Physiochemical and Antibacterial Activity Investigation on Noble Schiff Base Cu(II) Complex

Schiff base ligand and its Cu(II) complex had been synthesized by the condensation reaction of isatin with amino acids (cysteine / glycine / leucine / alanine ). The Structure and spectral properties of ligand and complex were confirmed by UV, FT-IR and some physiochemical measurements. The spectral properties showed that it was a distorted tetrahedral geometry with a tridentate ligand and chloride ion. IR spectral studies show the binding sites of the Schiff base ligand with the metal ion. Molar conductance data and magnetic susceptibility measurements give evidence for monomeric and non-electrolytic nature of the complexes. The Schiff base Cu(II) complex was subjected to antimicrobial studies screened by employing the Disc Diffusion method. All the synthesized complexes showed strong antibacterial activity.


Introduction
Multidentate ligands are extensively used for the preparation of metal complexes with interesting properties [1][2][3]. Among these ligands, Schiff bases containing nitrogen and phenolic oxygen donor atoms are of considerable interest due to their potential application in catalysis, medicine and material science [4][5][6][7]. Transition metal complexes of these ligands exhibit varying configurations, structural lability and sensitivity to molecular environments. The central metal ions in these complexes act as active sites for pharmacological agent. This feature is employed for modeling active sites in biological systems.
Amino acids and Isatin are important to the pharmaceutical industry, since they have antibacterial and antitubercular action. Schiff bases obtained by the condensation of Isatin and amino acids in presence of potassium hydroxide find application as antituberculosis compounds. They also find application in the biophysical and clinical studies as metal ligand luminescence probes [8]. Recently, few mixed ligand complexes containing heterocyclic amine as secondary ligands and few Schiff base containing complexes have studied in our laboratory [9][10][11]. Therefore, in view of our interest in synthesis of new Schiff base complexes, which might find application as pharmacological and as luminescence probes, we have synthesized and characterized Cu(II) metal ion complexes of noble Schiff base formed by the condensation of isatin and amino acids in presence of potassium hydroxide.

Experimental
Infrared spectra disc were recorded as KBr with a NICOLET 310, FTIR spectrophotometer, Belgium, from 4000-225 cm -1 . Magnetic measurements have been carried out in a Sherwood Scientific magnetic susceptibility balance at room temperature. The measurements of magnetic susceptibilities were made at about constant temperature. The electronic spectra of the ligand and complex in UV-Vis region were obtained in DMSO Solutions using a Shimadzu UV-1200 Spectrophotometer in the range of 200-800 nm.

Synthesis of Schiff Bases
To a stirring solution of isatin (0.735 g, 0.005 mole) dissolved in 25mL of ethanol, a solution of amino acids (cysteine 0.6058 g, glycine 0.3754 g, leucine 0.6559 g, alanine 0.4455 g, 0.005 mole) dissolved in 10mL water was added drop wise and in this mixture, a solution of potassium hydroxide (0.2805 g, 0.005 mole) dissolved in 10 mL water was added slowly. This has resulted a dark red solution, which was refluxed for 6h. The reaction mixture was cooled and kept for evaporation at room temperature leading to isolation of solid product. The product thus formed was filtered washed several times with ethanol and finally with diethyl ether and dried in vacuum over anhydrous CaCl 2 . The product was found to be soluble in DMF and DMSO. The target Schiff bases were synthesized according to

Synthesis of Metal Complexes
To a stirring solution of isatin (0.735 g, 0.005 mol) dissolved in 25mL of ethanol, a solution of amino acids (cysteine 0.6058 g / glycine 0.3754 g / leucine 0.6559 g / alanine 0.4455 g, 0.005 mol) dissolved in 10mL water was added drop wise and in this mixture, a solution of potassium hydroxide (0.2805 g, 0.005 mol) dissolved in 10 mL water was added slowly. This has resulted a dark red solution and a solution of cupric chloride (0.8525 g, 0.005 mol) dissolved in 10 mL water was added slowly to this solution. Then dark red color turns to gray color and the mixture was refluxed for 6 hours leading to the isolation of solid product. The complexes thus formed were filtered and washed several times with ethanol to remove any traces of unreacted starting materials and were further washed with diethyl ether and dried in vacuum over anhydrous CaCl 2 . The complexes were soluble in DMF and DMSO.

Physical Measurement
The melting point of the complexes prepared for this study is given in Table 1. All the complexes are non-electrolyte.
The observed values of effective magnetic moment (µ eff ) of the complexes at room temperature are given in Table 1. From the above data it is showed that all the complexes are paramagnetic in nature [11,12].

Characterizations by UV-Visible Spectra
Because of the relatively low symmetry of the environments in which the Cu 2+ ion is characteristically found, detailed interpretations of the spectra and magnetic properties are somewhat complicated, even though one is dealing with the equivalent of a one -electron case [16]. Virtually all complexes and compounds are blue or green. Exceptions are generally caused by strong UV bandscharge transfer bands -tailing off into the blue end of the visible spectrum, thus causing the substances to appear red or brown [17]. The observed λ max values are used to predict the geometry around the central metal ion in the complex. The electronic spectra of Ligand show similar absorption bands and obtain at 290 nm. These bands shows the presence of n→n* and π→π* transitions of their azomethines chromophore group and aromatic ring. But in the Spectra of complexes, slightly shifts are observed in the position and intensity of these bands as com-pare to that of ligand which might be due to the coordination of metal with the ligand. All the synthesized complexes showed d-d transitions at 410 nm which is due to 2 B 1g → 2 A 1g transition indicated the distorted tetrahedral structure [18].  Any chemical or biological agent that either destroys or inhibits the growth of microorganisms is called antimicrobial agent. The susceptibility of microorganism to antimicrobial agent can be determined in vitro by a number of methods. The disc diffusion technique [19] is widely acceptable for preliminary investigations of materials which are suspected to possess antimicrobial properties. Diffusion procedure, as normally used in essentially a qualitative test, which allocates organism of the susceptible, intermediate (moderately susceptible) or resistant categories. The antibacterial activity of the test complexes were determined by using the dose of 10 µg/disc. The results of antibacterial activity measured in terms of zone of inhibition is shown in Table-

Conclusion
Magnetic susceptibility data indicated that all the complexes are paramagnetic in nature. Conductivity measurement indicated that all the complexes are nonelectrolyte in nature. IR spectral data showed the ligand coordinate with metal complexes through O and N atoms. UV-Vis data showed the presence of d-d transition and paramagnetic nature nature of the complexes. There are two possibilities Cu(I) / Cu(II) state. Where, the Cu(II) oxidation state is more stable than Cu(I) for complexes with nitrogen or oxygen electron donating ligands because of the CFSE. The d 9 of Cu(II) configuration has more CFSE than d 10 of Cu(I) which is zero. Keeping this in mind and judging from all the experimental data it was concluded that the geometry around Cu(II) ions in the respective complexes might be distorted tetrahedral and structures of complexes have been proposed as shown in figures 5-8. All the complexes showed strong antibacterial activity.