Synthesis, characterisation, cytotoxicity, DNA binding and antimicrobial studies of binary and ternary metal complexes of Co (II)

Article abstract of DOI:10.1016/j.inoche.2019.107590

A series of Schiff's base ligand metal complexes of Co (II) with binary, formulae [Co (L)₂] (mc-a), and ternary, formulae [Co(L) (L₁) (H₂O)] (mc-b), [Co (L) (L₂) (H₂O)] (mc-c) where L is (2Z)-2-(2-Hyd

Full text of DOI:10.1016/j.inoche.2019.107590

InorganicChemistryCommunications110(2019)107590
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Synthesis, characterisation, cytotoxicity, DNA binding and antimicrobial
studies of binary and ternary metal complexes of Co (II)
⁎
Pilli Jyothia, Suneetha Koppua, V. Sumalathaa,c, B. Ushaiahb, C. Gyana Kumaria,
b Department of Chemistry, Nizam College, Osmania University, Hyderabad 500001, India
c Dept. of Chemistry, JMJ college for Women, Tenali, Guntur (Dist), Andhra Pradesh, 522202, India
a Department of Chemistry, Osmania University, Hyderabad 500007, India
G R A P H I C A L A B S T R A C T
A R T I C L E I N F O
A B S T R A C T
Keywords:
A series of Schiff’s base ligand metal complexes of Co (II) with binary, formulae [Co (L)2] (mc-a), and ternary,
Schiff’s base ligand
Metal complex
Cytotoxicity
formulae [Co(L) (L1) (H2O)] (mc-b), [Co (L) (L2) (H2O)] (mc-c) where
L is (2Z)-2-(2-Hydroxy-5-
BromoBenzylidine) Hydrazine N-methyl Carbo-Thioamide (Schiff’s base ligand), L1 is Ethylene Diamine and L2 is
Bipyridine were synthesized. The metal complexes have been characterized by Mass spectra, UV–Vis absorption,
Magnetic susceptibility, FT-IR, SEM, and Powder XRD. The Schiff’s base had been further identified by 1H NMR.
The complexes have been evaluated for their cytotoxicity, DNA binding studies, and antimicrobial studies. The
cytotoxic results found that the metal complexes showed IC50 values around 17.77–249.12 μg/ml. The DNA
DNA binding studies
Antibacterial
Antifungal
binding constants (kb) of the metal complexes were determined as, 0.9 × 104 M−1
,
0.5 × 104 M−1
,
2.0 × 104 M−1 for mc-a, mc-b, mc-c respectively, indicating that the complexes strongly bind to DNA.
Furthermore, these complexes showed significant activity against some bacteria & fungi.
1. Introduction
Thiosemicarbazides and their metal complexes display a wide range of
biological activities such as antitumor, antibacterial, antiviral and anti-
The chemistry of Schiff’s base is an important area of research with
increasing interest due to their simple synthetic process, versatility,
easy possible and application for their metal complexes [1].
malarial activities [2,3]. Ligands having Oxygen, Nitrogen, and Sulphur
as donors are widely studied to their complexes cover many areas
spacing from the effect of S and electron delocalization in Transition
⁎ Corresponding author.
E-mail address: prof.gyanach@gmail.com (C. Gyana Kumari).
https://doi.org/10.1016/j.inoche.2019.107590
Received 25 July 2019; Received in revised form 17 September 2019; Accepted 18 September 2019
Availableonline18October2019
1387-7003/©2019ElsevierB.V.Allrightsreserved.

P. Jyothi, et al.
InorganicChemistryCommunications110(2019)107590
Scheme 1. Synthetic route and structure of Schiff’s base ligand.
Scheme 2. Preparation of metal complexes.
Metal complexes [4]. Earlier studies had proven that transition metal
complexes of Thiosemicarbazides are a very powerful antitumor agent
than the free ligand.
resultant mixture was refluxed for 3 h; the resulting solid product was
isolated by filtration and recrystallized from methanol. Yield 80%; ESI-
MS(DMSO): m/z = 286 (calcd.286) (M); IR (KBr, cm−1):1627 (C]N),
1475 (C]C), 1654(eCH]N), 3275(eNH), 3390(eOH); 1H NMR
(400 MHz, CDCl3, ppm): 7.8–8.0 (d, Hc, 1H), 8.0–8.2 (d, Hd, 1H),
8.3–8.5 (s, Hf, 1H), 9.0–9.5 (s, eOH, 1H), 3–3.5 (s, eNH, 2H), 1.5–2.0
(s, eCH, 1H), 1.0–1.5 (s, eCH3, 3H) (Scheme1) Figs. S1 and S2.
Cytotoxicity study of the Schiff’s bases has been receiving con-
siderable attention ever since their effectiveness at inhibiting pro-
liferation of cells [5]. On the other hand use of Cisplatin, a medically
recognized antitumor drug, causes numerous side effects, which re-
mains a challenge to overcome and to prepare efficient anticancer drugs
for new chemotherapeutics [6].
2.2. Synthesis of complexes
Many transition metal complexes can bind and notch ds-DNA in a
physiological environment [7,8]. DNA binding studies of metal com-
plexes are a significant primary issue in life sciences and are very im-
portant in the investigation of DNA molecular probes and new ther-
apeutic reagents [9–11]. The non-covalent interactions including
intercalative, electrostatic and groove binding are the possible binding
modes of the complexes to the DNA.
2.2.1. Synthesis of [Co(L)2] complex
This complex was prepared by mixing CoCl2·6H2O (1 mM) in MeOH
(50 ml) and Schiff’s base (L) (1 mM) in 15 ml methanol in a 1:2 ratio
and the mixed solutions refluxed for 2–5 h at 70–80 °C. The product was
separated and washed with ethanol and dried in vacuum. Yield 80%;
ESI-MS (DMSO): m/z = 631 (calcd.630) (M+1). Fig. S3.
In present work we have studied on the synthesis, characterization,
cytotoxicity, DNA binding studies of Primary and Ternary Co (II)
complexes. DNA binding studies were studied by absorption spectra,
fluorescence spectral studies. Cytotoxicity experiments have been done
against HeLa & MCF7 cell lines using MTT assay. The complexes were
characterized by different spectral methods and also subjected to an-
timicrobial studies.
2.2.2. Synthesis of [Co(L)(L1)H2O] complex
This complex was prepared by mixing CoCl2 0.6 H2O (1 mM) in
MeOH (50 ml) and Schiff’s base (1 mM) in 15 ml Methanol. This mix-
ture was refluxed for 2 h. To this mixture Ethylene Diamine (1 mM) in
15 ml methanol was added and refluxed at refluxing temperature for
3 h. The resulting product was filtered, washed with cold ethanol and
dried in Vacuum. Yield 75%; ESI-MS (DMSO): m/z = 467 (calcd.428)
(M+K). Fig. S4.
2. Experimental
2.1. Synthesis of Schiff base ligand
2.2.3. Synthesis of [Co(L)(L2)H2O] complex
This complex was prepared by mixing CoCl2·6H2O (1 mM) in MeOH
(50 ml) and Schiff base (1 mM) in 15 ml Methanol and allowed to re-
fluxed for 2 h. To this mixture Bipyridine (1 mM) in 15 ml methanol was
added and refluxed at refluxing temperature for 3 h. The resulting
precipitate was filtered, washed with cold ethanol and dried in Vacuum
(Scheme 2). Yield 76%; ESI-MS (DMSO): m/z = 518 (calcd.518) (M).
Fig. S5.
The Schiff’s base ligand “(2Z)-2-(2-Hydroxy-5-Bromo Benzylidine)
Hydrazine N-Methyl Carbo-Thioamide” (L) has been synthesized by the
method that has been reported earlier by Aamer Saeed, Najim et al.
[12]. Methanolic solution of (40 ml) N-Methyl Thiosemicarbazide
(2.10 g, 0.02 mol) and few drops of sulphuric acid were added to a
Methanolic solution of 5-Bromo Salicyladehyde (3.13 g, 0.02 mol). The
2

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InorganicChemistryCommunications110(2019)107590
Fig. 1. (a) Images of scanning electron microscopy (SEM) (b) Energy-dispersive X-ray spectroscopy (EDAX) of the metal complexes for mc-a, mc-b, mc-c from the top
to bottom respectively.
3. Results and discussion
Further the appearance of broadband around 3370–3480 cm−1 and
weaker bands around 800–860 cm−1 range, which could be assigned to
OH stretching, rocking & wagging vibrations respectively indicating the
presence of water molecule that coordinated to the Co (II) metal ion in
the complexes [15] which also supported by elemental analysis. Figs.
S6–S9.
3.1. FT-IR analysis & mode of bonding
The IR spectra of a free ligand exhibited a broadband at 3390 cm−1
corresponding to phenolic OH group which was found disappeared in
the IR spectra of metal complexes, indicating co-ordination through
phenolic hydroxyl group and another important band in the IR spectra
of ligand appeared at 1552 cm−1 due to C]N group stretching vibra-
tion which was shifted to the extent of 10–20 cm−1 upon complexation
implying its coordination via azomethine nitrogen to the metal centre
[13,14]. Additionally, the strong band observed at the 1267 cm−1 due
to C]S stretching vibrations in the ligand spectrum were found to
shifted about 1284–1288 cm−1 in the IR spectra of metal complexes
indicating the involvement of the thioketo sulphur in the co-ordination.
Further, the formation of complexes was also ascertained by the pre-
sence of medium intensity bands in the region 576–578 cm−1 and
468–470 cm−1 and 372–439 cm−1 assigned to ʋ (CoeO), ʋ (CoeN) and
ʋ (CoeS) respectively.
The important absorption frequencies of all metal complexes with
the ligand and their assignments are listed in Table 1
3.2. Magnetic moments & electronic spectral data
The electronic spectral data gives information regarding the geo-
metry of metal complexes. The diffuse reflectance spectrum of the Co
(II) metal complexes showed bands in the region of 200–400 nm, which
is indicative of charge transfer transitions. Moreover the spectrum also
exhibits one broadband with the considerable fine structure that has
intensities consistent with the spin allowed d-d transition, which is
attributed to transitions ʋ1[(T1g(F) − T2g(F)] (700–800 nm), char-
acteristic of an octahedral geometry [16] further magnetic moment of
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3.3. XRD analysis
To obtain extra support about the structure of the metal complexes
X-ray diffraction was performed. The diffractograms obtained for the
metal complexes are given in (Fig. S14). The powder XRD of complexes
showed sharp crystalline peaks indicating its crystalline phase which
may be attributed to the formation of a well defined distorted crystal-
line structure. Probably this behaviour is due to the incorporation of
water molecules into the coordination sphere.
3.4. SEM analysis
The particle size, purity, morphology and the surface structure of
the synthesized metal complexes have been shown from the Scanning
Electron micrograph (SEM).
The SEM images revealed the metal complexes having the particle
are agglomerated with the controlled morphological structure and the
presence of irregular spherical structures in complexes (Fig. 1). “How-
ever, particle sizes less than 100 mm were also observed, which groups
to form agglomerates of larger size”. The elemental composition of
shown in EDX spectra (Table 2)
Fig. 2. Cytoxic activity of metal complexes showing Ic50 values in µg/ml
against HeLa and MCF7 cell lines.
3.5. Cytotoxic study
4.8B.M also suggest an octahedral symmetry. On the other hand, ligand
shows peaks in the region of 200–400 nm which are assigned to INCT
transitions. Figs. S10–S13.
An in vitro cytotoxic study is valuable tool in the screening of
chemotherapy agents and procures a preliminary data for further
Fig. 3. Electron spectra of three metal complexes in the absence and presence of increasing amounts of CT-DNA, DNA = 10–100 µM. Inset: Linear plots for the
calculation of intrinsic binding constant Kb.
4

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InorganicChemistryCommunications110(2019)107590
Fig. 4. Emission spectra of EB bound to DNA in the absence and presence of complexes (100 µm) Inset: Stern-Volmer quenching curves.
function which is followed by replication and transcription process
inhibition and eventually cell death i.e. what we can suppose [17].
The results were analyzed by cell viability curves and given with
IC50 values. The % of inhibition on the tested cell lines in the com-
pound concentration range of 5–100 µg/ml is given in Tables 4–6.
According to the result as the concentration of compound increased, the
cell viability is decreased, the viability of cells incubated without any
compound was considered as 100%.
The IC50 values obtained in this study are listed in Table 3. From the
Table 3 it is to be observed that metal complex-a, metal complex-c are
found to behave as a good antitumor agent on MCF7&HeLA respec-
tively (Fig. 2). Hence the higher cytotoxicity had shown by the com-
plexes may be due to relatively stronger interacting ability of the
complexes with DNA [18].
3.6. DNA binding studies
3.6.1. Electron absorption study
Fig. 5. Antibacterial and antifungal activity of metal complexes comparing with
Electron absorption spectroscopy was used to determine the binding
characteristics of metal complexes with DNA. The binding of Co (II)
complexes to the DNA helix was characterized by resulting hypo
chromic in intensity and red shift in wavelength due to strong stacking
interaction between an aromatic chromophore and the base pairs of
DNA [19,20] indicates intercalative mode of binding. “The electronic
absorption spectra consisting of all metal complexes are shown in
standards.
studies.
The cytotoxic activity of all metal complexes was examined on HeLa
&MCF7 cell lines adopting MTT assay. It depends on their ability to
bind DNA and damage its structure resulting in the impairment of its
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P. Jyothi, et al.
InorganicChemistryCommunications110(2019)107590
(Fig. 3)”. The intrinsic binding constant kb is calculated from a plot of
[DNA]/(Ea − Ef) Vs [DNA] using equation.
complexes of Co(II) and characterization by elemental data and spectral
analysis. SEM analysis of metal complexes revealed their homogenous
nature. The binding mode of complexes with CT-DNA was evaluated by
UV–Visible absorption spectroscopy & Fluorescence studies. The results
strongly favour the binding of the complex with CT-DNA via inter-
calation mode.
[DNA]/(Ea Ef) = [DNA]/(Eb Ef) + 1/kb(Eb Ef)
where Ea, Ef and Eb are the compound in the presence of DNA, free
compound and fully DNA-bound compound respectively [21]. The kb
values for metal complexes are found to be 0.9 × 104 M−1 for mc-a,
0.5 × 104 M−1 for mc-b, 2.0 × 104 M−1 for mc-c. With increasing DNA
concentration, “the resulting tendency to hypo chromic and slight red
shifts indicates that the complexes can bind with DNA through inter-
calative mode”. However, the binding affinity of all the complexes
against CT-DNA is less than that of potential intercalators like ethidium
bromide [EB] [22].
In MTT assay, cytotoxicity studies, the complexes exhibited antic-
ancer activity against MCF7 and HeLa cancer cells effectively.
Additionally, all the complexes are screened for antibacterial and an-
tifungal activities and it has observed that all complexes had shown
high antifungal activity than antibacterial activity.
Declaration of Competing Interest
3.6.2. Fluorescence study
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Fluorescence experiments were performed to get proof for the mode
of binding of metal complexes with DNA. The relative binding ability of
metal complexes with DNA has been investigated by Ethidium Bromide
(EB) displacement method. EB is one of the most useful fluorescent
probes that bind to DNA through intercalation and there is an en-
hancement in the intensity of fluorescent spectra of EB in the presence
of DNA [23]. The experiment results showed that by the addition of
metal complexes to EB-DNA, there is a decrease in the intensity of EB-
DNA due to complex competitive binding to the EB-bound DNA system
by displacement of bound EB from DNA [24]. As shown in (Fig. 4), the
fluorescence intensity at 590 nm decreased gradually on the increasing
concentration of metal complexes. The results showed that all the
compounds bind with DNA by the intercalation mode.
Acknowledgment
We thank the Head, Department of chemistry for providing the
necessary facilities, the Director, CFRD, Osmania University, and the
Director, IICT, Hyderabad.
This research did not receive any specific grant from funding
agencies in the public, commercial, or not -for-profit sectors.
Appendix A. Supplementary material
These results are expressed in terms of quenching constant KSV
calculated from equation I0/I = 1 + KSV. The relative binding constants
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.inoche.2019.107590.
of the complexes are found to be in between 1.4 and 3.1 × 104 M−1
.
From the results metal complex-c can bind DNA strongly than the other
complexes, consistent with the absorption spectral results were shown
in the order mc-c > mc-a > mc-b.
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4. Conclusion
In this paper, we reported the synthesis of Schiff’s base ligand & its
6