Inclusion complexes of cyclodextrins with galangin: A thermodynamic and reactivity study

Article abstract of DOI:10.1007/s10953-010-9574-1

The formation of the complexes of galangin (GAL) with native β-cyclodextrin (βCD), and with its substituted counterparts such as dimethyl-βCD (DMβCD) and hydroxypropyl-βCD (HPβCD), was studied by fluorescence spectra in aqueous medium. The binding association constants (K _a) of the complexes were determined at different temperatures. The formation constants obtained have the following trend upon complex formation at the three temperatures studied: HPβCD > DMβCD > βCD. The thermodynamic data for the inclusion of GAL in DMβCD and HPβCD indicated that is mainly enthalpy driven whereas for βCD it is an entropy-driven process. The antioxidant ability studies of GAL and CD complexes showed practically no change in its activity when the β-cyclodextrin complex is formed. The decrease in the T _eq observed for GAL-DMβCD and GAL-HPβCD in comparison with GAL-βCD could be due to effective protection of the phenol group in the cyclodextrin cavity, which is in agreement with molecular modeling studies.

Full text of DOI:10.1007/s10953-010-9574-1

J Solution Chem (2010) 39: 1168–1177
DOI 10.1007/s10953-010-9574-1
Inclusion Complexes of Cyclodextrins with Galangin:
a Thermodynamic and Reactivity Study
Carolina Jullian · Muriel Alfaro ·
Gerald Zapata-Torres · Claudio Olea-Azar
Received: 10 February 2010 / Accepted: 29 March 2010 / Published online: 14 August 2010
© Springer Science+Business Media, LLC 2010
Abstract The formation of the complexes of galangin (GAL) with native β-cyclodextrin
(βCD), and with its substituted counterparts such as dimethyl-βCD (DMβCD) and
hydroxypropyl-βCD (HPβCD), was studied by fluorescence spectra in aqueous medium.
The binding association constants (Ka) of the complexes were determined at different tem-
peratures. The formation constants obtained have the following trend upon complex forma-
tion at the three temperatures studied: HPβCD > DMβCD > βCD. The thermodynamic
data for the inclusion of GAL in DMβCD and HPβCD indicated that is mainly enthalpy
driven whereas for βCD it is an entropy-driven process.
The antioxidant ability studies of GAL and CD complexes showed practically no change
in its activity when the β-cyclodextrin complex is formed. The decrease in the Teq observed
for GAL-DMβCD and GAL-HPβCD in comparison with GAL-βCD could be due to effec-
tive protection of the phenol group in the cyclodextrin cavity, which is in agreement with
molecular modeling studies.
Keywords Galangin · Cyclodextrins · Inclusion complex · ORAC-FL · Thermodynamic
study · Docking
1 Introduction
Flavonoids are present in fruits, vegetables and beverages derived from plants (tea, red
wine) and in many dietary supplements or herbal remedies including ginkgo biloba, soy
C. Jullian ( ) · M. Alfaro
ꢀ
Departamento Química Orgánica y Fisicoquímica, Facultad de Ciencias Químicas y Farmacéuticas,
Universidad de Chile, Santiago, Chile
e-mail: cjullian@uchile.cl
G. Zapata-Torres · C. Olea-Azar
Departamento Química Inorgánica y Analítica, Facultad de Ciencias Químicas y Farmacéuticas,
Universidad de Chile, Santiago, Chile

J Solution Chem (2010) 39: 1168–1177
1169
β-cyclodextrin, R = H
2-hydroxypropyl β-cyclodextrin, R = CH CHOHCH or H
2
3
heptakis (2,6 O dimethyl) β-cyclodextrin, R = CH
2,6
R
3
= H
3
Scheme
1 (A) Molecular structure of galangin. (B) Schematic representation of β-cyclodextrin,
2-hydroxypropyl-β-cyclodextrin, and heptakis-2,6 O dimethyl-β-cyclodextrin
isoflavones, and milk thistle. Flavonoids have been described as health-promoting, disease-
preventing dietary supplements, and have activity as cancer preventive agents [1, 2]. In ad-
dition to being potential alternatives to the commonly used synthetic phenolics for the food
industry [3], they may have health benefits because epidemiological studies indicate that
adequate intakes of flavonoid-rich foods may decrease the risk of coronary heart disease and
certain cancers [4].
Galangin (Scheme 1A), a member of the flavonol class of flavonoid, is present in high
concentrations in medicinal plants (e.g. Alpinia officinarum), honey and propolis, a natural
beehive product. The increasing interest of this type of flavonol lies in their broad pharmaco-
logical activities (e. g., antimicrobial, spasmolytic, antiallergic, anti-inflammatory, antiviral,
anticarcinogenic) [5–9]. Despite the applicable qualities, biological activities and therefore
therapeutic usefulness of these substances, their bioavailability is limited because of their
unfavorable physicochemical properties, especially very poor water-solubility and low ox-
idative stability.
On the other hand, modern nanochemistry has offered a solution to this problem by in-
corporation of these substances into cyclodextrins (CDs). CDs are cyclic glucose oligomers
having six, seven or eight glucose units, linked by 1,4-α-glucosidic bonds and called re-
spectively α-, β- and γ -cyclodextrin. They have the ability to form inclusion complexes
with a wide variety of organic compounds, which enter partly or entirely into the relatively
hydrophobic cavity of CDs simultaneously expelling the few high-energy water molecules
from the inside. The size of the cavity of the CDs allows selectivity for the complexation
of guest molecules, therefore acting as molecular encapsulants [10]. In the pharmaceuti-
cal, cosmetics and food industries, CDs have been used as complexing agents for various
compounds, such as drugs, vitamins, and food colorants, increasing the solubility, stability,
and bioavailability of the guest molecule [11, 12]. Some indications of improvement of the
antioxidant activities of phenolic substances as guests of CD have been reported [13–15].
The present article is devoted to study the complexation of galangin with three different
cyclodextrins, (HPβCD, DMβCD and βCD, Scheme 1B). Several thermodynamic parame-
ters, determined from van’t Hoff plots, were analyzed so as to gain information about the
mechanisms involved in the association processes. Also, the effect that the cyclodextrin has
on the antioxidant capacity of galangin against reactive oxygen species (ROS) was studied
by the ORAC-fluorescein (ORACFL) methodology [16].

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2 Experimental
2.1 Materials
Galangin (3, 5, 7-trihydroxyflavone), was purchased from Sigma (USA). βCD (β-
cyclodextrin), DMβCD (heptakis-2,6-O-dimethyl-β-cyclodextrin), HPβCD (2 hydroxy-
propyl-β-cyclodextrin), AAPH (2,2’-azobis(2-methylpropionamidine) dihydrochloride), FL
(fluorescein disodium salt) and trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic
acid) were purchased from Sigma-Aldrich, Inc., St. Louis, MO. All solvents employed in
the spectrophotometric analyses were spectroscopic reagent grade, from Merck.
2.2 Methods
2.2.1 Determination of the Binding Constant Ka
300 µL of GAL solution having a concentration of 5.0×10−4 mol·L−1 was added to aqueous
solutions of CDs of various concentrations. The final volume of the system was kept constant
to 5 mL and buffered to pH = 8 (Britton-Robinson, 0.1 mol·L−1). The resulting mixture was
equilibrated in a Julabo thermostatic shaking water bath for 24 h at different temperatures
(298, 303 and 308 K) after which equilibrium was reached. Fluorescence emission spectra
were recorded with a Perkin-Elmer LS-55 spectrofluorometer, with an excitation wavelength
at 374 nm; the emission intensities were monitored at 524 nm. Excitation and emission
bandwidths were set at 15 nm.
2.2.2 ORACFL Assay
The ORAC analyses were carried out on a Synergy HT multidetection microplate reader,
from Bio-Tek Instruments, Inc. (Winooski, VT), using 96-flat polystyrene microplates with
clear bottoms, purchased from Nalge Nunc International. Fluorescence was read through the
clear bottom, with an excitation wavelength of 485/20 nm and an emission filter of 520/20
nm. The plate reader was controlled by KC4, version 3.4, software. The oxygen radical
absorbance capacity was determined as described by Dávalos et al., [17], with slight modifi-
cations. The reaction was carried out in 575 mmol·L−1 sodium phosphate buffer (pH = 7.4),
and the final reaction mixture volume was 200 µL. FL (150 µL; 52 nmol·L−1, final concen-
tration) and galangin solutions in the absence or presence of CDs (70 µL), were placed in the
wells of the microplate. The mixture was preincubated for 30 min at 37 ◦C, before rapidly
adding the AAPH solution (30 µL; 19 mmol·L−1, final concentration) using a multichannel
pipet. The microplate was immediately placed in the reader and the fluorescence recorded
every 1 min for 80 min. The microplate was automatically shaken prior to each reading.
A blank with FL and AAPH using sodium phosphate buffer instead of the antioxidant so-
lution, and eight calibration solutions using Trolox C (1, 2, 3, 4, 5 and 6 µmol·L−1) as
antioxidant, were also used in each assay. All reaction mixtures were prepared in triplicate,
and at least three independent assays were performed for each sample. In order to avoid a
temperature effect, only the inner 60 wells were used for experimental purposes, while the
outer wells were filled with 200 µL of distilled water. The results were expressed as relative
fluorescence with respect to the initial reading. The area under the fluorescence decay curve
(AUC) was calculated by the equation:
AUC = 1 + i=80
(1)
ꢀ
fi
f0
i=1

J Solution Chem (2010) 39: 1168–1177
1171
where f0 is the initial fluorescence reading at 0 min and fi is the fluorescence reading at
time i. The net AUC corresponding to the sample was calculated by subtracting the AUC
corresponding to the blank.
2.2.3 Molecular Modeling
In silico build-up of the β-CD and its derivative forms were carried out using the Builder
module of the InsightII program by adding to βCD 14 methyl groups in positions 2-, 6-
(DMβCD) and 7-hydroxypropyl (MS 1) groups (HPβCD). The models obtained were then
subjected to optimization using a protocol of 300 steps of conjugate gradients to avoid steric
hindrance and clashes that can appear in the building process. The galangin was build us-
ing Gaussview and then it was optimized using a semiempirical method such as PM3 as
implemented in the Gaussian98 package of programs [18].
Autodock3.0.5 [19] with the Lamarkian Genetic Algorithm (LGA) was used to generate
the starting complexes. The parameters used for the global search was an initial population
of 150 individuals, with a maximal number of energy evaluations of 1.5×107 and a maximal
number of generations of 5 × 106 as an end criterion. An elitism value of 1 was used, and
probabilities of mutation and crossing-over of 0.02 and 0.08, respectively, were used. The
best solutions obtained, according to these parameters, were further refined by a local search
method such as pseudo Solis and Wets “PSW”.
Autodock defines the conformational space implementing grids over all of the possible
solution space. With the aim of testing the ability of Autodock to converge into solutions that
are inside of the βCD, a grid of 80 Å by side and 0.3 Å spacing between each point was set
up in such a way that it covered both the external surface and the internal cavity of the βCD.
The following procedure was employed in the β-CD docking simulations: 250 runs were
done for each βCD. At the end of each run, the solutions were separated into clusters ac-
cording to their lowest RMSD and the best score based on a free energy function. Cluster
solutions whose average score was not over 1 kcal·mol−1(4.184 kJ·mol−1) above the best
energy obtained in the respective run were selected. Then, the solution that represented most
of the complexes obtained in the run was compared with the experimental NMR data, insur-
ing that this solution was able to reproduce it accurately.
The selected final complexes were optimized using the semiempirical PM3 method as a
refining procedure with Gaussian98.
3 Results and Discussion
The stoichiometry and the binding constant, Ka, were estimated from the fluorescence data
by using the modified Benesi-Hildebrand equation:
ꢁ
ꢂꢁ
ꢂ
1
ꢀF
1
ꢀFmax
1
1
ꢀFmax
=
+
(2)
Ka [CD]n
where ꢀF = Fx − Fo; Fx and Fo represent the fluorescence intensities of galangin in the
presence and absence of total added CDs concentration respectively. ꢀFmax is the maximum
change in fluorescence intensity, Ka is the binding constant for the galangin-cyclodextrin
complex, and n represents the stoichiometry of the complex formed. A typical double recip-
rocal plot for n = 1 is shown in Fig. 1 for galangin complexed with βCD, DMβCD and
HPβCD. For the three cyclodextrins the n = 1 plots exhibit good linearity whereas the

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J Solution Chem (2010) 39: 1168–1177
Fig. 1 Double reciprocal plots for galangin complexed with 2 βCD, Q HPβCD and " DMβCD for 1:1
binding stoichiometries
n = 2 plots (data not shown) deviate from linearity. From these results we can infer that
galangin forms 1:1 inclusion complexes with both substituted cyclodextrins and the native
cyclodextrin, which is in agreement with our previous work [20].
The binding constant Ka of the complexes with this methodology at 303 K are 748, 2455
and 2273 L·mol−1 for βCD, HPβCD and DMβCD, respectively. This apparent binding con-
stant was determined in an aqueous medium containing 10% methanol, which was needed to
improve ‘aqueous’ solubility of galangin in the CD-free medium. The Ka values calculated
by this spectroscopic method were found to be less than those obtained by the solubility
method [20–22], due to the fact that for this spectroscopic experiment we needed to dissolve
galangin in an organo-aquous medium to solubilize the flavonoid completely. Methanol was
the solvent of choice due to its low affinity for binding with CD [23]
The stability constant of the complexes of galangin with the three CDs at different tem-
perature (298, 303 and 308 K) are shown in Table 1. We note, that the stability constant for
GAL-HPβCD and GAL-DMβCD complexes decrease with increasing temperature as ex-
pected for an exothermic process, which indicates that the complexation process was favor-
able at lower temperature. As the temperature increased, the affinity between galangin and
HPβCD or DMβCD decreased. However, for GAL-βCD, the stability constant increases as
the temperature rises.
Thermodynamic parameters were calculated based on the temperature dependence of
the binding constant for galangin-CD binding. The thermodynamic parameters such as the
enthalpy changes (ꢀH) and entropy changes (ꢀS) of the binding reaction are important to
confirm the force of interactions of galangin with cyclodextrins. Four driving forces for the
inclusion of CDs with substrates were proposed, including: hydrogen bonding between the
hydroxyl groups of CDs and the guest, van der Waals interactions between host and guest
molecules, hydrophobic interaction, and the release of ‘high-energy water’ molecules from
the cavities of CDs to the bulk water. Hydrophobic interaction essentially involves favorable

J Solution Chem (2010) 39: 1168–1177
1173
Table 1 Apparent stability constant (K ), thermodynamic parameters and antioxidant capacity (T ) of
a
eq
galangin forming complexes with cyclodextrin
K /
a
K /
a
K /
a
ꢀH/
ꢀS/
ꢀG/
T
eq
−1
−1
−1
−1
−1 −1
−1
L·mol
L·mol
L·mol
kJ·mol
kJ·mol ·K
kJ·mol
T/K
298
303
308
GAL
4.57 0.37
4.60 0.34
3.40 0.58
3.11 0.26
GAL-βCD
589
748
2273
2455
893
1990
2111
31.78
−21.85
−22.03
0.160
−0.008
−0.008
−15.9
GAL-DMβCD 2650
GAL-HPβCD 2818
−19.47
−19.64
Fig. 2 Van’t Hoff plot (lnK
versus 1/T ) for
a
galangin-cyclodextrin association
positive entropy together with a slightly positive enthalpy change, whereas the other forces
involve negative ꢀH and ꢀS [24].
If the enthalpy change (ꢀH) does not vary significantly over the temperature range stud-
ied, then its value as well as that of the entropy change (ꢀS) can be determined from the
van’t Hoff equation:
ꢀH
RT
ꢀS
R
lnKa = −
+
(3)
where Ka is the associative binding constants corresponding to various temperatures, and R
is the gas constant (8.314 J·K−1·mol−1). The enthalpy change (ꢀH) can be calculated from
the slope of the van’t Hoff relationship and the Gibbs energy change (ꢀG) can be estimated:
ꢀG = ꢀH − T ꢀS.
(4)
A plot of lnKa versus 1/T for the three complexes formed were linear with correlation
coefficients R ≥ 0.996, Fig. 2. These thermodynamic parameters are listed in Table 1. By
careful inspection, the following conclusions can be obtained: the negative value for the
Gibbs energy (ꢀG) means that the binding process is a spontaneous process and thermody-
namically favored. ꢀH and ꢀS for GAL-HPβCD and GAL-DMβCD are negative in the
experimental temperature range, which indicates that the inclusion process was exothermic

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J Solution Chem (2010) 39: 1168–1177
Fig. 3 FL fluorescence decay curves induced by AAPH in the presence of galangin at different con-
−1
−1
−1
−1
centrations. 2 blank,
−1
0.13 µmol·L
,
0.27 µmol·L
,
0.40 µmol·L
,
0.54 µmol·L
,
0.67 µmol·L . Insets: net AUC of galangin on different concentration of galangin. The net
AUC = AUC
− AUC
; the AUC was calculated by Eq. 1
blank
sample
and an enthalpically controlled process. The negative enthalpy change arose from the van
der Waal’s interaction; while the negative entropy change can be explained considering that
the complex causes a decrease in translational and rotational degrees of freedom of the com-
plex molecule as compared with the free ones, giving a more ordered system. A different
behavior was observed for the GAL-βCD complex, where upon complexation both positive
enthalpic changes and positive entropic values are obtained, indicating that this inclusion is
mainly entropically driven. Apparently, when galangin is free in solution, it seems to have a
strong interaction with its solvent shell. Upon binding, this solvent shell is broken up, lead-
ing to the partly unfavorable enthalpic change. The same effect was observed [14] in the
complexation of morin with native and modified cyclodextrins; complexed with DMβCD
the inclusion is primarily enthalpically driven, while with βCD and HPβCD is an entropic
driven process. No reason for these differences was found.
The ORACFL assay expresses antioxidant activity relative to a standard (trolox) while
measuring the oxidation of the fluorescent substrate by peroxy radicals generated during the
reaction. This method follows a hydrogen atom transfer pathway, where the antioxidant and
a peroxy radical form a stable antioxidant radical that breaks the radical chain oxidation.
In order to discern any antioxidant effect of cyclodextrins per se, the disappearance of flu-
orescence signal of FL by the attack of the AAPH radical were measured in the presence
of increasing concentrations of CDs (in the absence of galangin or trolox). In this case, no
effect was observed as the CDs concentration increased indicating that CDs, at the studied
concentrations, do not have an antioxidant effect per se. Figure 3 shows the FL fluorescence
decay curves of galangin in the presence of AAPH. The linear relationship between the net
area and antioxidant concentration was calculated at different concentrations. The regres-

J Solution Chem (2010) 39: 1168–1177
1175
Fig. 4 Relative host-guest geometry corresponding to the minimum of the energy of the formation of
(A) GAL-βCD complex (B) GAL-DMβCD complex and (C) GAL-HPβCD complex
sion analysis points to a linear response between the galangin concentration and the net AUC
(R = 0.998). Table 1 reports the Trolox equivalent, Teq for free galangin and galangin inclu-
sion complexes with the different cyclodextrins referenced to Trolox. Practically no change
in the antioxidant activity is observed when galangin complexes with β-cyclodextrin. The
low Teq values obtained for GAL-HPβCD and GAL-DMβCD in comparison with GAL free
and complexed with βCD can be explained by the phenol group responsible for quenching
peroxyl radicals penetrating into the less polar CD cavity where there may be a modification
in the redox behavior of the phenol group or an effective protection of the phenol group due
to the complexation. Besides increasing the solubility of flavonoids, cyclodextrins may also
have an effect on their antioxidant activity. Moreover we have determined that the inclusion
geometry influences the antioxidant capacity. Our result indicated that for morin complexes
[14] the antioxidant activity increased due to the stabilization of the radical inside the apo-
lar cavity. However, for luteolin complexes [25] the antioxidant activity is maintained. This
must be taken into account when the antioxidant activity is determined by ORACFL utilizing
CD as an solubility enhancer for lipophilic compounds [26, 27]
To know more about the inclusion geometry of galangin complexes, molecular mod-
elling and docking studies were carried for the three complexes out. Autodock3.0.5 results
revealed a preferential relative orientation for all the complexes under study, in spite of their
different initial configurations. The better scored complexes obtained for βCD, DMβCD
and HPβCD are shown in Figs. 4A–C. All these complexes were further refined using a
semiempirical methodology such as PM3. The same trends in the inclusion geometries ob-
served by 2D-NMR [20] are noticeable here, where the inclusion in DMβCD and HPβCD
occurs in an opposite way. In the case of the GAL-βCD complex, the conformation ob-
tained has the B-ring of galangin oriented toward the primary rim, while both A and C rings
remain practically exposed to the external surface by the secondary rim. The theoretical re-
sults obtained for the GAL-DMβCD complex indicated that inclusion occurs in a similar
fashion to the GAL-βCD complex. In the latter, both the A- and C-rings are almost com-
pletely inserted in the interior of the DMβCD, with the OH-5 and OH-7 groups more buried
than in the GAL-βCD complex. In the case of the GAL-HPβCD complex, the results in-
dicated that the B-ring of galangin is oriented to the secondary rim, resulting in a complex
where galangin is located in the opposite direction compared to the previous complexes. Fig-
ures 4B and C show clearly that the OH-5 and OH-7 groups of galangin in GAL-HPβCD
and GAL-DMβCD remain protected. They are occupying the hydrophobic cavity of the
CD, a situation that does not occur in the βCD. These results could account for the observed

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J Solution Chem (2010) 39: 1168–1177
diminution of the antioxidant activity of these complexes in comparison with free galangin
and GAL-βCD.
4 Conclusions
The association constant and thermodynamic parameters for the inclusion complex were
evaluated by fluorescence spectroscopy. The formation constants obtained follow the same
trend under the three temperatures studied, in the order: HPβCD > DMβCD > βCD. Ther-
modynamic studies of cyclodextrin complexes indicated that for DMβCD and HPβCD in-
clusion is mainly an enthalpy driven process while for βCD it is an entropy driven process.
No changes in the antioxidant activity were observed when galangin forms the complex
with βCD. However, a diminution in antioxidant activity was observed upon complexation
with DMβCD and HPβCD. Molecular modelling studies showed that this behavior could
be explained by the GAL-βCD complex having the A and C rings of galangin exposed
to the external surface, while in the GAL-DMβCD and GAL-HPβCD complexes, the OH
groups of the chromone (OH-5 and OH-7), which are responsible for the quenching of the
peroxyl radicals, are protected and this could explain the diminution of antioxidant activity.
Finally, the study of the inclusion geometry is necessary to explain the changes produced in
antioxidant activity involving the complexes formed.
Acknowledgements Our thanks are to Fondecyt 11080038 and to Molecular Graphic Unit of the Faculty
of Chemical and Pharmaceutical Sciences, University of Chile.
References
1. Hollman, P.C., Katan, M.B.: Absorption, metabolism and health effects of dietary flavonoids in man.
Biomed. Pharmacother. 51, 305–310 (1997)
2. Stavric, B.: Antimutagens and anticarcinogens in foods. Food Chem. Toxicol. 32, 79–90 (1994)
3. Kochhar, S.P.: Deterioration of edible oils, fats and foodstuffs. In: Scott, G. (ed.): Atmospheric Oxidation
and Antioxidants, pp. 71–139. Elsevier Science, Amsterdam (1993)
4. Hertog, M.G.L., Feskens, E.J.M., Kromhout, D.: Antioxidant flavonols and coronary heart disease risk.
Lancet 349, 699–699 (1997)
5. Heo, M.Y., Lee, J.H., Sohn, S.J., Au, W.W.: Anticlastogenic effects of galangin against mitomycin C-
induced micronuclei in reticulocytes of mice. Mutat. Res. 360, 37–41 (1996)
6. Wall, M.E., Wani, M.C., Manikumar, G., Abraham, P., Taylor, H., Hughes, T.J., Warner, J., McGiveney,
R.: Plant antimutagenic agents. 2. Flavonoids. J. Nat. Prod. 51, 1084–1091 (1988)
7. Cholbi, M.R., Paya, M., Alcaraz, M.J.: Inhibitory effects of phenolic compounds on CCl4-induced mi-
crosomal lipid peroxidation. Experientia 47, 195–199 (1991)
8. Imamura, Y., Migita, T., Uriu, Y., Otagiri, M., Okawara, T.: Inhibitory effects of flavonoids on rabbit
heart carbonyl reductase. J. Biochem. 127, 653658 (2000)
9. Shih, H., Pickwell, G.V., Quattrochi, L.C.: Differential effects of flavonoid compounds on tumor
promoter-induced activation of the human CYP1A2 enhancer. Arch. Biochem. Biophys. 373, 287–294
(2000)
10. Szejtli, J.: Cyclodextrin Technology. Kluwer Academic, Dordrecht (1988)
11. Buschmann, H.J., Schollmayer, E.: Application of cyclodextrins in cosmetic products: a review. J. Cos-
met. Sci. 53, 185–191 (2002)
12. Loftsson, T., Brewster, M.E.: Pharmaceutical application of cyclodextrins: drug solubilisation and stabi-
lization. J. Pharm. Sci. 85, 1017–1025 (1996)
13. Alvarez-Parrilla, E., De la Rosa, L.A., Torres-Rivas, F., Rodrigo-Garcia, J., Gonzalez-Aguilar, G.A.:
Complexation of apple antioxidants: chlorogenic acid, quercetin and rutin by β-cyclodextrin (β-CD).
J. Incl. Phenom. Macrocycl. Chem. 53, 121–129 (2005)
14. Jullian, C., Orosteguis, T., Pérez-Cruz, F., Sánchez, P., Mendizabal, F., Olea-Azar, C.: Spectrochim. Acta
A 71, 269–275 (2008)

J Solution Chem (2010) 39: 1168–1177
1177
15. Ficarra, R., Tommasini, S., Raneri, D., Calabrò, M.L., Di Bella, M.R., Rustichelli, C., Gamberini, M.C.,
Ficarra, P.: Study of flavonoids/β-cyclodextrins inclusion complexes by NMR, FT-IR, DSC, X-ray in-
vestigation. J. Pharm. Biomed. Anal. 29, 1005–1014 (2002)
16. Ou, B., Hampsch-Woodill, M., Prior, R.L.: Development and validation of an improved oxygen radical
absorbance capacity assay using fluorescein as the fluorescent probe. J. Agric. Food Chem. 49, 4619–
4626 (2001)
17. Dávalos, A., Gómez-Cordovés, C., Bartolomé, B.: Extending applicability of the oxygen radical ab-
sorbance capacity (ORACFluorescein) assay. J. Agric. Food Chem. 52, 48–54 (2004)
18. Frisch, M.J., Trucks, G.W., Schlegel, H.B., Scuseria, G.E., Robb, M.A., Cheeseman, J.R., Zakrzewski,
V.G., Montgomery, J.A., Stratmann, R.E., Burant, J.C., Dapprich, S., Millam, J.M., Daniels, A.D., Kudin,
K.N., Strain, M.C., Farkas, O., Tomasi, J., Barone, V., Cossi, M., Cammi, R., Mennucci, B., Pomelli, C.,
Adamo, C., Cliford, S., Ochterski, J., Petersson, G.A., Ayala, P.Y., Cui, Q., Morokuma, K., Malick,
D.K., Rabuck, A.D., Raghavachari, K., Foresman, J.B., Cioslowski, J., Ortiz, J.V., Stefanov, B.B., Liu,
G., Liashenko, A., Piskorz, P., Komaromi, I., Gomperts, R., Martin, R.L., Fox, D.J., Keith, T., Al-Laham,
M.A., Peng, C.Y., Nanayakkara, A., Gonzalez, C., Challacombe, M., Gill, P.M.W., Johnson, B.G., Chen,
W., Wong, M.W., Andres, J.L., Head-Gordon, M., Replogle, E.S., Pople, J.A.: Gaussian 98 (revision a.7)
(1998)
19. Morris, G.M., Goodsell, D.S., Halliday, R.S., Huey, R., Hart, W.E., Belew, R.K., Olson, A.J.: Automated
docking using a Lamarckian genetic algorithm and an empirical binding free energy function. J. Comput.
Chem. 19, 1639–1662 (1998)
20. Jullian, C.: Improvement of galangin solubility using native and derivative cyclodextrins. An UV-vis and
NMR study. J. Chil. Chem. Soc. 54, 201–203 (2009)
21. Bergonzi, M.C., Bilia, A.R., Di Bar, L., Mazzi, G., Vincieri, F.F.: Studies on the interactions between
some flavonols and cyclodextrins. Bioorg. Med. Chem. Lett. 17, 5744–5748 (2007)
22. Kim, H., Choi, J., Jung, S.J.: Inclusion complexes of modified cyclodextrins with some flavonols. J. Incl.
Phenom. Macrocycl. Chem. 64, 43–47 (2009)
23. Mounoz de la Pena, A., Ndou, T.T., Zung, J.B., Greene, K.L., Live, D.H., Warner, I.M.: Alcohol size
as a factor in the ternary complexes formed with pyrene and beta-cyclodextrin. J. Am. Chem. Soc. 113,
1572–1577 (1991)
24. Zhang, Q., Jiang, Z., Guo, Y., Li, R.: Complexation study of brilliant cresyl blue with β-cyclodextrin
and its derivatives by UV-vis and fluorospectrometry. Spectrochim. Acta A 69, 65–70 (2008)
25. Jullian, C., Cifuentes, C., Alfaro, M., Miranda, S., Barriga, G., Olea-Azar, C.: Spectroscopic character-
ization of the inclusion complexes of luteolin with native and derivatized β-cyclodextrin. Bioorg. Med.
Chem. 14, 5025–5031 (2010)
26. Huang, D., Ou, B., Hampsch-Woodill, M., Flanagan, J.A., Deemer, E.K.: Development and validation
of oxygen radical absorbance capacity assay for lipophilic antioxidants using randomly methylated β-
cyclodextrin as the solubility enhancer. J. Agric. Food Chem. 50, 1815–1821 (2002)
27. Wu, X., Gu, L., Holden, J., Haytowitz, D.B., Gebhardt, S.E., Beecher, G., Prior, R.L.: Development of a
data base for total antioxidant capacity in foods: a preliminary study. J. Food Compos. Anal. 17, 407–422
(2004)