Synthesis, characterization, anticancer and DNA photocleavage study of novel quinoline Schiff base and its metal complexes

Sanjay K. Patil; Baliram T. Vibhute

doi:10.1016/j.arabjc.2021.103285

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Original article

2021

:14;

202108

doi:

10.1016/j.arabjc.2021.103285

Synthesis, characterization, anticancer and DNA photocleavage study of novel quinoline Schiff base and its metal complexes

Sanjay K. Patil, Baliram T. Vibhute^⁎

Department of Chemistry, C. K. T. ACS College, New Panvel, University of Mumbai, Maharashtra, India

⁎Corresponding author. vbtchem@gmail.com (Baliram T. Vibhute)

Received: 2021-5-19, Accepted: 2021-6-19,

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Abstract

This work reports synthesis of novel Quinoline Schiff base by condensation of 2-hydroxyquinoline-3-carbaldehyde and 4-methylbenzenesulfonohydrazide. Prepared Schiff base was further used for the formation of metal complexes with Cu (II), Ni (II), Co (II) & Cd (II). The complete formation of Schiff base and its metal complexes were confirmed by spectroscopic techniques i.e. FT-IR, ¹H NMR, ¹³C NMR, ESI-MS, UV–Visible, and EPR. Low conductivity data indicated that prepared compounds are non-electrolytic. FT-IR data suggested that ligand bears O, N, and O binding sites. Magnetic moment of the compounds indicated that Cu (II), Ni (II), and Co (II) metal complexes are paramagnetic. The synthesized compounds were further evaluated for their In vitro cytotoxicity against the A-549 and MCF-7 cell lines by using MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium Bromide] assay. Among all prepared compounds, Cu-complex has shown prominent results with IC₅₀ values 37.03 and 39.43, for A-549 and MCF-7 cancer cells respectively. Further, most active Cu-complex was subjected for photo-cleavage study with pBR322 DNA.

Keywords

Quinoline Schiff base

1H NMR

EPR

Cytotoxicity and DNA photo-cleavage

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1 Introduction

Schiff’s base has been recognized as a significant class of biologically active drug molecules, which has gained key attention of medicinal chemists due to their broad range of pharmacological properties. Many researchers have synthesized these compounds to battle various diseases with the minimum toxicity and maximum effects. These predictions have provided the therapeutic pathway to develop new effective biologically active Schiff’s base derivatives. Numerous Schiff bases have been reported as antitumor (Hu et al., 2012), DNA-binding (Bheemarasetti et al., 2018), antimycobacterial (Patole et al.. 2006), antibacterial (Shinde et al., 2014), the determination of Mg²⁺/Zn²⁺ in MCF-7 cells, Zebrafish larvae, syrup, and water samples (Wang et al. 2019), selectivity, and sensitivity toward human serum albumin (HSA) and Cu²⁺ & S^2- in living cells and biological system (Wang, 2020; Yan et al. 2020).

Quinoline and its derivatives have numerous applications in the biological field. Various derivatives of quinoline have been reported in their study in applications of biological fields. Meanwhile, it shows best antimicrobial (Nandhakumar et al. 2007; El Shehry et al., 2018), antiproliferative (Sumi Choi et al. 2010; Ökten et al., 2013; Ökten et al., 2017; Salih Okten et al., 2017; Chih-Hua Tseng et al. 2009 ), antineoplastic (González-Sánchez et al., 2011), antimalarial (Mishra et al., 2017), anticonvulsant (Guan et al., 2007; Xie et al., 2005) anti‐inflammatory (Pinz et al. 2017) and other activities (Abadi et al., 2005; Coa et al. 2015; Suresh Kumar et al. 2009; Mandewale et al., 2017 ). In addition to this quinoline derivative reported as an anticancer drug, its action of the mechanism involves apoptosis, cell cycle arrest, inhibition of angiogenesis, and disruption of cell migration (Afzal et al. 2015).

Metal complexes play an important role in cancer treatment, the discovery of cisplatin was the first hope for metal chemistry in the field of cancer treatment, cisplatin is widely used in various types of cancer treatment. However, it has some side effects like resistance in tumour cells and dose‐related adverse effects such as bone marrow destruction, kidney problems, vomiting, emotionlessness, trouble walking, hypersensitive reactions, heart disease (Huang et al. 2011; 2000). To overcome these side effects, numerous metal-based compounds are synthesized and used for clinical practice for treating cancer, while some are under clinical trials (Wong and Giandomenico, 1999; Angeles-Boza et al. 2004). Hence, a large number of metal complexes are developed and used as good anticancer drugs compared to cisplatin (Livia Viganor et al. 2017; Wehbe et al., 2017).

According to the current literature survey, rare research work occurs on quinoline-based metal complexes and its anticancer activity. In this work, we have prepared novel quinoline Schiff base and its metal complexes and evaluated for their In vitro cytotoxicity and photo-cleavage study with pBR322 DNA.

2 Materials and instruments

All the required chemicals and solvents were purchased from commercial source with high purity and were used as it is. The progress of the reaction was checked by thin-layer chromatography (TLC). Products were recrystallized using an appropriate solvent. FT-IR spectra were recorded on a Nicolet iS10, thermos Scientific, USA spectrophotometer using KBr pellets in the range of 4000–400 cm. Carry 100 UV–Visible spectrophotometer was used to record electronic spectra. ¹H NMR spectra were recorded on 400 MHz spectrometer using tetramethylsilane (TMS) as an internal standard. ¹³C NMR spectra were recorded at 100 MHz and chemical shifts were reported in parts per million (ppm) relative to TMS as an internal standard. The magnetic moment was measured by the Gouy method at 25 °C temperature using the MKl Johnson Matthey model. The effective magnetic moment was calculated using equation μ_effe = 2.828(xmT))1/2B.M. Waters Micromass Q-Tof Micro with electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) sources having a mass range of 4000 amu in quadruple and 20,000 amu in ToF was used to record ESI MS of the prepared compounds. EPR spectrum of Cu (II) complex was recorded on JES – FA200 ESR spectrometer.

3 General procedure for the synthesis of ligand and its metal complexes

3.1

3.1 Synthesis of ligand (LH): (E)-N'-((2-hydroxyquinolin-3-yl) methylene)-4-methylbenzenesulfonohydrazide

2-chloroquinoline-3-carbaldehyde was synthesized from starting material aniline by acylation followed by Vilsmeier-Haack reaction as reported method (Srivastava and Singh, 2005). A reaction of 2-chloroquinoline-3-carbaldehyde (10 mmol) and H₂O (1 mL) was dissolved in acetic acid (2 mL). The reaction mixture was refluxed for 4 h. The progress of the reaction was checked using TLC. After 4 h, the reaction mass was poured into ice-cold water. The obtained solid was filtered and washed with water. The crude solid was crystallized in ethanol to afford the corresponding pure product 2-hydroxyquinoline-3-carbaldehyde intermediate. The obtained intermediates were further used for the formation of the final ligand. An appropriate mixture of 2-hydroxy-3-carbaldehyde (1 mmol), 4-methylbenzenesulfonohydrazide (1 mmol), and acetic acid (5–10 drops) in ethanol (15 mL) was placed in a round bottom flask. The mixture was then refluxed at 70 °C for 4 h. The progress of the reaction was checked by TLC using ethyl acetate: hexane as a solvent system. The reaction mixture was quenched with crushed ice and extracted with ethyl acetate (2 × 15 mL). The organic extracts were washed with brine solution (2 × 15 mL) and dried over anhydrous sodium sulfate. The solvent was evaporated under reduced pressure to obtain the corresponding crude compounds. The obtained crude compounds were recrystallized using ethanol. Rout of ligand synthesis is given in Scheme 1.

Synthesis of ligand (E)-N'-((2-hydroxyquinolin-3-yl) methylene)-4-methylbenzenesulfonohydrazide.

3.2

3.2 ¹H NMR of ligand

In ligand ¹H NMR, signals observed at δ_H 11.99 & 11.61 ppm were due to NH and aromatic OH protons respectively. The signal at δ_H 2.333 ppm has confirmed the presence of the aromatic –CH₃ group. The formation of HC = N was confirmed by the signal at δ_H 8.09 ppm. Details of the aromatic proton signals are given as 8.09 (s 1H, Ar-H) 7.80–7.79 (d, 2H, Ar-H), 7.76–7.76 (d, 2H, Ar-H), 7.50–7.47 (t, 1H, Ar–H, J = 7.5 Hz), 7.39–7.37 (d, 1H, Ar–H, J = Hz 7.5), 7.27–7.25 (d, 1H, Ar–H, J = 7.3 Hz), 7.18–7.14(t, 1H, Ar-H J = 7.3 Hz). ¹H NMR spectrum of lignad is shown in Fig. 1.

1H NMR Spectrum of Ligand in DMSO‑d6 Solvent.

3.3

3.3 ¹³C NMR of ligand

In ¹³C NMR, the signal at δ_C 21.43 ppm was due to the presence of the aromatic –CH3 group. The C-O carbon was recorded at δ_C 161.13 ppm. The signals at δ_C 127.57 and 130.19 ppm are due to adjacent carbon atoms in the benzene ring. C = N carbon atom resonated at δ_C 143.94 ppm. The signal at δ_C 142.31 ppm was due to the C-S carbon atom. The signal at δ_C 136.60 ppm was due to the carbon of the benzene ring, which is attached to the methyl group. The signals appeared at δ_C 139.40, 135.02, 131.70, 123.51, 125.12, 122.77, 119.23 and 115.51 ppm was due to the quinoline ring carbon atoms.

3.4

3.4 Synthesis of metal complexes

Metal complexes were prepared by adding 25 mL hot ethanolic solution of metal salt (0.0015 mol) to the 30 mL hot ethanolic Schiff base solution (0.0030 mol) in 1:2 ratio for copper (II) chloride (CuCl₂), nickel (II) chloride (NiCl₂), cobalt (II) chloride (CoCl₂) and cadmium (II) chloride (CdCl₂). The reaction mixture was stirred for 30 min, then few drops of 5% NaOH solution were added to maintain basic conditions (pH = 8) of the reaction mixture. The reaction mixture was refluxed for 2hr and the colored precipitate metal complex was obtained. The obtained precipitate was filtered and washed with ethanol and dried in an oven for 90 min. at 80^οC, results in the formation of pure corresponding metal complex. The reaction and proposed structure of metal complexes are given in Scheme 2.

4 Biological activity

4.1

4.1 Cytotoxicity

The cells were seeded at a density of approximately 5 × 10³ cells well in a 96-well flat bottom microtitre plate and maintained at 37 °C overnight in 95% humidity and 5% CO₂. Different concentrations (50, 40, 30, 20, 10, 5 μM) of samples were treated to these cells and incubated for another 48 h. and then washed twice with phosphate buffer saline (PBS) and 20 μl of the MTT [3-(4,5-dimethythiazol-2-yl)-2,5 diphenyltetrazolium bromide] staining solution (5 mgmL⁻¹ in phosphate buffer saline) was added to each well and plate was incubated at 37 °C. Later 4 h, 100 μl of DMSO was added to each well to dissolve the formed crystals and absorbance was recorded at 570 nm using micro plate reader.

4.2

4.2 Photo cleavage study of pBR322 DNA

pBR322 plasmid DNA was used for all cleavage activities. In a typical experiment, 7 µl plasmid DNA (50 ng/µl) was mixed with different concentrations of complexes (5, 10, 20, 40, and 50 µM dissolved in DMF) to determine the optimum activation concentration. 5 µl H₂O₂ (5 mM) was added to the mixture to oxidize the reactant. Finally, the reaction mixture was diluted with the Tris buffer (100 mM Tris, pH: 8) to a total volume of 30 µl. After that reaction mixtures were incubated at 37 °C for two hours. Samples (20 µl) were then loaded with 4 µl loading dye (0.25% bromophenol blue, 0.25% xylene cyanol, 30% glycerol, 10 mmol EDTA) on a 1% agarose gel containing 1 µg/ml of EtBr. The gel was run at 100 V for 3 h in TBE buffer and photographed under UV light (Gup et al., 2015).

5 Results and discussion

Structure of Schiff base was confirmed by various physical and analytical methods. Synthesized Schiff base was further used to form metal complexes with Chlorides of Cu (II), Ni (II), Co (II) and Cd (II) metal salts in 1Metal ion: 2 Schiff base proportions. Obtained physical and analytical data agreed well for the proposed composition of Schiff base and its metal complexes. Colors of prepared metal complexes showed distinct differences from Schiff base color. Formed metal complexes were stable in air and insoluble in water and common organic solvent but, completely soluble in Dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) solvent. The molar conductance of the metal complexes was measured in DMF at a concentration 10^-3 M. and their values ranged from 35 to 51 Ohm⁻¹ cm² mol⁻¹ at room temperature, indicating that the metal complexes were non-electrolytic (Ali et al., 2013). Details of the molar conductance values are given in Table 2.

5.1

5.1 FT-IR spectroscopy

In FT-IR spectra, Schiff base showed peaks at 1660 cm⁻¹ and 3168 cm⁻¹ , which were due to C = N and OH stretching frequency, respectively. However, in case of metal complexes, C = N stretching frequency peaks were observed at 1652 cm⁻¹, 1620 cm⁻¹, 1647 cm⁻¹ and 1629 cm⁻¹ for Cu(II), Ni(II), Co(II) & Cd(II) metal complexes, respectively. The difference in FT-IR peak of C = N in Schiff base and its metal complexes clearly indicates that C = N of Schiff base was co-ordinated with metal ion. The peak observed at 3190 cm⁻¹ for OH in Schiff base was completely disappeared in metal complexes, this was due to the OH group takes part in bond formation with the central metal ion. Some additional peaks were observed in metal complexes in the range of 500–400 cm⁻¹ which also reveals that the central metal atom forms a bond with Schiff base through O-M and N-M. Details of the peaks are given in Table 1.

Table 1 FT-IR stretching frequency of ligand and its metal complexes in cm^−1.

Compounds	ν C = N	ν N-M	ν O-M (OH)	ν O-M (S = O)
C₁₇H₁₅N₃O₃S (LH)	1660	------	-------	-------
(C₁₇H₁₄N₃O₃S)₂Cu	1652	468	512	434
(C₁₇H₁₄N₃O₃S)₂Ni	1620	465	512	442
(C₁₇H₁₄N₃O₃S)₂Co	1647	467	516	431
(C₁₇H₁₄₇N₃O₃S)₂Cd	1629	463	506	440

Table 2 Physical and analytical data of Schiff base and its metal complexes.

Compounds	Yield in %	Color	M.P. in ^oC	λ_m (cm² Ω⁻¹ mol⁻¹)	μ_eff (B.M.)	Mol. Wt.	Elemental Composition in %
Compounds	Yield in %	Color	M.P. in ^oC	λ_m (cm² Ω⁻¹ mol⁻¹)	μ_eff (B.M.)	Mol. Wt.	C	N	H	S
C₁₇H₁₅N₃O₃S (LH)	89	Yellow	226–228	……	…..	342.08	59.61 (59.81)	12.42 (12.31)	4.42 (4.43)	8.36 (9.39)
(C₁₇H₁₄N₃O₃S)₂Cu	85	Green	275–277	38	1.73	743.08	54.71 (54.87)	11.05 (11.29)	3.31 (3.39)	8.43 (8.62)
(C₁₇H₁₄N₃O₃S)₂Ni	78	Green	>300	41	3.25	738.89	55.15 (55.23)	11.42 (11.37)	3.74 (3.82)	8.41 (8.67)
(C₁₇H₁₄N₃O₃S)₂Co	83	Brown	>300	35	4.85	739.08	55.02 (55.21)	11.12 (11.36)	3.74 (3.82)	8.53 (8.67)
(C₁₇H₁₄₇N₃O₃S)₂Cd	76	Buff	>300	51	Dimag-netic	794.05	51.48 (51.49)	10.45 (10.60)	3.40 (3.56)	7.92 (8.09)

*Values in parenthesis are calculated using ChemDraw application.

5.2

5.2 Electronic spectra and magnetic moment

Electronic spectrum of Schiff base was recorded in DMSO at the concentration of 10^-3 M. The transition bands was observed at 315 and 375 nm for π → π* and n → π* transition respectively, this was due to heterocyclic moiety and azomethine group of the Schiff base (Beyazit et al., 2017). In case of metal complexes, the transition band for π → π* and n → π* was observed at 330.5 and 380 nm, 339.5 and 386.5, 334.5 and 389.5, 342 and 394 nm for Cu(II), Ni(II), Co(II), & Cd(II) metal complexes, respectively. The shifting of transition band at longer wavelengths in metal complexes was due to coordination of Schiff base with a central metal ion (Tyagi et al., 2015). In the metal complexes, these bands were shifted to a longer wave length due to increasing its intensity. This shift may be caused due to the contribution of lone pair of electrons of nitrogen of azomethine of Schiff base compound to a metal ion.

Magnetic moment susceptibility of the metal complexes was recorded at room temperature for Cu (II), Ni (II) and Co (II) complexes and they were found to be paramagnetic. The observed magnetic moment for Cu (II) complex was 1.75 B.M. which was approximately equal to spin only value of one unpaired electron 1.73B.M. for octahedral geometry (Singh et al., 2007). The magnetic moment value of Ni (II) complex was observed as 3.25 B.M., which was in the range of expected value for octahedral geometry of metal complex 2.83–3.50 B.M. (Rao et al., 2005). For Co (II) complex, the observed magnetic moment was 4.85 B.M. which well agreed with the expected value for octahedral complexes of Cobalt (Greenwood and Earnshaw, 1997). The magnetic moment values are given in Table 2.

5.3

5.3 Elemental analysis

Ligand and its metal complexes were subjected for elemental analysis to get exact elemental composition. The analytical data for compositing carbon, nitrogen, hydrogen and sulphur in ligand and metal complexes were exactly matched with the actual composition of ligand and metal complexes, which reveals that compounds were completely formed. The detailed results are given in Table 2.

5.4

5.4 Mass spectrometry (MS)

To get a confirmation of complete formation of Schiff base and its metal complexes, all the prepared compounds were subjected to ESIMS spectra. For Schiff base, molecular ion peak was obtained at m/z⁺ 342.17, which is exactly equal to its molecular weight. In case of metal complexes, molecular ion peaks were obtained at m/z⁺ 742.99, 740.02, 740.10 and 794 for Cu(II), Ni(II), Co(II) and Cd(II), respectively. These observed peaks are equal to its corresponding molecular weight of the metal complexes. All the figures of ESIMS are given in the Supplementary data file (Fig. S8 to S12).

5.5

5.5 EPR spectra

X-band EPR spectra of Cu(II) complex were recorded in DMSO solvent at liquid nitrogen temperature (LNT) as shown in Fig. 2. From obtained EPR spectrum, we have calculated the g_|| and g⊥ values. From these values, we have obtained the geometry and types of bonding in the complex. To calculate the ground state of the Cu(II) complex, the Hamiltonian parameter was used. For octahedral geometry, the g -tensor parameter value is g _|| > g ⊥ > 2.0023 and g ⊥ > g _|| > 2.0023, which indicated that the unpaired electrons are present in the d_x²_-y² and d_z² orbitals, respectively (Thaker et al., 2005). If, the g _|| < 2.3 then bonding is covalent and g _|| > 2.3, then the bonding is ionic in nature (Kivelson, 1997). The calculated values of g || and g ⊥ were 2.0243 and 2.0058 respectively. Details of the values are given in Table 3 (Fig. 2).

Table 3 EPR spectral data of Cu (II) complex.

g ⊥	g _\|\|	g _avg.	G	µ _eff. (BM)
2.0058	2.0243	2.0119	4.18	1.74

5.6

5.6 In vitro cytotoxicity

Synthesized Schiff base and its metal complexes were evaluated for cytotoxicity against Human lung cancer cell line (A-549); Human breast cancer cell line (MCF-7) by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium Bromide] assay. Each reading was performed three times for each concentration. Results were expressed as mean ± standard deviation (n = 3).The % cell viability (% cell survival) of the cells was calculated using the relation,

% Viability = (Mean OD of test compound/Mean OD of negative control) × 100 Inhibiting cells (%) = 100 - Surviving cells.

The IC₅₀ was extrapolated from the dose–response curve. The synthesized compound concentration that reduced the viability of cells by 50% (IC₅₀) was calculated by plotting triplicate data points over a concentration range and calculating the values using GraphPad Prism Ver. 5.1 program. The results of MTT assay as shown in Table 4.

Table 4 In vitro cytotoxicity values.

Compound	IC₅₀ values in μM
Compound	A-549	MCF-7
LH	53.93	52.13
Co-complex	43.1	48.92
Cu-complex	37.03	39.43
Cd-complex	52.63	42.55
Ni-complex	52.19	44.24
Paclitaxcel (Ref.)	69.54	30.76

The metal complexes were found to be more active than ligand. Among the prepared metal complexes, the Cu-complex was found to be highly active. The Cu-complex has shown 37.03 μM and 39.43 μM IC₅₀ against A-549 and MCF-7, respectively.

5.7

5.7 Photocleavage study of pBR322 DNA

DNA is the primary pharmacological target of many antitumor compounds. The pBR322 plasmid exists in a compact supercoiled confirmation (Form I). Upon the formation of strand breaks, the supercoiled form of DNA is split into the nicked circular form (Form II) and the linear from (Form III). If only one DNA strand is cleaved, and the form I will relax to produce a nicked circular from. If both strands are cleaved, form III will be produced. These three plasmid DNA conformations are distinguishable when subjected to agarose gel electrophoresis since relatively fast migration is observed for supercoiled form when the plasmid DNA is subjected to electrophoresis. The nicked circular form migrates slowly and the linear form migrates between form I and form II. The ability of the Cu-complexes to cleave DNA in the presence and absence of H₂O₂ was studied. The synthesized Cu-complex has been tested for its cleavage DNA activity by converting the supercoiled DNA into the open circular and linear forms. Fig. 1 explains the effect of Cu-complex on pBR322 plasmid DNA in the presence and absence of H₂O₂. From Fig. 1 it can be seen that the DNA cleavage is concentration dependent. In presence of H₂O₂ and at the centration of 30 µM and 40 µM of the Cu-complex, the plasmid DNA is completely degraded into indistinguishable small fragments in lane 10 and 11. Similarly, for concentrations 30 µM and 40 µM of the Cu-complex, the complete plasmid DNA was reported to be degraded (Li et al., 2014) (Fig. 3).

Agarose gel electrophoresis images of Cu-complex in the presence and absence of hydrogen peroxide showing the effect on pBR322 DNA.

Lane 1: DNA control, Lane 2: Cu-complex (5 µM) + DNA, Lane 3: Cu-complex (10 µM) + DNA, Lane 4: Cu-complex (20 µM) + DNA, Lane 5: Cu-complex (30 µM) + DNA, Lane 6: Cu-complex (40 µM) + DNA, Lane 7: Cu-complex (5 µM) + DNA + H₂O₂, Lane. 8: Cu (10 µM) + DNA + H₂O₂, Lane 9: Cu (20 µM) + DNA + H₂O₂, Lane 10: Cu (30 µM) + DNA + H₂O₂, Lane 11: Cu (40 µM) + DNA + H₂O₂.

6 Conclusion

A novel Schiff base and their metal complexes that have been prepared are characterized by various physical and analytical techniques and results agreed well with synthesized compounds. Further, these compounds were tested for in vitro cytotoxicity with human lung cancer cell line (A-549); human breast cancer cell line (MCF-7). The metal complexes were found to be more active than ligand. Among these metal complexes Cu-complex was found to be more active. Further active Cu-complex was studied for Photocleavage of pBR322 DNA. The ability of the copper complexes to cleave DNA in the presence and absence of H₂O₂ was studied and it was observed that at high concentration, the plasmid DNA is almost degraded into indistinguishable small fragments in lane 10 and 11. It is thus concluded that Cu-complex can develop for further use as a lead drug for cancer.

Acknowledgement

The authors would like to extend their sincere appreciation to the Department of Chemistry, C.K.T. College, New Panvel, Mumbai for providing financial assistance under Rashtriya Uchchatar Shikshan Abhiyan (RUSA) scheme and laboratory facility.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Srivastava Ambika, Singh R.M., . Vilsmeier-Haack reagent: A facile synthesis of 2- chloro- 3-formylquinolines from N-arylacetamides and transformation into different functionalities. Indian J. Chem.. 2005;44:1868-1875.
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Appendix A

Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.arabjc.2021.103285.

Appendix A

Supplementary data

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[Google Scholar]

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[35] Prateek Tyagi, Sulekh Chandra, Saraswat, B.S., 2015. Ni(II) and Zn(II) complexes of 2- (thiophen-2-ylmethylene)amino)benzamide: Synthesis, spectroscopic characterization, thermal, DFT and anticancer activities. Spectrochimica Acta Part A: Mol. Biomol. Spectrosc., 134, 200–209.

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[39] Thaker B.T., Tandel P.K., Patel A.S., Vyas C.J., Jesani M.S., Patel D.M., . Synthesis and mesomorphic characterization of Cu(II), Ni(II) and Pd(II) complexes with azomethine and chalcone as bridging group. Indian J. Chem.. 2005;44:265-270.
[Google Scholar]

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Synthesis, characterization, anticancer and DNA photocleavage study of novel quinoline Schiff base and its metal complexes