Synthesis, Spectroscopic, Magnetic and Biological Activity of Cr(III) and Fe(III) Complexes with Amino Acids and Heterocyclic Amines

 

Md. Kudrat-E-Zahan¹*, Md. Abul Bashar², Md. Faruk Hossen² and M. Saidul Islam²

*¹Associate Professor, Dept. of Chemistry, Faculty of Science, Rajshahi University, Rajshahi-6205, Bangladesh.

Bangladesh.²Department of Chemistry, University of Rajshahi, Rajshahi-6205, Bangladesh.

*Corresponding Author E-mail: kudrat.chem@ru.ac.bd

The synthesis and investigation of the electronic properties of Cr(III) / Fe(III) metal complexes with amino acids and heterocyclic amines has been carried out on the basis of metal estimation, conductivity and magnetic measurements, infrared spectra and electronic spectra studies. The complexes were of [M(X)L] type, where M = Cr(III) / Fe(III) and X= deprotonated amino acids as a primary ligand, such as Glycine, Alanine, Leucine, Cysteine; L= heterocyclic amines as a secondary ligand, such as Pyridine, 8-hydroxyquinoline. Antibacterial activity of the complexes has been examined against six (gram positive and gram negative) pathogenic bacteria by disc diffusion method and compared with that of standard antibiotic (Kanamycin). The Fe(III) complexes was found to have strong antibacterial activity against the tested bacteria.

 

 

 

1. INTRODUCTION:

Coordination chemistry have been interested for many years due to the donor properties of amino acids as models for metal-ligand system and interaction [1]. Complexation has found various application in selective complexing agents based on amino carbon acids. Complexation plays an essential role in maintaining the metal –ligand balance in living organisms [2].

 

Chromium is the sixth most abundant element in the earth’s crust.   Trivalent chromium forms tight bonds with oxygen and sulfur some chromium complexes with histidine and cysteine are relatively inert because of these tight bonds [3]. Trivalent chromium potentiates the action of insulin, probably through a glutathione-like complex composed of niacin, trivalent chromium and amino acids [4]. Few structure analysis of amino acid complexes of Cr(III) have been reported.

 

On the other hand iron is one of the essential mineral that can function as regulators, activators, transmitters, and controllers of various enzymatic reactions. It is known that some naturally occurring substances, e.g., amino acids, form complexes with trace metal ions [5].

 

 

Thus, it seems desirable to quantitatively estimate the avidity of biologically significant trace metal ions such as Fe(III) for complex-forming agents such as glycine[5-7].

 

In our previous work, we studied electronic properties of N₂O₄ schiff base ligand containing metal complexes of Cd(II), Pd(II), Hg(II) and Zr(IV) [8-10]. In this study, we described a systematic investigation on preparation and characterization of mixed ligand Fe(III) / Cr(III) metal complexes, where amino acid used as a  primary ligand and heterocyclic amine as a secondary ligand 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)]:

M³⁺ + X + L ® [M(X)(L)]

Where, M³⁺ = Cr(III) and Fe(III) ions 

X = Amino acids such as Glycine, Alanine, Leucine, Cysteine,

L =  Amine bases, i.e, Pyridine, 8-hydroxyquinoline. 

Table 1. Physical properties of Cr(III) and Fe(III) complexes

Complexes	Colour	Melting point (± 0.52)	Molar conductance W-1 cm2 mol-1	Magnetic moment meff (B.M.)
[Cr(III)(Ala)2(Py)2]	Violet	260	7.53	3.78
[Cr(III)(Cyst)2(8-HQ)]	Brown	220	6.00	4.01
[Cr(III)(Leu)2(8-HQ)]	Violet	265	7.13	3.37
[Fe(III)(Gly)2 (8-HQ)]	Black	290	5.09	6.67
[Fe(III)(Leu)2 (8-HQ)]	Black	>300	4.49	6.12

 

Where, Gly = Glycine, Cyst= Cysteine, Leu= Leucine, Ala= Alanine Py = Pyridine, 8-HQ= 8-hydroxyquinoline

 

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

 

3. RESULTS AND DISCUSSION:

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

 

3.1 Elemental analysis and conductivity measurement 

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 4.49 to 7.53 (Table 1), W^–1 cm² mole^-1. These values are lower than expected for an electrolyte. Their 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

Infrared spectral data of the complexes are shown in Table 2. In the IR spectrum of the complexes showed strong adsorption band 1626-1571 and 1179-1102 cm^-1 due to ν(C=O) and ν(C-O) modes. The disappearance of the n(O-H) mode observed in the free amino acid molecule clearly indicated the loss of proton for O-H group upon coordination, revealing that acids are dinegative bidentate ligand coordinating through the carboxylate anion. All the complexes showed ν(N-H) bands from 3334-3258 cm^-1. The presence of metal nitrogen bonding in the complexes are evident from the appearance of n(M-N) modes at 498-540cm^-1 in the spectra of the complexes. 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 [11].The presence of metal nitrogen bonding in the complexes is evident from the appearance of n(M-N) modes at 493-410 in the spectra of the complexes and v(M-O) appearance at 673-760 cm^-1.

 

3.3 Magnetic Moment and Electronic Spectra

The magnetic moment (m_eff) of the complexes at room temperature are given in Table 1. The observed magnetic moment of all Cr(III) complexes are 4.01-3.78 B.M. which corresponds to three unpaired electron and indicated the paramagnetic and octahedral geometry [12]. The reflectance spectra of Cr(III) complexes consist of transition band 265 to 582 nm assignable to the transitions ⁴A_2g ® ⁴T_2g , ⁴A_2g ® ⁴T_1g (F) and ⁴A_2g ®⁴T_1g (P)  respectively, and the magnetic moment of Fe(III) complexes are 6.67 and 6.12 which correspond to 5 unpaired electrons and agreement with octahedral geometry [12] (Table 3). Electronic of [Fe(III)(Gly)₂ (8-HQ)]  and [Cr(III)(Cyst)₂(8-HQ)] is shown in Figure 1.

 

Figure 1. Electronic of [Fe(III)(Gly)₂ (8-HQ)] (A) and [Cr(III)(Cyst)₂(8-HQ)] (B)

 

 

Table 2. IR spectral data of Cr(III) and Fe(III)complexes

 

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, Leu= Leucine, Ala= Alanine Py = Pyridine, 8-HQ= 8-hydroxyquinoline

 

Table 3. Electronic spectral data of Cr(III) and Fe(III) complexes

Complexes	lmax (n.m)
[Cr(III)(Ala)2(Py)2]	278	410	565
[Cr(III)(Cyst)2(8-HQ)]	265	410	575
[Cr(III)(Leu)2(8-HQ)]	275	420	560
[Fe(III)(Gly)2 (8-HQ)]	265	380	475
[Fe(III)(Leu)2 (8-HQ)]	290	403	582

Where, Gly = Glycine, Cyst= Cysteine, Leu= Leucine, Ala= Alanine Py = Pyridine, 8-HQ= 8-hydroxyquinoline

 

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

Bacteria	Diameter of zone inhibition (in mm)
	[Cr(III)(Ala)2(Py)2] 100 mg/disc	[Cr(III)(Cyst)2(8-HQ)] 100 mg/disc	[Fe(Gly)2(8-HQ)] 100 mg/disc	[Fe(III)(Leu)2 (8-HQ)] 100 mg/disc	K- 30 mg/disc
Bacillus subtilis	5	6	8	17	22
Staphylococcus aureus	0	0	9	15	22
Streptococcus agalactiae	1	0	16	16	20
Escherichia coli	0	5	17	18	25
Shigella dysenteriae	0	0	19	16	21
Shigella sonnei	0	3	15	15	15

Where, Gly = Glycine, Cyst= Cysteine, Leu= Leucine, Ala= Alanine Py = Pyridine, 8-HQ= 8-hydroxyquinoline

 

 

4. ANTIBACTERIAL SCREENING:

Metal complexes play an important role in regulating biological activities. The disk diffusion method was employed for the in vitro study of antibacterial effects against six Gram positive and Gram negative bacteria. Preliminary screening of the compounds against the selected bacteria showed that the Fe(III) metal complexes are more microbial toxic than the free metal ions or ligands. The complex Cr(III)  less active than the standard drug kanamycin. Antimicrobial activities of the test samples are expressed by measuring the zone of inhibition observed around the area as shown in Table 4.

 

5. CONCLUSION:

Elemental analysis correspond to metal: ligand stoichiometry for Cr(III) and Fe(III) complexes are 1:2:2. Magnetic susceptibility measurement indicated the paramagnetic nature of the complexes. The IR spectral data shows the ligand coordinate with the metal through O and N atoms. The electronic spectral data are in conformity with the transitions of octahedral Cr(III) and Fe(III) complexes. Based on these facts structure of complex have been proposed as shown in Figure 2 and 3. Fe(III) complexes showed moderate to strong antimicrobial activity.

 

Figure 2. Proposed structure of complex [Cr(III)(Ala)₂(Py)₂]

 

Figure 3. Proposed structure of complex [Fe(III)(Gly)₂(8-HQ)]

 

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Received on 10.09.2014         Modified on 07.10.2014

Accepted on 27.10.2014         © AJRC All right reserved