Synthesis and spectral studies of 4,4′-(Hydrazine-1,2-diylidenedimethylylidene)-bis-(2-methoxyphenol) and its transition metal complexes with promising biological activities

Article abstract of DOI:10.14233/ajchem.2020.22703

The study describes the synthesis, characterization and biological activity of a novel Schiff base ligand and its transition metal complexes. The Schiff base ligand was obtained by a condensation reaction between 4-hydroxy-3-methoxybenzaldehyde (p-vanilli

Full text of DOI:10.14233/ajchem.2020.22703

Asian Journal of Chemistry; Vol. 32, No. 7 (2020), 1768-1772
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2020.22703
Synthesis and Spectral Studies of 4,4′-(Hydrazine-1,2-diylidenedimethylylidene)-bis-(2-
methoxyphenol) and Its Transition Metal Complexes with Promising Biological Activities
1
2,*
2
1
1
ANITA RANI , MANOJ KUMAR , HARDEEP SINGH TULI , ZAHOOR ABBAS and VINIT PRAKASH
1Department of Chemistry, Maharishi Markandeshwar University, Sadopur, Ambala-134007, India
2Department of Biotechnology, Maharishi Markandeshwar Deemed to be University, Mullana, Ambala-133207, India
*Corresponding author: E-mail: manojraju27@gmail.com
Received: 20 March 2020;
Accepted: 25 April 2020;
Published online: 27 June 2020;
AJC-19946
The study describes the synthesis, characterization and biological activity of a novel Schiff base ligand and its transition metal complexes.
The Schiff base ligand was obtained by a condensation reaction between 4-hydroxy-3-methoxybenzaldehyde (p-vanillin) and hydrazine
hydrate using ethanol as solvent. A new series of Ni(II) and Fe(III) complexes were also derived by reaction of prepared Schiff base ligand
with NiCl2 and FeCl3. Both the ligand and its metal complexes were characterized by solubility, melting point and elemental analysis.
These compounds were further identified by analytical techniques, FTIR, NMR and mass spectrometry. The ligand and its transition
metal complexes were also subjected to in vitro biological activities i.e. antimicrobial, antiangiogenic and DNA photo cleavage. For
antimicrobial activity compounds were tested against two strains of bacteria and two strains of fungi. Different concentrations of prepared
compounds were treated with fertilized chicken eggs and plasmid DNA to find out antiangiogenic and DNA photocleavage activity,
respectively.
Keywords: p-Vanillin, Schiff base, Hydrazine hydrate,Antimicrobial activity,Anti-angiogenic activity, DNA-photocleavage activity.
metals especially with transition metals due to availability of
vacant d-orbitals [5,6]. A wide range of Schiff base ligands
and their transition metal complexes has been prepared in last
many years but still there is a need to synthesize new Schiff bases
with unique activities.Actually due to regular use of antibiotics,
microbes have acquired resistance towards many available
antimicrobials. As a result, researchers have been forced to
increase the variety of drugs. So there is a need to incorporate
Schiff base ligands and their transition metal complexes into
variable and effective mode of medication. The researches have
proved that the spectrum of drugs can be increased by comp-
lexation of Schiff base ligands with transition metals [7,8].
Various types of carbonyl compounds and amines have been
used to prepare different Schiff base ligands. The study of
previous decades showed the high activity and efficiency of
vanillin compounds towards diseases like tumor, bacterial and
fungal growth regulators [9-11].
INTRODUCTION
Schiff bases has been characterized by presence of C=N
linkage and usually are prepared by condensation reaction
between carbonyl compound and primary amine. These conden-
sation reactions are very effective due to good electrophilic
property of the carbonyl toward amine group [1]. Hence Schiff
bases has been found to established a unique position in the
field of clinical and pharmaceuticals because of a wide range
of activities. The biological activity includes antibacterial, anti-
fungal, anti-inflammatory, antiproliferative, antiangiogenic,
DNA-photocleavage, herbicides, nematicides. etc. [2]. Generally,
Schiff bases have been widely used as ligands due to their high
stability upon complexation with transition metals and their
excellent solubility in common solvents [3]. Complexation
actually results in movement of electrons from ligand to vacant
d-orbitals of the metal atom or sometime from low oxidation
state metals to ligands thus establish strong bonding through
syngerstism [4]. That is why biological activity of many Schiff
bases has been found to be increased upon complexation with
This inspires to prepare a new novel Schiff base ligand
and metal complexes so that the choice of biological drugs
can be increase to reduce the effect of disease. 4-Hydroxy-3-
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Vol. 32, No. 7 (2020) Studies of 4,4′-(Hydrazine-1,2-diylidenedimethylylidene)-bis-(2-methoxyphenol) and Its Transition Metal Complexes 1769
H
O
methoxybenzaldehyde (p-vanillin) is a natural compound with
phenolic, aldehyde and ether group obtained from vanilla bean.
It exists in the form of position isomer and also induces muta-
tions which result in enhancement of chromosomal aberrations
in living system [12,13]. The condensation product of vanillin
and an amine exhibit excellent biological activity and very
good complexation ability with transition metal atoms [14-16].
Hence, a new Schiff base ligand has been prepared by conden-
sation reaction between 4-hydroxy-3-methoxybenzaldehyde
(p-vanillin) and hydrazine hydrate. The Schiff base ligand has
been reacted with NiCl2 and FeCl3 to synthesize its transition
metal complexes which shows very good complexation ability
[17-19].
H2N
NH2
2
+
CH3
O
OH
Refluxed for 6 h Ethanol
HO
OH
O
O
H3C
CH3
The structures of Schiff base ligands and its transition
metal complexes were assigned on the basis of solubility, melting
point, elemental analysis, FTIR, NMR and mass spectrometry.
The compounds were also screened for various biological acti-
vities.Antimicrobial activity was assayed by using disc diffusion
method against four different species of bacteria and fungi.
The compounds were also screened for antiangiogenic and
DNA-photocleavage activities, where antiangiogenic was done
by using fertilized chicken eggs while DNA-photocleavage
activity was observed by agarose gel electrophoresis method.
N
N
H
H
Scheme-I: Preparation of ligand
(C=O); 3408 (br, OH). 1H NMR (600 MHz, DMSO-d6) δ ppm:
6.8-7.7 (m, 3H, -Ph); 8.5 (s, 1H, CH=N) 8.2 (s, 1H, O-H); 3.8
(Br, 3H, O-CH3). MS (relative intensity): m/z value [M]+ calcd.
(found): 300.5 (300). Anal. calcd. (found) % for C16N2H16O4,
C, 64.00 (64.20), H, 5.33 (5.30), N, 9.33 (9.40), O, 21.30 (21.10).
Synthesis of nickel (II) complex: Schiff base ligand (2
mol) was introduced in 250 mL round bottom flask which contains
20 mL of hot ethanol. The content was mixed thoroughly. To
this mixture 1 mol NiCl2 was added and the resulting solution
was refluxed on water bath for 2.5 h using a water condenser.
The precipitate was filtered off, washed with methanol several
times and dried over silica in a vacuum desicator (Scheme-II).
The synthesized metal complex was soluble in DMSO and
DMF.Yield: 88%, IR (KBr, νmax, cm-1): 1614 (s), (C=N); 1250
(s), (C=O); 3465 (br, OH); 444 (s, M-N). 1H NMR (600 MHz,
DMSO-d6) δ ppm: 7.4-8.0 (m, 3H, -Ph); 8.4 (s, 1H, CH=N); 8.1
(s, 1H, O-H); 3.6 (Br, 3H, OCH3). MS (relative intensity): m/z
value [M]+ calcd. (found): 729.6 (730). Anal. calcd. (found)
% for C32N4H32O8NiCl2: C, 52.63 (52.60); H, 4.39 (4.40); N,
7.68 (7.66); O, 17.54 (17.53); Ni, 8.04 (8.07).
Synthesis of iron(III) complex: Schiff base ligand (2 mol)
was introduced in 250 mL round bottom flask which contains
20 mL of hot ethanol. The content was mixed thoroughly. To
this mixture 1 mol FeCl3 was added and the resulting solution
was refluxed on water bath for 2.5 h using a water condenser.
The precipitate was filtered off, washed with methanol several
times and dried over silica in a vacuum desicator (Scheme-II).
The synthesized metal complex was soluble in DMSO and
DMF. Yield: 53%, IR (KBr, νmax, cm-1): 1573 (s, C=N); 1599
(s, C=O); 3420 (br, OH); 455 (s, M-N). 1H NMR (600 MHz,
DMSO-d6) δ ppm: 7.2-7.9 (m, 3H, -Ph); 8.7 (s, 1H, CH=N);
8.0 (s, 1H, OH); 3.4 (Br, 3H, OCH3). MS (relative intensity):
m/z value [M]+ calcd. (found): 727.3 (727).Anal. calcd. (found)
% for C32N4H32O8FeCl3: C, 52.83 (52.80); H, 4.40 (4.42); N,
7.71 (7.73); O, 17.61 (17.59); Fe, 7.68 (7.66).
EXPERIMENTAL
All the chemicals used in synthesis were ofA.R. grade and
used as received without any further purification.All the chemical
reactions for preparation of Schiff base were performed on
magnetic stirrer equipped with a hot plate and all reactions to
synthesize metal complexes were performed on water bath
with water condenser using ethanol as solvent. The ligand was
purified with methanol before preparation of metal complexes.
The melting point of raw material was determined using open
capillary method. Micro spectra for determining C, H and N
were performed using Perkin-Elmer 2400 CHN elemental anal-
yzer. 1H NMR spectra were recorded on BRUKER AVANCE
II spectrophotometer at frequencies of 400 MHz using DMSO
as solvent and TMS as internal reference standard. The 1H NMR
chemical shifts were expressed in ppm. IR spectra were recorded
on Perkin Elmer FT-IR Spectrometer in 4000-400 cm-1 range
using KBr pellet. Mass spectra were obtained on WATERS,
Q-TOF MICROMASS (ESI-MS) mass spectrometer. Biolo-
gical activities viz. antimicrobial, antiangiogenic and DNA-
photocleavage activity were done by using disc diffusion assay,
CAM assay and agarose gel electrophoresis method, respec-
tively.
Synthesis of Schiff base ligand: 4-Hydroxy-3-methoxy-
benzaldehyde (2 mol) was added to 20 mL of ethanol in 100
mL round bottom flask. The content was dissolved at room
temperature with hand shaking. To this solution, 1 mol of
hydrazine hydrate was added. The content was refluxed on a
water bath with a water condenser for 6 h. A dark yellow solid
was obtained. The product was filtered and dried in a vacuum
desicator over silica (Scheme-I). The product was purified
several times by using methanol. The prepared Schiff base was
soluble in DMSO and DMF. Dark yellow crystals, yield: 70%,
m.p.: 256 ºC, IR (KBr, νmax, cm-1): 1650 (s), (C=N); 1235 (s),
Biological studies: As described [20,21], disc diffusion
assay was applied for antimicrobial activity, CAM assay was
adopted for antiangiogenic activity and agarose gel electro-
phoresis method by using supercoiled DNA pUC19 was applied
for DNA photocleavage activity.

1770 Rani et al.
Asian J. Chem.
HO
OH
O
O
H3C
CH3
HO
OH
O
O
Refluxed for 2.5 h
on water bath
N
N
H3C
CH3
H
H
2
M-X
+
ethanol
M
X
X
H
H
N
N
N
N
H
H
M = Ni, Fe
X = Cl
H3C
CH3
O
O
OH
OH
Scheme-II: Preparation of Ni and Fe complexes
corresponding to proton of azomethine group [26] and this
singlet was appear at δ 8.4 and δ 8.7 ppm after complexation
with metals. A multiplet between δ 6.8-7.7 ppm due to phenyl
protons of benzene ring was observed in spectra of ligand,
between δ 7.4-8.0 ppm for Ni(II) and between δ 7.2-7.9 ppm
was found in the spectra of Fe(III) complex [27]. Similarly, a
band at 8.2 confirmed the presence of -OH moiety on the
aromatic ring. Presence of methoxy group was shown by a
strong band at δ 3.8 ppm while this band occupied values at δ
3.6 and δ 3.4 ppm for methoxy groups of metal complexes
[28].
Mass spectral analysis: The mass spectral analysis confi-
rmed the molecular formula and proposed structure of Schiff
base ligand and its metal complexes. The molecular ion peak
attributed to parent ligand with molecular formula, C16H16N2O4
at 300 m/z, indicated the formation of a hydrazone Schiff base.
In addition to the peak due to molecular ion, the mass spectra
also exhibit peaks assigned to various fragments obtained after
thermal cleavage of ligand. The peaks at 268 m/z for C15H12N2O3
and at 151 m/z for C8H9NO2 give an idea about the stability of
fragments (Fig. 1). The mass spectra of metal complexes have
shown peak at m/z 729.6 and m/z 727.3 for nickel(II) and
iron(II) complexes, respectively which also has confirmed the
presence of metal atoms in ligand and hence prove that coordi-
nation indeed occur.
RESULTS AND DISCUSSION
Schiff base ligand was prepared by condensation reaction
between 4-hydroxy-3-methoxybenzaldehyde (p-vanillin) and
hydrazine hydrate. Synthesized Schiff base ligand was then
allowed to react with NiCl2 and FeCl3 to prepare respective metal
complexes. The synthesized Schiff base ligand and its transition
metal complexes were intensely coloured. The solubility test
for Schiff base and its metal complexes in different solvents,
established their solubility in ethanol, DMSO and DMF. Both
Schiff base and metal complexes were obtained in good yield.
After that spectroscopic and elemental analysis was done to
confirm the authenticity of the products. Hence, the structure
of the compound established on the basis of combined use of
IR, NMR spectroscopy and mass spectrometry.
FTIR spectral analysis: IR spectroscopy provides infor-
mation regarding the nature of functional groups present in
Schiff base ligand and metal complexes.A sharp peak at 1650
cm-1 for ν(>C=N) linkage supported the condensation reaction
between p-vanillin and hydrazine hydrate [22]. This value of
imine linkage get shifted to 1614 and 1573 cm-1, indicated that
the nitrogen atom take part in coordination with Ni and Fe
ion. In addition, broad band at 3465 and 3420 cm-1 confirmed
the existence of hydroxyl group i.e. ν(OH) in the spectra of
metal complexes [23]. However the corresponding strong
absorption of ν(OH) for ligand was found to exhibit at 3408
cm-1. Presence of these absorption bands in ligand and metal
complexes specify that the phenolic -OH did not participate
in bond formation with metals. The far IR spectra of complexes
have shown ν(OH) bands in the region 455-444 cm-1 region.
This occurrence indicates the coordination between metals and
lone pair of electron on nitrogen atom of the ligand [24,25].
NMR spectral analysis: Structures of Schiff base ligand
and its metal complexes were further confirmed on the basis
of NMR spectra where ligand shows a singlet at δ 8.5 ppm
Antimicrobial activity using disc diffusion assay: The
antimicrobial activity (Table-1) outlines the results obtained
for the inhibition zones generated by the synthesized Schiff
base and its transition metal complexes. The activity was
resolute in vitro against two different strains of bacteria (S.
aureus and K. pneumoniae) and two strains of fungi (A. niger
and Trichophyton rubrum) in terms of zone of inhibition in
mm. In the study, the zone of inhibition have been found
between 12-20 mm for ligand while in case of transition metal
complexes it ranged between 14-22 mm for Ni and 14-23 mm

Vol. 32, No. 7 (2020) Studies of 4,4′-(Hydrazine-1,2-diylidenedimethylylidene)-bis-(2-methoxyphenol) and Its Transition Metal Complexes 1771
.+
.+
OH
OH
O
OH
OH
H3C
O
H3C
O
H3C
O
O
CH3
- C7H4NO
- CH3OH
NH
N
N
N
N
H
H
H
H
H
m/z = 300
m/z = 269
m/z = 151
Fig. 1. Proposed mass fragmentation pattern of ligand
TABLE-1
ANTIMICROBIAL RESULT OF HYDRAZONE SCHIFF BASE LIGAND AND ITS NI AND FE COMPLEXES
Zone of inhibition (mm)
Hydrazone
Schiff base
Bacterial strains
K. pneumoniaae
Fungal strains
Trichophytonrubrum
S. aureus
150 200
14 15
0.7 0.4
15 17
0.7 0.6
18 18
0.7 0.6
A. niger
150 200
14 17
0.7 0.5
17 19
0.4 0.7
16 19
0.4 0.7
Dosages (ppm)
Ligand
100
12
0.5
14
0.5
16
0.5
250
100
150
200
250
19
0.7
22
0.6
21
0.6
100
13
0.5
14
0.6
14
0.6
250
100
150
200
16
0.5
19
0.7
19
0.7
250
20
0.6
21
0.4
20
0.4
18
0.6
13
0.5
15
0.7
16
0.5
18
0.5
12
0.7
13
0.5
20
0.4
16
0.5
17
0.5
20
0.7
21
0.7
15
0.6
17
0.5
Ni complex
Fe complex
23
0.4
15
0.5
17
0.5
20
0.7
21
0.7
17
0.6
18
0.5
Standards
solvent
21 mm (Neomycin,
250 ppm); 2 mm
23 mm (Neomycin,
250 ppm); 3 mm
24 mm (Fluconazole,
250 ppm); 1 mm
9 mm (Fluconazole,
250 ppm); 2 mm
Data represented as the average mean of three values with 0.5 to 0.7 standard deviation.
100
for Fe ion for each treatment [29]. It can be deduced from the
results that the Schiff base and its metal complexes exhibit
moderate to high activity on growth of tested bacterial and
fungal species when compared with common antibiotics i.e.
neomycin and antifungal i.e. fluconazole. The antimicrobial
results evidently show that the activity of metal complexes is
higher than that of corresponding ligand. It means that comple-
xation increases the antimicrobial activity, which can be expl-
ained on the basis of overtone and chelation theory.
Antiangeogenic activity using chorioallantoic membrane
(CAM) assay: Ex vivo CAM assay was used to find the anti-
angeogenic activity of prepared Schiff base and its transition
metal complexes. A scoring method was used to appraise the
level of antiangiogenic activity of compounds by counting total
number of blood vessels or undeveloped blood vessels over
CAM in terms of branch points. The results (Fig. 2) clearly
indicate that all the compounds were able to reduce the CAM
microvessel formation. The percentage of inhibition was found
to be 65, 77, 78 and 75, 85, 90 for 1 µg and 10 µg concentration
of synthesized compounds. The significant differences were
found on comparison with untreated control.
90
80
70
60
50
40
30
20
10
0
Control
1 µg &
10 µg ligand
1 µg & 10 µg
Ni complex
1 µg & 10 µg
Fe complex
Fig. 2. Antiangeogenic activity of ligand and its Ni and Fe complexes
Control 250 µg 300 µg 250 µg 300 µg
DNA photo-cleavage assay using agarose gel electro-
phoresis method: DNA cleavage activity of the synthesized
Schiff base and their transition metal complexes was studied
by agarose gel electrophoresis using supercoiled DNA from
plasmid such as pUC19. The result obtained after analysis
assures that proposed novel Schiff base ligand and their trans-
ition metal complexes have outstanding DNA cleaving and
binding potential in comparison to ligand. It has been observed
that (Fig. 3) metal complexes were able to convert super coiled
Fig. 3. DNA Photo-cleavage of transition metal complexes
plasmid DNA to open form, which was correlated with DNA
cleaving activity of hydrazinecarboxamide based Schiff base
using plasmid DNA [30,31]. Therefore, in near future novel
DNA cleaving agent could play an important role in designing
biological active drugs.

1772 Rani et al.
Asian J. Chem.
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as excellent antimicrobial agents. The synthesized compounds
are also acted as antiangeogenic and DNA photo-cleavage
agents. Hence, the study is also helpful in synthesis of new biol-
ogically active compounds and in understanding their use as
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Conclusion
A novel Schiff base and two new Schiff base complexes
of Ni(II), Fe(III), have been synthesized. The Schiff base was
synthesized by condensation reaction between 4-hydroxy-3-
methoxybenzaldehyde (p-vanillin) and hydrazine hydrate in
ethanol at 60 ºC.After that transition metal complexes of nickel
and iron were prepared by reacting Schiff base with corres-
ponding metal(II) chlorides. The Schiff base and its transition
metal complexes were characterized by IR, 1H NMR and mass
spectrometry. IR and NMR spectra indicate the formation of
expected hydrazone Schiff base ligand and transition metal(II)
complexes and mass spectra has confirmed it. The antimicro-
bial activity of Schiff base and its metal complexes have shown
that they act as good antimicrobial agents against four different
species of bacteria and fungi as well as a potent antiangio-
genesis and DNA-photo cleavage agent.
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CONFLICT OF INTEREST
https://doi.org/10.14233/ajchem.2019.22161
21. M. Kumar, A. Rani, R. Khare, H.S. Tuli, S. Arora and R. Kumar, Bulg.
J. Sci. Educ., 28, 141 (2019).
The authors declare that there is no conflict of interests
regarding the publication of this article.
22. M. Kumar, A. Rani, H.S. Tuli, R. Khare and V. Parkash, Asian J. Chem.,
31, 2331 (2019);
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