Preparation of octahedral Cu(II), Co(II), Ni(II) and Zn(II) complexes derived from 8-formyl-7-hydroxy-4-methylcoumarin: Synthesis, characterization and biological study

Article abstract of DOI:10.1016/j.molstruc.2020.128659

A series of octahedral Cu(II), Co(II), Ni(II) and Zn(II) complexes has been synthesized with ONO donor Schiff base ligand (L) derived from the reaction of 8-formyl-7-hydroxy-4-methyl coumarin and N-(4-phenylthiazol-2-yl)hydrazinecarboxamide. The chemical structures of the compounds were elucidated by elemental analysis and various physico-chemical techniques. Thermal analyses studies indicates the presence of coordinated water molecules in Cu(II) and Zn(II) complexes. The compounds were screened for their antibacterial and antifungal activities by MICs method and DNA cleavage activity by AGE method. Also, brine shrimp bioassay was also carried out to study the in vitro cytotoxic properties, the compounds reveals the significant activity.

Full text of DOI:10.1016/j.molstruc.2020.128659

Journal Pre-proof
Preparation of octahedral Cu(II), Co(II), Ni(II) and Zn(II) complexes derived from 8-
formyl-7-hydroxy-4-methylcoumarin: Synthesis, characterization and biological study
Nagesh Gunavanthrao Yernale, Mruthyunjayaswamy Bennikallu Hire Mathada
PII:
S0022-2860(20)30984-4
DOI:
https://doi.org/10.1016/j.molstruc.2020.128659
MOLSTR 128659
Reference:
To appear in: Journal of Molecular Structure
Received Date: 23 April 2020
Revised Date: 6 June 2020
Accepted Date: 8 June 2020
Please cite this article as: N.G. Yernale, M.B. Hire Mathada, Preparation of octahedral Cu(II),
Co(II), Ni(II) and Zn(II) complexes derived from 8-formyl-7-hydroxy-4-methylcoumarin: Synthesis,
characterization and biological study, Journal of Molecular Structure (2020), doi: https://doi.org/10.1016/
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Credit author statement
Nagesh Gunavanthrao Yernale: Conceptualization, Methodology, Software, Data curation,
Writing- Original draft, preparation, Validation, Writing- Reviewing and Editing.
Mruthyunjayaswamy
Bennikallu
Hire
Mathada:
Supervision
Visualization,
Investigation. Writing- Reviewing and Editing,

Research Article
Preparation of Octahedral Cu(II), Co(II), Ni(II) and Zn(II) Complexes Derived from 8-
formyl-7-hydroxy-4-methylcoumarin: Synthesis, Characterization and Biological study
1
,2
1,
Nagesh Gunavanthrao Yernale and Mruthyunjayaswamy Bennikallu Hire Mathada *
*1
Department of Studies and Research in Chemistry, Gulbarga University,
Kalaburagi - 585 106, Karnataka, INDIA.
2
Department of Chemistry, Guru Nanak PG Centre, Bidar – 585 403, Karnataka, INDIA.
Tel.: +91-9448830318; E-mail: bhmmswamy53@rediffmail.com
ABSTRACT
A series of octahedral Cu(II), Co(II), Ni(II) and Zn(II) complexes has been synthesized with
ONO donor Schiff base ligand (L) derived from the reaction of 8-formyl-7-hydroxy-4-methyl
coumarin and N-(4-phenylthiazol-2-yl)hydrazinecarboxamide. The chemical structures of the
compounds were elucidated by elemental analysis and various physico-chemical techniques.
Thermal analyses studies indicates the presence of coordinated water molecules in Cu(II) and
Zn(II) complexes. The compounds were screened for their antibacterial and antifungal
activities by MICs method and DNA cleavage activity AGE method. Also, brine shrimp
bioassay was also carried out to study the in vitro cytotoxic properties, the compounds
reveals the significant activity.
Key words: Transition metal complexes; Schiff base; in vitro cytotoxic; DNA cleavage;
coumarin; antimicrobial.
Address for correspondence: Prof. B. H. M. Mruthyunjayaswamy, Department of Studies
and Research in Chemistry, Gulbarga University, Kalaburagi - 585 106, Karnataka, INDIA.
Tel.: +91-9448830318; E-mail: bhmmswamy53@rediffmail.com
1

1. Introduction
It has long been known that many of the metal ions are actively involved in the
biological processes of life and have been a topic of interest. The mode of action of these
metal ions are often complex, but are believed to involve in bonding through the various
hetero atoms (ONO/S) of the heterocyclic residues of biological molecules, i.e., proteins,
enzymes, nucleic acids, etc. [1-3]. Some metal complexes have been used as the anticancer
drug in clinic. Currently Lanthanide (III) complexes are being investigated extensively for a
variety of functionalities and applications, such as medicine, optical probes, microelectronics,
and others [4-7]. Schiff base ligands with N and O donor atoms continue to occupy an
important role in metal coordination chemistry, resulting in an enormous number of
publications, ranging from pure synthetic work to modern physicochemical and
biochemically relevant studies of metal complexes [8-10].
Sulfa drugs have attracted the attention of the chemist because their therapeutic
significance as they were used against a wide spectrum of bacterial ailments. Also, some
sulfa drugs were used in the treatment of tuberculosis, malaria, cancer and leprosy [11,12].
The core molecule thiazole is an important class of heterocycles contains two hetero atoms (S
and N) placed in the heterocyclic ring at 1 and 3 positions respectively. Compounds
containing this moiety have wide range of applications in pharmaceutical, phytosanitary,
analytical industrial aspects and have diverse biological activities [13,14].
Coumarins are also an important class of compounds obtained from nature and
synthetic origin that possess diverse array of pharmacological and biological relevance such
as antitumor, anti-inflammatory, anticoagulant, anti-HIV, herbicidal and fungicidal activities
[
15-17]. Some of the coumarin derivatives are used as DNA intercalators used in cancer
treatment because of its planar chromophore [18]. Also, it has been proved that the naturally
occurring 7-hydroxy-4-methylcoumarin is potential lead molecule for cancer drug
development [19]. Also, the compounds containing this moiety form very stable complexes
with various metal ions due to the presence of phenolic hydroxyl group at its ortho-position,
which coordinates to the metals ion via deprotonation [20].
Herein, octahedral Cu(II), Co(II), Ni(II) and Zn(II) complexes has been synthesized
with ONO donor Schiff base ligand (L) derived from the reaction of 8-formyl-7-hydroxy-4-
methyl coumarin and N-(4-phenylthiazol-2-yl)hydrazinecarboxamide containing carbonyl
(C=O), azomethine (C=N) and hydroxyl group (OH) as potential chelating sites. The
structures of the complexes are elucidated using various physicochemical techniques. The
2

corresponding biological relevance of all the complexes have been compared with those of
the free Schiff base ligand (L) and standard drug.
2
2
. Experimental
.1. Materials and methods
All solvents and starting materials were purchased from commercial chemical
suppliers and used without further purification, unless otherwise stated. The precursor, 8-
formyl-7-hydroxy-4-methyl coumarin and N-(4-phenylthiazol-2-yl)hydrazinecarboxamide are
prepared as per literature methods [20-22].
2
.2. Instrumentation
The metal and chloride contents of the complexes were estimated gravimetrically as
per standard methods [23]. Carbon, Hydrogen and Nitrogen analysis was performed on Vario
EL III CHNS analyser. IR spectra were recorded on Perkin Elmer Spectrum RX-I FTIR
1
spectrophotometer. H NMR spectra were recorded on Bruker, 400 MHz spectrometer using
ꢀ6
-DMSO as solvent. ESI mass spectra were recorded on mass spectrometer equipped with
ESI source having mass range of 4000 amu in quadruple and 20,000 amu in Tof. Electronic
-
spectra were recorded on ELICO SL-164 double beam UV-visible spectrophotometer (ca. 10
3
M in DMF). Molar conductivity of metal complexes was measured on Elico-CM 180
-3
Conductivity Bridge (ca. 10 M DMF). ESR measurements of solid [Cu(L)(Cl)(H O) ]
2
2
complex was carried out on BRUKER Bio Spin spectrometer working at a microwave
frequency of 8.75-9.65 GHz using DPPH as reference with field set at 3000 Gauss using
tetracynoethylene as the ‘g’ marker (g = 2.00277). Thermo gravimetric analyses data were
measured on Perkin Elmer thermal analyser in nitrogen atmosphere with a heating rate of 20
-1
°
C min .
2
.3. Synthesis of Schiff base ligand (L)
A solution of 8-formyl-7-hydroxy-4-methyl coumarin and N-(4-phenylthiazol-2-
yl)hydrazinecarboxamide in absolute ethyl alcohol (30 mL) was refluxed on water bath for
about 5-6 with an addition of a catalytic amount of glacial acetic acid (2-3 drops). A light
yellow precipitate was collected by filtration, washed with absolute ethyl alcohol, and dried
in vacuo. The pathway for the synthesis of Schiff base ligand (L) is presented in Scheme 1.
O
O
O
O
H
H
OHC
N
EtOH/AcOH
Reflux, 5-6 h
H
H
H
N
N
C
O
+
N
N
N
C
NH2
C
O
N
CH3
HO
S
CH3
S
HO
Scheme 1- Synthesis of 2-((7-hydroxy-4-methyl-2-oxo-2H-chromen-8-yl)methylene)-N-(4-
phenylthiazol-2-yl)hydrazinecarboxamide (L)
3

2
.4. Preparation of metal complexes
Mixture of Schiff base ligand (L) (0.001 mol) and respective metal chlorides (0.001
mol) in 20 mL of absolute ethyl alcohol was refluxed on water bath for about 6-7 h and pH of
the reaction mixture was adjusted to ca.7.0-7.5 using sodium acetate (0.5 g) and reflux is
continued for about an hour more. The reaction mixture was cooled to room temperature and
poured in to distilled water the separated precipitates were filtered off, washed with distilled
water, then with hot ethanol and finally dried in a vacuum over fused calcium chloride.
2
2
.5. Biological Evaluation
.5.1. Antibacterial and antifungal assay
The antimicrobial activity of L and its [Cu(L)(Cl)(H O) ], [Co(L) ], [Ni(L) ] and
2
2
2
2
[
Zn(L)(Cl)(H O) ] complexes have been studied for their antibacterial and antifungal
2 2
activities using Muller-Hinton agar and potato dextrose agar (PDA) by disc and well
diffusion methods respectively. The activities were carried out in four different
-1
concentrations (100, 50, 25 and 12.5 μg mL in DMSO solvent). The antibacterial activity
was tested against four bacteria, S. aureus (MTCC 3160), B. subtilis (MTCC 736), E. coli
(
MTCC 46) and S. typhi (MTCC 98) and antifungal activity against four fungi, C. albicans
MTCC 227), C. oxysporum (MTCC 1777), A. flavus (MTCC 1883) and A. niger (MTCC
(
1
881) by MIC method [24].
The activity was carried out in accordance with the international recommendation
given by the CLSI. The minimum concentration of test compound with no visible growth of
bacteria/fungi is reported as MIC for their respective strains. Blank tests have shown that
DMSO in the preparation of the test solution does not affect the test organisms. The obtained
results were compared under similar conditions using Gentamycin and Fluconazole, a broad-
spectrum antibiotic for bacterial and fungal strains respectively.
2
.5.2. DNA cleavage studies
The DNA cleavage activity was performed using super coiled plasmid DNA pBR322
as a target molecule as per the literature method [25] and obtained results were compared
with the standard DNA marker.
2
.5.3. In vitro Cytotoxicity study
For the study, Brine shrimp nauplii (Artemia salina) were used for cytotoxicity assay
and followed the protocol given by Meyer et al. [26] with some modifications. Brine shrimp
nauplii eggs were hatched in a shallow rectangular dish (22 X 32 cm) filled with artificial sea
water. An unequal partition was made in the dish with the help of punctured device. About 50
4

mg of eggs were sprinkled into the large compartment, which was darkened and the minor
compartment was open to ordinary light. After two days nauplii were collected by a pipette
from the lighter side.
-1
The stock solutions of the each test compounds (1 mg mL ) were prepared by
dissolving 10 mg of each test compound in 10 mL of DMSO, different concentrations of the
test compounds were placed in separate vials and final volume is adjusted to 10 mL using
artificial sea water. After two days, when shrimp larvae were ready, 10 nauplii were then
placed in each vial, after 24 h incubation the vials were observed using a magnifying glass
and the number of survivors in each vial was counted. Tests were performed in duplicate and
the data were analysed by a Finney computer program to determine the LD values [27]. The
5
0
results were compared with a positive control Bleomycin, an anti-cancer drug.
3
3
. Results and discussion
.1. Chemistry
The synthesized [Cu(L)(Cl)(H O) ], [Co(L) ], [Ni(L) ] and [Zn(L)(Cl)(H O) ]
2
2
2
2
2
2
complexes are colored solids, stable at room temperature and infusible at high temperature.
The elemental analysis data provided in supplementary material Table S1 are agreeing well
with the proposed composition of L and its metal complexes. These data supports the metal
to ligand stoichiometric ratio of the complexes is 1:2 of the type [M(L) ] (M = Co and Ni)
2
and 1:1 stoichiometry of the type [M(L)(Cl)(H O) ] (M = Cu and Zn). The observed molar
2
2
conductance values for all the metal complexes are too low to account for any dissociation,
indicating their non-electrolytic nature.
3
.2. IR spectral studies
The IR spectrum of L, displayed a broad band at 3420 cm due to phenolic OH and
-1
-1
-1
-1
-1
showed high intensity strong bands at 1710 cm , 1692 cm , 1663 cm and 1270 cm are due
to lactone carbonyl, amide carbonyl, azomethine function and phenolic C-O respectively.
-1
-1
Also, medium intensity bands are observed at 3232 cm and 3048 cm due to amide NH and
NH attached to thiazole moiety respectively.
On comparing, the IR spectra of the L and its [Cu(L)(Cl)(H O) ], [Co(L) ], [Ni(L) ]
2
2
2
2
and [Zn(L)(Cl)(H O) ] complexes, it was clearly observed that, the absence of absorption
2
2
-1
band due to phenolic OH at 3420 cm of ligand in all the complexes indicates the formation
of coordination bond between metal ion and phenolic oxygen atom of coumarin moiety via
deprotonation. This is further confirmed by sharp increase in the absorption frequency about
-1
-1
2
1-45 cm of phenolic ν(C-O) which appeared in the region 1291-1315 cm in all the
5

complexes representing the involvement of oxygen atom of phenolic oxygen in coordination.
The most prominent change is the shift of amide carbonyl ν(C=O) to lower frequency side
-1
-1
about 05-66 cm which appeared in the region 1687-1626 cm in all the complexes confirms
the involvement of oxygen atom of amide ν(C=O) in coordination as such without
undergoing enolization. Also, the shift of azomethine function ν(C=N)to lower frequency
-1
-1
side about 32-81 cm and appeared in the region 1582-1631 cm in all the metal complexes
indicating the participation of nitrogen atom of azomethine function in coordination. The
-1
medium intensity weak bands appeared in all the metal complexes at 3201-3237 cm and
-1
3
050-3063 cm were due to amide NH and NH attached to thiazole moiety respectively,
which appeared almost at about the same region as in case of ligand, thus confirming their
non-involvement in coordination. Also, the absorption band due to lactone carbonyl function
-1
was appeared in all the complexes at 1700-1728 cm i.e., at about the same region as in the
case of ligand confirming its non-involvement in coordination.
Formation of metal complexes was further confirmed by the appearance of new weak
-1
-1
intensity, non-ligand bands in the region 509-540 cm , 449-495 cm in all the complexes and
-1
-1
peak at 366 cm and 343 cm (in case of Cu and Zn complexes) are assigned to frequencies
of ν(M-O), ν(M-N) and ν(M-Cl) bonds respectively. In case of [Cu(L)(Cl)(H O) ] and
2
2
-1
-1
[
Zn(L)(Cl)(H O) ] complexes, the appearance of broad band at 3430 cm and 3372 cm
2 2
respectively are due to coordinated water molecule. The prominent IR spectral data of L and
its metal complexes together with their assignments are presented in Table 1.
1
3
.3. H NMR spectra
1
The H NMR spectrum of L displayed (Supplementary data, Fig. S1) three singlets
each at 12.2, 11.4 and 11.1 ppm which are ascribed to protons of phenolic OH, amide NH and
NH of thiazole moiety respectively. A characteristic singlet appeared at 8.1 ppm is assigned
to azomethine proton (HC=N). In addition to this nine aromatic protons have resonated as
multiplet in the region 6.9-7.9 ppm and a signal at 2.4 ppm is due to three protons of methyl
1
group of coumarin moiety. The H NMR spectrum of diamagnetic [Zn(L)(Cl)(H O) ]
2
2
complex (Supplementary data, Fig. S2) displayed two singlets each at 11.1 and 10.5 ppm are
ascribed to protons of amide NH and NH of thiazole respectively. A singlet proton signal at
8
.3 ppm is assigned to azomethine proton (HC=N). In addition to this the nine aromatic
protons have resonated as multiplet in the region 7.1-8.0 ppm and a signal at 2.5ppm is due to
three protons of methyl group of coumarin moiety.
6

The phenolic OH signal of L, which was found at 12.2 ppm has completely
disappeared in [Zn(L)(Cl)(H O) ] complex confirming the involvement and bonding of
2
2
phenolic oxygen atom in chelation with metal ion via deprotonation. Also, appearance of a
new signal at 3.6 ppm corresponds to four protons of two coordinated water molecules.
3
.4. ESI mass spectral studies
The ESI mass spectrum (Supplementary data, Fig. S3) of L displayed a molecular ion
+
peak recorded at M 420 (100%) is equivalent to its molecular weight and which is also a base
peak.
The ESI mass spectrum of [Co(L) ] complex (Supplementary data, Fig. S4) displayed
2
+
+
M +1 peak recorded at 897 (7%). The molecular ion peak recorded at M 896 (5%)
underwent fragmentation in two routes (Scheme - S1). First, on loss of C H radical and CO
2
3
3
molecule of coumarin moiety gave a fragment ion peak recorded at m/z 813 (6%). In another
route, the molecular ion underwent fragmentation and gave a peak recorded at m/z 338
(
100%) which is also a base peak due to the loss of a deprotonated ligand, CO molecule,
2
benzene molecule, CH radical and two hydrogen radicals. The Schematic mass spectral
3
fragmentation pattern of [Co(L) ] complex is in consistency with its proposed structure which
2
is provided in the supplementary data, Scheme-S1.
The ESI mass spectrum of [Zn(L)(Cl)(H O) ] complex (Supplementary data, Fig. S5)
2
2
+
+
displayed M +1 peak recorded at m/z 556, 558 (9%, 3%). This molecular ion recorded at M
55, 557 (3%, 1%) underwent a fragmentation in two routes (Scheme - S2). First, on loss of
C H O molecule, C H radical of coumarin moiety and two coordinated water molecule
5
6
4
2
2
giving a fragment ion peak recorded at m/z 386, 388 (90%, 30%). Further this on
simultaneous loss of C H Ospecies of coumarin, Chloride radical and two hydrogen radicals
3
2
gave a fragment ion peak recorded at m/z 295 (80%). In another route, the molecular ion
underwent fragmentation and gave a peak recorded at m/z 364 (100%) which is also a base
peak, this is due to the loss of CO molecule, two coordinated water molecule and phenyl,
CH and Chloride radicals. This on further loss of C H O radical of coumarin moiety gave a
3
9
3
peak recorded at m/z 321 (31%). The Schematic mass spectral fragmentation pattern of
Zn(L)(Cl)(H O) ] complex is in consistency with its proposed structure which is provided in
[
2
2
the supplementary data, Scheme - S2.
3
.5. Electronic spectra and magnetic susceptibility studies
The green coloured [Cu(L)(Cl)(H O) ] complex displayed a low intensity single
2
2
-1
broad asymmetric band in the region 15149-17986 cm . The broadness of the band
7

2
2
2
2
2
2
designates the three transitions B → A (ν ), B → B (ν ) and B → E (ν ) which
1
g
1g
1
1g
2g
2
1g
g
3
are similar in energy and give rise to only one broad band and the broadness of the band may
be due to dynamic Jahn-Teller distortion. The obtained data suggests the distorted octahedral
geometry for [Cu(L)(Cl)(H O) ] complex [28]. The obtained µ
value of the
2
2
eff
[
Cu(L)(Cl)(H O) ] complex is 1.84 BM, which is slightly higher than the spin-only value due
2
2
to one unpaired electron 1.73 BM, indicates a octahedral geometry around the Cu (II) ion
[
29]. The electronic spectra of brown coloured [Co(L) ] complex displayed two absorption
2
-1
-1
4
4
bands at 16887 cm and 19695 cm . These bands are assigned to be T (F) → A (F) (ν )
1
g
2g
2
4
4
and T (F) → T (P) (ν ) transitions respectively, which are in good agreement with the
1
g
2g
3
reported values for octahedral geometry [30]. The lowest band, ν could not be observed due
1
to the limited range of the instrument used, but it could be calculated using the band fitting
procedure given by Underhill and Billing [31]. The transition values of ν , ν and ν suggest
1
2
3
the octahedral geometry arrangement for [Co(L) ] complex. The observed lower magnetic
2
moment value for [Co(L) ] complex is µ 5.02 BM, which is well within the range of µ
eff
2
eff
4
.70-5.20 BM for octahedral geometry [32]. The [Ni(L) ] complex under present
2
-1
-1
investigation exhibited two absorption bands in the region 14946 cm and 25168 cm , which
3
3
3
3
are assigned to A → T (F) (ν ) and A (F) → T (P) (ν ) transitions respectively,
2
g
1g
2
2g
1g
3
suggest an octahedral geometrical environment around Ni (II) ion [33]. The transition value
of band ν was calculated by using a band fitting procedure [31]. The observed magnetic
1
moment value for [Ni(L) ] complex is µ 2.94 BM, which is also well within the expected
2
eff
range of µ 2.83-3.50 BM, suggesting the consistency with its octahedral geometry [34]. The
eff
[
Zn(L)(Cal)(H O) ]complex is found to be accordingly diamagnetic in nature and it is
2 2
proposed to have a octahedral geometry.
The proposed geometry of [Cu(L)(Cl)(H O) ], [Co(L) ] and [Ni(L) ] complexes was
2
2
2
2
further confirmed by the calculated values of ligand field parameters such as, nephelauxetic
parameter (β), Racah inter electronic repulsion parameter (B’), ligand field splitting energy
(
10 Dq) and ligand field stabilization energy (LFSE) [35]. The calculated B’ values for the
Co(L) ] and [Ni(L) ] complexes are lower than the free ion values, which is due to the
[
2
2
orbital overlap and delocalization of d-orbitals. The β values are significant in determining
the covalency for the metal-ligand (M-L) bond and they were found to be less than unity,
suggesting a considerable amount of covalency for the M-L bonds. The β value for the
[
Ni(L) ] complexes was less than that of the [Co(L) ] complexes, indicating the greater
2 2
8

covalency of the metal-ligand bond. The position of absorption band maxima assignments
are presented in Table 2.
3
.6. Electronic Spin Resonance spectra
The ESR spectrum of [Cu(L)(Cl)(H O) ] complex (Fig. 1) at room temperature
2
2
exhibits anisotropic signals with g value g = 2.139 and g
⊥
= 2.034 which is characteristic for
values are closer to 2 and g > g suggesting an
⊥
> g > 2.0023 shows that the unpaired electron is
||
axial symmetry [36]. Since the g and g
⊥
⊥
||
||
octahedral geometry [37]. The trend g
||
2
2
–y
localized in the dx
orbital in the ground state. In addition, the exchange coupling
interaction between two Cu(II) ions is explained by Hathaway and Billing expression G = g -
||
2
⊥
.0023/g - 2.0023. When the G value is greater than 4, the exchange interaction between the
copper centres is negligible, whereas if its value is less than 4 and the exchange interaction is
noticed. In present study, that G value is 4.20, indicate the exchange coupling effects are not
operative. The ESR spectra of [Co(L) ], [Ni(L) ] and [Zn(L)(Cl)(H O) ] complexes at room
2
2
2
2
temperature do not show ESR signal because the rapid spin lattice relaxation of the [Co(L)2]
and [Ni(L) ] broadness the lines at higher temperatures [36] and the diamagnetic nature of the
2
[
Zn(L)(Cl)(H O) ] complex. The ESR spectra show signals that may be accounted for the
2 2
presence of free radicals that can result from the cleavage of any double bond and distribution
of the charge on the two neighbour atoms. The presence of unpaired electrons from any
source inside the molecule can be responsible for the appearance of these signals [38].
3
.7. Thermal analyses
The thermogram of [Cu(L)(Cl)(H O) ] complex (Fig. 2) showed that the complex is
2
2
decomposed in four successive stages. The first stage of degradation occurred at 165 °C, due
to the loss of two coordinated water molecules (Obs.5.84%, Calc. 6.50%). The resultant
complex on further degradation furnished a break at 310 °C by the loss of a coordinated
Chlorine atom and CH species of coumarin moiety (Obs. 10.27%, Calc. 9.66). Further,
3
thecomplex showed third stage of decomposition at 340 °C due to loss of C HO molecule of
5
2
coumarin moiety (Obs. 20.68%, Calc. 19.89%). Further, the complex at 430 °C showed the
break which was due to the loss of C H species of thiazole moiety (Obs. 24.42%, Calc.
8
6
2
7.23%). Thereafter, the complex showed a gradual weight loss up to 731 °C, due to loss of
remaining organic moiety. The final weight of the residue corresponds to cupric oxide.
The thermogram of [Co(L) ] complex indicated its degradation in three successive
2
stages. The first stage of decomposition represents the weight loss of a C H O species of
4
4
2
coumarin moiety at 358 °C (Obs. 9.33%, Calc. 9.36%). The resultant complex further
9

underwent degradation in second stage and gave break at 304°C (Obs. 46.35%, Calc.
5.14%) which corresponds to the loss of two moles of 2-amino-4-phenylthiazole molecules.
Further, the complex underwent third stage of decomposition and gave a break at 375 °C
Obs. 43.20%, Calc. 41.71%), which corresponds to the weight loss of C H O group of
4
(
11
6
3
coumarin moiety. Thereafter, the complex showed a gradual weight loss up to 632 °C, due to
remaining organic moiety. The weight of the residue corresponds to cobalt oxide.
Similarly, [Ni(L) ] and [Zn(L)(Cl)(H O) ] complexes underwent a decomposition in
2
2
2
three and four successive stages respectively and the final weight of the residue corresponds
to the formation of respective metal oxides. The proposed stepwise degradation pattern of
[
Cu(L)(Cl)(H O) ], [Co(L) ], [Ni(L) ] and [Zn(L)(Cl)(H O) ] complexes at different stages
2 2 2 2 2 2
are due to the loss of different organic moieties with respect to temperature, which is
illustrated in Table 3.
3
3
.8. Biological Evaluations
.8.1. Antibacterial and antifungal assay
The MIC values of the tested compounds and standards against the respective strains
are summarized in supplementary data Table S2 and S3. It is important to note that in most
of the cases, metal complexes exhibited a more inhibitory effect than the L. This activity was
found to be enhanced on coordination of the ONO donor atoms of the L with metal ions. This
enhancement in the activity of the complexes over the ligand can be explained on the basis of
chelation theory [39, 40]. It is also known that chelation enhances the ligand to act as more
powerful bactericidal/fungicidal agents by inhibiting the growth of bacteria/fungi, thus zone
of inhibition of metal complexes was found to be higher compared to the ligand. The
enhancement in the antimicrobial activity may be rationalized on the basis that ligands
mainly possess azomethine (C=N) bond. More over in metal complex, the positive charge of
the metal ion is partially shared with the hetero donor atoms (N and O) of the ligand and there
may be π-electron delocalization over the whole chelating system [41] as a result the
lipophilic character of the metal chelates was increased and favour their permeation through
the lipoid layer of the bacterial cell membranes and blocking of the metal binding sites in the
enzymes of microorganisms. In general, metal complexes are more active than the ligands
because metal complexes may serve as a vehicle for activation of ligands as the principal
cytotoxic species [42].
3
.8.2. DNA cleavage activity
From the DNA cleavage activity gel picture (Fig. 3), it is clearly evident that there
was a difference in the migration of the lanes (Lane 1 to 5) of L and its [Cu(L)(Cl)(H O) ],
2
2
1
0

[
Co(L) ], [Ni(L) ] and [Zn(L)(Cl)(H O) ] complexes respectively. Control experiments
2 2 2 2
clearly revealed that the untreated DNA does not show any cleavage (Lane C), whereas all
the compounds have exhibited cleavage of pBR322 DNA. On the basis of these outcomes, we
can infer that all the newly synthesized compounds under present study are good pathogenic
microorganism inhibitors. These compounds inhibit the growth of pathogenic organism by
cleaving the genome [43].
3
.8.3. Cytotoxicity
It is an excellent tool for monitoring the preliminary assessment of toxicity. Brine
shrimp lethality bioassay is a development in the assay procedure of bioactive compounds,
which indicates cytotoxicity as well as a wide range of pharmacological activities
(viz.antiviral, anti-cancer, insecticidal, pesticidal, AIDS, etc.) of the compounds [44]. Results
for the lethality were noted in terms of number of deaths of larvae. The summary of the
cytotoxicity assay results were presented in Table 4. The standard anti-cancer drug
-4
Bleomycin showed the LD value of 0.410 X 10 . Among all the tested compounds [Co(L) ]
5
0
2
-4
complex showed the highest cytotoxicity with LD50 value 1.106 X 10 , followed by
-4
[
Zn(L)(Cl)(H O) ] complex with LD value1.112 X 10 respectively. On the other hand, the
2 2 50
L and its [Cu(L)(Cl)(H O) ], [Ni(L) ] complexes were showed moderate activity.
2
2
2
4
. Conclusions
A new octahedral [Cu(L)(Cl)(H O) ], [Co(L) ], [Ni(L) ] and [Zn(L)(Cl)(H O) ]
2
2
2
2
2
2
complexes were synthesized with ONO donor Schiff base ligand 2-((7-hydroxy-4-methyl-2-
oxo-2H-chromen-8-yl)methylene)-N-(4-phenylthiazol-2-yl)hydrazinecarboxamide(L). The
spectral data suggest the octahedral coordination geometrical arrangement for all the
complexes having 1:2 stoichiometric ratio of the type [M(L) ] (M = Co and Ni) and
2
[
M(L)(Cl)(H O) ] (M = Cu and Zn). Thermal analyses data provides the information
2 2
regarding the presence of coordinated water molecules in [Cu(L)(Cl)(H O) ] and
2
2
[
Zn(L)(Cl)(H O) ] complexes. The antimicrobial activity of all the metal complexes was
2 2
found to be enhanced on the formation of complex. The results of DNA cleavage studies infer
that, all the newly synthesized compounds are able to carry out an efficient cleavage of
pBR322 DNA. In addition to that, the [Co(L) ]and [Zn(L)(Cl)(H O) ] complexes showed
2
2
2
good cytotoxic property. Hence from these observations, it was concluded that L and its
metal complexes gave remarkable, versatile and valuable information of coordination
compounds and also they are found to be powerful bioactive compounds. Based on the
spectral data following geometries have been proposed for the metal complexes:
1
1

Proposed structures of the [Cu(L)(Cl)(H O) ], [Co(L) ], [Ni(L) ] and [Zn(L)(Cl)(H O) ]
2
2
2
2
2
2
complexes
Acknowledgments
One of the authors (Nagesh Gunvanthrao Yernale) is grateful to DST New Delhi for the
award of DST-INSPIRE SRF [DST/AORC-IF/UPGRD/2014-15/IF120091]. Authors extend
their thanks to IIT Bombay, STIC Cochin University, SAIF Punjab University, for providing
spectral data. Authors are also thankful to BioGenics Research and Training Centre in
Biotechnology, Hubli for biological studies.
Supplementary Data
Supplementary data associated with this article i.e., Fig’s., Tables and Schemes are provided
in electronic form.
Declaration of interest
The authors declared no conflicts of interest.
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GRAPHICAL ABSTRACT
•
•
Synthesis of new class of bioactive metal complexes containing thiazole core.
All the newly prepared compounds showed complete cleavage of super-coiled DNA
pBR322.
1
5

-1
Table 1 - IR spectral data (cm ) of Schiff base ligand (L) and its metal complexes
Ligand/
Complexes
L
νOH
νH2O
νNH
νNH
νC=O
νC=O
νC=N
νC-O
νM-O νM-N νM-Cl
(phenolic)
(amide) (thiazole) (lactone) (carbonyl) (azomethine) (phenolic)
3420
--
--
3430
--
3232
3226
3237
3201
3225
3048
3050
3050
3050
3063
1710
1728
1709
1700
1705
1692
1683
1687
1626
1685
1663
1614
1631
1582
1619
1270
1291
1291
1295
1315
--
--
--
[
[
[
[
Cu(L)(Cl)(H O) ]
528
540
520
509
449 366
2
2
Co(L)2]
Ni(L)
Zn(L)(Cl)(H O) ]
--
495
465
--
--
2
]
--
--
3372
473 343
2
2
Table 2 - Electronic spectral data and ligand field parameter data
-1
′
Complexes
Transitions in cm
Dq
B
β
β%
ν2/ν1 LFSE
*
-1
-1
ν1
ν2
ν3
(cm ) (cm )
(k cal.)
[
[
[
Cu(L)(Cl)(H
2
O)
2
]
15149-17986
--
--
--
--
--
28.40
15.42
31.40
Co(L)2]
7887
9160
16887 19695
14946 25168
894
916
861
841
0.886 11.32 2.14
0.808 31.40 1.63
2
Ni(L) ]
*
Calculated values
16

Table 3 - Thermal degradation pattern of metal complexes with respect to temperature
Metal
Complexes
Temperature
( °C)
Weight loss
(%)
Metallic
residue (%)
Assignment
Obs. Calc. Obs. Calc.
[
Cu(L)(Cl)(H O) ]
165
5.84
6.50
--
--
Loss due to two coordinated water molecules
2
2
310
10.27 9.66
--
--
Loss due to a coordinated Chlorine atom and CH species of
3
coumarin moiety
3
4
40
30
20.68 19.89
24.42 27.23
--
--
--
--
Loss due to C
Loss due to C H species of thiazole moiety
5 2
HO molecule of coumarin moiety
8
6
Up to 731
--
--
11.22 12.90 Loss due to remaining organic moiety
[
Co(L)2]
Ni(L)2]
258
9.33
46.35 45.14
43.20 41.71
9.36
--
--
--
--
--
--
Loss of a C H O species of coumarin moiety
4 4 2
3
3
04
75
Loss of two moles of 2-amino-4-phenylthiazole molecules
loss of C11 group of coumarin moiety
6 3
H O
Up to 632
--
--
12.11 13.97 Loss due to remaining organic moieties.
[
154
11.59 11.04
36.73 36.85
--
--
--
--
Loss due to CH group and C H O species of coumarin moiety
3
4
4
2
3
58
72
7 2 2 9 8 2
Loss due to C H O molecule of coumarin and C H N S
molecule of thiazole moiety
Loss due to C H S species
3
26.95 26.60
--
--
8
6
Up to 380
--
--
10.14 12.13 Loss due to remaining organic moiety
[
Zn(L)(Cl)(H O) ]
160
7.02
9.78
6.48
9.62
--
--
--
--
Loss due to two coordinated water molecules
Loss due to coordinated Chlorine atom and methyl species of
coumarin moiety
2
2
220
3
4
34
90
36.44 37.49
26.34 23.51
--
--
--
--
Loss due to a molecule of 2-amino-4-phenylthiazole
Loss due to C H species and CO molecule
2 2
Up to 731
--
--
10.71 12.23 Loss due to remaining organic moiety.
17

Table 4 - Brine shrimp bioassay data
Compounds
LD (M/mL)
50
-4
-4
-4
-4
-4
-4
L
2.262 X 10
2.142 X 10
1.106 X 10
2.216 X 10
1.112 X 10
0.410 X 10
[
Cu(L)(Cl)(H O) ]
2 2
[
Co(L)2]
Ni(L)
Zn(L)(Cl)(H O) ]
[
2
]
[
2
2
Bleomycin
Fig. 1 - ESR spectrum of [Cu(L)(Cl)(H O) ] complex
2
2
1
8

Fig. 2 - The Thermogram of [Cu(L)(Cl)(H O) ] complex
2
2
Fig.3 - DNA cleavage on plasmid pBR 322
2 2 2
M: Standard DNA, C: Control DNA (untreated pBR 322), 1: L, 2:[Cu(L)(Cl)(H O) 3:[Co(L) ]
4
:[Ni(L) ] 5:[Zn(L)(Cl)(H O) ]
2 2 2
1
9

Figure captions:
1
2
3
2 2
. Fig. 1 - ESR spectrum of [Cu(L)(Cl)(H O) ] complex
. Fig. 2 - The Thermogram of [Cu(L)(Cl)(H O) ] complex
2
2
. Fig. 3 - DNA cleavage on plasmid pBR 322
M: Standard DNA, C: Control DNA (untreated pBR 322), 1: L, 2:[Cu(L)(Cl)(H O)
2
2
3
:[Co(L) ] 4:[Ni(L) ] 5:[Zn(L)(Cl)(H O) ]
2 2 2 2
2
0

Research Highlights:
•
•
Synthesis of Octahedral Metal (II) complextes.
The synthesized complexes shows promising antimicrobial activities compared to
ligands.
•
•
Thermogravimetric studies for Cu(II) and Zn(II) complexes indicated the presence of
coordinated water molecules.
The prepared complexes have good ability to cleave the pBR322 DNA.

Research Article
Preparation of Octahedral Cu(II), Co(II), Ni(II) and Zn(II) Complexes Derived from 8-
formyl-7-hydroxy-4-methylcoumarin: Synthesis, Characterization and Biological study
1
,2
1,
Nagesh Gunavanthrao Yernale and Mruthyunjayaswamy Bennikallu Hire Mathada *
*
1
Department of Studies and Research in Chemistry, Gulbarga University,
Kalaburagi - 585 106, Karnataka, INDIA.
2
Department of Chemistry, Guru Nanak PG Centre, Bidar – 585 403, Karnataka, INDIA.
Tel.: +91-9448830318; E-mail: bhmmswamy53@rediffmail.com
Conflict of Interests:
The authors do not have any agreement, financial assistance or sponsorship from any institution
except providing the data which are of purely academic interest and to encourage young
researchers in India. The IR spectra of compounds were recorded on Perkin Elmer-Spectrum
1
RX-I FTIR spectrophotometer using KBr disc technique, H NMR spectra were recorded on
Bruker Avance II 400 MHz NMR Spectrometer in ꢀ6-DMSO using TMS as an internal standard,
ESI mass spectra were recorded by electrospray ionization (ESI) on a Waters Micromass Q-Tof
Micro spectrometer, ESR spectrum was recorded on JES-FA200 ESR spectrometer, and so forth.
These names are mentioned in the experimental protocol as these are the instrument models and
it is mandatory for authors to mention the instrument models used to scan the spectra of
unknown compounds. Otherwise, the corresponding author or coauthor has no-direct financial
relationship with the commercial identity in any form of the institutes mentioned in our paper.