Synthesis, Characterization and Antimicrobial Activities of Copper(II) Complexes of Schiff Base Ligand 2-[(3′-N-salicylidinephenyl)benzimidazole]

Article abstract of DOI:10.14233/ajchem.2019.22067

CuX2·6H2O (X = Cl^–, Br^– or ClO4^–) reacted with a Schiff base ligand 2-[(3′-N-salicylidinephenyl)benzimidazole] in 1:2 mole ratio in methanol to yield brown colored complexes of types [CuCl2L]2, [CuBr1.5L1.5]2Br and [Cu(OCl

Full text of DOI:10.14233/ajchem.2019.22067

Asian Journal of Chemistry; Vol. 31, No. 9 (2019), 1979-1984
A
SIAN
J
OURNAL OF HEMISTRY
C
https://doi.org/10.14233/ajchem.2019.22067
Synthesis, Characterization and Antimicrobial Activities of Copper(II)
Complexes of Schiff Base Ligand 2-[(3′-N-salicylidinephenyl)benzimidazole]
1,*,
2,
B. ROOPASHREE
and V. GAYATHRI
1
Department of Chemistry, J.S.S.Academy of Technical Education, (Affiliated toVisvesvaraya Technological University), Bengaluru-560060,
India
2
Department of Post Graduate Studies in Chemistry, Central College Campus, Bangalore University, Bengaluru-560001, India
*
Corresponding author: Fax: +91 80 28612706; E-mail: roopajss@gmail.com
Received: 12 March 2019; Accepted: 17 April 2019;
Published online: 31 July 2019;
AJC-19485
–
–
–
CuX
2
·6H
2
O (X = Cl , Br or ClO
4
) reacted with a Schiff base ligand 2-[(3′-N-salicylidinephenyl)benzimidazole] in 1:2 mole ratio in
L] Br and [Cu(OClO )L (ClO ·4H O. The complexes were
methanol to yield brown colored complexes of types [CuCl
2
2
, [CuBr1.5
L
1.5
]
2
3
2
]
2
4
)
2
2
characterized by analytical and spectroscopic studies such as elemental analysis, conductivity and magnetic moment measurements,
thermogravimetric analysis, IR, far-IR, electronic, ESR and mass spectral studies. IR spectral studies suggested the coordination of ligand
to the central metal atom via tertiary nitrogen of benzimidazole and nitrogen of azomethine group. Based on these studies, binuclear
structure was proposed for all the copper complexes. The ligand and its copper(II) complexes were screened for antibacterial and antifungal
activities.
Keywords: Schiff base, Benzimidazole, Copper(II) complexes, Biological activity.
Schiff base of salicylaldehyde and its derivatives are studied
to a greater extent due to their unusual magnetic properties,
novel structural features and importance to biological systems
[12-16].
INTRODUCTION
Benzimidazoles are the promising class of biologically
significant N-heterocycles and are abundant in naturally occur-
ring drugs such as omeprazole, astemizole and emedastine
difumarate [1]. Transition metal complexes with biologically
important N-donor ligands have gained the significance for
their application in the pharmaceutical industry, interesting
magnetic properties, finding application as corrosion inhibitors
for metals and alloys. Transition metal complexes with 2-substi-
tuted benzimidazole ligands exhibit cytotoxic, antiviral and anti-
amoebic properties [2-6]. Schiff bases have the ability to
reversibly bind oxygen, catalytic activity in the hydrogenation
of olefins and exhibit photochromism and thermochromism
Copper is a vital trace element necessary for all the living
organisms. It plays significant role as a fundamental constituent
of many enzymes. Copper complexes display variations in coor-
dination geometry, excellent colours, unusual magnetic prop-
erties, technical application dependent molecular structures
and spectroscopic properties and their biochemical significance
[17,18]. Diverse geomentries are displayed by copper(II) ion
with the same ligand and is known as plasticity effect [17,19,20]
as a consequence of Jahn-Teller distortion of Cu(II) ion. Coordi-
nation complexes of copper(II) ion with benzimidazole ligands
are studied as models for copper proteins [21-25]. Copper salts
and copper complexes also exhibit antibacterial, antifungal
properties and have applications in ion exchange resins [26,27].
In view of this, we report herein the synthesis, structural charac-
terization and antimicrobial studies of copper(II) complexes
of Schiff base ligand formed by the condensation of m-amino-
phenyl benzimidazole and salicylaldehyde.
[
7] and hence have been used as ligands in coordination chemistry.
Metal complexes of biologically important ligands are many
a times more effective than uncoordinated N-heterocycles.
Metal complexes of Schiff-base ligands have significant appli-
cations in bioinorganic chemistry because many of these comp-
lexes serve as biological models in understanding the structure
of biologically important molecules and processes [8-11].
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1
980 Roopashree et al.
Asian J. Chem.
was prepared for the organisms. The medium was sterilized,
fresh culture of fungi and ampicillin were added to prevent
bacterial growth at a concentration 25 µg/30 mL of the culture
medium and the plates were prepared. In each petridish, five
wells were made using a sterile borer. 0.1 mL of test solution
of concentration 2.5 mg/0.1 mL, standard solution and DMSO
control were poured into separate wells in each plate. The petri-
dishes were covered and incubated at 28 ºC for 48 h. Zone
inhibitions were observed and average three readings were
recorded.
Synthesis of 2-[(3′-N-salicylidinephenyl)benzimidazole]:
A new Schiff base ligand, 2-[(3′-N-salicylidinephenyl)benzi-
midazole] was prepared by the condensation of methanolic
solution of m-aminophenyl benzimidazole [29] with salicyl-
aldehyde at refluxing temperature for 6 h. The reaction mixture
was concentrated to get yellow coloured compound (Fig. 1).
The solid was filtered, dried and recrystallized in methanol.
The X-ray crystallographic studies of the ligand is reported
elsewhere [30]. m.p. = 235 ºC, Yield = 76 %.
EXPERIMENTAL
All the reagents were of analytical grade. The solvents
used were purified according to standard procedure [28].
Hydrated copper halides were obtained from BDH. Hydrated
perchlorate was prepared by dissolving copper(II) carbonate
in 1:2 aqueous perchloric acid, evaporating the resulting solu-
tion to almost dryness under reduced pressure. Standard drugs
were obtained from Ranbaxy, India.
Microanalyses were obtained from ElementarVario EL
III and TGA was recorded on Perkin Elmer, Diamond TG/DTA
-1
with a heating rate of 15 ºC min in nitrogen atmosphere at
Sophisticated Test and Instrumentation Centre (STIC), Cochin,
India. IR (nujol mull) spectra were recorded on Shimadzu FTIR
8
400s spectrometer. Far-IR spectra were recorded on Thermo
Nicolet model; 6700 spectrometer and magnetic susceptibility
measurements were recorded by VSM method at Central
Instrumentation Facility, Pondicherry University, Pondicherry,
India. Electronic spectra were recorded in DMF on Shimadzu
UV 3101PC spectrophotometer. Molar conductivity measure-
ments were made on a Systronic conductivity meter 304-cell
Type CD-10. ESI mass spectra were recorded on a Micromass
Quattro II triple quadrupole mass spectrometer at SAIF, CDRI,
Lucknow. ESR spectra were recorded on ESR-SVarian,USA
make, E-112 ESR Spectrometer model at SAIF, IIT, Bombay.
Biological activity:Antimicrobial activities were carried
out by agar diffusion method. The ligand 2-[(3′-N-salicyli-
dinephenyl)benzimidazole], its Cu(II) complexes and standard
drug dissolved in DMSO (2.5 µg/0.1 mL) were used for testing
antimicrobial activity. Peptone (0.6 %), beef extract (0.15 %),
sodium chloride, dextrose and agar (2 %) were dissolved in
000 mL of distilled water at 7.4 pH to form nutrient agar
media. The medium was autocalved at 121 ºC for 15 min at
5 lb pressure/sq. inch. The mixture was cooled to 45 ºC. Fresh
culture (6 g of peptone, 1.5 g of beef extract, 1 g of dextrose,
5 g of agar and 5 g of sodium chloride in 1000 mL of distilled
water) was added, mixed well and the medium was allowed to
solidify. In each petridish, five wells were made using a sterile
borer. 0.1 mL of test solution (2.5 µg/0.1 mL), standard solution
and DMSO control were poured into separate wells in each
plate. The petridish was covered and incubated at 37 ºC for 24 h.
Zone inhibitions were observed and average three readings
were recorded.
Synthesis of [Cu(OClO
3
)L
2
]
2
(ClO
4
)
2
·4H
2 2
O, [CuCl L]
2
and [CuBr1.5
L
1.5 2
]
Br complexes: To 1 mmol of hydrated
−
−
−
CuX
2
·6H
2
O (X = Cl , Br or ClO ) in 12 mL of methanol and
4
triethyl orthoformate mixture (3:1), 10 mL of methanolic
solution of Schiff base ligand (2 mmol) was added. The reaction
mixture was heated under reflux for 6 h during which a brown
solids got separated. The solids were filtered, washed with
methanol and dried in a vacuum (Yield 60-70 %).
RESULTS AND DISCUSSION
Copper halides/perchlorate react with 2-[(3′-N-salicylidi-
nephenyl)benzimidazole] in 1:2 mole ratio in methanol/teof
1
mixture to yield brown coloured complexes of the types [CuCl
Br and [Cu(OClO )L (ClO ·4H O.
The complex, [CuCl L] was insoluble in common organic
solvents but soluble in DMF and DMSO in which it behaved
as non-electrolyte. The [CuBr1.5 Br exhibited 1:1 electro-
L]
2 2
1
[CuBr1.5
L
1.5
]
2
3
2
]
2
4
)
2
2
2
2
1
L
]
1.5 2
lytic behavior in DMSO and [Cu(OClO
exhibited 1:2 electrolytic behaviour [31].
3
)L
2
]
2
(ClO
4
)
2
·4H O
2
The TGA studies for the complex was restricted to 300
ºC to determine the nature of water molecules present in the
complex. The complex, [Cu(OClO
3
)L
2
]
2
(ClO
4
)
2
·4H O lost water
2
molecules within 100 ºC indicating the presence of lattice water
in the complex. The results are in accordance with the compo-
sition of the complex as determined by elemental analyses.
The physical properties and analytical data of the compounds
are listed in Table-1.
Pathogenic fungi were isolated by inoculating infec-
ted sample into corn meal agar. The inoculated plates were
incubated at 28 ºC for 2 days. The colonies thus formed were
selected for further screening. The Sabouraud′s agar medium
Fig. 1. Preparation of 2-[(3'-N-salicylidinephenyl)benzimidazole]

Vol. 31, No. 9 (2019)
Synthesis and Antimicrobial Activities of Copper(II) Complexes of Schiff Base Ligand 1981
TABLE-1
PHYSICAL PROPERTIES AND ANALYTICAL DATA
m.p../d.p.
°C)
Elemental analysis (%): Found (calcd.)
a
Complex
Ligand
Colour
Λ
eff
µ *
(
C
H
N
Yellow
Brown
Brown
Green
235
> 280
235
–
–
1.1
0.92
0.94
76.92 (76.66)
53.60 (53.60)
51.30 (51.66)
51.70 (51.93)
4.96 (4.83)
3.00 (3.30)
3.60 (3.25)
4.00 (3.70)
13.38 (13.42)
9.70 (9.40)
9.00 (9.03)
9.30 (9.08)
[
[
[
CuCl L]
28
2
2
b
CuBr L ] Br
38
88
1
.5 1.5 2
b
Cu(OClO )L ] (ClO ) ·4H O
> 280
3
2
2
4
2
2
-
1
2
-1
Λ in Ω cm mol ; a in DMF, b in DMSO, *Bohr magneton
IR spectral studies: The IR spectra of the ligand and its
copper(II) complexes were recorded as nujol mull (Table-2).
The spectra of all the complexes were similar to that of uncoor-
dinated N-heterocycle except for minor shifts in the position
of the peaks. The IR spectrum of the ligand showed the absence
was made through the combined use of 1-D and 2-D NMR
experiments such as COSY, HSQC and HMBC experiments
carried out for the ligand.
1
The H NMR spectrum of the ligand exhibited a singlet at
12.80 ppm due to imine and OH protons. A singlet at 8.20
ppm was assigned to 2′ proton. Spectrum exhibited a multiplet
at 7.23 ppm and a triplet at 7.01 ppm which were assigned to
4, 7 and 4′′, 3′′ protons of benzimidazole unit and salicylidine
unit, respectively. Phenylene ring proton 4′ exhibited a doublet
at 7.54 ppm. A triplet at 7.44 ppm was due to a proton at 5′′.
Protons 5, 6 and 5′ exhibited a multiplet at 7.62 ppm. Doublets
at 8.12 and 7.72 ppm were assigned to protons of 6′ of phenyl
and 6′′ of salicylidine moiety, respectively.Azomethine proton
exhibited a singlet at 9.08 ppm.
of peaks due to νNH or νC-O of the precursor m-aminophenyl
2
benzimidazole and salicyladehyde which suggested the
complete formation of azomethine linkage [32-35]. A peak at
-1
1
312 cm and shift in νC-N and νO-H compared to the vibrations
in usual Schiff bases suggested the presence of intramolecular
H-bonding between OH group and the azomethine nitrogen
atom [36]. Schiff base ligand can coordinate to central metal ion
through nitrogen of benzimidazole moiety and/or azomethine
nitrogen or oxygen of hydroxyl group after deprotonation. The
-1
13
free ligand displayed νC-N at 1618 cm due to benzimidazole
moiety and azomethine group. This peak was shifted upon
complexation, indicating the participation of the tertiary nitrogen
of benzimidazole moiety and/or azomethine group in the metal
coordination sphere. Hence, the Schiff base ligand can behave
as both monodentate as well as bridging bidentate ligand. The
The C NMR spectrum of ligand exhibited peaks in the
range 115 ppm to 165 ppm. Quaternary carbons 2, (8 & 9), (1′
& 1′′), 3′ & 2′′ exhibited peaks at 150.66, 131.36, 160.30,
148.34 and 119.30 ppm, respectively. The signals at 122.24
and 130.12 ppm were assigned to benzimidazole ring carbons
(4, 7) and (5, 6), respectively. Phenyl ring carbons 2′, 4′, (5′ & 6′)
exhibited signals at 119.40, 122.51 and 124.77 ppm, respectively.
The resonance signals at 119.23, 116.64, 133.50 and 132.54
ppm were due to salicylidine ring carbon atoms 3′′ 4′′, 5′′ and
6′′, respectively.A resonance signal at 163.97 ppm was assigned
to azomethine carbon atom.
ν
C-N and δN-H, νN-H and νO-H of the uncoordinated N-heterocycle
-1
appeared at 1312, 3157 and 3471 cm , respectively [37]. The
characteristic band of C-OH group of salicyladehyde lowered
-1
by the H-bonding, which was observed at 1115 cm in the
spectrum of ligand. The νO-H of the complexes was found in
-1
the range 3534-3300 cm which indicated that oxygen of O-H
was not involved in the coordination. The IR spectral data of
the complex containing water molecules displayed a broad
2D-Homonuclear and heteronuclear techniques have assisted
the complete analysis of the resonances of ligand. The COSY
spectrum of ligand showed the cross peaks between the protons
(4′ & 5′), (5′ & 6′), (3′′ & 4′′), (4′′ & 5′′), (5′′ & 6′′). In order to
make unambiguous assignments of the resonances, PFG-HSQC
and PFG-HMBC [39,40] experiments had been carried-out. The
-1
peak in the range 3534-3300 cm assigned for νO-H of water
molecule and salicylidine moiety. The perchlorato complex
of copper exhibited peaks at 1184, 1156, 1100, 1045 and 621
-1
13
cm indicative of the presence of both coordinated as well as
ionic perchlorate groups [38], which was also supported from
the conductivity data.
C NMR spectrum of ligand showed fifteen resonances for
the carbons. Cross peaks were observed for the protons 4, 5,
6, 7, 2′, 4′, 5′, 6′, 3′′, 4′′, 5′′, 6′′ and C-H proton of imine group
with the corresponding carbons. The PFG-HMBC experiment
of the ligand displayed carbon-proton correlation of long range
or multiple bonds. For multiple bonds connectivity or long-
range information, this provided support for the assignment
of resonances of the quaternary carbons 2, 8, 9, 1′, 3′, 1′′ and
2′′. The resonances due to the quaternary carbons 1′′ and 1′
The far-IR spectrum of chloro complex of copper displayed
-1
peak due to only terminal νCu-Cl at 282 cm while its bromo
analogue exhibited peaks corresponding to both bridging as
-1
well as terminal bromides at 188 and 259 cm , respectively.
NMR spectral studies of 2-[(3′-N-salicylidinephenyl)-
benzimidazole]: The structural and spectroscopic assignments
TABLE-2
IR AND FAR-IR SPECTRAL DATA (cm )
–1
ν
of
ν
C–N
&
δN–H
ν
M–X
(b)
ν
M–X
(t)
N–H
Complex
νO–H
νC=N
ν
ClO
4
benzimidazole
x = Cl/Br
x = Cl/Br
Ligand
3471
3400
3300-3182
3157
3138
3300-3182
1618
1615
1608
1312
1282
1310
–
–
188
–
282
259
–
–
–
[
[
CuCl L]2
2
CuBr L ] Br
1.5 1.5 2
1
184, 1156, 1100,
[
Cu(OClO )L ] (ClO ) ·4H O 3600-3451(b)
3186
1608
1303
–
–
3
2
2
4
2
2
1045, 621

1
982 Roopashree et al.
Asian J. Chem.
appeared at 160.30 ppm and the assignments were made with
the help of C-H proton of azomethine group in the HMBC
experiment. Further, hydroxyl proton showed cross peaks with
quaternary carbons 2′′, 1′′ and 1′.
mined by elemental analyses. IR spectral studies indicated the
coordination of the ligand to the central metal atom through
tertiary nitrogen of benzimidazole as well as nitrogen atom of
azomethine moiety behaving as both monodentate and bridging
bidentate.
Electronic spectral and magnetic moment studies: The
electronic spectra of ligand and its copper(II) complexes were
recorded in DMF. The spectra of free ligand displayed intense
Electronic spectra of the copper complexes indicated square
planar geometry around metal ion. Chloro complex of copper
*
bands in the range 297-354 nm which was assigned to π → π
was analyzed for the formula [CuCl
2
L] . ESR and mass spectral
2
*
and n → π transitions. The spectra of copper complexes of 2-
(3′-N-salicylidinephenyl)benzimidazole] displayed absor-
analysis supported dimeric structure. Far-IR spectrum indicated
the presence of terminal chlorides. Hence a binuclear structure
with ligand acting as bridging bidentate has been suggested
[
ption band in the range 707-778 nm which is attributed to d-d
transition arising out of square planar geometry [41]. The mag-
netic moment of copper(II) complexes are in the range 0.92-1.1
B.M. and is in consistence with one unpaired electron. The low
magnetic moment is characteristic of antiferromagnetic coupling
between two Cu(II) ions.
ESR spectral studies: ESR spectra of copper(II) complexes
recorded at ambient and liquid nitrogen temperature (Fig. 2)
showed no significant difference in the pattern. The ESR spectra
for the [CuCl
The bromo complex of copper analyzed for the formula
Br . ESR and mass spectral studies supported dimeric
2
L]
2
complex (Fig. 3a).
Cu
2
4
L
3
nature of the complex. Far-IR spectrum indicated the presence
of both bridging and terminal bromides and the complex showed
1:1 electrolytic behaviour. Based on these studies, binuclear
structure with one ligand acting as bridging bidentate and other
two as monodentate has been suggested (Fig. 3b).
of [CuCl
2
L]
while [CuBr1.5
. The g|| values were in the range 2.11-2.24 and g
2
and [Cu(OClO
3
)L
2
]
2
(ClO
Br showed only one peak due
in the
4
)
2
·4H
2
O displayed two
Perchlorato complex of copper analyzed for the formula
g
|| and a g
⊥
L
1.5
]
2
Cu
2
L
4
(ClO ) . ESR and mass spectral analysis revealed its dimeric
4
4
to g
⊥
⊥
nature. The complex showed 1:2 electrolytic behaviour. IR
spectrum indicated the presence of both ionic and monoden-
tately coordinated perchlorate groups. Based on these studies,
the complex has been assigned binuclear structure wherein
the two ligands acting as bridging bidentate and two as monoden-
tately coordinated to the metal ion (Fig. 3c).
range 2.04-2.09. The g|| < 2.3 for the copper complexes sugg-
ested considerable covalent character in the metal-ligand bond.
Further, g|| > g
⊥
implied a dx2-y2 ground state. The dimeric nature
of the complexes have been supported by the observation of a
weak ESR signal at g ≈ 4.2 corresponding to ∆Ms = ± 2 spin
forbidden transition in addition to a broad rhombic signal in
the g ≈ 2 region [42].
Mass spectral studies: Mass spectrum of ligand exhibited
m/z peak at 314 corresponding to the molecular formula of
Antibacterial activity: The ligand and the synthesized
complexes were screened against five different bacterial (Table-
3) strains. The compounds, control (DMSO) and standard drug
ampicillin were screened against two Gram-positive bacteria,
Staphylococcus aureus and Bacillus cereus, three Gram- negative
bacteria Escherichia coli, Salmonella typhi and Pseudomonas
aerugenosa. Varying degree of inhibitory effect was observed
against these bacteria. The Schiff base, 2-[(3′-N-salicylidine-
phenyl)benzimidazole] was not sensitive to bacterial strains
except for E. coli. In general, antibacterial activity increased
upon complexation [44].All the complexes did not show inhibi-
tion effect on Bacillus cereus.All the copper complexes exhibited
excellent antibacterial activity against P. aerugenosa and found
to be more effective than the standard drug. Perchlorato complex
of copper was found not sensitive towards Gram-positive bacteria,
Staphylococcus aureus and Bacillus cereus.Antibacterial activity
was found to increase with increase in the concentration of
the test solution. The increase in toxicity may be due to reduction
the ligand. Mass spectra of [CuCl
Cu(OClO )L (ClO ·4H O, have supported the binuclear
nature of the complexes [43]. These compounds exhibited mole-
cular ion peaks at 896, 1395 and 1579 corresponding to Cu Cl
Cu Br andCu (OClO , respectively supporting the binuclear
nature of these complexes.
2
L]
2
, [CuBr1.5
L
1.5
]
2
Br and
[
3
2
]
2
4
)
2
2
2
4 2
L ,
2
3 3
L
2
3
)
2 4
L
Stereochemistry:A new Schiff base ligand and its copper
complexes were synthesized. Conductivity measurements of
chloro complexes suggested non-electrolytic behaviour while
bromo complex exhibited 1:1 and for [Cu(OClO
3
)L
2
]
2
(ClO
4
)
2
·
4H O exhibited 1:2 electrolytic behaviour. Thermogravimetric
2
analysis data of perchlorato complex of copper suggested the
presence of lattice water molecules in the complex. The results
are in accordance with the composition of the complexes as deter-
[
CuCl L]2
2
[
Cu(OClO )L ] (ClO ) ·H O
[CuBr1.5
L
] Br
3 2 2 4 2 2
1.5 2
6
00 1000 1600 2000 2400 2800 3200 3600 4000600 1000 1400 1800 2200 2600 3000 3400 3800 600 1000 1400 1800 2200 2600 3000 3400 3800
Magnetic field (Gauss)
Magnetic field (Gauss)
Magnetic field (Gauss)
Fig. 2. ESR spectra of Cu(II) complexes

Vol. 31, No. 9 (2019)
Synthesis and Antimicrobial Activities of Copper(II) Complexes of Schiff Base Ligand 1983
(
a)
(
b)
(
c)
Fig. 3. Sterochemistry of the complexes
TABLE-3
ANTIBACTERIAL ACTIVITY
Concentration (ppm)
% Activity index
Concentration (ppm)
% Activity index
(100 ppm)
Complex
(
100 ppm)
25
50
75
100
25
50
75
100
Staphylococcus aureus
Escherichia coli
[
[
[
CuCl L]
12
13
–
12
13
–
13
16
–
13
17
–
62
81
–
–
12
–
–
13
–
–
14
–
–
14
–
–
70
–
2
2
CuBr L ] Br
1
.5 1.5 2
Cu(OClO )L ] (ClO ) ·4H O
3 2 2 4 2 2
Ligand
Ampicillin
–
14
–
15
–
18
–
21
–
100
15
14
15
16
16
17
17
20
85
100
Salmonella typhi
Pseudomonas aeruginosa
[
[
[
CuCl L]
–
–
–
–
–
–
–
15
13
13
–
75
65
65
–
29
15
25
–
29
15
27
–
31
24
27
–
33
25
30
–
132
100
120
–
2
2
CuBr L ] Br
13
12
–
1
.5 1.5 2
Cu(OClO )L ] (ClO ) ·4H O
3
2
2
4
2
2
Ligand
–
–
Ampicillin
Zone inhibition in mm
15
16
17
20
100
16
18
20
25
100
of polarity of the metal ion due to coordination of ligands and
π-electron delocalization. Such coordination enhances lipohilic
character of the central metal atoms that favours permeation
of the complexes through the lipid layers of cell membrane
and increases the antimicrobial activity.According to Overtone′s
concept of cell permeability [45], only lipid soluble materials
pass through the lipid membrane that surrounds the cell. Hence,
the antimicrobial activity depends on liposolubility.
Conclusion
Binuclear complexes of Cu(II) of a Schiff base ligand, 2-
[(3′-N-salicylidinephenyl)benzimidazole] were prepared and
characterized. Antibacterial and antifungal studies of these
complexes were investigated.All the sythesized copper complexes
exhibited excellent antibacterial activity against P. aerugenosa
and found to be more effective than the standard drug.
Antifungal activity: The complexes, DMSO control and
the standard drug were screened against two fungal species,
Aspergillus flavus and Trichoderma. Although the complexes
exhibited activity (Table-4) against Trichoderma, they did not
reach the effectiveness of the standard drug, fucanozole. Bromo
complex of copper showed activity against Aspergillus flavus.
ACKNOWLEDGEMENTS
The authors thank Spectroscopy Analytical Test Facility,
IISc, Bangalore, India for ESI-MS, Pondicherry University,
Puducherry, India, for far-IR spectra and magnetic susceptibility
measurements, SAIF, IIT, Bombay for ESR spectra, STIC,
CUSAT, Cochin, India for elemental and thermal analyses.
TABLE-4
CONFLICT OF INTEREST
ANTIFUNGAL ACTIVITY (ZONE INHIBITION IN mm)
The authors declare that there is no conflict of interests
regarding the publication of this article.
Aspergillus
Trichoderma
flavus
Complexes
%
Activity
index
%
Activity
index
1
00
ppm
100
ppm
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