Studies on aqueous solubility of 3,3′-diindolylmethane derivatives using cyclodextrin inclusion complexes

Article abstract of DOI:10.1016/j.molstruc.2012.09.036

The supramolecular interaction of 3,3′-diindolylmethane (DIM) and its derivatives with α-, β-, and γ-cyclodextrins (CDs) has been investigated to improve their aqueous solubility. A series of complexes of α-, β-, and γ-CDs with DIMs were prepared and thei

Full text of DOI:10.1016/j.molstruc.2012.09.036

Journal of Molecular Structure 1036 (2013) 1–6
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Studies on aqueous solubility of 3,30-diindolylmethane derivatives
using cyclodextrin inclusion complexes
Sutapa Roy a,c,1, Madhumita Mandal a,1, Churala Pal a,1, Prabal Giri b, Gopinatha Suresh Kumar a,b
,
Joydeep Mukherjee c, Parasuraman Jaisankar a,
⇑
a Chemistry Division, CSIR-Indian Institute of Chemical Biology, 4, Raja S. C. Mullick Road, Jadavpur, Kolkata 700 032, India
b Biophysical Chemistry Laboratory, CSIR-Indian Institute of Chemical Biology, 4, Raja S. C. Mullick Road, Jadavpur, Kolkata 700 032, India
c School of Environmental Studies, Jadavpur University, Jadavpur, Kolkata 700 032, India
h i g h l i g h t s
"
"
"
"
3,30-Diindolylmethanes (DIMs)-cyclodextrin (CD) inclusion complexes were prepared.
Spectroscopic analyses confirmed the supramolecular interaction of complexes.
1:1 Stoichiometry of the complexes of DIM-(
a, b, c)-CDs have been observed.
Aqueous solubility of DIMs in presence of CDs has been enhanced considerably.
a r t i c l e i n f o
a b s t r a c t
The supramolecular interaction of 3,30-diindolylmethane (DIM) and its derivatives with
cyclodextrins (CDs) has been investigated to improve their aqueous solubility. A series of complexes of
-, b-, and -CDs with DIMs were prepared and their inclusion complexation behavior in solution phase
assessed by fluorescence, UV–visible spectroscopy and circular dichroism. Circular dichroism spectra
revealed that incorporation of DIMs in the chiral environment of the CDs affecting their electric transi-
tions leading to the development of induced circular dichroism bands in the near UV region. A linear
increase of aqueous solubility of DIMs in presence of CDs was observed from their phase–solubility dia-
grams indicating the formation of soluble inclusion complexes. According to the continuous variation
method a 1:1 stoichiometry has been proposed for DIM cyclodextrins complexes.
a-, b-, and c-
Article history:
Received 11 June 2012
Received in revised form 13 September 2012
Accepted 13 September 2012
Available online 21 September 2012
a
c
Keywords:
Cyclodextrins
3,30-Diindolylmethane
Inclusion complex
Aqueous solubility
Supramolecular interaction
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
potent inhibitors of Leishmania donovani topoisomerase I [6].
DIM and its derivatives are required in very high doses to
3,30-Diindolylmethane (DIM), the most important self-
condensation product of indole-3-carbinol (I3C), is found in the
acidic environment of the stomach upon ingestion of I3C. The
I3C is formed by acid hydrolysis of glucobrassicin present in
common vegetables of the genus Brassicca such as cabbage, kale,
brussels sprouts, and broccoli [1]. DIM has been the subject of
much research due to its potential ability in promoting healthier
estrogen metabolism in patients with thyroid proliferative dis-
ease [2], preventing of human breast cancer [3], and prostate
cancer development in the transgenic adenocarcinoma mouse
prostate model [4]. Our recent studies have shown that DIM
and its derivatives are good plant growth promoters [5] and
provide satisfactory biological activity due to their low aqueous
solubility. Therefore, seeking an efficient and nontoxic carrier
for these DIM derivatives to overcome the problems of bioavail-
ability has become inevitable.
Among the various compounds generally used as drug carrier,
one of the most important ones are the cyclodextrins (CDs) [7], a
class of biodegradable cyclic oligosaccharides, mainly with six to
eight D-glucose units linked by a-1,4 glycosil units represented
as a truncated cone structure with a hydrophobic cavity [8]. Popu-
lar feature of CDs is the marked difference of polarity between the
internal and external surfaces; the inner part is made nonpolar by
the glycosidic oxygen and methylene protons, whereas the
external surface is polar by virtue of the presence of secondary
and primary hydroxyls on the large and small rims, respectively,
thus allowing their solubility in water [9]. Furthermore, this
particular structural feature of CDs allows various organic and
⇑
Corresponding author. Tel.: +91 33 2499 5790/774; fax: +91 33 2473 5197.
E-mail addresses: pjaisankar@yahoo.com, jaisankar@iicb.res.in (P. Jaisankar).
1
These authors contributed equally to this work.
0022-2860/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.molstruc.2012.09.036

2
S. Roy et al. / Journal of Molecular Structure 1036 (2013) 1–6
biological guests within their hydrophobic cavities to afford typical
host–guest complexes in aqueous solution [10–12]. A number of
inclusion complexes of cyclodextrins with drugs like paclitaxel
[13] and cinchona alkaloids [14] resulting in increasing their aque-
ous solubility have been reported.
prepared in methanol and 3.4
the buffer solution to maintain the final concentration of DIMs as
17.0 M in 2.0 ml. The -, b- and -CD (1.7 l) were added gradu-
ally to the cell to maintain the concentration of CD’s ranged from 0
to 18.7 ꢀ 10ꢁ3 mM. The solution was kept stirred continuously.
Fluorescence emission spectra were acquired on a Shimadzu RF-
5301PC fluorimeter (Shimadzu Corporation, Kyoto, Japan) by exci-
tation at the absorption maxima of each compound. Excitation and
emission bandwidths were set at 5 nm.
ll of this solution was added to
l
a
c
l
Herein, we report inclusion complexes of DIM derivatives 1–6
(Fig. 1), previously synthesized and characterized in our laboratory
[15], with
a-, b- and c-cyclodextrins, and characterization of the
mode of inclusion and stoichiometry of the complexes by means
of absorbance [16], fluorescence [17], circular dichroism and
phase–solubility studies.
2.4. Circular dichroism spectroscopy
Circular dichroism spectra of compound 2 (0.5 mM) in presence
a, b, c cyclodextrin (10.0 mM) were recorded on a JASCO J815
2. Experimental
of
spectropolarimeter (Jasco International Co., Hachioji, Japan) in
2.1. General procedures
rectangular quartz cuvettes of 1.0 cm path length at 20 0.5 °C.
Commercial a-, b- & c- CDs (Fluka) were dried in a desiccator in
vacuo over phosphorus pentoxide at 90 °C for at least 24 h and
stored in the same apparatus at 40 °C till use. Guests 5 and 6 were
prepared by the reaction of indole (Acros) and corresponding benz-
aldehyde (Acros) in presence of InCl3 (Aldrich). All other reagents
and chemicals were of analytical reagent grade. All solutions were
prepared using ultra pure water (MILLIQ). Sodium dihydrogen
phosphate and disodium hydrogen phosphate were dissolved in
double distilled, deionised water to make a 0.1 (M) buffer solution
of pH 7.2, which was used as solvent throughout the measurement.
All experiments were performed at 298.15 K.
2.5. Phase–solubility study
Phase–solubility studies were carried out according to the
method reported by Connors [18]. A fivefold molar excess of DIMs
were added to the aqueous solutions of a-, b- and c- cyclodextrins
with increasing concentrations of 0.1, 0.2, 0.3, 0.4, and 0.5 mM. The
resulting solutions, protected from light by wrapping with black
paper, were stirred for 72 h with similar stirring rates. After equil-
ibration, aliquots of the supernatant were filtered through a mem-
brane filter (0.45 lm). The filtrates were then analyzed using UV
spectrophotometer at kmax of each compound.
For the determination of stoichiometry of inclusion complexes
the total molar concentration of the different DIMs–CD solutions
(i.e. the combined concentrations of DIMs and CD) were kept
constant (3.0 mM), but the mole fraction of DIMs (i.e. [DIMs]/
[DIMs] + [CD]) were varied (0.2, 0.4, 0.6 0.8 mol fraction). The
solutions were stirred for 48 h. The absorbance of the resulting
solutions was measured at kmax of each compound by using spec-
trophotometer. The differences in absorbance in the presence of
2.2. Absorption spectral titrations
The inclusion complex formation phenomenon of CDs with
guest DIMs in aqueous phosphate buffer solutions was examined
at pH 7.2 by means of UV–visible spectral titration in a Shimadzu
1700 Spectrophotometer (Shimadzu Corporation, Kyoto, Japan). A
1.0 mM stock solution of DIMs (5.0 ml) was prepared in methanol,
and 6.0 ll of this stock solution was added to the phosphate buffer
CDs and in the absence of CDs (DA = A–Ao) were plotted against
molar ratio R; where R = [DIMs]/{[DIMs] + [CD]} for all solutions.
solution to maintain the final concentration of molecules as
2.5 ꢀ 10ꢁ7 mol dmꢁ3 in the cuvette. Then gradually
a-, b-, c-CD
were added in the cuvette so that the concentrations of CDs ranged
from 0 to 12.5 ꢀ 10ꢁ3 mol dmꢁ3. The absorption spectra were mea-
sured against an appropriate reagent blank.
3. Results and discussion
3.1. Absorption spectra
2.3. Fluorescence spectroscopy
The UV absorption spectrum of 2 in methanolic solution
(5 ꢀ 10ꢁ6 M) exhibited a kmax at 317 nm for
p ?
pꢂ transition with
Fluorescence eꢁm3ission spectra of DIM derivatives (1–4)
-CD (0–18.7 ꢀ 10ꢁ3 mM). 1.0 mM stock solutions of DIMs were
(17 ꢀ 10ꢁ6 mol dm ) were measured in presence of
a-, b- and
molar absorptivity of 55.272 ꢀ 103 dm3 molꢁ1 cmꢁ1. Qualitative
investigation of the inclusion complexation phenomenon of CDs
with guest DIMs was performed at various pH by means of UV–
visible spectral titration. The optimum results were obtained at
pH 7.2. Table 1 shows the UV spectral wavelength in terms of
the ratio of the initial absorbance (A1) to final absorbance (A2)
and the spectral wave length shift data for all the DIMs and
c
a-, b-, c- CDs complexes in aqueous phosphate buffer at pH 7.2.
Generally, in all cases, maximum absorption bands shifted in pres-
ence of CDs, while the absorption intensity gradually decreased
with the stepwise addition of CDs. The absorption intensity of com-
pound 2 gradually decreased with the increasing concentration of
CDs along with blue shifting of the absorption band. For compound
2 the absorption intensity varied from the initial 0.109 to 0.081
with
0.099 for
, b- and
ences harder environmental changes upon inclusion in the narrow-
est -CD cavity than in the b-CD and -CD cavity, respectively, in
agreement with the notion that the effectiveness of non-bonding
a
-CD and from 0.138 to 0.107 with b- and from 0.137 to
-CD. This corresponds to 26%, 23% and 28%, respectively,
-CD. This suggests that compound 2 in general experi-
c
c
a
a
c
Fig. 1. General structure of 3,30-diindolylmethane derivatives 1–6.

S. Roy et al. / Journal of Molecular Structure 1036 (2013) 1–6
3
Table 1
UV–vis spectral data of DIM–CDs complexes in phosphate buffer solution at pH 7.2 by
the excess addition of CDs [conc. 12.5 ꢀ 10ꢁ3 mol dmꢁ3
]
to the DIMs
[2.5 ꢀ 10ꢁ7 mol dmꢁ3].
DIMs and DIM–CDs
complexes
kmax
(nm)
Ratio of change in absorbance (A1/
A2)a
1
1 +
1 + b-CD
1 +
292
293
293
294
a
-CD
1.39
1.29
1.15
c
-CD
2
2 +
2 + b-CD
2 +
317
317
315
318
a
-CD
1.35
1.29
1.39
c
-CD
3
3 +
3 + b-CD
3 +
276
277
275
275
a
-CD
1.56
1.28
1.26
c
-CD
4
4 +
4 + b-CD
4 +
293
294
293
294
a
-CD
1.59
1.15
1.07
c
-CD
5
5 +
5 + b-CD
5 +
276
277
276
277
a
-CD
1.36
1.08
1.03
Fig. 2. Fluorescence spectral changes of compound 2 (17 ꢀ 10ꢁ6 mol dmꢁ3) in
presence of
a
-CD (0–18.7 ꢀ 10ꢁ3 mM) in aqueous phosphate buffer, pH 7.2 at
c
-CD
298.15 K (the excitation and emission wavelengths were 317 and 381 nm,
respectively). The arrows indicate the increase of fluorescence intensity with
increasing concentration of a-CD.
6
6 +
6 + b-CD
6 + -CD
295
295
285
295
a
-CD
1.32
2.07
1.42
c
a
A1 and A2 represent the initial and final absorbance values.
normally occur in bulk buffer solution and enhance the fluores-
cence efficiencies of guest molecules [20]. The fluorescence inten-
sity of 2 gradually increased with increase of concentration of CDs,
interactions in modifying the properties of an included guest
strictly depend on the distance from the host inner wall [19].
followed the order,
c > b > a and finally reached a saturation point
(Fig. 2, compound 2).
3.2. Fluorescence spectra
3.3. Determination of apparent association constant
Fluorescence emission spectra of DIM derivatives 1–4
A very well known way to determine the apparent association
constant of host–guest complexes is Benesi–Hildebrand method
[21] as per the following equation
(17 ꢀ 10ꢁ6 mol dmꢁ3) were measured in presence of
a-, b- and
c
-CD (0–18.7 ꢀ 10ꢁ3 mM) in aqueous phosphate buffer at pH 7.2
and 298.15 K. Compounds 5 and 6 were not fluorescent. The max-
imum absorption wavelengths of the DIMs were chosen for excita-
tion. The excitation and emission maxima of the DIM derivatives
1–6 are presented in Table 2. Accordingly, the maximum excitation
and emission wavelengths of compound 2 were 317 and 381 nm,
1=ðI—IoÞ ¼ 1=½ðIa ꢁ IoÞKꢃ þ 1=ðIa ꢁ IoÞ
ð1Þ
where I is the observed fluorescence intensity of the DIM solutions
at each -, b-, -CD concentration tested, Io and I are the fluores-
cence intensities in the absence of
DIMs molecules are complexed. It is presumed that: (i)
-CDs are in a large excess with respect to DIMs and therefore its
a
c
a
respectively. With the addition of
a-, b-, and c- cyclodextrins to
a-, b-,
c-CD and when all the
the solution of guest (DIMs, 1–4), the fluorescence intensity was
markedly enhanced (Fig. 2, compound 2). The increase of fluores-
cence intensity due to formation of complexes of CDs with DIMs
could be explained as the guest molecules were entrapped in the
cavity of CDs. The microenvironment around CDs with smaller
polarity and stronger rigidity would restrict the freedom of guest
molecules inside the cavity and increase the fluorescence quantum
yield. Furthermore, the steric hindrance of CDs torus can protect
the excited states from non-radiative and quenching process that
a-, b-,
c
free and analytical concentration are the same; (ii) the variation
in the fluorescence intensity are proportional to the complex con-
centration and (iii) at high a-, b- and c-CD concentration essentially
all of the DIMs molecule are complexed.
In case of DIM derivatives, a good linear relationship was ob-
tained when 1/(I–Io) was plotted against 1/[CD] (a-, b-, c-CD) sup-
ported the existence of a 1:1 complex (Fig. 3, compound 2) [22].
The apparent association constant K of compound 2 was deter-
mined to be 4.8 ꢀ 105 l molꢁ1 for
a
-CD and 6.89 ꢀ 105 l molꢁ1 for
Table 2
Excitation wavelength and emission maxima of DIM derivatives 1–6 in phosphate
buffer solution at pH 7.2.
b-CD. In contrary, for c-CD, the plot is best described by two linear
segments each giving association constants of 2.795 ꢀ 105 l molꢁ1
and 3.5 ꢀ 106 l molꢁ1. Thus, it can be observed that the DIM com-
pounds form only one type of complex with 1:1 stoichiometry with
all three cyclodextrins.
Compound
Excitation wavelength (nm)
Emission maxima (nm)
1
2
3
4
5
6
292
317
276
293
276
295
333
381
341
365
Change in Gibbs energy (DG°) associated with various DIM–CD
complexations was evaluated from their respective K values.
Table 3 reveals that there is a strong host–guest binding ability be-
tween cyclodextrins and DIMs quantitatively. It can be concluded
Non-fluorescent
Non-fluorescent

4
S. Roy et al. / Journal of Molecular Structure 1036 (2013) 1–6
Fig. 3. The change of 1/(I–Io) with 1/[
CD complexes for compound 2.
a-CD] (j), 1/[b-CD] (d), 1/[c-CD] (N) for DIM–
Table 3
Complex association constant K (dm3 molꢁ1) and Gibbs energy change (
DG°) for
inclusion complexation of host CDs with DIMs in aqueous buffer solution (pH 7.2) at
298 K.
Drug Drug + CD-
complexes
Association constant K
(dm3 molꢁ1
Gibbs energy change
G°) (kJ molꢁ1
)
(
D
)
1
2
3
4
1 +
1 + b-CD
1 +
2 +
2 + b-CD
2 +
3 +
3 + b-CD
3 +
4 +
4 + b-CD
4 + -CD
a
-CD
K1 = 4.2 ꢀ 103
K1 = 2.0 ꢀ 104
K1 = 1.9 ꢀ 104
K1 = 4.8 ꢀ 105
K1 = 6.9 ꢀ 105
K1 = 2.8 ꢀ 105
K1 = 17.2 ꢀ 105
K1 = 12.9 ꢀ 105
K1 = 8.6 ꢀ 105
K1 = 1.52 ꢀ 104
K1 = 2.44 ꢀ 104
K1 = 7.5 ꢀ 104
ꢁ20.58
ꢁ24.53
ꢁ24.40
ꢁ32.42
ꢁ33.31
ꢁ31.07
ꢁ35.55
ꢁ34.86
ꢁ33.86
ꢁ23.86
ꢁ25.03
ꢁ27.82
c
a
-CD
-CD
c
a
-CD
-CD
c
a
-CD
-CD
c
Fig. 4. Induced CD spectra of compound 2 in presence of
-CD (c).
a-CD (a), b-CD (b) and
c
that these complexation process is highly feasible, which is evident
from the negative values of G° of different DIM–CD complexes.
D
fluorescence study it has been observed that DIMs and CDs form
1:1 complex which is the most common type of association when
a single drug molecule is included in the cavity of a cyclodextrin
molecule, with a stability constant K1:1 for the equilibrium be-
tween the free and complexed ones. Fig. 5 presents the phase–sol-
ubility diagram for the DIMs studied. There is a linear increase in
3.4. Circular dichroism spectroscopy
Induced circular dichroism spectroscopy (ICD) study was per-
formed for compound 2 as a representative case in the presence
of CDs. Optical activity was induced at ꢄ317 nm for 2 manifested
by the appearance of a positive peak and the shape of the ICD spec-
tra is similar to the corresponding absorption spectra (Fig. 4). The
changes in optical activity of compound 2 could be attributed to
the perturbation its electronic transition caused its inclusion in
the cavity of CDs following complexation. According to Harata’s
rule, a positive ICD effect is expected for a parallel alignment of
the electric transition dipole moment relative to the CD axis, while
a negative effect should result from a perpendicular alignment
[23]. Thus, the results of circular dichroism spectroscopy revealed
that compound 2 is embedded in the asymmetric locus of CDs
cavity.
the solubility of DIMs with increasing concentration of
a-, b-, c-
CDs with a slope lower than unity indicating a 1:1 stoichiometry.
This is a feature of A-L type of complexes showing the formation
of water-soluble complexes between CDs and DIMs [24]. The
apparent stability constants (K1:1) values were calculated from
the phase solubility diagram (Fig. 5), using the following equation,
K1 : 1 ¼ Slope=Soð1 ꢁ SlopeÞ
ð2Þ
Here, slope is the value found in the linear regression and So is
the solubility of the drug previously determined in the absence of
CDs [25]. The stability constant values were evaluated to be
5400 Mꢁ1, 6130 Mꢁ1 and 6210 Mꢁ1 for compound 1, 4167 Mꢁ1
,
3.5. Solubility studies
5769 Mꢁ1 and 7000 Mꢁ1 for compound 2, 5530 Mꢁ1, 5710 Mꢁ1
,
and 4580 Mꢁ1 for compound 3, 7500 Mꢁ1 6370 Mꢁ1 and
Determination of the stability constants from the phase-solubil-
ity diagram is a widely accepted method for understanding the ef-
fect of CDs complexation on the drug solubility [18]. From
5150 Mꢁ1 for compound 4, 7900 Mꢁ1, 6320 Mꢁ1 and 5280 Mꢁ1
for compound 5, and 8300 Mꢁ1, 6320 Mꢁ1 and 5280 Mꢁ1 for com-
pound 6, respectively, with a-, b-, and c- CD.

S. Roy et al. / Journal of Molecular Structure 1036 (2013) 1–6
5
Fig. 5. Phase-solubility diagram of (a) a-CD–DIM, (b) b-CD–DIM and (c) c-CD–DIM
complexes in water at pH 7.2 and 298.15 K. Symbols (-j-), (-d), (-N-), (-.-), (-ꢀ-)
and (ð-J-Þ) represent the DIM derivatives 1–6.
Fig. 6. Job’s plot of the (a),
a
-CD–DIMs (b) b-CD–DIMs and (c)
c
-CD–DIMs
complexation. Six different colors indicate the plots of six different DIM derivatives
The apparent association constant from fluorescence studies
and the stability constants from solubilizations studies differ in
their values for many compounds studied here. This may be due
to use of the different CD and compound concentrations in the
two methods. Such differences are not uncommon and significant
variations in solubility and apparent association constants have
been recently reported for inclusion complexes of bromhexine
with CDs [26].
1–6 in presence of -, b- and -CD.
a
c
3.7. Possible structure of the DIMs–CD inclusion complexes
From the knowledge of theoretical studies of various cyclodex-
trin–indole inclusion complexes [27] it could be predicted that
DIMs penetrate inside the torus of the host molecules through
their one of the benzene ring of indole moieties, give rise to a
1:1 stoichiometry with the CDs, although the molecules are per-
fectly symmetrical in nature.
3.6. Stoichiometry of the complex: job plot
According to the continuous variation method, if a physical
parameter can be directly related to the concentration of the com-
plex and that parameter can be measured for a set of samples with
continuously variable molar fraction of components, the maximum
value of that parameter corresponds to the actual stoichiometry of
complex. The molar ratio R corresponds to the complexation stoi-
chiometry. The maximum absorbance variation of DIMs in pres-
ence of CDs were observed for R ꢅ 0.5 (Fig. 6), which indicates
that the inclusion stoichiometry in all cases is 1:1, in agreement
with the stoichiometry suggested from the phase solubility study.
4. Conclusions
Formation of host–guest inclusion complexes between DIM
derivatives (1–6) and
fluorescence spectroscopy. The ratio of DIM derivatives to
-CD in the inclusion complexes is 1:1, which is confirmed by their
a-, b-,
c
-CDs is revealed by absorption and
a-, b-,
c
phase solubility studies and Job’s plot analysis. Circular dichroism
spectroscopy results suggest that the DIMs entered into the

6
S. Roy et al. / Journal of Molecular Structure 1036 (2013) 1–6
[8] W. Saenger, Angew. Chem., Int. Ed. Engl. 19 (1980) 344.
[9] E.M. Martin Del Valle, Process Biochem. 39 (2004) 1033.
[10] A.J. Baer, D.H. Macartney, Org. Biomol. Chem. 3 (2005) 1448.
[11] L. Liu, Q.X. Guo, J. Incl. Phenom. Macro. Chem. 42 (2002) 1.
[12] A.A. Knyazev, I.N. Karpov, O.I. Mikhalev, M.V. Alfimov, J. Incl. Phenom. Macro.
Chem. 40 (2001) 77.
hydrophobic cavity of CDs, which enhance the solubility of DIMs in
water for their better bioavailability.
Acknowledgments
[13] E. Junquera, L. Peña, E. Aicart, J. Pharm. Sci. 87 (1998) 86.
[14] M. Wulff, M. Aldén, J. Tegenfeldt, Bioconjugate Chem. 13 (2002) 240.
[15] P.K. Pradhan, S. Dey, V.S. Giri, P. Jaisankar, Synthesis 11 (2005) 1779.
[16] N.V. Roik, L.A. Belyakova, J. Mol. Struct. 987 (2011) 225.
[17] Y. He, X. Shen, J. Photochem. Photobio A: Chem. 197 (2008) 253.
[18] K.A. Connors, The determination of the phase–solubility diagram in water.
Binding Constants: The Measurement of Molecular Complex Stability, John
Wiley and Sons, NewYork, 1987. p. 24.
Financial support from the Network Project (ORIGIN) by the
Council of Scientific and Industrial Research (CSIR), New Delhi, In-
dia is gratefully acknowledged. Authors C.P., M.M., and P.G. of CSIR-
Indian Institute of Chemical Biology received financial support in
the form of Research Fellowships from CSIR, India.
[19] Y. Liu, G.S. Chen, L. Li, H.Y. Zhang, D.X. Cao, Y.J. Yuan, J. Med. Chem. 46 (2004)
4634.
References
[20] M.V. Rekharsky, M.P. Mayew, R.N. Goldberg, P.D. Ross, Y. Yamashoji, Y. Inoue, J.
Phys. Chem B. 101 (1997) 87.
[21] S. Mizyed, H. Tarabsheh, D. Marji, Jordan. J. Chem. 2 (2007) 145.
[22] Q. Zhang, Z. Jiang, Y. Guo, R. Li, Spectrochim Acta, part A 69 (2008) 65.
[23] S. Allenmark, Chirality 15 (2003) 409.
[1] R.E. Staub, B. Onisko, L.F. Bjeldanes, Chem. Res. Toxicol. 19 (2006) 436.
[2] S. Rajoria, S. Suriano, P.S. Parmar, Y.L. Wilson, U. Megwalu, A. Moscatello, H.L.
Bradlow, D.W. Sepkovic, J. Geliebter, S.P. Schantz, R.K. Tiwari, Thyroid 21
(2011) 299.
[3] Y. Jin, X. Zou, X. Feng, Anticancer Drugs 21 (2010) 814.
[24] A. Durán-merás, F. Muñoz De La Peña, M.I. Salinas López, Rodriguez Ca´ceres, J.
[4] H.J. Cho, S.Y. Park, E.J. Kim, J.K. Kim, J.H. Park, Mol. Carcinog. 50 (2011) 100.
[5] C. Pal, S. Dey, S.K. Mahato, J. Vinayagam, P.K. Pradhan, V.S. Giri, P. Jaisankar, T.
Hossain, S. Baruri, D. Ray, S.M. Biswas, Bioorg. Med. Chem. Lett. 17 (2007) 4924.
[6] A. Roy, A. Ganguly, S.B. Dasgupta, B.B. Das, C. Pal, S. Dey, P. Jaisankar, H.K.
Majumder, Mol. Pharmacol. 74 (2008) 1292.
Incl. Phenom. Macrocycl. Chem. 51 (2005) 137.
[25] T. Higuchi, K.A. Connors, Adv. Anal. Chem. Instrum. 4 (1965) 117.
[26] M. Stojanov, H.M. Nielsen, K.L. Larsen, Int. J. Pharm. 427 (2012) 349.
[27] G. Fronza, A. Mele, E. Redenti, P. Ventura, J. Org. Chem. 61 (1996) 909.
[7] M.E. Davis, M.E. Brewster, Nat. Rev. Drug. Discov. 3 (2004) 1023.