Synthesis, characterization, and antimicrobial activity of a new pyrimidine Schiff base and its Cu(II), Ni(II), Co(II), Pt(II), and Pd(II) complexes

Article abstract of DOI:10.3906/kim-1104-2

A new Schiff base, {1-[(5-bromo-2-hydroxy-benzylidene)-amino]-4-phenyl-2- thioxo-1,2-dihyro-pyrimidin-5-yl}-phenyl-methanone, was synthesized from N-amino pyrimidine-2-thione and 5-bromsalicylaldehyde. Metal complexes of the Schiff base were prepared from acetate salts of Cu(II), Ni(II), Co(II), Pd(II), and PtCl₂ in methanol. The chemical structures of the Schiff base ligand and its metal complexes were confirmed by spectroscopic analysis. All of the compounds were evaluated for their antimicrobial against 4 grampositive bacteria, 1 gram-negative bacterium, and 3 yeast strains. The Schiff base and the Cu(II) and Co(II) complexes showed good biological activity against all tested bacteria and yeast strains. TUeBITAK.

Full text of DOI:10.3906/kim-1104-2

Turk J Chem
36 (2012) , 189 – 200.
¨
˙
c
ꢀ TUBITAK
doi:10.3906/kim-1104-2
Synthesis, characterization, and antimicrobial activity of
a new pyrimidine Schiff base and its Cu(II), Ni(II),
Co(II), Pt(II), and Pd(II) complexes
1
2,∗
˙
3
¨
¨
Mehmet GULCAN , Mehmet SONMEZ , Ismet BERBER
1Department of Chemistry, Faculty of Science, Yu¨zu¨ncu¨yıl University,
65080 Van-TURKEY
2Department of Chemistry, Faculty of Arts and Sciences, Gaziantep University,
27310 Gaziantep-TURKEY
e-mail: msonmez@gantep.edu.tr
3Department of Biology, Faculty of Science and Letters, Sinop University,
57000 Sinop-TURKEY
Received: 01.04.2011
A new Schiff base, {1-[(5-bromo-2-hydroxy-benzylidene)-amino]-4-phenyl-2-thioxo-1,2-dihyro-pyrimidin-
5-yl}-phenyl-methanone, was synthesized from N-amino pyrimidine-2-thione and 5-bromsalicylaldehyde.
Metal complexes of the Schiff base were prepared from acetate salts of Cu(II), Ni(II), Co(II), Pd(II), and
PtCl2 in methanol. The chemical structures of the Schiff base ligand and its metal complexes were confirmed
by spectroscopic analysis. All of the compounds were evaluated for their antimicrobial against 4 gram-
positive bacteria, 1 gram-negative bacterium, and 3 yeast strains. The Schiff base and the Cu(II) and Co(II)
complexes showed good biological activity against all tested bacteria and yeast strains.
Key Words: N-aminopyrimidine-2-thione, 5-bromosalicylaldehyde Schiff base, metal complexes, antimi-
crobial activity
Introduction
Schiff bases, products of the reaction of primary amines and carbonyl compounds, are involved in many metabolic
processes. Numerous products of further fragmentation and crosslinking are responsible for the color, flavor, and
∗Corresponding author
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Synthesis, characterization, and antimicrobial activity of..., M. GULCAN, et al.
taste of foods and drinks.1 Salicyliden- and 2-hydroxynaphthylideneamines have been the subject of particular
interest because some of their complexes are found in nature and biological activities have been recorded for
the synthesized ones.2 Pyrimidine is the parent heterocycle of a very important group of compounds that
have been extensively studied due to their occurrence in living systems. 3 Pyrimidines are reported to have
a broad spectrum of biological activities. Some are endowed with antitumor,4 antiviral,5 antiinflammatory,6
antipyretic,7 antimicrobial,8 and antifungal9 properties. Considerable attention has been given to the metal(II)
complexes of polydentate Schiff base ligands of the N-aminopyrimidine type, due to their structural richness and
electrochemical properties as well as their potential as a model for a number of important biological systems.10,11
This paper describes the synthesis of a new Schiff base ligand (Figure 1) containing a ring of pyrimidine
and its metal complexes. Spectral and magnetic studies were used to characterize the structure of the complexes.
IR, 1 H-NMR, 13 C-NMR, and mass spectra were obtained to determine the structure of the ligand (HL). All
of the synthesized compounds were evaluated for their antimicrobial activities against gram-positive and gram-
negative bacteria and fungi using the microdilution procedure.
Experimental
Elemental analyses (C, H, N, S) were performed using a LECO CHNS model 932 elemental analyzer. The
IR spectra were obtained using KBr disks (4000-400 cm−1) on a Bio-Rad-Win-IR spectrophotometer. The
electronic spectra, in the range of 200-900 nm, were obtained in DMF on a Unicam UV2-100 UV/Visible
spectrophotometer. Magnetic measurements were carried out by the Gouy method using Hg[Co(SCN)4 ] as the
calibrant. Molar conductance of the Schiff base ligand and the transition metal complexes were determined
in DMF at room temperature using a Jenway model 4070 conductivity meter. The 1 H-NMR and 13 C-NMR
spectra of the Schiff base were recorded with a Bruker 300 MHz UltraShield NMR instrument. LC/MS-API-ES
mass spectra were recorded using an Agilent model 1100 MSD mass spectrophotometer. Thermogravimetric
analysis (TGA) measurements were carried out with a Shimadzu-50 thermal analyzer. 1-Amino-5-benzoyl-
4-phenyl-1H -pyrimidine-2-thione was prepared according to the literature method.12 All other reagents and
solvents were of reagent-grade quality and were obtained from commercial suppliers.
Chemistry
Synthesis of Schiff base (HL)
The Schiff base ligand was prepared by the condensation of 1-amino-5-benzoyl-4-phenyl-1-H pirimidine-2-thione
(0.307 g, 1 mmol) with 5-bromosalicylaldehyde (0.201 g, 1 mmol) in n-butanol (40 mL), achieved by boiling
the mixture under reflux for 3 h. The precipitated ligand was filtered off, recrystallized from ethanol, and dried
in a vacuum desiccator. Yield was 295 mg (60%), mp 204 ◦ C. Anal. Calc. for C24 H16 BrN3 O2 S (490.37):
C, 58.78; H, 3.29; N, 8.57; S, 6.54. Found: C, 58.84; H, 3.43; N, 8.70; S, 6.74%. Selected IR data, ν (cm−1):
3200-3500 (O-H/H2 O-NH), 3059 (C-H), 1647 (C=O), 1616 (C=N), 1314 (C-O), 1180, 735 (C=S). UV-Vis [λ
(nm)]: 257, 285, 334, 368, 374. 1 H-NMR (δ): 7.33-7.97 (m, aromatic H), 8.96 (s, C(6)pyrim.), 9.08 (s, HC=N-),
11.035 (bs, OH). 13 C-NMR (δ): 191.99 (-CO-Ph), 176.25 (C=S), 165.16 (Ph-C-pyrim.), 164.39 (-C-OH), 146.55
(-HC=N-), 137.50 (HC-pyrim.), 137.5-111.05 (aromatic C). API-ES: m/z 492.4 [M+H].
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Synthesis of the complexes (1-5)
In 30 mL of methanol, 0.912 g (2.00 mmol) of the ligand was dissolved, and a solution of 1.00 mmol of the metal-
salt [Cu(AcO)2·H2 O (0.200 g), Co(AcO)2·4H2 O (0.250 g), Pd(AcO)2 (0.224 g), Ni(AcO)2·4H2 O (0.248 g),
and PtCl2 (0.266 g)] methanol was added dropwise with continuous stirring. The mixture was stirred further
for 1.5-2.5 h at 65 ◦ C. The precipitated solid was then filtered off, washed with cold methanol followed by
diethyl ether, and dried in vacuum desiccators.
[Cu(L)2 ]·4H2 O (1): Yield was 445 mg (40%), mp 254 ◦ C. Anal. Calc. for C48 H38 Br2 CuN6 O8 S2
(1114.33 g mol−1): C, 51.74; H, 3.44; N, 7.54; S, 5.76. Found: C, 51.43; H, 3.18; N, 7.69; S, 5.49%. Selected
IR data, ν (cm−1): 3356 (O-H/H2 O), 1657 (C=O), 1594 (C=N), 1350 (C-O), 1215 (C=S), 545 (M-O), 421
(M-N). UV-Vis [λ (nm)]: 241, 252, 283, 295, 312, 320, 338, 347, 355, 376, 462. μeff 1.92 BM, Λo (S cm2
mol−1) 12.95. API-ES: m/z 1043.0 [63 Cu(L)2 +1].
[Ni(L)2 ]·3H2 O (2): Yield was 510 mg (46%), mp 238 ◦ C. Anal. Calc. for C48 H36 Br2 NiN6 O7 S2
(1091.47 g mol−1): C, 52.82; H, 3.32; N, 7.70; S, 5.88. Found: C, 52.88; H, 3.22; N, 7.69; S, 5.75%. Selected
IR data, ν (cm−1): 3340 (O-H/H2 O), 1661 (C=O), 1600 (C=N), 1290 (C-O), 1224 (C=S), 522 (M-O), 434
(M-N). UV-Vis [λ (nm)]: 227, 251, 270, 296, 309, 321, 407, 560. μeff 2.88 BM, Λo (S cm2 mol−1) 3.95.
API-ES: m/z 1041.0 [58 Ni(L)2 +3].
[Co(L)2 ]·2H2 O (3): Yield was 450 mg (42%), mp 266 ◦ C. Anal. Calc. for C48 H34 Br2 CoN6 O6 S2
(1073.69 g mol−1): C, 53.69; H, 3.19; N, 7.83; S, 5.97. Found: C, 53.78; H, 3.33; N, 8.32; S, 6.03%. Selected IR
data, ν (cm−1): 3200-3500 (O-H/H2 O-NH), 1651 (C=O), 1596 (C=N), 1340 (C-O), 1220 (C=S), 545 (M-O),
429 (M-N). UV-Vis [λ (nm)]: 238, 283, 299, 306, 314, 453, 790. μeff 2.36 BM, Λo (S cm2 mol−1) 10.75.
API-ES: m/z 1019.8 [59 Co(L)2 -OH]+
.
[Pd(L)2 ]·H2 O (4): Yield was 435 mg (39%), mp 198 ◦ C. Anal. Calc. for C48 H32 Br2 N6 O5 PdS2
(1103.16 g mol−1): C, 52.26; H, 2.92; N, 7.62; S, 5.81. Found: C, 51.66; H, 3.15; N, 8.26; S, 6.56%. Selected
IR data, ν (cm−1): 3400 (O-H/H2 O), 1659 (C=O), 1596 (C=N), 1271 (C-O), 1175 (C=S), 538 (M-O), 432
(M-N). UV-Vis [λ (nm)]: 249, 307, 352, 376, 393, 407, 424, 442, 451, 463, 471, 481. μeff Dia, Λo (S cm2
mol−1) 5.19. API-ES: m/z 1083 [106 Pd(L)2 +1].
[Pt(LH)2 ]·Cl2 (5): Yield was 470 mg (37%), mp 210 ◦ C. Anal. Calc. for C48 H32 Br2 CI2 N6 O4 PtS2
(1246.73 g mol−1): C, 46.24; H, 2.59; N, 6.74; S, 5.14. Found: C, 45.40; H, 3.18; N, 7.47; S, 5.75%. Selected
IR data, ν (cm−1): 3400 (O-H/H2 O-NH), 1663 (C=O), 1595 (C=N), 1315 (C-O), 1217 (C=S), 533 (M-O),
410 (M-N). UV-Vis [λ (nm)]: 231, 278, 311, 335, 361, 386, 410, 438, 460. μeff Dia, Λo (S cm2 mol−1) 140.5.
API-ES: m/z 1031.8 [195 Pt(L)2 -(PhCO)2+35 (Cl)2 ]+ .
Biological assay
Compounds and cells
Test compounds were dissolved in DMSO (12.5%) at an initial concentration of 1280 μg mL−1 and then serially
diluted in culture medium. Bacterial strains were supplied by the American Type Culture Collection. Candida
strains were obtained from Refik Saydam Hıfzıssıhha Research Institute, Ankara, Turkey.
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Antibacterial assay
The newly synthesized compounds were screened for their antibacterial activity against 4 gram-positive (S.
aureus ATCC 6538, S. aureus ATCC 25923, B. cereus ATCC 7064, and M. luteus ATCC 9345) and 1 gram-
negative (E. coli ATCC 4230) bacteria, as described by the guidelines in NCCLS-approved standard document
M7-A4, using the microdilution broth procedure.13 Ampicillin trihydrate was used as the reference antibacterial
agent. Solutions of the compounds and reference drug were dissolved in DMSO at a concentration of 2560 μg
mL−1 . The 2-fold dilutions of the compounds and the reference drug were prepared (1280, 640, 320, 160, 80,
40, 20, 10, 5 μg mL−1). Antibacterial activities of the newly synthesized chemical compounds were performed
in Mueller-Hinton broth medium (Difco) at a pH of 7.2 with an inoculum of (1-2) × 103 cells mL−1 by the
spectrophotometric method, and an aliquot of 100 μL was added to each tube of serial dilution. The chemical
compounds-broth medium serial tube dilutions inoculated with each bacterium were incubated on a rotary
shaker at 37 ◦ C for 18 h at 150 rpm. The minimum inhibitory concentration (MIC) of each chemical compound
was recorded as the lowest concentration of each chemical compound in the tubes with no growth (i.e., no
turbidity) of inoculated bacteria.
Antifungal assay
The antifungal activities of the newly synthesized chemical compounds were tested against 3 yeast strains (C.
albicans ATCC 14053, C. krusei ATCC 6258, and C. parapsilosis ATCC 22019) according to the guidelines in
NCCLS-approved standard document M27-A2, using the microdilution broth procedure.14 Fluconazole was used
as the reference antifungal agent. Solutions of the test compounds and reference drug were dissolved in DMSO
at a concentration of 2560 μg mL−1 . The 2-fold dilutions of the compounds and reference drug were prepared
(1280, 640, 320, 160, 80, 40, 20, 10, 5 > μg mL−1). Antifungal activities of the yeast strains were performed in
RPMI 1640 medium (Sigma), which had been buffered to a pH of 7.0 with 0.165 M morpholinopropanesulfonic
acid (Sigma), as outlined in document M27-A. The stock yeast inoculum suspensions were adjusted to a
concentration of (0.5-2.5) × 103 cells mL−1 by the spectrophotometric method, and an aliquot of 100 μL
was added to each tube of the serial dilution. The chemical compound-broth medium serial tube dilutions
inoculated with yeast were incubated on a rotary shaker at 37 ◦ C for 18 h at 150 rpm. The MIC of each
chemical compound was recorded as the lowest concentration of each chemical compound in the tubes with no
growth (i.e., no turbidity) of inoculated yeast.
Results and discussion
Schiff base HL (Figure 1) was synthesized by the condensation of 1-amino-5-benzoyl-4-phenyl-1H-pirimidine-
2-thione12 with 5-bromosalicylaldehyde. The Schiff base ligand and its complexes are very stable at room
temperature in the solid state. The ligand is soluble in common organic solvents, but its metal complexes are
generally only soluble in DMF and DMSO. The elemental analytical data of the complexes reveal a metal:ligand
stoichiometry of 1:2 corresponding to the octahedral geometry of [M(L)2 ]·nH2 O (Figure 2), except for the
square-planar [Pd(L)2 ]·H2 O and [Pt(LH)2 ]·CI2 complexes (Figure 3). These analytical data are in good
agreement with the proposed stoichiometry of the complexes. The molar conductivities of compounds 1-4
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in DMF at 25 ◦ C were in the range of 3.95-12.95 Ω−1 cm2 mol−1 , indicating nonelectrolytes, except for
[Pt(LH)2 ]·CI2 , which behaved as a polar compound due to the electrolytic behavior of its chloride anions (Λo
= 40.5 Ω−1 cm2 mol−1).15
Br
OH
O
HC
N
Ph
N
Ph
N
S
Figure 1. Structure of the Schiff base ligand.
IR spectra
The IR spectra of the Schiff base ligand showed characteristic broad bands at the 3200 cm−1 ν (O–H),16−18
3059 cm−1 ν (C–H pyrimidine ring), l647 cm−1 ν (C=O benzoyl), 1616 cm−1 ν (C=N azomethine), 1314 cm−1
ν (C–O phenolic),16 and 1180 and 735 cm−1 ν (C=S) vibrations.19,20
The IR spectra of the complexes were compared with that of the free ligand to show changes during
complexation. In the spectra of the Cu(II), Ni(II), Co(II), and Pd(II) complexes, the phenolic (C–O) band at
1271-1350 cm−1 shifted to 25-43 cm−1 , the lower or higher frequency supporting bonding of the phenolic OH
after deprotonation.21,22 The azomethine vibration of the ligand at 1616 cm−1 shifted to 1594-1600 cm−1 after
complexation, confirming the formation of a bond from the imine nitrogen to the metal.16−18 The ν (C=S) at
1180 and 735 cm−1 in the free ligand shifted to a higher frequency after complexation, due to coordination
with the nitrogen of azomethine, the oxygen of hydroxyl, and the sulfur of the thione group for the Cu(II),
Co(II), and Ni(II) complexes (Figure 2). On the other hand, the ν (C=S) thione bands in the spectrum of the
Pd(II) complex remained at almost 1175 and 736 cm−1 , suggesting that the C=S group does not take part
in complexation17 and indicating bidentate coordination for the Schiff base through the phenolic oxygen and
nitrogen of the azomethine to the Pd(II) ion (Figure 3).
Bands observed at 410-435 and 520-545 cm−1 were due to ν (M–N) and ν (M–O), respectively.16,20 Broad
bands of the Cu(II), Ni(II), Co(II), and Zn(II) complexes from 3200-3500 cm−1 were assigned to the ν (OH) of
water;23 water content was also identified by thermal analyses.
NMR spectra
DMSO-d6 was used as a solvent to measure the 1 H-NMR and 13 C-NMR spectra of HL (Figure 4 and 5).
The 1 H-NMR spectra of the ligand did not show a signal corresponding to the primary amine, supporting the
complete condensation and formation of the Schiff base. The signal due to the imine group at δ 9.08 ppm (s,
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Synthesis, characterization, and antimicrobial activity of..., M. GULCAN, et al.
1H) provides evidence for the formation of the Schiff base.24 Sharp singlets at δ 11.05 and 8.96 ppm were due
to the phenolic proton and C6(H)-pyrimidine proton of the ligand. The phenyl proton multiplets were between
δ 7.33 and 7.97 ppm.11,24 The 13 C-NMR spectrum of the ligand had a cluster of peaks at δ 191.99 and 176.25
ppm due to benzoyl and thione carbons. The peak at δ 146.25 ppm may be attributed to CH=N. Peaks in the
region of δ 111.05–137.5 ppm were due to aromatic carbons.
Br
O
HC
N
S
N
Ph
O
O
nH2O
Ph
N
M
N
Ph
N
O
Ph
N
S
CH
Br
Figure 2. Proposed structure of the Cu(II), Co(II), and Ni(II) complexes.
Br
Br
HO
N
O
HC
N
O
HC
N
Ph
N
O
N
Ph
O
S
H2O
S
N
Ph
O
Pd
Ph
S
Ph
N
Cl2
N
N
Ph
Pt
O
N
Ph
N
CH
Ph
N
S
CH
Br
OH
Br
Figure 3. Proposed structures of the [Pd(L)2 ]·H2 O and [Pt(LH)2 ]Cl2 complexes.
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Synthesis, characterization, and antimicrobial activity of..., M. GULCAN, et al.
Figure 4. The 1 H-NMR spectrum of the ligand (in DMSO-d6 ).
Figure 5. The 13 C-NMR spectrum of the ligand (in DMSO-d6 ).
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Magnetic and electronic spectral studies
Electronic spectra were recorded in DMF. In the Schiff base, the band at 368 nm was attributed to the π −π * of
the azomethine. Bands between 334 and 257 nm are associated with phenyl and pyrimidine π − π * transitions.
In the spectra of the complexes, the π − π * of the azomethine shifted to 374 nm, indicating that the imino
nitrogen was involved in coordination. The electronic spectra of the Pd(II) and Pt(II) complexes had bands in
the range of 311-231 nm due to the n-π * and π − π * transitions of phenyl, pyrimidine, and azomethine. In
the spectra of the complexes, the less intense and broad bands in the range of 311-481 nm resulted from the
overlap of the low energy π → π * transitions, mainly localized within the azomethine group, and the LMCT
transitions from the lone pairs of the phenolate oxygen donor to Pd(II) and Pt(II).3
2
The UV-Vis spectrum of the Cu(II) complex had a strong band at 462 nm assigned to the 2 Eg → T2g
transition and tailing to a higher wavelength, which is well-known behavior for octahedral Cu(II) complexes.25,26
4
4
The Co(II) complex had 2 bands, 1 at 790 nm and the other at 453 nm, which were assigned to T1g → T2g
4
4
(F) and T1g → T1g (P) transitions, respectively.26,27 The Co(II) complex showed a magnetic moment of 2.36
BM.28,29
The observed magnetic moment of the Ni(II) complex (2.88 BM) indicates Oh geometry. 26 The spectrum
of the Ni(L2 ]·3H2 O complex was characteristic of octahedral geometry, and the bands at 560 and 407 nm can
3
3
3
3
be assigned to A2g → T1g (F) and A2g → T2g (F) transitions.
Mass spectra
The LC-API-ES mass spectrum of the Schiff base showed a molecular ion peak m/z at 491.4, which is equivalent
to its molecular ion weight. The fragmentation peaks, at m/z 245, 199, and 173, were ascribed to the
cleavage of C11 H8 N3 O2 S, C10 H6 N3 S, and C6 H6 OBr, respectively, and are well observed in the mass
spectrum. The spectra of [63 Cu(L)2 +1]+ , [58 Ni(L)2 +3H], [59 Co(L)2 -O]+ , [106 Pd(L)2 +1], and [195 Pt(L)2 -
(PhCO)2+35 (Cl)2 ]+ showed a molecular ion peak M+ at m/z 1043.9, 1041.0, 1019.8, 1083.0, and 1031.8,
respectively, equivalent to the molecular weight. All of the compounds were consistent with the molecular ion
fragment and support the proposed structure of the complexes. The spectrum of the Pd(II) complex is shown
in Figure 6.
Figure 6. API-ES spectrum of the Pd(II) complex.
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Thermogravimetric analysis
The TGA data agree with the formula suggested from elemental analyses. The thermal stabilities were
investigated using TGA at a heating rate of 10 ◦ C min−1 in N2 from 20 to 850 ◦ C. Mass losses corresponded
to H2 O, Ph–CO–, and the other organic moieties in the first, second, third, fourth, and fifth stages of
decomposition. The Cu(II), Ni(II), Co(II), and Pd(II) complexes suffered loss of H2 O in the first stage, 65-130
◦ C, and the ligands gradually decomposed from 220 to 580 ◦ C. The complexes contained 4, 3, 2, and 1 moles
of water of crystallization per complex molecule, respectively. The complexes decomposed to CuO, CoO, NiO,
PdS, and Pt at higher temperatures.30−32
Biological activity
The biological activities of the ligand and its series of metal complexes [Cu(II), Ni(II), Co(II), Pd(II), and
Pt(II)] were screened for antibacterial activity against S . aureus ATCC 6538, S . aureus ATCC 25923, B.
cereus ATCC 7064, M . luteus ATCC 9345, and E . coli ATCC 4230 and for antifungal activity against C .
albicans ATCC 14053, C . krusei ATCC 6258, and C . parapsilosis ATCC 22019 by using broth microdilution
procedures. Ampicillin trihydrate for bacteria and fluconazole for yeast were used as reference drugs. The
results of the antimicrobial activity of the ligand and its metal complexes against all tested bacterial and fungal
strains are shown in Tables 1 and 2. All compounds inhibited the growth of bacteria (gram-negative and
gram-positive), with MIC values in the range of 20-320 μg mL−1 , and exhibited antifungal activity with MICs
between 20 and 160 μg mL−1
.
According to the results of the antibacterial activity screening, the Co(II) and Cu(II) complexes possess
effective and selective antibacterial activity against 1 gram-positive spore-forming bacterium (B. cereus ATCC
7064), 1 gram-negative bacterium (E . coli ATCC 4230), and other gram-positive bacteria (S . aureus ATCC
6538, S . aureus ATCC 25923, and M . luteus ATCC 9345) with MIC values in range of 20-40 μg mL−1
.
On the other hand, other complexes had moderate antibacterial activity against all gram-positive and gram-
negative bacteria, with MICs between 80 and 160 μg mL−1 . Moreover, our findings indicate that all prepared
compounds had similar antibacterial efficacy against gram-positive and gram-negative bacteria.
Table 2 summarizes the antifungal activities of the free ligand and the complexes of compounds against 3
yeast strains (C. albicans ATCC 14053, C . krusei ATCC 6258, and C . parapsilosis ATCC 22019). According
to antifungal studies, the ligand and the Cu(II) and Co(II) complexes compounds displayed good antiyeast
efficacy against the tested fungal species (MICs: 20-40 μg mL−1). Other complexes exhibited weak antifungal
activities (MICs: 80-160 μg mL−1).
The results of this investigation revealed that the Co(II) and Cu(II) complexes possess higher antimicro-
bial activity; it is generally reported that free ligands show lower activity than complexes. 13,14,33,34 Additionally,
when all of the antimicrobial MIC values are compared, the ligand and Co(II) complex displayed the highest
antimicrobial efficacy, with MIC values ranging between 20 and 40 μg mL−1 . Finally, it is suggested that the
reason for this higher antimicrobial efficacy could be related to the inhibition of several structural enzymes that
play a key role in vital metabolic pathways of the microorganisms.
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Table 1. MICs of the ligand (HL) and its metal complexes [Cu(II), Ni(II), Co(II), Pd(II), Pt(II)] against gram-negative
and gram-positive bacterial strains.
Bacillus
Staphylococcus Staphylococcus Escherichia Micrococcus
cereus
aureus
aureus
coli
luteus
ATCC 7064
ATCC 6538
ATCC 25923
ATCC 4230 ATCC 9345
HL
160
40
160
40
80
80
5
160
40
80
20
80
80
5
160
40
80
20
80
80
10
160
80
160
20
80
20
80
80
10
1
2
160
40
3
4
160
160
20
5
Ampicillin
The MIC values were determined as μg mL−1 of active compound in medium.
Table 2. MICs of the ligand (HL) and its metal complexes [Cu(II), Ni(II), Co(II), Pd(II), Pt(II)] against fungal strains.
Candida albicans Candida parapsilosis Candida krusei
ATCC 14053
ATCC 22019
ATCC 6258
HL
160
40
160
40
80
20
80
80
5
160
40
80
20
80
80
10
1
2
160
40
3
4
160
80
5
Fluconazole
5
The MIC values were determined as μg mL−1 of active compound in medium.
Conclusions
We have described the synthesis and structure of a new heterocyclic Schiff base and its metal complexes in a
metal-to-ligand ratio of 1:2. The ligand is a bidentate or tridentate chelating agent coordinating through the
deprotonated phenolic group, azomethine nitrogen, and sulfur of the pyrimidine thione group. The analytical
data, electronic spectra, magnetic susceptibility, and IR, NMR, and API-ES mass spectral data revealed the
mononuclear octahedral configuration of the Cu(II), Co(II), and Ni(II) complexes, while Pd(II) and Pt(II)
are mononuclear and square-planar in configuration. The antibacterial activity results showed that all of the
complexes have moderate activity against gram-positive bacteria. They have weak activity against gram-
negative bacteria, except the Co(II) complex, which has moderate activity against E. coli. Generally, the
antibacterial activities of all of the complexes are greater than those of the free Schiff base ligand.
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Acknowledgements
We are grateful to the Yu¨zu¨ncu¨yıl University Research Foundation (2009-FBE-D006) for its support in this
research.
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