from Sigma. Anhydrous grade methanol and DMSO were purified according to standard procedures. Mic-roanalytical data and FAB mass spectra of the compounds were recorded at the Regional Sophisticated Instrumentation Center (Central Drug Research Institute (RSIC, CDRI), Lucknow).
The FAB mass spectrum of the complex was recorded on a JEOL SX 102/DA-6000 mass spectrometer/data system using argon/xenon (6 kV, 10 mA) as the FAB gas. The accelerating voltage was 10 kV, and the spectra were recorded at room temperature using m-ni-trobenzyl alcohol (NBA) as the matrix.
The IR spectra of the samples were recorded on a Perkin-Elmer 783 spectrophotometer in 4000-200 cm-1 range using KBr pellets.
The UV-Vis spectra were recorded on a Shimadzu UV-1601 spectrophotometer using DMSO as solvent at 300 K.
The X-band ESR spectra of the complexes were recorded at 300 and 77 K at the IIT (Mumbai) using TCNE (tetracyanoethylene) as the g-marker.
Magnetic susceptibility measurements for the solid complexes were carried on the Guoy balance using copper sulfate as the calibrant at room temperature.
Electrochemical studies were carried out using EG&G Princeton Applied Research Potentiostat/Gal-vanostat Model 273A controlled by the M270 software.
Cyclic voltammetry measurements were performed using a glassy-carbon working electrode, a platinum wire auxiliary electrode, and an Ag/AgCl reference electrode. All solutions were purged with N2 for 30 min prior to each set of experiments. The molar conductance of the complexes was measured using a Systronic conductivity bridge. Solutions of CT-DNA in 50 mM Tris-HCl/18 mM NaCl (pH 7.0) gave a ratio of UV absorbance at 260 and 280 nm, ^260/^280 of ca. 1.8-1.9, indicating that the DNA was sufficiently free of protein contamination. The DNA concentration was determined by the UV absorbance at 260 nm after
1 : 100 dilutions. Stock solutions were kept at 4°C and used after not more than 4 days. Doubly distilled H2O was used to prepare the buffer. The antimicrobial activities of the ligands and their complexes were carried out by the well-diffusion method.
Designing of the Schiff base ligands. The Schiff base of the ligand was synthesized by an alcoholic solution of benzaldehyde/cinnamaldehyde/2-chloroben-zaldehyde (0.01 M) with 4-aminoantipyrine (0.01 M) in the 1 : 1 ratio with vigorous magnetic stirring. The yellow-colored solid Schiff base was isolated by filtration, washed, and recrystallized from ethanol.
Designing the vanadium complexes. 4[(Ben-zylidene/cinnamalidene/2-chlorobenzylidene)amino] antipyrine (2 mmol) in an alcohol-acetonitrile mixture, 1,10-phenanthroline (2 mmol) in alcohol, and vanadium sulfate (2 mmol) in distilled water were refluxed for
2 h using the template method and then cooled. The
green-colored precipitate was filtered off, washed with water and ethanol, and dried in vacuo. The proposed structure of the complexes is the following:
HsCN .CHs
NI
N=CH—R
/Vv
NN
2+
SO4
(Ia)
(Ib)
R==-
Cl (Ic)
Gel electrophoresis. The gel electrophoresis experiments were performed by incubation at 35°C for 1.5 h as follows. The test solution containing CT DNA (30 |M), a complex (50 |M), H2O2 (500 |M) in tris-HCl buffer (50 mM) (pH 7.2) was electrophoresized for 4 h at 40 V on 1% agarose gel using tris-acetic acid-EDTA buffer (pH 8.3). After electrophoresis, the gel was stained using 1 |g/cm3 EB and photographed under UV light.
RESULTS AND DISCUSSION
All the complexes are stable at room temperature, non-hygroscopic, insoluble in water but slightly soluble in methanol, ethanol, DMF and soluble in DMSO and chloroform. The analyses of the proposed [VO(Phen)(L)]SO4 complexes are consistent with the stoichiometry VO : (Phen) : (L) = 1 : 1 : 1) and are summarized in Table 1. High molar conductance values of all the complexes in DMSO indicate that the sulfate ion is present outside of the coordination sphere, which is confirmed by the barium chloride test. It is known that five-coordinated vanadyl species are blue or green in color, while the six-coordinated complexes are orange or red [18]. Our synthesized complexes are green in color, which favors the five-coordinate geometry.
Effective magnetic moments of all the complexes after the appropriate diamagnetic correction values (1.73-1.84 |B) are very close to spin only values for a
Table 1. Physical characterization, analytical, molar conductance, and magnetic susceptibility data of the complexes
Compound Content (found/calcd) % Ohm 1 cm2 mol 1
M C H N
V[C30H25N5O2]SO4 8.1/8.2 56.7/56.6 3.8/3.9 11.1/11.0 170
V[C32H27N5O2]SO4 7.5/7.6 57.2/57.4 4.1/4.0 10.4/10.4 210
V[C30H24N5O2Cl]SO4 7.6/7.7 54.3/54.5 3.5/3.6 10.5/10.6 160
d1 case [19]. These values are suited for the oxovanadi-um monomeric complex with one unpaired electron.
The FAB mass spectra of the complexes are used to identify their stoichiometric composition. The mass spectrum of complex Ia gives two important fragmentations, which are given below. The base peaks appeared at m/z 292 and 181 correspond to the 4[(benzylidene)amino]an-tipyrine and 1,10-phenanthroline moieties. The molecular ion peak of complex Ia was observed at m/z 635, which confirms the stoichiometry of the metal complex as [VO(Phen)L]SO4.
The Schiff bases show a prominent peak at ca. 1715 cm1 corresponding to v(C=O) of 4-aminoantipyrine and another band at 1630 cm1 corresponding to v(C=N). In the spectra of all the complexes, a sharp band observed at 1663 cm1 is due to v(C=O) of 4-aminoantipyrine. Two sharp peaks observed at 1597 and 966 cm1 are due to v(C=N) and v(V=O), respectively. The observed down-field shifts, going from the free Schiff base ligands to the complexes, suggest coordination of the carbonyl group to the metal and also the involvement of the azomethine nitrogen. The new medium intensity bands in regions of 410 and 500 cm1 are due to v(V -— N) and v(V -— O), which indicate coordination of the ligand to the metal ion.
The electronic absorption spectra often can provide quick and reliable information about the ligand arrangement in the transition metal complexes. The vanadyl complexes, recorded in DMSO at 300 K, exhibit bands in the regions 33500, 14500, and 24600 cm1, which are assigned as INCT, 2B2 —► 2E, and 2B2 —► 2A1 transitions, respectively, which are consistent with that of five-coordinate square pyramidal geometry [20-21].
Cyclic voltammetry is the most versatile electroana-lytical technique for the study of electroactive species. The important parameters of a cyclic voltammogram are the magnitudes of the anodic peak current (ipa), cathodic peak current (ipc), anodic peak potential (Epa), and cathodic peak potential (Epc). The cyclic voltammogram of the oxovanadium complex recorded in DMSO at 300 K in the potential range from +1.2 to -1.3 V is depicted in Fig. 1. In the cathodic side, the peak at Epc = = 0.065 V is assigned to the reduction of VO(I)/VO(0). In the anodic side, the peak at Epa = 0.948 V is assigned to the oxidation of VO(II)/VO(III) [22].
ESR spectral technique is a powerful tool to investigate the nature of bonding in the oxovanadium(IV) complexes [23-24]. Its simplicity due to high isotropic purity and the absence of interaction effects makes studies interesting. Vanadium has a large nuclear moment with a nuclear spin of 7/2. The ESR spectrum of metal chelates provides information about the hyper-fine and superfine structures, which is of importance in studying the metal ion environment in metal complexes, i.e., the geometry, nature of the ligating sites from the Schiff base to metal, and the degree of covalency of the M-L bonds.
The ESR spectra of the complexes were recorded as polycrystalline samples at room temperature and at the liquid-nitrogen temperature. ESR signals are readily observed for the VO(IV) complex. The spectra of the polycrystalline sample gave one signal at room temperature and eight lines are observed at the liquid-nitrogen temperature due to isotropic intramolecular dipolar interactions between the electron and the vanadyl ion (I = = 7/2). As expected, the g-values are invariably lower than the free-electron value (ge = 2.0023). This lowering is related to the spin-orbital interaction of the ground state, d^, with low lying excited states, thus lowering from ge, which is an approximate measure of the ligand field strength. The ESR spectrum of oxovanadium
< s
<D 3
U
1.2
E, V(Ag/AgCl)
-1.3
Fig. 1. The cyclic voltammogram of the the oxovanadium complex in DMSO solution at 300 K (0.1 M TBAP, scan rate 100 mV s-1).
Table 2. Antibacterial activity of the ligand and its complexes (zone formation in mm)
Compounds B. subtilis S. aureus E. coli P. putita
V[C30H25N5O2]SO4 9 13 16 8
V[C32H27N5O2]SO4 12 25 28 16
V[C30H24N5O2Cl]SO4 10 19 20 10
Penicillin 7 10 14 9
at room temperature in the solid state recorded at frequency of 9.1 GHz, and the field set of 2000 G exhibited axial symmetry with hyperfine splitting in both parallel and perpendicular components with partial overlap. The calculated g||, g±, and G values are 1.8, 1.9, and 4.98, respectively. The A|| and values for the complex are 178 and 76 G, respectively, indicating that the complex is of square-pyramidal geometry. The g values are lower than the free-electron value (g < g± < ge) shows that the unpaired electron is in the dy-orbital of the vanadium ion. The lowering of the g value is due to the spin-orbital interaction of the ground state dxy with low-lying excited state.
The molecular orbital coefficients a2 and |2 were also calculated for the complex (Ia) using the following equations:
a2 = (2.0023 - g||)£/(-8À|2), |2 = 7/6(-A||/P + AJP + g||(-5/14)g± - 9/14ge).
In these equations, P = 128 x 10-4 cm-1, X = 135 cm-1 and E is the electronic transition energy of 2B2 —» 2E. We used the simplified molecular orbital theory [25, 26] to calculate the molecular orbital coefficients. The calculated values for in-plane c-bonding a2 = 0.68 and for in-plane n-bondin
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.