Synthesis, characterization, X-ray crystal structure, DFT calculation and antibacterial activities of new vanadium(IV, V) complexes containing chelidamic acid and novel thiourea derivatives

Article abstract of DOI:10.1016/j.jinorgbio.2015.02.007

Three new thiourea ligands derived from the condensation of aroyl- and aryl-isothiocyanate derivatives with 2,6-diaminopyridine, named 1,1′-(pyridine-2,6-diyl)bis(3-(benzoyl)thiourea) (L1), 1,1′-(pyridine-2,6-diyl)bis(3-(2-chlorobenzoyl)thiourea) (L2) and

Full text of DOI:10.1016/j.jinorgbio.2015.02.007

Synthesis, characterization, X-ray crystal structure, DFT calculation and an-
tibacterial activities of new vanadium(IV, V) complexes containing chelidamic
acid and novel thiourea derivatives
Javad Farzanfar, Khaled Ghasemi, Ali Reza Rezvani, Hojat Samareh
Delarami, Ali Ebrahimi, Hona Hosseinpoor, Amir Eskandari, Hadi Amiri
Rudbari, Giuseppe Bruno
PII:
DOI:
Reference:
S0162-0134(15)00050-1
doi: 10.1016/j.jinorgbio.2015.02.007
JIB 9668
To appear in:
Journal of Inorganic Biochemistry
Received date:
Revised date:
Accepted date:
1 November 2014
13 February 2015
13 February 2015
Please cite this article as: Javad Farzanfar, Khaled Ghasemi, Ali Reza Rezvani, Ho-
jat Samareh Delarami, Ali Ebrahimi, Hona Hosseinpoor, Amir Eskandari, Hadi Amiri
Rudbari, Giuseppe Bruno, Synthesis, characterization, X-ray crystal structure, DFT
calculation and antibacterial activities of new vanadium(IV, V) complexes containing
chelidamic acid and novel thiourea derivatives, Journal of Inorganic Biochemistry (2015),
doi: 10.1016/j.jinorgbio.2015.02.007
This is a PDF file of an unedited manuscript that has been accepted for publication.
As a service to our customers we are providing this early version of the manuscript.
The manuscript will undergo copyediting, typesetting, and review of the resulting proof
before it is published in its final form. Please note that during the production process
errors may be discovered which could affect the content, and all legal disclaimers that
apply to the journal pertain.

ACCEPTED MANUSCRIPT
Synthesis, characterization, X-ray crystal structure, DFT calculation and
antibacterial activities of new vanadium(IV, V) complexes containing
chelidamic acid and novel thiourea derivatives
a
a
a,*
a
Javad Farzanfar, Khaled Ghasemi, Ali Reza Rezvani, Hojat Samareh Delarami, Ali
a
a
a
b
c
Ebrahimi, Hona Hosseinpoor, Amir Eskandari, Hadi Amiri Rudbari, Giuseppe Bruno
a
Department of Chemistry, University of Sistan and Baluchestan, Zahedan 98135-674, Iran
b
Faculty of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran
c
Universita degli Studi di Messina, dip. Scienze Chimiche. Viale Ferdinando S. d’Alcontres, 98166 Messina, Italy
*
- Corresponding author Tel: +98 54 33447010; Fax: +98 54 33443388, E-mail address: Ali@hamoon.usb.ac.ir,
javadfr@pgs.usb.ac.ir;
1

ACCEPTED MANUSCRIPT
Abstract
Three new thiourea ligands derived from the condensation of aroyl- and aryl-isothiocyanate
derivatives with 2,6-diaminopyridine, named 1,1'-(pyridine-2,6-diyl)bis(3-(benzoyl)thiourea)
(
L1), 1,1'-(pyridine-2,6-diyl)bis(3-(2-chlorobenzoyl)thiourea) (L2) and 1,1'-(pyridine-2,6-
diyl)bis(3-(4-chlorophenyl)thiourea) (L3), their oxido-vanadium(IV) complexes, namely
'
'
'
[
VO(L1)(H O)] (C1), [VO(L2)(H O)] (C2) and [VO(L3)(H O)] (C3), and also, dioxo-
2 2 2
vanadium(V) complex containing 4-hydroxy-2,6-pyridine dicarboxylic acid (chelidamic acid,
H dipic-OH) and metformin (N,N-dimethylbiguanide, Met), named [H Met][VO (dipic-
2
2
2
1
OH)] ·H O (C4), were synthesized and characterized by elemental analysis, FTIR and H NMR
2
2
and UV-visible spectroscopies. Proposed structures for free thiourea ligands and their vanadium
complexes were corroborated by applying geometry optimization and conformational analysis.
Solid state structure of complex [H Met][VO (dipic-OH)] ·H O (triclinic, Pī) was fully
2
2
2
2
determined by single crystal X-ray diffraction analysis. In this complex, metformin is double
protonated and acted as counter ion. The antibacterial properties of these compounds were
investigated in vitro against standard Gram-positive and Gram-negative bacterial strains. The
experiments showed that vanadium(IV) complexes had the superior antibacterial activities than
novel thiourea derivatives and vanadium(V) complex against all Gram-positive and Gram-
negative bacterial strains.
Keywords: Thiourea; 4-hydroxy-2,6-pyridine dicarboxylic acid; N,N-dimethylbiguanide; Oxo-
vanadium(IV, V) complex; Antibacterial activity
2

ACCEPTED MANUSCRIPT
1
. Introduction
In recent years, many research efforts are directed to the development of effective antimicrobial
agents caused by the variety of drug-resistant strains and inhibition of the growth of them [1-5].
On the basis of the pharmacological studies of the compounds containing carbonyl and
thiocarbonyl groups such as urea, thiourea and their related analogues, it is proposed that the
thiourea derivatives and their transition metal complexes represent a wide diversity of biological
functions including antibacterial [6-16], antifungal [17-21], anti-diabetic [22-24], antitubercular
[
[
25], anti-human immunodeficiency virus (anti-HIV) [26-28], anti-Hepatitis C virus (anti-HCV)
29], Antitumor [30-31], antithyroid, anthelmintic, rodenticidal, insecticidal, herbicidal, and
plant-growth regulator properties [32-34]. In many investigations, coordination of thiourea
derivatives as potential donor ligands to a range of metal ions have led to increment in the
biological activity of these compounds, hence showing that complexation can be a novel
approach for the reduction of dose [35]. Vanadium is present in trace amounts as physiologically
essential element with wonderful biological properties. There are suggestions that vanadium
plays important roles in cells such as regulation of phosphoryl transfer enzymes and cell’s redox
potential [36]. Pharmacologically, vanadium compounds with oxidation states +4 (IV) and +5
(V) have demonstrated anti-diabetic and anti-carcinogenic effects in humans [37]. Considering
the biological properties of vanadium and the antimicrobial activities of thiourea derivatives, it
can be concluded that the combination of them can lead to the generation of novel improved
antimicrobial agents. In spite of extensive investigations on insulin-enhancing properties and
anti-diabetic effects of vanadium compounds, a few researchers have studied antimicrobial
activity of vanadium complexes, particularly, with thiourea derivatives as ligands [38-42].
Furthermore, 4-hydroxypyridine-2,6-dicarboxylic acid, which obtains from the substitution of
3

ACCEPTED MANUSCRIPT
dipicolinic acid (2,6-pyridine dicarboxylic acid) with a hydroxyl group in position 4 and forms
−
the [VO (dipic-OH)] complexes with various organic or inorganic counterions, has recently
2
revealed the range of biological functions [43-45]. In view of this, we focused on the synthesis,
characterization and antibacterial activity of three novel thiourea derivatives and their oxido-
vanadium(IV) complexes. Moreover, we fully investigated a new dioxo-vanadium(V) complex
with metformin, which has lately exhibited an appreciable biological activity, as a counterion
namely [H Met][VO (dipic-OH)] ·H O. Based upon the previous studies, the protonation of the
2
2
2
2
metformin as a relatively strong base leads to activate it in some biological processes [46]. Since
appropriate crystals from pure solid thiourea compounds were not available for X-ray
measurements, we carried out geometry optimization and conformational analysis to all free
ligands and oxido-vanadium(IV) complexes as a supplementary tool to validate the proposed
structures. The antibacterial properties of all compounds were screened in vitro against two
standard Gram-positive (Staphylococcus aureus and Enterococcus faecalis) and two standard
Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacterial strains.
2
2
. Experimental
.1. Materials and instrumentation
All starting reagents and solvents were purchased from Sigma-Aldrich and Merck and used as
received. Elemental analyses were performed on a Leco, CHNS-932 elemental analyzer. Fourier
transform infrared spectra were recorded on a FT-IR JASCO 680-PLUS spectrometer as KBr
−
1
pellets in the 4000–400 cm spectral range. Proton NMR spectra at room temperature were
obtained on a Bruker 400 spectrometer. Electronic spectra (UV-visible (UV-Vis)) were recorded
on a UV-JASCO-570 spectrometer using 10 mm pass length quartz cells at room temperature.
4

ACCEPTED MANUSCRIPT
2
2
.2. Synthesis
.2.1. Synthesis of thiourea ligands and their oxido-vanadium(IV) complexes
The ligands L1 and L2 were synthesized using a procedure similar to that described in the
literature [8, 47] by the reaction of benzoyl chloride (2 mmol) and 2-chlorobenzoyl chloride (2
mmol) separately with NH SCN (2 mmol) in acetone to produce benzoyl-isothiocyanate and 2-
4
chlorobenzoyl-isothiocyanate, respectively, followed by condensation of each of them with 2,6-
diaminopyridine (1 mmol). The ligand L3 was directly synthesized by condensation of 4-
chlorophenyl-isothiocyanate (2 mmol) with 2,6-diaminopyridine (1 mmol). The oxido-
vanadium(IV) complexes were also prepared according to the method described in the literature
[
48] by the reaction of aqueous solutions (10 ml) of the ammonium metavanadate ((NH )VO , 1
4 3
mmol) separately with an ethanol solution (10 ml) of each of the ligands (1 mmol) in the
presence of triethyl amine. The reaction mixtures were refluxed for 48 h and then the complexes
were isolated as the solids. All the resulting solid products (ligands and complexes) were soluble
in acetone, ethanol, dichloromethane, DMSO and N,N-dimethylformamide (DMF) and were re-
crystallized from an ethanol-dichloromethane mixture (1:2).
-1
L1: Light yellow, m.p.: 156 °C. Anal. Calc. For C H N O S (%; FW: 435.520 g.mol ): C,
2
1
17
5
2 2
-
5
7.91; H, 3.93; N, 16.08; S, 14.72; Found: C, 57.83; H, 3.99; N, 16.05; S, 14.78. FTIR (KBr, cm
1
): 3330.7, 3107.5, 3032.8, 1667.6, 1599.7, 1580.0, 1552.4, 1537.9, 1531.6, 1515.2, 1489.0,
1
7
451.0, 1399.3, 1325.4, 1319.4, 1239.6, 1152.6, 1100.5, 1072.6, 1021.9, 1000.7, 837.8, 796.4,
1
72.5, 734.8, 710.9, 687.9, 671.9, 661.8, 648.6, 606.7, 547.8, 476.7, 456.0, 412.9. H NMR
(
DMSO-d , ppm): 13.21 (br s, 2H, NH), 11.72 (br s, 2H, NH), 7.95-8.84 (m, 10H, phenyl
6
protons), 7.08-7.63 (m, 3H, pyridyl protons). UV-Vis (DMSO, nm): 262, 274, 326.
5

ACCEPTED MANUSCRIPT
-1
L2: Light yellow, m.p.: 148 °C. Anal. Calc. For C H Cl N O S (%; FW: 504.404 g.mol ): C,
21
15
2
5
2 2
-
5
0.01; H, 3.00; N, 13.88; S, 12.71; Found: C, 50.08; H, 2.97; N, 13.91; S, 12.75. FTIR (KBr, cm
1
): 3390.1, 3221.1, 3180.1, 3111.7, 3046.6, 1676.4, 1592.1, 1577.3, 1556.6, 1536.4, 1477.3,
1
7
449.1, 1440.1, 1402.1, 1328.4, 1305.8, 1250.8, 1239.9, 1161.7, 1097.5, 1044.8, 1022.2, 844.4,
1
98.6, 771.6, 745.1, 726.7, 711.5, 692.9, 650.7, 617.9, 570.3, 467.9, 438.8. H NMR (DMSO-d ,
6
ppm): 12.84 (br s, 2H, NH), 11.15 (br s, 2H, NH), 7.83-8.66 (m, 8H, phenyl protons), 7.18-7.69
m, 3H, pyridyl protons). UV-Vis (DMSO, nm): 260, 271, 323.
L3: Yellow, m.p.: 153 °C. Anal. Calc. For C H Cl N S (%; FW: 448.384 g.mol ): C, 50.90;
(
-1
1
9
15
2
5 2
-1
H, 3.37; N, 15.62; S, 14.30; Found: C, 50.84; H, 3.31; N, 15.71; S, 14.24. FTIR (KBr, cm ):
3
1
5
7
2
397.8, 3373.7, 3325.7, 3197.9, 3030.3, 1582.9, 1532.3, 1484.2, 1448.1, 1401.2, 1350.9, 1305.2,
260.0, 1222.9, 1195.9, 1156.6, 1089.3, 1013.4, 824.6, 789.7, 771.1, 717.0, 670.1, 627.8, 613.4,
1
79.0, 495.4, 442.3. H NMR (DMSO-d , ppm): 11.20 (br s, 2H, NH), 10.86 (br s, 2H, NH),
6
.71-8.63 (m, 8H, phenyl protons), 7.11-7.59 (m, 3H, pyridyl protons). UV-Vis (DMSO, nm):
60, 274, 332.
-1
C1: Green. Anal. Calc. For C H N O S V (%; FW: 518.460 g.mol ): C, 48.65; H, 3.31; N,
2
1
17
5
4 2
-
1
1
3
1
6
5
3.51; S, 12.37; Found: C, 48.63; H, 3.29; N, 13.55; S, 12.38. FTIR (KBr, cm ): 3431.7, 3332.9,
165.1, 3107.6, 3032.3, 1667.1, 1603.2, 1579.8, 1514.9, 1489.4, 1448.0, 1399.7, 1309.0, 1218.2,
206.1, 1186.5, 1152.6, 1101.9, 1073.9, 1020.6, 999.7, 981.3, 826.3, 795.5, 734.8, 711.4, 687.6,
71.3, 661.5, 648.7, 631.4, 606.9, 547.9, 525.4, 479.2, 411.7. UV-Vis (DMSO, nm): 268, 320,
76, 867.
-1
C2: Dark green. Anal. Calc. For C H Cl N O S V (%; FW: 587.343 g.mol ): C, 42.94; H,
2
1
15
2
5
4 2
-1
2
.57; N, 11.92; S, 10.92; Found: C, 42.88; H, 2.51; N, 12.96; S, 10.96. FTIR (KBr, cm ):
471.8, 3337.8, 3219.3, 3178.4, 3111.2, 3043.9, 1676.2, 1592.1, 1577.6, 1556.5, 1533.1, 1477.5,
3
6

ACCEPTED MANUSCRIPT
1
7
448.8, 1402.5, 1305.4, 1221.5, 1161.2, 1097.2, 1044.4, 1021.6, 986.1, 882.7, 844.3, 798.5,
44.9, 726.5, 711.1, 692.6, 650.5, 618.1, 570.3, 528.7, 496.7, 468.1, 438.4. UV-Vis (DMSO,
nm): 269, 322, 569, 862.
C3: Dark green. Anal. Calc. For C H Cl N O S V (%; FW: 527.291 g.mol ): C, 43.28; H,
-1
1
9
11
2
5
2 2
-1
2
.10; N, 13.28; S, 12.16; Found: C, 43.22; H, 2.08; N, 13.32; S, 12.19. FTIR (KBr, cm ):
428.3, 3183.4, 3053.2, 1638.6, 1566.3, 1460.1, 1397.1, 1157.9, 985.8, 799.1, 611.0. UV-Vis
3
(
DMSO, nm): 267, 324, 560, 859.
.2.2. Synthesis of dioxo-vanadium(V) complex with chelidamic acid and metformin
hydrochloride
-Hydroxypyridine-2,6-dicarboxylic acid (1.0 mmol) and NaOH (2.0.mmol) were dissolved in
2
4
the mixture of ethanol/water (20 ml) and dropwise added, under continuous stirring, to an
aqueous solution (10 ml) of VOSO (1.0 mmol). Afterward metformin hydrochloride (0.50
4
mmol) was added to the resulting mixture and was refluxed for18 h until the light green solution
obtained. After 6 days, green crystals suitable for X-ray structural analysis from the title dioxo-
vanadium(V) complex, C4, were obtained.
-1
C4: pale green, Anal. Calc. For C H N O V (%; FW: 677.283 g.mol ): C, 31.92; H, 3.13; N,
1
8
21
7
15
2
-
1
1
1
4.48; Found: C, 31.53; H, 3.07; N, 14.55. FTIR (KBr, cm ):3341,3163, 2749, 1681, 1609,
1
572, 1463, 1376, 1290, 1126, 1056, 948, 884, 803, 756, 639, 576, 453. H NMR (DMSO-d ,
6
2−
2−
2−
ppm): 8.30 (s, dipic-OH ), 7.61 (s, dipic-OH ), 7.35 (s, dipic-OH ), 3.00 (s, 6H, H Met). UV-
2
Vis (DMSO, nm): 220, 285.
2
.3. Theoretical calculations
To gain an accurate understanding of the molecular structures of thiourea derivatives and their
oxido-vanadium(IV) complexes, geometry optimization and conformational analysis performed
7

ACCEPTED MANUSCRIPT
in the gas phase with the Gaussian 09 suite of programs and the Beck’s three-parameter hybrid
method B3LYP with the 6-31G(d,p) basis set. Vibrational frequency analyses were also
performed at the same level to ensure the structures are local minima. The natural bond orbital
(
NBO) method on the wave functions was obtained at the same level of theory by NBO 3.1
program [49-55].
.4. X-ray crystal structure determination dioxo-vanadium(V) complex C4
The crystal structure of [H Met][VO (dipic-OH)] ·H O was obtained by the single-crystal X-ray
2
2
2
2
2
diffraction technique. Data for the dioxo-vanadium(V) complex C4 were collected on a Bruker
APEX II area-detector diffractometer using graphite monochromated Mo Kα radiation, λ =
0
.71073 Å at 298(2) K. Data was analyzed with APEX2 software, reduced using SAINT
program and the empirical absorption corrections were applied using the SADABS program
56]. The structure was solved by direct methods and refined using the least-squares method in
[
SHELXTL software package [57]. All non-hydrogen atoms were refined anisotropically. Outlier
reflections were omitted during the final refinement. Materials for publications were prepared
with SHELXTL [58], PLATON [58], WinGX [59] and Mercury [60]. Details of the X-ray data
collection are reported in Table 1.
2
.5. Antibacterial assay
The antibacterial test was done in vitro against two Gram-negative standard strains of bacteria
Escherichia coli; E. coli ATCC 25922 and Pseudomonas aeruginosa; P. aeruginosa ATCC
7853) and two Gram-positive standard strains of bacteria (Staphylococcus aureus; S. aureus
ATCC 25923 and Enterococcus faecalis; E. faecalis ATCC 11700).
(
2
2
.5.1. Determination of minimum inhibitory concentration
8

ACCEPTED MANUSCRIPT
Minimum inhibitory concentrations for all synthesized thioureas and vanadium(IV, V)
complexes were investigated against all above-named standard bacterial strains by the broth
macrodilution assay in sterile test tubes [61]. The Muller Hinton Broth (MLB) medium was used.
Since DMSO has no effect on the microorganisms, DMSO was used as solvent for preparation of
stock solutions and further dilutions were done with distilled water. The concentrations of
assayed compounds were 1024, 512, 256, 128, 64, 32, 16, 8, 4, 2 and 1 µg/ml. DMSO was
utilized as negative control. In nutrient broth medium 24 h fresh bacterial culture was prepared.
In order to compare the turbidity of bacterial culture, McFarland Standard 0.5 solution was used
as turbidity standard. All the inoculated tubes were incubated at 36 °C and results were assessed
after 18 h for bacteria. The minimum inhibitory concentration (MIC) was defined as the lowest
concentration of the compounds that prevents the visible growth of bacteria after incubation for
1
8 h, at 36 °C.
2
.5.2. Determination of inhibition zone
The inhibition zones of the synthesized compounds were determined in vitro against all aforesaid
standard bacterial strains by the disk diffusion method. Sterilized paper disks (diameter = 6 mm)
were immersed in DMSO solution of tested compounds in the concentration equivalent to most
obtained MIC for 5 min. Then, they were taken out and attached to the surface of Muller Hinton
3
Agar (MHA) plates, which were inoculated with a loop (0.01 cm ) of the adequate inoculum of
6
-3
the bacteria (10 CFUs cm ). DMSO was used as a negative control while Amikacin (AMK-30
µg) and Gentamycin (GEN-10 µg) were used as positive controls for Gram positive antibacterial
activity and Gram negative antibacterial activity, respectively. All plates were incubated for 24 h
at 36 °C and the resulting diameter of each inhibition zone showing no bacterial growth was
measured.
9

ACCEPTED MANUSCRIPT
3
3
3
. Results and Discussion
.1. Characterization of thiourea ligands and their oxido-vanadium(IV) complexes
.1.1. Infrared spectroscopy
The solid state properties of three new thiourea ligands and their oxido-vanadium(IV) complexes
were investigated by infrared spectroscopy. The infrared spectra of these samples exhibit all the
expected frequency regions of the ν(N─H), ν(C═S), ν(C═O) and ν(C─N). The thiourea
derivatives can display thione-thiol tautomerism. In the IR spectra of the ligands, the ν(S─H)
-1
band at around 2500-2600 cm is absent and, vice versa, multiple absorption bands related to the
asymmetric and symmetric stretching vibrations of the (N─H) groups in the range of 3100–3400
-1
cm are present, consequently, exhibiting formation of the thione tautomer in the solid state of
-1
thiourea derivatives. The absorption band at about 3030 cm is assigned to ν(Ph─H) stretching
mode. The characteristic IR bands associated with the stretching vibrations of thionyl (C═S)
groups of the free thiourea ligands are appeared in the region of 1325-1351, 1239-1260 and 824-
-1
8
44 cm . The multiple high or medium intensity absorption bands in the range of 1000–1200
-1
cm are attributed to the ν(C─N) stretching vibrations. The ν(C=C) + ν(C=N) vibration
-1
frequencies of the pyridine ring found at around 1515-1600 cm . The ring wagging vibrations of
-
1
the pyridine group are observed in the range of 670-692 and 789-798 cm . The absorption band
-1
at around 610 cm is from the in-plane ring deformation of the pyridine ring. For two thiourea
-1
ligands L1 and L2, the sharp absorption band at about 1670 cm is responsible for the stretching
-1
vibration of carbonyl (C═O) group. Besides, the absorption band observed at around 710 cm
corresponds to ν(C─Cl) stretching vibration of phenyl ring in two thiourea ligands L2 and L3
47-48].
[
10

ACCEPTED MANUSCRIPT
In the suggested structures of the complexes C1 and C2 (Figures 1 and 2), two thiourea ligands
L1 and L2, respectively, behave as binegative tridentate chelating agents coordinating through
2
+
the nitrogen of the pyridyl group and two CS groups in the thiol form to vanadyl ([VO] ) ion.
The environment around the vanadium atom is penta-coordinate. In the IR spectra of these
-1
complexes, two ν(C═S) bands of free thiourea ligands at around 1325 and 1239 cm underwent
-1
a shift into lower frequencies at about 1305 and 1220 cm and the ν(C═S) band of free thiourea
-1
ligands at around 840 cm weakened upon complexation. These observations suggest the
participation of the C=S groups in the coordination, which are in acceptable agreement with the
proposed structures of the complexes C1 and C2 [7].
The synthesis of complex C3 starts with the reaction of the sulfur atoms in thionyl (C═S) groups
with carbon atoms (C17 and C28) in the phenyl rings of the free thiourea ligand L3, which
eliminates four hydrogen atoms and forms two new five-membered rings. In the suggested
structure of the complex C3 (Fig. 3), the oxidized cyclization form of thiourea ligand L3 acts as a
binegative tridentate chelating ligand coordinating through the nitrogen atoms of pyridine and
2+
thiourea to vanadyl ([VO] ) ion. Similarly with the complexes C1 and C2, The environment
around the vanadium atom of complex C3 is penta-coordinate. In the IR spectrum of this
-1
complex, the ν(C═S) band of free thiourea ligand L3 at 824 cm is absent and the new
-1
absorption band observed at 799 cm corresponds to ν(C─S) stretching vibration upon
cyclization [47].
According to the literature, the oxido-vanadium(IV) complexes display the IR band related to the
-1
stretching vibration of vanadyl (V═O) group in the region of 995-940 cm . This characteristic
band for the square pyramidal oxido-vanadium(IV) complexes emerges at higher wave numbers,
-1
while for octahedral oxido-vanadium(IV) complexes appears at 960–940 cm . For example,
11

ACCEPTED MANUSCRIPT
Bakir J.A. Jeragh et al. studied three monomeric square pyramidal oxido-vanadium(IV)
complexes containing para-substituted phenyl-2-picolylketone. The IR band of vanadyl group for
-1
these complexes was observed in the range of 977–993 cm [62]. In the IR spectra of present
oxido-vanadium(IV) complexes (C1, C2 and C3), the characteristic IR absorption band
-1
associated with the stretching vibration of vanadyl (V═O) group is appeared at around 985 cm
-1
and the broad absorption band at around 3425 cm is attributed to the ν(H O) stretching
2
vibrations of coordinated water molecule. Their wide broadness is representative of an intensive
H-bonding [63].
3
.1.2. Electronic absorption spectroscopy
DMSO solutions of three new thiourea ligands and their oxido-vanadium(IV) complexes were
prepared, and their electronic absorption spectra were recorded in the range of 200-1000 nm.
Electronic excitation study of these samples in DMSO solution display several absorption bands
in the UV and visible regions. For all thiourea ligands, in the UV region, three intense absorption
bands in the range of 260-262, 271-274 and 323-332 nm were assigned to intra-ligand π→π* and
n→π* charge transfer transitions from phenyl and pyridine rings of the free thiourea ligands.
According to the literature, the square pyramidal oxido-vanadium(IV) complexes display three
characteristic d–d transition bands with low intensities in the visible region. Electronic excitation
study of oxido-vanadium(IV) complexes in DMSO solution result in the addition of DMSO trans
to the oxygen in the vanadyl moiety. Therefore, the third band in DMSO is mostly absent due to
a blue shift for the d–d transitions [64]. For example, Bakir J.A. Jeragh et al. observed that their
monomeric square pyramidal oxido-vanadium(IV) complexes exhibit two d–d transition bands in
the visible region and the third band is absent [62]. For present oxido-vanadium(IV) complexes
(C1, C2 and C3), in the UV region, two strong bands at around 268 and 322 nm are related to
12

ACCEPTED MANUSCRIPT
intra-ligand charge transfer transitions within the thiourea moiety of the complexes and in the
visible region, the weak bands in the range of 560-867 nm are assigned to d–d transitions within
the oxido-vanadium(IV) moiety of the complexes [7, 65].
3
.1.3. NMR spectroscopy
Proton NMR spectroscopy was recorded in CDCl3 at room temperature at 400.00 MHz on a
1
Bruker 400 instrument. H NMR spectra of three new thiourea ligands manifested the expected
characteristic resonances, multiplicity and integration consistent with the corresponding
1
structures. In the H NMR spectra of the all free thiourea ligands, the characteristic signals for
the protons on the pyridyl ring were observed at around δ 7.08-7.69 ppm, while the
H
characteristic signals for the protons on the phenyl rings were recognized in downfield about δH
7
.71-8.84 ppm. Moreover, the NH resonances notably were downfield from other resonances and
as seen, NH signals were observed in the range of δ 10.86-13.21 ppm as two broad singlet
H
1
signals in the H NMR spectra.
3
.1.4. Theoretical studies
The optimization of the molecular structures of the free thiourea ligands and their oxido-
vanadium(IV) complexes were performed at the DFT (Density Functional Theory) level of
theory. The most important geometrical parameters of the target compounds are gathered in
Tables 2 and 3. The configurations of transition metal complexes with five-coordinate atoms
around metal ion can range from regular trigonal-bipyramidal (RTBP) to regular square-based
pyramidal (RSBP) coordination. According to N6-V-O25 (145.84° in C1 and 127.52° in C3),
N14-V-N27 (158.40° in C3), S13-V-S26 (149.07 ° in C1) angles, configurations of complexes
are RSBP and coordination is occurred through the nitrogen of the pyridyl group and two CS
2
+
groups in the thiol form with vanadyl ([VO] ) ion. As can been seen from Tables 2 and 3, N10-
13

ACCEPTED MANUSCRIPT
C12 bond length in C1 and C2 is shorter than that in L1 and L2. Also, C12-S13 and N6-C5 bond
lengths in these complexes are longer than those in the corresponding ligands. These results
confirm suggested coordination through the nitrogen of the pyridyl group and two CS groups in
the thiol form with vanadyl ion. On the other hand, contraction of N10-C12 and C12-N14 bonds
with the elongation of N6-C5 and C12-S13 bonds confirm the mentioned coordination in C3
complex.
The frontier molecular orbitals (HOMO and LUMO) of thiourea ligands and their complexes are
presented in Fig. 4. In addition, some considerable electronic features such as calculated natural
charges of atoms, dipole moments and energies of HOMO and LUMO for all thiourea ligands
and complexes are listed in Table 4. As can be seen, in the HOMO molecular orbitals, the higher
negative charge density is around sulphur atoms of thiourea ligands, which can increase
probability of nucleophilic attack from those to metal ion. It can be found that more negative
charge on S13 and simultaneously less negative charges on N10 and N14 have led to
nucleophilic attack of the sulfur atoms in thionyl (C═S) groups to carbon atoms (C17 and C28)
in the phenyl rings and formation of two new five-membered rings in the free thiourea ligand L3.
The higher energy of HOMO and the lower energy of LUMO facilitate the interaction between
the donor and acceptor of electron. On the basis of the obtained results from previous
antibacterial studies [6], the quantity of difference between LUMO and HOMO energies (∆EL-H
)
and the level of the LUMO energies (ELUMO) play important roles in the antibacterial activities of
these compounds.
3
.2. Characterization of dioxo-vanadium(V) complex with chelidamic acid and metformin
hydrochloride
3
.2.1. Infrared spectroscopy
14

ACCEPTED MANUSCRIPT
The solid state properties of the dioxo-vanadium(V) complex C4 was investigated by infrared
spectroscopy. The infrared spectrum of complex C4 shows strong, broad and branched
−
1
absorption bands at 2749–3500 cm because of the O–H stretching vibrations of the
crystallization water molecules, aliphatic C–H’s of metformin, aromatic C–H’s of pyridyl ring
+
and NH stretching vibrations of metformin. The strong characteristic absorption bands at 1681
2
–
1
and 1376 cm corresponds to the asymmetric and symmetric stretching vibrations of carboxyl
groups, respectively. Furthermore, this complex exhibited one strong absorption band at 1056
−
1
cm , which is attributed to the C–O (hydroxy) vibration of dipic-OH ligand. In the IR spectrum
of the dioxo-vanadium(V) complex C4, two characteristic absorption bands associated with the
symmetric and asymmetric stretching vibrations of (V═O) group are observed at 948 and 884
-1
cm , respectively. This behavior is consistent with previously reported dioxo-vanadium(V)
complexes of the dipicolinic acid and derivatives [66-67].
3
.2.2. Electronic absorption spectroscopy
DMSO solution of the dioxo-vanadium(V) complex C4 was prepared, and its electronic
spectrum was recorded in the range of 200-1000 nm. Electronic excitation study of this sample in
DMSO solution shows two absorption bands in the UV region. The absorption bands at 220 and
285 nm were assigned to the intra-ligand π→π* and n→π* charge transfer transitions in the dipic-
OH ligand. The band at 220 nm was probably superimposed with the O→V charge transfer involving the
double bonded oxo group.
3
.2.3. NMR spectroscopy
Proton NMR spectrum of the dioxo-vanadium(V) complex C4 confirms the presence of both Met
2
−
and (dipic-OH) fragments in this complex and gives four signals in DMSO-d at δ 3.00, 7.35,
6
H
7
.61 and 8.30 ppm. The resonance at δ 3.00 ppm is assigned to methyl protons of metformin
H
15

ACCEPTED MANUSCRIPT
and the remaining three resonances correspond to aromatic protons of the pyridyl ring in (dipic-
2
−
OH) .
.2.4. Description of the crystal structure of the dioxo-vanadium(V) complex C4
3
The molecular and crystal structure of dioxo-vanadium(V) complex C4 was fully elucidated by
single crystal X-ray diffraction methods. The ORTEP view of the molecular structure of C4 is
shown in Fig. 5, together with the atomic labelling scheme. A list of the most important bond
distances and angles is reported in Table 5.
The vanadium atom shows a penta-coordinate environment, achieved by two oxo ligands and by
2
−
the tridentate (dipic-OH) moiety. The configurations of transition metal complexes with five-
coordinate atoms can range from regular trigonal-bipyramidal (RTBP, D ) to regular square-
3
h
based pyramidal (RSBP, C ) coordination. In order to assign the corrected geometrical
4v
environment as trigonal-bipyramidal or squared pyramidal to the vanadium atom, the τ parameter
defined in [68] can be considered. However, the numerical value of 0.32 in compound C4 didn’t
allow assigning unambiguously the corrected geometrical coordination.
2
−
The (dipic-OH) ligands are planar and the mean plane of the ligand bisects the dioxo-vanadium
V=O double bonds whose lengths are range from 1.603(3) to1.617(3) Å (average 1.61 Å). The
V-N and VO bond distances are V1-N6 2.072(3) Å, V1-O1 1.977(3) Å, V1-O3 1.990(2) Å
py
carb
and V2-N7 2.076(3) Å, V2-O12 1.606(3) Å, V2-O13 1.603(3) Å (Table 5).
The asymmetric unit of compound C4 is constituted by two molecular anion [VO (dipic-OH)] , a
−
2
2+
molecular cation [H Met] and a water molecule. The cation lies on a symmetry center. The
2
crystal packing is build up by several mediums to strong hydrogen bond interactions (Table 6
2
+
and Fig. 6). In particular the nitrogen atom of the cation [H Met] is involved in two hydrogen
2
−
bonds with two carboxylic oxygen atom of the anion [VO (dipic-OH)] [N(1)···O(2) 2.933(4) Å,
2
16

ACCEPTED MANUSCRIPT
N(1)−H(1B)···O(2) 148(3)° and N(1)···O(11) 2.869(4) Å, N(1)−H(1A)···O(11) 162(4)°].
Moreover, the water molecule is involved in three hydrogen bonds with two oxo and a
carboxylic oxygen atoms, [O15···O5 3.028(4) Å, O(15)−H(15B)···O(5) 148(6)°, O15···O6
3
1
3
.026(4) Å, N(15)−H(15B)···O(6) 139(6)° and O15···O10 2.554(1) Å, O(15)−H(15A)···O(10)
57(4)°].
.3. Antibacterial activities
All studied compounds were screened for antibacterial activity in terms of the minimum
inhibitory concentration (MIC) by the broth macrodilution procedure and the zone of inhibition
by the disk diffusion method against different types of bacterial strains. The experiments were
repeated three parallel times. The values of minimum inhibitory concentrations and inhibition
zones of the all compounds are reported as means of at least three determinations and are
represented in Table 7. As is apparent from the table all compounds revealed relatively good
inhibitory activities against the all bacterial strains, compared to standard drugs as positive
controls used for comparison purposes. It can also be drawn from the table that relative to
negative control DMSO, all compounds have stronger antibacterial activities. The antibacterial
activities of oxo-vanadium(IV, V) complexes are relatively higher than those of three new
thiourea ligands, hence verifying that coordination with vanadium ion leads to increment in the
biological activity of these thiourea derivatives. This increment in the antibacterial activity may
be because of the formation of the chelate, which decreases the polarity of the compound and
thereby increases the lipophilic properties. The improved lipophilic characteristics facilitate the
interaction of these complexes with cell components and processes. Moreover, the antibacterial
activities of the oxido-vanadium(IV) complexes are the highest against all types of bacterial
strains. All compounds inhibited the growth of bacteria with MIC values ranging between 64 and
17

ACCEPTED MANUSCRIPT
1
024 µg/ml. On precise examination of the theoretical results, it can be found that antibacterial
activities have some relationship with the LUMO energies and the difference between LUMO
and HOMO energies (Figures 7 and 8). We find that the thickness of inhibition zones for above-
named standard bacterial strains is linear with these features in some samples. For example, the
differences between the LUMO and HOMO energies in L2, L3, C1, C2, C3 and C4 compounds
are linear with the thickness of inhibition zones for P. aeruginosa, namely, the lower difference
between LUMO and HOMO energies leads to higher antibacterial activity. The linear equation is
y = -101.2x + 33.61, R² = 0.872. These relations may attribute to the more appropriate
interaction of these complexes with cell components and processes because of the accessibility
of the suitable orbitals. Figures 7 and 8 demonstrate more instances of these connections.
4
. Conclusions
Present research investigated the synthesis, characterization, crystal structure, theoretical
calculation and antibacterial properties of three thiourea ligands, their oxido-vanadium(IV)
complexes and dioxo-vanadium(V) complex containing chelidamic acid and metformin. From
the chemical structures of the resulting oxido-vanadium(IV) complexes, it can be concluded that
the configurations of oxido-vanadium(IV) complexes around the vanadium atom are square-
based pyramidal coordination. Theoretical calculations show that the antibacterial activities of
thiourea ligands and their oxido-vanadium(IV) complexes have some relation with the LUMO
energy and the difference between LUMO and HOMO energies. The results of antibacterial
experiments show that all the synthesized compounds have good ability to inhibit growth of the
bacteria. Considering the antibacterial activities of these compounds, we are currently working
18

ACCEPTED MANUSCRIPT
on the vanadium complexes with other thiourea ligands for the investigation of their biological
properties.
5
. Abbreviations
L1
1,1'-(pyridine-2,6-diyl)bis(3-(benzoyl)thiourea)
L2
1,1'-(pyridine-2,6-diyl)bis(3-(2-chlorobenzoyl)thiourea)
L3
1,1'-(pyridine-2,6-diyl)bis(3-(4-chlorophenyl)thiourea)
'
C1
[VO(L1)(H O)]
2
'
C2
[VO(L2)(H O)]
2
'
C3
[VO(L3)(H O)]
2
C4
[H Met][VO (dipic-OH)] ·H O
2
2
2
2
HIV
HCV
Human immunodeficiency virus
Hepatitis C virus
H dipic-OH
4-Hydroxy-2,6-pyridine dicarboxylic acid
N,N-Dimethylbiguanide
N,N-dimethylformamide
Density functional theory
Melting point
2
Met
DMF
DFT
m.p.
MLB
MHA
MIC
AMK
GEN
Muller Hinton Broth
Muller Hinton Agar
Minimum inhibitory concentration
Amikacin
Gentamycin
19

ACCEPTED MANUSCRIPT
RTBP
RSBP
HOMO
LUMO
FW
Regular trigonal-bipyramidal
Regular square-based pyramidal
Highest Occupied Molecular Orbital
Lowest Unoccupied Molecular Orbital
Formula weight
Acknowledgement
The authors are grateful to the University of Sistan and Baluchestan (USB) for financial support.
Appendix A. Supplementary materials
Full crystallographic data for the structural analysis have been deposited with the Cambridge
Crystallographic Data Center, CCDC No. 1031492. This data can be obtained free of charge via
www.ccdc.cam.ac.uk or from Cambridge Crystallographic Data Center, 12 Union Road,
Cambridge, CB2, 1EZ, UK (fax: +44 (0)1223 336033 or email: deposit@ccdc.cam.ac.uk).
References
[
1] A. Khalaj, M. Nakhjiri, A.S. Negahbani, M. Samadizadeh, L. Firoozpour, S. Rajabalian, N.
Samadi, M.A. Faramarzi, N. Adibpour, A. Shafiee, A. Foroumadi, Eur. J. Med. Chem. 46 (2011)
5–70.
2] M.S. Karthikeyan, D.J. Prasad, B. Poojary, K.S. Bhat, B.S. Holla, N.S. Kumari, Bioorg. Med.
Chem. 14 (2006) 7482–7489.
3] X.S. Cui, C. Jing, K.Y. Chai, J.S. Lee, Z.S. Quan, Med. Chem. Res. 18 (2009) 49–58.
6
[
[
20

ACCEPTED MANUSCRIPT
[
(
[
4] J. Chen, X.Y. Sun, K.Y. Chai, J.S. Lee, M.S. Song, Z.S. Quan, Bioorg. Med. Chem. 15
2007) 6775–6781.
5] X.J. Chen, F. Niyonsaba, H. Ushio, D. Okuda, I. Nagaoka, S. Ikeda, K. Okumura, H. Ogawa,
J. Dermatol. Sci. 40 (2005) 123–132.
[
[
[
[
[
6] W. Yang, H. Liu, M. Li, F. Wang, W. Zhou, J. Fan, J. Inorg. Biochem. 116 (2012) 97–105.
7] U. El-Ayaan, J. Mol. Struct. 998 (2011) 11–19.
8] H. Arslan, N. Duran, G. Borekci, C.K. Ozer, C. Akbay, Molecules 14 (2009) 519-527.
9] Z. Zhong, R. Xing, S. Liu, L. Wang, S. Caia, P. Li, Carbohydr. Res. 343 (2008) 566–570.
10] M.Kh. Rauf, I. Din, A. Badshah, M. Gielen, M. Ebihara, D.D. Vos, S. Ahmed, J. Inorg.
Biochem. 103 (2009) 1135–1144.
[
[
11] S.A. Khan, N. Singh, K. Saleem, Eur. J. Med. Chem. 43 (2008) 2272-2277.
12] G. Binzet, H. Arslan, U. Flörke, N. Külcü, N. Duran, J. Coord. Chem. 59 (2006) 1395–
1
406.
[
13] S. Cunha, F.C. Macedo Jr., G.A.N. Costa, M.T. Rodrigues Jr., R.B.V. Verde, L.C.D.S. Neta,
I. Vencato, C. Lariucci, F.P. Sa, Monatsh. Chem. 138 (2007) 511–516.
14] A.A. Isab, S. Nawaz, M. Saleem, M. Altaf, M. Monim-ul-Mehboob, S. Ahmad, H.S. Evans,
Polyhedron 29 (2010) 1251–1256.
15] A. Saeed, U. Shaheen, A. Hameed, S.Z. Haider Naqvi, J. Fluorine Chem. 130 (2009) 1028–
034.
16] G.S. Kurt, F. Sevgi, B. Mercimek, Chem. Pap. 63 (2009) 548–553.
17] E. Rodrıguez-Fernández, E. Garcıa, M.R. Hermosa, A. Jiménez-Sánchez, M.M. Sánchez, E.
[
[
1
[
[
ꢀ
ꢀ
Monte, J.J. Criado, J. Inorg. Biochem. 75 (1999) 181–188.
18] Z. Weiqun, Y. Wen, X. Liqun, C. Xianchen, J. Inorg. Biochem. 99 (2005) 1314–1319.
[
21

ACCEPTED MANUSCRIPT
[
19] R.D. Campo, J.J. Criado, R. Gheorghe, F.J. Gonzalez, M.R. Hermosa, F. Sanz, J.L.
Manzano, E. Monte, E. Rodriguez-Fernandez, J. Inorg. Biochem. 98 (2004) 1307–1314.
[
[
20] F. Bilek, T. Krizova, M. Lehocky, Colloids Surf B Biointerfaces 88 (2011) 440-447.
21] R.D. Campo, J.J. Criado, E. Garcia, M.R. Hermosa, A. Jimenez-Sanchez, J.L. Manzano, E.
Monte, E. Rodriguez-Fernandez, F. Sanz, J. Inorg. Biochem. 89 (2002) 74–82.
[
[
[
[
[
22] H. Pluempe, W. Pulls, Chem. Abstr. 74 (1971) 1251154n.
23] H.M. Faidallah, K.A. Khan, A.M. Asiri, J. Fluorine Chem. 132 (2011) 131–137.
24] H.M. Faidallah, K.A. Khan, A.M. Asiri, J. Fluorine Chem. 132 (2011) 870–877.
25] S. Karakus, S. Rollas, Il Farmaco 57 (2002) 577–581.
26] S.B. Tsogoeva, M.J. Hateley, D.A. Yalalov, K. Meindl, C. Weckbecker, K. Huthmacher,
Bioorg. Med. Chem. 13 (2005) 5680–5685.
[
[
[
27] O.J. DCruz,Y. Dong, F.M. Uckun, Biochem. Biophys. Res. Commun. 302 (2003) 253–264.
28] T.K. Venkatachalam, E.A. Sudbeck, F.M. Uckun, Tetrahedron Lett. 42 (2001) 6629–6632.
29] I.J. Kang, L.W. Wang, C.C. Lee, Y.C. Lee, Y.S. Chao, T.A. Hsu, J.H. Chern, Bioorg. Med.
Chem. Lett. 19 (2009) 1950–1955.
30] W. Hermindez, E. Spodine, L. Beyer, U. Schrtider, R. Richter, J. Ferreira, M. Pavani,
Bioinorg. Chem. Appl. 3 (2005) 3-4.
31] W. Hermindez, E. Spodine, J.C. Mufioz, L. Beyer, U. Schrtider, R. Richter, J. Ferreira, M.
Pavani, Bioinorg. Chem. Appl. 1 (2003) 3-4.
32] E. Rodríguez-Fernández, J.L. Manzano, J.J. Benito, R. Hermosa, E. Monte, J.J. Criado, J.
Inorg. Biochem. 99 (2005) 1558–1572.
33] M.K. Rauf, I.A. Badshah, M. Gielen, M. Ebihara, D. de Vos, S. Ahmed, J. Inorg. Biochem.
03 (2009) 1135–1144.
[
[
[
[
1
22

ACCEPTED MANUSCRIPT
[
(
[
(
[
[
[
34] H.J. Zhang, X. Qin, K. Liu, D.D. Zhu, X.M. Wang, H.L. Zhu, Bioorg. Med. Chem. 19
2011) 5708–5715.
35] I.C. Mendes, M.A. Soares, R.G. dos Santos, C. Pinheiro, H. Beraldo, Eur. J. Med. Chem. 44
2009) 1870–1877.
36] F.H. Nielsen, FASEB J. 5 (1991) 2661–2667.
37] M. Anke, H. Illing-Gunther, U. Schafer, Biomed. Res. Trace Elem. 16 (2005) 208–214.
38] G. Müller, H. Benkhai, R. Matthes, B. Finke, W. Friedrichs, N. Geist, W. Langel, A.
Kramer, Biomaterials 35 (2014) 5261–5277.
39] I.O. Adriazola, A.E. doAmaral, J.C. Amorim, B.L. Correia, C.L.O. Petkowicz, A.L.R.
Mercê, G.R. Noleto, J. Inorg. Biochem. 132 (2014) 45–51.
40] Z.H. Chohan, S.H. Sumrra, M.H. Youssoufi, T.B. Hadda, Eur. J. Med. Chem. 45 (2010)
739–2747.
41] T. Rosu, E. Pahontu, M. Reka-Stefana, D.C. Ilies, R. Georgescu, S. Shova, A. Gulea,
Polyhedron 31 (2012) 352–360.
[
[
2
[
[
[
42] S.H. Sumrra, Z.H. Chohan, Spectrochim. Acta, Part A 98 (2012) 53–61.
43] D.C. Crans, M. Mahroof-Tahir, M.D. Johnson, P.C. Wilkins, L. Yang, K. Robbins,
A.Johnson, J.A. Alfano, M.E. Godzala, L.T. Austin, G.R. Willsky, Inorg. Chim.Acta 356 (2003)
65-378.
3
[
[
[
44] L. Yang, A. la Cour, O.P. Anderson, D.C. Crans, Inorg. Chem. 41 (2002) 6322-6331.
45] T.G. Porter and D.L. Martin, Biochem. Pharmacol. 34 (1985) 4145–4150.
46] I. Sánchez-Lombardo, E. Sánchez-Lara, A. Pérez-Benítez, Á. Mendoza, S. Bernès, E.
González-Vergara, Eur. J. Inorg. Chem. (2014) 4581–4588.
47] G. Li, D.J. Che, Z.F. Li, Y. Zhu, D.P. Zou, New J. Chem. 26 (2002)1629–1633.
[
23

ACCEPTED MANUSCRIPT
[
[
48] C.K. Ozer, H. Arslan, D. VanDerveer, G. Binzet, J. Coord. Chem. 62 (2009) 266-276.
49] A.D. Becke, Density-Functional Thermochemistry. III. The Role of Exact Exchange. J.
Chem. Phys. 98 (19993) 5648–5652.
50] C. Lee, W. Yang, R.G. Parr, Development of the Colle-Salvetti Correlation-Energy Formula
into a Functional of the Electron Density. Phys. Rev. B 37 (1988) 785–789.
51] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman, G.
[
[
Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H.P.
Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, J.A.
Montgomery, J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N.
Staroverov, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar,
J. Tomasi, M. Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C.
Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C.
Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth, P. Salvador,
J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman, J.V. Ortiz, J. Cioslowski,
D.J. Fox, Gaussian 09, Revision A.1, Gaussian, Inc., Wallingford CT, 2009.
[
52] E.D. Glendening, A.E. Reed, J.E. Carpenter, F. Weinhold, NBO 3.1; Theoretical Chemistry
Institute, University of Wisconsin: Madison, 1990.
[
[
[
[
[
53] G. Micera and E. Garribba, Int. J. Quantum Chem. 112 (2012) 2486–2498.
54] G. Micera, V.L. Pecoraro, E. Garribba, Inorg. Chem. 48 (2009) 5790–5796.
55] S. Gorelsky, G. Micera, E. Garribba, Chem. Eur. J. 16 (2010) 8167 – 8180.
56] Bruker, SAINT and SMART, Bruker AXS Inc., Madison, Wisconsin, USA, 2009.
57] G.M. Sheldrick, Acta Crystallogr.,Sect. A 64 (2008) 112–122.
24

ACCEPTED MANUSCRIPT
[
[
[
58] A.L. Spek, Acta Crystallogr.,Sect. D 65 (2009) 148–155.
59] L.J. Farrugia, J. Appl. Crystallogr. 45 (2012) 849–854.
60] C.F. Macrae, P.R. Edgington, P. McCabe, E. Pidcock, G.P. Shields, R. Taylor, M. Towler,
J.V.D. Streek, J. Appl. Crystallogr. 39 (2006) 453–457.
[
[
[
61] I. Wiegand, K. Hilpert, R.E.W. Hancock, Nature Protocols 3 (2008) 163-175.
62] B.J.A. Jeragh and A. El-Dissouky, Transition Met. Chem. 29 (2004) 579–585.
63] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Compounds.
Wiley-Interscience, New York, 1997.
[
[
64] C.J. Ballhausen and H.B. Gray, Inorg. Chem. 1 (1962) 111–122.
65] H.Y. Zhao, Y.H. Zhang, Y.H. Xing, Z.P. Li, Y.Z. Cao, M.F. Ge, X.Q. Zeng, S.Y. Niu,
Inorg. Chim. Acta 362 (2009) 4110–4118.
66] B.S. Parajo´n-Costa, O.E. Piro, R. Pis-Diez, E.E. Castellano, A.C. Gonza´lez-Baro,
Polyhedron 25 (2006) 2920–2928.
67] D.C. Crans, M. Mahroof-Tahir, M.D. Johnson, P.C. Wilkins, L. Yang, K. Robbins, A.
Johnson, J.A. Alfano, M.E. Godzala, L.T. Austin, G.R. Willsky, Inorg. Chim. Acta 356 (2003)
65–378.
68] A.W. Addison, T.N. Rao, J. Reedijk, J. van Rijn, G.C. Verschoor, J. Chem. Soc., Dalton
Trans. (1984) 1349.
[
[
3
[
25

ACCEPTED MANUSCRIPT
Figure legends
Fig. 1. The minimum energy structures of the ligand L1 and complex C1.
Fig. 2. The minimum energy structures of the ligand L2 and complex C2.
Fig. 3. The minimum energy structures of the ligand L3 and complex C3.
Fig. 4. HOMO and LUMO Molecular orbitals of the thiourea ligands and their complexes.
Fig 5. ORTEP representation of C4. Displacement ellipsoids are drawn at the 50% probability
level and H atoms are shown as small spheres of arbitrary radii.
Fig. 6. The intermolecular hydrogen bonds between the biguanidium groups and the carboxylate
groups of the dipic-OH, between the oxo groups and the water molecules, as well as between the
carboxylate groups of dipic-OH and water molecules with donor. . .acceptor distance.
Fig. 7. The linear relations between the energies of LUMOs and the inhibition zones (a) for P.
aeruginosa in L1, C1, C2 and C3 samples; (b) for E. faecalis in C1, C2 and C3 samples and (c)
for P. aeruginosa in C1, C2 and C3 samples.
Fig. 8. The linear relations of the differences between the LUMO and HOMO energies and the
inhibition zones (a) for P. aeruginosa in L2, L3, C1, C2, C3 and C4 samples; (b) for E. faecalis in
L1, L2, L3, C1, C2 and C3 samples; (c) for S. aureus in L2, C1, C2 and C3 samples and (d) for
E. coli in C1, C2 and C3 samples.
26

ACCEPTED MANUSCRIPT
Fig. 1.
27

ACCEPTED MANUSCRIPT
Fig. 2.
28

ACCEPTED MANUSCRIPT
Fig. 3.
29