Synthesis, characterization and antimicrobial activity of 3,5-di-tert-butylsalicylaldehyde-S-methylthiosemicarbazones and their Ni(II) complexes

Article abstract of DOI:10.1007/s11243-011-9518-7

Ni(II) complexes were prepared by the reactions of 3,5-di-tert- butylsalicylaldehyde-S-methylisothiosemicarbazone (L) with salicylaldehyde or 2-hydroxy-1-naphthaldehyde in the presence of NiCl₂?6H ₂O. The complexes and starting material L were characterized by physic-chemical analysis and spectroscopic techniques such as ¹HNMR, ¹³CNMR, IR and UV-VIS. Antimicrobial activity studies of L and the two complexes standards strains of bacteria (Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), Bacillus cereus, Enterococcus faecalis, Streptococcus pneumoniae, Listeria monocytogenes, Escherichia coli, Salmonella typhi and Candida albicans) and 22 clinically isolated microorganisms, including multidrug resistant pathogenic microorganisms, were carried out. The free thiosemicarbazone L showed a significant inhibition of the growth all of Gram-positive bacteria tested.

Full text of DOI:10.1007/s11243-011-9518-7

Transition Met Chem (2011) 36:679–684
DOI 10.1007/s11243-011-9518-7
Synthesis, characterization and antimicrobial activity
of 3,5-di-tert-butylsalicylaldehyde-S-methylthiosemicarbazones
and their Ni(II) complexes
•
•
˘
Baki Tu¨rkkan Bahtiyar Sarıboga
˘
Nezaket Sarıboga
Received: 24 March 2011 / Accepted: 12 July 2011 / Published online: 26 July 2011
Ó Springer Science+Business Media B.V. 2011
Abstract Ni(II) complexes were prepared by the reactions
of 3,5-di-tert-butylsalicylaldehyde-S-methylisothiosemi-
carbazone (L) with salicylaldehyde or 2-hydroxy-1-naph-
thaldehyde in the presence of NiCl2Á6H2O. The complexes
and starting material L were characterized by physic-
chemical analysis and spectroscopic techniques such as
1HNMR, 13CNMR, IR and UV–VIS. Antimicrobial activity
studies of L and the two complexes standards strains of
bacteria (Staphylococcus aureus, methicillin-resistant
Staphylococcus aureus (MRSA), Bacillus cereus, Entero-
coccus faecalis, Streptococcus pneumoniae, Listeria mon-
ocytogenes, Escherichia coli, Salmonella typhi and Candida
albicans) and 22 clinically isolated microorganisms,
including multidrug resistant pathogenic microorganisms,
were carried out. The free thiosemicarbazone L showed a
significant inhibition of the growth all of Gram-positive
bacteria tested.
considered to be due to substituent effects on their aromatic
aldehyde or ketone rings and their ability to form chelates
with trace metals [12]. Among the metal complexes of
thiosemicarbazones, the copper(II) and palladium(II)
chelates have been studied especially, regarding their
antitumor potential. Some palladium(II) complexes of
thiosemicarbazones are also known as antiviral agents.
[13] Considerable attention has recently been focused on
S-alkyl thiosemicarbazone derivatives due to their inter-
esting biological activities. A number of studies on the
synthesis and characterization of these compounds have
been published [14, 15]. Many metal-templated compounds
synthesized from S-alkyl to thiosemicarbazones with var-
ious carbonyl compounds have been studied [16–18].
However, to date, the microbial activities of 3,5-di-tert-
butylsalicylaldehyde-S-methylthiosemicarbazones have not
been reported in the literature. The present work deals
with the synthesis and antimicrobial activities of 3,5-di-tert-
butylsalicylaldehyde-S-methylthiosemicarbazone and its
Ni(II) complexes (Figs. 1, 2).
Introduction
Thiosemicarbazones and their transition metal complexes
are of considerable interest because of their biological
activities such as antiviral, antifungal, antibacterial, anti-
tumor, anticancerogenic and insulin mimetic properties
[1–11]. The biological activities of thiosemicarbazones are
Experimental
All chemicals and solvents were of reagent grade. Iodo-
methane, 3,5-di-tert-butylsalicylaldehyde (DTBSA), ethanol,
methanol, thiosemicarbazide, 2-hydroxy-1-naphthaldehyde,
salicylaldehyde, DMSO and NiCl2Á6H2O were purchased
from Sigma to Aldrich.
B. Tu¨rkkan (&)
IR spectra were recorded (KBr disks) on a Perkin–Elmer
FTIR spectrometer. 1H and 13CNMR spectra were obtained
on a Bruker 200 MHz spectrometer. UV–VIS spectra were
recorded using a Perkin–Elmer PTP–1 Petier system UV
spectrophotometer. A Carlo-Erba 1106 Elemental Analyser
was utilized for elemental analysis.
Department of Chemistry, Harran University,
63300 Osmanbey, Sanlurfa, Turkey
e-mail: bakiturkkan@harran.edu.tr
˘
˘
B. Sarıboga Á N. Sarıboga
Department of Chemistry, Nevs¸ehir University, Nevsehir,
Turkey
123

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Transition Met Chem (2011) 36:679–684
t-Bu
Fig. 1 Synthesis of NiL1
c
d
f
a
t-Bu
OH
a
EtOH
t-Bu
O
O
e
NiCl2.6H2O
+
HO
O
+
t-Bu
Ni
4
N
1
b
4
N
1
b
N
NH2
N
2
2
N
S
NiL1
L
S
t-Bu
Fig. 2 Synthesis of NiL2
c
d
a
t-Bu
a
EtOH
e
t-Bu
O
O
NiCl2.6H2O
+
HO
+
t-Bu
OH
f
Ni
4
1
b
4
N
N
S
1
O
h
b
g
N
NH2
N
2
2
N
NiL2
L
S
Synthesis of 3,5-di-tert-butylsalicylaldehyde-S-
methylisothiosemicarbazone (L)
stirred for 24 h at room temperature. A mixture of L
(0.321 g, 1 mmol) and salicylaldehyde (0.122 g, 1 mmol)
in ethanol (30 mL) was added. After 24 h, the dark red
precipitate was filtered off, washed with ethanol and
diethyl ether and then dried in vacuum. Dark red yield,
0.289 g, 60%, m.p, 260–262 °C, Anal. Calc. for
(C24H29N3NiO2S) (482.26 g/mol): C, 59.77; H, 6.06; N,
8.71; S, 6.65, Found: C, 59.80; H, 6.07; N, 8.75; S, 6.45,
1HNMR (DMSO-d6, 25 °C, ppm): 8.03,(s, 1H, HC=N1),
7.84 (s, 1H, HC=N4), 7.40 (s, 1H, a), 7.03 (s, 1H, b),
7.35–7.24 (m, 3H, c, d, f), 6.62, 6.58 (m, 1H, e), 2.61 (s,
3H, S=CH3), 1.30 (s, 18H, t-Bu), 13CNMR (DMSO-d6,
25 °C): 169.8, 163.48, 161.0 ppm (C=N2, N1, N4), 156.2,
154.6, 140.6, 136.9, 136.5, 134.0, 129.8, 125.7, 123.3,
119.5, 117.0, 116.5 ppm (phenyl), 35.6, 31.2, 29.4 ppm,
(t–Bu), 15.18 ppm (S–CH3), FTIR (KBr, cm-1): m(C=N1)
1,615, m(N2=C) 1,582, m(N4=C) 1,593, m(C–H) 2,953,
2,902, 2,864 cm-1. UV–VIS (CHCl3): 247, 252 nm (p–
p*), 298, 330 nm, (n–p*), 404, 424 nm (MLCT), 498,
590 nm (d–d).
The S-methylisothiosemicarbazone of 3,5-di-tert-butylsa-
licylaldehyde was prepared with a small modification of
the general method [19].
Thus, mixing thiosemicarbazide (0.91 g, 0.01 mol) and
iodomethane (0.76 mL, 0.012 mol) were mixed in ethanol
(40 mL). The mixture was refluxed water bath for 2–3 h.
A solution of 3,5-di-tert-butylsalicylaldehyde (2.34 g,
0.01 mol) in ethanol (10 mL) was then added. The reaction
mixture was refluxed for a further 4 h, and the clear solution
was cooled to room temperature. An aqueous solution of 5%
NaHCO3 was added to the reaction mixture for neutraliza-
tion. The mixture, containing a yellowish oily layer, was poured
into water and stirred vigorously for 3 h. The resulting cream
precipitate was filtered off, washed with water and diethyl
ether and finally dried in a vacuum desiccator.
Cream yield 2.56 g, 80%, m.p, 120–122 °C, Anal. Calc.
for (C17H27N3OS) (321.48 g/mol): C, 63.51; H, 8.47;
N, 13.07; S, 9.97, Found: C, 63.59; H, 8.45; N, 13.21; S,
9.75, 1HNMR (DMSO-d6, 25 °C, ppm): 11.65 (s, 1H, OH),
8.47,8.31 (syn/anti ratio: 1/4, s, 1H, CH=N1), 5.08 (s, 2H,
NH2), 7.34, 7.23 (syn/anti ratio:1/3, s, 1H, a), 7.09,7.05 (syn/
anti ratio:1/3s, 1H, b), 2.48, 2.45 (cis/trans ratio: 3/2, s, 3H,
S–CH3), 1.28 (s, 18H, t–Bu). 13CNMR (DMSO-d6, 25 °C):
159.6, 157.2 ppm (C=N2, N1), 141.0, 136.2, 126.4, 125.8,
117.7 ppm (phenyl), 35.0, 31.4, 29.4 ppm (t–Bu), 13.0 ppm
(S–CH3), FTIR (KBr, cm-1): mas (NH2) 3,494, ms (NH2) 3,386,
3,296, m (OH) 3,130, d (NH2) 1,641, m (C=N1) 1,612, m (N2=C)
1,582, m (C–O) 1,174, m (C–H) 2,955–2,856 cm-1. UV–VIS
(CHCl3): 242–298 nm (p–p*), 310–342 nm, (n–p*).
Synthesis of N1-3,5-di-tert-butylsalicylidene-N4-2-
hydroxy-1-naphthylidene-S-methylthiosemi-
carbazidato nickel(II) (NiL2)
The complex NiL2 was obtained in a similar manner to
NiL1. Dark red yield, 0.266 g, 50%, m.p, [340 °C, Anal.
Calc. for (C28H31N3NiO2S) (531.15 g/mol): C, 63.18; H,
5.87; N, 7.89; S, 6.02, Found: C, 63.20; H, 5.85; N, 7.92;
1
S, 5.87, HNMR (DMSO-d6, 25 °C, ppm): 8.71, (s, 1H,
HC=N1), 8.11 (s, 1H, HC=N4), 7.24 (s, 1H, a), 7.15–7.06
(m, 1H, b),7.34–7.21 (m, 1H, c),7.41–7.39 (m, 1H, d),
7.94–7.90 (m, 1H, e),7.45 (m, 1H, f), 7.53–7.49 (m, 1H, g),
7.71–7.62 (m, 1H, h), 2.72 (s, 3H, S–CH3), 1.29 (s, 18H,
t–Bu), 13CNMR (DMSO-d6, 25 °C): 156.3, 156.0 ppm
(C=N2, N1), 147.0, 142.0, 137.5, 137.0, 136.0, 136.5,
134.0, 131.3, 130.0, 129.5, 126.0, 125.0, 124.5, 124.0,
119.4, 116.0 ppm (phenyl), 35.6, 34.01, 31.29 ppm (t–Bu),
29.51 ppm (S–CH3), FTIR (KBr, cm-1): m(C=N1) 1,616,
Synthesis of N1-3,5-di-tert-butylsalicylidene-N4-
salicylidene-S-methylthiosemicarbazidato-nickel(II)
(NiL1)
NiCl2Á6H2O (0.237 g, 1 mmol) was dissolved in ethanol
(25 mL) containing orthoformic ester (1.33 g, 9 mmol) and
123

Transition Met Chem (2011) 36:679–684
681
m(N2=C) 1,577, m(N4=C) 1,598, m(C–H) 2,950, 2,902,
2,863 cm-1. UV–VIS (CHCl3): 242, 262 nm (p–p*), 320,
30 nm, (n–p*), 404, 428 nm (MLCT), 491, 581 nm (d–d).
(Himedia) and Ceftazidime (Sigma) were used as reference
inhibitors for bacterial strains and Amphotericin B (Sigma)
for fungal strains.
Antimicrobial activities
Results and discussion
Standard strains of microorganisms, namely S. pneumoniae
(ATCC 29212), S. aureus (ATCC 6538), methicillin-
resistant S. aureus MRSA (ATCC 43300), B. cereus
(ATCC 7064), E. faecalis (ATCC 29212), S. typhi (CCM
5445), L. monocytogenes (ATCC 19114), E. coli (ATCC
8739), were studied along with the fungal strain C. albi-
cans (ATCC 10231). Ten MRSA, two MSSA and ten
E. faecalis strains were clinical isolates supplied by Ond-
okuz Mayis University, Medical School Department of
Microbiology and Infectious Disease. MRSA, MSSA and
E. faecalis isolates were concurrently processed using a
Phoenix instrument version 5.75A and Epicenter software
version V5.75A/V4.85A systems for genus and species
identification and the determination of the antimicrobial
susceptibility category.
Spectroscopic characterization
In the infrared spectra of 3,5-di-tert-butylsalicylaldehyde-
S-methylisothiosemicarbazone (L), bands at 3,494–3,386,
3,130 and 1,641 cm-1 were attributed to NH2 and OH,
stretches and the N–H bend, respectively. These bands are
absent after coordination of the ligand to the metal through
the phenolic oxygen atom and reaction of the N4H2 group
with aldehyde to give the complex. The (C–H) stretching
vibrations of the S–CH3 and t–Bu groups were observed
at 2,955–2,856 cm-1. The S-methylisothiosemicarbazone
L exhibits strong bands at 1,612 and 1,582 cm-1 which
correspond to the azomethine system (C=N1 and N2). An
additional azomethine group (C=N4) is observed after con-
densation of a second aldehyde to the thioamide nitrogen,
positioned at 1,594 cm-1 for NiL1 and 1,597 cm-1 for
NiL2 [17].
The 1HNMR spectra of the compounds showed
the expected signals [22–24]. Peaks corresponding to the
azomethine groups were observed for the ligand L. The
observed syn-anti isomerism is associated with the double
bond of the azomethine (HC=N1) [17, 25]. Syn- and anti-
isomers of L were defined by dual peaks with the 1:4
integral ratios. Such cis–trans isomerism is common for
such (C=N2) [17, 26, 27]. The chemical shifts of the methyl
protons of L are 2.48 and 2.45 ppm (cis/trans ratio 3:2).
The HC=N1 and N4 protons of NiL1 and NiL2 are observed
at 8.03, 7.84 and 8.71, 8.11 ppm, respectively. The spectra
of the complexes contain no isomer peaks, consistent with
single coordination geometry.
Each compound was dissolved in DMSO. Antibacterial
and antifungal activities were evaluated using the mini-
mum inhibitory concentration (MIC) by micro-dilution.
The antibacterial activity assays of all compounds were
performed according to the Clinical and Laboratory Stan-
dards Institute (CLSI) protocols [20]. The antifungal
activities of all compounds were evaluated according to the
National Committee for Clinical Laboratory Standards
(NCLS) [21].
The bacteria were incubated in Muller Hinton Broad
(MHB, Oxoid) at 37 °C for 24 h. The yeast was incubated
in RPMI-1640 medium (Biological Industries) at 35 °C for
48 h. All experiments were performed in duplicate and
confirmed by three separate experiments. The MIC (lg/
mL) was defined as the lowest concentration of compound
inhibiting the growth of each strain. Vancomycine
Table 1 Antimicrobial activity
of the compounds and
L
NiL1
NiL2
DTBSA
Vancomycine
antibiotics evaluated by
MIC (lg mL-1
G. positive
)
B. cereus
E. faecalis
S. aureus
MRSA
0.062
0.062
0.062
0.062
0.062
0.062
32
[256
[256
[256
64
32
[256
[256
[256
32
[256
8
0.5
1
32
32
4
0.5
0.125
0.125
0.5
S. pneumoniae
L. monocytogenes
G. negative
E. coli
[256
[256
64
[256
[256
[256
[256
[256
[256
[256
[256
MICs of Ceftazidime; E. coli
0.5 lg mL-1, S. typhi
1 lg mL-1
S. typhi
Yeast
MICs of Amphotericin B; C.
albicans 0.5 lg mL-1
C. albicans
128
128
64
32
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Transition Met Chem (2011) 36:679–684
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Transition Met Chem (2011) 36:679–684
683
The 13CNMR spectrum of L showed peaks at 157.2 and
159.60 ppm which could be assigned to the azomethine
carbon, while signals at 117.7 and 141.0 ppm were assigned
to the phenyl ring carbons. In addition, signals at 31.5, 35.03
and 13.07 ppm were assigned to the t–Bu and S–CH3 car-
bons, respectively.
With reference to this data, clinically isolated bacteria are
defined in Table 2 as both MRSA and VRSA for 1,
MRSA for 2–10, SRSA for 11–12, streptomycin-resistant
E. faecalis (SREF) and gentamicin-resistant E. faecalis
(GREF) for 13, 14, 16, 20, 21 and 22, SREF for 17, 18 and
19, susceptible E. faecalis for 15.
The 13CNMR spectra of NiL1 and NiL2 exhibited sig-
nals at 163.5, 169.9, 156.0 and 147.0 ppm, respectively,
which were assigned to the azomethine carbons. Signals
at 116.5, 161.02, 119.4–141.0 ppm were assigned to the
aromatic carbons, respectively. Signals at 31.3, 35.6, 31.3,
35.7, 15.2 and 15.3 ppm can be assigned to the t–Bu and
S–CH3 groups, respectively.
Conclusion
In this study, we have presented the synthesis and char-
acterization of a new S-methylthiosemicarbazone and two
of nickel(II) complexes of Schiff base derivatives. Fur-
thermore, the antifungal and antibacterial properties of
these compounds were investigated. The free thiosemi-
carbazone showed much better activity than the other
compounds and is even superior to some standard antibi-
otics. It can be concluded that this compound merits further
investigation as an alternative antibiotic. The high activi-
ties obtained for the free thiosemicarbazone were, how-
ever, not observed for the complexes. However, in order to
explain the effects of metal coordination on the activity, the
MIC values of other metal complexes formed by the same
ligand must be investigated. We aim to clarify this situation
in our next study.
The electronic spectrum of the free thiosemicarbazone L
in chloroform solution exhibited absorption bands at 298
and 242, 342, 310 nm, corresponding to p–p* and n–p*
transitions, respectively. Bands at 342 and 310 nm are
assigned to the n–p* transitions of azomethine nitrogen.
Other absorption bands at 298–242 nm were due to phenyl
p–p* transitions. The electronic spectrum of NiL1 in
chloroform exhibited bands at 590, 498, 424, 404 nm
assigned to d–d and MLCT, respectively, while bands at
330 and 298 nm are assigned to the n–p* transitions of the
azomethine nitrogens, and bands at 252 and 247 nm arise
from phenyl p–p* transitions. Similarly, assigned bands
were observed for NiL2 at 581, 491, 428, 404, 340, 320,
262 and 242 nm [16, 17].
Acknowledgments This work was supported by the Research Fund
of the University of Nevs¸ehir.
Antimicrobial activity
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