КООРДИНАЦИОННАЯ ХИМИЯ, 2009, том 35, № 10, с. 752-756
SYNTHESIS, SPECTRAL AND ANTIBACTERIAL STUDIES OF BIVALENT TRANSITION METAL ION MACROCYCLIC COMPLEXES
© 2009 D. P. Singh1*, V. Malik1, R. Kumar1, K. Kumar1, and J. Singh2
1 Department of Chemistry, National Institute of Technology, Kurukshetra 136119, India 2D.M. Division, National Dairy Research Institute, Karnal 132001, India * E-mail: firstname.lastname@example.org. in Received November 17, 2008
A new series of the macrocyclic complexes of type [M(C18H16N4O2)]X2, where M = Co(II), Ni(II), Cu(II),
Zn(II), Cd(II) and X = Cl-, NO-, CH3COO-, has been synthesized by the condensation of succinyldihydrazide
with benzil in the presence of bivalent metal ions. The complexes have been characterized with the aid of elemental analyses, conductance measurements, and electronic, NMR, and infrared spectral studies. On the basis of these studies, a six-coordinate distorted octahedral geometry in which two nitrogen and two carbonyl oxygen atoms are suitably placed for coordination toward metal ion has been proposed for all the complexes. The complexes were tested for their in vitro antibacterial activity. Some of the complexes showed remarkable antibacterial activity against some selected bacterial strains.
Research on diverse aspects of new macrocyclic compounds has evoked considerable worldwide interest in recent years. The condensation reaction between diketones and primary diamines in the presence of metal ion has played a vital role in the development of macrocyclic complexes (MCC). MCC are thermodynamically more stable and more selective ion bindes than open-chain analogs. The multifarious role is played by the naturally occurring macrocycles in biological systems. The chemistry of synthetic MCC is also of great importance due to their use as dyes and pigments, MRI contrast agents, and models for naturally occurring macrocycles [1-4]. Macrocyclic nickel complexes find use in DNA recognition and oxidation , while macrocyclic copper complexes find use in DNA-binding and cleavage . Some MCC have been reported as showing antibacterial, antifungal, and anti-inflammatory activities [7-9]. Macrocyclic metal chelating agents are useful to detect tumor lesions . Prompted by these, in the present paper a new series of macrocyclic complexes of Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) obtained by the template condensation reaction of succinyldihydrazide and benzil has been reported. The complexes have been characterized with the help of various physicochemical techniques like elemental analyses, IR, NMR, magnetic susceptibilities, electronic spectra, and molar conductance. These macrocyclic complexes were also screened for their in vitro antibacterial activity.
Synthesis of complexes. All the reported MCC were prepared by the template method. To a stirring methanolic solution (~50 cm3) of succinyldihydrazide (10 mmol) was
added bivalent cobalt, nickel, copper, zinc, and cadmium salts (10 mmol) dissolved in a minimum quantity of methanol (20 cm3). The resulting solution was refluxed for 0.5 h. After that benzil (10 mmol) dissolved in ~20 cm3 of methanol was added, and the mixture was again refluxed for 6-8 h. On overnight cooling light colored complexes were formed, which were filtered, washed with methanol, acetone, and ether, and dried in vacuo (the yield was 65%). The complexes were soluble in DMF and DMSO but insoluble in common organic solvents and water. They were found to be thermally stable up to ~250°C and then decomposed.
The template syntheses of the complexes may be represented by the scheme.
Analytical and physical measurements. The microanalyses of C, H, and N were carried out at the Sophisticated Analytical Instrument Facility (CDRI, Lucknow). The metal contents were determined by standard EDTA methods. Electronic spectra (DMF) were recorded on a Cary 14 spectrophotometer. The magnetic susceptibility measurements were carried at the IIT Roorkee. The IR spectra were recorded on a infrared spectrophotometer in the range 4000-200 cm-1 using Nujol mulls. The NMR spectra were recorded on a Bruker NMR spectrometer (300 MHz). The conductivity was measured on a digital conductivity meter (HPG System, G-3001).
Biological assay. Some of the synthesized macrocyclic complexes were tested for in vitro antibacterial activity against some bacterial strains using spot-on-lawn on Muller Hinton Agar .
Four test pathogenic bacterial strains viz., Bacillus cereus (MTCC 1272), where MTCC - Microbiol Type Culture Collection, Salmonella typhi (MTCC 733), Escherichia coli (MTCC 739) and Staphylococcus au-
z \ / z
Methanol 2 (6-8 h)"
:^C6H5 :n C6H5
where M = Co(II), X = Cl- (I), Co(II), X = NO- (II), Co(II), X = CH3COO- (III), Ni(II), X = CH3COO- (IV),
Cu(II), X = Cl- (V), Cu(II), X = NO- (VI), Zn(II), X = CH3COO- (VII), Cd(II), X = CH3COO- (VIII).
reus (MTCC 1144), were considered for determination of minimum inhibitory concentration (MIC) of selected complexes.
The test pathogens were subcultured aerobically using Brain Heart Infusion Agar (HiMedia, Mumbai, India) at 37°C/24 h. Working cultures were stored at 4°C in Brain Heart Infusion (BHI) broth (HiMedia, Mumbai, India), while stock cultures were maintained at -70°C in BHI broth containing 15% (v/v) glycerol (Qualigens, Mumbai, India) an organism was grown overnight in 10 ml BHI broth, and centrifuged at 5.000 g for 10 min and the pellet was suspended in 10 ml of a phosphate saline buffer (PBS, pH 7.2). The optical density at 545 nm (OD-545) was adjusted to obtain 108 cfu/ml followed by plating serial dilution onto plate count agar (HiMedia, Mumbai, India).
The MIC is the lowest concentration of the antimicrobial agent that prevents the development of viable growth after overnight incubation. Antimicrobial activity of the compounds was evaluated using spot-on-lawn on Muller Hinton Agar (MHA, HiMedia, Mumbai, India). Soft agar was prepared by adding 0.75% agar in Muller Hinton Broth (HiMedia, Mumbai, India). Soft agar was inoculated with 1% of 108 cfu/ml of the test pathogen and 10 ml was overlaid on MHA. From 1000X solution of the compound
(1 mg/ml of DMSO) 1, 2, 4, 8, 16, 32, 64, and 128X solutions were prepared. Dilutions of standard antibiotics (Lin-ezolid and Cefaclor) were also prepared in the same manner: 5 ^l of the appropriate dilution was spotted on the soft agar and incubated at 37°C for 24 h. The zone of inhibition of compounds as considered after subtraction of the inhibition zone of DMSO. Negative control (with no compound) was also observed.
RESULTS AND DISCUSSION
The analytical data suggest the formula of macrocyclic complexes as [M(C18H16N4O2)X2], where M = Co(II),
Ni(II), Cu(II), Zn(II), and Cd(II) and X = Cl-, NO3, and CH3COO-. The test for anions is positive after decomposing the complexes with concentrated HNO3, indicating their presence inside the coordination sphere. Conductivity measurements in DMSO indicate them to be nonelec-trolytic in nature  (10-20 Ohm-1 cm2 mol-1). All compounds give satisfactory elemental analyses results as shown in Table 1.
A close perusal of IR spectra exhibits a pair of strong bands at ~3200 and ~3250 cm-1 corresponding to v(N-H),
Table 1. Analytical data of the bivalent cobalt, nickel, copper, zinc, and cadmium complexes derived from succinyldihy-drazide and benzil
Complex Contents (found/calcd), % Color F.w.
C H N M
[C0(Ci8Hi6N4O2)Cl2] (I) 48.i9/48.00 3.73/3.55 i2.52/i2.44 i3.i6/i3.ii Bluish green 450
[Co(Ci8Hi6N4O2)(NO3)2] (II) 42.80/42.94 3.i3/3.i8 i6.95/i6.69 ii.79/ii.72 Orange 503
[C0(Ci8Hi6N4O2)(OAc)2] (III) 53.i9/53.ii 4.i9/4.42 ii.29/ii.26 ii.89/ii.87 Dark red 497
[Ni(Ci8Hi6N4O2)(OAc)2] (IV) 53.3i/53.22 4.33/4.43 ii.27/ii.29 ii.27/ii.69 Dark gray 496
[Cu(Ci8Hi6N4O2)Cl2] (V) 46.86/46.70 3.59/3.52 i2.35/i2.32 i3.69/i3.97 Bluish green 455
[Cu(Ci8Hi6N4O2)(NO3)2] (VI) 42.69/42.56 3.25/3.i5 i6.64/i6.55 i2.62/i2.5i Brown 507
[Zn(Ci8Hi6N4O2)(OAc)2] (VII) 52.5i/52.48 4.23/4.37 ii.27/ii.i3 i2.99/i2.92 White 503
[Cd(Ci8Hi6N4O2)(OAc)2] (VIII) 47.88/47.96 3.93/3.99 i0.i0/i0.i7 20.56/20.42 Off white 550
which is present in the spectrum of succinyldihydrazide but absent in the spectra of all the complexes . However, a broad peak at ~3350-3400 cm1 observed in the spectra of all the complexes is due to v(NH) stretching vibrations [14, 15]. A strong peak at ~1665 cm1 in the spectrum of succinyldihydrazide is attributed to the CO group of the CONH moiety. This peak is shifted to a lower frequency (~1625-1640 cm1) in the spectra of all the complexes , suggesting the coordination of oxygen of the carbonyl group with the metal. Further no strong absorption band was observed near 1690 cm-1 in the IR spectra of the complexes as observed in the spectrum of benzil. This indicates the absence of the >C=O group of the benzil moiety. This confirms the condensation of the carbonyl group of benzil and the amino group of succinyldihydrazide [17, 18]. This fact is also supported by the appearance of a new strong absorption band in the region ~1590-1610 cm-1, which may be attributed to v(C=N) stretching vibrations [19, 20]. These results provide strong evidence for the formation of macrocyclic frame . The lower values of v(C=N) indicate coordination of azomethine nitrogen to metal . The bands present at ~1350-1000 cm-1 may be assigned due to the v(C-N) vibration. The bands present at ~2900-3130 cm-1 may be assigned to v(C-H) vibrations of the benzil moiety and methylene moiety. The far-infrared spectra show bands in the region ~420-460 cm-1 corresponding to v(M-N) vibrations in all the complexes . The presence of bands in all the complexes in the region ~420-460 cm-1 originates from (M-N) azomethine vibration modes and gives an idea about coordination of azomethine nitrogen . The bands presen
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