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Amine-Based Zinc(II), Copper(II), and Oxidovanadium(IV) Complexes: SOD Scavenging, DNA Binding, and Anticancer Activities

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Amine-Based Zinc(II), Copper(II), and Oxidovanadium(IV) Complexes: SOD Scavenging, DNA Binding, and Anticancer Activities Int. J. Electrochem. Sci., 7 (2012) 7526 - 7546 International Journal of ELECTROCHEMICAL SCIENCE www.electrochemsci.org Synthesis, Characterization, and Electrochemical Properties of Bis(2-benzimidazolylmethyl-6-sulfonate)amine-based zinc(II), copper(II), and oxidovanadium(IV) Complexes: SOD Scavenging, DNA binding, and Anticancer Activities Mohamed M. Ibrahim1,2, Gaber A. M. Mersal1,3, Samir A. El-Shazly4,5, Abdel-Motaleb M. Ramadan2 1 Department of Chemistry, Faculty of Science, Taif University, Taif, Saudi Arabia 2 Departmentof Chemistry, Faculty of Science, Kafr El-Sheikh University, Egypt 3 Department of Chemistry, Faculty of Science, South Valley University, Qena, Egypt 4 Departmentof Biochemistry, Faculty of Veterinary Medicine, Kafr El-Sheikh University, Egypt 5 Department of Biotechnology, Faculty of Science, Taif University, Taif, Saudi Arabia *E-mail: [email protected] Received: 8 June 2012 / Accepted: 9 July 2012 / Published: 1 August 2012 The synthesis of a tridentate ligand, bis(2-benzimidazolylmethyl-6-sulfonate)amine H2SBz is described together with its zinc(II), copper(II), and oxidovanadium(IV) complexes [SBz-M(H2O)2] (M = Zn2+ 1, Cu2+ 2, and VO2+ 3). The ligand and its metal complexes 1-3 were characterized based on elemental analysis, conductivity measurements, spectral, and magnetic studies. The magnetic and spectroscopic data indicate a square pyramidal geometry is proposed for all complexes. The redox properties of the ligand and its complexes 1-3 were extensively investigated by using cyclic voltammetry. Complexes 1 and 2 exhibited quasi-reversible single electron transfer process. Whereas in complex 3, only one electron oxidation peak was observed at + 0.72 V, which is due to the oxidation of VIV to VV. The SOD-like activity of complexes 2 and 3 has been investigated and showed that both complexes possess the capability to dismutase the superoxide anion generated in nitrobluetetrazolium/superoxide system. The electrochemical DNA binding studies by using oxidovanadium(IV) complex 3 was investigated and showed that the modified electrode with DNA causes the peak potentials, Epc, and Epa shifted to more positive values. This may be attributed to diffusion of the metal complex bound to the large, slowly diffusing DNA molecule and the resulted peak current due the equilibrium of free and DNA-bound oxidovanadium(IV) complex to the electrode surface. Complexes 2 and 3 were also assessed for their cancer chemotherapeutic potential towards colon cancer cell line (Caco-2) and showed that these complexes have the potential to act as an effective anticancer drug with IC50 values of 4.0 and 2.5 M for complexes 2 and 3, respectively Keywords: Benzimidazole-containing ligand; Cyclic voltammetry; Electrochemical DNA binding studies; SOD mimic;; Antitumor activities. Int. J. Electrochem. Sci., Vol. 7, 2012 7527 1. INTRODUCTION The reactive superoxide free radical anion O•2- is generated in cells as an avoidable sub-product of aerobic metabolism [1]. The intracellular concentration of O•2- and consequently tissue damage is normally controlled by the superoxide dismutase (SODs), a group of metalloenzymes which play an important role in protecting cells through catalysis of superoxide disproportionation [2,3] into O2 and H2O2 through a one-electron redox cycle involving its metal center. It is known that cancer cells have less than normal SODs activity and the treatment with bovine native Cu-SOD decreased the growth of several solid tumors [4]. It is difficult, however, to employ SODs because they are readily cleared by the kidney and are unable to enter cells because of their high molecular weight [5]. The presence of copper, manganese, and iron at the active site of SODs led many investigators [6-13] to search for low molecular weight complexes of these metals having SOD activity. Although many copper complexes catalyze the •- dismutation of O2 in vitro [14-21], their activities are attenuated in vivo by chelating agents ordinarily found in living cells [22]. Useful SOD mimics should be capable of crossing cell membranes and should be stable, active, and nontoxic. One general strategy for the research on new anticancer agents has been the therapeutic use of metal containing compounds [23,24]. Specially, in the search of less toxic metal-based antineoplastic drugs, essential metal complexes such as copper-based drugs have been developed [25]. The cytotoxicity of these complexes can be explained by different mechanisms of action. In particular, the report by Oberley and Buettner showed that cancer cells have a less than normal superoxide dismutase SODs activity and the treatment with bovine native Cu-SOD decreased the growth of several solid tumors [26]. H N N H H N H N N H N H N N N M N - O H2O OH2 O Bis(2-benzimidazolylmethyl)amine (Bz) S S O O O -O M = Zn 2+ (1) H N H N H N 2+ = Cu (2) N N 2+ -O O = VO (3) S S O O O -O Bis(2-benzimidazolylmethyl-6-sulfonate)amine (SBz) Scheme 1. The ligand SBz and its metal complexes 1-3 The synthesis and study of structural models can lead the understanding of fundamental mechanistic aspects of enzymes as well as the development of structure reactivity relationship. The major task in designing these model compounds depends on the proper choice of ligands as well as the Int. J. Electrochem. Sci., Vol. 7, 2012 7528 steriochemical environment surrounding the metal centers. The water soluble ligand bis(2- benzimidazolylmethyl-6-sulfonte)amine), SBz is a tridentate NNN donor ligand (Scheme 1) with donor groups suitable placed for forming two five-membered chelate rings. The mononuclear complexes 1-3 show penta-coordinated metal ions with a square pyramidal coordination geometry. Herein we report the synthesis and structural characterization of new water soluble zinc(II), copper(II), 2+ 2+ 2+ and oxidovanadium(IV) complexes viz., [SBz-M(H2O)2] (M = Zn 1, Cu 2, and VO 3. Since the possible biomimetic activity of metal complexes can be evaluated from the electrochemical behavior and spectroscopic studies. The electrochemical behavior of all complexes by cyclic voltammetry was studied because of their applications as SOD mimetic complexes are related to the redox properties, in which their general physicochemical and both SOD and cytotoxic activities were investigated. 2. EXPERIMENTAL 2.1. Materials and instrumentations All chemical used were of analytical grad. The starting material, 4-sulfo-o-phenylenediamine was synthesized by the method of Nakata [27]. The IR spectra were recorded as KBr disks in the 4000- 400 cm-1 range on FT-IR Prestige-21 Shimadzu spectrophotometer. The electronic absorption spectra were obtained in methanolic solution with Shimadzu spectrophotometer UV-240. Magnetic moments were measured by Gouy’s method at room temperature. ESR measurements of the polycrystalline samples at room temperature were made on Varian E9 X-band spectrometer using a quartz Dewar vessel. All spectra were calibrated with DPPH (g = 2.0027). The specific conductance of the complexes were measured using freshly prepared (0.001 M) solutions in the electrochemically pure MeOH or water at room temperature, using YSI Model 32 conductance meter. The copper content was determined by using atomic absorption technique, after destruction of the complexes with concentrated H2SO4/H2O2 mixture. 2.2. Syntheses 2.2.1. Synthesis of, N, N bis-(2-benzimidazolylmethyl-5(6)-sulfo)amine H2SBz The ligand H2SBz was synthesized by the method of Nakata [27] as follows: 7.52 mmol (1.69 g) of 4-sulfo-o-phenylenediamine and 3.76 mmol (0.50 g) iminodiacetic acid in 150 mL 6 M HCl was stirred for 4 hours and cooled. The yielded blue precipitate was filtered, and dissolved in 0.1 M NaOH, decolorized on active carbon. After removing (filtering) the active carbon, 0.1 M HCl was added in little portions, and H2SBz precipitate was formed. 0.56 g (34% yield). 2.2.2. Synthesis of the metal complexes 1-3 A general procedure for the synthesis of the metal complexes 1-3 is as follows: a solution of 373 mg (1.0 mmol) of Zn(ClO4)2 • 6H2O or 370 mg (1.0 mmol) of Cu(ClO4)2 • 6H2O, or 163 mg (1.0 Int. J. Electrochem. Sci., Vol. 7, 2012 7529 mmol) of VOSO4 dissolved in water (10 mL) was added to a solution of Na2SBz, made up from (438 mg, 1.0 mmol) of the protonated ligand H2SBz and NaOH (80 mg, 2.0 mmol) in water (10 mL). The resulting solution was stirred for 4 h at room temperature and then evaporated to dryness. yielded 0.427 mg (77%) of 1 as colorless crystals, 0.468 mg (82%) of 2 as blue crystals, and 0.426 mg (74%) of 3 as grey crystals. 2.3. Electrochemical measurements The electrochemical behavior of the ligand SBz and its zinc(II), copper(II), and oxidovanadium(IV) complexes 1-3 was studied using cyclic voltammetry (CV) and square wave voltammetry (SWV) using auto lab potentiostat PGSTAT 302 (Eco Chemie, Utrecht, The Netherlands) driven by the General Purpose Electrochemical Systems data processing software (GPES, software version 4.9, Eco Chemie). The electrochemical cell used in this work contains three electrodes; platinum wire was used as a working electrode, SCE as a reference electrode, and a platinum wire was used as a counter electrode. Stock solutions of the ligand SBz and its complexes were freshly prepared daily in Britton–Robinson (BR). BR buffer was prepared via mixing 0.04 M H3BO3, 0.04 M H3PO4, and 0.04 M CH3COOH. The desired pH was adjusted by the addition of 0.2 M NaOH. 2.4. SOD-like activity assay The SOD-like activity of the two complexes were determined by NBT/NADH/PMS (Nitroblue Tetrazolium/reduced Nicotinamide/Phenazine methosulphate) system [28]. The superoxide radicals were produced by NADH, PMS and NBT in phosphate buffer (pH = 8.5).
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