A novel oxido-vanadium(V) Schiff base complex: Synthesis, spectral characterization, crystal structure, electrochemical evaluation, and biological activity

Article abstract of DOI:10.1007/s11164-015-2045-y

A new oxido-vanadium(V) complex, [VO(L)(PrOH)(OPr)] (L = [(3-methoxy-2oxidobenzylidene)benzohydrazidato], PrOH = propanol, OPr = propanolato) has been synthesized and characterized by means of elemental analysis, Fourier transform infrared (FTIR), proton

Full text of DOI:10.1007/s11164-015-2045-y

Res Chem Intermed
DOI 10.1007/s11164-015-2045-y
A novel oxido-vanadium(V) Schiff base complex:
synthesis, spectral characterization, crystal structure,
electrochemical evaluation, and biological activity
S. Yousef Ebrahimipour1 Maryam Mohamadi2
•
•
Iran Sheikhshoaie1 Sebastian Suarez
Ricardo Baggio4 Moj Khaleghi5
3
•
•
´
´
•
Received: 10 November 2014 / Accepted: 2 April 2015
Ó Springer Science+Business Media Dordrecht 2015
Abstract
A new oxido-vanadium(V) complex, [VO(L)(PrOH)(OPr)] (L =
[(3-methoxy-2oxidobenzylidene)benzohydrazidato], PrOH = propanol, OPr =
propanolato) has been synthesized and characterized by means of elemental analysis,
Fourier transform infrared (FTIR), proton nuclear magnetic resonance (1HNMR),
ultaviolet-visible (UV–Vis) spectroscopy, voltammetry and molar conductivity
measurement. The structure of the complex has also determined using single crystal
X-ray diffraction. The geometric structure around the V(V) ion has been found to be
octahedral in which the positions around the central ion are occupied by ONO ligand
donors, oxido groups, and oxygen atoms of coordinated propanol and propoxide
group. Electrochemical behavior of this complex is also discussed in more details.
In vitro antimicrobial effect of the title complex has investigated exhibiting significant
activities against some Gram-positive (Staphylococcus aureus, Micrococcus luteus,
Bacillus cereus, Eterococcus faecalis) and Gram-negative bacteria (Pseudomonas
aeruginosa, Escherichia coli, Klebsiella sp, Pseudomonas sp) and fungus strain
(Candida albicans).
&
S. Yousef Ebrahimipour
Ebrahimipour@ymail.com; Ebrahimipour@uk.ac.ir
1
Department of Chemistry, Faculty of Science, Shahid Bahonar University of Kerman,
76169-14111 Kerman, Iran
2
3
Department of Chemistry, Payame Noor University (PNU), 19395-4697, Tehran, Iran
´
´
´
´
´
Departamento de Quımica Inorgınica, Analıtica y Quımica, Fısica/INQUIMAE–CONICET,
Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos Aires,
Argentina
4
5
´
Gerencia de Investigacion y Aplicaciones, Centro Atomico Constituyentes, Comision Nacional
de Energıa Atomica, Buenos Aires, Argentina
´
´
´
´
Department of Biology, Faculty of Science, Shahid Bahonar University of Kerman, Kerman,
Iran
123

S. Yousef Ebrahimipour et al.
Keywords Schiff base ligand Á V(V) complex Á Electrochemical behavior Á Anti-
microbial activity Á Biofilm formation
Introduction
In coordination chemistry, Schiff bases are versatile ligands due to their ease of
synthesis, multi-denticity and their combining of donor atoms [1]. Also, Schiff base
complexes possess high stability in different oxidation states, resulting in wide
application of these compounds [2].
The interest in coordination chemistry of vanadium has increased in the last
decades because of its catalytic and medicinal importance. Different enzymes,
including nitrogenases and haloperoxidases [3–5], phosphate-metabolizing enzymes
[6] and phosphomutases [7], are in close relationship to vanadium. Vanadium
compounds participate in a variety of non-enzymatic, industrially important
reactions like oxidation of sulfides and thioethers [8, 9], epoxidation of allylic
alcohols, phenols and catechol [10–12], and hydroxylation of alkenes [13]. One of
the most important impetuses to the coordination chemistry of vanadium in the
context of medical applications has arisen from the ability of vanadium complexes
to promote insulin mimetic activity in the pathophysiological state of diabetes
mellitus in humans [14–16]. Also, some oxido-vanadium complexes have been
found to exhibit important anticancer properties [17, 18].
The wide spectrum of physiological effects of vanadium is concentrated on the
biologically relevant oxidation states (IV and V) and is associated with the
interactions in which it is involved with physiological ligands [19]. The rich
chemistry of vanadium(V) is probably due to its ability to exist in three different
forms: viz. mononuclear VO3? and VO2? motifs, and dinuclear V2O3 motif.
4?
Herein, a tridentate ONO hydrazine Schiff base ligand [HL] and its oxido-
vanadium(V) complex [VO(L)(PrOH)(OPr)] have been synthesized and fully char-
acterized by means of physicio-chemical and spectroscopic methods. The electro-
chemical behavior of the oxido-vanadium(V) complex has also discussed.
Furthermore, the antimicrobial activities of [HL] and [VO(L)(PrOH)(OPr)] have
been investigated against microorganisms.
Experimental
Materials and instrumentation
All chemicals and solvents used were of analytical reagent grade and were used as
received. Micro analyses for C, H and N were determined on a Thermo Finnigan
Flash Elemental Analyzer 1112EA. Melting points were measured on an
Electrothermal-9100 apparatus and were uncorrected. FTIR spectra were recorded
on a Shimadzu FTIR-8400S with KBr discs in the range of 400–4000 cm-1. Molar
conductance measurements were made by means of a Metrohm 712 Conductometer
in EtOH. 1H-NMR spectra were recorded at 25 °C on Bruker AVANCE III 500 and
123

A novel oxido-vanadium(V) Schiff base complex: synthesis…
100 MHz spectrometers using dimethyl sulfoxide (DMSO)-d6 or CDCl3 as solvents
and tetramethylsilane (TMS) as the internal standard. Electronic spectra in ethanolic
solutions of the compounds were recorded with
spectrophotometer.
a Cary 50 UV–Vis
Synthesis of [(2-hydroxy-3-methoxybenzylidene)benzoydrazide] [HL]
An ethanolic solution (5 ml) of benzohydrazide (0.14 g, 1 mmol) was added drop
wise to 5 ml of ethanolic solution of 3-methoxy-2 hydroxy benzaldehyde (0.15 g,
1 mmol) with constant stirring. After 15 min, the resulted precipitate was filtered,
washed with cold ethanol and dried in vacuum over silica gel.
Yield: 0.224 g, 83 %. m.p.: 116 °C. Anal. Calc. for C15H14N2O3
(270.28 g mol-1): C, 66.66; H, 5.22; N, 10.36. Found: C, 66.18; H, 5.30; N,
10.53 %. FT-IR (KBr), cm-1: m(NH) 3571, m(OH) 3367, m(CHar) 2839–3062, m(C=O)
1647, m(C=N) 1610, m(C=Cring) 1470, m(C–O) 1296, m(N–N) 1149, doopb(OH) 733. 1H-
NMR (500 MHz, DMSO-d6, 25 °C, ppm): d = 12.10 (s, 1H; NH), 11.03 (s, 1H; OH),
8.67 (s, 1H; CH=N), 6.85–7.96 (m, 8H, rings), 3.82 (s, 3H, OCH3). UV/Vis (EtOH)
k
max, nm (loge, L mol-1 cm-1): 225 (4.53), 305 (4.60), 343 (4.07).
Synthesis of [(3-methoxy-2oxidobenzylidene)benzohydrazidato] propanol
propanolato oxido-vanadium(V) [VO(L)(PrOH)(OPr)] (1)
VO(acac)2 (0.1 mmol, 0.03 g) and HL (0.1 mmol, 0.03 g) were added to 5 ml of
propanol and the mixture was refluxed at 100 °C for 30 min. After 3 days, suitable
single crystals appeared due to slow evaporation of the solvent. The resultant
product was isolated, and dried in a vacuum desiccator over silica gel.
Yield: 61 %. m.p.: 201 °C. Molar conductivity (1.0 9 10-3 M, EtOH):
7 X-1 cm2 mol-1. Anal. Calc. for C21H27N2O6V (454.39 g mol-1): C, 55.51; H,
5.99; N, 6.17. Found: C, 55.65; H, 5.89; N 6.09 %. FT-IR (KBr), cm-1: m(OH) 3447,
m(CHar) 2868–3060, m(C=N) 1601, m(C=Cring) 1452, m(C–O) 1284, m(N–N) 1173,
m(V=O) 972, doopb(OH) 733, m(V–O) 600, m(V–N) 429. 1H-NMR (100 MHz, CDCl3,
25 °C, ppm): d = 8.9 (s, 1H; CH=N), 6.9–8.02 (m, 8H, rings), 3.82 (s, 3H, OCH3), 5.3
(s, 1H, OH), 0.8–2.4 (m, 14H, C16H2, C17H2, C18H3, C19H2, C20H2, C21H3). UV/Vis
(EtOH), kmax, nm (log(e), L mol-1 cm-1): 271 (4.51), 319 (4.39), 340 (4.34), 422
(3.80).
Crystal structure determination
Single-crystal X-ray diffraction data were collected at 294(2) K on an Oxford
˚
Diffraction CCD diffractometer using Mo-Ka radiation (k = 0.71073 A) with x
scan technique. An empirical absorption correction was applied to the raw
intensities [20].
The structures were solved by direct methods (SHELXS-97) [21] and refined
with a full-matrix least-squares technique on F2 using SHELXL-2014 [21]. On
refinement, the large propanol/propoxy tails showed a pronounced vibration, with
123

S. Yousef Ebrahimipour et al.
large anisotropic displacement parameters leading to unrealistic C–C distances due
to libration. Attempts to refine them as disordered moieties proved unsuccessful.
Hydrogen atoms were spotted in a difference map; those attached to carbon were
further idealized, riding in coordinates and thermal factors on their host atoms; those
˚
attached to the oxygen of propoxy were refined with restrained O–H = 0.85(1)A.
Full details of crystallographic data and structure refinement parameters can be
found in Table 1.
Electrochemical measurements
Cyclic voltammetry measurements were performed using a Sama-500 electro-
chemical system (Isfahan, Iran) in conjunction with a personal computer for data
storage and processing. A three-electrode system composed of an Ag/AgCl/3 M
KCl reference electrode, a Pt wire as a counter electrode and a glassy carbon
electrode as a working electrode were employed for the electrochemical studies.
Table 1 Crystal, collection and refinement data for (I)
Crystal data
Chemical formula
Mr
C21H27N2O6V
454.38
Crystal system, space group
Temperature (K)
Monoclinic, P21/c
295
˚
a, b, c (A)
10.8345 (3), 18.4298 (6), 22.7242 (6)
b (°)
V (A )
93.167 (2)
4530.6 (2)
8, 2
3
˚
Z, Z’
Radiation type
l (mm-1
Mo Ka
0.48
)
Data collection
Diffractometer
Oxford Diffraction Gemini CCD S Ultra
Diffractometer
Absorption correction
Multi-scan CrysAlis PRO [1], Oxford
diffraction (2009)
No. of measured, independent and observed [I [ 2r(I)] 30214, 10642, 5737
reflections
Rint
0.057
0.688
-1
˚
(sin h/k)max (A
)
Refinement
R[F2 [ 2r(F2)], wR(F2), S
0.063, 0.180, 0.98
No. of reflections
10,642
555
No. of parameters
No. of restraints
50
-3
)
˚
Dqmax, Dqmin (e A
0.55, -0.47
123

A novel oxido-vanadium(V) Schiff base complex: synthesis…
Microorganism strains and culture
In this study, we used five standard bacteria (Pseudomonas aeruginosa ATCC
27853; Staphylococcus aureus PTCC 1112; Micrococcus luteus PTCC 1110,
Bacillus cereus PTCC 1015 and Escherichia coli PTCC 1330) that three of them
were isolated from clinical samples (Pseudomonas sp; Klebsiella sp and Eterococ-
cus faecalis) and one from yeast (Candida albicans PTCC 5027). Brain-heart
infusion medium (BHI-Merck) was used for E. faecalis, whereas other bacteria were
cultured on Mueller–Hinton medium (Merck). Also, yeast extract glucose
chloramphenicol (YGC) medium (Merck) for the yeast strain was used as the test
medium.
Determination of antimicrobial activity
Antimicrobial assays were performed using the agar well diffusion method [22] for
[HL] and [VO(L)(PrOH)(OPr)]. The agar media were inoculated with 100 ll of the
inoculums which were prepared using an overnight culture of each bacterium, and
yeast strain (18–24 h) adjusted to a turbidity equivalent to a 0.5-McFarland standard
[23]. Wells were cut and then 50 ll of the synthesized compounds (50 mg/ml;
DMSO was used as the solvent) was added. The plates were then incubated at 37 °C
for 24–48 h. The antibacterial activity was assayed by measuring the diameter of the
inhibition zone in millimeter (mm) formed around the well. DMSO, as solvent, was
used as a negative control, whereas ciprofloxacin (standard antibiotic) and
fluconazole (standard antifungal drug) were used as the positive controls. The
experiments were performed in triplicate.
Determination of minimum inhibitory and bactericidal concentration
Microtiter minimum inhibitory concentration (MIC) and minimal bactericidal
concentration (MBC) tests were carried out according to standard techniques
(NCCLS, 2008). Briefly, serial two-fold dilutions of each compound were
performed in media broth. A suspension of each organism was added to wells at
a concentration of 5 9 105 CFU/ml, and the microtiter plates were incubated
aerobically at 37 °C for 24 h. The MIC was defined as the lowest concentration of
antibiotic in which there was no visible growth after overnight incubation. In the
wells in which no visible growth was observed, 10 ll of the compound was sub-
cultured and the agar plate was incubated aerobically at 37 °C for the colony count.
MBC was defined as the highest dilution showing a C99.9 % kill rate after 24 h of
incubation. Serial dilutions ranging from 100 mg/ml to 0.39 mg/ml were prepared
in the medium.
Biofilm formation assessment
Those bacteria that have good adhesion to the surface are appropriate for biofilm
production. For detection of the microbial adhesion to the surface in the presence of
the vanadium complex, the microtitre plates were prepared as described previously
123

S. Yousef Ebrahimipour et al.
[24]. Briefly, a culture of the bacteria and yeast were grown overnight in the broth
media. Then, the overnight cultures were diluted 1:100 into fresh medium for
biofilm assays. 200 ll of the diluted solution was added to a 96-well dish. After the
growth phase, the medium was carefully removed with a pipette, the wells of the
microtitre plates were then rinsed three times with 200 ll of sterile PBS. After
washing, wells were filled with 96 % ethanol for 15 min. The microtitre plates were
dried in air and then, 200 ll of 1 % crystal violet were added for 5 min. Then, the
microtitre plates were washed with distilled water, and then dried. Finally, 200 ll of
33 % glacial acetic acid were added to the wells and absorbance was measured at
540 nm with an ELISA reader.
Data for biofilm formation of all strains were compared with the data obtained for
the negative control. S. aureus PTCC 1431 was used as positive control and
microbial medium without microorganisms was used as the negative control.
Results and discussion
A new oxido-vanadium(V) complex, [VO(L)(PrOH)(OPr)], containing tridentate
ONO hydrazone ligand HL was synthesized in propanol as the solvent. This
complex was stable in air and soluble in most common solvents, except n-hexane,
diethyl ether and water. The molar conductivity value of this complex was
consistent with its non-electrolyte nature.
Spectral characterization
Selected frequencies and vibrational assignments of [HL] and its oxido-vanadi-
um(V) complex are listed in the experimental section. In the free ligand spectrum,
the bands observed at 3367 and 734 cm-1 are corresponded to stretching and out-of-
plane vibrations of OH, respectively while in the spectrum of the complex, these
bands appeared at 3447 and 733 cm-1, respectively. Disappearance of C=O and NH
vibrations in the FTIR spectrum of [VO(L)(PrOH)(OPr)] indicates HL contributes
an enolic form on complexation [25]. After coordination, the red shift of (-C=N)
from 1610 cm-1 to 1601 cm-1 shows that the azomethine nitrogen atom
coordinates to the metal center [26–29]. A shift in C-O bond energy of the
complex from 1296 cm-1 in HL to a lower frequency (1284 cm-1) indicates the
ligand coordinates to the metal through the phenolic oxygen atom [30]. The strong
band at 972 cm-1 is ascribed to stretching vibration of the the vanadyl moiety [31,
32].
The electronic spectra of the compounds were recorded in EtOH. In the UV–Vis
spectrum of HL, the band observed at 225 nm is ascribed to p ? p* transitions of
the aromatic rings. Two bands at 305 and 343 nm can be assigned to p ? p* and
n ? p* of the azomethine and carbonyl moieties [33]. In the electronic spectrum of
the V(V) complex, intra-ligand transitions show a red shift in comparison with free
ligand, indicating enolization followed by deprotonation of the ligand. Moreover,
the band at about 422 nm is assignable to N(p)/O(p) ? V(d) charge transfer
(LMCT) [30].
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A novel oxido-vanadium(V) Schiff base complex: synthesis…
X-ray structure characterization
The crystal and molecular structure of [(3-methoxy-2oxidobenzylidene)benzohy-
drazidato] propanol propanolato oxido-vanadium(V) was determined using single
crystal X-ray diffraction. The asymmetric unit is composed of two independent
moieties (Ia and Ib), which are identical in formulation [VO(L)(PrOH)(OPr)] , but
show inverted configurations. Figure 1a, b show ellipsoid plots of both independent
moieties Ia and Ib. The coordination geometry around the vanadium(V) ion shows a
distorted octahedral environment with an NO5 chromophore. Some selected bond
distances and angles are also listed in Table 2.
Searching in Cambridge structural database, (CSD, V5.34 [34]) we found two
oxido-vanadium(V) alcohol-alkoxy complexes [35, 36] similar to the title
synthesized complex, Scheme 1 depicts the structures of these complexes along
with the complex synthesized here.
In spite of differences in the alcohol chain, the coordination sphere around
vanadium(V) ion is extremely similar in the complexes I, II and III. A comparison
of the selected bond distances and angles of the complexes are given in Table 2.
Moreover, Fig. 2 presents an L.S. fit of the four molecules (Ia, Ib, II and III)
showing an identical coordination sphere around the central ion .
In the title complex, V=O6 and V-O3 bonds which are trans to each other and
occupy the apical sites, are the shortest and longest VO bonds, respectively. While
the basal plane is determined by the donor atoms of the tridentate L2- (O1, O2, and
N1) and the oxygen atom of the coordinated propoxy (O4). The basic descriptors of
this geometry are (in Ia/Ib sequence): max. deviation from the basal L.S. plane,
˚
˚
0.020(2)/0.019(2) A for N1 and 0.306(3)/0.323(4) A for vanadium ion deviated
towards O6.
There are few intermolecular H-bonding interactions in the structure. All of them
are presented in Table 3. Entries #1 and #2 described O-H...N type and entries #3
and #4 described C-H...O type, define chains running along ‘‘a’’ (Fig. 3a). These
chains, in turn, are weakly linked to dual-chain slabs (Fig. 3a) by the remaining
C-H...O bond (entry #5 in Table 3). As shown in Fig. 3b, these slabs are almost non-
interacting.
Fig. 1 Ellipsoid plots of both independent moieties Ia and Ib
123

S. Yousef Ebrahimipour et al.
˚
Table 2 Selected geometric parameters (A, 8) for Ia, Ib, II and III
Bond/angle
Ia
Ib
II(30)
III(31)
V1—O6A
1.592 (2)
1.575 (3)
1.578 (4)
1.769 (3)
1.580 (3)
1.761 (3)
V1—O4A
1.761 (2)
1.847 (2)
1.768 (2)
1.836 (2)
V1—O1A
1.839 (3)
1.850 (3)
V1—O2A
1.946 (2)
1.957 (2)
1.966 (2)
1.954 (3)
V1—N1A
2.118 (3)
2.111 (3)
2.109 (4)
2.122 (3)
V1—O3A
2.338 (2)
2.396 (3)
2.346 (4)
2.367 (3)
O6A—V1—O4A
O6A—V1—O1A
O4A—V1—O1A
O6A—V1—O2A
O4A—V1—O2A
O1A—V1—O2A
O6A—V1—N1A
O4A—V1—N1A
O1A—V1—N1A
O2A—V1—N1A
O6A—V1—O3A
O4A—V1—O3A
O1A—V1—O3A
O2A—V1—O3A
N1A—V1—O3A
103.44 (12)
100.86 (12)
101.42 (10)
95.45 (11)
94.29 (10)
153.95 (10)
95.57 (11)
158.75 (12)
83.96 (9)
103.77 (14)
101.58 (13)
102.77 (10)
96.56 (12)
91.76 (10)
153.19 (10)
96.72 (13)
156.42 (12)
84.12 (10)
74.22 (10)
174.94 (11)
80.60 (11)
79.72 (10)
80.62 (9)
104.17 (19)
100.97 (17)
103.20 (15)
96.48 (17)
91.66 (16)
153.41 (13)
96.11 (18)
156.54 (17)
84.05 (14)
74.22 (14)
173.89 (18)
80.39 (15)
81.71 (13)
79.17 (13)
78.63 (15)
103.23 (14)
100.22 (16)
101.65 (12)
97.38 (16)
94.21 (12)
152.84 (13)
96.49 (13)
158.23 (12)
83.58 (13)
73.97 (12)
175.37 (14)
80.75 (11)
81.11 (11)
79.84 (10)
79.21 (11)
74.29 (9)
174.05 (10)
82.12 (10)
79.86 (10)
81.89 (9)
78.60 (9)
78.50 (10)
Scheme 1 The structures of the synthesized complex (I) and two similar vanadium(V) alcohol-alkoxy
complexes (II and III)
Electrochemical activity
Cyclic voltammograms of 10-3 M of the [VO(L)(PrOH)(OPr)] were recorded in
DMSO containing 0.1 M tetra-n-butylammonium bromide (TBAB) as the support-
ing electrolyte by scanning the potential from -0.8 to 0.7 V. Figure 4 reveals the
123

A novel oxido-vanadium(V) Schiff base complex: synthesis…
Fig. 2 L.S. fit of the four molecules (Ia, Ib, II and III)
˚
Table 3 Hydrogen-bond geometry (A, 8) for (I)
Code
D—HÁÁÁA
D—H
HÁÁÁA
DÁÁÁA
D—HÁÁÁA
#1
#2
#3
#4
#5
O3A—H3AOÁÁÁN2B
O3B—H3BOÁÁÁN2Aa
C7A—H7AAÁÁÁO1Bb
C7B—H7BAÁÁÁO1A
C3B—H3BAÁÁÁO6Ac
0.84 (3)
0.85 (4)
0.93
1.99 (3)
2.10 (4)
2.55
2.824 (3)
2.824 (3)
3.059 (4)
3.181 (4)
3.470 (4)
170 (3)
143 (4)
115
0.93
2.57
124
0.93
2.56
166
a
b
c
Symmetry codes: x ? 1, y, z; x - 1, y, z; - x ? 1, -y ? 2, -z?1
Fig. 3 Representation of intermolecular H-bonding interactions
123

S. Yousef Ebrahimipour et al.
Fig. 4 Cyclic voltammograms of the title V(V) complex at scan rates of 30, 100 and 200 mV/s
corresponding voltammograms obtained at scan rates of 30, 100 and 200 mV/s. An
irreversible oxidation peak is observed at 500 mV corresponded to the ligand. Two
separate peaks obtained in the reverse direction of the scan at -41 and -641 mV, are
assigned to V(V)/V(IV) and V(IV)/V(III). Investigation of the effect of scan rate
indicates that with increasing the scan rate from 30 to 200 mV, the currents of both
cathodic peaks increase accompanied with negative shifts in their peak potentials, as
expected for irreversible electrode processes [37].
Antimicrobial activity
Antimicrobial activities of [VO(L)(PrOH)(OPr)] and free ligand [HL] against
Pseudomonas sp; Klebsiella sp, E. faecalis, isolated from a clinical sample, P.
aeruginosa ATCC 27853, S. aureus PTCC 1112, M. luteus PTCC 1110, B. cereus
PTCC 1015, E. coli PTCC 1330, and C. albicans PTCC 5027, were assessed by
evaluating the presence of inhibition zone (IZ), MIC and MBC values. The results
obtained are reported in Table 4. As seen the oxido-vanadium(V) complex
possessed a great potential of antibacterial activity, while [HL] didn’t show any
antimicrobial effects. Also, the antibacterial effect of the complex on Gram-positive
bacteria was more than its effect on Gram-negative ones. In addition, the complex
was found to be effective on C. albicans PTCC 5027. However, according to the
obtained results, the bacteria isolated from clinical samples were resistant to
[VO(L)(PrOH)(OPr)] and ciprofloxacin antibiotic.
The MIC and MBC values for the title complex were in the range of 100–0.39 mg/
ml. The results of our study showed that the title oxido-vanadium(V) complex was
effective on Gram-positive bacteria and yeast. It was observed that the complex not
only inhibited the growth of the microorganisms, but also killed C. albicans PTCC
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A novel oxido-vanadium(V) Schiff base complex: synthesis…
Table 4 In vitro antimicrobial activity of the compounds, 50 mg/mL (IZ)
Microorganism
[VO(L)(PrOH)
(OPr)] dia. of
clear zone (mm)
[HL] dia.
of clear
zone (mm)
Ciprofloxacin
dia. of clear
zone (mm)
Fluconazol
dia. of clear
zone (mm)
P. aeruginosa ATCC 27853
S. aureus PTCC 1112
M. luteus PTCC 1110
B. cereus PTCC 1015
E. coli PTCC1330
Pseudomonas sp*
0
24
20
24
0
0
0
0
0
0
0
0
0
0
22
25
31
24
27
0
0
0
0
0
0
0
0
Klebsiella sp*
0
0
0
E. faecalis*
0
0
0
C. albicans PTCC 5027
22
0
35
* Clinical bacteria
Table 5 In vitro antimicrobial
activity of [VO(L)(PrOH)(OPr)]
(MIC and MBC, mg/mL)
Microorganism
[VO(L)(PrOH)(OPr)]
MIC
MBC
S. aureus PTCC 1112
M. luteus PTCC 1110
B. cereus PTCC 1015
C. albicans PTCC 5027
–
1.563
6.25
–
–
6.25
6.25
12.5
Table 6 Comparison of anti-biofilm formation effect, MIC and MBC of [VO(L)(PrOH)(OPr)], (mg/ml)
Compound
Microorganisms
S. aureus PTCC
1112
M. luteus PTCC
1110
B. cereus PTCC
1015
C. albicans PTCC
5027
ABF*
MBC
1.563
ABF
MBC
6.25
ABF
MBC
6.25
ABF
MIC
6.25
[VO(L)(PrOH)(OPr)] 0.39
3.125
1.563
3.125
* Anti-biofilm formation effect
5027. We found that the V(V) complex is a bactericidal compound, capable of killing
bacteria at a minimum lethal concentration (Table 5).
According to the biofilm formation results, it was found that the title complex
repressed biofilm formation in S. aureus PTCC 1112 (0.39 mg/mL), M. luteus
PTCC 1110 (3.125 mg/mL), B. cereus PTCC 1015 (1.563 mg/mL) and C. albicans
PTCC 5027 (3.125 mg/mL). Moreover, the formation of the biofilm was inhibited
by the complex at a concentration lower than minimum lethal and inhibitory
concentration (Table 6).
123

S. Yousef Ebrahimipour et al.
Conclusion
A new oxido-vanadium(V) complex containing a tridentate ONO Schiff base ligand
(2-hydroxy-3-methoxybenzylidene)benzoydrazide was synthesized and character-
1
ized using physico-chemical and spectroscopic methods of CHN, FTIR, HNMR,
UV–Vis as well as voltammetry. The structure of the complex was also determined
with single crystal X-ray diffraction. According to the obtained data, vanadi-
um(V) ion was found to be coordinated by the di-negative and tridentate chelating
agent through its oxygen and nitrogen moieties. Other positions around the central
ion are occupied by oxygen atoms of oxido group, propanol and propoxide group.
Antimicrobial assay showed that the [VO(L)(PrOH)(OPr)] complex posesses
significant activities against both Gram-positive and Gram-negtive bacteria as well
as fungus species.
Supplementary data
CCDC 1025915 contains the supplementary crystallographic data for [VO(L)(PrO-
H)(OPr)]. A copy of this information may be obtained free of charge from: Director,
CCDC, 12 Union Road, Cambridge, Cb2 1EZ, UK (fax: ?44 1223 336 033); web
page: http://www.ccdc.cam.ac.uk/cgibin/catreq.cgi.
Acknowledgments The authors gratefully acknowledge the financial support provided for this work by
the Shahid Bahonar University of Kerman.
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