Binding studies of curcumin to polyvinyl alcohol/polyvinyl alcohol hydrogel and its delivery to liposomes

RESEARCH ARTICLES

Binding studies of curcumin to polyvinyl
alcohol/polyvinyl alcohol hydrogel and its
delivery to liposomes

C. P. Shah, B. Mishra, M. Kumar, K. I. Priyadarsini and P. N. Bajaj*
Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Mumbai 400 085, India

the drug to a target tissue efficiently at a steady therapeutic
Binding of curcumin, an antioxidant and anti-tumour
concentration, with minimum exposure to non-target
agent from turmeric, with polyvinyl alcohol (PVA) has
tissues. The rate of release of the drug into the external
been characterized by monitoring changes in the ab-
sorption and the fluorescence spectra. The product of
environment can be controlled, depending on the com-
the number of binding sites in PVA and the binding
patibility between the drug molecule and the external
constant (K) was determined to be 2.4 × 105 and fluid, and cross-linking density of the hydrogel10. PVA, a
1.9 × 105 M–1 by optical absorption and fluorescence
biocompatible polymer, is used for making hydrogel
techniques respectively. The hydrogel of PVA, pro-
dressings11. Aqueous PVA solution can be easily cross-
duced by γ-irradiation of aqueous solution, also could be
linked by γ-radiation to produce hydrogels with different
loaded with curcumin to a maximum extent of cross-linking densities. Many drugs can be incorporated
215 nmol/g. The binding constant of curcumin to PVA
in such hydrogel matrices for their controlled release.
hydrogel and the number of binding sites were deter-
Since ancient times, curcumin, a yellow poly phenolic
mined to be 2.6 × 104 M–1 and 2.5 respectively. Studies
pigment from turmeric, has been used for skin protection.
on the release of curcumin in liposomes indicated that
It is applied, in combination with other ayurvedic formu-
hydrogel could be used as an effective vehicle for
transferring curcumin to model lipid membranes, lations, for the treatment of several superficial skin infec-
liposomes.
tions and burns. Curcumin suppresses the growth of many

bacteria. It is a good cleansing agent. Curcumin is used
commercially in several skin-lotion formulations. Cur-
Keywords: Curcumin, drug delivery, hydrogel, lipo-
somes, polyvinyl alcohol.
cumin and its derivatives are also known to exhibit a

wide range of pharmacological activities, including anti-
H
inflammatory, antioxidant, anti-carcinogenic and anti-
YDROGELS are hydrophilic polymer networks having the
capacity to absorb water, ranging from about twenty to HIV protease activity12–15. It is a hydrophobic molecule,
thousand times their dry weight1. Hydrogels can be pre-
and is practically insoluble in aqueous medium. Because
pared by: (a) cross-linking of water-soluble polymers, (b)
of its hydrophobic nature and poor solubility in water, its
conversion of cross-linked hydrophobic polymers, or (c) bioavailability, after oral administration, is inadequate
conversion of hydrophobic polymers to hydrophilic poly-
and, therefore, needs a carrier vehicle to transport to the
mers, followed by cross-linking to form networks. Hy-
desired targets. A suitable delivery system, such as PVA
drogels are widely used in areas, such as drug delivery, hydrogel, needs to be employed to deliver curcumin to
immobilization of enzymes, de-watering of protein, etc. the required target for treatment.
As these have a marked cooling effect and can also release
With this aim, the loading of curcumin to PVA hydro-
water at the desired site, they are often used on dehydrated
gel, and its release from the hydrogel into phosphatidyl-
wounds, such as minor burns, grazes and pressure sores2.
choline (PC) liposome, were studied. Further, its binding
Synthetic polymers, such as polyacrylic acid (PAA), capacity with aqueous PVA solution and PVA hydrogel
polyacryl amide (PAAm), poly
was determined by spectroscopic techniques.
n-isopropyl acrylamide
(PNIPAAm), polyvinyl pyrrolidone (PVP) and polyvinyl
alcohol (PVA), form hydrogels3–9. Some of these hydrogels
Materials and method
have a lower critical solution temperature (LCST), above
which they release the imbibed water. These hydrogels PVA (mol. wt. ~125,000; S.D. Fine Chemicals) and spe-
can adsorb different drugs, depending on the nature of the
ctrograde methanol (Sisco Research Laboratory), were
drug, the polymer and the pore size. One of the important
used in the study. Curcumin, cholesterol, acrylamide and
requirements for the drug delivery systems is to deliver egg yolk phosphatidylcholine were from Sigma. Rest of
the chemicals used were obtained from local market, and
*For correspondence. (e-mail: pnbajaj@barc.gov.in)
were of the highest purity available. Aqueous solutions
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RESEARCH ARTICLES

were prepared, using water obtained from Millipore-Q Since [S] = n[PVA],
water purification system, and were purged with nitrogen,

wherever required, to minimize degradation. 60Co γ-
[Curcumin : S]
source, with a dose rate of 2.6 kGy/h, was used for irra-
K =
. (3)
[PV
n
A][Curcumin]
diation of the polymer solution. Absorption and fluo-

rescence spectra were recorded, using Spectroscan UV As optical absorption measurements were carried out in
2600-spectrophotometer and Hitachi F-4010 fluorimeter the presence of excess PVA, thus assuming n[PVA] >
respectively.
[Curcumin], the above equation can be written as,

Results and discussion
[Curcumin : S]
K
=
. (4)
[P
n VA]
−
0 ([Curcumin 0
]
[Curcumin : S])
Binding of curcumin with PVA solution

Equation (4) is rearranged to give [Curcumin : S].
Optical absorption method: Aqueous solution of cur-

cumin (10 μM), containing 5% methanol, shows maxi-
nK[PVA] [Curcumin]
mum absorption at 426 nm. On addition of PVA, in the

0
0
[Curcumin : S] =
. (5)
1 + nK[PVA]
concentration range of 10–100 μM, the absorption maxi-
0
mum was blue shifted from 426 to 420 nm, with simulta-

neous increase in absorbance at 420 nm (Figure 1). These
The initial absorbance A0, is due to curcumin and PVA.
changes in the absorption spectra indicate an interaction However, the final absorbance Aeq is the sum of absor-
between the ground states of curcumin and PVA. The bance due to complex, Aeq(Curcumin : S); free curcumin,
process of binding of curcumin to PVA can be repre-
Aeq (Curcumin), and PVA, Aeq(PVA).
sented by the following:


Aeq = Aeq(Curcumin : S) + Aeq(Curcumin)
Curcumin
+
S
Curcumin : S, (1)
+ Aeq(PVA). (6)


where S is the binding site in the polymeric chain, and [S]
Differential absorption method (linear fitting): Since
is the product of the number of binding sites in the poly-
absorbance due to PVA at 420 nm is negligible, it can be
meric chain
neglected. Therefore, eq. (6) becomes
n, and [PVA], i.e. [S] = n[PVA].
The binding constant (

K) for the above equilibrium is
given by:
Aeq = Aeq (Curcumin : S) + Aeq (Curcumin).
(7)


Maximum absorption changes were seen at 420 nm; hence
[Curcumin : S]
K
=
. (2)
the binding constant was estimated by following the
[Curcumin][S]
absorbance changes at the same wavelength, as a function

of PVA concentration. Therefore, the change in absor-

bance at 420 nm can be given as:

ΔA = Aeq(Curcumin : S) + Aeq (Curcumin)
– A0 (Curcumin), (8)

ΔA = ε (Curcumin : S)l[Curcumin : S] + ε (Curcumin)l
× [Curcumin] – ε (Curcumin)l[Curcumin]0, (9)

ΔA = Δεl [Curcumin : S], (10)

where l is the optical path length, which is 1 cm, and Δε
corresponds to the differential extinction coefficient at
420 nm. From eqs (5) and (10), we get


nK[PVA] [Curcumin]



0
0
ΔA = Δε l
(11)
+
Figure 1. Absorption spectra of curcumin (10 μM) in aqueous solu-
1 nK[PVA 0
]
tion in 5% methanol, in the absence and presence of varying concentra-

tions of PVA (10–100 μM), at pH 7. Inset: Double reciprocal plot, in
accordance with eq. (12).
which is rearranged to give,
CURRENT SCIENCE, VOL. 95, NO. 10, 25 NOVEMBER 2008
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1
1
⎛
1
⎞
1
not shown), was found to be 2.1 ± 0.1 × 105 M–1. The
=
⎜
⎟ +
.
Δ
results obtained from both the linear and the nonlinear
A
nKlΔε [Curcumin
⎝
⎠ Δε
0
]
[PVA 0
]
l[Curcumin 0
]
regression match reasonably well.

(12)


The absorbance values at the respective PVA concentra-
Fluorescence method: Curcumin exhibits medium-
sensitive fluorescence properties. In an aqueous buffer, it
tions were fitted to a double reciprocal plot (eq. 12), the exhibits a broad, weak fluorescence band, with maximum
modified Benesi–Hildebrand plot. Figure 1 (inset) shows at ~550 nm, but in a hydrophobic environment, its fluo-
the double reciprocal plot, 1/ΔA vs 1/[PVA]0, and the rescence intensity is found to increase, with a blue shift
linear fit. The slope and intercept of the plot are in the fluorescence maximum. This photophysical prop-
1/(nKΔεl[Curcumin]0) and 1/(Δεl[Curcumin]0), respecti-
erty of curcumin was utilized to estimate the mode of
vely. The ratio of the intercept and the slope gives the binding and the binding constant of curcumin with PVA.
product of the number of the binding sites and the bind-
For this study, curcumin was excited at 380 nm, as the
ing constant (nK). The differential extinction coefficient absorption intensity at this wavelength does not change
was calculated from the reciprocal of the intercept. Under
much with PVA concentration. Figure 2 shows that the
this condition, the product nK and the differential extinc-
fluorescence intensity of curcumin increases significantly
tion coefficient estimated at 420 nm, were found to in presence of PVA, along with a blue shift in the fluores-
be 2.4 ± 0.2 × 105 M–1 and 2.7 ± 0.2 × 104 M–1 cm–1 res-
cence maximum. In the presence of the highest studied
pectively. Using the value of the extinction coefficient of
concentration of 100 μM PVA, the fluorescence maxi-
free curcumin at 420 nm to be 4.88 × 104 M–1 cm–1, the mum shifted towards the blue region by ~20 nm, from a
extinction coefficient of PVA-bound curcumin was de-
broad, weak band (λem
termined to be 7.58 × 104 M–1 cm–1.
max ~ 550 nm) to a well-defined fluo-
rescence band (λem

max ~ 530 nm). The observed blue shift
in the fluorescence spectrum indicates probable binding
Alternate absorption method (non-linear fitting): Non-
of curcumin to the hydrophobic pockets of PVA. Similar
linear least-squares regression is an alternative approach to the case of absorbance, eq. (16), the binding constant
of data analysis, which is used to fit the data directly into
the relevant equations. For this approach, eq. (7) can be K is related to the fluorescence intensities as given
below16.
written as


F + F (Curcumin : S ) nK[PVA]

[Curcumin : S]
[Curcumin]
=
+

0
0
=
eq
F
, (17)
eq
A
(C
A
urcumin : S)
0
A
,
1+ nK[PVA]
[Curcumin
0
0
]
[Curcumin 0
]
(13)


where F0 and Feq are the respective fluorescence intensi-
ties from curcumin at 530 nm, in the absence and the
where A(Curcumin : S) represents the absorbance at presence of different concentrations of PVA (10–100 μM),
420 nm at saturating concentration of PVA, and eq. (13)
can be written as,



[Curcumin : S]

=
eq
A
(C
A
urcumin : S)

[Curcumin 0
]
[Curcumin] −[Curcucmin : ]
S

0
+ 0
A
, (14)
[Curcumin 0
]

[Curcumin : S]
A − A

0
eq
=
. (15)
[Curcumin
−
0
]
0
A
(C
A
urcumin : S)

From eqs (5) and (15), after rearrangement, we get

A + (
A Curcumin : S) nK[PVA]

0
0
=
eq
A
.
(16)
1+ nK[PVA 0]



The binding constant was evaluated using the nonlinear Figure 2. Fluorescence spectra of curcumin (10 μM) in aqueous solu-
fitting, in accordance with eq. (16). The value of
tion, containing 5% methanol, in the absence and presence of varying
nK, deter-
concentrations of PVA (10–100 μM), at pH 7. The samples were exci-
mined by nonlinear least-squares fitting of the data (plot ted at 370 nm.
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and F(Curcumin : S) is the saturating fluorescence inten-
phores, one of which may not be easily accessible to the
sity of curcumin in the presence of the highest PVA con-
quencher17.
centration. Nonlinear least-square fitting of the data (plot Curcumin has phenolic OH groups, which can be ion-
not shown) using eq. (17), gave nK as 1.9 ± 0.1 × 105 M–1,
ized, with pK ~ 8 and at pH 7, it has contributions from
a
which is slightly lower than the value obtained by the ab-
both the ionized and the non-ionized forms. It is possible
sorption methods.
to evaluate the fraction of curcumin located in the hydro-
phobic and hydrophilic pockets inside PVA, by following
the quenching of fluorescence from PVA-bound curcu-
Nature of binding sites in PVA
min, using acrylamide and iodide as quenchers at pH 7.
For this, the curcumin–PVA solutions were incubated in
Quenching studies of fluorescence intensity of curcumin quartz cells at 30°C, at different concentrations of iodide
bound to PVA were carried out using iodide and acryla-
(I–) and acrylamide as quenching agents, separately, in
mide as quenchers. These studies were carried out to 10 mM phosphate buffer. The fluorescence intensity
evaluate the location and nature of the curcumin-binding changes (Δ
sites inside PVA chains. Iodide is a hydrophilic quencher
F = F0 – F) due to curcumin were treated with
the modified Stern–Volmer equation, according to the
that can access curcumin bound in the hydrophilic part of
procedure given in Kunwar
PVA, while acrylamide, being hydrophobic, can access
et al.18:

curcumin only when inserted inside the hydrophobic part
of PVA. The concentrations of the quenchers were varied
F
⎛
1
⎞ ⎛ 1 ⎞

0 = ⎜
⎟ + ⎜
⎟ , (19)
from 0 to 0.3 M, keeping the ionic strength constant at
ΔF
f
′
⎝ a Kd[Q]
f
⎠ ⎝ a ⎠
0.3 M. The fluorescence data were analysed according to
the Stern–Volmer equation:
where F0 and ΔF are the fluorescence intensity in the ab-

sence and change in fluorescence in the presence of the

0
F =1+
quencher Q respectively, f
K
a is the fraction of the initial
d [Q] , (18)
F
fluorophore that is accessible to the quencher and K′d is

the modified Stern–Volmer collision constant, which
where F
measures the stability of the quencher–probe complex,
0 and F are the intensities of the fluorescence
(curcumin bound to PVA) in the absence and the pre-
and is related to the separation distance in the excited
sence of the quencher Q respectively, and K
state complex. Experimental results are plotted in Figure
d is the Stern–
Volmer collision constant. Figure 3 (inset a and b) shows
3 c for I–, and in Figure 3 d for acrylamide titrations. On
the Stern–Volmer plot obtained by monitoring quenching
fitting the data obtained from quenching in the presence
of curcumin fluorescence at 420 nm, in the presence of of iodide to eq. (19), we found fa = 0.25 ± 0.01 and
iodide and acrylamide quenchers respectively. The Stern–
K′d = 19.1±1.7 M–1 at pH 7. Similarly, fitting the data
Volmer plots for both the quenchers show deviation from
obtained from quenching in the presence of acrylamide to
linearity, indicating the presence of two types of fluoro- eq. (19), fa value of 0.20 × 0.01 and K′d value of 17.3 ±

2.11 M–1 were determined at pH 7. The sum of the frac-

tions of the curcumin embedded in hydrophilic and
hydrophobic cavities does not equate to one, which indi-
cates that curcumin may not be uniformly present in the
gel, and some fraction of the curcumin in the hydrophobic
interior is not accessible to acrylamide17. The above two
sets of experiments confirmed that at pH 7, which is close
to physiological pH, curcumin is embedded in both
hydrophobic and hydrophilic sites of PVA. Whereas the
hydrophobic nature of curcumin and the observed blue
shift in the fluorescence spectrum in the presence of PVA
indicate preferential binding of curcumin to hydrophobic
pockets of PVA. Therefore, it may be concluded that
hydrophobic sites of PVA chains are mainly responsible
for binding of curcumin, along with some contribution
from the hydrophilic sites.


Binding of curcumin with PVA hydrogel
Figure 3. (Inset) Stern–Volmer plot for quenching of curcumin–PVA
complex with iodide (a) and acrylamide (b) at pH 7, (c) and (d) repre-
sent modified Stern–Volmer plots obtained on quenching of curcumin–
Aqueous PVA solution as such cannot be used for con-
PVA complex with iodide and acrylamide respectively, at pH 7.
trolled drug delivery. It has to be cross-linked either by γ-
CURRENT SCIENCE, VOL. 95, NO. 10, 25 NOVEMBER 2008
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radiation method or by a chemical method to form hydro-
incubating hydrogel with different concentrations of cur-
gel. Several reports have shown the use of hydrogel as an
cumin (20–250 μM), the amount of curcumin loaded was
efficient drug-delivery agent19–22. Hydrogels have the estimated to be in the range 20–215 nmol/g of the hydro-
ability to absorb solutes, or drugs, from solutions and can
gels. Figure 4 (inset, a) shows the amount of curcumin
release them in a controlled manner in a suitable medium,
adsorbed in one gram of hydrogel as a function of the initial
to have application as drug-delivery systems. Therefore, curcumin concentration. The amount of curcumin loaded
binding of curcumin to PVA hydrogel, produced by γ-ray
in the hydrogel was found to increase with increasing
induced cross-linking method, was also studied.
concentration of curcumin in the solution. Figure 4 (inset,
For this purpose, hydrogel was prepared by exposing b) also shows the number of nanomoles of curcumin
5 ml of 5% aqueous PVA solution to a total γ-radiation
adsorbed from 100 and 150 μM curcumin solution by one
dose of ~13 kGy, in a closed container of cross-sectional gram of hydrogel as a function of time.
area 1 × 1 cm2. The PVA gel samples were washed with At equilibrium, the concentration of curcumin in the
nanopure water to remove uncross-linked polymer fra-
solution is given by the equation:
ction, and kept in nanopure water. A known weight (~1 g)

of the swollen gel was immersed in 10 ml solution of kb(1 – θ)[Curcumin] = kdθ, (20)
known concentration of curcumin (typically around 20–

250 μM), dissolved in 5% methanol–water (v/v) mixture. where kb and kd are rate coefficients of the binding and
It was incubated for nearly 8 h. The loading of curcumin dissociation reactions respectively, and θ is the fraction
into the hydrogel was monitored by recording the absorp-
of the binding sites occupied at equilibrium.
tion spectrum of the supernatant solution as a function of
time. Figure 4 shows the absorption spectra of the super-
Moles of curcumin bound
θ =

natant solution, with initial concentration of 150 μM cur-
Moles of binding sites
cumin for different incubation times. From the absorption

spectra, it is clear that the absorbance in the methanol–
Moles of curcumin bound
water solution at 426 nm decreases with time, indicating =
,
loading of curcumin into the hydrogel. After 8 h, there
n × Moles of PVA in the gel
was not much change in the absorption spectrum, indicat-

ing an equilibrium state. The amount of curcumin loaded where n is the number of the binding sites in a polymer
into the hydrogel was calculated from the difference in chain. Equation (20) can be rearranged to give the Lang-
absorbance of the curcumin solution at 426 nm, before muir equation23:
and after incubating with hydrogel, and using the extin-

ction coefficient value of 4.88 × 104 M–1 cm–1. Thus, on
nK[Curcumin]

r =
, (21)
1+ K[Curcumin]


where K (kb/kd) is the binding constant and r (= θn) is the
binding ratio which is defined as the ‘ratio of the moles of
curcumin bound with hydrogel to the moles of PVA’. To
get the best values for binding parameters, linearization
methods of eq. (21) developed by Klotz has been used.
Reciprocal of eq. (21) gives the Klotz plot, i.e.

1
1
1

= +
(22)
r
n
nK[Curcumin]

The plot of 1/r vs 1/[Curcumin], as shown in Figure 5,
gives a straight line, with slope 1/nK and intercept 1/n.
The binding constant was found to be 2.6 × 104 M–1 and
the number of binding sites was 2.5 per polymer chain.

The nK value of the PVA hydrogel (6.5 × 104 M–1) was

lower than that of aqueous PVA. This difference could be
Figure 4. Absorption spectra of supernatant solution at different
due to lower value of
times, at an interval of 30 min (with initial curcumin concentration of
n or K, or both, in the PVA hydro-
150 μM). Inset: a, Nanomoles of curcumin adsorbed per gram of hy-
gel because of configurational constraints. Figure 6 shows
drogel as a function of curcumin concentration at saturation stage (in-
a representative piece of PVA hydrogel loaded with cur-
cubation time 8 h). b, Number of nanomoles of curcumin adsorbed per
cumin. Uniform loading of curcumin throughout the
gram of hydrogel, as a function of time, with initial curcumin concen-
tration of (I) 100 μM and (II) 150 μM.
hydrogel is clearly visible.
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Release of curcumin from hydrogel into
Liposomes, having a bilayer lipid-like structure, are being
liposomes
used as models for cell membrane. The phosphatidylcho-
line lipid, in the presence of water, arranges itself to form
To utilize biocompatible hydrogel for delivery of cur-
liposome. Therefore, release of curcumin from the PVA
cumin into a targetted bio-system, it is important to study
hydrogel into the liposomal solution was used to evaluate
its releasing characteristics from the curcumin–hydrogel its releasing capacity. In an earlier work from our labora-
system into a suitable medium. It is also important to tory18, the binding constant of curcumin to PC liposome
check whether curcumin is released into water from the was found to be in the order of 104 to 105 M–1. Since in
hydrogel. Therefore, a known weight (~0.2 g) of curcu-
this work the binding constant of curcumin to the PVA
min-loaded PVA hydrogel was incubated with 5 ml of hydrogel has been estimated to be in the order of 104 M–1,
water. The solution was checked spectrophotometrically one could expect its release in the presence of PC lipo-
for curcumin release, by monitoring the absorbance at some. Therefore, the release of curcumin from hydrogel
426 nm at different time intervals up to 5 h. No trace of was studied in the presence of different concentrations of
curcumin was observed in the water. The same procedure
liposome, ranging from 0.5 to 1.5 mg/ml.
was repeated with 5 and 10% methanol–water mixtures, Liposomes were prepared by the reported procedure18.
and even in these solvent mixtures, no release of curcu-
Briefly, phosphatidylcholine and cholesterol were dis-
min was observed. Further, increase in methanol con-
solved in chloroform in the weight ratio of 2 : 1, followed
centration resulted in hydrogel deformation. Therefore, by solvent evaporation in rotavapour. The resulting thin
higher concentration of methanol was not tested for re-
film was solubilized in 10 mM phosphate buffer (pH 7.4),
lease of curcumin.
and sonicated for 5 min, using a bath type sonicator. The

concentration of the phospholipids in liposomal solution

was determined according to the method reported earlier.
The curcumin-loaded hydrogel samples were kept in
5 ml of 0.5–1.5 mg/ml liposome solution, and the sam-
ples were incubated at 37°C, using a thermostated water-
bath. After 15 min intervals, the solution was checked
spectrophotometrically for curcumin release, by monitor-
ing the absorbance at 426 nm. Figure 7 shows the per-
centage of curcumin released, on incubation of liposome
solutions with curcumin-loaded hydrogel. The progress
of the release of curcumin was monitored as a function of
time up to 5 h. It can be seen from Figure 7 that in
0.5 mg/ml of liposome, only about 40% of curcumin is




Figure 5. Linear Klotz plot for binding of curcumin to PVA hydro-
gel.




Figure 7. Plot of percentage of curcumin released (from hydrogel
loaded with 250 μM curcumin solution) as a function of liposome con-
centration at equilibrium. (Inset) Percentage of curcumin released in

0.5 and 1.5 mg/ml liposome solution from the curcumin-loaded

hydrogel obtained by equilibrating with 250 μM curcumin solution as
Figure 6. Uniformly loaded PVA hydrogel with curcumin.
function of time.
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released in 4½ h. But, at higher concentration, 1.5 mg/ml
alcohol) in aqueous solution in the absence and presence of oxy-
of liposome, almost 50% of curcumin is released in the
gen. A pulse radiolysis and product study. Macromol. Chem.
same time-period.
Phys., 1994, 195, 1443–1461.
7. Karadag, E., Saraydin, D., Sahiner, N. and Guven, O., Radiation
The release of curcumin in the liposome was also studied
induced acrylamide/citric acid hydrogels and their swelling behav-
at different concentrations of curcumin loaded in 1 g of
iors. J. Macromol. Sci. – Pure Appl. Chem. A, 2001, 38, 1105–
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1121.
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Sci., 2002, 85, 1787–1794.
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9. Nagaoka, N., Safranji, A., Yoshida, M., Omichi, H., Kubota, H.
in the hydrogel, more curcumin was released in the lipo-
and Kotakai, R., Synthesis of poly (N-isopropylacrylamide) hydro-
some.
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Deliv. Rev., 2002, 43, 3–12.
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We have studied the binding of curcumin to PVA by ab-
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sorption and fluorescence techniques. The product nK
12. Aggarwal, B. B., Sundaramm, C., Malani, N. and Ichikawa, H.,
and the differential extinction coefficient were deter-
Curcumin: The Indian solid Gold. Adv. Exp. Med. Biol., 2007,
mined to be 2.4 × 105 M–1 and 2.7 × 104 M–1 cm–1 respec-
595, 1–75.
tively, by absorption technique, whereas the nK was 13. Singh, S., From exotic spice to modern drug? Cell, 2007, 130,
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765–768.
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ACKNOWLEDGEMENTS. C.P.S. is grateful to Department of Ato-
5. Ruiz, J., Mantecon, A. and Cadiz, V., Synthesis and properties of
mic Energy, for awarding research fellowship. The authors also wish to
hydrogels from poly (vinyl alcohol) and ethylenediaminetetraace-
acknowledge Drs T. Mukherjee and S. K. Sarkar for their encourage-
tic dianhydride. Polymer, 2001, 42, 6347–6354.
ment during the course of the study.
6. Ulanski, P., Bothe, E., Rosaik, J. M. and Sonntag, C. V., OH-

radical induced crosslinking and strand breakage of poly (vinyl
Received 15 October 2007; revised accepted 22 September 2008


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