Investigation on the inclusion behaviour of baicalein with β-cyclodextrin and derivatives and their antioxidant ability study

Article abstract of DOI:10.1080/10610278.2011.593630

The formation of the complexes of baicalein (Ba) with β-cyclodextrin (β-CD) and β-CD derivatives (HP-β-CD and Me-β- CD) was studied by UV-vis absorption spectroscopy, fluorescence method, nuclear magnetic resonance spectroscopy and phase-solubility measurement. The solid-inclusion complexes of Ba with CDs were synthesised by the co-precipitation method. The characterisations of the solid-inclusion complexes have been proved by infrared spectra and differential scanning calorimetry. Experimental conditions including the concentration of various CDs and media acidity were investigated in detail. The results suggested that the inclusion ratio of HP-β-CD with Ba was the highest among the three kinds of CDs. The binding constants (Ks) of the inclusion complexes were determined by fluorescence method and phasesolubility measurement. Kinetic studies of DPPHz with Ba and CDs complexes were also done. The results indicated that the Ba/HP-β-CD complex was the most reactive form.

Full text of DOI:10.1080/10610278.2011.593630

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Investigation on the inclusion behaviour of baicalein
with β-cyclodextrin and derivatives and their
antioxidant ability study
Jianbin Chao a , Jian Su a , Jinxia Li a , Wei Zhao a , Shuping Huang a & Rui Du b
a The Institute of Applied Chemistry of Shanxi University , Taiyuan , 030006 , China
b Department of Engineering , Shanxi Coal Mining Administrators College , Taiyuan , 030006 ,
China
Published online: 25 Jul 2011.
To cite this article: Jianbin Chao , Jian Su , Jinxia Li , Wei Zhao , Shuping Huang & Rui Du (2011) Investigation on the
inclusion behaviour of baicalein with β-cyclodextrin and derivatives and their antioxidant ability study, Supramolecular
Chemistry, 23:9, 641-649, DOI: 10.1080/10610278.2011.593630
To link to this article: http://dx.doi.org/10.1080/10610278.2011.593630
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Supramolecular Chemistry
Vol. 23, No. 9, September 2011, 641–649
Investigation on the inclusion behaviour of baicalein with b-cyclodextrin and derivatives and
their antioxidant ability study
Jianbin Chaoa*, Jian Sua, Jinxia Lia, Wei Zhaoa, Shuping Huanga and Rui Dub
b
aThe Institute of Applied Chemistry of Shanxi University, Taiyuan 030006, China; Department of Engineering, Shanxi Coal Mining
Administrators College, Taiyuan 030006, China
(Received 14 January 2011; final version received 9 May 2011)
The formation of the complexes of baicalein (Ba) with b-cyclodextrin (b-CD) and b-CD derivatives (HP-b-CD and Me-b-
CD) was studied by UV–vis absorption spectroscopy, fluorescence method, nuclear magnetic resonance spectroscopy and
phase-solubility measurement. The solid–inclusion complexes of Ba with CDs were synthesised by the co-precipitation
method. The characterisations of the solid–inclusion complexes have been proved by infrared spectra and differential
scanning calorimetry. Experimental conditions including the concentration of various CDs and media acidity were
investigated in detail. The results suggested that the inclusion ratio of HP-b-CD with Ba was the highest among the three
kinds of CDs. The binding constants (Ks) of the inclusion complexes were determined by fluorescence method and phase-
solubility measurement. Kinetic studies of DPPHz with Ba and CDs complexes were also done. The results indicated that the
Ba/HP-b-CD complex was the most reactive form.
Keywords: cyclodextrins; baicalein; inclusion complex
1. Introduction
water solubility (13–15). However, parent CDs have
relatively low solubility and molecular binding abilities,
which limit their further use. On this basis, modification of
CDs is one of the ‘hot’ topics in recent host–guest
supramolecular chemistry, and CD derivatives have been
successfully utilised to extend the natural CD (16, 17).
Hydroxypropyl-beta-cyclodextrin (HP-b-CD), which is a
water-soluble derivative of b-CD, and methyl-beta-cyclo-
dextrin (Me-b-CD), which is no harm to human, were
selected as other two host molecules.
Herbal medicines have a long history in medical practice
and health care, especially in a number of Asian and African
countries. Now, herbal medicines have expanded globally
and gained considerable attention because of low toxicity
and good therapeutical performance. Scutellaria baicalen-
sis Georgi is one commonly used herbal medicine in China
and other East Asian countries. Baicalein (Ba, Figure 1) is
one of the main active components, which has a variety of
interesting activities such as antibacterial (1), anti-HIV
activity (2), attenuating oxidative stress (3–5), inhibiting
the growth of several types of cells (6–8) and inducing cell
death in human hepatocellular carcinoma cell (9) and in
human promyelocytic leukaemia HL-60 cells (10).
However, one disadvantage of this compound is its
low-water solubility, leading to limited use in pharmaceu-
tical field.
The inclusion of Ba with biomacromolecule, for
example, DNA (18) has been researched by many groups,
but the inclusion of Ba with CDs has not been investigated.
As such, this paper has definite guidance purport in clinic
pharmaceutics. In this study, not only the inclusion process
was characterised by fluorescence and NMR, but also the
solubility was improved and the effect of the complexation
process on their antioxidant capacity was determined. A new
theory based on new drug carrier system is demonstrated.
Cyclodextrins (CDs) are polysaccharides made of six to
eight D-glucose monomers connected at one and four carbon
atoms. They have the property of forming inclusion complex
with various guests’ molecules with suitable polarity and
dimension because of their special molecular structure –
hydrophobic internal cavity and hydrophilic external
surface. They have been widely used in pharmaceutical
industries, in analytical purposes and as models for protein
and enzymes (11, 12). Formation of the inclusion complex
can increase the guest’s stability against hydrolyses,
oxidation, photodecomposition and dehydration, and the
2. Experimental section
2.1 Apparatus and materials
The absorption and fluorescence measurements were
performed with a UV-757CRT spectrophotometer
(Shanghai Precision & Scientific Instrument Co., Ltd,
Shanghai, China) and a F-2500 FL spectrofluorometer
(Hitachi, Tokyo, Japan), respectively. Both excitation and
emission bandwidths were at 20 nm obtained with Bruker
*Corresponding author. Email: chao@sxu.edu.cn
ISSN 1061-0278 print/ISSN 1029-0478 online
q 2011 Taylor & Francis
http://dx.doi.org/10.1080/10610278.2011.593630
http://www.tandfonline.com

642
J. Chao et al.
3'
B
A
1600
1400
1200
1000
800
2'
4'
7
1
8
1
HO
HO
O
5'
2
1'
7
6'
A
C
3
6
600
5
4
400
O
OH
Baicalein
200
320
340
360
380
400
420
Wavelength (nm)
Figure 1. The chemical structure of Ba.
B
Avance DRX 300 MHz superconducting NMR spec-
trometer, and D2O was used as the solvent. Infrared (IR)
spectra were obtained with PerkinElmer FT-1730 IR
spectroscopy using KBr pelleting. The range of spectra
was from 400 to 4000 cm21. Differential scanning
calorimetry (DSC) analyses were carried out in the
temperature range from 30 to 5008C in a stream of nitrogen
atmosphere on DSC-60 thermal analyzer (Shimadzu,
Japan). During experiments, aluminium crucibles were
used. The weight of the sample was 5 mg. The heating rate
was 108C/min, and the flow rate of nitrogen atmosphere
was 20 ml/min.
1600
1400
1200
1000
800
7
1
600
400
200
350
400
450
The stock solution of 1.0 £ 1024 mol/l Ba (purchases
from Nanjing Tcm Institute of Chinese Materia Medica,
Nanjing, China; .99%) was prepared by dissolving and
dilutingitscrystalsinwater.ThestockconcentrationsofCDs
were 1.0 £ 1022 mol/l. Phosphate-buffered saline (PBS;
0.2 mol/l)was usedtocontrol the pHvalue ofthe media. CDs
and 2,2-diphenyl-1-picrylhydrazyl (DPPH) were purchased
from Sigma-Aldrich, Inc. (St Louis, MO, USA). All other
reagents were of analytical-reagent grade and were used
without purification. Double distilled water was used
Wavelength (nm)
C
1200
1000
800
5
1
600
400
200
0.30
7
0.28
0.26
320
340
360
380
400
420
440
Wavelength (nm)
0.24
1
Figure 3. Fluorescence emission spectra of 1.0 £ 1025 mol/l Ba
in three kinds of CDs solution. (A) b-CD; (B) HP-b-CD and
0.22
0.20
0.18
0.16
0.14
0.12
0.10
0.08
(C) Me-b-CD. CD concentration (M): 0–6.0 £ 1023
.
throughout. All experiments were carried out at room
temperature.
250
300
350
400
2.2 Procedure
Wavelength (nm)
A 1 ml aliquot of the stock solution (1.0 £ 1024 mol/l) of
Ba was transferred into a 10 ml volumetric cuvette, and an
appropriate amount of 1.0 £ 1022 mol/l CDs (b-CD, HP-b-
CD and Me-b-CD) was added. The pH was controlled by
Figure 2. The absorption spectra of 1.0 £ 1025 mol/l Ba in
the presence of b-CD. The concentration of b-CD (M):
0–6.0 £ 1023
.

Supramolecular Chemistry
643
A
0.016
0.014
0.012
0.01
0.40
0.38
0.36
0.34
0.32
0.30
0.28
0.26
0.24
0.22
0.20
0.18
0.16
0.14
7
1
F
0.008
0.006
0.004
0.002
0
F
0.12
0.10
0.08
0
200
400
600
800
1000
1200
1/CCD (L/mol)
250
300
350
400
Wavelength (nm)
Figure 4. Double reciprocal plots of Ba complexes to b-CD or
HP-b-CD or Me-b-CD. (V) b-CD; (B) HP-b-CD and (O) Me-b-
CD.
B
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
8
1
Table 1. Apparent stability constants (Ks) of Ba inclusion.
CDs complex
Linear equation
Ks (M21
)
r 2
b-CD
HP-b-CD
Me-b-CD
y ¼ 1E-05x þ 0.0005
y ¼ 2E-06x þ 0.0023
y ¼ 5E-06x þ 0.0023
50
1150
460
0.9974
0.9981
0.9949
0.2 M PBS. The mixed solution was diluted to the final
volume with distilled water and ultrasonically handled for
30 min, and then equilibrated for 30 min at room
temperature. Excitation bandwidth was obtained at
270 nm, and fluorescence emission was obtained at about
360 nm. All measurements of absorption and fluorescence
were made against a blank solution treated in the same way
but without a CD in a 1.0 cm quartz cell.
250
300
350
400
Wavelength (nm)
0.65
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
C
5
1
2.3 NMR measurements
All the concentrations of Ba and CDs solution were
1.0 £ 1024 mol/l, and Ba solution is diluted with CDs
solutions, respectively, at the volume ratio of 1:1. 1H NMR
of Ba solution as well as its inclusion complexes solutions
was also performed to get further evidence.
250
300
330
Wavelength (nm)
Figure 5. Absorption of 1.0 £ 1025 mol/l Ba at different pH
values in HP-b-CD. The pH is (A) 3.1; (B) 6.5 and (C) 8.9.
2.4 Phase-solubility study
Solubility measurements were based on the phase-
solubility technique (19). For example, an excess amount
of solid Ba (6 mg) was added to a series of 10 ml stopper
volumetric cuvette that contained an increasing amount of
CDs (1.0 £ 1022 mol/l, 0–9 ml, including b-CD and
HP-b-CD). These obtained suspensions were shaken by
ultrasonic method for 3 h at room temperature, and then
filtered after being placed for 7 days. This filtrate was
diluted and analysed through UV method. Phase-solubility
profile was obtained by plotting the solubility of Ba versus
the concentration of CDs.
The apparent stability constant (K) of the complexes
was calculated according to the following equation:
slope
K ¼
;
ð1Þ
S0ð1 2 slopeÞ
where S0 is the solubility of Ba at room temperature in the
absence of CDs and slope means the corresponding slope
of the phase-solubility diagrams.

644
J. Chao et al.
A
4
3.5
3
1400
5
1
1200
1000
800
2.5
2
1.5
1
0.5
0
600
0
2
4
6
8
10
–0.5
C
CDs (10–4 mol/L)
400
Figure 7. Phase-solubility diagram of Ba and CDs. (B) b-CD
and (V) HP-b-CD.
200
350
400
450
500
Table 3. Apparent stability constants (Ks) of Ba inclusion.
Wavelength (nm)
CDs complex
Linear equation
Ks (M 21
)
r 2
B
b-CD
HP-b-CD
Me-b-CD
y ¼ 0.1362x þ 0.1941
y ¼ 0.3784x 2 0.0183
y ¼ 0.2331x þ 0.2291
500.29
5247.86
613.79
0.9962
0.9914
0.9914
800
700
600
500
400
300
200
100
8
1
350
400
450
500
Wavelength (nm)
C
1000
900
800
700
600
500
400
300
200
100
5
1
Figure 8. 1H NMR spectra of Ba (d), and Ba complexed with
Me-b-CD (a), HP-b-CD (b), and b-CD (c).
2.5 Determination of antioxidant activity by the
scavenging of the stable radical DPPHz
The antioxidant activity was measured, wherein the
bleaching rate of a stable free radical, DPPHz is monitored
at a characteristic wavelength in the presence of the
sample. In its radical form, DPPHz absorbs at 517–520 nm,
but upon reduction by an antioxidant or a radical species
its absorption decreases.
350
400
450
500
Wavelength (nm)
Figure 6. Fluorescence emission spectra of 1.0 £ 1025 mol/l Ba
at different pH values in b-CD. The pH is (A) 3.1, (B) 6.5 and
(C) 8.9.
A volume of 2 ml of 1.0 £ 1025 M DPPHz was used.
Furthermore, DPPHz is insoluble in aqueous solution, and
the scavenging study was performed in a mixture of
ethanol–water (20:80).
Table 2. The binding constants (Ks) at different pH value
solutions.
PH
The reaction was started by the addition of 1 ml of Ba
(1.0 £ 1025 M), Ba/b-CD and Ba/HP-b-CD complex
samples, which correspond to the 3 mM CD concentration
from the phase-solubility studies. The bleaching of DPPHz
was followed at 520 nm.
CD
Ks
50
1150
460
3.1
6.5
8.9
b-CD
HP-b-CD
Me-b-CD
312
1150
300
132
900
100
344
–
200

Supramolecular Chemistry
645
Table 4. 1H NMR chemical shifts corresponding to Ba in the absence and presence of CDs in D2O.
dfree (ppm)
dcomplexed (ppm)
H-b-CD
ed (dcomplexed 2 dfree) (ppm)
Ba
b-CD
Me-b-CD
b-CD
H-b-CD
Me-b-CD
8-H
3-H
304050-H
2060-H
6.613
6.671
7.454
7.905
6.597
6.654
7.501
7.828
6.641
6.763
7.481
7.823
6.572
6.675
7.517
7.766
0.034
0.017
20.047
0.077
20.028
20.092
20.027
0.082
0.041
20.004
20.063
0.139
Table 5. 1H NMR chemical shifts CDs and the inclusion complexes in D2O.
dfree (ppm)
H-b-CD
dcomplexed (ppm)/Ba
ed (dcomplexed 2 dfree) (ppm)
b-CD
Me-b-CD
b-CD
H-b-CD
Me-b-CD
b-CD
H-b-CD
Me-b-CD
3-H
5-H
6-H
3.817
3.727
3.727
3.858
3.720
3.607
3.702
3.502
3.502
3.814
3.727
3.696
3.857
3.707
3.586
3.695
3.490
3.472
0.003
0.000
0.031
0.001
0.013
0.021
0.007
0.012
0.030
The decrease in absorbance at 520 nm was measured
a 50 ml beaker and 10 ml of distilled water was added and
electromagnetically stirred until it was dissolved. Then
CDs solution was poured slowly into stirred Ba solution,
which was continuously stirred for 12 h at room
temperature. The reaction mixture was put into refrigerator
for 24 h. Precipitate was filtrated by G4 sand filtering
funnel and washed with distilled water. After drying in an
oven at 608C, white powdered products were obtained.
This is inclusion complex of Ba with CDs.
against a blank of ethanol–water (20:80) with 1 and 2 ml
1.0 £ 1025 M DPPHz to estimate the radical scavenging
capacity of each antioxidant sample. The results were
expressed as percentage DPPHz elimination calculated
according to the following equation (20):
ꢀ
ꢁ
As
A0
AU ¼ 1 2
£ 100;
ð2Þ
where AU is the radical scavenging activity, As is the
absorbance of sample and A0 is the absorbance of the blank
sample.
3. Results and discussion
3.1 UV spectroscopy
The putative formation of complex of Ba with b-CD in
aqueous solution was characterised by UV spectroscopy.
Figure 2 shows the absorption spectra of Ba in the absence
and presence of b-CD. The absorption peaks of Ba itself
were 272 and 319 nm. With an increasing concentration of
b-CD from 1 to 6 mmol/l, an increasing absorption that
depended on the concentration of b-CD was observed.
Simultaneously, with an increasing concentration of b-CD,
weak blue shift appeared in the absorption wavelength of
272 nm and a line was formed in the absorption wavelength
of 319 nm. These changes might be partly attributed to the
shielding of chromophore groups in Ba molecule due to the
complex formation between Ba and b-CD through
hydrophobic interaction. The nuclear energy is counter-
acted partially because of the repellency between the
electrons. So, these changes might be partly attributed to
the shielding of chromophore groups in Ba molecule due to
the complex formation between Ba and b-CD through
hydrophobic interaction. Similar phenomena were
observed for the other two CDs. The absorption peaks of
the inclusion of Me-b-CD were 260 and 359 nm, whereas
the absorption peaks of the inclusion of HP-b-CD were the
same as that of b-CD. All of these suggested that the
inclusion complexes were formed between Ba and CDs.
2.6 Preparation of solid complexes of Ba with CDs
Accurately, weighed 0.0567 g b-CD or 0.069 g HP-b-CD
was placed into a 50 ml conical flask and 10 ml of distilled
water was added, stirred, then 0.0135 g Ba was added into
4.8
4.6
4.4
4.2
4.0
3.8
3.6
3.4
3.2 ppm
Figure 9. 1H NMR spectra of b-CD and Ba/b-CD inclusion
complex from the bottom to the top.

646
J. Chao et al.
for Ba molecule, which increases the quantum yield of the
fluorescence of Ba.
A
3′
6′
The formation constant (K) and the ratio of the
complex were calculated from these data by using the
modified Benesi–Hildebrand equation (21)
2′
4′
1
8
HO
HO
2
O
5′
1′
7
1
1
1
¼
þ
;
ð3Þ
F 2 F0 ½CDsꢀKa
a
3
6
5
4
where F and F0 represent the fluorescence intensity of Ba
in the presence and absence of CDs, respectively, K is a
forming constant and a is a constant. Figure 4 shows the
double reciprocal plots of 1/(F 2 F0) versus 1/[CD]. They
exhibit good linearity. These implied that the inclusion
complexes have a stoichiometry of 1:1. The values of K are
shown in Table 1. As such, the inclusion ability was HP-b-
CD . Me-b-CD . b-CD.
OH
O
3′
B
2′
4′
1
8
HO
HO
O
2
5′
1′
7
6′
3
3.3 Influence of pH
6
5
4
Figure 5 shows the effect of pH on the absorption spectra of
Ba in the presence of HP-b-CD. At pH 3.1, the absorption
peaks were kept at constant and compared with that without
any PBS, while at pH 6.5 and pH 8.9, the absorption peaks
of 272 and 319 nm formed different shifts, respectively. At
the same time, adding CDs to Ba solution resulted in
noticeable increase in absorption signals.
O
OH
Figure 10. The structure of inclusion complexes between Ba
and CDs. (A) Ba/b-CD and (B) Ba/HP-b-CD.
80.0%
70.0%
60.0%
50.0%
40.0%
30.0%
20.0%
10.0%
0.0%
Figure 6 shows the effect of pH on the fluorescence
spectra on Ba in the presence of b-CD. The excitation
wavelengths were 270 nm. At pH 3.1 and pH 6.5, the
emission wavelengths were the same as that without any
PBS, whereas at pH 8.9, the emission wavelength shifted
to lower wavelength at 355 nm. Simultaneously, the
increasing concentration of CDs resulted in the enhance-
ment of fluorescence signals. The ability of inclusion in
different pH values is shown in Table 2.
3.4 Phase-solubility measurements
Ba
In Figure 7, it can be seen that CDs enhanced the
poor aqueous solubility of Ba, thus proving a certain degree
of its inclusion complexation in aqueous solutions.
The results observed showed a linear behaviour for b-CD
(r 2 ¼ 0.9962) and HP-b-CD (r 2 ¼ 0.9914), and consistent
with 1:1 molecular complex formation for CDs and Ba.
The binding constant (K) of the complexes is shown in
Table 3. As shown in Table 3, the binding constant and
solubility of Ba determined with CDs followed the rank
order HP-b-CD . b-CD. The results were the same as that
of fluorescence results.
Ba/β-Ba Ba/Hp-β-Ba Ba/Me-β-Ba
Figure 11. Consumption percentage of DPPHz in the presence
of free and complex Ba forms.
3.2 Fluorescence study
Figure3 shows the fluorescence spectra of Ba in the absence
and presence of CDs (including b-CD, HP-b-CD and Me-
b-CD). The maximum excitation and emission wave-
lengths were 270 and 363 nm, respectively. Addition of
different CDs (b-CD, HP-b-CD and Me-b-CD) caused
significant enhancement of Ba fluorescence intensity. From
Figure 3, it can be seen that fluorescence intensity was
enhanced with an increasing concentration of CDs. These
data suggested that stable complexes were formed between
CDsandBa. TheCDcavityprovidedanapolarenvironment
3.5 NMR measurements
To ascertain the structure of the inclusion complexes
between Ba and CDs, 1H NMR spectroscopy studies of free
drug and inclusion complexes were therefore undertaken.

Supramolecular Chemistry
647
A
105
90
75
60
45
30
15
0
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
FTIR 8400S
1/cm
B
105
90
75
60
45
30
15
0
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
1/cm
FTIR 8400S
C
105
90
75
60
45
30
15
0
4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 400
FTIR 8400S
1/cm
Figure 12. IR spectra of (a) Ba, (b) HP-b-CD and (c) Ba/HP-b-CD inclusion complex.

648
J. Chao et al.
the molecule of Ba entered into the cavity of b-CD from
A
0.00
–1.00
–2.00
–3.00
–4.00
–5.00
the large port; whereas the H-5 of HP-b-CD had larger
chemical shift than H-3, which illustrated that the
molecule of Ba entered into the cavity of HP-b-CD from
the vintage port.
From the above discussion, the mechanism of inclusion
complexes between Ba and CDs is shown in Figure 10.
3.6 Scavenging study of DPPHz by free or complexed Ba
DPPHz is a stable free radical generating a deep violet
solution in organic solvents. Its progressive discolouration
when in the presence of Ba indicated that it is acting as an
antioxidant.
0.00
100.00
100.00
100.00
200.00
200.00
200.00
300.00
Tem (C)
400.00
400.00
400.00
500.00
500.00
500.00
Furthermore, since the mechanism of DPPHz reduction
is known, the amount remaining from both the reagents
may be determined.
B
0.00
–2.00
–4.00
–6.00
TherateoftheDPPHz scavengingreactionwasmeasured
by monitoring the decrease in absorbance at 520 nm due to
DPPHz. Figure 11 shows the consumption of DPPHz, which
indicates that the complexed Ba/CDs were more effective
than the free Ba, with the HP-b-CD complex (72.22) . Me-
b-CD complex(69.24) . b-CD complex (66.67) . free Ba
(33.33). The scavenging ability was measured as a relative
scavenging in the presence of free or complex Ba. Figure 11
shows the scavenging ability related to the enhanced
solubility of Ba. Also, these results indicated that the
complexes formed maintained the Ba antioxidant activity.
The antioxidant activity of phenolic compounds depends
on the position and degree of hydroxylation, as well as on the
nature of radicals of the ring structure. Antioxidative activity
is intensified by the presence of a second hydroxy group
through the formation of an intramolecular hydrogen bond
(22). It might be that the ZOH positions of Ba molecules are
close enough to secondary ZOH groups of CDs to form
hydrogen bonds and contribute to antioxidant activity (23).
Therefore, the formation of an ‘intramolecular’ hydrogen
bond of the inclusion complex is possible, and consequently
an increase in antioxidant capacity is expected.
0.00
300.00
Tem (C)
C
0.00
–1.00
–2.00
–3.00
–4.00
0.00
300.00
Tem (C)
3.7 IR spectra studies
Compared IR spectra of Ba, HP-b-CD and complex of HP-
b-CD with Ba, as in Figure 12, showed that the absorption
intensity of CvO group and phenyl ring gave rise to
changes. The absorption intensity of CvO and phenyl ring
in inclusion complex were weaker than in Ba and have a
right shift; therefore, it can be deduced that CvO and
phenyl ring in Ba were included into the cavity of HP-b-
CD. And the same phenomenon was observed for b-CD
(the figure has not been given).
Figure 13. Thermal spectra of (a) b-CD, (b) Ba and (c) Ba/b-
CD inclusion complex.
Figures 8 and 9 illustrate the change of hydrogen atom of
Ba and CDs before and after forming the inclusion
complexes. The difference in hydrogen chemical shift
values between Ba in the free and in the complexed state is
presented in Table 4. Table 5 shows the hydrogen chemical
shift change values of CDs after forming the complexes.
It can be seen from the figures that the H-8, H-3, H-30,
H-40, H-50 and H-20, H-60 of Ba exhibited larger chemical
shifts, namely the A, B and C rings of Ba were all entered
into the cavity of b-CD and HP-b-CD. The H-3 of b-CD
had larger chemical shift than H-5, which illustrated that
3.8 DSC studies
The DSC curves of Ba, HP-b-CD and inclusion complex
are shown in Figure 13. From Figure 13, it can be seen that

Supramolecular Chemistry
649
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DSC curves of inclusion complex with the DSC curves of
Ba and HP-b-CD were different. This proved that the new
inclusion complex was formed. And the same phenomenon
was observed for b-CD (the figure has not been given).
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4. Conclusion
This study has demonstrated the inclusion complex
interaction between Ba with b-CD and its derivatives.
The major factors of affecting guest/host binding are size
matching between CD and guest, and the hydrophobicity
of the guest molecule. Among the CDs examined, HP-b-
CD was the most suitable for the inclusion of Ba,
which suggested that HP-b-CD cavity supplies a more
hydrophobic environment. And the activities of eliminat-
ing free radical DPPHz were HP-b-CD inclusion
complex . b-CD inclusion complex . free Ba.
In addition, the fluorescence spectroscopy and phase-
solubility measurement data have shown the formation of
a stable 1:1 stoichiometric complex of Ba with CDs (b-
CD, HP-b-CD and Me-b-CD). CDs can be used as a guest
complex agent, which act as a substrate reservoir in a
dosage-controlled manner and can increase the solubility,
stability and antioxidant activity of guest molecule.
Moreover, this study demonstrated that CDs served as
drug carrier systems.
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Acknowledgements
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This work was supported by the National Natural Science
Foundation of Shanxi Province (No. 2006011017).
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(20) Strazisar, M.; Andrensek, S.; Smidovnik, A. Food Chem.
2008, 110, 636–642.
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