Synthesis, characterization and their antimicrobial activity of crystalline materials of nickel (II) complexes with substituted 2-amino-benzimidazole

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ScienceDirect Materials Today: Proceedings 5 (2018) 25862–25866

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ICAST-2018

Synthesis, characterization and their antimicrobial activity of crystalline materials of nickel (II) complexes with substituted 2amino-benzimidazole P. Mangaveni*, G. Durga, P. Bhushanavathi, P. Sarada Department of Chemistry, St. Joseph' College for Women, Visakhapatnam, Andhra Pradesh, India-530004

Abstract Majority of bio-molecules exist in nature are complex compounds and exhibits profound biological activity. The crystalline Nickel complexes are gained lot of attraction due their strong anti leukemic activity. The synthetic protocol of 2-Aminobenzimidazole (I) condensation with acetyl acetone, ethylcyanoacetate and 3, 4-dimethoxy benzaldehyde established to develop Schiff Bases ((IIa) C19H18N6, (IIb) C12H12N4O & (II c) C16H15N3O2). Schiff Bases were condensed with Nickel(II) Chloride to form Nickel complexes (IIIa,IIIIb,.IIIc). The prepared Ni (II) complexes were characterized by elemental analysis and spectroscopic analysis with IR, 1HNMR, UV-Visible. The antimicrobial activity of the ligands [IIa, IIb and IIc] and their Ni(II) complexes [IIIa, IIIb, IIIc] against bacterial strains and fungal strains were investigated. The antimicrobial activity of the prepared crystalline metal complexes and the ligands were also discussed. © 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Applied Sciences and Technology (ICAST-2018). Keywords:2 -Amino-benzimidazole, Nickel (II) complexes, antimicrobial activity;

* Corresponding author. Tel.:+91-9396468093. E-mail address: [email protected] 2214-7853© 2018 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Conference on Applied Sciences and Technology (ICAST-2018).

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1. Introduction In the process of condensation of primary amines and active carbonyl Compounds generates–C=N- (azomethine group) which are usually are known as Schiff bases. Schiff bases are important class of compounds in the branch of medicinal and allied fields. These compounds are being widely studied because of increasing recognition of their role in biological systems [1]. These compounds involved in metal complexation, which are used in chemical processes as catalysts and also the biological models for understanding the structures of bio-molecules.Schiff bases [2] are promising ligands because of their synthetic accessibility, diversity and structural varieties. 2-amino benzimidazoles chelated with Nickel metal and the resulting complexes has shown’ abroad spectrum of activity viz antiviral, antibacterial, anti-cancerous, antioxidant activity [3]. Imidazole and its derivatives are very important from a biological point of view. Benzimidazole, as the 5, 6-dimethyl derivative is present in vitamin B12 and related biomolecules and other benzimidazole complexes has been in wide use as antihelmintic agent for human and veterinary purposes [4]. Coordination compounds exhibit varied characteristic physical and chemical properties. These properties are mainly varied with the change in the metal ion and donor atoms, as well as on the structure of the ligand and the metal ligand interaction [5]. These complex compounds find extensive applications in various fields. In this work, we have synthesized 2-Amino-benzimidazole (I) by condensation with acetyl acetone (AcAc) ethylcyanoacetate (ECA) and 3, 4-dimethoxy benzaldehyde (DMB) established to develop Schiff Bases ((IIa) C19H18N6, (IIb) C12H12N4O & (II c) C16H15N3O2). Schiff Bases were condensed with Nickel (II) Chloride to form Nickel complexes (IIIa,IIIIb,.IIIc). The prepared Ni (II) complexes were characterized by elemental analysis and spectroscopic analysis with IR, 1HNMR, UV-Visible spectral. The antimicrobial activity of the ligands [IIa, IIb and IIc] and their Ni(II) complexes [IIIa, IIIb, IIIc] against bacterial strains and fungal strains were investigated. The antimicrobial activity of the prepared crystalline metal complexes and the ligands were also discussed. 2. Experimental 2.1. Synthesis of Schiff bases (IIa, IIb and IIc) General Methodology N NH2 N H

N H H N

II a

CH3

Reflux 6-7 hrs

OC2H5

H3CO

CHO N N NH

N N

N

O

H3CO

CH3

s hr

N

N

7 6-

N

s hr

x flu

x flu Re

7 6-

Re

O O

N

OC2H5

OCH3

N H NC

OCH3

II c

II b Scheme -1: Synthesis of Schiff Bases

Schiff bases were synthesized [6] by mixing an ethanolic solution (20ml) of 2-amino benzimidazole (1.5g, 10 mmole) with acetyl acetone (AcAc) (0.510ml , 5mmol in ethanol(20ml)) for the preparation of compound (IIa); Ethylcyanoacetate (ECA) (1.1ml,10 mmole in ethanol(20ml)) for the preparation of compound(IIb) and 3, 4-

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dimethoxy benzaldehyde(DMB) (1.7g,10 mmole in ethanol (20ml) for the preparation of compound (IIc) in separate reactions. The reaction mixture was refluxed with continuous stirring for 5-6 hrs. The crude product was separated by filtration under vacuum and washed several times with diethyl ether. The product was recrystallized from hot ethanol and dried in desiccators over anhydrous CaCl2. The synthesized ligands were presented in Scheme -1. 2.2. General Procedure for Synthesis of Nickel Complexes: To an ethanolic solution(10ml) of ligands (IIa (0.32g, 1mmol), IIb (0.456g, 2mmol), IIc (0.562g, 2mmol) NiCl2.6H2O (0.237, 1mmol) (for the preparation of complexes IIIa, IIIb and IIIc) was added drop wise in separate reactions in ethanol(10ml) while stirring followed by the addition of 2 to 3 drops of triethylamine (Et3N). Furtherthe reaction mixture was refluxed for about 3-4 hrs. It was then cooled in the refrigerator overnight [7]. The crystalline product was then recovered byfiltration,successive washings with ethanol: ether and then dried in vacuum. Ni(II) complexes were determined by employing gravimetric procedure. The percentage of carbon, hydrogen, nitrogen was determined by using CHN analyzer. 3. Results and Discussions 3.1. IR Spectral Studies The solid state IR spectra of the free ligands and their complexes were recorded in the region 4000-400 cm-1 (υmax,KBr Pellet in cm-1).The bands appeared at the range 1633-1598 cm-1, assigned as the azomethine group frequency present in the Schiff bases. The common observationin all the complexes was that the IR bands were shifted to lower frequency at the range 1624-1575 cm-1 indicating that coordination was through the azomethine nitrogen to the metal. The band at the range 3351-3221 cm-1 represents` coordinated water molecules in the complex IIIa. In the complexes IIIb IR absorption at the range 2158-2151cm-1was due the presence of (-C≡N). This value was less than the ligand IIb. The low frequency of (-C≡N) upon complexation could be understood in view of the participation of their π electrons in coordination with the metal ions. The metal oxygen and metal nitrogen stretching frequencies were often very difficult to assign. The coordination of the azomethine nitrogen confirms with the presence of new bands in the range 555-520 cm-1 for all complexes [8]. M-O bonds for the synthesized complexes would beat 472-400 cm-1. The weak bands are in the range 2968-2954 cm-1cold be due to stretching vibrations of the methoxy group in the Schiff base (IIc), complex IIIc. 3.2. UV visible spectra The electronic spectral data of Ni (II) complexes of the ligands were recorded in DMF as shown in Table -1. The electronic spectra of ligands (IIa, IIb and IIc) showed strong bands in the range 41,250-42,310cm-1 and 33,19033,450cm-1 which were attributed to π→π* and n →π* respectively. The electronic spectra of Ni(II) complexes IIIa, IIIb and IIIc showed bands at 15,228-15,430cm-1 and 21,118-21,280cm-1 which have existence 3A2g(F)→3T1g(F)(√2) and 3A2g(F)→3T1g(P)(√3) transitions. Therefore an octahedral geometry around Ni (II) ion is confirmed [9]. The ratio √3/√2 was found to be well within the range (1.37 to 1.45) and was indicative of octahedral geometry for these Ni (II) complexes [10]. Table 1. Electronic Special Data of Synthesized Complexes in DMF Solution Compound

√2

√3

√3/√2

λmax(nm)

λmax Cm-1

λmax(nm)

λmaxCm-1

III a

652

15326

471

21190

1.38

III b

656

15228

473

21118

1.38

III c

648

15430

469

21280

1.38

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3.3. Thermal Analysis The thermal properties of the prepared complex IIIb were examined by thermo gravimetric (TG) and differential thermo gravimetric analysis (DTG). The Nickel complex with ligand was heated up to 14000C in a nitrogen atmosphere. The TG and DTG curve results were in good agreement with the proposed chemical formula. The decomposition of the complex proceeded with an exothermic peak at 112.70C. The first stage at 153.2 0C - 686.0 0C with the mass loss of 29% (calcd: 28.6%) corresponded to the loss of two chlorine atoms and Schiff base ligand moiety C2H7NO (EthylCyanoacetate). The second stage at 686.0 0C-1057.1 0C with mass loss of 12 %( calcd 13.1%) corresponded to the loss of ligand molecule C3H5N; the third stage at 1057.1 0C-1198.7 0C with a mass loss of 27%( calcd 26.7%) C3H3N3O and finally at 1269.3 0C the TGA curve have shown that total decomposition of organic molecule with the formation of stable metal oxide (NiO) as the final product [11]. Thestructures of complexes are proposed as in (Fig-1) based on the above physical, analytical and spectral data.

Fig. 1. Proposed Structures of Complexes IIIa-IIIc

3.4. Screening of synthesized Nickel complexes for Antimicrobial Activity The synthesized ligands IIa-IIc and their Ni(II) metal complexes IIIa-IIIc compounds were screened for their antibacterial activity.The screening was carried out with gram +ve Micrococcus luteus (ML), Micrococcus proteus (MP), Bacillus subtilis (BS), gram –ve bacterial strains klepsiellapneumonia (KP), Escherichia coli (EC) and Pseudomonas syringae (PS) and three fungal strains Rhizopus stolonifer (RS), Candida albicans (CA), Aspergillus niger (AN). The well diffusion method was adopted for screening [12]. Standard antibacterial drug (Ampicillin) and antifungal drug (Nystatin) were used for comparison under similar conditions. DMSO was used as solvent to dissolve the compounds and used as control drug. The activity was determined by measuring the diameter of the Zone of Inhibition in (mm). Table 2. Biological activity of synthesized compounds against bacterial and fungal strains (Zone of Inhibition in mm)(1mg/ml)50μl of compound from 1mg/ml

Compounds

ML

II a

NA

NA

NA

10

14

14

NA

11

NA

II b

15

NA

NA

NA

13

12

NA

NA

NA

II c

11

NA

NA

10

NA

10

NA

NA

NA

III a

21

21

11

20

19

20

33

18

20

III b

25

24

22

20

26

21

30

14

34

III c

17

NA

NA

18

12

19

34

17

13

Ampicelline/

35

-

36

-

38

-

40

25

36

MP

BS

KP

EC

PS

RS

CA

AN

Micrococcus luteus (ML), Micrococcus proteus (MP), Bacillus subtilis (BS), Klepsiellapneumonia (KP), Escherichia coli (EC) and Pseudomonas syringe (PS),Rhizopus Stolonifer(RS), Candida albicans (CA) and Aspergillus niger (AN) NA-Not active

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The Ni(II) metal complexes exhibited a higher activity than the free ligands against both bacterial and fungal strains. The complexes IIIa, IIIb and IIIc exhibited significant antibacterial as well as antifungal activity against almost all bacterial and fungal strains except IIIa which was less active against the bacterial strain Bacillus subtilis; IIIc against bacterial strains Micrococcus proteus, Bacillus subtilis, Escherichia coli and the fungal strain Aspergillus niger. It can be concluded that Ni (II) metal complexes exhibited greater significant activity than the Schiff bases. The values of the tested compounds are shown towards bacterial strains and fungal strains in Table -2 and Table-3 respectively. Table 3.Biological activity of synthesized compounds against fungal strains (Zone of Inhibition in mm) (1mg/ml) 50μl of compound from 1mg/ml

Compounds II a II b II c III a III b III c Nystains

RS NA NA NA 33 30 34 40

CA 11 NA NA 18 14 17 25

AN NA NA NA 20 34 13 36

Rhizopus Stolonifer(RS); Candida albicans (CA);Aspergillus niger (AN); NA-Not active

4. Conclusions We have synthesized 2-Amino-benzimidazole by condensation with acetyl acetone, ethylcyanoacetate and 3, 4dimethoxy benzaldehyde established to develop the Schiff Bases. The prepared Schiff Bases were condensed with Nickel (II) Chloride to form Nickel complexes. The prepared Ni (II) complexes were characterized by elemental analysis and spectroscopic analysis with IR, 1HNMR, UV-Visible spectral. The antimicrobial activity of the ligands and their Ni(II) complexes against bacterial and fungal strains were investigated. References [1] J.A. McCleverty, T.J. Meyer, Comprehensive coordination chemistry II from Biology to Nanotechnology (2004) 411. [2] M. Mikuria, Y. Hatno, E. Asato, Bull. Chem.Soc. Japan 70, (1997) 2495. [3] E. Yousif, A. Majeed, K. Sammarrae, N. Salih, J. Salimon, B. Abdulah, Arabian Journal of Chemistry 10 (2017) S1639-S1644 [4] R.N. Preston, Chem. Rev. 74 (1974) 279. [5] O.V.S. Heath, J.E. Clark, Nature 178 (1957) 600. [6] S. Deepa, K. T. Anjani, S. Sweta, European J. of Medicinal Chem. 43 (2008) 160. [7] L. Mishra, A. Jha, Trans Met. Chem.18 (1993) 559. [8] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination compounds, 5th Ed.,Wiley, New York, 1997. [9] B.N. Fiffis, J. Lewis, Progress in inorganic chemistry, 6th Ed., Inter Science publisher, New York, 1964. [10] J.T. Makode, A.S. Aswar, J. Indian Chem. Soc. 80 (2003) 44. [11] T.H. Rakha, K.M. Ibrahim, M.I. Khalija, Thermochimica Acta 53 (1989) 144. [12] F.C. Odds, J. Antimicrobial chemotha. 24 (1989) 533. [13] Ky. Lau, A. Mayr, K.K. Cheung , Inorganicachimica Acta 285 (1999) 223. [14] Z.H. Chohan, Synthesis and reactivity in Inorganic and metal Organic chemistry 34 (2004) 833.