1. INTRODUCTION:

There is a substantial interest in the coordination chemistry of Cd (II)due to its ability to form stable complexes with coordination numbers 4, 5 and 6^1-3. Metal complexes of quinoxaline derivatives have attracted attention because of their versatile biological^4-7, electroluminescent ⁸ and catalytic activities ⁹.

The literature survey reveals that the coordination chemistry of Cd (II)complexes of Schiff bases derived from 3-hydrazinylquinoxalin-2(1H)-one¹¹ is not well explored. Therefore, in the present paper we report the synthesis, characterization DNA binding and anti bacterial studies of Cd (II) complex of the tridentate Schiff base (VHQO) derived from 3-hydrazinylquinoxalin-2(1H)-one and 2-hydroxy-3-methoxybenzaldehyde.

2. EXPERIMENTAL:

2.1. Materials and methods:

All the chemicals used were purchased from commercial sources. Elemental analysis was carried out using Flash Ea 1112 Series CHNS analyzer.¹H NMR spectra were recorded on Bruker 400 MHz spectrometer using DMSO d₆ solvent. Electronic absorption spectra were recorded on Shimadzu UV-3600 spectrophotometer. IR spectra were recorded using Shimadzu FTIR-5300 spectrometer in KBr pellets from 250 to 4000 cm^-1. Thermo gravimetric analysis was carried using TG/DTA Extar 6300 under nitrogen atmosphere in the temperature range of 25°C to 800°C with a heating rate of 10°C/min. Electrical conductance measurements were recorded using 10^-3M solution of the complex in DMSO with an Elico conductivity bridge and dip type cell calibrated with KCl solution. Magnetic susceptibilities were measured on a Faraday balance model 7550 at room temperature using Hg [Co (NCS)₄] as calibrant.

2.2.Synthesis of 3-(2-(2-hydroxy-3-methoxybenzylidene) hydrazinyl) quinoxalin-2(1H)-one (VHQO):

3-(2-(2-hydroxy-3-methoxybenzylidene) hydrazinyl) quinoxalin-2(1H)-one (VHQO) was prepared by a 3 step procedure involving the Synthesis of quinoxaline-2,3 (1H,4H)-dione¹⁰ and 3-hydrazinylquinoxalin-2(1H)-one¹¹.

3-hydrazinylquinoxalin-2(1H)-one (100 m moles) in methanol was condensed with 2-hydroxy-3-methoxybenzaldehyde (100 m moles) with a catalytic amount of acetic acid by stirring at room temperature for 30 min. The yellow solid obtained was collected by filtration, washed with methanol and n-hexane and dried over anhydrous calcium chloride. Yield 89%, M.P. 224°C.

2.3. Synthesis of Cd (II) Complex of VHQO:

To a hot methanolic suspension of the ligand VHQO (100 m moles) in a two necked round bottom flask, a hot methanolic solution of Cd (II) chloride (50 m moles) was added in small increments and the pH of the clear solution obtained was adjusted to ≈8 using alcoholic ammonium hydroxide solution. The reaction mixture was refluxed on a water bath for about four hours. The bright yellow colored solid obtained was filtered in hot condition, washed with methanol and n-hexane and dried over anhydrous calcium chloride in a desiccator at room temperature.

2.4. DNA binding studies:

The stock solution of CT-DNA was prepared in KH₂PO₄ and K₂HPO₄ buffer. The purity of DNA was verified by monitoring the ratio of absorbance at 260 nm to that at 280 nm, which was in the range of 1.8–1.9.The concentration of DNA per nucleotide was determined from the known molar absorption coefficient value (e=6600 M -1 cm-1) at 260 nm¹². Electronic absorption titrations were performed by adding increments of CT-DNA to the solution of the metal complex of fixed concentration in DMSO. The solution after each addition of DNA was incubated for 10 minutes before recording the absorption spectra. The intrinsic binding constant (Kb) was determined using the equation

[DNA]/ (ea-ef) = [DNA]/ (eb-ef) +1/ Kb (eb-ef)

Where, [DNA] represents the concentration of DNA in base pairs, ea,eb and ef are apparent extinction coefficient, extinction coefficient for free metal complex and extinction coefficient for the metal complex in fully bound form respectively¹³. The ratio of the slope to intercept in the plot of [DNA]/ (ea - ef) versus [DNA] gives the value of Kb.

2.5. Antibacterial studies:

The antibacterial activity of the complex was carried out by measuring the zone of inhibition against Gram positive bacteria, Bacillus subtillis and Staphyloccocus aureus and Gram negative bacteria Pseudomonas aeroginosa, Proteus vulgaris, Escherichia coli and Klebsiella pneumonia in the nutrient agar media by using DMSO as negative control.

3. RESULTS AND DISCUSSION:

The Cd(II) complex is dark yellow in color, stable in air at room temperature, non hygroscopic, insoluble in water and common organic solvents but soluble in DMF and DMSO. The elemental analysis Calc. for C₁₆H₁₃N₄O₃CdCl: C 42.04%, H 2.84% and N 12.25%, Found: C 42.26%, H 2.78% and N 12.08%. The LC-MS shows a well defined molecular ion peak of m/Z=457.The mass and elemental analysis data are in good agreement with the formula [Cd (C₁₆H₁₃N₄O₃) Cl]. Volhard’s test indicated the presence of chloride ion inside the coordination sphere¹⁴. The molar conductance value 4.4 W-1Cm2 mol-1 of the complex indicates that the complex is non-electrolyte.

3.1. IR Spectra:

The characteristic azomethine ʋ (-CH=N-) peak observed at 1614 cm-1 in the IR spectrum of the ligand VHQO is shifted to 1608 cm-1 in the complex suggesting the coordination of azomethine nitrogen to the metal ion¹⁵. Negative shift of ʋ (C=N)ring from 1465 cm-1 to 1436 cm-1 indicates the participation of ring nitrogen in coordination. Involvement of phenoxide group in coordination is evidenced by the disappearance of ʋ (OH) band in the complex, which is observed at 3581 cm-1in the ligand. This is further supported by the fact that the peak at 1344 cm-1 in the ligand assigned to ʋ (C-O) experiences a positive shift by 19 cm-1 in the complex¹⁶. The peaks in Far IR region indicate the presence of ʋ (M-O), ʋ (M-N) and ʋ (M-Cl) bands in the complex.

3.2. Electronic Spectra:

Electronic absorption spectra of the ligand and its cadmium (II) complex were recorded in DMSO at room temperature over the range of 200-1200nm. The ligand exhibits strong peaks at 266 and 276nm corresponding to π-π* transitions and at 358,377 and 397nm corresponding to n-π* transitions. The new peaks at 444 and 476 nm in the absorption spectrum of the complex can be attributed to intraligand transitions, as the Cd (II) complex has d10 configuration and is diamagnetic.

3.3. Thermo gravimetric analysis:

Thermo gravimetric analysis of the Cd (II) complex [Fig.1] indicates the absence of lattice water as well as coordinated water¹⁷. The complex decomposes beyond 300 0C. The residue left at 7740C (25.03%) corresponds to the metal (cal 24.058%).

Based on the spectral and analytical data, the proposed structure for the complex is given in Fig.2.

Fig.1 Thermogram of the Cd (II) complex

Fig.2 Structure of the Cd (II) complex

3.4. DNA binding studies:

Electronic absorption spectroscopy is an effective method to investigate the binding mode of DNA with the metal complexes¹⁸. In general, hypochromism and red-shift are associated with the intercalative mode of binding of the complex to the DNA helix involving stacking interaction of the aromatic chromophore of the complex between the base pairs of DNA¹⁹. The absorption spectra of Cd (II) complex in the presence and absence of CT DNA are shown in Fig.3. The peak at 377 nm indicates a considerable hypochromism. The calculated value of the intrinsic binding constant, K_b (6.63 x 10⁵) indicates that the Cd (II) complex has strong binding affinity for CT- DNA. The observed absorption spectral changes are predictive of intercalative mode of interaction of complex with the CT -DNA involving insertion of its aromatic rings between the base pairs of DNA^20,
21.

3.5. Antibacterial activity:

Antibacterial screening of the complex against gram positive bacteria, Staphyloccocus aureus and Bacillus subtillis and gram negative bacteria Escherichia coli, Pseudomonas aeroginosa, Klebsiella pneumonia and Proteus vulgaris revealed that the complex exhibits a moderate antibacterial activity against Staphyloccocus aureus and Bacillus subtillis with a zone of inhibition of 13 mm each and is inactive against the other bacteria.

Fig.3. Absorption spectra of Cd (II) complex in the presence and absence of CT DNA

4. CONCLUSIONS:

Cd (II) complex of the tridentate Schiff base ligand, 3-(2-(2-hydroxy-3-methoxybenzylidene) hydrazinyl) quinoxalin-2(1H)-one (VHQO) has been prepared and characterized by various spectral and analytical techniques. The ligand formed four coordinated, 1:1, monomeric complex with the metal ion coordinating through ring nitrogen, azomethine nitrogen and phenolic oxygen. The absorption spectroscopy indicated the ability of the complex to bind with CT- DNA through intercalation and the intrinsic binding constant (Kb) was found to be 6.63 x 105 M-1. Antibacterial screening studies indicated that the complex is active against Staphyloccocus aureus and Bacillus subtillis with a zone of inhibition of 13 mm each and is inactive against the Escherichia coli, Pseudomonas aeroginosa, Klebsiella pneumonia and Proteus vulgaris.

5. REFERENCES:

1. Halehatty S. Bhojya Naik, Parasuramapura R. Chetana, Hosakere D. Revanasiddappa .Synthesis, Spectral and Thermal Degradation Kinetics of Divalent Cadmium Complexes of Dothiepine and Diphenhydramine. Turk.J.Chem. 26; 2002: 565 -572.

2. Alfonso Castin eiras, Isabel Garcia, Elena Bermejo, Douglas X. West. Structures of 2-pyridineformamide thiosemicarbazone and its complexes with cadmium halides .Polyhedron.19; 2000: 1873-1880.

3. Lotf A. Saghatforoush, Ali Aminkhani, Sohrab Ershad, Ghasem Karimnezhad, Shahriar Ghammamy and Roya Kabiri. Preparation of Zinc (II) and Cadmium (II) Complexes of the Tetradentate Schiff Base Ligand 2-((E)-(2-(2-(pyridine-2-yl)-ethylthio) ethylimino)methyl)-4-bromophenol (PytBrsalH). Molecules.13; 2008: 804-811.

4. Rogier A. Smits, Herman D. Lim, Agnes Hanzer, Obbe P. Zuiderveld, Elena Guaita, Maristella Adami, Gabriella Coruzzi, Rob Leurs, Iwan J. P. de Esch .Fragment Based Design of New H4 Receptor-Ligands with Anti-inﬂammatory Properties in Vivo.J. Med. Chem. 51; 2008: 2457-2467.

5. Nelilma C.Romero, Gabriela Aguirre, Paola Hernandez, Mercedes Gonzalez, Hugo Cerecetto, Ignacio Aldona, Silvia Perez-Silanes, Antonio Monge, Eliezer J. borreiro, Lidia M. Lima .Synthesis, trypanocidal activity and docking studies of novel quinoxaline-N-acylhydrazones, designed as cruzain inhibitors candidates. Bioorg. Med. Chem. 17; 2009: 641–652.

6. Andres Jaso, Belen Zarranz, Ignacio Aldana, Antonio Monge. Synthesis of new 2-acetyl and 2-benzoyl quinoxaline 1,4-di-N-oxide derivatives as anti-Mycobacterium tuberculosis agents. Eur. J. Med. Chem. 38; 2003: 791-800.

7. Reinhard Sarges, Harry R. Howard, Ronald G. Browne, Lorraine A. Lebel, Patricia A. Seymour, B. Kenneth. Koe 4-Amino[1,2,4]triazolo[4,3-a Iquinoxalines.A novel class of potent adenosine receptor antagonists and potential rapid-onset antidepressants. J. Med. Chem. 33; 1990: 2240-2254.

8. K. R. Justin Thomas, Marappan Velusamy, Jiann T. Lin, Chang-Hao Chuen, and Yu-Tai Tao. Chromophore-Labeled Quinoxaline Derivatives as Efficient Electroluminescent Materials. Chem. Mater. 17; 2005: 1861.

9. Manju sebatian,V.Arun, P.P.Robinson, Annu Anna Varghese, Rani Abraham, E. Suresh, K. K. Mohammed Yusuff. Synthesis, structural characterization and catalytic activity study of Mn(II), Fe(III), Ni(II), Cu(II) and Zn(II) complexes of quinoxaline-2-carboxalidine-2-amino-5-methylphenol: Crystal structure of the nickel(II) complex. Polyhedron .29; 2010: 3014-3020.

10. Montague Alexandra Phillips. The formation of 2-substituted benziminazoles. J.Chem.Soc. 1928: 2393-2399

11. G.W.H.Cheeseman and M. Rafiq, Quinoxalines and related compounds. Part VIII. The reactions of quinoxaline-2(1H)-ones and -2,3(1H,4H)-diones with hydrazine. J.Chem.Soc.C.1971:452-454.

12. D. Kannan, M.N. Arumugham. Synthesis, Characterisation. DNA-Binding Studies and antimicrobial activity of Copper (II) Complex with 1,10 Phenanthroline, L-Tyrosine and Thiourea as Ligands. International Journal of Research in Controlled Release. 2 (4); 2012:10-17.

13. Farukh Arjmand, Shazia Parveen, Mohd Afjal, Mohd Shahid. Synthesis, characterization, biological studies (DNA binding, cleavage, antibacterial and topoisomerase I) and molecular docking of copper (II) benzimidazole complexes .J. Photochem. Photobiol B. 114; 2012: 15-26.

14. Vogel, A. I. A Text Book of Qualitative Inorganic Analysis. Longman Elbs, London, 1968.

15. P.Sukanya and Ch.Venkata Ramana Reddy. Synthesis, characterization, antibacterial and DNA binding studies of Mn (II) Complex of 3-(2-(2-Hydroxy-3-Methoxybenzylidene) Hydrazinyl) Quinoxalin-(1H)-One. IOSR Journal of Applied Chemistry .10 (1); 2017: 59-62.

16. P.V.A. lakshmi, D.Sandhya Rani, V. Jayatyagaraju .Structural elucidation studies on transition metal complexes of new hydrazino quinoxaline derivatives. Asian J. Chem. 7(2); 1995: 296-306.

17. Mendu Padmaja, J. Pragathi, B. Anupama, C. Gyana Kumari. Spectral Characterization, Molecular Modeling, and Antimicrobial Studies of Cu(II), Ni(II), Co(II), Mn(II), and Zn(II) Complexes of ONO Schiff Base. E-Journal of Chemistry. 9(4); 2012:2145-2154.

18. Yuan Cai-Xia, Wei Yi-Bin, Yang Pin .DNA-Binding and Cleavage Studies of Zinc (II) Mixed-polypyridyl Complex. Chin. J. Chem. 24; 2006: 1006-1012.

19. Nagababu, J. Naveena Lavanya Latha, Y. Prashanthi, S. Satyanarayana. DNA-binding and photocleavage studies of cobalt (III) ethylenediamine complexes: [Co (en) 2phen]3+ and [Co(en)2bpy]3+. J. Chem. Pharma. Res. 1(1); 2009: 238-249.

20. Balaraman Selvakumar, Venugopal Rajendiran, Palanisamy Uma Maheswari, Helen Stoeckli-Evans, Mallayan Palaniandavar. Structures, spectra, and DNA-binding properties of mixed ligand copper (II) complexes of iminodiacetic acid: The novel role of diimine co-ligands on DNA conformation and hydrolytic and oxidative double strand DNA cleavage. J. Inorg. Biochem. 100(3); 2006: 316-330.

21. Sangeetha Gowda K.R, Blessy Baby Mathew, C.N. Sudhamani, H.S. Bhojya Naik. Mechanism of DNA Binding and Cleavage. Biomedicine and Biotechnology. 2(1); 2014: 1-9.

Received on 30.01.2017 Modified on 08.02.2017

Asian J. Research Chem. 2017; 10(1):54-57.

DOI: 10.5958/0974-4150.2017.00010.4