Fabrication of 2D nanosheet through self assembly behavior of sulfamethoxypyridazine inclusion complexes with α- And β-cyclodextrins

Article abstract of DOI:10.1016/j.saa.2013.12.053

A 2D nanosheet was fabricated through the supramolecular self assembly of sulfamethoxypyridazine (SMP) and β-cyclodextrin (β-CD) inclusion complexes. HRTEM image exhibited 2D nanosheet morphology with a length of 1200 mm and the sheet thickness of 60 mm. It is noted that the nanosheet did not form a single layer aggregation but a bulk aggregation of SMP/β-CD inclusion complex. The formation of this multilayer 2D nanosheet based on the self assembly of SMP/β-CD inclusion complexes is proposed by the topological transformation as well as molecular modeling calculations. But, nanorods are formed in SMP/α-CD inclusion complex indicated that the nature of the CD determined the shape of the self assembled supramolecular architecture. The formation of nanomaterial was characterized by using FT-IR, DSC, PXRD, ¹H NMR, absorption, fluorescence and lifetime measurements.

Full text of DOI:10.1016/j.saa.2013.12.053

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 158–166
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Fabrication of 2D nanosheet through self assembly behavior
of sulfamethoxypyridazine inclusion complexes
with
a
- and b-cyclodextrins
⇑
N. Rajendiran , G. Venkatesh, T. Mohandass
Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamilnadu, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
ꢀ
ꢀ
2D nanosheet structures are formed
in sulfamethoxypyridazine/b-CD
inclusion complex.
Self assembled nanorods are formed
in sulfamethoxypyridazine/
inclusion complex.
a-CD
Self assembly
Intermolecular hydrogen bonding
play a vital role in the supramolecular
self assembling process.
The size of the CD determined the
shape of the supramolecular
architecture.
2D nano sheet
SMP/ -CD inclusion
complexes
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 October 2013
Received in revised form 26 November 2013
Accepted 4 December 2013
Available online 18 December 2013
A 2D nanosheet was fabricated through the supramolecular self assembly of sulfamethoxypyridazine
(SMP) and b-cyclodextrin (b-CD) inclusion complexes. HRTEM image exhibited 2D nanosheet morphol-
ogy with a length of 1200 mm and the sheet thickness of 60 mm. It is noted that the nanosheet did
not form a single layer aggregation but a bulk aggregation of SMP/b-CD inclusion complex. The formation
of this multilayer 2D nanosheet based on the self assembly of SMP/b-CD inclusion complexes is proposed
by the topological transformation as well as molecular modeling calculations. But, nanorods are formed
Keywords:
Sulfamethoxypyridazine
Cyclodextrins
Molecular modeling
2D nanosheet
in SMP/a-CD inclusion complex indicated that the nature of the CD determined the shape of the self
assembled supramolecular architecture. The formation of nanomaterial was characterized by using FT-
IR, DSC, PXRD, 1H NMR, absorption, fluorescence and lifetime measurements.
Ó 2013 Elsevier B.V. All rights reserved.
Supramolecular architecture
Pseudopolyrotaxane
Introduction
obtained by grafting aliphatic chains on the primary or secondary
face exhibit self-organizational properties yielding stable nano-
In the past decade, considerable interest has been shown in the
development of new vectors based on different hydrophobic CD
derivatives. These macrocyclic amphiphiles can form a variety of
supramolecular assemblies, such as micelles [1,2], vesicles [3,4],
spheres or nanocapsules [8–10]. A good knowledge of the nanoag-
gregate ultra structure is essential to the development of drug
carriers. It is worth reminding that the ability to encapsulate drugs
is partly related to the internal structure of nanosystems.
and nanoparticles [5–7]. In this area, amphiphilic
a
-cyclodextrins
The studies of inclusion complexes are important in fundamen-
tal research since it furnishes valuable information about noncova-
lent intermolecular forces [11]. Apart from this, research in the
field of characterization of inclusion complexes has experienced a
⇑
Corresponding author. Tel.: +91 94866 28800; fax: +91 41442 38080.
E-mail address: drrajendiran@rediffmail.com (N. Rajendiran).
1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.12.053

N. Rajendiran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 158–166
159
flasks. To this, varying concentration of CD solution (1.0 ꢁ 10ꢂ3
to 1.0 ꢁ 10ꢂ2 M) was added. The mixed solution was diluted to
10 ml with triply distilled water and shaken thoroughly. The final
concentration of SMP in all the flasks was 4 ꢁ 10ꢂ5 M. The experi-
ments were carried out at room temperature at 300 K.
O
H
N
N
N
H3C
O
S
NH2
O
Fig. 1. Chemical structure of SMP.
Instruments
splendid evolution because of its potential ability in a diverse
range of applications. These inclusion complexes can serve as min-
iature models for studying the mode of action of enzymes [12]
mimicking the reactions in biosystems [13] and so forth. These,
have promising prospects in future applications like drug delivery
[14], nanometer-sized electronic devices, and development of en-
ergy storage devices [15]. In this article, we report the fabrication
of 2D nanosheet through self assembly of b-cyclodextrin with sul-
famethoxypyridazine (Fig. 1) drug. The self assembled morphology
was observed using transmission electron microscope (TEM) and
scanning electron microscope (SEM). We proposed a reasonable
formation mechanism for the formation of the 2D nanosheet. The
inclusion complexes were subsequently characterized by FT-IR,
differential scanning calorimeter (DSC), powder X-ray diffraction
(PXRD), 1H NMR, absorption and fluorescence emission spectros-
copy techniques. The sulfamethoxypyridazine (SMP) belongs to a
class of sulfonamide drugs, which is frequently used in pharmaceu-
tical preparation, especially in veterinary practices. Interest in the
field of drug studies are not only for gaining some fundamental in-
sight into the determination of pharmaceutical samples, but also
obtaining information about the structure as well as the cheating
behavior of the drugs.
Scanning electron microscopy (SEM) photographs were col-
lected on a JEOL JSM 5610LV instrument. Morphology of the SMP
inclusion complexes was investigated by transmission electron
microscopy (TEM) using a TECNAI G2 microscope with accelerating
voltage 200 kV. Carbon coated copper TEM grid (200 mesh) was
used for TEM analysis. FT-IR spectra of SMP,
a-CD, b-CD and the
inclusion complexes were recorded 4000–400 cmꢂ1 on Nicolet
Avatar 360 FT-IR spectrometer. 1H NMR spectra for SMP and its
inclusion complexes were recorded on
a Bruker AVANCE
400 MHz spectrometer using DMSO-d6 as a solvent. The differen-
tial scanning calorimeter (DSC) was recorded using Mettler Toledo
DSC1 fitted with STRe software (Mettler Toledo, Switzerland). The
temperature scanning range was from 25 to 220 °C with a heating
rate of 10 °C/min. Powder X-ray diffraction (PXRD) spectra were
recorded with a BRUKER D8 advance diffractometer (Bruker AXS
GmbH, Karlsruhe, Germany), The XRD patterns were measured in
the 2h angle range between 5° and 80° with a scan rate 5°/min.
Absorption spectral measurements were carried out with a Shima-
dzu (model UV 1650 PC) UV–visible spectrophotometer and stea-
dy-state fluorescence measurements were made by using
a
Shimadzu spectrofluorimeter (model RF-5301). The fluorescence
lifetime measurements were performed using a picosecond laser
and single photon counting setup from Jobin-Vyon IBH.
The aim of the present work was to study the self assembly
behavior of SMP drug (Fig. 1) with a-CD and b-CD. The absorption
and fluorescence characteristics of few sulfa drugs with different
solvents, pH and b-CD were already reported [16,17]. In our previ-
ous study we investigated inclusion complexation of some sulfon-
amide derivatives with b-CD. In the present work, we prepared
Molecular modeling studies
The theoretical calculations were performed with Gaussian
solid inclusion complexes of the SMP drug with
a-CD and b-CD
03W package. The initial geometry of the SMP, a-CD and b-CD
and the inclusion complexation behavior was characterized by
UV–visible, fluorescence, life time, FTIR, DSC, PXRD, 1H NMR, SEM
and TEM and techniques.
was constructed with the aid of Spartan 08 and then optimized
by the semiempirical PM3 method at vacuum. The CD was fully
optimized by PM3 without any symmetry constraint [18]. The gly-
cosidic oxygen atoms of CD were placed onto the XY plane and
their center was defined as the center of the coordinate system.
The primary hydroxyl groups were placed pointing toward the po-
sitive Z axis. The inclusion complex was constructed from the PM3
optimized CD and guest molecules. The longest dimension of the
guest molecule was initially placed onto the Z axis. The position
of the guest was determined by the Z coordinate of one selected
atom of the guest. The inclusion process was simulated by putting
the guest on one end of the CD and then letting it pass through the
CD cavities. Since the semiempirical PM3 method has been proved
to be a powerful tool in the conformational study of CD inclusion
complexes and has high computational efficiency [19], we selected
semiempirical PM3 method to study the inclusion process of CDs
with the SMP drug.
Experimental section
Materials
SMP, a-CD and b-CD was purchased from Sigma–Aldrich chem-
ical company and used without further purification. The purity of
the compound was checked for similar fluorescence spectra when
excited with different wavelengths.
Preparation of nanomaterials
CD (1 mmol) was dissolved in 30 ml distilled water and SMP
(1 mmol) in 20 ml methanol and was slowly added to the CD solu-
tion. This solution was stirred at 50 °C overnight. The above solu-
tion was refrigerated overnight at 5 °C. The precipitated SMP/CD
complexes were recovered by filtration and washed with a small
amount of ethanol and water to remove uncomplexed drug and
CD, respectively. This precipitate was dried in vacuum at room
temperature for two days and stored in an airtight bottle. This
powder sample was used for further analysis.
Results and discussion
Micromorphological observations
The surface morphology of powder samples of SMP,
SMP/ -CD and SMP/b-CD complexes were assessed by SEM. As
illustrated in Fig. 2 SMP existed in a microcrystalline structure,
whereas SMP/ -CD inclusion complex appeared in the form of
irregular particles in which the original morphology of both the
SMP and -CD components disappeared and tiny aggregates of
amorphous pieces of irregular shape were present. The SMP/b-CD
a-CD, b-CD,
a
Preparation of CD solution
a
The concentration of stock solution of the drug was 2 ꢁ 10ꢂ3 M.
a
The stock solution (0.2 ml) was transferred into 10 ml volumetric

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20 µm
(a)
50 µm
200 µm
(b)
(c)
1 mm
5 µm
(e)
(d)
Fig. 2. SEM images of (a) SMP, (b)
a-CD, (c) SMP/
a-CD complex, (d) b-CD and (e) SMP/b-CD complex.
inclusion complex appeared as a micro-sheet like structure, which
was formed by SMP and b-CD mixed with excipient particles or ad-
hered to their surface. The comparison of these images revealed
gation proceeds mainly from the contribution of hydrogen bonding
or electrostatic interactions. Further, the above reports indicate that
the aggregation between CDs inclusion complexes is not only
hydrogen bonding and nonbonding interactions like van der Waals
forces, hydrophobic interaction, etc., and that they are also respon-
sible for the formation of the well defined supramolecular architec-
ture. Through these intermolecular forces, SMP/b-CD inclusion
complexes are aggregated and form a 2D nanosheet like structure
with the length of approximately 1200 nm.
Recently Chandrasekar and his co-workers [22] studied and
demonstrated the reversible shape-shifting of organic nanostruc-
tures that have dimensionally dependent optical waveguides.
And they were fabricated with organic rhombus shaped nanosheet
by self assembling of novel triazole derivative in acetonitrile solu-
tions. Besides, they reported that the triazole ring nitrogen atoms
participate in the intermolecular hydrogen bonding, thus playing
a crucial role in the supramolecular self assembling process. In
the present case also the intermolecular hydrogen bonding interac-
tion is the dominant driving force of the self assembling process.
that the SMP/
turally distinct from the isolated components. The size and shape
of the SMP/ -CD inclusion complex were different from that
a-CD and SMP/b-CD inclusion complexes were struc-
a
SMP/b-CD inclusion complex, which confirmed the formation of
different nanomaterials.
The HRTEM images in Fig. 3c shows the perfect architecture of
the 2D nanosheet formed by the self aggregation of SMP/b-CD
inclusion complexes, whereas the SMP/a-CD shows a nanotube like
structure (Fig. 3a and b). The SMP/b-CD inclusion complex act as a
building blocks and has unique structural features for hierarchical
supramolecular self assembly. The a-CD and b-CD have two types
of hydroxyl groups on the end of the cavities; one is a primary hy-
droxyl group (tail) and another is a secondary hydroxyl group
(head). Probably, there are three types of arrangement modes in
which CDs can have interacted with each others, namely head-to-
head, tail-to-tail and head-to-tail. So, the intermolecular hydrogen
bonding between the SMP/b-CD inclusion complexes play a vital
role in the supramolecular self assembly. The primary and second-
ary hydroxyl groups of the CDs play an essential role in the forma-
tion of these types of 2D hybrid nanosheet through hydrogen
bonding. According to the previous reports [20,21], the self-aggre-
Formation mechanism of 2D nanosheet
Based on our observations from the micromorphological
images, we proposed the self assembling mechanism of 2D

N. Rajendiran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 158–166
161
100 nm
100 nm
0.5 µm
(a)
(c)
(b)
1200 nm
60 nm
50 nm
0.5 µm
(d)
Fig. 3. TEM photographs of (a and b) SMP/a-CD complex and (c and d) SMP/b-CD complex.
nanosheet formation. A closer examination of the nanosheet edges
(Fig. 3d) showed that the thickness of the nanosheet is approxi-
mately 60 nm, which confirms that the nanosheet was not a single
layer aggregation of SMP/b-CD inclusion complex, but it is a multi-
layer bulk assembly of these complexes. The proposed mechanism
is shown in Fig. 4. In the first stage, the individual SMP/b-CD com-
plexes are arranged at one dimensionally (a-axis) to form a pseud-
opolyrotaxane like structure through intermolecular hydrogen
bonding. These pseudopolyrotaxane further aggregates in the same
molecular axis to form a single or a 1D molecular level layer
(Fig. 4c). Again every primarily assembled single molecular level
monolayer’s are tightly stacked along another one molecular axis
(b-axis). This process can go ahead to form 2D nanosheet like
supramolecular self aggregates of SMP/b-CD inclusion complexes.
To find out the number of SMP/b-CD molecular level layers that
make up the nanosheet, we performed molecular modeling studies
we observed that on the single or individual SMP/b-CD inclusion
complex. From the molecular modeling studies a single SMP/b-
CD inclusion complex has an average height about 10.02 Å
(1.002 nm). Hence, the 1D molecular level layer has a thickness
of approximately 1.002 nm, because these individual inclusion
complexes were arranged in one direction to form the 1D molecu-
lar level layer. Comparison of the molecular modeling studies and
HRTEM data showed that the nanosheet approximately 60 nm
thickness is composed of approximately 60 single molecular level
layers (60 ꢁ 1.002 nm = 60.12 nm).
SMP/a-CD complex nanomaterial definitely stem from the replica-
tion of the cylindrical shape of pseudopolyrotaxane structure
shown in Fig. 3b. So the same line of proposed mechanism has
been taken in explaining the formation of nanorod structure of
SMP/
earlier not much extended between the SMP/
SMP/ -CD complex having nanorod self assembly. The same type
a-CD complexes. Further, intermolecular forces as discussed
a-CD that is why
a
of results was reported by Chen and his co-workers [23], when
they fabricated mesoporous silica microtubes through the self
assembly behavior of b-CD and Triton X-100 micelles. Their reports
indicate that b-CD acts as a structure directing agents to construct
the mesoporous silica microtube.
FT-IR spectral analysis
FT-IR spectra in the region from 4000 to 400 cmꢂ1 of the
uncomplexed SMP and the corresponding inclusion complexes
are recorded (Fig. S1 in Supplementary material). It can be seen
from the FT-IR spectra peak at 3466 cmꢂ1 in SMP molecule assign
to the ANH2 stretching vibration, which can be moved to lower fre-
quencies at 3402 cmꢂ1 for SMP/ -CD complex and 3377 cmꢂ1 in
a
SMP/b-CD complex. Such lower frequency shift for ANH2 stretch-
ing is due to the overlapping of this vibration into AOH stretching
frequency of CDs. The frequency appeared at 2939 cmꢂ1 is assigned
to the aromatic ACAH stretching vibration of free SMP molecules,
and is moved to lower frequency of 2928 cmꢂ1 and 2926 cmꢂ1 for
However, instead of b-CD, if
with SMP, the obtained SMP/
nanorod like morphology, which is shown in Fig. 3a and b. The
preparation method of SMP/ -CD inclusion complex was same as
that stated in the experimental part but the self assembling mor-
phology of SMP/ -CD and SMP/b-CD were different. This demon-
a
-CD is used as the host molecule
both a-CD and b-CD inclusion complexes respectively. Another
a-CD inclusion complexes have a
characteristic vibration in SMP molecule is AS@O stretching ap-
peared at 1035 cmꢂ1 which strongly affected in both inclusion
complexes (ꢃ1028 cmꢂ1). The shift in the above frequency is due
to the hydrogen bond formation between this sulfonyl group and
CDs hydroxyl group. The stretching vibration at 2843 cmꢂ1 is due
to the aliphatic ACH3 stretching of the SMP molecule and it com-
pletely vanished from the inclusion complexes. In the present
study, there are difference between uncomplexed SMP and com-
plexes with CDs in the relative intensity of the various peaks in
spectrum region 1500–1200 cmꢂ1. This probably provides evi-
dence for the inclusion complex formation.
a
a
strates that the self assembled 2D nanosheet architecture of the
SMP/b-CD complex depending on the supramolecular assembly
of b-CD with SMP drug, and the type of CD determines the shape
of the self assembled architectures. The height of the nanorods
varied from 225 nm to 640 nm and diameter of the nanorods
varied from 75 nm to 200 nm. The short nanorod like structure of

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N. Rajendiran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 158–166
(c)
(a)
(b)
b-axis
a-axis
(e)
(d)
b-axis
a-axis
b-axis
a-axis
(g)
(f)
Fig. 4. Proposed mechanism for the formation of 2D nanosheet: (a and b) inclusion complexes of SMP/b-CD, (c and d) randomly oriented pseudopolyrotaxanes of SMP/b-CD
inclusion complexes formed by hydrogen bonding, (e and f) a molecular layer level (1D nanosheet) aggregation of pseudopolyrotaxanes of SMP/b-CD inclusion complexes at
molecular axis-a, (g) 1D molecular level layers are tightly staked with another one molecular axis-b and form 2D nanosheet.
DSC thermograms
endothermic peaks of both CDs and SMP drug thus implying com-
plex formation. The SMP/ -CD complex show one endothermic
a
Encapsulation of SMP into both the CDs cavity has been con-
firmed by the DSC thermograms. Since the disappearance of ther-
mal events of SMP molecule is considered as a proof of inclusion
complex formation. Fig. S2 in Supplementary material shows the
peak at 96.4 °C and SMP/b-CD complex show two endothermic
peaks at 84.6 °C, 128.6 °C. All the above endothermic peaks appear
due to loss of water molecules from the CDs. The disappearance of
the characteristic endothermic peak of SMP drug in the corre-
sponding inclusion complexes thermogram is taken as an evidence
for the formation of inclusion complexes.
details about the DSC thermograms of
a-CD, b-CD, SMP and its
inclusion complexes. The DSC scans of SMP show an exothermic
peak at 181.6 °C, which corresponds to melting point of the free
SMP drug (Fig. S2c). The DSC curves of b-CD shows a broad endo-
Powder X-ray diffraction analysis
thermic peak around 128.6 °C and a-CD shows three endothermic
peaks at 79.2 °C, 109.1 °C and 137.5 °C. These endothermic peaks
are associated with crystal water loss from CDs. The thermogram
of SMP/CD inclusion complexes prepared by co-precipitation
method show the complete disappearance of the characteristic
Powder X-ray diffraction patterns of SMP and their inclusion
complexes are shown in Fig. S3 in Supplementary material. The
diffraction peak of uncomplexed drug molecules and complexes
with CDs are entirely different, suggesting that SMP drug forms

N. Rajendiran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 158–166
163
inclusion complexes with both CDs. Sharp peak observed in the
600
(a)
diffractograms of the uncomplexed SMP confirmed the crystalline
nature of the drugs. It is also revealed, from the diffractograms that
the SMP enter into the CD cavity and modify the crystal lattice
structure of the CD. Hence, the characteristic new peaks have
appeared and become clearly distinct. A similar result was reported
by Neoh and his co-workers [24] in complexation between CO2
650
550
450
If
335 nm
10
7
1
300
0
15
5
[ -CD] × 10-3
M
with
a-CD. The major diffraction peaks at an angle of 2h = 8.7°,
12.2°, 13.4°, 18.1°, 22.6°, 32.2°, 35.4° in the diffractogram of SMP
(Fig. S3a) is significantly higher in intensity than that of the diffrac-
tograms of inclusion complexes with
a-CD (Fig. S3b) and b-CD
(Fig. S3c). The present study implies that the significantly higher/
lower intensities of the diffracted peaks are a result of the inclusion
complex formation of these SMP drugs with both CDs. A new sharp
0
270
385
500
Wavelength (nm)
peak appeared at angle 18.6° in the diffractogram of SMP/a-CD,
which was absent in the free SMP diffractograms indicating
the formation of the inclusion complexes. The above result due
to the inclusion of guest into the CDs cavity could cause the
changes in the host and guest shape, which modified the diffrac-
tion patterns of the respective systems.
800
400
0
850
650
(b)
If
335 nm
10
[ -CD] × 10-3
450
0
15
5
M
1H NMR analysis
7
1H NMR is one of the most powerful tools for the identification
of the formation of inclusion complexes and for the demonstration
of total or partial inclusion in the CDs cavities that occurs in liquid
medium. In the inclusion complexes, it is important to explain
whether the guest molecule is fully or partially included in the
CD cavity. During complex formation the chemical environment
of the guest molecule changed, and this resulted in change in
chemical shift of the 1H NMR line of the guest protons that are
due to the shielding or deshielding effects. The internal protons
of the CD cavity (H-3 and H-5 protons) were responsible for the
changes in the 1H NMR peak position of the guest protons. 1H
NMR spectra of SMP and its complexes were recorded at 25 °C in
DMSO-d6, the chemical shift values for the SMP and its inclusion
1
270
400
550
Wavelength (nm)
Fig. 5. Fluorescence spectra of SMP in different a-CD and b-CD concentrations (M):
(1) 0, (2) 0.001, (3) 0.002, (4) 0.004, (5) 0.006, (6) 0.008 and (7) 0.01 (Excitation
wavelength: 260 nm).
inclusion complexes. The LW emission may correspond to an energy
stabilization of emitting species and it is characteristic for the
fluorescence of an intramolecular charge transfer (ICT) or twisted
intramolecular charge transfer (TICT). The LW emission of SMP
drugs originates from the TICT state and twisting occur SAN bond
between aniline moiety (electron donor) and SO2 moiety (electron
acceptor). Further we reported [25–30] that when two aromatic
rings are separated by a group like ASO2, ACH2, AC@O and ANH,
those molecules show TICT emission. Thus, it can be speculating
than enhancement of LW emission should originate from the TICT
state. The addition of CDs with aqueous solution of SMP and SMD
the TICT band shows an enhancement with slight red shift,
whereas the LE band shows a strong enhancement without chang-
ing its band position (Fig. 5).
complexes (in parentheses first value corresponds to
a-CD and
the second corresponds to b-CD inclusion complex) are as follows,
OCH3 = 3.859 (3.813/3.886); NH2 = 5.952 (5.313/5.251); Ar–H =
6.564 (6.659/6.631); Ar–H = 7.251 (7.237/7.241); Ar–H = 7.512
(7.548/7.569). The above results shows the chemical shift value
of amino protons of SMP shift up to -0.639 ppm (in a-CD complex)
and ꢂ0.701 ppm (in b-CD complex) as compared with correspond-
ing free SMP molecule. These results indicated that the amino part
of the SMP molecule interacts strongly with CD cavities.
Absorption and fluorescence spectral studies
Figs. 5 and S4 depicts the absorption and emission spectra of
SMP (4 ꢁ 10ꢂ5 M) in pH ꢃ7 solutions containing different concen-
The b-CD concentration dependent TICT emission intensities of
SMP (Fig. 5) shows large enhancement when compared to aqueous
trations of
a-CD and b-CD. The inset Figs 5 and S4 depicts the
a
-CD solution. In two ways the TICT emission could be possible
changes in the absorbance and fluorescence intensity was observed
as a function of the concentration of CD added. In both CD solu-
tions, the absorbance was not significantly increased. In b-CD solu-
tion a slight red shift was observed in SMP (320, 262, 230 nm to
323, 266, 232 nm), whereas no significant shift was observed in
when these drug molecules complex with b-CD. First the less polar
medium of the inside cavity or the TICT state goes up causing an
increase in the energy barrier for the transition from the LE to TICT
state. So, in the event of non-radiative transition form LE gets tram-
meled, the TICT emission enhanced. Secondly the SMP drug feels
less geometrical restriction inside the b-CD cavity when compared
a-CD solution. The above results indicate that both the drugs were
transformed to more polar aqueous medium into less polar CDs
cavities. The changes in the absorption band and molar extinction
coefficient with the addition of both CDs suggest the formation of
to the a-CD cavity. Hence, the free rotation of donor group was less
hindered as this would cause further enhancement of the TICT
emission. Earlier we have observed that TICT emission is strongly
polarity sensitive [25–30] and very little enhancement TICT emis-
inclusion complexes between SMP with a-CD and b-CD [25–30].
In aqueous medium SMP shows single emission maxima around
sion in
a
-CD solutions suggest that this drug does not experience
-CD cavity when com-
ꢃ330 nm, this corresponds to the locally excited (LE) state. Upon
any major change in its polarity inside the
a
addition of both a-CD and b-CD to aqueous solutions of SMP they
pared to that outside. From the above results it can be concluded
show a new structured longer wavelength (LW) emission around
ꢃ430 nm. This LW emission is attributed to the formation of
that large enhancement of the TICT brand of the SMP drug in

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N. Rajendiran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 158–166
aqueous b-CD solution is due to less geometrical restriction and due
Semiempirical quantum mechanical calculations
0
to the larger size of the b-CD cavity (ꢃ6.2 ÅA) than that of
a-CD cavity
0
(ꢃ5.0 ÅA). Benesi–Hildebrand plots pointed out that only a single
In order to support the inclusion process, we applied semiem-
pirical quantum mechanical calculations at PM3 level of theory.
Binding energies, complexation enthalpy, entropy, free energy
changes and HOMO–LUMO energy levels of the SMP drug and its
inclusion complexes are listed in Table 1. The data presented in
Table 1 clearly indicates that these SMP/CD inclusion complexes
were formed because of their negative binding energies and
that the bigger absolute negative values led to the higher stability
of these complexes. Fan and his co-workers [32] proved that
the higher negative binding energy values of complexes have
higher stability than others. The complexation energies of
type of 1:1 inclusion complexes are formed with the SMP with
a
-CD and b-CD. Binding constant (K) and free energy change values
G) SMP/ -CD and SMP/b-CD inclusion complexes are calculated
by Benesi–Hildebrand equation. The calculated binding constant
(D
a
values for SMP/a
-CD complex are Kabs = 328 Mꢂ1; Kflu = 735 Mꢂ1
and SMP/b-CD complex are Kabs = 412 Mꢂ1; Kflu = 783 Mꢂ1. The
higher binding constant of SMP/b-CD inclusion complex suggests
that SMP molecule form stable more inclusion complex with
b-CD than compared with
a-CD. The experimental DG values
for SMP/
a
-CD complex are given below:
D
Gabs = ꢂ3.49 kcal molꢂ1
;
D
Gflu = ꢂ3.97 kcal molꢂ1 and SMP/b-CD complex are
D
Gabs
=
SMP/a
-CD = ꢂ19.63 kcal molꢂ1 and SMP/b-CD = ꢂ22.50 kcal molꢂ1
.
ꢂ3.62 kcal molꢂ1
;
D
Gflu = ꢂ4.01 kcal molꢂ1. The negative
D
G of
Among the two complexes SMP/b-CD complex was more stable
than SMP/a-CD. This higher stability of the complexes was depen-
dent upon the number of hydrogen bonds formed between the
the inclusion complexes suggest that the inclusion preceded spon-
taneously at room temperature.
host and guest molecules. Since the SMP/b-CD complex have two
hydrogen bonds (Fig. 6), it is more stable than SMP/a-CD. Moro-
Fluorescence decay spectral analysis
kuma [33] have demonstrated that the hydrogen bonding effects
the formation of the energy of the complexes and also their report
revealed that the PM3 level of semiempirical calculations is more
suitable for the study of these types of inclusion complex process.
Further, the complexation energy of SMP/CD inclusion complexes
is higher negative values than the corresponding free SMP mole-
cule which suggests that the formed complexes are more stable
than the corresponding free molecules. In addition to the hydrogen
bonds, the hydrophobic interaction also contributed in a major
way toward the stabilities of the complexes. The hydrophobic CD
cavities behaved as a binding acceptor to aromatic rings like ben-
zene and naphthalene moiety of guests which is also one of the fac-
tors that stabilized the inclusion complexes.
The fluorescence decay behavior of aqueous SMP and its inclu-
sion complexes were monitored by picosecond time correlated sin-
gle photon counting spectrometer. Respective fluorescence decay
profiles of aqueous SMP and corresponding complexes at pH
ꢃ7.0 were monitored at 300 nm excited by SMP. Visual inspection
of weighted residuals and reduced chi-square values indicate the
necessity two exponentials to properly fit experimentally observed
data points. Multi-exponential decays were significant for organic
heterocyclics in solution and it is often difficult to mechanically as-
sign the various components of decay. In the aqueous medium,
four hydrogen bonding sites were present in the SMP molecule.
The above behavior gives rise to different charge distribution struc-
tures with varying fluorescence decay life times. As an alternative
of giving importance to individual decay components, we defined
The HOMO energies, LUMO energies and HOMO–LUMO energy
gap of free SMP and its inclusion complexes were listed in Table 1.
The HOMO, LUMO energy orbital pictures of the SMP molecule is
the second order average life time h i SMP in solution using as de-
s
shown in Fig. 7. The HOMO and LUMO energy gap of the SMP/
inclusion complex was more negative (ꢂ8.1 eV) than SMP/b-CD.
Therefore, SMP/ -CD complex is more stable than others. The
a-CD
scribed in Paul and Guchhat [31]. The SMP drug in water shows an
average lifetime of 0.77 ns, which comparatively is very lower than
that of SMP/a-CD (2.54 ns) and SMP/b-CD (1.65 ns). These results
a
above higher energy gap was due to the hydrogen bonding interac-
tion between the host and guest. This interaction changed the elec-
tronic structure of the complexes to a certain extent, leading to the
elevation of HOMO energy and the depression of LUMO energy in
indicated that the nonradiative transition of SMP drug was affected
in the corresponding CD solution, which is in turn responsible for
the increase in the lifetime of the CD solution. The overall result
suggests that SMP complexes with
system.
a-CD and b-CD form stable
the SMP/a-CD complex. The net Mulliken charges of these four
Table 1
Energetic features, thermodynamic parameters and HOMO–LUMO energy calculations for SMP, SMD and its inclusion complexes by PM3 method.
Properties
SMP
a-CD
b-CD
SMP/a-CD
SMP/b-CD
EHOMO (eV)
ELUMO (eV)
EHOMO–ELUMO (eV)
l
ꢂ9.03
ꢂ0.68
ꢂ8.35
ꢂ4.85
4.17
ꢂ10.37
1.26
ꢂ11.63
ꢂ4.56
5.81
ꢂ10.35
1.23
ꢂ11.58
ꢂ4.56
5.79
ꢂ9.35
ꢂ1.17
ꢂ8.18
ꢂ5.26
4.10
ꢂ9.01
ꢂ0.92
ꢂ8.09
ꢂ4.96
4.04
g
x
2.82
1.78
1.79
3.13
3.05
S
0.23
0.17
0.17
0.24
0.25
Dipole (D)
5.64
ꢂ26.06
11.34
ꢂ1247.62
12.29
ꢂ1457.63
6.81
5.94
Ea
ꢂ1254.05
ꢂ19.63
ꢂ533.57
56.32
ꢂ1506.19
ꢂ22.50
ꢂ701.13
1.92
ꢂ558.91
ꢂ7.54
0.476
ꢂ0.075
887.33
0.00
D
Ea
Ga
86.47
128.91
0.142
ꢂ676.37
ꢂ570.84
0.353
ꢂ789.52
ꢂ667.55
0.409
D
Ha
D
Sb
Ga
ꢂ405.33
Ha
36.60
0.430
D
Sb
ꢂ0.065
795.54
0.00
Zero point vibrational energya
Mulliken properties
142.99
0.00
635.09
0.00
740.56
0.00
a
kcal moleꢂ1
kcal/mol K.
.
b

N. Rajendiran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 158–166
165
2.67 Å
1.78 Å
3.52 Å
1.77 Å
(a)
(b)
Fig. 6. PM3 optimized structure of (a) SMP/
a-CD and (b) SMP/b-CD inclusion complexes; Colors of the atoms denotes: Blue ꢃ nitrogen, yellow ꢃ sulphur, red ꢃ oxygen,
white ꢃ hydrogen, and grey ꢃ carbon of the molecules respectively. (For interpretation of the references to colour in this figure legend, the reader is referred to the web
version of this article.)
Fig. 7. Optimized structure and HOMO–LUMO energy structures of SMP; Colors of the atoms denotes Blue ꢃ nitrogen, yellow ꢃ sulphur, pale red ꢃ oxygen,
white ꢃ hydrogen, grey ꢃ carbon and whereas the green and dark red colors indicate negative and positive phase of the molecules respectively. (For interpretation of the
references to colour in this figure legend, the reader is referred to the web version of this article.)
complexes were zero and this result indicates that there is no
charge transfer interaction present in these complexes. The CD cav-
ities could offer a nonpolar environment but also attract the elec-
trons if the guests were matched with host (CD) both in space
and in electric charges which pronounces the binding process. Fur-
ther the dipole moments of both the inclusion complexes were ly-
ing between the dipole moments of the free guest and host. For
and SMP/b-CD inclusion complexes and (iv) no significant differ-
ence in the stability of the SMP/CD complexes.
The global minimum energy geometries were used to estimate
the thermodynamic quantities (DG, DH and DS) of the inclusion
process of SMP/CD inclusion complexes. The thermodynamic
quantities of both the inclusion complexes are listed in Table 1.
The lower level of the computational calculation method was not
able to reproduce absolute free energy changes of the complexa-
tion process were due to the limitations of the semiempirical cal-
culations at PM3 level. Quantitatively, the miscalculation seems
to be addressed to a systematic over estimation of the free energy
example, the dipole moment value of SMP/a-CD complex is 6.81
D, lies between the values of free SMP (5.64 D) and
a-CD (11.34
D). The above result is due to the guest molecule where transferred
polar environment to less polar or even nonpolar CD cavities.
Chemical potential (
philicity ( ) of the isolated SMP and it inclusion complexes were
listed in Table 1. From Table 1 following points can be observed
(i) SMP/ -CD complex having higher negative chemical potential
than others, (ii) hardness of the SMP molecule is decreased in the
SMP/ -CD and SMP/b-CD inclusion complexes, (iii) whereas the
electrophilicity of the SMP molecule is increased in the SMP/ -CD
l
), stability (S), hardness (
g
) and electro-
changes (DG) of the inclusion complexes as displayed in Table 1.
x
From Table 1, it can be observed that the complex process have po-
sitive free energy change values which suggests that these inclu-
sion processes are not spontaneous processes. But generally the
inclusion processes are spontaneous occurrence at room tempera-
ture. The above contradict results are arise not only due to the lim-
itations of PM3 level calculations but also due to optimization of
a
a
a

166
N. Rajendiran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 123 (2014) 158–166
Table 2
observed from SEM, TEM and molecular modeling calculations. In
order to confirm the interactions between SMP and CDs a detailed
characterization was carried out by using FT-IR, P-XRD, DSC, 1H
NMR, absorption spectroscopy, fluorescence emission spectros-
copy and lifetime measurements.
Geometrical parameters of SMP before and after inclusion with
most stable inclusion complexes.
a
-CD and b-CD for the
SMP
SMP/a-CD SMP/b-CD
Bond length (Å)
H4AH9
H3AH9
H6AH1
H4AC11
10.26
11.05
9.86
4.33
10.54
3.43
11.53
10.02
4.32
9.06
3.42
9.41
4.36
9.31
3.48
Acknowledgements
This work was supported by the Council of Scientific and Indus-
trial Research [No. 01(2549)/12/ EMR-II] and the University Grants
Commission [F.No. 41-351/2012 (SR)] New Delhi, India. One of the
authors, G. Venkatesh is thankful to the University Grants Commis-
sion, New Delhi, India for the award of BSR-SAP fellowship. The
authors thank Dr. P. Ramamurthy, Director, National Centre for
ultrafast processes, Madras University for allowing the fluores-
cence lifetime measurements for this work.
H11AN4
H-bond length (Å)
(ANH)H--O (glycoside)
3.52
1.77
2.67
1.78
(ASO2)O---H(20 OH)
Bond angle (°)
H4AN1AC4
C1AS1AO1
S1AN2AC7
C8AO3AC11
112.74
112.38
128.93
101.67
113.63
111.35
124.59
116.90
113.24
112.99
127.23
118.06
Dihedral angle (°)
C1AS1AN1AC7
C1AS1AN1AH7
H4AN1AC4AC5
Appendix A. Supplementary material
78.41
ꢂ128.09
27.94
107.62
ꢂ109.38
24.03
72.69
ꢂ137.26
28.52
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2013.12.053.
inclusion complexes in a vacuum. Since, we neglect the solvent
parameters in the thermodynamic calculations that become the
factors for the above controversial results.
References
[1] R. Auzely-Velty, S. Djedaini-Pilard, S. Desert, B. Perly, T.H. Zemb, Langmuir 16
(2000) 3727–3734.
[2] B.J. Ravoo, R. Darcy, P. Gambadauro, F. Mallamace, Langmuir 18 (2002) 1945–
1948.
[3] R. Donohue, A. Mazzaglia, B.J. Ravoo, R. Darcy, Chem. Commun. (2002) 2864–
2865.
[4] B.J. Ravoo, R. Darcy, Angew. Chem. 112 (2000) 4494–4496.
[5] D. Duchene, G. Ponchel, D. Wouessidjewe, Adv. Drug Deli. Rev. 36 (1999) 29–
40.
[6] E. Memisoglu, A. Bochot, M. Sen, D. Charon, D. Duchene, A.A. Hincal, J. Pharm.
Sci. 91 (2002) 1214–1224.
[7] A. Geze, S. Aous, I. Baussanne, J.L. Putaux, J. Defaye, D. Wouessidjewe, Int. J.
Pharm. 242 (2002) 301–305.
The negative enthalpy changes
(DH) of the SMP/b-CD
(ꢂ7.54 kcal molꢂ1) complex reveals that this complexation process
is an enthalpy driven process. Similarly the negative entropy
changes (DS) were observed in the thermodynamic calculations,
where the quantity of the entropy changes is very minimal for both
inclusion complexation processes. The SMP/b-CD complex shows a
high entropy change (ꢂ0.075 kcal molꢂ1) than SMP/
a-CD complex.
The above result suggests that the inclusion processes are not only
enthalpy driven but also entropy co-driven processes.
[8] V.K. Lamer, R.H. Dinegar, J. Am. Chem. Soc. 72 (1950) 4847–4854.
[9] H. Fessi, F. Puisieux, J.P. Devissaguet, N. Ammoury, S. Benita, Int. J. Pharm. 55
(1989) R1–R4.
[10] A. Geze, J.L. Putaux, L. Choisnard, P. Jehan, D. Wouessidjewe, J.
Microencapsulation 21 (2004) 607–613.
[11] M.V. Rekharsky, Y. Inoue, Chem. Rev. 98 (1998) 1875–1918.
[12] R. Villalonga, R. Cao, A. Fragoso, Chem. Rev. 107 (2007) 3088–3116.
[13] K. Ukeama, F. Hirayama, T. Irie, Chem. Rev. 98 (1998) 2045–2076.
[14] Y. Xia, K.E. Rodgers, J. Paul, G.M. Whitesides, Chem. Rev. 99 (1999) 1823–1848.
[15] S.J. Hashimoto, J.K. Thomas, Am. Chem. Soc. 107 (1985) 4655–4662.
[16] J. Premakumari, G. Allan Gnana Roy, A. Antony Muthu Prabhu, G. Venkatesh,
V.K. Subramanian, N. Rajendiran, Phys. Chem. Liq. 49 (2011) 108–132.
[17] A. Antony Muthu Prabhu, G. Venkatesh, N. Rajendiran, J. Soln. Chem. 39 (2010)
1061–1086.
Table 2 depicts the selected geometrical parameters like bond
distance, bond angles, dihedral angles and hydrogen bonding dis-
tances of SMP before and after inclusion with CDs. From Table 2
it can be seen that only minimum changes are formed in the bond
distance and bond angles, but a significant change can be observed
in the dihedral angles. For example, the verti0cal distance of the
0
SMP molecule is 10.26 ÅA but it changes 11.64 ÅA in the
a-CD com-
plexes. Likewise, the dihedral angle of bonds between C1AS1AN1-
AC7 in free SMP is ꢂ29.4°, but this is considerably changed to
ꢂ54.6° in
a-CD complexes. The overall annotation from the geo-
metrical parameters (Table 2) suggests that the SMP molecules
[18] T. Steiner, G.J. Koellner, Am. Chem. Soc. 116 (1994) 5122–5128.
[19] A.A. Rafati, S.M. Hashemianzadeh, Z.B. Nojini, M.A. Safarpour, J. Mol. Liq. 135
(2007) 153–157.
adopt a specific conformation in the CDs cavities.
[20] P. Das, A. Mallick, D. Sarkar, N. Chattopadhyay, J. Phys. Chem. C 112 (2008)
9600–9603.
Conclusions
[21] J.H. Park, S. Hwang, J. Kwak, ACS Nano 4 (2010) 3949–3958.
[22] N. Chandrasekhar, R. Chandrasekar, Angew. Chem. Int. Ed. 51 (2012) 3556–
3561.
[23] D. Chen, Q. Lu, X. Jiao, Chem. Mater. 17 (2005) 4168–4173.
[24] T.L. Neoh, H. Yoshi, T.J. Furta, J. Incl. Phenom. Macrocycl. Chem. 56 (2006) 125–
133.
[25] A.A. Smith, K. Kannan, R. Manavalan, N. Rajendiran, J. Fluorescence 20 (2010)
809–820.
[26] K. Sivakumar, T. Stalin, N. Rajendiran, Spectrochim. Acta 62A (2005) 991–999.
[27] A. Antony Muthu Prabhu, R.K. Sankaranarayanan, G. Venkatesh, N. Rajendiran,
A. Antony, J. Phys. Chem. B 166 (2012) 9061–9074.
In summary, we have fabricated that a supramolecular 2D
nanosheet aggregate in aqueous solution composed of SMP and
b-CD. The inclusion complexes of SMP/b-CD first formed a pseud-
opolyrotaxane like structure through hydrogen bonding interac-
tions and then these pseudopolyrotaxanes were primary
assembled to form 1D molecular level nanosheet. Further, these
1D molecular level nanosheets are secondary self assembled to
form 2D nanosheet through staking interaction between the
[28] A. Antony Muthu Prabhu, R.K. Sankaranarayanan, S.SivaN. Rajendiran,
Spectrochim. Acta A 74 (2009) 484–497.
sheets. But in the case of SMP/a-CD inclusion complexes form
the nanorods through self assembly process. The intermolecular
hydrogen bonding and van der Waals forces are the main dominant
driving force for the construction of this type of supramolecular
architecture. The reasonable self assembling mechanism of the
formation of this 2D nanosheet is suggested based on the results
[29] A. Anton Smith, K. Kannan, R. Manavalan, N. Rajendiran, J. Inclusion Phenom.
Macrocyclic Chem. 58 (2007) 161–167.
[30] A.A.M. Prabhu, N. Rajendiran, J. Fluorescence 22 (2012) 1461–1474.
[31] B. Kumar Paul, N. Guchhait, J. Colloid Interface Sci. 353 (2011) 237–247.
[32] X.X. Fan, Y. Yang, S. Shung, C. Dong, Spectrochim. Acta A 61 (2005) 953–959.
[33] K. Morokuma, Acc. Chem. Res. 10 (1977) 294–300.