O A

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Journal of Applied Sciences Research, 9(3): 2268-2278, 2013
ISSN 1819-544X
This is a refereed journal and all articles are professionally screened and reviewed
ORIGINAL ARTICLES
Synthesis, characterization and biological activity of some transition metal complexes
of Pyrrolidine derivatives
1
Eman A.M. El-Zahany, 1,2Ahmed M.A. El-Seidy, 1Sayed A. Drweesh, 1Nabil S. Youssef, 3Bakr
F. Abdel-Wahab, 4Ahmed Atef El-Beih
1
Inorganic Chemistry Department, National Research Centre, Giza, Egypt
Chemistry Department, Faculty of Science, Al Imam Mohammad Ibn Saud Islamic University (IMSIU), Riyadh
11432, Saudi Arabia.
3
Applied Organic Chemistry Department, National Research Centre, , Giza, Egypt
4
Department of Chemistry of Natural and Microbial Products, Division of Pharmaceutical Industries, National
Research Center, Giza, Egypt.
2
ABSTRACT
Two ligands: 4-hydrazinyl-1-(4-methoxyphenyl)-2,5-dihydro-1H-pyrrole-3-carbonitrile (H2L1) and 4-(2(1H-pyrrol-2-yle)hydrazinyl)-1-4(4-methoxyphenyl)-2,5-dihydro-1H-pyrrol-3-carbonitrile (H2L2) have been
prepared and characterized. Their copper(II), nickel(II), cobalt(II), manganese(II) and zinc(II) complexes have
been also synthesized and characterized by infrared, electronic spectra, magnetic and conductivity
measurements in addition to elemental and thermal analyses. Octahedral structures are suggested for the H2L1
complexes of Cu(II) and Mn(II) and the H2L2 complexes of Cu(II), Ni(II) and Mn(II), whereas tetrahedral
structures are proposed for the H2L1 complexes of Co(II) and Zn(II) and the H2L2 complex of Co(II). Moreover,
the results showed that both ligands are tetradentate in all of their complexes. They also indicated that the
complexes exhibit higher antimicrobial activity than their ligands and Mn(II) exhibits a wide range of
antimicrobial activity against gram positive, gram negative bacteria and yeast .
Key words: metal complexes, Schiff base, cyano group, biological study.
Introduction
The condensation of an amine with an aldehyde or ketone, forming what is called a Schiff base, is one of
the oldest reactions in chemistry. Schiff base ligands coordinate to a metal through the imine nitrogen and
another group, usually oxygen, situated on the original carbonyl compound (Prasanta Bhowmik, 2011).
Active and well-defined Schiff base ligands are considered as "privileged ligands" because they are easily
prepared and are able to stabilize different metals in various oxidation states, (Mohammad Shakir, 2011). Schiff
base complexes are extensively studied due to synthetic flexibility, selectivity and sensitivity towards variety of
metal ions. Schiff bases are potentially biologically active compounds and have been reported to possess
antifungal,(Iqbal et al., 2007) antitumor (Singh, 2001) and anticancer activities,(Offiong, 1997). Schiff base
metal complexes are more biologically active than their uncoordinated Schiff base molecules (Sau, 2003).
The biological aspects of pyrrolidine derivatives have got attention as they show potential for anti-cancer
therapy (Chen et al., 2008; Fiaux et al., 2008), antibacterial agents (Hu et al., 2003), inhibitors of the Psubstance (Wu et al., 2000), anti-amnesic agents, affecting the nervous system(Thamotharan et al., 2003),
antiepileptic substances (Kenda et al., 2004), selective inhibition activity against matrix metalloproteinase-2
(Cheng et al., 2008), inhibitors of the reverse transcriptase enzyme of the HIV (Tamazyan et al., 2004), and
characteristics of potent anti-tumor agents (Li et al., 2006).
Cyanide is an efficient ligand for the stabilization of the transition metals in either low or high oxidation
states. This high electronic and coordinative versatility prompts its terminal coordination to almost all transition
metals, and permits a wide number of binding modes in cyanide bridged complexes (Potočňák et al., 2006). In
addition, some of N-(p-substituted phenyl)4-cyanopyrrolidin-3-ones derivatives were prepared and screened for
their serotonin antagonistic and antianexity activities, and they showed high activities compared to buspirone
and diazepam as controls. (Abdalla et al., 2009)
In view of these observations and in continuation of our previous work on Schiff base stransition metal
complexes, we report herein the synthesis and characterization of some Schiff bases complexes of4-hydrazinyl1-(4-methoxyphenyl)-2,5-dihydro-1H-pyrrole-3-carbonitrile (H2L1) and 4-(2-(1H-pyrrol-2-yle) hydrazinyl) -14(4-methoxy phenyl)-2,5-dihydro-1H-pyrrol-3-carbonitrile.(H2L2) for their pharmacological screening.
Corresponding Author: Eman A.M. El-Zahany, Inorganic Chemistry Department, National Research Centre, Giza, Egypt
E-mail: [email protected]
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J. Appl. Sci. Res., 9(3): 2268-2278, 2013
Materials:
All the reagents employed for the preparation of the ligands and their complexes were of the best grade
available and used without further purification. They include copper(II) acetate (Cu(CH3COO)2), Nickel(II)
acetate tetrahydrate (Ni(CH3COO)2.4H2O),Cobalt(II)acetatetetrahydrate(Co(CH3COO)2.4H2O), Zinc acetate
dihydrate(Zn(CH3COO)2.4H2O), Manganese(II) acetate tetrahydrate (Mn(CH3COO)2.4H2O).
Experimental:
The ligands and their metal complexes were analyzed for C, H, N, and metal contents at the Micro
analytical Laboratory, Faculty of Science, Cairo University, Egypt.). IR spectra of the ligands and their metal
complexes were measured using KBr discs with a Jasco FT/IR 300E Fourier transform infrared
spectrophotometer covering the range 400-4000 cm-1 and in the 500-100 cm-1 region using polyethylenesandwiched Nujol mulls on a Perkin Elmer FT-IR 1650 spectrophotometer. Electronic spectra of the ligands and
their complexes were obtained in Nujol mulls using a Shimadzu UV–240 UV–Vis recording spectrophotometer.
Magnetic susceptibilities were measured at 25oC by the Gouy method using mercuric tetra thiocyanato
cobaltate(II) as the magnetic susceptibility standard. Diamagnetic corrections were estimated from Pascal’s
constant. (Salama et al., 2006) The magnetic moments were calculated from the equation:
. Molar conductances were measured on a Tacussel type CD6NG conductivity bridge
 eff .  2.84  corr
M .T
using10-3M DMF solutions. 1H NMR spectrum was obtained on BruckerAvance 400-DRX spectrometers.
Chemical shifts (ppm) are reported relative to TMS. ESR measurements of solid complexes at room
temperature were made using a Varian E-109 spectrophotometer, with DPPH as a standardmaterial.
Synthesis of ligands:
A mixture of 4-hydrazinyl-1-(4-methoxyphenyl)-2,5-dihydro-1H-pyrrole-3-carbonitrile (0.46 g, 2 mmol)
and methyl ketone, namely o-hydroxyaceteophenone in case of H2L1 or 2-acetylpyrrole in case of H2L2 (2
mmol) in 20 cm3 absolute ethanol containing a few drops of acetic acid was heated under reflux for 1 h .
(Abdalla et al., 2009). The formed solid was filtered off, dried and recrystallized to afford the target ligands,(
Fig1).
NH
OH
OCH3
N
N
N
HN
HN
N
N
OCH3
N
H2
L1
H 2L2
Fig. 1: Strucure of the H2L1 and H2L2 ligands.
Synthesis of metal complexes:
All complexes were prepared by refluxing hot ethanolic solution of the ligand H2L1 or H2L2 with a hot
ethanolic solution of the corresponding metal salt in a ratioL:M (1:2). The reaction mixtures were refluxed with
constant stirring for a time depending on the transition metal salt used. The resulting precipitates were filtered
off, washed with hot ethanol (40C) and dried in a vacuum desiccator over P4O10.
In-vitro Antibacterial and Antifungal Activities:
Antimicrobial activity of the synthesized compounds (1-10) in comparison with that of control drugs
Chloramphenicol (Chemical Industries Development Company (CID), Cairo, Egypt) was evaluated against
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J. Appl. Sci. Res., 9(3): 2268-2278, 2013
Gram positive (Bacillus subtilis NRRL-B-4219 and Staphylococcus aureusATCC 29213), Gram-negative
bacteria (Escherichia coli ATCC 25922, Alcaligenesfaecalis B-170) and fungi (Candida albicansATCC 10321
and Aspergillusniger NRRL-363) by the agar diffusion technique(Domig et al., 2007). All microorganisms used
were obtained from the culture collection of the Department of Chemistry of Natural and Microbial Products,
National Research Center, Cairo, Egypt. The microorganisms were passaged at least twice to ensure purity and
viability. The compounds were mounted on a concentration of 500 μg/disc. The bacteria were maintained on
nutrient agar medium while yeast and fungi were maintained on potato dextrose agar medium. DMSO showed
no inhibition zone. The agar media were incubated with different microorganism cultures tested. After 24 h of
incubation at 30 C for bacteria and yeast and 72 h of incubation at 28 C for fungi, the diameter of inhibition
zone in mm was measured (Table 3). Chloramphenicol was used as a positive control for antimicrobial activity
in a concentration of 100 μg/disc.
Preparation of the discs:
Compounds 1-10 together with the positive control Chloramphenicol were mounted on a paper
discprepared from blotting paper (5 mm diameter) with the help of a micropipette on a concentration of 500
μg/10μL DMSO/disc. The discs were applied on the microorganism-grown agar plates.
Preparation of agar plates:
Minimal agar was used for the growth of specific microbial species. The preparation of agar plates for
Bacillus subtilis, Staphylococcus aureusandEscherichia coli (bacteria) utilized nutrient agar (2.30 g; obtained
from PanreacQuimica SA, Spain) suspended in freshly distilled water (100 ml), and potato dextrose agar
medium (3.9 g/100 ml; obtained from Merck) for Candida albicansandAspergillusniger (fungi). This was
allowed to soak for 15 min and then boiled on a water bath until the agar was completely dissolved. The mixture
was autoclaved for 15 min at 120 ◦C and then poured into previously sterilized Petri dishes and stored at 30 ◦C
for inoculation.
Procedure of inoculation:
Spore suspension was prepared with the help of a platinum wire loop to reach a microbial concentration
equivalent 0.5 Mac-Farland.
Application of the discs:
Sterilized forceps were used for the application of the paper disc on previously inoculated agar plates.
When the discs were applied, they were incubated at 37 ◦C for 24 h for bacteria and yeast, and at 28 ◦C for 48 h
for fungi. The zone of inhibition around the disc was then measured in millimetres.
Results and Discussion
The analytical and physical data of the ligands and their metal complexes reported in (Table 1) and spectral
data shown in (Tables 2-3 , Fig 2), are compatible with the suggested structures (Fig. 3). The complexes are
colored, stable in air and insoluble in H2O, ethanol and non-polar solvents such as benzene. However, they
dissolve in polar solvents such as DMF and DMSO. All the complexes are non-electrolytes as shown in (Table
1).
Infrared spectra:
The most characteristic vibrational frequencies and their tentative assignments forthe ligands H3L1, H2L2
and their transition metal complexes are listed in Table 2. The assignments were made by comparison with the
vibrational frequencies of the free ligand (Fig.2).
The IR data obtained for the ligand (H2L1) showed that the ligand behaves as a neutral tetra dentate
coordinating through C–OH, C=N, NHhyd and C≡N groups in its complexes, and the mode of coordination was
suggested by the following pieces of evidence:i) The weakness and shift of υOH band to lower wave number
which is further supported by the shift in the stretching frequency of phenolic oxygen υ(C–O) in the
complexes(Naresh Kumar et al., 2005).;ii) The imines bands are shifted to lower wave number by 23-33 cm1
(Pal et al., 2002; Ramesh et al., 2003); iii) The ν(C≡N) shifts to higher frequencies and the range forterminal
cyano ligands extends from 9-29 cm-1(Vavra et al., 2009).; iv) The shift of υN–N to higher wave number(
Chandra et al., 2005).
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J. Appl. Sci. Res., 9(3): 2268-2278, 2013
The IR data obtained for the H2L2 ligand suggested that this ligand can behave as a neutral tetra dentate
coordinating through NHhydr, C= N,NHpyr and C≡N groups. In these complexes, the mode of coordination was
suggested by the following pieces of evidence: i) In the spectra of all the compounds the υ(NH) band due to the
pyrrolic ring is influenced on complexation. ii)The imines bands are negative shifted by 10-40 cm−1(Youssef et
al., 2012).; iii) The positive ν(C≡N) shift in the range forterminal cyano ligands extends from 35-37cm-1(Vavra
et al., 2009).; iv) The positive υN–N shift by 8-18 cm−1 (Chandra et al., 2005).
Table 1: Analytical and physical data of the ligand H2L1, H2L2 and their metal complexes.
No.
Ligands/Complexes
Color
FW
Yield
Anal./found (calc.) (%)
(%)
1
2
3
4
5
6
7
8
9
10
H2L1
C19H18N4O2
[Cu2H2L1(OC(O)CH3)4.4H2O].
2H2O
C27H42Cu2N4O16
Co2H2L1(OC(O)CH3)4
C27H30Co2N4O10
[Mn2H2L1(OC(O)CH3)4.4H2O].
3H2O
C27H44Mn2N4O17
1
[Zn2H2L (OC(O)CH3)4].5H2O
C27H40N4O15Zn2
H2L2
C18H19N5O
Cu2H2L2(OC(O)CH3)4.4H2O
C26H39Cu2N5O13
[Co2H2L2(OC(O)CH3)4].3H2O
C26H37Co2N5O12
[Ni2H2L2(OC(O)CH3)4].4H2O
C26H39N5Ni2O13
[Mn2H2L2(OC(O)CH3)4
.4H2O].2H2O
C26H43Mn2N5O15
334.37
80
805.73
75
688.41
72
806.53
66
791.44
70
321.38
75
756.71
72
729.46
76
747.00
66
775.52
80
Molar
conductance
m
(-1 cm2
mol-1)
C
67.60
(68.25)
41.11
(40.25)
H
4.95
(5.43)
5.85
(5.25)
N
16.30
(16.76)
16.72
(15.75)
6.02
(6.95)
17
46.55
(47.11)
40.70
(40.21)
3.85
(4.39)
6.20
(5.50)
8.55
(8.14)
13.95
(13.62)
17.65
(17.12)
7.50
(6.95)
12
40.15
(40.97)
64.55
(67.27)
41.80
(41.27)
41.55
(42.81)
40.16
(41.80)
41.15
(40.27)
4.55
(5.09)
5.62
(5.96)
4.40
(5.19)
6.50
(5.11)
5.70
(5.26)
6.36
(5.59)
8.25
(7.08)
20.90
(21.79)
9.50
(9.26)
8.65
(9.60)
10.10
(9.38)
13.85
(14.17)
17.15
(16.53)
-
15
16.15
(16.80)
14.85
(16.16)
14.88
(15.71)
8.20
(9.03)
14
Table 2: IR frequencies of the bands (cm-1) of ligands H2L1, H2L2, their metal complexes and their assignments.
No.
Ligand/ Complexes
Ν
ν(NH)pyr
ν(OH)
Ν
ν(C=N)
ν(CN)
(OH)H2O
(NH)hydr
phenolic
ν(N-N)
M
-
νs(OAc), νas(OAc),
1
H2L1
-
-
3067
3210
2197 s
1644 v.s
1116 m
-
2
[Cu2H2L1(OC(O)CH3)4.4H
2O]. 2H2O
Co2H2L1(OC(O)CH3)4
3412
-
3055
2224w
1611 s
1125 m
1534, 1323, 211
-
3060
3212
vw
3220br
2226 w
1621 s
1122 m
1533, 1340, 203
[Mn2H2L1(OC(O)CH3)4.4
H2O].3H2O
[Zn2H2L1(OC(O)CH3)4].5
H2 O
H2L2
3362
-
3042
3221 w
2206 w
1614 s
1123 m
1539, 1332, 207
3
4
5
6
7
8
9
10
Cu2H2L2(OC(O)CH3)4.4H2
O
[Co2H2L2(OC(O)CH3)4].3
H2 O
[Ni2H2L2(OC(O)CH3)4].4H
2O
[Mn2H2L2(OC(O)CH3)2)4
.4H2O].2H2O
-
15
-
13
16
18
ν (C-O)
1242 vs
1248 m
1246 m
1249 m
3415 br
-
3056
3230 m
2196 w
1616 s
1129 w
1534, 1330, 204
-
3440v.s 3278
-
3238 m
2190v.s
1644 s
1102 w
-
3460
3460 br 3355
-
3278 br
2226w
1604 m
1111 m
3410
3387 br 3127
-
3280 br
2225w
1614 sh
1111 m
1532, 1314,
218
1558-1341
2171551-1344
207
1545, 1342,
203
1247 m
--
3466
3400
3390
3282
3400
-
3287 sh
2226w
1625 sh
1120 m
3390 br
-
3282 m
2227w
1634 m
1110 m
-
Table 3: The electronic absorption spectral bands (nm) and magnetic moment (B.M) for the ligands H2L1, H2L2 and its complexes.
No.
Ligand/Complexes
λmax (nm)
eff inBM
1
H2L1
366, , 302, 270
2
[Cu2H2L1(OC(O)(CH3)2)4 ]. 4H2O
650, 398, 366, 330, 296
1.55
1
3
Co2H2L (OC(O)(CH3)2)4
621, 366, 328, 300
4.00
4
Mn2H2L1(OC(O)(CH3)2)44H2O
650, , 390, 320, 299
4.87
5
[Zn2H2L1(OC(O) ] (CH3)2)4]. 5H2O
412, 366, 328, 296
6
H2L2
346, 262
7
Cu2H2L2(OC(O)(CH3)2)4 . 4H2O
645, 388, 352, 296
1.65
8
[Co2H2L2(OC(O)(CH3)4 ]. 4H2O
615, 348, 328, 288
3.90
9
[Ni2H2L2(OC(O)(CH3)4] .3H2O
630, 450, 354, 286
2.45
2
10
[Mn2H2L (OC(O)(CH3)2)4 ] . 4H2O
625, 375, 328, 290
4.98
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J. Appl. Sci. Res., 9(3): 2268-2278, 2013
Fig. 2: IR spectra of H2L1, H2L2 and their metal complexes.
The acetato group in all complexes acted as a mono dentate ligand, which is supported by the appearance of
two new bands in the ranges 1558-1532cm-1 and 1342-1314 cm-1, which may be attributed to νasym.(COO-) and
νsym.(COO-), respectively (Karbasanagouda et al., 2008),where the difference between them is more than 200cm1
. The broad bands in the 3400-3466 cm-1 region in all complexes are due to anti symmetric and symmetric OH
stretching of water molecules.
Mass Spectra of the ligand (H2L1):
The mass spectra of the Schiff base ligand (H2L1) exhibit the molecular ion peak at m/e 334 which is
coincident with the formula weight of this ligand. Its proposed pathway fragmentation pattern is described
(Scheme1), which supports the identity of its structure.
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J. Appl. Sci. Res., 9(3): 2268-2278, 2013
OH
Y
OCH 3
X
OH
Y
M
N
X
.nH2O
N
HN
N
M
N
NH
Y
N
X
Complex 2: M=Cu, X=OC(O)CH3, Y=H2O, n=2
Complex 4: M=Mn, X=OC(O)CH3, Y=H2O, n=3
Complex 3: M=Co X=OC(O)CH3 , n=0
Complex 5: M=Zn, X=OC(O)CH 3 , n=5
NH
X
M
N
X
Y
M
X
N
Y
X
.nH 2O
.nH2 O
HN
M
N
X
Y
M
X
Y
.nH 2O
X
HN
X
Y
X
OCH3
X
M
HN
X
M
N
X
OCH3
N
X
N
Complex 7: M=Cu, X=OC(O)CH 3, Y=H2O, n=0
Complex 10: M=Mn, X=OC(O)CH 3, Y=H 2O, n=2
OCH3
N
Complex 8: M=Co, X=OC(O)CH 3, n=3
Complex 9: M=Ni, X=OC(O)CH3, n=4
Fig. 3: The proposed structures of H2L1 and H2L2 complexes.
1
H NMR Spectra:
The 1H NMR spectrum of the free ligand (H2L1) in DMSO solution showed proton signals appearing at
8.9,9.95 and 11.09 ppm for the azomethine (CH=N), N-H, phenolic OH protons, respectively(Bacchi et al.,
1998), whereas in case of ligand H2L2the 1H NMR and masss pectra have been characterized before(Abdalla et
al., 2009).
Molar conductivity:
The molar-conductance of the metal complexes (Table 1) are in the 8-18-1 cm2 mol-1 range, indicating
their non-electrolytic nature(Golcu et al., 2005).
Electronic spectra and magnetic moments:
The UV–Vis spectra of H2L1 and H2L2 exhibits an intense absorption peak at 270-366 and 262-346 nm,
respectively (Table 3) assigned to overlap of π→π* and n→π* transitions. The electronic spectra of the copper
complexes 2 and 7 showed one broad absorption band due to the 2T2g(G)← 2Eg transition. This band lie at 650
and
645 nm in complexes 2 and 7, respectively, suggesting octahedral geometry(Emara et al., 2006; Swamy
et al., 2008).The magnetic moments of copper complexes 2 and 7 are 1.55 and 1.65BM, respectively,which
indicate the presence of an unpaired electron on Cu(II) ion in an octahedral geometry environment(Emam et
al., 2009; Rosu et al., 2010). The lower magnetic moment values of these complexes may be attributed to the
exchange existing between the metal ions(Youssef et al., 2009).
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J. Appl. Sci. Res., 9(3): 2268-2278, 2013
OH
OCH3
N
N
HN
H2 L1
N
m/z 334
OCH3
OH
N
HN
N
m/z 120
m/z 214
-HCN
N
N
-NH2
OCH3
OH
-CN
m/z 93
-N
N
-OH
OCH3
m/z 198
-O
N
m/z 77
C2H5
+H
+H
N
OCH3
OCH3
N
m/z 93
m/z 108
-OCH3
m/z 77
Scheme 1: The pathway fragmentation pattern of the mass spectrum of the ligand H2L1
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J. Appl. Sci. Res., 9(3): 2268-2278, 2013
In the tetrahedral environment, cobalt(II) complexes are reported to consist of only one transition, due to
A2(F)→4T1(F)(Lever, 1984). The spectrum of cobalt(II) complexes 3 and 8, showed only one band in the
visible region at 621 and 615 nm, respectively. This indicates the tetrahedral geometry for these cobalt(II)
complexes(Joseyphus et al., 2006). The lower magnetic moment values of these complexes (4.00 and 3.90
B.M), respectively, may be attributed to the antiferromagnetic exchange existing between the metal
ions(Youssef et al., 2009)
The spectrum of the Zn(II) complex 5 exhibited bands assigned to of π→π*and n→π* transitions(AlJeboori et al., 2010). This complex is diamagnetic as expected. The zinc metal ion normally prefers tetrahedral
coordination. The electronic spectra of the nickel complex showed a band at 630 nm arising from the transition
3
T1(F) →3T1(P) transition which is consistent with a tetrahedral geometry around the nickel(II) ion . The
observed magnetic moment of 2.45 B.M lies lower than the normal range found for a tetrahedral environment
(µeff 3.02 B.M )which may be due to the antiferromagnetic exchange contribution(Zaky et al., 2011).
Mn complexes 4 and 10 showed µeff of 4.87 and 4.98 B.M), respectively, indicating the presence of five
unpaired electrons in these complexes. Their electronic spectra showed absorption bands at 625-650, 375-390
and 320-328nm, respectively. The first band shown at 625-650 nm is assigned to the 6A1g→4T1g, transition for a
high spin octahedral geometry around Mn (II) (Singh et al., 2009). The high energy bands at 375-390 and 320328 nm may be assigned to the intraligand/charge transfer transition. The lower magnetic moment values of
these complexes may be due to the antiferromagnetic exchange between Mn (II) ions ( Youssef et al., 2009).
4
Thermal analyses (DTA and TGA):
Complex 2 : TGA % found (% Calc., temp.): H2O 4.59(4.47, 82 oC), H2O 8.81(8.95, 128 oC), acetate
30.01(29.29,
264 oC), CuO 19.64 (19.75, 510 oC).
Complex 3 : TGA % found (%Calc., temp.): acetate 35.03 (34.28 , 285 oC), Co2O3 24.17 (24.09, 601 oC).
Complex 4: TGA % found (%Calc., temp.): H2O 6.99 (6.70, 77 oC), H2O 8.97(8.93, 125 oC), acetate
30.57(29.26,
281 oC), Mn2O3 19.86 (19.57, 585oC).
Complex 5 : TGA % found (%Calc., temp.): H2O 11.52 (11.37, 87 oC), acetate 30.56 % (29.82 %, 292oC),
ZnO 20.41 %(20.57 %, 510oC).
Complex 7 : TGA % found (%Calc., temp.): H2O 9.68 (9.53, 137 oC), acetate 31.59 (31.19 , 295 oC), CuO
21.18 (21.03, 515oC).
Complex 8 : TGA % found (%Calc., temp.): H2O 7.58 (7.41, 73oC), acetate 32.77 (32.35, 287oC), Co2O3
22.86 (22.74, 585oC).
Complex 9 : TGA % found (%Calc., temp.): H2O 9.83 (9.65, 78oC), acetate 32.77(31.59, 315 oC), NiO
20.16(20.06, 522oC).
Complex 10 : TGA % found (%Calc., temp.): H2O 4.6 (4.64, 84oC), H2O 9.39 (9.29, 126oC), acetate
31.09(30.43, 325 oC), Mn2O3 40.90 (40.71, 608 oC).
The thermogravimetric analysis (TG) was measured in the temperature range of 20-800 oC. The results
were in good agreement with the proposed structures. Dehydration of lattice water in lie in the range of 67-78
o
C, while removal of coordinated water lie at higher values in the range of 125-137oC. The removal of acetate
lie in the range of
264-325 oC. The last stage in all complexes comprises the decomposition of the
organic constituents of the complexes leaving the metal oxides at 510-608 oC.
Suggested Structural Formulae of the Complexes:
From the spectral data and the elemental analyses, the structure of the prepared complexes may be
formulated as shown in ( Fig. 3).
Antibacterial and Antifungal Screening:
A comparative study of the antimicrobial activity values for ligands and their complexes indicates that the
complexes exhibit higher antimicrobial activity than the ligand. The results shown in Table 4 revealed that
compound 10 exhibited a wide range of antimicrobial activity against gram positive, gram negative bacteria and
yeast. Moreover, compounds 2 and 3 exhibited a moderate antimicrobial activity against A. niger and C.
albicans. Such an increased activity of the complexes can be explained on the basis of Overtone’s
concept(Knopp et al., 1990) and Tweedy’s chelation theory(Dharmaraj et al., 2001).This would suggest that the
chelation could facilitatethe ability of a complex to cross a cell membrane and chelation considerably reduces
the polarity of the metal ion mainly because of partial sharing of its positive charge with the donor groups and
possible electron delocalization over the whole chelate ring. Such chelation could also enhance the lipophilic
character of the central metal atom, which subsequently favors its permeation through the lipid layer of the
cell membrane.
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J. Appl. Sci. Res., 9(3): 2268-2278, 2013
Table 4: Antimicrobial activity of compounds 1-10.
Compound No.
Inhibition zone (mm)
E. coli
S. aureus
B. subtilis
A.. faecalis
C. albicans
A. niger
1
2
++++
++++
3
++
+
4
5
++
6
7
8
9
+
10
++
+
+++
+
+
++
Chloramphenico
++++
++++
++++
++++
++++
l
Inhibition zone diameter (% inhibition): +, 6–9 mm (33–50%); ++, 10–12 mm (55–67%); +++, 13–15 mm (72–83%); ++++, 16–18 mm
(89–100%). Percentage inhibition values were relative to inhibition zone (18 mm) with 100% inhibition.
Conclusion:
We report here the syntheses and characterization of two Schiff bases ligands, H2L1 and H2L2 and their
Cu(II), Ni(II), Co(II), Zn(II) and Mn(II) metal complexes. All their data collected are in agreement with their
proposed structures. The results indicated that the complexes showed higher antimicrobial activity than their
parents ligands whereas Mn (II) exhibited a wide range of antimicrobial activity against gram positive, gram
negative bacteria and yeast .
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