DNA interaction, in vivo and in vitro cytotoxicity, reactive oxygen species, lipid peroxidation of –N, S donor Re(I) metal complexes

Article abstract of DOI:10.1007/s11030-020-10040-2

Abstract: N, S donor ligands (L¹–L⁵){L¹–L⁵ = 1,5-bis(4-chlorophenyl)-3-(thiophen-2-yl)-4,5-dihydro-1H-pyrazole (L¹), 1-(4-bromophenyl)-5-(4-chlorophenyl)-3-(thiophen-2-yl)-4,5-dihydro-1H-pyrazole (L²), 5-(4-chlorophenyl)-3-(thiophen-2-yl)-1-(p-tolyl)-4,5-dihydro-1H-pyrazole (L³), 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(thiophen-2-yl)-4,5-dihydro-1H-pyrazole (L⁴), 5-(4-chlorophenyl)-1-(4-nitrophenyl)-3-(thiophen-2-yl)-4,5-dihydro-1H-pyrazole (L⁵)} were synthesized by Claisen–Schmidt condensation and characterized by spectrometric methods. The complexes (I–V) were synthesized by ligand combination followed by metal chelation. The binding of the rhenium complexes to Herrin sperm DNA was monitored by UV spectroscopy and viscosity measurements. The groove binding was suggested as the most possible mode, and the K_b values of the complexes were calculated. The mode of interaction was furthermore confirmed by molecular docking. Brine shrimp lethality and Saccharomyces cerevisiae cytotoxicity against the eukaryotic and prokaryotic cells showed the toxic nature of the synthesized compounds. All compounds were found active against S. cerevisiae, which was confirmed by increased ROS production, and DNA damage as compared to untreated yeast cell culture. The oxidative harm to cell structures was affirmed by lipid peroxidation. An antimicrobial study was carried out by estimating minimum inhibitory concentration against two Gram-positive and three Gram-negative bacteria. All complexes show good antiproliferative activity against the HCT 116 cell line. All synthesized complexes are biologically more active than the corresponding ligands. Graphic abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s11030-020-10040-2

Molecular Diversity
https://doi.org/10.1007/s11030-020-10040-2
ORIGINAL ARTICLE
DNA interaction, in vivo and in vitro cytotoxicity, reactive oxygen
species, lipid peroxidation of –N, S donor Re(I) metal complexes
Reena R. Varma1 · Juhee G. Pandya2 · Jyoti Sharma3 · Chandramani Pathak3 · Mohan N. Patel1
Received: 16 June 2019 / Accepted: 20 January 2020
© Springer Nature Switzerland AG 2020
Abstract
N, S donor ligands (L1–L5){L1–L5 = 1,5-bis(4-chlorophenyl)-3-(thiophen-2-yl)-4,5-dihydro-1H-pyrazole (L1),
1-(4-bromophenyl)-5-(4-chlorophenyl)-3-(thiophen-2-yl)-4,5-dihydro-1H-pyrazole (L2), 5-(4-chlorophenyl)-3-(thiophen-
2-yl)-1-(p-tolyl)-4,5-dihydro-1H-pyrazole (L3), 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(thiophen-2-yl)-4,5-dihydro-1H-
pyrazole (L4), 5-(4-chlorophenyl)-1-(4-nitrophenyl)-3-(thiophen-2-yl)-4,5-dihydro-1H-pyrazole (L5)} were synthesized by
Claisen–Schmidt condensation and characterized by spectrometric methods. The complexes (I–V) were synthesized by ligand
combination followed by metal chelation. The binding of the rhenium complexes to Herrin sperm DNA was monitored by UV
spectroscopy and viscosity measurements. The groove binding was suggested as the most possible mode, and the Kb values
of the complexes were calculated. The mode of interaction was furthermore confrmed by molecular docking. Brine shrimp
lethality and Saccharomyces cerevisiae cytotoxicity against the eukaryotic and prokaryotic cells showed the toxic nature of
the synthesized compounds. All compounds were found active against S. cerevisiae, which was confrmed by increased ROS
production, and DNA damage as compared to untreated yeast cell culture. The oxidative harm to cell structures was afrmed
by lipid peroxidation. An antimicrobial study was carried out by estimating minimum inhibitory concentration against two
Gram-positive and three Gram-negative bacteria. All complexes show good antiproliferative activity against the HCT 116
cell line. All synthesized complexes are biologically more active than the corresponding ligands.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11030-020-10040-2) contains
supplementary material, which is available to authorized users.
* Mohan N. Patel
jeenen@gmail.com
1
Department of Chemistry, Sardar Patel University,
Vallabh Vidyanagar, Gujarat 388 120, India
2
B. R. Doshi School of Bioscience, Sardar Patel University,
Vallabh Vidyanagar, Gujarat 388 120, India
3
Department of Cell Biology, School of Biological Sciences
and Biotechnology, Indian Institute of Advanced Research,
Koba Institutional Area, Gandhinagar, Gujarat 382007, India
Vol.:(0123456789)
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Molecular Diversity
Graphic abstract
Keywords DNA binding · Cytotoxicity · Saccharomyces cerevisiae cell · HS-DNA · ROS · Lipid peroxidation · HCT116
[8]. The fpronil is a broad spectrum insecticide that dis-
rupts the insect central nervous system by blocking the
passage of chloride ions through the GABA receptor
and glutamate gated chloride channels (Glu Cl), compo-
nents of the central nervous system [9]. The fomepizole
or 4-methylpyrazole is used as an antidote in suspected
methanol or ethylene glycol poisoning [10]. A part from
medicinal uses the role of 4-methylpyrazole in coordina-
tion chemistry has been widely studied [11].
Introduction
Metal carbonyls are coordination complexes of transition
metals having carbon monoxide as a ligand. In the last
decade, the use of CO as a cytoprotective and homoeo-
static molecule has received increasing attention in medi-
cine due to its documented benefcial therapeutic efects
[1, 2]. Several carbon monoxide releasing molecules based
on transition metals are important due to their ease of
fragmentation by consecutive losses of CO in a controlled
manner [3]. Carbon monoxide under the physiological
condition to cause vasodilation, anti-infammatory, anti-
coagulant efects [4].
The focus of our research on transition metal com-
plexes with pyrazoline products is due to the theoretical
and practical signifcance of these compounds. Their rep-
resentatives expressed antipyretic [12], antirheumatic [13]
and antimicrobial [14] actions. Some of them are active
components of products with potential antitumour activity
[15–17]. In this study, we report the synthesis of orga-
nometallic Re(I) complexes (I–V) with ligands (L1–L5)
and characterization by diferent spectroscopy. The mode
of DNA binding with the complexes was confrmed by
Heterocyclic moiety represents the core structure for
the number of drugs [5]. The well known pyrazoline-based
drug betazole is a H2 receptor agonist. The celecoxib is
a non-steroidal infammatory drug (NSAID) used in the
treatment of osteoarthritis [6], rheumatoid arthritis [7],
acute pain, painful menstruation and menstrual symptoms
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Molecular Diversity
UV–visible, and viscosity measurement. The cytotoxic-
ity of compounds was evaluated by brine shrimp assay,
and the genotoxicity was performed on Saccharomyces
cerevisiae to fnd the percentage viability, the DNA was
extracted and further used for the gel electrophoresis to
fnd toxicity of compounds on DNA. Finding ROS activity
of synthesized compounds against the yeast DNA can be
a better future application to kill tumour cell by reactive
oxygen species in the presence of UV radiation and lipid
peroxidation process. The efect of compounds on cancer
cells was checked by cell proliferation against HTC 116
cell line.
Synthesis
of 3‑(thiophen‑2‑yl)‑4,5‑dihydro‑1H‑pyrazole
ligands (L1–L5)
The synthesis and characterization details of ligands and
Re(I) complexes are shown in supplementary material 2.
The general reaction for the synthesis of ligands (L1–L5)
1
and Re(I) complexes (I–V) is shown in Fig. 1. H NMR
and 13C NMR spectra of ligands are shown in supplemen-
tary material 3 and 4, respectively.
Results and discussion
Materials and methods
Fourier transform infrared spectroscopy
magnetic moments, conductance measurements
and electronic spectral analysis
Details of materials, and methods are shown in supple-
mentary material 1.
Consequences of the FT-IR spectra of the thiophene-based
1,3,5-trisubstituted pyrazole subsidiaries free ligands
(L1–L5) demonstrate the peak for pyrazole ring contain
ν(> C=N) extending groups at 1543–1596 cm−1 range, yet
Fig. 1 General reaction scheme
for synthesis of ligands and
complexes
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Molecular Diversity
for the complexes (I–V), ν(> C=N) groups are moved to
higher frequencies at 1597 cm−1. In free ligands, the thio-
phene heterocyclic ring contains ν(C–S–C) band is seen in
the scope of 1011–1088 cm−1. In complexes, the ν(Re–N)
and ν(Re–S) bands are observed at around 520–565 cm−1
and 440–510 cm−1, respectively [18]. Each compound
indicates (–CO) peaks at around 2030–1860 cm−1, typical
of a pseudo-C3v symmetry resulting from a facial arrange-
ment of carbonyls [19].
charge transfer (π–π*) (Fig. 2). From these, Re(I) metal
complexes demonstrate an octahedral geometry [20].
Biological applications of synthesized ligands
and complexes
Cellular level bioassay using Saccharomyces cerevisiae cells
(Saccharomyces cerevisiae yeast)
At room temperature magnetic moment values of
rhenium(I) complexes are found to be zero, indicates it
has no unpaired electron i.e. low spin t2g6 eg0 confgura-
tion, which suggest that all the rhenium(I) complexes are
diamagnetic in nature and +1 oxidation state of metal ion.
The molar conductance values of all the low spin
rhenium(I) complexes are 2.03–20.0 Ω−1 cm2 mol−1. It
suggests that the Re(I) complexes are non-ionic and non-
electrolytic in nature.
The cellular level cytotoxicity of ligands L1–L5 and com-
plexes (I–VI) was carried out using Saccharomyces cerevi-
siae cells in terms of % viability. Cell passing brought about
by lethality of the chemically synthesized compounds could
be efectively seen by vital staining which is appeared in
Fig. 3. The in vitro toxicity was found to vary with the type
of substituent present and concentrations of the synthesized
complexes i.e. 20 µg/mL, 40 µg/mL, 60 µg/mL, 80 µg/mL,
100 µg/mL, respectively. The results show that an increase
in the concentration of compounds increases the cytotoxic
nature of compounds and decreases % viability of cells
(Fig. 4). The metal salt does not have ability to release the
CO, but the presence of heterocyclic molecules as coordi-
nation ligands may potentiate the CO-releasing ability of
complexes; therefore, complexes show good activity as com-
pared to ligands. Complex-V, shows maximum cytotoxic,
while complex-I and II exhibit moderate cytotoxic, and
complex-III, and IV exhibit less cytotoxic. The increasing
order of % viability of ligands and complexes is L4 < L3 <
L2 < L1 < L5 < IV < III < II < I < V, respectively.
The electronic spectra of the synthesized compounds
were recorded at room temperature in the DMSO solution
as the standard solution. Three bands were observed in
electronic spectra of complexes (I–V): one band ranging
in 355–502 nm region assign to metal to ligand charge
transfer (MLCT), second going from 310 to 355 nm region
attributed to the ligand to metal charge transfer (n–π*)
and third ranging from 255 to 310 relegate to ultra-ligand
In vivo bioassay (brine shrimp lethality bioassay)
The BSLB is a valuable method for assurance of lethal
nature of synthesized compounds and furthermore demon-
strate the pharmacological exercises of the compounds, it is
widely used in the bioassay [21–23]. The in vivo cytotoxicity
was performed by using potassium dichromate as positive
Fig. 3 Efect of compounds on S. cerevisiae cells, dead cells are seen
Fig. 2 Electronic spectra of the ligands and their metal complexes
dark whereas live cells are seen transparent
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Molecular Diversity
Fig. 4 Efect of compounds on
Saccharomyces cerevisiae cells
control [22, 23]. The result for the toxicity means lethality
regarding the demise of the larvae.
graph, the LC50 value of the compounds was calculated,
complex-IV is the most potent amongst all the compounds.
The complexes are increasingly cytotoxic as compared to
the ligands.
The demise rate of nauplii was observed with increas-
ing the concentration of the compounds. A plot of the log
of the sample’s concentration versus percentage (%) of
mortality showed a linear correlation (Fig. 5). The syn-
thesized ligands have less death rate as compared to the
synthesized complexes. The increasing mortality rate of
ligand and complexes is IV > I>II > V>L4 < L3 > III >
L2 > L1 > L5 > DMSO > potassium dichromate. From the
In vitro antimicrobial screening
The antimicrobial efcacies of the ligands and the com-
plexes were tested against two Gram-positive (S. aureus,
B. subtilis) and three Gram-negative (S. marcescens, P.
Fig. 5 Plot of LC50 values of diferent compounds in µg/mL using Brine shrimp. A plot of log concentration versus percentage of mortality in
linear correlation
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Molecular Diversity
Fig. 6 Efect of diferent
concentrations (μM) of metal
salt, free ligands and their
rhenium(I) complexes on two
gram(+ve) and three gram(−ve)
microorganisms
Table 1 Minimum inhibitory
concentration (MIC) values of
the rhenium(I) complexes (I–V)
and ligand (L1–L5)
Compounds
Gram positive
Gram negative
S. aureus
B. subtilis
S. marcescens
P. aeruginosa
E. coli
Metal salt
L1
>2500
305
310
315
265
292
78
>2500
315
318
312
315
290
80
>2500
322
308
305
272
275
70
>2500
295
299
300
265
284
60
>2500
298
296
285
275
270
63
L2
L3
L4
L5
Complex-I
Complex-II
Complex-III
Complex-IV
Complex-V
60
90
72
62
69
86
82
68
74
82
60
73
76
72
70
66
78
80
68
72
Fig. 7 Generation of H2O2
by Saccharomyces cerevisiae
after treatments of synthesized
compounds
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Molecular Diversity
Fig. 8 Generation of MDA
(malondialdehyde) by Sac-
charomyces cerevisiae after
treatments of synthesized
compounds
Fig. 9 Efect of synthesized
Re(I) complexes conjugate on
(HCT116) cancer cell prolif-
eration (MTT assay). Error
bar represent mean of three
independent experiments
aeruginosa, E. coli) bacteria. Bacterial culture with DMSO
in the absence of compounds was used as positive control
in in vitro antibacterial activity. The data reveals that all
complexes have less MIC values than neutral bidentate
ligands and penta-carbonyl chloro rhenium(I). For the syn-
thesized complexes, two variables are applicable, the nature
of ligands which are bound to metal ions in a multidentate
fashion, and presence of CO group in complexes [24]. We
observed that the antimicrobial activity of all complexes
against various microorganisms is superior to that of the
particular ligands, as shown in Fig. 6. The MIC values of the
complexes, ligands, and penta-carbonyl chloro rhenium(I)
are observed in the range of 60–90 μM, 280–320 μM, and >
Table 2 IC50 value of synthesized complexes and platinum-based
drugs
Complexes
IC50 values (μg/mL)
I
II
III
IV
12.42
104.06
125.62
>500.00
<10.00
15.49
V
Cisplatin
Carboplatin
Oxaliplatin
>111.37
22.66
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Molecular Diversity
concentration increased with increasing the test sample con-
centration. The increasing order of H2O2 accumulation is L3
< L4 < L2 < L1 < L5 < III < IV < II < I < V (Fig. 7). From
the results, complexes show comparatively higher toxic
efect than ligands and it means ROS depends on the metal
concentration, functionality on compounds. These was fur-
ther confrmed by observing their efects on DNA integrity
of Saccharomyces cerevisiae as higher H2O2 causes DNA
damage.
Lipid peroxidation
Hemoproteins and transition metals related with biological
membrane improve the colour formation in the thiobarbi-
turic corrosive measured by advancing the development of
oxy and peroxy radicals from the metal-catalysed break-
down of hydro peroxides amongst the warming of the layer
with the TCA–TBA–HCI reagent [26]. Unadulterated lipid
emulsions and liposomes are especially helpless to improve
metal-catalysed autoxidation [27]. In addition, malondial-
dehyde responds with tissue parts to frame cross-connected
lipofusion pigments, in this way diminishing its intracel-
lular concentration (Fig. 8). Therefore, the in vivo malondi-
aldehyde concentration isn’t probably going to refect per-
oxidatives events happening inside biological membranes
[28]. From the result the MDA (malondialdehyde) content
higher in complexes than the ligands, which means the toxic
nature of complexes is higher than the ligands, the data are
summarized in supplementary material 6. The presence of
rhenium metal carbonyl with heterocyclic ligands enhanced
the H2O2 production in complexes as compared to ligands.
Greater ability of metal complexes to release CO may be the
reason for enhancing the production of H2O2. Complex-V
have highest malondialdehyde concentration than other due
to the presence of a nitro group. The increasing order of
MDA (malondialdehyde) accumulation is L3 < L4 < L2 <
L1 < L5 < III < IV < II < I < V.
Fig. 10 Absorption spectra of ligand (L1) and complex(I), Inset: plot
of [DNA]/(εa−εf) versus [DNA], the change in absorption with
increase in concentration of DNA
Fig. 11 The Kb (binding constant) values of ligand (L1–L5) and their
metal complex (I–V)
2500 μM, respectively (Table 1). Complex-V and complex-
IV are the most active amongst all the complexes, due to the
presence of the nitro and chlorine group in the thiophen-
2-yl-4,5-dihydro-1H-pyrazole ligands. The increasing order
of MIC value is Re(CO)5Cl < L4 < L3 < L2 < L1 < L5 < IV
< III < II < I < V.
Antiproliferative study
The antiproliferative study of Re(I) complexes against sev-
eral cancer and normal cell lines were determined by MTT
assay (Fig. 9). The subsequent IC50 qualities are determined
and listed in Table 2. It tends to be seen that Re(I) complexes
show a lot higher cytotoxicity than cisplatin against all the
human malignant growth cell lines. Increasing order of the %
cell proliferation value of the Re(I) complexes is: V > I > II
> cisplatin > oxaliplatin > carboplatin > III > IV > vehicle
control (0.8% DMSO) > DMSO. Complexes V and I show
good antiproliferative activity than cisplatin, oxaliplatin and
carboplatin.
Reactive oxygen species (ROS)
The toxic efect of synthesized compounds on growth inhi-
bition of Saccharomyces cerevisiae was evaluated by quan-
tifcation of H2O2, a reactive oxygen species (ROS) [25].
Here, we found that treated cells were showing increased
accumulation of H2O2 in contrasted with untreated cells,
data are summarized in supplementary material 5. The H2O2
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Molecular Diversity
Table 3 Binding constant (Kb), percentage hypochromicity (%H), bathochromicity (Δλ), and Gibb’s free energy (ΔG°) values of free ligands and
synthesized complexes
Compounds
λmax
Δλ (nm)a
Kb (M−1)×105b
H%c
ΔG° (Jmol−1 K−1 d
)
ΔH (Jmol−1 K−1 e
)
ΔS (Jmol−1 K−1 f
)
Bound
Free
L1
L2
L3
L4
L5
I
278.5
282.5
278
291.5
265.5
240
291.5
281
265.5
292
277.5
281.5
277
290.5
264
238.5
287
279
1
1
1
1
1.5
1.5
4.5
2
3.5
5
0.63
0.46
0.4
0.63
0.52
1.15
1.18
0.8
37.7
20.0
39.2
37.4
17.2
28.3
28.2
28.9
22.6
18.4
−36,567.1
−35,526.4
−35,064.0
−36,567.1
−35,932.1
−38,558.4
−38,643.6
−37,357.6
−40,040.9
−40,389.6
−6543.5
−6357.29
−6274.54
−6543.5
−6429.8
−6899.8
−6915.1
−6684.9
−7155.1
−7227.5
−100.75
−97.88
−96.60
−95.70
−99.0
−106.23
−106.47
−102.92
−110.35
−111.28
II
III
IV
V
262
287
1.77
2
aΔλ=diference between bound wavelength and free wavelength
bKb =intrinsic DNA binding constant determined from the UV–visible absorption spectral titration
cH%=[(Afree −Abound)/Afree]×100%
dΔG°=change in Gibb’s free energy
fΔS=entropy change
DNA interactions
Absorption titration
Binding of metal complexes with base pair of DNA via
intercalation normally fallouts hypochromism and a red shift
(bathochromism) of the absorption band [29]. Four type of
interaction of complexes with DNA i.e. the intercalation
is a direct result of a strong stacking cooperation between
an aromatic moiety of the ligand and the base pair of the
DNA, complex binds to DNA through covalent binding
generally results in hyperchromism (increase in absorption
intensity) with bathochromic shift, groove binging shows
hypochromism and small red shift, electrostatic interac-
tion shows hypochromism with no bathochromic shift [20,
30–33]. For neutral Re(I) complex showed groove binding
[34], as the successive addition of DNA (100 μL) at 10 min
time interval, there was observed decrease in absorption
(hypochromism) and a red shift (bathochromism) (Fig. 10).
The decreasing order of binding constant is V > IV > II >
I>III > L4 > L1 > L5 > L2 > L3, respectively. The binding
constant (Kb) of a complex towards DNA gives an idea about
the strength of interaction, which can be obtained by study-
ing UV–Vis. The binding constant (Kb) values were evalu-
ated from the proportion of the ratio of the slope to intercept
(Fig. 11). The absorption spectral changes were monitored at
around 273–296 nm for the investigation of the DNA bind-
ing mode and strength. As the DNA concentration increase,
the transition bands of the complexes (I–VI) exhibited
Fig. 12 The impact of expanding amounts of complexes on the rela-
tive viscosity of HS-DNA at 27 ( 0.1) °C in phosphate bufer at pH
7.2
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Molecular Diversity
Fig. 13 Molecular docking of complex-I (ball and stick) and dactinomycin with the DNA duplex (lacorice) of sequence d(ACCGACGTCGGT)2.
The complex and dactinomycin is docked inside the DNA groove
Fig. 14 Photogenic view of the cleavage of Saccharomyces cerevisiae DNA with a series of compounds using 1% agarose gel containing
0.5 μg cm−3 EtBr for 24 h at 37 °C
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Molecular Diversity
hypochromicity [hypochromicity, H% = [(Afree − Abound)/
Afree] × 100%] of about 17.2–39.2%, and bathochromicity
of 1–5 nm. The complex (IV) and the ligand (L4) exhibit the
highest percentage of hypochromicity (IV-28.9%, L4-39.2%).
Thermodynamic parameters for the interaction of complex
and HS-DNA were calculated from the thermodynamic
functions (Table 3). The negative estimation of enthalpy
change shows that the interaction process of the complex
with HS-DNA is exothermic. The negative sign for ΔG and
ΔH demonstrate that the interaction process is unconstrained
additionally the negative ΔS value indicates that hydrogen
bonding forces might play a notable role in the binding of
metal complex towards DNA [35].
Efect of compounds on the integrity of DNA
of Saccharomyces cerevisiae cells
Agarose gel electrophoresis is helpful technique to assess the
cleavage of DNA by metal-based drugs [41], to determine
the DNA damaging potential of the compounds, to decide
the components infuencing the nucleolytic efectiveness of
a compound and to think about the nucleolytic properties
of various compounds. A characteristic picture of comets
was observed, when yeast cells were exposed to increas-
ing concentrations of compounds, increase in smearing was
observed. Figure 14 shows the electrophoretic separation of
Saccharomyces cerevisiae DNA, when reacted with com-
pounds under aerobic conditions. It clearly shows that the
efectiveness of the relative binding of the complexes to
DNA is much higher than the binding efcacy of pyrazoline
ligands. The diference in the DNA cleavage efciency of
the complexes and ligands is due to the diference in binding
afnity of the ligands and complexes to the DNA. Ligands
show lesser smearing as compared to the complexes. The
damage occurs due to the toxic nature of the compound,
it suggests that the cleavage efciency of DNA is higher
in complexes than the ligands whereas control cell DNA
appeared normal as an intact band. Complexes II, III, and V
shows better cleavage efect of DNA because of the presence
of electron withdrawing (-Br, –OCH3, and –NO2), complex-I
shows moderate cleavage efect of DNA and complex-IV are
show lesser cleavage efect of DNA.
Hydrodynamic volume or viscosity measurement
Viscosity measurement was carried out on DNA by varying
the concentration of the added Re(I) complex to get an idea
of the binding mode. Groove binding typically causes less
defnitive or only a minor change in the viscosity [36]. The
values of relative specifc viscosity (η/η0)1/3 {η and η0 are the
specifc viscosities} of DNA in the presence and absence
of the Re(I) complex, respectively, are plotted against
[Re(I)complex]/[DNA] (Fig. 12).The ability to increase the
(η/η0)1/3 of DNA varies in the order V > III > I > IV > II >
L4 > L3 > L2 > L1 > L5, which parallels the DNA binding
afnity. These show that complex-I–V, is more likely to have
a DNA groove binding propensity [20, 37].
Molecular modelling with DNA sequence d(ACCGACGTC
GGT)2
Final remark
Molecular docking study was attempted to have an idea
on the binding sites and favoured orientation of the ligand
inside the DNA groove [38, 39]. The complexes and ligands
are shown by ball and stick model and DNA base pair shown
by VDW sphere using Hex 8.0 software. Structure of ligands
and complexes are drawn in .CDX format using Chem-
BioDraw Ultra 14.0, then converted to PDB format using
Chem3D (Cambridge Soft). For docking study the struc-
tural coordinates of HS-DNA were obtained from the protein
data bank (pdb id: 423D) [40]. All the docking images and
values are shown in supplementary material 7. To validate
the procedure, we carried out the molecular docking study
using dactinomycin, a known DNA groove binder. Figure 13
shows that Re(I) complexes and dactinomycin bind with the
base pair A–T, C–G, G–C, A–T (B-DNA) minor grooves of
the DNA. The increasing order of energy is L2 < L1 < L5 <
L2 < L4 < I<II < III < IV < V. The study validate the groove
binding region as the binding site for all the compounds.
A series of substituted thiophene-based 1,3,5-trisubstituted
derivative-based organometallic rhenium(I) complexes
were synthesized and well characterized. The organometal-
lic complexes show better antibacterial, cytotoxicity, reac-
tive oxygen species, lipid peroxidation, genotoxicity, DNA
binding and DNA cleavage activities. Binding constant (Kb)
values of complexes are higher than the ligands, it shows
the higher binding capability of complexes with DNA and
groove binding mode of interaction. There was a minor
change in the relative specifc viscosity (η/η0)1/3 (η and η0 are
the specifc viscosities) of DNA in presence and absence of
the Re(I) complex, which validates the groove binding mode
as suggested by UV–visible studies. In molecular modelling,
docking energy of complexes are higher than the ligands.
The presence of a diferent substitution in thiophene-based
1,3,5-trisubstituted environment and presence of carbon-
yls directly linked to rhenium(I) improves the antibacterial
activity. All the complexes show potential in vitro cytotoxic
nature as confrmed by cellular level bioassay, reactive oxy-
gen species and lipid peroxidation studies compared to free
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Molecular Diversity
diperoxovanadate complex and pyrazole-like ligands. Spectrochim
Acta A 75:1095–1099. https://doi.org/10.1016/j.saa.2009.12.063
12. Ivanenkov Y, Balakin K, Tkachenko S (2008) New approaches to
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https://doi.org/10.2165/0126839-200809060-00005
ligands. It is probable that in the near future a range of new
drugs will be developed based on CO-releasing molecules
for the treatment of cardiovascular function, as well as neu-
rodegenerative and infammatory-related diseases. All syn-
thesized compounds showed promising hope for application
in pharmaceuticals.
13. Graneto MJ, Kurumbail RG, Vazquez ML, Shieh HS, Pawlitz
JL, Williams JM, Stallings WC, Geng L, Naraian AS, Koszyk FJ
(2007) Synthesis, crystal structure, and activity of pyrazole-based
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org/10.1021/jm0611915
Acknowledgements The authors are thankful to the Head, Department
of Chemistry, Sardar Patel University, Vallabh Vidyanagar, Gujarat,
India, for providing necessary research facilities, Sardar Patel Uni-
versity, Vallabh Vidyanagar, CPEPA, UGC, New Delhi for providing
chemicals facility, DST-PURSE Sardar Patel University, Vallabh Vidy-
anagar for LC–MS analysis.
14. da Silva PEA, Ramos DF, Bonacorso HG, Agustina I, Oliveira
MR, Coelho T, Navarini J, Morbidoni HR, Zanatta N, Martins MA
(2008) Synthesis and in vitro antimycobacterial activity of 3-sub-
stituted 5-hydroxy-5-trifuoro [chloro] methyl-4, 5-dihydro-1H-1-
(isonicotinoyl) pyrazoles. Int J Antimicrob Agents 32:139–144.
https://doi.org/10.1016/j.ijantimicag.2008.03.019
15. Reisner E, Arion VB, Keppler BK, Pombeiro AJ (2008) Electron-
transfer activated metal-based anticancer drugs. Inorg Chim Acta
361:1569–1583. https://doi.org/10.1016/j.ica.2006.12.005
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J, Opolski A, Wietrzyk J, Wojdat E (2002) Rhodium(III) com-
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Compliance with ethical standards
Conflict of interest The authors declared that they have no confict of
interest.
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