Present work describes the synthesis of Schiff bases and their metal complexes. For the synthesis of these compounds, different glass wares are used which were oven and flame dried. All the commercially available reagents and chemicals were used as such without further purification. By using standard procedures solvents were dried, where necessary. Thin-layer chromatography was used to determine the progress and completion of reactions. In thin-layer chromatography (TLC) commercial aluminium backed Merck plates, coated with silica gel GF254 (0.25 mm thick), was used having a fluorescent indicator which was active at 254 nm wavelength. UV light at 254 nm was used to visualize the chromatograms.
5-aminosalicylic acid (9.7 mmol) was dissolved in 15 ml methanol in beaker, (9.7 mmol) of 2-hydroxy-3-methoxybenzaldehyde was also dissolved in 15 ml methanol. Mix these two solutions in round bottom flask and 3-4 drops of acetic acid was also added. Reflux it for about two and half hours. Reddish orange colour precipitate appeared. Reaction mixture was cooled to room temperature and placed in refrigerator for about 24 hours. The precipitated solid was filtered and washed with methanol.
Schiff base (3.5 mmol) was dissolved in 10 ml ethanol in a beaker and metal salt (1.75 mmol) was dissolved in 10 ml ethanol in a beaker. Mix these two solutions in round bottom flask. Reflux it for four hours. Metal to ligand ratio was 1:2 (w/w). Coloured precipitates appear. Filter these precipitate and washed with ethanol.
Disc diffusion method was used to determine the antibacterial activities against two gram positive bacteria (B. subtillus, S. aureus) and two Gram negative bacteria (E. coli, P. multocida). Nutrient agar media was prepared by suspending the 28 g nutrient agar in one liter distilled water. The media was autoclaved for 15 min at 121°C. Nutrient media (100 mL) was taken in beaker, to the media 100 µL of inocula was added and mixed well. Transfer the mixture (media and inocula) to the petri plate. Sample (100 µL) was applied on each flat paper discs. These discs were laid on the growth medium having bacterial strain in petri plates and incubated it for 37°C for 24 hours for the growth of bacteria. The active samples inhibit the growth of bacteria and clear zone were formed. Zone reader was used to measure the zone of inhibition .
Disc diffusion method was used to determine the antifungal activities against Ganoderma lucidum, Alterharia lterhata, Penicillium notatum and Aspergillus flavus. Potato dextrose agar media was prepared. The media was autoclaved for 15 min at 121°C. Potato dextrose agar media (100 mL) was taken in beaker, to the media 100 µL of inocula was added and mixed well. Transfer the mixture (media and inocula) to the petri plate. Sample (100 µL) was applied on each flat paper discs. These discs were laid on the growth medium having fungal strain in petri plates and incubated it for 28°C for 48 hours for the growth of fungus. The active samples inhibit the growth of fungus and clear zone were formed. Zone reader was used to measure the zone of inhibition .
|Sample code||R1||R2||Physical state||Molecular formula||Molecular mass (g/mol)||Melting Point (°C)||Yield (%)|
|Schiff base 1||5-aminosalicylic acid||2-hydroxy-3-methoxybenz-aldehyde||Reddish orange solid||C15H13O5N||287||207-211||71|
|1Cu||Schiff base 1||Copper acetate||Greenish solid||C30H24O10N2Cu||635.5||291-294||68|
|1Cd||Schiff base 1||Cadmium acetate||Light orange Solid||C30H24O10N2Cd||684.4||314-319||65|
|1Co||Schiff base 1||Cobalt acetate||Dark yellowish Solid||C30H24O10N2Co||631||301-304||71|
|1Zn||Schiff base 1||Zinc acetate||Light yellowish Solid||C30H24O10N2Zn||637.4||321-325||69|
|1Ni||Schiff base 1||Nickel Chloride||Yellowish solid||C30H24O10N2Ni||630||333-337||73|
|Sample Code||Dist. Water||Methanol||Ethanol||Ethyl acetate||n-Hexane||CHCl3||DMF||DMSO|
|Schiff base 1||I||I||S||S||PS||S||S||S|
I = Insoluble
S = Soluble
PS = Partially soluble
The Schiff bases and complexes were screened for their antibacterial activity against four bacterial strains by using disc diffusion method. Two of which, gram positive bacteria (B. subtillus, S. aureus) and two gram negative bacteria (E. coli, P. multocida). Results are summarized in (Table 3). In order to compare the results, Ampicillin is used as standard control drug. It was observed from the tabulated data of that the antibacterial activity of the Schiff bases are lower than the standard drug Ampicillin and the complexes showed higher activity than that of Schiff bases which are used as ligands. From the results, it is clear that complexes showed more activity towards Gram positive bacteria such as B. subtillus and S. aureus as compare to Gram negative strains such as E. coli and P. multocida due to the fact that structures of cell wall of Gram negative bacteria’s are more complex as compare to Gram positive bacteria’s.
|Sample No.||Bacterial inhibition zone (mm)|
|E. coli||S. aureus||B. subtilis||P. multocida|
|Schiff base 1||14.5||15.5||22.5||16|
Values are mean of three individual replicates
Concentration = 10 mg/ml of DMSO - = No activity
In vitro tests for antifungal activity of Schiff bases and their complexes were screened against four fungal strains Ganoderma lucidum, Alterharia lterhata, Penicillium notatum and Aspergillus flavus by using disc diffusion method. Fluconazole was used as standard control drug for the determination of antifungal activity. The results of antifungal activity were shown in (Table 4). According to results, complexes (1Cd, 1Ni) show more activity against Ganoderma lucidum, Alterharia lternaria and Penicillium notatum. The increased activity of complexes may be due to coordination of Schiff base with transition metals .
|Sample No.||Fungal inhibition zone (mm)|
|G. lucidum||A. lternaria||P. notatum||A. flavus|
|Schiff base 1||26||19.5||24||17.5|
Values are mean of three individual replicates
Concentration = 10mg/ml of DMSO - = No activity
The infrared spectroscopy of Schiff base 1 and complexes (1Cu-1Ni) were recorded in the range 4000-250 cm-1 as KBr pellets. IR spectra of Schiff bases and their complexes showed remarkable broad bands as shown in (Table 5). The IR spectra provide valuable information regarding the nature of functional groups attached to ligand and metal atom in complexes. In order to study the bonding bond of Schiff base and metal complexes, IR spectrum of free ligand was compared with the spectra of complexes. A band in free Schiff base appeared at 1638.06 cm-1 was due to C=N vibrational frequency. The azomethine peak (1638.06 cm-1) in Schiff base 1 was shifted to lower value 1610.56-1623.64 cm-1 suggesting the coordination. The shifting of this group to lower frequency in the metal complexes when compared to free Schiff base, suggested the coordination of metal ion through nitrogen atom of azomethine group. It is expected that coordination of metal atom would reduce the electron density in the azomethine link and thus lower the –HC=N absorption. Peaks in the range 540.07-582.50 cm-1 in complexes were due to M-N bonding and peaks in the range 435.04-480.82 cm-1 in complexes were due to M-O bonding .
|Sample code||ʋ (C = N) (cm-1)||ʋ (-OCH3) (cm-1)||ʋ (M-N) (cm-1)||ʋ (M-O) (cm-1)|
|Schiff base 1||1638.06||1242.16||-||-|
Authors are cordially thankful to Chairman, Department of Chemistry, Government College University, and Faisalabad-Pakistan for providing chemical of AR grade and instrumentations.
Authors declare that they have no conflict of interest.
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