In vitro antibacterial and antifungal activities of binuclear transition metal complexes of ONNO Schiff base and 5-methyl-2,6-pyrimidine-dione and their spectroscopic validation

Abhay Nanda Srivastva; Netra Pal Singh; Chandra Kiran Shriwastaw

doi:10.1016/j.arabjc.2014.10.004

View/Download PDF

Buy Reprints

PDF

Translate this page into:

Original article

9 (

); 48-61

doi:

10.1016/j.arabjc.2014.10.004

In vitro antibacterial and antifungal activities of binuclear transition metal complexes of ONNO Schiff base and 5-methyl-2,6-pyrimidine-dione and their spectroscopic validation

Abhay Nanda Srivastva, Netra Pal Singh^⁎, Chandra Kiran Shriwastaw

Department of Chemistry, Meerut College, Meerut 250001, India

⁎Corresponding author. Tel.: +91 9411226479. npsmcm.in@gmail.com (Netra Pal Singh),

Received: 2013-2-8, Accepted: 2014-10-8, Published: 2014-01-01

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

Novel binuclear metal complexes of general formula [M₂(PymL)X₃] (where: M = Cu(II), Ni(II), Co(II) or Zn(II); X = Cl⁻ or CH₃CO₂⁻ and PymL = C₁₃H₁₇N₄O₆) were synthesized by template condensation of Schiff base (L) derived from glycine using 2,3-butanedione, 5-methyl-2,6-pyrimidine-dione and metal chloride/acetate salt in 1:1:2 stoichiometric ratio. Synthesized compounds were characterized by elemental analysis, conductance measurement, magnetic measurement, IR, UV–visible, ¹H NMR, ¹³C NMR, EPR and ESI-MS spectral studies. IR spectral data suggest that Schiff base (L) behaves as tetradentate ligand with two nitrogen and two oxygen donor sites of the azomethine group and carboxylic group, respectively and 5-methyl-2,6-pyrimidine-dione behaves as tridentate ligand with two oxygen atoms of the carbonyl group and one nitrogen atom of pyrimidine ring as binding sites. Physico-chemical data suggest octahedral geometry and non-electrolytic nature of metal complexes. The compounds were evaluated for their antimicrobial property by in vitro antimicrobial screening against bacteria Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Salmonella typhi and fungi Candida albicans and Candida parapsilosis. The results indicate that metal complexes exhibit more activity than free Schiff base (L) against studied bacteria and fungi.

Keywords

5-Methyl-2,6-pyrimidine-dione

Binuclear complexes

Octahedral geometry

Antimicrobial property

Show Related Articles from PubMed

1 Introduction

After the discovery of cis-platin, there has been considerable exploration of other transition metal complexes. Enormous interest of coordination compounds of transition metal ions is due to their various biological significance as well as unique catalytic, photochemical and optical properties (Parashar et al., 1988; Suslick and Reinert, 1985; Gamba et al., 2013; Prakash and Natarajan, 2003; Harriman et al., 2007; Singh and Singh, 2014 ). Recently synthesized transition metal complexes have been used for the study of biological activities viz. antibacterial, antifungal, toxicity and DNA interaction (Srivastava et al., 2014; Bagihalli and Patil, 2010; Alagha et al., 2011; Singh and Pal, 2010; Singh and Srivastava, 2010; Tabassum et al., 2001; Patel et al., 2011 ). Pyrimidines, being an integral part of DNA and RNA, play an essential role in several biological processes and have considerable chemical and pharmacological importance. Due to multifunctional coordinating ability of pyrimidines and its derivatives, they have been used for the synthesis of mononuclear and binuclear transition metal complexes (Khali et al., 2002; Mastropietro et al., 2008; Weitzer and Brooker, 2005; Lumme and Knuuttilla, 1995 ). There are many bibliographic data available which display coordination modes of pyrimidine moiety (Faus et al., 1993; Colacio et al., 1995; Masoud et al., 2004 ). Most of the transition metal complexes containing purine or pyrimidine base have been used to understand biological phenomena as well as to get new biologically active metallodrugs (Sikova and Rowan, 2005; Navarro and Lippert, 2001; Sharaby et al., 2007; Sonmez et al., 2010 ). Amino acid Schiff base readily forms complexes with metal ions which play an important role as the basic compounds for modelling more complicated Schiff base (Pyrz et al., 1985; Martell and Szpoganicz, 1989; Aminabhavi et al., 1985; Arbaoui et al., 2011 ). Importance of coordination chemistry of amino acid Schiff bases and other Schiff bases is clear by the study of antifungal, antibacterial and anticancer activities of some reported mononuclear and binuclear complexes (Patil et al., 2010; Gudasi et al., 2006; Tabassum et al., 2010; Shi et al., 2008; Revenco et al., 2011; Singh et al., 2012; Singh and Srivastava, 2012 ). The prime aim of the present work is to prepare binuclear metal complexes of ONNO Schiff base (L) derived from glycine using 2,3-butanedione and 5-methyl-2,6-pyrimidine-dione. Synthesized compounds were characterized by various analytical and spectral studies like elemental analysis, magnetic moment measurement, molar conductance measurement, IR, UV–visible, NMR, EPR and ESI-MS. In vitro antibacterial and antifungal activities of synthesized compounds against some specific microbes were also studied.

2 Experimental

2.1

2.1 Reagents

All chemicals and solvents were of AR grade and used without further purification. MeOH, EtOH, diethyl ether, DMF, DMSO and metal salts were purchased from Qualigens. 2,3-butanedione was purchased from Aldrich. Glycine and 5-methyl-2,6-pyrimidine-dione were purchased from CDH.

2.2

2.2 Synthesis of Schiff base (L)

To an aqueous solution of glycine (20 mmol, 1.50 g), ethanolic solution of 2,3-butanedione (10 mmol, 0.87 ml) was added drop-wise with constant stirring. The resulting solution was stirred at 55 °C for 45 min and refluxed at 60 °C for 1 h. The completion of reaction was monitored by thin layer chromatography (TLC). The solution was cooled in refrigerator overnight. Yellow coloured solid product (L) was precipitated, filtered off, washed with water, MeOH, EtOH and diethyl ether and dried in vacuum desiccator over anhydrous calcium chloride (Scheme 1).

Yield 78%; m.p.: 194 °C; yellow solid. Anal. calc. for C₈H₁₂N₂O₄ (200.18): C 47.99, H 6.04, N 14.00%. Found: C 47.84, H 5.98, N 13.87%.

2.3

2.3 General procedure for synthesis of the binuclear metal complexes (1–4)

To a methanolic solution of Schiff base (L) (1 mmol, 0.20 g), methanolic solution of corresponding metal chloride/acetate salt (2 mmol) [CuCl₂·2H₂O (0.34 g), NiCl₂·6H₂O (0.47 g), CoCl₂·6H₂O (0.48 g) and Zn(CH₃CO₂)₂·H₂O (0.44 g)] was added drop-wise with continuous stirring and solution mixture was stirred at 60 °C for 30 min. Subsequently, a hot aqueous ethanolic solution of 5-methyl-2,6-pyrimidine-dione (1 mmol, 0.126 g) was added drop-wise and stirred at 65 °C for 2 h and refluxed at 75 °C for ∼10–12 h. The completion of reaction was monitored by thin layer chromatography (TLC). The solutions were cooled in refrigerator overnight. Coloured solid products (except Zn(II) complex) of metal complexes were isolated, filtered off, washed with hot water, MeOH, EtOH and diethyl ether and dried in vacuum desiccator over anhydrous calcium chloride (Scheme 2).

Synthesis of binuclear metal complexes [M2(PymL)X3] (1–4).

2.3.1

2.3.1 Binuclear metal complex [Cu₂(PymL)Cl₃] (1)

Yield 64%; m.p.: 258 °C (dec.); dark brown solid. Anal. calc. for C₁₃H₁₇N₄O₆Cl₃Cu₂ (558.72): C 27.92, H 3.04, N 10.02, Cu 22.75, Cl 19.06%. Found: C 27.86, H 2.98, N 9.96, Cu 22.68, Cl 18.97%. Molar conductance Λ_M: 8.20 Ω⁻¹ cm² mol⁻¹. μ_eff: 1.92 BM. UV–visible (DMSO), λ_max: 602 nm.

2.3.2

2.3.2 Binuclear metal complex [Ni₂(PymL)Cl₃] (2)

Yield 68%; m.p.: 244 °C (dec.); brown solid. Anal. calc. for C₁₃H₁₇N₄O₆Cl₃Ni₂ (548.92): C 28.41, H 3.10, N 10.20, Ni 21.39, Cl 19.40%. Found: C 28.36, H 3.07, N 10.13, Ni 21.31, Cl 19.32%. Molar conductance Λ_M: 7.60 Ω⁻¹ cm² mol⁻¹. μ_eff: 3.08 BM. UV–visible (DMSO), λ_max: 378, 466, 633, 708 nm.

2.3.3

2.3.3 Binuclear metal complex [Co₂(PymL)Cl₃] (3)

Yield 61%; m.p.: 272 °C (dec.); reddish brown solid. Anal. calc. for C₁₃H₁₇N₄O₆Cl₃Co₂ (549.40): C 28.40, H 3.12, N 10.20, Co 21.45, Cl 19.35%. Found: C 28.36, H 3.06, N 10.16, Co 21.41, Cl 19.30%. Molar conductance Λ_M: 5.20 Ω⁻¹ cm² mol⁻¹. μ_eff: 4.86 BM. UV–visible (DMSO), λ_max: 382, 400, 660, 732 nm.

2.3.4

2.3.4 Binuclear metal complex [Zn₂(PymL)(CH₃CO₂)₃] (4)

Yield 67%; m.p.: 238 °C (dec.); colourless. Anal. calc. for C₁₉H₂₆N₄O₁₂Zn₂ (633.16): C 36.04, H 4.14, N 8.85, Zn 20.65%. Found: C 35.98, H 4.10, N 8.78, Zn 20.60%. Molar conductance Λ_M: 3.10 Ω⁻¹ cm² mol⁻¹. UV–vis (DMF), λ_max: 322 nm.

2.4

2.4 Physical measurements

Elemental analysis (C, H, and N) was performed using a VarioEL elementar analysensysteme. Metals and chlorides were estimated volumetrically (Reilley et al., 1959) and gravimetrically (Vogel, 1961), respectively. Melting points were recorded on an electro-thermal melting point apparatus and are uncorrected. IR spectra were recorded as KBr discs using a Shimadzu 8300 IR spectrophotometer covering the frequency range 4000–400 cm⁻¹. Electronic absorption spectra in the 200–900 nm range were obtained in DMF on a Systronic UV–visible spectrophotometer at room temperature. ¹H NMR and ¹³C NMR spectra (at room temperature, in DMSO-d₆) were recorded on a Bruker Avance II 400 NMR spectrometer. The chemical shift (δ) was measured down field with reference to TMS (tetramethylsilane, 0.0 ppm). ESI-MS spectra were obtained on an AB-Sciex Q-Star LCMS-MS spectrometer. Molar conductance measurements were determined in DMSO (∼10⁻³ M) at room temperature using a Jenway Model 4070 conductivity meter. Magnetic moment measurements were carried out by the Gouy method using Hg[Co(SCN)₄] as calibrant. EPR spectra of Cu(II) and Co(II) complexes were recorded as polycrystalline sample on a Varian E-112 spectrometer at the X-band region with frequency of 9.1 GHz under the magnetic field strength 3200 G using TCNE (tetracyanoethylene) as field marker (g = 2.0027).

2.5

2.5 In vitro antimicrobial activities

2.5.1

2.5.1 In vitro antibacterial activity

Synthesized Schiff base (L) and binuclear complexes were screened for their in vitro antibacterial activities against two Gram positive (Staphylococcus aureus and Bacillus subtilis) and two Gram negative (Escherichia coli and Salmonella typhi) bacteria by using the Agar well diffusion method (Sadan et al., 2003; Rahman et al., 2001). Streptomycin was used as reference antibacterial drug. Bacterial strains stored in Mueller–Hinton broth (Merck), were subcultured for testing in the same medium and grown at 37 °C. The test compounds (Schiff base, metal complexes and streptomycin) were dissolved in DMSO at a concentration of 2 mg/ml. Stock solutions were prepared and dilutions were made according to the guidelines in NCCLS (National Committee for Clinical Laboratory Standards, 1997) approved standard document M7-A4 using the micro-dilution broth procedure. Microbial cells were suspended according to the 0.5 McFarland protocol in saline solution to produce a suspension of 10⁴–10⁶ CFU (colony forming unit) per ml. Serial dilutions of test compounds were prepared in test tubes to final concentrations of 1024, 512, 256, 128, 64, 32, 16, 8, 4, 2 μg/ml. All strains were incubated at 37 °C for 24 h with different concentrations of compounds in Mueller–Hinton broth. Wells were created in medium with the help of a sterile metallic borer of 6 mm diameter and nutrient agar media was prepared in 1000 ml of distilled water. The pH of solutions was adjusted to 7.1 by adding appropriate amount of sodium hydroxide. The resulting solution was autoclaved for 35 min at 12 psi and seeded with 100 μl of prepared inocula containing approximately 10⁶ CFU/ml. 70 ml of seeded nutrient agar was poured to prepare petriplates. The antibacterial activity was determined by measuring the diameter of the inhibition zone (in mm). For quantitative measurement of growth inhibition, calculation was done according to procedure described in the literature (Rahman et al., 2001). The minimum inhibition concentrations of each compound were recorded as the lowest concentration of each chemical compound in the tubes with no growth (i.e., no turbidity) of inoculated bacteria. Each assay was performed in duplicate and repeated three times.

2.5.2

2.5.2 In vitro antifungal activity

Poisoned food technique was used to check the in vitro antifungal activity of synthesized Schiff base and binuclear complexes against two fungi Candida albicans and Candida parapsilosis (Al-Burtamani et al., 2005). Fungal strains were grown on Sabouraud dextrose agar (SDA) at 28 °C for 7 days. For performing antifungal activity of test compounds one week old fungal culture was used as inoculums. Fluconazole was used as reference antifungal drug and the medium with DMSO as solvent was used as a negative control. Solution of the test compounds (Schiff base and metal complexes) and reference drug were dissolved in DMSO at a concentration of 2 μg/ml. Molten SDA was poisoned by the addition of 100 μl of prepared inocula and poured into sterile petriplates. The prepared plates containing the test compound were inoculated with fungal plugs (6 mm diameter) obtained from the activity growing margins of fungal plates. Plates were inoculated at 28 °C for one week. Each assay was performed in duplicate and repeated three times. Antifungal activity data of compounds were expressed as percent inhibition calculated from the diameter of inhibition zone. The percent inhibition was determined using the formula: $% Inhibition = (C - T) . 100 / C$ where C is the diameter of the fungal colony in the control plate and T is the diameter of the microbial colony in the tested plate after same incubation period.

3 Results and discussion

The Schiff base (L) was synthesized by the condensation of an aqueous solution of glycine and ethanolic solution of 2,3-butanedione in 2:1 M ratio. Template condensation of synthesized Schiff base (L), 5-methyl-2,6-pyrimidine-dione and corresponding metal chloride/acetate salt in 1:1:2 M ratio gives binuclear metal complexes (1–4) of general formula [M₂(PymL)X₃]. The newly synthesized Schiff base (L) and metal complexes are stable at room temperature in solid state. Schiff base is soluble in MeOH and EtOH but metal complexes are soluble in DMF and DMSO. Analytical and spectral data are consistent with the proposed molecular formula and structure of Schiff base (L) and binuclear metal complexes. The positions of the molecular ion peaks in the mass spectra of compounds are consistent with their empirical molecular formulae and formula weight. Molar conductance measurement values show non-electrolytic nature of complexes as the value falls in the range 3.10–8.20 Ω⁻¹ cm² mol⁻¹ (Geary, 1971). On the basis of electronic spectral data, EPR spectral data and magnetic moment values, octahedral geometry was assigned for all binuclear metal complexes.

3.1

3.1 IR spectra

The most relevant IR spectral bands of Schiff base (L) and binuclear complexes (1–4) are given in Table 1. In the IR spectrum of Schiff base (L), there are no bands of the free –NH₂ group (3400 cm⁻¹) and ketonic group (1720 cm⁻¹) (Fig. 1). The absence of these bands and appearance of a new band at 1618 cm⁻¹ which may be assigned to the azomethine group [ν(—C⚌N)] vibration, indicate the condensation of the amino group of glycine with the carbonyl group of 2,3-butanedione and formation of proposed Schiff base (Singh et al., 2006; Majumdar et al., 2002; Dolze et al., 2004 ). The appearance of band at 1768 cm⁻¹ and 3648 cm⁻¹ may be assigned to the ν(—C⚌O) and ν(—OH) group of carboxylic acid group, respectively. The IR spectra of all metal complexes show significant changes compared to free Schiff base (L) (Figs. 2–5 ). The appearance of band in the range 1582–1596 cm⁻¹ suggests participation of the azomethine group [υ(C⚌N)] in complex formation (Singh et al., 2010). The appearance of band in the range of 1248–1276 cm⁻¹ may be assigned for the coordinated [⚌C—N] group of pyrimidine ring (Nakamoto, 1986). The participation of N-atom of the azomethine group and (⚌C—N) group of pyrimidine ring in coordination is further supported by the presence of new bands in the range 480–498 cm⁻¹ which are assignable to ν(M-N) vibration (Srivastava et al., 2014; Bellamy, 1978). The participation of the C⚌O group in the complex formation was ascertained by the shift of the band at 1728–1742 cm⁻¹ and the presence of new band in the range 1654–1678 cm⁻¹, which appears at 1768 cm⁻¹ in (L) and 1690 cm⁻¹ in 5-methyl-2,6-pyrimidine-dione, respectively (Tabassum et al., 2010; Masoud et al., 2004). This is further supported by the appearance of new band in the range 512–532 cm⁻¹ which may be assigned for ν(M-O) vibration (Kumar et al., 2010). The band in the range 3645–3650 cm⁻¹ may be assigned to non-coordinated ν(—OH) vibration of the carboxylic acid group. A band in the range 3070–3078 cm⁻¹ may be due to stretching vibration of the heterocyclic —NH group of pyrimidine ring. In the IR spectrum of [Zn₂(PymL)(CH₃CO₂)₃], two characteristic bands appeared at 1560 cm⁻¹ and 1304 cm⁻¹ which may be assigned to ν(COO⁻) symmetric and ν(COO⁻) asymmetric stretching vibrations of acetate ion, respectively. A difference between (ν_as − ν_s) is 256 cm⁻¹ which is greater than 144 cm⁻¹ indicates the coordination of the acetate ion in mono-dentate fashion with central metal ion (Singh and Srivastava, 2013; Nakamoto, 1986).

Table 1 IR spectral data (υ, cm⁻¹) of the Schiff base (L) and metal complexes (1–4).

Compounds	υ(C⚌N) azo.	υ(C⚌O) carbox.	υ(C⚌O) pym.	υ(⚌C—N) pym.	υ(M—N)	υ(M—O)
(L)	1618	1768	–	–	–	–
[Cu₂(PymL)Cl₃] (1)	1594	1738	1664	1248	498	526
[Ni₂(PymL)Cl₃] (2)	1592	1732	1678	1276	494	532
[Co₂(PymL)Cl₃] (3)	1582	1728	1654	1265	480	512
[Zn₂(PymL)(OAc)₃] (4)	1596	1742	1672	1252	488	528

azo. = azomethine group, carbox. = carboxyl group, pym. = pyrimidine ring, OAc = CH₃COO.

IR spectrum of complex [Zn2(PymL)(CH3CO2)3].

3.1.1

3.1.1 ¹H and ¹³C NMR spectra

The ¹H NMR and ¹³C NMR spectral data of the Schiff base (L) and [Zn₂(PymL)(CH₃CO₂)₃] complex were recorded in DMSO-d₆ (Table 2). The absence of the signal corresponding to primary amine proton in the ¹H NMR spectrum of Schiff base (L) suggests the formation of proposed Schiff base (L) (Fig. 6). In the ¹H NMR spectrum of Zn(II) complex, signals of the (CH₃—C⚌N) and (—CH₂—) protons of Schiff base (L) as well as the (—NH) and (—CH) protons of pyrimidine ring shifted compare to the starting material which suggests coordination through nitrogen atom of the azomethine group and (C—N) group of pyrimidine ring and oxygen atom of the (C⚌O) group of (L) and 5-methyl-2,6-pyrimidine-dione (Fig. 7). The presence of sharp singlet at 11.32 ppm suggests that the (—OH) group did not participate in coordination and broad singlet at 10.90 ppm for one proton suggests that only one (—NH) group participated in complex formation (Silverstein et al., 1974). In the ¹³C NMR spectrum of Zn(II) complex, change in the chemical shift values compared to the starting materials revealed coordination through nitrogen atom of the azomethine group and (C—N) group of pyrimidine ring and oxygen atom of the (C⚌O) group of (L) and 5-methyl-2,6-pyrimidine-dione (Fig. 8). Thus, ¹H and ¹³C NMR spectral data support proposed structure of Schiff base and metal complexes (Srivastava et al., 2014; Silverstein et al., 1974).

1H NMR spectrum of complex [Zn2(PymL)(CH3CO2)3].

3.2

3.2 Mass spectra

The formation of Schiff base (L) and metal complexes (1–4) was studied with ESI-MS spectra. The proposed molecular formula of these compounds was confirmed by comparing their molecular formula weight with m/z values. In the mass spectra of compounds, peaks were attributed to the molecular ions; m/z: 201.16 [M+1]⁺ for compound (L), m/z: 559.56 [M+1]⁺ for compound (1), m/z: 549.90 [M+1]⁺ for compound (2), m/z: 550.32 [M+1]⁺ for compound (3) and m/z: 634.16 [M+1]⁺ for compound (4). These data are in good agreement with the proposed molecular formula of synthesized compounds. In addition to the peaks due to the molecular ion, the spectra exhibit peaks assignable to various fragments arising from the thermal cleavage of the compounds. The mass spectrum of Schiff base (L) is shown in Fig. 9.

3.3

3.3 Electronic absorption spectra and magnetic moment measurements

The electronic absorption spectrum of [Cu₂(PymL)Cl₃] complex (1) exhibits only one broad band at 602 nm assigned to ²E_g → ²T_2g transition which is in conformity with octahedral geometry around the Cu(II) ion (Patil et al., 2010; Lever, 1968). The obtained magnetic moment value (μ_eff) for Cu(II) complex is 1.92 BM indicating that magnetic exchange occurs between the two copper sites and also supports octahedral geometry of Cu(II) complex. The electronic absorption spectrum of [Ni₂(PymL)Cl₃] complex (2) displays bands at 708 nm, 633 nm and 466 nm due to ³A_2(g)(F) → ³T_2g(F), ³A_2(g)(F) → ³T_1g(F) and ³A_2(g)(F) → ³T_1g(P) transitions, respectively (Patil et al., 2010; Lever, 1968; Shukla et al., 2008 ). The absorption spectra of complex also display a band at 378 nm assigned to charge transfer transition from ligand to metal ion (LMCT). The Ni(II) complex showed the magnetic moment value (μ_eff) 3.08 BM which is consistent with octahedral geometry of complex (Alaghaz and Ammar, 2010). The electronic absorption spectrum of [Co₂(PymL)Cl₃] complex (3) exhibits absorption bands at 732 nm, 660 nm and 400 nm which may be assigned to ⁴T_1g(F) → ⁴T_2g(F), ⁴T_1g(F) → ⁴A_2g(F) and ⁴T_1g(F) → ⁴T_1g(P) transitions, respectively, indicating octahedral geometry of Co(II) complex (Patil et al., 2010; Lever, 1968; Chandra and Gupta, 2002 ). In addition, a band observed at 382 nm attributed to charge transfer transition from the ligand to metal ion (LMCT). Furthermore, octahedral geometry for Co(II) complex is also supported by its magnetic moment value (μ_eff) at room temperature which is 4.86 BM (Alaghaz and Ammar, 2010; Alaghaz, 2008). The electronic absorption spectrum of [Zn₂(PymL)(CH₃CO₂)₃] complex (4) exhibits only a high intense band at 322 nm assignable to charge transfer transition from the ligand to metal ion (LMCT) (Lever, 1968). The Zn(II) complex is diamagnetic as expected and its geometry is most probably octahedral similar to Cu(II), Ni(II) and Co(II) complexes.

3.4

3.4 EPR spectra of [Cu₂(PymL)Cl₃] and [Co₂(PymL)Cl₃] complexes

The X-band EPR spectrum of Cu(II) complex was recorded at frequency of 9.1 GHz under the magnetic field strength 3200 G at room temperature (298 K) and Co(II) complex at liquid nitrogen temperature (77 K) as polycrystalline sample and their $g_{‖}$ and g_⊥ values were determined from EPR spectra and g_av values were calculated from the formula g²_av = ( $g_{‖}^{2}$ + 2 g²_⊥)/3. The analysis of the EPR spectrum of Cu(II) gives $g_{‖}$ 2.0822, g_⊥ 2.0814 and g_av 2.080. The Cu(II) complex shows a single absorption band. The absence of hyperfine lines in the spectrum of complex may be due to the strong dipolar and exchange interaction between the Cu(II) ions in the unit cell. The trend $g_{‖}$ > g_⊥ > 2.002 observed for the complex under the study indicates that the unpaired electron is localized in the dx² − y² orbital of Cu(II) ion (Herrera et al., 2003). The analysis of the EPR spectrum of Co(II) gives $g_{‖}$ 2.3142, g_⊥ 2.0042 and g_av 2.112. The trend $g_{‖}$ > g_⊥ > 2.002 observed for the Co(II) complex under the study is due to a large angular momentum contribution. Thus, EPR values also support octahedral geometry of Cu(II) and Co(II) complexes (Srivastava et al., 2014; Chandra et al., 2010).

3.5

3.5 In vitro antibacterial activity

In vitro antibacterial activity of synthesized compounds and standard drug Streptomycin were screened separately against two Gram positive bacteria (Staphylococcus aureus and B. subtilis) and two Gram negative bacteria (E. coli and S. typhi). Agar well diffusion technique was used to evaluate antibacterial activity of compounds (Ferrari et al., 1999) and antibacterial activity data are given in Table 3. Antibacterial activity data show that the binuclear metal complexes were more toxic than Schiff base (L) and it is also concluded that metal complexes show more toxicity towards Gram positive strains than Gram negative strains. The reason is the difference in the complexity of structure of the cell walls of Gram positive and Gram negative bacteria. The zones of inhibition (ZOI) values obtained indicate that Schiff base (L) has a significant activity against Staphylococcus aureus but moderate activity against B. subtilis, E. coli and S. typhi. Complex [Cu₂(PymL)Cl₃] exhibits an excellent activity against Staphylococcus aureus and B. subtilis, and good activity against E. coli and S. typhi. Complex [Ni₂(PymL)Cl₃] shows a good activity against Staphylococcus aureus, B. subtilis and S. typhi but a significant activity against E. coli. Complex [Co₂(PymL)Cl₃] exhibits a good activity against B. subtilis, significant activity against Staphylococcus aureus and S. typhi but moderate activity against E. coli. Complex [Zn₂(PymL)(CH₃CO₂)₃] exhibits a significant activity against Staphylococcus aureus and B. subtilis but moderate activity against E. coli and S. typhi. The variation in the antimicrobial activity of different metal complexes against different microorganisms depends on the impermeability of the cell or the differences in ribosomes in microbial cell (Sengupta et al., 1998). The lipid membrane surrounding the cell wall favours the passage of any lipid soluble materials and it is known that liposolubility is an important factor controlling antimicrobial activity (Parekh et al., 2005).

Table 3 Antibacterial screening data of Schiff base (L), binuclear metal complexes (1–4) and standard drug. Agar well diffusion technique was used to evaluate the antibacterial activity of synthesized compounds.

Microorganism	(L)	Metal complexes				Streptomycin
		1	2	3	4
Gram-positive
Staphylococcus aureus	++	++++	+++	++	++	++++
Bacillus subtilis	+	++++	+++	+++	++	++++

Gram-negative
Escherichia coli	+	+++	++	+	+	++++
Salmonella typhi	+	+++	+++	++	+	++++

++++ = excellent activity (90–100% inhibition), +++ = good activity (60–70% inhibition), ++ = significant activity (30–50% inhibition), + = moderate activity (10–20%), size of well = 6 mm (diameter), (L) = Schiff base, complex 1 = [Cu₂(PymL)Cl₃], complex 2 = [Ni₂(PymL)Cl₃], complex 3 = [Co₂(PymL)Cl₃], complex 4 = [Zn₂(PymL)(CH₃CO₂)₃], streptomycin = standard drug.

3.6

3.6 Minimum inhibitory concentration (MIC)

The antibacterial screening concentrations of the compounds were estimated from the minimum inhibitory concentration (MIC) value. The MIC values of compounds against Staphylococcus aureus, B. subtilis, E. coli and S. typhi were found to be 64, 64, 128 and 128 μg/ml for Schiff base (L); 16, 16, 32 and 32 μg/ml for [Cu₂(PymL)Cl₃] complex; 32, 16, 32 and 32 μg/ml for [Ni₂(PymL)Cl₃] complex; 32, 16, 32 and 64 μg/ml for [Co₂(PymL)Cl₃] complex; 32, 32, 64 and 64 μg/ml for [Zn₂(PymL)(CH₃CO₂)₃] complex; 4, 4, 8 and 8 μg/ml for standard drug Streptomycin, respectively. The values of MIC show that the [Cu₂(PymL)Cl₃] complex was found more potent as compared to other studied complexes (Table 4).

Table 4 Minimum Inhibition Concentration (MIC)^∗ values of Schiff base (L), binuclear metal complexes (1–4) and standard drug.

Microorganism	Ligand	Metal complexes				Streptomycin
		1	2	3	4
Gram positive
Staphylococcus aureus	64	16	32	32	32	4
Bacillus subtilis	64	16	16	16	32	4

Gram negative
Escherichia coli	128	32	32	32	64	8
Salmonella typhi	128	32	32	64	64	8

^∗ = μg/ml, (L) = Schiff base, complex 1 = [Cu2(PymL)Cl3], complex 2 = [Ni2(PymL)Cl3], complex 3 = [Co2(PymL)Cl3], complex 4 = [Zn2(PymL)(CH3CO2)3], streptomycin = standard drug.

3.7

3.7 In vitro antifungal activity

In vitro antifungal activities of synthesized Schiff base (L) and binuclear metal complexes were carried out against two fungi C. albicans and C. parapsilosis and compared with standard antifungal drug Fluconazole at the same concentration. Antifungal activity data are given in Table 5 which indicate that metal complexes are more toxic than Schiff base (L). Among all synthesized compounds, [Ni₂(PymL)Cl₃] complex is the most active against studied fungi and shows the highest activity against C. albicans. The activity is greatly enhanced at higher concentrations. DMSO control has shown a negligible activity as compare to the metal complexes and Schiff base. All the metal complexes exhibited a good antifungal activity against C. albicans and C. parapsilosis as compared to the standard drug Fluconazole. Antifungal activity data show that activity of complexes depends upon the type of metal ion present in the complex and it is observed that [Ni₂(PymL)Cl₃] complex is the most active and [Zn₂(PymL)(CH₃CO₂)₃] complex is the least active, whereas [Cu₂(PymL)Cl₃] and [Co₂(PymL)Cl₃] complexes are active against the studied fungi. In the present study low activity of some metal complexes may be due to their low lipophilicity, because of which penetration of the complex through the lipid membrane was decreased and hence, they could neither block nor inhibit the growth of the microorganism. Increased activity of the metal chelates can be explained on the basis of chelation theory. On chelation, the polarity of the metal ion will be reduced to a greater extent due to overlap of the ligand orbital and partial sharing of the positive charge of the metal ion with donor groups. Further, it increases the delocalization of π-electrons over the whole chelate ring and enhances the penetration of the complexes into lipid membranes and blocking of the metal binding sites in enzymes of microorganism. These complexes also disturb the respiration process of the cell and thus block the synthesis of proteins, which restricts further growth of microorganism (Dharmaraj et al., 2002).

Table 5 Antifungal screening data of Schiff base (L), binuclear metal complexes (1–4) and standard drug. Poison food technique was used to evaluate the antifungal activity of synthesized compounds.

Compounds	Mycelial growth inhibition (%)
	a	b
(L)	38.2	36.3
[Cu₂(PymL)Cl₃] (1)	56.2	51.3
[Ni₂(PymL)Cl₃] (2)	59.6	56.4
[Co₂(PymL)Cl₃] (3)	54.8	54.5
[Zn₂(PymL)(CH₃CO₂)₄] (4)	48.3	42.8
Fluconazole	79.8	85.3

(L) = Schiff base, a = Candida albicans, b = Candida parapsilosis, fluconazole = standard drug.

The biological activity of compounds also depends on the nature of the ligand, concentration, nature of metal ion, nature of anion surrounding the metal ion, coordinating sites and geometry of complexes. As the mechanism of inhibition by [Zn₂(Pym)L.(CH₃CO₂)₃] complex might be different, it was observed that Zn(II) complex showed lesser antimicrobial activity as compared to other synthesized metal complexes (Vanpariya et al., 2010).

4 Conclusion

Binuclear complexes of Cu(II), Ni(II), Co(II) and Zn(II) metal ions were synthesized by template condensation of a novel Schiff base derived from glycine using 2,3-butanedione and 5-methyl-pyrimidine-2,6-dione promoted by the corresponding metal chloride/acetate salt. A comparative physicochemical and spectral study of synthesized compounds has been done which provides excellent data which is in the agreement with the proposed structure and composition of Schiff base and metal complexes. IR spectral data reveal that Schiff base coordinates through two nitrogen atoms of azomethine groups and two oxygen atoms of carboxylic groups, whereas pyrimidine moiety coordinates with metal ion through two oxygen atoms of carbonyl groups and one nitrogen atom of pyrimidine ring. Electronic absorption spectra, EPR spectra and magnetic moment values suggest octahedral geometry around metal ions. Low molar conductance values show non-electrolyte nature of metal complexes. In vitro antibacterial and antifungal studies show that Schiff base (L) and binuclear metal complexes are biologically active. [Cu₂(PymL)Cl₃] complex (1) shows the best activity against bacteria and [Ni₂(PymL)Cl₃] complex (2) shows the best activity against fungi studied.

Acknowledgements

Authors are thankful to the ACBR, Delhi for providing spectral data, IIT Roorkee, for providing elemental analysis data, SAIF, Punjab University, Chandigarh for providing NMR spectral data and SARC, Meerut for providing biological activity facility. Authors are also thankful to authorities of the Meerut College, Meerut for providing necessary research facilities.

References

Alagha A., Parthasarathi L., Gaynor D., Muller-Bunz H., Starikova Z.A., Farkas E., Brien C.O.E., Gil M.J., Nolan K.B., . Metal complexes of cyclic hydroxamates. Synthesis and crystal structures of 3-hydroxy-2-methyl-3H-quinazolin-4-one (ChaH) and of its Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) complexes. Inorg. Chim. Acta. 2011;368:58-66.
[Google Scholar]
Alaghaz A.N.M.A., . Preparation and biological activity of some novel tetrachlorocyclodiphosph(V)azane pyridazine derivatives and its metal complexes. Phosphorus, Sulfur Silicon Relat. Elem.. 2008;183:2373-2390.
[Google Scholar]
Alaghaz A.N.M.A., Ammar R.A., . New dimeric cyclodiphosph(V)azane complexes of Cr(III), Co(II), Ni(II), Cu(II), and Zn(II): Preparation, characterization and biological activity studies. Eur. J. Med. Chem.. 2010;45:1314-1322.
[Google Scholar]
Al- Burtamani S.K.S., Fatope M.O., Marwah R.G., Onifade A.K., Al- Saidi S.H., . Chemical composition, antibacterial and antifungal activities of the essential oil of Haplophyllum tuberculatum from Oman. J. Ethanopharmacol.. 2005;96:107-112.
[Google Scholar]
Aminabhavi T.M., Birader N.S., Patil S.B., Roddabasanagoudar V.L., Rudzinski W.E., . Amino acid schiff base complexes of dimethyldichlorosilane. Inorg. Chim. Acta. 1985;107:231-234.
[Google Scholar]
Arbaoui A., Redshaw C., Sanchez-Ballester N.M., Elsegood M.R.J., Hughes D.L., . Bimetallic copper(II) and zinc(II) complexes of acrylic Schiff base ligands derived from amino acids. Inorg. Chim. Acta. 2011;365:96-102.
[Google Scholar]
Bagihalli G.B., Patil S.A., . Synthesis, physico-chemical investigations of Co(II), Ni(II) and Cu(II) complexes and their in vitro microbial, cytotoxic, DNA cleavage studies. J. Enzyme Inhib. Med. Chem.. 2010;25:430-439.
[Google Scholar]
Bellamy L.J., . The Infrared Spectra of Complex Molecules. London: Chapmann and Hall; 1978.
Chandra S., Gupta K., . Chromium(III), manganese(II), iron(III), cobalt(II), nickel(II) and copper(II) complexes with a pentadentate, 15-membered new macrocyclic ligand. Transition Met. Chem.. 2002;27:196-199.
[Google Scholar]
Chandra S., Tyagi M., Agrawal S., . Synthesis and characterization of a tetraaza macrocyclic ligand and its cobalt(II), nickel(II) and copper(II) complexes. J. Serb. Chem. Soc.. 2010;75:935-941.
[Google Scholar]
Colacio E., Dominguez-Vera J.M., Romerosa A., Kivekas R., Klinga M., Escuer A., . A heterodinuclear anti oximate-bridged copper(II)-nickel(II) complex: crystal structure and magnetic properties. Inorg. Chim. Acta. 1995;234:61-65.
[Google Scholar]
Dharmaraj N., Viswanathamurthi P., Natarajan K., . Ruthenium(II) complexes containing bidentate Schiff bases and their antifungal activity. Transition Met. Chem.. 2002;26:105-109.
[Google Scholar]
Dolze M., Tumer M., Digrak M., . Synthesis, spectroscopic characterization and properties of new metal complexes. Transition Met. Chem.. 2004;29:516-522.
[Google Scholar]
Faus J., Julve M., Lloret F., Munoz M.C., . Bis(dimethylviolurato)(phenanthroline)cobalt(II), a low-spin octahedral cobalt(II) complex. Crystal structure of [Co(dmvi)2phen].2CHCl₃. Inorg. Chem.. 1993;32:2013-2017.
[Google Scholar]
Ferrari M.B., Capacchi S., Pelosi G., . Synthesis, structural characterization and biological activity of helicin thiosemicarbazone monohydrate and a copper(II) complex of salicylaldehyde thiosemicarbazone. Inorg. Chim. Acta. 1999;286:134-141.
[Google Scholar]
Gamba I., Mutikainen I., Bouwman E., Reedijk J., Bonnet S., . Synthesis and characterization of copper complexes of a tetrapyridyl ligand, and their use in the catalytic aerobic oxidation of benzyl alcohol. Eur. J. Inorg. Chem. 2013:115-123.
[Google Scholar]
Geary W.J., . The use of conductivity measurements in organic solvents for the characterisation of coordination compounds. Coord. Chem. Rev.. 1971;7:81-122.
[Google Scholar]
Gudasi K.B., Patil M.S., Vadavi R.S., Shenoy R.V., Patil S.A., . N-(salicylidene)nitrosophenylglycine Schiff base as NOOO-donor towards transition metal ions. Transition Met. Chem.. 2006;31:986-991.
[Google Scholar]
Harriman A., Khatyr A., Ziessel R., . The photophysical properties of short, linear arrays of ruthenium(II)tris(2,2′-bipyridine) complexes. Res. Chem. Intermed.. 2007;33:49-62.
[Google Scholar]
Herrera A.M., Staples R.J., Kryotov S.V., Nazarenko A.Y., Vakimova E., . Nickel(II) and copper(II) complexes with pyridine-containing macrocycles bearing an aminopropyl pendant arm: synthesis, characterization, and modifications of the pendant amino group. Dalton Trans. 2003:846-856.
[Google Scholar]
Khali S.E.M., Saleem H.S., El-Shetary B.A., Shebl M., . Mono- and bi-nuclear metal complexes of Schiff-base hydrazone (ONN) derived from o-hydroxyacetophenone and 2-amino-4-hydrazino-6-methyl pyrimidine. J. Coord. Chem.. 2002;55:883-899.
[Google Scholar]
Kumar G., Kumar D., Devi S., Johri R., Singh C.P., . Synthesis, spectral characterization and antimicrobial evaluation of Schiff base Cu(II), Ni(II) and Co(II) complexes. Eur. J. Med. Chem.. 2010;45:3056-3062.
[Google Scholar]
Lever A.B.P., . Inorganic Electronic Spectroscopy. New York: Elsevier; 1968.
Lumme P.O., Knuuttilla H., . Studies on coordination compounds-VIII: syntheses, structural, magnetic, spectral and thermal properties of some cobalt(II), nickel(II) and copper(II) complexes of 2-aminopyrimidine. Polyhedron. 1995;14:1553-1563.
[Google Scholar]
Majumdar K., Butcher R.J., Bhattacharya S., . Chemistry of some amino acid complexes of ruthenium. Synthesis, characterization, and DNA binding properties. Inorg. Chem.. 2002;41:4605-4609.
[Google Scholar]
Martell A.E., Szpoganicz B., . Zinc(II), aluminum(III), and gallium(III) complexes of Schiff bases of 3-amino-3-phosphonopropionic acid and 5’-deoxypyridoxal. Inorg. Chem.. 1989;28:4199-4206.
[Google Scholar]
Masoud M.S., Khalil E.A., Hindawy A.M., Ali A.E., Mohamed E.F., . Spectroscopic studies on some azo compounds and their cobalt, copper and nickel complexes. Spectrochim. Acta. 2004;60(A):2807-2817.
[Google Scholar]
Mastropietro T.F., Armentano D., Grisolia E., Zanchini C., Lloret F., Julve M., Munno G.D., . Guanine containing copper(II) complexes: synthesis, X-ray structures and magnetic properties. Dalton Trans. 2008:514-520.
[Google Scholar]
Nakamoto K., . Infrared and Raman Spectra of Inorganic and Coordination Compounds. New York: John Wiley; 1986.
National Committee for Clinical Laboratory Standards, 1997. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically, Approved Standard M7-A4, NCCLS: Villanova, PA, USA.
Navarro J.A.R., Lippert B., . Simple 1:1 and 1:2 complexes of metal ions with heterocycles as building blocks for discrete molecular as well as polymeric assemblies. Coord. Chem. Rev.. 2001;222:219-250.
[Google Scholar]
Parashar R.K., Sharma R.C., Kumar A., Mohan G., . Stability studies in relation to IR data of some Schiff base complexes of transition metals and their biological and pharmacological studies. Inorg. Chim. Acta. 1988;151:201-208.
[Google Scholar]
Parekh J., Inamdhar P., Nair R., Baluja S., Chandra S., . Synthesis and antibacterial activity of some Schiff bases derived from 4-aminobenzoic acid. J. Serb. Chem. Soc.. 2005;70:1155-1161.
[Google Scholar]
Patel M.N., Parmar P.A., Gandhi D.S., Thakkar V.R., . Ternary copper(II) complexes of levofloxacin and phenanthroline derivatives: in-vitro antibacterial, DNA interactions and SOD-like activity. J. Enzyme Inhib. Med. Chem.. 2011;26:359-366.
[Google Scholar]
Patil M., Hunoor R., Gudasi K., . Transition metal complexes of a new hexadentate macroacyclic N₂O₄-donor Schiff base: inhibitory activity against bacteria and fungi. Eur. J. Med. Chem.. 2010;45:2981-2986.
[Google Scholar]
Prakash H., Natarajan P., . Flash photolysis studies of charge transfer photochemistry of nickel(II) and Cobalt (II) complexes. Res. Chem. Intermediat.. 2003;29:349-364.
[Google Scholar]
Pyrz J.W., Roe A.L., Stem L.J., Qui L. Jr., . Model studies of iron-tyrosinate proteins. J. Am. Chem. Soc.. 1985;107:614-620.
[Google Scholar]
Rahman A., Choudhary M.I., Thomsen W.J., . Bioassay Techniques for Drug Development. Netherlands: Harwood Academic Publishers; 2001.
Reilley C.N., Schmid R.W., Sadek F.S., . Chelon approach to analysis (II). Illustrative experiments. J. Chem. Edu.. 1959;36:619-625.
[Google Scholar]
Revenco M.D., Palamarciuc O.V., Bourosh P.N., Lipkowski J., Gdaniec M., Simonov Y.A., Clerac R., . New template reactions of salicylaldehyde S-methyl-isothiosemicarbazone with 2-formylpyridine promoted by Ni(II) or Cu(II) metal ions. Inorg. Chim. Acta. 2011;368:157-164.
[Google Scholar]
Sadan A.K., Mirza Y., Aneja A.R., Prakash O., . Hypervalent iodine mediated synthesis of 1-aryl/hetryl-1,2,4-triazolo[4,3-a] pyridines and 1-aryl/hetryl 5-methyl-1,2,4-triazolo[4,3-a] quinolines as antibacterial agents. Eur. J. Med. Chem.. 2003;38:533-536.
[Google Scholar]
Sengupta S.K., Pandey O.P., Srivastava B.K., Sharma V.K., . Synthesis, structural and biochemical aspects of titanocene and zirconocene chelates of acetylferrocenyl thiosemicarbazones. Transition Met. Chem.. 1998;23:349-353.
[Google Scholar]
Sharaby C.M., Mohamed G.G., Omar M.M., . Preparation and spectroscopic characterization of novel cyclodiphosph(V)azane of N1-2-pyrimidinylsulfanilamide complexes: magnetic, thermal and biological activity studies. Spectrochim. Acta. 2007;66(A):935-948.
[Google Scholar]
Shi L., Fang R.Q., Xue J.Y., Xiao Z.P., Tan S.H., Zhu H.L., . Synthesis, characterization and antibacterial and cytotoxic study of metal complexes with Schiff base ligands. Aust. J. Chem.. 2008;61:288-296.
[Google Scholar]
Shukla D., Gupta L.K., Chandra S., . Spectroscopic studies on chromium(III), manganese(II), cobalt(II), nickel(II) and copper(II) complexes with hexadentate nitrogen–sulfur donor [N2S4] macrocyclic ligand. Spectrochim. Acta. 2008;71(A):746-750.
[Google Scholar]
Sikova S., Rowan S.J., . Nucleobases as supramolecular motifs. Chem. Soc. Rev.. 2005;34:9-21.
[Google Scholar]
Silverstein R.M., Bassler C.M., Morrill T.C., . Spectrometric Identification of Organic Compounds (third ed.). New York: John Wiley; 1974.
Singh K., Pal D., . Synthetic, structural and biological studies of organosilicon(IV) complexes of Schiff bases derived from pyrrole-2-carboxaldehyde. J. Serb. Chem. Soc.. 2010;75:917-927.
[Google Scholar]
Singh L.J., Singh R.K.H., . Synthesis and photophysical properties of new Ln (III) (Ln = Eu(III), Gd(III), or Tb(III)) complexes of 1-amidino-O-methylurea. Chem. Pap.. 2014;68:223-232.
[Google Scholar]
Singh N.P., Srivastava A.N., . Synthesis, characterization and spectral studies of noble heterobinuclear complexes of transition metal ions and their biological activity. E-J. Chem.. 2010;8:809-814.
[Google Scholar]
Singh N.P., Srivastava A.N., . Physico-chemical and biological studies of Cu(II), Co(II) and Ni(II) complexes of an N₄ coordinating ligand derived from the Schiff base of diacetyl with ethylenediamine and benzoic acid. J. Serb. Chem. Soc.. 2012;77(5):627-637.
[Google Scholar]
Singh N.P., Srivastava A.N., . Synthesis and characterization of novel binuclear transition metal complexes of a schiff base ligand derived from 1-amino-5-methyl-2,6-pyrimidine-dione and 2,3-butanedione and their antimicrobial studies. Asian J. Chem.. 2013;25:533-537.
[Google Scholar]
Singh D.P., Kumar R., Tyagi P., . Template synthesis, spectroscopic studies and biological screening of macrocyclic complexes derived from thiocarbohydrazide and benzyl. Transition Met. Chem.. 2006;31:970-973.
[Google Scholar]
Singh D.P., Kumar K., Sharma C., . New 14-membered octaazamacrocyclic complexes: synthesis, spectral, antibacterial and antifungal studies. Eur. J. Med. Chem.. 2010;45:1230-1236.
[Google Scholar]
Singh K., Kumar Y., Puri P., Kumar M., Sharma C., . Cobalt, nickel, copper and zinc complexes with 1,3-diphenyl-1H-pyrazole-4-carboxaldehyde Schiff bases: Antimicrobial, spectroscopic, thermal and fluorescence studies. Eur. J. Med. Chem.. 2012;52:313-321.
[Google Scholar]
Sonmez M., Celebi M., Berber I., . Synthesis, spectroscopic and biological studies on the new symmetric Schiff base derived from 2,6-diformyl-4-methylphenol with N-aminopyrimidine. Eur. J. Med. Chem.. 2010;4:1935-1940.
[Google Scholar]
Srivastava A.N., Singh N.P., Shriwastaw C.K., . Synthesis and characterization of bioactive binuclear transition metal complexes of a Schiff base ligand derived from 4-amino-1H-pyrimidin-2-one, diacetyl and glycine. J. Serb. Chem. Soc.. 2014;79:421-433.
[Google Scholar]
Suslick K.S., Reinert T.J., . The synthetic analogs of O₂-binding heme proteins. J. Chem. Edu.. 1985;62:974-984.
[Google Scholar]
Tabassum S., Singh N.P., Arjmand F., . Synthesis, characterization and toxicity of heterobinuclear complexes of transition metal ions. Synth. React. Inorg. Met. Org. Chem.. 2001;31:1803-1815.
[Google Scholar]
Tabassum S., Sharma G.C., Arjmand F., Azam A., . DNA interaction studies of new nano metal based anticancer agent: validation by spectroscopic methods. Nanotechnology. 2010;21:195102-195112.
[Google Scholar]
Vanpariya S.F., Patel T.S., Sojitra N.A., Jagani C.L., Dixit B.C., Patel P.S., Dixit R.B., . Synthesis, characterization and antimicrobial study of novel 4-{[(8-Hydroxyquinoline-5-yl)methyl]amino}benzenesulfonamide and its oxinates. Acta Chim. Slov.. 2010;57:660-667.
[Google Scholar]
Vogel A.I., . A Text Book of Quantitative Inorganic Analysis. London: Logmans; 1961.
Weitzer M., Brooker S., . Dimetallic complexes of a structurally versatile pyridazine-containing Schiff-base macrocyclic ligand with pendant pyridine arms. Dalton Trans. 2005:2448-2454.
[Google Scholar]

Show Sections

[1] Alagha A., Parthasarathi L., Gaynor D., Muller-Bunz H., Starikova Z.A., Farkas E., Brien C.O.E., Gil M.J., Nolan K.B., . Metal complexes of cyclic hydroxamates. Synthesis and crystal structures of 3-hydroxy-2-methyl-3H-quinazolin-4-one (ChaH) and of its Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) complexes. Inorg. Chim. Acta. 2011;368:58-66.
[Google Scholar]

[2] Alaghaz A.N.M.A., . Preparation and biological activity of some novel tetrachlorocyclodiphosph(V)azane pyridazine derivatives and its metal complexes. Phosphorus, Sulfur Silicon Relat. Elem.. 2008;183:2373-2390.
[Google Scholar]

[3] Alaghaz A.N.M.A., Ammar R.A., . New dimeric cyclodiphosph(V)azane complexes of Cr(III), Co(II), Ni(II), Cu(II), and Zn(II): Preparation, characterization and biological activity studies. Eur. J. Med. Chem.. 2010;45:1314-1322.
[Google Scholar]

[4] Al- Burtamani S.K.S., Fatope M.O., Marwah R.G., Onifade A.K., Al- Saidi S.H., . Chemical composition, antibacterial and antifungal activities of the essential oil of Haplophyllum tuberculatum from Oman. J. Ethanopharmacol.. 2005;96:107-112.
[Google Scholar]

[5] Aminabhavi T.M., Birader N.S., Patil S.B., Roddabasanagoudar V.L., Rudzinski W.E., . Amino acid schiff base complexes of dimethyldichlorosilane. Inorg. Chim. Acta. 1985;107:231-234.
[Google Scholar]

[6] Arbaoui A., Redshaw C., Sanchez-Ballester N.M., Elsegood M.R.J., Hughes D.L., . Bimetallic copper(II) and zinc(II) complexes of acrylic Schiff base ligands derived from amino acids. Inorg. Chim. Acta. 2011;365:96-102.
[Google Scholar]

[7] Bagihalli G.B., Patil S.A., . Synthesis, physico-chemical investigations of Co(II), Ni(II) and Cu(II) complexes and their in vitro microbial, cytotoxic, DNA cleavage studies. J. Enzyme Inhib. Med. Chem.. 2010;25:430-439.
[Google Scholar]

[8] Bellamy L.J., . The Infrared Spectra of Complex Molecules. London: Chapmann and Hall; 1978.

[9] Chandra S., Gupta K., . Chromium(III), manganese(II), iron(III), cobalt(II), nickel(II) and copper(II) complexes with a pentadentate, 15-membered new macrocyclic ligand. Transition Met. Chem.. 2002;27:196-199.
[Google Scholar]

[10] Chandra S., Tyagi M., Agrawal S., . Synthesis and characterization of a tetraaza macrocyclic ligand and its cobalt(II), nickel(II) and copper(II) complexes. J. Serb. Chem. Soc.. 2010;75:935-941.
[Google Scholar]

[11] Colacio E., Dominguez-Vera J.M., Romerosa A., Kivekas R., Klinga M., Escuer A., . A heterodinuclear anti oximate-bridged copper(II)-nickel(II) complex: crystal structure and magnetic properties. Inorg. Chim. Acta. 1995;234:61-65.
[Google Scholar]

[12] Dharmaraj N., Viswanathamurthi P., Natarajan K., . Ruthenium(II) complexes containing bidentate Schiff bases and their antifungal activity. Transition Met. Chem.. 2002;26:105-109.
[Google Scholar]

[13] Dolze M., Tumer M., Digrak M., . Synthesis, spectroscopic characterization and properties of new metal complexes. Transition Met. Chem.. 2004;29:516-522.
[Google Scholar]

[14] Faus J., Julve M., Lloret F., Munoz M.C., . Bis(dimethylviolurato)(phenanthroline)cobalt(II), a low-spin octahedral cobalt(II) complex. Crystal structure of [Co(dmvi)2phen].2CHCl₃. Inorg. Chem.. 1993;32:2013-2017.
[Google Scholar]

[15] Ferrari M.B., Capacchi S., Pelosi G., . Synthesis, structural characterization and biological activity of helicin thiosemicarbazone monohydrate and a copper(II) complex of salicylaldehyde thiosemicarbazone. Inorg. Chim. Acta. 1999;286:134-141.
[Google Scholar]

[16] Gamba I., Mutikainen I., Bouwman E., Reedijk J., Bonnet S., . Synthesis and characterization of copper complexes of a tetrapyridyl ligand, and their use in the catalytic aerobic oxidation of benzyl alcohol. Eur. J. Inorg. Chem. 2013:115-123.
[Google Scholar]

[17] Geary W.J., . The use of conductivity measurements in organic solvents for the characterisation of coordination compounds. Coord. Chem. Rev.. 1971;7:81-122.
[Google Scholar]

[18] Gudasi K.B., Patil M.S., Vadavi R.S., Shenoy R.V., Patil S.A., . N-(salicylidene)nitrosophenylglycine Schiff base as NOOO-donor towards transition metal ions. Transition Met. Chem.. 2006;31:986-991.
[Google Scholar]

[19] Harriman A., Khatyr A., Ziessel R., . The photophysical properties of short, linear arrays of ruthenium(II)tris(2,2′-bipyridine) complexes. Res. Chem. Intermed.. 2007;33:49-62.
[Google Scholar]

[20] Herrera A.M., Staples R.J., Kryotov S.V., Nazarenko A.Y., Vakimova E., . Nickel(II) and copper(II) complexes with pyridine-containing macrocycles bearing an aminopropyl pendant arm: synthesis, characterization, and modifications of the pendant amino group. Dalton Trans. 2003:846-856.
[Google Scholar]

[21] Khali S.E.M., Saleem H.S., El-Shetary B.A., Shebl M., . Mono- and bi-nuclear metal complexes of Schiff-base hydrazone (ONN) derived from o-hydroxyacetophenone and 2-amino-4-hydrazino-6-methyl pyrimidine. J. Coord. Chem.. 2002;55:883-899.
[Google Scholar]

[22] Kumar G., Kumar D., Devi S., Johri R., Singh C.P., . Synthesis, spectral characterization and antimicrobial evaluation of Schiff base Cu(II), Ni(II) and Co(II) complexes. Eur. J. Med. Chem.. 2010;45:3056-3062.
[Google Scholar]

[23] Lever A.B.P., . Inorganic Electronic Spectroscopy. New York: Elsevier; 1968.

[24] Lumme P.O., Knuuttilla H., . Studies on coordination compounds-VIII: syntheses, structural, magnetic, spectral and thermal properties of some cobalt(II), nickel(II) and copper(II) complexes of 2-aminopyrimidine. Polyhedron. 1995;14:1553-1563.
[Google Scholar]

[25] Majumdar K., Butcher R.J., Bhattacharya S., . Chemistry of some amino acid complexes of ruthenium. Synthesis, characterization, and DNA binding properties. Inorg. Chem.. 2002;41:4605-4609.
[Google Scholar]

[26] Martell A.E., Szpoganicz B., . Zinc(II), aluminum(III), and gallium(III) complexes of Schiff bases of 3-amino-3-phosphonopropionic acid and 5’-deoxypyridoxal. Inorg. Chem.. 1989;28:4199-4206.
[Google Scholar]

[27] Masoud M.S., Khalil E.A., Hindawy A.M., Ali A.E., Mohamed E.F., . Spectroscopic studies on some azo compounds and their cobalt, copper and nickel complexes. Spectrochim. Acta. 2004;60(A):2807-2817.
[Google Scholar]

[28] Mastropietro T.F., Armentano D., Grisolia E., Zanchini C., Lloret F., Julve M., Munno G.D., . Guanine containing copper(II) complexes: synthesis, X-ray structures and magnetic properties. Dalton Trans. 2008:514-520.
[Google Scholar]

[29] Nakamoto K., . Infrared and Raman Spectra of Inorganic and Coordination Compounds. New York: John Wiley; 1986.

[30] National Committee for Clinical Laboratory Standards, 1997. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically, Approved Standard M7-A4, NCCLS: Villanova, PA, USA.

[31] Navarro J.A.R., Lippert B., . Simple 1:1 and 1:2 complexes of metal ions with heterocycles as building blocks for discrete molecular as well as polymeric assemblies. Coord. Chem. Rev.. 2001;222:219-250.
[Google Scholar]

[32] Parashar R.K., Sharma R.C., Kumar A., Mohan G., . Stability studies in relation to IR data of some Schiff base complexes of transition metals and their biological and pharmacological studies. Inorg. Chim. Acta. 1988;151:201-208.
[Google Scholar]

[33] Parekh J., Inamdhar P., Nair R., Baluja S., Chandra S., . Synthesis and antibacterial activity of some Schiff bases derived from 4-aminobenzoic acid. J. Serb. Chem. Soc.. 2005;70:1155-1161.
[Google Scholar]

[34] Patel M.N., Parmar P.A., Gandhi D.S., Thakkar V.R., . Ternary copper(II) complexes of levofloxacin and phenanthroline derivatives: in-vitro antibacterial, DNA interactions and SOD-like activity. J. Enzyme Inhib. Med. Chem.. 2011;26:359-366.
[Google Scholar]

[35] Patil M., Hunoor R., Gudasi K., . Transition metal complexes of a new hexadentate macroacyclic N₂O₄-donor Schiff base: inhibitory activity against bacteria and fungi. Eur. J. Med. Chem.. 2010;45:2981-2986.
[Google Scholar]

[36] Prakash H., Natarajan P., . Flash photolysis studies of charge transfer photochemistry of nickel(II) and Cobalt (II) complexes. Res. Chem. Intermediat.. 2003;29:349-364.
[Google Scholar]

[37] Pyrz J.W., Roe A.L., Stem L.J., Qui L. Jr., . Model studies of iron-tyrosinate proteins. J. Am. Chem. Soc.. 1985;107:614-620.
[Google Scholar]

[38] Rahman A., Choudhary M.I., Thomsen W.J., . Bioassay Techniques for Drug Development. Netherlands: Harwood Academic Publishers; 2001.

[39] Reilley C.N., Schmid R.W., Sadek F.S., . Chelon approach to analysis (II). Illustrative experiments. J. Chem. Edu.. 1959;36:619-625.
[Google Scholar]

[40] Revenco M.D., Palamarciuc O.V., Bourosh P.N., Lipkowski J., Gdaniec M., Simonov Y.A., Clerac R., . New template reactions of salicylaldehyde S-methyl-isothiosemicarbazone with 2-formylpyridine promoted by Ni(II) or Cu(II) metal ions. Inorg. Chim. Acta. 2011;368:157-164.
[Google Scholar]

[41] Sadan A.K., Mirza Y., Aneja A.R., Prakash O., . Hypervalent iodine mediated synthesis of 1-aryl/hetryl-1,2,4-triazolo[4,3-a] pyridines and 1-aryl/hetryl 5-methyl-1,2,4-triazolo[4,3-a] quinolines as antibacterial agents. Eur. J. Med. Chem.. 2003;38:533-536.
[Google Scholar]

[42] Sengupta S.K., Pandey O.P., Srivastava B.K., Sharma V.K., . Synthesis, structural and biochemical aspects of titanocene and zirconocene chelates of acetylferrocenyl thiosemicarbazones. Transition Met. Chem.. 1998;23:349-353.
[Google Scholar]

[43] Sharaby C.M., Mohamed G.G., Omar M.M., . Preparation and spectroscopic characterization of novel cyclodiphosph(V)azane of N1-2-pyrimidinylsulfanilamide complexes: magnetic, thermal and biological activity studies. Spectrochim. Acta. 2007;66(A):935-948.
[Google Scholar]

[44] Shi L., Fang R.Q., Xue J.Y., Xiao Z.P., Tan S.H., Zhu H.L., . Synthesis, characterization and antibacterial and cytotoxic study of metal complexes with Schiff base ligands. Aust. J. Chem.. 2008;61:288-296.
[Google Scholar]

[45] Shukla D., Gupta L.K., Chandra S., . Spectroscopic studies on chromium(III), manganese(II), cobalt(II), nickel(II) and copper(II) complexes with hexadentate nitrogen–sulfur donor [N2S4] macrocyclic ligand. Spectrochim. Acta. 2008;71(A):746-750.
[Google Scholar]

[46] Sikova S., Rowan S.J., . Nucleobases as supramolecular motifs. Chem. Soc. Rev.. 2005;34:9-21.
[Google Scholar]

[47] Silverstein R.M., Bassler C.M., Morrill T.C., . Spectrometric Identification of Organic Compounds (third ed.). New York: John Wiley; 1974.

[48] Singh K., Pal D., . Synthetic, structural and biological studies of organosilicon(IV) complexes of Schiff bases derived from pyrrole-2-carboxaldehyde. J. Serb. Chem. Soc.. 2010;75:917-927.
[Google Scholar]

[49] Singh L.J., Singh R.K.H., . Synthesis and photophysical properties of new Ln (III) (Ln = Eu(III), Gd(III), or Tb(III)) complexes of 1-amidino-O-methylurea. Chem. Pap.. 2014;68:223-232.
[Google Scholar]

[50] Singh N.P., Srivastava A.N., . Synthesis, characterization and spectral studies of noble heterobinuclear complexes of transition metal ions and their biological activity. E-J. Chem.. 2010;8:809-814.
[Google Scholar]

[51] Singh N.P., Srivastava A.N., . Physico-chemical and biological studies of Cu(II), Co(II) and Ni(II) complexes of an N₄ coordinating ligand derived from the Schiff base of diacetyl with ethylenediamine and benzoic acid. J. Serb. Chem. Soc.. 2012;77(5):627-637.
[Google Scholar]

[52] Singh N.P., Srivastava A.N., . Synthesis and characterization of novel binuclear transition metal complexes of a schiff base ligand derived from 1-amino-5-methyl-2,6-pyrimidine-dione and 2,3-butanedione and their antimicrobial studies. Asian J. Chem.. 2013;25:533-537.
[Google Scholar]

[53] Singh D.P., Kumar R., Tyagi P., . Template synthesis, spectroscopic studies and biological screening of macrocyclic complexes derived from thiocarbohydrazide and benzyl. Transition Met. Chem.. 2006;31:970-973.
[Google Scholar]

[54] Singh D.P., Kumar K., Sharma C., . New 14-membered octaazamacrocyclic complexes: synthesis, spectral, antibacterial and antifungal studies. Eur. J. Med. Chem.. 2010;45:1230-1236.
[Google Scholar]

[55] Singh K., Kumar Y., Puri P., Kumar M., Sharma C., . Cobalt, nickel, copper and zinc complexes with 1,3-diphenyl-1H-pyrazole-4-carboxaldehyde Schiff bases: Antimicrobial, spectroscopic, thermal and fluorescence studies. Eur. J. Med. Chem.. 2012;52:313-321.
[Google Scholar]

[56] Sonmez M., Celebi M., Berber I., . Synthesis, spectroscopic and biological studies on the new symmetric Schiff base derived from 2,6-diformyl-4-methylphenol with N-aminopyrimidine. Eur. J. Med. Chem.. 2010;4:1935-1940.
[Google Scholar]

[57] Srivastava A.N., Singh N.P., Shriwastaw C.K., . Synthesis and characterization of bioactive binuclear transition metal complexes of a Schiff base ligand derived from 4-amino-1H-pyrimidin-2-one, diacetyl and glycine. J. Serb. Chem. Soc.. 2014;79:421-433.
[Google Scholar]

[58] Suslick K.S., Reinert T.J., . The synthetic analogs of O₂-binding heme proteins. J. Chem. Edu.. 1985;62:974-984.
[Google Scholar]

[59] Tabassum S., Singh N.P., Arjmand F., . Synthesis, characterization and toxicity of heterobinuclear complexes of transition metal ions. Synth. React. Inorg. Met. Org. Chem.. 2001;31:1803-1815.
[Google Scholar]

[60] Tabassum S., Sharma G.C., Arjmand F., Azam A., . DNA interaction studies of new nano metal based anticancer agent: validation by spectroscopic methods. Nanotechnology. 2010;21:195102-195112.
[Google Scholar]

[61] Vanpariya S.F., Patel T.S., Sojitra N.A., Jagani C.L., Dixit B.C., Patel P.S., Dixit R.B., . Synthesis, characterization and antimicrobial study of novel 4-{[(8-Hydroxyquinoline-5-yl)methyl]amino}benzenesulfonamide and its oxinates. Acta Chim. Slov.. 2010;57:660-667.
[Google Scholar]

[62] Vogel A.I., . A Text Book of Quantitative Inorganic Analysis. London: Logmans; 1961.

[63] Weitzer M., Brooker S., . Dimetallic complexes of a structurally versatile pyridazine-containing Schiff-base macrocyclic ligand with pendant pyridine arms. Dalton Trans. 2005:2448-2454.
[Google Scholar]

Compounds	¹H NMR (δ/ppm)	¹³C NMR (δ/ppm)
(L)	1.32 [⚌C—CH₃ (s, 6H)], 3.54 [—CH₂ (s, 4H)], 11.22 [—OH (s, 2H)]	13.40 [C-4, 6], 46.90 [C-2, 7], 161.50 [C-3, 5], 173.40 [C-1, 8]
[Zn₂(PymL)(CH₃CO₂)₃] (4)	1.12 [⚌C—CH₃ (s, 6H)], 1.74 [-CH₃ (pym.) (s, 3H)], 2.17 [—CH₃COO (br, s, 9H)], 3.68 [—CH₂ (s, 4H)], 7.34 [—CH (s, 1H), (pym.)], 10.90 [—NH (pym.) (br, s, 1H)], 11.32 [—OH (s, 2H)]	13.10 [C-4, 6], 15.20 [C-13], 18.96 [C-15, 15‘, 17], 46.20 [C-2, 7], 106.30 [C-11], 138.40 [C-10], 158.90 [C-3, 5], 160.80 [C-12], 169.80 [C-1, 8], 173.20 [C-14, 14‘, 16], 178.10 [C-9]

In vitro antibacterial and antifungal activities of binuclear transition metal complexes of ONNO Schiff base and 5-methyl-2,6-pyrimidine-dione and their spectroscopic validation

Abstract

Keywords

5-Methyl-2,6-pyrimidine-dione

Binuclear complexes

Octahedral geometry

Antimicrobial property

1 Introduction

2 Experimental

2.1 Reagents

2.2 Synthesis of Schiff base (L)

2.3 General procedure for synthesis of the binuclear metal complexes (1–4)

2.3.1 Binuclear metal complex [Cu2(PymL)Cl3] (1)

2.3.2 Binuclear metal complex [Ni2(PymL)Cl3] (2)

2.3.3 Binuclear metal complex [Co2(PymL)Cl3] (3)

2.3.4 Binuclear metal complex [Zn2(PymL)(CH3CO2)3] (4)

2.4 Physical measurements

2.5 In vitro antimicrobial activities

2.5.1 In vitro antibacterial activity

2.5.2 In vitro antifungal activity

3 Results and discussion

3.1 IR spectra

3.1.1 1H and 13C NMR spectra

3.2 Mass spectra

3.3 Electronic absorption spectra and magnetic moment measurements

3.4 EPR spectra of [Cu2(PymL)Cl3] and [Co2(PymL)Cl3] complexes

3.5 In vitro antibacterial activity

3.6 Minimum inhibitory concentration (MIC)

3.7 In vitro antifungal activity

4 Conclusion

Acknowledgements

References

Suggested read for related articles:

2.3.1 Binuclear metal complex [Cu₂(PymL)Cl₃] (1)

2.3.2 Binuclear metal complex [Ni₂(PymL)Cl₃] (2)

2.3.3 Binuclear metal complex [Co₂(PymL)Cl₃] (3)

2.3.4 Binuclear metal complex [Zn₂(PymL)(CH₃CO₂)₃] (4)

3.1.1 ¹H and ¹³C NMR spectra

3.4 EPR spectra of [Cu₂(PymL)Cl₃] and [Co₂(PymL)Cl₃] complexes