# Spectroscopic and Biological Studies on Newly Synthesized Cobalt (II) and Nickel (II) Complexes with 2-Acetyl Coumarone Semicarbazone and 2-Acetyl Coumarone Thiosemicarbazone

Authors: Sanjay Goel; Sulekh Chandra; Sudhanshu Dhar Dwivedi
Journal: Journal of Chemistry
 (2013)

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## Abstract

Co(II) and Ni(II) complexes of general composition ML2X2 (M = Co(II), Ni(II); X = Cl−, NO3−) were synthesized by the condensation of metal salts with semicarbazone/thiosemicarbazone derived from 2-acetyl coumarone. The ligands and metal complexes were characterized by NMR, elemental analysis, molar conductance, magnetic susceptibility measurements, IR, and atomic absorption spectral studies. On the basis of electronic, molar conductance and infrared spectral studies, the complexes were found to have square planar geometry. The Schiff bases and their metal complexes were tested for their antibacterial and antioxidant activities.


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## Body

## 1. Introduction

Research on the coordination chemistry, analytical applications, and biological activities of Schiff base complexes has increased steadily for many years. A large number of Schiff bases and their complexes have been studied for their interesting and important biological properties, for example, antimicrobial (El-Wahab et al. [1]), antiviral (Kolocouris et al. [2]), antifungal (Rodríguez-Argüelles et al. [3]), antitumour (Ainscough et al. [4]), and other biological activities (Bharamagouclar et al.  [5]; Zhu et al. [6]; Shalin et al. [7]; Kothari and Sharma [8]) particularly with first row of transition metal complexes. The formation of variety of metal complexes with Schiff base ligands as mentioned in our earlier studies (Chandra and Kumar [9]; Chandra and Kumar [10]; Chandra and Gupta [11]) indicates the spectacular progress in coordination and bioinorganic chemistry. It has been demonstrated through several studies that the biological activity of Schiff’s bases is enhanced on chelation with a metal ion (Sengupta et al. [12]). In the view of the facts that the metal complexes are better therapeutic agents (Chandra et al. [13]; Kumar and Chandra [14]) as compared to the Schiff bases, the aim of this study is to synthesize the new class of metal complexes with newly synthesized Schiff base ligands and different metal salts, to find their biological activity such as antioxidant and antibacterial activities and to observe the impact of complexation on their therapeutic values.


## 2. Experimental

All the chemicals used in the present work were of high purity, Anala R grade, and procured from Sigma-Aldrich. Metal salts were purchased from E. Merck and used as received. The solvents used were either spectroscopic pure from SRL/BDH or purified by the recommended methods (Vogel [15]).


### 2.1. Synthesis of 2-Acetyl Coumarone Semicarbazone (SCL)

An aqueous solution of semicarbazide HCl (1.11 g, 0.01 mol) was added to an ethanolic solution of 2-acetyl coumarone (1.60 g, 0.01 mol) in the presence of sodium acetate (0.82 g, 0.01 mol). The reaction mixture was stirred vigorously for 2 h. The completion of the reaction was confirmed by the TLC. The yellow product formed was collected by filtration which was washed several times with hot water and dried in vacuum over P4O10. The characterization details are tabulated in Table 1. (See Scheme 1).Table 1
Molar conductance and elemental analysis data.
Ligand/complex
Λ
M
Atomic mass
Colour
M.P (°C)
Yield            (%)
Elemental analysis data (%) found (calculated)
M
C
H
N
SCL
—
217
Yellow
224
72
—
59.83 (60.82)
4.97 (5.10)
19.12 (19.34)
[Co(SCL)2](Cl)2
152
563
Brown
230
72
10.42 (10.44)
46.92 (46.83)
3.97 (3.93)
14.92 (14.89)
[Co(SCL)2](NO3)2
184
616
Brown
219
71
9.53 (9.55)
43.89 (42.80)
3.62 (3.59)
18.37 (18.15)
[Ni(SCL)2](Cl)2
158
564
Light brown
226
79
10.40 (10.41)
46.92 (46.85)
3.99 (3.93)
15.18 (14.90)
[Ni(SCL)2](NO3)2
179
617
Light brown
218
73
9.50 (9.51)
43.14 (42.82)
3.64 (3.59)
18.53 (18.16)
TSCL
—
233
light yellow
197
70
—
56.21 (56.63)
4.59 (4.75)
17.81 (18.01)
[Co(TSCL)2](Cl)2
168
595
Brown
205
74
9.84 (9.88)
45.19 (44.30)
3.97 (3.72)
13.87 (14.09)
[Co(TSCL)2](NO3)2
180
648
Light brown
210
81
9.05 (9.07)
39.98 (40.68)
3.37 (3.41)
17.82 (17.25)
[Ni(TSCL)2](Cl)2
174
596
Light yellow
199
71
9.84 (9.84)
45.15 (44.32)
3.86 (3.72)
13.89 (14.10)
[Ni(TSCL)2](NO3)2
187
649
Brown
198
78
9.02 (9.04)
40.16 (40.70)
3.84 (3.42)
17.54 (17.26)
Λ
M: molar conductance (Ω−1cm2mol−1).Scheme 1


### 2.2. Synthesis of 2-Acetyl Coumarone Thiosemicarbazone (TSCL)

Hot ethanolic solution of 2-acetyl coumarone (1.60 g, 0.01 mol) was mixed with hot ethanolic solution of thiosemicarbazide (0.91 g, 0.01 mol) in the presence of 0.5 mL acetic acid. The contents were refluxed at 70–80°C for about 3-4 h. The completion of the reaction was confirmed by the TLC. The solvent was removed using a rotary evaporator and light yellow coloured solid was obtained. It was washed with cold ethanol and dried under vacuum over P4O10. The characterization details are tabulated in Table 1. (See Scheme 2).Scheme 2


### 2.3. Preparation of Metal Complexes

Hot ethanolic solution of metal salts (1 mmol), for example, nickel chloride hexahydrate (0.238 g), nickel nitrate hexahydrate (0.292 g), cobalt chloride hexahydrate (0.237 g), or cobalt nitrate hexahydrate (0.291 g), was mixed with hot ethanolic solution of the corresponding ligand (2 mmol), for example, SCL (0.434 g) or TSCL (0.466 g). The mixture was refluxed for 4-5 hours at 70–80°C. On cooling the contents, the complex separated out in each case. It was filtered, washed with 50% ethanol, and dried under vacuum over P4O10. The characterization details are tabulated in Table 1.


### 2.4. Physical Measurements

The C, H, and N were analyzed on a Carlo-Erba 1106 elemental analyzer. Metal contents were determined by Atomic Absorption studies. Molar conductance was measured on an ELICO (CM82T) conductivity bridge. Magnetic susceptibilities were measured at room temperature on a Gouy balance using CuSO4·5H2O as calibrant. IR spectra (KBr) were recorded on a FTIR spectrum BX-II spectrophotometer. The electronic spectra were recorded in DMSO on a Shimadzu UV mini-1240 spectrophotometer. The 1H NMR spectrums were recorded on a Jeol FT-NMR Spectrometer using DMSO as a solvent. Thermogravimetry (TG) and Differential Thermogravimetric (DTA) analysis for the metal complexes were carried out on a Perkin Elmer (Diamond) TG-DTA spectrometer for the determination of complex entrapped water.


## 2.1. Synthesis of 2-Acetyl Coumarone Semicarbazone (SCL)

An aqueous solution of semicarbazide HCl (1.11 g, 0.01 mol) was added to an ethanolic solution of 2-acetyl coumarone (1.60 g, 0.01 mol) in the presence of sodium acetate (0.82 g, 0.01 mol). The reaction mixture was stirred vigorously for 2 h. The completion of the reaction was confirmed by the TLC. The yellow product formed was collected by filtration which was washed several times with hot water and dried in vacuum over P4O10. The characterization details are tabulated in Table 1. (See Scheme 1).Table 1
Molar conductance and elemental analysis data.
Ligand/complex
Λ
M
Atomic mass
Colour
M.P (°C)
Yield            (%)
Elemental analysis data (%) found (calculated)
M
C
H
N
SCL
—
217
Yellow
224
72
—
59.83 (60.82)
4.97 (5.10)
19.12 (19.34)
[Co(SCL)2](Cl)2
152
563
Brown
230
72
10.42 (10.44)
46.92 (46.83)
3.97 (3.93)
14.92 (14.89)
[Co(SCL)2](NO3)2
184
616
Brown
219
71
9.53 (9.55)
43.89 (42.80)
3.62 (3.59)
18.37 (18.15)
[Ni(SCL)2](Cl)2
158
564
Light brown
226
79
10.40 (10.41)
46.92 (46.85)
3.99 (3.93)
15.18 (14.90)
[Ni(SCL)2](NO3)2
179
617
Light brown
218
73
9.50 (9.51)
43.14 (42.82)
3.64 (3.59)
18.53 (18.16)
TSCL
—
233
light yellow
197
70
—
56.21 (56.63)
4.59 (4.75)
17.81 (18.01)
[Co(TSCL)2](Cl)2
168
595
Brown
205
74
9.84 (9.88)
45.19 (44.30)
3.97 (3.72)
13.87 (14.09)
[Co(TSCL)2](NO3)2
180
648
Light brown
210
81
9.05 (9.07)
39.98 (40.68)
3.37 (3.41)
17.82 (17.25)
[Ni(TSCL)2](Cl)2
174
596
Light yellow
199
71
9.84 (9.84)
45.15 (44.32)
3.86 (3.72)
13.89 (14.10)
[Ni(TSCL)2](NO3)2
187
649
Brown
198
78
9.02 (9.04)
40.16 (40.70)
3.84 (3.42)
17.54 (17.26)
Λ
M: molar conductance (Ω−1cm2mol−1).Scheme 1


## 2.2. Synthesis of 2-Acetyl Coumarone Thiosemicarbazone (TSCL)

Hot ethanolic solution of 2-acetyl coumarone (1.60 g, 0.01 mol) was mixed with hot ethanolic solution of thiosemicarbazide (0.91 g, 0.01 mol) in the presence of 0.5 mL acetic acid. The contents were refluxed at 70–80°C for about 3-4 h. The completion of the reaction was confirmed by the TLC. The solvent was removed using a rotary evaporator and light yellow coloured solid was obtained. It was washed with cold ethanol and dried under vacuum over P4O10. The characterization details are tabulated in Table 1. (See Scheme 2).Scheme 2


## 2.3. Preparation of Metal Complexes

Hot ethanolic solution of metal salts (1 mmol), for example, nickel chloride hexahydrate (0.238 g), nickel nitrate hexahydrate (0.292 g), cobalt chloride hexahydrate (0.237 g), or cobalt nitrate hexahydrate (0.291 g), was mixed with hot ethanolic solution of the corresponding ligand (2 mmol), for example, SCL (0.434 g) or TSCL (0.466 g). The mixture was refluxed for 4-5 hours at 70–80°C. On cooling the contents, the complex separated out in each case. It was filtered, washed with 50% ethanol, and dried under vacuum over P4O10. The characterization details are tabulated in Table 1.


## 2.4. Physical Measurements

The C, H, and N were analyzed on a Carlo-Erba 1106 elemental analyzer. Metal contents were determined by Atomic Absorption studies. Molar conductance was measured on an ELICO (CM82T) conductivity bridge. Magnetic susceptibilities were measured at room temperature on a Gouy balance using CuSO4·5H2O as calibrant. IR spectra (KBr) were recorded on a FTIR spectrum BX-II spectrophotometer. The electronic spectra were recorded in DMSO on a Shimadzu UV mini-1240 spectrophotometer. The 1H NMR spectrums were recorded on a Jeol FT-NMR Spectrometer using DMSO as a solvent. Thermogravimetry (TG) and Differential Thermogravimetric (DTA) analysis for the metal complexes were carried out on a Perkin Elmer (Diamond) TG-DTA spectrometer for the determination of complex entrapped water.


## 3. Results and Discussion

### 3.1. Infrared Spectra of SCL

The IR spectrum of ligand SCL (Figure1) shows bands at 3456 and 3144 cm−1 which may be assigned to [υ(NH2)] and [υ(NH)] groups, respectively. The bands due to [υ(C=O)] appeared at 1720 cm−1 and the bands at 1562 or 1446 cm−1 may be assigned to symmetric or asymmetric [υ(C=N)] group (Kothari and Sharma [8]; Chandra and Gupta [11]).Figure 1
IR spectra of SCL.


### 3.2. The1H NMR Spectra of SCL

The1H NMR spectrum of the ligand SCL (Figure 2) was recorded in DMSO. It shows signals at δ 2.21 ppm (3H, CH3–C, s), δ 6.52 ppm (2H, NH2–CO, s), δ 9.62 ppm (1H, N–NH–CO, s), δ 7.36 ppm (1H, Ph–CH–C, s), δ 7.62 (1H, Ph, d), δ 7.57 ppm (1H, Ph, d), δ 7.32 (1H, Ph, m), and δ 7.25 ppm (1H, Ph, m).Figure 2
NMR spectra of SCL.


### 3.3. Infrared Spectra of TSCL

The IR spectrum of the ligand TSCL (Figure3) shows bands at 3310 and 3148 cm−1 which may be assigned to [υ(NH2)] and [υ(NH)] groups, respectively. The bands due to [υ(C=S)] appeared at 1598 cm−1 and the bands at 1497 or 1257 cm−1 may be assigned to symmetric or asymmetric [υ(C=N)] group (Kothari and Sharma [8]; Chandra and Gupta [11]).Figure 3
IR spectra of TSCL.


### 3.4. The1H NMR Spectra of TSCL

The1H NMR spectrum of the ligand TSCL (Figure 4) was recorded in DMSO. It shows signals at δ 2.33 ppm (3H, CH3–C, s), δ 7.82 ppm (2H, NH2–CO, s), δ 10.51 ppm (1H, N–NH–CO, s), δ 7.56 ppm (1H, Ph–CH–C, s), δ 7.65 (1H, Ph, d), δ 7.59 ppm (1H, Ph, d), δ 7.35 (1H, Ph, m), and δ 7.26 ppm (1H, Ph, m).Figure 4
NMR spectra of TSCL.


### 3.5. Infrared Spectra of Metal Complexes

The assignments of the significant IR spectral bands of the metal complexes are shown in Figures5, 6, 7, and 8 which clearly show the shifting of the bands corresponding to υ(–C=N) and υ(–C=S) in thiosemicarbazone or υ(–C=O) in semicarbazone towards the lower side (around ca. 20–50 cm−1) on complexation. This suggests that both the ligands act as bidentate chelating agents coordinating through nitrogen of C=N group and sulphur of C=S group or oxygen of C=O (Kothari and Sharma [8]; Chandra and Gupta [11]).Figure 5
IR spectra of [Co(SCL)2](Cl)2.Figure 6
IR spectra of [Ni(SCL)2](Cl)2.Figure 7
IR spectra of [Co(TSCL)2](NO3)2.Figure 8
IR spectra of [Ni(TSCL)2](NO3)2.


### 3.6. The1H NMR Spectra of Nickel Complexes

The1H NMR spectra of the nickel complexes were recorded in DMSO. They show shifting of signals corresponding to CH3, NH2–CO and N–NH–CO coordination as compared to the 1H NMR spectra of the corresponding ligand. It indicates the chelation of the ligand through nitrogen of C=N group and sulphur of C=S group or oxygen of C=O.


### 3.7. Elemental Analysis Data and Molar Conductance of Metal Complexes

The metal contents (Table1) were determined by the Atomic Absorption studies as shown in Figures 9 and 10. The C, H, and N contents in the metal complexes were analyzed by the Elemental Analyzer and are tabulated in Table 1. The molar conductance measurements (Table 1) of the complexes in DMSO correspond to 1 : 2 electrolytic nature (Shakir et al. [16]). On the basis of elemental analysis data and molar conductance of the complexes, the metal complexes may be formulated as [ML2]X2 (where M = Co(II), Ni(II); X = Cl−, NO3-).Figure 9
Calibration curve for Co metal complexes for Atomic Absorption studies. The solutions of cobalt complexes (10 ppm), that is, [Co(SCL)2](Cl)2, [Co(SCL)2](NO3)2, [Co(TSCL)2](Cl)2, and, [Co(TSCL)2](NO3)2, show the absorbance of 0.0396, 0.0362, 0.0374, and 0.0344, respectively. % of Cobalt = Absorbance × 10/Slope (where slope = 0.038).Figure 10
Calibration curve for Ni metal complexes for Atomic Absorption studies. The solutions of nickel complexes (10 ppm), that is, [Ni(SCL)2](Cl)2, [Ni(SCL)2](NO3)2, [Ni(TSCL)2](Cl)2, and [Ni(TSCL)2](NO3)2, show the absorbance of 0.0520, 0.0475, 0.0492, and 0.0451, respectively. % of Nickel = Absorbance × 10/Slope (where slope = 0.050).


### 3.8. Magnetic Moment and Electronic Spectral Data of Metal Complexes

At room temperature Ni(II) complexes show diamagnetic character and Co(II) complexes show magnetic moment in the range 1.85–2.04 B.M. (Table2) corresponding to one unpaired electron. These values correspond to low spin configurations of the metal complexes. The electronic spectrum of chloride and nitrate complexes shows electronic spectral bands in the range 17100–17900 cm−1 and 22400–22800 cm−1 corresponding to the following transitions: υ1: 2B1g → 2A1g, υ2: 2B1g → 2Eg which indicates the square planar geometry of the complexes.Table 2
Magnetic moment and electronic spectral data of complexes.
Electronic spectral data
Complex
μ
eff (B.M.)
υ
1 (cm−1)
υ
2 (cm−1)
ε (Lmol−1 cm−1)
ε (Lmol−1 cm−1)
[Co(SCL)2](Cl)2
2.04
17267
22800
[Co(SCL)2](NO3)2
1.93
17648
22523
[Ni(SCL)2](Cl)2
Diamagnetic
17856
22270
[Ni(SCL)2](NO3)2
Diamagnetic
17245
22948
[Co(TSCL)2](Cl)2
2.01
17112
22842
[Co(TSCL)2](NO3)2
1.85
17402
22845
[Ni(TSCL)2](Cl)2
Diamagnetic
17813
22613
[Ni(TSCL)2](NO3)2
Diamagnetic
17534
22400


### 3.9. TG-DTA Data of Metal Complexes

All the metal complexes show major weight loss above 175°C which shows that they are free of any entrapped water. The peaks due to melting of complexes in TG-DTA curve agree well with the melting point of the complexes as determined by the MP apparatus (Make: BUCHI, Model: M-560).


## 3.1. Infrared Spectra of SCL

The IR spectrum of ligand SCL (Figure1) shows bands at 3456 and 3144 cm−1 which may be assigned to [υ(NH2)] and [υ(NH)] groups, respectively. The bands due to [υ(C=O)] appeared at 1720 cm−1 and the bands at 1562 or 1446 cm−1 may be assigned to symmetric or asymmetric [υ(C=N)] group (Kothari and Sharma [8]; Chandra and Gupta [11]).Figure 1
IR spectra of SCL.


## 3.2. The1H NMR Spectra of SCL

The1H NMR spectrum of the ligand SCL (Figure 2) was recorded in DMSO. It shows signals at δ 2.21 ppm (3H, CH3–C, s), δ 6.52 ppm (2H, NH2–CO, s), δ 9.62 ppm (1H, N–NH–CO, s), δ 7.36 ppm (1H, Ph–CH–C, s), δ 7.62 (1H, Ph, d), δ 7.57 ppm (1H, Ph, d), δ 7.32 (1H, Ph, m), and δ 7.25 ppm (1H, Ph, m).Figure 2
NMR spectra of SCL.


## 3.3. Infrared Spectra of TSCL

The IR spectrum of the ligand TSCL (Figure3) shows bands at 3310 and 3148 cm−1 which may be assigned to [υ(NH2)] and [υ(NH)] groups, respectively. The bands due to [υ(C=S)] appeared at 1598 cm−1 and the bands at 1497 or 1257 cm−1 may be assigned to symmetric or asymmetric [υ(C=N)] group (Kothari and Sharma [8]; Chandra and Gupta [11]).Figure 3
IR spectra of TSCL.


## 3.4. The1H NMR Spectra of TSCL

The1H NMR spectrum of the ligand TSCL (Figure 4) was recorded in DMSO. It shows signals at δ 2.33 ppm (3H, CH3–C, s), δ 7.82 ppm (2H, NH2–CO, s), δ 10.51 ppm (1H, N–NH–CO, s), δ 7.56 ppm (1H, Ph–CH–C, s), δ 7.65 (1H, Ph, d), δ 7.59 ppm (1H, Ph, d), δ 7.35 (1H, Ph, m), and δ 7.26 ppm (1H, Ph, m).Figure 4
NMR spectra of TSCL.


## 3.5. Infrared Spectra of Metal Complexes

The assignments of the significant IR spectral bands of the metal complexes are shown in Figures5, 6, 7, and 8 which clearly show the shifting of the bands corresponding to υ(–C=N) and υ(–C=S) in thiosemicarbazone or υ(–C=O) in semicarbazone towards the lower side (around ca. 20–50 cm−1) on complexation. This suggests that both the ligands act as bidentate chelating agents coordinating through nitrogen of C=N group and sulphur of C=S group or oxygen of C=O (Kothari and Sharma [8]; Chandra and Gupta [11]).Figure 5
IR spectra of [Co(SCL)2](Cl)2.Figure 6
IR spectra of [Ni(SCL)2](Cl)2.Figure 7
IR spectra of [Co(TSCL)2](NO3)2.Figure 8
IR spectra of [Ni(TSCL)2](NO3)2.


## 3.6. The1H NMR Spectra of Nickel Complexes

The1H NMR spectra of the nickel complexes were recorded in DMSO. They show shifting of signals corresponding to CH3, NH2–CO and N–NH–CO coordination as compared to the 1H NMR spectra of the corresponding ligand. It indicates the chelation of the ligand through nitrogen of C=N group and sulphur of C=S group or oxygen of C=O.


## 3.7. Elemental Analysis Data and Molar Conductance of Metal Complexes

The metal contents (Table1) were determined by the Atomic Absorption studies as shown in Figures 9 and 10. The C, H, and N contents in the metal complexes were analyzed by the Elemental Analyzer and are tabulated in Table 1. The molar conductance measurements (Table 1) of the complexes in DMSO correspond to 1 : 2 electrolytic nature (Shakir et al. [16]). On the basis of elemental analysis data and molar conductance of the complexes, the metal complexes may be formulated as [ML2]X2 (where M = Co(II), Ni(II); X = Cl−, NO3-).Figure 9
Calibration curve for Co metal complexes for Atomic Absorption studies. The solutions of cobalt complexes (10 ppm), that is, [Co(SCL)2](Cl)2, [Co(SCL)2](NO3)2, [Co(TSCL)2](Cl)2, and, [Co(TSCL)2](NO3)2, show the absorbance of 0.0396, 0.0362, 0.0374, and 0.0344, respectively. % of Cobalt = Absorbance × 10/Slope (where slope = 0.038).Figure 10
Calibration curve for Ni metal complexes for Atomic Absorption studies. The solutions of nickel complexes (10 ppm), that is, [Ni(SCL)2](Cl)2, [Ni(SCL)2](NO3)2, [Ni(TSCL)2](Cl)2, and [Ni(TSCL)2](NO3)2, show the absorbance of 0.0520, 0.0475, 0.0492, and 0.0451, respectively. % of Nickel = Absorbance × 10/Slope (where slope = 0.050).


## 3.8. Magnetic Moment and Electronic Spectral Data of Metal Complexes

At room temperature Ni(II) complexes show diamagnetic character and Co(II) complexes show magnetic moment in the range 1.85–2.04 B.M. (Table2) corresponding to one unpaired electron. These values correspond to low spin configurations of the metal complexes. The electronic spectrum of chloride and nitrate complexes shows electronic spectral bands in the range 17100–17900 cm−1 and 22400–22800 cm−1 corresponding to the following transitions: υ1: 2B1g → 2A1g, υ2: 2B1g → 2Eg which indicates the square planar geometry of the complexes.Table 2
Magnetic moment and electronic spectral data of complexes.
Electronic spectral data
Complex
μ
eff (B.M.)
υ
1 (cm−1)
υ
2 (cm−1)
ε (Lmol−1 cm−1)
ε (Lmol−1 cm−1)
[Co(SCL)2](Cl)2
2.04
17267
22800
[Co(SCL)2](NO3)2
1.93
17648
22523
[Ni(SCL)2](Cl)2
Diamagnetic
17856
22270
[Ni(SCL)2](NO3)2
Diamagnetic
17245
22948
[Co(TSCL)2](Cl)2
2.01
17112
22842
[Co(TSCL)2](NO3)2
1.85
17402
22845
[Ni(TSCL)2](Cl)2
Diamagnetic
17813
22613
[Ni(TSCL)2](NO3)2
Diamagnetic
17534
22400


## 3.9. TG-DTA Data of Metal Complexes

All the metal complexes show major weight loss above 175°C which shows that they are free of any entrapped water. The peaks due to melting of complexes in TG-DTA curve agree well with the melting point of the complexes as determined by the MP apparatus (Make: BUCHI, Model: M-560).


## 4. Antioxidant Activity

### 4.1. Assay of Initiation of Lipid Peroxidation

The details of the assay procedure are described in the earlier communication (Raj et al. [17]). The reaction mixture in a final volume of 2 mL consisted of 0.025 M Tris-HCI (pH 7.5), microsomes (1 mg protein) which were taken from the laboratory of Prof. H. G. Raj, Department of Biochemistry, VP Chest Institute and were prepared by adopting the method of Ernster and Nordenbrand [18] (protein was assayed by the method of Lowry et al. [19]), 3 mM ADP, and 0.15 mM FeCl3. The tubes were preincubated for 10 min at 37°C followed by the addition of the test compounds added at a concentration of 100 μM in 0.2 mL of DMSO and then again incubated for 10 min at 37°C. The reaction was started by the addition of 0.5 mM NADPH for initiation of enzymatic lipid peroxidation and incubated for different intervals. The reaction was terminated by the addition of 0.2 mL of 50% TCA followed by addition of 0.2 mL of 5 N HCI and 1.6 mL of 30% TBA. The tubes were heated in an oil bath at 95°C for 30 min, cooled, and centrifuged at 3000 rpm. The intensity of the colour of the thiobarbituric acid reactive substance (TBRS) formed was read at 535 nm. The lipid peroxidation was found to be linear up to 15 min under the conditions described here. The results (Table 3) illustrate the influence of ligands and metal complexes on the initiation of lipid peroxidation enzymatically. These results clearly indicate that metal complexes have higher antioxidant activities as compared to the schiff’s base ligands. Thiosemicarbazone metal complexes show higher antioxidant activities than semicarbazone metal complexes. Moreover, nickel metal complexes show higher antioxidant activities than cobalt metal complexes.Table 3
Influence of ligands and metal complexes on the initiation of lipid peroxidation.
Ligands/complexes
Percent of control
SCL
98
[Co(SCL)2](Cl)2
82
[Co(SCL)2](NO3)2
86
[Ni(SCL)2](Cl)2
72
[Ni(SCL)2](NO3)2
77
TSCL
96
[Co(TSCL)2](Cl)2
76
[Co(TSCL)2](NO3)2
79
[Ni(TSCL)2](Cl)2
58
[Ni(TSCL)2](NO3)2
63


## 4.1. Assay of Initiation of Lipid Peroxidation

The details of the assay procedure are described in the earlier communication (Raj et al. [17]). The reaction mixture in a final volume of 2 mL consisted of 0.025 M Tris-HCI (pH 7.5), microsomes (1 mg protein) which were taken from the laboratory of Prof. H. G. Raj, Department of Biochemistry, VP Chest Institute and were prepared by adopting the method of Ernster and Nordenbrand [18] (protein was assayed by the method of Lowry et al. [19]), 3 mM ADP, and 0.15 mM FeCl3. The tubes were preincubated for 10 min at 37°C followed by the addition of the test compounds added at a concentration of 100 μM in 0.2 mL of DMSO and then again incubated for 10 min at 37°C. The reaction was started by the addition of 0.5 mM NADPH for initiation of enzymatic lipid peroxidation and incubated for different intervals. The reaction was terminated by the addition of 0.2 mL of 50% TCA followed by addition of 0.2 mL of 5 N HCI and 1.6 mL of 30% TBA. The tubes were heated in an oil bath at 95°C for 30 min, cooled, and centrifuged at 3000 rpm. The intensity of the colour of the thiobarbituric acid reactive substance (TBRS) formed was read at 535 nm. The lipid peroxidation was found to be linear up to 15 min under the conditions described here. The results (Table 3) illustrate the influence of ligands and metal complexes on the initiation of lipid peroxidation enzymatically. These results clearly indicate that metal complexes have higher antioxidant activities as compared to the schiff’s base ligands. Thiosemicarbazone metal complexes show higher antioxidant activities than semicarbazone metal complexes. Moreover, nickel metal complexes show higher antioxidant activities than cobalt metal complexes.Table 3
Influence of ligands and metal complexes on the initiation of lipid peroxidation.
Ligands/complexes
Percent of control
SCL
98
[Co(SCL)2](Cl)2
82
[Co(SCL)2](NO3)2
86
[Ni(SCL)2](Cl)2
72
[Ni(SCL)2](NO3)2
77
TSCL
96
[Co(TSCL)2](Cl)2
76
[Co(TSCL)2](NO3)2
79
[Ni(TSCL)2](Cl)2
58
[Ni(TSCL)2](NO3)2
63


## 5. Antibacterial Activity

The antibacterial activities of the metal complexes were determined at different concentrations (30μg/disc) against different pathogenic bacteria (Table 4) by using disc diffusion technique and the results were compared with standard antibiotic, Kanamycin (30 μg/disc). It was found that the metal complexes were active against all of the test bacteria but the metal complexes [Co(TSCL)2](NO3)2 and [Ni(TSCL)2](NO3)2 were most effective against all pathogenic bacteria as shown in Table 4. The zones of inhibition of the complexes were, however, lesser as compared to standard Kanamycin. The metal complexes have higher antibacterial activities as compared to the Schiff’s base ligands. Thiosemicarbazone metal complexes show higher activities than semicarbazone metal complexes.Table 4
Antibacterial activity of ligands and metal complexes.
Test organism
Diameter of zones of inhibition (mm)
M1
M2
M3
M4
M5
M6
M7
M8
L1
L2
Kanamycin
Escherichia  coli
8
7
8
7
13
14
12
15
2
2
22
Klebsiella species
6
5
5
4
14
16
14
17
4
5
20
Shigella sonnei
7
4
6
8
12
15
13
14
3
4
25
Bacillus  subtilis
9
6
8
5
12
14
14
16
3
3
23
M1: [Co(SCL)2](Cl)2; M2: [Co(SCL)2](NO3)2; M3:  [Ni(SCL)2](Cl)2; M4: [Ni(SCL)2](NO3)2; M5: [Co(TSCL)2](Cl)2; M6: [Co(TSCL)2](NO3)2; M7: [Ni(TSCL)2](Cl)2; M8: [Ni(TSCL)2](NO3)2; L1:  SCL; L2: TSCL.


## 6. Conclusions

The present work describes the facile synthesis of metal complexes with newly synthesized Schiff base ligands and their biological activity. On the basis of elemental analysis data, molar conductance, magnetic susceptibility measurements, IR, and atomic absorption spectral studies, the resulting metal complexes may have square planar geometry and may be formulated as [ML2]X2 (where M = Co(II), Ni(II); X = Cl−, NO3-). The metal complexes show higher antioxidant and antibacterial activities as compared to the ligands. The nickel complexes derived from 2-acetyl coumarone thiosemicarbazone show remarkable antioxidant and antibacterial activities.



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*Source: 742915-2012-12-03.xml*