Antibacterial activity data of Schiff base (
Abstract
New Co(II), Ni(II) and Cu(II) metal complexes from an imidazolium ionic liquid supported Schiff base, 1-{2-(2-hydroxy-5-nitrobenzylideneamino)ethyl}-3-ethylimidazolium tetrafluoroborate were synthesized and characterized by different analytical and spectroscopic techniques such as elemental analysis (CHN analysis), UV-Visible, 1H NMR, 13C NMR, FT-IR, powder X-ray diffraction, mass-spectra, magnetic susceptibility measurements and molar conductance data. From these spectroscopic and analytical data, tetra coordinated 1:2 metal-ligand stoichiometry was suggested for the metal complexes. The molar conductance data of the complexes revealed their electrolytic nature (1:2). The synthesized complexes along with the ligand were screened for in vitro antibacterial applications against Gram-negative and Gram-positive bacteria to assess their inhibition potentials. The complexes were proved very effective against the tested organisms.
Keywords
- ionic liquid-based Schiff base
- Co(II) complex
- Ni(II) complex
- Cu(II) complex
1. Introduction
Ionic liquids (ILs) may be defined as “ionic materials,” with low melting points (below 100°C) generally composed of inorganic or organic anions paired with large, usually asymmetric organic cations. Ionic liquids (ILs) pose a plethora of unique physicochemical and solvation characteristics that can be tuned for specific applications and often producing interesting results when employed instead of traditional molecular solvents [1, 2]. In addition, most ILs show negligible vapor pressure [3] as well as high thermal stability [4, 5, 6]. Due to these attractive features they are termed as neoteric solvents or green solvents. In recent years, ILs were extensively studied for their wide electrochemical window, high ionic conductivity [7] and a broad temperature range of the liquid state. Moreover, the physical properties of ILs including density, melting point, polarity, Lewis acidity, viscosity and enthalpy of vaporization can all be tuned by changing their cation and anion pairing [8]. IL-based solvent system typically exhibits enhanced reaction kinetics resulting in the efficient use of time and energy [1]. Due to these properties, ILs are treated as a new generation of solvents for catalysis, ecofriendly reaction media for organic synthesis and a successful replacement for conventional media in chemical processes [1, 9]. Recently, many researchers have focused on the synthesis of new ionic liquids called functionalized ionic liquids (FILs) with different functional groups in the cationic moiety [10, 11, 12, 13, 14, 15]. Such functionalization of the cation can easily be done in a single reaction step and thus both the cationic and anionic moieties of the FILs can be altered as required for specific applications like increased catalytic stability and reduced catalyst leaching, etc. [16, 17].
Of note Schiff base being a salient class of multidentate ligand has played a key role in coordination chemistry. They exhibit varied denticities, chelating capability [18, 19, 20], functionalities [21] and diverse range of biological, pharmacological and antitumor activities. Schiff-bases containing hetero-atom such as N, O, and S are drawn special interest for their varied ways of coordination with different transition metal ions and having unusual configurations [22, 23, 24]. The present chapter describes the syntheses and physicochemical characterizations of an IL-supported Schiff base, 1-{2-(2-hydroxy-5-nitrobenzylideneamino)ethyl}-3-ethylimidazolium tetrafluoroborate and its Co(II), Ni(II) and Cu(II) complexes. The ligand and its metal complexes were screened for their
2. Materials and physical measurements
Analytical grade chemicals were used for synthesis without further purification. 1-ethyl imidazole, 2-bromoethylamine hydrobromide, 5-nitro-2-hydroxybenzaldehyde and NaBF4 (sodium tetrafluoroborate) were purchased from Sigma Aldrich, Germany. Metal acetates and other reagents were used as obtained from SD Fine Chemicals, India. CH3OH, petroleum ether, CHCl3, DMF and DMSO were used after purification by standard methods described in the literature. FT-IR spectra were recorded by KBr pellets on a Perkin-Elmer Spectrum FT-IR spectrometer (RX-1). 1H NMR and 13C NMR spectra were recorded on a FT-NMR (Bruker Avance-II 400 MHz) spectrometer by using D2O and DMSO-
2.1 Synthesis of 1-(2-aminoethyl)-3-ethylimidazolium tetrafluoroborate [2-aeeim]BF4 (1a)
The FIL was synthesized by following a literature procedure [25]. [2-aeeim]BF4 was obtained as yellow oil; (98 mg, 70%); 1H NMR (400 MHz, D2O, TMS):
2.2 Synthesis of imidazolium ionic liquid-supported Schiff base, LH (2a )
5-nitro-2-hydroxybenzaldehyde (1.67 g, 10 mmol) and [2-aeeim]BF4 (2.27 g, 10 mmol) were taken in methanol and stirred at 25°C for 4 h. After completion of reaction, the product was diluted using ethanol. The precipitate was filtered, washed with cold EtOH and dried properly to collect the expected ligand as a yellowish brown solid; (282 mg, 75%). mp. 95–97°C. 1H NMR: (400 MHz, DMSO-
2.3 Synthesis of the metal complexes (3a , 4a and 5a )
To an ethanolic solution of ligand, LH (2c) (0.376 g, 1 mmol) in round bottomed flask, metal acetate salt Co(II), Ni(II) and Cu(II),
2.3.1 Co(II)complex (3a )
Brown solid; (0.54 g, 67%), decomposes at ~293°C. IR (KBr): ʋ = 3386 (O▬H), 1648 (C═N), 1332 (N▬O), 1177 (C▬O), 1106 (B▬F), 651 (M▬O), 510 (M▬N). UV/vis (methanol, λmax/nm): 227, 246, 358. ESI-MS (CH3OH,
2.3.2 Ni(II)complex (4a )
Light green solid; (0.56 g, 69%), decomposes at ~293°C. IR (KBr): ʋ = 3396 (O▬H), 1637 (C═N), 1330 (N▬O), 1172 (C▬O), 1102 (B▬F), 646 (M▬O), 526 (M▬N). UV/vis (methanol, λmax/nm): 220, 340, 400. ESI-MS (CH3OH,
2.3.3 Cu(II) complex (5a )
Dark green solid; (0.57 g, 70%), decomposes at ~295°C. IR (KBr): ʋ = 3429 (O▬H), 1656 (C═N), 1334 (N▬O), 1175 (C▬O), 1103 (B▬F), 633 (M▬O), 471 (M▬N). UV/vis (methanol, λmax/nm): 226, 244, 354. ESI-MS (CH3OH,
2.4 Antibacterial assay
The synthesized ligand (
3. Results and discussion
All the isolated compounds were stable at room temperature to be characterized by different analytical and spectroscopic methods. The complexes are soluble in
3.1 FT-IR spectral studies
The assignments of the IR bands of the synthesized Co(II), Ni(II) and Cu(II) complexes had been made by comparing with the bands of ligand (LH) to determine the coordination sites involved in chelation. FT-IR spectra of LH (
3.2 1H NMR and 13C NMR spectral studies
1H NMR and 13C NMR spectra of Schiff base were recorded in DMSO-
3.3 PXRD analysis
The PXRD analysis of the synthesized compounds was carried out to find whether the particle nature of the samples was amorphous or crystalline. The PXRD spectrum of ligand (LH) exhibited sharp peaks because of their crystalline nature although the spectra of the two complexes did not show such peaks for their amorphous nature (as shown in Figures 11
3.4 Mass spectral studies
To get information regarding the structure of the synthesized compounds at the molecular level, electrospray ionization (ESI) mass spectrometry was performed using methanol as solvent. Mass-spectra of the LH (
3.5 Electronic spectra and magnetic moment
The UV-visible spectra of the Schiff base and its metal complexes (as depicted in Figure 15) were recorded at room temperature using methanol as solvent. The LH (
3.6 Molar conductance
The molar conductance (
3.7 Antimicrobial activity
Antibacterial study of LH (
Specimen | Concentration (μg/mL) | ||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
10 | 20 | 30 | 40 | 50 | 10 | 20 | 30 | 40 | 50 | 10 | 20 | 30 | 40 | 50 | |
LH | — | 6 | 7 | 8 | 12 | 7 | 9 | 10 | 10 | 12 | — | — | 6 | 8 | 12 |
Co(II) complex | — | — | 6 | 7 | 8 | 6 | 7 | 7 | 9 | 10 | — | 6 | 6 | 8 | 10 |
Ni(II) complex | 6 | 7 | 8 | 9 | 9 | — | — | 7 | 8 | 10 | — | — | 6 | 8 | 10 |
Cu(II) complex | 8 | 9 | 14 | 15 | 18 | 6 | 8 | 10 | 17 | 17 | — | — | — | — | 7 |
Specimen | Concentration (μg/mL) | ||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
10 | 20 | 30 | 40 | 50 | 10 | 20 | 30 | 40 | 50 | 10 | 20 | 30 | 40 | 50 | |
LH | — | 6 | 9 | 15 | 16 | — | 6 | 9 | 10 | 14 | — | 6 | 8 | 10 | 13 |
Co(II) complex | — | 7 | 9 | 10 | 13 | — | — | — | 6 | 7 | 8 | 10 | 13 | 15 | 17 |
Ni(II) complex | — | — | 6 | 7 | 9 | — | — | 6 | 7 | 8 | 8 | 10 | 12 | 12 | 16 |
Cu(II) complex | — | 6 | 12 | 12 | 14 | — | 7 | 7 | 8 | 16 | — | — | 6 | 7 | 10 |
4. Conclusion
Herein this chapter, new Co(II), Ni(II) and Cu(II) complexes of an ionic liquid-supported Schiff base, 1-{2-(2-hydroxy-5-nitrobenzylideneamino)ethyl}-3-ethylimidazolium tetrafluoroborate were synthesized and characterized by different spectral and analytical techniques. The Schiff base ligand played as a potential bidentate ligand coordinating through the N-atom of azomethine and O-atom of phenolic group to the metal ions and thus formed 1:2 (M:L) complexes. Spectral and magnetic susceptibility data revealed that the ligand was arranged in square planner geometry around the central metal ions. The antibacterial study of the synthesized compounds was performed and metal complexes have exhibited promising activity against the tested bacteria.
Acknowledgments
The authors are thankful to the Departmental Special Assistance Scheme, under the University Grants Commission, New Delhi (SAP-DRS-III, NO.540/12/DRS/2013) and SAIF, NEHU, Guwahati, India for 1H NMR, 13C NMR, ESI-MS and elemental analysis. Again authors are grateful to Annamalai University, Tamil Nadu, India for PXRD analysis.
Nomenclature
1-(2-aminoethyl)-3-ethylimidazolium tetrafluoroborate 1-{2-(2-hydroxy-5-nitrobenzylmine) ethyl}-3-ethylimidazolium tetrafluoroborate [Di(1-{2-(2-hydroxy-5-nitrobenzylidene amino)ethyl}-3-ethylimidazolium) Co(II)] tetrafluoroborate [Di(1-{2-(2-hydroxy-5-nitrobenzylidene amino)ethyl}-3-ethylimidazolium) Ni(II)] tetrafluoroborate [Di(1-{2-(2-hydroxy-5-nitrobenzylidene amino)ethyl}-3-ethylimidazolium) Cu(II)] tetrafluoroborate
References
- 1.
Welton T. Room-temperature ionic liquids. Solvents for synthesis and catalysis. Chemical Reviews. 1999; 99 :2071-2083 - 2.
Chiappe C, Pieraccini D. Kinetic study of the addition of trihalides to unsaturated compounds in ionic liquids. Evidence of a remarkable solvent effect in the reaction of ICl2−. The Journal of Organic Chemistry. 2004; 69 :6059-6064 - 3.
Earle MJ, Esperanc JMSS, Gilea MA, Lopes JNC, Rebelo LPN, Magee J, et al. The distillation and volatility of ionic liquids. Nature. 2006; 439 :831-834 - 4.
Rogers RD, Seddon KR. Ionic liquids—Solvents of the future? Science. 2003; 302 :792-793 - 5.
Sheldon R. Green solvents for sustainable organic synthesis: State of the art. Green Chemistry. 2005; 7 :267-278 - 6.
Wasserscheid P, Keim W. Ionic liquids—New “solutions” for transition metal catalysis. Angewandte Chemie, International Edition. 2000; 39 :3772-3789 - 7.
Sakaebe H, Matsumoto H. N -methyl-N -propylpiperidinium bis(trifluoromethane sulfonyl)imide (PP13–TFSI)—Novel electrolyte base for Li battery. Electrochemistry Communications. 2003;5 :594-598 - 8.
Freire MG, Santos LMNBF, Fernandes AM, Coutinho JAP, Marrucho IM. An overview of the mutual solubilities of water-imidazolium-based ionic liquids systems. Fluid Phase Equilibria. 2007; 261 :449-454 - 9.
Sheldon R. Catalytic reactions in ionic liquids. Chemical Communications. 2001; 23 :2399-2407 - 10.
Yi F, Peng Y, Song G. Microwave-assisted liquid-phase synthesis of methyl 6-amino-5-cyano-4-aryl-2-methyl-4 H -pyran-3-carboxylate using functional ionic liquid as soluble support. Tetrahedron Letters. 2005;46 :3931-3933 - 11.
Bates ED, Mayton RD, Ntai I, Davis JH. CO2 capture by a task-specific ionic liquid. Journal of the American Chemical Society. 2002; 124 :926-927 - 12.
Cole AC, Jensen JL, Ntai I, Tran KLT. Novel Brønsted acidic ionic liquids and their use as dual solvent-catalysts. Journal of the American Chemical Society. 2002; 124 :5962-5963 - 13.
Li J, Peng Y, Song G. Mannich reaction catalyzed by carboxyl-functionalized ionic liquid in aqueous media. Catalysis Letters. 2005; 102 :159-162 - 14.
Davis JH Jr, Forrester KJT, Merrigan J. Novel organic ionic liquids (OILs) incorporating cations derived from the antifungal drug miconazole. Tetrahedron Letters. 1998; 49 :8955-8958 - 15.
Jodry JJ, Mikami JK. New chiral imidazolium ionic liquids: 3D-network of hydrogen bonding. Tetrahedron Letters. 2004; 45 :4429-4431 - 16.
Fei Z, Geldbach TJ, Zhao D, Dyson PJ. From dysfunction to bis-function: On the design and applications of functionalised ionic liquids. European Journal of Chemistry. 2006; 12 :2122-2130 - 17.
Lee S. Functionalized imidazolium salts for task-specific ionic liquids and their applications. Chemical Communications. 2006; 14 :1049-1063 - 18.
Hadjikakou SK, Hadjiliadis N. Antiproliferative and anti-tumor activity of organotin compounds. Coordination Chemistry Reviews. 2009; 253 :235-249 - 19.
Garoufis A, Hadjikakou SK, Hadjiliadis N. Palladium coordination compounds as anti-viral, anti-fungal, anti-microbial and anti-tumor agents. Coordination Chemistry Reviews. 2009; 253 :1384-1397 - 20.
Liu CM, Xiong RG, You XZ, Liu YJ, Cheung KK. Crystal structure and some properties of a novel potent Cu2Zn2SOD model Schiff base copper(II) complex. Polyhedron. 1996; 15 :4565-4571 - 21.
Atkins AJ, Black D, Blake AJ, Marin-Bocerra A, Parsons S, Ruiz-Ramirez L, et al. Schiff-base compartmental macrocyclic complexes. Chemical Communications. 1996; 4 :457-464 - 22.
Goku A, Tumer M, Demirelli H, Wheatley RA. Cd(II) and Cu(II) complexes of polydentate Schiff base ligands: Synthesis, characterization, properties and biological activity. Inorganica Chimica Acta. 2005; 358 :1785-1797 - 23.
Mohindru A, Fisher JM, Rabinovitz M. Bathocuproine sulphonate: A tissue culture-compatible indicator of copper-mediated toxicity. Nature. 1983; 303 :64-65 - 24.
Palet PR, Thaker BT, Zele S. Preparation and characterisation of some lanthanide complexes involving a heterocyclic beta-diketone. Indian Journal of Chemistry Section A. 1999; 38 :563-567 - 25.
Song G, Cai Y, Peng Y. Amino-functionalized ionic liquid as a nucleophilic scavenger in solution phase combinatorial synthesis. Journal of Combinatorial Chemistry. 2005; 7 :561-566 - 26.
Ahmed I, Beg AJ. Antimicrobial and phytochemical studies on 45 Indian medicinal plants against multi-drug resistant human pathogens. Journal of Ethnopharmacology. 2001; 74 :113-123 - 27.
Yıldız M, Kılıc Z, Hökelek T. Intramolecular hydrogen bonding and tautomerism in Schiff bases, structure of 1,8-di[N-2-oxyphenyl-salicylidene]-3,6-dioxaoctane. Journal of Molecular Structure. 1998; 441 :1-10 - 28.
Yeap G-Y, Ha S-T, Ishizawa N, Suda K, Boey P-L, Mahmood WAK. Synthesis, crystal structure and spectroscopic study of para substituted 2-hydroxy-3-methoxybenzalideneanilines. Journal of Molecular Structure. 2003; 658 :87-99 - 29.
Abdel-Latif SA, Hassib HB, Issa YM. Studies on some salicylaldehyde Schiff base derivatives and their complexes with Cr(III), Mn(II), Fe(III), Ni(II) and Cu(II). Spectrochimica Acta Part A. 2007; 67 :950-957 - 30.
Wang J, Pei Y, Zhao Y, Hu Z. Recovery of amino acids by imidazolium based ionic liquids from aqueous media. Green Chemistry. 2005; 7 :196-202 - 31.
Han D, Row KH. Recent application of ionic liquids in separation technology. Molecules. 2010; 15 :2405-2426 - 32.
Kohawole GA, Patel KS. The stereochemistry of oxovanadium(IV) complexes derived from salicylaldehyde and polymethylenediamines. Journal of the Chemical Society Dalton Transactions. 1981; 6 :1241-1245 - 33.
Mahmoud MA, Zaitone SA, Ammar AM, Sallam SA. Synthesis, structure and antidiabetic activity of chromium(III) complexes of metformin Schiff-bases. Journal of Molecular Structure. 2016; 1108 :60-70 - 34.
Ulusoy N, Gürsoy A, Ötük G. Synthesis and antimicrobial activity of some 1,2,4-triazole-3-mercaptoacetic acid derivatives. II Farmaco. 2001; 56 :947 - 35.
Adams DM. Metal-Ligand and Related Vibrations: A Critical Survey of the Infrared and Raman Spectra of Metallic and Organometallic Compounds. England: Edward Arnold (Publishers) Ltd London; 1967 - 36.
Li B, Li YQ , Zheng WJ, Zhou MY. Synthesis of ionic liquid supported Schiff base. ARKIVOC. 2009; 11 :165-171 - 37.
Peral F, Gallego E. Self-association of imidazole and its methyl derivatives in aqueous solution. A study by ultraviolet spectroscopy. Journal of Molecular Structure. 1997; 415 :187-196 - 38.
Shakir M, Nasam OSM, Mohamed AK, Varkey SP. Transition metal complexes of 13-14-membered tetraazamacrocycles: Synthesis and characterization. Polyhedron. 1996; 15 :1283-1287 - 39.
Chem LS, Cummings SC. Synthesis and characterization of cobalt(II) and some nickel(II) complexes with N,N′-ethylenebis(p-X-benzoylacetone iminato) and N,N′-ethylenebis(p-X-benzoylmonothioacetone iminato) ligands. Inorganic Chemistry. 1978; 17 :2358-2361 - 40.
Silverstein RM. Spectrometric Identification of Organic Compounds. 7th ed. United States of America: John Wiley & Sons; 2005 - 41.
Natarajan C, Tharmaraj P, Murugesan R. In situ synthesis and spectroscopic studies of copper(II) and nickel(II) complexes of 1-hydroxy-2-naphthylstyrylketoneimines. Journal of Coordination Chemistry. 1992; 26 :205-213 - 42.
Dehghanpour S, Bouslimani N, Welter R, Mojahed F. Synthesis, spectral characterization, properties and structures of copper(I) complexes containing novel bidentate iminopyridine ligands. Polyhedron. 2007; 26 :154-162 - 43.
Lever ABP. Inorganic Electronic Spectroscopy. 2nd ed. Amsterdam: Elsevier; 1984 - 44.
Tweedy BG. Plant extracts with metal ions as potential antimicrobial agents. Phytopathology. 1964; 55 :910-915