Host-guest interaction of l-tyrosine with β-cyclodextrin

Article abstract of DOI:10.1016/j.saa.2007.10.054

The inclusion complexes of β-cyclodextrin (β-CD) with l-tyrosine (l-TYN) were investigated by using spectrophotometers. The absorption and fluorescence enhancement occurs with β-CD and l-TYN forms 1:1 inclusion complex. The unusual blue shift of hydroxyl ion in the β-CD medium confirms OH groups present in the interior part of the β-CD cavity and -COOH group present in the upper part of the β-CD cavity. A mechanism is proposed to explain inclusion process. The inclusion interaction was examined and the thermodynamic parameters of inclusion process ΔG, ΔH and ΔS were determined. The results indicated that the inclusion process was an exergonic and spontaneous process. Stable solid inclusion complexes were established and characterized by FT-IR, scanning electron microscope (SEM) methods.

Full text of DOI:10.1016/j.saa.2007.10.054

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Spectrochimica Acta Part A 71 (2008) 125–132
Host–guest interaction of l-tyrosine with ␤-cyclodextrin
M. Shanmugama, D. Ramesha, V. Nagalakshmia, R. Kavithaa,
R. Rajamohanb, T. Stalina,∗
a Department of Chemistry, Muthayammal College of Arts and Science, Rasipuram, Namakkal 637408,
Tamilnadu, India
b Department of Chemistry, Annamalai University, Annamalainagar 608002, Tamilnadu, India
Received 30 May 2007; accepted 30 October 2007
Abstract
The inclusion complexes of ␤-cyclodextrin (␤-CD) with l-tyrosine (l-TYN) were investigated by using spectrophotometers. The absorption and
fluorescence enhancement occurs with ␤-CD and l-TYN forms 1:1 inclusion complex. The unusual blue shift of hydroxyl ion in the ␤-CD medium
confirms OH groups present in the interior part of the ␤-CD cavity and –COOH group present in the upper part of the ␤-CD cavity. A mechanism
is proposed to explain inclusion process. The inclusion interaction was examined and the thermodynamic parameters of inclusion process ꢀG,
ꢀH and ꢀS were determined. The results indicated that the inclusion process was an exergonic and spontaneous process. Stable solid inclusion
complexes were established and characterized by FT-IR, scanning electron microscope (SEM) methods.
© 2007 Elsevier B.V. All rights reserved.
Keywords: l-Tyrosine; ␤-Cyclodextrin; Inclusion complex; pH effects
1. Introduction
Upon inclusion or partial inclusion of molecules within their
hydrophobic interior, CDs can effectively shielded the excited
singlet state of molecules from the processes and enhance
their fluorescence intensity [5]. The complexed molecules
have also been observed to be increased upon formation of
inclusion complexes with CDs [6]. Furthermore, these studies
seem to indicate differences in the extend of inter- and intra
molecular hydrogen bond for the molecules in aqueous solu-
tions of cyclodextrins. Applications of cyclodextrins and their
derivatives cover various areas of the chemistry, including the
sensing of organic molecules, analytical chemistry, pharmaceu-
ticals, food, encapsulation of drugs and other industrial areas
[7–9].
The excited state intramolecular charge transfer (ICT)/
intramolecular hydrogen bond (IHB) process has been attractive
topics of investigations as a primary function for basic mecha-
nisms of biological and chemical energy conversion [10–14].
The ICT process of organic molecules containing separating
electron donor and electron acceptor moieties has been stud-
ied in various homogeneous and heterogeneous media, and
many reports revealed that the excited state ICT emission could
be maximized by conformation change. The conformational
change (such as dimethylaminobenzonitrile derivatives) has
been proposed to induce the twist of the whole alkyl amino
group with respect to the benzene ring leading to a called
Cyclodextrins (CDs) have been used to perturb the physi-
cal and chemical properties of hydrophobic organic molecules
in aqueous solutions. The CDs are capable of incorporating
a high range of guest molecules based on hydrophobic and
geometrical (Scheme 1) [1]. Generally molecular recognition
by native and modified cyclodextrins is currently an interest-
ing in supramolecular chemistry [2], naturally occurring cyclic
oligosaccharides composed of six, seven or eight ␣-(1-4)-linked
d-glucosyl residues, generally called, ␣-, ␤-, ␥-CD, respec-
tively (Scheme 1). They have a toroidal shape with an internal
hydrophobic surface and external hydrophilic surface and it is
acting as a host molecule. These cyclodextrins are well known
as forming stable host–guest inclusion complexes which have
the interesting property of including organic, inorganic and
biologicalaminoacids(foundinproteins)moleculesintheircav-
ities [3,4]. The guests have several weak intramolecular forces
between host and guest molecules, i.e., dipole–dipole interac-
tion, electrostatic, Vander waals, hydrophobic and hydrogen
bonding interactions.
∗
Corresponding author.
E-mail address: tstalinphd@rediffmail.com (T. Stalin).
1386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.10.054

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M. Shanmugam et al. / Spectrochimica Acta Part A 71 (2008) 125–132
idazole [20]. This phase restrictions caused by the inclusion
has been used advantageously to probe the dual fluorescence
of 9-anthroic acid, controversy such emission spectra [21].
An alternative explanation to TICT has been proposed by
Zachariasseetal. [22]. Accordingtotheauthorsthephenomenon
is based on a solvent-induced locally excited (LE) and charge
transfer (CT) states achieved by a sufficiently small energy gap
between the two states. In that respect, CT can be explored by
variation of the donor and acceptor groups on either side of the
benzene moiety stabilizing the CT transfer state. This property
leadsto severalapplicationsof cyclodextrinsin differentfieldsof
analytical and synthetic chemistry. The spectroscopic and pho-
tochemical behaviors of such complexes are of interest and the
changes in fluorescence and electronic absorption properties,
excimer and exciplex formation in the excited state protolytic
equilibria and photoisomerization have been reviewed [23]. On
the other hand, in some molecules having a perpendicular con-
figuration in the ground state (e.g., 9,9ꢀbianthrayl) that visiting
relaxation needed to reach the TICT state is not necessary and
the overall ICT rate is determined only by the solvent relaxation
dynamics [17]. The charge separation in biological molecules
is known to be coupled to proton motion which may be pro-
ton transfer process [24]. Nevertheless the role of the specific
hydrogen bonding in the photo induced TICT (ICT) has not been
systematically investigated.
In this study, we report for the absorption and fluorescence
characteristics of l-tyrosin (l-TYN) in different ␤-cyclodextrin
concentrations. For the past one decade, the corresponding
author has largely been involved in studying photophysical prop-
erties [25,26] of various organic fluorophores. This molecule
shows intramolecular hydrogen bond/intramolecular charge
transfer emission in the excited singlet state. This stimulated
us to carry out a study on l-tyrosin.
l-Tyrosin is one of the amino acid, i.e., found in proteins of all
lifeforms. Recently, tyrosinwastwistedtoseeifitcouldimprove
the neuropsychological test performances of individuals with
phenylketonuria. Pregnant women and nursing mothers should
avoid supplementation with l-tyrosin. Ferand et al. [27] were
reported the absorption spectra of the amino acids including
l-tyrosin horizontal banded structure in their spectra.
The techniques of UV–vis, fluorimetry, FT-IR, Scanning
electron microscope and thermodynamic parameters have been
used to examine the effects of ␤-cyclodextrin upon complex-
ation of l-tyrosin. The formation constants of the complexes
have been estimated in order to predict and understand the fac-
tors affecting complexation between ␤-cyclodextrin and l-TYN
molecules in solution.
Scheme 1. Chemical structure of ␤-cyclodextrin, with oxygen• and hydroxyl•
groups marked. All glucoses are in C1 chair form, structure of ␤-cyclodextrin
and molecular dimensions of ␣-, ␤- and ␥-cyclodextrins.
“twisted intramolecular charge transfer (TICT) state [15,16],
respectively.
Also, it has been reported that the intramolecular hydrogen
bonding process is an important factor to facilitate the ICT pro-
cess by maintaining a large twist angle between the electron
donor and acceptor groups in the ground states [17]. The reac-
tivity in the excited state, for e.g., proton transfer can also be
altered in the presence of cyclodextrine due to interactions of a
protonable group with the hydrophilic borders of the cavity [18].
The cyclodextrins have also proven to restrict the twisting of
functional groups in molecules that display twisted intramolec-
ular charge transfer (TICT), for example 4-N,N-dimethyl-amino
cinnamic acid [19] or 2-(4ꢀ-N,N-dimethylaminophenyl) bezim-
2. Experimental
2.1. Instruments
Absorption spectral measurements were carried out with a
ELICO BL-198 Bio Spectrophotometer, and fluorescence mea-
surements were made a JASCO FP-550 Spectrofluorimeter. The
pH values in the range 2.0–12.0 were measured on ELICO pH
meter model LI 120. FT-IR spectra were obtained with Avatar-

M. Shanmugam et al. / Spectrochimica Acta Part A 71 (2008) 125–132
127
Table 1
330 FT-IR spectroscopy using KBr pelleting. The range of
spectra was from 500 to 4000 cm−1. Microscopic morpholog-
ical structure measurements were performed with JEOL JSM
5610 LV scanning electron microscope (SEM).
Absorption and fluorescence maxima (nm) of l-tyrosine at different concentra-
tions of ␤-CD
S. No.
1
Concentration of ␤-CD
Water (without ␤-CD)
λabs
log ε
λflu
273.5
223.7
4.19
4.50
305
405
2.2. Reagents and materials
2
3
4
5
6
7
0.002 M
0.004 M
0.006 M
0.008 M
0.010 M
0.012 M
272.3
223.5
4.29
4.55
306
405
l-TYN and ␤-CD were obtained from E-merck. The purity
of the compounds was checked by similar fluorescence spectra
when excited with different wave lengths. Triply distilled water
used for the preparation of aqueous solutions. Solution in the pH
range 2.0–12.0 was prepared by adding the appropriate amount
of NaOH and H3-PO4. The concentrations of the solutions were
of the order 10−4 to 10−5 mol dm−3. The concentration of ␤-CD
is varied from zero to 1.2 × 10−2 mol dm−3. The stock solution
271.6
270.6
267.8
265
4.45
4.50
4.67
4.67
4.78
305
407
307
403
307
402
308
401
of the l-TYN is 1 × 10−3 mol dm−3
.
263.9
309
403
2.3. Preparation of solid inclusion complex of l-TYN with
β-CD
Binding constant (M−1
ꢀG (kJ/mole)
ꢀH (kJ/mole)
)
60
119
−13.45
−69.0
0.19
−14.25
−69.20
0.18
Accurately weighed 1 g of ␤-CD was placed in to 50 ml coni-
calflaskand30 mltriplydistilledwateraddedandthenoscillated
this solution enough. After that, 0.3 g l-TYN was put in to a
50 ml beaker and 20 ml triply distilled water added and put over
electromagnetic stirrer to stir until it was dissolved. Then slowly
poured ␤-CD solutions in to l-TYN solution. The above mixed
solution was continuously stirred for 48 h at room temperature.
The reaction mixture was put in to refrigerator for 48 h. At this
time, we observed that white powder precipitated. The precipi-
tate was filtered by G4 sand filter funnel and washed with triply
distilled water. After dried in oven at 50 ◦C for 12 h, white pow-
der product was obtained. This is solid inclusion complex of
l-TYN with ␤-CD.
ꢀS (kJ/mole)
3. Results and discussions
3.1. Effect of β-cyclodextrin
The UV–vis absorption and emission spectral data of l-
tyrosine (l-TYN) in different concentrations of ␤-CD are
complied in Table 1. The absorption peaks of l-TYN in pH
7.0 appears (Fig. 1) at 273.5 and 223.7 nm. Upon increasing
the concentration of ␤-CD, the absorption maxima is regularly
blue shifted from 273.5 to 264 nm, where as the absorption
spectra of l-TYN is seen to undergo a marginal blue shift. How-
ever, the absorption intensities of pH 7.0 solutions are regularly
increases with increasing concentration of ␤-CD, no clear isos-
bestic point is observed in the absorption spectra. The absorption
spectra show the marginal change in absorption maxima even
in the presence of the highest concentration of ␤-CD used
(1.2 × 10−2 mol dm−3) and there is no change in the absorbance
by further addition of ␤-CD (Fig. 2). Increasing the concentra-
tion of ␤-CD the absorption maximum was slightly blue shifted
with a gradual increase in absorbance. This behavior has been
attributed to the enhanced dissolution of the guest molecule,
through the hydrophobic interaction between guest molecule
and non-polar cavity of ␤-CD [28–30], as observed others also
Fig. 1. The absorption spectra of l-tyrosine in different ␤-CD concentrations
(mol dm−3): (1) 0.0 M, (2) 0.002 M, (3) 0.004 M, (4) 0.006 M, (5) 0.008 M, (6)
0.010 M and (7) 0.012 M.
Fig. 2. The absorption intensity of l-TYN changes at 275 nm with different
␤-CD concentrations.

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M. Shanmugam et al. / Spectrochimica Acta Part A 71 (2008) 125–132
Fig. 3. Benesi–Hildebrand plot of 1/A − A0 vs. 1/[␤-CD] for l-TYN.
Fig. 4. Fluorescence spectra of l-TYN in different ␤-CD concentrations
(mol dm−3): (1) 0, (2) 0.002, (3) 0.004, (4) 0.006, (5) 0.008, (6) 0.010 and
(7) 0.012.
[31,32]. Since, this indicates the formation of 1:1 host–guest
type inclusion complex between ␤-CD and l-TYN molecule.
The guest is in a surrounding, i.e., poor in water molecules, and
this causes both the blue shift of the absorption and the increase
of its absorbance.
The fluorescence spectra of aqueous l-TYN solutions ␤-CD
concentration are presented in Fig. 4. The fluorescence char-
acteristics of l-TYN are entirely different from those compare
in absorption spectra. The fluorescence spectra observed two
effects; firstly, a dual luminescence is observed at 305 and
405 nm. Secondly, fluorescence intensity is decreases shorter
wavelength and increased in longer wavelength along with
increasing ␤-CD concentrations. The positions of the fluores-
cence maxima and of the isosbestic point located in water and
in up to 1.2 × 10−2 M ␤-CD solution. It was clear isosbestic
point observed at 345 nm. From Fig. 4 it is clear that the fluo-
rescence enhancement in ␤-CD. This suggests the formation of
an inclusion complex between l-TYN and ␤-CD.
Both the emission bands (longer wavelength LW 405 nm,
shorter wavelength SW 305 nm) of the full width at half of
maximum (FWHM) increases with increase in ␤-CD concen-
trations, indicating that intramolecular interactions are greater
than intramolecular hydrogen bond (IHB) interaction in ␤-
CD solution. The increase in FWHM observed in both bands
clearly establishes that the l-TYN (OH group) present in the
interior part, exterior part contain COOH group with water
molecule present in intramolecular hydrogen bond (or) ‘N’ atom
lone-pair of electron interact in carboxylic acid H-atom due
For 1:1 inclusion complex between ␤-CD and l-TYN, the
following equilibrium can be written,
K
l-TYN + ␤-CDꢀl-TYN : ␤-CD
The binding constant ‘K’ and stoichiometric ratios of the inclu-
sion complex of l-TYN can be determined according to the
Benesi–Hildebrand relation [33] assuming the formation of 1:1
host–guest complex
1
1
1
=
+
ꢀε K[l-TYN]0ꢀε[␤-CD]0
(1)
A − A0
Where, A and A0 is the difference between the absorption of
l-TYN in the presence and absence of ␤-CD, ꢀε is the differ-
ence between the molar absorption co-efficient of l-TYN and
the inclusion complex [l-TYN]0, [␤-CD]0 are the initial con-
centration of l-TYN and ␤-CD, respectively. Fig. 3 depicts a
plot of 1/A − A0 as a function of 1/[␤-CD] for l-TYN good lin-
ear correlations was obtained, confirming the formation of a 1:1
inclusion complex. From the intercept and slope values of this
plot, K is evaluate [K = 60.25 M−1] at 303 K.
Scheme 2. The proposed structure of inclusion complex of l-TYN with ␤-CD for 1:1 complex.

M. Shanmugam et al. / Spectrochimica Acta Part A 71 (2008) 125–132
129
gen bonding interaction inhibited. Thus, if the hydrogen bonding
interaction inhibited as in the ␤-CD inclusion complex the for-
mation of the ICT state by direct excitation at 260 nm also be
inhibited [34]. If in the case, l-TYN shows dual emission in ␤-
CD medium. For type-II encapsulation, the cavity will impose a
restrictionaboutthefreerotationoftheCH2 (alkylgroups)group
in its excited state. For this type of complex, making hydrogen
bond with the aqueous solution is very much possible as the
carboxyl group is available in the bulk solution [35]. Hence,
ICT emission intensity remains almost unaltered because the
ICT state not depends upon rotation of carboxyl attached alkyl
groups, but it depends only on hydrogen bonding between solute
and solvents. These features again support the idea that the ICT
state in water is further stabilized through exciplex formation
between l-TYN and water.
Fig. 5. The Fluorescence intensity of l-TYN changes at 410 nm with different
␤-CD concentrations.
to ␤-CD (Scheme 2). The formation of an inclusion complex
between l-TYN and ␤-CD, the complexation is complete at
1.2 × 10−2 mol dm3, ␤-CD and there is no change in the flu-
orescence intensity by ␤-CD and there is no change in the
fluorescence intensity by further addition of ␤-CD (Fig. 5).
The equilibrium constant ‘K’ assuming the formation of a 1:1
l-TYN/␤-CD can be calculated based on the Benesi–Hildebrand
[33] plots using florescence data.
3.2. The thermodynamics of inclusion process
The determination of thermodynamic parameters, here were
three parameters in the inclusion process The thermodynamic
parameters ꢀG, ꢀH and ꢀS for the association of the guest
molecule to ␤-CD is given in Table 1. The free energy change
can be calculated from the formation constant ‘K’ by Eq. (3).
1
1
1
=
+
(2)
I − I0
Iꢀ − I0
K[Iꢀ − I0][␤-CD]0
ꢀG = −RT ln K
(3)
Where [␤-CD] represents the initial concentration of ␤-CD ‘I0’
and ‘I’ are the florescence intensities in the absence and pres-
ence of ␤-CD, respectively, and Iꢀ is the limiting intensity of
florescence. The ‘K’ value where obtained from the slope and the
intercept of the plots. The Benesi–Hildebrand plot (Fig. 6) shows
excellent regression supporting the assuming 1:1 l-TYN/␤-CD
inclusion complex. From plot, ‘K’ is evaluated as 119.94 M−1 at
303 K. The binding constant is so small, as compared with other
guestmolecule␤-CDcomplexas[28–31]. Thisisprobablyinter-
and intramolecular hydrogen bond present in this molecule.
Naturally, two different types in the inclusion complex for-
mation between l-TYN and ␤-CD are possible. One is with the
–COOH group captured in ␤-CD cavity and the other is –OH
groups captured (Scheme 2). Let us now consider the type-I
arrangement, when the carboxyl group of l-TYN is entrapped
with in the ␤-CD cavity, the l-TYN molecule is no longer able to
make a H-bonding with the bulk aqueous solution (i.e.) hydro-
As can be seen from Table 1, ꢀG is negative which sug-
gested that the inclusion process proceeded spontaneously at
303 K. ꢀH and ꢀS are also negative in the experimental
temperature range which indicates that the inclusion pro-
cess was an exergonic and enthalpy controlled process. The
negative enthalpy change arose from the Vander Waal’s inter-
action, while the negative entropy change was the steric barrier
caused by molecular geometrical shape and the limit of ␤-
CD cavity to the freedom of shift and rotation of guest
molecule.
3.3. Effects of pH with β-CD medium
The absorption and fluorescence spectra of l-TYN have
been studied in the pH range H0 −1 to pH ≈ 11 in ␤-
CD medium (Table 2). There are six prototropic species
(dication, monocation, Zwitter ion, neutral, monoanion and
dianion) present in aqueous medium. But in the case of ␤-
CD medium present only two species (neutral and monocation)
in ␤-CD medium cannot determine pKa and pKa∗ values for
zwitter ion because zwitter ion does not exist consistency
pH value (Scheme 3). When compared to aqueous medium
some appreciable change in absorption maxima of neutral to
monocation.
The pH dependent changes in the absorption and fluores-
cence spectra of the l-TYN molecule in aqueous solution
containing ␤-CD have been recorded and are shown in Table 2
and Figs. 7 and 8. The equilibrium of l-TYN could be due
to the presence of different resonating structure as shown in
Scheme 3. The absorption and emission maxima of l-TYN have
been in 1.2 × 10−2 M ␤-CD aqueous solutions in the pH range
Fig. 6. Benesi–Hildebrand plot of 1/I − I0 vs. 1/[␤-CD] for l-TYN.

130
M. Shanmugam et al. / Spectrochimica Acta Part A 71 (2008) 125–132
Table 2
Various prototropic maxima (absorption and fluorescence) of l-TYN in with and without ␤-CD medium
Species
With ␤-CD
Without ␤-CD
λabs
pKa
λflu
pKa∗
λabs
pKa
λflu
pKa∗
266.9
216.0
–
–
–
–
−1.26
−1.15
Dication
Monocation
Neutral
411
274.5
222.5
422
302
241
218
435
325
−0.26
4.0
−0.20
−1.98
−2.24
266.5
225.6
408
390
275
225
440
336
4.0
–
4.5
–
4.3
–
277.7–267.0
243.2–222.8
Zwitter
ion
–
–
–
4.0–12.0
260
215
–
–
–
–
–
–
–
–
Monoanion
Dianion
12.98
15.40
422
–
14.8
285
Quench
Scheme 3. Various prototropic equilibria of l-TYN in aqueous and ␤-CD medium.

M. Shanmugam et al. / Spectrochimica Acta Part A 71 (2008) 125–132
131
Fig. 8. Fluorescence spectra of l-TYN in different prototropic species at 303 K:
concentration 1 × 10−5 M. (1) Neutral and (2) monocation.
Fig. 7. Absorption spectra of l-TYN in different prototropic species at 303 K:
concentration 1 × 10−5 M. (1) Neutral and (2) monocation.
monocation–neutral equilibrium of l-TYN in ␤-CD is higher
thanaqueousmedium, whereasneutral–monocationequilibrium
pKa (pKa∗) values is higher than aqueous medium. This finding
confirms l-TYN molecule encapsulated in the ␤-CD cavity.
pH ≈ 0.1–11. No noticeable change is observed in the absorp-
tion maxima of the monocation whereas blue shift is observed
in neutral and monocationic of l-TYN in ␤-CD, then aque-
ous medium. However, in the excited state, a small blue shift
is observed in neutral and monocation, where as the change in
emission maxima of monoanion are negligible. This behaviour
is different from its ground state, because in the excited state
amino group becomes more acidic, where as –COOH group
becomes more basic. Further, ICT emission also inhibited in the
␤-CD medium. Hence a small blue shift emission is observed
in neutral and monocation, further the pKa (pKa∗) values for the
3.4. FT-IR—spectral studies
The FT-IR spectra of l-TYN, ␤-CD and the solid inclusion
complex. In l-TYN, carboxylic acid OH stretching absorption
in the region 2596 cm−1 is shifted to 2601 cm−1 in the solid
inclusion complex. The phenolic OH group appears 1104 cm−1
in l-TYN whereas it is shifted 1108 cm−1 in solid inclusion
complex. Further, the absorption intensity in inclusion complex
Fig. 9. Scanning electron microscope photographs (Pt coated) of (a) ␤-CD × 500, (b) ␤-CD × 3000, (c) l-TYN × 100 and (d) l-TYN–␤-CD complex.

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M. Shanmugam et al. / Spectrochimica Acta Part A 71 (2008) 125–132
was significantly greater than in l-TYN. The inclusion complex
FT-IR peaks in the range 1000–2000 cm−1 are 30–50% than the
free l-TYN molecule. So we can deduce the phenolic group of
l-TYN is included into the cavity of ␤-CD.
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3.5. Microscopic morphological observation
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First, we observed powdered form of l-TYN and ␤-CD
by scanning electron microscope, then we also observed
powered form of inclusion complex (Fig. 8). ␤-CD shows
plated/sheeted structure, l-TYN shows irregular arrangement
structure and the solid inclusion complex structure is different
from ␤-CD and l-TYN. Pictures clearly elucidated the differ-
ence of powder of each other. Modification of crystal and powder
can be assumed as a proof of the formation of new solid inclusion
complex (Fig. 9).
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4. Conclusion
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Mater. 21 (1994) 501;
The following conclusion can be arrived at from the above
studies; (i) l-TYN forms 1:1 complex with ␤-CD; (ii) proton
transfer reactions in ␤-CD medium indicates, OH group present
in the interior (non-polar) of the ␤-CD cavity; (iii) whereas
COOH group present in the upper (polar) part of the ␤-CD cav-
ity; (iv) FT-IR and SEM results suggest l-TYN formed a solid
inclusion complex with ␤-CD; (v) the above studies demonstrate
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