Synthesis, crystal structures and antibacterial studies of oxidovanadium(IV) complexes of salen-type Schiff base ligands derived from meso-1,2-diphenyl-1,2-ethylenediamine

Article abstract of DOI:10.1007/s11243-014-9798-9

A series of new derivatives and previously reported Schiff base ligands and their oxidovanadium(IV) complexes were synthesized, characterized and tested as potential antibacterial agents against four human pathogenic bacteria. These N₂O₂ type Schiff base ligands were derived from the condensation of meso-1,2-diphenyl-1,2-ethylenediamine with different salicylaldehyde derivatives, and their metal complexes were obtained from the reaction of these ligands with bis(acetylacetonato)oxidovanadium(IV). Our studies showed that the metal complexes had moderate antibacterial activity, and this activity was higher than that of the free ligands against both Gram-positive and Gram-negative bacteria. Besides, it was found that the presence of more substituents on the ligands increases the antibacterial activities of both the free ligands and their complexes. The crystal structures of H₂L⁴ and its corresponding complex VOL⁴ were determined by X-ray crystallography.

Full text of DOI:10.1007/s11243-014-9798-9

Transition Met Chem (2014) 39:253–259
DOI 10.1007/s11243-014-9798-9
Synthesis, crystal structures and antibacterial studies
of oxidovanadium(IV) complexes of salen-type Schiff base ligands
derived from meso-1,2-diphenyl-1,2-ethylenediamine
•
Omid Taheri Mahdi Behzad Abolfazl Ghaffari Maciej Kubicki
•
•
•
•
Grzegorz Dutkiewicz Abolfazl Bezaatpour Hossein Nazari
•
•
•
Ali Khaleghian Abolfazl Mohammadi Mehdi Salehi
•
Received: 24 November 2013 / Accepted: 9 January 2014 / Published online: 21 January 2014
ꢀ Springer International Publishing Switzerland 2014
Abstract A series of new derivatives and previously
reported Schiff base ligands and their oxidovanadium(IV)
complexes were synthesized, characterized and tested as
potential antibacterial agents against four human patho-
genic bacteria. These N2O2 type Schiff base ligands were
derived from the condensation of meso-1,2-diphenyl-1,2-
ethylenediamine with different salicylaldehyde derivatives,
and their metal complexes were obtained from the reaction
of these ligands with bis(acetylacetonato)oxidovanadi-
um(IV). Our studies showed that the metal complexes had
moderate antibacterial activity, and this activity was higher
than that of the free ligands against both Gram-positive and
Gram-negative bacteria. Besides, it was found that the
presence of more substituents on the ligands increases the
antibacterial activities of both the free ligands and their
complexes. The crystal structures of H2L4 and its corre-
sponding complex VOL4 were determined by X-ray
crystallography.
Introduction
Vanadium chemistry has attracted great interest for several
decades [1–7]. An especially considered class of vana-
dium-containing compounds is oxidovanadium(IV) Schiff
base complexes. This interest comes from their antibacte-
rial [8–10], insulin mimetic [11–13], anticancer [14, 15]
and catalytic properties [16, 17]. The wide variety of Schiff
base ligands and their metal complexes, thanks to their
easy synthesis and structural diversity as well as to the
possibility of fine tuning of steric and electronic properties,
has made it possible to identify several factors affecting
such activities. This has led to the development of new
industrially important catalysts and novel antibacterial
agents relevant to global issues such as bacterial resistance
[18]. In continuation of our studies on the antibacterial
activity of transition metal complexes derived from Schiff
base ligands, herein, we report the synthesis, character-
ization and results of antibacterial activity studies on a
series of N2O2 type Schiff base ligands and their oxido-
vanadium(IV) complexes (Fig. 1). The Schiff base ligands
were synthesized from the condensation of meso-1,2-
diphenyl-1,2-ethylenediamine with salicylaldehyde deriv-
atives. The oxidovanadium(IV) complexes were synthe-
sized from the reaction between these ligands and
bis(acetylacetonato)oxidovanadium(IV). Crystal structures
of one of the ligands (H2L4) and the corresponding com-
plex (VOL4) were also determined. The in vitro antimi-
crobial activity of the complexes was tested against four
human pathogenic bacteria, namely Escherichia Coli
(Gram negative), Salmonella typhi (Gram negative),
Staphylococcus aureus (Gram positive) and Bacillus sub-
tilis (Gram positive). Our studies revealed that these
complexes were moderately active against both Gram-type
bacteria, although they were more active against the Gram
O. Taheri ꢀ M. Behzad (&) ꢀ A. Ghaffari ꢀ M. Salehi
Department of Chemistry, Semnan University,
35351-19111 Semnan, Iran
e-mail: mbehzad@semnan.ac.ir; mahdibehzad@gmail.com
M. Kubicki ꢀ G. Dutkiewicz
Department of Chemistry, Adam Mickiewicz University,
Grunwaldzka 6, 60-780 Poznan, Poland
A. Bezaatpour
Department of Chemistry, Faculty of Basic Science, University
of Mohaghegh, Ardabili 179, Ardabil, Iran
H. Nazari ꢀ A. Khaleghian ꢀ A. Mohammadi
Biochemistry Department, Faculty of Medicine, Semnan
University of Medical Science, Semnan, Iran
123

254
Transition Met Chem (2014) 39:253–259
Fig. 1 Schematic
representation of the synthetic
procedure of the ligands (H2Lx)
and complexes VOLx
Ligands or complexes
H2L1, VOL1
X
H
Y
H
H
H
H
H
H
H
Z
H
T
H
H
H
H
H
H
H
H2L2, VOL2
OCH3
H
H
H2L3, VOL3
OCH3
Br
H2L4, VOL4
H
H2L5, VOL5
H
Cl
H2L6, VOL6
OCH3
Br
Br
H2L7, VOL7
Cl
positive ones. Besides, VOL6 and VOL7 complexes with
more substituents on their ligands showed higher antibac-
terial activity.
instrument was employed to obtain cyclic voltammograms
in DMSO solutions at room temperature (25 ꢁC) under
nitrogen atmosphere using 0.1 M tetra-n-butylammonium
hexafluorophosphate (TBAHFP) as supporting electrolyte.
A platinum working electrode, a platinum auxiliary elec-
trode and an Ag/AgCl reference electrode were used to
obtain cyclic voltammograms.
Experimental
All chemicals were purchased from commercial sources
and were used as received. Meso-1,2-diphenyl-1,2-ethy-
lenediamine [19], the ligands [H2Lx, x = 1–5] and their
VO(IV) complexes [VOLx, x = 1–5] were synthesized as
described elsewhere [20, 21]. Melting points were obtained
on a thermoscientific 9,100 apparatus. Elemental analyses
were performed by using a Perkin-Elmer 2400II CHNS-O
Synthesis of N,N0-bis(3-methoxy-5-bromosalicylidene)-
1,2-diphenyle-1,2-ethylenediamine (H2L6)
This ligand was synthesized following a routine procedure
[20]. In a typical experiment, to a vigorously stirred solu-
tion of meso-1,2-diphenyl-1,2-ethylenediamine (0.21 g,
1 mmol) in ethanol (25 mL) was added a solution of
3-methoxy-5-bromosalicylaldehyde (0.46 g, 2 mmol) in
ethanol (40 mL). The reaction mixture was stirred and
refluxed for 1 h, then the heating source was removed and
the reaction mixture was left undisturbed overnight. The
orange crystals of the target ligand were collected by
1
analyzer. HNMR spectra were recorded on a 500 MHz
Bruker FT-NMR spectrometer using CDCl3 or DMSO-d6
as solvent; chemical shifts (d) are given in ppm. IR spectra
were obtained as KBr plates using a Bruker FT-IR instru-
ment. UV–Vis spectra were obtained on a Shimadzu UV-
1650PC spectrophotometer.
A
Metrohm 757 VA
123

Transition Met Chem (2014) 39:253–259
255
filtration, washed with diethyl ether and air dried. Yield:
1
0.60 g, 94 %. HNMR (CDCl3): 14.10 (br, 2H, OH); 7.98
C28H18Br2Cl2N2O3V, C: 47.2; H: 2.5, N: 3.9.Found, C:
47.5; H: 2.7, N: 3.7.
(s, 2H, CHN); 7.38–7.25 (m, 10H, HAr); 7.00 (d, 2H, HAr);
6.86 (d, 2H, HAr); 4.77 (s, 2H, CHPh); 3.92 (s, 6H, OCH3).
X-ray crystallography
Selected IR (cm-1): 1,627 (CH=N). UV–Vis. 10-4
M
solution in CH2Cl2 [kmax nm, (e M-1 cm-1)]: 279 (22,650),
347 (6,940). Anal. Calcd. for C30H26Br2N2O4, C: 56.4; H:
4.1, N: 4.4. Found C: 56.5; H: 4.1, N: 4.5.
Diffraction data were collected at room temperature by the
x-scan technique on an Oxford Diffraction Xcalibur four-
circle diffractometer with Eos CCD detector, equipped
with graphite-monochromatized MoKa radiation source
˚
(k = 0.71,073 A). The data were corrected for Lorentz-
Synthesis of N,N0-bis(3-bromo-5-chlorosalicylidene)-
polarization as well as for absorption effects [22]. Precise
unit-cell parameters were determined by a least-squares fit
of 1,430 (1) and 2,641 (2) reflections of the highest
intensity, chosen from the whole experiment. The struc-
tures were solved with SIR92 [23] and refined with the full-
matrix least-squares procedure on F2 by SHELXL97 [24].
1,2-diphenyle-1,2-ethylenediamine (H2L7)
This ligand was also synthesized following a procedure
similar to that of H2L6 except 3-bromo-5-chlor-
osalicylaldehyde was used instead of 3-methoxy-5-bro-
1
mosalicylaldehyde. Yield 0.62 g, 96 %. HNMR (DMSO-
The scattering factors incorporated in SHELXL97 were
d6): 7.91 (s, 2H, CHN); 7.51 (d, 2H, HAr); 7.33–7.23 (m,
10H, HAr); 7.02 (d, 2H, HAr); 4.76 (s, 2H, CHPh). Selected
IR (cm-1): 1,627 (CH=N). UV–Vis. 10-4 M solution in
CH2Cl2 [kmax nm, (e M-1 cm-1)]: 276 (18,980), 341
(12,150). Anal. Calcd. for C28H20Br2Cl2N2O2, C: 52.0; H:
3.1, N: 4.3. Found C: 52. 2; H: 3.2, N: 4.5.
P
used. The function
w(|Fo|2 - |Fc|2)2 was minimized,
with w-1 = [r2(Fo)2 ? (AꢀP)2 ? BꢀP] (P = [Max (F2o,
0) ? 2F2c]/3). All non-hydrogen atoms were refined
anisotropically. All hydrogen atoms—except OH H12
atom in 1, which was freely refined—were inserted in
idealized positions and refined riding with the atoms to
which they were bonded.
Synthesis of {N,N0-bis(3-methoxy-5-
bromosalicylaldiminato)-1,2-diphenyle-1,2-
ethylenediamine}oxidovanadium(IV) (VOL6)
Antibacterial activity studies
Bacterial strains
To a vigorously stirred solution of H2L6 (0.32 g, 0.5 mmol)
in boiling ethanol (50 mL) was added a solution of
bis(acetylacetonato)oxidovanadium(IV) (0.14 g, 0.5 mmol)
in ethanol (25 mL). The reaction mixture was refluxed for
1 h, and then the green solution was left undisturbed
overnight until the green microcrystalline target compound
precipitated. The crystals were collected by filtration,
washed with cold ethanol (20 mL) and air dried. Yield:
0.31 g, 88 %. Selected IR (cm-1): 1,612 (CH=N), 995
(V=O). UV–Vis. 10-4 M solution in CH2Cl2 [kmax nm, (e
M-1 cm-1)]: 283 (27,230), 299.5 (27,090), 401 (7,660),
609 (180). Anal. Calcd. for C30H24Br2N2O5V, C: 51.1; H:
3.4, N: 4.0. Found: C: 51.3; H: 3.7, N: 4.1.
The metal complexes were tested against a panel of
microorganisms, namely Salmonella typhi (ATCC 19430,
Gram negative); Escherichia Coli (ATCC 25922, Gram
negative); Staphylococcus aureus (ATCC 25923, Gram
positive); and Bacillus subtilis (ATCC No. 6633, Gram
positive).
Determination of minimum inhibitory concentrations
(MIC) and minimal bactericidal concentrations (MBC)
Minimum inhibitory concentrations (MICs, mg/mL) were
determined by the broth microdilution method following
the procedures recommended by the National Committee
for Clinical Laboratory Standards [25, 26]. MICs were
defined as the lowest concentrations of compounds which
inhibit the growth of microorganisms. All tests were per-
formed in triplicate. Minimal bactericidal concentrations
(MBCs) were also measured following a standard proce-
dure [27]. Then, 100 lL volumes of all clear (no growth)
tubes from a dilution MIC test were spread onto separate agar
plates and incubated at 37 ꢁC for 24 h. The MBC (mg/mL)
was defined as the lowest concentration of the complex at
which no growth occurred.
Synthesis of {N,N0-bis(3-Bromo-5-
chlorosalicylaldiminato)-1,2-diphenyle-1,2-
ethylenediamine}oxidovanadium(IV) (VOL7)
This compound was synthesized following a procedure
similar to that of VOL6 except H2L7 was used instead of
H2L6. Yield: 0.31 g, 86 %. Selected IR (cm-1): 1,604
(CH=N), 995 (V=O). UV–Vis. 10-4 M solution in
CH2Cl2[kmax nm, (e M-1 cm-1)]: 277 (19,790), 290.5
(19,950), 390.5(9,330), 606 (163). Anal. Calcd. for
123

256
Transition Met Chem (2014) 39:253–259
Table 1 Redox potential data for 10-3 mol L-1 solution of VOLx
(x = 4, 6, 7) in DMSO containing 0.1 mol L-1 TBAHFP and scan
rate 50 mV/s. Potentials are versus Ag/AgCl
Results and discussions
Synthesis
Complex
E0 (mV)
Epc (mV)
Epa (mV)
DE (mV)
The reaction between meso-1,2-diphenyl-1,2-ethylenedia-
mine and different salicylaldehyde derivatives yielded the
target Schiff base ligands in good yield. Typically, a color
change to yellow or orange showed the proceeding of the
reaction, and the completion of the reaction was deter-
mined by TLC. The reaction between the tetradentate
Schiff base ligands and bis(acetylacetonato)oxidovanadi-
um(IV) in ethanol gave the oxidovanadium(IV) Schiff base
complexes as green microcrystalline compounds. The
green color of the complexes is indicative of their mono-
meric form [28]. The elemental analyses also confirmed the
synthesis of the complexes.
VOL6
VOL4
VOL7
515
560
620
470
506
590
560
614
650
90
108
60
Electrochemistry
Cyclic voltammetry studies were performed in DMSO
solutions at room temperature (25 ꢁC) using 0.1 M tetra-n-
butylammonium hexafluorophosphate (TBAHFP) as sup-
porting electrolyte. A platinum working electrode, a plat-
inum auxiliary electrode and an Ag/AgCl reference
electrode were used to obtain cyclic voltammograms. The
electrochemical properties of VOL1–5 complexes are pre-
viously reported [20, 21]. The redox data for VOL6 and
VOL7 complexes are collected in Table 1. The electro-
chemical data for VOL4 in DMSO are also shown in this
table for comparison. Cyclic voltammetry studies of oxi-
dovanadium(IV) Schiff base complexes usually exhibit a
reversible or quasi-reversible redox wave for VIV/VV pro-
cess. It has been shown that the presence of electronegative
substituents on the Schiff base ligands shifts the E0 of the
occurred VIV/VV process to more positive values [20, 21].
The same results were observed in this study.
Spectroscopic characterization of the ligands
and complexes
In the 1HNMR spectra of the free Schiff base ligands, a broad
(br) band at around 14 ppm was assigned to the phenolic OH
protons. This signal was not observed for H2L7 which is
expected and is due to the broadening of the band by rapid
exchange processes. The sharp singlet (s) signals at around
8 ppm were assigned to the azomethine protons. The aro-
matic protons of the phenyl rings of the meso-diamine
appeared in the aromatic region at around 7.2–7.4 ppm as
multiplets (m). The aromatic signals of the salicylaldehyde
part of the Schiff base ligands were also observed in the
aromatic region of the spectra as doublets (d).
X-ray crystallography
In the IR spectra of the ligands, the presence of an
intense band at 1,627 cm-1 was indicative of the formation
and presence of iminic groups (CH=N). This band was
shifted to lower wave numbers upon coordination to the
metal center which meant that the iminic nitrogen atoms of
the Schiff base ligands were participating in coordination.
The vanadyl (V=O) stretching vibration at 995 cm-1 was
suggestive of the absence of any intermolecular
(…V=O…V=O…) interactions. This indicated the mono-
meric form of the complexes, while the polymeric forms
usually give this band at around 850–880 cm-1 [28]. The
UV–Vis spectra of the free ligands were similar to those of
previously reported spectra for similar ligands. The intense
bands at around 270 and 341 nm were assignable to the
p ? p* transitions in the Schiff base ligands. The second
band that was blue shifted by about 40 nm in VOLx
complexes was assigned to the p ? p* transitions of
azomethine groups. This blue shift was due to the coordi-
nation to the VO(IV) metal center. The bands at around
400 and 600 nm are also assigned to the LMCT and
d ? d transitions, respectively [29].
Description of the crystal structures
Crystallographic data and final structure refinement
parameters for both structures are collected in Table 2.
Selected bond lengths and angles for VOL4 are listed in
Table 3. Figure 2 shows a perspective view of the ligand
H2L4. The molecule is Ci-symmetrical, and the middle
point of the C1–C1 (-x, 1 - y, 1 - z) bond lies on the
center of inversion. There are classical intramolecular
N–HꢀꢀꢀO hydrogen bonds between the hydrogen atoms of the
OH groups and nitrogen atoms in meso-1,2-diphenyl-1,2-
ethylenediamine (Table 4). The dihedral angle between the
planes defined by the rings of the salicylidene fragment and
the phenyl substituent is 30.41(6)ꢁ, compared to just 23.8ꢁ
in H2L1 and 63.76ꢁ in the (-)-(1S,2S) isomer [30, 31]. An
ORTEP representation of VOL4 is shown in Fig. 3. The
asymmetric unit of VOL4 consists of two crystallographi-
cally independent, but chemically identical and geometri-
cally very similar complexes that, however, show some
differences in their environment. The V(IV) atom is five-
coordinated in a distorted square-pyramidal environment.
123

Transition Met Chem (2014) 39:253–259
257
Table 2 Crystal data, data collection and structure refinement
parameters for H2L4 and VOL4
Table 3 Selected geometrical parameters for VOL4
˚
Bond lengths (A)
Compound
H2L4
VOL4
O1A-V1A-O12A
O1A-V1A-O28A
O1A-V1A-N8A
O1A-V1A-N24A
O12A-V1A-O28A
Bond angles (ꢁ)
V1A-O1A
109.42 (17) O12A-V1A-N8A
86.23 (14)
108.33 (16) O12A-V1A-N24A 146.14 (15)
Empirical formula
Formula weight
Crystal system
Space group
C28H22Br2N2O2
578.30
C28H20ꢀBr2N2O3V
643.22
106.54 (17) O28A-V1A-N8A
103.95 (16) O28A-V1A-N24A
86.43 (14)
144.85 (15)
88.48 (15)
Triclinic
P-1
Triclinic
P-1
˚
Unit-cell dimensions (A, ꢁ)
1.593 (3)
1.919 (3)
2.043 (4)
V28A-O28A
V1A-N8A
1.928 (3)
2.049 (4)
a
6.5028 (9)
11.9421 (6)
13.1778 (8)
16.9847 (7)
91.345 (4)
96.935 (4)
100.877 (5)
2602.7 (2), 4
1.64
V1A-O12A
b
c
9.5765 (13)
11.1719 (16)
103.090 (12)
104.410 (12)
105.616 (12)
616.00 (17), 1
1.56
V1A-N24A
a
b
c
3
˚
Volume (A ), Z
Calculated density
(g cm-3
)
Absorption coefficient
(mm-1
F(000)
3.32
290
3.48
)
1,276
h Range for data collection 3.36–28.04
(ꢁ)
2.82–28.44
Limiting indices
-7 B h B 7
-15 B h B 13
-17 B k B 17
-22 B l B 22
-12 B k B 12
-13 B l B 14
Reflections
Fig. 2 Perspective view of the H2L4; displacement ellipsoids are
drawn at 50 % probability level, hydrogen atoms are shown as
spheres of arbitrary radii. Intramolecular hydrogen bonds are shown
as blue lines. The non-labeled part is related by the symmetry
operation -x, 1 - y, 1 - z to the labeled one. (Color figure online)
Collected
4,070
18,090
Unique (Rint)
With I [ 2r(I)
2,485 (0.030)
2,001
10,853 (0.040)
5,923
Number of parameters/
restrains
158/0
649/0
Goodness of fit on F2
1.032
1.03
˚
Table 4 Hydrogen bond geometry (A, ꢁ)
Final R index [I [ 2r(I)] R1 = 0.0392,
wR2 = 0.0794
R1 = 0.0651,
wR2 = 0.0935
D—HꢀꢀꢀA
D—H
HꢀꢀꢀA
DꢀꢀꢀA
DHA
H2L4
R index [all data]
R1 = 0.0540,
wR2 = 0.0874
R1 = 0.1391,
wR2 = 0.1162
O12-H12ꢀꢀꢀN8
0.72 (5) 2.02 (5) 2.640 (4) 145 (5)
Largest difference peak
-3
0.34/-0.45
1.055/-1.166
VOL4
˚
and hole (e A
)
C1A -H1AꢀꢀꢀO1Bi
C9A-H9BꢀꢀꢀO28Bi
C17B-H17BꢀꢀꢀO1Aii
C22A –H22AꢀꢀꢀO1Biii
0.98
0.93
0.98
0.93
2.30
2.58
2.44
2.44
2.34
3.255 (6) 166
3.474 (6) 161
3.390 (6) 162
3.147 (9) 133
3.260 (6) 170
The basal square plane is constituted by the two iminic
nitrogen atoms and two phenoxide oxygen atoms of the
Schiff base ligand, H2L4, which acts as a dianionic tetra-
dentate ligand. The apical position is occupied with the oxo
ligand. The bond angles in the basal plane of the complex
are all smaller than the ideal angle of 90ꢁ, whereas the
vertex angles are larger than 90ꢁ as a result of the central
vanadium atom deviating from the basal plane toward the
axial ligand. The average V–Oax and V–Oeq as well as
V–Neq bond lengths for this complex are quite similar to
the ones observed similar structures [28]. In the crystal
C25B –H25BꢀꢀꢀO12Aii 0.93
i
Symmetry codes: x,1 ? y, z; -1?x,y,z; -x, - y, - z
ii
iii
structure, VOL4 is connected with infinite chains along the
c axis by weak intermolecular hydrogen bonds (Table 4).
Antibacterial studies
The synthesized oxidovanadium(IV) Schiff base com-
plexes were screened for in vitro antibacterial activity
123

258
Transition Met Chem (2014) 39:253–259
enhances the penetration of the complexes into the lipid
membrane and increases their antibacterial activities.
These complexes showed broad spectrum antibacterial
activity against both Gram-positive and Gram-negative
bacteria. Comparison of the MIC values of these com-
plexes with those of similar ones in the literature shows
that the studied complexes are moderate antibacterial
agents [34]. It has been previously suggested that the pre-
sence of more electronegative or electron-donating groups
on the ligands results in increased antibacterial activity of
the ligands themselves and their metal complexes [35]. Our
studies also confirmed this suggestion. H2L1 with no sub-
stituents on the salicylaldehyde moiety has the least anti-
bacterial activity (Table 5). The presence of other
substituents on the ligands increased their antibacterial
activity and H2L6 and H2L7 with two substituents on the
salicylaldehyde moiety showed the highest activities. The
complexes also showed similar features, and VOL6 and
VOL7 showed highest antibacterial activities. This
increased activity could also be described by the penetra-
tion theory. The presence of more substituents, especially
halogen substituents, increases the lipophilicity of the
ligands and their complexes and hence increases the
membrane penetration and antibacterial activities. The
electrochemistry of the complexes could also affect the
antibacterial properties of the complexes. As it is previ-
ously stated, the presence of more electronegative substit-
uents shifts the E0 value of VIV/VV redox process to more
positive values. This is itself due to the electron deficiency
of the central metal atom. This electron deficiency may
increase the interaction of the complexes with the bacteria
and increase their antibacterial properties. However, more
Fig. 3 Perspective view of one (A) of the symmetry-independent
complexes of VOL4 with labeling scheme. Displacement ellipsoids
are drawn at 50 % probability level; hydrogen atoms are shown as
spheres of arbitrary radii
against two Gram-negative (E. coli and S. typhi) and two
Gram-positive (S. aureus and B. Subtilis) bacterial strains
according to the literature protocol [25–27], and the results
are collected in Table 5. According to this data, the com-
plexes showed higher antibacterial activities than the free
ligands. This increased activity results from coordination
and could be explained by Overtone’s concept [32] and
Tweedy’s theory [33]. According to Overtone’s concept of
cell permeability, lipo-solubility is an important factor that
governs the antimicrobial activity of antibacterial agents.
Chelation reduces the polarity of the metal ions to a greater
extent due to the overlap of the ligand orbitals and partial
sharing of positive charge of metal atom with donor
groups. Besides, it increases the delocalization of p-elec-
trons over the whole chelate ring and increases the lipo-
philicity of the complexes. This increased lipophilicity
Table 5 MIC and MBC values for the ligands and complexes against the studied bacteria (mgL-1
)
Escherichia coli Salmonella Typhi Staphylococcus aureus
Bacillus subtilis
MIC
MBC
MIC
MBC
MIC
MBC
MIC
MBC
L1
L2
L3
L4
L5
L6
L7
VOL1
VOL2
VOL3
VOL4
VOL5
VOL6
VOL7
4.75
4.50
4.00
3.75
2.50
2.00
2.25
3.50
3.75
3.25
3.00
3.50
2.00
2.75
5.00
4.75
4.25
4.00
3.00
2.50
2.75
4.00
4.00
3.75
3.50
4.00
2.25
3.00
4.25
4.00
3.50
3.25
2.00
1.25
1.25
3.25
3.25
2.75
1.75
2.75
1.25
2.50
4.75
4.25
4.00
3.50
2.50
1.50
1.50
3.75
3.50
3.25
2.00
3.00
1.50
2.75
2.50
1.50
1.25
1.25
0.50
0.22
0.25
1.50
0.75
0.62
0.25
0.62
0.02
0.08
2.75
1.75
1.00
1.75
0.75
0.25
0.38
1.75
1.00
0.75
0.50
0.70
0.05
0.12
2.75
2.00
1.75
1.50
0.50
0.40
0.50
1.50
1.00
0.75
0.50
0.75
0.08
0.12
3.00
2.25
2.00
1.75
0.75
0.65
0.75
1.75
1.25
1.00
0.75
1.25
0.10
0.25
123

Transition Met Chem (2014) 39:253–259
259
13. Adachi Y, Yoshida J, Kodera Y, Katoh A, Takada J, Sakurai H
(2006) J Med Chem 49:3251–3256
14. Lu J, Guo J, Sang W, Guo H (2013) Trans Met Chem 38:481–488
15. Bian L, Li L, Zhang Q, Dong J, Xu T, Li J, Kong J (2012) Trans
Met Chem 37:783–790
work is required to find clear structural, electronic and
electrochemical correlation with antibacterial properties of
such antibacterial agents. It might be also mentioned that
the complexes we have studied showed better activity
against Gram-positive bacteria.
16. DaSilva JAL, DaSilva JJRF, Pombeiro AJL (2011) Coord Chem
Rev 255:2232–2248
17. Licini G, Conte V, Coletti A, Mba M, Zonta C (2011) Coord
Chem Rev 255:2345–2357
Supplementary material
18. Theuretzbacher UJ (2013) Glob Antimicrob Resist 1:63–69
19. Irving MNH, Parkins RM (1965) J Inorg Nucl Chem 27:270
20. Ghaffari A, Behzad M, Dutkiewicz G, Kubicki M, Salehi M
(2012) J Coord Chem 65:840–855
21. Boghaei DM, Bezaatpour A, Behzad M (2007) J Coord Chem
60:973–983
22. Oxford Diffraction (2009) CRYSALIS PRO, Version
1.171.33.36d, Oxford Diffraction Ltd., Yarn ton, Oxford shire
23. Altomare A, Cascarano G, Giacovazzo C, Gualardi A (1993) J
Appl Crystallogr 26:343–350
CCDC 894215 and 894216 contains the supplementary
crystallographic data for H2L4 and [VOL4]. These data can
be obtained free of charge from The Cambridge Crystal-
lographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
24. Sheldrick GM (2008) Acta Crystallogr Sect A 64:112–122
25. Clinical and Laboratory Standards Institute (2009) Performance
standards for antimicrobial susceptibility testing: Nineteenth
informational supplement M100–S19. Clinical and Laboratory
Standards Institute, Wayne
26. Goldman E, Green LH (2009) Practical handbook of microbiology,
2nd Edn 37–39. CRC Press, Taylor & Francis Group, New York
27. Bauer AW, Kirby WM, Sheris JC, Turck M (1966) Am J Clin
Pathol 45:493–496
28. Kojima M, Taguchi H, Tsuchimoto M, Nakajima K (2003) Coord
Chem Rev 237:183–196
29. Boghaei DM, Bezaatpour A, Behzad M (2006) J Mol Catal A
245:12–16
30. Senn R, Nowacki W (1977) Z Kristallogr 145:16–27
31. Korendovych IV, Rybak-Akimova EV (2003) Acta Crystallogr
Sect E 59:o-1498-o1500
32. Knopp P, Weighardt K, Nuber B, Weiss J, Sheldrick WS (2009)
Inorg Chem 29:363–371
33. Tweedy BG (1964) Phytopathology 55:910–914
34. Dharmaraj N, Viswanathamurthi P, Natarajan K (2001) Trans
Met Chem 26:105–109
35. Salehi M, Kubicki M, Dutkiewicz G, Rezaei A, Behzad M,
Etminani S (2013) Russ J Inorg Chem 39:716–722
References
1. Rehder D (2008) Bioinorganic vanadium chemistry. Wiley,
London
2. Thompson KH, Orvig C (2001) Coord Chem Rev 219:1033–1053
3. Butler A, Walker JV (1993) Chem Rev 93:1937–1944
´
4. Noshiranzadeh N, Mayeli M, Bikas R, Slepokura K, Lis T, Trans
Met Chem. doi:10.1007/s11243-013-9769-6
5. Ou GC, Yuan XY, Li ZZ (2012) Trans Met Chem 37:705–711
6. Ponnusamy S, Thangarajan DA, Mariappan P, Kasi R (2010)
Trans Met Chem 35:1019–1025
7. Hosseini-Monfared H, Farrokhi A, Alavi S, Mayer P (2013)
Trans Met Chem 38:267–273
8. Rosu T, Pahontu E, Stefana MR, Ilies DC, Georgescu R, Shova S,
Gulea A (2012) Polyhedron 31:352–360
9. Rehder D, Santoni G, Licini GM, Schulzke C, Meier B (2003)
Coord Chem Rev 237:53–63
10. Rosu T, Negoiu M, Pasculescu S, Pahontu E, Poirier D, Gulea A
(2010) Eur J Med Chem 45:774–781
11. Sheela A, Vijayaraghavan R (2010) Trans Met Chem 35:865–870
12. Rangel M (2001) Trans Met Chem 26:219–223
123