Schiff base pyrazolone complexes of iron (III): synthesis, characterization, antimicrobial and antioxidant activity

Article abstract of DOI:10.1007/s00044-016-1649-0

A series of novel Schiff base tetradentate ligands and its iron (III) coordination compounds were synthesized, characterized and evaluated for antibacterial and antioxidant activity. All the synthesized ligands and complexes were characterized by spectroscopic and crystallographic techniques. Electronic spectra, M?ssbauer spectra, magnetic moment and conductance study evidence the fact of octahedral arrangement around iron (III). The in vitro antimicrobial Schiff base complexes bear polar and nonpolar properties together; this makes them suitable for permeation to the cells and tissues, it enhances the activity against the bacteria. The antioxidant properties were measured with DPPH (2,2’-diphenyl-2-picrylhydrazyl). These properties were due to the unique feature of ligands such as highest lipophilicity, lowest electron withdrawing power and highest polarisability.

Full text of DOI:10.1007/s00044-016-1649-0

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res
DOI 10.1007/s00044-016-1649-0
ORIGINAL RESEARCH
Schiff base pyrazolone complexes of iron (III): synthesis,
characterization, antimicrobial and antioxidant activity
Kiran R. Surati1 Pooja A. Sathe1
●
Received: 20 April 2015 / Accepted: 4 July 2016
© Springer Science+Business Media New York 2016
Abstract A series of novel Schiff base tetradentate ligands
and its iron (III) coordination compounds were synthesized,
characterized and evaluated for antibacterial and antioxidant
activity. All the synthesized ligands and complexes were
characterized by spectroscopic and crystallographic techni-
ques. Electronic spectra, Mössbauer spectra, magnetic
moment and conductance study evidence the fact of octa-
hedral arrangement around iron (III). The in vitro anti-
microbial Schiff base complexes bear polar and nonpolar
properties together; this makes them suitable for permeation
to the cells and tissues, it enhances the activity against the
bacteria. The antioxidant properties were measured with
DPPH (2,2’-diphenyl-2-picrylhydrazyl). These properties
were due to the unique feature of ligands such as highest
lipophilicity, lowest electron withdrawing power and
highest polarisability.
2007; Ali et al., 2002; Sabry, 2006; Zitouni et al., 2001;
Casas et al., 2008; Youseef and Abbady, 2014) Pyrazolone,
as a prominent structural motif is found in numerous bio-
logically active compounds (Qi and Ready, 2007; Kalluraya
et al., 2014). Typical pyrazole derivatives are pyrazole-3-
ones (pyrazolones) whose synthesis, reactivity and numer-
ous application are well-documented (Varvounis et al.,
2001). Due to the trouble-free preparation and its rich bio-
logical activity of broad-spectrum antibacterial action,
antisepsis (Wang et al., 2007; Yang et al., 2001; Kimata
et al., 2007; Costa et al., 2006), antipyretic and analgesics
(Uramaru et al., 2010), antitumor (Casas et al., 2008;
Camacho et al., 2013), antituberculosis (Botta et al., 2008),
antidepressant, and anticonvulsant activities (Aziz et al.,
2009), pyrazolone and its complexes have both received
considerable attention in coordination chemistry (Surati and
Thaker, 2006; Thaker et al., 2007) and medicinal chemistry
(Huang et al., 2012; Ruf et al., 2012).
●
●
Keywords Schiff base pyrazolone Iron (III) complexes
●
Antimicrobial Antioxidant
However, to best our knowledge, very little has appeared
on the antioxidant (Yang, 2002; George et al., 2014)
properties of Schiff base pyrazolone coordination com-
pounds, and its suitability against bacteria and fungus.
Many reports available about the antioxidant and anti-
microbial activity of antipyrine based derivatives (Vieirera
et al., 2010; Nakagawa et al., 2006).
Iron have also a critically important metal for a wide
variety of cellular events, indeed no life form is possible
without the presence of this element (Bailar et al., 1975).
Iron holds this central position by virtue of its facile redox
chemistry and its high affinity for oxygen (Liu and Hider,
2002; Andrews, 1999).
Introduction
Recently, one important branch of pharmaceutical chem-
istry-synthesis, and research of the Schiff base and their
metal complexes has attracted many attention. (Wang et al.,
Electronic supplementary material The online version of this article
(doi: 10.1007/s00044-016-1649-0) contains supplementary material,
which is available to authorized users.
* Kiran R. Surati
Due to the large structural variability, biological impor-
tance and our interest in this area is focused for a considerable
time on the investigation of coordination chemistry of tran-
sition metal with using pyrazolone-based ligands, (Surati and
kiransurati@yahoo.co.in
1
Department of Chemistry, Sardar Patel University, Vallabh
Vidyanagar 388120, Anand, Gujarat, India

Med Chem Res
Tanker, 2010; Surati et al., 2008; Surati, 2011; Vyas et al.,
2011) initiate us to design iron (III) Schiff base complexes
and evaluate systematically their antimicrobial and anti-
oxidant activity. The aim of this work is to evaluate and come
across the suitability of these coordination compounds for
antioxidant and antimicrobial activities.
Synthesis of ligands
3-Methyl-5-oxo-1-(p-tolyl)-4,5-dihydro-1H-pyrazole-4-car-
baldehyde (1a) and p-(4-formyl-4,5- dihydro-3-methyl-5-
oxopyrazol-1-yl)benzenesulphonic acid (1b) were prepared
by literature (David and Straley, 1961).
Synthesis of Schiff base ligands H2L1, H2L2, H2L3, and H2L4
Experimental
The Schiff bases were synthesized by refluxing for two and
half hour in methanolic solution of ethylenediamine (0.60 g,
0.01 mol) or o-phenylenediamine (1.08 g, 0.01 mol) with
(1a) (4.32 g, 0.02 mol) or (1b) (5.64 g, 0.02 mol) in 20 cm3
methanolic solution. A solid mass separated, was collected
and washed by ether. Crystallization was done with ethanol
and dried over CaCl2 (Surati and Tanker, 2010).
Materials and methods
The solvents were used after purification using the standard
method described in literature (Perrin et al., 2008; Gordon
et al., 1978). 1-Phenyl-3-methyl-2-pyrazoline-5-one (E-
Merck); ethylenediamine (BDH); o-phenylenediamine
(Fluka AG, Switzerland) and FeCl3·6H2O, (Aldrich) were
used as received.
Characterization of H2L1, H2L2, H2L3, and H2L4 (See
Supplementary Materials)
Instruments
Synthesis of Schiff base complexes of iron (III) with ligands
H2L1, H2L2, H2L3, and H2L4
Elemental analyses (C, H, N) were performed at CDRI,
Lucknow. Infrared spectra were recorded with a Perkin-
Elmer IR spectrophotometer (4000–50 cm−1) using KBr
All the iron (III) complexes of the Schiff base were prepared
by the following general method. The salt FeCl3·6H2O
(2.70 g, 0.01 mol) was dissolved in water (15 mL) and the
solution was added to a warm (∼65 °C), stirred solution of
the corresponding Schiff bases H2L1 (4.56 g, 0.01 mol),
H2L2 (5.88 g, 0.01 mol) or H2L3 (5.04 g, 0.01 mol), or H2L4
(6.36 g, 0.01 mol) in 1:1 mixed solvent (DMF + methanol)
(25 mL). The reaction mixture was refluxed for 3–4 h and
then concentrated to half of its volume. The resulting pre-
cipitate was filtered by suction and dried in vacuum over
anhydrous CaCl2.
1
pellets. H-NMR spectra of the compound was recorded
with Bruker-400 using CDCl3 as a solvent and Tetra-
methylsilane as an internal reference. Mass spectra (EI)
obtained on a JEOL D-300 mass spectrometer at SAIF, IIT
Madras, Chennai. The FAB mass spectra were recorded on
a JEOL SX 102 mass spectrometer using Argon/Xenon
(6kV, 10mA) as the Fast atom bombardment (FAB) gas.
The accelerating voltage was 10kV and the spectra were
recorded at room temperature with using m-nitrobenzyl
alcohol as matrix. Electronic spectra in the 200–800 nm
range were obtained in acetone on a “SHIMADZU” UV
160 A using quartz cell of 1 cm3. Magnetic measurements
were carried out at room temperature by the Gouy method
using Hg[Co(SCN)4] as calibrant. Molar conductance of the
Schiff base complexes was determined on Systronics direct
reading conductivity meter type CM-82T. Thermal gravi-
metric analysis (TGA) was carried out on universal V3.0G
Thermal Ananlysis (TA) instrument in the range 0–700 °C
at a heating rate of 10 °C/min under nitrogen. Differential
scanning calorimetry (DSC) was carried out on universal
V3.0G TA instrument in the range 0–300 °C. The Möss-
bauer spectra were collected using a Cryophysics MS-1
microprocessor-controlled spectrometer operating in the
constant acceleration mode. The source was 25 mCi 57Co/Rh
and spectra were fitted using a standard nonlinear least
square package. X-ray structure analyses Powder diffraction
diagrams were obtained on a Philips PW 1710 dif-
fractometer (Cu/Ka; scan rate 1 min−1) with a graphite
monochromator.
Results and Discussion
The newly synthesized tetradentate ONNO donor Schiff
base complexes of iron (III) are stable at atmospheric
temperature and pressure. They are insoluble in organic
solvents like methanol, ethanol, and acetone. However,
Schiff base ligand and its complexes are soluble in coor-
dinating solvents like DMF and DMSO, and mixed solvents
(DMF + methanol), (DMF + ethanol) etc. The analytical
data are in good evidence with the proposed structure of
Schiff base ligands as well as complexes (Scheme 1 and 2).
All the analytical data are summarized in Table 1.
1H-NMR Spectra
1
The H-NMR spectra of Schiff base ligands H2L1, H2L2,
H2L3, and H2L4 were carried out in DMSO-d6 at room

Med Chem Res
Scheme 1 Synthetic pathway
for tetradentate Schiff base
ligands H2L1, H2L2, H2L3, and
H2L4
temperature. Ligands H2L1 and H2L2 show triplet at ∼1.5
ppm for methylene proton of ethylenediamine. Ligands
H2L1 and H2L3 show two singlets with integration of six
protons near the δ ∼2.35 and ∼2.79 ppm for methyl group
attached to pyrazolone ring and phenyl ring, respectively
(Silverstein et al., 1991). The enolic nature of all Schiff base
ligand shows broad singlet at δ ∼10.52 ppm, due to rapid
exchange interaction of keto-enol tautomerism (Surati and
Tanker, 2010). The sharp singlet at δ ∼8.91 ppm, observed
due to aldehydic proton in all Schiff base ligand. The
phenyl multiplet observed in the range of δ ∼7.31-7.98
ppm.
cm−1. The bands at ∼1640, ∼1594, and ∼1300 cm−1 may be
assigned to υ (C=N) (azomethine), υ (C=N) (pyrazoline
ring), and υ(C–O), respectively (Surati and Thaker, 2006;
Thaker et al., 2007; Silverstein et al., 1991).
The ligands as well as its corresponding complexes show
absorptions in the regions 3000–2800 cm−1, which may be
due to υ(C–H). The Schiff base ligand of the present study
shows a strong band due to δ (O–H) in the region
1210–1270 cm−1. Although all of the metal complexes show
this band, its intensity is found to be lower than that of
ligand (Nakamoto, 1978; Raj et al., 1992). This may be due
to the deprotonation of the 5-OH group of the ligand
(Nakamoto, 1978; Surati et al., 2008). All of the metal
chelates show bands in the region 3100–3600 cm−1, which
may be due to the presence of water molecules (Dwyer and
Mellor, 1962). As shown by TGA of all the metal chelates,
this band may be assigned to the one coordinated water
molecules, which can be also inferred from bands at ∼710
cm−1 and may be due to the bending modes of vibrations of
the water (Dwyer and Mellor, 1962).
Infrared Spectra
Characteristic frequency of FT-IR spectra were summarized
as above in Table 2. The infrared spectra of the ligand
shows a broad band in a region 3100–3600 cm−1, which
may be due to υ (OH). Free υ (OH) is generally observed
between 3500–3600 cm−1. The low value of this band is due
to intermolecular or intramolecular H-bonding (Silverstein
et al., 1991; Jadeja et al., 2004), which suggests the pre-
sence of keto-enol tautomeric form, at least in the solid
state. The same is also inferred from its NMR signal at
about δ ∼10.52 ppm due to an enolic proton. The phenyl
group shows υ (CH) at 3060 cm−1 and υ (C=C) at 1540
A characteristic band of intermediate intensity is found at
∼1300 cm−1, which may be due to υ(C–O) (Figgis and
Lewis, 1960). On coordination, this band is shifted toward
higher frequency indicating that the oxygen of the 5-OH
group of the pyrazoline ring of the ligand has taken part in
the coordination (Figgis and Lewis, 1960; Surati and

Med Chem Res
Scheme 2 a Schiff base
complexes [Fe(L1)ClH2O];
R=CH3 and [Fe(L2)ClH2O];
R=SO3H, b Schiff base
complexes [Fe(L3)ClH2O];
R=CH3 and [Fe(L4)ClH2O];
R=SO3H
Tanker, 2010; Surati et al., 2008). The observed low-energy
shift of υ (C=N) (azomethine) in the metal chelates suggests
nitrogen coordination. While υ (C=N) (cyclic) observed at
the same energy in the chelates indicates the nonparticipa-
tion of the cyclic nitrogen in the coordination (Figgis and
Lewis, 1960; Dwyer and Mellor, 1962; Surati and Tanker,
2010; Surati et al., 2008). The Fe–N stretching vibration for
complexes was observed at 258 cm−1 and that for Fe–Cl is
seen at 381 cm−1 in the anion species. The stretching
vibrations of Fe–N in complexes are consistent with the
high-spin character of these complexes. Low spin fre-
quencies for Fe–N appear around 50–70 cm−1 higher fre-
quency to that of high-spin complexes (Raj et al., 1992).
fragments observed were good agreement with structure of
ligands (Johnstone, 1972; Mclafferty, 1973).
Molecular mass of all the metal complexes performed
with FAB mass spectrometer. A FAB mass spectrum of
representative complex [Fe(H2L1)·Cl·H2O] were recorded
and the largest m/z isotropic peak appeared at 547 which
corresponding to the composition [Fe(L1)·Cl] (563.88
molecular mass –H2O). Fragmentation of a weakly coor-
dinated molecule/ion in FAB mass spectrum is not unlikely.
To confirm the presence of weakly coordinating H2O
molecules in the complexes, we carried out thermogravi-
metric analyses of complexes. However, the coordinated ion
Cl was strongly coordinated to metal that confirmed with
M + 2 peak at half intensity at 549 m/z (Johnstone, 1972;
Mclafferty, 1973).
Electronic Spectra
UV-visible spectra of iron (III) Schiff base complexes were
carried out in DMF. The data are summarized in Table 2.
The electronic spectra of Schiff base complexes of iron
(III) exhibit d-d absorption bands at 427-445 and 523–599
nm. The first band may be assigned to the 6A1→4A1, 4E(G)
transition, while the second band would be due to the
6A1→4T2(G) transition, suggesting an octahedral arrange-
ment around the iron (III) ion (Lever, 1968). Also the
charge transfer bands observe at higher energy such as
∼276 and ∼367 nm. The band observed at ∼550 for [Fe
(L1)·(Cl)·(H2O)] and [Fe·(L3)·(Cl)·(H2O)], ∼556 for
[Fe·(L2)·(Cl)·(H2O)] and [Fe·(L4)·(Cl)·(H2O)]. Second band
observed at 613 nm for [Fe·(L3)·(Cl)·(H2O)] and ∼648 nm
for other iron (III) complexes.
Thermal Study
Thermal analyses of all the complexes were carried out by
the Thermogravimetry (TG), Differential thermal analysis
(DTA), and Differential scanning calorimetry (DSC) tech-
niques. The experimental results revealed that the degra-
dation occurred in multiple stages, following a complex
mechanism. For each stage the kinetic parameters and the
thermogravimetric characteristics have been estimated.
Thermal behavior of all complexes are explained below.
[Fe(L1)·Cl·H2O]
The TG and DTA curves of the [Fe(L1)·Cl·H2O] are given
following degradation scheme. The compounds slowly
started to decompose at 201 °C. The first mass loss (3.13 %
est.; 3.19 % calc) up to 231 °C is in good agreement with
loss of one coordinated water molecule. The DTA curve
shows an endothermic peak at 226 °C. This is immediately
followed by exothermic process at 319 °C with mass loss
(7.0 % est.; 6.47 % calc) between 294–328 °C, due to the
removal of HCl. In the temperature range 356–671 °C with
Mass Spectra
Mass spectra of tetradentate Schiff base ligands H2L1, H2L2,
H2L3, and H2L4 were good agreements with their proposed
structure. Melting point of all the ligands is higher (above
200 °C), as results of this, the mass spectra we carried out
by EI. Cleavage take place in the Schiff base ligands and

Med Chem Res
mass loss (71.20 est.; 72.18 % calc), due to the pyrolysis of
organic molecule. The DTA curve shows an exothermic
peak at 556 °C. The final product of the thermal decom-
position Fe2O3 was determined by metal analysis (Furman,
1962).
[Fe(L2)·Cl·H2O]
The TG and DTA curves of the [Fe(L2)·Cl·H2O] are given
following degradation scheme. The compound slowly
started to decompose at 211 °C. The first mass loss (2.96 %
est.; 2.58 % calc) upto 236 °C is in good agreement with
loss of one coordinated water molecule. The DTA curve
shows an exothermic peak at 246 °C. This is immediately
followed by exothermic process at 564 °C with mass loss
(75.62 % est.; 77.43 % calc) between 302–650 °C, due to
the removal of HCl and pyrolysis of organic molecule. The
final product of the thermal decomposition Fe2O3 was
determined by metal analysis (Furman, 1962).
[Fe(L3)·Cl·H2O]
The TG and DTA curves of the [Fe(L3)·Cl·H2O] are given
following degradation scheme. The compound slowly
started to decompose at 235 °C. The first mass loss (2.96 %
est.; 2.58 % calc) up to 257 °C is in good agreement with
loss of one coordinated water molecule. The DTA curve
shows an endothermic peak at 248 °C. This is immediately
followed by exothermic process at 329 °C with mass loss
(4.59 % est.; 5.96 % calc) between 330-365 °C, due to the
removal of HCl. In the temperature range 379–699 °C
observed with mass loss (72.90 est.; 74.31 % calc), due to
the pyrolysis of organic molecule. The DTA curve shows an
endothermic peak at 515 °C. The final product of the ther-
mal decomposition Fe2O3 was determined by metal analysis
(Furman, 1962).
[Fe(L4)·Cl·H2O]
The TG and DTA curves of the [Fe(L4)·Cl·H2O] are given
following degradation scheme. The compound slowly
started to decompose at 221 °C. The first mass loss (2.96 %
est.; 2.41 % calc) up to 232 °C is in good agreement with
loss of one coordinated water molecule. The DTA curve
shows an endothermic peak at 253 °C. This is immediately
followed by exothermic process at 329 °C with mass loss
(4.59 % est.; 5.02 % calc) between 285–342 °C, due to the
removal of HCl. In the temperature range 345–710 °C
observed with mass loss (76.90 est.; 78.73 % calc), due to
the pyrolysis of organic molecule. The DTA curve shows an
exothermic peak at 521 °C. The final product of the thermal
decomposition Fe2O3 was determined by metal analysis
(Furman, 1962).

Med Chem Res
Table 2 FT-IR and electronic spectral data of complexes and their assignments
Complexes ν H2O δ (H2O) ν C = N (Coordinated) ν C = N (cyclic) νC–O (Str.) d–d (nm) Charge transfer band (nm)
[Fe(L1) (Cl) (H2O)] 3486
[Fe(L2) (Cl) (H2O)] 3470
[Fe(L3) (Cl) (H2O)] 3470
713
710
710
—
1624
1624
1620
1624
1593
1594
1594
1598
1345
1345
1349
1348
442, 552
427, 543
445, 558
296,367
290, 367
295, 366
[Fe(L4)(Cl)(H2O)]
3470
441, 546, 293, 365
665
Table 3 The thermodynamic
and decomposition parameters
for complexes
Complex
ΔS*(JK−1 mol−1
Step Cp(KJ g−1
°
Ts
T1
T2
Tp
ΔH*(kJ
mol−1
C−1
)
)
)
ΔE*(kJ
mol−1
)
[Fe(L1) (Cl) (H2O)]
[Fe(L2) (Cl) (H2O)]
[Fe(L3) (Cl) (H2O)]
[Fe(L4) (Cl) (H2O)]
I
1.35
201 223 308 252 115.35
211 214 301 253 119.26
235 225 309 253 116.23
221 221 309 251 114.89
0.457
0.471
0.459
0.457
7.94
21.36
45.62
8.41
II
III
I
2.48
1.38
1.30
II
III
I
20.60
49.68
10.29
26.69
53.62
9.94
II
III
I
II
III
22.36
49.29
From above results it is confirmed that iron (III) com-
plexes contain one coordinated water molecule. Also one
coordinated ion chloride and acetate ions are present in iron
(III). Schiff base complexes of iron (III) shows similar
behavior except [Fe(L1)·Cl·H2O], in this complexes degra-
dation of chloride and organic ligand take place in single
step, while in other complexes of iron (III) shows three step
degradation. The thermal stability of these complexes is
mentioned in Table 3. From the above results, order of
thermal stability of these complexes can be given as
follows.
calculated from DSC results and are given in Table 3. The
heat capacities Cp of the complexes were calculated from
DSC results and are summarized in Table 3.
Mössbauer study
Mössbauer spectra were carried out in solid sample to study
the environment surrounding of the nucleus. This technique
now finds wide application in diverse fields, such as solid
state physics, metallurgy, chemistry, and biochemistry.
Mössbauer studies of iron containing complexes attended
more interest and are important to know the metal envir-
onment in metal complexes. (Greenwood and Gibb, 1971;
Gibb, 1976) Mössbauer spectra of representative complexes
[Fe(L3)·Cl·H2O] and [Fe(L4)·Cl·H2O] at room temperature
and liquid nitrogen temperatures have been studied. The
room temperature spectrum of [Fe(L3)·Cl·H2O] (Supple-
mentary Materials fig. 1S) shows two lines with isomer shift,
δ =0.46 mm s−1 and quadrupole splitting, ΔEq = 0.64 mm
s−1. The LNT spectrum also shows two lines with isomer
shift, δ = 0.58 mm s−1 and quadrupole splitting,
ΔEq = 0.73 mm s−1 (Supplementary Materials fig. 2S).
Similar mössbauer behavior is observed for complex
[Fe(L3)·Cl·H2O] with isomer shift, δ = 0.43 mm s−1,
½FeðL4Þ:Cl:H2Oꢀ > ½FeðL3Þ:Cl:H2Oꢀ
> ½FeðL2Þ:Cl:H2Oꢀ > ½FeðL1Þ:Cl:H2Oꢀ
Differential scanning calorimetry (DSC)
Differential scanning calorimetry (DSC) curves are show
exothermic process. The complexes of iron (III) exhibited
exothermic process at temperature ∼279 °C corresponds to
the melting point of the complexes (Bell, 1969). The area of
the endothermic peak corresponding to the heat of fusion
and the peak temperature corresponds to the melting point.
The melting (Tp), transition temperature (T1, T2), heat of
reaction (ΔH), and entropy (ΔS) of the complexes were

Med Chem Res
quadrupole splitting, ΔEq = 0.61 mm s−1 at room tempera-
ture and δ = 0.55 mm s−1 , ΔEq = 0.71 mm s−1 at LNT. The
results indicate that iron (III) complexes are high-spin with
octahedral geometry (Long, 1984).
Table 4 Powder X-ray diffraction data of the [Fe(L2) (Cl) (H2O)]
2θ Relative I
d2 d12/ d2 hkl N* acalc**
d
18.02 36.20
34.0 43.5
36.09 26.3
46.90 100
48.60 20.8
56.09 46.2
4.6362 21.494
1
111
3
8
8.030134
8.082796
2.8577 8.1664 2.6320
—
2.4890 6.1951 3.4695 310 10 7.870909
2.4465 5.9853 3.5911 311 10 7.736512
2.0212 4.0852 5.2614 400 16 8.0848
1.6520 2.7291 7.8758 422 24 8.093114
X-ray diffraction study
From X-ray diffraction analysis we have successfully cal-
culated the unit cell parameters and crystal systems of
Schiff base complexes of iron (III) by using Ito’s method
(Azaroff and Buerger, 1958). The d-spacing are listed in
Table 4 in a decreasing order of values. Iron (III) complexes
shows simple cubic crystal system with six coordinates the
a = b = c ; α = β = γ = 90. Relative intensity, d-spacing,
angle (2θ) and miller indices were calculated. All the data
are well summarized in Table 4.
* N=h2 + k2 + l2
** a=d(N)1/2
those that play role in food poisoning, e.g., Nissle studied
the probiotic strains of Escherichia coli in 1917 and referred
EcN who are non-uropathogenic and noninvasive as well
(Sonnenborn and Schulze, 2009). As well as serotypes
0157:H7 who are among the six pathotypes of E. coli
bacterial strain and can produce Verotoxins (VTEC) and
Shiga like toxin (SLTs) that are related to the vast range of
human infections like hemorrhagic colitis and hemolytic
uremic syndrome (Broseta, 2001), similarly K. pneumoniae
are important pathogens in nosocomial infections.
Molar conductance
The observed molar conductances of the iron (III) com-
plexes in 10−3 molar DMF solution are in the range 25–42
ohm−1 cm2 mol−1 summarized in Table 1, which are con-
sistent with the nonelectrolytic nature of all the complexes
(Geary, 1971).
The susceptibility of certain strains of bacteria to the
ligand and their corresponding Schiff base complexes were
evaluated by agar diffusion method (Singh and Kushawaha,
2001; Sakıyan et al., 2004); so depending upon the area or
zone of inhibition, with respect to the selected range of
concentration of our designed molecule to determine the
minimum inhibitory concentration aspects, at minimum
concentration our designed molecule showed considerable
increase in antibacterial activity. Table 5 shows the results
for all compounds and comparison of MIC value (in
µg cm−3) of iron (III) complexes and standard drug strep-
tomycin against those of different bacteria. The tetradentate
Schiff base ligand shows antibacterial activity starting from
150–350 µg cm−3 against four strains of bacteria. It is very
interesting that iron (III) complexes show higher activity as
compared with Schiff base (azomethine) ligands, because
iron (III) Schiff base complexes bear polar and nonpolar
properties together; this makes them suitable for permeation
to the cell and tissue (Rehder, 2003). Changing the hydro-
philicity and lipophilicity probably leads to bring down the
solubility and permeability barrier of cell, which in turn
enhances the bioavailability of chemotherapeutics on one
hand and potentiality at another. (Surati and Tanker, 2010;
Surati, 2011; Rehder, 2003)
Magnetic measurements
The magnetic moment (μeff) per metal atom of the iron (III)
complexes ∼5.61 B.M. falls in the range reported for high-
spin octahedral iron (III) complexes (Table 1). This state-
ment is also supported by the mössbauer results (Long,
1984; El-tabl et al., 2005).
Antibacterial activity
Antibacterial activity of Schiff base (H2L1–H2L4) and the
corresponding iron (III) complexes [Fe(L1)(Cl)(H2O)]-[ Fe
(L4)(Cl)(H2O] were studied against two Gram positive
bacteria B. subtilis, S. aureus (MTCC-619 and MTCC-69,
respectively), two Gram negative bacteria E. coli, K.
pneumonia (MTCC-722 and MTCC-109, respectively). The
reason behind the choice of selection of Gram positive
bacteria named S. aureus and B. subtilis, are normally
present in respiratory tract and skin of human plays
important role in nitrate reduction and catalase mechanism,
also ideal choice for chromosome replication in bacteria,
enzyme production, and Gram negative bacteria’s like
Escherichia coli who are harmless but have a significant
role in food poisoning by its serotypes, because according
to its serotypes they are categorized into enterohemorrhagic
or pathogenic form and probiotic or nonpathogemic form.
Probiotic forms are those who are unable to produce
enterotoxins or cytotoxins, whereas pathogenic forms are
Antioxidant activity
There are different methods used to evaluate the in vitro
antioxidant capacity of isolated compounds, mixtures of

Med Chem Res
Table 5 Antibacterial activity
(concentration 2.5–7.0 µg/mL)
of ligand and Iron (III)
complexes
Compounds
Gram positive
MTCC-619
Gram negative
MTCC-722
Scavenging activity (%)
MTCC-96
MTCC-109
H2L1
H2L2
H2L3
H2L4
[Fe(L1)(Cl)(H2O)]
[Fe(L2)(Cl)(H2O)]
[Fe(L3)(Cl)(H2O)]
[Fe(L4)(Cl)(H2O)]
Ref.
26
28
38
41
52
50
56
57
27
24
29
34
46
55
54
56
53
33
27
30
35
42
57
52
58
54
38
32
34
33
48
65
58
60
58
44
59
41
66
48
57
48
69
51
49
MTCC-619 – Bacillus subtilis, MTCC-96 – Staphylococcus aureus, MTCC-722 – Escherichia coli, MTCC-
109 – Klebsiella pneumonia, Ref. Streptomycin used as antibacterial standard
compounds, biological fluids, tissues, and synthetic com-
pounds that involve different mechanisms of determination
of antioxidant activity, e.g., chemical methods based on
scavenging of ROS or RNS such as peroxynitrite (Heijnen
et al., 2001), the hydroxyl radical and superoxide. Other
methods measure the disappearance of free radicals
using spectrophotometry, such as ABTS + (2,2´-azinobis-
(3-ethyl-benzothiazoline-6-sulphonate) cation radical (Van
den Berg et al., 2000; Manojkumar et al., 2009) or DPPH
(2,2’-diphenyl-1-picrylhydrazyl) (Benzie and Strain, 1996).
Other assays to determine the total antioxidant power
include techniques such as the ferric reducing/antioxidant
power method (Benzie and Strain, 1996) or use the in situ
electrochemically generated bromine (Abdullin et al.,
2001). The results in the measurement of antioxidant
capacity depend on the method used.
with complexation in case of [Fe(L4)·Cl·H2O] and [Fe
(L2)·Cl·H2O]. While in case of [Fe(L3)·Cl·H2O] and [Fe
(L1)·Cl·H2O] the activity were remarkable improve. The
effect of substituents on the phenyl ring of pyrazolone-
based ligands H2L1, H2L2, H2L3, H2L4 in producing anti-
oxidant activity in the descending order were found to be
H2L3> H2L1> H2L4> H2L2. These trends were observed
due to substituents having highest lipophilicity, lowest
electron withdrawing power and highest polarisability. In
the same way after complexation the antioxidant activity in
the decreasing order were found [Fe(L3)·Cl·H2O]>[Fe
(L1)·Cl·H2O]>[Fe(L4)·Cl·H2O]>[Fe(L2)·Cl·H2O], it indi-
cates that the antioxidant properties is largely due to the
Schiff base ligands (Van den Berg et al., 2000).
In the present paper, we have carried out scavenging
effect on DPPH. 1.5 mL methanolic solution of the syn-
thesized compounds (0.2 mM) was added to 1.5 mL
(0.2 mM) solution of DPPH radical in methanol (final
concentration of DPPH and synthesized compounds was
0.1 mM). The mixture was shaken vigorously and allowed
to stand for 30 min. After this the absorbance at 517 nm was
determined and the percentage of scavenging activity was
calculated using the formula shown below. Ascorbic acid
was used as the reference compound. All tests and analyses
were undertaken on three replicate and the results were
averaged. The results are given Table 5.
Conclusion
On the basis of above studies, the general structure of the Fe
(III) complexes are proposed as shown in Scheme 2. The
Schiff base ligands are behaving as O, N, N, O donor tet-
radentate ligands. Also the chloride and coordinated water
is coordinated with metal ion confirmed from FT-IR, ther-
mal study. Electronic spectra, Mössbauer spectra, magnetic
moment, and conductance study evidence the fact of octa-
hedral arrangement around iron (III). Moreover, biological
screening state this Schiff base complexes enhance the
activity against the bacteria and fungi due to Schiff base
complexes bear polar and nonpolar properties together, this
makes them suitable for permeation to the cells and tissues.
The antioxidant properties of ligands are due to highest
lipophilicity, lowest electron withdrawing power, and
highest polarisability.
Scavenging activity ð%Þ ¼ f½ðAb þ AsÞ ꢁ Amꢀ=AbgX 100%
Ab: absorbance of 0.1 mM methanolic solution of DPPH
at 517 nm, As: absorbance of 0.1 mM methanolic solution
of test compounds at 517 nm, Am: absorbance of metha-
nolic mixture of the drug and DPPH at 517 nm. All the
ligands and iron (III) complexes shows good antioxidant
activity though this activity are not change significantly
Acknowledgments The author expresses their sincere thanks to
University Grant Commission (UGC), New Delhi (Ref. No. F. 41-296/

Med Chem Res
2012 (SR) for providing financial support under major research pro-
ject. The author is also thankful to the Head, Department of Chemistry,
Sardar Patel University, CDRI, Lucknow and SAIF, IIT Madras for
providing instrumental facility. Pooja A. Sathe express her sincere
thanks to UGC for JRF F.17-120/98(SA-I) No.F.15-9(JUNE-2012)/
2012(NET).
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