Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954
Voltammetric Sensing of Dopamine at a Glassy Carbon Electrode Modified with Chromium (III) Schiff Base Complex1 K. Bharathi1, S. Praveen Kumar2, P. Supriya Prasab1, V. Narayanan2,a 1 – Department of Chemistry, DKM College for Women, Vellore, India 2 – Department of Inorganic Chemistry, University of Madras, Guindy Campus, Chennai, India a – vnnara@yahoo.co.in DOI 10.2412/mmse.66.65.502 provided by Seo4U.link
Keywords: dopamine, chromium (III) Schiff base complex, microwave irradiation, electrochemical polymerization, differential pulse voltammetry.
ABSTRACT. Dopamine is one of the most important neurotransmitters, which belongs the catecholamine family. It is widely distributed in brain and nervous system of mammals. It involves a crucial role in the function of central nervous, hormonal, renal and cardiovascular systems. It is also controlling brain activity, human metabolism and persistence of addiction. Due to the more functions in several organs are related with dopamine, such as brain, immune system, kidneys, and pancreas. The abnormal level of dopamine has numerous significant in health problems, it may cause Parkinson’s disease, drug addiction, psychosis and attention deficit hyperactivity disorder. Hence, it is very important to develop a selective and sensitive method for the determination of dopamine. Dopamine has good electrochemical activity, it can be determined electrochemically with better detection limit. In the present work chromium (III) Schiff base complex modified GCE was utilized for the detection of dopamine. Chromium (III) is an essential biological element and it is less toxic to human cell. The chromium (III) has better electrochemical activity and it can be an efficient electrocatalytic sensor for the dopamine detection. The chromium (III) Schiff base complex modified GCE shows the oxidation potential at 0.196 V and the peak current is 6.74 μA. The bare GCE exhibits the oxidation peak for dopamine at 0.316 V and the peak current is 5.79 μA. The chromium (III) Schiff base complex modified GCE shows better electroctalytic sensing activity for dopamine detection than bare GCE. Based on the above result the chromium (III) Schiff base complex can be used for the determination of dopamine in real samples.
Introduction. It is necessary to develop a simple, accurate, selective and sensitive analytical method for the determination of dopamine, that has great impact on clinical process. Since, dopamine (DA) is an important neurotransmitter in central nervous system of the mammals and it affects brain processes that control movement, emotional response, and the ability to experience pleasure and pain. The DA deficiency caused Parkinson’s disease, it is one of the most common diseases in the brain. A DA imbalance in the prefrontal cortex will lead to eating and sleeping disorders [1], [2]. DA is a simple organic molecule in catecholamine family and it has significant role in human metabolism. Up to date, several analytical methodologies with different principles are available for the DA quantification, such as titrimetry, spectrophotometry, chromatography, capillary electrophoresis, chemiluminescence, FTIR and Raman spectrometry, flow-injection analysis, thermo gravimetric analysis and Electrochemical methods [3]. But the electrochemical techniques was widely used for the determination of DA, due to its advantages of high sensitivity, better selectivity, faster response and low costs over other analytical methods. The DA also exhibits high electrochemical redox activity. However, at the bare electrode surface, DA exhibits sluggish electrocatalytic redox activity. Thus, to increase the detection quality considerable efforts have been develop with the aid of modified electrodes. The modified electrodes enhance the voltammetric response of bare GCE and exhibits better performance for DA detection. There are several methods have been used for the electrode modification chemical modification, spin coating method and electrochemical polymerization etc. 1
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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954
Based on the above factors in the present work we employed the electrochemically polymerization process for the bare glassy carbon electrode surface modification. The chromium (III) Schiff base complex were used for the substrate to modified the GCE surface. Electrochemical polymerization of redox-active species like symmetrical metal complexes, is an effective tool for the modification of the surface of bare glassy carbon electrode. The Schiff base metal complexes forms polymer-coated electrodes via anodic oxidation, for different types of applications in the electrochemical fields such as electrochemical catalysis and electrochemical analysis [4]. The chromium (III) Schiff base complex was synthesized by microwave irradiation method. It is one of the best synthetic method, it gives better yield and purity than other synthetic methods. It required minimum quantity of solvents, less amount of energy consumption and very short time duration. This microwave irradiation method is one of the green chemical synthetic method [5]. Chromium (III) forms stable metal complex with Schiff base ligands, +3 oxidation state is more stable due its d3 electronic configuration under physiological conditions. Chromium (III) complex is less cytotoxic than chromium (VI) complexes to human cells and it is an essential nutrient in the glucose tolerance factor (GTF) to maintain the normal level of glucose in carbohydrate and lipid metabolism. Insufficient of chromium (III) in take may cause the Type II diabetes and cardiovascular diseases. Chromium coordination polymers have great interest in biological, clinical, analytical and pharmacological fields because of its multifunction importance. Chromium (III) metal complexes are having combined photochemistry, electromagnetic property and electrochemical properties. The chromium Schiff base complex polymer are connected covalently through carbon-carbon linkage between the ligands and it has efficient energy transfer. The chromium (III) Schiff base complex has good electrochemical redox behaviour it can be an efficient electrocatakytic sensor for the determination of DA. The chromium (III) Schiff base complex modified GCE shows better linearity form 1×10-5 to 1×10-3 and good detection limit 110 nM with the sensitivity of 2.3698×10-6 μA/μM. The chromium (III) Schiff base complex modified GCE has better electrocatalytic sensing activity for the detection of DA than bare GCE it reveals from the results. From the result the chromium (III) Schiff base complex can be used for the analysis of dopamine in real samples. Experimental procedure.
Fig. 1. Synthesis of chromium (III) Schiff base complex. The Schiff base ligand was synthesied by the following procedure, 1 mM [0.1462 g] of Triethylenetetramine was added with 2 mM [0.2242 g.] of salicylaldehyde, gradually under stirred condition. An yellow colour solution was obtained and it was irradiated in the microwave oven at 320 W for 2-3 minutes. After the irradiation, the mixture was cooled to room temperature and then it was kept for 12 hr. at 100C. The obtained coloured solid product was filtered, washed with cold ethanol and dried overnight in a desiccator. The Schiff bases were recrystallized using 1:1 methanol and dichloromethane as solvent. 1:1 ratio of Schiff base ligand and chromium (III) chloride was mixed MMSE Journal. Open Access www.mmse.xyz
Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954
under stirring condition and it was employed for microwave irradiation at 320 W for 5 min, a brown colour solution was obtained and it was cooled to room temperature for 24 hrs., brown colour solid was obtained. The brown colour solid was recrystallized by 1:1 methanol and dichloromethane. The synthetic scheme was shown in Fig. 1. Result and Discussion FT-IR spectral analysis. The FT-IR spectrum of chromium (III) Schiff base complex was recorded in the range of 4000–400 cm-1 using KBr pellet. The FT-IR spectrum shows an important characteristic band at 1633 cm-1, which corresponds to the stretching vibration of imine group (C=N). A peak appeared at 610 cm-1 due to the bond formation of chromium and nitrogen [ν (Cr-N)]. The chromium and oxygen [ν (Cr-O)] bond shows a peak at 540 cm-1. This peak conforms the complex formation between Schiff base ligand and chromium (III) metal ion. A peak at 3425 cm-1 is exhibit due to the presence of O-H stretching vibrational bands, it shows that water molecules were solvated/coordinated in the metal complex. Other characteristic peaks also observed in the spectrum. The spectrum is shown in Fig. 2a. UV-Visible spectral analysis. The electronic spectrum of chromium (III) Schiff base complex was show in Fig. 2b, which is recorded in methanol solution at room temperature in the range of 200800 nm. The electronic spectrum shows an absorption at 225 nm for the π→π* transition in ligand. A peak at 286 nm explains the n→π* transition. The d-d transition of chromium (III) metal ion exhibits at 357 nm and 645 nm. The d-d transitions were observed due to 4T2g ← 4A2g (ν1) and 4T1g ← 4A2g (ν2) electron transitions in chromium (III) metal ion. It conforms the octahedral geometry of Cr (III) Schiff base complex and the magnetic momentum is 3.17 BM. Fluorescence spectral analysis. The fluorescence spectrum of chromium (III) Schiff base complex was recorded using methanol solution in ambient temperature and it was given in Fig. 2c. The chromium (III) Schiff base complex shows an emission peak at 600 nm, when it was excited at 475 nm. The emission band at 600 nm is attributed due to 4T1g → 4A2g electronic. It is both Laporte and spin forbidden in octahedral (Oh) symmetry. Electrochemical Studies. The electrochemical redox activity of the chromium (III) Schiff base complex was examined by using three electrode system. The glassy carbon electrode was working electrode, silver and silver chloride (Ag/AgCl) was reference electrode and platinum wire used as counter electrode. Voltammetry measurements was carried in the acetonitrile solution, in presence of tetrabutylammonium perchlorate (TBAP) as supporting electrolyte. The chromium (III) complex exhibits only a reduction peak at -0.85 V. It indicates that chromium (III) Schiff base complex has good electrochemical activity. The reduction behaviour of the chromium (III) metal complex attributed to electrons transfer from Cr (II) to electrode, it is one electron transfer, which can be calculated by using ip = nFQʋ/4RT [4]. Electrochemical polymerization. The glassy carbon electrode (GCE) was modified by the electrochemical polymerization of 0.1 M chromium (III) Schiff base complex in acetonitrile solution. It was shown in the Fig. 3a. The Cr (III) Schiff base complex shows a oxidation peak at -0.085 V. There is no considerable changes at the number of cycles increase for the polymerization. The polymerized Cr(III) Schiff base complex (poly-Cr-SBC) were deposited on the electrode surface. The modified surface coverage concentration was determined by using Γ=Q/nFA. The calculated modified electrode surface coverage concentration is 0.0234 × 10-11 mol cm-2. The poly-Cr-SBC/GCE was used for the sensing of dopamine (DA). The Cr complex modified GCE (poly-Cr-SBC/GCE) was dried and stored at 10 0C when it was not used.
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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954
Fig. 2. a) FT-IR spectrum, b) UV-Visible spectrum, c) Fluorescence spectrum, d) Cyclic voltammogram in 0.1 M TBAP at the scan rate of 50 mVs-1 of chromium (III) complex.
Fig. 3. a) Cyclic voltammogram of chromium (III) complex polymerization in 0.1 M TBAP, b) Cyclic voltammogram of Electrocatalytic sensing of dopamine in PBS at the scan rate of 50 mVs-1. Electrocatalytic Sensing of dopamine. The electrochemical behaviour of dopamine (DA) at GCE and poly-Cr-SBC/GCE were investigated by cyclic voltammetry (CV) in phosphate buffer as background electrolyte. Cyclic voltammograms of DA using GCE and poly-Cr-SBC/GCE as working electrodes are shown in Fig. 3b. In the voltammogram the oxidation peak of DA at pH 7 was appears at 0.317 V (vs SCE) for bare GCE and for modified electrode it exhibits at 0.194 V, which is about 123 mV more negative than that of GCE. A broad peak at bare GCE indicates that a slow electron transfer reaction was occurred for the DA oxidation. However, the modified GCE shows a sharp oxidation peak with 123 mV negative shift, it indicates that electron transfer rate was enhanced at MMSE Journal. Open Access www.mmse.xyz
Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954
modified GCE. It must be pointed out that the oxidation peak current of DA observed on modified GCE has increased than that of bare GCE. At modified GCE oxidation peak of DA is well defined sharp peak, enhanced peak current and more negative shift, it reveals that the modified GCE has better electrocatalytic active than bare GCE. The chromium (III) Schiff base complex enhanced the electrocatalytic sensing activity of dopamine. The fig. 4 explains the electrochemical reaction of DA at working electrode [6].
Fig. 4. Electrocatalytic redox mechanism of dopamine (DA). Summary. In this present work, we synthesized chromium Schiff base complex using microwave irradiation method. The synthesized complex was characterized by FT-IR, UV-Vis and Fluorescence spectral techniques. The electrochemical redox property of Cr (III) Schiff base complexes by using cyclic voltammetry. The chromium Schiff base complex was electrochemically polymerized on the GCE surface and the modified electrode was successfully used for the detection of dopamine. The modified electrode shows a better result than bare GCE. References [1] Y. L. Xie, J. Yuan, H. L. Ye, P. Song, S. Q. Hu, J. Electroanal. Chem., 749 (2015) 26–30. DOI 10.1016/j.jelechem.2015.04.035. [2] J. Chou, T. J. Ilgen, S. Gordon, A. D. Ranasinghe, E. W. McFarland, H. Metiu, S. K. Buratto, J. Electroanal. Chem., 632 (2009) 97–101. DOI 10.1016/j.jelechem.2009.04.002. [3] H. Yao, Y. Sun, X. Lin, Y. Tang, L. Huang, Electrochim. Acta, 52 (2007) 6165–6171, DOI 10.1016/j.electacta.2007.04.013. [4] S. P. Kumar, R. Suresh, K. Giribabu, R. Manigandan, S. Munusamy, S. Muthamizh, V. Narayanan, Spectrochim. Acta A, 139 (2015) 431–441. DOI 10.1016/j.saa.2014.12.012. [5]N. Fahmi, S. Shrivastava, R. Meena, S.C. Joshi, R.V. Singh, New J. Chem. 37(2013) 1445–1453. DOI 10.1039/C3NJ40907D. [6] F. Zhu, J. Yan, C. Sun, X. Zhang, B. Mao, J. Electroanal. Chem., 640 (2010) 51–55. DOI 10.1016/j.jelechem.2010.01.006.
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