Biological important Ni(II) ternary complexes derived from 2-substituted benzothiazoles and amino acids

Article abstract of DOI:10.1155/2011/612847

Biological important ternary complexes of the type [NiCl(L-L) (A-A)(H ₂O)] and [Ni(L-L')(A-A)(H₂O) ₂], where A-A = Glycine (Gly), Alanine (Ala), L-L = 2-(2'-aminophenyl)benzothiazole (APBT) and L-L' = 2-(2'-hydroxyphenyl)benzothiazole (HPBT), 2-(2'-mercaptophenyl) benzothiazole (MPBT) have been synthesized. These complexes have been characterized by elemental analysis, molecular weight determination, conductivity, magnetic measurements, infrared, electronic spectral and TGA studies. On the basis of above described studies an octahedral geometry has been suggested for these complexes. All these complexes are coloured, thermally stable, monomeric and non-electrolytic in nature. The ligands and their metal complexes were tested against pathogenic fungi Aspergillus niger and Fusarium oxysporum to assess their fungicidal properties, the antifungal activity data reveals that these metal complexes are found more fungitoxic than the parent ligands.

Full text of DOI:10.1155/2011/612847

ISSN: 0973-4945; CODEN ECJHAO
E-Journal of Chemistry
2011, 8(3), 1174-1179
http://www.e-journals.net
Biological Important Ni(II) Ternary
Complexes Derived from
-Substituted Benzothiazoles and Amino Acids
2
*
NARENDRA PAL, MAHESH KUMAR and GITA SETH
Department of Chemistry, University of Rajasthan, Jaipur, India
gita_seth@yahoo.co.in
Received 7 October 2010; Accepted 16 December 2010
Abstract: Biological important ternary complexes of the type [NiCl(L-L)
(
(
A-A)(H O)] and [Ni(L-L´)(A-A)(H O) ], where A-A = Glycine (Gly), Alanine
2 2 2
Ala), L-L = 2-(2´-aminophenyl)benzothiazole (APBT) and L-L´ = 2-(2´-
hydroxyphenyl)benzothiazole (HPBT), 2-(2´-mercaptophenyl)benzothiazole
MPBT) have been synthesized. These complexes have been characterized by
(
elemental analysis, molecular weight determination, conductivity, magnetic
measurements, infrared, electronic spectral and TGA studies. On the basis of
above described studies an octahedral geometry has been suggested for these
complexes. All these complexes are coloured, thermally stable, monomeric and
non-electrolytic in nature. The ligands and their metal complexes were tested
against pathogenic fungi Aspergillus niger and Fusarium oxysporum to assess
their fungicidal properties, the antifungal activity data reveals that these metal
complexes are found more fungitoxic than the parent ligands.
Keywords: Benzothiazole, Spectral studies, Amino acids, Antifungal activity.
Introduction
Compounds with a benzothiazole moiety have received considerable attention because of
their widespread occurrence in biologically active molecules such as antitumor, antimaleria,
1.3
fungicide, anti-HIV, antiviral and analgesic agents . Recently, radiolabeling of
benzothiazole derivatives have been developed for PET imaging in the detection of
4
alzheimer diseases . These compounds also have many industrial applications; for example
some 2-substitued benzothiazole are utilized as fluorescence agents in textile dyeing,
antioxidants and valcanization accelerators of rubber.
A large number of benzimidazole derivative have been synthesized and patented as
5
fungicide . The formation and structural aspects of some transition metal complexes of
.6
7
-substituted benzimidazole derivatives have been reported by Seth et al. and various other
2

1
175
GITA SETH et al.
8
,9
workers . We describe here the synthesis, characterization and biological activity of Ni(II)
ternary complexes derived from 2-substituted benzothiazole viz. 2-(2´-aminophenyl)-
benzothiazole (APBT), 2-(2´-hydroxyphenyl)benzothiazole (HPBT), 2-(2´-mercaptophenyl)-
benzothiazole (MPBT) and amino acids viz. glycine (Gly) and alanine (Ala) ligands. As the
biological activity is often augmented when a ligand form complexes. The resulting mixed
ligand complexes may be of potential biological importance. The structure of ligands used to
synthesize the Ni(II) ternary complexes are shown in Figure 1 and 2.
S
H N CH
2
C
O
OH
N
R
HX
APBT
NH
HPBT
O
MPBT
S
Gly
Ala
CH3
X
R
H
Figure 1. Structure of the ligands APBT, HPBT, MPBT, Gly and Ala
S
S
N
N
X
NH2
OH2
Ni
OH2
Cl
Ni
H O
2
H N
2
O
H N
2
O
CH
C
CH
C
R
O
R
O
Where X = O, S R = H, CH3
Figure 2. The suggested chemical structures of the Ni(II) ternary complexes
Experimental
All the solvents were distilled prior to use, o-aminothiophenol, anthranilic acid, salicylic
acid, thiosalicylic acid, NiCl .6H O were purchased from Merck and used as such.
2
2
Physical measurements
Microanalysis was carried out at the CDRI Lucknow, India. Melting points were determined
on a capillary melting point apparatus and are uncorrected, IR spectra were recorded (with
KBr pellets) on a SHIMADZU 8400 SPIR spectrophotometer. Electronic spectra were
recorded on a Varian-Cary UV-visible spectrometer. Magnetic moments were measured on a
–3
Gouy balance. Molar conductance were measured in 10 M DMF on a Systronics
conductivity bridge model 305. Molecular weights were determined by the Rast camphor
method. Nitrogen was determined by the Kjeldahl’s method and sulfur was estimated by the
Messenger’s method. Chloride was determined by the Volhard’s method. nickel was
19
estimated gravimetrically .
Synthesis of 2-substituted benzothiazoles (APBT, HPBT, MPBT)
The 2-substituted benzothiazoles viz. 2-(2´-aminophenyl) benzothiazole (APBT),
2
-(2´-hydroxyphenyl) benzothiazole (HPBT), 2-(2´-marceptophenyl)benzothiazole (MPBT)

Biological Important Ni(II) Ternary Complexes
1176
were prepared by condensation o-aminothiophenol (1.25 g, 0.01 mol) with anthranilic acid
1.37 g, 0.01 mol), salicylic acid (1.38 g, 0.01 mol) and thiosalicylic acid (1.54 g, 0.01 mol)
(
20
in polyphosphoric acid (20 mL) using the method reported in literature . The reaction
mixture was heated to 250° C under reflux with constant stirring for 4 h. The temperature
was brought down to 100 °C and the contents were poured into a large volume of rapidly
stirred water. The resultant slurry was made alkaline with 50% NaOH. The crude product
was collected by filtration and washed with sufficient amount of water, dried in vacuo and
recrystallized from ethanol.
Preparation of nickel(II) ternary complex
To a solution of NiCl .6H O (0.95 g, 0.004 mol) in dry EtOH (25 mL) was added APBT
2
2
(
(
0.90 g, 0.004 mol) / HPBT (0.91 g, 0.004 mol) / MPBT (0.97g, 0.004 mol) and glycine
0.30 g, 0.004 mol) / alanine (0.36 g, 0.004 mol) in dry EtOH (25 mL). The reaction mixture
was then refluxed in the presence of a drop of pyridine with constant stirring for 4 h, and
allowed to stand at room temperature overnight. These were filtered, recrystallized from
EtOH and dried in vacuo.
Results and Discussion
The Ni(II) ternary complexes were synthesized by NiCl .6H O with 2-substituted
2
2
benzothiazoles (APBT, HPBT and MPBT) and amino acids (Gly, Ala) in 1:1:1 molar ratio.
Ethanol
[
NiCl (L-L) (A-A) (H O)]
2
NiCl .6H O + (L-L) + (A-A)
2
2
Reflux
Ethanol
[Ni (L-L´) (A-A) (H O) ]
2 2
NiCl .6H O + (L-L´) + (A-A)
2
2
Reflux
Where
L-L = APBT, L-L´ = HPBT, MPBT and A-A = Gly, Ala
These reactions are processed easily and lead to the formation of coloured solids, which
are stable to air and moisture. The resulting Ni(II) ternary complexes are soluble in DMSO
–3
and DMF. The molar conductance values of 10 M solutions of these complexes lay in the
–1
2
–1
10
range 10-20 Ω cm mol in dry DMF, indicating their non-electrolytic behaviour . The
monomeric nature of these complexes has been confirmed by the molecular weight
determination. The analytical data and physical properties of the ligands and their Ni(II)
ternary complexes are given in Table 1. The compounds were characterized on the basis of
following studies.
Infrared spectra
The important IR spectral bands and their tentative assignments are presented in
Table 2. The ligands APBT, HPBT, MPBT, Gly and Ala act as bidentate ligands in these
Ni(II) ternary complexes using nitrogen, oxygen and sulfur as donor atoms. The IR spectra
–1
–1
of APBT, Gly/Ala shows two strong bands in the region 3400-3370 cm and 3310-3250 cm
due to v (N–H) and v (N–H) vibrations of NH of these ligands, respectively. These bands
as
s
2
–1
are shifted to lower frequency by 35-80 cm in the respective Ni(II) ternary complexes,
suggesting the coordination through nitrogen lone pair of the NH group to the Ni atom
2
11
without any deprotanation . It is further supported by appearance of the new bands in the
–
region 436-432 cm due to v(Ni←N) vibration. The appearance of absorption bands in the
1
–1
region 448-445 cm may be assigned to v(Ni–O) vibration. The occurrence of non-ligand
12
absorption band in the region 320-315 cm may be attributed to v(Ni–Cl) vibration .
–1

1
177
GITA SETH et al.
Table 1. The analytical data and physical properties of the ligands and their Ni(II) ternary
complexes
Molecular
weight
found
Elemental analysis found (calcd.) %
Cl Ni
Compound and
Colour
empirical formula
C
H
N
S
(
calcd.)
[
NiCl(APBT)(Gly)
Bluish
Green
43.58 3.87 10.12 7.70 8.50 14.18 410.01
(43.67) (3.91) (10.18) (7.77) (8.59) (14.23) (412.54)
1
2
3
4
5
6
.
.
.
.
.
.
60 225
62 230
61 240
65 245
68 258
64 262
(
16 3 3
H O)]NiC15H O N SCl
2
[
NiCl(APBT)(Ala)(H
2
O
)] Bluish
44.95 4.18 9.72 7.42 8.22 13.65 422.52
(45.05) (4.25) (9.85) (7.52) (8.31) (13.76) (426.57)
NiC H O N SCl
1
Green
6
18
3
3
[
Ni(MPBT)(Gly)
Yellowish
43.71 3.85 6.71 15.52
(43.82) (3.92) (6.81) (15.60)
14.22 409.10
-
-
-
-
(
(
(
(
H O) ]NiC H O N S
2
Green
(14.28) (411.15)
2
15 16
4
2
2
2
[
Ni(MPBT)(Ala)
Light
45.12 4.18 6.48 15.01
(45.20) (4.27) (6.59) (15.08)
13.70 422.02
H O) ]NiC H O N S
2
Green
(13.81) (425.18)
2
16 18
4
2
[
Ni(HPBT)(Gly)
Light
45.52 4.02 7.01 8.04
(45.60) (4.08) (7.09) (8.12)
14.75 392.50
H O) ]NiC H O N S
2 2
Green
(14.86) (395.08)
2
15 16
5
[
Ni(HPBT)(Ala)
Light
46.92 4.36 6.78 7.77
(46.98) (4.43) (6.85) (7.84)
14.27 406.02
H O) ]NiC H O N S
2 2
Green
(14.35) (409.11)
2
16 18
5
–1
Table 2. IR spectral data (cm ) of ligands (APBT, HPBT, MPBT) and Ni(II) ternary
complexes
v
v
v(NH2)
v
v
v
v
v
v
v
Compound
(
C=C) (C=N) Asym. Sym. (O-H) (S-H) (C=O) (Ni-N) (Ni-S) (Ni-O) (Ni-Cl)
1
2
3
.
.
.
APBT
HPBT
MPBT
1586 1615 3370 3250
-
3330
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
1590 1620
1582 1618
-
-
-
-
2560
[
(
[
(
NiCl(APBT)
Gly)(H O)]
2
4
5
6
7
8
9
.
.
.
.
.
.
1584 1608 3355 3240
1580 1606 3352 3235
1585 1612 3360 3242
1582 1610 3358 3238
1580 1606 3350 3230
1578 1604 3348 3228
-
-
-
-
-
-
-
-
-
-
-
-
1662 436
1660 432
1680 438
1675 435
-
-
-
-
448 320
445 315
NiCl(APBT)
Ala)(H O)]
2
[
Ni(HPBT)
Gly)(H O) ]
455
452
-
-
-
-
(
2
2
[
Ni(HPBT)
Ala)(H O) ]
(
2
2
[
Ni(MPBT)
Gly)(H O) ]
1670 430 335 440
1665 428 332 438
(
2
2
[
Ni(MPBT)
Ala)(H O) ]
(
2
2
–1
The broad band at 3330 cm due to v(O–H) phenolic mode of HPBT, disappears in the
Ni(II) ternary complexes, indicating the deprotonation of the OH group and coordination of
phenolic oxygen to the Ni atom with the formation of Ni-O bond. This gets further support
–
by the appearance of bond in the region 455-452 cm due to v(Ni–O) vibrations . The IR
1
13
–1
spectrum of MPBT shows a band at 2560 cm due to v(S–H) (thiophenolic) vibration,
which disappears in the Ni(II) ternary complexes, suggesting the deprotonation of -SH group
and coordination through thiophenolic sulfur with the Ni atom. It is further supported by the
–1
appearance of new band in the region 335-332 cm due to v(Ni–S) vibration.

Biological Important Ni(II) Ternary Complexes
1178
–1
A medium or relatively weak band in the 1620-1615 cm region in the IR spectra of
the free ligands (APBT, HPBT and MPBT) is due to v(C=N) vibration. This band is shifted
–1
to lower frequency by 10-20 cm in Ni(II) ternary complexes indicate the bonding of the
14
benzothiazole tertiary nitrogen with Ni atom . It is further confirmed by the appearance of
–1
band in the region 438-428 cm due to v(Ni←N) vibration.)
Electronic absorption spectra and magnetic studies
The electronic spectral data and magnetic moments of the Ni(II) ternary complexes are
given in Table 3. The electronic spectra of Ni(II) ternary complexes were recorded in nujol
mull. These complexes display three absorption band of low intensity due to d-d transitions
–1
–1
–1
in the region 9725-9830 cm , 18225-18655 cm and 28045-28245 cm are assigned to the
3
3
3
3
3
3
15
A (F) → T (F) (v ); A (F) → T (F) (v ) and A (F) → T (P)(v ) transition ,
2
g
2g
1
2g
1g
2
2g
1g
3
respectively. The position of these bands are similar to those reported for Ni(II) complexes
16
with an octahedral geometry . The room temperature magnetic moments of these
complexes indicates the paramagnetic nature of the Ni(II) ion the magnetic moments of
these complexes have been found in the range 3.26-3.32 B.M., which are in the consistent
with the high spin state at the Ni(II) ion and in the range expected for octahedral complexes.
Table 3. Magnetic moments (µ ) and electronic spectral data for the Ni(II) ternary
B
complexes of 2-substituted benzthiazole and amino acids
–
1
Magnetic Electronic transition and assignments cm
3
3
3
S.No.
Complex
moment
µB) B.M.
3.30
A2g (F) → A2g (F) →
T2g (F) (v1) T1g (F) (v2) T1g (P) (v3)
A2g (F) →
3
3
3
(
1
2
3
4
5
6
.
.
.
.
.
.
[NiCl(APBT)(Gly)(H O)]
2
9740
9745
9828
9830
9725
9730
18250
18255
18650
18655
18225
18230
28060
28065
28240
28245
28045
28050
[NiCl(APBT)(Ala)(H O)]
2
3.32
3.26
[Ni(HPBT)(Gly)(H O) ]
2
2
[Ni(HPBT)(Ala)(H O) ]
2
3.27
3.26
3.27
2
[Ni(MPBT)(Gly)(H O) ]
2
2
[Ni(MPBT)(Ala)(H O) ]
2
2
TGA studies of Ni(II) ternary complexes
The existence of coordinated water molecule in these Ni(II) ternary complexes is confirmed
by TGA studies. The coordinated water molecules are lost in the temperature range 100 to
3
10 °C. The ultimate product of the thermal decomposition in these complex is nickel oxide.
Thus, on the basis of analytical data and above describe studies, an octahedral geometry may
be assigned for these Ni(II) ternary complexes.
The toxicity increased as the concentration was increased. The antifungal activity data
also reveals that Ni(II) ternary complexes of MPBT and Gly/Ala are more fungitoxic than
18
the complexes of APBT and HPBT ligands, respectively.
Biological activity
The antifungal activity of ligands (APBT, HPBT and MPBT) and their Ni(II) ternary complexes
were carried out against pathogenic fungi, namely Aspergillus niger and Fusarium oxysporum by
radial growth methods. The solution of the test compound were prepared (50, 100 and 200 ppm)
in dimethylformamide. The linear growth of the fungus was recorded by measuring the diameter
of the fungus colony after 72 h and the percentage inhibition was calculated as 100 (C-T)/C,
where T are the diameter of the fungus colony in the control and text plates respectively. The
results of antifungal activity of the ligands and Ni(II) ternary complexes have been compared
with the conventional fungicide Bavistin taken as standards (Table 4).

1
179
GITA SETH et al.
Table 4. Fungicidal screening data for ligands (APBT, HPBT and MPBT) and their Ni(II)
ternary complexes
Concentration, ppm
Aspergillus niger
Fusarium oxysporum
Complex
Inhibition after 72 h, %
Inhibition after 72 h, %
5
0
100
52
46
58
74
75
68
69
85
86
98
200
62
58
68
88
89
78
80
94
96
100
50
43
36
48
65
66
54
55
73
74
87
100
55
48
61
78
79
70
71
87
88
99
200
64
60
70
90
92
80
82
96
98
100
APBT
HPBT
MPBT
40
34
46
62
63
52
53
72
73
86
[
NiCl(APBT)(Gly)(H O)]
2
[
NiCl(APBT)(Ala)(H O)]
2
[
Ni(HPBT)(Gly)(H O) ]
2 2
[
Ni(HPBT)(Ala)(H O) ]
2 2
[
Ni(MPBT)(Gly)(H O) ]
2 2
[
Ni(MPBT)(Ala)(H O) ]
2
2
Bavistin (Standard)
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2

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