Structural investigation, DNA interactions and in?vitro anticancer studies of transition metal complexes of 3-(2-(2, 4-dihydroxy benzylidene) hydrazinyl) quinoxalin-2(1H) -one

Article abstract of DOI:10.1080/07391102.2021.1877819

The Schiff base ligand, 3-(2-(2, 4-dihydroxybenzylidene) hydrazinyl) quinoxalin-2(1H)-one (RHQO) has been synthesized and characterized by spectral and single crystal X-ray analysis. The Mn(II), Ni(II) and Cu(II) complexes of RHQO have been synthesized and characterized by FT-IR, UV-VIS, mass, EPR spectra, CHN, thermo gravimetric analysis, magnetic susceptibility and conductivity measurements. The morphology of the ligand and complexes is studied by Scanning Electron Microscopy. The metal complexes formed were found to be polymeric in nature. The abilities of the ligand and its metal complexes to interact and bind with calf thymus DNA (CT-DNA) has been studied by electronic absorption spectroscopy and their quantitative binding strength was evaluated in terms of their intrinsic binding constant (K_b). The cleavage interaction of the ligand and its metal complexes with super coiled pBR 322 DNA has been investigated by agarose gel electrophoresis. Cytotoxicity of the Cu(II) and Ni(II) complexes was evaluated using various cancer cell lines, Human cervical cancer cell line (Hela), B16 melanoma F10(B16-F10), Human ovarian cancer cell (SKOV3) and Breast cancer cell line (MCF7) by MTT assay. The results indicated that the ligand and its metal complexes bind with CT-DNA by groove binding mode and cleaved the supercoiled pBR 322 DNA in to nicked form. The Ni(II) and Cu(II) complexes exhibited anticancer activity without affecting the normal CHO-K1 cell lines. Communicated by Vsevolod Makeev.

Full text of DOI:10.1080/07391102.2021.1877819

Journal of Biomolecular Structure and Dynamics
ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/tbsd20
Structural investigation, DNA interactions and
in vitro anticancer studies of transition metal
complexes of 3-(2-(2, 4-dihydroxy benzylidene)
hydrazinyl) quinoxalin-2(1H) -one
Panaganti Sukanya & Chittireddy Venkata Ramana Reddy
To cite this article: Panaganti Sukanya & Chittireddy Venkata Ramana Reddy (2021): Structural
investigation, DNA interactions and in vitro anticancer studies of transition metal complexes of 3-(2-
(2, 4-dihydroxy benzylidene) hydrazinyl) quinoxalin-2(1H) -one, Journal of Biomolecular Structure
and Dynamics, DOI: 10.1080/07391102.2021.1877819
To link to this article: https://doi.org/10.1080/07391102.2021.1877819
View supplementary material
Published online: 29 Jan 2021.
Submit your article to this journal
Article views: 25
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=tbsd20

JOURNAL OF BIOMOLECULAR STRUCTURE AND DYNAMICS
https://doi.org/10.1080/07391102.2021.1877819
Structural investigation, DNA interactions and in vitro anticancer studies
of transition metal complexes of 3-(2-(2, 4-dihydroxy benzylidene)
hydrazinyl) quinoxalin-2(1H) -one
Panaganti Sukanyaa,b
and Chittireddy Venkata Ramana Reddyb
b
aDepartment of Chemistry, Vasavi College of Engineering, Hyderabad, India; Department of Chemistry, Jawaharlal Nehru Technological
University Hyderabad, Hyderabad, India
Communicated by Vsevolod Makeev
ABSTRACT
ARTICLE HISTORY
Received 18 September 2020
Accepted 13 January 2021
The Schiff base ligand, 3-(2-(2, 4-dihydroxybenzylidene) hydrazinyl) quinoxalin-2(1H)-one (RHQO) has
been synthesized and characterized by spectral and single crystal X-ray analysis. The Mn(II), Ni(II) and
Cu(II) complexes of RHQO have been synthesized and characterized by FT-IR, UV-VIS, mass, EPR spec-
tra, CHN, thermo gravimetric analysis, magnetic susceptibility and conductivity measurements. The
morphology of the ligand and complexes is studied by Scanning Electron Microscopy. The metal com-
plexes formed were found to be polymeric in nature. The abilities of the ligand and its metal com-
plexes to interact and bind with calf thymus DNA (CT-DNA) has been studied by electronic absorption
spectroscopy and their quantitative binding strength was evaluated in terms of their intrinsic binding
constant (Kb). The cleavage interaction of the ligand and its metal complexes with super coiled pBR
322 DNA has been investigated by agarose gel electrophoresis. Cytotoxicity of the Cu(II) and Ni(II)
complexes was evaluated using various cancer cell lines, Human cervical cancer cell line (Hela), B16
melanoma F10(B16-F10), Human ovarian cancer cell (SKOV3) and Breast cancer cell line (MCF7) by
MTT assay. The results indicated that the ligand and its metal complexes bind with CT-DNA by groove
binding mode and cleaved the supercoiled pBR 322 DNA in to nicked form. The Ni(II) and Cu(II) com-
plexes exhibited anticancer activity without affecting the normal CHO-K1 cell lines.
KEYWORDS
Crystal structure; polymeric
metal complex; SEM;
anticancer activity; DNA
interaction
Abbreviations: B16-F10: B16 melanoma F10; CT-DNA: Calf thymus-Deoxyribonucleic acid; DMSO:
Dimethyl sulfoxide; Hela: Human cervical cancer cell line; IC50: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-
tetrazolium; MCF7: Breast cancer cell line; MTT: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium;
SEM: Scanning electron microscopy; SKOV3: Human ovarian cancer cell
1. Introduction
the transition metal complexes derived from ligands contain-
ing 2,4-dihydroxy benzaldehyde were also reported to exhibit
anti-candida activity (Creaven et al., 2009), cytotoxic (Tan et al.,
2012), DNA binding and DNA cleavage abilities (Mandal et al.,
1997). Therefore, the Schiff base ligand derived from 3-hydrazi-
nylquinoxalin-2(1H)-one and 2,4 -dihydroxybenzaldehyde and
its metal complexes may also exhibit enhanced biological
activity. Accordingly, we report the synthesis of N,N,O,O donor
Schiff base ligand, 3-(2-(2, 4-dihydroxybenzylidene) hydrazinyl)
quinoxalin-2(1H)-one (RHQO) and its Mn(II), Ni(II) and Cu(II)
complexes. The single crystal X-ray studies of the ligand and
the characterization and biological activity of the ligand and
its metal complexes are also presented.
The development of medicinal inorganic chemistry requires
an understanding of the biological activity of metal com-
plexes as drugs and their interaction with DNA, to provide a
rational basis for the design of new metal-based drugs. The
transition metal complexes of ligands with potential donor
sites continue to provide necessary support for the develop-
ment of new drugs with desired properties.
Quinoxaline derivatives are well-known precursors for the
development of ligands and have been used as building
blocks in the synthesis of transition metal complexes with
pharmacological properties such as antimicrobial (Tarallo
et al., 2010), cytotoxic (Torre et al., 2005), DNA binding (Xu
et al., 2002), DNA cleavage (Peng et al., 2009), renal function
2. Experimental
ꢀ
monitoring (Chinen et al., 2008) and insulin mimetic (Noblıa
2.1. Materials and methods
et al., 2006) activities. Owing to their coordinating capabilities
and potential biological activities, quinoxaline derivatives com-
All the chemicals used were procured from commercial sour-
mand a special status amongst heterocyclic ligands. Similarly, ces, of reagent grade and used as received. Calf-thymus (CT)
CONTACT Chittireddy Venkata Ramana Reddy
vrr9@jntuh.ac.in
Jawaharlal Nehru Technological University Hyderabad, Kukatpally, Hyderabad,
500085, India.
Supplemental data for this article can be accessed online at https://doi.org/10.1080/07391102.2021.1877819.
ß 2021 Informa UK Limited, trading as Taylor & Francis Group

2
P. SUKANYA AND C. V. R. REDDY
DNA was purchased from Sigma-Aldrich. Plasmid pBR322 gel electrophoresis (Raman & Raja, 2007; Yuan et al., 2006).
DNA was purchased from SRL. The cell lines used for in-vitro
anticancer activity studies, B16-F10, CHO-KI, Hela, MCF7 and
SKOV3 were purchased from the American Type Culture
Collection (ATCC) (Bethesda, MD, USA).
The pBR322 DNA was dissolved in 5 mM Tris.HCl/50 mM NaCl
buffer (pH 7.2) to which RHQO/its metal complex was added
and incubated for 2 h at 37 ꢁC. After incubation, 1 ml of a
loading buffer (1% bromophenol blue and 40% sucrose) was
added to it and the mixture was loaded on to a agarose gel
(0.8% w/v) containing 1 mg/ml ethidium bromide (EB).
Control solution (DNA solution) alone was also loaded. The
gel was run in Tris Acetate EDTA (TAE) (40 mM Tris base,
20 mM acetic acid, 1 mM EDTA) buffer of pH 8.3 at a constant
voltage of 60 V for about 2 h so that the bromophenol blue
has traveled through 70% of the gel. The photographs of the
bands were obtained under UV trans-illuminator.
IR spectra of the ligand and the metal ion complexes
were recorded from 250 to 4000 cmꢀ1 on Shimadzu FTIR-
5300 spectrometer in KBr pellets. Electronic absorption spec-
tra were recorded from 200 to 1200 nm in DMSO using
Shimadzu UV-3600 spectrophotometer. 1H NMR spectrum
was recorded using Bruker 400 MHz spectrometer in DMSO-
d6 solvent. Mass spectra were obtained on Shimadzu mass
spectrometer. Elemental analysis was carried out on FLASH
Ea 1112 SERIES CHNS analyzer. Thermogravimetric analysis
(TGA) and differential thermal analysis (DTA) in the tempera-
ture range of 25 ꢁC to 800 ꢁC, was carried out using TG/DTA
EXTAR 6300 under nitrogen atmosphere with a heating rate
of 10 ꢁC/min. EPR spectra were recorded at room tempera-
ture on Bruker Xenon EMX-ER073 spectrometer. Electrical
conductance values of the 10ꢀ3M solutions of metal(II) com-
plexes in DMSO were measured using an Elico conductivity
bridge with dip type cell calibrated using KCl solution. The
morphology of the ligand and its metal complexes was eval-
uated using MERLIN Compact SEM analyzer. Magnetic sus-
ceptibilities were measured on Sherwood scientific magnetic
susceptibility balance. DNA cleavage studies were carried out
using Biotech electrophoresis system and the bands were
visualized and photographed under Biotech Transilluminator.
2.4. Cytotoxicity test
Cytotoxicity assay of the Ni(II) and Cu(II) complexes was eval-
uated on four different cancer cell lines, Mouse skin melan-
oma (B16-F10) (ATCC CRL 6475TM), Homo sapiens cervix
R
V
adenocarcinoma (HeLa), Human Breast Adenocarcinoma
(MCF7) (ATCC HTB-22TM), Human Ovarian cancer (SKOV3)
R
V
(ATCC HTB 77TM) and normal mammalian cell line, Chinese
R
V
hamster ovary cells (CHO-K1) (ATCC CCL-61TM) by micro cul-
R
V
ture tetrazolium assay using 3-(4,5-dimethyl thiazol-2-yl)-2,5-
diphenyl tetrazolium bromide(MTT) (Bollu et al., 2016). The
cell lines, were maintained in Dulbecco’s Modified Eagle’s
medium (DMEM) containing the supplements, 100 U/ml peni-
cillin, 100 lg/ml streptomycin, 2 mM l-glutamine and 10%
fetal bovine serum (FBS) in a 5% CO2 incubator at 37 ꢁC. The
cells were seeded in a 96 well culture plate and allowed to
attach properly. The solutions of the Ni(II) and Cu(II) com-
plexes in DMSO of 1 to 50 mM concentrations were added in
triplicates and incubated for 24 h. The cells were then incu-
bated with 0.5 mg/ml of MTT for 3 h. To dissolve the insol-
uble formazan crystals, 100 ml DMSO was added to each well
and the absorbance of the plates was measured on a
Synergy H1 multi-mode plate reader, USA.
2.2. DNA binding studies
The interaction of RHQO and its metal complexes with CT-
DNA was studied by electronic absorption spectroscopic
method. The concentration of CT-DNA solution prepared by
using potassium dihydrogen phosphate (KH2PO4) and dipot-
tasium phosphate (K2HPO4) buffer (pH 7.2) was determined
from its absorption intensity (Reichman et al., 1954) at
260 nm and the value of extinction coefficient, e (6600 L
molꢀ1 cmꢀ1). The electronic absorption titrations were per-
formed by keeping the concentration of the ligand/metal
complex constant and by varying the concentration of CT-
DNA. After each addition of CT-DNA, the solutions were incu-
bated for 10 min and the spectra were recorded by scanning
each sample from 200 to 800 nm. The spectral changes were
monitored to study the mode of binding and their intrinsic
binding constant, Kb was evaluated using the following
equation (Arjmand et al., 2012):
2.5. Synthesis of the ligand
The Schiff base ligand, 3-(2-(2, 4-dihydroxybenzylidene)
hydrazinyl) quinoxalin-2(1H)-one (RHQO) was synthesized by
the following steps.
2.5.1. Synthesis of 3-hydrazinylquinoxalin-2(1H)-one
The 3-hydrazinylquinoxalin-2(1H)-one was prepared by a
reported procedure involving the following two steps
(Cheeseman & Rafiq, 1971; Phillips, 1928) (Scheme 1).
½DNAꢂ=ðeaꢀefÞ ¼ ½DNAꢂ=ðebꢀefÞ þ 1=KbðebꢀefÞ
where [DNA] represents the concentration of DNA, ea is the
apparent extinction coefficient, eb is the extinction coeffi-
cients of fully bound complex and ef is the extinction coeffi-
cients of free complex. Kb ¼ slope/Intercept
2.5.1.1. Synthesis of quinoxaline-2,3(1H,4H)-dione. A solu-
tion of 100 mmol each of O-phenylene diamine (10.80 g) and
oxalic acid (12.60 g) in HCl (4 N) were heated for 20 min on a
water bath. The reaction mixture was cooled and the crystal-
line product was filtered, washed repeatedly with water and
2.3. DNA cleavage studies
The ability of RHQO and its metal complexes to cleave the
super coiled pBR322 DNA has been investigated by agarose dried. M.P. >350 ꢁC.

JOURNAL OF BIOMOLECULAR STRUCTURE AND DYNAMICS
3
Scheme 1. Synthesis of 3-hydrazinylquinoxalin-2(1H)-one.
The sharp intense peak at 1685 cmꢀ1 is due to lactam car-
2.5.1.2. Synthesis of 3-hydrazinylquinoxalin-2(1H)-one. To
100 mmol of quinoxaline-2,3 (1H,4H)-dione (16.2 g), 50 ml bonyl group. The C ¼ N of hydrazone fragment and ring N-H
each of hydrazine hydrate and water were added and the are observed at 1621 and 1448 cmꢀ1, respectively. The peak
observed at 1338 cmꢀ1 is ascribed to m (C-O). The peak at
mixture was refluxed for 2 h. The yellow solid obtained on
cooling was filtered, washed repeatedly with water and
recrystallized using n-butanol. M.P. >350 ꢁC.
1116 cmꢀ1 is assigned to m (N-N).
The 1H NMR spectrum of RHQO (Figure 3) displays the
signal for quinoxaline ring –NH proton at d 12.37 ppm. Two
phenolic protons are identified at d 11.96 and d 9.91 ppm.
The -NH proton of hydrazone fragment resonates at d
11.45 ppm. The signal at d 8.58 ppm can be assigned to -CH
proton of the azomethine group (Khedr et al., 2005). The
seven aromatic protons are identified as multiplet in the
region of d 6.32–7.44 ppm.
2.5.2. Synthesis of 3-(2-(2, 4-dihydroxybenzylidene) hydra-
zinyl) quinoxalin-2(1H)-one (RHQO)
20 mmol of 3-hydrazinylquinoxalin-2(1H)-one (3.52 g) was dis-
solved in methanol, to which 20 mmol of 2,4 -dihydroxyben-
zaldehyde (2.76 g) was added and stirred at room
temperature for 2 h (Scheme 2). The reaction was monitored
using n-hexane and ethyl acetate (7:3) by TLC. The yellow
solid obtained was filtered, washed successively with metha-
nol and n-hexane. The product was recrystallized using
methanol. Yield: 81%, M.P. 350 ꢁC. The bright yellow single
crystals for X-ray diffraction studies were obtained by diffus-
ing of water slowly in to a saturated solution of RHQO
in DMF.
The electronic absorption spectrum of RHQO shows
ꢃ
p!p transitions associated with benzene at 270 nm (Yeap &
ꢃ
Heng, 2014), while n!p transitions are noticed at 327 and
382 nm. (The electronic absorption spectrum of RHQO is
reported in Figure S10, supplementary material).
The spectro-analytical data confirms the structure of
RHQO as shown in Figure 4.
3.1.2. Crystal structure of RHQO.H2O
2.6. Synthesis of Mn(II), Ni(II) and Cu(II) complexes
of RHQO
The conclusive evidence for the structure of RHQO is
obtained from the X-ray crystallographic data. Crystal struc-
ture analysis indicates the presence of two chemically
equivalent molecules of RHQO.H2O with a small variation in
their bond lengths and angles. The ORTEP view of the com-
pound, RHQO.H2O is shown in Figure 5. The compound crys-
tallizes in the monoclinic system with the space group P21/c.
Each unit cell contains four molecules of RHQO and four
molecules of H2O. The cell parameters are a ¼ 16.2621(18) Å,
The methanolic solution of corresponding metal (II) chloride
was heated in a two necked round bottom flask to which
hot methanolic suspension of RHQO was added in small
amounts. The pH of the reaction mixture was adjusted by
using alcoholic ammonia. The reaction mixture was refluxed
for about 4 h on a water bath. The colored solid formed in
each case was filtered in hot condition under suction,
washed with methanol followed by n-hexane and dried over
anhydrous calcium chloride in a desiccator.
b ¼ 13.3311(14)
b ¼ 114.066(2)
Å
and c ¼ 14.2303(15) Å, a ¼ 90ꢁ,
ꢁ
and c ¼ 90ꢁ. Comparison of the bond
lengths C11-O2 (1.361 Å), C26-O5 (1.359 Å), N4-N3 (1.373 Å),
N8-N7 (1.388 Å), C1-O1(1.229 Å), C16-O4 (1.246 Å) and bond
angles C9-N4-N3 (121.8ꢁ), C24-N8-N7 (116.5ꢁ), N3-C2-N2
(120.4ꢁ), N7-C17-N6 (122.5ꢁ), O1-C1-N1 (123.5ꢁ) and O4-C16-
N5 (123.6ꢁ) reveal that the two molecules are similar with a
little variation in bond lengths and angles. The values are
comparable to those in related structures (Tan et al., 2012).
Crystal data and structure refinement are listed in Table 1
and bond parameters are given in Table 2.
1D-packing diagram of the molecule (Figure 6) reveals the
presence of hydrogen bonding, involving solvated water
molecules and ring hydrogen, phenolic hydrogens and
carbonyl oxygen of RHQO. The bond lengths of N5-H5B-O9,
3. Results and discussion
3.1. Characterization of 3-(2-(2,4–dihydroxy
benzylidene) hydrazinyl) quinoxalin-2(1H)-
one (RHQO)
3.1.1. Spectral data
Analytical data suggests the formula of RHQO as C15H12N4O3.
Presence of m/z peak at 296.11631 in the mass spectrum
(Figure 1) confirms the molecular weight of the ligand corre-
sponding to the proposed molecular formula.
FTIR spectrum of RHQO (Figure 2) shows characteristic
peaks at 3412 and 3329 cmꢀ1 corresponding to the stretch-
ing frequencies of two hydroxyl groups (Abid et al., 2016). N1-H1A-O10, O9-H9A-O2 and O3-H3B-O6 are 1.795 Å, 1.899 Å,

4
P. SUKANYA AND C. V. R. REDDY
Scheme 2. Synthesis of RHQO.
Figure 1. Mass spectrum of RHQO.
1.925 Å and 2.023 Å, respectively. Details of the hydrogen indicate the non-electrolytic nature (Geary, 1971) of the com-
bonding in RHQOꢄH2O are presented in Table 3.
plexes, which is also confirmed by Volhard test.
3.2.3. Infrared spectra of the complexes
3.2. Characterization of metal complexes of RHQO
The IR spectra of the complexes are compared with that of
the ligand to understand the coordination mode of the lig-
and and the observations are summarized in the Table 5.
(The representative IR spectra of the Mn(II), Ni(II) and Cu(II)
3.2.1. Elemental analysis
Elemental analysis data suggests the metal to ligand ratio to
be 1:1 in all the complexes. The CHN analysis data of the
complexes and their molecular weights are presented in complexes are reported in Figures S1–S3, supplementary
Table 4.
material, respectively).
The characteristic stretching frequencies at 3412 and
3329 cmꢀ1 corresponding to the two hydroxyl groups of the
ligand, disappeared in all the complexes, indicating deproto-
3.2.2. Molar conductance of the complexes
The molar conductance values of 10ꢀ3 M solutions of Mn(II), nation of two phenolic groups (Yeap & Heng, 2014).
Ni(II) and Cu(II) complexes in DMSO were found to be 11.58, Appearance of broad bands in the region of 3000–3350 cmꢀ1
9.85 and 14.21 mho.cm2.molꢀ1
, respectively .The values corresponds to coordinated water, which is further confirmed

JOURNAL OF BIOMOLECULAR STRUCTURE AND DYNAMICS
5
Figure 2. IR spectrum of RHQO.
Figure 3. 1H NMR spectrum of RHQO.
by the non-ligand bands in the region of 980–991 cmꢀ1
,
et al., 2010) by an increase in the frequency of m N-N band by
assignable to rocking mode of coordinated water (Rani et al., 12–18 cmꢀ1. A shift of the medium intensity peak at
1994). Presence of water molecules in the complexes is 1448 cmꢀ1 attributed to m (C ¼ N) of the quinoxaline ring in
authenticated by the endotherms and weight loss in thermal the ligand to lower frequency confirms the participation of
analysis data. The sharp peak at 1621 cmꢀ1, characteristic of quinoxaline ring nitrogen in bonding with the metal ions.
azomethine group experienced a downward shift due to the
The peak observed at 1338 cmꢀ1 ascribed to m (C-O) in
involvement of nitrogen (Yeap & Heng, 2014) of hydrazone the ligand, experienced an upward shift (Kavitha & Lakshmi,
group in coordination with metal ions. Participation of azome- 2017) in all the complexes, inferring the deprotonation of
thine nitrogen in complexation is further supported (Hosney phenolic groups prior to complexation. Coordination of the

6
P. SUKANYA AND C. V. R. REDDY
ligand to the metal ion is substantiated by the weak, non lig-
and bands in the low frequency region of the spectra of
complexes corresponding to M-N and M-O bonds.
From the IR spectral analysis, it may be inferred that the
ligand contains four potential donor sites and all of them are
involved in the complexation.
3.2.4. Mass spectra of the complexes
The composition of the complexes was established by mass
spectra. The prominent m/z peaks observed at 385.2862,
389.3163 and 394.2864 in the mass spectra of the Mn(II), Ni(II)
and Cu(II) complexes, respectively, corresponds to the empirical
formulae assigned. The CHN analysis (Table 4) values and mass
spectral data are in agreement with the values calculated from
the empirical formulae assigned to the complexes. (The mass
spectra of the Mn(II), Ni(II) and Cu(II) complexes are reported,
respectively, in Figures S4–S6, supplementary material).
3.2.5. TGA and DTA of the complexes
The TGA curve of Mn(II) complex reveals a total weight loss
of 9.8% up to 139 ꢁC, associated with the expulsion of two
coordinated water molecules (Calcd.9.34%). A corresponding
endotherm in DTA curve of the complex also confirms the
presence of coordinated water (Gaber et al., 2018). On fur-
ther heating, the complex decomposes gradually.
The TGA of Ni(II) complex indicates loss of 9.33% mass up
to 156 ꢁC implying the expulsion of two coordinated water
molecules (Calcd.9.25%). The endotherm observed in the cor-
responding DTA curve at tmin 156 ꢁC indicates the presence
Figure 4. Structure of RHQO.
Figure 5. Crystal structure of RHQOꢄH2O.

JOURNAL OF BIOMOLECULAR STRUCTURE AND DYNAMICS
7
Table 1. Crystal data and structure refinement for RHQOꢄH2O.
Identification code
shelx
Empirical formula
Formula weight
Temperature
C30 H28 N8 O8
628.60
298(2) K
Wavelength
0.71073 Å
Crystal system
Space group
Unit cell dimensions
Monoclinic
P 21/c
a ¼ 16.2621(18) Å, a ¼ 90ꢁ
b ¼ 13.3311(14) Å, b ¼ 114.066(2)ꢁ
c ¼ 14.2303(15) Å, c ¼ 90ꢁ.
Volume
2816.8(5) Å3
Z
4
Density (calculated)
Absorption coefficient
F(000)
Crystal size
Theta range for data collection
Index ranges
Reflections collected
Independent reflections
Completeness to theta ¼ 24.999ꢁ
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2sigma(I)]
R indices (all data)
Extinction coefficient
Largest diff. peak and hole
1.482 mg/m3
0.111 mmꢀ1
1312
0.34 ꢅ 0.28 ꢅ 0.20 mm3
1.371 to 24.999ꢁ.
ꢀ19 < ¼ h < ¼ 19, ꢀ15 < ¼ k < ¼ 15, ꢀ16 < ¼ l < ¼ 16
26,585
4957 [R(int) ¼ 0.0786]
100.0%
Empirical
1.0000 and 0.7546
Full-matrix least-squares on F2
4957/14/463
0.992
R1 ¼ 0.0612, wR2 ¼ 0.1263
R1 ¼ 0.1200, wR2 ¼ 0.1519
n/a
0.274 and ꢀ0.215 e.Åꢀ3
Table 2. Bond lengths [Å] and angles [ꢁ] of RHQO.H2O.
Bond
Bond
length
Angle
Bond angle
Angle
Bond angle
O(1)-C(1)
1.229(3)
1.361(3)
1.367(4)
1.246(3)
1.359(3)
1.378(3)
1.347(4)
1.398(4)
0.893(17)
1.305(3)
1.387(4)
1.350(4)
1.373(3)
1.354(3)
1.343(3)
1.393(3)
1.00(3)
1.299(3)
1.389(3)
1.388(3)
1.373(4)
1.390(4)
1.246(3)
0.863(17)
1.293(3)
O(4)-C(16)-N(5)
O(5)-C(26)-C(27)
C(22)-C(21)-H(21)
N(2)-C(8)-C(7)
N(2)-C(2)-C(1)
N(3)-C(2)-C(1)
O(1)-C(1)-C(2)
N(1)-C(1)-C(2)
C(5)-C(6)-C(7)
N(4)-C(9)-C(10)
N(4)-C(9)-H(9)
C(10)-C(9)-H(9)
N(2)-C(2)-N(3)
N(7)-C(17)-N(6)
O(1)-C(1)-N(1)
O(3)-C(13)-C(12)
O(3)-C(13)-C(14)
C(12)-C(13)-C(14)
C(15)-C(14)-C(13)
C(15)-C(14)-H(14)
C(13)-C(14)-H(14)
C(14)-C(15)-C(10)
C(6)-C(7)-N(1)
123.6(3)
118.1(3)
120.1
C(11)-O(2)-H(2A)
C(13)-O(3)-H(3B)
C(26)-O(5)-H(5A)
C(28)-O(6)-H(6A)
C(1)-N(1)-C(7)
C(1)-N(1)-H(1A)
C(7)-N(1)-H(1A)
C(2)-N(2)-C(8)
101(2)
117(3)
107(3)
O(2)-C(11)
O(3)-C(13)
O(4)-C(16)
O(5)-C(26)
O(6)-C(28)
N(1)-C(1)
N(1)-C(7)
N(1)-H(1A)
N(2)-C(2)
122.4(3)
125.3(3)
114.3(3)
123.5(3)
123.0(3)
113.5(3)
118.2(3)
120.9
111(3)
124.5(3)
118.5(19)
117.0(19)
117.4(3)
118.0(3)
126.4(18)
115.4(18)
121.8(3)
123.8(3)
117.1(18)
118.7(18)
117.8(3)
118.6(3)
118(2)
116.5(3)
116.5(3)
122.3(3)
121.2(3)
122.4(3)
114.1(3)
119.7(3)
C(2)-N(3)-N(4)
C(2)-N(3)-H(3A)
N(4)-N(3)-H(3A)
C(9)-N(4)-N(3)
N(2)-C(8)
N(3)-C(2)
120.9
N(3)-N(4)
N(7)-C(17)
N(5)-C(16)
N(5)-C(22)
N(5)-H(5B)
N(6)-C(17)
N(6)-C(23)
N(7)-N(8)
C(29)-C(30)
C(10)-C(15)
O(4)-C(16)
N(7)-H(7A)
N(8)-C(24)
120.4(3)
122.5(3)
123.5(3)
121.7(3)
118.1(3)
120.2(3)
119.2(3)
120.4
C(16)-N(5)-C(22)
C(16)-N(5)-H(5B)
C(22)-N(5)-H(5B)
C(17)-N(6)-C(23)
C(17)-N(7)-N(8)
C(17)-N(7)-H(7A)
C(24)-N(8)-N(7)
C(15)-C(10)-C(11)
C(15)-C(10)-C(9)
C(11)-C(10)-C(9)
O(4)-C(16)-C(17)
N(5)-C(16)-C(17)
C(20)-C(21)-C(22)
120.4
122.6(3)
121.9(3)
116.9(3)
119.8(3)
C(8)-C(7)-N(1)
N(2)-C(8)-C(3)
of water. Further heating involves gradual loss in mass which 434 ꢁC in DTA curve indicates oxidation, phase transition and/
confirms the decomposition of the complex.
total weight loss of 9.86% observed between
or decomposition of the complex. The final residue obtained
(21.73%) corresponds to metal oxide (Calcd.20.18). (The ther-
mograms of the Mn(II), Ni(II) and Cu(II) complexes are reported,
respectively, in Figures S7–S9, supplementary material).
A
85.4–147.7 ꢁC in the TGA curve of Cu(II) complex, in single step
is attributed to the loss of two coordinated water molecules
(Calcd.9.14%). The corresponding endotherm at tmin 158 ꢁC in
DTA curve of the complex is an additional evidence for the
loss of coordinated water. A steep fall in the weight of the
complex at higher temperatures is ascribed to the decompos-
3.2.6. Magnetic moment data of the complexes
The meff values of Mn(II), Ni(II) and Cu(II) complexes are 6.2,
3.14 and 1.78 B.M., respectively, which are in agreement with
ition of the organic part of the complex. An exotherm at the presence of five, two and one electron, respectively.

8
P. SUKANYA AND C. V. R. REDDY
Figure 6. 1D-packing diagram of RHQOꢄH2O.
Table 3. Hydrogen bonds with H.A < r(A) þ 3.000 Angstroms and < DHA > 110ꢁ.
D-H
d(D-H)
d(H..A)
<DHA
d(D..A)
A
C6-H6
C9-H9
C17-H17A
N1-H1A
N3-H3A
0.930
0.930
0.960
0.872
0.866
2.777
2.371
2.768
1.979
2.110
129.93
143.54
118.20
162.57
155.45
3.449
3.167
3.331
3.823
3.919
O3
O1
O2
O3
O1
D ¼ Donor, H ¼ hydrogen, A ¼ Acceptor.
Table 4. Mass and elemental analysis data of metal complexes of RHQO.
Calcd. (Found)%
Empirical formula weight
Empirical formula of the complex
15H14N4O5Mn
Calcd. (Found)
Carbon
Hydrogen
Nitrogen
C
385.23
(385.2862)
388.98
(389.3173)
393.84
46.76
(46.62)
46.31
(46.22)
45.74
3.66
(3.41)
3.62
(3.54)
3.58
14.54
(14.48)
14.40
(14.31)
14.22
C15H14N4O5Ni
C15H14N4O5Cu
(394.2864)
(45.68)
(3.41)
(14.16)
Table 5. Significant IR frequencies of RHQO and its complexes in cmꢀ1
.
3.2.8. EPR spectra
Ligand/Complex
m (C ¼ N)
m(C ¼ N)
m (C-O)
ring
New bands
EPR spectrum of Mn(II) complex appears to be isotropic, sug-
gesting large spin lattice interactions resulting in broadening
of spectral line. The hyperfine structure is not resolved at
room temperature. The g value calculated is 2.19.
free
RHQO
1621
1610
1614
1606
1448
1394
1435
1432
1338
1354
1355
–
[Mn RHQO(H2O)2]n
[Ni RHQO(H2O)2]n
[Cu RHQO(H2O)2]n
610,555,468,383
605,565,468,412
1352 688,619,599,524,461
The EPR spectral parameters of the Cu(II) complex recorded
in solid state at room temperature, g║ (2.18) > g (2.12) >
?
2.0023 suggest tetragonal elongated geometry for the com-
plex (Adam et al., 2018). The value of g║ (<2.3) and axial sym-
metry parameter, G value (1.55) indicate covalent environment
in M-L bond and considerable exchange interactions in the
solid complex, respectively. (The EPR spectra are presented in
Figures S11 and S12, supplementary material).
3.2.7. Electronic spectra
The significant bands observed in the electronic absorption
spectra of metal complexes that are different from the ligand
spectral bands are due to d-d transitions. The variation in
the position and intensity of the bands characteristic of the
ꢃ
ꢃ
n!p and p !p transitions of free ligands in the absorp-
tion spectra of metal complexes indicate that these transi-
tions are affected by chelation.
3.2.9. Scanning electron microscopy (SEM)
The geometry of the complexes under study is estab-
lished by their electronic spectral data. Electronic spectrum
The SEM studies were carried out to ascertain the surface
morphology of the metal complexes. The SEM micrograph of
RHQO differs significantly from its complexes. The uniform
matrix indicates single phase formation of the complexes
with well defined shapes (Figure 7). The ligand shows rod-
like structure. Mn(II) complex has wrecked rock like structure.
The Ni(II) complex shows pyramidal particles while the Cu(II)
of Mn(II) complex exhibits a peak at 403 nm corresponding
6
to A1g
!
4A1g transitions suggesting an octahedral geom-
etry of the complex. The band at 437 nm in the Ni(II) com-
3
3
plex is in accordance with the A2g (F) ! T1g (P) transition
for six coordinated octahedral Ni(II) complex (Raman et al.,
2004). The electronic spectrum of Cu(II) complex shows
bands at 450 and 478 nm corresponding to B1g
transition, indicating distorted octahedral geometry around
Cu(II) ion (Ramadthan, 2013). (The electronic spectra of the
complexes are presented in Figure S10, supplemen-
tary material).
2
!
2E1g
€
complex has agglomerated morphology (Muller et al., 2014).
Since the ligand(RHQO) has four binding sites viz nitro-
gens of the quinoxalin ring, free azomethine group and
deprotonated oxygens of two phenolic groups, polymer
complexes were obtained (Kavitha & Lakshmi, 2017).

JOURNAL OF BIOMOLECULAR STRUCTURE AND DYNAMICS
9
Figure 7. SEM images of RHQO and its M(II) complexes.
Based on the results obtained, the general structure of
the polymeric coordination complexes under investigation is
formulated as in Figure 8.
3.3. Biological activity studies of metal complexes
3.3.1. DNA binding studies by electronic absorp-
tion titrations
During the titration of RHQO and its metal complexes with
CT-DNA, the hypochromic shift observed in the UV–Vis spec-
tra indicated the possible groove binding interaction
between the electronic states of the chromophores of RHQO,
its metal complexes and the bases of CT-DNA (Chakraborty
et al., 2019).
In the presence of CT-DNA, RHQO and its metal com-
plexes exhibited significant decreases in absorbance and
Figure 8. Structure of M(II) complexes of RHQO.

10
P. SUKANYA AND C. V. R. REDDY
Figure 9. Absorption spectrum of RHQO in absence and in presence of increasing amounts of DNA from top to bottom. Inset: Plot of [DNA]/(ea ꢀ ef) vs [DNA].
intensity of the peaks at 382, 437 and 450 nm, respectively,
with the corresponding binding constants 5.14 ꢅ 106,
6.9 ꢅ 106 and 8.07 ꢅ 105 Mꢀ1
.
Viscosity measurements could have been helpful to con-
firm the binding mode of DNA. However, when the metal
complexes are polymeric and DNA is also another polymer,
the changes in the viscosity can be due to changes in the
structures of both DNA and the polymeric complexes.
Therefore it may not be possible to predict the mode of
binding by viscosity measurements. In addition, poor solubil-
ity of polymeric complexes also could not help in viscosity
measurements (Kumar & Arunachalam, 2009).
Figure 10. Agarose gel electrophoresis pattern for the cleavage of supercoiled
pBR 322 DNA by RHQO and its M(II) complexes.
marginal shift in k
of absorption. It is known that a small
max
3.3.2. DNA cleavage studies
shift in k
is the most possible outcome of groove bind-
max
The ability of RHQO and its complexes to cleave super coiled
pBR 322 DNA to nicked circular form was studied by agarose
gel electrophoresis. When plasmid DNA is subjected to elec-
trophoresis, fastest migration can be observed for the super
coiled form (Form-I). If one strand is cleaved, the super coils
will relax to generate a relatively slow moving circular form
(Form-II).If both the strands are cleaved, a linear form (Form-
III) that moves in between will be produced (Raman & Raja,
2007; Sasmal et al., 2008). The gel electrophoresis patterns of
RHQO and its metal complexes are shown in Figure 10.
Lane-1 demonstrates the control experiment using DNA
alone and no significant cleavage was noticed even on pro-
longed exposure. Lane-2 (ligand) and Lane-3-5(complexes of
Mn(II), Ni(II) and Cu(II), respectively) demonstrate that the lig-
and and its complexes are able to cleave the super coiled
DNA (Form I) to open circular form (Form-II). However, Form-
III is not observed in any of these cases. Thus the ligand and
all the metal complexes efficiently cleaved the super coiled
pBR 322 DNA in to open circular form, in the absence of any
external reagents.
ing. Contrarily, large shift in k
is associated with intercal-
max
ation mode of binding. The absorption spectra of all these
molecules indicate the groove binding mode with CT- DNA
rather than intercalation (Moradi et al., 2018).
The CT-DNA induced spectral changes may also be due to
change in polarity in the vicinity of molecule under investi-
gation, which in turn may affect the stabilization of different
energy levels. With the addition of CT- DNA, the polarity of
the environment around the drug molecule (RHQO or its
metal complex) decreases and the energy gap between its
highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO) decreases. The absence
of an isosbestic point in the absorption spectra is also indica-
tive of groove binding rather than intercalation (Sahoo
et al., 2010).
Different modes of binding of the polymeric complexes
with the double stranded DNA can be due to their structure,
charge and type of ligands. As double helix DNA possesses
several sites for hydrogen bonding, which are accessible
both in the major and minor grooves, it is likely that the -NH
groups of the drug molecule forms hydrogen bonds with
DNA, which may contribute to the significant changes 3.3.3. Anticancer activity
observed in the absorption spectra (Ataci et al., 2018).
An in-vitro anticancer activity of the Cu(II) and Ni(II) com-
The binding constant of RHQO (Figure 9) is 1.82 ꢅ 106 plexes of RHQO was investigated by MTT assay, using four
Mꢀ1
. The Mn(II), Ni(II) and Cu(II) complexes (Figures cancer cell lines, Hela, B16-F10,SKOV3 and MCF7. Normal
S.13–S.15, supplementary material) show a decrease in mammalian cell line employed was Chinese hamster ovary

JOURNAL OF BIOMOLECULAR STRUCTURE AND DYNAMICS
11
cells (CHO-K1).The results are expressed as IC50 values, which
represent the concentration of the complex in lM, required
for the inhibition of the growth of 50% of the cells in-vitro
(Hermawan et al., 2012).
ORCID
Panaganti Sukanya
http://orcid.org/0000-0003-3374-2791
References
The IC50 values of Ni(II) complex are 23.92 0.21,
23.36 1.26 and 16.70 1.98 lM for Hela, B16-F10 and MCF7,
respectively, while it exhibited no activity against the cancer
cell line SKOV3 and normal mammalian Chinese hamster
ovary cell lines (CHO-K1).
The Cu(II) complex was active against the cancer cell lines
B16-F10 and MCF-7 with an IC50 value of 43.76 2.06 and
16.17 0.59 lM, respectively. The complex was not active
against the cancer cell lines, Hela and SKOV3 and also the
normal mammalian cell line, CHO-K1.
Abid, K., Al-Bayati, S., & Rasheed, A. (2016). Synthesis, Characterization,
Thermal Study and Biological Evaluation of Transition Metal
Complexes Supported by ONNNO – Pentadentate Schiff Base Ligand.
American Journal of Chemistry, 6, 1.
Adam, A. M. A., Alhadhrami, A., Saad, H. A., & Refat, M. S. (2018). Green
synthesis of silver nanoparticles using Thymus kotschyanus extract
and evaluation of their antioxidant, antibacterial and cytotoxic effects.
Applied Organometallic Chemistry, 32, 3950.
Arjmand, F., Parveen, S., Afzal, M., & Shahid, M. (2012). Synthesis, charac-
terization, biological studies (DNA binding, cleavage, antibacterial and
topoisomerase I) and molecular docking of copper(II) benzimidazole
complexes. Journal of Photochemistry and Photobiology B, 114, 15–26.
https://doi.org/10.1016/j.jphotobiol.2012.05.003
Ataci, N., Ozcelik, E., & Arsu, N. (2018). Spectrophotometric study on
binding of 2-thioxanthone acetic acid with ct-DNA. Spectrochimica
Acta, Part A, 204, 281–286. https://doi.org/10.1016/j.saa.2018.06.001
Bollu, V. S., Nethi, S. K., Krishna, D. R., Shiva, N. R. S., Misra, S., & Patra,
C. R. (2016). Evaluation of in vivo cytogenetic toxicity of europium
hydroxide nanorods (EHNs) in male and female Swiss albino mice.
Nanotoxicology, 10(4), 413–425. https://doi.org/10.3109/17435390.
2015.1073398
Chakraborty, A., Panda, A. K., Ghosh, R., & Biswas, A. (2019). DNA minor
groove binding of a well known anti-mycobacterial drug dapsone: A
spectroscopic, viscometric and molecular docking study. Archives of
Biochemistry and Biophysics, 665, 107–113. https://doi.org/10.1016/j.
abb.2019.03.001
Cheeseman, G. W. H., & Rafiq, M. (1971). Quinoxalines and related com-
pounds. Part VIII. The reactions of quinoxaline-2(1H)-ones and
-2,3(1H,4H)-diones with hydrazine. Journal of the Chemical Society C,
453.
The IC50 values demonstrate that both the Cu(II) and Ni(II)
complexes of RHQO have potential cytotoxic activity against
MCF-7 cell lines.
4. Conclusions
The Schiff base, RHQO behaves as dibasic, quadridentate,
N,N,O,O donor ligand, coordinate with the metal ions
through two deprotonated phenolic oxygens, free azome-
thine and quinoxaline ring nitrogens. Spectral and analytical
data suggest that all the complexes are polymeric with octa-
hedral geometry around the metal ions. The empirical formu-
lae indicate the metal to ligand ratio to be 1:1. All the
complexes were found to be non-electrolytes.
The Kb values from the electronic absorption spectro-
scopic titrations and hypochromism indicate that the ligand
and its metal complexes have strong affinity to bind with
DNA by groove binding mode. Agarose gel electrophoresis
indicates that the ligand and its complexes efficiently
cleaved the supercoiled pBR 322 DNA in to nicked form.
Cytotoxic activity studies indicated that the Ni(II) complex
was active against Hela, B16-F10 and MCF7, while Cu(II) com-
plex was active against B16-F10 and MCF-7 cell lines. Both
the complexes did not affect the normal mammalian Chinese
hamster ovary cell line (CHO-K1).
Chinen, L. K., Galen, K. P., Kuan, K. T., Dyszlewski, M. E., Ozaki, H., Sawai,
H., Pandurangi, R. S., Jacobs, F. G., Dorshow, R. B., & Rajagopalan, R.
(2008). Fluorescence-enhanced europium-diethylenetriaminepentaace-
tic (DTPA)-monoamide complexes for the assessment of renal func-
tion. Journal of Medicinal Chemistry, 51(4), 957–962. https://doi.org/10.
1021/jm070842þ
Creaven, B. S., Devereux, M., Karcz, D., Kellett, A., McCann, M., Noble, A.,
& Walsh, M. (2009). Copper(II) complexes of coumarin-derived Schiff
bases and their anti-Candida activity. Journal of Inorganic
Biochemistry, 103(9), 1196–1203. https://doi.org/10.1016/j.jinorgbio.
2009.05.017
Gaber, M., El-Ghamry, H. A., Fathalla, S. K., & Mansour, M. A. (2018).
Synthesis, spectroscopic, thermal and molecular modeling studies of
Zn2þ, Cd2þ and UO22þ complexes of Schiff bases containing tri-
azole moiety. Antimicrobial, anticancer, antioxidant and DNA binding
studies. Materials Science & Engineering C, 83, 78–89. https://doi.org/
10.1016/j.msec.2017.11.004
Geary, W. J. (1971). The use of conductivity measurements in organic sol-
vents for the characterisation of coordination compounds.
Coordination Chemistry Reviews, 7(1), 81–122. https://doi.org/10.1016/
S0010-8545(00)80009-0
Acknowledgements
The authors are thankful to Jawaharlal Nehru Technological University
Hyderabad, for providing research facilities and UGC networking
resource centre, University of Hyderabad, India, for extending spectral
and single crystal XRD facilities.
Hermawan, A., Nur, K. A., Sarmoko, Dewi, D., Putri, P., & Meiyanto, E.
(2012). Ethanolic Extract of Moringa oleifera Increased Cytotoxic Effect
of Doxorubicin on HeLa Cancer Cells. Journal of Natural Remedies, 12,
108.
Disclosure statement
The authors declare that there is no conflict of interest regarding the
publication of this paper.
Hosney, N. M., Mahmoud, M. A.,
& Aly, M. R. E. (2010). 2-
Hydroxybenzaldehyde-(4,6-Dimethylquinolin-2-yl)-Hydrazone (HBDH),
Synthesis, Characterization, and Ligational Behavior Towards Some
Metals. Synthesis and Reactivity in Inorganic, Metal-Organic and Nano
Metal Chemistry, 40, 439.
Funding
Kavitha, N., & Lakshmi, P. V. A. (2017). Synthesis, characterization and
thermogravimetric analysis of Co(II), Ni(II), Cu(II) and Zn(II) complexes
supported by ONNO tetradentate Schiff base ligand derived from
This research did not receive any specific grant from funding agencies in
the public, commercial or not-for-profit sectors.

12
P. SUKANYA AND C. V. R. REDDY
hydrazino benzoxazine. Journal of Saudi Chemical Society, 21, Raman, N., Ravichandran, S., & Thangaraja, C. (2004). Copper(II), cobalt(II),
S457–S466. https://doi.org/10.1016/j.jscs.2015.01.003
nickel(II) and zinc(II) complexes of Schiff base derived from benzil-2,4-
dinitrophenylhydrazone with aniline. Journal of Chemical Sciences,
116(4), 215–219. https://doi.org/10.1007/BF02708270
Khedr, A. M., Gaber, M., Issa, R. M., & Erten, H. (2005). Synthesis and spec-
tral studies of 5-[3-(1,2,4-triazolyl-azo]-2,4-dihydroxybenzaldehyde (TA)
and its Schiff bases with 1,3-diaminopropane (TAAP) and 1,6-diamino-
hexane (TAAH). Their analytical application for spectrophotometric
microdetermination of cobalt(II). Application in some radiochemical
studies. Dyes and Pigments, 67(2), 117–126. https://doi.org/10.1016/j.
dyepig.2004.11.004
Kumar, R. S., & Arunachalam, S. (2009). DNA binding and antimicrobial
studies of polymer-copper(II) complexes containing 1,10-phenanthro-
line and L-phenylalanine ligands. European Journal of Medicinal
Chemistry, 44(5), 1878–1883. https://doi.org/10.1016/j.ejmech.2008.11.
001
Mandal, S. S., Varshney, U., & Bhattacharya, S. (1997). Role of the central
metal ion and ligand charge in the DNA binding and modification by
metallosalen complexes. Bioconjugate Chemistry, 8(6), 798–812.
https://doi.org/10.1021/bc970121x
Moradi, S. Z., Nowroozi, A., Sadrjavadi, K., Moradi, S., Mansouri, K.,
Hosseinzadeh, L., & Shahlaei, M. (2018). Direct evidences for the
groove binding of the Clomifene to double stranded DNA.
International Journal of Biological Macromolecules, 114, 40–53. https://
doi.org/10.1016/j.ijbiomac.2018.03.040
Rani, D. S., Lakshmi, P. V. A., & Raju, V. J. (1994). Structural elucidation of
manganese(II), iron(III), cobalt(II), nickel(II), copper(II) and zinc(II) com-
plexes of a new multidentate dihydrazino quinoxaline derivative.
Transition Metal Chemistry, 19, 75.
Reichman, M. E., Rice, S. A., Thomas, C. A., & Doty, P. (1954). A further
examination of the molecular weight and size of desoxypentose
nucleic acid. Journal of the American Chemical Society, 76(11),
3047–3053. https://doi.org/10.1021/ja01640a067
Sahoo, D., Bhattacharya, P., & Chakravorti, S. (2010). Quest for mode of
binding of 2-(4-(dimethylamino)styryl)-1-methylpyridinium iodide with
calf thymus DNA. The Journal of Physical Chemistry B, 114(5),
2044–2050. https://doi.org/10.1021/jp910766q
Sasmal, P. K., Patra, A. K., & Chakravarty, A. R. (2008). Synthesis, structure,
DNA binding and DNA cleavage activity of oxovanadium(IV) N-salicyli-
dene-S-methyldithiocarbazate complexes of phenanthroline bases.
Journal of Inorganic Biochemistry, 102(7), 1463–1472. https://doi.org/
10.1016/j.jinorgbio.2007.12.031
Tan, K. W., Seng, H. L., Lim, F. S., Cheah, S., Ng, C. H., Koo, K. S., Mustafa,
M. R., Ng, S. W., & Maah, M. J. (2012). Towards a selective cytotoxic
agent for prostate cancer: Interaction of zinc complexes of polyhy-
droxybenzaldehyde thiosemicarbazones with topoisomerase I.
Polyhedron, 38(1), 275–284. https://doi.org/10.1016/j.poly.2012.03.014
Tarallo, M. B., Urquiola, C., Monge, A., Costa, B. P., Ribeiro, R. R., Costa-
Filho, A. J., Mercader, R. C., Pavan, F. R., Leite, C. Q. F., Torre, M. H., &
Gambino, D. (2010). Design of novel iron compounds as potential
therapeutic agents against tuberculosis. Journal of Inorganic
Biochemistry, 104(11), 1164–1170. https://doi.org/10.1016/j.jinorgbio.
2010.07.005
€
Muller, K. H., Motskin, M., Philpott, A. J., Routh, A. F., Shanahan, C. M.,
Duer, M. J., & Skepper, J. N. (2014). The effect of particle agglomer-
ation on the formation of a surface-connected compartment induced
by hydroxyapatite nanoparticles in human monocyte-derived macro-
phages. Biomaterials, 35(3), 1074–1088. https://doi.org/10.1016/j.bio-
materials.2013.10.041
ꢀ
Noblıa, P., Vieites, M., Torre, M. H., Costa-Filho, A. J., Cerecetto, H.,
ꢀ
Gonzalez, M., Lavaggi, M. L., Adachi, Y., Sakurai, H., & Gambino, D.
(2006). Novel vanadyl complexes with quinoxaline N(1),N(4)-dioxide
derivatives as potent in vitro insulin-mimetic compounds. Journal of
Inorganic Biochemistry, 100(2), 281–287. https://doi.org/10.1016/j.
jinorgbio.2005.11.012
Peng, B., Chen, X., Du, K., Yu, B., Chao, H., & Ji, L. (2009). Spectrochim.
Spectrochimica Acta, Part A, 74(4), 896–901. https://doi.org/10.1016/j.
saa.2009.08.031
Phillips, M. A. (1928). CCCXVII.—The formation of 2-substituted benzimi-
nazoles. Journal of the Chemical Society, 2393–2399. https://doi.org/10.
1039/JR9280002393
Ramadthan, E. M. (2013). Synthesis and Characterization of New Some
First Transition Metals Complexes of Schiff Base N,N’-bis [2-
Methylenethiophene]-1,2-phenylenediimine. Iraqi National Journal of
Chemistry, 50, 154.
ꢀ
Torre, M. H., Gambino, D., Araujo, J., Cerecetto, H., Gonzalez, M., Lavaggi,
M. L., Azqueta, A., Cerain, A. L., Vega, A. M., Abram, U., & Costa-Filho,
A. J. (2005). Novel Cu(II) quinoxaline N1,N4-dioxide complexes as
selective hypoxic cytotoxins. European Journal of Medicinal Chemistry,
40(5), 473–480. https://doi.org/10.1016/j.ejmech.2004.11.012
Xu, Z., Liu, H., Wang, M., Xiao, S., Yang, M., & Bu, X. (2002). Manganese(II)
complex of 6,7-dicycanodipyridoquinoxaline with antitumor activities:
Synthesis, crystal structure and binding with DNA. Journal of
Inorganic Biochemistry, 92(3–4), 149–155. https://doi.org/10.1016/
S0162-0134(02)00569-X
Yeap, G., & Heng, B. (2014). Mesogenic copper(II) complexes with [1,2,3]-
triazole-based bidentate Schiff bases. Journal of Chemical Sciences,
126(1), 247–254. https://doi.org/10.1007/s12039-013-0545-0
Yuan, C., Wei, Y., & Yang, P. (2006). DNA-binding and cleavage studies of
zinc(II) mixed-polypyridyl complex. Chinese Journal of Chemistry, 24(8),
1006–1012. https://doi.org/10.1002/cjoc.200690188
Raman, N., & Raja, S. J. (2007). DNA cleavage, structural elucidation and
anti-microbial studies of three novel mixed ligand Schiff base com-
plexes of copper(II). Journal of the Serbian Chemical Society, 72(10),
983–992. https://doi.org/10.2298/JSC0710983R