Studies on Synthetic, structural characterization, thermal, DNA cleavage, antimicrobial and catalytic activity of tetradentate (N4) schiff base and its transition transition metal complexes

Article abstract of DOI:10.14233/ajchem.2017.20416

A novel tetradentate chelate was synthesized by the condensation of cinnamaldehyde and triethylenetetramine. The chelate ligand was used to prepare mononuclear transition metal complexes of Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) ions. They were charactertized by elemental analyses, conductivity studies, magenetic properties, infrared spectra, UV-visble spectra, 1H NMR and 13C NMR spectra, electron spin resonance spectra, mass spectra and thermogram studies. Their ligand field parameters and LFSE have also been determind. Kinetic studies on the hydrolysis of ethyl acetate have been studied using Co(II) and Ni(II) complexes as homogeneous catalysts and oxidation of pyrocatechol to o-quinone using Co(II), Ni(II) and Cu(II) complexes. The deoxyribonucleic acid cleavage activities of pUC19 DNA examined against chelate ligand and its metal complexes have been evaluated by agarose gel electrophoreises method in the presence of H₂O₂. The antimicrobial studies of Schiff base and its metal complexes were tested against the fungi Candida albicans and Aspergillus Niger and bacteria Escherichia coli, Staphylococcus aureus and Bacillus cereus.

Full text of DOI:10.14233/ajchem.2017.20416

Asian Journal of Chemistry; Vol. 29, No. 5 (2017), 1076-1084
ASIAN JOURNAL OF CHEMISTRY
https://doi.org/10.14233/ajchem.2017.20416
Studies on Synthetic, Structural Characterization, Thermal, DNA Cleavage, Antimicrobial and
Catalytic Activity of Tetradentate (N4) Schiff Base and Its Transition Transition Metal Complexes
1
2
1
1,*
S. RAJIV GANDHI , D. SATHIS KUMAR , S. SYED TAJUDEEN and A.K. IBRAHIM SHERIFF
1PG and Research Department of Chemistry, C. Abdul Hakeem College (Autonomous), Melvisharam-632 509, India
2Department of Chemistry, King Nandhivarman College of Arts & Science, Thellar-604 408, India
*Corresponding author: E-mail: akmhi62@gmail.com; isisis_1@yahoo.co.in
Received: 17 November 2016;
Accepted: 31 January 2017;
Published online: 10 March 2017;
AJC-18303
A novel tetradentate chelate was synthesized by the condensation of cinnamaldehyde and triethylenetetramine. The chelate ligand was
used to prepare mononuclear transition metal complexes of Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) ions. They were charactertized by
1
elemental analyses, conductivity studies, magenetic properties, infrared spectra, UV-visble spectra, H NMR and 13C NMR spectra,
electron spin resonance spectra, mass spectra and thermogram studies. Their ligand field parameters and LFSE have also been determind.
Kinetic studies on the hydrolysis of ethyl acetate have been studied using Co(II) and Ni(II) complexes as homogeneous catalysts and
oxidation of pyrocatechol to o-quinone using Co(II), Ni(II) and Cu(II) complexes. The deoxyribonucleic acid cleavage activities of
pUC19 DNA examined against chelate ligand and its metal complexes have been evaluated by agarose gel electrophoreises method in the
presence of H2O2. The antimicrobial studies of Schiff base and its metal complexes were tested against the fungi Candida albicans and
Aspergillus niger and bacteria Escherichia coli, Staphylococcus aureus and Bacillus cereus.
Keywords:Tetradentate (N4) chelate ligand, Spectral characterization studies, Catalytic studies, DNA cleavage,Antimicrobial studies.
of cell membranes [10,11]. In this study, a new series of
transition metal complexes has been designed and synthesized
using a novel tetradentate Schiff base ligand derived from
condensation of cinnamaldehyde and triethylenetetramine. The
Schiff base and its metal complexes were characterized invol-
ving various spectroscopic studies, which indicate the magnetic
properties, geometry and coordination of the metal complexes.
The significant activities of DNA cleavage and antimicrobial
screening against the Schiff base and its metal complexes is
also studied. The Co(II), Ni(II) and Cu(II) metal complexes
have behaved as moderate homogeneous catalysts in the oxida-
tion of pyrocatechol to o-quinone and hydrolysis of ethyl acetate
[12,13].
INTRODUCTION
The coordination behaviour of bi-, tri- and tetradentate
chelating Schiff base ligands has been a subject of study for
several years [1]. Some of them with the interest to exhibit a
variety of activities like antimicrobial, antimalarial, anti-
tubercular, anticancer activities, etc. [2-4]. In recent research,
aluminum, copper, silver and gold metal based Schiff base
complexes have been used to cure theAlzheimer’s disease [5].
They exhibit a broad physico-chemical property of corrosion
inhibition, hydroformylation, hydrogenation of olefins, oxi-
dation of alcohols, nonlinear optical activity and fluorescence
behaviour [6-8]. The iron and cobalt complexes have been
employed as homogeneous catalysts in fragmentation of heavy
oils. Transition metal complexes with N and O donor Schiff
bases were of particular interest of structural ability and sensi-
tive molecular environments. The azomethine or imines highly
interact with deoxyribonucleic acid of microorganism which
leads to disruption in replication and protein synthesis to resist
the growth of microorganisms [9].
EXPERIMENTAL
All the reagents were of AR grade. The FT-IR spectra
(4000-400 cm-1) had been recorded on KBr pellette using a
Perkin Elmer Spectrum ONE-N017-1159 spectrophotometer.
The elemental analyses of the synthesized compounds were
recorded and the magnetic moments were measured at room
temperature on vibrating sample magnetometer EG&G Model:
155 using Hg[Co(CN)4] as standard. The potential for electrical
conductance of the complexes were measured on a systronic
conductivity meter, type 304 in DMSO with a dip type cell
Cinnamaldehyde is known to inhibit E. coli and Salmonella
typhimurium’s growth. Possible modes of action include dis-
ruption of cell membranes, inhibition of essential enzymes,
chelation of essential trace elements such as iron and targeting

Vol. 29, No. 5 (2017)
Studies of Tetradentate (N4) Schiff Base and Its Transition Transition Metal Complexes 1077
fitted with a platinum electrode. The UV-visible spectra were
run on a carry-5E spectrometer (200-900 nm). The electro-
chemical character of the complexes had been studied with
the help of cyclic voltammetry obtained on a CHI-600A
electrochemical analyzer in the absence of oxygen employing
glassy carbon as a working electrode, calomel electrode as a
reference electrode and platinum wire as an auxiliary electrode
in the presence of NaClO4 as the background electrolyte. The
nuclear magnetic spectra of 1H and 13C were recorded on JKM-
ECS 400 in DMSO-d6 and and CDCl3 solvents respectively.
The electron spray ionization spectrum was recorded using
WATERS-Q-TOF of premier-HAB213. The X-band EPR
spectrum of Cu(II) complex was recorded at 300 K on Bruker
BioSpin GmbH using 2,2-diphenyl-1-picrylhydrazyl as the g-
indicators. The thermograms were obtained by tapping
NETZCH STA-409C/CD thermal analyzer. Catalytic oxidation
of catechol was estimated in 10-3 M DMSO solution and reactions
were monitored spectrophotometrically with the strongest
absorption band of o-quinone.
monitored by UV-visible spectrophotometer. The 10-3 M metal
complex solutions were prepared using DMSO solvent and
added to catechol solution together in the spectrophotometric
cell at room temperature [19,20]. The reactions were carried
out spectrophotometrically with the appearence of absorption
band of o-quinone at 390 nm for 45 min at time intervals of
5 min by noticed the increase in absorbance. A plot of log
(A∞/A∞ –At) vs. ‘t’was obtained the complex and rate constants
were determined.
DNA cleavage studies: The DNA cleavage studies of
chelating ligand and its metal complexes were conducted using
pUC19 DNA by agarose electrophoresis in the presence of H2O2
as an oxidant. The oxidative cleavage of DNA was examined
by keeping the concentration of the compound 30 µM and
pUC19 DNA as 2 µL to make up the volume to16 µL with 5
mM tris-HCl/5 mM NaCl buffer solution. The resulting mixture
was incubated at 37 °C for 2 h and electrophoresed for 2 h at
50V in tris-acetate-EDTA(TAE) buffer (pH 8.3) using 1 % agarose
gel containing 1.0 µg/mL ethidium bromide and photographed
under UV light at room temperature [21].
Preparation of quadridentate chelate ligand (L):A hot
ethanolic solution of cinnamaldehyde (0.2 M, 0.7 mL) and
triethylenetetramine (0.1 M, 0.25 mL) in 2:1 molar ratios and
stirred well for about 1 h. Then the mixtures cooled and ice
was added.The product was filtered, washed with ethanol and
recrystallized from hot solution of ethanol and chloroform
[14,15]. The yield was quantitative and the purity of the product
was checked by thin layer chromatography.
Antimicrobial activity: The in vitro biological screening
effects of the synthesized chelating ligand and its metal comp-
lexes were examined against the bacteria S. aureus, E. coli
and B. cereus by the well-diffusion method using agar nutrient
as the medium. The holes of 5 mm diameter were punched
carefully using a sterile cork borer and were filled with the
test solution (1 mg/mL in DMSO). The plates were incubated
for 24 h at 37 °C. The zone of inhibition for all the test com-
pounds were measured and the results were compared with
the standard drug ciprofloxacin under identical conditions [22].
The antifungal activity of the compounds were estimated
by the well-diffusion method against the fungi C. albicans and
A. niger cultured on potato dextrose agar as medium by the
above method. The plates were incubated at 37 °C for 72 h.
The diameters of the zone of inhibition for chelate ligand and
its complexes were estimated and the results were compared
with standard fluconazole under similer conditions.
The stock solutions (10-6 M) were prepared by dissolving
the chelating ligand and its metal complexes in DMSO and
the solutions were diluted to find MIC values. In a typical
procedure, a well was made on the agar medium inoculated
with microorganisms. It was filled with the test solution using
a micropipette and the plate was incubated for 24 h in case of
bacteria and 72 h for fungi at 37 °C [23]. During this period, it
was noticed that the test solution started diffusing, affecting
the growth of the inoculated microorganisms. The inhibition
zone was developed and its diameter was measured.
Preparation of metal chelate complexes: The metal
complexes were prepared by a refluxed hot solutions of chela-
ting ligand and the respective metal salts in 1:1 molar ratios
[16,17]. The concentrated solution was cooled to room tempe-
rature. The coloured metal complexes were filtered, washed
with ethanol and recrystallized from hot solution of alchol
and chloroform. The yield was quantitative and the purity of
the product was checked thoroughly by TLC.
Hydrolysis of esters: A known amount of Co(II) and
Ni(II) complex solutions were prepared by dissolving in a
solvent mixture of 20 mL DMSO and 20 mL distilled water
(and whose pH was adjusted to 2.5) and then by adding 5 mL
of ethyl acetate and the contents mixed thoroughly. The amount
of the reaction was determined by pipette out 5 mL of the
reaction mixture at regular time intervals and then titrated it
against standard NaOH solution using phenolphthalein as an
indicator. The reaction was carried out at 25, 35 and 45 °C in
a thermostat with an accuracy of 0.01 °C. The quantity of
catalysts used was in the range 0.01-0.05 g [18].
The reaction rates of catalyses of metal complexes were
compared with the rates obtained by using HCl as a catalyst.
40 mL of HCl of known strength was taken in a stoppered
bottle in which 5 mL of ester was added and the degree of
reaction was dermined as above. The reaction was carried out
at 25, 35 and 45 °C using 0.001, 0.01, 0.02 and 0.03 M HCl.
The activation energy (E) was measured from the Arrhenius
plots. The kinetic parameters, change in the enthalpy of acti-
vation (∆H≠), entropy of activation (∆S≠) and free energy of
activation (∆G≠) were also determined.
RESULTS AND DISCUSSION
The chelating ligand (L) and its metal complexes were
insoluble in common organic solvents but soluble in DMSO
and DMF. The elemental analyses data of the chelating ligand
and its metal complexes were in good agreement with calcu-
lated value are given in Table-1.
The electrolytic conductivity studies of the Mn(II), Fe(III),
Co(II), Ni(II) and Cu(II) complexes are 140.2, 214.0, 139.5,
149.3 and 134.5 S cm2 mol-1, respectively. The molar conduc-
tance values were calculated using a DMSO as solvent and
Catecholase activity: The catalytic oxidation of catechol
to o-quinone by Co(II), Ni(II) and Cu(II) complexes were

1078 Gandhi et al.
Asian J. Chem.
TABLE-1
ELEMENTAL ANALYSIS OF SCHIFF BASE AND METAL COMPLEXES
Elemental analysis (%): Calcd. (Found)
Λm
(S cm2 mol-1)
Compound
m.w.
µeff (BM)
M
C
H
N
L = C24H30N4
375.670
561.556
572.760
593.497
540.155
545.008
–
79.97 (79.94)
51.33 (51.26)
50.33 (50.29)
53.88 (53.84)
53.37 (53.33)
52.89 (52.83)
8.07 (7.99)
6.10 (6.07)
5.98 (5.94)
5.77 (5.72)
6.34 (6.31)
6.29 (6.26)
14.96 (14.91)
9.98 (9.94)
9.78 (9.72)
14.16 (14.10)
10.37 (10.34)
10.28 (10.24)
–
–
[Mn(L)(H2O)2]SO4
[Fe(L)(H2O)2]Cl3
[Co(L)(H2O)2](NO3)2
[Ni(L)(H2O)2]Cl2
[Cu(L)(H2O)2]Cl2
9.78 (9.72)
9.75 (9.69)
9.93 (9.90)
10.86 (10.82)
11.66 (11.59)
5.87
5.84
4.22
2.89
1.81
140.2
214.0
139.5
149.5
134.5
value indicates that these complexes have electrolytic nature
[24]. The Fe(III) complex shows the 1:3 electrolyte. The Mn(II),
Co(II), Ni(II) and Cu(II) complexes behave as 1:2 electrolyte.
Hence, there is an ionic sphere in these complexes.
NH
N
NH
N
M+, m/z 375(95%)
The magnetic susceptibility studies of the complexes were
carried at 300 K. The magnetic moments are in good agreement
with the theoretical values. The µeff values of Mn(II), Fe(III),
Co(II) and Ni(II) complexes are 5.86, 5.84, 4.22 and 2.89 BM
corresponding to 5, 5, 3 and 2 unpaired electrons respectively
[25]. These values suggest a high spin octahedral environment
of donor atoms around the metal ions. The magnetic moment
of the Cu(II) complex is 1.82 BM due to the presence of one
unpaired electron, which suggests a distorted octahedral
geometry because of John-Teller effect [26].
NH
NH
N
N
S2, m/z 298(7%)
Mass spectral and fragmentation of the chelate ligand
(L): The mass spectrum of the Schiff base ligand (Fig. 1) shows
a molecular ion peak (M+H)+ at m/z 375.52 which is equivalent
to its proposed molecular formula (L = C22H25N3). In the
fragmentation of ligand the peaks at m/z 298 (7 %), 216 (17 %),
174 (73 %) and 105 (3 %) are due to the elimination of C6H6,
C7H14N2, C2H7N and C3H8N2, respectively (Fig. 2).
NH
N
NH2
N
S3, m/z 216(17%)
100
376.670
174.0640
H2N
HN
349.170
%
S4, m/z 174(73%)
216.1494
235.1124
NH2
N
298.229
399.165
166.1248
105.0328
0
50
100
150
200
250
300
350
400
Fig. 1. Mass spectrum of Schiff base (L)
S5, m/z 105(3%)
FT-IR spectra: The FT-IR spectral data of chelating
ligand and its metal complexes are given in Table-2. In the ligand
the peak at 1656 cm-1 is due to the appearance of azomethine
group (-CH=N-) and is shifted to lower frequency region
around 1641-1635 cm-1 in all the metal complexes [27]. This
shows that the azomethine nitrogen of the ligand is complexed
with metal ions.
Fig. 2. Mass fragmentation of Schiff base
cating the coordinate of nitrogen of N-H group. The appearance
of new bands in the spectra of the complexes in the regions
3440-3414, 531-514 and 491-464 cm-1 were assigned to
ν(M-OH2), ν(M-N) and ν(M-O) respectively, which are absent
in the free Schiff base [28]. The presence of these band give
evidence for the bonding of nitrogen atoms with the metal
ions in tetradentate chelating environment.
A band at 3312 cm-1 in the ligand is due to N-H group. On
complexation this group is shifted to lower frequency indi-

Vol. 29, No. 5 (2017)
Compound
Studies of Tetradentate (N4) Schiff Base and Its Transition Transition Metal Complexes 1079
TABLE-2
KEY INFRARED SPECTRAL BAND (cm–1) OF SCHIFF BASE AND ITS METAL COMPLEXES
ν(N-H) (in-plane
bending)
ν(M-OH2)
ν(N-H)
ν(C=N)
ν(M-N)
ν(M-O)
L = C24H30N4
–
3312
3280
3275
3279
3278
3276
1656
1641
1633
1639
1636
1635
1494
–
–
[Mn(L)(H2O)2]SO4
[Fe(L)(H2O)2]Cl3
[Co(L)(H2O)2](NO3)2
[Ni(L)(H2O)2]Cl2
[Cu(L)(H2O)2]Cl2
3414
3416
3435
3436
3414
1450
514
531
514
518
521
461
481
469
474
474
1413
1449
1461
1416
UV-visble spectra:The electronic absorption spectral data
of chelating ligand and its metal complexes were recorded in
DMSO. The absorption region, ligand field parameters and
ligand field stabilization energy (LFSE) of the complexes are
shown in Table-3.They have been studied with the view to
obtain more information on stereochemistry of the complexes
and procure more support for the conclusion. The electronic
absorption spectrum of the Schiff base shows a band at 29850
cm-1 which attributes to n→π* transition of the azomethine
(-C=N-) chromophore. This transition can be found again in
the complexes but shifts towards lower frequencies which
indicates the coordination of the ligand with metal ions. The
electronic spectrum of Mn(II) complex exhibits three bands
at 11682 cm-1 (ν1), 16103 cm-1 (ν2) and 19121 cm-1 (ν3) which
are assigned to the transitions 6A1g→4A1g (G),6A1g→4T2g (G) and
6A1g→4Eg(G), respectively. The ligand field parameters, ligand
field splitting energy (Dq), inter electronic repulsion parameter
(B′), nephelauxetic ratio (β), β % and LFSE have been
calculated using the equations given by Konig [29]. The values
of ligand field parameters Dq, B′, β, β % and LFSE for this
complex are 1168.2 cm-1, 865.3 cm-1, 0.901, 9.86 and 139.81
KJ mol-1, respectively. The inter electronic repulsion parameter
(B′) is less than free metal ion (960 cm-1) and the nephelauxetic
ratio (β) is less than one which indicates a moderate covalent
character of the metal-ligand bonds with high spin octahedral
environment.
respectively. The values of ligand field parameters Dq and
LFSE value for this complex are 1344 cm-1 and 160.85 KJ
mol-1, respectively. These values suggest a high spin octahedral
environment for the central metal ion.
The absorption spectrum of Co(II) complex shows three
bands at 10764 cm-1 (ν1), 19305 cm-1 (ν2) and 26815 cm-1(ν3)
4
4
which are assigned to the transitions T1g (F)→4T2g (F), T1g
(F)→4A2g (F) and T1g (F)→4T2g (P), respectively. The
4
appearance of intense band around 31400 cm -1 may be a charge
transfer band. The ligand field parameters Dq, B′, β, β % and
LFSE for Co(II) complex have been calculated and their
respective values correspond to 1076.4 cm-1, 839.90 cm-1,
0.864, 13.50 and 128.83 KJ mol-1.The inter electronic repulsion
parameter (B′) is less than free metal ion (971 cm-1) and the
nephelauxetic ratio (β) is less than one which indicates a
moderate covalent character of the metal-ligand bonds with
octahedral geometry.
The electronic spectrum of Ni(II) complex gives two bands
at 15673 cm-1 (ν2) and 24937 cm-1 (ν3) assignable to 3A2g→3T1g
(F) and 3A2g→3T1g (P) transitions, respectively in an octahedral
environment. The lowest band ν1 ≈ (10 D q) was not observed
due to limited range of the instrument used. The ligand field
parameters Dq, B′, β, β % and LFSE for Ni(II) complex have
been calculated and their respective values correspond to
1170.4 cm-1, 838.80 cm-1, 0.805, 19.42 and 140.80 KJ mol-1.
The inter electronic repulsion parameter (B′) is less than free
metal ion (1040 cm-1) and the nephelauxetic ratio (β) is less
than one which indicates a moderate covalent character of the
metal-ligand bonds in an octahedral environment [30].
The absorption spectrum of Fe(III) complex obtained three
bands at 13440 cm-1 (ν1), 17790 cm-1 (ν2) and 19520 cm-1 (CT)
6
6
due to the transitions A1g→4T1g(G) (ν1), A1g→4T2g(G) (ν2),
TABLE-3
UV-VISIBLE SPECTRA OF SCHIFF BASE AND ITS METAL COMPLEXES
Frequency
(cm-1)
LFSE
(KJ mol-1)
Compound
Assignment
Dq (cm-1)
–
B' (cm-1)
–
β
β %
L= C24H30N4
29850
–
–
–
n → π*
6A1g → 4A1g (G)
6A1g → 4T2g (G)
6A1g → 4Eg (G)
11682 (ν1)
16103 (ν2)
19121 (ν3)
Mn(II)
Complex
1168.2
865.30
0.901
9.86
139.81
13440 (ν1)
17790 (ν2)
19520 (CT)
6A1g → 4T1g (G)
6A1g → 4T2g (G)
LMCT
4T1g → 4T1g (F)
4T1g → 4A2g (F)
4T1g → 4T1g (F)
3A2g → 3T2g (F)
3A2g → 3T1g (F)
3A2g → 3T1g (P)
2Eg → 2T2g
LMCT
Fe(III)
Complex
1344.0
1076.0
-
-
-
160.85
128.83
10764 (ν1)
19305 (ν2)
26815 (ν3)
9363 (ν1)
Co(II)
Complex
839.90
0.864
13.50
Ni(II) Complex
1170.4
1436.5
838.80
–
0.805
–
19.42
–
140.08
171.93
15673 (ν2)
24937 (ν3)
Cu(II)
Complex
14365 (ν1)
25157 (CT)

1080 Gandhi et al.
Asian J. Chem.
103
20
The electronic spectrum of Cu(II) complex exhibits three
bands, a low intense broad band in the region 16411-12320
2
cm-1 with maxima at 14365 cm-1 due to Eg→2T2g transition,
the high intense band in the region 22900-27100 cm-1 with
maxima at 25157 cm-1 due to symmetry forbidden ligand to
metal charge transfer transition (LMCT). The band above
27150 cm-1 was assigned for the ligand.A distorted octahedral
geometry around Cu(II) ion due to John-Teller effect is proposed
[31]. The ligand field splitting energy (Dq) and LFSE values
are 14365.0 cm-1 and 171.93 KJ mol-1, respectively.
10
0
1H and 13C nuclear spin resonace spectra of the chelate
-10
-20
1
ligand (L): The H NMR spectrum of chelating ligand was
recorded in DMSO-d6 solvent using tetramethylsilane (TMS)
as an internal standard. The Schiff base showed broad signal
at 7.3 ppm due to aromatic protons, while the azomethine group
protons was observed at 7.71 ppm. The N-H proton at 3.43
ppm indicates the presence of secondary amine in the Schiff
base [32].
0
2000
4000
(G)
6000
8000
The 13C NMR spectrum of chelating ligand was recorded
in CDCl3 solvent. The chemical shift for aromatic carbons
region was a set of peak at 128.78 ppm, while the chemical
shift of -C=N-carbons were seen in the range 162.73 ppm.
The chemical shift for aliphatic carbons was a set of multiples
in the range 56.91-57.55 ppm were given Table-4.
Fig. 3. ESR spectrum of Cu (II) complex
TABLE-5
ESR SPECTRAL DATA OF Cu(II) COMPLEX
A|| × 10-4
140
g||
gav
G
g⊥
α2
2.263
2.101
2.155
2.64
0.732
If the value of α2 = 0.5, it indicates complete covalent
bonding while the value of α2 = 1.0 suggests complete ionic
bonding. The observed value of α2 (0.732) of the complex is
less than unity, which indicates that the complex has some
covalent character in the ligand environment. The EPR spectral
study thus suggests the distorted octahedral geometry of the
Cu(II) complex [34].
TABLE-4
1H NMR AND 13C NMR SPECTRUM
DATA OF SCHIFF BASE LIGAND
Chemical shift
Compound
Assignment
(δ, ppm)
1.2509
2.3712
(m, 2H, -CH2-CH2-)
(s, 1H, -NH-)
2.715-2.5059
3.4345
5.3712
(m, 2H, -NH-CH2-)
(m, 1H, -CH=CH-)
(s, 1H, -CH-Ar)
TGA and DTA analysis: The TGA and DTA studies of
Mn(II), Fe(III), Co(II), Ni(II) and Cu(II) complexes were carried
out from room temperature to 1400 °C. In the first stage all
the metal complexes have shown (Figs. 4 and 5) an endothermic
peak at 100-160 °C. This indicates the presence of two coordi-
nated aqua molecules in these complexes [35]. The second
and third stages are found in the temperature range 180-600
°C and above 600 °C the formation of metal oxides as final
product. The data reveals that all the metal complexes are of
octahedral geometry formed by a tetradentate (N4) Schiff base
chelate ligand and two coordinated aqua molecules.
L= C24H30N4
7.3097
7.7127
(m, 5H, ArH)
(d, 1H, -N=CH-, azomethine H)
-C-C-(aliphatic)
-C=C-(aromatic)
57.91-57.55
128.78
162.73
-C=N-(azomethine)
Eelctron spin resonace spectrum: The EPR spectrum of
the Cu(II) complex was recorded at 300 K using DMSO, on the
X-band at the frequency 9.27 GHz under a magnetic field strength
about 3360G. The EPR spectrum of Cu(II) complex showed a
anisotropically broad signal as given in Fig. 3. The analysis of
spectrum gives A||, g|| and g⊥ values as 140 × 10-4 cm-1, 2.263 and
2.101, respectively. These values indicate that the ground state
DTA (mW/mg)
exo 0
TG (%)
100
-5
2
of Cu(II) is predominantly dx -y . The trend g|| > g⊥ > 2.0023 that
2
80
has been observed for the complex indicates that the unpaired
-10
2
2
electron is localized in the dx -y orbital of the Cu(II) ion and is a
characteristic of the axial symmetry. The gav value has been
calculated as 2.155 using the equation gav =1/3[g|| +2 g⊥]. The
deviation of gav from that of free electron (2.0023) is due to the
covalence character. The parameter ‘G’ is calculated by using
expression G= g|| -2/g⊥-2. The G value indicates the interaction
between metal centers in solid complex consistent with Hathaway
approach [33]. The covalency parameter α2 has been calculated
and given in Table-5 as:
60
-15
-20
40
-25
20
-30
0
200
400
600
800
Temperature (°C)
1000
1200
1400
α2 =(A||/0.036) + (g||-2.0023) + (3/7)(g⊥ -2.0023) + 0.04
Fig. 4. TGA-DTA thermogram of Co(II) complex

Vol. 29, No. 5 (2017)
Studies of Tetradentate (N4) Schiff Base and Its Transition Transition Metal Complexes 1081
DTA (mW/mg)
1.4
TG (%)
100
exo
-5
1.2
90
80
70
60
50
40
Co(II)
Ni(II)
-10
-15
-20
-25
-30
1.0
0.8
0.6
0.4
0.2
200
400
600
Temperature (°C)
Fig. 5. TGA-DTA Thermogram of Cu(II) complex
800
1000
1200
Electrochemical studies: The electrochemical behaviour
of the Fe(III) and Cu(II) complexes have been examined in
DMSO with 0.1 M NaClO4 about the range of +2.0 V to -2.0
V using cyclic voltammetry with glassy carbon as working
electrode (Fig. 6). The electrochemical data of the complexes
are given in Table-6. The Fe(III) and Cu(II) complexes shows
that one electron transfer process it gives a quasi-reversible
redox behaviour [36].
0.010
0.015
0.020
0.025
Amount (g)
0.030
0.035
0.040
Fig. 7. Plot of rate of reaction versus amount of catalysts at 313 K, Volume
of ethyl acetate: 5 mL
2.4
Co(II)
Ni(II)
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
5.0
4.0
3.0
2.0
1.0
0
-1.0
-2.0
-3.0
-4.0
-5.0
-6.0
-7.0
300
305
310 315
Temperature (K)
320
325
2.0 1.6 1.2 0.8 0.4
0
-0.4 -0.8 -1.2 -1.6 -2.0
Fig. 8. Plot of rate of reaction versus temperature
Potential (V)
Fig. 6. Cyclovoltammogram of Fe(III) complex
The rate constants for the hydrolysis of ethyl acetate
obtained by using different catalysts at various temperatures
are given in Tables 7 and 8. Keeping the quantity of the catalyst
and ester as constant it has been observed that when the tempe-
rature is varied in the range 303-313 K, the value of k increases
with increase in temperature. HCl is more efficient catalyst
than the Co(II) and Ni(II) complexes.It is observed that ∆H≠
values are closer to E values in accordance with absolute
TABLE-6
ELECTROCHEMICAL DATA OF
SCHIFF BASE METAL COMPLEXES
Epc
(V)
E1/2
(V)
ipa
(µA)
ipc
(µA)
∆E
(mV)
Complexes
Epa (V)
Fe(III)/Fe(II) 0.628
Cu(II)/Cu(I) 0.215
-0.776 0.702
0.510 0.363
148
295
30.82 -0.625
14.26 10.12
TABLE-7
Hydrolysis of esters: The ester hydrolysis of ethyl acetate
were studied by complexes as homogeneous catalysts. The
concentrations of ester, the amount of the catalyst has been
varied in the range 0.01-0.04 g. The obtained value of k is
proportional to the amount of the catalyst [37].
INFLUENCE OF THE AMOUNT OF CATALYST ON THE
HYDROLYSIS OF ETHYL ACETATE BY REPRESENTATIVE
COMPLEXES [Co(L)(H2O)2](NO3)2 AND [Ni(L)(H2O)2]Cl2
Amount of
catalyst (g)
Specific reaction rate
(k × 10-4, min-1)
Complexes
The plot of rate constant versus the quantity of catalyst is
linear showing that the rate constant is directly proportional to
the quantity of catalyst used in the reaction (Fig. 7). Hydrolysis
of ethyl acetate in presence of HCl is first order. In the present
study, it is found that Co(II) and Ni(II) complexes show first
order kinetics as shown by the linear plot of log (a-x) against
‘t’ (Fig. 8).
0.010
0.020
0.030
0.040
0.010
0.020
0.030
0.040
0.36
0.54
0.99
1.24
0.23
0.46
0.79
0.93
[Co(L)(H2O)2](NO3)2
[Ni(L)(H2O)2]Cl2

1082 Gandhi et al.
Asian J. Chem.
TABLE-8
KINETICS OF HYDROLYSIS A OF ETHYL ACETATE IN PRESENCE OF SCHIFF BASE METAL COMPLEXES AS
HOMOGENEOUS CATALYSTS (VOLUME OF ESTER: 5 mL, AMOUNT OF CATALYST: 50 mg)
k × 10-2 (min-1)
E (kJ mol-1)
∆H≠ (kJ mol-1)
∆S≠ (J K-1 mol-1)
∆G≠ (kJ mol-1)
Complexes
T (K)
303
313
323
303
313
323
0.63
1.24
2.31
0.54
0.90
1.52
Co(II)
52.852
50.250
-121.48
88.274
Ni(II)
42.171
39.569
-157.84
88.976
reaction rate theory for solution. The value of ∆G≠ is found to
be higher in all the cases. The values of ∆S≠ were found to be
negative in all the cases indicating that molecules in transition
state are more ordered than the reactants in the ground state.
Catecholase activity: The oxidation of catechol to the
corresponding quinine formation is known as catecholase
activity. In catecholase activity studies pyrocatechol has been
employed as substrate [38]. The catecholase activity of the
Co(II), Ni(II) and Cu(II) complexes were carried out using
pyrocatechol as the substrate. Solutions (10-3 mol dm-3) of
complexes in dimethyl sulfoxide were treated with 100
equivalents of pyrocatechol in the presence of air. The reaction
was carried out spectrophotometrically at 390 nm for 45 min
at time intervals of 5 min are given in Table-9. The slope was
determined by the method of initial rates by monitoring the
growth of the product o-quinone at the absorption band 390
nm. Plots of log (A∞/A∞-At) versus time for catecholase activity
results drawn for the metal complexes (Figs. 9 and 10).
The observed kinetics show a first order dependence on
the complex concentration and the initial rate constant values
show that Cu(II), Ni(II) and Co(II) complexes were 5.72 ×
10-3 min-1, 0.33 × 10-3 min-1 and 0.40 × 10-3 min-1, respectively
[39]. The Cu(II) complex exhibits higher activity than the other
metal complexes due to redox potential of the Cu(II) metal
ion and the binding of the catechol with ligand molecules.
0.11
0.10
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0
Co(II)
Ni(II)
Cu(II)
0
10
20
Time (min)
Fig. 10. Plot of log (A∞ /A∞-At) versus time
30
40
50
The metal having negative reduction potential to decreased the
catalytic efficiency of metal complexes due to a more difficult
to reduction of metal ions.
DNA cleavage studies: The DNA cleavage activity of the
chelating ligand and its metal complexes has been compared
with that of the control. The chelating ligand and its metal
complexes could able to convert super coiled DNA into open
circular DNA [40]. The oxidative cleavage involves the
oxidation of deoxyribose by absorption of sugar hydrogen or
oxidations of nucleobases in the presence of an oxidative agent.
The oxidative cleavage implies by hydroxyl radical species of
O2(OH). In the present study, the pUC19 DNA gel electro-
phoresis experiment has been studied in the presence of the
oxidant H2O2 (50 µg/mL) with chelating ligand and its metal
complexes [41]. The results show that Fe(III), Co(II), Ni(II)
and Cu(II) complexes have effectively degraded the pUC19
DNA in presence of the oxidant and chelating ligand and
Mn(II) complex does not show any significant cleavage. The
descending order of DNA cleavage results are:
TABLE-9
KINETICS STUDIES OF OXIDATION OF PYROCATECHOL
IN PRESENCE OF Co(II), Ni(II) AND Cu(II) COMPLEXES
AS HOMOGENEOUS CATALYSTS
log (A∞/A∞
)
Time
(min)
-t
Co(II) complex
0
Ni(II) complex
0
Cu(II) complex
0
0
5
0.0007
0.0015
0.0022
0.0030
0.0038
0.0043
0.0050
0.0056
0.0061
0.0009
0.0018
0.0026
0.0033
0.0042
0.0050
0.0058
0.0065
0.0072
0.013
0.029
0.042
0.050
0.057
0.068
0.081
0.094
0.104
10
15
20
25
30
35
40
45
[Cu(II) complex+ DNA+ H2O2] > [Co(II) complex+
DNA+ H2O2] > [Fe(III) complex+ DNA+H2O2] >
[Ni(II) complex+ DNA+ H2O2] > [Schiff base+
DNA+ H2O2] > [ Mn(II) complex+ DNA+ H2O2]
Antimicrobial activity: The in vitro antimicrobial activity
of the synthesized chelating ligand and its metal complexes
had been tested against bacteria and fungi and the zone of
inhibition values are given in the Table-10. The minimum
inhibitory concentration (MIC) values of the synthesized
compounds were given in Table-11. The synthesized chelating
ligand shows inhibitory effect (MIC values of 50-100 µg/mL)
H2O
1/2 O2
OH
O
O
Metal complexes
OH
Fig. 9. Catalytic oxidation of catechol to o-quinone

Vol. 29, No. 5 (2017)
Studies of Tetradentate (N4) Schiff Base and Its Transition Transition Metal Complexes 1083
TABLE-10
ANTIMICROBIAL ACTIVITY OF SCHIFF BASE AND ITS METAL COMPLEXES
Antibacterial inhibition (mm)
Antifugal inhibition (mm)
Compound
S. aureus
E. coli
09
B. cereus
C. albicans
A. niger
10
L
Mn(II)
10
11
14
12
11
21
28
–
10
11
13
12
11
22
28
–
09
10
12
12
11
24
–
12
12
Fe(III)
15
14
Co(II)
11
13
Ni(II)
10
11
Cu(II)
24
20
Ciprofloxacin
Fluconazole
32
–
–
36
30
TABLE-11
DETERMINATION OF MIC FOR ANTIMICROBIAL ACTIVITIES
Concentration (µg/mL)
Compound
S. aureus
50.0
25.0
12.5
12.5
25.0
12.5
6.25
–
E. coli
100.0
25.0
25.0
12.5
25.0
12.5
6.25
–
B. cereus
50.0
50.0
12.5
25.0
50.0
12.5
6.25
–
C. albicans
100.0
50.0
A. niger
100.0
25.0
12.5
12.5
25.0
12.5
–
L
Mn(II)
Fe(III)
25.0
Co(II)
25.0
Ni(II)
25.0
Cu(II)
12.5
Ciprofloxacin
Fluconazole
–
12.5
6.25
on growth of the tested bacterial strains.All the metal complexes
have shown greater bactericidal activities against E. coli (MIC
12.50-25 µg/mL), S. aureus (MIC 12.50-50 µg/mL) and B.
cereus (MIC 12.50-50 µg/mL) than the Schiff base. In the
fungal studies, the Schiff base had an inhibitory effect (MIC
values in range 50-100 µg/mL) on the growth of the tested strains
[42]. The metal complexes also have shown greater fungicidal
activities against C. albicans (MIC 12.50-50 µg/mL) and A.
niger (MIC 12.50-50 µg/mL).
On chelation theory the polarity of metal ion will be reduced
due to the positive charge of the metal ion with donor groups.
The delocalization of π-electrons increases the whole chelate
ring and enhances the lipophilicity of the complexes. This
increased lipophilicity enhances the penetration of the complexes
into lipid membrane and restricts further multiplicity of the
microorganisms. The variation in the effectiveness of complexes
against different microorganisms, depends either on the imper-
meability of the microbe’s cells. The Cu(II) complex has exhi-
bited better activity when compared to Schiff base and other
metal complexes due to higher polarity reduction and partial
sharing with donor groups which enhances the lipophilic
character.
The values indicate that the metal complexes posses higher
antimicrobial activity than the free ligand. Such increased
activity of the metal chelates can be explained by Overtone’s
[43] and Tweedy chelation theory [44].According to overtone’s
concept of cell permeability, the lipid membrane that surrounds
the cell favours the passage of only the lipid soluble materials
due to which liposolubility is an important factor, which controls
the antifungal activity.
Conclusion
A novel tetradentate (N4) chelate ligand and its mono-
nuclear metal complexes were synthesized by the condensation
H2O
H2O
3+
2+
HN
NH
HN
NH
HN
NH
M
M
N
N
N
N
N
N
H2O
H2O
M = Fe(III) metal ion
M = Mn(II), Co(II), Ni(II) and Cu(II) metal ions
Fig. 14. Proposed structure of Schiff base (L) and its metal complexes

1084 Gandhi et al.
Asian J. Chem.
14. S.R. Gandhi, D.S. Kumar, R. Srinivasan and A.K.I. Sheriff, Asian J.
Chem., 28, 1721 (2016);
https://doi.org/10.14233/ajchem.2016.19800.
of cinnamaldehyde and triethylenetetramine. The spectral
characterization and results of analytical techniques reveals
that the chelate ligand acts as a N4 donor. The results showed
that the chelate ligand would coordinate in a tetradentate manner
with the metal ions and the geometry of Mn(II), Fe(III), Co(II)
and Ni(II) complexes were octahedral geometry and the Cu(II)
complex showed a distorted octahedral geometry.All the metal
complexes are of paramagnetic in nature. The TGA-DTA study
had shown the presence of two coordinated water molecules.
The proposed structure of the chelating ligand and its metal
complexes was shown in Fig. 11. The catalytic study of the
metal complexes followed a first order kinetics with higher
∆G≠ in mild acidic medium. The copper complex shows higher
catalytic activity against oxidation of catechol than the other
complexes.All the metal complexes except Mn(II) had shown
strong DNA damage. The Cu(II) complex exhibited powerful
antimicrobial activity where as the other molecules showed a
moderate activity.
15. B. Kersting and U. Lehmann, Adv. Inorg. Chem., 61, 407 (2009);
https://doi.org/10.1016/S0898-8838(09)00207-4.
16. M.N. Ibrahim, K.J. Hamad and S.H. Al-Joroshi, Asian J. Chem., 18,
2404 (2006).
17. H.B. Silber and M.A. Murguia, Inorg. Chem., 24, 3794 (1985);
https://doi.org/10.1021/ic00217a020.
18. S.P. Walweakar and A.B. Halgeri, J. Indian Chem. Soc., 50, 246 (1973).
19. A. Zerrouki, R. Touzani and S. El Kadiri, Arab. J. Chem., 4, 459 (2010);
https://doi.org/10.1016/j.arabjc.2010.07.013.
20. R.A. Sheldon and J.K. Kochi, Metal Catalyzed Oxidation of Organic
Compounds, Academic Press, New York (1981).
21. Y. Jin and J.A. Cowan, J. Am. Chem. Soc., 127, 8408 (2005);
https://doi.org/10.1021/ja0503985.
22. C. Jayabalakrishnan and K. Natarajan, Transition Met. Chem., 27, 75
(2002);
https://doi.org/10.1023/A:1013437203247.
23. C.J. Dhanaraj and M.S. Nair, Mycobiology, 36, 260 (2008);
https://doi.org/10.4489/MYCO.2008.36.4.260.
24. N. Singh, S. Hingorani, J. Srivastava, V. Puri and B.V. Agarwala, Synth.
React. Inorg. Met.-Org. Chem., 22, 1283 (1992);
https://doi.org/10.1080/15533179208017841.
ACKNOWLEDGEMENTS
25. B.N. Figgis, Indroduction to Ligand Fields, Interscience, New York,
(1966).
The authors thank to the Management, P.G and Research
DepartmentofChemistry, C.AbdulHakeemCollege, Melvisharam,
India, for providing the research facilities. The authors also
thanks SAIF, IIT Kanpur for spectral, TGA-DTA and magnetic
susceptibility analysis. Thanks are also due to P.G and Research
Department of Chemistry, Muthurangam Govt. Arts College
(Autonomous),Vellore, India for providing cyclic voltammetry
facility. The authors extended their heartfelt gratitude to VIT
University providing antimicrobial and DNA cleavage studies.
26. A. Syamal, Asian J. Chem. Rev., 2, 79 (1991).
27. K. Nakamoto, Infrared Spectra of Inorganic and Coordination
Compounds, John Wiley, New York, edn 5 (1997).
28. F. Calderazzo, L. Labella and F. Marchetti, J. Chem. Soc., Dalton Trans.,
9, 1485 (1998);
https://doi.org/10.1039/a707623a.
29. E. König, Struct. Bonding, 9, 175 (1971);
https://doi.org/10.1007/BFb0118887.
30. A.B.P. Lever, Inorganic Electronic Spectroscopy, Elsevier, New York,
edn 2 (1984).
31. M. Dolaz, M. Tümer and M. Digrak, Transition Met. Chem. 29, 528 (2004);
https://doi.org/10.1023/B:TMCH.0000037520.05914.66.
32. K. Krishnankutty and J. Michael, J. Coord. Chem., 22, 327 (1990);
https://doi.org/10.1080/00958979009408232.
REFERENCES
1. V. Alexander, Chem. Rev., 95, 273 (1995);
https://doi.org/10.1021/cr00034a002.
33. B.J. Hathaway and A.A.G. Tomlinson, Coord. Chem. Rev., 5, 1 (1970);
https://doi.org/10.1016/S0010-8545(00)80073-9.
34. A. Syamal and M.M. Singh, Indian J. Chem., 31A, 110 (1992).
35. P. Martin-Zarza, P. Gili, A. Mederos, A. Medina, C. Valenzuela and A.
Bernalte, Thermochim. Acta, 155, 231 (1989);
2. P. Domadia, S. Swarup, A. Bhunia, J. Sivaraman and D. Dasgupta,
Biochem. Pharmacol., 74, 831 (2007);
https://doi.org/10.1016/j.bcp.2007.06.029.
3. J. Selbin, J. Coord. Chem. Rev., 1, 293 (1966);
https://doi.org/10.1016/S0010-8545(00)80142-3.
https://doi.org/10.1016/0040-6031(89)87190-4.
36. S.S. Djebbar, B.O. Benali and J.P. Deloume, Polyhedron, 16, 2175
(1997);
4. S. Beniz Gündüz, E. Maltas and S. Yildiz, Anal. Lett., 43, 2392 (2010);
https://doi.org/10.1080/00032711003763673.
https://doi.org/10.1016/S0277-5387(96)00555-4.
37. V.C. Haskell and L.P. Hammett, J. Am. Chem. Soc., 71, 1284 (1949);
https://doi.org/10.1021/ja01172a040.
5. F. Rahaman, B. Hiremath, S.M. Basavarajaish, B.H.M. Jayakumaraswamy
and B.H.M. Mruthyunjayaswamy, J. Indian Chem. Soc., 85, 381 (2008).
6. E. Fujita, B.S. Brunschwig, T. Ogata and S. Yanagida, Coord. Chem.
Rev., 132, 195 (1994);
38. S. Sreedaran, K. Shanmuga Bharathi, A. Kalilur Rahiman, K. Rajesh,
G. Nirmala and V. Narayanan, J. Coord. Chem., 61, 3594 (2008);
https://doi.org/10.1080/00958970802087425.
https://doi.org/10.1016/0010-8545(94)80040-5.
7. R. Than,A.A. Feldmann and B. Krebs, Coord. Chem. Rev., 182, 211 (1999);
https://doi.org/10.1016/S0010-8545(98)00234-3.
39. V.K. Bhardwaj, N. Aliaga-Alcalde, M. Corbella and G. Hundal, Inorg.
Chim. Acta, 363, 97 (2010);
https://doi.org/10.1016/j.ica.2009.09.041.
8. K. Hussain Reddy, M. Radhakrishna Reddy and K. Mohan Raju, Indian
J. Chem., 38A, 299 (1999).
40. A. Sitlani, E.C. Long, A.M. Pyle and J.K. Barton, J. Am. Chem. Soc.,
114, 2303 (1992);
https://doi.org/10.1021/ja00033a003.
9. M. Sarangapani andV.M. Reddy, Indian J. Pharm. Sci., 56, 174 (1994).
10. H.T. Chifotides and K.R. Dunbar, Acc. Chem. Res., 38, 146 (2005);
https://doi.org/10.1021/ar0302078.
41. K. Samejima and W.C. Earnshaw, Nat. Rev. Mol. Cell Biol., 6, 677 (2005);
https://doi.org/10.1038/nrm1715.
11. K. Samejima and W.C. Earnshaw, Nat. Rev. Mol. Cell Biol., 6, 677 (2005);
https://doi.org/10.1038/nrm1715.
42. L. Mishra, A.K. Pandey and U.C. Agarwala, Indian J. Chem., 32A,
442 (1993).
12. N. Raman, R. Jeyamurugan, R. Senthilkumar, B. Rajkapoor and S.G.
Franzblau, Eur. J. Med. Chem., 45, 5438 (2010);
https://doi.org/10.1016/j.ejmech.2010.09.004.
43. S. Belaid, A. Landreau, S. Djebbar, O. Benali-Baitich, G. Bouet and
J.-P. Bouchara, J. Inorg. Biochem., 102, 63 (2008);
https://doi.org/10.1016/j.jinorgbio.2007.07.001.
44. B.G. Tweedy, Phytopathology, 155, 910 (1964).
13. N.S. Venkataramanan, G. Kuppuraj and S. Rajagopal, Coord. Chem.
Rev., 249, 1249 (2005);
https://doi.org/10.1016/j.ccr.2005.01.023.