Synthesis, Characterization and antimicrobial activity of Co(II), Ni(II), Cu(II) and Zn(II) complexes N- O- S donor ligands.

Vinita Gupta¹, Sanchita Singh¹, Y.KGupta²*

¹Department of Chemistry, Agra College, Agra, U.P, India

²Head Department of Chemistry, B K Birla Institute of Engineering and Technology, Pilani, Rajasthan, India

*Corresponding Author E-mail: ykgbkbiet@rediffmail.com, ykgbkbiet123@gmail.com

ABSTRACT:

The Co(II), Ni(II), Cu(II) and Zn(II) complexes of the composition 1:1:1 molar ratio, (ML₁L₂) (where L₁=diphenylamine-2-mercapto-2-carboxylic acid and L₂=2-furyl glyoxalanthranilic acid have been synthesized and characterized by elemental analyses, ¹H-NMR, IR, electronic spectral data and magnetic susceptibility measurements. The synthesized ligands and their metal complexes were screened for their antimicrobial activity against two bacteria Staphylococcus aureus (gram +ve) and Escherichia coli (gram -ve) and two fungi Aspergillus niger and Apergillus flavus by Serial Dilution Method. Metal complexes are more active than their ligands.

KEYWORDS: Mixed ligand complexes, Antimicrobial Activity.

INTRODUCTION:

The Co(II), Ni(II), Cu(II) and Zn(II) complexes contain nitrogen, oxygen and sulphur donor ligands due to their versatile application in the biological studies including antifungal[1-3] antibacterial[4-5] anti-inflammatory[6] antipyretic, herbicidal[7] anticancer[8] and antiulcer[9] activities. They also play an important role in the activation of enzymes and are used for storage as well as for transport of active materials [10]. The study of mixed ligand complex formation is relevant in the field of analytical chemistry. They also play the important role in the field of biological and environmental chemistry [11,12]. These facts prompted us to synthesize new mixed ligand transition metal complexes, especially biologically important cobalt, nickel, copper and zinc complexes, to study the combined antimicrobial activity effect of ligands in conjugation with the metal ions [13,14].

EXPERIMENTAL:

Physical and analytical measurements

All chemicals used were of A.R. Grade. Molecular weights of the compounds were determined by Cryoscopic method [14] in DMSO. Co, Ni, Cu, and Zn were estimated by precipitating them as pyridine complex [15]. ¹H-NMR spectra were recorded on Bruker Biospin spectrometer DPX-300MHz in DMSO-d₆ solvent. IR spectra were recorded on Jasco Model JR report-100 spectrophotometer in KBr medium. The electronic spectra of metal complexes were recorded in dry DMF/DMSO at room temperature on Shimadzu digital double beam spectrophotometer (Model UV 150-150.02).The magnetic susceptibilities were measured at room temperature on Gouy balance using CuSO₄.5H₂O as calibrant.

Synthesis of furyl-2-glyoxal

15 ml ethanolic solution of 6.87 g (0.062 mol) SeO₂ was mixed with 6.22 ml (0.062 mol) 2- acetyl furan in 20 ml ethanol .This mixture was refluxed for 6 hr. The reduced Se metal was removed by filtration. The solvent obtained was removed from the filtrate by distillation. On fractionation, the residue under 30 cm vigreux column yielded a dark yellow colored furan-2-glyoxal.

Synthesis of 2-furyl glyoxal-anthranilic acid (L₁)

2.7 ml (0.025 mol) furyl-2-glyoxal was dissolved in 15 ml ethanol. To this, 3.42 g (0.025 mol) anthranilic acid dissolved in 20 ml ethanol was added and refluxed for 4 h. The solution thus obtained was concentrated to one third of its volume and allowed to cool in refrigerator. The obtained solid was filtered and washed with ethanol and recrystallized from benzene. It was finally dried in a vacuum desiccator over anhydrous CaCl₂.

Synthesis of diphenylamine-2-mercapto-2’-Carboxylic acid (L₂)

3.75 g (0.03 mol) o-aminothiophenol and 4.69 g (0.03 mol) o-chloro-benzoic acid was suspended in 75 ml of distilled water in the presence of copper oxide. Aqueous solution of this mixture, K₂CO₃ was added in slightly excess to neutralize. The mixture was reflux on an oil bath for 4 h and again refluxes for 1 h after adding 1 g of activated charcoal to decolorize. The contents of flask were filtered, while hot and concentrated to its one fourth of original volume on a water bath and allow to cool and dilute HC1 was added for precipitation. The obtained precipitate was filtered, washed with water and dried in a desiccator over anhydrous CaC1₂ and recrystallized from alcohol to obtain grey colored compound.

Synthesis of mixed ligand complexes

0.123 g (0.0005 mol) diphenylamine-2-mercapto-2’-Carboxylic acid dissolved in 10 ml ethanol was mixed with 10 ml ethanolic solution of 0.122 g (0.0005 mol). The mixture, an ethanolic solution (0.0005 mol) of 0.125 g cobalt acetate tetrahydrate / 0.098 g copper acetate monohydrate / 0.124 g nickel acetate tetrahydrate / 0.109 g zinc acetate dihydrate was added with continuous stirring. The contents were refluxed about 2 - 3 h at pH 6-7. The products obtained were washed with ethanol, filtered, and dried over anhydrous CaC1₂ in vacuum desiccator.

Antimicrobial activity

Antimicrobial activities of the synthesized compounds were screened by determining their Minimum Inhibitory Concentration (MIC) values against two bacteria Escherichia coli (gram-ve) and Staphylococcus aureus (gram+ve) keeping incubation period 24 hours at 37°C and two fungi Aspergillus flavus and Apergillus niger, (Incubation period 96 hours at 28°C) using Serial Dilution Method[16] in suitable nutrient medium (6.0 g peptone, 1.5 g beef extract, 3.0 g yeast extract, 1.0 g dextrose and 1.5 g agar only for slant in 1 litre distill water for bacteria and 10.0 g peptone, 20.5 g agar only for slant, 20.0 g dextrose in one litre distilled water for fungi).

RESULTS AND DISCUSSION:

All the compounds were stable and colored at room temperature. Physical and analytical data of metal complexes and ligands have been given in Table 1.

IR Spectral studies

IR spectra of ligand 2-furyl glyoxal-anthranilic acid (L₁) exhibited bands in the region 1620 cm^-1(>C=N-) [17], 1490 m^{- 1}(furan ring breathing vibrations) and 1755cm^-1 (>C=O stretching vibrations[18]). In the IR spectra of complexes >C=O and >C=N stretching vibrations of the ligand have been shifted towards lower region by 30-40 cm^-1 which indicated the participation of oxygen of >C=O and nitrogen of >C=N- moieties in the coordination with metal ions. The ligands, 2-furyl glyoxal-anthranilic acid (L₁) and diphenylamine-2-mercapto-2 -Carboxylic acid (L₂), exhibit bands in the region 3490-3480 cm^-1 and 1710-1705 cm^-1 due to -OH and >C=O stretching vibrations of-COOH [19] groups. In the IR spectra of metal complexes the bands due to –OH stretching vibrations have disappeared which indicated the coordination of ligands with the metal ion via deprotonation of carboxylic groups. In the case of diphenylamine-2-mercapto-2’-Carboxylic acid (L₂), a band at 3140 cm^-1 due to -NH stretching vibrations has been observed which has shifted towards higher frequency region by 30 cm^-1, in the IR spectra of metal complexes, indicating the involvement of NH group in the coordination with metal ions. A weak band at 2650 cm^-1 due to –SH stretching vibrations [19] has been appeared in the ligand diphenylamine-2-mercapto-2’-Carboxylic acid (L₂). The position of this band has shifted towards lower region by 40 cm^-1, in metal complexes, which indicate the involvement of –SH group in the coordination with metal ions. The appearance of new bands in the region 545-535, 450-445 and 330-325 cm^-1 due to MO, M-N and M-S bonds respectively [20] further indicated the coordination of ligands with metal ions through nitrogen, sulphur and oxygen atoms.

Table 1: Physical and Analytical data of ligands and their Mixed Ligand Complexes

S. No.	Compounds.	Molecular formula	Colour	% Analysis : Found / (Calcd.)					Mol. weight found/ (Cal.)
				C	H	N	S	M
1.	L1	C13H9O4N	Black	65.00 (64.19)	3.88 (3.70)	5.57 (5.76)	-	-	237 (243)
2.	L2	C13H11O2NS	Grey	64.12 (63.67)	4.60 (4.48)	5.45 (5.70)	12.50 (13.06)	-	238 (245)
3.	Co- L2- L1	Co (C26H18O6N2S)	Brown	58.40 (57.14)	3.80 (3.29)	5.79 (5.12)	5.60 (5.68)	10.81 (10.98)	554 (545)
4.	Ni- L2- L1	Ni (C26H18O6N2S)	Greenish black	57.76 (57.24)	3.60 (3.30)	5.53 (5.13)	5.43 (5.87)	11.90 (10.82)	553 (547)
5.	Cu- L2- L1	Cu(C26H18O6N2S)	Black	57.82 (56.77)	3.18 (3.27)	4.78 (5.09)	6.76 (5.82)	11.90 (11.55)	555 (549)
6.	Zn- L2- L1	Zn(C26H15O6N2S)	Brown	57.56 (56.62)	3.17 (3.26)	5.69 (5.08)	5.47 (5.80)	11.39 (11.79)	561 (551)

¹H- NMR spectral studies

¹H- NMR spectra of ligand 2-furyl glyoxal-anthranilic acid (L₁) showed two multiplets in the region d 7.72-6.61 ppm , d 8.14 -7.64 ppm and one singlet at d 7.54 ppm due to furyl ring protons, aromatic ring protons and >CH=N proton respectively. The ligand diphenylamine-2-mercapto-2’-Carboxylic acid (L₂) exhibited two multipltes in the region d 6.83-6.30 ppm , d 7.88-6.86 ppm and two singlets at d 4.12 ppm and d 3.23 ppm due to–SH and–NH- protons respectively. Both the ligands show singlets in the region d 11.34- 11.24 ppm due to –OH proton of –COOH group. ¹H-NMR spectra of complexes showed a complex multiple in the region d 7.94- 6.28 ppm which is due to four different types of protons of aromatic rings. The singlets due to protons of >CH=N , -NH , and -SH have shifted to downfield in the range d 7.98-7.96, d 4.66-4.51 and d 3.40-3.35 ppm respectively which is due to decrease electron density and deshielding of protons, as a result of participation of the >CH=N, -NH and –SH, groups in coordination[21-22]. The singlets due to -COOH proton have disappeared in the spectra of complexes which indicated the deprotonation of this group in both ligands during coordination with metal ions [23].

Electronic spectra studies and magnetic susceptibility measurements Cobalt (II) complex

The electronic spectra of Co(II)- L₂- L₁ complex displayed three bands at 8250, 15640 and 19670 cm^-1 corresponding to the transitions ⁴T_1g → ⁴T_2g(F), ⁴T_1g → ⁴A_2g(F), and ⁴T_1g → ⁴T_1g (P) respectively[24]. These transitions and the measured value of magnetic moment 4.82 BM suggest the octahedral geometry for this complex.

Nickel (II) complex

The electronic spectra of Ni(II)- L₂- L₁ complex exhibited three bands in the region 10800, 16700 and 25670 cm^-1 resultant to the transitions ³A_2g → ³T_2g, ³A_{2g →}³T_1g and ⁴A_{2g →}³T_lg (P) respectively for octahedral geometry[24]. The magnetic moment value of the complex was found 3.16 BM which was close to the value of octahedral environment.

Copper (II) complex

The electronic spectra of Cu(II) - L₂- L₁ complex displayed three bands at 12000, 16500 and 20000 cm^-1due to ²B_1g→²B_2g, ²B_1g →²A_2g and ²B_1g →²E_1g transitions respectively which suggested that Cu(II) complex has distorted octahedral geometry[25]. The magnetic moment of the complex was found 1.83 BM which confirmed the octahedral geometry.

Zinc (II) complexes

The mixed ligand complex of Zn(II) have no significant absorption bands in electronic spectra were obtained due to its diamagnetic nature. On the basis of elemental analyses, ¹H-NMR, IR, magnetic moment values and electronic spectral data suggest the probable structure of complexes shown in Fig. 1.

Fig.1

Where M = Co(II),Ni (II),Cu(II) and Zn(II)

The MIC values (Table.2) in general infer that the metal complexes as whole are more active than their fragments. The basis for the increased antimicrobial activity [26] of the complexes as compared to the ligands may be due to the fact that the chelation reduces the polarity of the metal ion by partial sharing of its positive charge with the donor groups and possibly π-electron delocalization within the whole chelate ring. This process thus increases the lipophilicity of the complexes, therefore enhances the penetration through the lipid layer of cell membrane and restricts further multiplicity of the microorganism. Among the metal complexes Cu (II) complex was found most active against both bacteria and fungi. The high antimicrobial activity of Cu (II) complex may be due to their higher stability constant of copper complexes.

Table 2: The Minimum Inhibitory Concentration (X 1O^-3) values of ligands and Mixed Ligand Complexes.

S. No.	Compounds.	Bacteria		Fungi
		Staphylococcus aureus	Escherichia coli	Aspergillus niger	Aspergillus flavus
1.	L1	20.57	20.57	10.28	10.28
2.	L2	20.40	20.40	10.20	10.20
3.	Co- L2- L1	5.47	5.47	2.73	2.73
4.	Ni- L2- L1	5.39	5.39	2.69	2.69
5.	Cu- L2- L1	5.18	5.18	2.59	2.59
6.	Zn- L2- L1	5.26	5.26	2.63	2.63

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Received on 06.12.2014 Accepted on 20.12.2014

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