Water Soluble Nickel – metformin ternary complexes: Thermal, DNA binding and molecular docking studies

Article abstract of DOI:10.1002/aoc.5351

The Nickel (II) complexes [Ni(Cl)₂(metf)(o-phen)] (1), [Ni(Cl)₂(metf)(opda)] (2), [Ni(Cl)₂(metf)(en)](3), [Ni(Cl)₂(metf)(2,2'-bipy)](4), (metf = metformin, o-phen = ortho-phenanthroline, opda = ortho-phenylenediamine, en = ethylenediamine, 2–2′ bipy = 2–2′ bipyridyl) were synthesized and characterized using LC–MS, elemental analysis, molar conductance measurements, TGA-DTA, IR spectroscopy, magnetic moment measurements and electronic spectroscopy. The central Ni²⁺ was found to be in octahedral geometry. The DNA interaction of these complexes have been studied by UV–visible absorption studies, fluorescence emission technique and viscosity measurement. The complexes showed absorption hyperchromism in UV–visible spectra with calf thymus DNA. The binding constants from UV–visible absorption studies were 7.42 × 10⁴, 0.74 × 10⁴, 3.19 × 10⁴, 5.9 × 10⁴ M^?1 for 1, 2, 3 and 4, respectively and Stern-Volmer quenching constants from fluorescence studies were 0.16, 0.41, 0.23, 0.18, respectively. Viscosity measurements revealed that the binding of the complexes with DNA could be surface binding, mainly due to groove binding. The highest DNA cleavage activity of the complexes is recorded for complex 1. The complexes were docked in to B-DNA sequence, 5′(D*AP*CP*CP*GP*AP*CP* GP*TP*CP*GP*GP*T)-3′ retrieved from protein data bank (PDB ID: 423D), using Discovery Studio 2.1 software. C Docker Intectraction energy of 1, 2, 3 and 4 complexes is 32.027, 31.427, 35.393 and 30.521 respectively. The highest docking score is seen for complex 3.

Full text of DOI:10.1002/aoc.5351

Received: 13 July 2019
DOI: 10.1002/aoc.5351
Revised: 1 October 2019
Accepted: 20 October 2019
F U L L P A P E R
Water Soluble Nickel – metformin ternary complexes:
Thermal, DNA binding and molecular docking studies
K. Rajeshwari1 | P. Vasantha1 | B.S. Kumar2 | B. Shekhar2 | P.V.A. Lakshmi2
1Department of Chemistry, University
The Nickel (II) complexes [Ni(Cl)2(metf)(o-phen)] (1), [Ni(Cl)2(metf)(opda)]
(2), [Ni(Cl)2(metf)(en)](3), [Ni(Cl)2(metf)(2,2'-bipy)](4), (metf = metformin,
o-phen = ortho-phenanthroline, opda = ortho-phenylenediamine, en = eth-
ylenediamine, 2–20 bipy = 2–20 bipyridyl) were synthesized and characterized
using LC–MS, elemental analysis, molar conductance measurements, TGA-
DTA, IR spectroscopy, magnetic moment measurements and electronic spec-
troscopy. The central Ni2+ was found to be in octahedral geometry. The DNA
interaction of these complexes have been studied by UV–visible absorption
studies, fluorescence emission technique and viscosity measurement. The com-
plexes showed absorption hyperchromism in UV–visible spectra with calf thy-
mus DNA. The binding constants from UV–visible absorption studies were
7.42 × 104, 0.74 × 104, 3.19 × 104, 5.9 × 104 M−1 for 1, 2, 3 and 4, respectively
and Stern-Volmer quenching constants from fluorescence studies were 0.16,
0.41, 0.23, 0.18, respectively. Viscosity measurements revealed that the binding
of the complexes with DNA could be surface binding, mainly due to groove
binding. The highest DNA cleavage activity of the complexes is recorded for
complex 1. The complexes were docked in to B-DNA sequence,
50(D*AP*CP*CP*GP*AP*CP* GP*TP*CP*GP*GP*T)-30 retrieved from pro-
tein data bank (PDB ID: 423D), using Discovery Studio 2.1 software. C Docker
Intectraction energy of 1, 2, 3 and 4 complexes is 32.027, 31.427, 35.393 and
30.521 respectively. The highest docking score is seen for complex 3.
College for Women, Osmania University,
Koti, Hyderabad, Telangana State, 500095,
India
2Department of Chemistry, Osmania
University, Tarnaka, Hyderabad,
Telangana State, 500007, India
Correspondence
Anantha Lakshmi, Department of
Chemistry, Osmania University, Tarnaka,
Hyderabad. Telangana State, 500007,
India.
Email: pvanantha.ou@gmail.com
Funding information
Department of Science and Technology,
Ministry of Science and Technology,
Grant/Award Number: PURSE II
K E Y W O R D S
DNA, docking, groove binding, metformin, nickel complexes
1 | INTRODUCTION
by binding with DNA, thereby altering DNA replication,
blocking the division of cancer cells and resulting in cell
Bioinorganic chemistry usually is the study of the interac-
tion of inorganic elements with organisms at molecular
level.[1] The interaction of biological macromolecules like
DNA with transition metal complexes has become an
important research topic and helps us to understand the
life processes at molecular level.[2,3] Many transition
metal complexes act as excellent chemotherapeutic
agents and exert their biological activity like anticancer,
death.[4] Interaction with DNA are not the only factors
that determine the biological activity of these complexes,
but their reactivity and selectivity are often correlated
with their mode of binding with DNA. Therefore it is
essential to understand the various factors that govern
the interaction of small molecules with DNA. In general,
drugs interact with DNA in three distinct modes of
noncovalent interactions, groove binding through a
Appl Organometal Chem. 2019;e5351.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5351

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RAJESHWARI ET AL.
combination of hydrophobic, electrostatic, and hydrogen-
bonding interactions; intercalative association in which a
planar, aromatic moiety slides between the DNA base
pairs; and external binding by electrostatic attraction.[5,6]
Metformin.HCl (Chemically known as N,N-
dimethylbiguanide) is chosen as primary ligand because
of its wide spread applications in medicinal field and its
ability to chelate metal strongly. Metformin is a powerful
oral antihyperglycemic drug that has been used in many
countries for over 40 years for treating diabetic patients
application, metformin and its ternary complexes have
received less attention. Hence, it is focused to synthesize,
characterize and study DNA binding properties of Ni (II)-
metformin ternary complexes.
The aim of this paper is to report the synthesis, char-
acterization and DNA binding studies of Nickel (II)-
metformin complexes containing 1,10-phenanthroline or
o-phenylenediamine or ethylenediamine or 2,20-
bipyridyl as auxiliary ligand. The binding properties of
the Nickel (II) complexes with CT-DNA in Tris -HCl
buffer (PH = 7) were investigated by multi- spectroscopic
methods. From the results of UV absorbtion spectra, vis-
cosity and fluorescence displacement experiments, the
binding mode of interaction between Ni (II) complexes
and DNA were obtained.
with
non-insulin
dependent
diabetes
mellitus
(NIDDM).[7] Metformin acts as glucose lowering agent,
analgesic, anti-malarial and anti-metabolite for organ-
isms that inhibit the metabolism of folic acid. It is well
known that these biguanide derivatives exhibit both bio-
logical and coordinative properties.[8] Recently, it was
found that vanadyl complex with metformin shows
potential synergistic insulin mimics,[9] while platinum
(IV) complexes reveals antitumor activity.[10] The interac-
tion of metformin with calf thymus DNA (CT-DNA) has
been investigated by Shahabadi and Heidari.[11] The
DNA binding studies of Pt (II) Complexes with metfor-
min. HCl (metf) as ligand have been studied by Nahid
Shahabadi et al. They have reported the interaction of Pt
(II) Complex with DNA via groove binding mode.[12]
Nickel is an essential trace element for human body
and the metalloenzymes containing Nickel (II) play
important physiological functions in the organisms.[13]
Nickel (II) complexes have been reported to act as anti-
convulsant and antiepileptic agents or vitamins, they
have also presented antibacterial,[14] antifungal,[15]
antimicrobial,[16] antioxidant[17] and anticancer activi-
ties.[18] Therefore the research of Nickel (II) complexes
has attracted more attention and become more important
in the field of bioinorganic and co-ordination chemis-
try.[19] The interaction of Nickel (II) complexes with
DNA has become an important research topic. These
Nickel (II) complexes exhibit anticancer activity by bind-
ing to DNA base pairs, there by altering DNA replication,
blocking the division of cancer cells and resulting in cell
death. For example Nickel (II) Complexes of Benzoic acid
(2-hydroxy- benzylidine)-hydrazide ligands bind to DNA
base pairs via intercalation and π-π stacking interactions.
Nickel (II) complexes containing N-substituted heterocy-
clic thiosemicarbazones have been found to exhibit
remarkable DNA/protein binding and antioxidant activi-
ties.[20] In addition Nickel (II) complexes have attracted
the attention of researchers because of their superoxide
scavenger activities and broad biological activities.[21]
A literature survey reveals that Nickel complexes
have various DNA binding properties and biological
properties. So, we planned the synthesis of complexes
using Nickel metal ion. In spite of its widespread
2 | EXPERIMENTAL
2.1 | Materials and methods
All the chemicals used were either of AR grade or chemi-
cally pure grade. Metformin was procured from
Emmennar Pharma Pvt Ltd. CT (Calf Thymus) DNA was
purchased from Himedia (stored at −20 ꢀC) and was used
as received. Supercoiled pUC19 plasmid DNA (stored at -
ꢀ
20 C) was obtained from Fermentas Life Sciences and
agarose from Genei.
For preparing various buffers, double-distilled water
was used. Binding studies of the complexes with CT-
DNA were conducted using Tris -HCl buffer (5 mM Tris -
HCl, 50 mM NaCl; pH = 7.2). A ratio of UV absorbance
of CT- DNA solution at 260 and 280 nm of 1.8–1.9 indi-
cated that the DNA was sufficiently free of protein.[22]
The DNA concentration per nucleotide was determined
by absorption spectroscopy using the molar absorption
coefficient (6600 M−1 cm−1) at 260 nm.[23] Stock solutions
ꢀ
were stored at 4 C and used after no more than four
days. Concentrated stock solutions of metal complexes
were prepared in buffer for all experiments.
2.2 | Instrumentation
UV–visible spectra were recorded with a Shimadzu 240A
spectrophotometer. Fluorescence spectra were recorded
with Shimadzu 5301 spetrofluorophotometer. Infrared
(IR) spectra were recorded using KBr discs in the range
400-4000 cm−1 with a Perkin Elmer FT-IR spectrometer.
Solid-state UV–visible spectra of the complexes were
recorded with a Shimadzu 160A spectrophotometer
(200-800 nm). Elemental microanalysis (C, H and N) was
carried out with a Perkin Elmer 240 elemental analyser.

RAJESHWARI ET AL.
3 of 18
Chloride analysis was carried out using Mohr's method.
The metal contents were estimated using a Shimadzu
AA-6300 atomic absorption spectrophotometer. Mass
spectra were recorded with a Shimadzu LCMS-2010 A
spectrometer. Molar conductance was measured using an
Elico Digital conductivity bridge (model CM-180) with a
dip-type cell. Magnetic susceptibilities were recorded at
room temperature with a Faraday magnetic susceptibility
mill balance (model 7550), using Hg[Co (NCS)4] as the
standard. Diamagnetic corrections were made using Pas-
cal's constants.[24] Thermal analysis was carried out using
a TGA Q 5000 V3.13 build 261 instrument.
titrated with varying concentrations of the complexes.
The DNA concentration was always 130 μM DNA-phos-
phate. The concentrations of the complexes were in the
range 0-100 μM and EB concentration was 40 μM. The
solutions were excited at 540 nm and fluorescence emis-
sion, which corresponds to 598 nm, was recorded. The
Stern-Volmer quenching constant was obtained from
classical Stern-Volmer equation[26]: I0/I = 1+ K.r. (I0 and
I are the fluorescence intensities in the absence and pres-
ence of complexes, respectively, K is a linear quenching
constant, which depends on the concentration ratio of
bound EB to DNA, and r is the concentration ratio of
complex to DNA). In the plot of Io/I Vs [complex]/
[DNA], K is given by the ratio of slope to intercept.
2.3 | Synthesis of metal complexes
Emission titration experiments were performed by
maintaining a constant metal complex concentration
(10 μM) and varying the DNA concentration (10–200 μM)
in the buffer. After each addition of DNA to the metal
complex, the resulting solution was allowed to equilibrate
Metformin (0.166 g, 1 mmol) was dissolved in 5 ml of
0.1 N KOH solution. NiCl2.6H2O (0.238 g, 1 mmol) in
5 ml of water was added to the metformin solution, in
the presence of 1,10-phenanthroline (0.198 g, 1 mmol) or
ꢀ
at 25 C for 5 min, then excited in the intense LMCT
o-phenylenediamine (0.108 g,
1
mmol) or eth-
band between 350 and 400 nm, and the emission was
measured at 550–700 nm. The fraction of the ligand
bound was calculated from the relation Cb = Ct[(F-F0)/
(Fmax-F0)], where Ct is the total complex concentration, F
is the observed fluorescence emission intensity at a given
DNA concentration, F0 is the intensity in the absence of
DNA and Fmax is the intensity when the complex is fully
bound to DNA. Binding constant (Kb) was obtained from
a modified Scatchard plot of r/Cf versus r, where r = Cb/
[DNA] and Cf is the concentration of free complex.[27]
Nonlinear least-squares fitting of the data yields Kb.
Viscosity measurements were performed with an Ost-
wald viscometer at room temperature. The concentration
of DNA was 20 μM and complex concentration varied
from 0 to 100 μM. The flow times were measured with a
digital timer and each sample was measured three times
for accuracy, and an average flow time was calculated.[28]
Data were presented as (η/η0)1/3 versus [complex]/
[DNA], where η is the viscosity of DNA in the presence
of complex and η0 that of DNA alone. Viscosity values
were calculated from the observed flow time of DNA-
containing solutions (t) corrected for buffer (5 mM Tris–
HCl/ 50 mM NaCl) alone (t0): η = (t - t0).
To perform DNA Cleavage studies of the complexes
pUC19DNA was used and the studies were performed by
using gel electrophoresis technique. Buffer solutions used
in this technique are TE buffer (1 mM Na2EDTA and
10 mM Tris–HCl) and TAE buffer (Tris-acetate EDTA,
1 mM EDTA, Tris-base, 20 mM acetic acid) and TE and
TAE buffer is maintained at pH 8.0. To prepare
pUC19DNA stock solution TE buffer solution was used.
pUC19 DNA (0.1 g μL−1) was allowed to react with vary-
ing concentration of complexes (1, 2, 3 and 4) and the
ylenediamine (0.133 g, 1 mmol) or 2,20- bipyridyl
(0.156 g, 1 mmol) at room temperature. The reaction mix-
ture was heated for 1 hr using a water bath and the com-
plexes that separated out were filtered and dried. The
purity of the complexes was determined by TLC using
various solvent mixtures. The melting points of the com-
plexes were above 300 ꢀC.
2.4 | DNA binding studies
Absorption titration experiments were performed by
maintaining a constant metal complex concentration
(20 μM) and varying the DNA concentration (0-100 μM)
in the buffer. After each addition of DNA to the metal
complex, the resulting solution was allowed to equilibrate
ꢀ
at 25 C for 5 min, after which the change in absorption
intensity of the ligand to metal charge transfer (LMCT)
band was recorded. The intrinsic binding constant, Kb,
was determined from the spectral data using the Wolfe-
Shimmer equation:[25] [DNA/(ɛa- ɛf) = [DNA]/ (ɛb- ɛf)
+1/Kb (ɛb- ɛf), where [DNA] is the concentration of the
DNA in base pairs, ɛa the apparent extinction coefficient
(= Aobsd/[complex]), ɛf the extinction coefficient for free
metal complex and ɛb the extinction coefficient for free
metal complex in fully bound form. From plots of
[DNA]/(ɛa- ɛf) versus [DNA], gave a slope of 1/(ɛb- ɛf) and
Y-intercept equal to1/Kb (ɛb- ɛf); Kb is given by the ratio
of slope to intercept.
Fluorescence quenching experiments were carried
out in 5 mM Tris -HCl/50 mM NaCl (pH = 7.5). A solu-
tion containing DNA and ethidium bromide (EB) was

4 of 18
RAJESHWARI ET AL.
volume of the solution was made to 16 μL by using Tris-
HCL buffer solution. To the above solution 1 mM H2O2
was addedꢀ and the resulting solution was incubated for
2 hr at 37 C. A dye containing 30, 300, 50, 500- tetra bromo
phenolsulfonphthalein (bromophenol blue, 0.30%), glyc-
erol(45%), xylene cyanol (30%) and 2 mM EDTA were
added to the above incubated solution in order to quench
the reaction. The sample mixtures were carefully placed
into wells of gel. Electrophoresis was performed for 2 hr
at 100 V using 1% agarose gel in TAE (Tris acetic acid
EDTA) buffer and ethidium bromide (1.0 μg/ml) was
used to stain the gel. When the dye front reaches the end
of the gel, electrophoresis was stopped and the images
were photographed under UV light.
3 | RESULTS AND DISCUSSION
3.1 | Characterization of metal
complexes
All the complexes are colored and quite stable to air and
moisture. The complexes are soluble in water, ethanol
and dimethylsulfoxide. Characterization of the complexes
using liquid chromatography-mass spectrometry (LC–
MS), elemental analysis, molar conductance measure-
ments, thermal analysis, IR spectroscopy, magnetic
measurements, electronic spectroscopy, and geometrical
studies confirm the coordination mode of the ligands.
The LC–MS spectra recorded at room temperature
resolve M + 1 peaks at m/z 439, 319 and 415 for com-
plexes 1, 3, 4 respectively and M - 1 peak at m/z 365 for
complex 2. Analysis of carbon, hydrogen, nitrogen, chlo-
ride and Nickel reveals the formulae NiC16H19N7Cl2,
NiC10H19N7Cl2, NiC6H19N7Cl2, NiC14H19N7Cl2 for com-
plexes 1, 2, 3 and 4 respectively. The ratio of metformin,
auxiliary ligand and Nickel (II) in these complexes is
1:1:1. The analytical data of prepared complexes are pres-
ented in the Table 1. The conductivity of metformin com-
plexes was measured for aqueous solution at room
temperature. The complexes show molar conductance
values of 2 to 4 Ω−1cm2mol−1 for 10−3 M concentration,
indicating that the complexes are non-electrolytes[29] and
the presence of chloride ions within the coordination
sphere of the complexes.
Thermogravimetric analysis (TGA) of 1, 2, 3, 4 was
conducted. They are thermally decomposed in decompo-
sition steps mainly within the range 25–1000 ꢀC.[30] Com-
plex 1 is thermally decomposed in five suꢀccessive
decomposition steps within the range 29–1000 C. The
ꢀ
first step (obs. = 9.82%, calc. = 9.80%) at 29–200 C may
be attributed to the removal of the CN2H3 fragment. The
second step at 200–300 ꢀC (obs. = 18.08%, calc. = 18.12%)

RAJESHWARI ET AL.
5 of 18
is accounted for the removal of C2H6N and chloride ion.
The third step at 300–500 ꢀC (obs. = 24.35%, calc. =
23.47%) is accounted for the rꢀemoval of C7NH5 fragment.
The fourth step at 500–700 C (obs. = 12.93%, calc. =
11.62%) is accounted for the removal of C4H3 fragment.
The fifth step at 700–1000 ꢀC (obs. = 7.80%, calc. =
8.09%) is attributed to the removal of chloride ion. The
decomposition ends with a C2H2N3 and Ni ion residue
(obs. = 27%, calc. = 28.88%). The TGA curve of complex
2 indicates that the mass change begins at 36 ꢀC and con-
tinues up to 1000 ꢀC. It is thermally decomposed in
mainly five decomposition steps. The first step occurs in
(obs. = 3.94%, calc. = 3.61%) is accounted for the
removal of NH fragment. The final step of decomposi-
tion of the complex at 600–1000 C is attributed to the
liberation of NH2. This decomposition ends with a
final residue of C11H9N4 and Nickel ion (obs. = 61.30%,
calc. = 61.63%).
ꢀ
The IR Spectra of 1, 2, 3 and 4 were analyzed in com-
parison of their free ligand spectra.[31] The characteristic
IR spectral bands assigned to the stretching frequencies
of amine and imine groups of metformin are shifted in
the spectra of all three complexes when compared with
free metformin.[32] The shifting of imine band C=N of
metformin at 1568 cm−1 to 1583,1571,1558, and
1591 cm−1 for complexes 1, 2, 3,and 4 respectively, indi-
cates that coordination takes place through the imine
nitrogen.[33] A six-membered ring possibly also exists
from coordination involving amino nitrogens; however,
M─N (imino) bond formation takes priority over M─N
(amino) bond formation possibly due to π conjugation of
the C-N-C system involving the imino nitrogen.[33] The
new band at around 1340,1342,1315 and 1311 cm−1 in
the spectra of 1, 2, 3, and 4 respectively, could be associ-
ated with the chelate ring formation for the metformin
complexes.[34] The shifting of the NH2(as), NH and
NH2(s) bands of metformin at 3371, 3294 and 3172 cm−1
to 3369, 3298, 3176; 3369, 3271, 3199; 3362, 3290,
3167 cm−1; and 3365, 3298, 3172 cm−1 for 1, 2, 3 and
4 respectively, indicates the coordination of metformin to
metal. In the spectrum of 1, the peaks corresponding to
the ring stretching frequencies υ(C=C) and υ(C=N) of o-
phen at 1505 and 1421 cm−1 are shifted to higher fre-
quencies (ca 1514 and 1479 cm−1), indicating the coordi-
nation of the heterocyclic nitrogen atoms to the metal
ion. The characteristic out-of-plane hydrogen-bonding
modes of free o-phen observed at 853 and 738 cm−1 are
shifted to 850 and 727 cm−1, respectively, upon complex-
ation.[35] The shifting of the υ (NH2) band of free opda at
3386 to 3309 cm−1 for complex 2 indicates the coordina-
tion of opda to Nickel (II) through NH2 groups.[36] The υ
(CN) band at 1060 cm−1 of free en is shifted to 1035 cm−1
for 3.The stretching frequencies of the chelate en are
observed in the region 1500–1700 cm−1 for NH2 bending
and in the region 850–950 cm−1 for rocking. In the spec-
trum of 3, NH2 bending is observed at 1678 cm−1 and
ꢀ
the range 36–100 C and corresponds to the liberation of
NH2 (obs. = 3.98%, calc. = 4.36%). The second step at
ꢀ
100–200 C (obs. = 6.32%, calc. = 7.36%) is accounted
for the removal of the CNH fragments. Theꢀthird step
(obs. = 28.551%, calc. = 29.44%) at 200–300 C may be
attributed to the liberation of the opda. The fourth
decompoꢀsition step of the complex occurs in the range
300–400 C and corresponds to the loss of 2Cl fragments
(obs. = 18.84%, calc. = 19.35%). The fifth step (obs. =
ꢀ
23.07%, calc. = 19.35%) at 400–1000 C and corresponds
to the loss of C3H7N2 fragment. This fragmentation ends
with a final residue of Ni-NH fragment (obs. = 19.23%,
calc. = 20.09%). The TGA curve ofꢀcomplex 3 indicates
that the mass change begins at 37 C and continues up
to 1000 ꢀC. The complex is thermally decomposed in
mainly five decomposition steps. The first step occurs in
ꢀ
the range 37–200 C and corresponds to the loss of C-
NH2 fragment. (obs. = 8.48%, calc. = 8.70%). The second
step at 200–300 ꢀC (obs. = 26.04%, calc. = 26.98%) is
accounted for the removal of (C3N3H8) fragment. Tꢀhe
third step (obs. = 21.83%, calc. = 22.27%) at 300–400 C
may be attributed to the loss of the 2Cl fragments. The
ꢀ
fourth step occurs in the range 400–600 C and corre-
sponds to the loss of (C2NH6) fragment (obs. = 16.256%,
calc. = 13.80%). The fifth step occurs in the range
600–1000 ꢀC and is accounted for the removal of NH
and NH2 (obs. = 10.16%, calc. = 9.73%). This fragmenta-
tion ends with a final residue of Nickel metal (obs. =
17.22%, calc. = 18.42%). The TGA curve of Complex
4 indicates that the mass change begins at 36 ꢀC and
continues up to 1000 ꢀC. It is thermally decomposed
mainly in six decomposition steps. The first step occurs
in the range 36–200 C and corresponds to the loss of
CH2 rocking at 933 cm−1 [37]
peaks corresponding to ring stretching frequencies of
υ(C=N), υ(C-H) and υ(C=C) of bipyridyl at 1600 cm−1
3050 cm−1 and 1450 cm−1 are shifted to
1558 cm−1,3070 cm−1 and 1446 cm−1 [38]
The υ (Ni-N)
.
In the spectrum of 4, the
ꢀ
(C-H) fragment (obs.ꢀ= 2.72%, calc. = 3.13%). The sec-
ond step at 200–300 C (obs. = 9.32%, calc. = 8.55%) is
accounted for the removal of the Cl fragment. The third
,
ꢀ
step (obs. = 8.3%, calc. = 8.55%) at 300–400 C may be
.
attributed to the loss of Cl fragment. The fourth decom-
band of bipyridyl complexes is observed in the range of
180–290 cm−1. In the spectrum of 4 this band is observed
at 277 cm−1. The low frequency region of the spectra of
all complexes reveals the presence of medium intensity
position step of the complex occurs in the range
ꢀ
400–500 C and corresponds to the loss of C2NH6 (obs.
ꢀ
= 10.42%, calc. = 10.60%). The fifth step at 500–600 C

6 of 18
RAJESHWARI ET AL.
bands in the region 300–600 cm−1 due to υ(M-N) and also
υ(M-Cl) vibrations.[39] Thus, the IR data suggest that met-
formin and the auxiliary ligands are bound to the metal
ion through nitrogen donor atoms.
The Racah inter-electron repulsion parameter B observed
for these complexes is less than that for the free ion. The
nephelauxetic parameter β = B/B0 is less than one for
these complexes.[44] All these observations suggest that
the metal -ligand bond in the complexes is covalent in
nature.
Complexes 1, 2, 3, and 4 show magnetic moments of
2.8, 2.7, 2.9 and 2.7 BM respectively, which are in good
agreement with the presence of 2 unpaired electrons. The
electronic spectra of all metal complexes were recorded.
Electronic absorption spectroscopy is very useful in the
evaluation of the results furnished by other methods of
structure investigation. The electronic spectral measure-
ments were used for assigning the stereochemistry of
metal ions in the complexes based on the position and
number of d-d transition bands. The electronic spectra of
complexes 1, 2, 3 and 4 show bands at 8319, 17543,
22270; 8620, 12722, 22222; 11587, 18939, 23201 and 8389,
14513, 20449 cm−1 respectively corresponding to the tran-
3.2 | Geometrical structure of metal
complexes
Geometrical structures of complexes 1, 2, 3 and 4 were
calculated by optimizing their bond lengths, bond angles
and torsional angles. The geometrical structures are pres-
ented in Figure 1. Selected geometric values (bond
lengths and bond angles) of the metal complexes are
presented in Table 2. Both the highest occupied molecu-
lar orbital (HOMO) and the lowest unoccupied molecular
orbital (LUMO) are the main orbitals that take part in
chemical stability. The HOMO represents the ability to
donate an electron. The LUMO represents the electron
accepting capacity. Molecular orbital structures (HOMO
and LUMO) for metal complexes 1, 2, 3 and 4 are pres-
ented in Figure 2. Quantum chemical parameters of 1, 2,
3 and 4, were obtained from calculations, such as ener-
gies of the HOMO (EHOMO) and the LUMO (ELUMO), as
listed in Table 3. Additional parameters such as HOMO-
LUMO energy gap, e.g., absolute electronegativity, χ,
3
3
3
3
sitions A2g(F) ! T2g(F) (υ1), A2g(F) ! T1g(F) (υ2)
and A2g(F) ! T1g(P) (υ3)[40,41] which are characteristic
of six-coordinate octahedral geometry of Nickel
(II) complexes. A moderately intense band, seen at
29411, 29069, 28653, 27173 cm−1 for 1, 2, 3 and 4, respec-
tively, can be assigned to ligand -to-metal charge transfer
transition. The structure is also further confirmed by the
ratio of υ2/υ1 = 2.10, 1.50, 1.63 and 1.73 for 1, 2, 3 and 4,
respectively, which are close to the value expected for
octahedral structure.[42,43] The ligand field parameters,
10Dq and B, have been calculated for all four complexes.
3
3
FIGURE 1 Molecular
structures with atomic
numbering for complexes (1–4)

RAJESHWARI ET AL.
7 of 18
TABLE 2 Selected geometric bond lengths and bond angles of complexes
Complex
Bond lengths (Ao)
Bond angles (o)
[Ni (Cl)2(metf)(o-phen)]
Ni(1) - Cl(26)
Ni(1) - Cl(25)
Ni(1) - N(20)
Ni(1) - N(16)
Ni(1)- N(12)
Ni(1)- N(2)
2.15
2.15
1.84
1.83
1.85
1.85
Cl(26)-Ni(1)-N(20)
Cl(26)-Ni(1)-N(16)
Cl(26)-Ni(1)-N(12)
Cl(26)-Ni(1)-N(2)
Cl(25)-Ni(1)-N(20)
Cl(25)-Ni(1)-N(16)
Cl(25)-Ni(1)-N(12)
Cl(25)-Ni(1)-N(2)
N(20)-Ni(1)-N(16)
N(20)-Ni(1)-N(12)
N(16)-Ni(1)-N(2)
N(12)-Ni(1)-N(2)
84.03
84.09
98.16
98.22
87.74
88.01
91.13
91.34
95.90
93.65
93.78
76.63
[Ni (Cl)2(metf)(opda)]
Ni(1)-Cl(20)
Ni(1)-Cl(19)
Ni(1)-N(14)
Ni(1)-N(10)
Ni(1)-N(5)
Ni(1)-N(2)
2.15
2.15
1.83
1.83
1.83
1.83
Cl(20)-Ni(1)-N(14)
Cl(20)-Ni(1)-N(10)
Cl(20)-Ni(1)-N(5)
Cl(20)-Ni(1)-N(2)
Cl(19)-Ni(1)-N(14)
Cl(19)-Ni(1)-N(10)
Cl(19)-Ni(1)-N(5)
Cl(19)-Ni(1)-N(2)
N(14)-Ni(1)-N(10)
N(14)-Ni(1)-N(5)
N(10)-Ni(1)-N(2)
N(5)-Ni(1)-N(2)
88.42
90.41
90.36
90.54
90.53
89.08
90.28
90.57
98.30
89.68
89.77
82.24
[Ni (Cl)2 (metf)(en)]
Ni(1)-Cl(16)
Ni(1)-Cl(15)
Ni(1)-N(10)
Ni(1)-N(6)
Ni(1)-N(5)
Ni(1)-N(2)
2.16
2.17
1.85
1.85
1.38
1.38
Cl(16)-Ni(1)-Cl(15)
Cl(16)-Ni(1)-N(10)
Cl(16)-Ni(1)-N(5)
Cl(16)-Ni(1)-N(2)
Cl(15)-Ni(1)-N(10)
Cl(15)-Ni(1)-N(6)
Cl(15)-Ni(1)-N(2)
N(10)-Ni(1)-N(6)
N(10)-Ni(1)-N(5)
N(6)-Ni(1)-N(5)
N(6)-Ni(1)-N(2)
N(5)-Ni(1)-N(2)
86.66
85.27
92.02
92.23
78.74
82.64
84.20
84.78
85.61
96.09
94.64
111.43
[Ni (Cl)2(metf)(2,2’-bipy)]
Ni(1)-Cl(24)
Ni(1)-Cl(23)
Ni(1)-N(18)
Ni(1)-N(14)
Ni(1)-N(10)
Ni(1)-N(2)
2.15
2.15
1.83
1.83
1.84
1.84
Cl(24)-Ni(1)-N(18)
Cl(24)-Ni(1)-N(14)
Cl(24)-Ni(1)-N(10)
Cl(24)-Ni(1)-N(2)
Cl(23)-Ni(1)-N(18)
Cl(23)-Ni(1)-N(14)
Cl(23)-Ni(1)-N(10)
Cl(23)-Ni(1)-N(2)
N(18)-Ni(1)-N(14)
N(18)-Ni(1)-N(10)
N(14)-Ni(1)-N(2)
N(10)-Ni(1)-N(2)
86.16
84.55
91.35
93.04
90.85
88.07
96.21
91.64
95.47
87.75
97.87
78.78
Eg = ELUMO −EHOMO
ð1Þ
ð2Þ
chemical potential, π, absolute hardness, η, absolute soft-
ness, σ, global electrophilicity, ω, global softness, S, and
additional electronic charge, ΔNmax, were calculated
using the following equations:[45]
EHOMO + ELUMO
χ = −
2

8 of 18
RAJESHWARI ET AL.
the reactivity of a compound.[46] It was found that com-
plex 1 is more reactive than the other complexes, where
the value of Eg for 1, 2, 3 and 4 is 1.57, 1.64, 3.82 and
2.07 eV, respectively.
3.3 | Kinetic studies
Thermodynamic activation parameters of decomposition
processes of samples, namely activation energy, enthalpy,
entropy, and Gibbs free energy change of the decomposi-
tion were evaluated graphically in Figure 3 by employing
the Coats-Redfern relation for complexes 1, 2, 3 and
4.[47,48] Data for kinetic thermal studies were shown in
Table 4. The high values of the activation energy illus-
trated to the thermal stability of the complexes. ΔG is
positive for reaction for which ΔH is positive and ΔS
is negative. The reaction for which ΔG is positive and ΔS
is negative considered as unfavorable or non-spontaneous
reaction. Reactions are classified as either exothermic
(ΔH < 0) or endothermic (ΔH > 0) on the basis of
whether they give off or absorb heat. Reactions can also
be classified as exergonic (ΔG < 0) or endergonic (ΔG > 0)
on the basis of whether the free energy of the system
decreases or increases during the reaction. The correla-
tion coefficients of the Arrhenius plots of the thermal
decomposition steps were lie in the range of 0.914 to
0.998 showing good fit with linear function. It is clear that
the thermal decomposition process of complexes 1, 2, 3
and 4 are non-spontaneous, i.e., the complexes are ther-
mally stable.
FIGURE 2 Molecular orbital structures (HOMO and LUMO)
for complexes (1–4)
E
LUMO −EHOMO
η =
ð3Þ
2
1
σ =
η
ð4Þ
ð5Þ
ð6Þ
π = −χ
3.4 | DNA binding studies
1
S =
2η
3.4.1 | Absorption spectroscopic studies
of DNA-complex interactions
π2
ω =
ð7Þ
ð8Þ
2η
Electronic absorption titration is one of the most useful
techniques for DNA binding studies. Nickel complexes in
water-buffer mixtures show bands in the region
230–300 nm, are assigned to LMCT transitions. When the
DNA concentration is increased, the intensity of charge
transfer band is also shifted, due to either hypochromism
π
ΔNmax = −
η
The HOMO and LUMO energy gap is an important
stability index. The smaller the value of e.g., the greater is
TABLE 3 The calculated quantum chemical parameters of the complexes
Complex
HOMO
−7.175
−7.955
−6.283
−7.401
LUMO
−5.597
−6.307
−2.459
−5.326
Eg
c
n
s
p
s
w
DNmax
1
2
3
4
1.578
1.648
3.824
2.075
6.386
7.131
4.371
6.363
0.789
0.824
1.912
1.037
1.267427
1.213592
0.523013
0.963855
−6.386
−7.131
−4.371
−6.363
0.633714
0.606796
0.261506
0.481928
25.84347
30.85629
4.996245
19.51524
8.093790
8.654126
2.286088
6.133494

RAJESHWARI ET AL.
9 of 18
FIGURE 3 Plots of ln[g(α)/
T2] vs 1/T2 of [Ni(Cl)2(metf)(o-
phen)] for different CR models
TABLE 4 Kinetic parameters using Coats- Redfern (CR) method
Parameters
Complex
Stage
E (J mole−1
4.72 x 104
6.06 x 104
8.48 x 104
1.05 x 105
)
A (S−1
)
ΔS (J mole−1 K−1
−1.2 x 102
−1.4 x 102
−8.0x 101
−2.1 x 101
)
ΔH (J mole−1
4.65x 104
5.8 x 104
8.33x 104
1.04x 105
)
ΔG
r
1
2
3
4
I
9.16x105
3.45x105
2.33x108
2.81x1011
5.71x104
9.71x104
9.7 x104
1.08x105
0.993
0.998
0.914
0.997
III
II
II
or hyperchromism. The complexes 1, 2, 3 and 4 in the
presence of DNA show hyperchromism with slight red
shift (Figure 4). The complexes can bind to double-
stranded DNA in different binding modes on the basis of
their structure, charge and type of ligand. As the DNA
double helix possesses many hydrogen-bonding sites
which are accessible both in minor and major grooves, it
is likely that the NH groups of the complexes form hydro-
gen bonds with N of adenine or O of thymine in DNA,
which may contribute to the hyperchromism observed in
the absorption spectra.[49] The hyperchromic effect may
also be due to an electrostatic interaction between posi-
tively charged complex and negatively charged phosphate
backbone at the periphery of the double helix of CT-
DNA.[50] Also, a coordination bond of DNA base with
Nickel can occur through replacement of the chloride
ligand in the complex, probably through aquation as has
been observed with cisplatin.[51] From a plot of [DNA]/
(ɛa-ɛf) versus [DNA], Kb is given by the ratio of slope to
intercept. The values of kb are 7.42 × 104, 0.74 × 104,
3.19 × 104 and 5.96 × 104 M−1 for complexes 1, 2, 3 and
4 respectively. The intrinsic binding constant (Kb) is
influenced by planarity of the complex, electron
releasing/electron withdrawing groups on ligand and
additional Hydrogen bonding.
The difference in the binding constant of the com-
plexes 1, 2, 3 and 4 is due to different ancillary ligands.
Complex 1 shows more binding strength to double helical
DNA than complex 4 due to increased planar aromatic
surface area and hydrophobiciy of ancillary ligand from
bipy to o-phen. Therefore Kb of complex 1 is greater than
complex 4. The least Kb value of complex 2 is due to elec-
tron releasing group NH2 present on opda ligand, may
enhance the electron density on complex moiety and

10 of 18
RAJESHWARI ET AL.
FIGURE 4 Absorption spectra of 1, 2, 3 and 4 in Tris-HCl buffer upon addition of CT-DNA in absence (lower) and presence (upper) of
CT-DNA. ([complex] = 20 μM; [DNA] = 0–100 μM). Inset plots of DNA/(εa-εf) versus [DNA] for the titration of Ni(II) complexes with DNA.
Arrow shows change in absorption with increasing DNA concentrations
makes electron rich. The electron deficient rings inter-
acts more strongly with polyanion (DNA) than electron
rich rings. Therefore the electron rich opda ancillary
ligand binds less effectively to polyanion (DNA). Like-
wise the decreasing order of Kb values of the four com-
complexes and DNA. The emission intensity of com-
plexes 1, 2, 3 and 4 from their LMCT excited states at
around 600 nm is found to depend on the DNA concen-
tration. These four complexes in the absence of DNA
emit luminescence in Tris–HCl buffer. Upon addition of
CT-DNA, the emission intensities increase as shown in
Figure 5 This implies that the complexes can strongly
interact with DNA and be protected by DNA efficiently.
The hydrophobic environment inside the DNA helix
reduces the accessibility of solvent water molecules to the
duplex and the complex mobility is restricted at the bind-
ing site, which leads to a decrease in the vibrational
modes of relaxation. To obtain intrinsic binding con-
stants, fluorescence data were cast into a modified Scat-
chard equation[27] through a plot of r/Cf versus r, where r
is the binding ratio of Cb/[DNA] and Cf is the free ligand
plexes i.e. 1
4
3
2 is justified from their chemical
structures.[35,38] The observed binding constant is more
in keeping with groove binding, as reported in the
literature.[10,52–54] Our results illustrate that the Nickel
(II) complexes may bind to DNA via groove binding.
3.4.2 | Steady-state emission studies
The emission spectra of the complexes in the presence of
DNA allow an investigation of the interaction between

RAJESHWARI ET AL.
11 of 18
FIGURE 5 Emission spectra of 1, 2, 3 and 4 in Tris-HCl buffer at 25 ꢀC upon addition of CT-DNA, ([Complex] = 10 μM; [DNA] =
10–200 μM). The arrow shows the increase in intensity upon increasing CT-DNA concentrations
concentration. The binding constants (Kb) are 2.51 × 104,
2.17 × 104, 2.24 × 104 and 2.32 × 104 M−1 for complexes
1, 2, 3 and 4 respectively. The calculated binding con-
stants are also comparable with UV absorption data. The
binding constants obtained from luminescence titration
are different from those obtained from absorption
studies.[55] This small difference between the two sets of
binding constants is due to the different spectroscopic
techniques and different calculation methods; however,
they are comparable.
the complexes to CT-DNA with respect to EB. It is
well-known that free EB displays a decrease in emis-
sion intensity in Tris–HCl buffer medium because of
quenching by solvent molecules. However EB strongly
fluoresces in the presence of DNA due to complete
intercalation between adjacent DNA base pairs, a pro-
cess that can be reversed by the addition of a compet-
ing agent. The quenching curves of EB bound to DNA
in the absence and presence of 1, 2, 3 and 4 are shown
in Figure 6. The addition of the complexes to DNA
pre-treated with EB causes appreciable reduction in the
emission intensity. This result is also in favor of groove
binding of the complexes to CT-DNA.[56] These data
were analyzed by means of Stern -Volmer equation.
The quenching plots (insets of Figure 6) illustrate that
the fluorescence quenching of EB bound to DNA by 1,
3.4.3 | Quenching studies
Fluorescence quenching experiments were performed to
obtain an estimate of the relative binding affinity of

12 of 18
RAJESHWARI ET AL.
FIGURE 6 Emission spectra of EB bound to CT-DNA in the absence and presence of complexes (1-4) ([Complex] = 0-100 μM, [DNA]
= 130 μM, [EB] = 40 μM). Insets: Stern–Volmer quenching curves
2, 3 and 4 is in linear agreement with the Stern-Volmer
relationship, which corroborates that the complexes
bind to DNA. From a plot of I0/I versus [complex]/
[DNA], Ksq is given by the ratio of slope to intercept.
The Ksq values for 1, 2, 3 and 4 are 0.16, 0.40, 0.23 and
0.18 respectively. To quantify the displacement, the
concentration of the complex at which EB fluorescence
decreases by 50% (assumed to be 50% displacement of
EB) is calculated, from a plot of I/Io vs [complex]
using regression analysis (Figure 7). The apparent DNA
binding constant values for 1, 2, 3 and 4 were calcu-
lated from a competitive binding model with equation,
Kapp = KEB × [EB]50% /[complex]50%, where Kapp is the
apparent DNA binding constant of the complex, KEB is
the binding constant of EB i.e. 1.25 × 106 M−1, [EB]50%
3 and 4 are 1.19 × 105, 2.38 × 105, 1.45 × 105,
1.12 × 105 M−1
.
3.4.4 | Light switch studies
Light switch studies were conducted using a literature
method.[57] As shown in Figure 8, upon addition of DNA
to complexes 1, 2, 3 and 4, its emission intensity is
increased (light switch on). This is because the complexes
bind to DNA to form DNA-[Ni (II)complex]. The emis-
sion of bound complex is quenched by cobalt (II) ion,
thus turning the light switch off,[58,59] due to formation of
heterometallic complex Co+2-[Ni (II) complex]. When
EDTA is added into the buffer system containing heter-
ometallic complex, emission intensity is recovered
and [complex]
are the concentrations of EB and
50%
complex at 50% fluorescence. Kapp values for 1, 2,
(switch on) again. This is due to the formation of [Co+2
-

RAJESHWARI ET AL.
13 of 18
FIGURE 7 Competitive DNA binding- Kapp plots of complexes 1, 2, 3 and 4
EDTA] complex and free Nickel (II) complex (1, 2, 3 and
4) again interacts with DNA. The change in the lumines-
cence of the DNA-bound complex in the presence of
Co+2 and EDTA reveals a potential in the modulation of
drug therapy.
by changes in conformation, flexibility or solvation of the
DNA molecule. This behavior is similar to that of metfor-
min -DNA binding studies reported by Shahabadi and
Heidari.[11]
3.4.6 | Photo-cleavage studies
3.4.5 | Viscosity studies
Many Nickel (II) complexes can cleave DNA under
irradiation by UV or visible light. When circular plas-
mid DNA is subjected to electrophoresis, relatively fast
migration will be observed in the intact supercoiled
form (Form I). When scission occurs on one strand
(nicked), the supercoil relaxes to generate a slower-
moving open circular form (Form II). Finally, when
both strands are cleaved, a linear form (Form III) is
obtained, which migrates at a speed between those of
Forms I and Form II.[63] Figure 10 shows the extent of
DNA photo -cleavage at four different concentra-
tions(10 μl, 20 μl, 30 μl, 40 μl) of the complexes 1, 2,
3 and 4 at 360 nm for 1 hr. No DNA cleavage is
observed in controls in which complex is absent. All
A classical intercalation model demands that the DNA
helix must lengthen as base pairs are separated to accom-
modate a binding ligand, leading to an increase in DNA
viscosity.[60] In contrast, a partial and/or non -classical
intercalation ligand could bend (or kink) the DNA helix,
reducing its effective length and concomitantly reducing
its viscosity, while ligands that bind exclusively in DNA
grooves (e.g. netropsin, distamycin), under the same con-
ditions, typically cause less pronounced changes (positive
or negative) or no changes in DNA solution viscosity.[61]
The slow increase in relative viscosity of CT-DNA with
increasing amount of 1, 2, 3 and 4 (Figure 9) indicates
groove binding.[62] In principle, this could be explained

14 of 18
RAJESHWARI ET AL.
FIGURE 8 DNA light switch on and off experiments showing the luminescence changes upon addition of Co2+, EDTA to
[Ni(Cl)2(metf)(o-phen)] + DNA
the four complexes exhibit DNA photocleavage activity,
with the increasing concentration of complexes(1, 2,
3 and 4) the amount of form I is decreased whereas
that that of form II is increased. The cleavage effect
was found to be concentration dependent. Among all
the four complexes, complex 1 exhibits higher effi-
ciency of DNA cleavage than other three complexes.
The role of Oxidant H2O2 is to oxidise metal complex
and releases OH free radical. This OHfree radical par-
ticipates in the oxidation of the deoxyribose moiety,
followed by hydrolytic cleavage of sugar phosphate
backbone.[64] The delivery of high concentration of
metal ion to the helix, in locally generating oxygen or
hydroxide radicals lead to an efficient DNA cleavage
reaction.
3.5 | In Silico molecular docking study
FIGURE 9 Effect of increasing amount of complexes 1,2,
3 and 4 on the relative viscosities of CT-DNA at room temperature
in 5 mM Tris–HCl buffer. The total concentration of DNA = 20 μM,
[complex]= 0-100 μM
Discovery Studio 2.1 software was used to perform dock-
ing between the metal complex. (ligand) and B-DNA

RAJESHWARI ET AL.
15 of 18
FIGURE 10 Changes in the Agarose gel electrophoresis pattern by oxidative cleavage of supercoiled pUC19 plasmid DNA, induced by
H2O2 in the absence and presence of metal complexes 1, 2, 3 and 4 at four different concentrations of 10 μl, 20 μl, 30 μl, 40 μl after 60 min
irradiation at 360nm
TABLE 5 Docking energy and ligand interaction data of the compound
CDocker Intectraction
energy
H-Bond
No. of
H-bonds
Complex
Interacting atoms
Distance (Ao)
Donor
H34
H35
H34
H20
H26
H22
H21
H20
H23
H4’
Acceptor
O4’
1
32.027
ophen: H34 - B:DC18:O4’
ophen: H35 - B:DG19:O4’
ophen: H34 - B:DC18:H4’
opda: H20 - B:DG19:O4’
opda: H26 - B:DA17:N3
en: H22 - B:DC18:O4’
en: H21 - B:DG19:O4’
en: H20 - A:DC9:O4’
2.265000
1.939000
1.677000
1.988000
2.437000
2.413000
2.216000
2.380000
1.839000
1.751000
1.917000
2.174000
1.806000
2
O4’
H4’
2
3
31.427
35.393
O4’
2
4
N3
O4’
O4’
O4’
en: H23 - B:DG19:O4’
A:DC9:H4’ - en: H20
O4’
H20
O4’
4
30.521
bipy: H32 - B:DG19:O4’
bipy: H33 - B:DC18:O4’
B:DC18:H1’ - bipy: H33
H32
H33
H1’
2
O4’
H33
(Continues)

16 of 18
RAJESHWARI ET AL.
TABLE 5 (Continued)
CDocker Intectraction
energy
H-Bond
No. of
H-bonds
Complex
Interacting atoms
A:DG7:H21 - Met:N3
Met:H16 - B:DG19:O4’
Met:H19 - B:DC18:O2
Met:H20 - B:DC18:O4’
Distance (Ao)
Donor
H21
Acceptor
N3
Metformin
37.561
2.472000
2.408000
2.127000
2.078000
4
H16
O4’
H19
O2
H20
O4’
(receptor) sequence. Input used for the docking is B-DNA
sequence 50-D(*AP * CP * CP * GP * AP * CP * GP * TP
* CP * GP * GP * T)-30 retrieved from protꢀein data bank
(PDB ID: 423D) at a resolution of 1.6 A and the 3D
models of the metal complexes. Receptor was prepared
by deleting all the heteroatoms including water and by
adding polar hydrogen atoms, docking energy (CDocker
Intectraction energy) of title derivatives were explored
towards target. From the docking analysis of B-DNA
sequence with the synthesized complexes, unveiled their
docking scores and interaction patterns. The docked com-
plexes 1, 2, 3 and 4 exhibited fitness scores with a range
of 35.393 to 30.521 as compared to metformin 37.561
(Table 5). Among all the compounds, Compound 3 was
ranked highest docking score of 35.393. These results
indicate that both the compounds bound within the bind-
ing site pocket of metformin similar binding pattern with
one of the binding site (DG19) nucleotide residue. The
protein–ligand interaction visualization of the com-
pounds is shown in Figure 11.
FIGURE 11 Receptor-ligand hydrogen bonds (green colour) and bumps (pink colour) of complexes (1-4) and Metformin with B-DNA
sequence (PDB : 423D)

RAJESHWARI ET AL.
17 of 18
[10] R. Olar, M. Badea, E. Cristurean, C. Parnau, D. Marinescu,
J. Therm. Anal. Calorim. 2006, 1, 53.
4 | CONCLUSIONS
[11] N. Shahabadi, L. Heidari, Spectrochim. Acta A 2012, 97, 406.
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Four new Ni (II) ternary complexes of metformin were
synthesized and the structure of these complexes were
proposed based on the analytical, conductance, thermal,
spectral and magnetic moment data. Finally, octahedral
geometry has been suggested for all four complexes. The
non-electrolytic nature of these complexes was confirmed
on the basis of their molar conductance values. Elemental
analysis shows the ratio of metformin, auxiliary ligand,
Nickel (II) in the complexes as 1:1:1. The stability of all
the complexes was discussed and kinetic parameters
(E*, A, ΔH*, ΔS* and ΔG*) of all thermal decomposition
stages have been estimated using the Coats–Redfern
method. From the kinetic studies it is clear that the ther-
mal decomposition process of these complexes are non-
spontaneous, i.e. the complexes are thermally stable. Geo-
metrical optimized structures of these complexes is given
by optimizing their bond lengths, bond angles and tor-
sional angles. The experimental results of DNA binding
studies suggest that complexes 1, 2, 3 and 4 bind to DNA
via groove binding with activity in the order 1 4 3 2.
The Fluorescence quenching studies gives Ksq values for
1, 2, 3 and 4 are 0.16, 0.40, 0.23 and 0.18 respectively. The
molecular docking technique was employed to determine
the binding affinity of the complexes with DNA and pro-
tein molecules. Complex 3 was ranked with highest dock-
ing score of 35.393. Nuclease studies showed that, upon
irradiation these complexes show effective cleavage of
pUC19DNA using H2O2 as an oxidant.
[14] M.
Alexion,
I.
Tsivikas,
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A. A. Pantazaki, P. Trikalitis, N. Lalioti, D. A. Kyriakidis,
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