Main Group Chemistry 11 (2012) 217–222 DOI 10.3233/MGC-2012-0074 IOS Press
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Synthesis, characterization and biological activity of a new long-chain imine ligand and some transition metal complexes in solvent-free conditions Fikriye Tuncel Elmalia,∗ , Berkay S¨utayb , Berna Ozbekc and Nebahat Demirhana a
Chemistry Department, Yildiz Technical University, Istanbul, Turkey Department of Chemistry, Istanbul Technical University, Maslak, Istanbul, Turkey c Faculty of Pharmacy, Department of Pharmaceutical Microbiology, University of Istanbul, Istanbul, Turkey
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Abstract. A new N-alkyl long-chain alkyl imine ligand (N-dodecyl-N1-dacanimine) has been synthesized by the reaction of dodecylamine (laurylamine) with decanal in molar 1 : 1 ratio and its Cu(I), Cu(II), Ni(II) and Co(II) complexes have been prepared under solvent-free conditions. The newly synthesized compounds have been verified by FTIR, UV-vis. and mass spectra. All of the compounds were tested for antimicrobial activity against Staphylococcus aureus ATCC 6538, meticillin resistant Staphylococcus aureus (MRSA) ATCC 33591, Staphylococcus epidermidis ATCC 12228, Escherichia coli ATCC 8739, Klebsiella pneumoniae ATCC 4352, Pseudomonas aeruginosa ATCC 1539, Proteus mirabilis ATCC 14153 and the yeast, Candida albicans ATCC 10231. Among the compounds, the ligand was found the most active compound against all strains. The Cu(II)complex exhibited very strong antibacterial activity against bacteria except for Pseudomonas aeruginosa ATCC 1539, Proteus mirabilis ATCC 14153. Also, all compounds showed very strong antifungal effects against C. albicans ATCC 10231.
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Keywords: Complex, imine, solvent-free condition, biological activity
1. Introduction Compounds with the structure of –C=N– (azomethine group) are known as imines, and are usually synthesized from the condensation of primary amines and active carbonyl groups. Imines bases are important class of compounds in medicinal and pharmaceutical field. They show biological applications including antibacterial, antifungal, antitumor activity [1–5]. This publication relates to a novel process for the preparation of aliphatic imines which can be used as intermediates for the preparation of agrochemical or pharmaceutical active substances. In contrast to the synthesis of aromatic imines, the preparation of ∗ Corresponding author: Fikriye Tuncel Elmali, Chemistry Department, Yildiz Technical University, Esenler 34210, Istanbul, Turkey. E-mail:
[email protected].
ISSN 1024-1221/12/$27.50 © 2012 – IOS Press and the authors. All rights reserved
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aliphatic imines, especially long chain aliphatic imines is known to be relatively difficult [6]. The only known method for the preparation of aliphatic imines in moderate yields is the solvent-free reaction of aldehydes with amines in the presence of solid potassium hydroxide. This method is poorly suited to industrial needs because the yield and quality of the products are unsatisfactory in many cases, the by products cannot easily be separated, and large amounts of potassium hydroxide have to be disposed of [7–11]. In the present study, we report to the synthesis of a new N-alkyl long-chain Schiff base ligand in a solvent environment. Cu(I), Cu(II), Ni(II) and Co(II) metal complexes were synthesized with the ligand with appropriate metal salts in solvent-free conditions. In order to investigate the relationships between antimicrobial activity and structure, the compounds were tested in vitro using the microbroth dilution technique according to Clinical and Laboratory Standards Institute (CLSI) [12, 13]. The minimum inhibitory concentration (MIC) of the synthesized compounds were determined against the bacteria and the yeast C. albicans. 2. Experimental 2.1. Materials and methods
2.2. Syntheses
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The FTIR spectra were recorded as KBr disks on a Perkin Elmer Spectrum One Bv 5.0 spectrophotometer. Mass spectra (ESI-MS) were determined on a Finnigan™ LCQ™ Advantage MAX spectrometer. Absorption spectra were recorded on an Agilent 8453 UV-visible spectrophotometer. Elemental analyses were determined on a Thermo Finnigan Flash EA 112. Melting points were obtained with a B¨uchi Melting point B-540 apparatus in open capillaries. Dodecylamine(laurylamine) CH3 (CH2 )11 NH2 , Decanal C10 H20 O, CuCl, Cu(CH3 COO)2 ·H2 O, NiCl2 ·6H2 O, Co(CH3 COO)2 ·4H2 O, methanol (Merck) was used as purchased. In this study, broth dilution method was used for antimicrobial activity. Mueller-Hinton broth for bacteria, RPMI-1640 medium for yeast strain were used as the test medium.
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2.2.1. Preparation of the Schiff base ligand Decanal (0.780 g, 5 mmol) solution in 50 mL absolute methanol, was added dropwise to dodecylamine (0.926 g, 5 mmol) in 30 mL absolute methanol during 30 min. After refluxing this mixture for 12 hours and evaporated under vacuum. The evaporation process was repeated two more times by the addition of 50 mL methanol. The pale yellow oily product washed with water and methanol. It was soluble in methanol, hexane, ether, chloroform and ethanol. Yield 86%. Mp 2◦ C, d: 1.2 g/cm3 and diffraction index: 1.4637; FTIR (KBr): 2916–2852(CH2 ), 1678(C=N) cm−1 . Anal. Calcd. for C22 H45 N (323.59 g/mol): C, 81.66; H, 14.02; N, 4.32. Found: C, 81.20; H, 14.82; N, 4.22. m/z: 324 (M + 1). 2.2.2. Solvent-free preparation of Cu(II) complex Cu(CH3 COO)2 ·H2 O (0.0199 g, 0.1 mmol) was added to the Schiff base ligand (0.0647 g, 0.2 mmol), stirred and heated to 60◦ C for 48 hours under a nitrogen atmosphere in solvent free conditions. The product was cooled and washed with water. The Cu (II) complex was green. The long-chain Schiff base complexes are highly soluble polar and even in non-polar solvents such as petroleum ether, diethyl ether and n-hexane. Yield 92%; FTIR (KBr): 2920–2850(CH2 ), 1642(C=N) cm−1 . Anal. Calcd. for C48 H96 CuN2 O4 (829 g/mol): C, 69.48; H, 11.58; N, 3.37. Found: C, 69.20; H, 11.02; N, 3.22. m/z: 830 [M + 1].
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Other metal complexes were obtained in the same procedure. The spectroscopic results of the other complexes: 2.2.2.1. Ni(II) complex. Yield 86%; FTIR (KBr): 2921–2852(CH2 ), 1643(C=N) cm−1 . Anal. Calcd. for C44 H90 NiN2 Cl2 (776 g/mol): C, 68.04; H, 11.59; N, 3.60. Found: C, 67.86; H, 11.22; N, 3.52. m/z: 799 [M + Na].
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2.2.2.2. Cu(I) complex. Yield 82%; FTIR (KBr): 2921–2852(CH2 ), 1640(C=N) cm−1 . Anal. Calcd. for C44 H90 CuN2 Cl2 (782 g/mol): C, 67.52; H, 11.50; N, 3.58. Found: C, 67.08; H, 11.72; N, 3.29. m/z: 829 [M + H + 2Na].
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2.2.2.3. Co(II) complex. Yield 90%; FTIR (KBr): 2921–2852(CH2 ), 1640(C=N) cm−1 . Anal. Calcd. for C46 H95 CoN2 O3 (783 g/mol): C, 70.49; H, 12.13; N, 3.57. Found: C, 69.82; H, 12.58; N, 3.20. m/z: 782 [M-1].
3. Results and discussion
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2.2.3. Antimicrobial activity Serial two-fold dilutions ranging from 5 mg/mL to 0.004 mg/mL were prepared in medium. The inoculum were prepared using a 4–6 h broth culture of each bacteria and 24 h culture of yeast strains adjusted to a turbidity equivalent to a 0.5 Mc Farland standard, diluted in broth media to give a final concentration of 5 × 105 cfu/mL for bacteria and 0.5 × 103 to 2.5 × 103 cfu/mL for yeast in the test tray. The trays were covered and placed in plastic bags to prevent evaporation. The trays containing Mueller-Hinton broth were incubated at 35◦ C for 18–20 h and the trays containing RPMI-1640 medium were incubated at 35◦ C for 46–50 h. The MIC was defined as the lowest concentration of compound giving complete inhibition of visible growth.
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3.1. Preparation of the ligand and its complexes
The imine ligand (N-dodecyl-N1-dacanimine) was synthesized by the reaction of dodecylamine (laurylamine) with decanal in molar 1 : 1 ratio in methanol. However, metal complexation reactions were carried out under solvent-free conditions. Among the solvents tested for this reaction (i.e. EtOH and MetOH), it was found that the best result (short reaction time and maximum yield of the product) was obtained under solvent-free condition, which is also economically and environmentally favorable. The complexes have been prepared by treating the imine ligand with the corresponding metal salt in 2 : 1 (shown in Scheme) ratio, under solvent-free condition yield 82–92%. 3.2. Characterization of the ligand (LH2 ) and the complexes FTIR spectra gave useful information on the structure of the imine ligand (L) and its complexes. Synthesis reaction of the ligand confirmed by the presence of strong C=N at 1678 cm−1 . This band shifted 1640 to 1643 cm−1 in the complexes (Table 1). The shifting of C=N from higher frequency to lower frequency suggested that the co-ordination of the Schiff-bases occurred through the nitrogen of the azomethine (C=N) groups. All results are in agreement with the expected molecular formula of the ligand and complex.
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H3C
H3C
O CH OH 3
H3C
N
H3C
-H2 O
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NH2
H3C
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N M
H3C
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M : Cu (I), Cu (II), Ni (II) and Co (II) in solvent free conditions
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Scheme 1. Formation of the ligand and complexes of Cu(I), Cu(II), Ni(II) and Co(II) under solvent-free conditions. Table 1 IR spectrum of the ligand and complexes C = N (Cm−1 )
2916–2852 2921–2852 2920–2850 2921–2852 2921–2852
1678 1643 1642 1640 1640
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L Ni(II) Cu(II) Co(II) Cu(I)
CH2 (Cm−1 )
The long-chain imine complexes are highly soluble polar and even in non-polar solvents such as petroleum ether, diethyl ether and n-hexane [14]. In the mass spectrum of the ligand, the peak observed at m/z 324 was assigned to the [M + 1] ion. The metal complexes were also identified by mass spectra (peaks at m/z 799 [M + Na] nickel(II), 829 [M + H + 2Na] copper(I), 830 [M + 1] copper(II) and 782 [M-1] cobalt(II)). These peaks are consistent with the molecular weight of the ligand. The electronic absorption spectral data for ligand and complexes were obtained in methanol solutions. The electronic spectrum of ligand showed three types of transition. The first one appeared at 206 nm which can be assigned to -* transition was due to transition involving orbitals located on the longchain. The second type of transition appeared at 230 nm which can be assigned to -* transition was due to transition involving molecular orbital of the C=N group. The third type of transition appeared at 280 nm which can be assigned to n-* transition was due to the C=N chromophore. The spectra of the complexes show another type of transition different from the ligand. The transition was at 312–320 nm which can be assigned to ligand to metal charge transfer. The elemental analysis of the ligand had good agreement with the proposed structure.
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Table 2 Antimicrobial activity results (MIC values in mg/mL) of synthesized compounds Mikroorganizma
MIC of Cu(I) complexes
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Co(II)
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0.009 0.009 0.009 0.009 0.039 0.156 0.156 0.009
0.039 0.039 0.039 0.156 0.156 – – 0.156
0.039 0.078 0.009 – 0.625 – – 0.039
0.009 0.009 0.009 0.156 0.078 – – 0.009
0.009 0.078 0.009 0.078 0.078 – – 0.009
Cefuroxime (1,200) Vancomycin (2,000) Cefuroxime (9,800) Cefuroxime (4,900) Cefuroxime (4,900) Ceftazidime (2,400) Cefuroxime (2,400) Clortrimazole (4,900)
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Staphylococcus aureus ATCC 6538 MRSA ATCC 33591 Staphylococcus epidermidis ATCC 12228 Escherichia coli ATCC 8739 Klebsiella pneumoniae ATCC 4352 Pseudomonas aeruginosa ATCC 1539 Proteus mirabilis ATCC 14153 Candida albicans ATCC 10231
Ligand
4. Conclusions
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The ligand and complexes exhibited remarkable antimicrobial activity against the tested microorganism. All the MIC results are presented in Table 2. The compounds were able to inhibit the growth of the selected microorganisms in vitro showing MIC values between 0.156 and 0.009 mg/mL. Among the synthesized compounds ligand and Cu(II) were found the most active derivatives at an MIC value of 0.009 mg/mL against S. aureus, MRSA and S. epidermidis. The ligand and the Cu(II) and Co(II) complexes showed the higest antimicrobial effect against C. albicans (0.009 mg/mL). Similarly other Ni(II), Cu(I) and Cu(II) comlexes showed good antimicrobial effect against C. albicans (MIC values between 1.56–0.078 mg/mL). Except for ligand, none of the it’s compleses exhibited activity against Pseudomonas aeruginosa ATCC 1539, Proteus mirabilis ATCC 14153.
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New bis-imine complexes have been synthesized at high yield in solvent-free conditions. Avoiding the use of solvents in synthesis can reduce environmental contamination and even be more convenient than using solvent-based synthesis. The higher concentration of reactants in the absence of solvents usually leads to more favorable kinetics than in solution. Solvent-free reactions obviously reduce pollution and bring down handling costs because of the simplification of experimental procedure and workup technique. These would be especially important during industrial production, and make synthetic processes clean, safe, high-yielding, and inexpensive. Field of solvent-free organic synthesis covers all branches of organic chemistry. Also, antimicrobial screening indicated that the tested compounds exhibited remarkable antimicrobial activity against the tested microorganism. Thus, the new imine ligand and bis-imine complexes could be lead compounds for further molecular modifications in the search for novel antibacterial agents. References [1] P.A.S. Smith, The Chemistry of Open-Chain Organic Nitrogen Compounds, Vol. 1, W.A. Benjamin, New York, 1965, pp. 291–313. [2] R.W. Layer, The Chemistry of Imines, B.F. Goodrich Co., Research Center, Brecksville, Ohio, 1962, pp. 490–495.
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[3] E.H. Rodd, Rodd’s Chemistry of Carbon Compounds, Aliphatic Compouds, Vol. 1, Elsevier Scientific Publishing Company, Amsterdam, 1962, pp. 1–493. [4] R.S. Monson and J.C. Shelton, Fundamentals of Organic Chemistry, New York, 1974, pp. 1–438. [5] P.G. More, R.B. Bhalvankar and S.C. Pattar, Synthesis, Spectral and Microbial Studies of Some Novel Schiff Base Derivatives of 4-Methylpyridin-2-amine, J Indian Chem Soc 78(9) (2001), 474–475. [6] R. Layer, The chemistry of Imines, Chem Reviews 63 (1963), 489–510. [7] O. Meth-Cohn, J Chem Soc Perkin Trans 1 (1984), 1173–1182. [8] R. Layer, The Chemistry of Imines in Chem Rev 63 (1967), 489–493. [9] B.M. Smith and J. March, March’s Advanced Organic Chemistry; Reactions, Mechanisms and Structure, 5 edition, John Wiley & Sons, Inc., New York, 2001, pp. 1–242. [10] R.T. Morrison and R.N. Boyd, Organic Chemistry, Englewood Cliffs, New Jersey, 1992, pp. 517–520. [11] E.E. Royals, Advanced Organic Chemistry, Englewood Cliffs, N.J. Prentice-Hall, Inc, U.S.A., 1954, pp. 787–790. [12] Clinical and Laboratory Standards Institute (CLSI) Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically: Approved Standard, M7-A5. Wayne, CLSI, PA, 2006. [13] Clinical and Laboratory Standards Institute Reference Method for broth dilution antifungal susceptibility testing of yeasts; Third Informational Supplement, M27-S3. Clinical and Laboratory Standards Institute, Wayne, CLSI, PA, 2008. [14] A. Mentes¸, M. Sarbay, B. Hazer and H. Arslan, Applied Organometallic Chemistry 19(1) (2005), 76–80.
