A modern technique for preparation of zinc(II) and nickel(II) nanometric oxides using Schiff base compounds: Synthesis, characterization, and antibacterial properties

Article abstract of DOI:10.1007/s11164-013-1049-8

The purpose of the work reported in this paper was the preparation and characterization of Zn(II) and Ni(II) nanometric oxides by using a simple Schiff compound as precursor for complexation then thermal degradation at 600 °C. Metal complexes [Ni(L)₂(Cl)₂] and [Zn(L) ₂](NO₃)₂, where L is the Schiff base formed by condensation of 2-thiophenecarboxaldehyde with phenylhydrazine, were prepared and characterized by elemental analysis and by magnetic and spectroscopic measurements (infrared, Raman, X-ray powder diffraction, and scanning electron microscopy). Elemental analysis of the chelates suggests the stoichiometry is 1:2 (metal-ligand). Infrared spectra of the complexes are indicative of coordination of the nitrogen of the phenylhydrazine (-Ph-NH-) group and the sulfur atom of the thiophene ring with the central metal atom. Magnetic susceptibility data and electronic and ESR spectra suggest a distorted octahedral structure for the Ni(II) complex and tetrahedral geometry for the Zn(II) complex. The Schiff base and its metal chelates were screened for in-vitro activity against four bacteria, two Gram-positive (Bacillus subtilis and Staphylococcus aureus) and two Gram-negative (Escherichia coli and Pseudomonas aeruginosa), and two strains of fungus (Aspergillus flavus and Candida albicans). The metal chelates were shown to have greater antibacterial activity than the free Schiff-base chelate.

Full text of DOI:10.1007/s11164-013-1049-8

Res Chem Intermed
DOI 10.1007/s11164-013-1049-8
A modern technique for preparation of zinc(II)
and nickel(II) nanometric oxides using Schiff base
compounds: synthesis, characterization,
and antibacterial properties
•
Adel S. Megahed M. S. Al-Amoudi M. S. Refat
•
Received: 15 December 2012 / Accepted: 11 January 2013
Ó Springer Science+Business Media Dordrecht 2013
Abstract The purpose of the work reported in this paper was the preparation and
characterization of Zn(II) and Ni(II) nanometric oxides by using a simple Schiff
compound as precursor for complexation then thermal degradation at 600 °C. Metal
complexes [Ni(L)2(Cl)2] and [Zn(L)2](NO3)2, where L is the Schiff base formed by
condensation of 2-thiophenecarboxaldehyde with phenylhydrazine, were prepared
and characterized by elemental analysis and by magnetic and spectroscopic mea-
surements (infrared, Raman, X-ray powder diffraction, and scanning electron
microscopy). Elemental analysis of the chelates suggests the stoichiometry is 1:2
(metal–ligand). Infrared spectra of the complexes are indicative of coordination of
the nitrogen of the phenylhydrazine (–Ph–NH–) group and the sulfur atom of the
thiophene ring with the central metal atom. Magnetic susceptibility data and elec-
tronic and ESR spectra suggest a distorted octahedral structure for the Ni(II)
complex and tetrahedral geometry for the Zn(II) complex. The Schiff base and its
metal chelates were screened for in-vitro activity against four bacteria, two Gram-
positive (Bacillus subtilis and Staphylococcus aureus) and two Gram-negative
(Escherichia coli and Pseudomonas aeruginosa), and two strains of fungus
(Aspergillus flavus and Candida albicans). The metal chelates were shown to have
greater antibacterial activity than the free Schiff-base chelate.
Keywords Nanometric oxides ꢀ Complexes ꢀ Schiff base ꢀ Thermal analysis ꢀ
Biological evaluation
A. S. Megahed ꢀ M. S. Al-Amoudi ꢀ M. S. Refat (&)
Department of Chemistry, Faculty of Science, Taif University, Taif 888, Saudi Arabia
e-mail: msrefat@yahoo.com
M. S. Refat
Department of Chemistry, Faculty of Science, Port Said University, Port Said, Egypt
123

A. S. Megahed et al.
Introduction
Nanotechnology offers unique approaches for investigation and control of a variety
of biological and medical processes that occur at nanometer length scales, and is
expected to have a revolutionary effect on biology and medicine. Among the
approaches used to exploit nanotechnology in medicine, nanoparticles have unique
advantages as sensing, image-enhancement, and delivery agents. Several varieties of
nanoparticle with biomedical relevance are available including, polymeric nano-
particles, metal nanoparticles, liposomes, micelles, quantum dots, dendrimers, and
nanoassemblies. To further the application of nanoparticles in disease diagnosis and
therapy, it is important that the systems are biocompatible and capable of being
functionalized for recognition of specific target sites in the body after systemic
administration [1].
Schiff bases are regarded as ‘‘privileged ligands’’ because they are easily
prepared by condensation of aldehydes with imines. Stereogenic centers or other
elements of chirality (planes, axes) can be introduced in the synthetic design. Schiff
base ligands are able to coordinate with many different metals [2], and to stabilize
them in different oxidation states. Schiff base complexes have been used in catalytic
reactions [3] and as models for biological systems [4]. Chiral Schiff bases prepared
by condensation of salicylaldehydes with 2-amino alcohols have found widespread
use as ligands in asymmetric synthesis. These compounds act as tridentate ONO
ligands, and many metallic complexes derived from them have been described in the
literature [5]. Depending upon the nature of the metal center, these chiral complexes
can promote a variety of enantioselective transformations. It has been reported that
the structure of the substituent bonded to the imino nitrogen affects the coordination
geometry of the complex [6]. During the past two decades, much attention has been
devoted to the chemistry of the metal complexes of Schiff bases containing nitrogen
and other donors [7]. This may be attributed to their stability, biological activity [8],
and potential applications in many fields, for example oxidation, catalysis, and
electrochemistry [9]. The complexes make these compounds effective and
stereospecific catalysts for oxidation, reduction, hydrolysis, and other transforma-
tions in organic and inorganic chemistry. They also have biological activity. It is
well known that some drugs are more active when administered as metal complexes
than as free ligands [10].
Nickel(II) complexes containing sulfur donors have received much attention
because of identification of a sulfur-rich coordination environment in biological
nickel centers, for example the active sites of some ureases, methyl-S-coenzyme-M-
methyl reductase, and hydrogenases [11].
The zinc(II) ion is known to have a high affinity for nitrogen and sulfur donor
ligands. Dowling and Perkin investigated Zn(II) complexes with mixed N, O, and S
coordination to understand the reactivity of the pseudotetrahedral zinc center in
proteins [12]. The transition metals zinc and copper are two of the most frequently
occurring elements in essential biochemical pathways. They are present in the active
sites of several biologically important molecules with catalytic activity [13] or
molecules involved in transfer processes, for example oxygen transfer. In contrast
with zinc(II), copper(II) ions are redox active and are extremely important in the
123

Synthesis, characterization and antibacterial properties
catalytic sites of oxidoreductases. The cyclic redox process enables these ions to act
as pro or anti-oxidants. Published results on the structure and pro or anti-oxidant
activity relationships are, however, quite inconsistent [14]. We report herein the
results of our studies on the metal complexes of a Schiff base derived from
2-thiophenecarboxaldehyde and phenylhydrazine, used in a modern technique for
preparation of nanometric oxides using Schiff base compounds. Tentative structures
have been proposed on the basis of analytical, spectral, magnetic, and conductance
data. For determination of the biological role of metals, the Schiff base and its metal
chelates were screened for biological activity against both Gram-positive and Gram-
negative bacterial and fungi.
Experimental
Chemicals
Reagent grade 2-thiophenecarboxaldehyde, phenylhydrazine, and transition metal
salts (nickel(II) chloride hexahydrate, and zinc(II) nitrate hexahydrate) were
obtained from BDH and Aldrich; other chemicals and solvents were purchased and
used as received.
Synthesis of the bi-dentate Schiff base (PTMH)
The Schiff base (PTMH, Fig. 1) was prepared as reported elsewhere [15, 16]. An
ethanolic solution of 2-thiophenecarboxaldehyde (1 mmol, 25 mL) was added to an
ethanolic solution of phenylhydrazine (1 mmol, 25 mL) and heated under reflux for
2 h in a water bath. After concentration of the solution, the precipitate which
separated, was isolated by filtration, re-crystallization from ethanol, and dried under
vacuum over anhydrous calcium chloride. Anal.: Calcd. For PTMH: C, 65.32; H,
4.98; N, 13.85; S, 15.85. Found: C, 65.12; H, 4.78; N, 13.74; S, 15.59. The
calculated mass spectrum was: m/e: 202.056 (100.0 %), 203.060 (12.2 %), 204.052
(4.4 %).
Synthesis of the ML2X2 Schiff base complexes
A mixture of PTMH (2 mmol, 50 mL) in ethanol was added to an ethanolic solution of
nickel(II) chloride hexahydrate or zinc(II) nitrate hexahydrate (1 mmol, 50 mL). The
mixturewasheatedunderrefluxfor2 hthenexcesssolventwasremovedbydistillation.The
precipitatedcompoundsthatseparatedwereisolatedbyfiltration,washedwithethanol,and
driedinvacuumoverCaCl2.Anal.:Calcd.For[Ni(L)2(Cl)2]:color(greenishbrown);mp
235 °C:C,49.47;H,3.77;N,10.49;S,12.01.Found:C,49.43;H,3.64;N,10.32;S,11.89.
Anal.:Calcd.For[Zn(L)2](NO3)2:color(darkbrown);mp210 °C:C,44.49;H,3.39;N,
14.15;S,10.80.Found:C,44.21;H,3.19;N,14.09;S,10.54.
123

A. S. Megahed et al.
C(1)
C(2)
C(3)
S(5)
H(10)
N(9)
C(4)
C(16)
C(15)
C(6)
C(11)
N(8)
H(7)
C(14)
C(12)
C(13)
S
NH
N
CH
Fig. 1 Structure of the Schiff base N-phenyl-N0-thiophen-2-ylmethylenehydrazine (PTMH)
Measurements
Elemental analyses of carbon, hydrogen, nitrogen, and sulfur content was performed
with a Perkin Elmer CHNS 2400 (USA). The molar conductivities of freshly prepared
1.0 9 10-3 mol/cm3 dimethyl sulfoxide (DMSO) solutions of the PTMH Schiff base
complexes were measured by use of Jenway 4010 conductivity meter. The electronic
absorption spectra of the PTMH Schiff base complexes were recorded in DMSO as
solvent in the range 900–200 nm by use of a UV2 Unicam UV/Vis Spectrophotometer
fitted with a quartz cell of 1.0 cm path length. Infrared spectra, as KBr discs, were
recorded with a Bruker FT-IR Spectrophotometer (4,000–400 cm-1). Laser Raman
spectra of the samples were measured with a Bruker FT-Raman with 50 mW laser.
Magnetic data were obtained by use of a Sherwood Scientific (Cambridge Science
Park, Cambridge, UK) magnetic susceptibility balance at 25 °C. Thermal studies up to
300 °C were performed with a Shimadzu DTG–50H thermogravimetric analyzer
under static air. Scanning electron microscopy (SEM) images were obtained with
Quanta FEG 250 equipment. The X-ray diffraction patterns for the Ni(II) and Zn(II)
123

Synthesis, characterization and antibacterial properties
Schiff base complexes were recorded with X’Pert PRO PANalytical X-ray powder
diffraction equipment, target copper, with secondary monochromator.
Antibacterial and antifungal evaluation
Antimicrobial activity of the complexes was determined by use of a modified
Kirby–Bauer disc-diffusion method [17]. Briefly, 100 ll test bacteria/fungi were
grown in 10 mL fresh media until they reached a count of approximately 108 cells/
mL for bacteria or 105 cells/mL for fungi [18]. This microbial suspension (100 ll)
was spread on to agar plates prepared with the broth in which they were maintained.
Isolated colonies of each organism were selected from primary agar plates and
tested for susceptibility by the disc diffusion method [19, 20].
The disc diffusion test for filamentous fungi was the approved standard method
(M38-A) developed by the NCCLS [21] for evaluation of the susceptibility of
filamentous fungi to antifungal agents. The disc diffusion method for yeast was
standard method M44-P developed by the NCCLS [22]. Plates inoculated with the
filamentous fungus Aspergillus flavus were incubated at 25 °C for 48 h. Plates
inoculated with the Gram(?) bacteria Staphylococcus aureus and Bacillus subtilis
and the Gram(-) bacteria Escherichia coli and Pseudomonas aeruginosa were
incubated at 35–37 °C for 24–48 h. Plates inoculated with the yeast Candida
albicans were incubated at 30 °C for 24–48 h. The diameters of the inhabitation
zones were then measured in millimeters [17]. Standard discs of tetracycline
(antibacterial agent) and amphotericin B (antifungal agent) served as positive
controls for antimicrobial activity. Filter discs impregnated with 10 ll solvent
(distilled water and DMSO) were used as a negative controls.
The agar used was Mueller–Hinton agar, which is rigorously tested for composition
and pH. The depth of the agar in the plate is a factor to be considered in the disc
diffusion method. This method is well documented and standard zones have been
determined for susceptible species. Blank paper disks (Schleicher and Schuell, Spain)
with a diameter of 8.0 mm were impregnated with 10 ll of the tested concentration of
the stock solutions. When a filter paper disc impregnated with a tested chemical is
placed on the agar the chemical will diffuse from the disc into the agar. This diffusion
will place the chemical in the agar only around the disc. The solubility of the chemical
and its molecular size will determine the size of the area of chemical infiltration around
the disc. If an organism is placed on the agar it will not grow in the area around the disc
if it is susceptible to the chemical. This area of no growth around the disc is known as a
‘‘zone of inhibition’’ or ‘‘clear zone’’. In the disc diffusion method zone diameters are
measured by use of slipping calipers meeting the National Committee for Clinical
Laboratory Standard [19]. Agar-based methods, for example the disk diffusion test,
can be good alternatives to broth methods because they are simpler and faster [23, 24].
Results and discussion
The synthesized complexes of Ni(II) and Zn(II) with the Schiff base PTMH (Fig. 1)
were obtained as high-melting-point powders. They are not soluble in ethanol,
123

A. S. Megahed et al.
diethyl ether, or chloroform, but are soluble in DMSO and DMF. Elemental analysis
suggests the complexes have 1:2 (metal–ligand) stoichiometry. On the basis of the
elemental analysis the formula, ML2X2, was suggested for all compounds.
Some characteristic infrared absorption bands of PTMH and its Ni(II) and Zn(II)
complexes, with their assignments, are listed in Table 1. The infrared spectrum of
the ligand (Fig. 2) contains a band at 1599 cm-1, assignable to m(C=N) of the
azomethine group, and intense bands at 1,536, 1,507, and 1,447 cm-1 correspond-
ing to C=C stretching of the benzene and thiophene rings. Comparison of the
positions of these bands with those observed in the IR spectra of the nickel(II) and
zinc(II) complexes indicated that the band at 1,599 cm-1 had no marked shift,
implying the azomethine group is not involved in complexation with the nickel(II)
and zinc(II) ions. The band at 3,322 cm-1, however, assigned to –NH of
phenylhydrazine, decreased slightly in intensity and shifted to slightly lower
wavenumber (by approx. *5 cm-1). This behavior suggests coordination of PTMH
through the Ph–NH nitrogen of phenylhydrazine. Proof of coordination to the N
atom is provided by the occurrence of the new bands at *415 cm-1 in the IR
spectra of the complexes. The observed medium intensity band at 910 cm-1 in the
free ligand, which is ascribed to m(CSC) of the thiophene ring stretching vibration
[16], shifted to lower values for the two complexes, suggesting involvement of the
sulfur atom in bonding with the metal ions. The band assigned to the asymmetric
m(C-S) is similarly shifted. This also confirms that the sulfur atom is taking part in
complex formation [16].
On the other hand, the Raman spectra of PTMH and the [Ni(L)2(Cl)2] and
[Zn(L)2](NO3)2 Schiff base complexes (Fig. 3) contain sharp peaks on a broad
background of distorted stretching and vibration bands. This can be explained on the
basis of the knowledge that Raman analysis of fluorescent materials and compounds
is a challenging task experimentally, because of the overlap of fluorescence which,
even when very weak, can overwhelm the inherently weak Raman scattering signal
[25, 26].
It is tentatively suggested that the Schiff base ligand coordinates through the
nitrogen of the phenylhydrazine moiety and the sulfur of the thiophene ring,
forming a stable chelating structure. According to the above discussion, distorted
octahedral structure for Ni(II) complex and tetrahedral structure for Zn(II) complex
are deduced (Fig. 4).
In the electronic spectrum of the N-phenyl-N0-thiophen-2-ylmethylenehydrazine
(PTMH) Schiff base ligand, absorption bands observed at 266, 361, and 436 nm and
assigned to the transitions n ? p*, p ? p*, and metal-to-ligand charge transfer,
respectively. These transitions also existed in the spectra of the complexes, but they
Table 1 Infrared characteristic band frequencies (cm-1) of the ligand complexes
Compound
m(C=N)
m(C=C) phenyl ? thiophene
m(CSC)
mas(C-S)
m(M-N)
PTMH
1599
1599
1598
1536, 1507, 1447
1531, 1503, 1447
1535, 1489, 1445
910
884
884
705
690
691
–
[Ni(L)2(Cl)2]
[Zn(L)2](NO3)2
415
415
123

Synthesis, characterization and antibacterial properties
Fig. 2 a Infrared spectrum of
the Schiff base PTMH as the
free ligand. b Infrared spectrum
of [Ni(L)2(Cl)2] Schiff base
complex. c Infrared spectrum of
[Zn(L)2](NO3)2 Schiff base
complex
A
4000 3500 3000 2500 2000 1500 1000 500
-1
Wavenumbers (cm
)
B
4000 3500 3000 2500 2000 1500 1000 500
-1
Wavenumbers (cm
)
C
4000 3500 3000 2500 2000 1500 1000 500
-1
Wavenumbers (cm
)
123

A. S. Megahed et al.
Schiff base
NiII
0.6
0.5
0.4
0.3
0.2
0.1
0.0
ZnII
4000 3500 3000 2500 2000 1500 1000 500
-1
Wavenumbers (cm )
Fig. 3 Raman spectra of PTMH and the [Ni(L)2(Cl)2] and [Zn(L)2](NO3)2 Schiff base complexes
Fig. 4 Proposed structures
of [Ni(L)2(Cl)2] and
[Zn(L)2](NO3)2 Schiff base
CH
N
HC
N
S
S
complexes
Cl Ni Cl
HN
NH
CH
N
HC
S
S
Zn
N
HN
NH
.2(NO3)
shifted to lower intensities, confirming coordination of the ligand with the metal ions.
Information concerning the geometry of these compounds was obtained from the
electronic spectra and from magnetic moments. The electronic spectrum of the
[Ni(PTMH)2Cl2] complex was indicative of octahedral geometry. The solid
reflectance spectrum of the Ni(II) complex contained two identified bands at
123

Synthesis, characterization and antibacterial properties
Fig. 5 a Scanning electron microscope image of synthesized NiO nanoparticles. b Scanning electron
microscope image of synthesized ZnO nanoparticles
3
3
16,667 and 24,691 cm-1, assigned to the transitions A2g(F) ? T1g(F) and,
3A2g(F) ? T1g(P) respectively [27]. We determined the magnetic moment,
3
configuration, stereochemistry, hybrid orbitals, number of unpaired electrons, and
spin-only and expected magnetic values for the Ni(II) complex by means of magnetic
susceptibility measurements at room temperature; the results were 3.12 B.M., d8,
octahedral, sp3d2, n = 2, and 2.83 B.M. and 3.32 B.M., respectively. The magnetic
moment (3.1 MB) lies within the region expected for octahedral complexes. The
molar conductance of the [Ni(PTMH)2Cl2] and [Zn(PTMH)2](NO3)2 Schiff base
complexes in DMSO are 35 and 96, indicating the non-electrolytic nature for
nickel(II) with two chloride ligands inside coordination sphere. The zinc(II)
complex, however, is a 1:2 electrolyte.
Zinc(II) and nickel(II) oxide nanoparticles were synthesized at 600 °C from
[Ni(PTMH)2Cl2] and [Zn(PTMH)2](NO3)2 Schiff base complexes as precursors.
Their properties were studied by use of scanning electron microscopy (SEM) and
123

A. S. Megahed et al.
A
2000
1500
1000
500
0
10
20
30
40
50
60
2θ
B
1200
1000
800
600
400
200
0
10
20
30
40
50
60
2θ
Fig. 6 a XRD patterns of NiO nanoparticles. b XRD patterns of ZnO nanoparticles
X-ray diffraction. Figure 5 show the SEM image of the synthesized ZnO and NiO
nanoparticles. The equipment was attached to a computer running software to
analyze the mean size of the particles in the samples. It should be noted that particle
diameter is always overestimated because of the distortion of SEM images [28].
Scanning electron micrographs were obtained for both NiO and ZnO oxides
prepared at 600 °C. A homogeneous phase because of uniform of grain size is
apparent. It is also clearly apparent the nanometric oxides have characteristic
surface morphology which is different for each oxide—caves and crushed ice for
NiO and ZnO, respectively.
The XRD patterns of the NiO and ZnO nanoparticles are shown in Fig. 6a, b. The
X-ray diffraction data were recorded by use of Cu Ka radiation (1.5406 Angstrom).
The intensity data were collected over a 2h range of 5–60°. X-ray diffraction studies
123

Synthesis, characterization and antibacterial properties
50
A 12
0
10
8
-50
-100
-150
-200
-250
-300
6
4
2
0
250
300
350
50
100
150
200
Temp.[oC]
B
0
0.8
0.7
0.6
0.5
0.4
0.3
0.2
-10
-20
-30
-40
-50
-60
-70
50
100
150
200
250
300
Temp.[oC]
C
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0
-20
-40
-60
-80
-100
0
50
100
150
200
250
300
Temp.[oC]
Fig. 7 a TGA/DTA curves of PTMH Schiff base ligand. b TGA/DTA curves of [Ni(PTMH)2Cl2] Schiff
base complex. c TGA/DTA curves of [Zn(PTMH)2](NO3)2 Schiff base complex
confirmed that the synthesized materials were NiO and ZnO and all the diffraction
peaks agreed with reported standard data. No characteristic peaks were observed
other than ZnO. The mean average grain size (D) of the samples was estimated by
123

A. S. Megahed et al.
Table 2 Antimicrobial activity data of PTMH and its Ni(II) and Zn(II) complexes
Sample Inhibition zone diameter (mm/mg sample)
Bacillus Escherichia Pseudomonas Staphylococcus Aspergillus Candida
coli (G-)
subtilis
(G?)
aeruginosa
(G-)
aureus (G?)
flavus
(fungus)
albicans
(fungus)
Control: DMSO 0.0
Standard
0.0
32
0.0
34
0.0
30
0.0
–
0.0
–
Tetracycline
antibacterial
agent
34
Amphotericin
B antifungal
agent
–
–
–
–
18
19
PTMH
Ni(II)
Zn(II)
9
8
12
10
14
11
9
5.0
19
21
3.0
12
18
12
14
14
11
16
use of the Scherrer equation (Eq. 1) from XRD line broadening, and from the
intensities of the diffraction peaks:
D ¼ 0:89k=ðb cos hÞ:
ð1Þ
where k is the wavelength (Cu Ka), b is the full width at half-maximum (FWHM) of
the NiO or ZnO line, and h is the diffraction angle. Obvious broadening of the
diffraction peaks is an indication that the synthesized materials are in the nanometer
range. Calculated lattice parameters were also in agreement with reported values.
The reaction temperature greatly affects particle morphology of as-prepared NiO
and ZnO powders. The results from nanoparticle size measurement of the samples
by XRD and SEM indicate that the size of the NiO and ZnO nanoparticles was
approximately 30 and 50 nm, respectively.
The thermal behavior of N-phenyl-N0-thiophen-2-ylmethylenehydrazine Schiff
base ligand was also studied (Fig. 7a). Three endothermic peaks were observed at
DTAmax = 165, 203, and 280 °C with weight loss of 100 % in static air at steady
state at 300 °C. Thermal decomposition of the synthetic nickel(II) and zinc(II)
PTMH Schiff base complexes was also studied. The TGA and DTA curves obtained
from the [Ni(PTMH)2Cl2] Schiff base complex heated from 30 °C to 300 °C are
shown in Fig. 7b. Thermal decomposition of the nickel(II) complex furnishes three
strong-to-weak peaks in the DTA curve at 118, 203, and 283 °C. These steps are
endothermic and assigned to loss of 2PTMH and Cl2 gas, with weight loss of 75 %.
Thermal analysis of the [Zn(PTMH)2](NO3)2 Schiff base complex confirmed its
thermal stability and several degradation steps corresponding to the DTA peak
maxima. According to the TG and DTA curves (Fig. 7c) at least two decomposition
steps are observed at 142 and 236 °C. Both are endothermic processes assigned to
the complete decomposition of 2PTMH and loss of 2NO3, with weight loss of
123

Synthesis, characterization and antibacterial properties
A
Candida albicans
Aspergillus flavus
Staphylococcus aureus
Pseudomonas aeruginosa
Escherichia coli
Bacillus subtilis
16.7%
25%
18.8%
6.25%
22.9%
10.4%
B
Candida albicans
Aspergillus flavus
Staphylococcus aureus
Pseudomonas aeruginosa
Escherichia coli
Bacillus subtilis
13.2%
18.4%
11.8%
15.8%
25%
15.8%
C
Candida albicans
Aspergillus flavus
Staphylococcus aureus
Pseudomonas aeruginosa
Escherichia coli
Bacillus subtilis
14.9%
11.7%
17%
14.9%
22.3%
19.1%
Fig. 8 a Antimicrobial activity of PTMH. b Antimicrobial activity of [Ni(PTMH)2Cl2] Schiff base
complex. c Antimicrobial activity of [Zn(PTMH)2](NO3)2 Schiff base complex
123

A. S. Megahed et al.
60 %. This is an interesting result—calcination furnishing the metal oxide in the
pure form occurs at low temperature when the Schiff base complexes are used as
precursors.
The antibacterial activity of the Schiff base and its nickel(II) and zinc(II)
complexes against Gram-positive (B. subtilis and S. aureus) and Gram-negative
(E. coli and P. aeruginosa) bacteria and two strains of fungus (A. flavus and C.
albicans) was studied. The results are shown in Table 2 and Fig. 8a–c.
The Schiff base complexes had different inhibitory effects on the growth of the
bacteria. Table 2 shows that the activity of the Schiff base was more pronounced
when coordinated with the metal ions. The biological activity of the complexes
follows the order: Zn(II) [ Ni(II). Furthermore, the data in Table 2 show that A.
flavus was strongly inhibited by the Zn(II) and Ni(II) complexes.
Conclusions
We report the preparation, isolation, and characterization of a new bidentate Schiff
base derived from 2-thiophenecarboxaldehyde and phenylhydrazine, its complexes
with Zn(II) and Ni(II), and the use of these complexes as precursors for preparation
of oxides with nano-sized particles. The synthesized metal complexes, in
comparison with the un-complexed Schiff base ligand, were screened for their
antibacterial and antifungal activity. The activity of the Schiff base became more
pronounced when coordinated with the metal ions.
Acknowledgments This work was supported by grants from Vice President for Graduate Study and
Research, Taif University, Saudi Arabia, under project no. 1971-433-1.
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