Synthesis, characterization and biological activity of some platinum(II) complexes with Schiff bases derived from salicylaldehyde, 2-furaldehyde and phenylenediamine

Article abstract of DOI:10.1016/j.saa.2006.06.031

Four platinum(II) complexes of Schiff bases derived from salicylaldehyde and 2-furaldehyde with o- and p-phenylenediamine were reported and characterized based on their elemental analyses, IR and UV-vis spectroscopy and thermal analyses (TGA). The complex

Full text of DOI:10.1016/j.saa.2006.06.031

Spectrochimica Acta Part A 67 (2007) 114–121
Synthesis, characterization and biological activity of some platinum(II)
complexes with Schiff bases derived from salicylaldehyde,
2-furaldehyde and phenylenediamine
Akmal S. Gaballaa,∗, Mohsen S. Askerb, Atiat S. Barakatc, Said M. Telebc
a Faculty of Specific Education, Zagazig University, Zagazig, Egypt
b Microbial Biotechnology Department, National Research Center, P.O. 12622, Egypt
c Chemistry Department, Faculty of Science, Zagazig University, Zagazig, Egypt
Received 12 June 2006; accepted 27 June 2006
Abstract
Four platinum(II) complexes of Schiff bases derived from salicylaldehyde and 2-furaldehyde with o- and p-phenylenediamine were reported and
characterized based on their elemental analyses, IR and UV–vis spectroscopy and thermal analyses (TGA). The complexes were found to have the
general formula [Pt(L)(H2O)2]Cl2·nH2O (where n = 0 for complexes 1, 3, 4; n = 1 for complex 2. The data obtained show that Schiff bases were
interacted with Pt(II) ions in the neutral form as a bidentate ligand and the oxygens rather than the nitrogens are the most probable coordination
sites. Square planar geometrical structure with two coordinated water molecules were proposed for all complexes The free ligands, and their
metal complexes were screened for their antimicrobial activities against the following bacterial species: E. coli, B. subtilis, P. aereuguinosa, S.
aureus; fungus A. niger, A. fluves; and the yeasts C. albican, S. cervisiea. The activity data show that the platinum(II) complexes are more potent
antimicrobials than the parent Schiff base ligands against one or more microorganisms.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Salicylaldehyde; 2-Furaldehyde; Phenylenediamine Schiff base; Platinum(II) complexes; IR; Thermal analysis; UV–vis; Biological activity; Antimicrobial
activity
1. Introduction
plexes with Schiff bases have been synthesized [12], the number,
detailed vibrational and thermal studies of this class of com-
pounds appear to be very limited in the literature.
In this paper, we report the synthesis of four new com-
plexes of platinum(II) with Schiff bases, N,Nꢀ-o-phenylenebis
(salicylideneimine) (sal-o-phdnH2), N,Nꢀ-p-phenylene-bis
(salicylideneimine) (sal-p-phdnH2), N1,N2-bis((furan-2-yl)
methylene)benzene-1,2-diamine (fur-o-phdn) and N1,N4-bis
Schiff bases are considered as a very important class of
organic compounds which have wide applications in many bio-
logical aspects [1]. These wide applications of Schiff bases have
generated a great deal of interest in metal complexes. Schiff
base–transition metal complexes are one of the most adapt-
able and thoroughly studied systems [2,3]. These complexes
have also applications in clinical [4] and analytical fields [5].
Some of Schiff base complexes are used as model molecules for
biological oxygen carrier systems [6]. Tetradentate Schiff base
complexes are well known to form stable complexes, where the
coordination takes place through the N2O2 donor set [7–9].
The coordination chemistry of platinum(II) has attracted a
considerable attention due to its biological applications and
tumor treatment based on the early discovery of antitumer activ-
ity of cis-platin [10,11]. Although analogues platinum com-
((furan-2-yl)methylene)benzene-1,4-diamine
(fur-p-phdn),
Scheme 1. Their infrared and electronic spectra were recorded
and fully assigned along with the complexes thermal properties
as well as screening for their antimicrobial activities and mode
of action.
2. Experimental
2.1. Materials and spectral measurements
∗
Analytical reagent grade chemicals were used throughout
Corresponding author. Tel.: +20 55 2376777; fax: +20 55 2345452.
E-mail address: akmalsg@yahoo.com (A.S. Gaballa).
this investigation. K2PtCl4, o-phenylenediamine, p-phenylene-
1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.06.031

A.S. Gaballa et al. / Spectrochimica Acta Part A 67 (2007) 114–121
115
Scheme 1.
diamine, salicylaldehydeand2-furaldehydewereBDHorMerck
chemicals.
Infrared spectra of the reactants and the obtained com-
2.3. Preparation of platinum complexes
2.3.1. [Pt(sal-o-phdnH2)(H2O)2]Cl2 (1),
[Pt(sal-p-phdnH2)(H2O)2] Cl2·H2O (2)
[Pt(fur-o-phdn)(H2O)2]Cl2 (3), [Pt(fur-p-phdn)(H2O)2]Cl2
(4)
To a solution of K2PtCl4 (124.5 mg, 0.30 mmol) in methanol
(10 ml), a methanolic solution (10 ml) of the respective Schiff
base (0.30 mmol) was added. The reaction mixtures were stirred
several hours at ca. 40 ◦C. The formed powdery precipitates of
complexes 1–4 were left to cool to room temperature, filtered
off, washed several times with methanol and dried in vacuo.
The analysis results came in good consistence with the proposed
formulas as follows.
plexes were recorded from KBr bellets (4000–400) using a
Buck scientific 500-IR spectrophotometer. Microanalyses were
performed using CHNS-932 (LECO) and vario-EL elemen-
tal analyzers. Chlorine was determined by burning the sub-
stance in oxygen with platinum contact and subsequent titra-
tion with mercuric nitrate towards diphenylcarbazide. Ther-
mal analysis, TG was carried out using a Shimadzu TGA-50
H computerized thermal analysis system. The rate of heat-
ing of the samples was kept at 10 ◦C min−1. Sample masses
varied between 2.7 and 4.0 mg were analyzed under N2 flow
of 30 ml min−1. Electronic spectra of solutions of ligands,
and platinum(II) complexes in methanol were recorded on a
UV–vis Recording Spectrophotometer, UV-2401PC Shimadzu
at 25 ◦C.
[Pt(sal-o-phdnH2)(H2O)2]Cl2 (1): (C20H20Cl2N2O4Pt,
618.37); yield = 91.6%; C, 39.44 (38.85); H, 3.66(3.26); N,
4.58(4.53); Cl, 11.49(11.47).
[Pt(sal-p-phdnH2)(H2O)2]Cl2·H2O
(2):
(C20H22Cl2N2O5Pt, 636.38); yield = 83.8%; C, 38.56(37.75);
H, 3.59(3.48); N, 4.54(4.40); Cl, 11.38(11.14).
2.2. Preparation of Schiff base ligands
[Pt(fur-o-phdn)(H2O)2]Cl2
566.29); yield = 76.5%; C, 34.43 (33.93); H, 3.01(2.85); N,
5.19(4.95); Cl, 12.77(12.52).
[Pt(fur-p-phdn)(H2O)2]Cl2
(566.29); yield = 83.8%; C, 34.52(33.93); H, 3.11(2.85); N,
5.22(4.95); Cl, 12.79(12.52).
(3):
(C16H16Cl2N2O4Pt,
Schiff base ligands were prepared according to the known
method [13] from the condensation of the respective diamine
with the corresponding aldehyde in a molar ratio of 1:2, respec-
tively, using methanol as a solvent at ca. 45 ◦C. The reac-
tion mixture was stirred for 3 h. The precipitate were filtered
off, washed several times with methanol and finally dried in
a desiccator over phosphorous pentoxide. The Schiff bases
were obtained in good yields (above 90.0%). The infrared
and elemental analysis measured for the obtained products are
consistent very well with the corresponding Schiff base for-
mula.
(4):
(C16H16Cl2N2O4Pt
2.4. Antimicrobial activity
The antimicrobial activities were carried out according to the
conventional agar diffusion test [14] using cultures of Bacillus

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A.S. Gaballa et al. / Spectrochimica Acta Part A 67 (2007) 114–121
subtilis NRRL B-94, E. coli NRRL B-3703, Pseudomonas
aereuguinosa NRRL B-32, Staphylococcus aureus NRRL B-
313, Aspergillus niger NRRL 599, A. fluves NRC, Saccha-
romyces cervisiea NRC and Candida albicans NRRL 477. The
bacterial strains were cultured on nutrient medium, while the
fungi and yeast strains were cultured on malt medium and yeast
medium, respectively. Broth media included the same contents
except for agar. For bacteria and yeast, the broth media were
incubated for 24 h. As for fungus, the broth media were incu-
bated for approximately 48 h, with subsequent filtering of the
culture through a thin layer of sterile Sintered Glass G2 to
remove mycelia fragments before the solution containing the
spores was used for inoculation. For preparation of plates and
inoculation, 1.0 ml of inocula were added to 50 ml of agar media
(50 ◦C) and mixed. The agar was poured into 120 mm petri
dishes and allowed to cool to room temperature. Wells (6 mm in
diameter) were cut in the agar plates using a proper sterile tubes.
Then, fill wells were filled up to the surface of agar with 0.1 ml
of the test compounds dissolved in DMSO (200 ␮mol/ml). The
plates were left, on a leveled surface, incubated for 24 h at 30 ◦C
for bacteria and yeast and 48 h for fungi and the diameter of the
inhibition zones were read. DMSO (0.1 ml) alone was used as
control under the same conditions for each organism. By sub-
tracting the diameter of inhibition zone resulting with DMSO
from that obtained in each case. The results were compared
with a similar run of Tetraceycline as an antibacterial and Flu-
conazol as an antifungal. Both antimicrobial activities could be
calculated as a mean of three replicates.
3. Results and discussion
Schiff bases sal-o-phdnH2, sal-p-phdnH2, fur-o-phdn and
fur-p-phdn interact as neutral ligands with potassium tetra-
chloroplatinum(II) in methanol to form the corresponding plat-
inum(II) complexes, [Pt(sal-o-phdnH2)(H2O)2]Cl2 (1), [Pt(sal-
p-phdnH2)(H2O)2] Cl2·H2O (2), [Pt(fur-o-phdn)(H2O)2]Cl2
(3), [Pt(fur-p-phdn)(H2O)2]Cl2 (4), respectively. The formula-
tion of these complexes were based on the elemental analysis
which agrees quite well with 1:1 (Pt(II):Schiff base) stoichiom-
etry, as well as on qualitative chemical analysis (test of the
ionic chloride by AgNO3 solution), vibrational, and electronic
spectra and thermal analysis. Tables 1 and 2 give assignments
of the characteristic infrared bands of Schiff bases together
with their corresponding Pt(II) complexes 1–4, respectively.
The results enable us to characterize the complexes and make
an assessment of the bonding and structures inherent in them.
The C N in an open chain system characterizes by a sharp
band definitely assigned in the region of 1690–1640 cm−1
.
Aryl conjugation causes a shift towards longer wavelengths
regardless of the substituent is located on N or C. The strong
interaction between C C and C N stretching vibrations in
olefin-substituted azomethine systems makes the assignment
of a band due to ν(C N) is rather tentatively. Furthermore,
the C N band of Schiff bases is mostly overlapped from
the aromatic bands ν(C C) and therefore difficult to assign
[19].
The infrared spectra of sal-o-phdnH2 and sal-p-phdnH2
(Table 1) show two well resolved bands around 1632(s) and
1592(m) cm−1, in addition to two weak bands lying in the region
around 3253 and 3182 cm−1 which may be attributed to N+–H
bond vibration. Such situation could be explained on the basis
of a partial protonation on the nitrogen atom of azomethine
groups and the formation of Zwitter ion (form (II), as shown
in Scheme 2, which is the more stable during complexation with
Pt(II).
2.5. MIC determination
The minimum inhibitory concentration (MIC) was determi-
nation by the serial dilution method [15]. About 200 ␮mol of the
active compounds were dissolved in 1.0 ml DMSO. Serial dilu-
tions of the compounds were prepared to obtain concentrations
rang from 37.5 to 200 ␮mol. The inocula of B. subtilis NRRL
B-94, E. coli NRRL B-3703, P. aeueuguinosa NRRL B-32, S.
aureus NRRL B-313, A. niger NRRL 599, A. fluves NRC, S.
cervisiea NRC and C. albicans NRRL 477, were obtained from
24 h old cultures. The plates were finally incubated at 30 ◦C for
24 h.
The infrared spectra of the two complexes reveal in compar-
ison with the free ligands spectra the following observations.
(i) The band around 1632 cm−1 in the free ligands is observed
at almost the same region around 1620 cm−1 in complexes
spectra. This band can be attributed to the ν(C C) and the
slight change in wavenumbers may be understood as a result
of changing the electron density of the aromatic system due to
complexation. (ii) The medium–strong band around 1592 cm−1
of the free ligands which may be assigned due to the partially
2.6. The mode of action
protonated azomethine (C N+–H) is shifted (50–60 cm−1
)
The effect of different concentrations of complex 3 on the
growth rate and some biochemical activities was studied. Imme-
diately after incubating the flasks with B. Subtilis NRRL B-94,
cells were harvested during the middle logarithmic phase; the
active compound was applied in a concentration of the MIC and
its folds (2 and 3) in three replicates. Subsequently, the flasks
were shaken using a rotary shaker of 120 rpm at 30 ◦C. Samples
were withdrawn at the onset of the experiment and after incu-
bation periods of 10, 30, 50, 70, 90, 120, 150 and 180 min. The
bacterial cells were subjected to the following determinations:
acid soluble phosphorus compounds [16], total lipids [17] and
total protein [18].
to lower wavenumber, around 1540 cm−1 in the complexes
spectra as expected for fully protonated form of the azomethine
group (form II, Scheme 2). (iii) The two bands around 3253
and 3182 cm−1 assigned to ν(N+–H) are observed at almost the
same frequencies but their intensity were changed from weak
to strong. It should be mentioned here that protonation at the
nitrogen of azomethine groups of Schiff bases was previously
reported in literature [19,20]. (iv) The free Schiff bases spectra
show two strong sharp bands in the region 3386–3365 cm−1
Taking into consideration an expected intramolecular hydrogen
bonding, these two bands can be quietly assigned due to ν(O–H)
.

A.S. Gaballa et al. / Spectrochimica Acta Part A 67 (2007) 114–121
117
Table 1
Characteristic infrared frequenciesa (cm−1) and tentative assignments for the Schiff bases, sal-o-phdnH2 and sal-p-phdnH2 together with their complexes, 1 and 2
sal-o-phdnH2
sal-p-phdnH2
1
2
Assignmentsb
3401 m
3446 vs
ν(O–H); H2O
3386 s
3365 s
3295 s
3375 s
3366 s
3253 s
3255 m
3185 sh
3060 w
2926 w
1650 m
1615 s
ν(N+–H)
3182 m
3065 m
2927 m
1686 w
1623 m
1531 vs
3045 sh
2926 w
–
3052 sh
2927 w
–
1631 s
1588 m
1515 s
1438 vs
1389 vs
1262 m
1127 w
ν(C–H); aromatic
ν(C–H); aliphatic
δ(H2O); coordinated H2O
ν(C C)
ν(C N+)
1632 s
1592 m
1501 s
1456 vs
1401 s
1273 s
1249 sh
1154 w
1151 vw
1059 vw
927 w
1547 s
1502 s
Phenyl breathing modes (quadrant vibrations) and C–H deformation
1442 m
1353 s
1237 w
1150 m
1401 w
1323 w
1260 w
1236 m
1124 w
ν(C–O), ν(C–C) and ν(C–O) chelating ring
1062 w
883 w
830 m
1020 w
1079 w
1011 vw
In plane CH-deformation
875 sh
841 w
762 m
574 w
828 m
735 vw
673 vw
δr (H2O)
750 s
707 m
673 w
515 m
In plane CH-quadrant deformations; phenyl
539 w
455 w
535 w
467 vw
ν(Pt–O); O of Schiff base
ν(Pt–O); O of coord. Water
a
s, strong; m, medium; v, very; w, weak; br, broad.
ν, stretching; δ, deformation.
b
even so they are observed at lower wavenumbers than expected.
The corresponding complexes spectra 1 and 2 reveal no bands
in this region, but instead a new broad band characteristic for
with Pt(II). Furthermore, two additional new bands are
observed around 1650 and 850 cm−1 due to the bending and
rocking motions of H2O [21]. The latter band is characteristic
for coordinated water molecules. The stretching vibrations
ν(Pt(O) (oxygen of the Schiff base) in complexes 1 and 2
H2O molecules is observed in the region above 3400 cm−1
.
This indicate that oxygen atoms are involved in coordination
Scheme 2.

118
A.S. Gaballa et al. / Spectrochimica Acta Part A 67 (2007) 114–121
are in the region 539(498 cm−1 while the ν(Pt(O) (oxygen of
Table 2
coordinated water) assigned at 455 and 467 cm−1, respectively
[19,21].
Characteristic infrared frequenciesa (cm−1) and tentative assignments for the
Schiff bases, fur-o-phdn and fur-p-phdn along with their complexes 3 and 4
Schiff bases fur-o-phdn and fur-p-phdn in contrary lack such
acidic protons, Scheme 1, and therefore, protonation in such a
way is not expected in this case. The infrared spectra of the free
ligands and their correspondence complexes 3 and 4 (Table 2)
show the same pattern with some shift in bands frequencies as
a result of coordination with Pt(II). The strong and relatively
broad band around 1618 cm−1 in the spectra of the free lig-
ands which is assigned due to ν(C N) + ν(C C) [19,20] and
is observed at nearly the same frequencies in their Pt(II) com-
plexes. This observation indicate at once that nitrogen atoms
are not the binding sites and oxygen atoms should be the most
probable sites to coordinate with the Pt(II) atom. In addition to
the ligands bands, complexes spectra show a set of new bands at
3425, 1640 and 800 cm−1 (Table 2) due to stretching, bending
and rocking motions of the coordinating water molecules [21].
Furthermore, two new bands are observed in complexes spectra
above 500 cm−1 and around 450 cm−1 and can be assigned due
to ν(Pt(O) (oxygen of the Schiff base) and ν(Pt(O) (oxygen of
coordinated water), respectively [21].
The infrared spectra of the four ligands and their complexes
show the stretching vibrations, ν(C–H) of the phenyl groups
are in the region 3113–3025 cm−1, while, ν(C–H) vibrations
of the CH– groups are observed as expected in the region
2970–2860 cm−1 [22,23]. A group of strong to week bands
falling in the region 1554–1337 cm−1 should be associated as
expected with the phenyl, quadrant, semicircular and sextant
vibrations [24,25]. The ν(C–O), ν(C–C) and ν(C–O) stretching
vibrations in both complexes are observed as a number of bands
lying in the region 1280–1147 cm−1. The C–H bends of the
phenyl groups in the three complexes are assigned to a number
of bands lying in the range 1072–576 cm−1. These assignments
agree quit well with those known for related systems [24–32].
fur-o-phdn fur-p-phdn
3
4
Assignmentsb
3425 s, br 3445 s, br ν(O–H); H2O
3200 w
3190 w
3111 m
3058 sh
3205 s
3196 s
3122 w
3059 w
2928 w
3109 m
3022 w
2973 w
2879 w
3113 m
3025 sh
2970 m
2925 m
1650 m
1618 s
1610 m
1508 vs
1460 w
1418 s
ν(C–H); aromatic
ν(C–H); aliphatic
2927 vw
1641 m
1614 s
1608 s
1509 s
δ(H2O)
νas(C N); ν(C C)
1618 m
1620 vs
1509 s
1554 m
1469 vs
Phenyl breathing modes
(quadrant vibrations) and
C–H deformation
1457 m
1422 m
1377 m
1339 m
1284 w
1458 vs
1392 m
1337 m
1280 m
1397 vw
1337 vw
1280 vw
1340 vw
1284 w
ν(C–O), ν(C–C) and
ν(C–O) chelating ring
1258 m
1225 w
1148 m
1070 w
1011 s
925 w
1200 m
1227 m
1198 vw
1147 m
1109 w
1069 w
1013 s
957 w
933 s
1147 m
1072 w
1011 s
923 w
1155 m
1102 w
1017 m
935 vw
In plane CH-deformation
907 w
886 w
865 s
884 w
826 w
882 vw
835 m
δr(H2O)
In plane CH-quadrant
deformations; phenyl
820 w
742 vs
593 w
819 s
762 vs
733 sh
590 m
552 m
745 vs
591 m
559 w
442 w
760 w
576 w
509 w
462 w
421 vw
ν(Pt–O); O of Schiff base
ν(Pt–O); O of Coord.
water
a
s, strong; m, medium; v, very; w, weak; br, broad.
ν, stretching; δ, deformation.
b
Table 3
The maximum temperature values for the decomposition along with the species lost in each step of the decomposition reactions of complexes 1, 2 and 4
Complex
Decomposition
Tmax (◦C)
Lost species
% Weight loss
Found
Calculated
First step
Second step
Total loss
Residue
201
347
2H2O
sal-o-phdnH2
6.20
52.00
58.20
41.80
5.82
51.16
56.98
43.03
[Pt(sal-o-phdnH2)(H2O)2]Cl2 (1)
First step
Second step
Third step
Total loss
Residue
111
240
384
H2O
2H2O
sal-p-phdnH2
2.90
5.80
47.5
56.20
43.80
2.83
5.66
49.71
58.2
41.80
[Pt(sal-p-phdnH2)(H2O)2]Cl2·H2O (2)
[Pt(fur-p-phdn)(H2O)2]Cl2 (4)
First step
Second step
Total loss
Residue
279
442
2H2O
fur-p-phdn
6.80
47.50
54.30
45.70
6.36
46.67
53.03
46.97

A.S. Gaballa et al. / Spectrochimica Acta Part A 67 (2007) 114–121
119
Table 4
According to the above discussion, Schiff bases interact
Electronic spectral data of the Schiff bases and their Pt(II) complexes
with Pt(II) as a neutral bidentate ligand and oxygen rather than
nitrogen atoms are the most probable coordination sites. With
two water molecules inside the coordination sphere of the Pt(II)
ion a square planar geometry is proposed in the four complexes.
The presence of coordinated and uncoordinated water was
further investigated by thermal analysis. Table 3 gives the max-
imum temperature values for the decomposition along with
the species lost in each step of the decomposition reactions
of the complexes [Pt(sal-o-phdnH2)(H2O)2]Cl2 (1), [Pt(sal-p-
phdnH2)(H2O)2]Cl2·H2O (2) and [Pt(fur-p-phdn)(H2O)2]Cl2
(4). The data obtained support the proposed structures and indi-
cate that complexes 1and 4 undergo two steps degradation reac-
tion, while complex 2 undergoes three steps in good agreement
with their structures, see Table 3. The first step in complexes 1
and 4, and the second step in complex 2 occur at a maximum
lying in the region above 200 ◦C. The weight loss associated
with this step agrees quite well with the loss two coordinated
water molecules. The first step in the decomposition reaction of
complex 2 was observed at relatively lower temperature 111 ◦C
with weight loss consistent with the loss of the uncoordinated
water molecules. The last step in the degradation of the three
complexes occurs in the region around 400 ◦C and should be
associated with the loss of the ligand as the found and calcu-
lated weight loss are in good agreement (Table 3). The weight
of the residue is found to be in consistent with the formation of
PtCl2 as final thermal decomposition product.
Compound
λmax (nm)
*
*
␲ → ␲
n → ␲
d → d transition
(sal-o-phdnH2)
1
(sal-p-phdnH2)
2
(fur-o-phdn)
3
(fur-p-phdn)
4
249
249
222
251
216
244
222
222
295
285
432
448
354
359
333
308
308
273
bial active than the other two. Moreover, complex 3 shows
the highest antibacterial activity against all bacteria tests. The
highest inhibition of growth occurred on complex 3 against the
bacterium B. subtilis NRRL B-94 (as gram positive bacteria),
Table 5. It may conclude that most of complexes have antibacte-
rial effect except complex 4, which have less antibacterial effect.
On the other hand, complex 3 showed the best activity towards
fungi against A. fluves NRC (27.00 0.19 mm) and the lowest
against S. cervisiea NRC (6.7.00 0.094 mm). All complexes
showed antifungal activities against A. niger NRRL 599 and
A. fluves NRC. Therefore, the inhibition zone diameter results
were mostly found to be dependant on both the type of Schiff
bases and/or position of Pt(II) (o- or p-). The activities of com-
plexes 1 and 3 may be explained on the basis of chelation theory;
chelation reduces the polarity of the metal atom mainly because
of partial sharing of its positive charge with the donor groups
and possible ␲ electron delocalization within the whole chalete
ring. Also, chelation increases the lipophelic nature of the cen-
tral atom which subsequently favors its permeation through the
lipid layer of the cell membrane [35].
Electronic absorption spectra of the Schiff bases and their
Pt(II) complexes, 1–4 were recorded in methanol as a solvent.
Table 4 show the observed absorption bands and their assign-
ments. The complexes spectra generally show the characteristic
bands of the free ligands with some changes both in frequencies
(λmax) and intensity together with appearances of new bands at
longer wavelengths. This could be taken as an evidence for the
complexation of Schiff bases with Pt(II) [33,34].
The results of minimum inhibitory concentration (MIC) of
some active complexes against B. subtilis NRRL B-94, S. aureus
NRRL B-313, P. aereuguinosa NRRL B-32, A. niger NRRL
599 and A. fluves NRC are shown in Table 6. The concentration
(75.00 ␮mol/ml) was major in about all microorganisms tested
except the complex 3 for which the MIC against S. aureus NRRL
3.1. Antimicrobial activity
The results revealed that complexes are more microbial toxic
than the ligands. Complexes 1 and 3 are much more micro-
Table 5
Antimicrobial activity of Schiff bases and their platinum(II) complexes
Diameter of inhibition zone (mm)
Bacteria
Fungus
Yeast
B. subtils
S. aureus
E. coli
P. aereuguinosa
A. niger
A. fluves
C. albicans
S. cervisiea
1
2
3
4
L1
L2
L3
L4
R1
R2
14.3 0.094
11.6 0.120
27.0 0.091
00.0 0.000
04.6 0.047
00.0 0.000
04.6 0.047
00.0 0.000
32.3 0.205
00.0 0.000
19.0 0.094
14.0 0.250
26.0 0.120
00.0 0.000
04.3 0.047
00.0 0.000
08.0 0.140
00.0 0.000
30.6 0.047
00.0 0.000
19.0 0.169
11.6 0.094
19.0 0.047
00.0 0.000
00.0 0.000
00.0 0.000
00.0 0.000
00.0 0.000
29.6 0.094
00.0 0.000
18.0 0.160
13.6 0.047
22.0 0.170
00.0 0.000
00.0 0.000
00.0 0.000
00.0 0.000
00.0 0.000
30.3 0.170
00.0 0.000
18.6 0.120
16.3 0.047
25.0 0.140
15.0 0.047
04.6 0.094
00.0 0.000
04.3 0.047
00.0 0.000
00.0 0.000
27.6 0.094
25.0 0.094
09.6 0.094
27.0 0.190
13.0 0.020
04.3 0.047
00.0 0.000
04.7 0.094
00.0 0.000
00.0 0.000
29.3 0.094
06.0 0.094
00.0 0.000
11.0 0.081
04.7 0.047
00.0 0.000
00.0 0.000
00.0 0.000
00.0 0.000
00.0 0.000
25.6 0.047
04.6 0.120
00.0 0.000
06.7 0.094
05.3 0.047
00.0 0.000
00.0 0.000
00.0 0.000
00.0 0.000
00.0 0.000
28.0 0.124
Each value represents mean of sample S.D., L1, L2, L3 and L4 represent the Schiff base ligands, respectively. R1 and R2 represent tetraceycline and fluconazol,
respectively.

120
A.S. Gaballa et al. / Spectrochimica Acta Part A 67 (2007) 114–121
Table 6
Minimum concentration inhibitory (MIC, ␮mol/ml) of active complexes (1–3)
against some microorganisms
Complex Bacteria
Fungus
B. subtils S. aureus P. aeroeuguinosa A. niger A. fluves
1
2
3
75.0
75.0
75.0
75.0
75.0
50.0
75.0
100.0
50.0
100.0
100.0
50.0
100.0
100.0
75.0
Fig. 3. Effect of different concentrations of complex 3 on total lipids content of
B. subtilis NRRL B-94.
Fig. 1. Effect of different concentrations of complex 3 on growth rate of B.
subtilis NRRL B-94.
B-313, P. aereuguinosa NRRL B-32 and A. niger NRRL 599 was
50.00 ␮mol/ml. The aforementioned results indicate that com-
plex 3 exhibited antimicrobial activities higher than that of other
complexes. The variation in the effectiveness of different com-
plexes against different organisms depend either on differences
in the permeability of the cells of the microbes or on difference
in ribosome’s of the microbes [36].
From the results illustrated in Figs. 1–4, it could be concluded
that complex 3 reduced the growth rate, acid soluble phospho-
rus content, intracellular lipids and proteins content of B. subtilis
NRRL B-94. The mode of action may involve the formation of a
hydrogen bonds through the nitrogen atom in interference with
the active contents of the cell constituents, resulting in interfer-
ence with the normal cell process [37]. The inhibition growth
may be due to the effect on the biosynthesis of phospholipids in
cell membrane and proteins.
Fig. 4. Effect of different concentrations of complex 3 on total protein content
content of B. subtilis NRRL B-94.
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