luo, H. Fa, 3DGH-Fc based electrochemical sensor for the simultaneous determination of ascorbic acid, dopamine and uric acid, J. Electroanal. Chem. 799 (2017) 459–467, https://doi. org/10.1016/j.jelechem.2017.07.004. [40] C.R. Raj, T. Ohsaka, Electroanalysis of ascorbate and dopamine at a gold electrode modified with a positively charged self-assembled monolayer, J. Electroanal. Chem. 496 (2001) 44, https://doi.org/10.1016/S0022-0728(00)00335-1.
dopamine and hydrogen peroxide, J. Electroanal. Chem. 802 (2017) 78–88, https://doi.org/10.1016/j.jelechem.2017.08.016. P.C. Pandey, D.S. Chauhan, V. Singh, Effect of processable polyindole and nanostructured domain on the selective sensing of dopamine, Mater. Sci. Eng. C 1 (2012) 1–11, https://doi.org/10.1016/j.msec.2011.08.020. H. Cheng, H. Qiu, Z. Zhu, M. Li, Z. Shi, Investigation of the electrochemical behavior of dopamine at electrodes modified with ferrocene-filled double-walled carbon nanotubes, Electrochim. Acta 63 (2012) 83–88, https://doi.org/10.1016/j. electacta.2011.12.083. M. Sajid, M.K. Nazal, M. Mansha, A. Alsharaa, S.M.S. Jillani, C. Basheer, Chemically modified electrodes for electrochemical detection of dopamine in the presence of uric acid and ascorbic acid, Trends Anal. Chem. 76 (2016) 15–29, https://doi.org/10.1016/j.trac.2015.09.006. M. Sajid, N. Baig, Chemically modified electrodes for electrochemical detection of dopamine: challenges and opportunities, Trends Anal. Chem. 118 (2019) 368–385, https://doi.org/10.1016/j.trac.2019.05.042. L. Xiao, L. Jia, S. Zhao, X. Tang, C. Zhu, H. Huang, J. Jiang, M. Li, Solvent-free synthesis of sheet-like carbon coated MnO with three-dimensional porous structure for simultaneous detection of dopamine and uric acid, J. Electroanal. Chem. (2020) 113823, https://doi.org/10.1016/j.jelechem.2020.113823. A. Thamilselvan, P. Manivel, V. Rajagopal, N. Nesakumar, V. Suryanarayanan, Improved electrocatalytic activity of Au@ Fe3O4 magnetic nanoparticles for sensitive dopamine detection, Colloids Surf., B 180 (2019) 1–8, https://doi.org/ 10.1016/j.colsurfb.2019.04.034. X. Zhang, Y.C. Zhang, L.X. Ma, One-pot facile fabrication of graphene-zinc oxide composite and its enhanced sensitivity for simultaneous electrochemical detection of ascorbic acid, dopamine and uric acid, Sensor. Actuator. B Chem. 227 (2016) 488–496, https://doi.org/10.1016/j.snb.2015.12.073. T. Daeneke, T.H. Kwon, A.B. Holmes, N.W. Duffy, U. Bach, L. Spiccia, Highefficiency dye-sensitized solar cells with ferrocene-based electrolytes, Nat. Chem. 3 (2011) 211, https://doi.org/10.1038/nchem.966. R. Sun, L. Wang, H. Yu, Z.U. Abdin, Y. Chen, J. Huang, R. Tong, Molecular recognition and sensing based on ferrocene derivatives and ferrocene-based polymers, Organometallics 18 (2014) 4560–4573, https://doi.org/10.1021/ om5000453. M. Tropiano, N.L. Kilah, M. Morten, H. Rahman, J.J. Davis, P.D. Beer, S. Faulkner, Reversible luminescence switching of a redox-active ferrocene–europium dyad, J. Am. Chem. Soc. 31 (2011) 11847–11849, https://doi.org/10.1021/ja203069s. J. Elbert, M. Gallei, C. Rüttiger, A. Brunsen, H. Didzoleit, B. Stühn, M. Rehahn, Ferrocene polymers for switchable surface wettability, Organometallics 32 (20) (2013) 5873. J.M. Chen, Z.J. Lu, G.Q. Pan, Y.X. Qi, J.J. Yi, H.J. Bai, Synthesis of hydroxylterminated polybutadiene possessing high content of 1, 4-units via anionic polymerization, Chin. J. Polym. Sci. 28 (5) (2010) 715–720. R.M. Sankar, T.K. Roy, T. Jana, Functionalization of terminal carbon atoms of hydroxyl terminated polybutadiene by polyazido nitrogen rich molecules, Bull. Mater. Sci. 34 (4) (2011) 745.
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