Synthesis and Characterization of Biologically Active Mixed Ligand complexes of 8-Hydroxyquinoline and Salicylaldehyde.

 

Dnyaneshwar S. Wankhede¹*, P. A. Kulkarni², Nikhil S. Jadhav¹, Manisha D. Gurle¹, Pradip B. Wagh¹, and Omkar Shankarrao³

¹School of Chemical Sciences, Swami Ramanand Teerth Marathwada University, Nanded-431606, Maharashtra State, India.

²Yeshwant Mahavidyalaya, Nanded-431605, Maharashtra State, India.

³School of Life Sciences, Swami Ramanand Teerth Marathwada University, Nanded-431606, Maharashtra State, India.

*Corresponding Author E-mail: dswchem@yahoo.co.in

In this communication the synthesis of mixed ligand transition metal complexes of Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) with 8-hydroxyquinoline as a primary ligand and salicylaldehyde as a secondary ligand is reported. The synthesized complexes were characterized using instrumental techniques IR, UV, Magnetic measurements and conductivity measurements in DMSO. All complexes show very low conductance values indicating their non electrolytic nature and they have an octahedral geometry. These complexes have been screened in vitro for their  antimicrobial activity.  In the present  series of mixed ligand metal complexes, the Cu(II) Complex (C₁₇H₁₃Cl₂CuNO₃) and Zn(II) Complex (C₁₇H₁₃Cl₂ZnNO₃) showed good antibacterial as well as antifungal activity.

 

 

 

INTRODUCTION:

The interest in the synthesis of mixed ligand complexes has been increased to a great extent recently. The role of mixed ligand metal complexes in biological process has been well recognized^1-2. The interest may be due to the ease of preparation of these complexes and their wide applications in various fields.

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Some 8-hydroxyquinoline ligand complexes possess antibacterial and antifungal properties and are widely used in creams and ointments for the treatment of skin diseases³. Patel and Kharadi have synthesized a series of 8-hydroxyquinoline derivatives and their transition metal complexes^4-8. It has been found that a majority of the metal complexes with 8-hydroxyquinoline possess biological activity⁹. Anti-tumor activity of some mixed ligand complexes has also been reported. The antibacterial and anti-fungal properties of a range of copper (II) complexes have been evaluated against several pathogenic bacteria and fungi^10-11.

 

Bhodke et al. reported 8-hydroxyquinoline and various amino acids mixed ligand metal complexes¹². The use of 8-Hydroxyquinoline as an in vivo agent in micro biological system has been reviewed¹³. Mashalya et al.¹⁴ reported mixed ligand transition metal complexes of                            8-hydroxyquinoline and oxalic acid.

 

Literature survey reveals that although a lot of work has been done in this area of synthesis and characterization of mixed ligand metal complexes, still no report has been published on mixed ligand metal complexes of transition metals with 8-hydroxyquinoline and salicylaldehyde. Hence herein we report, synthesis and characterization of mixed ligand metal complexes of transition metals such as Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) with biologically active 8-hydroxyquinoline and salicyaldehyde. The synthesized complexes are well characterized from spectral data such as IR, Electronic spectra and with magnetic susceptibility and molar conductance measurements. The synthesized complexes are also screened for their antimicrobial activities such as antibacterial and antifungal.

                                                                                                              

 

MATERIALS AND METHODS:

The chemicals used in the present study such as salicylaldehyde and metal chlorides were purchased from  S. D. Fine chemicals. 8-hydroxyquinoline was purchased from Qualigens chemicals. Methanol used as a solvent was purchased from Merck and was used after distillation. Molecular sieves were used for the drying purpose of solvent.

 

Infrared spectra were recorded as KBr pellets in the region 400-4000 cm^-1 on Shimadzu Spectrometer. The electronic spectra were recorded in DMSO on a Shimadzu UV-1600 spectrophotometer. The molar conductance measurements were performed in DMSO solvent using Equiptronics conductivity meter with inbuilt magnetic stirrer (Model Eq-664) [cell const. = 1] at room temperature. The magnetic susceptibility values were measured at room temperature on a Gouy balance using CuSO₄.5H₂O as a Calibrant.

 

Synthesis of mixed ligand metal complexes:

The mixed ligand transition metal complexes were synthesized by the reaction of metal chlorides with 8-Hydroxyquinoline and salicylaldehyde. Methanolic solutions of metal chlorides, 8-hydroxyquinoline and salicyladehyde were prepared by dissolving appropriate quantities of the reactants so as to give 1:1:1 mole ratio. The hot methanolic solutions were mixed and the reaction mixture was refluxed up to 2 hrs, on rotamantle with magnetic stirring at 40-60 °C. The progress of the reaction was monitored using thin layer chromatography technique in a solvent system 20% (Ethylacetate + Pet ether).  After completion of the reaction, the obtained coloured complexes were cooled to room temperature and filtered. The complexes were washed with methanol 2-3 times and air dried. All the mixed ligand metal complexes were stable at room temperature, were recrystalized from ethanol and melting point was checked. The yield of the reaction was found to be 80-85 %. Scheme for the synthesis of mixed ligand metal complexes is as shown below.  The physical and analytical data for the synthesized complexes is shown below in Table 1.

 

 

Scheme 1: Synthesis of mixed ligand metal complexes, where, M = Fe(III), Co(II), Ni(II), Cu(II) & Zn(II).

 

Table 1: Analytical data of synthesized metal complexes

Sr.No.	Molecular formula	Molecular weight (g)	Colour	Melting point °C	Yield (%)	pH
1.	Fe Complex C17H13Cl2FeNO3	406.04	Black	280-285	85	7
2.	Co Complex C17H13Cl2CoNO3	409.13	Dark yellow	190-195	80	7
3.	Ni Complex C17H13 Cl2NiNO3	408.89	Dark green	275-280	84	7
4.	Cu Complex C17H13Cl2CuNO3	413.74	Green	240-245	82	7
5.	Zn Complex C17H13Cl2ZnNO3	415.59	Green	230-235	85	7

Bioassays of mixed ligand metal complexes:

The total four pathogenic test strains were selected on the basis of their clinical importance and their systematic position. Of two fungi, one unicellular fungi (Candida albicans, ATCC 14053) and a filamentous fungi (Aspergillus niger, MTCC 1781) and of two bacteria, one gram positive bacteria (Staphylococcus aureus, ATCC 10832) and one gram negative bacteria (Escherichia coli, ATCC 33684) were selected. The microbial cultures were purchased from National Collection of Industrial Microorganisms (NCIM), NCL, Pune 411 008, India. The bacterial cultures were subcultured and maintained on Nutrient agar, whereas fungi on Potato dextrose agar medium.

 

Minimum Inhibitory Concentration (MIC):

The stock solution of each test compounds were prepared by dissolving 5mg of compound in methanol (5ml) to give a solution of 1000 μg/ml and further concentrations of  100-900 μg/ml obtained  by serial dilution factors.

 

The MIC for series of mixed ligand metal complexes against the S. aureus, E. coli and C. albicans were determined by tube dilution method¹⁵. A series of culture tubes was prepared (Nutrient broth for bacteria and Sabouraud’s dextrose broth for C. albicans) and inoculated with the same number of microorganisms (10⁶ cfu/ml). Each tube contains medium with an increasing concentration of the compounds (100-1000 μg/ml). After incubation, at 30⁰ C for 24 hrs the tubes were checked for visible growth (turbidity). The MIC value of each compound was considered having lowest concentration of agent that completely inhibits the growth of the test organism. The MIC for the mixed ligand metal complexes against A. niger was determined by disc diffusion technique¹⁵. 0.1 ml of A. niger (10⁶ cfu/ml) culture medium was inoculated into Petri plate containing potato dextrose agar medium. After aseptically spreading of culture by glass spreader on agar medium, known amounts of (100-1000 μg/ml) mixed ligand metal complexes were added to filter paper discs, which were then placed on the surface of the agar. During incubation, at 30⁰ C for 48 hrs, the complex compound diffuses from the disc into the agar, establishing a gradient; further the chemical diffuses away from the filter paper, the lower is the concentration of the agent. At some distance from the disc, the effective MIC is reached. Beyond this point the microorganism grows, but closer to the disc, growth was absent.

 

Antimicrobial activity:

Antifungal and antibacterial activity of mixed ligand metal complexes was determined by agar well diffusion method¹⁶. All the microbial cultures were adjusted to 0.5 McFarland standards, which is visually comparable to a microbial suspension of approximately 1.5 × 10⁸ cfu/ml. 20-25 mL of nutrient agar and potato dextrose agar medium was poured into each Petri plate and plates were swabbed with 100 μl inocula of the test microorganisms, nutrient agar plates for bacteria and potato dextrose agar plates for fungi. Inoculated plates, kept for 15 min for adsorption. Using sterile cork borer, 10 mm diameter, wells were bored into the seeded agar plates and these were loaded with a 100 μl (1000 μg/ml) of each test compound reconstituted in the methanol.

 

All the plates were incubated at 30 ⁰C. The zone of inhibition was measured around the well after 24-48 hrs for antibacterial and 48 to 72 hrs for antifungal activity. The only methanol was used as a negative control. The standard Tetracycline (200 μg/ml) and Amphotericin B (200 μg/ml) was used as positive control for antibacterial and antifungal activity respectively.

 

RESULT AND DISCUSSION:

Thin layer chromatography:

TLC of the all mixed ligand metal complexes was performed by the using silica gel G in polar solvent system pet-ether and ethyl acetate (20%) and iodine vapors as the spray reagent. The starting materials were disappeared and all the mixed ligand complexes showed single spot at the completion of reaction.

 

Solubility:

Solubility of all the synthesized mixed ligand metal complexes along with 8-hydroxyquinoline was checked by using different solvents. The synthesized complexes are soluble in MeOH, EtOH, DMF, DMSO , partially soluble in chloroform and insoluble in CCl₄ and DCM except  Zinc complex, that  is partially soluble in DMF and DMSO.  (Table 2.)

 

 

Table 2: Solubility of synthesized metal complexes

Sr. No.	Compounds	MeOH	EtOH	CHCl3	CCl4	DCM	DMF	DMSO
1	8-HQ L1	S	S	S	S	S	S	S
2	Fe Complex C17H13Cl2FeNO3	S	S	PS	I	I	S	S
3	Co Complex C17H13Cl2CoNO3	S	S	PS	I	I	S	S
4	Ni Complex C17H13 Cl2NiNO3	S	S	PS	I	I	S	S
5	Cu Complex C17H13Cl2CuNO3	S	S	PS	I	I	S	S
6	Zn Complex C17H13Cl2ZnNO3	S	S	PS	I	I	PS	PS

S= Soluble, PS= Partially Soluble, I= Insoluble

 

Molar conductance:

The molar conductance of synthesized mixed ligand metal complexes were measured using 10^-3 M solution prepared in DMSO at the room temperature, the conductance values are in the range of 10-30 [ohm^-1mol^-1 Cm^2‑]. The obtained values are very much low to account for any dissociation of complexes in DMSO solvent, hence indicating towards the nonelectrolytic nature of the complexes¹⁷.

 

Infrared spectra:

In the IR spectra of mixed ligand complexes absorption frequency at 3300, 1276, 868, 740 Cm^-1 are attributed to OH stretching, bending, rocking and wagging vibrations respectively due to the presence of water molecule. The presence of rocking band indicate coordinated water molecule by the metal complexes. The n(C-O) appeared at 1106.22 Cm^-1 and the position of the bands slightly varies with the metal. The n(C-O) is observed in the free oxine molecule at 1090 Cm^-1. This is shifted to higher frequency in the all mixed ligand complexes in between 1090 Cm^-1-1110 Cm^-1. The keto frequency of free salicylaldehyde  n(C=O), have been reported at 1660,1650,1640 Cm^-1,  these bands shifted to lower wave numbers on the chelation with metal ions¹⁸. Above information clearly indicates that the co-ordination of 8-hydroxyquinoline complexes is in octahedral in nature.

 

Electronic spectra:

The electronic spectra of mixed ligand metal complexes have been measured in DMSO solvent between the 200-600 nm at room temperature.  The spectrum of Fe(III) complex show two bands at 265 and 345 nm which can be assigned to P®P* and n®P* transitions of the primary ligand 8-hydroxyquinoline. A spin forbidden band ⁶A_1g®⁴T_1g expected^19,20 in the region 450-600 nm for Fe (III) high spin complex is observed in the region 465-575 nm, indicating towards high spin Fe(III) complex formation. In the spectrum of Co(II) complex two bands at 275 and 320 nm are observed which can be assigned to the primary ligand. The third band observed at 420 nm can be ascribed to ⁴T_1g® ⁴T_1g (P) transition, indicating towards octahedral Co(II) complex formation which is also supported with the magnetic property measurements. The spectrum of Ni(II) complex show two bands at 275 and 335 nm assigned to transitions of the primary ligand. The third band observed at 540 nm can be assigned to ³A_2g®³T_1g (F) transition, indicating towards octahedral Ni(II) complex formation. Similar type of observation in case of Co(II) and Ni(II) complexes is also reported by Ababei et al²¹. In case of Copper (II) complex two bands observed at 270 and 365 nm can be assigned to the primary ligand. The only expected band in case of copper (II) complexes is usually observed at 650 nm region, which is not scanned in this study. In case of Zinc (II) complex no d-d transition is expected and the bands observed at 270 and 335 nm can be assigned to ligand.

 

Bioassays of mixed ligand metal complexes:

The 8-Hydroxyquinoline L₁ and their mixed ligand metal complexes were screened for antibacterial and antifungal activity. All the tested metal complexes possessed variable antibacterial activity against S. aureus and E. coli as well as  antifungal activity against A. niger and C. albicans. In the whole series, the MIC (minimum inhibitory concentration) of metal complexes was ranged between 100-700 µg/ml against bacteria and 200-1000 µg/ml against fungi (figure 1). Among all tested mixed ligand metal complexes, the Cu(II) Complex (C₁₇H₁₃Cl₂CuNO₃) showed remarkable MIC values, 300, 200,100 and 100 µg/ml against A. niger, C. albicans, S. aureus and E. coli respectively. The Ndosiri reported, the MIC value  of Mn(II), Co(II), Cu(II), and Zn(II) mixed-ligand complexes against the unicellular fungi Candida and Cryptococcus of various species viz. C. albicans, C. parapsilosis, C. krusei and C. neoformis in the range 3-80 mg/ml²². For remaining mixed ligand metal complexes MIC values against bacterial and fungal pathogens are represented in figure 1.

 

Positive controls produced significantly sized inhibition zones against the tested bacteria and fungi; however, negative control produced no observable inhibitory effect against any of the test organism. The tested chemical compounds showed zone of inhibition ranging between 12-22 mm against the bacteria and 10-16mm against the fungi (figure 2). On the basis of zone of inhibition produced against the test bacterium, Cu(II) Complex (C₁₇H₁₃Cl₂CuNO₃) and Zn (II) Complex (C₁₇H₁₃Cl₂ZnNO₃) were found to be most effective against S. aureus with zone of inhibition ranging between 22 mm and 20 mm respectively Biological activities of mixed ligand Zr(IV) complexes against S. aureus, E. faecium, C. albicans, C. krusei and A. fumigates  indicates the zone of inhibition in the range of  12-28 mm for antibacterial and 10-22mm for antifungal activity determined by using agar well diffusion method²³. Copper(II)-Pyridine-2,5-dicarboxylate Complexes with 2-Aminomethylpyridine and 8-Hydroxyquinoline  showed antimicrobial activity against S. aureus, E. coli, S. epidermidis, P. aeroginosa and C. albicans with the diameters of zone inhibition ranging between 7–10 mm at 200 μg/disc concentration²⁴. Overall, among all complexes, the Cu(II) Complex (C₁₇H₁₃Cl₂CuNO₃) and Zn(II) Complex (C₁₇H₁₃Cl₂ZnNO₃) showed good antifungal and antibacterial activity as shown  (figure 1 and 2).

 

 

Table 3: Infrared spectral data of the mixed ligand metal complexes

Compound	C=O(cm-1)	C-O (cm-1)	M-O(cm-1)	M-N(cm-1)
Fe Complex  C17H13Cl2FeNO3	1614.49	1106.22	523.70	450
Co Complex  C17H13 Cl2CoNO3	1663.68	1108.15	555.90	455
Ni Complex  C17H13 Cl2NiNO3	1661.75	1105.06	598.92	423
Cu Complex  C17H13Cl2CuNO3	1663.68	1104.29	570.04	450
Zn Complex  C17H13Cl2ZnNO3	1663.61	1107.19	541.06	442

 

Table 4: Electronic spectral data, molar conductance and Magnetic moments for complexes

Figure 1:  The MIC (µg/ml) of mixed ligand metal complexes against A.niger , C. albicans, S. aureus and  E. coli.

 

Figure 2:  The antifungal (against A.niger and C. albicans) and antibacterial (against S. aureus  and  E. coli) activity of mixed ligand metal complexes

The antimicrobial studies suggested that the 8-Hydroxyquinoline L₁ was found to be biologically active and their metal complexes showed significantly enhanced antibacterial and antifungal activity in comparison to the free ligands. The increased activity of mixed ligand complexes was may be due to its enhanced lipophilicity than free ligand as consequences rapidly penetration of the compound into the lipid membranes of cell and target to block the metabolic pathways leads to death of microorganisms²⁵.

 

CONCLUSION:

The complexes were obtained as coloured powder and were characterized using IR spectra, electronic spectra, magnetic measurements and molar conductance. From the antimicrobial activity data it is observed that the complexes exhibit higher activity than the free ligands, metal salts. The increased antimicrobial activity of the complexes observed may be due to the metal chelation. All metal complexes are more potent biocidal than the ligand. Cu(II) and Zn(II) are highly active metal complexes as compared to other metal complexes. 

 

ACKNOWLEDGEMENTS:

Corresponding author Dr. D. S. Wankhede is thankful to Dr. B. R. Arbad, Professor, Department of Chemistry,      Dr. B. A. M. University, Aurangabad, for his constant encouragement during the research work of this paper. The authors are grateful to analytical facilities provided by the sophisticated analytical instrumentation facility center Chandigarh.

 

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Received on 16.04.2013       Modified on 20.05.2013

Accepted on 25.05.2013      © AJRC All right reserved