Thermal properties, antimicrobial activity and DNA binding of Ni(II) complexes of azo dye compounds

Article abstract of DOI:10.1016/j.molliq.2016.11.047

A novel series of nickel(II) azo dye complexes of 5-(4-methoxyphenylazo)-2-thioxo-4-thiazolidinone (HL₁), 5-(4-methylphenylazo)-2-thioxo-4-thiazolidinone (HL₂), 5-(phenylazo)-2-thioxo-4-thiazolidinone (HL₃) and 5-(4-nitrophenylazo)-2-thioxo-4-thiazolidinone (HL₄) were prepared and characterized elemental analyses, IR, UV–Visible spectra, X-ray diffraction analysis and mass spectrum as well as thermogravimetric analysis (TGA). The magnetic measurements of Ni(II) complexes (1–4) lie in 3.05–3.20 BM., as anticipated for octahedral geometry. Quantum chemical parameters and molecular structures of the complexes were theoretically computed and the results were studied. IR spectra show that HL_n ligands (n?=?1–4) act a monobasic bidentate ligands by coordinating via the oxygen atom of the deprotonated [sbnd]OH group moiety and nitrogen atom of azo group. The interaction between Ni(II) complexes and calf thymus DNA (CT-DNA) shows hyperchromism effect coupled with obvious bathochromic shift. The value of binding constant (K_b) obtained from the absorption spectral technique for Ni(II) complexes (1–4) was calculated and found to be 1.20?×?10⁵, 1.17?×?10⁵, 7.22?×?10⁴ and 6.65?×?10⁴?M^??1, respectively. The antimicrobial activities of Ni(II) complexes (1–4) were investigated. It was found that the Ni(II) complexes have low antibacterial activity against Klebsiella pneumoniae. Complex (1) has antifungal activity against Penicillium italicum. All the Ni(II) complexes have more antibacterial activity than the penicillin against Klebsiella pneumoniae. The thermodynamic parameters were calculated using Coats–Redfern and Horowitz–Metzger methods. From the values of the thermal activation energy for decomposition (E_a) of Ni(II) complexes (1–4), it was found that the E_a value for the complex (4) is higher compared to the other complexes. The positive value of Gibbs free energy of decomposition (ΔG^?) for the Ni(II) complexes is non-spontaneous processes.

Full text of DOI:10.1016/j.molliq.2016.11.047

Thermal properties, antimicrobial activity and DNA binding of Ni(II) com-
plexes of azo dye compounds
A.Z. El-Sonbati, M.A. Diab, Sh.M. Morgan
PII:
DOI:
Reference:
S0167-7322(16)32966-X
doi:10.1016/j.molliq.2016.11.047
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14 November 2016
15 November 2016
Please cite this article as: A.Z. El-Sonbati, M.A. Diab, Sh.M. Morgan, Thermal proper-
ties, antimicrobial activity and DNA binding of Ni(II) complexes of azo dye compounds,
Journal of Molecular Liquids (2016), doi:10.1016/j.molliq.2016.11.047
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ACCEPTED MANUSCRIPT
Thermal properties, antimicrobial activity and DNA binding of Ni(II) complexes
of azo dye compounds
A.Z. El-Sonbati a, M.A. Diab a, Sh.M. Morgan b,*
a Chemistry Department, Faculty of Science, Damietta University, Damietta, Egypt
b Environmental Monitoring Laboratory, Ministry of Health, Port Said, Egypt
Abstract
A novel series of nickel(II) azo dye complexes of 5-(4-methoxyphenylazo)-2-
thioxo-4-thiazolidinone (HL1), 5-(4-methylphenylazo)-2-thioxo-4-thiazolidinone
(HL2), 5-(phenylazo)-2-thioxo-4-thiazolidinone (HL3) and 5-(4-nitrophenylazo) -2-
thioxo-4-thiazolidinone (HL4) were prepared and characterized elemental analyses,
IR, UV-Visible spectra, X-ray diffraction analysis and mass spectra as well as
thermogravimetric analysis (TGA). The magnetic measurements of Ni(II) complexes
(1-4) lie in 3.05-3.20 BM., as anticipated for octahedral geometry. Quantum chemical
parameters and molecular structures of the complexes were theoretically computed
and the results were studied. IR spectra show that HLn ligands (n = 1-4) act a
monobasic bidentate ligands by coordinating via the oxygen atom of the deprotonated
-OH group moiety and nitrogen atom of azo group. The interaction between Ni(II)
complexes and calf thymus DNA (CT-DNA) shows hyperchromism effect coupled
with obvious bathochromic shift. The value of binding constant (Kb) obtained from
the absorption spectral technique for Ni(II) complexes (1-4) was calculated and found
to be 1.20 x 105 , 1.17 x 105 , 7.22 x 104 and 6.65 x 104 M-1, respectively. The
antimicrobial activities of Ni(II) complexes (1-4) were investigated. It was found that
the Ni(II) complexes have low antibacterial activity against Klebsiella pneumoniae.
Complex (1) has antifungal activity against Penicillium italicum. All the Ni(II)
complexes have more antibacterial activity than the penicillin against Klebsiella
pneumoniae. The thermodynamic parameters were calculated using Coats–Redfern
and Horowitz–Metzger methods. From the values of the thermal activation energy for
decomposition (Ea) of Ni(II) complexes (1-4), it was found that the Ea value for the
complex (4) is higher compared to the other complexes. The positive value of Gibbs
free energy change of the decomposition (ΔG*) for the Ni(II) complexes is non-
spontaneous processes.
Keywords: Ni(II) complexes; Calf thymus DNA; X-ray diffraction analysis; Thermal
analysis; Thermodynamic parameters; Antimicrobial activity.
_______________
*Corresponding author: E-mail: shimaa_mohamad2010@yahoo.com (Sh.M. Morgan).
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1.
Introduction
Coordination chemistry is basically the chemistry of the electron accepting
behavior of metal ions surrounded by ligands. The wide range of color exhibited by
coordination compounds and their structures which are signs of the coordination
number of the metal ion and the ligational behavior of the complexing agents, make
their investigation very challenging and at the same time interesting [1-3]. The azo
compounds are characterized by the presence of one or more azo groups. The
formation of azo compounds usually involves the reaction between a diazo species
and a coupling agent.
Rhodanine azo dye compounds are the most widely used class of coloring
materials because of the huge demand in the various fields of technology and science
[3,4]. A lot of investigation has been carried out in recent years on the synthesis and
spectral the characteristics of this group of dyes [2,5]. Besides, the azo compounds are
known to be involved in some biological reactions such as inhibition of DNA and
biological activity against bacteria and fungi [2,4,6]. The rhodanine compounds were
effectives against Gram positive and Gram negative bacteria [4] that can be used in a
wide range of application. Advancement of metal complexes as artificial nucleases
was an area of interest. Various reports have additionally pointed out several cases of
complexes due to their vast potential utilities through their interactions against bacteria
and fungi activity [4,7]. Chemical properties of rhodanine compounds are of interest
due to coordination capacity and their use as metal extracting agents and as analytical
reagents [8,9].
Rhodanine and its derivatives are quite interesting which have gained special
attention in the last decade, not only because of the structural chemistry and their
importance in medical chemistry. Rhodanine derivatives have broad spectra of
pharmacological activities and these compounds were used in the pharmaceutical
industry and applications in many vital areas. Rhodanine and its derivatives are
known to possess biological activities [10,11] such as potential antimycobacterial
[12], antifungal [13], antibacterial [14], antiviral [15] and antidiabetic mechanism
[16]. The studies revealed that such type of molecule exhibit as inhibitors of
numerous targets such as histidine decarboxylase [17], β-lactamase [18], JNK
Stimulatory Phosphatase-1 (JSP-1) [19] in addition to rhodanine derivatives were also
reported as hepatitis C virus (HCV) protease inhibitor [20,21].
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Recently in our laboratory, numerous azo/hydrazone complexes of rhodanine
and its derivatives have been reported [2,7]. In this paper, we investigate the molecular
structures, elemental analyses, IR spectra, spectral studies, molar conductance,
magnetic measurements, mass spectra, X-ray diffraction analysis, thermal study and
thermodynamics parameters of nickel(II) azo dye complexes with
5-(4-
methoxyphenylazo)-2-thioxo-4-thiazolidinone (HL1), 5-(4-methylphenylazo)-2-
thioxo-4-thiazolidinone (HL2), 5-(phenylazo)-2-thioxo-4-thiazolidinone (HL3) and 5-
(4-nitrophenylazo) -2-thioxo-4-thiazolidinone (HL4). The molecular structures of
Ni(II) complexes are discussed and quantum chemical parameters are calculated.
Ni(II) complexes are screened for their antimicrobial activity against bacteria and
fungi species. The calf thymus DNA (CT-DNA) binding activity of Ni(II) complexes
are studied by absorption spectra.
2. Experimental
2.1. Materials
All the chemicals used were of British Drug House (BDH) quality and were
used without any further purification. The calf thymus DNA (CT-DNA) was acquired
from SRL (India). Double distilled water was utilized to prepare all the buffer
solutions.
2.2. Preparation of the ligands (HLn)
HLn ligands were prepared according to the method [1-4]. Azo dye compounds
are prepared by an aqueous diazotization and coupling procedure, which lead to a
pure product in high yield and in a physical form suitable for application [22,23]. The
purity of ligands was checked by Thin-layer chromatography (TLC). TLC analysis
was performed on silica gel utilizing the dissolvable framework benzene/acetone (1:2)
as solvent.
2.3. Preparation of Ni(II) complexes
The Ni(II) complexes were prepared by refluxing a hot ethanolic solution
containing azo dye rhodanine derivatives was mixed with a hot ethanolic solution of
Ni(CH3COO)2.4H2O (1 mmol). The mixture was then refluxed on a water bath for ~
6-8 hrs and allowed to cool then the solid complexes are separated, filtered, washed a
few with ethanol, diethyl ether and finally dried in a vacuum desiccators over
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anhydrous CaCl2. The yields of the final products were 78-88%. Table 1 shows the
analytical data of Ni(II) complexes (Fig. 1).
2.4. Biological activity investigation
For this examination was applied the method of agar well diffusion [4]. The
antibacterial activities of the investigated compounds were tested against two local
Gram positive bacterial types (Staphylococcus aureus and Bacillus cereus) and two
local Gram negative types (Escherichia coli and Klebsiella pneumoniae) on nutrient
agar medium. As well, the antifungal activities were tested against four local fungal
types (Penicillium italicum, Alternaria alternata, Aspergillus niger and Fusarium
oxysporium) on DOX agar medium. The concentrations of every solution of
compound were 50, 100 and 150 µg/mL in dimethyl formamide (DMF). Utilizing a
sterile cork borer (10 mm diameter), wells was made in medium of agar plates
previously seeded with the test microorganism. 200 µL of every compound was
applied in every well. The agar plates were kept at 4 °C for at least 30 min to allow
the diffusion of the compound to agar medium. The plates were then incubated at 37
°C or 30 °C for bacteria and fungi, respectively. The diameters of inhibition zone
were specified after 24 h and 7 days for days for bacteria and fungi, respectively,
taking the consideration of the control values (DMF). Penicillin and miconazole were
used as standard drugs against bacteria and fungi, respectively.
2.5. DNA binding experiments
The binding properties of Ni(II) complexes to CT-DNA are studied using
electronic absorption spectroscopy. The stock solution of CT-DNA is prepared in 5
mM Tris-HCl / 50 mM NaCl buffer (pH=7.2), which a ratio of UV absorbance at 260
and 280 nm (A260/A280) of calculated 1.8 -1.9, indicating that the DNA is sufficiently
free of protein [24], and the concentration is determined by UV absorbance at 260 nm
(Ɛ = 6600 M-1 cm-1) [25]. Electronic absorption spectra are carried out using 1 cm
quartz cuvette at room temperature by fixing the concentration of complex (1.00 × 10-
3 mol L-1), while progressively increasing the concentration of calf thymus DNA (CT-
DNA) (0.00 to 1.30 × 10-4 mol L-1). An equivalent amount of CT-DNA is added to
both the solutions of compound and the references buffer solution to eliminate the
absorbance of CT-DNA itself. The intrinsic binding constant Kb of the compound
with CT-DNA is determined using the following equation (1) [24]:
[DNA] / (єa–єf) = [DNA] / (єb –єf) + 1 / Kb(єa–єf)
(1)
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where [DNA] is the concentration of CT-DNA in base pairs, єa is the molar extinction
coefficient observed for the Aobs/[compound] at the given DNA concentration, єf is
the molar extinction coefficient of the free compound in solution and єb is the molar
extinction coefficient of the compound when fully bond to DNA. In plots of
[DNA]/(єa–єf) versus [DNA] and Kb is given by the ratio of the slope to the intercept.
2.6. Measurements
Elemental microanalyses of the complexes for C, H, N and S were analyzed on
Automatic Analyzer CHNS Vario ELIII, Germany. Infrared spectra were recorded
using a Perkin-Elmer 1340 spectrophotometer as KBr discs. Mass spectra were
recorded using MS-5988 GS-MS Hewlett-Packard by the EI technique at 70 eV. X-
ray diffraction analysis of complexes was recorded on X-ray diffractometer analysis
in the range of diffraction angle 2θo = 4–80o. This analysis was done utilizing CuKα
radiation (λ = 1.540598 Ả). The tube current and the applied voltage are 30 mA and
40 kV, respectively. Ultraviolet-visible spectra of the complexes were registered in
nujol mulls using a Unicom SP 8800 spectrophotometer. The magnetic moment of the
complexes was determined using the Gouy`s method at room temperature.
Mercury(II) (tetrathiocyanato)cobalt(II), [Hg{Co(SCN)4}], was utilized for the
calibration of the Gouy tubes. Corrections of diamagnetic were calculated from the
values given by Selwood [26] and Pascal’s constants. Magnetic moments were
computed utilizing the equation, µeff. = 2.84 [TcMcoor.]1/2. The thermal studies were
computed on Simultaneous Thermal Analyzer (STA) 6000 system using
thermogravimetric analysis method. Thermal properties of the samples were
anatomized at the heating rate of 10 oC/min under dynamic nitrogen atmosphere in the
temperature range from 30 to 800 °C. Molecular structures of the compounds were
optimized by HF technique with 3-21G basis set. The molecules were built with the
Perkin Elmer ChemBio Draw and optimized utilizing Perkin Elmer ChemBio3D
software [7].
2.7. Statistical Analysis
Data were statistically analysed for variance and the least significant difference
(LSD) at 0.05 level using one-way analysis of variance (ANOVA) were carried out by
SPSS software version 17.
3.
Results and discussion
3.1. The structure and molecular geometry optimization of Ni(II) complexes
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All complexes were found to form readily from the reaction mixture of the
appropriate nickel(II) acetate and the ligand (HLn) in hot ethanolic. The analytical data
of the experimental and theoretical data of (%C, %H, %N, %S and %Ni) are in a good
agreement with suggests the formulation [Ni(Ln)(CH3COO)(OH2)2].nH2O as shown in
Table 1 and Fig. 1. Nickel(II) complexes are stable with highly melting points (> 300
oC), insoluble in H2O and soluble in warm DMSO and DMF. The molar conductance
values of all complexes in 10-3 M solution in DMF are found to be less than 20 Ω-1
mol-1 cm2, showing that they are non-electrolytes indicating its non-electrolytic nature
[7] which indicate that the anion and the ligand are coordinated to the central
nickel(II). The magnetic moment of Ni(II) complexes was estimated at room
temperature and has a paramagnetic nature octahedral geometry.
Molecular modeling and quantum chemical parameters of Ni(II) complexes (1-
4) were calculated theoretically and listed in Table 2 (Fig. S1). Also, corresponding
geometric parameters bond lengths and bond angles of Ni(II) complexes (1-4) are
listed in Tables S1-S4. The quantum chemical parameters were calculated and the
calculated parameters are identified as follows [5]:
 The highest occupied molecular orbital energy (EHOMO
)
 The lowest unoccupied molecular orbital energy (ELUMO
)
 The HOMO–LUMO energy gap (the difference between HOMO and LUMO
energy levels) (ΔE)
 Absolute electronegativities (χ)
 Chemical potential (Pi)
 Absolute hardness (η)
 Absolute softness (σ)
 Global electrophilicity (ω)
 Global softness (S)
 Electronic charge (∆Nmax
)
Figure 2 shows the HOMO and LUMO orbital's for Ni(II) complexes (1-4). As
indicated the frontier molecular orbital theory, FMO, the chemical reactivity is a
function of interaction between HOMO and LUMO levels of the reacting species
[5,7]. The EHOMO frequently connected with the electron donating ability of the
molecule to donate electrons to appropriated acceptor molecules with low-energy,
empty molecular orbital [5]. Likewise, ELUMO indicates the ability of the molecule to
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accept electrons. The higher is the value of EHOMO of the complexes; the easer is its
offering electrons. The value of low energy gap performs to soft molecules which is
more reactivity and high flexibility. The calculation of absolute softness (σ) parameter
is useful to recognize the molecular stability and reactivity. It was found that the
stability of the Ni(II) complexes increase with the order: complex (4) < complex (3) <
complex (2) < complex (1) related to ΔE values (Table 2), as expected electron
donating group has lower energy gap and higher stability compared with electron
withdrawing group as shown in Fig. 3.
3.2. Structure of ligands (HLn)
Classic-azo-enol dyes are prepared by an aqueous diazotization and coupling
procedure, which lead to a pure product in high yield and in a physical form suitable
for application [27-29]. The azo dyes prepared in this study may exist in tautomeric
forms as shown in azo-keto (Fig. 1A), azo-enol (Fig. 1B) and keto-hydrazone
(Fig. 1C).
El-Sonbati et al. [27,28] found that three types of hydrogen bonds may exist in
equilibrium with each other. The hydrogen bond in this case is of intramolecular type
either with (B) or (C) and intermolecular hydrogen bonding can form cyclic dimmer
through the (E) and/or (F) as shown in Fig. 1. The azo dye ligands have been
demonstrated conclusively from a series of investigations using a variety techniques,
such as IR spectra, the HLn ligands exist exclusively in azo-enol form in solution
[1A↔1B] (Fig. 1) [2]. The six-membered intramolecular hydrogen bonding ring is
possible in the azo-enol tautomer (Fig. 1).
The infrared spectra are consistent with the formation of HLn ligands. The
vibrational assignments were aided by comparison with the vibrational frequencies of
the related compounds as p-derivative aniline and 2-thioxo-4-thiazolidinone. The
fundamental stretching mode of the azo dye moiety, υ(N=N), is readily assigned by
comparison with the infrared spectra of derivatives of aniline and ligands (HLn). The
absorption bands due to amino (NH2) of stretching vibration disappeared and instead a
new band assigned to azo dye υ(N=N) linkage appeared at ~ 1540 cm-1 [7] (Fig. 1).
The ligands under investigation are capable of exhibiting azo-enol (Fig. 1B) and
keto-hydrazone (Fig. 1C) tautomerism. It has been reported that azo dye rhodanine
derivatives exist predominantly in the azo-enol form [30].
3.3. Structure of the metal chelates
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 Infrared spectra of the ligand (HLn) exhibited a broad medium intensity band
ranging ~ 3340-2980 cm-1 and centered at ~3210 cm-1, which could be
assigned to hydrogen bonded enolic υ(C–O) stretching vibration [31]. A
strong band at ~1275-1265 could be attributed to υ(C–O) vibration of C–O
group [32]. A medium intensity band at ~ 1540 cm-1 was assignable to the
stretching vibration of N=N group [2,7].
 In all complexes, the hydrogen bonded enolic –OH band disappeared,
attributed to the deprotonation and formation of metal-oxygen bond. This is
supported by the shifting of υ(C–O) towards higher frequencies as compared
to the free ligands due to the conversion of hydrogen bonded structure into a
covalent metal bonded structure [2].
 The N=N stretching frequency of the azo group is shifted to lower frequencies
by ~25-30 cm-1 attributed to the involvement of one of the azo nitrogen atom
in coordination with metal ion [7]. This lowering of frequency can be
explained by the transfer of electrons from the nitrogen atom to the metal ion
due to coordination.
 From infrared spectra of the metal complexes show several non ligand bands
of low intensity appearing in the region 515-540 and 445-460 cm-1 can be
assigned to υ(M–O) and υ(M–N), respectively, [2,7].
 Absence of υ(M–S) band in the far IR spectra gives added evidence for the
non participation of ring sulfur atom in bond formation.
 Ni(II) complexes exhibits distinct bands at 1590 and 1450 cm-1 due to the
asymmetric and symmetric modes of vibration characteristic of CH3COO,
respectively, and with υ = 140 cm-1 which is consistent with the bidentate
nature of the acetate group [33], this is further supported by the appearance of
(O–C–O) wagging modes of acetate around 680 and 620 cm-1 [34]. A broad
band around 3410 cm-1 is attributed to υ(O–H) aqua of coordinated water. On
complex formation, the new peak observed at 565 may be assigned to chelate
ring deformation [35].
 The appearance of a new bands around 2450 cm-1 in the prepared Ni(II)
complexes may be taken as a strong evidence for the presence of coordinated
water and also suggest that H-bonding interaction exists between the water
molecule and the carboxylate oxygen of acetate group. Such region, however,
is not initially present in the free ligands. This is confirmed by the elemental
analysis of these complexes (Table 1).
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 Molecular structure of all complexes could be suggested based on: (i) the
presence of one anion, (ii) the disappearance of C=O, (iii) the coordination of
azo group and (iv) the coordination of water molecules.
Based on these information's obtained from the spectra and other investigations,
the bonding in Ni(II) complexes may be represented as shown in Fig. 1.
3.4. Magnetic moment and spectral studies
Azo dye ligands (HLn) react with freshly prepared solutions of nickel(II) acetate
to give complexes of the type [Ni(Ln)(CH3COO)(OH2)2].nH2O. The magnetic
measurements of Ni(II) complexes (1-4) lie in the range of 3.05-3.20 BM., as
expected for octahedral geometry around the metal ions. The reflectance spectra of the
Ni(II) complexes are characterized by three main bands in the regions 3A2g → 3T2g(υ1)
3
3
3
3
(12770-13280 cm-1), A2g → T1g(υ2) (14640-18580 cm-1) and A2g→ T1g(P)(υ3)
(24210-27625 cm-1) transition in an idealized Oh-symmetry [36]. The computed
values of υ2/υ1 are proportionate with an octahedral configuration proposing strong
T1g-term interactions of nickel(II) complexes [37]. The low values of υ2/υ1 are due to
3
3
the strong interaction between T1g(P) and T1g(F) states. The value of B are lower
than the free ion, there is due to orbital overlap and delocalization of d-orbital. Ligand
field stabilization energy (LFSE kcal mol-1) has been calculated [38]. The energies of
these bands were used to calculate the electronic spectral parameters of the nickel(II)
complexes according to Lever's method [38] and the electronic parameters are listed
in Table 3. The Dq/B value was taken to measure the extent of distortion in this
symmetry The covalency factor (β) is less than unity, this can be assigned upon the
metal-ligand bonds have a considerable of covalent character. The percentage
lowering of energy in free gaseous ion (βo % = 41.6 – 87.4%) are calculated (Table 3).
The reduction of the Racah parameter (B) can be calculated from the following
equation [39]:
2
2
Bcomplex = (2υ1 + υ2 – 3υ1υ2)(15υ2 – 27 υ1)
(2)
(3)
The covalency factor was calculated from the following equation:
β = B/B` (B` is the free nickel ion = 1038 cm-1).
The relation between Dq and Hammett’s substituent coefficients (σR) is shown in
Fig. S2, it is clear that the value of Dq increase with decreasing the value of σR. The
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values of Dq the order of binding complex is as follows: complex (1) > complex (3) >
complex (4).
3.5. Mass spectra
The mass spectrum of [Ni(L3)(CH3COO)(OH2)2]H2O (3) complex (Scheme 1)
exhibits a parent molecular ion peak at m/z 407.69 (1.0%) which is equal to the
formula weight of the complex [NiC11H13N3O5S2]H2O. The peak at m/z 338.69 (9%)
formed from complex (3) through the removal of 3H2O molecules and methyl group
(structure I). The spectrum shows molecular ion peaks at m/z 262.69 (17%), 99 (28%)
and 71 (34%) corresponding to the [NiC9H6N3OS] (structure II), [C3HNOS] (structure
III) and [C2HNS] (structure IV) fragments, respectively. The information gathered
from mass spectrum data of Ni(II) complex (3) is good agreement with the proposed
molecular formula for this complex.
3.6. X-ray diffraction analysis
The X-ray diffraction, XRD, patterns of Ni(II) complexes (2-4) powder forms
are shown in Fig. 4. The XRD patterns show a broad peak in the range of 2θo = 23- 26o
indicating a completely amorphous structures.
3.7. DNA binding studies
Absorption titration is a standout amongst the most generally utilized methods to
study the binding modes and binding extent of compounds to DNA. Absorption
titration experiments are performed with fixed concentrations of Ni(II) complexes (1-
4) (40 μM) while gradually increasing the concentration of calf thymus DNA (CT-
DNA) (10 mM). While measuring the absorption spectra, an equivalent value of DNA
was added to both the compound solution and the reference solution to eliminate the
absorbance of DNA itself. We have determine the intrinsic binding constant to CT-
DNA by monitoring the absorption intensity of the charge transfer spectral bands near
427, 425, 428 and 440 nm for Ni(II) complexes (1-4), respectively. Absorption spectra
of Ni(II) complexes (1-4) increase with increasing the volume of CT-DNA are in the
range 300-600 nm as shown in Fig. 5 and Fig. S3.
The interaction between Ni(II) complexes (1-4) and calf thymus DNA (CT-
DNA) has been studied by UV Visible spectroscopy electronic absorption spectra.
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After interaction of Ni(II) complexes (1-4) and with increasing the amount of calf
thymus DNA (CT-DNA), it was found that all the peaks increased gradually and the
wavelengths have minor red shift (bathochromic shift) of 2 nm. The binding involves a
typical intercalative mode, a hyperchromism effect coupled with obvious
bathochromic shift for the distinguishing peaks of the small molecules will be found
due to the strong stacking between the chromophore and the base pairs of DNA [40].
Therefore, based on this viewpoint, the interaction between Ni(II) complexes (1-4) and
calf thymus DNA could be noncovalent intercalative binding.
Plot of [DNA]/(εa − εf) as function of DNA concentration as determined from
the absorption spectral data was shown in Fig. 6 and Fig. S4. The value of binding
constant (Kb) obtained from the absorption spectral technique for Ni(II) complexes (1-
4) was calculated and found to be 1.20 x 105, 1.17 x 105, 7.22 x 104 and 6.65 x 104 M-1,
respectively. Binding constant values are related to the nature of the substituent as they
increase according to the following order p-(OCH3 > CH3 > H > NO2). That is
attributed to the p-substituent's of azo moiety as electron donating group which
increases the electron density in the benzene ring by its high electron donating
mesomeric or inductive effects; there by stronger hydrogen bond is formed. The
relation between binding constant (Kb) and Hammett’s substituent coefficients (σR) is
shown in Fig. 7, it is clear that the value of Kb increase with decreasing the value of
σR, is due to exists donating group. From these results it may be generalized that the
more binding complex has more high value of binding constant (Kb) so that from the
values of Kb the order of binding complex is as follows: Ni(II) complex (1) > Ni(II)
complex (2) > Ni(II) complex (3) > Ni(II) complex (4).
3.8. Thermal analysis of Ni(II) complexes
Thermal analysis is useful in determining the water molecules content in the
complexes and their thermal stability. The thermal stability properties were evaluated
by TG method whose results revealed good thermal stability for all the complexes. In
general, it was observed that the sequence of degradation that takes place in these
complexes starts with dehydration of lattice water molecules followed by the release
of coordination water and then fragments of a part of the ligand. Thermogravimetric
analysis (TGA) curves of Ni(II) complexes (1-4) are displayed in Fig. 10 and the
thermal decomposition results are listed in Table 4. The first stage of decomposition
in the range ~35-110 ºC for Ni(II) complexes can be attributed to loss of lattice water
molecule [7] (Fig. 8). The second stage of decomposition corresponds to the loss of
11

ACCEPTED MANUSCRIPT
coordinated water molecule and coordinated acetate group and decomposition of a
part of the ligand. The third stage is attributed to loss of a part of the ligand. The
remaining final product is nickel oxide residue with contaminated carbon atoms
(Table 4).
In conclusion, the thermal studies were significantly helpful for the elucidation
of crystallisation of water, degradation temperature and thermal stability of complexes
for every decomposition step in thermal analysis processes.
3.9. Thermodynamic studies
The thermodynamic parameters are calculated using the Coats-Redfern and
Horowitz-Metzger methods [41,42]. The thermal activation energy for decomposition
(Ea) and entropy (ΔS*) were calculated. The enthalpy (ΔH*) and Gibbs free energy
change of the decomposition (ΔG*) were calculated from H  E  RT
*
a
*
*
*
and G  H  T S , respectively.
The thermodynamic data obtained with the two methods for Ni(II) complexes
(1-4) are listed in Table 5 and Figures 9 and 10. The thermodynamic results obtained
from the Coats-Redfern and Horowitz-Metzger methods are comparable and can be
considered in good agreement with each other [43]. From the values of the thermal
activation energy for decomposition (Ea) of Ni(II) complexes (1-4), it was found that
the Ea value for the complex (4) is higher compared to the other complexes.
The entropy reflects the thermal stability of the compounds. The entropy is
found to be negative values in the Ni(II) complexes (1-4) which indicates more
ordered activated complex than the reactants or the reaction is slow [7,44]. The
positive value of ΔG* for the Ni(II) complexes (1-4) is non-spontaneous processes.
Also, the values of ΔG* increases significantly for the subsequent decomposition
stages of a given complex. This is due to increasing the values of T ΔS* significantly
from one stage to another which overrides the values of ΔH* [45].
3.10. Antimicrobial studies
The antimicrobial activity was assessed based on the size of inhibition zone
around dishes. Antimicrobial activity of rhodanine azo dye derivatives and their metal
complexes may be significantly enhanced by the presence of nitrogen, oxygen and
sulfur atoms which have chelating properties [2,7]. These properties may be used in
metal transport across the bacterial membranes or to append to the bacterial cells at a
particular site from which it can meddle with their growth.
12

ACCEPTED MANUSCRIPT
Antibacterial and antifungal activities of Ni(II) complexes (1-4) were tested
against Gram positive bacteria as Staphylococcus aureus and Bacillus cereus and
Gram negative bacteria as Escherichia coli and Klebsiella pneumoniae and fungi
species as Aspergillus niger, Fusarium oxysporium, Penicillium italicum and
Alternaria alternata. The results of the antibacterial activity of Ni(II) complexes (1-4)
were recorded in Table 6. All the Ni(II) complexes (1-4) have low antibacterial
activity against K. pneumoniae and have no antibacterial activity against S. aureus
and B. cereus. It was found that Ni(II) complexes (1-4) have more antibacterial
activity than the penicillin against K. pneumoniae at all tested concentrations (Fig.
11).
The antifungal activity results of the Ni(II) complexes (1-4) were listed in Table 7.
It was found that the Ni(II) complexes (1-4) have no antifungal activity against F.
oxysporum and A. alternata. While the complexes (1) and (3) have antifungal activity
against P. italicum (Fig. 12). The complexes (3) and (4) have antifungal activity than
the other complexes against A. niger. The complex (1) has more antifungal activity
than the miconazole against P. italicum at 50 and 100 µg/ml. Our results are similar to
Habib et al. [46] who studied the antimicrobial activities of some rhodanine
derivatives and they revealed that the most pronounced activity was the antifungal
activity against A. niger and Penicillium sp.
Conclusions
The molecular structures, elemental analyses, IR spectra, spectral studies, molar
conductance, magnetic measurements, mass spectra, X-ray diffraction analysis,
thermal study and thermodynamics parameters of Ni(II) complexes have been
discussed. It was found that the stability of the Ni(II) complexes (1-4) increase with
the order: complex (4) < complex (3) < complex (2) < complex (1) related to ΔE
values, as expected electron donating group has lower energy gap and higher stability
compared with electron withdrawing group. The values of the thermal activation
energies for decomposition (Ea) of complexes [Ni(Ln)(CH3COO)(OH2)2].nH2O (1-4),
are found to be in the rang 38-60 kJ/mol. Ni(II) complexes are screened for their
antimicrobial activity against bacteria and fungi species. It was found that Ni(II)
complexes (1-4) have more antibacterial activity than the penicillin against Klebsiella
pneumoniae. The tested complex (1) has antifungal activity against Penicillium
italicum.
13

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Acknowledgement
The authors would like to thank Prof. Dr. M.I. Abou-Dobara, Botany Department,
Faculty of Science, Damietta University, Egypt for his help during testing antimicrobial
activity.
Appendix A: Supplementary material
See the attached file.
14

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Med. Chem. 32 (1997) 759–762.
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Table 1. Elemental analyses of Ni(II) complexes (see Fig. 1).
Complexes
Experimental (calculated) (%)
C
H
N
S
M
[Ni(L1)(CH3COO)(OH2)2] H2O
32.74
3.31
9.41
14.36
13.38
(1)
(32.90) (3.43)
(9.60)
(14.62)
(13.41)
[Ni(L2)(CH3COO)(OH2)2] 2H2O
32.55
3.23
9.35
14.43
13.67
(2)
(32.75) (3.41)
(9.55)
(14.56)
(13.35)
[Ni(L3)(CH3COO)(OH2)2] H2O
32.25
3.00
10.02
15.54
14.62
(3)
(32.38) (3.19) (10.30)
(15.70)
(14.40)
[Ni(L4)(CH3COO)(OH2)2] H2O
29.04
2.54
12.19
13.86
12.70
(4)
(29.16) (2.65) (12.37)
(14.14)
(12.96)
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Table 2. Quantum chemical parameters of Ni(II) complexes.
Complexa EHOMO ELUMO
(eV) (eV)
ΔE
χ
η
σ
Pi
S
ω
(eV)
∆Nmax
(eV) (eV) (eV) (eV)-1 (eV)
(eV)-1
-6.086 -4.417 1.669 5.252 0.835 1.198 -5.252 0.599 16.524 6.293
-6.120 -4.424 1.696 5.272 0.848 1.179 -5.272 0.590 16.388 6.217
-6.154 -4.440 1.714 5.297 0.857 1.167 -5.297 0.583 16.370 6.181
-6.665 -4.936 1.729 5.801 0.865 1.157 -5.801 0.578 19.459 6.709
(1)
(2)
(3)
(4)
aNumbers as given in Table 1
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Table 3. Ligand field parameters of the Ni(II) complexes.
Complexa
Dq
B
β
βo %
Dq/B
LFSE
(kcal mol-1)
(cm-1) (cm-1)
1328
1312
1277
526
131
606
0.507 49.3
0.126 87.4
0.584 41.6
2.52
10.02
2.11
45.64
45.09
43.89
(1)
(3)
(4)
aNumbers as given in Table 1
20

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Table 4. Thermal analysis data of the Ni(II) complexes.
Complexa
(1)
Temp. range
(ºC)
Found mass loss Assignment
(calc.) %
60-96
4.07 (4.11)
Loss of one water molecule in outside of the coordination
sphere
96-408
40.64 (39.07) Loss of two coordinated water molecules and loss of one
coordinated acetate group, further decomposition of a part
of the ligand (CS2)
408-800
27.17 (28.79) Decomposition of a part of the ligand (C5H8N3O)
> 800
28.12 (28.03) 4C atoms + NiO
35-107
8.41 (8.19)
Loss of two water molecules in outside of the coordination
sphere.
(2)
107-404
37.32 (38.89) Loss of two coordinated water molecules and loss of one
coordinated acetate group, further decomposition of a part
of the ligand (CS2).
404-800
> 800
30.43 (30.48) Decomposition of a part of the ligand (C7H8N3)
23.84 (22.45) 2C atoms + NiO
45-99
4.81 (4.42)
Loss of one water molecule in outside of the coordination
sphere
(3)
99-400
37.43 (37.77) Loss of two coordinated water molecules and loss of one
coordinated acetate group, further of a part of the ligand
(CSNH).
21

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400-800
> 800
29.65 (30.66) Decomposition of a part of the ligand (C5H5N2S)
28.11 (27.15) 3C atoms + NiO
45-109
3.24 (3.98)
Loss of one water molecule in outside of the coordination
sphere
(4)
109-408
47.18 (46.61) Loss of two coordinated water molecules and loss of one
coordinated acetate group, further of a part of the ligand
(C2S2N2).
408-800
> 800
25.47 (24.96) Decomposition of a part of the ligand (C4H5N2O2).
24.11 (24.45) 3C atoms + NiO
aNumbers as given in Table 1
Table 5. Thermodynamic data of the thermal decomposition of Ni(II) complexes.
Complexa
Decomposition Method
temperature
Parameter
Correlation
coefficient
(r)
Ea
A
∆S*
∆H*
∆G*
(oC)
(kJ mol−1)
(s−1)
(J mol-1 K-1 (kJ mol−1) (kJ mol−1)
)
150-400
400-555
CR
39.9
49.7
8.56×100
3.17×102
35.3
45.9
163
157
0.99707
0.99761
(1)
-232
-202
HM
CR
131
145
4.29×106
9.83×107
-126
125
139
220
214
0.99681
0.99850
HM
-99.6
158-395
395-533
CR
43.2
53.1
1.91×101
5.87×102
38.6
48.6
163
157
0.99817
0.99195
(2)
(3)
-225
-197
HM
CR
88.8
99.4
3.14×103
6.04×104
-186
-161
82.6
93.2
219
212
0.99872
0.99931
HM
145-400
400-535
160-410
410-550
CR
38.7
49.5
5.54×1000
2.61×102
34.2
45.0
163
157
0.99771
0.99361
-236
-204
HM
CR
101
114
2.38×104
6.93×105
-169
-141
94.8
108
220
212
0.99784
0.99800
HM
CR
58.1
68.4
4.36×102
1.67×104
53.4
63.8
165
158
0.99723
0.99580
(4)
-200
-169
HM
CR
118
3.80×105
22
111
221
0.99557
-146

ACCEPTED MANUSCRIPT
HM
131
8.06×106
124
215
0.99841
-120
aNumbers as given in Table 1
Table 6. Antibacterial activity data of Ni(II) complexes and standard drug. The results
were recorded as the average diameter of inhibition zone (mm) ± standard deviation.
Compounda
Conc.
Gram positive bacteria
Gram negative bacteria
(µg/mL)
Bacillus Staphylococcus Escherichia
Klebsiella
cereus
-ve
aureus
-ve
coli
-ve
pneumoniae
(1)
50
100
150
50
2 ± 0 *
2 ± 0.14 *
3 ± 0.28 *
2 ± 0.14 *
3 ± 0 *
-ve
-ve
-ve
-ve
-ve
-ve
(2)
(3)
(4)
1 ± 0
1 ± 0.14
1 ± 0
-ve
-ve
-ve
100
150
50
-ve
-ve
1 ± 0
-ve
-ve
3 ± 0.14 *
2 ± 0.28 *
2 ± 0.14 *
3 ± 0 *
1 ± 0
1 ± 0
1 ± 0
-ve
100
150
50
-ve
-ve
-ve
-ve
1 ± 0
-ve
-ve
2 ± 0.14 *
2.025 ± 0.035 *
100
150
50
-ve
-ve
-ve
-ve
-ve
2 ± 0.14 *
-ve
1 ± 0.14
2 ± 0
1 ± 0
Penicillin
3 ± 0.28
3 ± 0.14
2 ± 0.14
2 ± 0
23
3 ± 0
3 ± 0
-ve
-ve
100
150

ACCEPTED MANUSCRIPT
aNumbers as given in Table 1.
* Indicate significant different value from that of penicillin.
Table 7. Antifungal activity data of Ni(II) complexes and standard drug. The results
were recorded as the average diameter of inhibition zone (mm) ± standard deviation
Aspergillus Fusarium Alternaria Penicillium
Compounda
Conc.
niger
oxysporum alternata
italicum
(µg/mL)
(1)
(2)
(3)
(4)
50
100
150
50
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
-ve
5 ± 0 *
6 ± 0.14 *
2 ± 0
-ve
-ve
-ve
100
150
50
-ve
2 ± 0
-ve
2 ± 0.14
1 ± 0
2 ± 0.14
2 ± 0.14
1 ± 0
1 ± 0
-ve
100
150
50
5 ± 0.28
5 ± 0.14
-ve
100
150
50
-ve
2 ± 0.14
1 ± 0
-ve
-ve
-ve
2 ± 0
5 ± 0
1 ± 0
Miconazole
100
3 ± 0.14
3 ± 0
6 ± 0
1 ± 0
24

ACCEPTED MANUSCRIPT
150
4 ± 0
3 ± 0
6 ± 0.14
2 ± 0
aNumbers as given in Table 1.
* Indicate significant different value from that of miconazole.
25

ACCEPTED MANUSCRIPT
S
S
N
N
-3H2O
N
N
H2O
S
S
H2O
O
-CH3
O
Ni
NH
Ni
NH
O
O
O
O
H3C
OH2
m/z = 338.69 (9%)
m/z = 407.69 (1.0%)
Structure I
-CO2S
S
S
N
S
N
- CO
- C6H5N2Ni
NH
Ni
NH
O
HN
O
m/z = 99 (28%)
m/z = 262.69 (17%)
m/z = 71 (34%)
Structure II
Structure IV
Structure III
Scheme 1. Fragmentation patterns of complex (3).
26

ACCEPTED MANUSCRIPT
S
S
O
HN
NH
O
+
N
-
X
N
Cl
alkaline solution
0-5 oC
N
X
S
N
S
Diazonium Salt
(A)
Azo-keto form
R
O
O
H
HN
S
N
HN
H
N
S
nH2O
X
HN
O
N
X
S
H
N
O
S
S
N
Ni
NH
S
O
O
(C)
(B)
H3C
O
H
Keto-hydrazone form
Azo-enol form
H
X
X
X
S
N
N
S
S
N
N
S
S
N
H
O
NH
HN
S
NH
H
N
HO
NH
OH
O
O
S
HN
S
OH
N
HN
S
N
NH
S
N
N
N
S
S
X
X
X
(D)
(E)
(F)
n=1, R = OCH3 (HL1); n=2, CH3 (HL2); n=3, H (HL3) and n=4, NO2 (HL4)
Fig. 1. Structure of intramolecular and intermolecular hydrogen bonds of azo dye
ligands and their Ni(II) complexes.
27

ACCEPTED MANUSCRIPT
HOMO
LUMO
Complex (1)
Complex (2)
Complex (3)
28

ACCEPTED MANUSCRIPT
Complex (4)
Fig. 2. Molecular structures (HOMO & LUMO) of Ni(II) complexes.
29