научная статья по теме SYNTHESIS, CHARACTERIZATION, ELECTROCHEMICAL STUDIES AND ANTIBACTERIAL ACTIVITIES OF COBALT(III) COMPLEXES WITH SALPN-TYPE SCHIFF BASE LIGANDS. CRYSTAL STRUCTURE OF TRANS-[COIII(L1)(PY)2]CLO4 Химия

Текст научной статьи на тему «SYNTHESIS, CHARACTERIZATION, ELECTROCHEMICAL STUDIES AND ANTIBACTERIAL ACTIVITIES OF COBALT(III) COMPLEXES WITH SALPN-TYPE SCHIFF BASE LIGANDS. CRYSTAL STRUCTURE OF TRANS-[COIII(L1)(PY)2]CLO4»

КООРДИНАЦИОННАЯ ХИМИЯ, 2013, том 39, № 10, с. 606-612

УДК 541.49

SYNTHESIS, CHARACTERIZATION, ELECTROCHEMICAL STUDIES AND ANTIBACTERIAL ACTIVITIES OF COBALT(III) COMPLEXES WITH SALPN-TYPE SCHIFF BASE LIGANDS. CRYSTAL STRUCTURE

OF trans-[Com(L1)(Py)2]ClO4

© 2013 M. Salehi1 *, M. Kubicki2, G. Dutkiewicz2, A. Rezaei3, M. Behzad1, and S. Etminani1

department of Chemistry, College of Science, Semnan University, Semnan, Iran 2Department of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, Poznan, 60-780 Poland 3School of Biological Science, Damghan University, Damghan, Iran *E-mail: msalehi@sun.semnan.ac.ir Received February 24, 2012

The synthesis, characterization, spectroscopic and electrochemical properties of trans-[CoIII(L1)(Py)2]ClO4 (I) and trans-[CoIII(L2)(Py)2]ClO4 (II) complexes, where H2L1 = N,N'-bis(5-chloro-2-hydroxyben-zylidene)-1,3-propylenediamine and H2L2 = N,N'-bis(5-bromo-2-hydroxybenzylidene)-1,3-propylenedi-amine, have been investigated. Both complexes have been characterized by elemental analysis, FT-IR, UV-Vis, and 1H NMR spectroscopy. The crystal structure of I has been determined by X-ray diffraction. The coordination geometry around cobalt(III) ion is best described as a distorted octahedron. The electrochemical studies of these complexes revealed that the first reduction process corresponding to Co(III/II) is elec-trochemically irreversible accompanied by dissociation of the axial Co-N(Py) bonds. The in vitro antimicrobial activity of the Schiff bse ligands and their corrsponding complexes have been tested against human pathogenic bacterias such as Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, and Escherichia coli. The cobalt(III) complexes showed lower antimicrobial activity than the free Schiff base ligands.

DOI: 10.7868/S0132344X13100083

INTRODUCTION

Schiff bases are widely used as analytical reagents since they allow simple and inexpensive preparation of a number of organic and inorganic compounds [1]. There is a growing interest in the chemistry of chelate complexes of Schiff bases because of the wide range of applications of these complexes in various fields. Numerous studies are also devoted to the synthesis and characterization of the metal complexes with bioactive organic ligands in order to produce novel potential chemotherapeutic agents. Particularly important is the pressing need for the new antibacterial agents which could replace those losing their effectiveness because of the fast development of microorganisms' resistance [2]. Therefore, the discovery of brand new antimicrobial compounds or finding the ways to increase the effectiveness of previously known drugs is important. Some cobalt complexes with tetradentate Schiff bases are known to exhibit antibacterial activity, amongst their many other applications, such as reversible oxygen transport, potent antiviral or antitumor agents, in enantioselective and asymmetric catalysis, or as the models for vitamin B12 [3—8]. In our ongoing studies on the synthesis, structural, spectroscopic and electrochemical studies of cobalt(III) complexes with Schiff base ligands [9, 10], we report here the synthesis

and characterization of ira«s-[CoIII(L1)(Py)2]ClO4 (I) and trans-[Com(L2)(Py)2]ClO4 (II) complexes. Their spectral properties were investigated by FT-IR, UV-Vis, and 1H NMR spectra. The X-ray crystal structure of I has been determined. Electrochemical properties of these complexes are reported and discussed. Antibacterial activities of the Schiff base ligands and their complexes against Bacillus subtilis (Gram-positive), Staphylococcus aureus (Gram-positive), Escherichia coli (Gram-negative), and Pseudomonas aeruginosa (Gram-negative) are investigated for the first time.

EXPERIMENTAL

Materials and methods. All solvents and chemicals were used as received, except the amines which were distilled under reduced pressure prior to use. Elemental analyses were performed by using a PerkinElmer 2400II CHNS-O elemental analyzer. 1H NMR spectra were recorded on a 500 MHz Bruker FT-NMR spectrometer using CDCl3 solvent; chemical shifts (8) are given in ppm. IR spectra were obtained as KBr plates using a Bruker FT-IR instrument and UV-Vis spectra were obtained on a Shimadzu UV-1650PC

spectrophotometer. A Metrohm 757 VA computerace instrument was employed to obtain cyclic voltammo-grams in acetonitrile at room temperature (25°C) using 0.1 M tetra-n-butylammonium hexafluorophos-phate solution as supporting electrolyte.

Synthesis of Schiff base ligands. The Schiff base ligands, N,N'-bis(5-chloro-2-hydroxybenzylidene)-1,3-propylenediamine (H2L1) and N,N'-bis(5-bro-mo-2-hydroxybenzylidene)-1,3-propylenediamine (H2L2), were prepared as described in [11].

Synthesis of complex I. Co(CH3COO)2 • 4H2O (0.125 g, 0.5 mmol), dissolved in 10 mL of methanol, was added to a methanolic solution (20 mL) of H2L1 (0.175 g, 0.5 mmol) with constant stirring. To the resulting solution was added 4 mmol of pyridine, and air was bubbled through the reaction mixture for about 3 h. Then 0.5 mmol of NaClO4 was added to the resulting brown solution and stirred for 5 min. A brown microcrystalline solid was produced by slow evaporation of methanol at room temperature. The precipitate was washed with and redissolved in methanol. The single crystals suitable of compound I were obtained by slow evaporation of the methanol solution of this compound after 3 days. The crystals were filtered off and washed with a small amount of cold methanol and dried under vacuum. The yield of I was 50%.

For C27H24N4O6Cl3Co

anal. calcd., %: C, 48.71; H, 3.63; N, 8.42. Found, %: C, 48.50; H, 3.58; N, 8.35.

FT-IR (KBr; v, cm-1): 1609 (C=N), 1082 (Cl-O) UV-Vis (CH3CN; Xmax, nm (s, L mol-1 cm-1)): 226 (59300), 250 (48300), 392 (6990), 575 (380). 1H NMR. (500 MHz; CDCl3; 8, ppm): 1.30 (s., 2Ha), 3.87 (m., 4Hb), 7.02-7.40 (m., 10H, Ar), 8.45 (s.,

2Hc).

Synthesis of complex II. The complex was prepared by the same method as for I except that H2L2 was used instead of H2L1. The compound recrystallised from methanol, but no suitable single crystals were grown for complex II. The yield was 55%.

For C27H24N4O2Br2Co

anal. calcd., %: Found, %:

C, 68.20; C, 68.05;

H, 5.72; H, 5.65;

N, 9.94. N, 9.78.

FT-IR (KBr; v, cm-1): 1618 (C=N), 1084 (Cl-O) UV-Vis (CH3CN; ^max, nm (s, L mol-1 cm-1)): 224 (58500), 251 (47400), 329 (6570), 575 (381). 1H NMR. (500 MHz; CDCl3; 8, ppm): 1.23 (s., 2Ha), 3.79 (m., 4Hb), 7.05-7.78 (m., 10H, Ar), 8.36 (s.,

2Hc).

X-ray structure determination. Diffraction data of complex I were collected at room temperature by the

«-scan technique on an Agilent Technologies Xcali-bur four-circle diffractometer with Eos CCD-detector and graphite-monochromatized MoZ„ radiation source (X = 0.71073 A). The data were corrected for Lorentz-polarization as well as for absorption effects [12]. Precise unit-cell parameters were determined by a least-squares fit of 30159 reflections of the highest intensity, chosen from the whole experiment. The structure was solved with SIR92 [13] and refined with the full-matrix least-squares procedure on F2 by SHELXL-97 [14]. The scattering factors incorporated in SHELXL-97 were used. The function Zw(|Fo|2 - |Fc|2)2 was minimized, with w-1 = [a2(Fo)2 + (0.0840P)2 +

+ 3.2183P] (P = [Max(FO, 0) + 2F] /3) [14]. All non-hydrogen atoms were refined anisotropically, the hydrogen atoms were placed geometrically in idealized positions and refined as rigid groups with their Uiso's as 1.2 or 1.5 (methyl) times Ueq of the appropriate carrier atom. The large residual electron density has been interpreted as the half-occupied solvent (methanol) molecule, which did not interact specifically with the rest of the structure. Hydrogen atoms from this molecule have not been found and no attempts to determine their positions have been performed. Relevant crystal data are listed in Table 1 together with refinement details. A full detail of data collections and structure determinations has been deposited with the Cambridge Crystallograph-ic Data Centre (146366 (I); deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).

Bacterial strains. The metal complexes and ligands were individually tested against a penal of microorganisms (Gram negative and Gram positive), namely Bacillus subtilis (B. subtilis; PTCC no. 1023; ATCC 6633); Staphylococcus aureus (S. aureus; PTCC no. 1431; ATCC 25923), Escherichia coli (E. coli; PTCC no. 1399; ATCC 25922), and Pseudomonas aeruginosa (P. aeruginosa; PTCC no. 1430; ATCC 27853). The organisms were purchased from Iranian Research Organization for Science and Technology (IROST).

Disc diffusion assay. Single-disk diffusion as a qualitative assay was performed according to Bauer et al. [15]. Briefly, four to five colonies of each organism were inoculated into 4 ml of broth and incubated for 4 to 6 h at 37°C. A suspension of each organism was then standardized against a turbidity standard of 0.5 McFarland [16]. Bacteria were cultured on to agar plates using a sterile absorbent cotton swabs. Then plates were incubated at 35 °C and the zones of inhibition were measured after 24 h. Each organism was tested in duplicate on different days to measure the repro-ducibility of the test. Ampicillin (10 Mg/disc), Chloramphenicol (30 Mg/disc), and Kanamycin (30 Mg/disc), purchased from PadtanTeb Company (Iran), were used as reference antibacterial agents. A set of assay tubes containing only inoculated medium was kept as negative control and likewise solvent con-

SALEHI et al.

608

trols were also done simultaneously. All assays were performed in duplicate.

Minimum inhibitory concentration (MIC) of chemicals were determined by the broth twofold dilution method as a quantitative assay [17]. Briefly, serial diluted chemical compounds in the range of 0.04—0.29 mg/mL were added to a final inoculum of approximately 1.5 x x 106 organisms per ml in log phase growth. The cultures were incubated on a rotary shaker at 37°C for 24 h. M

Для дальнейшего прочтения статьи необходимо приобрести полный текст. Статьи высылаются в формате PDF на указанную при оплате почту. Время доставки составляет менее 10 минут. Стоимость одной статьи — 150 рублей.

Показать целиком