Synthesis, characterization and antimicrobial studies of Cd(II), Hg(II), Pb(II), Sn(II) and Ca(II) complexes of curcumin

Article abstract of DOI:10.1515/mgmc-2013-0023

Cd(II), Hg(II), Pb(II), Sn(II) and Ca(II) complexes of curcumin have been prepared and characterized on the basis of their analytical, spectral and conductance data. In all the complexes, curcumin behaved as a monobasic bidentate ligand in which the intramolecularly hydrogen-bonded enolic proton is replaced by the metal ion. The antifungal (with Aspergillus niger, Aspergillus flavus, Aspergillus heteromorphus and Penicillium verruculosum ) and antibacterial (with Bacillus cereus ) studies reveal that metal complexation considerably increased the activity of curcumin, and among the complexes, Sn(II) complex exhibited maximum activity except for A. flavus where Hg(II) complex is more active.

Full text of DOI:10.1515/mgmc-2013-0023

ꢁꢁꢁꢂ
DOI 10.1515/mgmc-2013-0023ꢀ ꢀMain Group Met. Chem. 2013; 36(3-4): 123–127
Radhika Pallikkavil, Muhammed Basheer Ummathur*, Sajith Sreedharan and
Krishnannair Krishnankutty
Synthesis, characterization and antimicrobial
studies of Cd(II), Hg(II), Pb(II), Sn(II) and Ca(II)
complexes of curcumin
Abstract: Cd(II), Hg(II), Pb(II), Sn(II) and Ca(II) complexes 2009), and anticancer (Wilken et al., 2011) activities
of curcumin have been prepared and characterized on the and thus has a potential against various malignant dis-
basis of their analytical, spectral and conductance data. eases, diabetes, allergies, arthritis, Alzheimer’s disease
In all the complexes, curcumin behaved as a monobasic (Mishra and Palanivelu, 2008) and other chronic ill-
bidentate ligand in which the intramolecularly hydro- nesses. The biological activity of curcumin is associated
gen-bonded enolic proton is replaced by the metal ion. with phenolic and methoxy groups in conjunction with
The antifungal (with Aspergillus niger, Aspergillus flavus, the 1,3-diketone-conjugated diene system (Anand et al.,
Aspergillus heteromorphus and Penicillium verruculosum) 2008). Recent studies have shown that metal complexa-
and antibacterial (with Bacillus cereus) studies reveal that tion enhances the biochemical activities of curcumin
metal complexation considerably increased the activity (Thompson et al., 2004; Tajbakhsh et al., 2008; Lou
of curcumin, and among the complexes, Sn(II) complex et al., 2010; Zhao et al., 2010; Modi, 2011). Even though
exhibited maximum activity except for A. flavus where the literature is extensive on the antimicrobial studies of
Hg(II) complex is more active.
curcumin (Hariharan, 2012; Singh and Jain, 2012; Hamed
et al., 2013) and its transition/inner transition metal
Keywords: antifungal and antibacterial activities; cur- complexes (Sumathi et al., 2012; Refat, 2013), reports are
cumin; metal complexes; spectral studies.
scanty on such studies of its complexes with main group
metals. In continuation of our previous studies on metal
complexes of curcumin and its derivatives (John and
Krishnankutty, 2005, 2011), we report here the synthesis,
structural characterization and some biological proper-
ties of Cd(II), Hg(II), Pb(II), Sn(II) and Ca(II) complexes
of curcumin.
*Corresponding author: Muhammed Basheer Ummathur,
Department of Chemistry, KAHM Unity Women’s College, Manjeri,
Kerala 676122, India, e-mail: mbummathur@gmail.com
Radhika Pallikkavil and Krishnannair Krishnankutty: Department of
Chemistry, University of Calicut, Kerala, India
Sajith Sreedharan: Department of Botany, University of Calicut,
Kerala, India
Results and discussion
Introduction
The observed elemental analytical data (Table 1) of the
metal complexes of curcumin (HL) suggest [ML2] stoi-
Turmeric, derived from the plant Curcuma longa, is a chiometry. All the complexes behave as nonelectrolytes
gold-colored spice commonly used in the Indian subcon- [specific conductance <10 Ω cm-1; 10-3 m solution in
-1
tinent not only for health care but also for the preserva- dimethylformamide (DMF)]. Magnetic measurements
tion of food and as a yellow dye for textiles (Lampe, 1918; indicate that all the complexes are diamagnetic in nature,
Kapoor et al., 2008). Extensive research within the past as expected. The spectral data of the complexes are in
half century has proven that most of these activities are conformity with Figure 1.
due to curcumin [1,7-bis(4-hydroxy-3-methoxyphenyl)-
1,6-heptadiene-3,5-dione] (Danie et al., 2004; Miriyala
et al., 2007). Curcumin has been shown to exhibit antioxi- Infrared spectra
dant (Ak and Gulcin, 2008), anti-inflammatory (Jurenka,
2009), antiviral (Singh et al., 2010), antibacterial (Martin The infrared (IR) spectra of curcumin show a strong band
et al., 2009), antifungal (Negi et al., 1999; Wang et al., at 1619 cm-1 and a broad band in the range 2800–3500 cm-1
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124ꢀ ꢀR. Pallikkavil et al.: Antimicrobial studies of curcumin complexes
Table 1ꢁPhysical and analytical data of the metal complexes of curcumin.
Complex/
molecular formula
Color
Yield (%)
M.p. (°C)
Elemental analysis: found (calculated) (%)
C
H
M
[CdL2] C42H38CdO12
[HgL2] C42H38HgO12
[PbL2] C42H38O12Pb
[CaL2] C42H38CaO12
[SnL2] C42H38O12Sn
Greenish yellow
Dark red
Reddish brown
Red
Black
58
82
62
56
43
>300
>300
184
59.40 (59.55)
53.76 (53.93)
53.40 (53.55)
65.26 (65.12)
59.06 (59.18)
4.50 (4.49)
4.03 (4.07)
3.99 (4.04)
4.88 (4.91)
4.44 (4.46)
13.15 (13.28)
21.55 (21.46)
21.84 (22.01)
5.15 (5.17)
170
>300
13.85 (13.94)
due to the stretching of the chelated carbonyl and the intra- appearance of two medium-intensity bands at ~420 and
molecularly hydrogen-bonded enol functions, respec- ~470 cm-1 assignable to νM-O (Nakamoto, 1997). Important
tively (John and Krishnankutty, 2011). The absence of any bands that appeared in the spectra are given in Table 2.
band assignable to a normal α,β-unsaturated carbonyl
group in the region 1640–1740 cm-1 indicates the existence
of the compound entirely in the enolic form (Bellamy,
1H NMR spectra
1980). In the IR spectra of the metal complexes, the band
at 1619 cm-1 of the ligand is absent and, instead, a strong
1
The H NMR spectrum of curcumin displayed a one-
band assignable to the stretching of the coordinated car-
proton signal at δ 16.30 ppm due to the intramolecu-
bonyl moiety appeared at ~1580 cm-1. The broad band in
larly hydrogen-bonded enolic proton (Roughley and
the region 2800 to 3500 cm-1 disappeared in the spectra,
Whiting, 1973; Jiang et al., 2011). The trans orientation
indicating the replacement of enolic proton by the metal
of the -CH=CH- group is evident from the observed J
cation during complexation (Nakamoto, 1997; John and
1
values (16 Hz). In the H NMR spectra of the diamag-
Krishnankutty, 2005). However, spectra of all the com-
netic complexes, the low field signal due to the enol
plexes exhibited bands at ~3400 cm-1 due to the stretching
proton of the ligand disappeared, indicating its replace-
of the OH group in the phenyl ring (Nakamoto, 1997). This
ment by the metal ion during complexation (John and
suggests that only the enol proton is replaced by metal ion
Krishnankutty, 2005). The methine proton signal shifted
and the phenolic OH is excluded from coordination. The
appreciably to low field due to the deprotonation of the
prominent band at ~975 cm-1 is typical of a trans -CH=CH-
OH group. The integrated intensities of various signals
group, which remained unaltered in the spectra of metal
agree well with Figure 1 of the complexes. That the phe-
complexes (Nakamoto, 1997; John and Krishnankutty,
nolic (~δ 10 ppm) and methoxy (~δ 3.7 ppm) groups on
2005). That the carbonyl groups are involved in bonding
the aryl ring are not involved in bonding with the metal
with the metal ion as in Figure 1 is further supported by the
ion is clearly indicated (John and Krishnankutty, 2005)
in the spectra where the signals remain unaltered. The
assignments of various proton signals observed are
assembled in Table 2.
HO
OH
H3CO
OCH3
Mass spectra
O
O
O
M
The mass spectrum of curcumin (Baar et al., 1998; John
and Krishnankutty, 2005) showed an intense molecular
ion peak at m/z 368. The fast atom bombardment (FAB)
mass spectra of the metal complexes showed intense
molecular ion peaks corresponding to their formulae.
Peaks correspond to successive removal of aryl groups,
[ML]+, L+ and fragments of L+ are also present in the
spectra. Important fragments appeared in the spectra and
their probable assignments are given in Table 3.
O
OCH3
OH
H3CO
HO
Figure 1ꢀStructure of the metal complexes of curcumin. M=Cd(II),
Hg(II), Pb(II), Sn(II) and Ca(II).
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R. Pallikkavil et al.: Antimicrobial studies of curcumin complexesꢀ
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Table 2ꢁIR and 1H NMR spectral data of the metal complexes of curcumin.
Complex
IR stretching bands (cm-1)
1H NMR spectral data (δ, ppm)
Chelated C=O
CH=CH trans
M-O
Methine
CH=CH
Phenyl
Aryl substituents
[CdL2]
[HgL2]
[PbL2]
[CaL2]
[SnL2]
1574
1582
1589
1585
1586
970
978
978
966
980
422, 479
418, 466
424, 476
424, 467
426, 474
6.78
6.74
6.78
6.68
6.82
8.16, 8.26
8.12, 8.20
8.14, 8.22
8.10, 8.20
8.14, 8.20
7.02–7.98
6.90–7.80
6.98–7.78
7.12–8.02
7.22–7.90
10.02, 3.73
10.04, 3.71
10.06, 3.75
10.04, 3.70
10.08, 3.68
presence of nistatin and the medium DMF are included in
Table 4. The results clearly suggest that curcumin showed
Ultraviolet spectra
The ultraviolet (UV) spectrum of curcumin shows two appreciable antifungal activity compared to nistatin. Metal
broad bands with maxima at 380 and 270 nm due to the complexation considerably increased the activity of the
various n→π* and π→π* transitions (Bong, 2000). The free ligand. Among the complexes, Sn(II) complex exhi-
spectra of the complexes bear close resemblance to that of bited maximum activity toward Aspergillus niger, Aspergil-
the free ligand, indicating that no structural alteration of lus heteromorphus, Penicillium verruculosum and Bacillus
the ligand took place during complexation. However, the cereus, whereas Hg(II) complex showed maximum acti-
two free ligand spectral absorption maxima are shifted to vity toward Aspergillus flavus.
longer wavelength in the spectra of the complexes. This
indicates the involvement of the metal ion (John and
Krishnankutty, 2005).
Conclusions
The Cd(II), Hg(II), Pb(II), Sn(II) and Ca(II) complexes of
Antimicrobial studies
curcumin with [ML2] stoichiometry were synthesized and
1
characterized by UV, IR, H NMR and mass spectral data.
Various biological activities exhibited by curcumin have In complexes, curcumin behaved as monobasic bidentate
been the subject of numerous physiological and clinical in which the intramolecularly hydrogen-bonded enolic
studies (Negi et al., 1999; Ak and Gulcin, 2008; Anand proton is replaced by the metal ion. The compounds were
et al., 2008; Mishra and Palanivelu, 2008; Jurenka, 2009; investigated for their possible antimicrobial activities. The
Martin et al., 2009; Wang et al., 2009; Singh et al., 2010; results clearly reveal that Sn(II) complex shows maximum
Wilken et al., 2011). In the present study, the antifungal activity toward A. niger, A. heteromorphus, P. verruculosum
and antibacterial activities of the metal complexes of and B. cereus, whereas Hg(II) complex shows maximum
curcumin were investigated. The data obtained in the activity toward A. flavus.
Table 3ꢁMass spectral data of the metal complexes of curcumin.
Assignments
m/z
[CdL2]
[HgL2]
[PbL2]
[CaL2]
[SnL2]
P+
846
479
935
568
941
574
774
407
853
486
[ML]+
[P-Ar]+
723
812
818
651
730
[P-2Ar]+
[P-3Ar]+
[P-4Ar]+
L+
600
689
695
528
607
477
566
572
405
484
354
443
449
282
361
367
367
367
367
367
Ligand fragments
244, 123
244, 123
244, 123
244, 123
244, 123
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126ꢀ ꢀR. Pallikkavil et al.: Antimicrobial studies of curcumin complexes
Table 4ꢁAntimicrobial activity (diameter inhibition zone in millimeters) of curcumin (HL) and its metal complexes.
Compound
P. verruculosum
A. niger
A. heteromorphus
A. flavus
B. cereus
a
b
c
a
b
c
a
b
c
a
b
c
a
b
c
DMF
Nystatin
HL
[CdL2]
[PbL2]
[HgL2]
[SnL2]
[CaL2]
11
12
14
18
15
17
22
17
11
12
16
19
17
18
23
19
11
12
20
23
22
23
27
22
10
12
15
13
13
19
20
15
10
12
16
15
14
21
22
17
10
12
21
20
19
25
26
23
10
13
15
18
15
17
19
15
10
13
16
21
17
19
21
17
10
13
22
24
22
24
26
21
12
13
13
20
19
24
15
14
12
13
14
22
21
26
18
14
12
13
19
27
26
31
24
21
11
13
15
19
14
17
20
16
11
13
17
20
16
18
21
17
11
13
24
26
20
25
27
23
a=500 ppm; b=1000 ppm; c=5000 ppm.
Belkys et al., 2006) was employed for both antifungal and antibac-
terial studies. Nutrient agar medium was used for maintaining pure
bacterial culture and to lawn the bacteria for detecting the antimicro-
bial activity. It was prepared by dissolving peptone (0.5 g), beef extract
(0.3 g), NaCl (0.5 g) and agar (2 g) in 100 mL of distilled water. Potato
dextrose agar (PDA) was used to maintain pure fungal culture and to
lawn fungus for detecting antimicrobial activity. It was prepared by
dissolving PDA (0.36 g) and agar (2 g) in 100 mL of distilled water.
Normal saline was used as a suspension of fungal/bacterial spores for
lawning. It was prepared by dissolving NaCl (0.95 g) in 100 mL of dis-
tilled water. Solutions of the test compounds were prepared in DMF,
and for sterilizing, all the media used were autoclaved at 121 °C for
20 min. The Petri plates were made with PDA media for antifungal
activity. The PDA solution was poured into the Petri plates afer au-
toclaving at 121 °C for 20 min. Plates were allowed to dry for 20 min.
Using an agar punch, wells (10 mm) were made on these plates. The
fungal suspensions of spores were prepared in normal saline.
To prepare the mat growth of fungi on Petri plates, this spore
suspension was swabbed on the surface of the plates and the com-
pounds in DMF were added into each well at different concentrations
(500 ppm, 1000 ppm, 5000 ppm) for each sample. Each plate has a
well for the control (solvent DMF) and one for the reference antibiotic
nistatin. These wells were properly labeled, and the plates were in-
cubated at room temperature for 24–28 h. The antifungal activity was
detected by measuring the diameter of the inhibiting zone around
each well (mm). The greater diameter shown by the compound other
than the control indicates their antifungal activity. In the case of an-
tibacterial activity, a uniform lawn of bacteria B. cereus was spread
evenly in the Petri plates as in the case of fungi. Compounds in DMF
were placed in the well and the antibacterial activity was measured
from the diameter of the zone of inhibition (mm).
Experimental
Methods, instruments and materials
Carbon and hydrogen percentages were determined by microanalyses
(Heraeus Elemental analyzer, RSIC, Central Drug Research Institute,
Lucknow, India) and metal contents of complexes by atomic absorption
spectroscopy (Perkin Elmer 2380, Euclid, OH, USA). The UV spectra of
the compounds in methanol (10-4 mol/L) were recorded on a UV-Visible
spectrophotometer (UV-1601 PC, Shimadzu, Kyoto, Japan), IR spectra
(KBr discs) on an FTIR spectrophotometer (FT-IR-8101 A, Shimadzu,
Kyoto, Japan), 1H NMR spectra (CDCl3 or DMSO-d6) on a NMR spectro-
meter (Mercury Plus 300 MHz NMR spectrometer, Varian, USA) and
mass spectra on a JEOL USA SX-102 mass spectrometer (FAB using ar-
gon and meta-nitrobenzyl alcohol as the matrix). Molar conductance
of the complexes was determined in DMF (~10-3 mol/L) at 28 1°C. Mag-
netic susceptibilities were determined at room temperature on a Guoy
type magnetic balance, Sherwood Scientific Ltd., UK.
Synthesis of curcumin
Curcumin was prepared by the condensation of vanillin with acety-
lacetone-boric oxide complex in ethylacetate medium in the presence
of tri(sec-butyl)borate and n-butylamine as reported (Pabon, 1964).
Synthesis of metal complexes
A methanolic solution of metal acetate (0.001 mol, 25 mL) was added
slowly with stirring to a methanolic solution of curcumin (0.002 mol,
25 mL). The mixture was refluxed gently for ~1 h and the volume was
reduced to half. The precipitated complex on cooling to room temper-
ature was filtered, washed with 1:1 aqueous methanol, recrystallized
from hot methanol and dried in vacuum.
Acknowledgements: Dr. Muhammed Basheer Ummathur
is thankful to University Grants Commission, New Delhi,
India, for financial assistance [Research Project No.
MRP(S)-865/10-11/KLCA045/UGC-SWRO dated February 10,
2011] and Dr. C. Saidalavi, principal, KAHM Unity Women’s
College, Manjeri, for providing the necessary facilities.
Determination of antimicrobial activity
The four different fungal strains used were A. niger, A. flavus, A. hetero-
morphus and P. verruculosum. The organism selected for antibacterial
study was B. cereus. The well diffusion method (Prescott et al., 1990; Received April 14, 2013; accepted June 10, 2013
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