КООРДИНАЦИОННАЯ ХИМИЯ, 2015, том 41, № 5, с. 312-318
УДК 541.49
SYNTHESIS, STRUCTURE, AND PHARMACOLOGICAL EVALUATION OF Co(III) COMPLEX CONTAINING TRIDENTATE SCHIFF BASE LIGAND
© 2015 S. Jone Kirubavathy1, R. Vèlmurugan1, R. Karvembu2, N. S. P. Bhuvanesh3, K. Parameswari4, and S. Chitra4, *
department of Chemistry, Kongunadu Arts and Science College, Coimbatore, 641029 India 2Department of Chemistry, National Institute of Technology, Tiruchirappalli, 620015 India 3Department of Chemistry, Texas A&M University, College Station, TX 77842 USA 4Department of Chemistry, P.S.G. R. Krishnammal College for Women, Coimbatore, 641004 India
*E-mail: chitrapsgrkc@gmail.com Received October 16, 2014
A Co(III) Schiff base complex with the formula [Co(L)2]Cl • H2O (I) (L = monoanionic tridentate Schiff base ligand derived from salicylaldehyde and ethylene diamine) has been synthesized and characterized by elemental analysis and spectroscopic techniques. The structure of I was confirmed by single crystal X-ray diffraction studies (CIF file CCDC no. 1009967), which showed the presence of two Schiff base molecules in an octahedral fashion. The complex has been screened for its in vitro antibacterial and anticancer activities. Complex I was found to be more active in anti-microbial and anti-cancer activity than the ligand.
DOI: 10.7868/S0132344X15050047
INTRODUCTION
Schiff bases and their complexes have a variety of applications including biological, clinical and analytical, and have been extensively studied over the past few decades [1—3]. Schiff base metal complexes are very popular due to their diverse chelating ability [4]. They play an important role in both synthetic and structural research, because of their preparative accessibility and structural diversity [5]. Due to variable magnetic property and catalytic activity, they can also serve as efficient models for the metalloproteins and enzymes [6, 7]. In view of the interest involved in the Schiffbase complexes, many cobalt Schiff base complexes have been synthesized and characterized [8, 9]. We report herein the synthesis and biological evaluation of Schiff base complexes of cobalt.
EXPERIMENTAL
Materials, methods and measurements. All the
chemicals were purchased from Sigma Aldrich. Elemental analyses of the compounds were carried out using the ElementarVario EL III CHN analyzer. The FT-IR spectra were recorded on a Shimadzu FT-IR spectrophotometer in the 4000—400 cm-1 region. The UV-Vis spectra were recorded on an Elico SL 159 UV-Vis spectrophotometer. The molar conductance of the complex was measured using a Systronics conductivity bridge at room temperature in DMSO solution. The thermal behavior of Co(III) complex was studied using PerkinElmer STA 6000 thermo analyzer. The antimicrobial activity of the ligand and its Co complex was
carried out by disc diffusion method. The Schiff base ligand was prepared from salicylaldehyde and ethylene diamine according to the reported procedure [10, 11]. The human cervical cancer cell line (HeLa) was obtained from National Centre for Cell Science (NCCS), Pune and grown in Eagles Minimum Essential Medium (EMEM) containing 10% fetal bovine serum (FBS). All cells were maintained at 37°C, 5% CO2, 95% air and 100% relative humidity.
Synthesis of Co(III) complex (I). The Schiff base ligand (0.0328 g, 0.2 mmol) in ethanol (10 mL) was added to a solution of CoCl2 • 6H2O (0.0237 g, 0.1 mmol) in ethanol (10 mL), and the mixture was heated under reflux for 5 h. The product obtained was filtered, washed and dried. The yield was 67%, m.p. = 218°C, orange so-lid.
For C18H24N4O3ClCo
anal. calcd., %: C, 49.22; H, 5.46; N, 12.76, Found, %: C, 49.22; H, 5.47; N, 12.76.
IR (KBr; v, cm-1 ) 3380 s, 3420 s, 1634 s, 1448 w, 1386 w, 1298 w, 1154 w, 1123 w, 673 s, 598 m, 553 m, 548 m.
X-ray determination of structure I. A Bruker APEX 2 X-ray (three-circle) diffractometer was employed for crystal screening, unit cell determination, and data collection. The X-ray radiation employed was generated from a Mo sealed X-ray tube (X = 0.70173 A with a potential of 40 kV and a current of 40 mA) fitted with a graphite monochromator in the parallel mode (175 mm collimator with 0.5 mm pinholes). Systematic reflection conditions and statistical tests of the data suggested the space group Pbca. A solution was obtained
Table 1. Crystal data and structural refinement parameters for I
Parameter Value
Formula weight 438.79
Temperature, K 110.15
Crystal system Orthorhombic
Space group Pbca
Unit cell dimensions:
a, A 10.036(3)
b, A 11.842(3)
c, A 32.425(8)
Volume, A3 3853.6(16)
Z 8
Pcalcd mg/m3 1.513
Absorption coefficient, mm-1 1.056
F(000) 1824
Crystal size, mm 0.32 x 0.24 x 0.18
9 Range for data collection, deg 2.387-27.478
Index ranges -13 < h < 13, -15 < k < 15, 0 < l < 40
Reflections collected 14280
Independent reflections (Rint) 4282 (0.0290)
Data/restraints/parameters 4282/0/247
Goodness-of-fit on F2 1.052
Final R indices (I> 2a(I)) Rx = 0.0293, wR2 = 0.0730
R indices (all data) R1 = 0.0352, wR2 = 0.0751
Largest diff. peak and hole, e A-3 0.348 and -0.399
readily using SHELXTL (XS) [12]. Hydrogen atoms were placed in idealized positions and were set riding on the respective parent atoms. All non-hydrogen atoms were refined with anisotropic thermal parameters. The structure was refined (weighted least squares refinement on F2) to convergence [13]. Olex2 was employed for the final data presentation and structure plots. The crystal data and structural refinement parameters are summarized in Table 1. Bond lengths and bond angles for the complex have been incorporated in Table 2. A few selected H-bonding parameters are given in Table 3.
Supplementary material for the crystal structure has been deposited with the Cambridge Crystallo-graphic Data (no. 1009967; deposit@ccdc.cam.ac.uk or http://ccdc.cam.ac.uk).
Antimicrobial activity. The antibacterial activity of the ligand and the Co(III) complex was tested against the bacteria S. aureus, B. subtilis, S. paratyphi and K. pneumoniae by the disc diffusion method using agar nutrient medium. The antifungal activity was screened for
Table 2. Selected bond lengths (A) and bond angles (deg) for I
Bond d, Â
Co(1)-O(2) 1.8979(11)
Co(1)-O(1) 1.8894(12)
Co(1)-N(2) 1.9547(14)
Co(1)-N(3) 1.8978(14)
Co(1)-N(1) 1.8960(14)
Co(1)-N(4) 1.9600(14)
Angle ro, deg
O(2)Co(1)N(2) 89.23(6)
O(2)Co(1)N(4) 177.90(5)
O(1)Co(1)O(2) 90.77(5)
O(1)Co(1)N(2) 179.99(7)
O(1)Co(1)N(3) 88.74(5)
O(1)Co(1)N(1) 94.76(5)
O(1)Co(1)N(4) 87.17(6)
N(2)Co(1)N(4) 92.83(6)
N(3)Co(1)O(2) 94.22(6)
N(3)Co(1)N(2) 91.26(6)
N(3)Co(1)N(4) 85.36(6)
N(1)Co(1)O(2) 87.58(6)
N(1)Co(1)N(2) 85.24(6)
N(1)Co(1)N(3) 176.05(6)
N(1)Co(1)N(4) 92.97(6)
C(15)O(2)Co(1) 124.20(10)
C(6)O(1)Co(1) 124.20(11)
the organisms A. niger and C. albicans cultured on potato dextrose agar medium, by the disc diffusion method. The plates were incubated for 24 and 72 h for bacteria and fungi respectively. Then, the test solutions were diffused and the growth of the inoculated microorganisms was affected. The inhibition zone was developed, at which the concentration of the samples was noted [14].
Anticancer activity-cell treatment procedure and MTT assay. The monolayer cells were detached with trypsin-ethylenediaminetetraacetic acid (EDTA) to make single cell suspensions and viable cells were counted using a hemocytometer and diluted with medium containing 5% FBS to give final density of 1 x 105 cells/mL. Cell suspensions were seeded into 96-well plates at plating density of 10000 cells/well and incubated to allow for cell attachment at 37°C. After 24 h, the cells were treated with serial concentrations of the test samples. They were initially dissolved in DMSO and diluted to twice the desired final maximum test concentration with serum free medium. Additional four, 2 fold serial dilutions were made to pro-
Table 3. Geometric parameters of hydrogen bonds of I*
D H-A Distance, Ä Angle DHA, deg
D-H H-A D-A
O(1w)-H(1w^)-Cl(1)#1 0.85 2.30 3.1489(16) 174
N(2)-H(2^)-Cl(1)#2 0.99 2.31 3.2237(15) 154
N(2)-H(25)-Cl(1) 0.99 2.29 3.2455(15) 160
N(4)-H(4^)-Cl(1)#2 0.99 2.35 3.3308(17) 173
N(4)-H(45)-O(1w) 0.99 1.95 2.927(2) 169
* Symmetry transformations used to generate equivalent atoms: #1 x — 1, y, z; #2 x - 1/2, y, -z + 3/2.
vide a total of five sample concentrations. Aliquots of 100 ^L of these different sample dilutions were added to the appropriate wells already containing 100 ^L of medium, resulted the required final sample concentrations. Following drug addition, the plates were incubated for an additional 48 h at 37°C. The medium containing without samples was served as control and triplicate was maintained for all concentrations.
3-[4,5-Dimethylthiazol-2-yl]2,5-diphenyltetrazolium bromide (MTT) is a yellow water soluble tetrazolium salt. A mitochondrial enzyme in living cells, succinate de-hydrogenase, cleaves the tetrazolium ring, converting the MTT to an insoluble purple formazan. Therefore, the amount of formazan produced is directly proportional to the number of viable cells. After 48 h of incubation, 15 ^L of MTT (5 mg/mL) in phosphate buffered saline (PBS) was added to each well and incubat-
ed at 37°C for 4 h. The medium with MTT was then flicked off and the formed formazan crystals were sol-ubilized in 100 ^L of DMSO and then measured the absorbance at 570 nm using micro plate reader. The % cell inhibition was determined using the formula, % cell Inhibition = 100 — Abs (sample)/Abs (control) x 100. Nonlinear regression graph was plotted between % cell inhibition and log10 (concentration) and IC50 was determined using graph pad prism software.
RESULTS AND DISCUSSION
An octahedral Co(III) complex was prepared from the reaction between CoCl2 • 6H2O and Schiff base (derived from the condensation of salicylaldehyde with ethylene diamine):
The analytical and spectral data of the complex revealed monoanionic tridentat
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