New Cu(II), Co(II), Ni(II) complexes with aroyl-hydrazone based ligand. Synthesis, spectroscopic characterization and in vitro antibacterial evaluation

Article abstract of DOI:10.1016/j.ejmech.2010.01.033

A new aroyl-hydrazone, N-(2-pyridinecarbaldehyde)-N′-[4-(4-chloro-phenylsulfonyl) benzoyl]-hydrazone (L) and its Cu(II), Co(II) and Ni(II) complexes have been prepared. The structure of these compounds has been investigated by using elemental analysis, magnetic susceptibility, molar conductance, thermal and spectral (IR, UV, NMR, LC-MS, EPR) measurements. The semi-empirical method MM2, LC-ESI-MS, NMR and IR spectra indicate that the ligand behaves as mononegative bidentate/tridentate with NO/NON donor sequence in E isomeric form towards the metal ions. The magnetic and spectral data indicate a square-planar geometry for Ni²⁺ complex and an octahedral or pseudo-tetrahedral geometry for Co²⁺ and Cu²⁺ complexes. Bacterial activity of acyl-hydrazone (L) and its complexes were studied against gram-positive bacteria: Staphylococcus aureus, Bacillus subtilis and gram-negative bacteria: Pseudomonas aeruginosa, Escherichia coli by using minimum inhibitory concentrations (MICs) method.

Full text of DOI:10.1016/j.ejmech.2010.01.033

European Journal of Medicinal Chemistry 45 (2010) 2055–2062
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Short communication
New Cu(II), Co(II), Ni(II) complexes with aroyl-hydrazone based ligand. Synthesis,
spectroscopic characterization and in vitro antibacterial evaluation
Madalina Veronica Angelusiu a, Stefania-Felicia Barbuceanu b, Constantin Draghici c,
,
Gabriela Laura Almajan b
*
a University of Bucharest, Faculty of Chemistry, Inorganic Chemistry Department, Dumbrava Rosie Street 23, 020462 Bucharest, Romania
b University of Medicine and Pharmacy, Faculty of Pharmacy, Organic Chemistry Department, Traian Vuia Street 6, 020956 Bucharest, Romania
c C.D. Nenitescu Institute of Organic Chemistry, Romanian Academy, Splaiul Independentei 202B, 060023 Bucharest, Romania
a r t i c l e i n f o
a b s t r a c t
A new aroyl-hydrazone, N-(2-pyridinecarbaldehyde)-N0-[4-(4-chloro-phenylsulfonyl) benzoyl]-hydra-
zone (L) and its Cu(II), Co(II) and Ni(II) complexes have been prepared. The structure of these compounds
has been investigated by using elemental analysis, magnetic susceptibility, molar conductance, thermal
and spectral (IR, UV, NMR, LC-MS, EPR) measurements. The semi-empirical method MM2, LC-ESI-MS,
NMR and IR spectra indicate that the ligand behaves as mononegative bidentate/tridentate with NO/NON
donor sequence in E isomeric form towards the metal ions. The magnetic and spectral data indicate
a square-planar geometry for Ni2þ complex and an octahedral or pseudo-tetrahedral geometry for Co2þ
and Cu2þ complexes. Bacterial activity of acyl-hydrazone (L) and its complexes were studied against
gram-positive bacteria: Staphylococcus aureus, Bacillus subtilis and gram-negative bacteria: Pseudomonas
aeruginosa, Escherichia coli by using minimum inhibitory concentrations (MICs) method.
Ó 2010 Elsevier Masson SAS. All rights reserved.
Article history:
Received 16 November 2009
Received in revised form
15 January 2010
Accepted 18 January 2010
Available online 25 January 2010
Keywords:
[(phenylsulfonyl)benzoyl]-hydrazone
Cu(II), Co(II), Ni(II) complexes
Antibacterial activity
1. Introduction
Starting from these premises, this paper presents the synthesis
and characterization of a new aroyl-hydrazone, N-(2-pyridine-
Hydrazones are organic compounds characterized by the
presence of –NH–N]CH– group in their molecule. Acyl-hydra-
zones have an additional donor site like C]O, which determine
the versatility and flexibility of these compounds. Such molecules
show various biological effects: anticonvulsant, antidepressant,
analgesic, antimicrobial, antitumor, anti-platelet, vasodilator,
antiviral [1–8].
carbaldehyde)-N0-[4-(4-chloro-phenylsulfonyl)benzoyl]-hydrazone
(L) and studying its ligating behavior by coordinating to Cu(II), Co(II)
and Ni(II) ions (Scheme 1). The study also includes antibacterial
activity of the newly synthesized compounds.
2. Chemistry
Usually, by reaction with salts of transition metals, acyl-
hydrazones can coordinate metal ions bidentate, through carbonyl
oxygen and azomethinic nitrogen atoms. The structural changes of
the segment attached to the hydrazone will affect the metal
binding of the ligand and exhibit interesting coordination with
transition metal ions: octahedral to tetrahedral to square-planar
[9,10]. Furthermore, metal complexes of acyl-hydrazones (i.e.
Cu(II), Co(II), Pt(II) complexes) are known for wide spectrum of
biological and pharmaceutical activities, such as inhibition of
tumor growth [11,12], antioxidative effect [13,14], antimicrobial
and antiviral [15,16].
The precursor 4-(4-chloro-phenylsulfonyl)benzohydrazide was
prepared by reaction of 4-(4-chloro-phenylsulfonyl)benzoic acid
and hydrazine monohydrate in absolute ethanol as described in
literature [17].
N-(2-pyridinecarbaldehyde)-N0-[4-(4-chloro-phenylsulfonyl)ben-
zoyl]-hydrazone (L) was obtained through a condensation reaction of
4-(4-chloro-phenylsulfonyl)benzohydrazide with 2-pyridinecarbal-
dehyde in ethanol medium, at 1:1 molar ratio. The structure of the
formed aroyl-hydrazone (L) was established by elemental analyses
and IR, UV, NMR, LC-ESI-MS spectra.
For the synthesis of complex combinations of Cu(II), Co(II) and
Ni(II), we have used the following ethanolic metal salts: CuCl2 anh.,
Cu(OCOCH3).2H2O, CuSCN, CoCl2. 6H2O and NiCl2. 6H2O, which were
added over the ethanolic solution of the ligand, in a 1:1 or 1:2, M:L
molar ratio. CuSCN was dissolved in NH3 and for precipitation of the
* Corresponding author. Tel.: þ40 741 095490; fax: þ40 21 3180729.
E-mail address: laura.almajan@gmail.com (G.L. Almajan).
0223-5234/$ – see front matter Ó 2010 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2010.01.033

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M.V. Angelusiu et al. / European Journal of Medicinal Chemistry 45 (2010) 2055–2062
Scheme 1. Synthesis of N-(2-pyridinecarbaldehyde)-N0-[4-(4-chloro-phenylsulfonyl)benzoyl]-hydrazone (L) and their Cu(II), Co(II) and Ni(II) complexes.
complex was added hydrogen peroxide, which oxidized Cu(I) to
Cu(II). Co(II) and Ni(II) complexes were stabilized at pH ¼ 8–8.5 by
adding sodium acetate. All the complexes were characterized on the
basis of IR, UV, EPR spectral studies, elemental analyses, magnetic
susceptibility, molar conductance and thermal measurements.
4. Results and discussion
4.1. Chemistry
4.1.1. The structure of the ligand
The resulting double bond –N2]C3H– following the condensa-
tion reaction, contributes to the formation of geometrical isomers Z
and E for the ligand (L). Geometrical isomerism may have some
important role in the bioactivity of the acyl-hydrazones hence their
studies are very crucial to develop synthetic methods for selective
synthesis of a particular isomer.
3. Antibacterial activity
The in vitro antibacterial activity of the free ligand (L) and its
complexes were tested against the gram-positive bacteria: Staph-
ylococcus aureus ATCC 12600, Bacillus subtilis ATCC 6633 and gram-
negative bacteria: Pseudomonas aeruginosa ATCC 9027, Escherichia
coli ATCC 11775 using the paper disc diffusion method [18] (for the
qualitative determination) and the serial dilutions in liquid broth
method [19,20] for determination of MIC. Streptomycin was used as
control drug.
Electrospray mass spectra (Fig 1) showed high purity of the acyl-
hydrazone, however the proton NMR spectra (not shown) indicated
the presence of some additional peaks in the compound. Signals of
all the additional peaks were of low intensity and appeared at the
footstep of each proton signal. One distinctive feature is the amide
Fig. 1. ESI-MS spectra of N-(2-pyridinecarbaldehyde)-N0-[4-(4-chloro-phenylsulfonyl) benzoyl]-hydrazone (L).

M.V. Angelusiu et al. / European Journal of Medicinal Chemistry 45 (2010) 2055–2062
2057
Fig. 2. Interconversion of Z and E isomers of the ligand (L).
proton resonance which is well downfield of all other peaks. Thus,
the 1H NMR spectra show an intense singlet signal at 12.29 ppm
assigned to N1H proton of E isomer accompanied by a weak singlet
signal at approximately 14 ppm. This greater deshielding effect is
most likely caused by intramolecular H bonding of the type seen in
the solid-state structure of the Z isomer (Fig. 2) [21].
The distinctly different proton chemical shifts of N-(2-pyr-
idinecarbaldehyde)-N0-[4-(4-chloro-phenylsulfonyl)benzoyl]-
hydrazone (L) indicate that this chelator adopt an E isomeric form
in solution [22,23].
The geometrical isomers were resolved by LC-MS method
(Fig 3). Above observations indicated the presence of both Z and E
isomers of the ligand. The formation of both isomers is thermo-
dynamically controlled which has been reflected in NMR spectra as
difference in intensities of proton signals corresponding to both
isomers. There was a significant difference between the intensities
of the two peaks and one of the isomers was formed in excess,
which must have lower minimum energy stabilization and heat of
formation than the other one. MM2 calculation [24] indicated that
the minimum energy stabilization of E isomer (ꢀ1.2521 kcal/mol)
and heat of formation (157.942 kcal/mol) were lower than that of Z
isomer (ꢀ0.7655 kcal/mol and 308.161 kcal/mol, respectively)
(Table 1).
Hence E isomer should form predominantly and should corre-
spond to the larger peak in the LC-MS profile. But this calculation is
not self sufficient to designate the more intense peak as E isomer,
because the peak intensity in positive ESI mode is dependent not
only up on the concentration of the molecule but also up on its
proton accepting capability. If we consider the equal proton
acceptability of both isomers, then peak intensity of LC-MS peak
should be dependent only up on concentration of the molecule and
peak at Rt ¼ 2.413 min was due to E isomer and at 2.648 min was
due to Z isomer.
atom N1H to neighbor carbonyl oxygen atom and formation of
imide bond (Fig. 4).
The ability of this ligand to coordinate a metal ion is influenced
by changing the configuration and conformation, stability in
different working conditions and especially by the density of
negative charge, which can be partially transferred during the
process of complexation of metal ion. Using molecular orbital
method (Hu¨ckel calculation) [24] was determined the charge
density per heteroatom (Fig. 5).
The obtained values show that the donor site is on the fragment
–CO–N1H–N2]CH– and the ligand coordinate to the metal ions
into E isomeric form. In this form, the pyridyl radical has a good
geometric position in order to bind metal ion by non-bonding
electron doublet of nitrogen atom. In these conditions, in obtained
complex combinations, the metal ion can adopt different geome-
tries, due to the capacity of N-(2-pyridinecarbaldehyde)-N0-[4-(4-
chloro-phenylsulfonyl) benzoyl]-hydrazone (L) to act as a bidentate
or tridentate ligand.
The obtained complexes are microcrystalline solids which are
stable in air, are soluble in DMF and DMSO, but insoluble in other
organic solvents and have melting points higher than 300 ꢁC. The
molar conductance values in DMSO (10ꢀ3 M) are too low to account
for any dissociation, therefore the complexes are considered to be
non-electrolytes [25].
The elemental analyses data along with some physical proper-
ties of the ligand and its complexes are reported in Table 2.
4.1.2. IR spectra
In the IR spectra of the complexes (Table 3) the
n
N1H
(3375 cmꢀ1) and C]O (1661 cmꢀ1) stretching vibrations corre-
n
sponding to the free ligand are not observed. This fact, along with
the presence of a medium intensity band in 1489–1509 cmꢀ1 range,
assignable to
predominantly in the enolate form (B) in the complexes. On
complex formation, the position of
CH]N2 is shifted to the higher
n C–O, indicates that the deprotonated ligand is
Ligand presents keto-enol tautomerism, which is manifested
especially in solution by proton migration from hydrazine nitrogen
n
Fig. 3. LC-ESI-MS chromatogram of N-(2-pyridinecarbaldehyde)-N0-[4-(4-chloro-phenylsulfonyl) benzoyl]-hydrazone (L).

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M.V. Angelusiu et al. / European Journal of Medicinal Chemistry 45 (2010) 2055–2062
Table 1
Cobalt(II) complex (4) exhibits a typical electronic spectrum for
octahedral species in the solid state [35,36]. Two main bands are
observed at 13,550 cmꢀ1 and 18,365 cmꢀ1, which are assigned to
the [4A2g(F) ) 4T1g(F)] (n2) and [4T1g(P) ) 4T1g(F)] (n3) transitions.
The band n1, due to transition [4T2g(F) ) 4T1g(F)] which is usually
Experimental and theoretical data of the isomers of N-(2-pyridinecarbaldehyde)-N0-
[4-(4-chloro-phenylsulfonyl)benzoyl]-hydrazone (L).
Isomer
Retention
Emin stab
D
Hf0
ELUMO
EHOMO
time (min)
(kcal/mol)
(kcal/mol)
(eV)
(eV)
under 10,000 cmꢀ1, as ligand field parameters, 10Dq, B and
b
were
Z
E
2.648
2.413
ꢀ1.2521
ꢀ0.7655
308.162
157.192
ꢀ1.350
ꢀ3.689
ꢀ2.771
ꢀ9.179
calculated using the following equations:
10Dq ¼ 1=3ð2n2
ꢀ
n3Þ þ 5B
wave numbers, shift which indicates that the azomethine nitrogen
atom is coordinated to the metal ion [26,27].
h
i
ꢀ
ꢁ
1=2
B ¼ 1=510 7ðn3 ꢀ 2n2Þ ꢂ 3 81n23 ꢀ 16n2
ð
n2
ꢀ
n3
Þ
(A)
This coordination behavior of the ligand is also proved by the
10Dq ¼ n2
ꢀ
n1
appearance of IR bands due to
n M–O and n M–N vibrations in the
range 474–502 cmꢀ1 and 429–456 cmꢀ1, respectively [28,29].
340Dq2 ꢀ 18ðn2
þ
n3ÞDq þ n2n3 ¼ 0
(B)
The IR spectra of the complex (2) derived from copper acetate,
B ¼ 1=15ðn3
þ
n2 ꢀ 30DqÞ
show an absorption band at 1489 cmꢀ1 which is assigned to
n
(C–O)
anti-symmetric stretching of acetate group and another at
The calculated values of the ligand field parameters
10Dq ¼ 7263 cmꢀ1 and B ¼ 869 cmꢀ1 are in good agreement with
the predicted values for octahedral complexes of Co(II) [37]. The
1450 cmꢀ1 which can be assigned to
vibration of acetate. Difference
n (C–O) symmetric stretching
D
¼ 39 cmꢀ1 indicates the mono-
nephelauxetic ratio
b
¼ B/B0 ¼ 0.89 for the complex (4) suggesting
negative bidentate coordination of the acetate group [30].
The pyridine-ring-stretching, in-plane-ring-bending and out-
of-plane-ring-bending vibrations are found at 1510, 628 and
502 cmꢀ1, respectively. These absorptions are highly affected when
nitrogen atom of pyridine ring takes part in coordination. In the
complex (1) the position of these absorption bands is shifted to
higher region. This indicates that the nitrogen of pyridine ring is
involved in coordination. The above discussion reveals that the
ligand coordinates to the metal atom as a tridentate chelate. The
complex combinations [Cu(L)(NCS)(H2O)] (3) and [Co(L)2(H2O)2]
an ionic character of cobalt(II)-ligand bonds [38]. The room
temperature magnetic moment value, 5.10 B.M., demonstrates that
the Co(II) complex is paramagnetic and has a high-spin octahedral
configuration with 4T1g(F) ground state [39].
For the diamagnetic Ni(II) complex (5) the electronic spectra
showed a typical of square-planar monoligated Ni(II) complexes
bands [35,40]: a medium intensity board band at 20,040 cmꢀ1 and
this may be regarded due 1A2g ) 1A1g transition and a shoulder
band at 23,923 cmꢀ1 which may be attributed to 1E1g ) 1A1g. The
radial parameters values es (11,961.5 cmꢀ1) and ep (8480 cmꢀ1
which were calculated with Lever’s relations [41] indicate
a pronounced character for Ni(II)-ligand bond [42–44].
)
(4) exhibit
n (OH) and r (H2O) bands in the 3400–3452 and 680–
695 cmꢀ1 regions which are indicative of coordinated water in the
complexes [31,32]. In the IR spectrum of (3) (prepared from CuSCN),
two absorption bands at 2059 and 795 cmꢀ1 specific to the
N-coordination of the thiocyanate group are detected [30].
s
4.1.4. EPR spectra
EPR spectra of the complexes (2) and (3), recorded in DMSO
solution at room temperature, are similar and show only an intense
and broad signal without hyperfine splitting (giso ¼ 2.14 and 2.15,
respectively). The shape of the spectra are consistent with the
tetrahedral geometry around the Cu(II) environment and the
higher g values obtained in case of these complexes, when
compared to the g value of a free electron, (g ¼ 2.0023), indicate an
increase of the covalent nature of the bonding between the metal
ion and the ligand molecule [45, 46].
4.1.3. Electronic spectra and magnetic studies
The electronic spectra of the ligand, recorded by diffuse-reflec-
tance technique, shows two bands at 39,062 cmꢀ1 and 29,850 cmꢀ1
due to the benzene ring and to the
p / p* transition of the chro-
mophore (–C]N–NH–CO–), respectively. These bands shift to wave
numbers in the electronic spectra of the complexes (38,760–
37,010 cmꢀ1 and 29,120–28,740 cmꢀ1, respectively).
On the basis of electronic spectra, distorted octahedral geometry
around Cu(II) ion in complex (1) is suggested [33]. The spectrum
shows a low intensity broad band at 13,069 cmꢀ1 (dx2ꢀy2 /dxy
transition) and a second band at 17,580 cmꢀ1 which is assigned to
dx2ꢀy2 /dxy;yz transition. This complex has magnetic moment 1.98
BM, which is higher than the spin-only value (1.73 BM) expected for
one unpaired electron and offers possibility of an octahedral
geometry [34].
The gII and gt values determined from the EPR spectra of the
complex (1) recorded in microcrystalline powder at room
temperature (2.220 and 2.085) suggest that the unpaired electron is
localized in the dx2ꢀy2 orbital of the Cu(II) ion and are characteristic
for the axial symmetry [46]. The axial symmetry parameter
G ¼ 2.58 which has less than 4.0 indicates considerable exchange
interaction between metal ions [47]. EPR spectrum of the complex
(1) recorded in DMSO solution at room temperature is character-
istic of monomer Cu(II) complexes with axial symmetry and pres-
ents clear bands, without highlighting any hyperfine splitting. The
constants a and b which show ionic or covalent nature of M–L bond
In the electronic spectra of complexes (2), (3), the broad band
which was observed at 13,227–13,495 cmꢀ1 region due to
dxy/dz2 ; dx2ꢀy2 transition, suggesting a pseudo-tetrahedral
configuration around the central metal ion [35]. The complexes
were found paramagnetic with magnetic moments in 1.75–1.98
BM range, which is normal for Cu(II) with pseudo-tetrahedral
stereochemistry.
and the covalency parameters a2 b2 d2 were calculated using
, ,
spectral parameters values determined from this spectrum
(gII ¼ 2.25, gt ¼ 2.06, AII ¼ 157 and At ¼ 15) and transition energy
Fig. 4. Tautomerism of N-(2-pyridinecarbaldehyde)-N0-[4-(4-chloro-phenylsulfonyl) benzoyl]-hydrazone (L).

M.V. Angelusiu et al. / European Journal of Medicinal Chemistry 45 (2010) 2055–2062
2059
0.589 (Z)
0.429 (E)
0.147 (Z)
0.167 (E)
-0.132 (Z)
-0.145 (E)
O
S
O
S
H
N
H
Cl
C
O
C
O
N
H
N
C
H
Cl
N
C
O
N
O
-0.343 (E)
-0.316 (Z)
N
-0.950 (E)
-0.980 (Z)
M2+
0.422 (Z)
0.940 (E)
0.388 (Z)
0.122 (E)
M2+ = Cu2+, Co2+, Ni2+
Fig. 5. The charge density per heteroatom and the donor site of N-(2-pyridinecarbaldehyde)-N0-[4-(4-chloro-phenylsulfonyl)benzoyl]-hydrazone (L).
D
Exy (13,069 cmꢀ1) and
D
Exz (17,580 cmꢀ1) from electronic spec-
(3.29% of the sample weight). Exothermic peak at 245 ꢁC corre-
sponds to elimination of SCN fragment (exp. 10.37%, calc. 10.80%).
Organic part is lost in the 250–700 ꢁC range and the experimentally
obtained residue of CuO determining the percentage of 11.53%
copper. The thermal decomposition of Co(II) complex (4) occurs in
three distinct stages. First, in 160–195 ꢁC range corresponds to loss
of two water coordinating molecules. The organic part is lost in two
stages, with maximum at 380 ꢁC and 500 ꢁC, respectively, which
corresponding to (phenylsulfonyl)benzoyl fragment and the
residue hydrazone, respectively. Ni(II) complex (5) is stable up to
280 ꢁC and it decomposes in two cumulative stages, which corre-
sponds of the loss of the ligand. Over 690 ꢁC the thermogram
registers a plateau region, which corresponding to NiO residue.
Thus, based on these analytical and physico-chemical data, the
proposed structures for the complexes are shown in Fig. 6.
trum by the following formula [48]:
ꢂ
ꢂ
ꢃ
gII ¼ 2:0023 ꢀ 8
=
l D
Exy a2
$
b2
ꢃ
gt ¼ 2:0023 ꢀ 2
=
l D
Exz a2
$
d2
a2 ¼ ꢀAII=P þ ðgII ꢀ 2:0023Þ þ 3=7ðgt ꢀ 2:0023Þ þ 0:04
where: P ¼ ꢀ0.036 ꢃ 10ꢀ4 cmꢀ1 and
l
¼ ꢀ828 cmꢀ1 (spin–orbit
coupling constant for Cu2þ
)
The obtained values for a and b (1.92 and 0.67 respectively)
show a pronounced distortion from octahedral symmetry by
elongation along the z axis. The calculated value for parameter b2
(0.65) indicates a predominantly covalent character for in-plane
4.1.6. Antibacterial activity
p
-bonding, while out-of-plane p-bonding has a pronounced ionic
character (d2 ¼ 0.91) [49].
All the synthesized compounds were screened for their anti-
bacterial activity. All the tested complexes possessed variable
antibacterial activity against both Gram-positive (S. aureus, B. sub-
tilis) and Gram-negative (P. aeruginosa, E. coli) bacteria. To compare
the antibacterial activities shown by the synthesized complexes,
standard drug namely Streptomycin was used (Table 4).
By careful study of the obtained results, we can see that the
ligand (L) has a weak action on all the tested microorganisms. The
activity of N-(2-pyridinecarbaldehyde)-N0-[4-(4-chloro-phenyl
sulfonyl)benzoyl]-hydrazone (L) becomes more pronounced when
coordinated to the metal ions. All metal ions have varying anti-
bacterial influence on bacterial species. The action of the tested
4.1.5. Thermogravimetric analysis
Thermal stability up to 260 ꢁC for complex combinations (1) and
(2) indicated lack of coordination water. Above this temperature
thermal decomposition begins. For the complex (1), there is
a single, exothermic process, between 280 and 650 ꢁC, which
corresponds to the loss of ligand. Weight loss, which occurs, for
compound (2), in 260–320 ꢁC range (10.98% of the sample weight),
corresponds to loss of acetate fragment. In the 320–650 ꢁC range
there is total loss of the organic ligand. Complex (3) is stable up to
160 ꢁC. In the 160–200 ꢁC range there is coordination-water loss
Table 2
Analytical data and physical properties of N-(2-pyridinecarbaldehyde)-N0-[4-(4-chloro-phenylsulfonyl)benzoyl]-hydrazone (L) and its Cu(II), Co(II) and Ni(II) complexes.
Comp. Molecular formula
MW (g/mol) Colour
Elemental analysis (calc/exp)
L
(ohmꢀ1 cm2 moleꢀ1
)
m
(BM)
C
H
N
M
L
C19H14ClN3O3S
[Cu(L)2] (C38H26Cl2CuN6O6S2)
[Cu(L)(AcO)] (C23H19ClCuN3O5S)
[Cu(L)(NCS)(H2O)] (C20H15ClCuN4O4S2) 538.49
[Co(L)2(H2O)2] (C38H30Cl2CoN6O8S2)
[Ni(L)2] (C38H26Cl2NiN6O6S2)
399.85
861.23
548.48
white
green
57.07 (56.94) 3.53 (3.43) 10.51 (10.43)
–
–
9.50
–
1
2
3
4
5
52.99 (53.11) 3.04 (3.16)
9.76 (9.68)
7.66 (7.56)
7.38 (7.21)
11.59 (11.38) 8.70
1.98
1.75
1.98
5.10
diam.
brick-red 50.37 (50.46) 2.91 (2.97)
brick-red 44.61 (44.73) 2.81 (2.93) 10.40 (10.31) 11.80 (11.71) 4.50
reddish
orange
892.65
856.38
51.13 (51.02) 3.39 (3.25)
53.29 (53.16) 3.06 (2.97)
9.41 (9.32)
9.81 (9.74)
6.60 (6.50)
6.85(6.78)
9.50
12.10
Table 3
IR bands and their assignments for N-(2-pyridinecarbaldehyde)-N0-[4-(4-chloro-phenylsulfonyl)benzoyl]-hydrazone (L) and its Cu(II), Co(II) and Ni(II) complexes.
Comp.
n
OH
n
N1H
nC]O
n
CH]N2
nC–O
nC]Caryl
(
nC]N)
nPy
nacetate (nSCN)
nC–Cl
nM–O, nM–N
L
–
–
–
3375m
1661s
1600m
1617m
1619s
1620m
1622s
–
1587m, 1552s
1581s
1566s
1591s
1580m
1580s
1510m, 628s, 502m
1524m, 661s, 517m
1509m, 627m, 500m
1508m, 629i, 503m
1509m, 626s, 501m
1511m, 625s, 502m
–
–
768vs
769s
771s
766s
758vs
756s
–
1
2
3
4
5
–
–
–
–
–
–
–
–
–
–
1492m
1489m
1509m
1497m
1494m
474m, 447m
502m, 433m
478m, 429m
502m, 438m
474m, 456m
1489m, 1450m
2059m, 795m
–
–
3410m, 680m
3452m, 695m
–
1615m
m ¼ medium; s ¼ strong; vs ¼ very strong.

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M.V. Angelusiu et al. / European Journal of Medicinal Chemistry 45 (2010) 2055–2062
Table 4
Antibacterial activities of ligand L and its Cu(II), Co(II) and Ni(II) complexes.
Cl
N
H
C
Compd.
Gram-positive
bacteriaa
Gram-negative
bacteriab
O
S
N
N
O
N
O
Sa
Bs
Pa
Ec
28
Cu
(L)
(1)
(2)
(3)
(4)
(5)
Strept.
512
256
128
128
256
128
8
512
512
128
256
512
128
8
256
128
64
64
64
O
N
128
32
64
128
64
8
O
N
S
C
H
[Cu(L)2]
(1)
O
Cl
128
16
Cl
Strept. ¼ streptomycin.
a
O
CH3
Sa (Staphylococcus aureus ATCC 12600); Bs (Bacillus subtilis ATCC 6633).
O
b
S
Pa (Pseudomonas aeruginosa ATCC 9027); Ec (Escherichia coli ATCC 11775).
O
O
Cu
O
donor atoms; the total charge on the complex ion; the nature of the
metal ions and the geometrical structure of the complex.
Since all the complexes have the same donating atoms (N, O),
containing metals with the same oxidation state (M2þ), which form
5-membered chelating rings with ligand, therefore the more
effective factors that influence the antibacterial activity are the
geometrical shape and the nature of the central atoms.
N
N
C
[Cu(L)(OCOCH3)]
(2)
N
H
H
H
O
The tetracoordinated complexes have better action than the
hexacoordinated compounds. The tetrahedral of (2), (3) increases
the lipophilicity for the central atom by decreasing the effective
nuclear charge (polarity) of the Cu(II) more than the square-planar
structure of Ni(II) (5).
N
Cu
C
C
N
N
N
S
O
H
The most active is [Cu(L)(OCOCH3)] (2) which presents a good
inhibitory action against all the tested bacterial species. Cu(II)
complexes (2) and (3) inhibit the growth of P. aeruginosa and E. coli
O
[Cu(L)(NCS)(H2O)]
(3)
S
O
(MIC ¼ 32–64
mg/mL) and have no significant effect against
S. aureus and B. subtilis comparative with the control drug. The
octahedral Co(II) complex (4) was more antibacterial as compared
to the Cu(II) complex (1) which has also distorted octahedral
geometry, probably due to the presence of two molecules of water
in the coordination sphere of the metallic ion.
Cl
Cl
O
S
H
H
H
Furthermore, chelation reduces the polarity of the metal ion
because of partial sharing of its positive charge with the donor
groups and possibly the p-electron delocalization within the whole
O
O
C
N
O
N
Co
N
chelate ring system that is formed during coordination [50]. These
factors increase the lipophilic nature of the central metal atom and
hence increasing the hydrophobic character and liposolubility of
the molecule favoring its permeation through the lipid bilayer of
the bacterial membrane. This enhances the rate of uptake/entrance
and thus the antibacterial activity of the testing compounds.
Our future studies were to determine the mechanism by which
the complexes of acyl-hydrazones inhibit growth and development
of various bacterial species.
N
N
O
C
O
O
H
N
H
S
H
O
[Co(L)2(H2O)2]
(4)
Cl
Cl
5. Conclusions
H
N
C
O
S
We have synthesized Cu(II), Co(II) and Ni(II) complexes using the
aroyl-hydrazone formed by the condensation of 4-(4-chloro-phe-
nylsulfonyl)benzohydrazide with 2-pyridinecarbaldehyde. The
ligand behaves as mononegative bidentate/tridentate with NO/NON
donor sequence in E isomeric form towards the metal ions. The
complexes were characterized by analytical and physico-chemical
measurements, which led to the proposal of a square-planar
geometry for Ni2þ complex and an octahedral or pseudo-tetrahedral
geometry for Co2þ and Cu2þ complexes. The ligand and its
complexes were screened for their antibacterial activity against
gram-positive and gram-negative bacteria. A comparative study of
MIC values indicates that the complexes exhibit higher antibacterial
activity against Gram-negative bacteria than the free ligand, but it is
weak compared with the standard drug.
N
O
N
O
Ni
O
N
O
N
S
C
N
[Ni(L)2]
(5)
H
O
Cl
Fig. 6. Proposed structures of the complexes (1)–(5).
complexes on Gram-negative bacteria is better than that on Gram-
positive bacteria.
The antibacterial activity of the complexes is governed by the
following factors: the chelate effect of the ligand; the nature of the

M.V. Angelusiu et al. / European Journal of Medicinal Chemistry 45 (2010) 2055–2062
2061
6. Experimental protocols
In case of CuSCN (1 mmol) a blue solution (obtained in 5 mL
NH3) was mixed with stirring with a hot clear ethanolic solution
of the ligand (L) (2 mmol/20 mL ethanol) and after was added
few drops of hydrogen peroxide, which oxidized Cu(I) to Cu(II).
The obtained mixture was refluxed 2.5–3 h and the obtained
precipitate was filtered, washed successively with water, hot
ethanol, cold ethanol and diethylether and finally dried under
vacuum.
6.1. Chemistry
The content of metallic ions was determined by atomic
absorption spectroscopy with Varian-A240 spectrometer; C, H, and
N were done with ECS-40-10-Costeh microdosimeter, after drying
the compounds at 105 ꢁC. The molar conductivity was determined
in DMSO (3 ꢃ 10ꢀ3 M), at room temperature, using OK-102/1
Radelkis conductometer. Electronic spectra were recorded by the
diffuse-reflectance technique, using MgO as diluting matrix, on
a JASCO UV–VIS 540 spectrophotometer. IR spectra were recorded
with Vertex 40 Brucker FTIR spectrophotometer in the 4000–
400 cmꢀ1 region using KBr pellets. The thermal analysis of the
complexes was carried out in static air atmosphere, with a sample
heating rate of 5 ꢁC/min using TGA V5-1A DuPont 2000 thermo-
balance. ESR spectra were recorded with an ART-6 IFIN, X-band
spectrometer (9.1 GHz) online with a PC equipped with a 100 kHz
field modulation unit. The melting points were determinated with
Boetius apparatus and are uncorrected. The NMR spectra were
registered on a Varian Gemini 300 BB spectrometer working at
300 MHz for 1H and 75 MHz for 13C in DMSO-d6. All chemical shifts
6.2. Antibacterial activity
Antibacterial activity was evaluated by minimum inhibitory
concentration (MIC) using the serial macrodilution test. S. aureus
ATCC 12600, B. subtilis ATCC 6633, P. aeruginosa ATCC 9027 and
E. coli ATCC 11775 stored in Muller-Hinton broth (Merck), were
subcultured for testing in the same medium and grown at 37 ꢁC.
Then the cells were suspended, according to the McFarland
protocol, in saline solution, to produce a suspension of about
10ꢀ5 CFU mLꢀ1 (colony-forming units per mL). Serial dilutions of
the test compounds, previously dissolved in dimethylsulfoxide
(DMSO), were prepared in test tubes to final concentrations of
1024; 512; 256; 128; 64; 32; 16; 8; 4; 2 mg/mL. 100 mL of a 24 h
are reported in d (ppm) using TMS as an internal standard. The mass
old inoculum was added to each tube. The MIC, defined as the
lowest concentration of the test compound, which inhibits the
visible growth after 18 h, was determined visually after incuba-
tion for 24 h at 37 ꢁC. Tests using DMSO as negative control were
carried out in parallel. Streptomycin was used as control drug.
Because the MIC values are not spectacular, no statistical calcu-
lations were made.
spectra were registered with a triple quadrupole mass spectrom-
eter Varian 1200 L/MS/MS coupled with a high performance liquid
chromatograph with Varian ProStar 240 pump and a Varian ProStar
410 automatic injector. For the obtainment of ions was used an
electrospray interface (ESI) or a atmospheric pressure chemical
ionization (APCI). The solvent used was DMSO; the liquid chro-
matography was performed on a Hypersil Gold (Thermo) column
with precolumn, and the mobile phase was 30% water and 70%
methanol. The required chemicals were purchased from Merck and
Sigma–Aldrich and all manipulations were performed using
materials as received.
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