Hindawi Publishing Corporation
Bioinorganic Chemistry and Applications
Volume 2010, Article ID 292760, 8 pages
Stabilization of Curcuminby ComplexationwithDivalent
Bachar Zebib,1Z´ ephirinMouloungui,1and VirginieNoirot2
1Universit´ e de Toulouse-UMR 1010, Laboratoire de Chimie Agro-Industrielle, ENSIACET, INPT, INRA, 4 all´ ee Emile Monso,
31432 Toulouse Cedex 4, France
2Laboratoires Phod´ e S.A.S., ZI Albipole 81150 Terssac, France
Correspondence should be addressed to Bachar Zebib, email@example.com
Received 20 January 2010; Accepted 6 April 2010
Academic Editor: Enrico Rizzarelli
Copyright © 2010 Bachar Zebib et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The purpose of present study was to stabilize curcumin food pigment by its complexation with divalent ions like
were prepared by mechanical mixture of curcumin and sulfate salts of each metal (metal:curcumin1/1mol) into unconventional
and nontoxic glycerol/water solvent. Two stoichiometry of complex were obtained, 1:1 and 1:2 (metal/curcumin), respectively.
On evaluation of in vitro stability, all complexes were found to provide a higher stability from curcumin alone.
Natural pigment is a vital quality attribute of foods, and
plays an important role in sensory and consumer accep-
tance of products [1–3]. Curcumin, a naturally occur-
ring polyphenolic phytoconstituent, isolated from the rhi-
zomes (Figure 1) of Curcuma longa Linn, is an impor-
tant permitted natural colorant used in food, nutri-
tious, and pharmaceutical preparations among others [4–
8]. Curcumin is chemically (1E,6E)-1,7-bis(4-hydroxy-3-
methoxyphenyl)hepta-1,6-dienne-3,5-dione. It has a pKa1,
pKa2, and pKa3 value of 7.8, 8.5, and 9.0, respectively, for
three acidic protons . It is insoluble in water under acidic
or neutral conditions but dissolves in alkaline conditions.
Curcumin is unstable undergoing rapid hydrolytic degrada-
ferulic acid . Since it is insoluble in aqueous medium
and has poor stability towards oxidation, light, alkalinity,
enzymes and heat, it cannot really be widely used in food
and pharmaceutical processing industry [11, 12]. Although,
exposure of the curcumin pigment to alkaline foods or
ingredients may be difficult to avoid. For these reasons, it
should be protected curcumin in certain forms from physical
and chemical damage before its industrial application.
Complexation of curcumin with transition metals has
attracted much interest over the past years as one of the
useful requirements for the treatment of Alzheimer’s disease
[13, 14] and in vitro antioxidant activity .
Moreover, several metallocomplexes of curcumin have
been synthesized characterized and evaluated for various
biological activities [15–19]. However, all these metallocom-
plexes of curcumin have been prepared under relatively high
temperature synthesis conditions (reflux at 100◦C under
nitrogen gas for 3 hours) in the presence of organic solvent
like ethanol, methanol, or acetone. Other recent studies
[20, 21] suggest the preparation of curcumin-phospholipid
complex under smooth synthesis conditions (temperature
not exceeding 60◦C for 2 hours) for hepatoprotective
application. However, organic solvents like dichloromethane
and hexane are not excluded from experimental preparation
of curcumin-phospholipid complex.
routes” to protect and stabilize natural biomolecules using
glycerol chemistry for food, pharmaceutical, agriculture, and
cosmetic applications. In this paper, we investigate a com-
plexation of curcumin with divalent ions such (Zn2+, Cu2+,
Mg2+, Se2+) by mechanical mixture, without any conven-
2 Bioinorganic Chemistry and Applications
Figure 1: Photo of rhizomes of Curcuma longa Linn plant and chemical structure of polyphenolic curcumin compound.
was carried out in presence of water/glycerol solvent at
25◦C. Obtained complex was characterized by IR and UV
spectroscopic methods. Supportive evidence of obtained
stoichiometry has been suggested from TG-DTA thermal
2.1. Materials. Curcumin (95%), glycerol (99%), zinc sulfate
(ZnSO4·7H2O; 22%), Copper sulfate (CuSO4·5H2O; 25%),
Magnesium sulfate (MgSO4·7H2O; 49.1%), Sodium selenite
(Na2SeO3; 45%), were procured from Phod´ e Laboratory
S.A.S. (Albi, France).
2.2. Preparation of M2+-Curcumin Complex. Zinc sulfate
(ZnSO4·7H2O; 22%) was mechanically mixed in mortar
with curcumin (M2+: Curcumin 1/1mol) until homogenous
powder mixture was obtained. Then glycerol/water (1:1v/v)
solution was added to mixture followed by mechanical
pasty product was dried in room temperature at 50◦C until
water evaporation. Free glycerol was eliminated by washing
with distilled water. Powder complex of Zn2+-curcumin was
obtained. Other complexes derived from another ion sulfate
source were prepared by the same method.
2.3. Assay. The contents of curcumin in complex were
determined spectrophotometrically. 5mg of the complex
was dissolved in 10mL of DMSO (Dimethylsulfoxide) and
stirred for 1 hour on a magnetic stirrer. The concentration
of curcumin in complex was determined by measuring the
absorbance of the solution so obtained at 435nm.
2.4. FT-IR Spectroscopy. FT-IR spectroscopy of curcumin
and Zn-curcumin complex was performed on fourrier-
transformed infrared spectrophotometer (Bruker VECTOR
22) equipped with a detector DTGS witch resolution is fixed
to 4cm−1. The pellets of sample (10mg) and potassium bro-
mide (200mg) were prepared by compressing the powders
at 5 bars for 5 minutes on KBr press and the spectra were
scanned on the wave number range of 4000–850cm−1.
UV/visible spectrophotometer was used to record spectra
of curcumin and curcumin complex in DMSO solvent.
The spectra were scanned on the wave number range of
UV-Visible Spectroscopy. HP8452diodearray
2.6. Thermogravimetric Analysis. Thermograms of cur-
cumin complexes were recorded using differential scanning
calorimeter (Seiko SSC 5200H). The samples (20–40mg)
were sealed in the platinum crimp pan, and heated at the
speed of 10◦C /min from 25◦C to 600◦C in air atmo-
2.7. In Vitro Stability. In vitro kinetic degradation of cur-
cumin from all curcumin complexes was followed spec-
trophotometrically between 350 and 600nm. 10mg of
curcumin complex was incubated at 37◦C in 100mL of
buffer solutions at various pH from 2.0 to 10.0. Kinetic
degradation reaction of curcumin and its complexes was
followed between 0–120 minutes and 0–24 hours, respec-
3.Results and Discussion
The method of preparation of curcumin complexes was
found to be reproducible yielding 98% of product. On
assaying the complex, it was found to contain about
45%, 60%, 61%, and 50% of curcumin for Mg-curcumin,
Cu-curcumin, Zn-crucumin, and Se-curcumin complexes,
Bioinorganic Chemistry and Applications3
Table 1: Wave length changes of main vibration modes from infrared (KBr pellets) spectral data of curcumin and curcumin complexes.
Vibrational modes: (ν) stretching; (δ) in-plane bending; (—) not observed.
1762———1738 (Δν = 13)
1778 (Δν = 53)
1725 1800 (Δν = 75)
1795 (Δν = 70)
1800 (Δν = 75)
39503700 3450 3200 2950 2700 2450 2200
Wave number (cm−1)
19501700 1450 1200
(Ar–OH ; RHC=C–OH)
Figure 2: Normalized FT-IR spectra of curcumin complexes com-
pared with that of curcumin alone.
3.1. FT-IR Characterization. Figure 2 compares the IR spec-
tra of curcumin and all curcumin complexes. The spectrum
of curcumin may be assigned as follows:
(i) Two broad band’s at 3600 and 3560cm−1attributed
to vibrations of free hydroxyl-group of phenol
(Ar−OH) and alcohol group (R−OH), respectively,
tions of C−H bond of alkenes groups (RCH=CH2),
(iii) An intense band at 1725cm−1attributed to the
vibration of the carbonyl bond (C=O) accompanied
by a small shoulder at 1762cm−1due to Keto-enol
tautomerism of curcumin compound,
compared with that of curcumin in DMSO solvent.
(iv) Tree bands at 1406, 1332, 1320cm−1attributed to
vibrational mode of C−O elongation of alcohol and
Compared with the reference spectrum of curcumin,
all complexes shows a great decrease in the intensity of
(C=O) carbonyl band, accompanied by a shift (Δν
53–75cm−1) to high wave values (Table 1). In addition, a
net decrease in the intensity of the free (OH) hydroxyl
group of curcumin was observed in the caseof Mg-curcumin
and Cu-curcumin complexes, but totally disappeared for Se-
curcumin and Zn-curcumin complexes. These two above
phenomena indicating that some interaction has occurred
at these sites and its involvement in complexation by new
created link between metal and curcumin compound.
4Bioinorganic Chemistry and Applications
0 50100 150 200 250 300 350
400 450 500 550 600
Weight loss (%)
050 100 150 200 250 300 350
400 450 500 550 600
Heat flow (μv)
Figure 4: TG and ATG analysis of curcumin and curcumin com-
plexes. Conditions: heating speed 10◦C/min. under air atmosphere.
3.2. UV-Visible Characterization. Curcumin is soluble in
most of the organic solvents, lipids, and micellar solutions,
is insoluble in organic solvents like methanol and acetoni-
charged micellar solutions. It is also soluble in lipids and
A UV-visible spectrum of the complexes in DMSO
showed absorption maximum at 435nm assigned to the
→ π∗of curcumin (Figure 3). Compared with
curcumin, the complexes in DMSO shows a maximum
absorption shifted by (1–8nm), which varies between (427–
434nm), and the shoulders at (410–413nm) and (448–
451nm) are attributed to a curcumin → metal (M2+)
charge transfer, specific complex formed. We believe that the
variation of the absorption peak of curcumin and shoulders
apparition in different complexes depend on the nature of
metal (M2+) ion implication.
3.3. Thermogravimetric Analysis. Supporting evidence of the
structure of complexes is suggested by thermal analysis. The
TG-DTA measurements of all the complexes were performed
in air over the temperature range of 25–600◦C (Figure 4).
3.3.1. Curcumin. It was thermally stable up to 160◦C.
Above this temperature we observe an endothermic peak at
174◦C (weight loss: found 3.3%, calcd. 3.1%) related to the
deshydroxylation of OH groups by elimination of two water
molecules. After 400◦C curcumin was totally decomposed.
3.3.2. Zn-Curcumin and Mg-Curcumin Complex. They were
thermally stable up to 65◦C. Above this temperature one
molecule of crystalline water is eliminated in one step at
93◦C and 102◦C, respectively, (weight loss: found 3.2%,
calcd. 3.0%). The existence of an anhydrous complexes
[Mg(L)(H2O)] and [Zn(L)(H2O)] can be evident from the
plateau between 90 and 150◦C. Then, the sample weight
of two complexes decreases up to 205◦C which is probably
connected with the elimination of the coordinated water
molecule, leading to the formation of [Mg(L)] and [Zn(L)]
species (weight loss: found 11.2%, calcd. 11.4%). The
intermediate is stable within the interval of 160–220◦C. After
250◦C we observe a chemical decomposition of curcumin
without formation of thermally stable intermediates up to
600◦C. At this temperature ZnO and MgO oxides can be
3.3.3. Cu-Curcumin Complex. It was thermally stable up to
60◦C. Above this temperature one molecule of crystalline
water is eliminated in two steps at 88◦C and 122◦C (weight
existence of an anhydrous complexe [Cu(L)(H2O)] can be
evident. Then, the sample weight of complexe decreases up
to 185◦C which is probably connected with the elimination
of the coordinated water molecule, leading to the formation
of [Cu(L)] specie (weight loss: found 11.0%, calcd. 11.2%).
At 237◦C we observe a small endothermic peak which
can be related to the elimination of coordinated Ligand.
Chemical decomposition of curcumin between 350–500◦C
was obtained. A thermally stable decomposition product
exists after 500◦C. It may be related with the formation of
3.3.4. Se-Curcumin Complex. It was thermally stable up to
150◦C. One molecule of crystalline water is eliminated in
range of 80–150◦C. In the range of 152–190◦C (weight loss:
found 1.78%, calcd.1.80%) we observe an endothermic peak
centered at 165◦C which can be related to the deshydroxyla-
selenium atom by the elimination of four water molecules
Bioinorganic Chemistry and Applications5
Figure 5: Proposed structures of curcumin complexes based on experimental calculation from TG and DTA measurements.
(deduced by obtained weight loss). Next decomposition at
487◦C is exothermic which can be related to the degradation
of total curcumin ligand compounds. Selenium oxide (SeO)
can be formed after 550◦C.
Thermograms of curcumin complexes were showed in
Figure 4. Thermal analysis proves that two stoichiome-
try of complexes were obtained (Figure 5), 1:1 and 1:2
(metal/ion), respectively. This difference of coordination
geometry is probably due to the various physicochemical
properties of each metal ion involved in complexation reac-
tion, like electro-negativity, nuclear ray, polarity, solubility,
and electronic configuration. However, previous study [16,
17] suggest that other factors such, molar ratio of reactants,
the nature of solvent used, or the chemical source of metal
ion, are implicated in the coordination geometry of resulting
6Bioinorganic Chemistry and Applications
7080 90 100 110 120
Residual curcumin (%)
pH = 2
pH = 7
pH = 6
pH = 10
Figure 6: Kinetic degradation of curcumin in various pH of 0.1M
buffer at 37◦C. The data are normalized to a value of 100 at zero
3.4. Stability Evaluation
3.4.1. Curcumin. It has been shown that curcumin has a
poor light stability. About a 5% decrease in absorbance
due to curcumin has been measured during the time for
typical sample preparation when clear rather than amber
glassware is used . Curcumin decomposes when exposed
to sunlight, both in ethanolic and methanolic extracts
and as a solid, vanillin, vanillic acid, ferulic aldehyde and
ferulic acid have been identified as the degradation products
When curcumin was added to 0.1M phosphate buffer,
pH = 7 (physiological condition in vitro), the majority of
curcumin was degraded after 1 hour. A series of pH values
from 2 to 10 in buffer solutions were assayed for this degra-
dation. Figure 6 shows the kinetics of curcumin degraded at
various pH values, 37◦C, using HP 8452 diode UV/visible
concentration versus time were reasonably linear at all pH
values tested, indicated that degradation followed apparent
first-order kinetics at 37◦C.
In present work, we found that more than 90% of
curcumin decomposed rapidly in buffer systems at neutral-
basic pH conditions. The increased stability of curcumin
in acidic pH condition may be contributed by the conju-
gated diene structure. However, when the pH is adjusted
to neutral-basic conditions, proton removed from the
phenolic group, leading to the destruction of this struc-
3.4.2. Curcumin Complex. The kinetics of demetallation of
curcumin complex was carried out in various pH buffers.
pH = 7
6 8 10 12 14 16
18 20 22 24 26 28 30 32
Residual complex (%)
pH = 2
68 10 12 14 16
18 20 22 24 26 28 30 32
Residual complex (%)
Figure 7: Kinetic degradation of curcumin complexes in water (pH
= 6.5) and at pH 2 and 7 of 0.1M buffer at 37◦C. The data are
normalized to a value of 100 at zero time.
The complexes decompose via general reaction
− → (x −1)M2++n(x −1)L(degraded)+ yMLn(residual),
where degraded curcumin (L(degraded)) entity is not measured
Bioinorganic Chemistry and Applications7
60 180360 780 1260 1800
Kinetic stability of zinc-curcumin complex in pH 7 of
0.1M buffer at 37◦C compared to curcumin alone
Residual ( %)
Figure 8: Kinetic stability of zinc-curcumin complex compared to
curcumin alone in pH 7.0 of 0.1M buffer at 37◦C.
In acidic media, complexes are decomposed via
ML(total)+2H+− → M2++H2L(degraded),
where M = Metal ion and L = Ligand = curcumin.
It was found that all complexes were very stable in
purified water (pH = 6.5) up to 30 hours at 37◦C. All
complexes rapidly decomposed at acidic pH 2 (Figure 7)
and the dissociation of complexes was decreased in higher
of complexes was dependent on proton concentration. As
presented in Figure 7, the dissociation of complexes was
in equilibrium by 50% degradation in buffer pH 7.0. The
dissociation was found to be 90% in acidic buffer (pH 2).
level after 13 hours in buffer pH 2.0 and 7.0.
However, stability of these complexes compared to
curcumin alone, for the same time interval, is much higher.
As an indication, at buffer pH 7.0, curcumin was totally
degraded after 1 hour, while in the same conditions; less
than 5% of complex was degraded (Figure 8). Therefore, the
stability of curcumin at pH 7 has been multiplied by a factor
of 20 after its complexation with metal ions.
For the first time, curcumin complexes with divalent ions
were successfully prepared in “green media” glycerol/water
solvent. Complexes were characterized by spectroscopic (IR,
UV) and thermogravimetric analysis. Their physicochemical
stability was evaluated “in vitro,” where conditions are
close to those physiological. In FT-IR, metal-curcumin link
was highlighted by the decrease of carbonyl band (CO)
intensity of curcumin coupled with a shift (70nm) to high
wave numbers. The linkage was also confirmed by UV
analysis where charge transfer between curcumin and metal
(curcumin→ M2+) is observed. Supporting structure of
synthesized complexes was suggested by thermal analysis
which shows two different stoichiometry (1:1 and 1:2
(ion/curcumin)). Indeed, we prejudge each structure has
different physicochemical properties such a conductivity,
polarity, electro-negativity, molecular size, and carrying and
effect on the biological applications.
Furthermore, the created connection between molecules
is based on electrostatic links between curcumin and oli-
goelements, which is reversible on the action field, for
“in vitro” studies that they are able to protect curcumin
against chemical degradation in neutral and basic media for
long period of time (30 hours), which gives much hope for
its industrial application.
On the other hand, we believe that curcumin complex
synthesis in an unconventional and nontoxic solvent, for
example, glycerol and its derivatives (glycerol fatty esters)
opened a new path for stabilization of active ingredients in
food and pharmaceutical field were complex can be formed
“in situ” inside the product formulation health without the
requirement of solvent isolation. Beside, glycerol and its
derivatives can play a good role in the solubilization and
diffusion of many organic molecules insoluble or poorly
soluble in water without forgotting its other conventional
roles that comes in many applications.
The authors express their sincere thanks to a CRMP cen-
ter (Conseil R´ egional de la r´ egion Midi-Pyr´ en´ ees DAER-
RECH/08005118) for its financial support for this work.
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