Synthesis and characterization of new metal complexes containing Triazino[5,6–b]indole moiety: In vitro DNA and HSA binding studies

Article abstract of DOI:10.1016/j.molstruc.2021.131203

The present study reports the synthesis, structural characterization of Ni(II) (1,3) and Cu(II) (2,4) metal complexes of Schiff-base (L) derived from 5H-[1,2,4]triazino[5,6-b]indol-3-amine and salicylaldehyde moiety. The coordination sphere of Cu(II)/Ni(I

Full text of DOI:10.1016/j.molstruc.2021.131203

Journal of Molecular Structure 1246 (2021) 131203
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Synthesis and characterization of new metal complexes containing
Triazino[5,6–b]indole moiety: In vitro DNA and HSA binding studies
∗
Reem L.B. Alanazi, Mehvash Zaki , Wafa A. Bawazir
Department of Chemistry, King Abdulaziz University, P.O. Box 80203, Jeddah, Saudi Arabia
a r t i c l e i n f o
a b s t r a c t
Article history:
The present study reports the synthesis, structural characterization of Ni(II) (1,3) and Cu(II) (2,4) metal
complexes of Schiff-base (L) derived from 5H-[1,2,4]triazino[5,6-b]indol-3-amine and salicylaldehyde moi-
Received 18 March 2021
Revised 24 July 2021
Accepted 27 July 2021
Available online 28 July 2021
ꢀ
ety. The coordination sphere of Cu(II)/Ni(II) was completed by tethering secondary ligand 2,2 –Bipyridine
and 1,10 phenanthroline to obtain the final complexes 1–4, respectively. The spectral analysis of com-
plexes 1 and 3 suggested square planar geometry while complexes 2 and 4 acquire the octahedral geom-
etry around the metal centers. In vitro DNA binding profiles of the newly synthesized metal complexes
1–4 with calf thymus DNA (CT DNA) were explored by employing electronic absorption titrations and
fluorescence spectral studies. The results revealed that complexes 1–4 bind to DNA through electrostatic
surface binding mode along with partial intercalation in the minor groove. Moreover, complexes 3 and 4
Keywords:
Triazino[5,6–b]indole
Cu(II)/Ni(II) metal complexes
In vitro DNA binding
HSA binding
4
have stronger DNA binding propensity with higher intrinsic binding constant Kb values of 1.9 × 10 and
FRET
4
–1
4.8 × 10
M , respectively. Additionally, HSA binding studies of ligand L and metal complexes 1–4 sup-
Molecular docking
port the static quenching mechanism and alterations in the microenvironment around Trp–214 residues
causing conformational distortions in the HSA secondary structure. Furthermore, molecular docking stud-
ies of complexes 3 and 4 with DNA and HSA confirms that both specifically binds in G–C rich regions of
the DNA minor groove and subdomain IIA pocket of HSA near the Trp–214 residue.
©
2021 Elsevier B.V. All rights reserved.
1
. Introduction
to its resemblance with purines and broad biological properties
such as anti-inflammatory, antimicrobial and antitumor activity [7–
9]. The combination of 1,2,4 triazine moieties with other hete-
rocyclic structures such as indole, pyrazole and thiophene rings
leads to the generation of ligand scaffold with enhanced phar-
macological properties [10]. This synthesized triazino[5,6b]indole
amine and its derivatives exhibited a wide range of biological
activities such as antiparasitic, antihypertensive, antimalarial, an-
tibacterial, and antifungal activities [11–15]. In vitro studies of tri-
azino[5,6b] indoles had shown that most of them act as antivi-
ral agents specifically against rhinovirus [16]. Moreover, the for-
mation of Schiff base molecule by the condensation of bioactive
triazino[5,6b]indole amine with salicylaldehyde leads to the de-
velopment of new chemotherapeutic agents. Furthermore, tether-
ing the biologically active Schiff base ligand with transition metal
ions increases the pharmacological activity manyfold, facilitates the
DNA interaction and improves the therapeutic potential [17]. In the
past decade, the interaction of many Schiff base transition metal
complexes with DNA has been investigated because DNA is eas-
ily prone to damage thereby inducing the cellular degradation in
diseased cells [18]. In particular, Schiff base Cu(II) and Ni(II) metal
complexes exhibited interesting biological properties (such as an-
tipyretic, anti-inflammatory, anti-diabetic, anti-bacterial, anti-HIV
The interaction of metal complexes with DNA is one of the
most emerging areas of inorganic medicinal chemistry. In the re-
cent years, rapid advances has been made for the development
of the new improved metal based drugs whose ultimate target
is DNA [1–3]. The design of an organic framework that enhances
the DNA binding ability of metal complexes is necessary in order
to overcome the drawbacks related to platinum drugs. The litera-
ture revealed that many DNA binding agents that bind with DNA
through non–covalent interactions such as groove binding, interca-
lation and electrostatic interaction is crucial for the development
of chemotherapeutic drugs [4–6]. Therefore, an approach to im-
prove the DNA binding potential of metal complexes is the use
of planar aromatic pharmacophore containing heteroatom’s that
provides the coordinating center for the metal ion in order to
structurally feature the molecule for the better stacking interac-
tion within the base pairs of the DNA helix. This brings about
conformational changes in DNA. In this regard, 1,2,4 triazine moi-
eties are considered as the attractive heterocyclic scaffold owing
∗
Corresponding author.
E-mail address: mehvashzaki@gmail.com (M. Zaki).
https://doi.org/10.1016/j.molstruc.2021.131203
0
022-2860/© 2021 Elsevier B.V. All rights reserved.

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
and anti-cancer), structural versatility and the ability to mimic
metallo-enzymes used in the catalytic oxidation/reduction in bio-
logical reactions [19–21].
600 Ultrashield NMR 600/S4/MKS spectrometer. IR spectrum was
measured on Interspec 2020 FTIR spectrometer in KBr pellets from
400–4000 cm–1. Electrospray mass spectra were conducted on the
Micromass Quattro II mass spectrometer. The electronic spectrum
was taken on Shimadzu MultiSpec–1501 UV–vis spectrophotome-
ter in DMF using 1 cm path length cuvettes. The information was
recorded in λmax/nm. Fluorescence measurements were resolute on
Hitachi (F–7000) fluorescence spectrophotometers. A complete set
of experiments dealing with the interaction of ligand and com-
plexes with CT–DNA was accomplished in buffer (5 mM Tris–HCl,
50 mM NaCl, pH = 7.3).
Apart from this, the selectivity of complexes can be further in-
creased by using some carrier molecules that can safely deliver
the complexes inside the tumor cells. The human serum albu-
min (HSA), which is abundantly available biomacromolecular car-
rier present in our circulatory system helps in the biodistribution
of various exogenous and endogenous molecules. These molecules
includes vitamins, hormones, metabolites, fatty acids, and drug
molecules. Furthermore, HSA also contribute in the transportation
of metal ions like Cu2 and Ni to regulate the osmotic pressure of
blood [22,23]. The HSA acts as biomacromolecular carrier by bind-
ing to the molecules in its binding site. In general, HSA has two
binding sites present inside its structure called Sudlow’s site I and
Sudlow’s site II present in hydrophobic cavities in subdomain IIA
and IIIA, respectively. But in some cases molecule also prefers a
third binding site III located in the hydrophobic pocket of subdo-
main IB [24]. Therefore, the binding interaction of metal complexes
with HSA is extremely important in the path of the drug develop-
ment process as it is well known that HSA selectively accumulates
inside the tumor cells leaving the healthy cells thereby reducing
the toxicity caused by the drug in the human body [25].
+
2+
2.3. Synthesis
2.3.1. Synthesis of the ligand (L)
The solution of isatin (1.47 g, 10 mmol) dissolved in ethanol
was added to a solution of aminoguanidine (1.10 g, 10 mmol) also
dissolved in 10 ml methanol and the resulting mixture was re-
fluxed continuously for 5 h to obtain the required ligand in good
yield. The molecule obtained was isolated and further reacted with
salicylaldehyde (1.22 g, 10 mmol) until the dark yellow color pre-
cipitate of ligand L was obtained in the required amount. The
dark yellow color precipitate was carefully filtered by Buchner and
washed several times with methanol and hexane, dried in a desic-
cator.
Herein, we describe the synthesis, characterization of new
Cu(II)/Ni(II) transition metal complexes [Ni(L)(Bipy)]1/2SO (1),
4
[
Cu(L)(Bipy)]1/2SO (2), [Ni(L)(Phen)]1/2SO (3) and [Cu(L)(Phen)]1/
Yield = 92%, M.P. 285 °C. Anal. (%) Calc. for C16 H11 N O: C,
4
4
5
2
SO (4)derived from new ligand (E)–2–(((5H–[1,2,4]triazino[5,6–
4
66.43; H, 3.83; N, 24.21. Found: C, 66.35; H, 3.41; N, 24.27. IR
(KBr) (νmax /cm–1): 3430.69 υ(O–H)stretch; 3197.98, 3067.66 υ(C–H)
stretch; 1157.91 υ(C–H)bend {in–plane aromatic}; 751.60 υ(C–H)bend
{out–plane aromatic}; 1616.56 υ(C=N); 1537.86 υ(C=C); 1256.20
b]indol–3–yl)imino)methyl)phenol(L). This new Schiff base ligand
scaffold is not reported in the literature and thus requires exten-
sive investigation in the field of medicinal chemistry. The newly
designed pharmacophoric ligand framework was mainly achieved
by the reaction of isatin and aminoguanidine which further re-
acted with salicylaldehyde to produce ligand L. In this regard, a
comparative in vitro DNA binding pattern of ligand L and com-
plexes 1–4 was thoroughly studied by employing biophysical stud-
ies. Furthermore, in order to get insight into the delivery pro-
cess by serum protein HSA, the in vitro HSA of ligand L and
metal complexes 1–4were conducted under physiological condi-
tions. Finally, the molecular docking studies of complex 4 showing
stronger binding affinity with DNA and HSA were performed to de-
termine the specific interaction of complex within the binding site
of biomacromolecules.
υ(C–O). 1H NMR (400 MHz, DMSO–d , δ): 12.57 (–OH); 10.26 (–
6
NH, indole); 8.91 (–CH=N); 6.53, 6.68, 7.0, 7.08, 7.11, 7.51, 7.67, 8.04
13
(aromatic–H, L); 3.4 (CH –DMSO). C NMR (100 MHz, DMSO–d ,
3
6
δ): 164.8 (–CH=N); 109.9, 113.7, 115.5, 120.1, 125.9, 129.6, 133.6,
137.1, 143.8, 147.8, 153.4 (Ar C–triazine); 161.3, 116.1, 117.7, 122.95,
–
3
127.3, 131.4, 133.6, (Ar C–salicylaldehyde). Uv–vis (1 × 10
M,
∗
∗
DMF, nm): 280 (π –π , strong), 320 (n–π , strong). ESI–MS (m/z,
+
+
DMF) 290.3 [C16 H11 N O + H ] (Fig. S2).
5
2.3.2. Synthesis of the complex (1)
The solution of Triazino[5,6–b]indole ligand L (0.289 g, 1.0
mmol) was obtained in 5 ml of DMF after 10 min of heating. The
metal salt NiSO .6H O (0.31 g, 1.2 mmol) dissolved in a minimum
4
2
2
. Experimental section
amount of distilled water was added to the hot solution of ligand
L. On the addition of metal salt, the color of the solution changes
from orange to brown along with the appearance of some pre-
2
.1. Reagents and materials
ꢀ
cipitate. The resulting solution was refluxed for 3 h and the 2,2 –
All reagents were commercially purchased and used as provided
Bipyridine (0.18 g, 1.2 mmol) dissolved in DMF was slowly added to
the refluxing solution which causes a slight change in color along
with the disappearance of the precipitate. The solution obtained
was further refluxed for 4 h at 80 °C and finally, the solution was
reduced and left for 7 days in the cupboard. After a week brown
color crystalline product was obtained and this complex 1 was
washed several times with a 1:1 methanol and dichloromethane
solution and dried in vacuo.
without extra purification. Nickel sulfate hexahydrate, Copper sul-
fate hexahydrate salicylaldehyde (Sigma–Aldrich), Isatin (Sigma–
Aldrich), Aminoguanidine (Sigma–Aldrich), 1,10 Phenanthroline,
ꢀ
2
,2 –Bipyridine (Sigma–Aldrich) and disodium salt of calf thymus
DNA (purely polymerized stored at 4°C). Trisaminomethane (TRIS)
buffer was also handled as received from Sigma–Aldrich. The sol-
vents were purchased from Merck in high purity. All reagents were
of the optimal financial grade and were used without any addi-
tional purification.
Yield = 75%, M.P. 279 °C, Anal. (%) Calc. for C26H18 N NiO S0.5:
7
5
C, 62.06; H, 3.61; N, 19.49. Found: C, 62.35; H, 3.41; N, 19.27.
–
3
M, DMF): 110 ꢁ–1 cm2 mol–1. IR (KBr) (νmax
ꢀM (1 × 10
2
.2. Methods and instrumentation
/cm–1): 3078.14 υ(C–H) stretch; 1099.08 υ(C–H)bend {in–plane aro-
matic}; 765.81 υ(C–H)bend {out–plane aromatic}; 1599.91 υ(C=N);
Carbon, hydrogen, and nitrogen percentage were resolved using
1564.77 υ(C=C); 1262.35 υ(C–O); 417.19 υ(Ni–N), 523.16 υ(Ni–
1
the CHNSO Elemental Analyzer Elementar Vario EL III model. Mo-
lar conductance was calculated using CON 510 Bench conductivity
TDS Meter at room temperature. The melting point of compounds
has been measured on the Sanyo GallenKamp melting point appa-
ratus. The 1H and 13C NMR spectra have been recorded on Bruker
O). H NMR (400 MHz, DMSO–d , δ): 9.50 (–NH, indole); 8.98
6
(–CH=N); 7.90–6.70 (aromatic–H, L and phen); 3.44 (H O); 2.49
2
13
(CH –DMSO). C NMR (100 MHz, DMSO–d , δ): 173.0 (–CH=N);
3
6
125.9, 129.6, 132.18, 134.2, 148.0, 156.9 (Ar C, Phenan); 110.7,
112.0, 115.5, 117.7, 118.8, 122.0, 127.5, 128.3, 131.8, 132.1, 134.9,
2

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
1
34.4, 140.3, 143.4, 147.5, 152.8, 160.4 (Ar C–ligand L); Uv–vis
to the hot solution of ligand L until a dark color solution was ob-
tained. The resulting solution was refluxed for 4 h and after this,
the 1,10 phenanthroline (0.21 g, 1.2 mmol) dissolved in DMF was
added drop by drop to the refluxing solution leading to the forma-
tion of a dark green color precipitate. The solution obtained was
further refluxed for 2.5 h at 80 °C and the precipitate obtained
was left overnight. The next day the dark green color precipitate
was filtered and washed several times with a 1:1 methanol and
dichloromethane solution and dried in vacuo.
–
3
∗
∗
(
1 × 10 M, DMF, nm): 275 (π –π ), 325 (n–π ), 480 (LMCT),
1
1
1
1
5
35 ( A g→ A g), 620 ( A g→ B g). ESI–MS (m/z, DMF) 552.03
1
2
1
1
+
+
[
C
H
N NiO S + H ] .
2
6
18
7
5 0.5
2
.3.3. Synthesis of the complex (2)
Similarly, the solution of Triazino[5,6–b]indole ligand L (0.289
g, 1.0 mmol) was obtained in 5 ml of DMF after 10 min of heat-
ing. The CuSO .6H O (0.32 g, 1.2 mmol) solution prepared in 3 ml
4
2
Yield = 90%, M.P. 195 °C, Anal. (%) Calc. for C28H22N CuO S0.5:
7
5
of DMF, was gradually added to the hot solution of ligand L un-
C, 59.20; H, 3.90; N, 17.26. Found: C, 59.35; H, 3.12; N, 17.50.
til a dark green color solution was obtained. The resulting solution
–
3
M, DMF): 125 ꢁ–1 cm2 mol–1. IR (KBr) (νmax
ꢀ
ꢀ
M
(1 × 10
was refluxed for 4 h and the 2,2 –Bipyridine (0.18 g, 1.2 mmol) dis-
/
cm–1): 3430.63 υ(O–H)stretch; 3056.98 υ(C–H) stretch; 1164.69 υ(C–
solved in DMF was slowly added to the refluxing solutions which
cause the appearance of the dark green color precipitate. The so-
lution obtained was further refluxed for 2 h at 80 °C and the pre-
cipitate obtained was left overnight. The next day, the dark green
color product was filtered and washed several times with a 1:1
methanol and dichloromethane solution and dried in vacuo.
Yield = 89%, M.P. 125 °C, Anal. (%) Calc. for C26H22N CuO S0.5:
H)bend {in–plane aromatic}; 856.77 υ(C–H)bend {out–plane aro-
matic}; 1593.42 υ(C=N); 1609.22 υ(C=C); 1220.63 υ(C–O); 420.31
–
3
υ(Cu–N), 520.13 υ(Cu–O). Uv–vis (1 × 10 M, DMF, nm): 285 (π
∗
∗
2
2
–
π , strong), 320 (n–π , strong), 492 (LMCT), 635, 695 ( Eg→ T g,
2
+
+
broad). ESI–MS (m/z, DMF) 617.43 [C28
H
N CuO S + H ] .
22
7
5 0.5
7
5
2
.4. DNA binding evaluations
C, 57.40; H, 4.08; N, 18.02. Found: C, 57.35; H, 4.02; N, 18.10.
–
3
M, DMF): 112 ꢁ–1 cm2 mol–1. IR (KBr) (νmax
ꢀM (1 × 10
cm–1): 3429.81 υ(O–H)stretch; 3050.21 υ(C–H) stretch; 1123.67 υ(C–
Absorption spectral study experiments were conducted by grad-
/
ually adding increasing DNA concentration to a constant volume of
H)bend {in–plane aromatic}; 770.71 υ(C–H)bend {out–plane aro-
matic}; 1589.21 υ(C=N); 1603.08 υ(C=C); 1257.91 υ(C–O); 427.92
complexes (50 μM) in each set. The intrinsic binding constant (Kb)
–
3
were calculated from the changes in the variations in absorbance
υ(Cu–N), 525.80 υ(Cu–O). Uv–vis (1 × 10 M, DMF, nm): 280 (π
∗
∗
2
2
at the maximum wavelength of the intra ligand band and the Kb
value was evaluated by using Wolf–Shimmer Eq. (1) [26];
–
π , strong), 300 (n–π , strong), 490 (LMCT), 600, 680 ( Eg→ T g,
2
+
+
broad). ESI–MS (m/z, DMF) 595.51 [C
H
N CuO S + 3H ] .
2
6
22
7
5 0.5
[
DNA]
[DNA]
1
=
+
(1)
ε
a − εf
εb − ε
Kb(εa − εf )
2
.3.4. Synthesis of the complex (3)
Similar to complex 1, Triazino[5,6–b]indole ligand L (0.289 g,
.0 mmol) was dissolved in 5 ml of DMF after 10 min of heating.
The metal salt NiSO .6H O (0.31 g, 1.2 mmol) dissolved in a min-
f
where, [DNA], εa, εf and εb are the amount of the DNA added,
apparent extinction coefficient, extinction coefficient, apparent ex-
tinction coefficient for free complex and fully bound complex, re-
spectively. However, the Kb values were calculated from the ratio
1
4
2
imum amount of distilled water was added to the hot solution of
ligand L. On the addition of metal salt, the color of the solution
changes from orange to brown along with the appearance of the
precipitate. The resulting solution was refluxed for 3 h and the 1,10
phenanthroline (0.21 g, 1.2 mmol) dissolved in DMF was slowly
added to the refluxing solution which causes the disappearance of
the precipitate and the change in color from light brown to dark
brown. The clear solution obtained was further refluxed for 4 h at
of slope to intercept in the [DNA]/(εa–ε ) vs [DNA] graph.
f
Steady state fluorescence emission studies in the range of 300–
8
00 nm were also performed by employing a methodology iden-
tical to the electronic absorption titration studies and the bind-
ing propensity of complexes were evaluated using the Scatchard
Eq. (2) and (3) [27];
C = CT (I/Io − P)(1 − P)
(2)
8
0 °C and was reduced and left for 7–8 days in the cupboard. Af-
f
ter a week brown color product obtained was isolated and washed
several times with a 1:1 methanol and dichloromethane solution
and dried in vacuo.
r/C = K(n − r)
(3)
f
Yield = 87%, M.P. >300 °C, Anal. (%) Calc. for C28H18 N NiO S0.5:
7
3
where CT is the total concentration of the complex, C is the con-
f
C, 63.79; H, 3.44; N, 18.60. Found: C, 63.35; H, 3.41; N, 18.27. ꢀ
M
centration of free complex, added, I and Io are fluorescence intensi-
ties in the presence and absence of CT–DNA, respectively, and P is
the ratio of the observed fluorescence intensity of the bound com-
plex to that of the free complex. The value of P was determined
from the intercept by plotting the graph of I/Io vs. 1/[DNA], r indi-
cates the ratio of CB (= C – C ) to the concentration of DNA, where
1 × 10 M, DMF): 120 ꢁ–1 cm2 mol–1. IR (KBr) (νmax /cm–1):
–3
(
3
8
054.01 υ(C–H) stretch; 1122.67 υ(C–H)bend {in–plane aromatic};
53.43 υ(C–H)bend {out–plane aromatic}; 1581.38 υ(C=N); 1607.51
1
υ(C=C); 1215.95 υ(C–O); 426.12 υ(Ni–N), 525.45 υ(Ni–O). H NMR
(
400 MHz, DMSO–d , δ): 9.57 (–NH, indole); 8.99 (–CH=N); 7.94,
6
T
f
7
.59, 7.39, 7.19, 6.95, 6.83 (aromatic–H, L and phen); 3.37 (H O);
2
Cb represents the concentration of complex in the bounded DNA (r
.49 (CH –DMSO). 1 C NMR (100 MHz, DMSO–d , δ): 173.55 (–
3
2
3
6
=
Cb/[DNA]). The binding parameters K is the binding constant was
CH=N); 126.2, 129.7, 132.7, 134.5, 148.4, 156.01 (Ar C, Phenan);
10.2, 112.0, 115.9, 117.7, 118.7, 122.2, 127.3, 128.4, 131.2, 132.7,
33.9, 134.4, 140.1, 143.2, 147.4, 151.3, 160.7 (Ar C–ligand L). Uv–vis
calculated from the slope and “n” is the binding site number was
1
determined from the intercept from the Plot of r/C versus r.
f
1
Similarly, in Ethidium bromide displacement studies, the EB–
DNA solution was prepared by mixing 100 μM CT–DNA and 100
μM EB in an aqueous buffer incubated for 30 min before being
used for titrations with metal complexes. The competitive inter-
action studies of complexes towards CT–DNA were evaluated by
gradually adding the volume of interacting complexes to the so-
lution of EB–DNA in each set where EB is almost fully bound to
DNA helix. The impact of the EB–DNA solution on adding the in-
creasing concentration of ligand/ metal complexes was directly im-
pacted the change in the emission profile of EB–DNA [28]. For this
–
3
∗
∗
(
1 × 10 M, DMF, nm): 281 (π –π , strong), 319 (n–π , strong),
1
1
1
1
4
80 (LMCT) 550 ( A g→ A g, broad), 625 ( A g→ B g, broad).
1
2
1
1
+
+
ESI–MS (m/z, DMF) 576.34 [C
H
N NiO S + H ] .
2
8
18
7
3 0.5
2
.3.5. Synthesis of the complex (4)
Similar to complex 2, the solution of Triazino[5,6–b]indole lig-
and L (0.289 g, 1.0 mmol) was obtained in 5 ml of DMF after 10
min of heating in a round bottom flask. In the beaker CuSO .6H O
4
2
(
0.32 g, 1.2 mmol) dissolved in 3 ml of DMF was gradually added
3

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
cm–1 range in ligand L and metal complexes 1–4. The other aro-
matic ring stretching vibrations of the ν(C=C) bond of medium
intensity were found at 1537.86 cm–1 for ligand L and 1537.86–
1603.08 cm–1 for metal complexes 1–4. The ν(C–O) stretching vi-
brations appeared as a sharp peak at 1256.20 cm–1 in ligand L
while in metal complexes the intensity of this peak was expectedly
reduced and shifted at 1262.35–1215.95 cm–1 [35]. Additionally, in
metal complexes 1–4 weak intensity peaks in the range 417.19–
experiment Stern–Volmer equation was employed to calculate the
Stern–Volmer quenching constant from the graph of Fo/F versus
[
Q]. In this Eq. (4), Fo and F is the fluorescence intensity in the
absence and the presence of the complex, respectively and [Q] is
the concentration of quencher i.e the ligand or metal complex.
Fo
=
1 + KSV[Q]
(4)
F
4
27.92 cm–1 and 523.16–520.13 cm–1 were assigned to the ν(M–
2
.5. Molecular docking studies
N) and ν(M–O) vibrations, respectively, confirming the formation
of complexes [36,37].
The inflexible molecular docking studies were executed by us-
ing HEX 6.1 software [29]. Structures of the ligand/complexes
were drawn using CHEMSKETCH (http://www.acdlabs.com) which
was changed into PDB format from mol format by OPENBA-
BEL (http://www.vcclab.org/lab/babel/). Furthermore, B–DNA dode-
camer d(CGCGAATTCGCG)2 crystal structure (PDB ID: 1BNA) was
taken from protein data bank (http://www.rcsb.org./pdb). All com-
putation studies were conducted on Intel Pentium 4 operating sys-
tem having a 2.4 GHz based system containing running MS Win-
dows XP SP2. Finally, the insight view of docked pose model was
visualized by using two molecular graphics programs i.e. CHIMERA
3
.2. NMR spectral studies
The 1H NMR spectra of the ligand L displayed a strong char-
acteristic peak at 8.91 ppm due to the presence of azomethine
–
HC=N proton thus confirming the formation of ligand L [38].
Moreover, the signals at 10.25 ppm were attributed to the –NH
groups suggesting the presence of the free –NH in ligand L [39].
The upfield shift of the phenolic –OH group signal at 12.57 ppm
suggests the existence of the intramolecular hydrogen bonding be-
tween the hydrogen atom of the phenolic –OH and the nitrogen
atom of the azomethine group [40]. The multiplets in the range of
(
http://www.cgl.ucsf.edu/chimera/).
3. Results and discussion
6
.53 to 8.04 ppm corresponds to the combined signals of aromatic
New metal-based molecular modalities 1–4 were obtained,
hydrogen atoms of both the triazino[5,6–b]indole ring and salicy-
laldehyde moieties present in ligand L. However, in the 1H NMR
followed by the stoichiometric addition of new (E)–2–(((5H–
[
1,2,4]triazino[5,6–b]indol–3–yl)imino)methyl)phenol ligand L and
spectra of complexes 1 and 3 the peak for the azomethine –HC=N
proton was slightly shifted downfield at 8.98 and 8.99 ppm, re-
spectively thus suggesting the coordination of N–atom to the metal
ion [41]. In contrast, the signal for the –OH group at 12.57 ppm
was completely disappeared in both complexes which further con-
firms the deprotonation of the hydroxyl group and the direct co-
ordination of the –OH group with the metal ion. In addition, the
signal for the –NH group present in triazino[5,6–b]indole ring was
shifted upfield at 9.50 and 9.57 ppm in complexes 1 and 3, respec-
tively. Furthermore, the peaks in the aromatic region from 6.78–
ꢀ
2
,2 –Bipyridine/1,10 phenanthroline to Ni(II)/Cu(II) metal sulfates
(
Scheme 1). Proposed structures of the complexes were established
by CHN analysis and various spectroscopic methods. In complexes
and 3 displayed square planar geometry, whereas complexes 2
1
and 4 acquired octahedral environments and were stable toward
air and moisture. Conductance values of all the complexes suggest
their 1:1 electrolytic nature in DMF solution.
3
.1. IR spectra
7.90 ppm and 6.83–7.94 ppm were broad and merged in both com-
The IR spectrum of ligand L and metal complexes 1–4 were
recorded in the range of 4000–400 cm–1 at room temperature.
plexes 1 and 3, respectively. The broadness in these signals were
observed mainly due to the presence of metal ions, so it is quite
difficult to differentiate the signals of the triazino[5,6–b]indole lig-
The IR spectra of the ligand L shows a characteristic peak at
616.56 cm–1 for the azomethine ν(C=N) group which was shifted
and L and 2,2 –Bipyridine/1,10 phenanthroline separately in the
ꢀ
1
to lower frequencies in metal complexes 1–4 in the range 1599.91–
aromatic region. Additionally, a strong peak at 3.40 ppm in the
case of ligand L and a very broad peak at 3.44 and 3.37 ppm
in complexes 1 and 3 in the 1H NMR spectra suggested the as-
1
581.38 cm–1 confirming the coordination of azomethine group to
the central metal ion [30]. Apart from this ligand L also shows a
medium intensity broad band at 3430.69 cm–1 due to the pres-
ence of the ν(O–H) group attached with the salicylaldehyde moi-
ety [31]. However, the absence of this ν(O–H) band in complexes
sociation of water molecules. The strong broadening of the H O
2
molecule signal in the case of metal complexes indicates the dy-
namic processes such as proton exchange or the presence of water
molecules in the solvent [42]. On the other hand, a sharp peak ob-
served at 2.51 ppm, 2.45 and 2.49 ppm was due to the presence
of DMSO solvent in ligand L and complexes 1 and 3, respectively
[43] (Fig. S1).
In the 13C NMR spectra of ligand L, a characteristic peak at
164.8 was observed for the azomethine carbon atom. The reso-
nance signals for the aromatic triazino[5,6–b]indole ring was found
in the range of 109.99–153.4 ppm [44]. The signals for the car-
bon atoms of the aromatic salicylaldehyde ring were observed in
the 116.12–133.66 ppm range except for the carbon atom that is
bonded to the –OH group which was observed at 161.36 ppm
[45]. However, in complexes 1 and 3 the azomethine carbon was
shifted downfield at ~173 ppm suggesting the formation of com-
plexes [46]. The resonance signals for the aromatic carbon atoms
of ligand L were assigned in the range 110.21–160.74 ppm. The
characteristic signatures for the aromatic 1, 10 phenanthroline ring
were identified in the 126.25–156.01 ppm range [47].
1
and 3 confirms the coordination by the deprotonation of the hy-
droxyl group. But in complexes 2 and 4 the broadness and inten-
–
1
sity of the ν(O–H) band nearly at ∼3429.18 cm was increased
indicating the presence of coordinated water molecules thus mak-
ing it difficult to analyze the deprotonation of the hydroxyl group
[
32]. Furthermore, the band for the ν(N–H) of the triazino[5,6–
b]indole ring was observed in the range of 3200.98–3262.28 cm–1
in both ligand L and metal complexes 1–4 [33]. For the heteroaro-
matic structures, the ν(C–H) stretching vibrations of the aromatic
ring were expected in the region of 3100–3000 cm–1. Therefore,
the characteristic ν(C–H) stretching vibration in ligand L was de-
picted at 3197.98 and 3067.66 cm–1 [34]. These –C–H stretching vi-
brations in metal complexes 1–4 were shifted at 3078.14, 3050.21,
3
054.01, 3056.98 cm–1, respectively. Moreover, the peaks in the re-
gion 1099.08–1164.69 cm–1 were assigned to the ν(C–H) in–plane
bending mode of vibration. Similarly strongly intense ν(C–H) out–
of–plane bending vibrations were observed in the 751.60–856.77
4

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
Scheme 1. Synthetic route to ligand L and metal complexes 1–4.
3
.3. Electronic spectra
tronic spectra of complexes 2 and 4, respectively were assigned
to the combination of LMCT (N→ Cu ) and 2Eg→ T g transitions
2
+
2
2
The UV–vis spectra of the ligand L and the metal complexes 1–
[51]. In addition, the effective magnetic moment of complex 4 was
calculated from the magnetic susceptibility by using the equation
μeff = 2.828 [χm.T]1/2 where χm is the molar susceptibility and T
is the absolute temperature. For complex 4 the magnetic moment
was obtained to be 1.92 B.M which is slightly higher than the the-
oretical value (i.e 1.73 B.M) thus indicating the monomeric nature
and octahedral geometry of Cu(II) complex [52]. Unfortunately, the
magnetic moment value of complex 2 cannot be recorded due to
the slight hygroscopic nature of the complex. On the other hand,
the Ni(II) complexes 1 and 3 exhibited a high intensity band at
275–281 nm, respectively and a slight shoulder at 325–319 nm
which is more pronounced in the case of complex 3 [53]. Apart
from this, a strong peak at 480 nm at higher concentrations in
complexes 1 and 3 corresponds to the LMCT transitions. Complex 1
exhibited two absorption bands at 535 and 620 nm whereas com-
plex 3 shows the bands at 550 and 625 nm corresponding to the
4
were measured in a DMF solution (10–3 to 10–4 M) in the range
of 200 to 800 nm at room temperature. The ligand L exhibited
two strong intensity peaks at 280 and 320 nm mainly attributed to
∗
∗
the intraligand transitions π –π and n–π of the heterocyclic aro-
matic framework and non-bonding electrons of the nitrogen atom
of –C=N groups attached with the triazino[5,6–b]indole moiety, re-
spectively [48,49]. Similarly, the electronic spectra of complexes
2
and 4 displayed an intense absorption band in the range 280–
2
85 nm with a shoulder at 300–320 nm, respectively, affirming
the presence of ligand L in metal complexes. At higher concentra-
tion complex 2 and 4 shows two low energy d–d bands centered
at 600,680 nm and 635,695 nm, respectively corresponding to the
2
2
Eg→ T g transitions suggesting the tetragonally distorted octahe-
2
dral geometry around Cu(II) ion attributed to the John–Teller effect
[
50]. However, a shoulder band at 490 and 492 nm in the elec-
5

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
spin forbidden 1A g→ A g and A g→ B g transitions character-
1
1
1
loss of both water molecules from complexes 2 and 4 correspond-
1
2
1
1
+
+
istic of the square planar Ni(II) complexes. Furthermore, very low
magnetic susceptibility values in complexes 1 and 3 suggested the
diamagnetic nature of Ni(II) complexes consistent with the square
planar arrangement.
ings to the [C26H22N7CuO3–2H2O] and [C28H22N7CuO3–2H2O]
observed at m/z 507.20 and 532.36, respectively. In the next step,
there will be complete removal of bipyridine/phenanthroline lig-
ands as evidenced from the appearance of peaks at m/z 351.10
+
and 351.64 corresponding to [C26H22N CuO –2H O–C H N ] and
7
3
2
10
8
2
+
C28H22N CuO –2H O–C H N ] fragments. After this, the copper
7 3 2 12 8 2
[
3
.4. Thermal gravimetric analysis (TGA)
metal ion is lost giving a peak at nearly m/z 288 in both com-
plexes 2 and 4 attributed to the [C26H22N CuO –2H O–C H N –
7
3
2
10
8
2
To determine the thermal stability of metal complexes 1–4, the
+
+
Cu] and [C28H22N CuO –2H O–C H N –Cu] fragments, respec-
7
3
2
12
8
2
TGA analysis has been carried out over the temperature range
of 25–800 °C (Fig. S3). In complex 1, the decomposition of the
complex occurs in four steps in the temperature range of 85.72–
tively. Moreover, in ligand L and metal complexes 1–4 high inten-
sity peaks were seen at m/z 185 and 106 due to the presence of
indole triazine and salicylaldehyde moiety, respectively. Therefore,
in the metal complexes 1–4, the complex ions are the main species
responsible for the interaction with DNA and HSA as the counter
ion is very easily lost in the first step of the mass fragmentation
process.
159.96, 159.96–223.43, 223.43–464.93, 464.93–690.92 °C. However,
in complexes 2–4, the weight loss has been observed in three
steps over the temperature range of 94.03–206.23, 176.77–395.54,
5
39.64–652.64 °C. In the case of complexes 1 and 3, a loss of sul-
fate molecules accompanied by a % weight loss of 7.37% and 7.03%
calculated%: 8.71 and 8.34) was observed in the first step in tem-
(
3
3
.6. DNA binding studies
perature range 85.72–159.96 and 108.76–206.23 °C, respectively. In
the second step in complex 1 (159.96–223.43 °C), there was the
elimination of CO2 from the molecule with a weight loss of 7.88%
.6.1. Electronic absorption titration
The DNA binding interaction of ligand and metal complexes
(
calculated%: 8.74) whereas in complex 3 (206.23–395.54 °C) there
was commonly studied by employing the electronic absorption
technique. The electronic absorption spectra were evaluated for
the ligand L and complexes 1–4 by monitoring the changes in
the maximum absorption band at 271 nm assigned to the intrali-
gand π→π∗ transitions of the aromatic rings [54,55]. Moreover,
a very weak band nearly in the region of 330–360 nm in ligand
L and complexes 2–4 was attributed to the n→π∗ transitions of
the heterocyclic rings. When a complex is bound to DNA, either
hypochromism or hyperchromism was observed with or without
any red or blue shift in the position of the absorption band. The
hypochromism mainly represents the stacking of the aromatic pla-
nar residues inside the base pairs of the DNA helix thereby show-
ing the intercalative binding mode. However, hyperchromism was
associated with the electrostatic interaction of the molecule with
the sugar phosphate backbone and the stabilization of the DNA
secondary structure. The absorption spectra of ligand L and com-
plexes 1–4 in the absence and presence of DNA in 5mM Tris HCl/
NaCl buffer were depicted in Fig. 1. The incremental addition of
DNA concentration to a constant volume of ligand L, metal com-
plexes 1 and 2 shows hyperchromism of 44.2%, 91.5% and 67.85%,
respectively in the absorption profile with a slight red shift of 3–5
nm in 1 and 2 in the range 265–271 nm. The spectral characteris-
tics such as red shift and hyperchromic effect suggested both co-
valent binding via the N7 atom of guanine and non–covalent bind-
ing mode through the breakage of hydrogen bonds between the
DNA base pairs leading to the overall contraction and stabilization
of the DNA secondary structure [56]. Similarly, hyperchromism of
45.97% and 73.91% was also observed in the absorption profile of
complexes 3 and 4, respectively but with a strong blue shift of 6–9
nm in the maximum absorption band. The concomitant blue shift
along with hyperchromism in the absorption intensity inferred the
interaction of metal complexes with DNA through the groove bind-
ing or external contact by electrostatic interaction with the phos-
phate backbone of the DNA helix [57,58]. In order to access the
binding propensity of ligand and metal complexes, the intrinsic
binding constant Kb was quantitatively determined by using the
Wolfe–Shimer Eq. (1). The value of Kb evaluated from the ratio
is a weight loss of 18.43% (calculated%: 19.93) corresponding to the
removal of salicylaldehyde moiety. However, in complex 1 (223.43–
4
64.93 °C) the decomposition of salicylaldehyde moiety occurs in
the third step assigned to the weight loss of 26.71% (calculated%:
5.94). In the last step in complexes, 1 and 3, the weight loss of
9.22% and 20.60% (calculated%: 19.20 and 20.30) in the temper-
2
1
ature range 395.54–690.92 °C, respectively were assigned to the
further decomposition of organic ligand leading to the generation
of NiO as final residue. Similarly, in complexes 2 and 4 (94.03–
176.77), there is a loss of two coordinated water molecules caus-
ing a weight loss of 6.76% and 5.63% (calculated%: 6.08 and 5.84),
respectively. In the second step in complex 2 (201.57–263.46 °C)
there is a weight loss of 16.20% (calculated%: 16.56) due to the
elimination of sulfate ion and CO2 molecule while in complex 4
(176.77–342.04 °C), a greater weight loss of 37.41% (calculated%:
3
6.40) was observed which indicated the removal of sulfate ion,
CO2 and salicylaldehyde moiety from the molecule. In the third
step in the temperature range of 263.46–634.45 °C in complexes
2
and 4 there is a decomposition of the remaining organic ligand
accompanied with weight loss of 40.64 and 20.52% (calculated%:
0.08 and 20.12), respectively ultimately forming the CuO at the
end.
4
3
.5. Mass spectra
The ESI mass spectra of ligand L and metal complexes 1–4 ex-
hibited a prominent molecular ion peak at 290.3, 552.03, 595.51,
76.34, and 617.43, respectively in support of our chemical struc-
5
tures. In the case of metal complexes 1–4, the loss of the counter
ion (1/2SO 2–) is observed leading to the formation of complex
4
ion observed at m/z 504.16, 543.99, 528.31 and 568.43, respec-
+
tively. In complexes 1 and 3, the complex ions [C26H18 N NiO]
7
+
and [C28H18 N NiO] were further fragmented giving peaks at m/z
7
+
3
46.10 and 346.35 corresponding to the [C26H18 N NiO–C H N ]
7 10 8 2
+
2
and [C28H18 N NiO–C H N ] fragments indicating the removal of
7
12
8
bipyridine and phenanthroline, respectively. The peaks at 289.10
+
and 289.62 were ascribed to [C26H18 N NiO–C H N –Ni] and
of slope to intercept in a plot of [DNA]/(εa − ε ) Vs [DNA] fol-
7
10
8
2
f
+
[
C28H18 N NiO–C H N –Ni] fragments clearly showing the sep-
lows the order 4>3>2>1>L (Table 1). These results revealed that
all metal complexes 1–4 exhibited higher binding constant Kb val-
ues as compared to the ligand L and thus we can say that com-
plexation of organic ligands with metal ions increases the bind-
ing ability thereby acting as stronger DNA binding agents. Finally,
it can be concluded that hyperchromism in the absorption spec-
7
12
8
2
aration of nickel metal ion leaving behind the Schiff base ligand
L. Similarly in complexes 2 and 4 the resulting loss of the sul-
fate counter ion in the first step give rise to the complex ions
+ +
C26H22N CuO ] and [C28H22N CuO ] appearing at m/z 543.20
7 3 7 3
[
and 568.43 in the mass spectra. In the second step, there will be
6

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
Fig. 1. Absorption spectra of ligand L and metal complexes 1–4 in 5mM Tris HCl/ 50 mM NaCl buffer upon the addition of calf thymus DNA; Inset: Plots of [DNA]/(εa–εf) vs
–6
–4
[
DNA] for the titration of CT DNA with complexes, experimental data points; full lines, linear fitting of the data. [Complex] = 6.42 × 10 M, [DNA] = 1.14 × 10 M. Arrow
shows a change in intensity with increasing concentration of DNA.
Table 1
DNA binding parameters of ligand L and metal complexes 1–4 obtained from the elec-
tronic absorption studies.
Complex/Ligand
λ
max (nm)
࢞λ (nm)
% Hyperchromism
Kb (M–1
)
3
4
4
L
1
2
3
4
271
265
275
269
265
6 (Blue)
5 (Red)
3 (Red)
9 (Blue)
6 (Blue)
44.2%
8.45 × 10
1.04 × 10
1.14 × 10
91.5%
67.85%
45.97%
73.91%
4
1.9 × 10
4
4.8 × 10
7

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
tra in both ligand metal complexes was mainly attributed to the
non–covalent electrostatic binding and groove binding through the
formation of hydrogen bonds with the –OH and –NH group of
the ligand L with the accessible hydrogen bonding sites present
in the major and minor grooves. However, Cu(II) complexes 2 and
Moreover, the binding constant ‘K’ and number of binding sites
‘n’ for ligand L and complexes 1–4 were calculated from slope and
intercept of the Scatchard plot of r/Cf versus r, respectively. The
binding constant values follow the order 4>3>2>1>L in agree-
ment with electronic absorption studies (Table 2). This result indi-
cated the structure–activity relationship in complexes and reveals
that the nature of the metal ion and the increase in molecular pla-
narity of the ligands can affect the binding propensity of metal
complexes with CT DNA.
4
exhibited greater binding affinity when compared to their cor-
responding analogs Ni(II) complexes 1 and 3. The higher binding
propensity of complexes 2 and 4 is mainly due to the presence of
selective Cu(II) endogenous metal ion which acts as a promising
alternative to platinum-based drugs because it is highly selective
towards N7 of guanine residue and strongly interacts with can-
cerous DNA thereby blocking the uncontrolled replication of DNA
which ultimately leads to cell death [59]. Apart from this, Cu(II) is
an essential metal ion that is present at the active site of various
proteins/enzymes which is involved in many important biological
processes in the human body such as respiration, electron transfer,
energy metabolism and DNA synthesis [60]. Additionally, the ge-
ometry of metal complexes plays a key factor in determining the
binding affinity of metal complexes. The literature revealed that
octahedral geometry of copper(II) complexes containing aromatic
ligands [61,62] are quite fluxional and labile that allows the inter-
calation of complex inside the DNA base pairs making it a more
suitable DNA probe for the development of novel chemotherapeu-
tic agents [63,64].
3.6.3. Ethidium bromide displacement experiment
An ethidium bromide displacement experiment was carried out
to further get detailed insight into the intercalative behavior of
complexes with DNA. The ethidium bromide (EB) is basically a sen-
sitive fluorescent probe that emits fluorescence in the presence
of DNA; this is due to its highly planar aromatic structure that
easily intercalates inside the stacked base pairs of the DNA he-
lix [69]. This staking interaction of EB dye with DNA leads to a
very high emission intensity due to the decrease in the quench-
ing effect by solvent molecules. However, the emission intensity
of this EB dye decreases when replaced by another molecule at
the same intercalating site. Therefore, any molecule that replaces
this dye will have the intercalating mode of binding depending
upon the ability of intercalation and hence reflected by a decrease
in emission intensity [70]. The emission spectra of EB dye show
an intense emission peak at 595 nm when excited at 525 nm
wavelength in the presence of the DNA molecule, thereby con-
firming the formation of DNA–EB adducts. As shown in Fig. 3,
the increasing concentration of ligand L and metal complexes 1–
4 quenches the emission intensity of DNA–EB adducts [71]. The
results revealed only quenching of the fluorescent intensity with
no shift in the position of the band. In both ligand and metal
complexes, since EB was not completely displaced from its bind-
ing site, it can be concluded that our molecule competes with EB
for its binding site and undergo partial intercalation [72]. There-
fore, quenching in the fluorescence indicates the partial intercala-
tive behavior of both ligand L and metal complexes 1–4, but the
extent of intercalative nature was determined from the quench-
ing constant Ksv by using the Stern–Volmer Eq. (1). The quenching
constant was calculated from the slope of the plot of Io/I verses
[Complex] follows the order 4>3>2>1>L (Table 3). Furthermore,
the apparent binding constant Kapp values at the 50% quenching
of the fluorescent intensity of DNA–EB adduct by ligand L and
metal complexes 1–4 were calculated by using the equation [73]:
Kapp × [ligand/complex]50 = KEB × [EB], where [ligand/complex]50
is the concentration of molecule at 50% quenching, KEB is the bind-
ing constant of Ethidium bromide (KEB = 1.0 × 10 M–1) and [EB]
3
.6.2. Fluorescence spectral studies
Fluorescence spectroscopy is one of the most sensitive and ac-
curate techniques to determine the mode of binding of molecules
with DNA. The fluorescence emission spectra of ligand L and com-
plexes 1–4 exhibited a strong emission band in the range 364–376
nm when excited at a maximum wavelength of 265–275 nm in
0.01 Tris–HCl/50 mM NaCl buffer at room temperature. The fluo-
rescence titration studies of ligand L and complexes 1–4 have been
–
4
performed in the absence and presence of CT DNA (1.10 × 10
M). The changes in the fluorescence intensity and difference in the
wavelength shift determine the mode of binding of these com-
plexes with CT DNA. As depicted in Fig. 2, the ligand L, com-
plexes 3 and 4 show an increase in the fluorescence intensity in
the emission peak at 380 nm on continuous addition of increasing
concentration of CT–DNA to a constant volume of complex 1. The
complexes 3 and 4 exhibited 43.84% and 51.01% hyperchromism at
a ratio of [DNA]/[complex] is 2.4, respectively with a slight blue
shift of 2–3 nm (Fig. 2). However, the ligand L only shows hy-
perchromism with no shift in the position of the emission peak.
The enhancement in the emission intensity and red/blue shift in-
dicates the electrostatic interaction of complexes 3 and 4 towards
the negatively charged phosphate backbone of DNA [65]. This type
of behavior was also expected due to the highly planar structure
of the phenanthroline present in complexes. Furthermore, the in-
crease in the emission intensity is the characteristic of intercalator
molecules; therefore our complexes 3 and 4 due to the presence of
highly planar phenanthroline ring will also undergo partial interac-
tion inside the adjacent base pairs of DNA helix. This will lead to a
decrease in the collisional frequency due to the less accessibility of
solvent molecules at the binding site thus proving a hydrophobic
environment around the complex molecule [66]. However, in the
case of complexes, 1 and 2, quenching in the intrinsic fluorescence
by 11.29% and 19.88% with a red and blue shift of 3 and 5 nm, re-
spectively was observed in the emission peak appearing at 364 nm
on incremental addition of CT DNA. This quenching in the fluores-
cence intensity can be either static quenching or dynamic quench-
ing. The static quenching represents the formation of the ground
state complex between the fluorophore and quencher whereas dy-
namic quenching refers to the interaction of the quencher with a
molecule in the excited state [67,68].
7
–
6
is the concentration of ethidium bromide (3.33 × 10 M) [74]. The
Kapp values for ligand L and metal complexes 1–4 are mentioned
in Table 3. These Ksv and Kapp values suggested that complex 4
has a stronger ability to intercalate partially inside the DNA helix
as compared to the other complexes and ligands alone.
3.7. HSA binding studies
3.7.1. Absorption spectral studies
To investigate the changes in the secondary structure of HSA
on interaction with ligand/ complexes, electronic absorption stud-
ies were conducted under physiological conditions. The electronic
absorption spectrum of HSA shows a strong peak at 280 nm due to
the tryptophan amino acid residues present in HSA. It is well es-
tablished in the literature that any changes in the absorption spec-
tra of HSA were mainly due to the formation of the ground state
complex and unfolding of the polypeptide chain thus supporting
the static fluorescence quenching mechanism. However, the dy-
namic quenching only affects the excited state of the molecule
8

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
Fig. 2. Emission spectra of ligand L and metal complexes 1–4 in Tris–HCl buffer (pH 7.3) in the presence and absence of CT DNA at room temperature. The arrow shows a
change in intensity with the increasing concentration of DNA.
Table 2
DNA binding constant (K) values, percent hypo–/hyperchromism and shift in the wavelength (࢞λ) for the interaction of
ligand L and metal complexes 1–4.
Complex/Ligand
Emission wavelength λem (nm)
࢞λ (nm)
% Hypo–/ Hyperchromism
K (M–1
)
3
4
4
4
4
L
1
2
3
4
376
364
364
364
366
No shift
3.06%
6.56 × 10
1.81 × 10
3.03 × 10
6.03 × 10
7.12 × 10
3 (Red shift)
5 (Blue shift)
8 (Red shift)
9 (Blue shift)
11.29%
19.88%
43.84%
51.01%
9

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
–4
–5
Fig. 3. Emission quenching spectra of CT DNA (1.10 × 10 M) bound ethidium bromide (3.33 × 10 M) in the presence of ligand L and metal complexes 1–4 in buffer 5
mM Tris–HCl/50 mM NaCl, pH = 7.2 at room temperature. The arrow depicts a change in intensity with the increasing concentration of dye ethidium bromide.
Table 3
and did not alter the absorption spectra of fluorophore [75,76].
Binding parameters for the competitive ethidium bromide displacement
The electronic absorption spectra were recorded of on incremen-
studies for ligand L and metal complexes 1–4.
–
5
tal addition of ligand L and complexes 1–4 (0.12–1.26 × 10 M)
Ksv (M–1
–5
Complex/Ligand
% Hypochromism
)
Kapp
to a fixed amount of HSA (2.27 × 10 M) in 5 mM Tris– HCl/
4
4
4
4
4
6
6
6
6
6
NaCl buffer at room temperature (Fig. 4). The results revealed hy-
perchromism in the intensity along with a blue shift of 5 nm
in the absorption spectra of complexes 1 and 2 whereas a red
shift of 3 nm in the case of complexes 3 and 4. In contrast, no
shift in the wavelength was observed in the absorption profile
of HSA showing no alteration in the microenvironment around
the tryptophan residue on increasing the concentration of ligand
L [77]. In complexes 1 and 2, a substantial increase in the ab-
L
1
2
3
4
39.61
46.94
41.65
43.04
48.87
1.73 × 10
2.25 × 10
2.50 × 10
3.36 × 10
4.38 × 10
1.08 × 10
1.80 × 10
1.92 × 10
2.01 × 10
2.58 × 10
10

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
Fig. 4. UV absorption spectra of the ligand L and metal complexes 1–4 in the presence and absence of HSA in 5 mM Tris– HCl/50 mM NaCl buffer, pH 7.3, at room
–5
–5
temperature: [HSA] = 2.27 × 10 M; [Complex] = 0.12–1.26 × 10 M. Arrows show the intensity changes upon the increasing concentration of the complex 1. Inset: Plot
of 1/A–Ao vs. 1/ [Complex].
sorbance and blue shift in the wavelength indicated an increase
in the polarity around the tryptophan residues thereby reducing
the hydrophobicity leading to conformational changes in the pep-
tide strands of HSA [78]. Similarly, in complexes 3 and 4, the
marked red shift and hyperchromism also indicated changes in
the microenvironment in Trp–214 residue due to the formation
of ground state complex with HSA leading to structural changes
in the secondary structure of HSA [79,80]. Overall, we concluded
that the observed increase in the absorption intensity suggests the
non–covalent interaction probably through the formation of hydro-
gen bond between the complexes and HSA molecule. The intrinsic
cept to slope from the linear double reciprocal plot of 1/(A–Ao)
versus 1/[ligand/complex] by using Eq. (1). The Kb values were
3
4
4
4
found to be 2.36 × 10 , 1.29 × 10 , 6.33 × 10 , 7.32 × 10 ,
4
8.57 × 10 for L and complexes 1–4, respectively. These results
showed that complexes 2 and 4 containing Cu(II) ions exhibited
a stronger binding affinity towards HSA than its analogous Ni(II)
complexes 1 and 3. It can be expected as 15% of the total cop-
per content in blood plasma was transported by HSA under nor-
mal conditions. Since HSA acts as a carrier and shows high se-
lectivity towards Cu(II) ions in the human body, therefore, the
Cu(II) complexes possess high HSA binding affinity [81]. It is re-
ported that the copper-binding site in the HSA is the amino N-
terminal site with the sequence Asp-Ala-His which binds easily to
binding constants (K ) for the HSA binding of ligand L and metal
b
complexes 1–4 have been evaluated from the ratio of the inter-
11

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
Fig. 5. The fluorescence quenching spectra of HSA in the presence of ligand L and metal complexes 1–4 at excitation wavelength at 280 nm in 5 mM Tris–HCl/50 mM NaCl
–
5
–6
–6
buffer, pH 7.3, at room temperature: [HSA] is 2.27 × 10 M; the concentration of complex increases from 0.73 × 10 to 8.06 × 10 M, respectively. The arrow shows the
intensity changes upon the increasing concentration of the quencher at an emission wavelength of 350 nm.
the Cu(II) ion and delivers to the tissues and organs in the human
body [82].
due to the presence of tryptophan (Trp–214) residue with a sub-
stantial contribution from tyrosine (Tyr), and phenylalanine (Phe)
residues. The Trp–214 residue is located in the subdomain IIA of
HSA which also contains a large hydrophobic cavity near Trp–214
that acts as a binding site for many drugs [85]. The fluorescence
spectra of HSA have been recorded in the range of 200–800 nm
with excitation wavelength at 280 nm in the absence and pres-
ence of an increasing concentration of ligand L and metal com-
3
.7.2. Fluorescence quenching studies
The affinity of drug molecules to bind with the carrier protein
HSA which is freely accessible inside the blood helps in the dis-
tribution, metabolism and pharmacological properties of the blood
[
83,84]. The binding interaction of ligand/metal complexes with
HSA protein was studied by the highly sensitive fluorescence spec-
troscopy technique. The intrinsic fluorescence of HSA was mainly
–5
plexes 1–4 (Fig. 5). The HSA (2.27 × 10 M) shows a strong emis-
12

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
Table 4
ligand L and metal complexes 1–4 was found to be in the range
The HSA binding constants and parameters derived for ligand L and
complexes 1–4.
0
.82–1.4 revealing that there is only one binding site available for
interaction with HSA. The value of binding constant K for all ligand
L and metal complexes 1–4 are in the optimum range to bind with
HSA molecule but quite less than the association constant of non–
Compound
Ksv (M–1
)
Kq (M–1 s–1
)
K (M–1
)
n
4
4
4
5
5
12
12
12
13
13
4
4
4
5
5
L
1
2
3
4
6.06 × 10
6.22 × 10
9.89 × 10
1.33 × 10
2.50 × 10
6.06 × 10
6.22 × 10
9.89 × 10
1.33 × 10
2.50 × 10
0.65 × 10
1.11 × 10
1.31 × 10
1.51 × 10
1.72 × 10
0.82
1.05
1.10
1.38
1.40
15
−1
covalent avidin–ligands bonds (K ≈ 10
M
) [90]. This suggests
a possible release of the complex at the target site. The results re-
vealed that among the metal complexes 1–4, complex 4 shows the
greater interaction with HSA due to the presence of Cu(II) metal
ion which is well known for its specific interaction and transporta-
tion by HSA inside the human body [91,92]. Therefore, the nature
of metal ions directly affects the bioactivity of metal complexes to-
gether with the coexistence of the synergetic effect of ligand [93].
sion peak at 355 nm which was specifically quenched along with
the slight blue shift of 5–6 nm on gradual addition of an increas-
–
6
ing amount of ligand L and metal complexes 1–4 (0.73 × 10 to
–
6
8
.06 × 10 M). This quenching in the fluorescence intensity and
3
.7.3. Forster resonance energy transfer (FRET)
the blue shift indicates Trp–214 residues are less exposed to the
solvent molecules and are buried in the more hydrophobic en-
vironment after binding with the ligand/ metal complexes [86].
However, the quenching in the case of complex 4 was more as
compared to complex 1, 2, 3 and ligand L due to the presence of a
highly planar phenanthroline ring causing greater interaction with
HSA. The overall results suggest perturbations in the microenviron-
ment around Trp–214 residues leading to the conformational alter-
ations in the secondary structure of HSA [87].
The energy transfer between the donor fluorophore (HSA) and
acceptor (metal complexes) was observed due to the significant
overlap of the emission spectra of HSA and the absorption spec-
tra of the metal complexes 1–4 (Fig. 7). This non–radiative transfer
of energy through intermolecular dipole–dipole is also called the
Forster resonance energy transfer (FRET). In general, FRET mainly
occurs due to the interaction of the acceptor molecule with donor
HSA in the excited state leading to the transfer of energy from
donor to acceptor molecule [94]. However, the extent of the en-
ergy transfer depends on the amount of overlap between the donor
HSA and acceptor metal complexes. For efficient energy transfer
between donor and acceptor molecules by FRET mainly three cri-
teria’s are required: (a) the donor molecule must have some flu-
orescence, (b) there must be significant overlap between emission
spectra of donor and absorption spectra of acceptor and (c) the dis-
tance between donor and acceptor molecule must be less than 8
nm [95]. The efficiency of energy transfer (E) and the distance (r)
between the tryptophan residue of donor HSA and acceptor metal
complexes were evaluated by employing the Eq. (7):
To analyze the quenching mechanism of HSA by ligand L and
metal complexes 1–4, the fluorescence data were evaluated by em-
ploying the Stern–Volmer Eq. (5):
Fo
=
1 + Kq
τ
o[Q] = 1 + KSV[Q]
(5)
F
where Fo and F are the emission intensities of HSA in the ab-
sence and presence of quencher (ligand/metal complex), respec-
tively, kq is a bimolecular quenching rate constant of HSA (equal
to Kq = KSV/ τo), τ0 is the average lifetime of fluorophore in
the absence of quencher (τo = 10− s), KSV is the Stern–Volmer
quenching constant and [Q] is the concentration of a quencher
8
6
F
Ro
6
(
ligand/metal complex). The Stern–Volmer quenching constant KSV
calculated from the plot of Fo/F verses [Q] follows the order
>3>2>1>L. Furthermore, bimolecular quenching rate constant Kq
E = 1 −
=
(7)
Fo
6
Ro + ro
4
Where F and Fo represent the fluorescence intensity of HSA in the
presence and absence of the metal complexes 1–4, r is the actual
distance between the donor HSA and acceptor metal complexes
and Ro signifies the critical distance at 50% energy transfer which
can be computed from the Eq. (8).
given in Table 4 was calculated from the Stern–Volmer quench-
ing constant Ksv by employing the equation Kq = K / τo and
SV
12
13
was obtained in the order of magnitude 10
to 10 , which
was much greater than the limiting diffusion constant Kdif of the
10
−1 −1
biomolecules (Kdif = 2 .0 × 10
M s ). The greater values of
Ro = 8.78 × 10−25K N ϕJ
6
2
−4
(8)
Kq>Kdif for ligand L and metal complexes 1–4 confirmed that flu-
orescence quenching takes place through a static quenching mech-
anism [88,89]. The static quenching supports the formation of the
ground state complex between the HSA and ligand L/metal com-
plexes 1–4 due to specific interaction in agreement with UV–vis
absorption results. For a static quenching mechanism, the binding
constant (K) and the number of binding sites (n) can be calculated
using the modified Stern–Volmer Eq. (6):
Where K2 is the spatial orientation factor of the donor and accep-
tor dipoles depending on their geometry, N is the refractive index
of the medium, ϕ is the donor HSA fluorescence quantum yield
and J is the overlap integral of the HSA donor fluorescence and ab-
sorption spectrum of acceptor metal complexes calculated by using
the Eq. (9).
∞
ꢂ
ꢀ
ꢁ
4
Fo − F
F(λ)ε(λ)λ ꢂλ
log
= logK + nlog[Q]
(6)
0
F
J =
(9)
∞
ꢂ
F(λ)ꢂλ
Where, Fo and F are the fluorescence intensities of HSA in the
0
absence and presence of quencher (ligand/metal complex), K is the
binding constant, n is the number of binding sites and [Q] is the
quencher concentration (ligand/metal complex). By employing this
Eq. (2), a double logarithm regression graph of log(Fo − F/F) ver-
sus log[Q] has been plotted and the binding constant (K) was de-
termined from the intercept and the number of binding sites (n)
was calculated from the slope (Fig. 6). The values of K and n for
ligand L and metal complexes 1–4 are mentioned in Table 4. The
binding constant K values were found to be in the appropriable
range of 10 –105 M–1 indicating the excellent interaction between
complex 1–4 and HSA. Moreover, the number of binding sites for
Where F(λ) is the fluorescence intensity of the HSA donor with-
out acceptor at wavelength λ and ε(λ) is the molar absorption
coefficient of the acceptor metal complexes at wavelength λ. In
the present circumstances the value of K2 = 2/3, N = 1.336 and
ϕ = 0.118 for HSA. The parameters of the Forster resonance en-
ergy transfer (FRET) such as E, J, Ro and r for the interaction of the
acceptor metal complexes 1–4 with donor HSA were determined
by using Eqs. (1) to (3). The calculated values show that the dis-
tance between donor and acceptor ‘r’ is less than that of the criti-
cal distance ‘Ro’ for all the metal complexes thereby confirming the
4
13

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
Fig. 6. Double logarithm regression plot of fluorescence quenching of HSA for the calculation of binding constant (K) and the number of binding (n) for ligand L and
complexes 1–4 with HSA at room temperature.
14

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
Fig. 7. Spectral overlap (J(λ)) of UV absorption spectra of complexes 1–4 with fluorescence emission spectra of HSA. The red line shows the fluorescence emission spectrum
–6
–6
of HSA (0.67 × 10 M), the blue line UV absorption spectrum of metal complexes 1–4 (0.67 × 10 M).
Table 5
to their higher binding propensity towards DNA. We have per-
Forster resonance energy transfer (FRET) obtained parameters
formed the rigid molecular docking studies with duplex DNA
d(CGCGAATTCGCG)2 dodecamer (PDB ID: 1BNA) to study the bind-
ing interaction and proper orientation of our complex at the bind-
ing site of the macromolecule [97]. The minimum energy docked
poses of our complexes 3 and 4 with DNA revealed that the com-
plex binds in the minor groove in the GC-rich region together with
the hydrogen bonding and van der Waal interactions in the groove
for energy transfer between HSA and metal complexes 1–4.
−1
Complex
J (cm3
M
)
Ro (nm)
E
r (nm)
1
1
1
1
3
1
2
3
4
1.27 × 10
2.18 × 10
2.48 × 10
6.07 × 10
2.11
2.25
2.74
2.97
0.107
0.136
0.173
0.374
3.12
3.13
3.14
3.17
3
3
3
(
Fig. 8). Moreover, the phenanthroline ring bends in such a man-
ner to allow intercalative π–π stacking interaction with the dou-
ble helix in agreement with the EB displacement studies [98]. The
H–bonding has been observed with the oxygen atom of pheno-
late and the nitrogen atoms of the triazine ring with the phos-
phate backbone present in the GC-rich region provides stabiliza-
tion to the docked pose. Furthermore, the relative binding energy
of complexes 3 and 4 in the docked pose of DNA was found to be
static quenching mechanism. Moreover, the good value of ‘E’ re-
vealed the excellent transfer of energy from the tryptophan residue
of the HSA to the metal complexes 1–4 along with substantial in-
teraction. For an appropriate energy transfer process the value of r
must obey the criteria 0.5Ro < r < 1.5Ro which can be simplified
in general to 2 < r < 8 nm [96]. Our all complexes have followed
this condition as their r value is observed in the range of 3.02–3.17
nm, therefore, suggesting the exemplary transfer of energy in the
order of 4>3>2>1 (Table 5).
–
6.82 and –7.53 Kcal/mol respectively. The more negative binding
energy indicates a more stabilized structure in the docked posed,
thus the values of the binding energy evidenced that complex 4
more strongly binds with DNA as compared to complex 3. This
is in agreement with the same order as obtained from the ex-
perimental electronic absorption studies. Overall these results are
in close correlation with the DNA binding results which confirms
the partial intercalation along with groove binding for complexes
3 and 4.
3
.8. Molecular docking studies with DNA
To further get detailed information on the binding mode
of metal complexes with DNA biomolecules, molecular docking
studies have been performed for only complexes 3 and 4 due
15

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
Fig. 8. Molecular docked poses of complex 3 and complex 4 with DNA dodecamer of sequence d(CGCGAATTCGCG)2 (PDB ID: 1BNA).
Fig. 9. Molecular docked poses of (a) complex 3 and (b) complex 4 lying in the hydrophobic cavity in subdomain IIA of HSA.
3
.9. Molecular docking studies with HSA
cal motifs joined together by an extended polypeptide chain [99].
The binding sites for the drugs are located in the subdomain IIA
and IIIA also known as the Sudlow site I and II, respectively. Apart
from this, there is another site located in the subdomain IB which
binds the heme, protoporphyrin IX and other synthetics porphyrins
[100]. The docked conformation of complexes 3 and 4 with HSA
protein revealed that both the complexes were exactly fitted into
the hydrophobic cavity of site I located in the subdomain IIA. As
depicted in Fig. 9, complex 4 was more embedded in the cavity
Molecular docking studies of complexes 3 and 4 have been con-
ducted to determine the exact binding location with HSA as it is
considered as the main blood carrier protein (60%) for the trans-
portation of the drugs and other endogenous substances. It is well
established that HSA is a helicoidal protein and contains three ho-
mologous domains denoted as I, II and III. Each domain is further
divided into two subdomains A and B which shared common heli-
16

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
as compared to complex 3 indicating the stronger interaction of
complex 4 with HSA. It is observed that both the molecules are
closely located to Trp–214 residue which is also lying in the bind-
ing pocket of subdomain IIA. Besides the hydrophobic interaction,
the complexes were also stabilized with the pocket by the hydro-
gen bonding interactions promoted by the phenolate oxygen and
the nitrogen atoms of the triazine ring with the various amino acid
groups. The binding affinity score in the optimum pose was found
to be −7.02 and −7.34 kcal/mol for complexes 3 and 4, respec-
tively. Overall the molecular docking studies are consistent with
the experimental studies and help us to get insight into the bind-
ing sites of metal complexes within the particular subdomain.
[2] P.C. Bruijnincx, P.J. Sadler, New trends for metal complexes with anticancer
activity, Curr. Opin. Chem. Biol. 12 (2008) 197–206, doi:10.1016/j.cbpa.2007.
11.013.
[3] K. Abdi, H. Hadadzadeh, M. Salimi, J. Simpson, A.D. Khalaji, A mononuclear
copper (II) complex based on the polypyridyl ligand 2, 4, 6-tris (2-pyridyl)-1,
+
3
, 5-triazine (tptz),[Cu (tptz)2]2 : X-ray crystal structure, DNA binding and in
vitro cell cytotoxicity, Polyhedron 44 (2012) 101–112, doi:10.1016/j.poly.2012.
6.089.
0
[4] K. Zhang, V. Wing–Wah Yam, Platinum (ii) non-covalent crosslinkers for
supramolecular DNA hydrogels, Chem. Sci. 11 (2020) 3241–3249, doi:10.1039/
C9SC05910E.
[
5] A. Kellett, Z. Molphy, C. Slator, V. McKee, N.P. Farrell, Molecular methods for
assessment of non-covalent metallodrug–DNA interactions, Chem. Soc. Rev.
48 (2019) 971–988, doi:10.1039/C8CS00157J.
[
6] W. Xi, F.Q. Song, X.L. Xia, X.Q. Song, Tuned structure and DNA binding prop-
erties of metal complexes based on a new 4-acylpyrazolone derivative, New
J. Chem. 44 (2020) 2281–2290, doi:10.1039/C9NJ05948B.
4. Conclusion
[7] M. Shoeb, R. Shaikh, Synthesis, spectral characterization and antibacterial ac-
tivity of quinolone incorporating 1, 2, 4-triazine rings, Chem. Biol. Inter. 10
(
2020) 51–55.
In this investigation, we have discussed the comparative
[
8] S. Cascioferro, B. Parrino, V. Spano, A. Carbone, A. Montalbano, P. Barraja,
P. Diana, G. Cirrincione, An overview on the recent developments of 1, 2, 4-
triazine derivatives as anticancer compounds, Eur. J. Med. Chem. 142 (2017)
DNA and HSA binding profile of the newly synthesized metal
complexes [Ni(L)(Bipy)]1/2SO4 (1), [Cu(L)(Bipy)]1/2SO4 (2),
3
28–375, doi:10.1016/j.ejmech.2017.08.009.
[
Ni(L)(Phen)]1/2SO4 (3) and [Cu(L)(Phen)]1/2SO4 (4) derived
[9] M.H. El–Wakil, A.F. El–Yazbi, H.M.A. Ashour, M.A. Khalil, K.A. Ismail,
from
new
ligand
(E)–2–(((5H–[1,2,4]triazino[5,6–b]indol–3–
I.M. Labouta, Discovery of a novel DNA binding agent via design and synthe-
sis of new thiazole hybrids and fused 1, 2, 4-triazines as potential antitumor
agents: Computational, spectrometric and in silico studies, Bioorg. Chem. 90
ꢀ
yl)imino)methyl)phenol (L) and 2,2 –Bipyridine/1,10 phenan-
throline. The analysis of DNA binding of ligand L and metal
complexes 1–4 from vivid biophysical techniques revealed that
metal complexes 1–4 exhibited higher binding propensity than
ligand (L) and prefer the electrostatic mode of interaction followed
by partial intercalation. Complexes 3 and 4 containing the planar
(2019) 103089, doi:10.1016/j.bioorg.2019.103089.
[10] A. Lauria, A. Alfio, R. Bonsignore, C. Gentile, A. Martorana, G. Gennaro,
G. Barone, A. Terenzi, A.M. Almerico, New benzothieno [3, 2-d]-1, 2, 3-
triazines with antiproliferative activity: Synthesis, spectroscopic studies, and
biological activity, Bioorg. Med. Chem. Lett. 24 (2014) 3291–3297, doi:10.1016/
j.bmcl.2014.06.007.
ꢀꢀ ꢀꢀ ꢀ ꢀ
1,10 phenanthroline ring displayed greater binding affinity as
[11] R.S. Ali, H.A. Saad, Synthesis of some novel fused pyrimido[4 ,5 :5 ,6 ]-
ꢀ
ꢀ
[
1,2,4]triazino[3 ,4 :3,4] [1,2,4]triazino[5,6-b]indoles with expected anticancer
activity, Molecules 23 (2018) 693, doi:10.3390/molecules23030693.
12] K. Ramesh, S.N. Murthy, K. Karnakar, Y.V.D. Nageswar, facile, aqueous
phase green synthetic protocol for the synthesis of 5,9b-dihydro-1H-
1,2,4]triazino[5,6-b]indole-3-ols/5,9b-dihydro-1H-[1,2,4]triazino[5,6-b]indole-
compared to 1 and 2 which contain bipyridine rings. Additionally,
the HSA binding studies showed that complexes 3 and 4 interact
efficiently with Trp–214 residues of HSA located in the subdomain
IIA.
[
A
[
3
-thiols, Tetrahedron Lett. 52 (2011) 4734–4737, doi:10.1016/j.tetlet.2011.06.
98.
0
Declaration of Competing Interest
[13] J.L. Kgokong, P.P. Smith, ad G.M. Matsabisa, 1,2,4-Triazino-[5,6b]indole deriva-
tives: effects of the trifluoromethyl group on in vitro antimalarial activity,
Bioorg. Med. Chem. 13 (2005) 2935–2942, doi:10.1016/j.bmc.2005.02.017.
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared to
influence the work reported in this paper.
[
14] A. Keivanloo, S. Sepehri, M. Bakherad, M. Eskandari, Click Synthesis of 1,2,3-
Triazoles-Linked 1,2,4-Triazino[5,6-b]indole, antibacterial activities and molec-
ular docking studies, ChemistrySelect 5 (2020) 4091–4098, doi:10.1002/slct.
202000266.
[
15] A.G. Al Osaimi, R.S. Ali, H.A. Saada, M.R. El Sayed Aly, Synthesis and antimi-
crobial activity of novel fused [1, 2, 4]triazino[5, 6-b]indole derivatives, Russ.
J. Gen. Chem. 87 (2017) 1246–1255, doi:10.1134/S1070363217060202.
CRediT authorship contribution statement
[
16] J.M.Z. Gladych, R. Hornby, J.H. Hunt, D. Jack, J.J. Boyle, R.J. Ferlauto, R.F. Haff,
C.G. Kormendy, F.J. Stanfield, R.C. Stewart, Antiviral agents. 5H-as-Triazino[5,6-
b]indoles, J. Med. Chem. 15 (1972) 277–281, doi:10.1021/jm00273a017.
Reem L.B. Alanazi: Data curation, Investigation. Mehvash Zaki:
Conceptualization, Methodology, Validation, Visualization, Formal
analysis, Supervision, Writing – original draft, Writing – review &
editing. Wafa A. Bawazir: Methodology, Resources, Project admin-
istration.
[
17] L. Pathaw, T. Khamrang, A. Kathiravan, M. Velusamy, Synthesis, crystal struc-
ture, bovine serum albumin binding studies of 1, 2, 4-triazine based copper
(
I) complexes, J. Mol. Struc. 1207 (2020) 127821, doi:10.1016/j.molstruc.2020.
127821.
[
18] E. Bulatov, R. Sayarova, R. Mingaleeva, R. Miftakhova, M. Gomzikova, Y. Ig-
natyev, A. Petukhov, P. Davidovich, A. Rizvanov, N.A. Barlev, Isatin-Schiff base-
copper (II) complex induces cell death in p53-positive tumors, Cell Death Dis-
cov. 4 (2018) 103, doi:10.1038/s41420-018-0120-z.
Acknowledgments
[
19] M. Lashanizadegan, H.A. Ashari, M. Sarkheil, M. Anafcheh, S. Jahangiry, New
Cu (II), Co (II) and Ni (II) azo-Schiff base complexes: synthesis, characteri-
zation, catalytic oxidation of alkenes and DFT study, Polyhedron 200 (2021)
115148, doi:10.1016/j.poly.2021.115148.
Dr. Mehvash Zaki and Wafa A. Bawazir acknowledges with
thanks King Abdulaziz University and King Fahad Medical Research
Center for technically supporting this work. The author Reem
Alanazi is grateful to King Abdulaziz University and Hafr Al–Batin
University for financial support. The authors are highly thankful to
Dr. Mohd Afzal, King Saud University, Saudi Arabia for his valuable
suggestions during the revision process of this manuscript.
[20] H. Kargar, A.A. Ardakani, M.N. Tahir, M. Ashfaq, K.S. Munawar, Synthesis, spec-
tral characterization, crystal structure determination and antimicrobial activ-
ity of Ni (II), Cu (II) and Zn (II) complexes with the Schiff base ligand de-
rived from 3, 5-dibromosalicylaldehyde, J. Mol. Struct. 1229 (2021) 129842,
doi:10.1016/j.molstruc.2020.129842.
[
21] N. Amir, Y. Miyashita, K. Fujisawa, K.-I. Okamoto, Nickel (II) complexes
with Schiff bases derived from salicylaldehyde or pentanedione and 3-
aminopropanethiol, J. Coord. Chem. 59 (2006) 1527–1536, doi:10.1080/
Supplementary materials
0
0958970500537796.
[
22] O.A. Chaves, L.B. Menezes, B.A. Iglesias, Multiple spectroscopic and theoreti-
cal investigation of meso-tetra-(4-pyridyl) porphyrinruthenium (II) complexes
in HSA-binding studies. Effect of Zn (II) in protein binding, J. Mol. Liq. 294
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.2021.131203.
(2019) 111581, doi:10.1016/j.molliq.2019.111581.
References
[23] C. Zhu, F. Liu, Y. Wei, F. Zhang, T. Pan, Y. Ye, Y. Shen, Evaluating the potential
risk by probing the site-selective binding of rutin-Pr (III) complex to human
serum albumin, Food Chem. Toxicol. 148 (2021) 111927, doi:10.1016/j.fct.2020.
[
1] A. Barve, A. Kumbhar, M. Bhat, B. Joshi, R. Butcher, U. Sonawane, R. Joshi,
Mixed-ligand copper (II) maltolate complexes: synthesis, characterization,
DNA binding and cleavage, and cytotoxicity, Inorg. Chem. 48 (2009) 9120–
111927.
[24] F. Shen, Y.–X. Liu, S.–M. Li, C.–K. Jiang, B.–F. Wang, Y.–H. Xiong, Z.–W. Mao,
X.–Y. Le, Synthesis, crystal structures, molecular docking and in vitro cy-
9132, doi:10.1021/ic9004642.
17

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
totoxicity studies of two new copper (ii) complexes: special emphasis on
their binding to HSA, New J. Chem. 41 (2017) 12429–12441, doi:10.1039/
C7NJ02351K.
amino acids and salicylaldehyde-5-sulfonates, Spectrochim. Acta A 67 (2007)
944–949, doi:10.1016/j.saa.2006.09.012.
[47] L.F. Hernandez–Ayala, M. Flores–Alamo, S. Escalante–Tovar, R. Galindo–
Murillo, J.C. Garcia–Ramos, J. Garcia–Valdes, V. Gomez–Vidales, K. Resendiz–
Acevedo, Y. Toledano–Magana, L. Ruiz–Azuara, Synthesis, characterization,
theoretical studies and biological activity of coordination compounds with es-
sential metals containing N4-donor ligand 2, 9-di (ethylaminomethyl)-1, 10-
phenanthroline, Inorg. Chim. Acta 470 (2018) 187–196, doi:10.1016/j.ica.2017.
06.040.
[
[
[
25] H. Shi, T. Fang, Y. Tian, H. Huang, Y. Liu, A dual-fluorescent nano-carrier for
delivering photoactive ruthenium polypyridyl complexes, J. Mater. Chem. B 4
(2016) 4746–4753, doi:10.1039/C6TB01070A.
26] A. Wolfe, G.H. Shimer, T. Meehan, Polycyclic aromatic hydrocarbons physically
intercalate into duplex regions of denatured DNA, Biochemistry 26 (1987)
6392–6396, doi:10.1021/bi00394a013.
27] H.G. Weder, J. Schildknecet, R.A. Lutz, P. Kesselrinu, Determination of binding
parameters from Scatchard plots: theoretical and practical considerations, Eur.
J. Biochem. 42 (1974) 475–481, doi:10.1111/j.1432-1033.1974.tb03361.x.
28] C. Tan, J. Liu, W.Zheng H.Li, S. Shi, L. Chen, L. Ji, Differences in structure,
physiological stability, electrochemistry, cytotoxicity, DNA and protein bind-
ing properties between two Ru (III) complexes, J. Inorg. Biochem 102 (2008)
[48] R. Kalarani, M. Sankarganesh, G.G. Vinoth Kumar, M. Kalanithi, Synthesis,
spectral, DFT calculation, sensor, antimicrobial and DNA binding studies of Co
(II), Cu (II) and Zn (II) metal complexes with 2-amino benzimidazole Schiff
base, J. Mol. Struct. 1206 (2020) 127725, doi:10.1016/j.molstruc.2020.127725.
[49] I. Nawrot, B. Machura, R. Kruszynski, Thiocyanate cadmium (II) complexes of
2, 4, 6-tri (2-pyridyl)-1, 3, 5-triazine–Synthesis, structure and luminescence
properties, J. Lumin. 156 (2014) 240–254, doi:10.1016/j.jlumin.2014.08.022.
[50] C.E. Satheesh, P. Raghavendra Kumar, P.A. Suchetan, H. Rajanaika, S Foro, New
(N, O) Schiff bases of 2-hydroxynaphthaldehyde and their homoleptic Zn (II)
and Cu (II) complexes–Synthesis, structural characterization, Hirshfeld sur-
face analysis and antimicrobial activity studies, Inorg. Chim. Acta 515 (2021)
120017, doi:10.1016/j.ica.2020.120017.
[
347–358, doi:10.1016/j.jinorgbio.2007.09.008.
[
29] D. Mustard, D.W. Ritchie, Docking essential dynamics eigenstructures, Pro-
teins Struct. Funct. Bioinform. 60 (2005) 269–274, doi:10.1002/prot.20569.
30] N. Ganji, S. Daravath, A. Rambabu, K. Venkateswarlu, D.S. Shankar, Shiv-
araj, Exploration of DNA interaction, antimicrobial and antioxidant studies
on binary transition metal complexes with isoxazole Schiff bases: Prepara-
tion and spectral characterization, Inorg. Chem. Commun. 121 (2020) 108247,
doi:10.1016/j.inoche.2020.108247.
[
ꢀ
[51] A.M. Mansour, O.R. Shehab, Spectroscopic and TDDFT studies of N-phenyl-N -
(3-triazolyl) thiourea) compounds with transition metal ions, Arab. J. Chem.
14 (2021) 102932, doi:10.1016/j.arabjc.2020.102932.
[
31] S.–Z. Zhang, G. Guo, W.–M. Ding, J. Li, Y. Wu, H.–J. Zhang, J.–Q. Guo, Y.–X. Sun,
Synthesis and spectroscopic properties of two different structural Schiff base
Zn (II) complexes constructed with/without auxiliary ligands, J. Mol. Struct.
[52] T.A. Fayed, M. Gaber, M.N. El–Nahass, H.A. Diab, M.M. El–Gamil, Synthesis,
Structural characterization, thermal, molecular modeling and biological stud-
ies of chalcone and Cr (III), Mn (II), Cu (II) Zn (II) and Cd (II) chelates, J. Mol.
Struct. 1221 (2020) 128742, doi:10.1016/j.molstruc.2020.128742.
[53] A. Gusev, V. Shulgin, E. Braga, E. Zamnius, M. Kryukova, W. Linert, Lumi-
nescent properties of Zn complexes based on tetradentate N2O2-donor pyra-
zolone schiff bases, Dyes Pigm 183 (2020) 108626, doi:10.1016/j.dyepig.2020.
108626.
1230 (2021) 129627, doi:10.1016/j.molstruc.2020.129627.
[
32] B. Vivekanand, K.M. Raj, B.H.M. Mruthyunjayaswamy, Synthesis, characteriza-
tion, antimicrobial, DNA-cleavage and antioxidant activities of 3-((5-chloro-
2
-phenyl-1H-indol-3-ylimino) methyl) quinoline-2 (1H)-thione and its metal
complexes, J. Mol. Struct. 1079 (2015) 214–224, doi:10.1016/j.molstruc.2014.
8.033.
0
[
33] K.M. Raj, B.H.M. Mruthyunjayaswamy, Synthesis, spectroscopic characteriza-
tion, electrochemistry and biological activity evaluation of some metal (II)
complexes with ONO donor ligands containing indole and coumarin moieties,
J. Saudi Chem. Soc. 21 (2017) S202–S218, doi:10.1016/j.jscs.2014.01.001.
34] H. Arslan, A. Demircan, Structure and Vibrational Spectra of Tert-butyl
N-(2-bromocyclohex-2-enyl)-N-(2-furylmethyl)carbamate, Acta Phys. Chim.
Sinica 23 (2007) 1683–1690 10.1016/S1872-1508(07)60082-5.
[54] H. Farrokhpour, H. Hadadzadeh, F. Darabi, F. Abyar, H.A. Rudbari, T. Ahmadi–
Bagheri, A rare dihydroxo copper (II) complex with ciprofloxacin; a com-
bined experimental and ONIOM computational study of the interaction of the
complex with DNA and BSA, RSC Adv. 4 (2014) 35390–35404, doi:10.1039/
C4RA04634J.
[
[
[
[55] E.S. Aazam, M. Zaki, Synthesis and Characterization of Ni (II)/Zn (II) Metal
complexes derived from Schiff base and Ortho-phenylenediamine: In vitro
35] B.C. Smith, IR spectral interpretation workshop alcohols the rest of the
story, Spectroscopy 32 (2017) 19–23 https://www.spectroscopyonline.com/
view/alcohols-rest-story-alf3.
DNA binding, molecular modeling and RBC hemolysis, ChemistrySelect
(2020) 610–618, doi:10.1002/slct.201903583.
5
[56] P. Alreja, N. Kaur, DNA and copper (II) governed fluorescence tuning of
phenanthroline possessing Ru (II) complex. Interplay of electrostatic interac-
tions, Inorg. Chem. Commun. 77 (2017) 51–54, doi:10.1016/j.inoche.2017.01.
033.
2
+
2+
36] R. Fouad, O.M.I. Adly, Novel Cu
and Zn nanocomplexes drug based on
hydrazone ligand bearings chromone and triazine moieties: Structural, spec-
tral, DFT, molecular docking and cytotoxic studies, J. Mol. Struct. 1225 (2021)
1
29158, doi:10.1016/j.molstruc.2020.129158.
[57] B. Kaya, Z.K. Yilmaz, O. Sahin, B. Aslim, B. Ulkuseven, Structural characteriza-
tion of new zinc (ii) complexes with N 2 O 2 chelating thiosemicarbazidato
ligands; investigation of the relationship between their DNA interaction and
in vitro antiproliferative activity towards human cancer cells, New J. Chem. 44
(2020) 9313–9320 10.1039/D0NJ02149K.
[
37] O.A. EL–Gammal, H. Alshater, H.A. El–Boraey, Schiff base metal complexes
of 4-methyl-1H-indol-3-carbaldehyde derivative as a series of potential an-
tioxidants and antimicrobial: Synthesis, spectroscopic characterization and
3D molecular modeling, J. Mol. Struct. 1195 (2019) 220–230, doi:10.1016/j.
molstruc.2019.05.101.
[58] B.K. Kundu, S.M.Mobin Pragti, S. Mukhopadhyay, Studies on the influence of
the nuclearity of zinc (ii) hemi-salen complexes on some pivotal biological
applications, Dalton Trans. 49 (2020) 15481–15503, doi:10.1039/D0DT02941F.
[59] H. Irving, R.J.P. Williams, The stability of transition-metal complexes, J. Chem.
Soc. 637 (1953) 3192–3210, doi:10.1039/JR9530003192.
[
[
[
38] S. Alyar, U.O. Ozmen, S. Adem, H. Alyar, E. Bilen, K. Kaya, Synthesis, spectro-
scopic characterizations, carbonic anhydrase II inhibitory activity, anticancer
activity and docking studies of new Schiff bases of sulfa drugs, J. Mol. Struct.
1223 (2021) 128911, doi:10.1016/j.molstruc.2020.128911.
39] M.H. Abdelrahman, A.S. Aboraia, B.G.M. Youssif, B.E.M. Elsadek, Design, syn-
thesis and pharmacophoric model building of new 3-alkoxymethyl/3-phenyl
indole-2-carboxamides with potential antiproliferative activity, Chem. Biol.
Drug Des. 90 (2017) 64–82, doi:10.1111/cbdd.12928.
[60] R. Loganathan, S. Ramakrishnan, M. Ganeshpandian, N.S. Bhuvanesh, M. Pala-
niandavar, A. Riyasdeen, M.A. Akbarsha, Mixed ligand copper(ii) dicarboxy-
late complexes: the role of co-ligand hydrophobicity in DNA binding, double-
strand DNA cleavage, protein binding and cytotoxicity, Dalton Trans. 44 (2015)
10210–10227, doi:10.1039/C4DT03879G.
40] Y. Sun, Y. Liu, W. Guo, Fluorescent and chromogenic probes bearing salicy-
laldehyde hydrazone functionality for cyanide detection in aqueous solution,
Sens. Actuators B Chem. 143 (2009) 171–176, doi:10.1016/j.snb.2009.09.038.
[61] R. Patel, N. Singh, K. Shukla, J. Niclos-Gutierrez, A. Castineiras,
V. Vaidyanathan, B.U. Nair, Characterization and biological activities of
ꢀ
[
41] Z.H.A. El–Wahab, Mononuclear metal complexes of organic carboxylic acid
derivatives: Synthesis, spectroscopic characterization, thermal investigation
and antimicrobial activity, Spectrochim. Acta A 67 (2007) 25–38, doi:10.1016/
j.saa.2006.05.038.
two copper(II) complexes with diethylenetriamine and 2,2 -bipyridine or
1,10-phenanthroline as ligands, Spectrochim. Acta, Part A 62 (2005) 261–268,
doi:10.1016/j.saa.2004.12.034.
[62] I. Turel, The interactions of metal ions with quinolone antibacterial agents,
Coord. Chem. Rev. 232 (2002) 27–47, doi:10.1016/S0010-8545(02)00027-9.
[63] M. Sharma, M. Ganeshpandian, M. Majumder, A. Tamilarasan, M. Sharma,
R. Mukhopadhyay, N.S. Islam, M. Palaniandavar, Octahedral copper (ii)-
diimine complexes of triethylenetetramine: effect of stereochemical fluxional-
ity and ligand hydrophobicity on Cu II/Cu I redox, DNA binding and cleavage,
cytotoxicity and apoptosis-inducing ability, Dalton Trans. 49 (2020) 8282–
8297, doi:10.1039/D0DT00928H.
[
42] Y. Xu, T. Watermann, H.–H. Limbach, T. Gutmann, D. Sebastiani, G. Bun-
tkowsky, Water and small organic molecules as probes for geometric confine-
ment in well-ordered mesoporous carbon materials, Phys. Chem. Chem. Phys.
16 (2014) 9327–9336, doi:10.1039/C4CP00808A.
[
43] H.E. Gottlieb, V. Kotlyar, A. Nudelman, NMR chemical shifts of common lab-
oratory solvents as trace impurities, J. Org. Chem. 62 (1997) 7512–7515,
doi:10.1021/jo971176v.
[
44] M.S. Almutairi, S. Xavier, M. Sathish, H.A. Ghabbour, S. Sebastian, S. Periandy,
Reem I. Al–Wabli, Mohamed I. Attia, Spectroscopic (FT-IR, FT-Raman, UV, 1H
and 13C NMR) profiling and computational studies on methyl 5-methoxy-1H-
indole-2-carboxylate: A potential precursor to biologically active molecules, J.
Mol. Struct. 1133 (2017) 199–210, doi:10.1016/j.molstruc.2016.12.004.
[64] T.H. Sanatkar, H. Hadadzadeh, Z. Jannesari, T. Khayamian, M. Ebrahimi,
H.A. Rudbari, M. Torkzadeh-Mahani, M. Anjomshoa, Characterization, photo-
cleavage, molecular modeling, and DNA-and BSA-binding studies of Cu (II)
and Ni (II) complexes with the non-steroidal anti-inflammatory drug meloxi-
cam, Inorg. Chim. Acta 423 (2014) 256–272, doi:10.1016/j.ica.2014.08.060.
[65] A.A. Ensafi, R. Hajiana, S. Ebrahimi, Study on the interaction between
morin-Bi (III) complex and DNA with the use of methylene blue dye as
[
45] M. Yildiz, O. Karpuz, C.T. Zeyrek, B. Boyacioglu, H. Dal, N. Demir, N. Yildirim,
H. Unver, Synthesis, biological activity, DNA binding and anion sensors,
molecular structure and quantum chemical studies of a novel bidentate Schiff
base derived from 3, 5-bis (triflouromethyl) aniline and salicylaldehyde, J.
Mol. Struct. 1094 (2015) 148–160, doi:10.1016/j.molstruc.2015.03.047.
a
fluorophor probe, J. Braz. Chem. Soc. 20 (2009) 266–276, doi:10.1590/
S0103-50532009000200011.
[66] V.G. Vaidyanathan, B.U. Nair, Synthesis, characterization, and DNA binding
studies of a chromium (III) complex containing a tridentate ligand, Eur. J. In-
org. Chem. (2003) 3633–3638, doi:10.1002/ejic.200300170.
[
46] D.M. Boghaei, M. Gharagozlou, Spectral characterization of novel ternary zinc
(
II) complexes containing 1, 10-phenanthroline and Schiff bases derived from
18

R.L.B. Alanazi, M. Zaki and W.A. Bawazir
Journal of Molecular Structure 1246 (2021) 131203
[
67] N. Shahabadi, S. Mohammadi, R. Alizadeh, Bioinorg. DNA interaction studies
of a new platinum(II) complex containing different aromatic Dinitrogen lig-
ands, Chem. Appl. (2011) 429241, doi:10.1155/2011/429241.
[83] V.K.A. Kalalbandi, J. Seetharamappa, 1-[(2 E)-3-Phenylprop-2-enoyl]-1 H-
benzimidazoles as anticancer agents: synthesis, crystal structure analysis and
binding studies of the most potent anticancer molecule with serum albumin,
Med. Chem. Commun. 6 (2015) 1942–1953, doi:10.1039/C5MD00293A.
[84] N. Chadha, D. Singh, M.D. Milton, G. Mishra, J. Danield, A.K. Mishra, A.K. Ti-
wari, Computational prediction of interaction and pharmacokinetics profile
study for polyamino-polycarboxylic ligands on binding with human serum al-
bumin, New J. Chem. 44 (2020) 2907–2918, doi:10.1039/C9NJ05594K.
[85] C.–L. Zhang, Y.–X. Liu, X.–M. Zhang, S. Chen, F. Shen, Y.–H. Xiong, W. Liu,
Z.–W. Mao, X.–Y. Le, Synthesis, characterization, DNA/HSA interactions and
in vitro cytotoxic activities of two novel water-soluble copper (II) complexes
with 1, 3, 5-triazine derivative ligand and amino acids, Mater. Sci. Engineer. C
91 (2018) 414–425, doi:10.1016/j.msec.2018.05.065.
[
68] H. Liu, C. Hao, Z. Nan, H. Qu, X. Zhang, Z. Zhang, R. Sun, Fabrication of
graphene oxide and sliver nanoparticle hybrids for fluorescence quenching
of DNA labeled by methylene blue, Spectrochim. Acta A 243 (2020) 118802,
doi:10.1016/j.saa.2020.118802.
[
69] A. Petrovic, M. Zivanovic, R. Puchta, D. Cocic, A. Scheurer, N. Milivojevic,
J. Bogojeski, Experimental and quantum chemical study on the DNA/protein
binding and the biological activity of a rhodium (III) complex with 1, 2, 4-
triazole as an inert ligand, Dalton Trans 49 (2020) 9070–9085, doi:10.1039/
D0DT01343A.
[
70] N. Ganji, S. Daravath, A. Rambabu, K. Venkateswarlu, D.S. Shankar, Shiv-
araj, Exploration of DNA interaction, antimicrobial and antioxidant studies
on binary transition metal complexes with isoxazole Schiff bases: Prepara-
tion and spectral characterization, Inorg. Chem. Commun. 121 (2020) 108247,
doi:10.1016/j.inoche.2020.108247.
[86] O.A. Chaves, L.B. Menezes, B.A. Iglesias, Multiple spectroscopic and theoreti-
cal investigation of meso-tetra-(4-pyridyl) porphyrinruthenium (II) complexes
in HSA-binding studies. Effect of Zn (II) in protein binding, J. Mol. Liq. 294
(2019) 111581, doi:10.1016/j.molliq.2019.111581.
[
[
[
71] N.N. Rao, E. Kishan, K. Gopichand, R. Nagaraju, A.M. Ganai, P.V. Rao, De-
sign, synthesis, spectral characterization, DNA binding, photo cleavage and
antibacterial studies of transition metal complexes of benzothiazole Schiff
base, Chem. Data Collec. 27 (2020) 100368, doi:10.1016/j.cdc.2020.100368.
72] R.R. Kumar, M.K.M. Subarkhan, R. Ramesh, Synthesis and structure of nickel
[87] A. Bhattacharjee, S. Das, B. Das, P. Roy, Intercalative DNA binding, protein
binding, antibacterial activities and cytotoxicity studies of
a mononuclear
copper (II) complex, Inorg. Chim. Acta 514 (2021) 119961, doi:10.1016/j.ica.
2020.119961.
[88] F.F. Tian, J.H. Li, F.L. Jiang, X.L. Han, C. Xiang, Y.S. Ge, L.L. Li, Y. Liu, Investigat-
ing the interactions of a novel anticancer delocalized lipophilic cation and its
precursor compound with human serum albumin, RSC Adv. 2 (2012) 501–513,
doi:10.1039/C1RA00521A.
(
II) thiocarboxamide complexes: effect of ligand substitutions on DNA/protein
binding, antioxidant and cytotoxicity, Rsc Adv. 5 (2015) 46760–46773, doi:10.
039/C5RA06112A.
1
73] P. Adak, B. Ghosh, A. Bauza, A. Frontera, S.R. Herronc, S.K. Chattopadhyay,
Binuclear and tetranuclear Zn (II) complexes with thiosemicarbazones: syn-
thesis, X-ray crystal structures, ATP-sensing, DNA-binding, phosphatase activ-
ity and theoretical calculations, Rsc Adv. 10 (2020) 12735–12746, doi:10.1039/
C9RA10549B.
[89] D. Yinhua, M.M. Foroughi, Z. Aramesh–Boroujeni, d S. Jahani, M. Peydayesh,
F. Borhani, M. Khatami, M. Rohani, M. Dusek, V. Eigner, The synthesis, charac-
terization, DNA/BSA/HSA interactions, molecular modeling, antibacterial prop-
erties, and in vitro cytotoxic activities of novel parent and niosome nano-
encapsulated Ho (III) complexes, RSC Adv. 10 (2020) 22891–22908, doi:10.
1039/D0RA03436C.
[90] O.H. Laitinen, V.P. Hytonen, H.R. Nordlund, M.S. Kuloma, Genetically engi-
neered avidins and streptavidins, Cell. Mol. Life Sci. 63 (2006) 29920–23017,
doi:10.1007/s00018-006-6288-z.
[
74] V.A. Kawade, A.A. Kumbhar, A.S. Kumbhar, C. Nather, A. Erxleben, U.B. Son-
awane, R.R. Joshi, Mixed ligand cobalt (II) picolinate complexes: synthesis,
characterization, DNA binding and photocleavage, Dalton Trans. 40 (2011)
639–650, doi:10.1039/C0DT01078B.
[
75] G. Devagi, F. Reyhaneh, F. Dallemer, R. Jayakumar, P. Kalaivani, R. Prabhakaran,
Morphological and in vitro evaluation of programmed cell death in MCF-7
cells by new organoruthenium (II) complexes, New J. Chem. 41 (2017) 8620–
[91] T. Peters, F.A. Blumenstock, Copper-binding properties of bovine serum albu-
min and its amino-terminal peptide fragment, J. Biol. Chem. 242 (1967) 1574–
1578, doi:10.1016/S0021-9258(18)96130-2.
8
636, doi:10.1039/C7NJ01707C.
[92] T. Kirsipuu, A. Zadoroznaja, J. Smirnova, M. Friedemann, T. Plitz, V. Tougu,
P. Palumaa, Copper(II)-binding equilibria in human blood, Scientific Rep. 10
(2020) 5686, doi:10.1038/s41598- 020-62560-4.
[93] H. Kabeer, S. Hanif, A. Arsalan, S. Asmat, H. Younus, M. Shakir, Structural-
dependent N, O-donor imine-appended Cu(II)/Zn(II) complexes: synthesis,
spectral, and in vitro pharmacological assessment, ACS Omega 5 (2020) 1229–
1245, doi:10.1021/acsomega.9b03762.
[
76] F. Shen, Y.–X. Liu, S.–M. Li, C.–K. Jiang, B.–F. Wang, Y.–H. Xiong, Z.–W. Mao,
X.–Y. Le, Synthesis, crystal structures, molecular docking and in vitro cy-
totoxicity studies of two new copper (ii) complexes: special emphasis on
their binding to HSA, New J. Chem. 41 (2017) 12429–12441, doi:10.1039/
C7NJ02351K.
[
77] K. Karami, N. Jamshidian, A. Bagheri, A. Hajiaghasi, A.A. Momtazi–Borojeni,
E. Abdollahi, A. Shahpiri, N. Azizi, J. Lipkowski, Novel fluorescence palladium-
alkoxime complexes: Synthesis, characterization, DNA/BSA spectroscopic and
docking studies, evaluation of cytotoxicity and DNA cleavage mechanism, J.
Mol. Struct. 1206 (2020) 127595, doi:10.1016/j.molstruc.2019.127595.
[94] S. Bhunia, S. Adhikary, P. Purkayastha, Energy transfer from luminescent gold
nanoclusters to non-luminescent silver nanoparticles from a new perspective,
J. Mol. Liq. 318 (2020) 114048, doi:10.1016/j.molliq.2020.114048.
[95] M. Dehkhodaei, M. Khorshidifard, H.A. Rudbari, M. Sahihi, G. Azimi, N. Habibi,
S. Taheri, G. Bruno, R. Azadbakht, Synthesis, characterization, crystal struc-
ture and DNA, HSA-binding studies of four Schiff base complexes derived
from salicylaldehyde and isopropylamine, Inorg. Chim. Acta 466 (2017) 48–
60, doi:10.1016/j.ica.2017.05.035.
[
78] M.B. Dukic, M.S. Jeremic, I.P. Filipovic, O.R. Klisuric, V.V. Kojic, D.S. Jakimov,
R.M. Jelic, V. Onnis, Z.D. Matovic, Synthesis, characterization, HSA/DNA inter-
6
actions and antitumor activity of new [Ru (η -p-cymene)Cl2(L)] complexes, J.
Inorg. Biochem. 213 (2020) 111256, doi:10.1016/j.jinorgbio.2020.111256.
79] X.–Bing. Fu, G.–Tian. Weng, D.–D. Liu, X.–Y. Le, Synthesis, characterization,
DNA binding and cleavage, HSA interaction and cytotoxicity of a new cop-
[
[96] P. Kumar, R.J. Butcher, A.K. Patra, Ternary Co (II), Ni (II) and Cu (II) complexes
containing dipyridophenazine and saccharin: Structures, reactivity, binding
interactions with biomolecules and DNA damage activity, Inorg. Chim. Acta
506 (2020) 119532, doi:10.1016/j.ica.2020.119532.
ꢀ
per(II) complex derived from 2-(2 -pyridyl)benzothiazole and glycylglycine, J.
Photochem. Photobiol. A 276 (2014) 83–95, doi:10.1016/j.jphotochem.2013.12.
0
02.
[97] R. Rohs, I. Bloch, H. Sklenar, Z. Shakked, Molecular flexibility in ab initio drug
docking to DNA: binding-site and binding-mode transitions in all-atom Monte
Carlo simulations, Nucl. Acids Res. 33 (2005) 7048–7057 10.1093/nar/gki1008.
[98] A. Jayamania, N. Sengottuvelan, G. Chakkaravarthi, Synthesis, structural, elec-
trochemical, DNA interaction, antimicrobial and molecular docking studies
on dimeric copper (II) complexes involving some potential bidentate ligands,
Polyhedron 81 (2014) 764–776, doi:10.1016/j.poly.2014.05.076.
[
80] S.U. Parsekar, P. Velankanni, S. Sridhar, P. Haldar, N.A. Mate, A. Banerjee,
P.K.S. Antharjanam, A.P. Koley, M. Kumar, Protein binding studies with hu-
man serum albumin, molecular docking and in vitro cytotoxicity studies us-
ing HeLa cervical carcinoma cells of Cu (II)/Zn (II) complexes containing
a carbohydrazone ligand, Dalton Trans. 49 (2020) 2947–2965, doi:10.1039/
C9DT04656A.
[
81] S. Al-Harthi, J.I. Lachowicz, M.E. Nowakowski, M. Jaremko, L. Jaremko, To-
wards the functional high-resolution coordination chemistry of blood plasma
human serum albumin, J. Inorg. Biochem. 198 (2019) 110716, doi:10.1016/j.
jinorgbio.2019.110716.
[99] S. Curry, H. Mandelkow, P. Brick, N. Franks, Crystal structure of human serum
albumin complexed with fatty acid reveals an asymmetric distribution of
binding sites, Nature Struct. Biol. 5 (1998) 827–835, doi:10.1038/1869.
[100] T.R.C. Guizado, Analysis of the structure and dynamics of human serum albu-
min, J. Mol. Model 20 (2014) 2450, doi:10.1007/s00894-014-2450-y.
[
82] M. Sendzik, M.J. Pushie, Ew. Stefaniak, K.L. Haas, Structure and Affinity of
Cu(I) bound to human serum albumin, Inorg. Chem. 56 (2017) 15057–15065
DOI: 10.1021/acs.inorgchem.7b02397.
19