Studies on Synthesis, Characterization and Biological Activity of Mixed Ligand Coordinating Co (II) Complexes

 

Md. Abul Bashar¹, Shejuty Aktar¹, Md. Jahangir Alam², Md. Faruk Hossen¹, M. Saidul Islam¹ Md. Kudrat-E-Zahan^*1

¹Department of Chemistry, University of Rajshahi, Rajshahi-6205, Bangladesh.

²Department of Agronomy and Agricultural Extension, University of Rajshahi, Rajshahi-6205, Bangladesh.

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

The mixed ligand complexes of Co(II) with amino acids and heterocyclic amines have been synthesized and characterized on the basis of metal estimation, conductivity and magnetic measurements, infrared spectra and electronic spectra studies. The complexes were of [M(X)L] where M = Co(II) and X= deprotonated amino acids as a primary ligand, such as glycine and cysteine; L= heterocyclic amines as a secondary ligand, such as quinoline, isoquinoline pyridine, 1,10-phenanthroline, 8-hydroxyquinoline, 2-picoline, 4-picoline. 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 complexes have been found to have moderate to strong antibacterial activity against the tested bacteria.

 

 

 

1. INTRODUCTION:

The bonding nature of the α-amino acid complexes of Co(II) ion and their spectroscopic investigation have been the subject of much interest since long time perhaps because of their biochemical importance. A knowledge of the interaction between biologically active molecules and metals is needed when preparing biomaterials or considering certain aspects of biocompatibility. The study of model species such as the simple amino acids can assist in the interpretation of more complex system. Amino acid (glycine and alanine) has the neutral donor N at one end and acidic replaceable H at the other end and are sufficient length to span two adjacent coordinating site and the resulting complexes is a non electrolyte chelate or inner complex compound. Such metal chelates are characterized by great thermal stability [1, 2], are intensely colored, insoluble in water but soluble in organic solvents are of practical importance. Cis- and trans-bis-(glycino)-platinum(II), Pt(NH₂CH₂CO₂)₂, were prepared by Pinkard and co-workers and were twice recrystallized from water. Bis-(glycino)-copper (II) monohydrate, (Cu(C₂H₄NO₂)₂·H₂O) was prepared by Abderhalden and Schnitzler [3].

 

There are three complexes of cysteine with cobalt (III) ion were isolated in the solid state by Segbert such as Bis-cysteine of cobalt (III). Shubert concluded that the sulfhydral and carboxyl groups of cysteine were co-ordinated to the cobalt atom. The ultimate goal is to simultaneous synthesis of facial and meridional isomer of some cobalt-amino acid complexes and their characterization. Two isomers of Co(III)-glycine complex are exist; a violet and a red. Both of these two isomers were prepared by the method of Shibata et al. [1, 4], here allowing glycine to reacts with aqueous potassium tri(carbonato)cobalt (III).  Worldwide spread of drug-resistant bacteria is now a critical problem in global health. Of particular importance are severe infections caused by drug-resistant Gram-positive and RTIa (respiratory tract infection) causative Gram-negative bacteria in hospital and community care. Infectious and parasitic diseases are responsible for 20% of the mortality worldwide, followed by malignant neoplasms with about 13% [5]. Thus, the emergence of antibiotic-resistant bacteria is nowadays a serious challenge to the clinical treatment of infections. Drug resistance is also a problem in the treatment of cancer. Previously, we studied electronic properties of N₂O₄ schiff base ligand containing metal complexes of Cd(II), Pd(II), Hg(II) and Zr(IV) [6-8]. In this study, we described a systematic study of preparation and characterization of mixed ligand Co(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⁺ =  Co(II)  ion

X = Amino acids such as, Glycine and Cysteine

L = Heterocyclic amine bases such as Pyridine, Quinoline, Isoquinoline; 2-Picoline, 8-hydroxyquinoline etc.  An ethanolic solution of Co(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 Co(II) complexes are insoluble in common organic solvents but are soluble in DMSO, DMF and CHCl₃.

 

3.1 Elemental analysis and conductivity measurement: 

The analytical data and their physical properties of the complexes are given 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 1.43 to 4.12 (Table 1) W^–1 cm² mole^-1. The molar conductance values indicates that the compound are non electrolytic in nature [9, 10].

 

3.2 IR spectral studies:

The infrared spectral data are presented in Table 2. The IR spectrum of the complexes shows strong adsorption band 1647-1575 and 1170-1112 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 indicate the loss of proton for O-H group upon coordination, revealing that acids are dinegative bidentate ligand coordinating through the carboxylate  anion .The complexes shows ν(N-H) bands from 3166-3350 cm^-1 (3500cm^-1). The presence of metal nitrogen bonding in the complexes is evident from the appearance of n(M-N) modes at 371-529 cm^-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 cm^-1 in the spectra of the complexes and v(M-O) appearance at 673-760).

 

3.3 Magnetic Moment and Electronic Spectra:

The Co(II) complexes magnetic moment were found in the range 4.81 to 5.56 B.M.( Table 3) at room temperature, in agreement three unpaired electron (paramagnetic) with octahedral geometry[12]. The three transitions observed in the electronic spectra of the Co(II) complexes indicate the octahedral environment around the metal ion. The electronic spectrum of Co(II) complexes shows strong peak between 260 to 560 nm assignable to the transition⁴A_2g ® ⁴T_1g (F) and ⁴T_2g  ®⁴T_1g  (P).

 

Table 1: Physical properties of Co(II) complexes

Complexes	Colour	Melting point (± 0.52)	Molar conductance W-1 cm2 mol-1	Magnetic moment  meff (B.M.)
[Co(II)(Gly) 2(Py)2]	Black	193	1.43	4.37
[Co(II)(Cyst)2(8-HQ)]	Brown	215	2.13	4.80
[Co(II)(Gly) 2 (IQ) 2]	Ash	187	2.23	4.34
[Co(II)(Gly)2(2-Pico) 2]	Violet	198	4.12	5.56
[Co(II)(Leu)2(2-Pico)2]	Deep blue	245	3.19	5.20
[Co(II)(Gly) 2(Q) 2]	Black	194	3.45	4.81

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

Table 2: IR spectral data of Co(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
[Co(II)(Gly)2(Py)2]	3350 br	1575 m	3060 m	-	824 s	529 s
[Co(II)(Cyst)2(8-HQ)]	3283br	1590s	3034m	1126m	847s	394m
[Co(II)(Leu)2(2-Pico)2]	3232br	1650s	2958s	-	840s	424m
[Co(II)(Gly)2(2-Pico)2]	3242 br	1600 vs	3171 m	-	813 s	371 m
[Co(II)(Gly)2(IQ)2]	3166 br	1647 s	3105s	-	834 s	415 s
[Co(II)(Gly)2(Q)2]	3254 br	1610 vs	3143 s	-	871 s	403 s

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, 8-HQ= 8-hydroxyquinoline

 

 

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

Complexes	lmax (n.m)
[Co(II)(Gly)2(Py)2]	280	425	535
[Co(II)(Cyst)2(8-HQ)]	260	310	413
[Co(II)(Leu)2(2-Pico)2]	263	450	560
[Co(II)(Gly)2(2-Pico) 2]	275	425	520
[Co(II)(Gly)2(IQ) 2]	287	440	494
[Co(II)(Gly) 2(Q) 2]	264	465	560

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

 

4. ANTIBACTERIAL SCREENING:

Metal complexes play an important role in regulating biological activities. Many coordination compounds present activity against tuberculosis, influenza, and rheumatism or are suggested as pesticides and fungicides. The disk diffusion method was employed for the in vitro study of antibacterial effects against six Gram positive and Gram negative bacteria. The results revealed that the complexes are more microbial toxic than the free metal ions or ligands. Antimicrobial activities of the test samples are expressed by measuring the zone of inhibition observed around the area as shown in Table 4.

 

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

Bacteria	Gram Staining	Diameter of zone inhibition (in mm)
		[Co(II)(Gly) 2(Q) 2] 100 mg/disc	[Co(II)(Gly)2(2-Pico) 2]  100 mg/disc	[Co(II)(Gly)2(IQ) 2] 100 mg/disc	K- 30 mg/disc
Bacillus subtilis	Positive	6	22	30	22
Staphylococcus aureus	Positive	8	23	27	22
Bacillus cereus	Positive	6	24	31	20
Escherichia coli	Negative	5	25	29	25
Shigella dysenteriae	Negative	4	26	27	21
Shigella sonnei	Negative	4	31	27	15

Where, Gly = Glycine, Q = Quinoline, IQ = Isoquinoline, 2-Pico = 2-Picoline.

 

4. CONCLUSION:

Elemental analysis correspond to metal: ligand stoichiometry for Co(II) complexes were found as 1:2:2. Magnetic susceptibility measurement indicated the paramagnetic nature of the complexes. The IR spectral data showed the ligand coordinate with the metal through O and N atoms. The electronic spectral data were in conformity with the transitions of octahedral Co(II) complexes. Based on these facts a structure of complex has been proposed as shown in Figure 1.

 

Figure 1: Proposed structure of the complex  [Co(II)(Gly)₂ (Py) ₂]

 

5. REFERENCES:

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2.         M. M. Rahman, Transition met. Chem. (Dordrecht Neth)., 24(2), 193, 1996.

3.         A. J. Saraceno, I. Nakagawa, S. Mizushima, Columba Curran, and J. V. Quagliano, J. Am. Chem. Soc. 80, 5018 (1958).

4.         M. Mori, M. Shibata, E. Kyuno, and T. Adachi, Bull. Chem. Soc. Jpn. 29, 883 (1956).

5.         World Health Organization, The World Health Report 2004: Chang- ing History. http://www.who.int/whr/2004/en/report04_en.pdf, 2004

6.         Md.Kudrat-E-Zahan and Hiroshi Sakiyama, Asian Journal of Research in Chemistry, 7(13): 278 (2014).

7.         Md.Anarul Islam, Roksana khatun, M.Monirul Islam and Md.Kudrat-E-Zahan, Asian Journal of Research in Chemistry, 7(2):(2014).

8.         Md.Kudrat-E-Zahan, and Hiroshi Sakiyama, Asian Journal of Research in Chemistry, 6(11): 1072 (2013).

9.         J. C. De Andrade, Yoshitaka Gushikem J. inorg nucl Chem., 38, 961 (1977).

10.         Gina Carlo pellacani, Giorgio peyronel, Wanda Malavasi and Ladi Minabue, J. inorg nucl Chem., 39, 1855 (1977).

11.         Abdul Hamid and Muhammad, Pak. J. Sci. Ind. Res.,28(2), 75 (1985).

12.         Raju, K.C., Radhakrishnan, P.K., 32, 1719 (2002)

 

 

 

Received on 03.09.2014         Modified on 10.09.2014

Accepted on 19.09.2014         © AJRC All right reserved