1. INTRODUCTION:

Proteins are the basis of protoplasm and are present in all living organisms. All proteins are polymers, composed of amino acids. The monomers that are covalently linked in sequence to each other by peptide bond. Proteins exhibit enormous diversity of biological function and are the most important final products of the informal pathways. The biological importance of the amino acids includes specific functions involving the metabolism of individual amino acids.

The heterocyclic amines, although they contain tertiary nitrogen [1-7], coordinate readily with the metal ion. Most of the heterocyclic amines are used as corrosion inhibitor [8-10] and their complexes with platinum and copper have been tested as antitumor [11]and antibacterial agents [12]. 3- amino pyridine has strong anticonvulsive effects [13-14].

The chlorinated species of 8-hydroxy quinoline has been proved as antibacterial and antifungal agents [15], and the imido derivatives are administered to overcome zinc deficiency in animals [16]. Derivatives of copper and tin of 8-hydroxyquinoline are antifouling agents [17-18] and 8-hydroxyquinoline itself protects the industrial oil from the growth of bacteria and fungi in them [19-20]. Studies on the metal complexes of heterocyclic amine bases have been carried out by many other workers and thus confirmed the complexation ability of amine with metal [21-31].

Previously, we studied electronic properties of N₂O₄ schiff base ligand containing metal complexes of Cd(II), Pd(II), Hg(II) and Zr(IV) [32-34]. In this study, we described a systematic study of preparation and characterization of mixed ligand Cu(II) metal complexes and also their functions as antimicrobial actions.

2. EXPERIMENTAL:

2.1 Measurements and materials

Electronic spectra were recorded on a Thermoelectron Nicolet evolution 300 UV-Vis spectrophotometer. All chemicals were commercial products and were used as supplied.

2.2. General method for the preparation of the complexes of the type [M(X)(L)]:

M²⁺ + X + L ® [M(X)(L)]

Where,

M²⁺ = Cu(II) ion

X = Amino acids such as, Glycine and Cysteine Heterocyclic amine bases such as Pyridine, Quinoline, Isoquinoline; 2-Picoline, 4-picoline, 8-hydroxyquinoline etc.

An ethanolic solution of Cu(II) chloride salts (2 m mol) and ethanolic potassium hydroxide solution of ‘X’ acid (4 m mol) were mixed and heated gently with stirring for half an hour. No precipitate was observed, and then secondary ligand in calculated ratio was added and stirring until complex precipitated. The precipitate were filtered, washed several times with alcohol and then dried in a vacuum desiccator over phosphorus pentaoxide (P₂O₅).

3. RESULTS AND DISCUSSION:

All the complexes are non-hygroscopic and stable at room temperature. The Cu(II) complexes are insoluble in common organic solvents but are soluble in DMSO, DMF and CHCl₃.

3.1 Elemental analysis and conductivity measurement

The physical properties of the complexes are tabulated in Table 1. The molar conductance of 10^-3M solution of the complexes in DMSO were measured at 30°C. The molar conductance values are in the range 0.98 to 2.45 W^–1 cm² mole^-1 (Table 1). These values are lower than expected for an electrolyte. There observations suggest that all the complexes are non-electrolyte in DMSO at room temperature and proved that the anions are covalently bonded in all the cases.

3.2 IR spectral studies

Outstanding features of the IR spectra of the complexes are tabulated in the Table 2. The complexes display bands in the regions 1575-1642 and 1106-1140 cm^-1 due to ν(C=O) and ν(C-O) respectively, significantly lower than that of free ligand ν(C=O) =1760 cm^-1 and ν(C-O) =1220 cm^-1 respectively indicating the coordination of metal ion through its carboxylate anion. The disappearance of the n(O-H) mode observed in the free amino acid molecule clearly indicate the loss of proton for O-H group upon coordination, revealing that acids are di-negative bidentate ligand coordinating through the carboxylate anion .The complexes show ν(N-H) and v(-NH₂) bands respectively from 3212-3400cm^-1 and 3058-3239 cm^-1 which is significantly lower than the free ligand (amines bands 3500 cm^-1 and amino band 3200-3400 cm^-1) clearly suggest the coordination of amines group through nitrogen atoms of amine bases.

The in-plane and out-of-plane ring deformation modes of heterocyclic amines observed at 680 and 620 cm^-1 respectively undergo a positive shift in mixed ligand complexes confirming their coordination through nitrogen [35].The presence of metal nitrogen bonding in the complexes is evident from the appearance of n(M-N) modes at 493-410 cm^-1 in the spectra of the complexes and v(M-O) appearance at 673-760).

Table 1: Physical properties of Cu(II) complexes

Complexes	Colour	Melting point (± 0.52)	Molar conductance W^-1 cm² mol^-1	Magnetic moment m_eff (B.M.)
[Cu(II)(Cyst) (Py)₂]	Blue	220	1.25	1.93
[Cu(II)(Gly)(8-HQ)]	Green	200	2.23	1.79
[Cu(II)(Gly)(IQ)₂]	Ash	230	1.43	1.87
[Cu(II)(Gly)(Py)₂]	Ash	187	2.45	1.63
[Cu(II)(Gly)(4-Pico)₂]	Blue	190	0.98	2.00
[Cu(II)(Gly)(Q)₂]	Green	210	1.25	1.79

Where, Gly = Glycine, Cyst= Cysteine, Py = Pyridine,Q = Quinoline, IQ = Isoquinoline, 2-Pico = 2-Picoline, 8-HQ= 8-hydroxyquinoline

Table 2: IR spectral data of Cu(II) complexes

Complexes	n(N-H) cm^-1	n(C=O) cm^-1	V(-NH₂) cm^-1	n(C-O) cm^-1	n(M-O) cm^-1	n(M-N) cm^-1
[Cu(II)(Gly)(8-HQ)]	3289m	1642s	3218m	1114s	744s	487m
[Cu(II)(Cyst)(Py)₂]	3304br	1630vs	3239m	-	688s	410w
[Cu(II)(Gly)(4-Pico)₂]	3400 br	1575 vs	3058br	-	742 s	416 s
[Cu(II)(Gly)(Py)₂]	3212 br	1633 s	3205s	-	673 s	489 w
[Cu(II)(Gly)(IQ)₂]	3216 br	1640 vs	3111 m	-	731s	493 s
[Cu(II)(Gly)(Q)₂]	3387 br	1624 s	3217s	-	760 s	468 m

Related band intensities are denoted by vs, s, m, w and br representing very strong, strong, medium, weak and broad band respectively.

Where, Gly = Glycine, Cyst= Cysteine, Py = Pyridine, Q = Quinoline, IQ = Isoquinoline, 2-Pico = 2-Picoline, 4-Pico = 4-Picoline, 8-HQ= 8-hydroxyquinoline

3.3 Magnetic Moment and Electronic Spectra

The observed values of effective moment (m_eff) of the complexes at room temperature are given in Table 3. All the compounds under investigation are found to be paramagnetic. Cu(II) complexes have m_eff values (1.79 to 2.00 B.M.) shows the presence of one unpaired electron. The electronic spectra of Cu(II) complexes exhibits a broad band between 425 to 485 nm which is assigned to transition²A_2g ® ²T_2g in square planar configuration. The other band observed at 275 to 378 nm due to charge transfer band only.

Table 3: Electronic spectral data of Cu(II) complexes

Complexes	l_max(nm)
[Cu(II)(Gly)(8-HQ)]	270	400	527
[Cu(II)(Cyst) (Py)₂]	260	380	550
[Cu(II)(Gly)(4-Pico)₂]	263	462	519
[Cu(II)(Gly)(Py)₂]	287	410	530
[Cu(II)(Gly)(IQ) 2].	295	462	519
[Cu(II)(Gly)(Q)₂]	315	426	550

Where, Gly = Glycine, Cyst= Cysteine, Py = Pyridine, Q = Quinoline, IQ = Isoquinoline, 2-Pico = 2-Picoline, 4-Pico = 4-Picoline, 8-HQ= 8-hydroxyquinoline

4. Antibacterial Screening:

Antimicrobial activities of the test samples are expressed by measuring the zone of inhibition observed around the area as shown in Table 4. The results revealed that the complexes are more microbial toxic than the free metal ions or ligands. All the complexes of metals under investigations showed more or less activities against the six pathogenic bacteria tested. The results also revealed that among all the tested samples, these metal complexes showed strong activity against both the Gram positive and Gram negative bacteria.

4. CONCLUSION:

i) Elemental analysis correspond to metal: Ligand stoichiometry for Cu(II) to ligands in complexes are 1:1:1.

ii) Magnetic susceptibility measurement indicates the paramagnetic nature of the complexes.

iii) The IR spectral data shows the ligand coordinate with the metal through O and N atoms.

Based on these facts and literature review, structure of complex has been proposed as shown in Figure 1.

Figure 1: Probable structure of the complex [Cu(II)(Gly)(8-HQ)]

Table 4: Antibacterial activities of the compounds and Kanamycin (K-30).

Bacteria	Gram Staining	Diameter of zone inhibition (in mm)
Bacteria	Gram Staining	[Cu(II)(Gly)₂(8-HQ)] 100 mg/disc	[Cu(II)(Gly) (Q)₂] 100 mg/disc	[Cu(II)(Gly) (IQ)₂] 100 mg/disc	K- 30 mg/disc
Bacillus subtilis	Positive	6	22	22	22
Staphylococcus aureus	Positive	21	23	9	22
Bacillus cereus	Positive	19	24	7	20
Escherichia coli	Negative	20	25	7	25
Shigella dysenteriae	Negative	19	26	5	21
Shigella sonnei	Negative	15	31	5	15

Where, Gly = Glycine, Q = Quinoline, IQ = Isoquinoline, 8-HQ= 8-hydroxyquinoline

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Received on 29.08.2014 Modified on 11.09.2014

Asian J. Research Chem. 7(11): November, 2014; Page 909-912