Determination of Uric Acid with the Aid of N, N'-Bis (Salicylaldimine)-Benzene

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Determination of Uric Acid with the Aid of N, N'-Bis (Salicylaldimine)-Benzene1, 2-Diamine Cobalt (II) Schiff Base Complex Modified GCE1 G.B. Hemalatha1, S. Praveen Kumar1, S. Munusamy1, S. Muthamizh1, A. Padmanaban1, T. Dhanasekaran1, G. Gnanamoorthy1, V. Narayanan1,a 1 – Department of Inorganic Chemistry, University of Madras, Guindy Campus, Chennai, India a – vnnara@yahoo.co.in DOI 10.2412/mmse.72.76.83 provided by Seo4U.link

Keywords: cobalt (II) Schiff base complex, microwave irradiation, uric acid, electrochemical polymerization, differential pulse voltammetry.

ABSTRACT. Uric acid (UA) is the principal end product of purine metabolism and it is biologically important oxypurine present in body fluids such as blood or urine. The abnormal level of uric acid is associated with several disorders such as gout, Lesch–Nyhan syndrome and Hyperuricemia. The elevation of uric acid concentrations may indicate other medical conditions such as kidney injury, leukemia and pneumonia. The determination of UA is an essential topic in clinical research because it is related with several diseases. A selective and sensitive accurate method should be developed for the uric acid determination with reliable concentration. Uric acid has good electrochemical activity, which under goes irreversibly oxidized in an aqueous solution and forms allantoin as the major product. Among the various methods, which are available for the determination uric acid, electrochemical method gives fast response, high selectivity and sensitivity with low detection limits. It is one of the cost effective methods for uric acid determination in human fluids. In the present work we utilized cobalt (II) Schiff base complex as an effective electrocatalytic sensor for uric acid determination. The cobalt (II) Schiff base complex was deposited on the glassy carbon electrode by electrochemical polymerization process.

The modified GCE shows better electrocatalytic sensing activity for uric acid determination. The cobalt (II) Schiff base complex modified GCE exhibits an irreversible anodic peak at 0.48 V with peak current 7.03 μA and the bare GCE shows the uric acid oxidation potential at 0.556 V with peak current 6.59 μA. The result reveals that cobalt (II) Schiff base complex modified GCE has better electrocatalytic activity than bare GCE. So that the cobalt (II) Schiff base complex can be used as efficient electrocatalytic sensor for uric acid determination in real samples.

Introduction. The Schiff base ligands are having wide range of applications in several biological, chemical and pharmacological activities. These Schiff base ligands have simple synthetic process and better stability in complex formation they have more interest in research field. The Schiff base metal complexes were widely used in analytical chemistry, biochemistry, medicinal chemistry and electrochemistry. The Schiff base complex activities were mostly depends on the nature of the ligands [1]. The Schiff base structural arrangements and their coordination sites may attribute variety of functions in the metal complexes. The structure and function relationships play major role in Schiff base and their metal complex synthesis and its studies in research field. The synthesis of Schiff base ligands and their metal complexes in various kinds of structural arrangements was getting great interest. It has variety of applications in different fields like electrochemical sensors, ionic ferroelectrics, highly efficient catalysts in different synthetic chemical reactions, and biologically active compounds. The salen type tetradentate Schiff base ligands have more attention among the various types of Schiff ligands. It forms stable complexes through the coordination of transition metal imine nitrogen and phenolic oxygen. The salen type Schiff base ligands provides planar coordination sites for better stability of metal complexes. Cobalt metal is an important trace element in human and living things, which is present in many enzymes and vitamin B12 complex. The cobalt metal complex plays a major role in biological function, chemical processes and it also been used in various 1

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

analytical measurements. The cobalt metal has two stable oxidation states +2 and +3, due to variable oxidation states these cobalt complexes have better catalytic and electrochemical activity [2]. In the present work cobalt(II) Schiff base complex was synthesized by microwave irradiation method [3].

In this method reaction completed in a very short period and it gives more yields when compared with other synthetic methods. The microwave irradiation method requires minimum quantity of solvents and less energy consumption. It is one of the green chemical synthetic routes in the synthetic chemistry. The cobalt(II) Schiff base complex was utilized for the electrocatalytic sensing of uric acid (UA). Uric acid is the final end product of purine metabolism, it is necessity to maintain constant level in human body. The abnormal level of uric acid may lead to some diseases in human. The excesses urinary elimination is leads to hyperuricemia. The high level uric acid in human blood serum is leads to diabetes, hypertension, Lesch–Nyhan syndrome and gout. The level of UA in human fulides indicates various diseases in clinical process. Hence there is a necessity for the determination of UA in human physiological fluids. There are several methods available and reported for the UA determination such as, enzymatic, high-performance liquid chromatography (HPLC), capillary electrophoresis (CE), colorimetric and electrochemical methods. Among the available determination methods, the electrochemical method better than other determine methods of UA. This electrochemical method has high sensitivity, selectivity, low detection limit, inexpensive, faster response and simple procedure. Therefore electrochemical method has been chosen for the determination of UA [4].

Experimental procedure. An absolute methanol solution of 2 mmol of salicylaldehyde (0.123 g) was taken in a beaker and subjected to stirring and then 1 mmol o-phenylenediamine (0.108 g) in methanol was added to aldehyde solution under stirring. The stirring was continued for 1 hr. and employed for microwave irradiation at 320 W for 2-3 min. A yellow colour solution was obtained it was collected and recrystallized by ethanol. Then 1 mmol of Schiff base ligand was taken and 1 mmol of cobalt(II) chloride (0.238 g) was added in the Schiff base ligand. It was continuously stirred for about 2 h and it was subjected for the microwave irradiation at 320 W, for 5 min. A brown colour precipitate was obtained, it was collected and recrystallized by using hot ethanol. The cobalt(II) Schiff base complex synthetic procedure was given in Scheme-1.

Instrumentation. UV-Visible spectrum was recorded in PerkinElmer lambda 35 UV-visible spectrophotometer, FT-IR spectral data was recorded on a Perkin-Elmer FT-IR 8300 using KBr pellet disk and electrochemical studies were obtained using CHI-1103A electrochemical analyser with three-electrode cell. Glassy carbon electrode was used as working electrode, silver and silver chloride electrode and saturated calomel electrode were used as reference electrode, platinum wire was used as counter electrode. Tetrabutylammonium perchlorate (TBAP) used as supporting electrolyte in complex studies. The phosphate buffer solution pH 7.4 (PBS) was used as back ground electrolyte for uric acid sensing.

Fig. 1. Synthesis of Cobalt (II) Schiff base complex.

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Result and Discussion FT-IR analysis. The FT-IR spectrum of cobalt (II) Schiff base complex was recorded using KBr disk in the IR range of 4000–400 cm-1 and the spectrum was given in Fig. 2 (a). The IR spectrum explains valuable characteristic information about the cobalt (II) Schiff base complex. In the IR spectrum a peak shows at 3536 cm-1 due to the solvated water molecules in the complex [ν (Co. . . .OH2)]. The imine group [ν (C=N)] exhibit its vibrational frequency, in the spectrum at 1610 cm -1. This C=N vibrational band has been shifted towards the lower region in the spectrum, due to coordination of cobalt metal ion with the imine nitrogen. The lone pair electrons presented in imine nitrogen was involved in the bond formation, so that bond order was decreased. The [ν (C=N)] normally observed in free Schiff base ligand at above 1650 cm-1. It has blue shift in the IR spectrum, when compare with free Schiff base ligand C=N stretching frequency. The complex formation between Schiff base ligand and cobalt (II) metal ion was further confirmed by two major peaks in the region of 400-600 cm-1, the metal nitrogen and metal oxygen bonds. The metal nitrogen [ν (Co-N)] bond exhibits at 570 cm- 1 and the metal oxygen bond [ν (Co-O)] was appeared at 480 cm-1. The FT-IR spectrum clearly indicates that the complex formation between cobalt (II) metal ion and Schiff base ligand. The other characteristic peaks also observed in the spectrum [5].

UV-Visible analysis. The UV-Visible spectrum of the cobalt (II) Schiff base complex was recorded in methanol solution, in the range of 200-800 nm at room temperature and the spectrum was shown in Fig. 2 (b). The electronic spectrum of cobalt(II) Schiff base complex shows three absorption bands, a peak at 248 nm is due to π → π* transition in the phenyl ring. The second absorption band appeared at 305 nm was assigned to n → π* transition. This n → π* transition appeared due to the C=C in the aromatic ring in ligand field. The d → d transitions of cobalt (II) metal ion shows two absorption peaks at visible region. The d-d transition exhibits its absorption peaks at 400 nm and 605 nm. The electronic transitions in the cobalt (II) Schiff base complex was explains the geometry and magnetic momentum of the complex. The UV-Visible spectrum of cobalt (II) Schiff base complex confirm the octahedral geometry and the magnetic moment value is 3.78 BM. Electrochemical studies The electrochemical redox behaviour of the cobalt (II) Schiff base complex was examined in 0.1 M acetonitrile solution with the aid of cyclic voltammetry (CV) technique. The cyclic voltammetry technique has three electrodes, such as glassy carbon electrode (GCE), silver- silver chloride (Ag/AgCl) and platinum wire were used as working, reference and counter electrodes respectively.

In the electrochemical studies of cobalt (II) Schiff base complex tetrabutylammonium perchlorate (TBAP) as supporting electrolyte. The cyclic voltammogram of cobalt (II) Schiff base complex was shown in Fig. 2 (c). In the CV cobalt (II) Schiff base complex exhibits an oxidation peaks due to electronic transition from Co (II) state to Co (III) state. The anodic peak observed at 1.294 V corresponds to the oxidation of Co (II)/Co (III). The number of electron transfer in the electrochemical redox process of cobalt (II) Schiff base complex was calculated using equation: ip = nFQʋ/4RT It shows that cobalt (II) Schiff base complex has good electrochemical activity, it is an one electron transfer electrochemical redox behaviour.

Electrochemical polymerization. The cobalt (II) Schiff base complex was electrochemically polymerized for the modification of glassy carbon electrode (GCE). The modified GCE was utilized for UA electrocatalytic sensing. The electrochemical polymerization was carried out in 0.1 M acetonitrile solution of cobalt (II) Schiff base complex, in the potential range of 0 to 1.6 V working potential. The electrochemical polymerization of cobalt (II) Schiff base complex also shows the same kind of electrochemical redox process. The electrochemical polymerization was carried at 50 mVS-1 MMSE Journal. Open Access www.mmse.xyz

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

scan rate for 20 cycles. The polymerized cobalt (II) Schiff base complex was deposited on the surface of GCE, the cyclic voltammogram of electrochemical polymerization was shown in the Fig. 2 (d).

The poly cobalt (II) Schiff base complex modified GCE [ploy-Co-SBC/GCE] was utilized for the determination of UA.

Fig. 2. (a) FT-IR spectrum, (b) UV-Visible spectrum, (c) Cyclic voltammogram in 0.1 M TBAP at the scan rate of 50 mVs-1 of cobalt(II) complex and (d) Cyclic voltammogram of cobalt(II) Schiff base complex polymerization in 0.1 M TBAP. Electrocatalytic Sensing of Uric Acid. The electrocatalytic sensing of UA at both bare GCE and poly-Co-SBC/CE were investigated with the aid of cyclic voltammetry (CV) in phosphate buffer (pH = 7.4). The Cyclic voltammograms of UA sensing at bare and poly-Co-SBC/GCE modified electrodes were shown in Fig. 3 (a). In cyclic voltammogram the UA exhibits only an oxidation peak for both the electrodes. The bare GCE shows the UA anodic peak at 0.552 V (vs SCE), with the anodic peak current of 6.59 μA. The cobalt (II) Schiff base complex modified GCE shows the UA anodic peak at 0.483 V with the peak current of 7.15 μA. The modified GCE shows the anodic peak of UA at low potential and higher peak current than the bare GCE. The increasing electrocatalytic sensing activity of modified GCE is due to the polymerized cobalt (II) Schiff base complex on the working electrode surface. The UA oxidation was facile by the cobalt (II) redox activity. The modified GCE exhibits 69 mV negative shift with higher anodic peak current. The UA oxidation was exhibits as a broad peak at bare GCE, it explains that a slow electron transfer, but the modified GCE shows a sharp peak it indicates faster electron transfer reaction. The electrocatalytic oxidation of UA at modified GCE has well defined sharp peak, enhanced peak current and more negative shift, it clearly shows that modified GCE has better electrochemical active than bare GCE. The scan rate effect was also studied for the UA sensing [6], [7]. The different scan rate shows the UA sensing process is adsorption process. The scan rate effect was shown in Fig. 3 (b).

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Fig. 3. (a) Cyclic voltammogram of electrocatalytic sensing of UA in PBS at the scan rate of 50 mVs-1, (b) scan rate effect of UA sensing at poly-Co-SBC/GCE in PBS. Summary. The microwave irradiation method was successfully used for the synthesis of cobalt (II) Schiff base complex. The synthesized cobalt (II) Schiff base complex was characterized by FT-IR and UV-Vis. spectral techniques. These spectral techniques confirm the cobalt (II) Schiff base complex. The electrochemical redox activity of cobalt (II) Schiff base complex was examined in acetonitrile solution with the aid of cyclic voltammetry. The CV gives additional information about the cobalt (II) metal ion, it confirms the cobalt at +2 oxidation state. The cobalt (II) Schiff base complex was electrochemically polymerized on GCE surface and fabricated for electrocatalytic sensing of UA. The cobalt(II) Schiff base complex was successfully utilized for the electrochemical determination of UA. The poly-Co-SBC/GCE shows better electrocatalytic activity for determination of UA. Hence, it can be utilized for the UA determination in real sample analysis.

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