DNA binding properties and antibacterial activity of heterolyptic transition metal complexes with 2,2-bipyridyl and 2-acetylthiophene thiosemicarbazone

Article abstract of DOI:10.14233/ajchem.2019.22018

Metal complexes having the composition M(Bipy)Cl2 (where, M = Cu(II), Ni(II) and Co(II); Bipy = 2,2-bipyridyl) are reacted with 2-acetylthiophene thiosemicarbazone (ATT) to produce heteroleptic transition metal complexes with molecular formula [M(Bipy)ATT]. The complexes are characterized by mass spectra, molar conductivity, infrared and electronic spectra. Electrochemical behaviour of these metal complexes was investigated by cyclic voltammetric studies. The metal complexes show quasi reversible cyclic voltammetric responses for the Cu(II)/Cu(I) couple. The binding properties of these complexes with calf-thymus DNA have been investigated by using absorption spectrophotometry. Metal complexes are screened for their antibacterial activity by using agar well diffusion method against pathogenic bacterial strains viz. Escherichia coli and Staphylococcus aureus. Antibacterial activity of the present complexes are comparable with the activity of ciprofloxacin. The Cu(Bipy)Cl2 complex inhibits bacteria more strongly than any other complex. The Ni(Bipy)ATT complex shows more activity than the parent complex, Ni(Bipy)Cl2.

Full text of DOI:10.14233/ajchem.2019.22018

Asian Journal of Chemistry; Vol. 31, No. 9 (2019), 1905-1912
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2019.22018
DNA Binding Properties and Antibacterial Activity of Heterolyptic Transition
Metal Complexes with 2,2-Bipyridyl and 2-Acetylthiophene Thiosemicarbazone
1
1,*
1
1
2
KUMMARA SRINIVASULU , KATREDDI HUSSAIN REDDY , K. ANUJA , D. DHANALAKSHMI and GOLLA RAMESH
1
2
Department of Chemistry, Sri Krishnadevraya University, Ananthapuramu-515003, India
Department of Studies and Research in Chemistry, University College of Science, Tumkur University, Tumkur-572103, India
Corresponding author: E-mail: khussainreddy@yahoo.co.in
Received: 21 February 2019; Accepted: 30 March 2019;
*
Published online: 31 July 2019;
AJC-19475
Metal complexes having the composition M(Bipy)Cl
2
(where, M = Cu(II), Ni(II) and Co(II); Bipy = 2,2-bipyridyl) are reacted with
2
-acetylthiophene thiosemicarbazone (ATT) to produce heteroleptic transition metal complexes with molecular formula [M(Bipy)ATT].
The complexes are characterized by mass spectra, molar conductivity, infrared and electronic spectra. Electrochemical behaviour of these
metal complexes was investigated by cyclic voltammetric studies. The metal complexes show quasi reversible cyclic voltammetric responses
for the Cu(II)/Cu(I) couple. The binding properties of these complexes with calf-thymus DNA have been investigated by using absorption
spectrophotometry. Metal complexes are screened for their antibacterial activity by using agar well diffusion method against pathogenic
bacterial strains viz. Escherichia coli and Staphylococcus aureus. Antibacterial activity of the present complexes are comparable with the
activity of ciprofloxacin. The Cu(Bipy)Cl
2
complex inhibits bacteria more strongly than any other complex. The Ni(Bipy)ATT complex
shows more activity than the parent complex, Ni(Bipy)Cl
2
.
Keywords: Heterolyptic transition metal complexes, 2,2-Bipyridyl, ATT, DNA binding, Antibacterial activity.
attention due to the widespread application in the chemothera-
INTRODUCTION
peutic field. Thiosemicarbazones and their metal complexes
are a broad class of biologically active compounds [3,4]. The
group N–C=S is of considerable chemotherapeutic interest and
is responsible for pharmacological activity. Thiosemicarbazones
and their metal complexes present a wide range of applications
that stretch from their use in analytical chemistry [5-8], through
pharmacology [9-11] to nuclear medicine [12].Transition metal
complexes of thiosemicarbazone showed antibacterial [13,14],
antimalarial [15], antitrypanosomal [16], antiviral [17], anti-
tumor [18] and anticancer [19,20] activities.
Transition metal complexes with assorted ligands conta-
ining hetero donor atoms (N, S) are known to exhibit interesting
stereochemical, electrochemical and electronic properties
[21,22]. Mixed ligand metal complexes with 2,2-bipyridine
and acetylacetone [23]; 2,2-bipyridine and maltolate [24] have
been investigated. But no report is available on mixed ligand
metal complexes with 2,2-bipyridine and thiosemicarbazone.
Pharmacological activity of metal complexes is traced to their
ability to bind/interact with DNA, ladder of life. The heterocyclic
Thiosemicarbazones are prepared by the condensation of
thiosemicarbazides with aldehydes or ketones in the presence
of a few drops of glacial acetic acid. Thiosemicarbazones with
general formula R
1
R
2
C=N–NH–C(S)–NR
3
R usually react as
4
chelate with transition metal ions by bonding through the sulfur
and hydrazinic nitrogen atoms in ligands. Thiosemicarbazones
are versatile ligands in both neutral (HL) and anionic forms
(
L–). They are extensively delocalized systems, especially
when aromatic radicals are bound to the azomethine carbon
atom. The R and R groups may provide additional donor
atoms and R and R
1
2
4
3
4
are the N substituents. Thiosemicarba-
zones have emerged as an important class of sulfur containing
ligands particularly for transition metal ions. The real impetus
towards developing their coordination chemistry was due to
their physicochemical properties [1,2] and significant biolo-
gical activities [3,4].
Thiosemicarbazones are thiourea derivatives and the studies
on their chemical and structural properties have received much
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1
906 Srinivasulu et al.
Asian J. Chem.
ligand, 2,2-bipyridyl is known as potential intercalating com-
pound due to its planar structure.
and carbonyl compound viz. 2-acetylthiophene. A methanolic
solution of thiosemicarbazide (5 mmol), 2-acetylthiophene
(5 mmol) in methanol was mixed in a round bottom flask.
Bipyridine chelators act as potential antitumor agents [25].
The choice of bipyridine is mainly due to two factors. (i) The
ligand is rigid, planar and provides two aromatic nitrogens
whose unshared electron pairs can act co-operatively in binding
cations (ii) The π-electron deficiency makes 2,2-bipyridyl an
excellent π-acceptor ligand The metal complexes of bipyridine
are of considerable due to their biological or pharmacological
properties.
Structural and spectral studies on 2-acetylthiophene thio-
semicarbazones (ATT) have been reported [26,27]. Platinum
and palladium complexes ofATT) are also reported in the lite-
rature [28]. 2-Acetylthiophene thiosemicarbazones has been
used for the spectrophotometric determination of copper(II)
in alloys, edible oils and seeds [29]. However, transition metal
complexes with polypyridyl ligands and thosemicarbazone
have not been much investigated [30].
Two drops of HCl/CH COOH were added to the reaction
3
mixture. This reaction mixture was refluxed for 3 h and the
reaction mixture was cooled to room temperature. The ligand
ATT was obtained as yellow coloured crystalline product, which
are subsequently used for the synthesis of metal complexes.
-1
Yield 65 %, m.p. 155-157 °C, IR spectra (cm ) 3404, 3207,
-1
3126, 1605. 1232 cm are assigned to ν(N-H asym), ν(N-H
sym), ν(C-H thiophene), ν(C=N) and ν(C=S) stretching vibra-
tions respectively. NMR spectra (δ) 8.773 (singlet 1H), 7.030-
7.371 (multiplet 3H), 6.521 (singlet 2H broad), 2.311(singlet
3H) are assigned to >NH, thiophene H, -NH
2
and CH protons
3
respectively. Mass spectrum (Fig. 1) ofATT shows molecular
ion peak at 199. The structure of ligand is shown in Fig. 2.
199
100
It is of interest to study mixed ligand transition metal com-
plexes. This is because they are the most general and probable
form of coordination compounds in the biological system.
Therefore studies of mixed ligand complexes of biologically
important compounds may serve as models for biochemical
processes [31-33]. They are also characterized by their extreme
stability and the properties of the central metal ion is more
pronounced in these complexes. In the light of the above and
in continuation of our ongoing research on transition metal
complexes, herein we report synthesis, characterization and
DNA binding properties of heterolyptic Cu(II), Ni(II) and
Co(II) complexes with 2,2-bipyridyl and 2-acetylthiophene
thiosemicarbazone (ATT).
1
82
39
124
09
1
60
139
150
84
50
100
200
250
Fig. 1. Mass spectrum of ATT ligand
CH3
S
N
EXPERIMENTAL
NH
Thiosemicarbazide, 2-acetylthiophene, 2,2-bipyridyl,
were purchased from Sigma-Aldrich.All other chemicals were
of AR grade and used as provided. The solvents used for the
synthesis were distilled before use. Calf-thymus DNA (CT-
DNA) was purchased from Genio Bio labs, Bangalore, India.
Elemental analyses were carried out on a Heraeus Vario EL
III Carlo Erba 1108 instrument. Magnetic measurements were
taken at 298K using lakeshore VSM 7410 instrument. Molar
conductivity measurements at 298 ± 2 K in dry and purified
DMF were carried out using a CM model 162 conductivity
cell (ELICO). The electronic spectra were recorded in DMSO
with a UV lamda50 (Perkin-Elmer) spectrophotometer. IR
S
C
NH2
Fig. 2. Structure of ATT ligand
Preparation of complexes: The complexes, Cu(Bipy)Cl
Ni(Bipy)Cl , Co(Bipy)Cl were prepared by mixing one equi-
2
,
2
2
valent of 2,2′-bipyridine in 30 mL of ethanol to one equivalent
of respective metal chlorides in 15 mL of ethanol.
PreparationofCu(Bipy)ATT, Ni(Bipy)ATT, Co(Bipy)ATT
complexes: A 1.2 g of ATT ligand (0.006 mol) was dissolved
in 15 mL of 0.05 N NaOH in ethanol solvent in 100 mL beaker.
A 1.0 g Cu(Bipy)Cl
2
(0.003 mol) was dissolved in 15 mL of
-1
spectra were recorded in the range 4000–400 cm with a Perkin-
Elmer spectrum100 spectrometer on KBr discs. ESR spectra
were recorded on a Varian E-112 X-band spectrophotometer
at room temperature and liquid nitrogen temperature (LNT)
in solution (DMF) state. Cyclic voltammetric measurements
were taken on a CH instruments assembly equipped with an
ethanol solvent in 100 mL beaker. Ligand solution and Cu(Bipy)Cl
2
solution were transferred into 100 mL round bottom flask and
heated under reflux for 1 h. On cooling the contents of flask,
dark green coloured complex was formed. It was collected by
filtration, washed with small quantities of ethanol and dried
in air. Ni(Bipy)ATTand Co(Bipy)ATT complexes are prepared
similarly.
DNA binding experiments: The electronic spectra of
metal complexes were monitored in the absence and presence
of CT-DNA. The interaction of the complexes with DNA was
carried out in tris-buffer. Solution of calf thymus DNA (CT-
DNA) in (50 mM NaCl/5 mM Tris-HCl; pH =7.0) buffer gave
absorbances ratio at 260 nm and 280 nm of 1.85, indicating
X–Y recorder. Measurements were taken on degassed (N
2
-3
bubbling for 5 min) solutions (10 M) containing 0.1 M Bu
4
NPF
6
as the supporting electrolyte. The three-electrode system
consisted of glassy carbon (working), platinum wire (auxiliary)
and Ag/AgCl (reference) electrodes.
Preparation ofATT: The ligand, 2-acetylthiophene thio-
semicarbazone (ATT) was prepared using thiosemicarbazide

Vol. 31, No. 9 (2019)
Metal Complexes with 2,2-Bipyridyl and 2-Acetylthiophene Thiosemicarbazone 1907
that the DNA was sufficiently free of proteins [34,35]. The DNA
concentration per nucleotide was determined by absorption
are reacted (Scheme-I) with 2-acetylthiophene thiosemicarba-
zone (ATT) to produce heteroleptic transition metal complexes
with molecular formula [M(Bipy)ATT].
3
-1
-1
coefficient (6600 dm mol cm ) at 260 nm. Stock solutions
stored at 4 °C were used after no more than 4 days. The electronic
spectra of metal complexes were monitored in the absence and
presence of CT-DNA. Absorption titrations were performed
CH3
N
N
S
-5
Cl
Cl
by maintaining the metal complex concentration 2 × 10 M
and varying nucleic acid concentration. Absorption spectra
were recorded after each successive addition of DNA solution.
N
M
M(Bipy)(ATT)Cl2
NH
S
C
The intrinsic binding constant (K
equation:
b
) was calculated by the
NH2
M(Bipy)Cl2
ATT
Scheme-I: Synthesis of mixed ligand metal complexes [where, M = Cu(II),
[
DNA]/ε
where [DNA] is the molar concentration of DNA in base pairs,
, ε , ε are apparent extinction coefficient (Aobs/[M], the
a
-ε
f
= [DNA]/ε
a
-ε
f
+ 1/K
b
(ε
a
-ε
f
)
Ni(II), Co(II)]
ε
a
b
f
All the complexes are stable at room temperature, non-
hygroscopic, insoluble in water, slightly soluble in methanol
and ethanol but readily soluble in DMF and DMSO. The physico-
chemical data for the complexes are summarized in Table-1.
Analytical data support the compositions of the comp-
lexes. For 1:1 electrolyte the molar conductivity values are in
extinction coefficient for the metal (M) complex in the fully
bound form and the extinction coefficient for free metal (M)
respectively.A plot of [DNA]/(ε
of 1/(ε -ε )x K is the ratio of the intercept.
Evaluation of antibacterial activity: The pathogenic
bacterial strains were purchased from National Chemical Labo-
ratory (NCL) Pune, India.Antibacterial activity of compounds
a
f
-ε ) versus [DNA] gave a slope
a
f
b
-1
2
-1
the range 65-90 Ω cm mol in dimethylformamide. The
observed values indicate non-electrolytic nature [36] of comp-
lexes.
such as Cu-Bipy-Cl
2 2
, Cu-Bipy-ATT, Ni-Bipy-Cl , Ni-Bipy-ATT,
Co-Bipy-Cl and Co-Bipy-ATT were screened byAgar well diffu-
2
Electronic spectra: The electronic spectra of the comp-
lexes are recorded in DMF. The significant bands obtained
from electronic spectral data are presented in Table-2.A Strong
sion method against bacterial strains such as Gram-negative
bacteria such as Escherichia coli [NCIM-5051] and Gram-
positive bacteria Staphylococcus aureus [NCIM-5022]. Nutrient
agar (NA) plates were prepared using sterile nutrient agar
medium was poured into sterile petri-dishes and allowed to
solidify.After, 100 µL of 24 h mature broth culture of individual
pathogenic bacterial strains while spreading all over the surface
of agar plates using sterilized L-shaped glass rod.About 6 mm
well are made in each nutrient agar plate using sterile cork
borer. Different concentrations of compounds (100, 200 and
-1
sharp band is observed in the region of 33898-31847 cm for
*
the metal complexes is associated with π→π transition of
aromatic chromophore [37]. Medium intensity band is obtained
-1
in the range of 30211-28089 cm which corresponds to charge
transfer spectra caused by ligand to the metal ion [38]. A
-1
weak band in the region of 13106-16806 cm region may be
assigned to d-d transition. The electronic spectrum of complex
Co(Bipy)(ATT)Cl is shown in Fig. 3.
2
3
00 µg/well) were used to assess the dose dependent activity
IR spectra: IR spectral data of the 2-acetylthiophene
thiosemicarbazone (ATT) and its metal complexes along with
assignment of peaks are given in Table-3. A strong band is
of the product. The metal complexes were dissolved in 10 %
dimethyl sulfoxide and micropipettes were used for the addi-
tion of compounds into the wells. Simultaneously the standard
antibiotics (ciprofloxacin used as a positive control) are tested
against the pathogenic bacterial strains. Then the plates were
incubated at 37 °C for 36 h. After incubation, the zone of inhi-
bition of each well was measured and the values were noted.
The experiments were carried out in triplicates with each com-
pound and the average values were calculated for determining
the zone of inhibition.
-1
observed in the IR spectrum of ATT at 1605 cm , which is
assigned to ν(C=N) group. In all the complexes, this band is
-1
shifted to lower frequency (11-27 cm ) indicating the parti-
cipation of azomethine nitrogen atom in coordination [39,40].
A medium band is appeared in the spectrum of ATT ligand at
-1
1
232 cm , which is assigned to ν(C=S) group. In all the
complexes, this peak disappears and a new band is formed in
68-759 cm region due to ν(C-S). These changes suggest
-1
7
the enolization of >C=S to >C-SH. In the enolic form, subse-
quently the ligand (ATT) undergoes deprotonation and binds
metal by forming covalent bond between sulphur and metal.
In far IR region, new peaks are observed in 506-498 and 457-
RESULTS AND DISCUSSION
Metal complexes having the composition M(Bipy)Cl
where, M = Cu(II), Ni(II) and Co(II); Bipy = 2,2-bipyridyl)
2
(
TABLE-1
PHYSICO-CHEMICAL AND ANALYTICAL DATA OF Cu(II), Ni(II) AND Co(II) COMPLEXES
Molar conductivity
Complex
Cu(Bipy)Cl2
Cu(Bipy)(ATT)Cl2
Ni(Bipy)Cl2
Colour
Yield (%)
ESI-MS
f.w.
-1
2
-1
(
Ω cm mol )
30.90
Light green
Dark green
Parrot green
Dark brown
Blue
71.56
89.03
81.93
86.26
72.77
88.43
289.41
487.60
281.30
496.10
282.32
480.95
291
490
285
496
286
485
15.64
27.75
40.46
46.05
Ni(Bipy)(ATT)Cl ·0.5H O
2
2
Co(Bipy)Cl2
Co(Bipy)(ATT)Cl2
Black
67.36

1
908 Srinivasulu et al.
Asian J. Chem.
1
1
1
1
1
0
0
0
0
0
.8
.6
.4
.2
.0
.8
.6
.4
.2
.0
0
.5
.4
0
(a)
(b)
0.3
0
.2
0
.1
0
.0
-
0.2
2
50
300
350
400
450
500
500
600
700
Wavelength (nm)
complex (a) in lower concentration and (b) in higher concentration
800
900
Wavelength (nm)
Fig. 3. Electronic spectrum of Co(Bipy)(ATT)Cl
2
TABLE-2
1
000
ELECTRONIC SPECTRAL DATA FOR
Cu(II), Ni(II) AND Co(II) COMPLEXES
500
λ
Frequency
(cm )
max
Complex
-1
Assignment
(
nm)
01
312
0
3
33222
32015
13106
31847
28735
16806
33557
32786
16260
32679
30211
33898
19305
14814
10101
33783
28089
16611
14992
π-π* transition
CT transition
d-d transition
-500
Cu(Bipy)Cl2
7
3
63
14
-1000
π-π* transition
CT transition
d-d transition
π-π* transition
CT transition
d-d transition
π-π* transition
CT transition
Cu(Bipy)(ATT)Cl2
348
-1500
-2000
5
2
95
98
Ni(Bipy)Cl2
305
-2500
615
306
331
295
518
675
990
296
356
602
667
100
150
200
Field strength (mT)
Fig. 4. ESR spectrum of Cu(Bipy)(ATT)Cl
250
300
350
400
450
Ni(Bipy)(ATT)Cl ·0.5H O
2
2
π-π* transition
CT transition
d-d transition
d-d transition
2
complex (LNT)
Co(Bipy)Cl2
given in Table-4. The g|| and g are computed from the spectra
using TCNE free radicals as g marker. The observed g|| values
forcomplexes are less than or equal to 2.3 suggesting signi-ficant
covalent character of metal ligand bond in agreement with
π-π* transition
CT transition
d-d transition
d-d transition
Co(Bipy)(ATT)Cl2
⊥
observation of Kivelson and Neiman [43]. The g|| and g were
more than 2, corresponding to an axial symmetry. The trend The
g > g > g (2.0023) observed for these complexes suggests that
-
1
||
⊥
e
4
49 cm regions, which are assigned to ν(M-N) and ν(M-S)
the unpaired is localized in the dx2-y2 orbital [43] of the copper
ion. The axial symmetry parameter G is defined as [44]:
[g − 2.0023]
vibrations [41,42] respectively.
ESR spectra: The ESR spectra of copper complexes were
recorded in DMF solution at room temperature and at liquid nitro-
gen temperature.A typical ESR spectrum of Cu(Bipy)(ATT)Cl
recorded at LNT is shown in Fig. 4. The spin Hamiltonian,
orbital reduction and bonding parameters of complexes are
|
|
G =
2
[g − 2.0023]
⊥
The calculated G values for these complexes are less than
.0, which indicates the presence of small exchange coupling
4
TABLE-3
-
1
IR THIOSEMICARBAZONE (ATT) SPECTRAL BANDS (cm ) OF Cu(II), Ni(II) AND Co(II)
COMPLEXES OF BIPYRIDINE AND 2-ACETYLTHIOPHENE
ATT
Cu(Bipy)(ATT)Cl2
Ni(Bipy)(ATT)Cl ·0.5H O
Co(Bipy)(ATT)Cl2
Assignment
ν(C=N) Azomethine
ν(C-C) thiophene
ν(C=S) thione
ν(C-S)
2
2
1
1
578, 1513
448, 1284
1594
1587
1423, 1301
1152, 1006, 850
768
1605
1439, 1309
1112, 989
759
1095
7
4
4
68
98
57
1232
506
457
ν(M-N)
ν(M-S)
449

Vol. 31, No. 9 (2019)
Complex
Metal Complexes with 2,2-Bipyridyl and 2-Acetylthiophene Thiosemicarbazone 1909
TABLE-4
ESR SPECTRAL DATA† OF COPPER COMPLEXES
In DMF at LNT
-
5
-5
2
g||
g
⊥
gavg
G
A × 10
A
⊥
× 10
K||
K
⊥
λ
α
||
2
.28
2.05
(2.08)
1.99
(2.06)
2.13
(2.10)
2.10
(2.08)
4.87
(1.74)
3.96
(2.21)
Cu(Bipy)Cl2
0.0016
0.0013
–
0.995
1.027
0.181
463
0.2997
(
2.14)
.33
2.13)
2
Cu(Bipy)(ATT)Cl2
0.00093
0.304
693
0.0495
(
†ESR data in DMF at room temperature are given in parenthesis.
and misalignment of molecular axes. The g||,
complexes and the energies of the d-d transitions are used to
calculate the orbital reduction parameters (K , K ), the bonding
parameter (α ). The factor α which is usuallytaken as a measure
of covalency and it is evaluated by the expression:
⊥
g⊥||, A of
H C
3
⊥
⊥
S
2
2
Cl
N
N
N
2
α = –A||/p + (g|| – 2.0023) + 3/7(g
⊥
– 2.0023) + 0.04
NH
M
Hatchway pointed out that for pure σ bonding K|| ≈K ≈
⊥
0
.77, for in-plane π-bonding K|| < K
⊥
, while out of plane π-
S
C
Cl
bonding K|| > K
⊥
the following simplified expressions were
used to calculate K|| and K
⊥
:
NH2
(
g|| − 2.0023)
2
K =
×d-d transition
×d-d transition
|
|
Fig. 5. Structure of M(Bipy)(ATT)Cl
2
complex
8
×λo
(
g⊥ − 2.0023)
2
K =
–5
⊥
3.0×10
8
×λo
The observed K|| < K
indicates the significant out of plane π-bonding and K|| > K
relation for Cu(Bipy)(ATT)Cl complex indicates the significant
⊥
relation for Cu(Bipy)Cl complex
2
–
5
2.0×10
⊥
2
out of plane π-bonding.
–5
1.0×10
Based on analytical, physico-chemical and spectral data,
a general structure (Fig. 5) is proposed for the complexes.
Cyclic voltammetry: The redox behaviour of the comp-
lexes has been investigated by cyclic voltammetry in DMF
using 0.1 M tetrabutylammonium hexafluorophosphate as
supporting electrolyte. The cyclic voltammogram of Ni(Bipy)
0
1
2
–5
-1.0×10
3
(
ATT)Cl complex is shown in Fig. 6 and the electrochemical
2
0.0
-0.5
-1.0
-1.5
data of complexes are summarized in Table-5.
Potential (V) vs. 150 Hz
Fig. 6. Cyclic voltammogram of Ni(Bipy)(ATT)Cl 0.5 H
The cathodic peak current function values were found to
be independent of the scan rate. Repeated scans at various scan
rates suggest that the presence of stable redox species in solu-
2
2
O, at different
-1
scan rates (1) 0.05 (2) 0.1 (3) 0.2 mV s
tion. It has been observed that cathodic (Ip
c
) and anodic (Ip
a
)
quasi-reversible behaviour [45]. The difference, ∆Ep in all the
complexes be better than the Nerstian requirement 59/n mV
(n = number of electrons involved in oxidation reduction),
which demonstrate quasi-reversible character of electron transfer
[46]. The complexes show large separation between anodic
and cathodic peaks indicating quasi-reversible character.
peak currents were not equal. The E1/2 values of copper(II)
complexes are noticed at potential range of 0.179–0.298 V. It
may be concluded that all the bivalent metal complexes undergo
one electron reduction to their respective M(I) complexes. The
non-equivalent current in cathodic and anodic peaks indicates
TABLE-5
CYCLIC VOLTAMMETRIC DATA OF Cu(II), Ni(II) AND Co(II) COMPLEXES
Redox
couple
C
v
cathodic
Epc
C
v
anodic
Epa
0.488
0.523
∆Ep
a
b
Complex
Cu(Bipy)Cl2
Cu(Bipy)(ATT)Cl2
Ni(Bipy)Cl2
Ni(Bipy)(ATT)Cl ·0.5H O
Co(Bipy)Cl2
E1/2
-i i
log Kc
-∆G
c/ a
(mV)
II/I
II/I
II/I
II/I
II/I
II/I
-0.047
-0.072
-1.291
-1.196
-1.034
-1.370
535
595
548
691
308
693
0.267
0.297
-1.017
-0.850
-0.880
-1.023
1.510
1.432
2.740
2.381
0.895
2.950
0.062
0.056
0.061
0.048
0.010
0.048
362
323
354
280
629
279
-0.743
-0.505
-0.726
-0.677
2
2
Co(Bipy)(ATT)Cl2
a
b
log K = 0.434ZF/RT∆E ; ∆Gº = -2.303RT log K
c
p
c

1
910 Srinivasulu et al.
Asian J. Chem.
DNA binding studies: The binding interaction of the
complexes with DNA was monitored by comparing their absor-
ption spectra with and without CT-DNA. Typical absorption
of the Ni(II) and Co(II) complexes suggest that these comp-
lexes bind DNA through intercalation involving a strong
π-stacking interaction between the aromatic chromophore and
base pairs of DNA [48].
spectra of Ni(Bipy)(ATT)Cl complex in the absence and in the
2
presence of CT DNA are shown in Fig. 7. It has been observed
that molar absorptivity of complexes decreases (hypochromism,
Antibacterial activity:All the metal complexes are scree-
ned for their antibacterial activity by using agar well diffusion
method against pathogenic bacterial strains such as E. coli
and S. aureus. Inhibition zones are determined in the presence
of different amounts (100, 200 and 300 µg/well) of complexes
with reference to the positive control viz. ciprofloxacin. The
diameters of inhibition of zone were measured with Vernier
callipers in mm and its values are depicted in the Table-7.
Antibacterial activity of present complexes is quite comparable
to the standard compound (Fig. 8) as shown in bar graph. The
∆
ε, +11.91 to +38.8 %, Table-6) for each addition of CT-DNA
*
of the π-π absorption band as well as a hypsochromic shift in
the case of Cu(II) complexes and bathochromic shift for Ni(II)
and Co(II) complesxes of a few nanometers (0.5-2.0 nm). The
intrinsic binding constants (K ), were determined by using the
b
equation. The intrinsic binding constants of copper complexes
are given in Table-6.
[
DNA] [DNA]
1
=
+
(ε − ε )
zone of inhibition by Cu(Bipy)Cl
ficant. The data indicates that the parent complexes {Cu(Bipy)Cl
and Co(Bipy)Cl } show more activity than the ternary comp-
lexes Cu(Bipy)(ATT)Cl and Co(Bipy)(ATT)Cl . However, the
ternary Ni(Bipy)(ATT)Cl complex shows higher activity than
2
complexes is highly signi-
a
f
(1)
εa − εf εa − εf Kb
2
Hyperchromic effect and hypochromic effect are the
special features of DNA concerning its double helix structure.
Hypochromism results from the contraction of DNA in the
helix axis as well as from the change in conformation on DNA
while hyperchromism emerges from the damage of the double
helix structure [47]. Hypochromism was observed due to inter-
calative mode involving strong stacking interactions between
aromatic chromophore of metal complexes and nitrogenous
bases of DNA [47]. Where the hyperchromism due to the
dissociation of ligand accumulated and the breakage of
intermolecular hydrogen bonds when metal complex bound
to DNA [34]. Hypochromism and bathochromic shift in case
2
2
2
2
the parent complexes possibly due to synergistic interactions
of two organic ligands with bacteria.
Conclusion
Mixed ligand transition metal complexes with 2,2-bipyridyl
(Bipy) and 2-acetylthiophene thiosemicarbazone (ATT) have
been synthesized and characterized based on mass spectra,
molar conductivity, infrared and electronic spectra. Electro-
chemical properties of these complexes are uncovered by using
24
22
20
18
16
14
12
10
8
6
4
2
0
0.35
0.30
0.25
0.20
0.15
0.10
(
a)
(b)
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
2
60
280
300
320
340
360
–6
Wavelength (nm)
[DNA] × 10
Fig. 7. Absorption spectra of Ni(Bipy)(ATT)Cl
2
0.5H
2
O. In the absence and in the presence of increasing concentration of CT-DNA; [(a)
-ε ) vs.
most spectrum is recorded in the absence of CT-DNA and (b) spectra on addition 20 µL DNA each time] A plot [DNA]/(ε
a
f
-6
[
DNA] × 10 is shown
TABLE-6
ELECTRONIC ABSORPTION DATA UPON ADDITION OF CT-DNA TO THE COMPLEX
λmax (nm)
-1
Complex
∆λ
H (%)
K [M ]
b
Free
300.5
302.0
306.0
306.0
295.0
302.0
Bound
300.0
300.0
306.5
306.5
296.5
303.5
5
5
5
5
5
5
Cu(Bipy)Cl2
0.5
2.0
0.5
0.5
1.5
1.5
38.80
11.91
36.60
13.43
17.77
11.91
3.50 × 10
4.00 × 10
3.56 × 10
4.37 × 10
3.12 × 10
4.34 × 10
Cu(Bipy)(ATT)Cl2
Ni(Bipy)Cl2
Ni(Bipy)(ATT)Cl ·0.5H O
2
2
Co(Bipy)Cl2
Co(Bipy)(ATT)Cl2

Vol. 31, No. 9 (2019)
Metal Complexes with 2,2-Bipyridyl and 2-Acetylthiophene Thiosemicarbazone 1911
TABLE-7
CONFLICT OF INTEREST
ANTIBACTERIAL ACTIVITY OF DIFFERENT METAL
COMPLEXES AGAINST PATHOGENIC BACTERIAL STRAINS
The authors declare that there is no conflict of interests
regarding the publication of this article.
Treatment
E. coli
Mean±SE) (Mean±SE)
S. aureus
Complex
conc.
µg/µL)
5
(
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