INTRODUCTION:
Metal complexes play an essential role in agriculture, pharmaceutical and industrial chemistry. Ligand, a metal surrounded by a cluster of ions or molecules is used for the preparation of complex compounds named as Schiff base1 which are condensation products of primary amines and aldehydes or ketones.
The Schiff bases are widely studied because of increasing recognition of their role in biological systems2, 3. Their complexes have been studied for their interesting and important properties such as complexing ability towards some toxic metals4, their ability to reversibly bind oxygen5. The interaction between metal ions and amino acids is of considerable interest as metals for metal - protein reactions and models in a variety of biological systems6. Schiff base complexes have remained an important and popular area of research due to their simple synthesis, versatility and diverse range of applications7. Many potent antibacterial and antifungal Schiff base compounds were reported8 - 11. Some heterocyclic Schiff bases12 - 14 can act as antibacterial agent.
This paper describes the synthesis, characterization and antimicrobial studies of Schiff base complexes of 3-pyridine carboxaldehyde and amino acids. The amino acids used were histidine and tryptophan.
The resulting complexes were studied by magnetic measurements and IR spectra. The new Schiff base and its complexes were tested for antibacterial activity against pathogenic bacterial species. Klebsiella Pneumonia, Pseudomonas aeroginosa, E.Coli, Staphylococcus aureus, Proteus and also for antifungal activity against Aspergillus niger.
MATERIALS AND METHODS:
MATERIALS
All the chemicals and solvents used were of A R grade. All the reagents used for the preparation of the Schiff bases were obtained from Sigma Aldrich. Metal salts were purchased from Loba Chemie.
Elemental analyses of the ligand and complexes were done on a Perkin-Elemer 240 analyzer. IR spectra of the ligands and their complexes have been recorded in KBr pellets at Shimadzu FT – IR 8201 spectrophotometer in 4000 – 200 cm‑1. Magnetic susceptibility measurements on powder form of the complexes were recorded with a Gouy’s balance by using mercuric tetrathiocyanato cobaltate (II) as a calibrant at 250C.
General procedure for preparation of Schiff bases
Schiff bases have been synthesized by adding the methanolic solution of aldehyde with amino acids in equimolar ratio. The reaction mixture was then refluxed on a water bath for about 4 - 5 hrs. The condensation product was filtered, thoroughly washed with ethanol, ether and dried in vacuum.
General procedure for preparation of metal complexes
All the complexes were prepared by mixing hot ethanolic solution of Schiff base ligand with the corresponding metal salts with constant stirring. The resulting mixture was refluxed on a water bath for about 6 – 12 hrs. A coloured product appeared on standing and cooling the solution. The complexes were filtered, washed with ether and dried under reduced pressure over anhydrous CaCl2.
Preparation of Schiff base
i) 3-Pyridine carboxaldehyde with histidine (L1)
Ligand (L1)
Scheme - 1
ii) 3-pyridine carboxaldehyde with Tryptophan (L2)
Ligand (L1)
Scheme – 2
Preparation of metal complexes
Hot methanolic solution of ligand L1, L2 (0.05 mol) and hot methanolic solution of the Cu (II), Ni (II) metal salts (0.05 mol) were mixed with stirring. The mixture was refluxed for 2 – 3 hours at 70 – 800 C on a water bath. On cooling coloured solid metal complex were precipitated out. The product was filtered, washed with cold methanol and dried under vacuum over P4O10.
Biological activity
The invitro biological activity of the Schiff base and its metal complexes were tested against the bacteria Klebsiella pneumonia, Pseudomonas aeroginosa, E. Coli, Staphylococcus aureus and Proteus by disc diffusion method using nutrient agar as medium and Amikacin as control. The antifungal activities of the compounds were also tested by the invitro well diffusion method against the fungi Aspergillus niger on potato dextrose agar as the medium and Flucanazole as control. Each of the compounds was dissolved in dimethyl sulfoxide and solutions of the concentrations were prepared separately. In a typical procedure, a well was made on agar medium inoculated with microorganisms. The well was filled with the test solution using a micro pipette and the plate was incubated 24 hrs for bacteria at 370C and 72 hrs for fungi at 300C. During this period, the test solution diffused and the growth of the inoculated microorganisms was affected. The inhibition zone was developed at which the concentration was noted.
RESULT AND DISCUSSION:
All the complexes are stable at room temperature, non - hygroscopic, insoluble in water but slightly soluble in methanol and ethanol and soluble in DMF and DMSO.
Elemental Analysis:
The Schiff base and metal complexes are subjected to elemental analysis. The results of elemental analysis (C, H and N) with molecular formula are presented in Table. 1 The results obtained are in good agreement with those calculated for suggested formula.
The results of the selected IR measurements were tabulated in Table II.
The free Schiff base show the characteristic of 3 - substituted pyridine ring (774 cm-), imino group – C = N
( 1590 cm-1 ), – 
– group in the acid (
1631 cm-1 ), free – OH group of the carboxyl group ( 3319 cm-1
). The IR spectrum of the ligand is compared with the spectra of complexes
(fig. 1 and 2). The presence of
bond
of the imidazole ring at 3063 cm-1 confirms the unbounded nature of
the NH group. The C = N bond 1590 cm-1 is shifted to lower frequency
suggesting coordination of both the N atoms to metal. Another absorption band
at 1022.96cm-1 is assigned to the coordinated nitrato group with the
central metal atom. The absorption band around 3319 cm-1 is assigned
to the free OH group of the carboxyl group.
