Spectroscopic, thermal and antimicrobial properties of the copper(II) complex of Schiff base derived from 2-(salicylidene) aminopyridine

Article abstract of DOI:10.1002/aoc.2872

Schiff bases and their complex combinations with metallic ions represent a class of compounds with antimicrobial activity. A ligand was prepared by condensation of the salicylaldehyde with 2-aminopyridine obtaining 2-(salicylidene) aminopyridine (SB) with

Full text of DOI:10.1002/aoc.2872

Full Paper
Received: 30 January 2012
Revised: 18 March 2012
Accepted: 9 April 2012
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.2872
Spectroscopic, thermal and antimicrobial
properties of the copper(II) complex of Schiff
base derived from 2-(salicylidene) aminopyridine
a
b
a
Gladiola Tantaru , Maria-Cristina Popescu *, Veronica Bild ,
c
d
b
Antonia Poiata , Gabriela Lisa and Cornelia Vasile
Schiff bases and their complex combinations with metallic ions represent a class of compounds with antimicrobial activity. A
ligand was prepared by condensation of the salicylaldehyde with 2-aminopyridine obtaining 2-(salicylidene) aminopyridine
(
(
SB) with a high capacity for complexing Cu(II) ions. The new compound has been characterized by physical constants
1
melting point, solubility, stability) and the chemical structure was confirmed by elemental, spectral (IR, UV–visible, H NMR
1
3
and C-NMR) and thermal analyses. The elemental analysis gives a coordination ratio of 1:2 metal:Schiff base. Lethal dose
0 (DL50) values of new Schiff base and their complex with metallic ions were established. The antimicrobial activity of this
5
complex was tested in comparison with the activity of the corresponding Schiff base on strains of Staphylococcus aureus,
Bacillus cereus, Bacillus subtilis, Escherichia coli, Candida albicans, and Klebsiella. These were compared with the activity of
the reference drugs (chloramphenicol, tetracycline, ofloxacin and nystatin) on the above-mentioned strains. It has been
established that all compounds tested were very active against both Gram-positive and Gram-negative bacteria. Copyright
©
2012 John Wiley & Sons, Ltd.
Keywords: Schiff base; 2-(salicylidene) aminopyridine; Cu(II) complex; antimicrobial activity; toxicity
by bond length changes and deviations from expected ligand
Introduction
geometry. So-called ’stepped’ or ’umbrella’ distortions are well
documented, with deviations from planarity and unexpected bond
lengths in the aromatic ring of salicylaldiminato (salim) groups.
Schiff bases can form a new class of drugs through mechanisms
of immune potentiation and therapeutic potential. The complex
combination of Schiff bases with metallic ions represents a class
of compounds with the most interesting properties, both from
the point of view of chemical and biological behavior. The literature
data quotes the antimicrobial, anti-inflammatory and antioxidant
action of the complex combinations of Schiff bases with
Investigation of metal organic complexes represents one of the
most active areas of material science and chemical research.
Major advances have been made in these materials because of
their interesting properties and potential in various applications,
e.g. electrical conductivity, magnetism, host guest chemistry,
[
1]
ion exchange, catalysis, nonlinear optics. Synthesis of new
Schiff bases and their metal complexes is still the aim of many
recent investigations. Schiff bases have played an important role
in the development of coordination chemistry as they readily
form stable complexes with most of the transition metals. They
show interesting properties, e.g. their ability to reversibly bind
[
10,11]
different cations.
Several Schiff base complexes of copper(II), such as N,N′-1,
2-phenylene-bis(salicylideneiminato)copper(II), bis(N-phenylpyridox-
ylideneiminato)copper(II), aqua(5-phosphopyridoxylidene-DL-pheny-
lalanineato)copper(II) were reported in the literature data. No
studies were found on the Cu(II) complexes of the Schiff base derived
[
2]
[3]
oxygen, catalytic activity in hydrogenation of olefins, transfer
[4]
[5]
of an amino group, photochromic properties and complexing
ability towards toxic metals.
Schiff bases continue to have an important role as ligands in
[
6]
[
7]
metal coordination chemistry, even almost a century since their
discovery. These applications were generated by the possibility of
formation of some complex combinations with transition metals.
Most of the metal complex model studies of Schiff base ligands
containing salicylaldehyde and amino acids have focused upon
*
Correspondence to: Maria-Cristina Popescu, ’Petru Poni’ Institute of Macromo-
lecular Chemistry, 41A Grigore Ghica Voda Alley, RO 700487, Iasi, Romania.
E-mail: cpopescu@icmpp.ro
[
8,9]
the binding mode of these ligands
are related on their applications.
and only a few studies
a ’Gr. T. Popa’ University of Medicine and Pharmacy, Faculty of Pharmacy, Iasi,
Romania
Ligands derived from substituted salicylaldimine have played
an important part in revealing the preferred coordination
geometries of metal complexes. Of particular interest were those
involving copper(II) since they reveal surprising molecular diver-
sity not only in coordination geometry but also in more subtle
changes in the ligands. Thus complexes with four, five or six
donors or with marked tetrahedral ’distortions’ are accompanied
b ’Petru Poni’ Institute of Macromolecular Chemistry, Iasi, Romania
c ’Gr. T. Popa’ University of Medicine and Pharmacy, Faculty of Medicine, Iasi,
Romania
d ’Gh. Asachi’ Technical University, Department of Chemical Engineering, Iasi,
Romania
Appl. Organometal. Chem. 2012, 26, 356–361
Copyright © 2012 John Wiley & Sons, Ltd.

Properties of the Cu(II) complex of SB derived from SAP
[
12]
from 2-(salicylidene) aminopyridine.
Schiff bases and their
Methods
[13]
[14]
[15]
complexes have a variety of biological, clinical and analytical
Elemental analyses
applications. Earlier works have shown that some drugs had
increased activity when administered as metal chelates rather than
as organic compounds.
Elemental analyses (C, H, N) were carried out with an Elemental
Vario EL analyzer. The quantitative determination of Cu(II) ions from
the synthesized complexes was performed using an AAS- IN atomic
absorption spectrometer (Carl Zeiss, Jena, Germany).
This work deals with the study of the physicochemical
characterization of a Schiff base derived from 2-(salicylidene)
aminopyridine and its complex with Cu(II) ions. The antimicrobial
activity of this complex was compared with that of Schiff base on
strains of Staphylococcus aureus ATCC 25923, methicillin-resistant
S. aureus (MRSA), Bacillus cereus ATCC 14579, B. subtilis ATCC6633,
Escherichia coli ATCC25922, Candida albicans ATCC 10231 and
Klebsiella spp. This activity was also compared with that of the
reference drugs (chloramphenicol, tetracycline, ofloxacin and
nystatin) on the above-mentioned strains.
FT-IR spectroscopy
FT-IR spectra were recorded on a solid sample in a KBr pellet by
means of an FT-IR DIGILAB, Scimitar Series Spectrometer (USA)
with a resolution of 4 cm . The concentration of the sample
was 5 mg/500 mg KBr. Processing of the spectra was performed
using the Grams/32 program (Galactic Industry Corporation).
ꢀ1
ꢀ
1
UV–visible spectroscopy
The electronic spectra were obtained on a Hewlett- Packard 8453
Materials and Methods
Materials
UV–visible spectrophotometer.
NMR spectroscopy
All chemicals used in this work were reagent grade (by Merck
and Chimopar Bucharest), including Cu(OAc) .H O, salicylalde-
2 2
hyde, 2-aminopyridine, DMSO and methanol. Double-distilled
water was used.
1
13
H and C-NMR spectra were recorded on Bruker 400 MHz
equipment, using DMSO as solvent.
Thermogravimetry
Thermogravimetric analysis (TGA) was carried out under constant
ꢁ
ꢀ1
Synthesis of Ligand and Complex
nitrogen flow at a heating rate of 15 C min , using a Mettler
Toledo TGA/SDTA 851 balance. The heating scans were performed
on 3–5 mg of sample, in the temperature range 25–900 C.
Synthesis of Schiff base
ꢁ
The Schiff base used as ligand has been prepared by condensing
salicylaldehyde with 2-aminopyridine in methanol, in a 1:1 molar
ratio, at room temperature. The precipitate was collected after
Biological Activity
4
8 h by filtration, washed with water, ethanol–water mixture
1:1, v/v) and absolute ethanol, and recrystallized from methanol.
A fine, intense yellow crystalline powder of 2-[salicylidene]-
Toxicity study
(
Acute toxicity was estimated by oral administration of SB and
SB-Cu(II), using sodium carboxymethyl cellulose (Na-CMC)
[
16]
aminopyridine (SB) type NNO was obtained. The product yield
for the schiff base was 85%.
0
.1% suspension as carrier, to groups of 6–10 Swiss male mice
(
each mouse weighing 20–25 g). Administration was made
[
17]
Synthesis of the complex
according to classical laboratory methodology.
The animals
received food and water ad libitum. Three hours before testing their
access to water was discontinued. Acute toxicity was evaluated,
using geometrically progressing doses (ratio 2) in single administra-
tions. Death of animals and their behavioral reactions were
To 2 M (0.396 g) Schiff base (50 ml) methanolic solution was
added 1.001 mM (0.2 g) Cu(OAc) .H O methanolic solution. The
2
2
resulting solution was refluxed for 1.5 h and left to rest at room
temperature for 48 h; it was filtered, then left to dry on filter
paper. Finally, it was recrystallized from dimethylformamide. A
light-green crystalline powder was obtained. The product yield
for the complex was about 65%. See Fig. 1 for structures of the
ligand and complex.
followed during 10 days. The testing was made in accordance with
[18,19]
the international legislation and the internal regulations
of the
University of Medicine and Pharmacy concerning experiments
using lab animals.
Statistics: the interpretation of the results was made by
analyzing the regression lines, and the data were submitted for
ANOVA testing.
Antibacterial activity
The newly prepared compounds were screened for their antibac-
terial activity against Gram-positive and Gram-negative bacteria
(
S. aureus ATCC 25923, MRSA, B. cereus ATCC 14579, B. subtilis
ATCC 6633, E. coli ATCC 25922, Klebsiella spp., C. albicans ATCC
[
20]
10231) using disc diffusion assay.
Suspensions in sterile
peptone water from 24 h cultures of microorganisms were
Figure 1. Structure of the ligand (a) and complex (b)
adjusted to 0.5 McFarland. Muller–Hinton Petri dishes of 90 mm
Appl. Organometal. Chem. 2012, 26, 356–361
Copyright © 2012 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/aoc

G. Tantaru et al.
were inoculated using these suspensions. The tested compounds
ꢀ
1
were dissolved in DMSO to a final concentration of 1000 mg ml
.
The discs (6 mm in diameter) were impregnated with 10 ml of
each compound and placed on the inoculated peptone water.
DMSO-impregnated discs were used as negative controls.
Toxicity tests of the solvent, DMSO, showed that the concen-
trations used in antibacterial activity assays did not interfere with
[
21]
microorganism growth.
Results and Discussion
The synthesized compounds are crystalline and non-hygroscopic.
They are insoluble in water, partially soluble in ethanol, and
soluble in acetone, DMF and DMSO. Composition and identity
of the assembled compounds were deduced from elemental
analyses, spectroscopic techniques (IR, UV–visible, NMR) and
thermal studies. The analytical data of the complex indicated
Figure 2. Adsorbance versus molar ratio M/L for SB/Cu(II) complex
The observed bands in the SB-Cu(II) complex spectrum can be
classified into those originating from the ligand and those arising
from the bonds formed between metal ions and the coordinating
sites. The infrared spectrum of the ligand shows a broad band
1
:2 metal to ligand stoichiometry. The composition of the ligand
and complex (Table 1) was calculated and compared with the
experimental values.
For the characterization of coordination compounds, an
important study is related to the complex stability of Cu(II) with
ꢀ
1
between 3200 and 3450 cm , which can be attributed to the
ꢀ
1
stretching vibration of the phenolic OH (3436 cm ) and to
(SAP) ligand.
The stability constant was determined following the method of
Harvel and Manning, and the dissociation degree according to
the relations
2
Ki ¼ a C=1 ꢀ a; a ¼ Am ꢀ As=Am
where a = dissociation degree, A = maximum absorbance,
m
As = equilibrium absorbance, and C = concentration of the
solutions of Cu(II) and SB.
ꢀ
6
5
a = 0.1118;
K = 1.407 ꢂ 10
;
K = 7.1 ꢂ 10 ꢂ e = 1.20 ꢂ
i
s
5
ꢀ1
ꢀ1
ꢀ2
ꢀ1
1
0 mol L cm . Solubility = 1.09 ꢂ 10 mol L
.
Combination rate was established by isomolar series method
(Fig. 2).
The SB-Cu(II) complex has a higher K than other Cu(II) complexes,
s
5
4
ꢀ1
ꢀ1 [22]
which have K =4.3ꢂ 10 and e =1.08ꢂ 10 mol Lcm
.
s
By comparing the K value of our complex with that of an
i
ꢀ
5 [23]
SB-Mn (II) complex, which is 2.943 ꢂ 10
,
it can be observed
that the first one is more stable than the last one. From Fig. 2,
the M/L ratio evidenced that every Cu ion needs two ligands.
FT-IR and UV–Visible Spectroscopy
IR spectroscopy is a powerful method for highly sensitive and
selective concentration determination and identification of
chemical species. The specific absorption of the substance in
the ’fingerprint’ region enables the distinct recognition of various
chemical species and even of structural isomers.
IR spectra of SB along with its complex are displayed in Fig. 3.
Figure 3. FT-IR spectra of SB and SB-Cu(II) complex
Table 1. Analytical and physical data of ligand and its Cu (II) complex
ꢁ
Sample
Color
Elemental analysis
M.p. ( C)
C
H
N
Cu
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
Exp.
Calc.
SB (C12
H
10
N
2
O)
Intense yellow crystalline powder
Light-green crystalline powder
78.5
63.2
78.3
63.0
5.7
4.0
5.4
3.9
8.0
7.6
—
—
69
SB-Cu(II) (C24
H
18
N
4
O
2
Cu)
12.4
12.2
13.9
13.8
160
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Copyright © 2012 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2012, 26, 356–361

Properties of the Cu(II) complex of SB derived from SAP
ꢀ1
the stretching vibrations of H-bonded OH groups (3325 cm ).
The first band decreases and is shifted to lower wavenumbers
in the SB-Cu(II) complex, suggesting the involvement of phenolic
OH groups in coordination. In the Schiff base complex spectrum a
ꢀ
1
new band at 1663 cm was evidenced, which can be assigned to
physical bonded water molecule stretching vibrations. Also, one
can observe a shifting of the bands, corresponding to aromatic
CH stretching vibrations, to higher wavenumbers.
Figure 4. Numbering of carbon atoms in SB
The involvement of a deprotonated phenolic moiety in the
SB-Cu(II) complex is confirmed by the shifting of n(C-O) stretching
In the sample SB-Cu(II) spectrum the bands are broad, indicating
complex formation, especially because this is only partially soluble
in DMSO and has paramagnetic properties.
ꢀ
1
band (observed at 1276 cm in the ligand) to a lower frequency
ꢀ
1
with 14cm . This shifting suggests the weakening of C-O bonds
and formation of Cu-O bonds. The free Schiff base ligand showed
ꢀ
1
ꢀ1
strong bands at 1610 cm and 1586 cm , which are characteristic
of the azomethine (-HC N) groups. Coordination of the Schiff base
to the metal through the nitrogen atom is expected to reduce
electron density in the azomethine link and shift to a lower
frequency of n(C-N) absorption. This phenomenon was observed,
proving the coordination of the azomethine nitrogen to metal ions.
Coordination of the azomethine nitrogen is further supported by
Thermogravimetry
The thermal analysis of SB and its metal complex were recorded
ꢁ
in a nitrogen atmosphere from 25 to 900 C using a TGA instru-
ment. Based on the thermograms, decomposition stages, tem-
perature ranges, decomposition product as well as weight loss
percentages were evaluated.
The TG/DTG curves are given in Fig. 5 and the characteristic
thermogravimetric data are summarized in Table 2.
ꢀ
1
the appearance of bands in the range of 536 cm due to n(Cu-N).
The electronic spectra of the free ligand in DMF solution,
recorded in the 250–800 nm region, exhibit bands in the range
The TG curves showed that the thermal decomposition of the
ligand takes place in two steps, indicating that the different
groups lead to a decrease in stability. There was no evidence of
2
50–280 and 350 nm, which can be assigned to the p!p* and
n!p* transitions, respectively, of the azomethine group. The
spectrum of SB-Cu(II) showed three absorption bands. The first
one, at 340–350 nm, can be assigned to the O-Cu charge-
transfer transition. The band situated at 420–430 nm can be
attributed to the N-Cu charge-transfer transition, being over-
lapped by the p*!p or n!p transitions of the ligand. A new
band observed as a shoulder in the spectrum at 540–550 nm
can be assigned to the d!d transition of the divalent copper(II)
ꢁ
weight loss before 100 C, indicating absence of water in the SB.
ꢁ
The mass loss within the 100–350 C temperature range indicates
the decomposition of the fully organic part and may be
attributed to the loss of N and aliphatic groups.
2
[
24]
with square-planar geometry.
NMR Spectroscopy
1
The H NMR spectrum of the ligand and the SB-Cu(II) complex were
recorded to confirm the binding of the Schiff base to the metal
ions. The spectrum of the complex showed a peak at 9.52 ppm,
which has been assigned to the azomethine proton (-HC N). The
position of the azomethine signal in the complex is downfield in
comparison with that of the free ligand, suggesting deshielding
of the azomethine proton due to its coordination to metal ions
through the azomethine nitrogen. The 6.70–7.90 ppm region was
assigned to chemical shifts for hydrogen of the ligand symmetrical
aromatic ring and peaks in the 6.2–6.7ppm region were assigned
[
25]
1
to the chemical shift of the pyridine hydrogen. In the H NMR
spectrum of the Schiff base, the phenolic OH signal at 13.99 ppm
is evidenced. This signal disappeared in the spectrum of the
complex, indicating deprotonation of phenolic proton and
confirming coordination through phenolic oxygen. A weak peak
in the 4.5–5.2 ppm region, characteristic of the physical bonded
[
25]
water molecule, is observed in the spectrum of the complex.
13
C NMR of SB shows signals at 164.41 ppm assigned to C7
carbon, 160.8 ppm assigned to C1 carbon, 157.47 ppm assigned
to C12 carbon, 148.95 ppm assigned to C8 carbon, 138.98 ppm
assigned to C6 carbon, 134.03 ppm assigned to C10 carbon,
1
33.19 ppm assigned to C3 carbon, 122.88 ppm assigned to C4
carbon, 119.68 ppm assigned to C11 carbon, 119.3 ppm assigned
to C5 carbon, 118.98 ppm assigned to C2 carbon and 116.67 ppm
assigned to C9 carbon (Fig. 4).
Figure 5. TG/DTG curves of SB (black line) and SB-Cu (II) complex (red line)
Appl. Organometal. Chem. 2012, 26, 356–361
Copyright © 2012 John Wiley & Sons, Ltd.
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G. Tantaru et al.
Table 2. Thermogravimetric data of SB and SB Cu(II) complex
Sample
SB
SB-Cu (II)
ꢁ
Step I
T
T
T
T
T
onset ꢀ Tpeak ꢀ Tendset ( C)
—
41.1 ꢀ 63.4 ꢀ 120.6
ΔW (%)
—
2.3
ꢁ
Step II
Step III
Step IV
Step V
onset ꢀ Tpeak ꢀ Tendset ( C)
—
120.6 ꢀ 165.2 ꢀ 187.3
ΔW (%)
—
6.4
ꢁ
onset ꢀ Tpeak ꢀ Tendset ( C)
100 ꢀ 201.6 ꢀ 237.9
187.3 ꢀ 200.2 ꢀ 243.8
ΔW (%)
39.7
5.1
ꢁ
onset ꢀ Tpeak ꢀ Tendset ( C)
237.9 ꢀ 263.8 ꢀ 350.5
243.8 ꢀ 290.0 ꢀ 347.7 infl-567.0
ΔW (%)
34.6
—
34.2
ꢁ
onset ꢀ Tpeak ꢀ Tendset ( C)
597.7 ꢀ 672.2 ꢀ 794.1
ΔW (%)
—
6.6
Residue
25.7
45.4
ΔW, weight loss.
The thermogram of Cu(II) complex exhibits several thermal
a
Table 3. Antimicrobial activity of the tested compounds
ꢁ
events. The first weight loss of 2.31% in the 40–110 C temperature
ꢁ
Antimicrobial SB SB-Cu(II) C 30 mg T 30 mg OF 5 mg N 100 mg
range and second weight loss of 6.45% in the 120–180 C
agents
temperature range corresponded to the loss the physical bonded
ꢁ
water molecules. A rapid weight loss was observed after 180 C, in-
B. cereus
B. subtilis
S. aureus
MRSA
27
25
24
20
37
25
34
34
32
28
40
39
38
26
25
25
22
—
32
30
33
28
18
28
—
35
30
30
25
20
28
—
—
—
—
—
—
—
26
dicating the decomposition of coordinated ligand. The broad band
ꢁ
obtained after heating the complex above 570 C corresponds to
the formation of stable CuO.
Klebsiella spp. 28
E. coli
22
40
C. albicans
Toxicological Study
a
C, chloramphenicol; T, tetracycline; OF, oflloxacin; N, nystatin.
For SB and SB-Cu(II) complex (Fig. 6) several doses were used (100,
ꢀ
1
ꢀ1
2
00,400 and 800mgkg b.w.). The 800mgkg dose induced
sudden death due to convulsive phenomena. From analysis of
Regarding the ligand, we have noticed a efficient action of chlor-
amphenicol, tetracycline and ofloxacin on Staphylococcus aureus,
methicillin-resistant Staphylococcus aureus, Escherichia coli, and
Klebsiella spp. The SB- Cu(II) complex is more active than SB as a
bidentate ligand with coordination involving the -OH and the
nitrogen atom of C N groups. SB does not have a effective activity
in relation to B. cereus and B. subtilis. SB-Cu(II) is efficient against
B. cereus, S. aureus, MRSA, E. coli and Klebsiella spp. The strongest
activity is noticed in relation to C. albicans. The cations involved
in the complex intensify the action compared to Schiff base.
ꢀ
1
the regression lines the LD50 for SB = 115.39 ꢃ 88.16 mgkg b.w.
Y = 0.174 + 1.728X, R = 0.669) and for SB-Cu(II) = 620.62ꢃ 250.45
(
ꢀ
1
mgkg
b.w.(Y = 1.185 + 1.850X, R = 0.901), which indicates a
low toxicity for SB and a very low toxicity for SB-Cu(II). For SB and
SB-Cu(II) the use of doses higher than LD50 will induce central
nervous phenomena which create significant discomfort.
Antibacterial Activity
Conclusions
Antimicrobial activity is estimated by measuring the diameter of
the area inhibited by the tested compounds (Table 3). These
results, attributed to the structure of the tested compounds,
seemed to be the principal factor influencing antibacterial
activity. This property is certainly correlated with the ability of a
compound to diffuse through the biological membranes and
reach its site of action.
This research reports the successful synthesis and antimicrobial
activity of new Schiff bases complexes with Cu(II) ions. Schiff base
and its Cu(II) complex were physicochemically and chemically char-
1
acterized through elemental analyses, FT-IR, H and 13C NMR and
UV–visible spectroscopy. These confirmed the ratio of metal/ligand
combination, melting point, solubility and stability of the SB-Cu(II)
complex.
The antimicrobial activity of this complex was tested in
comparison with the activity of the Schiff base on the following
strains: S. aureus, MRSA, B. cereus, B. subtilis, E. coli, C. albicans
and Klebsiella spp. This activity was also compared with the
activity of the reference drugs (chloramphenicol, tetracycline,
ofloxacin and nystatin) on the above-mentioned strains.
All tested compounds were very active against both Gram-positive
and Gram-negative bacteria.
The comparative study of the antimicrobial activity of a new
Schiff base and of complex combination with metallic cations
proves the fact that both manifested an antimicrobial action
Figure 6. Regression line for SB and SB-Cu(II)
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Properties of the Cu(II) complex of SB derived from SAP
[
10] B. Geeta, K. Shravankumar, P. Muralidhar Reddy, E. Ravikrishna,
Spectrochim. Acta Part A 2010, 77, 911.
11] R. S. Hunoor, B. R. Patil, D. S. Badigera, R. S. Vadavi, K. B. Gudasi, V. M.
Chandrashekhar, I. S. Muchchandi, Spectrochim. Acta Part A 2010, 77,
838.
comparable with the reference drugs chloramphenicol, tetracy-
cline, ofloxacin and nystatin. However, the complex is more
active than the Schiff base, due to the complex generator and
structure.
[
[
12] N. Raman, Y. Pitchaikani Raja, A. Kulandaisamy, J. Chem. Sci. 2001,
1
13, 183.
Acknowledgments
[
13] P. Singh, R. L. Goel, B. P. Singh, J. Indian Chem. Soc. 1975, 52, 958.
M. C. Popescu acknowledges the financial support of the European
Social Fund ’Cristofor I. Simionescu’ Postdoctoral Fellowship
Programme (ID POSDRU/89/1.5/S/55216), Sectoral Operational
Programme Human Resources Development 2007–2013.
[14] A. M. Mahindra, J. M. Fisher, Rabinovitz Nature (London) 1983, 303,
4.
6
[
[
[
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1
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4 November, 1986.
[19] AVMA Guidelines on Euthanasia, June, 2007.
[
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