Ni(II), Pd(II) and Pt(II) complexes of (1H-1,2,4-triazole-3-ylimino)methyl]naphthalene-2-ol. Structural, spectroscopic, biological, cytotoxicity, antioxidant and DNA binding

Article abstract of DOI:10.1016/j.saa.2014.12.057

Metal complexes of the general formula [ML(H₂O)Cl]nH₂O; n = 1 for M = Ni and Pt and n = 2 for M = Pd, L = Schiff base (HL) derived from the condensation of 3-amino-1,2,4-triazole and 2-hydroxy-1-naphthaldehyde, were prepared. The syn

Full text of DOI:10.1016/j.saa.2014.12.057

Accepted Manuscript
Ni(II), Pd(II) and Pt(II) compleqxes of (1H-1,2,4-triazole–3 –ylimino)meth-
yl]naphthalene -2-ol. Structural, spectroscopic, biological, cytotoxicity, antiox-
idant and DNA binding
M. Gaber, H.A. El-Ghamry, S.K. Fathalla
PII:
S1386-1425(14)01837-X
http://dx.doi.org/10.1016/j.saa.2014.12.057
SAA 13107
DOI:
Reference:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
To appear in:
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Accepted Date:
15 October 2014
17 December 2014
Please cite this article as: M. Gaber, H.A. El-Ghamry, S.K. Fathalla, Ni(II), Pd(II) and Pt(II) compleqxes of
(1H-1,2,4-triazole–3 –ylimino)methyl]naphthalene -2-ol. Structural, spectroscopic, biological, cytotoxicity,
antioxidant and DNA binding, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi:
http://dx.doi.org/10.1016/j.saa.2014.12.057
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Ni(II), Pd(II) and Pt(II) complexes of (1H-1,2,4-triazole–3 –ylimino)methyl]naphthalene
-2-ol. Structural, spectroscopic, biological, cytotoxicity, antioxidant and DNA binding.
M. Gaber 1, H.A. El-Ghamry 1,2*, S.K. Fathalla 1
1 Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt
2 Department of Chemistry, Faculty of Applied Science, Umm Al–Qura University, Makkah,
Kingdom of Saudi Arabia
Abstract
Metal complexes of the general formula [ML(H2O)Cl]nH2O; n=1 for M=Ni and Pt and n=2
for M=Pd, L= Schiff base (HL) derived from the condensation of 3-amino-1,2,4-triazole and
2-hydroxy-1-naphthaldehyde, were prepared. The synthesized ligand and its metal complexes
were characterized on the basis of elemental analyses, spectral and magnetic studies as well as
thermal analysis. The IR spectra revealed that the ligand is coordinated to the metal ions in
bidentate manner via the N-atom of the azomethine group and the phenolic OH group. Square
planar geometry was proposed for Pd(II) and Pt(II) complexes and tetrahedral for Ni(II)
complex. The ligand and its metal complexes were screened against the sensitive organisms
Escherichia coli as Gram-negative bacteria, Staphylococcus aureus as Gram-positive bacteria,
Aspergillus flavus and Candida albicans as fungi. Moreover, the anticancer activity of the
ligand and its metal complexes was evaluated in liver cacinoma (HEPG2) cell line. The results
obtained indicated that the Schiff base ligand is more effective than its metal complexes
towards the tested cell line. Ni(II), Pd(II) and Pt(II) complexes as well as the free Schiff base
ligand were tested for their antioxidant activities. The DNA-binding properties of the studied
complexes have been investigated by electronic absorption and viscosity measurements.
Keywords: Ni(II), Pd(II), Pt(II) complexes, DNA binding, Antioxidant activity,
Cytotoxicity, Antimicrobial.
* Corresponding author e.mail: helghamrymo@yahoo.co

1. Introduction
The chemistry of Schiff base ligands and their metal complexes have attracted a lot of
interest due to their facile synthesis and wide range of applications. These compounds play an
important role in the development of coordination chemistry related to catalysis, organic
synthesis [1,2], antitumor, antimicrobial and cytotoxic activity[3-7.] Schiff bases derived from
1,2,4-triazoles and their metal complexes are biologically active having antiproliferative [ 8],
antibacterial and antifungal activity[9-17], antitumor [ 18] and anticancer [19]. DNA is an
important drug target and it regulates many biochemical processes that occur in the celluar
system. Small metal complexes that undergo hydrolytic DNA cleavage are useful in genetic
engineering molecular biotechnology and robust anticancer drug design [20]. Recently, there
has been a great interest on the binding of metal complexes with DNA [21-27] because it may
provide important information for new cancer therapeutic agents and potential probes of DNA
structure and conformation. Pd(II) and Pt(II) complexes have attracted considerable attention
in recent years because of their promising antibacterial and antitumor activity [28-39]
In the view of the above and our ongoing interest in the synthesis and biological properties of
various transition metal complexes [13, 40-42], we report herein the synthesis of the titled
Schiff base and its Ni(II), Pd(II) and Pt(II) complexes. The synthesized ligand and its metal
complexes were characterized by different techniques like elemental analyses, spectral
studies, TGA, magnetic and conductance measurements. The biological screening, antioxidant
and anticancer activities of the Schiff base ligand and its metal complexes are also described
here.
2. Experimental
2.1. Chemicals
All compounds used in the present study were of pure grade available from BDH, Aldrich
or Sigma. The solvents used for the spectral study were spectroscopic grade from Aldrich.
2.2. Preparation of Schiff-base ligand (SB)
The Schiff base ligand (Fig. 1) was prepared by the condensation of 3-amino1,2,4-
triazole with 2-hydroxy-1-naphthaldehyde, in 1:1 mole ratio in hot methanol as a solvent and
refluxed for 8 h according to the recommended method.[13,42] It was achieved by refluxing
0.01 mol (1.72 g) of 2-hydroxy-1-naphthaldehyde with 0.01 mol (0.84 g) of 3-amino-1,2,4-

triazole in methanol (100 mL) as a solvent. The condensation product separated on cooling
was filtered off, washed several times with methanol till constant melting point and finally
dried in a vacuum desiccator over anhydrous calcium chloride.
2.3. Preparation of the solid metal complexes
To a hot solution (1 mmol) of Schiff base ligand in (50 ml) methanol, a hot solution of
corresponding metal chlorides [NiCl2.6H2O, K2PdCl4 and K2PtCl4] (1 mmol, in 50 ml
methanol) were added slowly by the molar ratio 1:1 ( L:M ) in the presence of few drops of
triethyl amine as basic medium.. The resulting mixtures were stirred and refluxed on a hot
plate for 10 hours and then concentrated to a small volume; the solid complexes, which
separated out on hot, were filtered off, washed several times with methanol and finally deride
in a vacuum desiccator over anhydrous CaCl2.
2.4. Physical measurements
The elemental microanalyses of the prepared compounds were performed in the
microanalytical center, Cairo University using Perkin-Elmer 2400 CHN Elemental analyzer.
The Infrared spectra were recorded on a Perkin-Elmer 1430 IR spectrophotometer within the
1
range 4000-200 cm-1 as KBr discs. The HNMR spectra were carried out using a Varian
Mercury Oxford NMR 300 Hz spectrophotometer after dissolving the samples in DMSO d-6
using tetramethylsilane as internal standard. The electronic absorption spectra were recorded
using a Shimadzu Uv-Vis 240 spectrophotometer. The electron impact mass spectra of the
complexes were recorded at 70 eV. The magnetic susceptibility of the solid complexes was
carried out at room temperature by the Gouy's technique for magnetic susceptibility
instrument. The thermogravimetric analysis (TGA) of the solid complexes were performed
using the Schimadzu TG-50 thermogravimetric analyzer with heating rate 10°C /min under
nitrogen atmosphere, in the range 25-800 ºC.
2.5. DNA binding studies
The experiments were carried out in Tris-HCl buffer (5.0 mM of tris (hydroxymethyl)-
aminomethane and 50 mM NaCl) at pH 7.2. Tris–HCl buffer was prepared using deionized
and triple distilled water. Solutions of DNA in Tris–HCl gave a ratio of UV absorbance at 260

and 280 nm (A260/A280) of 1.8–1.9, indicating that the DNA was sufficiently free from
protein [43, 44]. The stock solution of DNA was prepared by dissolving DNA in Tris–HCl
buffer. Concentrated stock solutions of metal complexes were prepared by dissolving in DMF
and diluted suitably to required concentration. The spectroscopic titrations were carried out by
adding increasing amounts of DNA to a solution of the complex at a fixed concentration.
When measuring the absorption spectra, an equal amount of DNA was added to both the
complex solutions and the reference solution to eliminate the absorbance of DNA itself. The
intrinsic binding constant Kb was determined from the plot of [DNA]/(εa - εf) versus [DNA],
according to the following Eq.
[DNA]/(εa - εf) = [DNA]/(εb - εf) + 1/ [Kb(εb - εf)]
where [DNA] is the concentration of DNA in base pairs, the apparent absorption
coefficients εa, εf and εb correspond to Aobs/[complex], extinction coefficient for the free
complex and the extinction coefficient of the complex in the totally bound form, respectively.
The data were fitted to the above equation and graph was obtained with a slope equal to 1/(εb -
εf) and intercept equal to 1/[K(εb - εf)]. Hence Kb was obtained from the ratio of the intercept
to the slope [45].
Viscosities of CT-DNA at different complex concentrations in buffer solution were
measured using Ubbelodhe viscometer at the temperature of 30 0.1 ˚C in a thermostatic
water-bath. The DNA concentration was fixed, but the complex concentration was increased
each time. The average flow time was obtained after three times measurement for a sample
with a digital stopwatch. Data were presented as (η/η0)1/3 vs. mole ratio of [complex]/[DNA],
where η and η0 are the specific viscosity of DNA in presence and in absence of the complex,
respectively. The values of η and η0 were calculated by using the equation:
η = (t-t0)/t0
where "t" is the observed flow time of a solution containing DNA and the complexes and
"t0" is the flow time of the DNA solution alone. The relative viscosities for DNA were
calculated from the relation (η/η0) [46].
2.6. Biological activity

Antimicrobial activity of the synthesized compounds was determined using disc-agar
diffusion method [47] against the sensitive organisms Escherichia coli as Gram-negative
bacteria, Staphylococcus aureus as Gram-positive bacteria, Aspergillus flavus and Candida
albicans as fungi. Standard discs of Tetracycline (Antibacterial agent), Amphotericin B
(Antifungal agent) served as positive controls for antimicrobial activity but filter discs
impregnated with 10 µl of solvent (DMSO) were used as a negative control. Briefly, 100µl of
the test bacteria/fungi were grown in 10 ml of fresh media until they reached a count of
approximately 108 cells/ml for bacteria or 105 cells/ml for fungi [48]. 100 µl of microbial
suspension was spread onto agar plates corresponding to the broth in which they were
maintained. Plates incubated with filamentous fungi as Aspergillus flavus at 25 °C for 48 hours;
Gram (+) bacteria as Staphylococcus aureus and Gram (-) bacteria as Escherichia coli they were
incubated at 35-37 °C for 24-48 hours and yeast as Candida albicans incubated at 30 °C for 24-
48 hours and, then the diameters of the inhibition zones were measured in millimeters [47].
Blank paper disks (Schleicher & Schuell, Spain) with a diameter of 8.0 mm were impregnated
10µ of tested concentration of the stock solutions. When a filter paper disc impregnated with a
tested chemical is placed on agar the chemical will diffuse from the disc into the agar. This
diffusion will place the chemical in the agar only around the disc. Inhibition of the organisms
which evidenced by clear zone surround each disk was measured and used to calculate mean of
inhibition zones.
2.7. Measurement of Potential cytotoxicity by SRB assay
Liver carcinoma (HEPG2) Human cancer cell line was used for in vitro screening
experiments. This cell line was obtained frozen in liquid nitrogen (-180 ˚C) from the American
Type Culture Collection. The tumor cell line was maintained in the National Cancer Institute,
Cairo, Egypt, by serial sub-culturing. Potential cytotoxicity of the compounds was tested using
Skehan et al. method [49]. Cell was plated in 96-multiwell plate (104 cells/well) for 24 hrs
before treatment with the compound to allow attachment of cell to the wall of the plate.
Different concentrations of the compounds under study (0, 5, l2.5, 25 and 50 µg/ml) were added
to the cell monolayer triplicate wells prepared for each individual dose. The monolayer cell was
incubated with the compounds for 48 hrs at 37 °C and in atmosphere of 5% CO2. After 48 hrs,
Cell was fixed, washed and stained with the protein-binding dye Sulfo-Rhodamine-B (SRB)

[50]. Excess stain was washed with acetic acid and attached stain was recovered with Tris
EDTA buffer. Color intensity was measured in an ELISA reader. The relation between surviving
fraction and drug cone is plotted to get the survival curve of each tumor cell line after the
specified compound. Potential cytotoxicity of the compounds was measured in (Pharmacology
Unit, Cancer Biology Department, National Cancer Institute, Cairo University). Doxorubicin
was used as standard cytotoxins.
2.8. DPPH radical scavenging
The antioxidant activity of the investigated compounds and the standard ascorbic acid were
assessed on the basis of the radical scavenging effect of the stable DPPH (1,1-diphenyl-2-
picryl hydrazyl) free radical. The radical scavenging effects of antioxidants on DPPH are due
to their hydrogen donating ability which causes an absorbance drop at 517 nm.
In the DPPH radical scavenging, antioxidants react with the DPPH radical, which is a
stable free radical and exists naturally in deep violet color, to turn into a yellow colored
(diphenyl--picryl hydrazine). The degree of discoloration indicates the radical scavenging
potential of the antioxidant [51].
1µg of the studied samples and ascorbic acid (reference compound) were dissolved in
DMSO (1 ml). 250 µl of each solution was added to 1 ml DPPH/DMSO solution (6 mg/50 ml)
and the total volume was adjusted to 3 ml with DMSO. After vortexing the mixture was
incubated for 30 min at room temperature. Absorbance was measured at 517 nm. Absorbance
of blank sample containing the same amount of DMSO and DPPH solution was prepared and
measured as well. The experiment was carried out in triplicate. The scavenging potential was
compared with a solvent control (0% radical scavenging) and ascorbic acid. Radical
scavenging activity was calculated by the following formula:
% Reduction of absorbance = [(AB – AA)/AB] X 100
Where: AB – absorbance of blank sample; AA – absorbance of tested sample
3. Results and discussion
3.1. The elemental analysis and molar conductance results
On the basis of elemental analysis the complexes were assigned the composition shown in
Table 1. The results obtained are in good agreement with those calculated for the suggested
molecular formulae. The molar conductance values listed in Table 1 revealed that the

complexes are non-electrolytes in DMF [52]. Thus, the general formulae of the complexes is
[ML(H2O) Cl] nH2O, where n=1 for M= Pt or Ni; n=2 for M= Pd.
3.2. Infrared spectra
The IR spectra of the metal complexes are compared with that of the free Schiff base
ligand in order to determine the coordination sites that may be involved in chelation, Table 2.
The IR spectrum of the free ligand showed strong bands at 1614 cm-1 and 1575 cm-1 due to
υC=N of triazole moiety and azomethine group, respectively [53]. The υ (C=N) of the free
azomethine group is shifted to lower values (1538-1553 cm-1) indicating its involvement in
the coordination sphere [54]. The involvement of the deprotonated phenolic OH group in
complex formation is confirmed by the blue shift of the υ (C-O) stretching band (1280-1307
cm-1) in complex formation [55]. IR spectra of all complexes showed broad bands at (3378-
3413) cm-1 which can be assigned to υOH of lattice water molecules associated with complexes
[56]. The participation of oxygen and nitrogen atoms in coordination with the metal ion is
further supported by the appearance of new bands within the range (556- 611), (426- 535) cm-
1 due to υM-O and υM-N, respectively.
3.3. 1HNMR spectra
The 1HNMR spectrum of the Schiff base ligand showed singlet signals at 10.08 and 8.44
ppm due to phenolic (-OH) and azomethine (-CH=N-) protons, respectively. The signal due to
the phenolic proton is absent, while the signal due to the azomethine proton is shifted to 8.93
and 8.95 ppm in the spectra of Pd(II) and Pt(II) complexes, respectively. This observation
supported the involvement of the OH and azomethine nitrogen in complex formation, Table
3.
3.4. EI- Mass spectra
The EI-mass spectra of Schiff base complexes showed the molecular ion peaks at (m/z)
366, 433 and 503 for Ni(II), Pd(II) and Pt(II) complexes, respectively, which agree with the
formula weights of the complexes. The fragmentation patterns of the complexes are illustrated
in Schemes (S1- S3).
3.5. Electronic spectra and magnetic moments
The magnetic moment value of Ni(II) complex is 3.35 B.M corresponding to two
unpaired electrons which is consistent with the tetrahedral structure of the complex [57]. All

the Pd(II) and Pt(II) complexes exhibit diamagnetic character confirming the square-planar
geometry. The Nujol mull spectrum of Ni(II) complex (1) showed broad d–d transition band
at 23419 cm-1 attributed to 3T1→ 3T1(p) transition indicating tetrahedral geometry [58]. The
electronic spectrum of Pt(II) complex exhibited a low energy spin allowed band at 23364 cm-1
1
1
corresponding to the transition b2g (dxy) - d1g (dx2-y2) i.e A1g → A2g (υ1) comparable to the
-2
transition assigned by Jorgensen [59] for [PtCl4] ( 21500 cm-1 ). The bands at 28986 cm-
1and 28818 cm-1 for Pd(II) and Pt(II) complexes, respectively, are assignable to a combination
1
1
of eg ( dyz, dzx ) – b1g (dx2-y2 ) i.e A1g → Eg ( υ3 ) and MLCT indicating a square planar
geometry [60].
3.6. Thermogravimetric analysis (TGA) of the complexes
The thermal behavior of the metal complexes was studied using TG technique. The stages
of decomposition, temperature range, mass loss percentages as well as decomposition
products are given in Table S1.
The thermal decomposition of Ni(II) complex takes place in five steps, the first step of
°
decomposition within the temperature range 38-136 C with mass loss 9.80% (calc. 9.98 %
corresponded to elimination of tow water molecules. The second step at 136-410 °C with mass
loss 27.23% (calc. 28.16 %) can be assigned to elimination of (Cl and triazole ring). The third
°
step at 410- 467 C with mass loss 17.42 % (calc. 17.96 %) represents the loss of (C4H4N).
The fourth step at 467-533 °C with mass loss 13.79 % (calc. 13.33%) correspond to loss of
°
(C4H). The final step at 533- 660 C with mass loss 11.25 % (calc. 10.34 %) represents the
further dissociation of the ligand with the formation of NiO as a final product. The
°
thermogram of Pd(II) complex comprises three steps. The first step at 45-100 C with mass
loss 8.65 % (calc. 8.32 %) correspond to elimination of 2 hydrated water molecules. The
second step at 100- 337 °C with mass loss 28.33 % (calc. 28.09 %) can be assigned to the loss
of coordinated water molecule, Cl- anions and triazole ring. The third step at 337- 458 °C with
mass loss 27.44% (calc. 27.05%) represents the decomposition of the organic ligand with the
formation of PdO + 3C as a final product. The thermal decomposition of Pt(II) complex
°
comprises two steps. The first step at 40-103 C with mass loss 3.21 % (cal. 3.57 %)
°
correspond to elimination of hydrated water molecule. The second step at 103- 590 C with
mass loss 31.67 % (calc. 32.08%) can be assigned to the loss of coordinated water molecule,

Cl- anions and decomposition of the organic ligand with the formation of PtO + C8H4 as a
final product.
The kinetic parameters (the order n, pre-exponential factor A and activation energy ∆E)
for the thermal decomposition steps were evaluated graphically using the Coats-Redfern
equation [61], Fig 2.
The thermodynamic activation parameters (∆H), (∆S) and (∆G) were calculated using the
relationships:
∆H = ∆E - RT
∆S = R [ln(Ah/kT)-1]
∆G = ∆H - T ∆S
Where k is Boltezmann constant and h is Plank's constant.
From the results listed in Table 4:
1- The negative values of the activation entropies ∆S* indicate a more ordered activated
complex than the reactants and/or the reactions are slower than normal [62].
2- The positive values of ∆H mean that the decomposition processes are endothermic [63].
3- Kinetics of the thermal decomposition stages of all complexes under study obeys, in most
cases, the first order kinetics.
4- The values of activation energies increase as the maximum temperature of decomposition
increases reflecting higher stability of the formed complexes under investigation.
Based on the above results, the schematic structures of the metal complexes is shown in Fig. 3
3.7. DNA studies
To evaluate the DNA interaction properties of the synthesized compounds, the UV-Vis
absorption and viscosity titration techniques were performed using CT-DNA. Absorption
spectral titration experiments were performed by maintaining a constant concentration of the
complex and varying concentration of CT-DNA. Hypochromism and hyperchromism are both
spectral features of DNA connected with its double helix structure. Hypochromism means the
DNA binding mode of the complex is electrostatic which can stabilize the DNA duplex [64].
The extent of hypochromism is commonly consistent with the strength of intercalative
interaction [65]. The hyperchromism means the breakage of the secondary structure of DNA
[64,66]. Complex bind to DNA through intercalation usually results in hypochromism

(decrease in absorbance) and bathchromism (red shift) because intercalative mode involves a
strong staking interaction between aromatic chromophore and the base pairs of DNA [67].
The absorption spectra of the ligand and its Ni(II), Pd(II) and Pt(II) complexes in the absence
and presence of CT-DNA are shown in Fig. 4. The electronic absorption of the Schiff base
ligand and its Pd(II) and Pt(II) complexes showed an increase in intensity with increasing the
concentration of the DNA i.e upon addition of increasing amount of CT-DNA, a significant
hyperchromic effect was observed. This suggested the existence of strong interaction between
the Pd(II) and Pt(II) complexes and CT-DNA which is different from the classical
intercalation binding. The observed hyperchromism was 21 % and 61 % for Pd(II) and Pt(II)
complexes, respectively. The spectral change of the complexes C2 and C3 observed in the
presence of CT-DNA can be rationalized in terms of groove binding [68]. The addition of
increasing concentration of CT-DNA (0 - 60 x 10-6 M) to a fixed concentration of Ni(II)
complex (8×10-5 M) resulted in the hypochromism with red shift (∆λ = 2 nm). The spectral
characteristics suggested that Ni(II) complex interacted with CT-DNA by the intercalative
binding mode because intercalation leads to hypochromism and bathochromism in absorption
spectra.
The intrinsic binding constant (kb) for Ni(II), Pd(II) and Pt(II) complexes was found to be
(3.08 x 105, 17.68 X 105, 5.52 X 105 )M-1 respectively, Table S2. From the results listed in
Table S2, we could deduce that Ni(II), Pd(II) and Pt(II) complexes bind to DNA with high
affinities and the DNA binding affinity of Pd(II) complex is stronger than Ni(II) and Pt(II)
complex [69]. Non planarity of the Ni(II) complex may be the main reason for the lower kb
value of the Ni(II) complex compared to Pd(II) and Pt(II) complexes i.e the geometry of the
complex affects the magnitude of binding [70]
3.8. Viscosity measurements
To further make clear the interaction between the complex and DNA, viscosity
measurements were studied. A classical intercalative mode causes a significant increase in
viscosity of DNA solution due to increase in overall DNA length. In constract, complexes
those bind exclusively in the DNA grooves by partial and/or non-classical intercalation under
the same conditions, typically cause less pronounced (positive or negative) or no change in
DNA solution viscosity [71]. The effect of increasing amount of complexes on the relative

viscosity of DNA is shown in Fig. 5. The gradual increase in relative viscosity was observed
on addition of the metal complexes to DNA solution suggesting mainly intercalation mode of
binding with the complexes [71,72] i.e. the observed increase in the relative viscosity of
DNA could be as a result of a length increase of the duplex on intercalation of the complex.
This phenomenon may be explained by the insertion of the compounds in between the DNA
base pairs, leading to an increase in the separation of base pairs at intercalation sites and thus
an increase in overall DNA length [73].
3.9. Antimicrobial activity
The synthesized Schiff base (SB) and its Ni(II), Pd(II) and Pt(II) complexes have been
tested for their inhibitory effect on the growth of bacteria: E. coli and S. aureus and fungi: A.
flavus and C. albicans. The antibacterial and antifungal activity values of the investigated
compounds are tabulated in Table 5.
With regard to A. flavus, the results indicated that the Schiff base ligand and its complexes
showed no activity. With C. albicans, the Schiff base ligand showed moderate activity while
Ni(II), Pd(II) and Pt(II) complexes exhibited the lower activity. On the basis of inhibition zone
produced against the E. coli and S. aureus bacteria (9-13 mm), all the complexes have moderate
activity except Ni(II) complex with E. coli (9 mm) and S. aureus (9 mm) which has low
activity. A possible explanation for the poor activity of these complexes in comparison to the
Schiff base ligand may be due to their inability to chelate metals essential for the metabolism of
microorganisms and/or to form hydrogen bonds with the active centers of cell structures,
resulting in an interference with the normal cell cycle. It is also due to their low lipophilicity,
where the penetration of the complex through the lipid membrane is decreased and hence, they
cannot block or inhibit the growth of the microorganism [35]
3. 10. Anticancer activity
The anticancer activity of the SB ligand and its complexes was determined in vitro on
human tumor cell line (liver carcinoma HEPG2), Fig. 6. The IC50 (the concentration that
inhibited in 50% of the cellublar proliferation) was determined. According to Shier [74], the
compounds exhibited IC50 activity within the range of 10-25 µg/ml are considered weak
anticancer drugs, while those of IC50 activity between 5 and 10 µg/ml are moderate and
compounds of activity below 5.00 µg/ml are considered strong agents. It was found that the
ligand exhibited strong antitumor activity and its Ni(II), Pd(II) and Pt(II) complexes exhibited

a weak antitumor activity according to Shier scale. The results obtained indicated that the
Schiff base ligand is more effective than its complexes towards the cancer cell line. The
results showed the higher toxicity of Pd(II) (19.7 µg/ml) complex than Pt(II) (19.5 µg/ml) and
Ni(II) (15.5 µg/ml) complexes, Table 6.
3.11. Antioxidant
Hydroxyl radical is highly reactive oxygen centered radical formed from the reactions of
various hydroperoxides with transition metal ions. This radical is by far the most potent and
therefore the most dangerous oxygen metabolite and hence the elimination of this radical is
one of the major aims of antioxidant administration [75]. It attack proteins, DNA,
polysaturated fatty acid in membranes and most biological molecules [76]
Nowadays, antioxidants that exhibit DPPH radical scavenging activity are increasingly
receiving attention. The model of the scavenging of the stable DPPH radical is extensive used
to evaluate the antioxidant activities in less time than the other methods. The competition of
the complex with DMSO for hydroxyl radicals, generated by the Fe3+ / ascorbic acid system
expressed as the inhibition of formaldehyde production was used for the evaluation of their
hydroxyl radical scavenging activity.
Ni(II), Pd(II) and Pt(II) complexes as well as the free Schiff base ligand were tested for
their antioxidant activities. The radical scavenging activity of the investigated compounds was
tested against (the DPPH stable free radical) the hydroxyl radical generated by Fe3+ / ascorbic
acid system. In the present study, based on the IC50 values, scavenging activities of the free
Schiff base ligand and its Ni(II), Pd(II) and Pt(II) complexes are calculated. The comparison
of the antioxidant activity of the SB ligand (IC50 = 83.91 mg/ml) with those of the metal
complexes ( IC50 values of Ni(II), Pd(II) and Pt(II) complexes are 73.72, 57.39 and 86.64
mg/ml, respectively) indicated that (i) Ni(II) and Pd(II) complexes posses higher scavenging
activities towards the hydroxyl radical than the free ligand. (ii) Pd(II) complex showed more
scavenging activity than Ni(II) and Pt(II) complexes. In general, the antioxidant activity of the
SB ligand and its metal complexes was found to decrease in order of Pd(II) > Ni(II) > SB >
Pt(II).
4. Conclusion

Schiff base ligand derived from condensation of 3-amino-1, 2, 4-triazole with 2-hydroxy-1-
naphthaldehyde and its metal complexes with Ni(II), Pd(II) and Pt(II) have been described
and characterized by the combination of the elemental analysis, 1HNMR, IR, mass, electronic
spectra, magnetic susceptibility and thermal analysis. The metals are coordinated to the
nitrogen atoms of the azomethine and phenolic oxygen atom. The magnetic moment values of
the complexes display diamagnetic behavior for Pd(II) and Pt(II) complexes and tetrahedral
geometrical structure for Ni(II) complex. All the complexes have moderate activity towards
the E. coli and S. aureus bacteria except Ni (II) complex with E. coli and S. aureus which has
low activity. The Schiff base ligand and its complexes showed no activity against A. flavus.
With C. albicans, the Schiff base ligand showed moderate activity while Ni(II), Pd(II) and
Pt(II) complexes exhibited the lower activity. The free Schiff base ligand and its complexes
show anticancer activity against HEPG2 cell. The Schiff base ligand exhibited strong
antitumor activity while its Pd(II), Pt(II) and Ni(II) complexes exhibited a weak antitumor
activity. The results obtained indicated that the SB ligand is more effective than their
complexes towards the cancer cell line. The in vitro antioxidant of the ligand and its metal
complexes were also carried out. The order of the scavenging activity of the metal complexes
according to their IC50 values is Pd(II) > Ni(II) > Pt(II).
Acknowledgements
Financial support from Tanta University, Tanta, Egypt is gratefully acknowledged. The
authors would like to thank Prof. Dr. T. Mostafa and Dr. Mai M. El-Keiy, Chemistry
Department, Biochemistry Specialty, Faculty of Science, Tanta University, Egypt for their
help with the antioxidant activity studies.
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Figures
Fig. 1 The structure of the Schiff base ligand.
Fig. 2 The kinetic parameters
Fig. 3 The structure of the Schiff base metal complexes.
Fig. 4 The absorption spectra of the ligand and its Ni(II), Pd(II) and Pt(II) complexes
in the absence and presence of CT-DNA
Fig. 5 Effect of increasing amount of the prepared compounds on the viscosity of CT-
DNA (3x10-5M)
Fig. 6 Effect of prepared compounds on HEPG2 cell line
Tables

Table 1: The results of the elemental analyses and the molar conductance values of
the metal complexes.
Table 2: The IR spectra of the metal complexes
Table 3: 1HNMR of the Schiff base ligand, Pd and Pt complexes
Table 4: The thermodynamic parameters (∆E, ∆H, ∆S and ∆G) of Ni(II), Pd(II)
and Pt(II) complexes.
Table 5: The antibacterial and antifungal activity values of the investigated
compounds.
Table 6: In vitro antitumor activities of prepared compounds against HEPG2 cell line.
Table S1: The stages of decomposition, temperature range, weight loss percentages
and decomposition products of the metal complexes.
Table S2: Binding constants (Kb M-1) of the interaction between the complexes of the
Schiff-base and CT-DNA.

Table 1: Elemental analysis and physical properties of the prepared compounds
Compounds Molecular formula
(Emperical formula)
Mol.
wt.
(m.p.)
Yield
%
Elemental analysis
Calc / (found)
Λm
-
%C
65.5
%H
%M
C13H10N4O
SB
C1
(238)
240
92
89
4.2
-
(65.85) (4.8)
C13H13ClN4O3Ni
[NiLCl.H2O].H2O
367.5
> 300
42.45 3.54 16.05
(42.27) (3.91) (15.55)
5.98
(C13H15ClN4O4Pd)
[PdLCl.H2O].2H2O
C2
C3
432.5
> 300
70
72
36.07 3.47 24.51
8.23
(36.12) (3.02) (24.03)
30.98 2.58 38.73
(31.37) (2.89) (38.95)
C13H13ClN4O4Pt
[PtLCl.H2O].H2O
503.5
> 300
10.12
SB (Schiff base ligand)
Table 2: IR bands of the prepared compounds
Compounds νOH νNH
νC=N
(Traizole) (Schiff)
νC=N
νM-O νM-N νC-O
SB
C1
C2
C3
3437 3105
3378 3126
3413 3148
3405 3146
1614
1617
1621
1627
1575
1538
1545
1553
-
-
1318
556
600
611
426 1280
521 1307
535 1313
Table 3: The 1HNMR spectra of complexes under investigation recorded in d6- DMSO
at 25 oC.
Compounds
δNH
δHC=N
8.44
8.93
8.95
δOH
δaromatic
7.17-8.08
7.27-7.99
6.74-8.14
SB
C2
C3
14.16
10.935
10.809
10.08
-
-

Table 4: Temperature of decomposition and activation parameters (∆ H, ∆S, ∆G) for
decomposition of complexes
Complex
n
1
1
0
Step
1st
2nd
3rd
r
T (K)
360
E
∆ H
A
-∆S
∆ G
0.9901
0.9634
0.9827
0.9998
0.9980
0.9963
0.9986
0.9732
0.9946
0.9999
44.195
13.557
169.055
158.592
128.117
53.635
35.742
46.057
55.349
104.767
41.240
9.169
3718.5367
884107802.4
0.0789342
4.190
0.186
0.087
0.282
0.249
0.198
0.218
0.126
0.133
0.222
0.196
107.48
54.93
C1
546
711
163.158
152.082
121.013
50.758
30.966
40.443
52.487
98.634
362.84
347.31
290.53
126.21
103.33
130.28
128.92
242.92
0.33 4th
773
1
1
1
1
1
5th
1st
2nd
3rd
1st
869
2097.69
345.5
541.5
670.5
364.5
671
79.714
C2
C3
8569596.37
4291349.97
49.203
0.66 2nd
2538.11
E: the activation energy (KJ.mol-1), ∆H: the activation enthalpy (KJ.mol-1), ∆S: the entropy
(J.K-1.mol-1), A: the pre-exponential factor(s-1), ∆G: the free energy (KJ.mol-1).
Table 5: The antibacterial and antifungal activity values of the investigated compounds
Inhibition zone diameter (mm / mg sample)
Compound
Escherichia coli Staphylococcus
Aspergillus
Candida
(G-)
10
9
aureus (G+)
flavus (fungus) albicans (fungus)
SB
C1
13
10
13
12
29
0
0
0
0
-
11
9
C2
11
10
31
9
C3
9
Tetracycline
Antibacterial agent
Amphotericin B
Antifungal agent
-
-
-
16
19

Table 6: In vitro antitumor activities of prepared compounds against HEPG2 cell line
Compound
IC50 (µg/mL)
(HEPG2)
4.3
SB
C1
15.5
19.7
19.5
4
C2
C3
Dox.
Dox: doxorubicin, standard cytotoxin drug

HO
N
N
C
H
N
H
N
Fig.1. The structure of Schiff base ligand, [(1H-1,2,4-triazole-3-ylimino)methyl]naphthalene-
2-ol

-11.6
-12.0
-12.4
-12.8
-13.2
-13.6
-14.0
-14.4
Ni
(a)
(d)
(b)
(c)
(e)
1.2
1.6
2.0
2.4
2.8
1000 / T
Fig. 2a. Coats-Redfern plot for complex 1.
c) third step
a) first step b) second step
d) fourth step e) fiveth step
where, Y= [1-(1-α)1-n] / (1-n) T2 for n ≠ 1 or Y= [-ln(1- α)] / T2 for n = 1
-11.4
Pd
-11.7
(a)
-12.0
-12.3
(c)
-12.6
(b)
-12.9
1.6
2.0
2.4
2.8
1000 / T
Fig. b. Coats-Redfern plot for complex 2.
a) first step b) second step
c) third step
where, Y= [1-(1-α)1-n] / (1-n) T2 for n ≠ 1 or Y= [-ln(1- α)] /T2 for n = 1
23

-11.4
-11.7
-12.0
-12.3
-12.6
-12.9
-13.2
-13.5
Pt
(a)
(b)
1.2
1.6
2.0
2.4
2.8
3.2
1000 / T
Fig. 2c. Coats-Redfern plot for complex 3.
a) first step
b) second step
where, Y= [1-(1-α)1-n] / (1-n) T2 for n ≠ 1 or Y= [-ln(1- α)] / T2 for n = 1
24

Cl
Ni
H2O
O
N
N
.H2O
HC
N
N
H
Complex 1
Cl
H2O
Pd
O
N
N
.2 H2O
HC
N
N
H
complex 2
Cl
H2O
Pt
O
N
N
. H2O
HC
N
N
H
complex 3
Fig 3. The structures of the metal complexes.
25

20
18
16
14
12
10
8
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Kb = 3.40 X 105 M-1
L
6
4
2
0
0
10
20
30
40
50
60
[DNA] X 10-6
250
300
350
400
450
500
Wavelength (nm)
Fig. 4a. Electronic absorption spectra of the ligand in the absence and presence of
increasing amounts of CT DNA. Arrows show the changes in absorbance with respect
to an increase in the DNA concentration (Inset: Plot of [DNA] vs [DNA]/( εa - εf). (at
318 nm Kb = 3.40 X 105 M-1)
Ni
140
0.14
Kb = 3.08 X 105
120
100
0.12
80
60
0.10
40
0.08
20
0
10
20
30
40
50
[DNA] X 10-6
0.06
0.04
0.02
0.00
300
400
500
600
Wavelength (nm)
Fig. 4b. Electronic absorption spectra of Ni complex in the absence and presence of
increasing amounts of CT DNA. Arrows show the changes in absorbance with respect
to an increase in the DNA concentration (Inset: Plot of [DNA] vs [DNA]/( εa - εf). (at
319 nm Kb = 3.08 X 105 M-1)
26

60
50
40
30
20
10
0
0.30
0.25
0.20
0.15
0.10
0.05
0.00
pd
Kb = 17.675 X 105 M-1
0
10
20
30
40
50
[DNA] X 10-6
300
400
500
600
Wavelength (nm)
Fig. 4c. Electronic absorption spectra of Pd complex in the absence and presence of
increasing amounts of CT DNA. Arrows show the changes in absorbance with respect
to an increase in the DNA concentration (Inset: Plot of [DNA] vs [DNA]/( εa - εf). (at
288 nm Kb = 17.675 X 105 M-1)
0.06
Pt
20
Kb = 5.52 X 105 M-1
0.05
15
10
0.04
5
0.03
0
0
10
20
30
40
50
[DNA] X10-6
0.02
0.01
0.00
300
400
500
600
Wavelength (nm)
Fig. 4d. Electronic absorption spectra of Pt complex in the absence and presence of
increasing amounts of CT DNA. Arrows show the changes in absorbance with respect
to an increase in the DNA concentration (Inset: Plot of [DNA] vs [DNA]/( εa - εf). (at
320 nm Kb = 5.52 X 105 M-1)
27

1.07
1.06
1.05
1.04
1.03
1.02
1.01
1.00
L
Ni complex
Pd complex
Pt complex
0
2
4
6
8
10
12
14
[Complex] / [DNA]
Fig. 5. Effect of increasing amount of the prepared compounds on the viscosity of
CT-DNA (3x10-5M)
1.0
DOX
SB
C1
C2
C3
0.8
0.6
0.4
0.2
0
10
20
30
40
50
Conc. µg
Fig. 6. Effect of prepared compounds on HEPG2 cell line
28

Ni(II),
Pd(II)
and
Pt(II)
complexes
of
(1H-1,2,4-triazole–3
–
ylimino)methyl]naphthalene -2-ol. Structural, spectroscopic, biological, cytotoxicity
and DNA binding.
20
18
1.4
Kb = 3.40 X 105 M-1
16
14
1.2
1.0
0.8
0.6
0.4
0.2
0.0
12
10
8
L
6
4
2
0
0
10
20
30
40
50
60
[DNA] X 10-6
250
300
350
400
450
500
Wavelength (nm)
29