Metal based new triazoles: Their synthesis, characterization and antibacterial/antifungal activities

Article abstract of DOI:10.1016/j.saa.2012.08.026

A series of new triazoles and their oxovanadium(IV) complexes have been synthesized, characterized and evaluated for antibacterial/antifungal properties. The new Schiff bases ligands (L¹)-(L⁵) were prepared by the condensation reaction of 3,5-diamino-1,2,4-triazole with 2-hydroxy-1-naphthaldehyde, pyrrole-2-carboxaldehyde, pyridine-2-carboxaldehyde, 2-acetyl pyridine and 2-methoxy benzaldehyde. The structures of the ligands have been established on the basis of their physical, spectral (IR, ¹H and ¹³C NMR and mass spectrometry) and elemental analytical data. The prepared ligands were used to synthesize their oxovanadium(IV) complexes (1)-(5) which were also characterized by their physical, spectral and analytical data and proposed to have a square pyramidal geometry. The ligands and their complexes were screened for in vitro antibacterial activity against six bacterial species such as, Escherichia coli, Shigella flexneri, Pseudomonas aeruginosa, Salmonella typhi, Staphylococcus aureus, and Bacillus subtilis and for in vitro antifungal activity against six fungal strains, Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani, and Candida glabrata. Cytotoxic nature of the compounds was also reported using brine shrimp bioassay method against Artemia salina.

Full text of DOI:10.1016/j.saa.2012.08.026

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 53–61
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Metal based new triazoles: Their synthesis, characterization
and antibacterial/antifungal activities
⇑
Sajjad H. Sumrra, Zahid H. Chohan
Department of Chemistry, Bahauddin Zakariya University, Multan 60800, Pakistan
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
"
"
"
Novel series of triazole and its
vanadium metal complexes are
studied.
Characterization is made on the
basis of their physical, spectral and
analytical data.
Antibacterial and antifungal
correlation with vanadium metal is
established.
Bioactivity is enhanced upon
coordination with the vanadium
metal.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 June 2012
Received in revised form 28 July 2012
Accepted 12 August 2012
Available online 23 August 2012
A series of new triazoles and their oxovanadium(IV) complexes have been synthesized, characterized and
evaluated for antibacterial/antifungal properties. The new Schiff bases ligands (L1)–(L5) were prepared by
the condensation reaction of 3,5-diamino-1,2,4-triazole with 2-hydroxy-1-naphthaldehyde, pyrrole-2-
carboxaldehyde, pyridine-2-carboxaldehyde, 2-acetyl pyridine and 2-methoxy benzaldehyde. The struc-
tures of the ligands have been established on the basis of their physical, spectral (IR, 1H and 13C NMR and
mass spectrometry) and elemental analytical data. The prepared ligands were used to synthesize their
oxovanadium(IV) complexes (1)–(5) which were also characterized by their physical, spectral and analyt-
ical data and proposed to have a square pyramidal geometry. The ligands and their complexes were
screened for in vitro antibacterial activity against six bacterial species such as, Escherichia coli, Shigella
flexneri, Pseudomonas aeruginosa, Salmonella typhi, Staphylococcus aureus, and Bacillus subtilis and for
in vitro antifungal activity against six fungal strains, Trichophyton longifusus, Candida albicans, Aspergillus
flavus, Microsporum canis, Fusarium solani, and Candida glabrata. Cytotoxic nature of the compounds was
also reported using brine shrimp bioassay method against Artemia salina.
Keywords:
1,2,4-Triazole ligands
Oxovanadium(IV) complexes
Antibacterial
Antifungal
Cytotoxic activity
Crown Copyright Ó 2012 Published by Elsevier B.V. All rights reserved.
Introduction
is of great interest since its discovery of a role in biotic and abiotic
systems [12]. Another perspective application of vanadium com-
Triazoles occupy a unique position [1] amongst the potentially
used bioactive compounds due to different potential activities such
as antibacterial [2], antifungal [3], anticonvulsant [4], antiprolifer-
ative [5], antitumor [6], antitubercular [7], anticancer [8], anti HIV
[9] and antiviral [10]. The coordination behavior [11] of vanadium
pounds is their ability in promoting the biological properties like
antimicrobial [13], antitumor [14], antileukemic [15], spermicidal
[16], antiamoebic activity [17] and recently most significant insu-
lin mimetic activity [18]. Keeping in view the significant bioactive
nature of triazoles as well as biological functioning of vanadium
metal, it was thought valuable to merge the chemistry of triazoles
with the vanadium metal to form a novel class of vanadium metal
based triazoles that could serve as potential antibacterial and
⇑
Corresponding author. Tel.: +92 3006802791; fax: +92 619210083.
E-mail address: dr.zahidchohan@gmail.com (Z.H. Chohan).
1386-1425/$ - see front matter Crown Copyright Ó 2012 Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.08.026

54
S.H. Sumrra, Z.H. Chohan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 53–61
antifungal agent against resistant bacterial/fungal strains. For
accomplishment of this task, a series of oxovanadium(IV) com-
plexes with different new triazole Schiff base compounds have
been synthesized (Scheme 1) and characterized. These compounds
were then subjected to in vitro antibacterial activity against six
bacterial species such as, Escherichia coli, Shigella flexneri, Pseudo-
monas aeruginosa, Salmonella typhi, Staphylococcus aureus and Bacil-
lus subtilis and for in vitro antifungal activity against six fungal
strains, Trichophyton longifusus, Candida albicans, Aspergillus flavus,
Microsporum canis, Fusarium solani and Candida glabrata. Cytotoxic
nature of the compounds was also reported using brine shrimp
bioassay method against Artemia salina.
Elemental analysis was carried out on Perkin Elmer (USA model).
1H and 13C NMR spectra were recorded on a Bruker Spectrospin
Avance DPX-400 spectrometer using TMS as internal standard
and d6-DMSO as a solvent. Electron impact mass spectra (EIMS)
were recorded on JEOL MS route instrument. In vitro antibacterial,
antifungal and cytotoxic properties were studied at HEJ Research
Institute of Chemistry, International Centre for Chemical Sciences,
University of Karachi, Pakistan.
Synthesis
An equimolar solution of 3,5-diamino-1,2,4-triazole (0.99 g,
0.01 mol) and 2-hydroxynaphthaldehyde (1.72 g, 0.01 mol) in dry
methanol (50 mL) was refluxed for 3 h, a precipitated product
was formed during refluxing. It was then cooled to room tempera-
ture, filtered, washed with methanol (35 mL), then with diethyl
ether (2 ꢀ 5 mL) and dried under vacuum. Recrystallization in a
mixture of methanol:dioxane (1:4) gave TLC pure product (L1) in
83% yield. The same method was applied for the preparation of
all other ligands (L2)–(L5).
Experimental
Materials and methods
All the chemicals used were of analytical grades. 3,5-Diamino-
1,2,4-triazole was purchased from Sigma Aldrich. Fisher Johns
melting point apparatus was used for recording melting points.
IR spectra were recorded on SHIMADZU FT-IR spectrophotometer.
Scheme 1. Synthesis of the triazole ligands and their oxovanadium(IV) complexes.

S.H. Sumrra, Z.H. Chohan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 53–61
55
1-{(E)-[(5-Amino-1H-1,2,4-triazol-3-yl)imino]methyl}naphthalen-2-
ol (L1)
(d, 1H, J = 7.9 Hz, C3–H), 7.32 (t, 1H, J = 7.7 Hz, C4–H), 7.59 (d, 1H,
J = 8.1 Hz, C6–H), 8.36 (s, C11–H), 11.89 (s, 1H, NH); 13C NMR
(DMSO-d6): d 56.1 (OCH3), 113.7 (C6), 120.9 (C4), 122.5 (C2),
128.6 (C3), 133.8 (C5), 156.1 (C13), 159.6 (C1), 160.2 (C11), 163.1
(C12); EIMS (70 eV) m/z (%): 217 ([M]+, 28), 201 (100), 186 (19),
171 (12), 161 (32), 146 (9), 134 (23), 107 (9), 104 (43), 77 (13);
Anal. Calcd. for C10H11N5O (217.23): C, 55.29; H, 5.10; N, 32.24;
O: 7.37; Found: C, 55.26; H, 5.09; N, 32.22; O: 7.34%.
Yield: 83% (2.1 g); colour (yellow); m.p. 229–231 °C; IR (KBr,
cmꢁ1): 3436 (OH), 3348 (NH2), 3203 (NH, triazole), 1637 (HC@N),
1612 (C@N, triazole), 1028 (N–N); 1H NMR (DMSO–d6): d 6.02 (s,
2H, NH2), 7.11 (d, 1H, J = 9.1 Hz, C3–H), 7.39 (t, 1H, J = 7.5 Hz, C6–
H), 7.59 (t, 1H, J = 7.5 Hz, C7–H), 7.85 (d, 1H, J = 7.9 Hz, C4–H),
7.98 (d, 1H, J = 9.1 Hz, C5–H), 8.19 (d, 1H, J = 8.4 Hz, C8–H), 8.29
(s, 1H, C11–H), 10.22 (s, 1H, OH), 12.10 (s, 1H, NH); 13C NMR
(DMSO-d6): d 115.5 (C1), 123.2 (C6), 124.1 (C3), 125.8 (C8), 126.3
(C10), 127.6 (C7), 128.9 (C5), 133.5 (C9), 136.1 (C4), 156.3 (C13),
158.3 (C11), 159.2 (C2), 163.8 (C12); EIMS (70 eV) m/z (%): 253
([M]+, 14), 236 (100), 222 (16), 197 (11), 182 (17), 169 (68), 154
(11), 141 (12), 127 (43), 77 (9); Anal. Calcd. for C13H11N5O
(253.26): C, 61.60; H, 4.38; N, 27.65; O: 6.32; Found: C, 61.63; H,
4.35; N, 27.63; O: 6.30%.
Synthesis of oxovanadium(IV) complexes (1)–(5)
Vanadyl sulfate (0.163 g, 0.001 mol) in a dry methanol solution
(20 mL) was treated with Schiff base ligand 1-{(E)-[(5-amino-1H-
1,2,4-triazol-3-yl)imino]methyl}naphthalen-2-ol
(L1)
(0.51 g,
0.002 mol) in dry dioxane (40 mL). The reaction mixture was re-
fluxed for 3 h during which a precipitated product was formed.
The reaction mixture was then cooled to room temperature. The
precipitates thus formed were filtered, washed with methanol,
dioxane and then with diethyl ether and dried under vacuum.
N3-[(E)-1H-Pyrrol-2-ylmethylidene]-1H-1,2,4-triazole-3,5-diamine
(L2)
Yield: 78% (1.37 g); colour (light brown); m.p. 185–187 °C; IR
(KBr, cmꢁ1): 3343 (NH2), 3204 (NH, triazole), 3175 (NH, pyrrole),
1636 (HC@N), 1613 (C@N), 1030 (N–N); 1H NMR (DMSO-d6, d,
ppm): d 5.95 (dd, 1H, J = 3.9, 2.8 Hz, C4–H), 6.02 (s, 1H, NH2), 6.71
(d, 1H, J = 2.8 Hz, C5–H), 7.01 (d, 1H, J = 3.9 Hz, C3–H), 8.72 (s, 1H,
The precipitated product was recrystallized in
a mixture of
water:dioxane (1:3) to obtain TLC pure vanadium complex (1).
All other complexes (2)–(5) were prepared following the same
method (Scheme 1).
C
11–H), 9.46 (s, 1H, NH), 12.07 (s, 1H, NH); 13C NMR (DMSO-d6,
d, ppm): d 115.4 (C3), 121.4 (C4), 125.6 (C5), 132.1 (C2), 156.2
(C13), 157.9 (C11), 162.7 (C12); EIMS (70 eV) m/z (%): 176 ([M]+,
100), 160 (19), 146 (18), 134 (9), 120 (21), 105 (19), 93 (13), 79
(27), 66 (6), 52 (7); Anal. Calcd. for C7H8N6 (176.18): C, 47.72; H,
4.59; N, 47.70; Found: C, 47.68; H, 4.56; N, 47.66%.
Estimation of vanadium metal
The vanadium content present in complex (1) was determined
volumetrically by using 0.1 N KMnO4 solution as an oxidizing
agent in the presence of dil. H2SO4. For this purpose, sample of
the oxovanadium(IV) complex (1) (100 mg) was placed in a silica
crucible, decomposed by gentle heating and then by adding 1–
2 mL of conc. HNO3 two to three times. An orange colored mass
(V2O5) was obtained after decomposition and complete drying. It
was dissolved in miminum amount of dil. H2SO4 and solution so
obtained was diluted with distilled water to 100 mL in a measuring
flask. The amount of vanadium in the tested sample was calculated
[19] by using the standard relationship given below. All other oxo-
vanadium(IV) complexes (2)–(5), were estimated following the
same method.
N3-[(E)-Pyridin-2-ylmethylidene]-1H-1,2,4-triazole-3,5-diamine (L3)
Yield: 74% (1.39 g); colour (grey); m.p. 172–174 °C; IR (KBr,
cmꢁ1): 3347 (NH2), 3201 (NH, triazole), 1633 (HC@N), 1609
(C@N), 1030 (N–N); 1H NMR (DMSO-d6, d, ppm): d 6.01 (s, 2H,
NH2), 7.33 (ddd, 1H, J = 7.8, 5.2, 1.3 Hz, C5–H), 7.71 (dd, 1H,
J = 7.9, 1.3 Hz, C3–H), 8.04 (ddd, 1H, J = 7.9, 7.8, 1.9 Hz, C4–H),
8.68 (dd, 1H, 5.2, 1.9 Hz, C6–H), 8.95 (s, 1H, C11–H), 12.11 (s, 1H,
NH); 13C NMR (DMSO-d6, d, ppm): d 121.2 (C3), 126.8 (C5), 136.6
(C4), 149.6 (C6), 153.9 (C2), 156.1 (C13), 158.6 (C11), 162.3 (C12);
EIMS (70 eV) m/z (%): 188 ([M]+, 15), 172 (100), 161 (11), 133
(36), 118 (74), 105 (13), 92 (15), 78 (22), 51 (8); Anal. Calcd. for
C8H8N6 (188.19): C, 51.06; H, 4.28; N, 44.66; Found: C, 51.02; H,
4.26; N, 44.61%.
1 mL of 0.1 N KMnO4 = 0.005094 g vanadium.
Pharmacology
N3-[(1E)-1-(Pyridin-2-yl)ethylidene]-1H-1,2,4-triazole-3,5-diamine
(L4)
Antibacterial studies (in vitro)
Yield: 70% (1.42 g); colour (grey); m.p. 126–128 °C; IR (KBr,
cmꢁ1): 3349 (NH2), 3199 (NH), 1634 (HC@N), 1612 (C@N), 1033
(N–N); 1H NMR (DMSO-d6, d, ppm): d 2.36 (s, 3H, CH3), 6.04 (s,
2H, NH2), 7.33 (ddd, 1H, J = 7.8, 5.2, 1.3 Hz, C5–H), 7.71 (dd, 1H,
J = 7.9, 1.3 Hz, C3–H), 8.04 (ddd, 1H, J = 7.9, 7.8, 1.9 Hz, C4–H),
8.68 (dd, 1H, 5.2, 1.9 Hz, C6–H), 8.95 (s, 1H, C11–H), 12.11 (s, 1H,
NH); 13C NMR (DMSO-d6, d, ppm): d 16.8 (CH3), 121.2 (C3), 126.8
(C5), 136.6 (C4), 149.6 (C6), 153.9 (C2), 156.1 (C13), 158.6 (C11),
162.3 (C12); EIMS (70 eV) m/z (%): 202 ([M]+, 18), 186 (24), 172
(100), 161 (9), 146 (22), 133 (16), 118 (11), 105 (18), 92 (20), 78
(17), 51 (13); Anal. Calcd. for C9H10N6 (202.22): C, 53.46; H, 4.98;
N, 41.96; Found: C, 53.43; H, 4.96; N, 41.91%.
All newly synthesized triazole Schiff bases (L1)–(L5) and their
oxovanadium(IV) complexes (1)–(5) were screened in vitro for
their antibacterial activity against four Gram-negative (E. coli, S.
flexneri, P. aeruginosa, S. typhi) and two Gram-positive (S. aureus,
B. subtilis) bacterial strains by the agar-well diffusion method
[20]. The wells (6 mm in diameter) were dug in the media with
the help of a sterile metallic borer. Bacterial inocula (2–8 h old)
containing approximately 104–106 colony-forming units (CFU/
mL) were spread on the surface of the nutrient agar with the help
of a sterile cotton swab. The recommended concentration of the
test sample (1 mg/mL in DMSO) was introduced in the respective
wells. Other wells supplemented with DMSO and reference anti-
bacterial drug, imipenum served as negative and positive controls,
respectively. The plates were incubated at 37 °C for 24 h. Activity
was determined by measuring the diameter of zones showing com-
plete inhibition (mm). In order to evaluate the interfering effect of
DMSO on the biological screening, alternate studies on DMSO solu-
tion showed no activity against any bacterial strains.
N3-[(E)-(2-Methoxyphenyl)methylidene]-1H-1,2,4-triazole-3,5-
diamine (L5)
Yield: 73% (2.59 g); colour (reddish brown); m.p. 238–240 °C; IR
(KBr, cmꢁ1): 3346 (NH2), 3199 (NH), 2910 (OCH3), 1632 (HC@N),
1603 (C@N, triazole), 1027 (N–N); 1H NMR (DMSO-d6): d 3.86 (s,
3H, OCH3), 6.02 (s, 2H, NH2), 6.87 (t, 1H, J = 8.5 Hz, C5–H), 6.95

56
S.H. Sumrra, Z.H. Chohan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 53–61
Antifungal activity (in vitro)
IR spectra
IR spectral data of the ligands is reported in experimental sec-
Antifungal activities of all compounds were studied [20] against
six fungal strains (T. longifusus, C. albican, A. flavus, M. canis, F. solani
and C. glabrata). Sabouraud dextrose agar (Oxoid, Hampshire, Eng-
land) was seeded with 105 (CFU/mL) fungal spore suspensions and
tion and oxovanadium(IV) complexes in Table 2. All the triazole li-
gands have active donor sites such as, azomethine (–C@N) linkage,
hydroxyl (–OH), methoxy (–OCH3), pyrrole (N–H), pyridine nitro-
gen (–C–N) and triazole-N, for coordination with the vanadium
metalloelement. All the ligands showed bands at 3180–3204,
1594–1616 and 1016–1033 cmꢁ1 respectively due to N–H, C@N
and N–N vibrations of triazole [24] moiety. Originally, 3,5-diami-
no-1,2,4-triazole had two bands [25] at 3310 and 3350 cmꢁ1 due
to two amino groups present in the molecule. All the ligands
showed an absence of a band at 3310 cmꢁ1 emerging into a new
band of azomethine linkage [26] at 1626–1636 cmꢁ1 however, a
band at 3350 cmꢁ1 was remained unchanged giving thus an evi-
dence for condensation of only one amino group of the triazole
transferred to petri plates. Discs soaked in 20 mL (200 lg/mL in
DMSO) of the compounds were placed at different positions on
the agar surface. The plates were incubated at 32 °C for 7 days.
The results were recorded as percentage of inhibition and com-
pared with standard drugs miconazole and amphotericin B.
Minimum inhibitory concentration (MIC)
Compounds containing promising antibacterial (above 80%)
activity were selected for minimum inhibitory concentration
(MIC) studies. The minimum inhibitory concentration was deter-
mined using the disc diffusion technique [21] by preparing discs
containing 10, 25, 50 and 100 g mLꢁ1 concentrations of the com-
pounds along with standards at the same concentrations.
moiety [27]. The hydroxyl and methoxy, [
v(–OH) and v(OCH3)]
groups of ligands (L1) and (L5) appeared at 3436 and 2910 cmꢁ1
.
On comparison of the IR spectral data of all the oxovana-
dium(IV) complexes with the data of triazole Schiff base ligands,
the absorption modes indicated that the triazole Schiff base ligands
were principally coordinated to the vanadium(IV) metal ion biden-
tately. The coordination modes of bonding are discussed as under:
Cytotoxicity (in vitro)
Brine shrimp (Artemia salina leach) eggs were hatched in a
shallow rectangular plastic dish (22 ꢀ 32 cm), filled with artificial
seawater, which was prepared with commercial salt mixture and
double distilled water. An unequal partition was made in the plas-
tic dish with the help of a perforated device. Approximately 50 mg
of eggs were sprinkled into the large compartment, which was
darkened while the matter compartment was opened to ordinary
light. After two days a pipette collected nauplii from the lighted
side. A sample of the test compound was prepared by dissolving
20 mg of each compound in 2 mL of DMF. From this stock solutions
(1) All the ligands showed azomethine m(HC@N) bands at 1632–
1637 cmꢁ1 which shifted [28] to lower frequency (12–
15 cmꢁ1) at 1618–1624 cmꢁ1 indicating the coordination of
the azomethine-N with the vanadium(IV) metal atom.
(2) The appearance of a new band at 1387–1388 cmꢁ1 was
assigned [29] to m(C–O) in the spectra of vanadyl(IV) com-
plex (1) and (5), confirming deprotonation and coordination
of hydroxyl-OH to the vanadium(IV) metal.
(3) A new lower frequency bands at 518–522 were assigned to
m
(V–O) of complexes (1) and (5), and all complexes showed
500, 50 and 5 lg/mL were transferred to 9 vials (three for each
bands at 423–428 cmꢁ1 due to
m
(V–N) [30] respectively
dilutions were used for each test sample and LD50 is the mean of
three values) and one vial was kept as control having 2 mL of
DMF only. The solvent was allowed to evaporate overnight. After
two days, when shrimp larvae were ready, 1 mL of seawater and
10 shrimps were added to each vial (30 shrimps/dilution) and
the volume was adjusted with seawater to 5 mL per vial [22]. After
24 h the number of survivors were counted and analyzed by Finney
computer program to determine the LD50 values [23].
indicating the coordination of these ligands with the vana-
dyl(IV) metal ion.
(4) A new band at 960–970 cmꢁ1 which was only observed in all
the spectra of the complexes was assigned to the presence of
(V@O) [31]. The oxovanadium complexes (2)–(4), showed
bands at 1080–1086 due to the presence of (SO4) [32].
(5) The bands at 3343–3349, 3199–3204, 1603–1613 and 1027–
1033 cmꢁ1 respectively assigned to the vibrations,
(N–H), (C@N) and (N–N) of triazole moiety remained
v(NH2),
v
v
v
Results and discussion
unchanged in all the ligands indicating their non-involve-
ment in the coordination.
Chemistry
All the above mentioned evidences supported the coordination
of the ligands with the vanadium(IV) metal though azomethine-N,
pyridine-N, deprotonation of hyroxyl-OH and pyrrol-N.
The triazole Schiff base ligands (L1)–(L5) were prepared by the
condensation reaction of 3,5-diamino-1,2,4-triazole with 2-hydro-
xy-1-naphthaldehyde, pyrrole-2-carboxaldehyde, pyridine-2-car-
boxaldehyde, 2-acetyl pyridine and 2-methoxybenzaldehyde
respectively, under stirring. The prepared ligands were air, mois-
ture stable, different colored compounds and only soluble in diox-
ane, DMF and DMSO. All were amorphous solids which melted at
126–240 °C. The oxovanadium(IV) complexes (1)–(5) of the syn-
thesized ligands were prepared in a molar ratio 1:2 (metal:ligand).
All the oxovanadium(IV) complexes were green colored amor-
phous solid. All the complexes decomposed on heating rather than
melting. They were all only soluble in DMSO and DMF. The ele-
mental analysis and solubility data were consistent with mono-
mers and showed 1:2 stoichiometry of type ML2 where M is
metal and L is ligand. The analytical data given in (Table 1), also
agreed well with the proposed structure of the complexes. The
spectral data of the vanadyl(IV) complexes is reported in Tables 1
and 2.
1H NMR spectra
1H NMR spectral data of the triazole Schiff bases recorded in
DMSO-d6 along with its possible assignments is reported in the
experimental part. All the protons due to aromatic and heteroaro-
matic were found in their expected region [33]. All the ligands
(L1)–(L5) possessed a singlet at 12.07–12.11 and 8.29–8.95 ppm
due to NH proton of triazole moiety and azomethine protons
(C11–H). Also, all ligands demonstrated [34] characteristic amino
(NH2) protons at 5.98–6.08 ppm as a singlet which provided an evi-
dence for condensation of one mono group of triazole moiety. The
ligand (L1) possessed hydroxyl (OH) proton at 10.22 ppm as a sin-
glet. Other C3–H, C4–H, C5–H and C8–H protons were found as a
double doublet at 7.11, 7.85, 7.98 and 8.19 ppm, respectively, but
C6–H and C7–H protons appeared as
a triplet at 7.39 and

S.H. Sumrra, Z.H. Chohan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 53–61
57
Table 1
Physicaland microanalytical data of the oxovanadium(IV) complexes.
No.
Structure
MW (g/mol) Formula
M.P (dec.) (°C)
Yield (%) [colour]
Found (calculated)%
C
H
N
V
(1)
(2)
(3)
(4)
(5)
[VO(L1–H)2]
[VO(L2–H)2]
[VO(L3)2]
[571.44]
240–241
248–250
263–265
85
[Green]
74
[Sea-green]
72
[Light green]
74
[Light green]
81
[Sea-green]
54.69
(54.65)
40.33
(40.30)
35.59
(35.63)
38.14
(38.10)
40.17
(40.21)
3.51
(3.53)
3.36
(3.38)
2.99
(2.97)
3.51
(3.53)
3.65
(3.68)
24.48
(24.51)
40.25
(40.28)
31.13
(31.21)
29.57
(29.61)
23.41
(23.44)
8.81
C
26H20N10O3V
[417.28]
14H14N12OV
SO4 [539.31]
16H16N12O5SV
SO4 [567.37]
18H20N12O5SV
SO4 [597.46]
20H22N10O7SV
(8.85)
12.17
(12.21)
9.48
(9.44)
8.94
(8.98)
8.55
(8.53)
C
C
[VO(L4)2]
C
254–257
229–232
[VO(L5)2]
C
Table 2
Physical, spectral and IR data of oxovanadium(IV) complexes.
1
No.
M [cmꢁ (nm)]
B.M (eff
)
kmax [cmꢁ1 (nm)]
IR (cmꢁ1
)
(X )
ꢁ1 cm2 molꢁ1
(1)
(2)
(3)
(4)
(5)
41.8
39.5
88.9
85.8
87.5
1.75
1.73
1.78
1.73
1.68
12412 (806), 17541 (570), 24912 (401), 37256 (268)
12576 (795), 17534 (570), 24978 (400), 37364 (268)
12536(798), 17418(574), 25013 (400), 36751 (272)
12642 (791), 17639 (567), 25057 (399), 36632 (273)
12475 (801), 17498 (572), 24783 (404), 36712 (272)
1622 (C@N), 1388 (C–O), 960 (V@O), 518 (V-O), 428 (V-N)
1624 (C@N), 970 (V@O), 425 (V–N)
1623 (C@N), 1085 (SO4), 968 (V@O), 425 (V–N)
1622 (C@N), 1088 (SO4), 965 (V@O), 427 (V–N)
1618 (C@N), 1378 (C–O), 1085 (SO4), 965 (V@O), 522 (V–O), 422 (V–N)
7.59 ppm, respectively. The NH proton of pyrrolyl ring found in the
ligand (L2) exhibited a singlet at 9.46 ppm. Also, C5–H and C3–H
protons were found in the region at 6.71 and 7.01 ppm as a
doublet, and C4–H proton at 5.95 ppm as double of doublet. The
ligands (L3) and (L4) showed C3–H and C6–H protons at 7.71 and
8.68 ppm as double of doublet, and C4–H and C5–H protons ap-
peared as double of double doublet at 7.33 and 8.04 ppm, respec-
tively. The ligand (L5) showed (OCH3) proton at 2.86 ppm as a
singlet. Other protons, C4–H and C5–H appeared as a triplet at
6.87–7.32 ppm. The C3–H and C6–H protons were observed at
6.95–7.59 ppm as a doublet. The conclusions drawn from this
study provided further support to the modes of bonding discussed
earlier in IR spectra.
at m/z 172. In addition, the mass of ligand (L4) with molecular for-
mula [C9H10N6]+, was observed at m/z 202 (calcd. 202.22) and its
most stable fragment [C8H6N5]+ was shown at m/z 172. Moreover,
the mass of ligand (L5) with molecular formula [C10H11N5O] was
observed at m/z 217 (calcd. 217.22) and the most stable fragment
[C10H9N4O]+ was observed at m/z 201. All ligands fragmentation
pattern followed the cleavage of C@N (exocyclic as well as endocy-
clic), C–N, C–C, C@C and C–O bonds. The proposed mass fragmen-
tation pattern of (L1) has been shown in Fig. 1.
Conductance and magnetic susceptibility measurements
The molar conductance studies of the oxovanadium(IV) com-
plexes (1)–(5) were carried out in DMF solution and the results re-
ported in Table 2. The molar conductance values of compounds (1)
13C NMR spectra
and (2) fall in the range 39.5–41.8
non-electrolytic nature [35]. Conductance values of compounds
(3)–(5), however, fall in the range 85.8–88.9
ꢁ1 cm2 molꢁ1 indi-
X
ꢁ1 cm2 molꢁ1 showing their
The spectra of ligands (L1)–(L5) possessed the triazole carbons
C
12 and C13 in the region at 156.12–163.78 ppm. In addition to this,
X
the azomethine carbons C11 of all ligands appeared in the region at
157.9–160.23 ppm. Moreover, the aromatic and heteroaromatic
carbons of these two series were found at 115.35–159.17 ppm.
The peak for C2 of ligand (L1) was observed at 159.17 ppm due to
higher inductive effect of hydroxyl (OH) group. However, the
methoxy-C in the ligand (L5) appeared in the region at
55.39 ppm. The methyl-C in ligand (L4) was observed at
16.83 ppm. The results of these studies were found to be in agree-
ment with the results of IR and 1H NMR spectra of these
compounds.
cating their electrolytic [36] nature (Table 2). The effective mag-
netic moments of the oxovanadium(IV) complexes at room
temperature were found in the range 1.68–1.78 B.M. which are
indicative of the presence of a single electron consistent with
half-spin (S = 1/2) orbital contribution. These results gave a clue
for vanadium metal to possess +4 oxidation state which is indicative
of having square-pyramidal geometry of all these oxovanadium(IV)
complexes. These values were also compatible to the reported
values for the compounds having square-pyramidal geometry.
Electronic spectra
Mass spectra
The UV/Visible spectra of all the oxovanadium(IV) complexes in
DMF displayed three (Table 2) distinctive low to high intensity
The electron impact mass spectra (EIMS) of the synthesized tri-
azole Schiff bases is recorded in experimental part. The molecular
mass of ligand (L1) with molecular formula [C13H11N5O]+, was ob-
served at m/z 253 (calcd. 253.26) and its base peak stable fragment
[C13H10N5]+ was found at m/z 236. Similarly, the mass of ligand (L2)
with molecular formula [C7H8N6]+ was found at m/z 176 (calcd.
176.18) as a stable fragment. The ligand (L3) showed molecular
mass at m/z 188 (calcd. 188.19) with molecular formula
[C8H8N6]+ and its most stable fragment [C8H6N5]ꢂ+ was appeared
bands
p
(
m1
,
m2 and m3
)
which were assigned to b2ðdxyÞ !
e ðdxz; dyzÞ; b2ðdxyÞ ! b1ðd2 ꢁ y2Þ and b2ðdxyÞ ! a1ðd2Þ transitions,
x
z
respectively. The first band observed at 12412–12642 cmꢁ1 was
assigned to b2 ! e d–d transitions. The second band was observed
p
at 17418–17639 cmꢁ1 which can be attributed to b2 ? b1 and the
presence of third band at 24783–25057 cmꢁ1 can be assigned to
the transitions b2 ? a1. The fourth band of high intensity observed
at 36632–37251 cmꢁ1 was due to metal ? ligand charge transfer

58
S.H. Sumrra, Z.H. Chohan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 53–61
Fig. 1. Proposed mass fragmentation pattern of (L1).
(MLCT). All these observations provided a strong evidence for the
complexes to show a square-pyramidal geometry [37,38].
which displayed moderate (50%) activity. Likewise, significant
(55%) activity against (d) strain was observed by the ligands (L5)
and remaining strains demonstrated moderate (42–50%) activity.
All the oxovanadium(IV) complex (1)–(5) showed significant
(54–88%) activity against all bacterial strains. The antibacterial
studies revealed that all the Schiff base ligands and their oxovana-
dium(IV) complexes contributed significantly towards enhancing
the biological activity.
Biological activity
Antibacterial Bioassay
The results obtained from in vitro antibacterial studies are sum-
marized in (Table 3) and (Fig. 2). All the compounds were tested
against four Gram-negative (E. coli, S. flexneri, P. aeruginosa, S. typhi)
and two Gram-positive (S. aureus, B. subtilis) bacterial strains. The
results obtained were compared with that of the standard drug
imipenum. The percentage of activity was compared with the
activity of the standard drug considering its activity as 100%. All li-
gands and their oxovanadium(IV) complexes possessed wide-rang-
ing biological activity against all Gram-negative and Gram-positive
bacterial strains. The synthesized compounds showed varying de-
gree of inhibitory effects: low (up to 33%), moderate (up to 53%)
and significant (above 53%). The studies of results showed that
the ligand (L1) exhibited significant (55–59%) activity against (a),
(c) and (d) bacterial and moderate (45–50%) activity against (b),
(e) and (f). Also, the ligands (L2)–(L4) exhibited a significant (54–
72%) activity against all the strains except (b) of the ligand (L3)
Antifungal bioassay
The triazole ligands (L1)–(L5) and their oxovanadium(IV) com-
plexes (1)–(5) were subjected to screen against six fungal strains
(Table 4 and Fig. 3). It was indicated from the obtained antifungal
results that ligand (L1) possessed significant (61%) activity against
(c) and moderate (39–48%) against (b), (d)–(f) but inactive against
fungal strain (a). However, the ligand (L2) demonstrated overall
significant (55–63%) activity against all fungal strains except (c)
which showed moderate (49%) activity. Similarly, the ligand (L3)
exhibited significant (54–62%) activity against (d)–(f) and moder-
ate (47–52%) against (a)–(c) fungal strains. Furthermore, signifi-
cant (58–63%) activity was observed by the ligand (L4) against
(a), (d)–(f) and moderate (42–44%) against (b), (c) fungal strains.
Table 3
Antibacterial activity (concentration used 1 mg/mL of DMSO) of triazole Schiff base ligands and their oxovanadium(IV) complexes.
Bacteria
Compounds [Zone of Inhibition (mm)]
(L1)
(L2)
(L3)
(L4)
(L5)
(1)
(2)
(3)
(4)
(5)
(A)
SD
Gram-negative
(a)
(b)
(c)
(d)
16
14
16
17
16
17
16
20
17
19
17
19
18
17
20
21
12
14
13
16
17
18
21
19
19
22
18
27
24
25
20
24
25
22
24
25
20
16
17
18
10
12
11
10
29
31
30
29
Gram-positive
(e)
(f)
12
14
17
18
16
14
18
17
11
14
16
17
23
24
21
20
22
23
16
16
08
09
26
28
SA =
1.83
1.51
1.90
1.64
1.75
1.79
3.31
2.25
1.38
1.60
1.41
1.72
Average of bacterial strains
13.6
16.8
17.5
18.5
12.2
17
22.2
22.3
23.5
16.2
10
28.8
(a) E. coli, (b) S. flexneri, (c) P. aeruginosa, (d) S. typhi, (e) S. aureus, (f) B. Subtilis; <10 = weak; 11–15 = moderate; 16 and above = significant; (A) = simple triazole; SD = standard
drug = imipenum; SA = statistical analysis.

S.H. Sumrra, Z.H. Chohan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 53–61
59
Fig. 2. Comparison of antibacterial activity.
Table 4
Antifungal activity (concentration used 200
l
g/mL) of triazole Schiff base ligands and oxovanadium(IV) complexes.
Organism
Compounds
(L1)
(L2)
(L3)
(L4)
(L5)
(1)
(2)
(3)
(4)
(5)
SD
(a)
(b)
(c)
(d)
(e)
(f)
00
48
61
43
43
39
55
63
49
59
56
60
47
52
45
54
64
62
60
42
44
58
63
58
45
48
56
37
49
00
40
61
70
57
35
55
72
77
65
69
70
75
59
66
54
74
80
78
71
55
63
73
79
75
57
46
62
54
58
39
A
B
C
D
E
F
SA20.58
4.86
7.72
8.86
20.15
13.16
4.32
10.58
8.80
7.37
Average of fungal strains
39
57
54
54.2
39.2
53
71.3
68.5
69.3
51.5
(a) T. longifusus, (b) C. albicans, (c) A. flavu, (d) M. canis, (e) F. Solani, (f) C. glabrata, SD = standard drugs MIC
l
g/mL; a = miconazole (70
l
g/mL:1.6822 ꢀ 10ꢁ7 M/mL),
b = miconazole (110.8
l
g/mL:2.6626 ꢀ 10ꢁ7 M/mL), c = amphotericin B (20
l
g/mL:2.1642 ꢀ 10ꢁ8 M/mL), d = miconazole (98.4
l
g/mL:2.3647 ꢀ 10ꢁ7 M/mL), e = miconazole
(73.25
l
g/mL: 1.7603 ꢀ 10ꢁ7 M/mL), f = miconazole (110.8 g/mL: 2.66266 ꢀ 10ꢁ7 M/mL), SA = statistical analysis.
l
Fig. 3. Comparison of antifungal activity.
Beside this, (L5) showed significant (56%) activity against (c), and
moderate (37–49%) against (a), (b), (d) and (e) and showed no
activity against (f) fungal strains. The vanadyl complex (1) showed
moderate (35–40%) activity against (a) and (e) and rest of all
strains possessed significant (55–70%) activity. In addition to this,
the complexes (2)–(5) possessed significant (54–81%) activity
against all strains except (f) of complex (5) which displayed weak-
er (38%) activity. The comparison of the average antifungal activity
data revealed that the oxovanadium(IV) metal complexes dis-
played average value (60.4%) greater than the average value of
the ligands (49.2%). It was also concluded that the heterocyclic
aldehyde ring system and imine (–CH@N) group play a key role
in enhancing the activity. On the other hand, the comparison of
average values of the complexes versus ligands, a conclusion can
be drawn that the antifungal activity is overall enhanced upon che-
lation with the oxovanadium(IV) metal atom.
Minimum inhibitory concentration (MIC)
The synthesized ligands and their oxovanadium(IV) complexes
possessing promising antibacterial activity (above 80%) were se-
lected for MIC studies and obtained results are reported in Table 5.

60
S.H. Sumrra, Z.H. Chohan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 98 (2012) 53–61
Table 5
studies revealed that all the oxovanadium(IV) complexes showed
more biological activity against one or more bacterial and/or fungal
strains as compared to the parent ligands, hence showing better re-
sults of bioactivities rather than their uncomplexed parent ligands
[39]. Generally, it is claimed that functional groups present in the
compounds are responsible for enhancing antibacterial and anti-
fungal activities.
Minimum inhibitory concentration (mol/mL) of the selected compounds (2–4) against
selected bacteria.
Microorganisms
MIC (mol/mL)a
(2)
(3)
(4)
Gram-negative
E. coli
S. flexneri
P. aeruginosa
S. typhi
Gram-positive
S. aureus
B. subtilis
ND
ND
ND
1.435 ꢀ 10ꢁ6
6.378 ꢀ 10ꢁ3
ND
4.751 ꢀ 10ꢁ8
ND
4.117 ꢀ 10ꢁ7
5.223 ꢀ 10ꢁ4
2.383 ꢀ 10ꢁ2
3.832 ꢀ 10ꢁ3
Acknowledgments
3.132 ꢀ 10ꢁ7
1.879 ꢀ 10ꢁ6
1.391 ꢀ 10ꢁ4
4.237 ꢀ 10ꢁ5
5.688 ꢀ 10ꢁ7
The authors are thankful to Higher Education Commission
(HEC), Government of Pakistan for the award to carry out this re-
search work. We are also indebted to HEJ Research Institute of
Chemistry, University of Karachi, Pakistan, for providing their help
in taking NMR and mass spectra and, for the help in carrying out
antibacterial, antifungal and brine shrimp bioassays.
ND
a
Each compound was measured three times, with a standard deviation (SD) less
than 10% in all the cases. ND is not determined at tested concentrations.
Table 6
Brine shrimp bioassay of triazole Schiff
bases (L1–L5) and oxovanadium(IV) com-
plexes (1–5).
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