3. FOOD ChEMISTRy & bIOTEChNOLOGy 3.1. Lectures

Chem. Listy, 102, s265–s1311 (2008) Food Chemistry & Biotechnology
P83 ANTIMICRObIAL INVESTIGATIONS OF
NICKEL(II) COMPLExES wITh SOME 1bENZyLbENZIMIDAZOLE
DERIVATIVES
SAnJA O. PODUnAVAC-KUZMAnOVIć and
DRAGOLJUB D. CVETKOVIć
University of Novi Sad, Faculty of Technology, Bulevar cara
Lazara 1, 21000 Novi Sad, Serbia,
sanya@uns.ns.ac.yu
Introduction
Physiological activity and commercial applications of
many benzimidazole derivatives have received much attention.
Benzimidazole and its derivatives have different activities
as they can act as bacteriostats or bactericides and
fungicides. 1–10 Extensive biochemical and pharmacological
activities have confirmed that these molecules are effective
against RnA viruses and inhibit the formation of virus
induced RnA polymerase, thereby preventing or retarding
RnA synthesis various strains of microorganisms. 11–14 Antimicrobial
activity of these class of compounds against Helicobacter
pylori 15 and oral Streptococci 16 was also reported.
Synthesis of benzimidazoles fused to another heterocyclic
ring has attracted wide spread attention due to their diverse
application as antioxidant 17,18 , antifungal 19 , antitubercular 20 ,
anticancer 21,22 , and antiallergic drugs 23 . Also, some of these
compounds exhibited anti-HIV activity 24,25 .
The complexes of transition metals with benzimidazole
and related ligands have been extensively studied as models
of some important biological molecules 26 . It was found that
the complexes showed larger antimicrobial activitiy than the
ligands applied alone.
Following our studies of the reactivity of benzimidazole
derivatives with metallic halides 5–8 , we evaluated the antibacterial
activity of this type of complexes in this study. We
report in vitro inhibitory activities of 1-benzylbenzimidazoles
and their nickel (II) complexes against three gram-positive
bacterial strains: Bacillus cereus, Staphylococcus aureus
and Sarcina lutea, one gram-negative isolate: Pseudomonas
aeruginosa.
Experimental
In the present paper we evaluated the antibacterial
activity of nickel (II) complexes with the following starting
ligands: 1-(3-chlorobenzyl)-2-aminobenzimidazole (L 1 ),
1-(3-fluoro-benzyl)-2-aminobenzimidazole (L 2 ), 1-(3-chlorobenzyl)-2-amino-5,6-dimethylbenzimidazole
(L 3 ), 1-(3fluorobenzyl)-2-amino-5,6-dimethylbenzimidazole
(L 4 ) and
1-(3-methylbenzyl)-2-amino-5,6-dimethylbenzimidazole (L 5 ).
All the ligands were synthesized by Vlaović et al. according
to a procedure described earlier. 27 nickel (II) complexes
were prepared following the same procedure described in our
previous paper 7 .
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A n t i b a c t e r i a l a c t i v i t y
All the nickel (II) complexes were tested for their in
vitro growth inhibitory activity against Bacillus cereus ATCC
10876, Staphylococcus aureus ATCC 25923, Sarcina lutea
ATCC 9341 and Pseudomonas aeruginosa ATCC 27853.
Antibacterial activities of the complexes were tested by
the disc-diffusion method under standard conditions using
Mueller-Hinton agar medium as described by nCCLS 28 . Each
of the investigated isolates of bacteria was seeded in the tubes
with nutrient broth (nB). 1 ml of seeded nB was homogenized
in tubes with 9 ml of melted (45 °C) nutrient agar (nA).
The homogenous suspension was poured out in Petri dishes.
The discs of filter paper (diameter 5 mm) were ranged on cool
medium. After cooling on formed solid medium, 0.02 ml of
the investigated compounds (γ = 1000 µg ml -1 ) were placed
by micropipette. After incubation of 24 hours in thermostat at
25–27 °C, inhibition (sterile) zone diameters (including disc)
were measured (in mm). Inhibition zone diameter over 8 mm
indicates the tested compound is active against microorganisms.
Every test was done in three replications. Antimicrobial
activities of the free ligands against the same bacteria
were tested in our previous studies 8 .
Minimum inhibitory concentration (MIC) was performed
by the agar dilution method according to guidelines established
by the nCCLS standard M7-A5 29 . MIC was described
as the lowest concentration of the compound that visibly
inhibited colony’s growth. Stock solutions of the compounds
were prepared in dimethylformamide (DMF). Further dilutions
were performed with distilled water. The concentration
range of the compounds tested was between 60–750 µg ml –1
in two-fold dilution steps. The inoculated plates were than
incubated at 35 °C for 16–20 h. A control using DMF without
any test complex was included for each organisms. It was
determined that the solvent had no activity against any of the
test microorganisms.
Results
The results of antibacterial studies of the nickel (II) complexes
with two series of 1-benzylbenzimidazole derivatives
tested by the agar disc-diffusion method are summarized in
Table I.
As can be seen from the data, all the investigated compounds
displayed in vitro inhibitory activity against very
persistent bacteria. The complexes investigated were found
Table I
In vitro antibacterial activity of complexes at a concentration
of 1,000 μg ml –1
Complex Inhibition zone diameter [mm]
P.aeruginosa B. cereus S. aureus S. lutea
ni(L 1 ) 2 Cl 2 22 26 26 29
nI(L 2 ) 2 Cl 2 17 24 24 25
ni(L 3 ) 2 Cl 2 9 17 17 18
ni(L 4 ) 2 Cl 2 8 16 17 17
ni(L 5 ) 2 Cl 2 5 16 17 16