Synthesis characterization and antimicrobial activity studies of some transition metal complexes derived from 3-chloro-6-methoxy-N’-((2-thioxo-1, 2-dihydroquinolin-3-yl) methylene)benzo[b]thiophene-2-carboxyhydrazide

 

Vivekanand D. B. and Mruthyunjayaswamy B. H. M.*

Department of Studies and Research in Chemistry, Gulbarga University, Gulbarga- 585 106, Karnataka, India

*Corresponding Author E-mail: bhmmswamy53@rediffmail.com

 

ABSTRACT:

A series of new coordination complexes of Fe(III), Co(II), Ni(II), and Zn(II), with a new Schiff base 3-chloro-6-methoxy-N’-((2-thioxo-1,2-dihydroquinolin-3-yl)methylene) benzo[b] thiophene-2-carboxyhydrazide have been synthesized and characterized by elemental analysis, UV-Visible, IR spectra, ¹HNMR spectra, mass spectra, powder X-ray diffraction data, molar conductance, magnetic susceptibility and TGA. The new Schiff base has been synthesized by the reaction between 3-chloro-6-methoxy benzo[b]thiophene-2-carboxyhydrazide and 2-thioxo-1, 2-dihydroquinoline-3-carbaldehyde. The Schiff base behaves as tridentate ONS donor ligand and forms the complexes of the type ML2–stoichiometry in case of Fe(III), Co(II) and ML–stoichiometry in case of Ni(II), and Zn(II). The Fe(III), Co(II) and Ni(II) complexes have octahedral geometry, whereas Zn(II) complex exhibited square planar geometry. The ligand and its metal complexes have been screened for their antibacterial activity against Staphylococcus aureus and Pseudomonous aeruginosa, antifungal activity against Aspergillus niger and Aspergillus flavus by cup plate method respectively and antioxidant activity by free radical scavenging activity using 1, 1- diphenyl-2-picryl hydrazyl (DPPH), with standard compounds vitamin-C and vitamin-E and DNA cleavage activity.

 

KEYWORDS: Schiff base, metal complexes and antimicrobial, antioxidant activity and DNA cleavage activity.

 

1. INTRODUCTION:

The study of transition metal thiophene compounds is an area of great current interest. This is mainly due to the importance of the hydrodesulphurization reaction in the petroleum industry.^1-4 Hydrodesulphurization is a process whereby sulfur is removed from organic sulfur compounds present in petroleum based feed stocks; is an important commercial process for environmental and industrial reasons, i.e. this reaction converts the organic sulfur compounds which contaminate crude oil into alkanes, alkenes and hydrogen sulfide which can then be easily removed.

 

The importance of quinoline and its annulated derivatives are well recognized by synthetic and biological chemists.⁵ Compounds possessing this ring system have wide applications as drugs and pharmaceuticals.⁶

 

Pyranoquinolines are important class of compounds that constitute the basic frameworks of a number of alkaloids of biological significance, for example, geibalasine, ribalalinine, flindersine⁷ etc. Therefore, considerable efforts have been directed towards the preparation and synthetic manipulation of these molecules.⁸ As a result, a number of compounds have been obtained with diverse biological activities.

 

Quinoline, also known as L-azanaphthalene, 1-benzaine or benzo(b)pyridine is an aromatic nitrogen compound characterized by a double ring structure contains a benzene fused to pyridine at two adjacent carbons. Quinoline and its derivatives are widely used as a starting materials to make drugs (especially antimalarial medicine), fungicides, biocides, alkaloids, dyes, rubber, and chemicals, flavoring agents, antiseptic and antipyretic. Quinolinaldine and 2-methyl quinoline are used as antimalarial and for preparing other antimalarial drugs.  It is a fundamental structure in some antihypertensive agents such as prazosin and doxozosin which are peripheral vasodilator.

Quinoline derivatives have been reported to possesses anti-inflammatory,⁹ antibacterial,^10-12 antifungal,^13,14 antiallergy,¹⁵ antidepressant,¹⁶ antiasthmatic,¹⁷ antimalarial,^18-20 antiviral,^21,22 antitumor,²³ neuroleptic,²⁴ antihypertensive,^25,26 cytotoxic, ^27-29 antihistamine,³⁰ CVS,³¹ antiseptic, analgesic, anthelmintic,³²  hypnotic , sedative³³ and bronchodilator³⁴ activities.

 

The chemistry of coordination compounds with heterocyclic ligands containing oxygen and nitrogen as donor atoms has attracted increasing attention in recent years. It is well known that such ligands coordinate to metal atom in different ways in different media. Transition metal ions are essential in many biological systems in nature.³⁵ These metal complexes with bidentate and tetra dentate ligands containing both hard and soft donor groups have been used extensively in coordination and organometallic chemistry.³⁶ The chelating properties of Schiff bases display manifold applications in medicine, industry and agriculture.³⁷

 

In view of these findings and in continuation of our research work on 3-chloro-6-methoxy benzo[b]thiophene-2-carboxyhydrazide we have synthesized some coordination complexes with Schiff base 3-chloro-6-methoxy-N^’-((2-thioxo-1,2-dihydroquinolin-3-yl)methylene)benzo[b]thiophene-2-carboxyhydrazide  and study their antimicrobial, antioxidant and DNA cleavage activities.

 

2. EXPERIMENTAL:

2.1. General Remarks

All solvents and reagents were used as obtained from commercial sources with further purification according to standard procedures.³⁸ Melting points were determined in open glass capillary tubes and are uncorrected. Purity of the compounds was checked on TLC. The IR spectra of compounds were recorded on Perkin-Elmer spectrum one spectrophotometer using KBr disc technique. ¹HNMR spectrum was recorded on Bruker Advance 400MHz instrument in d₆-DMSO using TMS as an internal standard and mass spectra on a JEOL GC mate and Agilent 6330 ion trap mass spectrometer. Satisfactory C, H, N analysis was recorded for all the compounds.

 

Compounds 2-chloro-3-formylquinolines, 2-thioxo-1, 2-dihydroquinoline-3-carbaldehyde^39,40 and 3-chloro-6-methoxy benzo[b]thiophene-2-carboxyhydrazide were prepared according to reported methods.

 

2.2. Synthesis of ligand HL

An equimolar mixture of 3-chloro-6-methoxy benzo[b]thiophene-2-carboxyhydrazide (0.001 mol) and 2-thioxo-1, 2-dihydroquinoline-3-carbaldehyde (0.001mol) in ethanol (30 mL) was refluxed in presence of catalytic amount of glacial acetic acid (1-2 drops) for about 6-7 h on water bath. The reaction mixture was cooled to room temperature, the separated Schiff base collected by filtration, washed with ethanol, dried and recrystallized from 1, 4, dioxane.

 

2.3. Preparation of Fe(III), Co(II), Ni(II), and Zn(II), complexes with Schiff base 3-chloro-6-methoxy-N^’-((2-thioxo-1,2-dihydroquinolin-3-yl)ethylene)benzo[b] thiophene -2-carboxyhydrazide

To a hot solution of 3-chloro-6-methoxy-N^’-((2-thioxo-1, 2-dihydroquinolin-3-yl) methylene)benzo[b]thiophene-2-carboxyhydrazide (0.001 mol) in ethanol (20 mL) was added a hot ethanolic solution (10 mL) of respective metal chlorides (0.001 mol). The reaction mixture was refluxed on a steam bath for 4 h, then sodium acetate (0.5 g) added to it and refluxed for further 2h. It was then poured into distilled water. The resulting solid complexes were collected by filtration, washed with sufficient quantity of distilled water, then with hot ethanol to apparent dryness and dried in a vacuum over anhydrous calcium chloride in a desiccator (yield 75-80%) Table 1

 

 

Table 1: Physical, Analytical, Magnetic susceptibility and Molar conductance data of ligand HL and its complexes

Compd.	Molecular formula	Mol. Wt.	M.P 0C (Yield in %)	Elemental analysis (%) Calcd. (Found)					Molar cond. (ƛM) ohm-1 cm2 mol-1	µ eff (B.M)	Colour
				M	C	H	N	Cl
HL	C20H14N3O2S2Cl	427	294- 96 (65)	-	56.20 (56.07)	3.27 (3.20)	9.83 (9.78)	8.19 (8.10)	26	-	Orange
Fe-complex	Fe[C40H26N6O4S4Cl3]2H2O	978.85	280- 82 (80)	5.70 (5.61)	49.03 (48.95)	3.06 (3.01)	8.58 (8.49)	10.72 (10.66)	39	5.85	Brown
Co-complex	Co[C40H26N6O4S4Cl2]4H2O	982.93	320- 22 (73)	5.99 (6.05)	48.83 (48.70)	3.45 (3.39)	8.54 (8.48)	7.12 (7.05)	34	5.07	Brown
Ni-complex	Ni[C20H13N3O2S2Cl2]2H2O	555.89	> 360 (61)	10.59 (10.47)	43.17 (42.98)	3.05 (2.92)	7.55 (7.63)	12.59 (12.65)	25	2.88	Reddish brown
Zn-complex	Zn[C20H13N3O2S2Cl2]	524.39	306 (68)	12.46 (12.21)	45.76 (45.65)	2.47 (2.41)	8.00 (7.88)	13.34 (13.25)	18	Dimagnetic	Orange

HL = Ligand

 

 

2.4. Antimicrobial activity

The in vitro antibacterial screening of ligand and its complexes was undertaken against S. aureus and P. aeruginosa by the MIC cup-plate method using nutrient agar media. In a typical procedure molten agar nutrient kept at 45^oC was poured into petri dishes and allowed to solidify. Then wells of 4 mm diameter were punched carefully using a sterile cork borer and were filled with test solution 25 µL (1000 ppm, 500 ppm, 250 ppm, 125 ppm). The plates were incubated for 24 h at 37 ^oC. The diameter of the zone of inhibition for all the test compounds was measured and the results were compared with the standard drugs Gentamycin of the same concentration as that of the test compound under identical conditions.

 

The antifungal activity of the test compounds was evaluated against A. niger and A. flavus by the MIC cup plate method cultured on seberose dextrose agar (SDA) medium adopting the procedures as described above. The plates were incubated at 37 ^oC for 48 h, the diameter of the zone of inhibition for the entire test compounds were compared with standard drug, Fluconazole of the same concentration as that of the test compounds was tested under identical conditions. Since solutions of all the test compounds and standard drugs were prepared in freshly distilled DMF, its zone of inhibition was found to be negligible and taken as 0 mm.

 

2.5 Antioxidant activity by DPPH radical scavenging activity

1, 1- Diphenyl-2-picryl hydrazyl (DPPH) radical scavenging activity was measured by spectrophotometric method at 517 nm.^24-26 to a methanolic solution of DPPH (0.1 mmol) and standard compounds Vit-C and Vit-E and test compounds added separately in different concentrations and an equal amount of methanol (0.05 mL) was added to a control. After 30 min, absorbance was measured. The percentage of radical scavenging activity was calculated by comparing the activities of control and test samples with the following equation.

 

Where,  A_o corresponds to the absorbance of DPPH without sample and A_e corresponds to the absorbance of sample with complex or ligand. A_o is the absorbance of sample containing only DPPH (blank).

 

2.6 DNA cleavage activity

The DNA cleavage activity of ligand and its complexes was studied by using agarose gel electrophoresis. Nutrient broth media was used (Peptone 10 g, NaCl 10 g and yeast extract 5 g/L). The electrophoresis of the samples was done according to the following procedure⁴¹.

 

250 mg of agarose was dissolved in 25 mL of tris- acetate-EDTA (TAE)  buffer (4.84 g Tris base, pH 8.0, 0.5 M EDTA/1 Ltr) by boiling, when the gel attains ~55⁰C, it was poured into the gel cassette fitted with comb. The gel was allowed to solidify, and then carefully the comb was removed. The gel was placed in the electrophoresis chamber flooded with TAE buffer. Load 20 μL of DNA sample (mixed with bromophenol blue dye @ 1:1 ratio) was loaded carefully into the wells, along with standard DNA marker with the constant 50 V of electricity for 45 min. Later gel was removed carefully and stained with ethidium bromide (ETBR) solution (10 μg/mL) for 10-15 min and the bands were observed under UV gel documentation system.

 

3. RESULT AND DISCUSSION:

The physical and analytical data of the synthesized ligand HL and its Fe(III), Co(II), Ni(II) and Zn(II) complexes are given in the Table 1. The molar conductance of the complexes was measured in DMF at 10^-3 M concentration. Measured conductance values of these complexes are too low to account for their electrolytic behavior.

 

3.1 IR, ¹HNMR and mass spectra of ligand HL

The IR spectrum of ligand showed absorption band at 3361, 3129, 1644, 1176 and 1588 cm^-1 due to CO-NH, quinoline NH, C=O and C=S attached quinoline molecule respectively.

 

The ¹HNMR spectrum of the ligand HL in d₆-DMSO at room temperature, showed signals at δ14.00 (s, 1H, NH quinoline), δ12.34 (s, H-NHCO), δ9.45 (s, 1H, N=CH), δ7.39-9.23 (m, 8H, ArH) and δ4.02 (s, 3H, OCH₃ ), respectively.

 

Scheme I Synthesis of ligand HL

 

The mass spectrum of ligand HL showed a molecular ion peak at M^+. 427, 429 (9%, 3%) which on loss of chloride radical and C₈H₆NS radical simultaneously gave a fragment ion peak at m/z 244 (100%) which is also a base peak. This on loss of HC₂N species gave a fragment ion recorded at m/z 205 (40%) which on simultaneous loss of methoxy radical and NH=C=O species gave a fragment ion recorded at m/z 132 (7%).

 

This fragmentation pattern is in consistency with the structure of ligand HL. IR, ¹HNMR and mass spectral data proves the formation of ligand 3-chloro-6-methoxy-N^’-((2-thioxo-1, 2-dihydroquinolin-3-yl)methylene)benzo[b] thiophene-2-carboxyhydrazide by the reaction between 3-chloro-6-methoxy benzo[b]thiophene-2-carboxyhydrazide and 2-thioxo-1,2-dihydroquinoline-3-carbaldehyde.

 

Scheme 2 Synthesis of metal complexes of ligand HL

 

The probable fragmentation pattern of the mass spectrum of ligand is depicted in Scheme 3.

 

3.2 IR and mass data of the Complexes of ligand HL

All the complexes showed the absence of peaks at 3361 and 1644 cm^-1 in the complexes which were there in the IR spectrum of ligand clearly indicates enolization of amide carbonyl function and bonding of the enolized carbonyl oxygen to the metal atom via deprotonation. Appearance of new band due to C=N-N=C in all the complexes in the range 1594-1599 cm^-1 confirms the enolization of amide carbonyl during complexation. Appearance of peak in the range 3129-3152 cm^-1 in all the complexes at about the same region as in the ligand indicates the non-involvement of quinoline NH in complexation.

 

Scheme 3 Mass fragmentation pattern of ligand HL

 

Appearance of band in the region 1182-1165 cm^-1 indicates that the coordination of sulfur atom of quinoline 2-thione function to the central metal atoms in all the complexes. The decrease in the absorption frequency of C=N by 67-36 cm^-1 which appeared in the region  1552-1521 cm^-1 in all the complexes when compared to that of ligand indicates the involvement of nitrogen atom of azomethine group in coordination with the metal ions.

 

Appearance a broad hump in the range in the region 3419- 3411 cm^-1 in case of all the metal complexes except Zn(II) complexes of ligand indicates the presence of water molecule as water of lattice in Fe(III) and Co(II) and coordinated water molecules in case of Ni(II) complexes.

 

The IR regions are purely tentative because of various skeletal vibrations associated with metal and ligand vibrations. The bands of weak intensity observed in the region 560-531 cm^-1 in case of all the complexes of the ligand HL are assigned to M-O vibrations and the bands in the region 460-432 cm^-1 to M-N vibrations. The bands observed in the range 372-344 cm^-1 are due to M-S vibrations. The band in the region 318-307 cm^-1 are due to M-Cl vibrations of all the complexes except Fe(III) and Co(II) complex Table 2.

 

 

The mass spectrum of Fe(III) complex of ligand HL showed  M+1^+. peak at 980.82, 982.82 (70%, 38%) this on loss of hydrogen radical gave a fragment ion peak at 979.82,981.82 (100%, 33%) which is equivalent to its molecular weight and also a base peak. This on simultaneous loss of two water molecules, two molecules of C₁₀H₆NOSCl species, HCN radical, chloride radical and C₁₀H₆N₂S species gave a fragment ion recorded at m/z 248.82 (8%). This fragmentation pattern is in consistency with its structure. The probable fragmentation pattern of the mass spectrum of Fe(III) complex is depicted in Scheme 4.

 

The mass spectrum of Co(II) complex of ligand HL exhibited a molecular ion peak appeared at  M^+. 982.93, 984.93 (61%, 25%) which is equal to its molecular weight. This on simultaneous expulsion of 4 hydrogen radicals gave a fragment ion peak at 978.93, 980.93 (100%, 33%) which is also a base peak.

Table 2 IR Data of ligand HL and its complexes

HL = Ligand

 

Table 4 X-ray data of Co(II) Complex of ligand HL

Peak	2Ө	Ө	SinӨ	Sin2Ө	h k l	d		h2+k2+l2	a in Ao
						Calc.	Observ.
1	10.560	5.28	0.092	0.0084	1 0 0	8.3695	8.3705	1	8.37
2	10.850	5.42	0.094	0.0089	1 0 0	8.1567	8.1474	1	8.34
3	18.070	9.03	0.156	0.0246	1 1 1	4.9075	4.9051	3	8.38
4	22.350	11.17	0.193	0.0375	2 0  0	3.9752	3.9745	4	8.39
5	22.650	11.32	0.196	0.0384	2 0  0	3.9245	3.9225	5	8.38
6	22.840	11.42	0.197	0.0391	2 0 0	3.8908	3.8903	5	8.38
7	23.100	11.55	0.200	0.0400	2 1 0	3.8461	3.8471	5	8.39
8	25.290	12.64	0.218	0.0478	2 1 0	3.5191	3.5187	6	8.39
9	25.920	12.96	0.224	0.0502	2 1 1	3.4344	3.4346	6	8.39
10	26.110	13.05	0.225	0.0509	2 1 1	3.4100	3.4100	6	8.38
11	26.370	13.18	0.228	0.0519	2 1 1	3.3771	3.3770	6	8.38
12	27.590	13.79	0.238	0.0567	-	3.2312	3.2304	7	8.39
13	28.930	14.46	0.249	0.0623	-	3.0837	3.0837	7	8.39
14	29.310	14.65	0.252	0.0639	-	3.0446	3.0446	8	8.39
15	30.430	15.21	0.262	0.0688	2 2 0	2.9355	2.9351	8	8.39
16	30.560	15.28	0.263	0.0694	2 2 0	2.9222	2.9229	8	8.40
17	37.450	18.72	0.320	0.1029	2 2 2	2.3995	2.3994	12	8.39
18	40.750	20.37	0.348	0.1211	3 2 1	2.2126	2.2124	14	8.39
19	46.010	23.00	0.390	0.1526	4 1 1	1.9708	1.9710	18	8.39
20	50.420	25.21	0.425	0.1813	4 2 1	1.8079	1.8084	22	8.40
21	51.970	25.98	0.438	0.1918	-	1.7579	1.7581	23	8.40
22	56.640	28.32	0.474	0.2249	5 1 1	1.6234	1.6237	27	8.40
23	75.130	37.56	0.609	0.3714	6 2 2	1.2633	1.2635	44	8.40

 

Table 5 X-ray data of Zn(II) Complex of ligand HL

Peak	2Ө	Ө	SinӨ	Sin2Ө	h k l	d		h2+k2+l2	a in Ao
						Calc.	Obser.
1	5.820	2.91	0.0507	0.0025	1 -  -	15.187	15.172	1	15.17
2	6.100	3.05	0.0532	0.0028	1 -  -	14.473	14.477	1	15.19
3	6.390	3.19	0.0557	0.0031	1 -  -	13.824	13.820	1	15.13
4	6.580	3.29	0.0573	0.0032	1 1  1	13.438	13.421	1	15.12
5	10.370	5.18	0.0903	0.0081	1 1  1	8.527	8.523	3	15.17
6	10.560	5.28	0.0920	0.0084	1 1  1	8.369	8.370	3	15.18
7	10.920	5.46	0.0951	0.0090	2 1  0	8.096	8.095	4	15.16
8	13.340	6.67	0.1161	0.0134	-	6.632	6.631	5	15.18
9	22.980	11.49	0.1991	0.0396	3 2 2	3.867	3.866	15	15.18
10	23.530	11.76	0.2038	0.0415	3 2 2	3.789	3.777	16	15.18
11	23.930	11.96	0.2073	0.0429	-	3.714	3.715	17	15.18
12	25.580	12.79	0.2213	0.0489	-	3.479	3.479	19	15.18
13	26.350	13.17	0.2279	0.0519	4 2 0	3.378	3.379	20	15.18
14	26.600	13.30	0.2300	0.0529	4 2 0	3.347	3.348	21	15.18
15	27.690	13.84	0.2392	0.0572	3 3 2	3.219	3.218	22	15.18
16	27.860	13.93	0.2407	0.0579	3 3 2	3.199	3.199	23	15.19
17	28.410	14.20	0.2453	0.0601	-	3.139	3.139	23	15.18
18	28.570	14.28	0.2466	0.0608	-	3.122	3.121	24	15.18
19	30.090	15.04	0.2594	0.0672	5 1 0	2.968	2.967	26	15.18

 

This on simultaneous loss of 4 water molecules, C₁₀H₆NO₂SCl species, CN radical, chloride radical and NCS radical gave another fragment ion peak at m/z 548.93 (25%). This fragmentation pattern is in consistency with its structure. The probable fragmentation pattern of the mass spectrum of Co(II) complex is depicted in Scheme 5.

 

3.3 Electronic spectra of Fe(III), Co(II) and Ni(II) complexes of the ligand HL

Electronic spectral data of the Fe(III), Co(II) and Ni(II) complexes of the ligand HL are given in Table-3. Electronic spectral studies of all these complexes were carried out in DMF at 10^-3 M concentration.

Table 3 Electronic spectral data of complex of the ligand HL

Compounds	Electronic spectral data (in cm-1)
	ν1	ν2	ν3	ν4
Fe-complex	17645	19474	26008	-
Co-complex	10680	15880	19986	-
Ni-complex	10480	16328	25510	-

 

3.3.1 Fe(III) complex

The ground state of high spin octahedral coordinated Fe(III) complex is ⁶A_1g. The four lowest energy bands are due to the transition ⁶A_1g to ⁴T_1g, ⁴T_2g, ⁴E_g and ⁴A_1g excited states. For high spin Fe(III) complex three spin allowed transitions are reported⁴² around 16800 cm^-1 (ν₁), 20500 cm^-1 (ν₂) and 25900 cm^-1 (ν₃) which are characteristics of octahedral geometry. The iron complex of the ligand HL in the present study displayed three bands at 17645 cm^-1, 19474 cm^-1 and 26008 cm^-1 which corresponds to ν₁, ν₂ and ν₃ transitions respectively. These observed values for Fe(III) complex in its visible spectrum are in agreement with the literature values⁴³ and thereby proved octahedral geometry for the Fe(III) complex of the ligand HL.

 

3.3.2 Co(II) complex

Cobalt(II) is d⁷ ion exists both in octahedral and tetrahedral geometry. In octahedral Co(II) complexes three spin allowed transitions are expected corresponding to the transitions ⁴T_1g(F) → ⁴T_2g(F) (ν₁) (~ 8000 cm^-1),    ⁴T_1g(F) → ⁴A_2g(F) (ν₂) (~ 16000 cm^-1) and ⁴T_1g(F) → ⁴T_2g(P) (ν₃) (~ 20000 cm^-1).

Chandra⁴⁴  have reported three bands corresponding to ν₁, ν₂ and ν₃ transition around 9000 cm^-1, 14500 cm^-1, 20620 cm^-1 respectively for octahedral Co(II) complex. The Co(II) complex of the ligand HL  under present study has showed three bands at 10680 cm^-1, 15880 cm^-1 and 19986 cm^-1 due to ⁴T_1g(F) → ⁴T_2g(F) (ν₁), ⁴T_1g(F) → ⁴A_2g(F) (ν₂) and ⁴T_1g(F) → ⁴T_2g(P) (ν₃) transitions respectively. These transitions suggests octahedral geometry for Co(II) complex. The broad nature of ν₁ band which may be best assigned to the envelope of the transitions from ⁴E_g(⁴T_2g) to the component ⁴B_2g and ⁴E_g of ⁴T_2g  which is the characteristic of tetragonally distorted octahedral geometry.⁴²

 

3.3.3 Ni(II) complex

The ground state of Ni(II) in octahedral co-ordination is ³A_2g(t_2g ⁶eg²). Ni(II) complexes shows three transitions in an octahedral field viz., ³A_2g(F) → ³T_2g(F) (ν₁) (7000-13000 cm^-1), ³A_2g(F) → ³T_1g(F) (ν₂) (11000- 20000 cm^-1) and ³A_2g(F) → ³T_1g(P) (ν₃) (20000-27000 cm^-1).

 

Figgis⁴⁵ has reported bands in the region ~ 10000, ~12000 and ~ 25000 cm^-1 due to ³A_2g(F) → ³T_1g(P) (ν₃), ³A_2g(F) → ³T_1g(F) (ν₂) and ³A_2g(F) → ³T_2g(F) (ν₁) for the transitions mentioned above which are characteristics of octahedral geometry.⁴⁶

 

The electronic spectrum of Ni(II) complex of the ligand HL under present investigation exhibited three bands in the region 10480 cm^-1, 16328 cm^-1 and 25510 cm^-1 which are assigned to ³A_2g(F) → ³T_2g(F) (ν₁),  ³A_2g(F) → ³T_1g(F) (ν₂) and ³A_2g(F) → ³T_1g(P) (ν₃) transitions respectively. All these observations favor the octahedral geometry for Ni(II) complex of the present study.

 

3.4 Magnetic susceptibility data

Magnetic susceptibility measurements of the complexes were performed at room temperature. The magnetic moment values for the various Co(II) complexes is in the range 4.70-5.20 BM is for octahedral complexes. In the present investigation the observed magnetic moment value for Co(II) complex is 5.07 BM indicates octahedral geometry for the Co(II) complex.⁴³ For Ni(II)  complex the observed magnetic moment value is 2.88 BM which is well within the expected range 2.83-4.00BM.⁴⁴ For Ni(II) complex with octahedral stereochemistry. For Fe(III) complex the observed magnetic moment value is 5.85 BM which corresponds to high spin octahedral complex.⁴⁷ The Zn(II) complex is diamagnetic in nature, the magnetic moment value of Zn(II) complex are also consistent with a square planar geometry⁴⁸ Table 1.

 

3.5 Molar Conductance

The molar conductance of the complexes was measured in DMF at 10^-3 M concentration. Measured conductance values of these complexes are too low to account for their electrolytic behavior for their non-electrolytic behavior Table 1.

 

3.6 Powder X-ray diffraction (XRD) studies

The compounds were soluble in polar organic solvents (DMSO & DMF). We did not obtain crystals suitable for single crystal studies. In order to test the degree of crystallinity of the synthesized complexes, we obtained the powder XRD pattern of Co(II) and Zn(II) complexes.

 

The powder XRD pattern of Co(II) and Zn(II) complexes have provided in supplementary material. The Co(II) complex showed twenty three reflections in the range 10.56-75.13^o (2θ), arising the diffractions of X-ray by the planes of complex. The 2θ values with maximum intensity of peak for the complex is found to be 10.85^o which corresponds to d=8.14 Å is almost equal to calculated d=8.15 Å. All important peaks have been indexed and observed values of interplanar distance (d) have been compared with the calculated ones. The unit cell calculations were performed for cubic system and the (h²+ k²+ l²) values were determined. The presence of forbidden numbers (7 and 23) indicates that the Co(II) complex may belong to hexagonal or tetragonal system Table 4.

 

Similar calculations were performed for Zn(II) complex and this complex showed nineteen reflections in the range 5.82-30.09^o (2θ). The presence of forbidden numbers (15 and 23) indicates that the Zn(II) complex may belong to hexagonal or tetragonal system Table 5.

 

3.7 Thermal studies

From TG curve, information related to the thermal stabilities, composition of the initial sample, intermediate compounds that formed and the final residue could be obtained.

The TGA study on Ni[C₂₀H₁₇N₃O₄S₂Cl₂] was carried out in the temperature range 35 ^°C to 1000 ^°C.

 

3.7.1 Ni(II) complex

The decomposition studies of the Ni(II) complex Ni[C₂₀H₁₇N₃O₄S₂Cl₂] has been carried out. In the thermogram of the Ni [C₂₀H₁₇N₃O₄S₂Cl₂], the loss of 2H₂O was observed at 305 ^°C, with weight loss of 7%.

 

 

 

Table 6 Thermal decomposition of Ni(II) complex of ligand HL

 

 

Table 7 Antibacterial activity of ligand HL and its complexes

Compound	1000 ppm		500 ppm		250 ppm		125 ppm
	S. aureus	P.  aeruginosa	S. aureus	P.  aeruginosa	S.  aureus	P.  aeruginosa	S. aureus	P.  aeruginosa
HL	8	4	6	3	5	3	4	2
Fe-complex	6	5	5	5	4	3	2	3
Co-complex	4	4	3	3	3	2	2	2
Ni-complex	6	5	4	4	3	3	3	2
Zn-complex	5	5	4	3	3	3	2	2
DMF(Control)	-	-	-	-	-	-	-	-
Gentamycin	8	6	8	6	7	5	5	4

HL = Ligand

 

 

Table 8 Antifungal activity of ligand HL and its complexes

Compound	1000ppm		500ppm		250ppm		125ppm
	A. Niger	A. Flavus	A. Niger	A. Flavus	A. Niger	A. Flavus	A. Niger	A. Flavus
HL	6	8	6	6	4	6	4	6
Fe-complex	6	8	6	8	4	8	3	6
Co-complex	6	8	6	8	6	8	5	6
Ni-complex	12	6	10	6	8	6	6	4
Zn-complex	6	6	6	6	5	6	4	4
DMF(Control)	-	-	-	-	-	-	-	-
Fluconazole	10	10	8	10	8	10	8	8

HL = Ligand

 

 

This practical weight loss of 7% is in accordance with the theoretical weight loss 6.47%. The resultant intermediate complex underwent further degradation and gave another break at 340 ^°C with a weight loss of 33% which corresponds to the elimination of the HCl and C₁₀H₆N species from the above intermediate complex. This theoretical weight loss corresponds to 33.89% is agreeing well with the observed value 33%. The third stage of decomposition occurs at 463 ^°C, with weight loss of 17% which corresponds to the decomposition of N₂ and SH species. This practical weight loss 17% is in accordance with theoretical weight loss of 17.48%. Thereafter compound showed a gradual decomposition up to 1000 ^°C and onwards. The weight of residue corresponds to nickel oxide. The thermal decomposition of Ni [C₂₀H₁₇N₃O₄S₂Cl₂] with probable assignments is given in Table 6.

 

 

3.8 Antimicrobial activity

The antibacterial activity of the newly synthesized ligand and its complexes were studied in a series of dilutions 1000 ppm, 500 ppm, 250 ppm and 125 ppm by cup-plate method using nutrient agar as media. Ligand HL and Ni(II) complex exhibited high activity towards S. aureus in vitro tests at minimum inhibitory concentration of 125 ppm. Fe(III) and Co(II) complexes were active at minimum inhibitory concentrations of 250 ppm against S. aureus when compared with standard drug Gentamycin at 125 ppm.

 

Fe(III) complex exhibited high activity towards P. aeruginosa in vitro at minimum inhibitory concentration of 125 ppm. Ligand HL, Ni(II) and Zn(II) complexes were active at minimum inhibitory concentrations of 250 ppm against P. aeruginosa. Co(II) showed less activity 500 ppm when compared with standard drug Gentamycin 125 ppm Table 7.

 

The antifungal activity of all the ligand and its complexes were studied in a series of dilutions 1000 ppm/mL, 500 ppm, 250 ppm and 125 ppm by SDA method. Ni(II) complex exhibited high activity towards A. niger in vitro tests at minimum inhibitory concentration of 125 ppm. Co(II) and Zn(II) complexes were moderately active at minimum inhibitory concentrations of 250 ppm against A. niger. Ligand HL and Fe(III) complex showed less activity at 500 ppm when compared with standard drug Fluconazole at 125 ppm.

 

Ligand HL, Fe(III) and Co(II) complexes exhibited high activity towards A. flavus tests at minimum inhibitory concentration of 125 ppm. Ni(II) and Zn(II) complexes were moderately active at minimum inhibitory concentrations of 250 ppm against A. flavus when compared with standard drug Fluconazole at 125 ppm Table 8.

 

3.9 Antioxidant activity

The antioxidant activity results indicate that there is a great possibility of finding potent antioxidants in our newly synthesized compounds for free radical scavenging activity. The ligand HL has exhibited very good free radical scavenging activity, Fe(III), Co(II), Ni(II) and Zn(II) complexes of ligand HL showed less activity compared with standards Vit-C and Vit-E. The bar graph represents the percentage of free radical scavenging activities is shown in Fig. 1.

 

Fig.1: Antioxidant activity of ligand HL and its complexes

 

Fig 2 DNA-cleavage activity of ligand HL and its complexes

 

3.10 DNA cleavage activity

In the present study, the calf-thymus (CT) DNA gel electrophoresis experiment was conducted at 37 ^oC using our newly synthesized ligand and its complexes, as can be seen from the result all the samples showed complete cleavage of DNA as compared to control DNA at100 µg/mL.

 

4. CONCLUSION:

All the prepared complexes of the ligand HL are coloured, amorphous in nature and stable in air. The physical and analytical data of the ligand HL and its complexes are given in the Table-1. Analytical data justified 1:2 Stoichiometry with empirical formula (M(L)₂) to Fe(III) and Co(II) complexes. The Ni(II) and Zn(II) complexes of the ligand HL exhibited 1:1 stoichiometry with the empirical formula [M(L) (Cl) (2H₂O) and [M(L)(Cl)]  respectively.⁴⁹ Ligand and complexes showed good antimicrobial, antioxidant and DNA cleavage activities.

 

5. ACKNOWLEDGEMENTS:

The authors are thankful to Directors, Indian Institute Technology, Madras, Indian Institute of Science, Bangalore, BioGenics Reasearch and Training Center in Biotechnology Hubli. Chairmen, Department of Physics and Department of Material Science of Gulbarga University, Gulbarga for spectral data. Authors are thankful to Chairman, Department of chemistry, Gulbarga University, Gulbarga for providing the laboratory facilities.The authors are thankful to UGC-Research Fellowship for Science Meritorious Student (RFSMS) Delhi for providing fellowship.

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Received on 14.12.2012         Modified on 20.12.2012

Accepted on 22.12.2012         © AJRC All right reserved