Nanostructures formed by cyclodextrin covered aminobenzophenones through supramolecular self assembly

Article abstract of DOI:10.1016/j.saa.2014.02.024

Cyclodextrin (α and β) based nanostructures formed with 2-aminobenzophenone, 3-aminobenzophenone through the supramolecular self assembly are studied by absorption, fluorescence, time-resolved fluorescence, SEM, TEM, FT-IR, DSC, PXRD and ¹H NMR. The unequal layer by layer nanosheets and nanoribbons are formed through self assembly of 3ABP/CD inclusion complexes. 2ABP/α-CD complex nanostructures show the self assembly hierarchical thread structure and β-CD complexes displays a nanobrick structure. The formation of nanostructures are prearranged to HO-H, NH ₂-O and H₂N-H intermolecular hydrogen bond between individual complexes. The absorption and fluorescence spectral changes explicit formation of 1:1 inclusion complexes and solvent study demonstrate the ESIPT and TICT present in both molecules. The thermodynamic parameters (ΔH, ΔG and ΔS) of 2ABP and 3ABP molecule and the inclusion complexes were determined from semiempirical PM3 calculations.

Full text of DOI:10.1016/j.saa.2014.02.024

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 52–60
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Nanostructures formed by cyclodextrin covered aminobenzophenones
through supramolecular self assembly
⁄
N. Rajendiran , R.K. Sankaranarayanan, J. Saravanan
Department of Chemistry, Annamalai University, Annamalai Nagar 608 002, 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
ꢀ
ꢀ
2ABP and 3ABP guest molecule form
1:1 inclusion complex.
Intermolecular hydrogen bonding
play a vital role in the formation of
nanostructure.
ꢀ
2ABP/a-CD complex show the self
assembly hierarchical thread
nanostructures.
ꢀ
ꢀ
b-CD complexes displays a nanobrick
nanostructure.
Solvent study demonstrate the ESIPT
and TICT in both molecules.
a r t i c l e i n f o
a b s t r a c t
Article history:
Cyclodextrin (a and b) based nanostructures formed with 2-aminobenzophenone, 3-aminobenzophenone
Received 26 November 2013
Received in revised form 26 January 2014
Accepted 9 February 2014
through the supramolecular self assembly are studied by absorption, fluorescence, time-resolved fluores-
cence, SEM, TEM, FT-IR, DSC, PXRD and 1H NMR. The unequal layer by layer nanosheets and nanoribbons
are formed through self assembly of 3ABP/CD inclusion complexes. 2ABP/a-CD complex nanostructures
Available online 22 February 2014
show the self assembly hierarchical thread structure and b-CD complexes displays a nanobrick structure.
The formation of nanostructures are prearranged to HAOꢁ ꢁ ꢁH, NH2ꢁ ꢁ ꢁO and H2Nꢁ ꢁ ꢁH intermolecular
hydrogen bond between individual complexes. The absorption and fluorescence spectral changes explicit
formation of 1:1 inclusion complexes and solvent study demonstrate the ESIPT and TICT present in both
Keywords:
Aminobenzophenone
Cyclodextrin
molecules. The thermodynamic parameters (
sion complexes were determined from semiempirical PM3 calculations.
Ó 2014 Elsevier B.V. All rights reserved.
DH, DG and DS) of 2ABP and 3ABP molecule and the inclu-
Self assembly
Nanostructures
Molecular modeling
Solvent effects
Introduction
self-assembly of CDs and their derivatives are give more attention
in chemical, polymer and biological systems [4–9]. The molecular
The design of organic molecules permeates with specific
structural sequence that decides their spontaneous assembly into
organized nanoscale structures is a remarkable goal in supramolec-
ular chemistry [1,2]. The morphology of the assembly is regularly
determined by the structure of the individual components [3].
The molecular encapsulation and molecular assembly or
assembly based on
reversibly shuttled using a STM under ambient circumstances
[10]. The formation of nanotubes with -CD indicated that the
length of guest molecule is a key factor in the route of nanotube
formation [11]. Further, CD based nano-structures of linking b-
a-CD necklace in the polyrotaxane, which is
c
and
diphenyl-hexatrienes. These cyclodextrin-nanotubes were found
to consist of 20 b-CDs and 30–35 -CDs, respectively [12]. Further-
more, based on its dimension, CD cavity has to accommodate one
c-CD molecular nanotube aggregates by the encapsulation of
c
⁄ Corresponding author. Tel.: +91 94866 28800; fax: +91 4144 238080.
E-mail address: drrajendiran@rediffmail.com (N. Rajendiran).
http://dx.doi.org/10.1016/j.saa.2014.02.024
1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

N. Rajendiran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 52–60
53
or two guest molecules in the majority cases; if the guest is long
enough, three [13–15] or more numerous CD rings [16,17] can be
threaded along it. The micro rod formed by the secondary assem-
bly of b-CD nanotube induced by the guest molecule, the nanotube
of b-CD occupied by the guest molecule acted as a center for the
aggregation of b-CD to form the unfilled nanotube [18].
In this paper, the cyclodextrin covered 2ABP and 3ABP inclusion
complexes spectral properties are determined by UV–visible and
fluorescence measurements. Further, we summarize research on
nanomaterials formed by CDs with 3ABP and 2ABP possibly reflect-
ing the thought of nanoarchitectonics, according to classification of
unit nanostructures (nanorod, nanobelt, nanosheet, nanobrick),
prearranged assemblies (layer-by-layer (LbL) self-assembly) and
hierarchical structures, where research on inclusion complex is
developed into nanostructures through self-assembly is high-
lighted. The wrapping characteristics of 2ABP and 3ABP (Fig. 1)
onto CD nanomaterials are investigated by SEM, TEM, FTIR, DSC,
Powder X-RD and 1H NMR.
using KBr to pellets. 1H NMR spectra was recorded on a Bruker
AVANCE 400 MHz spectrometer (Germany) using D2O (99.9%) as
a solvent. The DSC were recorded using Mettler Toledo DSC1 fitted
with STRe software (Mettler Toledo, Switzerland), temperature
scanning range was from 25 to 250 °C with a heating rate of
10 °C/min. PXRD spectra were recorded with a BRUKER D8 advance
diffractometer (Bruker AXS GmbH, Karlsruhe, Germany) and the
pattern was measured in the 2h angle range between 5° and 80°
with a scan rate 5°/min.
Reagents and materials
2ABP, 3ABP,
a-CD and b-CD were purchased from Sigma–
Aldrich chemical company and used without further purification.
Triply distilled water was used for the preparation of aqueous
solutions. All solvents were used of the highest grade (spectrograde)
and all the spectral measurements were performed at the solute
concentrations of 4 ꢃ 10ꢂ5 M. The concentration of
a-CD and b-CD
solutions were varied from 1 ꢃ 10ꢂ3 to 10 ꢃ 10ꢂ3 M.
Experiments
Preparation of nanomaterials
Instruments
a
-CD or b-CD (1 mmol) was dissolved in 40 ml distilled water
and 2ABP or 3ABP (1 mmol) in 10 ml methanol was slowly added
to the CD solution. This mixture was sonicated at 40 °C for 2 h.
Then the solution was refrigerated overnight at 5 °C. The precipi-
tated 2ABP/CD and 3ABP/CD inclusion complexes were filtered
and the precipitate was washed with little amount of ethanol
and water to remove uncomplexed ABPs and CDs, respectively.
These precipitates were dried in vacuum at room temperature
for two days and stored in an airtight bottle. These powder samples
were using for further analysis.
Absorption spectral measurements were carried out with a
Shimadzu (Model UV 2600) UV–visible spectrophotometer and
steady-state fluorescence measurements were made by using a
Shimadzu spectrofluorometer (Model RF-5301). The fluorescence
lifetime measurements were performed using a picoseconds laser
and single photon counting setup from Jobin–Vyon IBH (Madras
University, Chennai). Scanning electron microscopy (SEM)
photographs were collected on a JEOL JSM 5610LV instruments.
The morphology of 2ABP and 3ABP encapsulated CD inclusion
complexes were investigated by TEM using a TECNAI G2 micro-
scope with accelerating voltage 100 kV and 200 kV, using carbon
coated copper TEM grid (200 mesh). FT-IR spectra of 2ABP, 3ABP,
Molecular modeling studies
a
-CD, b-CD and the inclusion complexes were measured from
The theoretical calculations were performed with Gaussian
03W. The preliminary geometry of the guest and CDs were
4000 cmꢂ1 to 400 cmꢂ1 on Nicolet Avatar 360 FT-IR spectrometer
A
B
A
B
11.02 Å
9.99 Å
(b)
(a)
1.37 nm
1.53 nm
0.65 nm
0.53 nm
H-3’
H-3’
H-3’
H-3’
0.79 nm
H-5’
H-5’
H-5’
H-5’
(d)
(c)
Fig. 1. The optimized structure with the numbering system of (a) 2ABP and (b) 3ABP obtained by PM3 level of theory and truncated cone shaped molecular structure of (c)
CD and (d) b-CD. The values represent dimensions of the corresponding molecules.
a-

54
N. Rajendiran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 52–60
constructed with Spartan 08 and then optimized by PM3 method.
-CD and b-CD were completely optimized by PM3 without any
kabs ꢄ 375, 236 nm, kflu ꢄ 429, 455s nm, water: kabs ꢄ 369,
226 nm, kflu ꢄ 425, 452 ws nm) is red shifted than that of 3ABP
a
symmetry limit [19,20]. Because the semiempirical PM3 method
has been shown to be a powerful tool in the conformational study
of cyclodextrin complexes and has high computational efficiency
in calculating CD systems, [19,20] it was selected to study the
inclusion process of CD with 2ABP and 3ABP in this work.
(cyclohexane: kabs ꢄ 328, 238 nm, kflu ꢄ 365 nm, methanol: kabs
ꢄ 340, 243 nm, kflu ꢄ 396, 339 nm, water: kabs ꢄ 328, 236 nm, kflu
-
-
ꢄ 421, 372 nm). The molar extinction coefficient is extremely high
(ꢄ10ꢂ4 cmꢂ1) and the absorption wavelength was blue shifted in
water which entail that excited state intramolecular proton trans-
fer (ESIPT) in 2ABP and twisted intramolecular charge transfer
(TICT) band in 3ABP is affected by the polar solvents. It is well
known that in ABPs, LW fluorescence band originates from the
ESIPT tautomer species of keto and enol form of 2ABP [24,25]
and TICT form of 3ABP molecule. Further it is already reported,
whenever two phenyl rings are split by the groups like SO2, CH2,
CO, NH, etc. they form a TICT state [19,23,26].
Results and discussion
Effect of CDs on ABPs in ground and excited states
The ground and excited state spectra of 2ABP and 3ABP
(4 ꢃ 10ꢂ5 M) were recorded in the absence and presence of differ-
The binding constant (K) of the inclusion complex nanomateri-
als of ABPs can be determined according to the double reciprocal
relation assuming the formation of a 1:1 [ABP:CD] complex [27].
ent
a
-and b-CD concentrations (pH ꢄ 6.5) and are shown in Table 1
and Figs. 2 and 3 respectively. The absorption maxima of 2ABP and
3ABP appear at ꢄ369, 226 nm and 331, 237 nm respectively in
aqueous solution. No significant spectral shift was observed an
addition of both CDs into the 2ABP and 3ABP aqueous solution.
1
1
a
1
¼
þ
ð1Þ
In 3ABP, the absorbance increases with increasing the
a-CD con-
ðI ꢂ I0Þ
ð
a
K½CDsꢅÞ
centration, where as it decreases in b-CD. However, in 2ABP, the
absorbance increases along with both CD concentrations. The
above changes in the absorption spectra with admire to concentra-
tion of CDs has been attributed to the improve dissolution of the
guest molecules through the detergent action of CDs [20–23].
Moreover, the variation in the absorption spectra is efficient as
being indicative the inclusion complex nanomaterial formation.
In addition to this a obvious isosbestic point was observed, desig-
nates a well-defined formation of 1:1 inclusion complex nanoma-
terial between ABPs and CDs. Fig. 3 shows the emission spectra
of 2ABP and 3ABP in aqueous solution containing various concen-
trations of CDs. The effects of CDs on the emission spectra of ABPs
are more pronounced than the absorption spectra with respect to
the concentration of CDs. In aqueous solution, the weak fluores-
cence of 2ABP and 3ABP molecules were observed at ꢄ425,
452s nm and 372, 421 nm respectively. The introduction of ABPs
where I0 and I are the absorption/emission intensities of ABPs in the
absence and in the presence of CDs, respectively; K is the binding
constant and
a is a constant. The free energy change can be calcu-
lated from the formation constant K by equation
D
G ¼ ꢂRT ln K
ð2Þ
The thermodynamic parameter
D
G for the binding of ABPs
molecule to CD is given in Table 1. As can be seen from Table 1,
the negative values for free energy change ( G) of these complexes
D
means that the binding process is a spontaneous and thermody-
namically favor in the experimental temperature range (303 K)
[20].
Encapsulation of ABPs into the CDs nanocavity, the ABP mole-
cule ‘A’ ring is deeply entrapped in the nonpolar b-CD cavity than
into CDs solution, the emission intensity of 2ABP/
a-CD and
that of a-CD cavity. The enhancement of TICT emission seems to
3ABP/ -CD was increased without changing the emission maxima
a
the position that C@O group present wider rim edge of b-CD cavity
while red shift was observed in 2ABP/b-CD and 3ABP/b-CD. Fur-
ther, in b-CD, the rate of enhancement of the longer wavelength
(LW) emission is higher than that of shorter wavelength (SW)
and amino substituted ‘B’ ring present in the highly polar aqueous
phase. However, in a-CD, 3ABP molecule ‘A’ ring does not encapsu-
late deeply into the CD cavity and the ‘B’ ring with C@O group is
band, where as in
a-CD, the enhancement is very small. These phe-
present into hydrophilic aqueous phase. If the ‘A’ ring is deeply en-
nomena would be suggested that guest molecules are deeply
encapsulated into the b-CD cavity and a highly binding complex
have been formed. Further, the CD cavity provided an apolar envi-
ronment for the guest and motion of the guest in the cavity was
largely confined. Thus, the enhanced rigidity of ABPs resulted is
an increase in its fluorescence quantum yield.
trapped in the a-CD cavity it should have given enhancement of
TICT (longer wavelength ꢄ447 nm) emission like ABPs/b-CD. In
addition to that, the amino group positioned to hydrophilic phase
of the CDs, thus can be form an intermolecular hydrogen bond
(IHB) with the another CD hydroxyl group; hence various nano-
structure complexes may be formed. The above discussions entail
that both ABPs forms unrelated 1:1 inclusion complexes with
CDs which directed to the formation of nanostructures.
In all the solvents, the absorption and emission maxima of 2ABP
(cyclohexane: kabs ꢄ 363, 236 nm, kflu ꢄ 416, 453s nm, methanol:
Table 1
Absorption and fluorescence maxima (nm) of 2ABP and 3ABP at different concentrations of
a- and b-CD.
Concentration of CD M
2ABP
-CD
3ABP
-CD
a
b-CD
a
b-CD
kabs
loge
kflu
kabs
loge
kflu
kabs
loge
kflu
kabs
loge
kflu
Water
0.002
0.010
369
226
369
227
369
228
345
ꢂ3.51
3.73
4.33
3.74
4.34
3.77
4.35
425
369
226
369
227
369
228
1015
ꢂ3.70
3.79
4.31
3.82
4.32
3.87
4.37
425
331
237
330
236
330
237
295
ꢂ3.42
4.12
4.30
4.13
4.31
4.15
4.33
421
372
421
373
421
374
350
ꢂ3.52
331
237
330
240
330
245
250
ꢂ3.32
4.12
4.30
4.09
4.28
4.03
4.26
421
372
442
374
447
376
273
ꢂ3.37
452s
425
452s
425
179
ꢂ3.33
452
428s
452
Binding constant (Mꢂ1
G (kcal molꢂ1
)
656
ꢂ3.38
D
)
Ws – weak shoulder; s – shoulder.

N. Rajendiran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 52–60
55
1.0
0.5
1.0
0.24
0.23
Abs
0.22
0.31
0.29
0.27
0.25
2ABP-β-CD
2ABP-α-CD
Abs
360 nm
8
360 nm
8
7
1
0.21
12
4
0
7
1
12
0
4
[β-CD] x 10-3
M
0.5
[α-CD] x 10-3 M
0
200
0
480
200
340
480
340
1.2
1.0
0.27
0.26
0.25
0.24
0.27
329 nm
8
0.25
0.23
0.21
Abs
Abs
329 nm
7
1
0
4
0
12
12
4
8
[β-CD]×10 -3
M
[α-CD] ×10-3
M
0.6
0.5
1
3ABP-α-CD
3ABP-β-CD
7
0
200
0
200
300
Wavelength (nm)
400
300
400
Wavelength (nm)
Fig. 2. Absorption spectra of 2ABP and 3ABP in different
a-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. Insert Fig.: plot
of absorbance vs. CD concentration.
180
1000
180
165
1000
2ABP-β-CD
2ABP-α-CD
If
If
500
0
150
7
1
0
4
8
12
0
12
4
8
[β-CD] x 10-3 M
[α-CD] x 10-3 M
500
90
7
1
0
380
0
380
200
505
If
630
460
580
920
460
0
200
3ABP-α-CD
850
425
3ABP-β-CD
If 185
170
423 nm
7
1
372 nm
0
0
0
4
8
12
4
8
12
[β-CD] x 10-3 M
[α-CD] x 10-3
M
100
7
1
0
340
460
580
340
460
Wavelength (nm)
580
Wavelength (nm)
Fig. 3. Fluorescence spectra of 2ABP and 3ABP in different
a 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. Insert Fig.:
fluorescence intensity vs. CD concentration. (2ABP-kexcitation: 370 nm, 3ABP-kexcitation: 330 nm).
Excited singlet state life time analysis
nanocavity. In
number of 2ABP and 3ABP molecules are leftover complex.
The 1 value of 2ABP and 3ABP in pure water is due to monomer
of guest and 2 is attributed to a hydrogen bonding interaction and
s3 value is attributed to the feasible aggregates of ABP molecules.
In the CD medium, s1 value are imputed to the free species of
2ABP and 3ABP in aqueous solution and s2 value is suitable to
hydrogen bonding interactions and s3 value concurs to the com-
a-CD and b-CD solution s1 designated certain
The lifetimes of the 2ABP and 3ABP molecules were measured
in water and 0.01 M CDs (Table 2). The excitation wavelength is
350 nm and emission wavelength is 450 nm for both ABP
molecules. The triexponential decay curve might be fitted for both
aqueous and CD medium. However, it was identified that the three
components of lifetime become slow with decreasing polarity.
This is because both guest molecules are entrapped into the CD
s
s
plex formation. Further, the guest molecules can induce
a-CD

56
N. Rajendiran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 52–60
Table 2
Time resolved fluorescence spectral data of 2ABP and 3ABP (excitation wavelength = 350 nm).
Compound
2ABP
Medium
Lifetime (ns)
Preexponential
hsfi
s1
s2
s3
a1
a2
a3
Water
0.61
0.09
0.09
2.01
1.28
2.65
5.42
4.28
4.93
0.58
1.38
0.09
0.02
0.03
0.05
0.01
0.03
0.02
1.31
2.09
3.50
a-CD
b-CD
3ABP
Water
0.56
0.05
0.04
1.94
1.18
1.87
5.98
4.07
4.67
0.65
1.3
0.11
0.03
0.04
0.05
0.01
0.02
0.02
1.39
2.01
3.19
a-CD
b-CD
and b-CD to form a various type of nanostructures, the excited sin-
glet state life time of 2ABP and 3ABP in -CD nanocavity was long-
er than that of b-CD nanocavity. The higher life time of CD medium
corresponds to a formation of inclusion complexes nanomaterial,
probably an extension of various types of nanostructures.
observed in a perpendicular bond distance, bond angles and dihe-
dral angles extremely altered at C8AC7AC1 and C8AC7AC1AC2
atom of ABPs molecules. The intermolecular hydrogen bonding
interactions in both inclusion complexes are shown in Fig. S1. In
a
3ABP/a-CD complex, one intermolecular hydrogen bond have been
recognized (distance of 2.94 Å) between the amino group nitrogen
and secondary hydroxyl group hydrogen atom of CD. In 3ABP/b-CD
complex, one intermolecular hydrogen bond has been identified
(distance of 2.66 Å) between the keto group oxygen and glucopyr-
anose ring hydrogen atom of CD. In 2ABP, the length of the hydro-
gen bond with the distance of 2.50 Å and 3.00 Å was recognized
Molecular modeling
The least energy of the molecular geometries was analyzed by
means of the stabilization energy (
DE) between 2ABP, 3ABP with
a-CD and b-CD, according to the following equation:
between hydrogen atom of the secondary OH of
a-CD and the
D
E ¼ EC ꢂ ðECD þ EABPs
The thermodynamically more favorable 1:1 inclusion
Þ
ð3Þ
nitrogen atom of NH2 group. The 2.72 Å length is recognizable be-
tween the hydrogen atom of the secondary OH of CD and the keto
group of 2ABP molecule. Further, in isolated 2ABP an intramolecu-
lar hydrogen bond is identified between NH2 group and C@O group
complexes identified by the negative energies. The complexation
energy is favorable in a wider rim side orientation of ABP mole-
cules with CDs. The energy of 3ABP with
ꢂ1245.27 kcal/mol, ꢂ1452.2 kcal/mol,
with the length of 1.88 Å which is extended in a-CD (2.49 Å) and b-
a
-CD and b-CD was
while 2ABP was
CD (2.57 Å) complexes due to twisting of the guest molecule dur-
ing encapsulation. The hydrogen bonds make attractive forces,
causing complexes stabilization and can be considered as the driv-
ing forces of the ABPs/CDs complexes. The non bonded interaction
between the ABPs phenyl ring and CDs might be liable for the dif-
ference in structure stability of the inclusion complex.
The energies of HOMO and LUMO are essential parameters in
quantum mechanical calculations. HOMO is the electron donor
and LUMO is the electron acceptor. The energies of HOMO, LUMO
and their orbital energy gaps were calculated by PM3 method are
summarized in Table 3. The 3D plots of the frontier orbital in the
S0 state HOMO and LUMO are shown in Fig. S2. The complex energy
gap is higher than the isolated ABPs molecules. In the molecular
orbital diagram, red color is shown in positive phase and green is
in negative phase. The 3D plots of HOMO level in ABPs were extend
to the entire B ring along with amino group, LUMO levels are
spread over the ABP molecules but somewhat low in amino group
[30]. In ABP/CD complexes, HOMO and LUMO energies levels on
ꢂ1244.93 kcal/mol and ꢂ1455.03 kcal/mol respectively (Table 3
and Fig. S1). The stabilization energy of 2ABP/CD and 3ABP/CD
complexes leads to exclusively negative values, which reveals the
energy of complex is lower than the sum of the isolated guest mol-
ecule energy [20,28,29]. The negative values demonstrate the pos-
sibility of complex development with ABPs incorporated in both
CD cavities. The ABP molecules cannot completely encapsulate into
the CD cavity, because t0he length of the guest molecule (3AB0P:
0
11.02 ÅA and 2ABP: 9.99 ÅA) are higher than the CD cavity (7.8 ÅA).
In ABP molecules, ‘A’ ring is completely positioned into the CD cav-
ity, the C@O group encapsulated in wider rim edge of the CD and
‘B’ ring with NH2 group positioned completely outside of the CD
cavity.
The bond distances, bond angles of ABPs were derived before
and after complexation are complied in Table 4, a small extent of
dimensions changes was observed and a significant dihedral angle
changes also predicted in ABP molecules. The changes were
Table 3
HOMO–LUMO energies and thermodynamic parameters calculations for 2ABP and 3ABP the inclusion complexes using PM3 method.
Parameters
2ABP
3ABP
a-CD
b-CD
2ABP:
a-CD
2ABP: b-CD
3ABP:
a
-CD
3ABP: b-CD
EHOMO (eV)
ELUMO (eV)
ꢂ8.10
ꢂ0.57
ꢂ7.53
0.67
ꢂ8.24
ꢂ0.53
ꢂ7.71
2.01
ꢂ10.37
1.26
ꢂ10.35
1.23
ꢂ9.36
ꢂ0.67
ꢂ8.69
8.27
ꢂ9.23
ꢂ9.28
ꢂ0.64
ꢂ8.64
8.55
ꢂ1245.27
ꢂ24.47
ꢂ428.26
116.12
ꢂ9.04
ꢂ0.67
ꢂ0.34
EHOMO – ELUMO (eV)
Dipole moment (D)
E*
ꢂ11.63
ꢂ11.58
ꢂ8.56
ꢂ8.70
11.34
12.29
11.37
13.92
26.86
26.82
ꢂ1247.62
ꢂ1457.63
ꢂ1244.93
ꢂ24.17
ꢂ550.23
ꢂ7.41
ꢂ1455.03
ꢂ24.26
ꢂ661.82
ꢂ5.84
ꢂ1452.52
ꢂ21.71
ꢂ522.78
133.91
ꢂ664.61
ꢂ159.86
0.475
D
E*
G*
133.54
163.13
0.991
132.83
162.80
0.100
ꢂ676.37
ꢂ570.84
0.353
ꢂ789.52
ꢂ667.55
0.409
D
G*
H*
ꢂ427.85
ꢂ20.14
0.410
ꢂ524.98
ꢂ20.56
0.458
ꢂ550.601
ꢂ142.56
0.410
D
S**
D
ZPVE*
H*
S**
ꢂ0.934
ꢂ0.942
ꢂ0.043
ꢂ0.034
129.24
128.76
635.09
740.57
766.96
873.13
766.85
871.88
*
kcal molꢂ1
.
**
kcal/mol-Kelvin, ZPVE – zero point vibrational energy.

N. Rajendiran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 52–60
57
Table 4
Geometrical parameters of 2ABP and 3ABP before and after inclusion with
a
-CD and b-CD for the stable inclusion complexes.
Parameters
3ABP
2ABP
2ABP:
a-CD
2ABP: b-CD
3ABP:
a-CD
3ABP: b-CD
Bond length (Å)
H9AH3
9.99
11.02
9.38
6.32
4.71
2.70
9.12
9.14
8.03
4.02
3.88
2.56
6.49
9.05
8.06
3.91
3.97
2.56
6.28
10.13
9.30
5.97
5.15
2.56
8.33
9.92
8.25
5.89
5.23
2.54
8.10
H
10AH2
8.08
4.42
3.45
2.70
6.49
NAC8
OAH2
C8AC1
C
11AN
Bond angle (°)
C8AC7AC1
OAC7AC1
H2ANAC3
C2AC3AN
128.41
28.16
87.30
127.50
116.38
120.08
119.93
118.25
119.97
85.23
118.40
119.25
85.38
118.52
119.50
111.21
119.40
116.93
120.89
111.66
119.93
116.78
118.37
30.72
Dihedral angle (°)
C8AC7AC1C2
OAC7AC1AC6
OAC7AC8AC13
H2ANAC3AC4
180.00
0.00
0.00
0.00
180.00
0.00
ꢂ119.89
30.09
ꢂ114.39
ꢂ89.31
17.23
ꢂ118.76
ꢂ116.64
5.23
ꢂ112.29
ꢂ112.77
ꢂ49.99
155.15
ꢂ3.83
180.00
180.00
35.29
19.24
146.17
each atom were slightly altered whereas amino group LUMO levels
spread very low. The energy gap of both CDs complex (Table 3) give
details of the charge transfer interaction within the ABP molecules,
the higher energy indicates the stability of the inclusion complex.
e, and h). Fig. S3g, 3ABP/b-CD complex shows spherical shape
agglomerated with needle like micro level morphology. The above
morphological changes concerning to the influence of guest host
complexes.
3ABP and 2ABP frontier orbital energy gap of
a-CD and b-CD com-
Figs. 4 and 5 TEM images show 2ABP/CD and 3ABP/CD inclusion
plexes was established to be ꢂ8.64 eV, ꢂ8.70 eV and ꢂ8.69 eV,
complex nanostructures. The shape and size of 3ABP/
a-CD com-
ꢂ8.56 eV respectively.
plex shows nanosheet (length ꢄ1 m, thickness ꢄ50 nm) structure
l
Further dipole moment value of both the inclusion complexes
were laying between the free guest and host, because CD cavity
polarity was decreased after the guest molecule entered into the
and two types of nanorods were identified with the thickness of
ꢄ10 nm and ꢄ50–70 nm. 3ABP/b-CD displayed various dimension
of nanoribbon with thickness of 65–75 nm and width of 100–
320 nm and did not show macroscopic agglomeration. Similarly,
a micro level dimension ribbon and needle was also observed in
the field of SEM images (Fig. S3d and e), which communicated to
the two dimensional expansion of single ribbon in TEM images.
cavity. For example, the dipole moment (8.55 D) of 3ABP/
a-CD
complex was lower than the isolated -CD (11.34 D) dipole
a
moment. However 3ABP/b-CD complex (13.92 D) is higher
than the isolated b-CD (12.59 D). As a result, one can conclude that
the dipole moment values explicit the strong association with the
complexation behavior.
Further, TEM images of 2ABP/a-CD complex revealed hierarchical
thread like structure with different width about 5–50 nm (Fig. 4a
and b), while 2ABP/b-CD TEM image displayed which was resem-
ble to brick morphology (Fig. 4c and d). The nanostructures forma-
tion of 2ABP/CD, 3ABP/CD complexes are ascribed to difference of
relative formation rates of various crystalline faces. The inclusion
complex act as a building blocks and it has unique structural fea-
ture for hierarchical supramolecular self assembly.
2ABP/CD and 3ABP/CD inclusion complexes nanostructure are
not absolutely indistinguishable since the template has some dis-
crepancy. The different ABPs/CDs complex self assembly led to var-
ious template effects, so the nanoarchitecture shape also have
dissimilar. The density of nanostructures is unequal (Figs. 4 and
The thermodynamic properties are summarized in Table 3. The
enthalpy changes (
energy ( G), were also calculated from the association of ABPs
with CDs. It can be observed that 3ABP bind to both CDs with an
unfavorable Gibbs free energy ( G > 0) but 2ABP molecule encap-
sulated with ( G < 0) favorable Gibbs free energy which confirmed
that the inclusion process of 3ABP/CD was non spontaneous pro-
cess and 2ABP/CD was spontaneous one. The higher negative
DH), entropy contribution (DS) and Gibbs free
D
D
D
D
H
values are observed for the ABP/CD complexes explain a favorable
number of connections relative to the tight binding of the guest
molecules to the CD cavity, because C@O group bond angle and
dihedral angle highly changed due to the restricted rotation of
the guest molecule. Further, the complex formation of ABP with
5), for example the 3ABP/a-CD complex nanosheet (Fig. 5a–c)
shows a layer by layer uneven sheet. The thickness of nanosheet
approximately ꢄ30–50 nm, and nanoribbon is ꢄ65–75 nm which
confirms the nanosheet and ribbon was not a single layer aggrega-
tion of 3ABP/CD inclusion complex. A closer judgment of a nano-
sheet boundary confirmed the presence of thin layers, which
have stacked together due to bulk assembly of these complexes
all CDs were exothermic and most enthalpy-driven (
process.
DH > DS)
Micro and nanolevel morphological study
SEM microphotographs of 2ABP, 3ABP,
a-CD, b-CD and binary
or numerous nanorod assemblies. In 3ABP/a-CD, we found that
solid systems are shown in Fig. S3. 3ABP is characterized by ball
like agglomerated type (Fig. S3c), 2ABP displays cashewnut mor-
phology (Fig. S3f), a-CD and b-CD consists of amorphous character
with prismatic and plated shape structure was observed respec-
tively in Fig. S3a and b [31,32]. 2ABP and 3ABP inclusion complex
nanomaterials were clearly visible, confirming the presence of
the layer by layer nanosheet which was bounded by ꢄ10 nm thick-
ness of nanorod (Fig. 5b and c). While the 3ABP/b-CD complex for-
mation show the knife like structure with unequal dimension
(Fig. 5d). Such nanodimensions were formed due to the effect of
various driving forces (Figs. 4 and 5). Further, the 3ABP/CD mech-
anism followed in 2ABP/CD complex, which shows hierarchical
thread like structure and perfect dimensions of nanobrick structure
(Fig. 4a–c). The brick structure was assembled through layer by
layer (LbL) arrangement (Fig. 4c and d), which conforms the brick
was not a single layer aggregation of nanosheet but it was
characteristic crystalline morphology. 2ABP/a-CD and 3ABP/a-CD
complex nanomaterials show micro rod and ribbon like sheet mor-
phology respectively whereas 2ABP/b-CD showed the disparity size
and shape of the microcrystal structures were identified (Fig. S3d,

58
N. Rajendiran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 52–60
(a)
(b)
(c)
(d)
Fig. 4. TEM images of (a and b) 2ABP/a-CD and (c and d) 2ABP/b-CD nanostructure.
multilayer bulk assembly sheet. The above nanostructures were
confirmed that the ratio of 1:1 [ABP:CD] inclusion complex has
been developed a miniature nanorods (Fig. 5) [33,34].
ꢄ500 units of 2ABP/b-CD initially form a primary single nanorod
(head to head arrangement) the consequences of such a nanorod
(a-axis) leads to the substantial growth of ꢄ300 number of adja-
cent nanorods were formed through secondary self assembly by
the way of b axis (Fig. S4). The termination of this arrangement
ended with the formation of nanosheet. Further, the above individ-
ual nanosheets were arranged layer by layer through the stacking
forces (c-axis). As cited above, the same theory was applicable to
The shape and size of nanostructures is controlled by steric hin-
drance and the polarity of host and guest. The 2ABP/CD and 3ABP/
CD complexes have high activity, they tend to form a nanostruc-
tures through intermolecular hydrogen bonding with nearby com-
plexes. The hydrogen bond possibility concern to the CD and guest
molecules polar hydroxyl, oxygen, amino and keto groups. Further,
many factors influence the growth of the inclusion complex nano-
structures which are followed by the arrangement of head–head,
tail–tail or head–tail [10], in other words the 2ABP/CD and 3ABP/
CD individual complex are deliberately prearranged to HOꢁ ꢁ ꢁH,
NH2ꢁ ꢁ ꢁO and H2Nꢁ ꢁ ꢁH intermolecular hydrogen bonds are present
in the supramolecular assembly.
the formation of nanosheet by 3ABP/a-CD complex and nanosheet
by 3ABP/b-CD complex. All the above individual complexes are ar-
ranged at one dimensionally (a-axis) to form a pseudopolyrotaxane
like structure through intermolecular hydrogen bondings. These
pseudopolyrotaxane further aggregate into brick, ribbon and sheet
type nanostructures.
From the above discussion nanoribbon, nanorod, nanosheet,
hierarchical thread and nanobrick may be related to the weaker
supramolecular interaction such as van der Waals force, inter
molecular hydrogen bond between neighboring inclusion
complexes, and also between host and guest molecules. Liu et al.
reported that a linear structure was attained from 4-hydroxyazo-
benzene and 4-aminoazobenzene with b-CD complex by intra-
FT-IR spectral studies
The host guest complex in their solid state has been analyzed by
FTIR spectra (Fig. S5). The interaction between the guest and the
host often leads to identifiable changes in the infrared profile of
complexes. In isolated 2ABP and 3ABP, the intense peak appeared
around 3330 cmꢂ1 are due to NH2 asymmetric and symmetric
stretching modes may be shrouded by the huge number of CD
hydroxyl groups in the inclusion complexes. The aromatic CAH
and inter-dimer hydrogen bonding, intradimer
p–p interactions
and wave-type structure was attained respectively [35]. Thus, we
believe that the hydrogen bonding interaction of ABP–CD complex
which is a driving force for self-assembly process and strengthen
the secondary assembly of cyclodextrin. Schematic representation
of supramolecular structure consisting of nanorods, nanobrick and
nanosheets are shown in Fig. S4. The 2ABP/CD and 3ABP/CD com-
plexes form five type of self-assembly nanostructure and can be
visualize by using molecular modeling.
stretching appears as
a weak absorption band at 3000–
3100 cmꢂ1 was disappeared in the CD complexes. The aromatic
ring skeletal vibration is observed around 1450 cmꢂ1 was diffused
and slightly distorted due to inclusion complexes (3ABP:
a-
CD:1455 cmꢂ1 b-CD:1454 cmꢂ1 -CD:1408 cmꢂ1
,
,
2ABP: b-
a
,
CD:1436 cmꢂ1). The sharp C@O group stretching frequency
(ꢄ1647 cmꢂ1) is slightly shifted to ꢄ10 cmꢂ1 in both complex
forms. The CAC@O stretching frequency of 3ABP and 2ABP ap-
peared at 518 cmꢂ1, 536 cmꢂ1 is slightly altered in the inclusion
complexes. The C@C stretching frequency of 3ABP, 2ABP at
From Fig. S1, the thickness and length of b-CD complexes of
2ABP and 3ABP is found to be 1.50 nm, 1.20 nm respectively, the
thickness and length of
a-CD complex is 1.30 nm, 1.15 nm. The

N. Rajendiran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 52–60
59
(a)
200 nm
(b)
(c)
Layer by layer sheet
Bounded nano rod
100 nm
50 nm
(e)
(d)
1μnm
2 μm
Fig. 5. TEM images of (a, b, and c) 3ABP/
a-CD and (d and e) 3ABP/b-CD nanostructure.
ꢄ1587 cmꢂ1 is moved to longer wave number and the intensity
was diffused in the complex. These changes confirmed that the
aromatic part of ABPs was included into the hydrophobic cavity
of CDs. The disparity of the shape, shift and intensity of the IR spec-
tral signals in the complex proves the formation of inclusion which
was in good unity with the NMR results.
Powder X-ray diffraction
The complexation of 3ABP and 2ABP with CD was further inves-
tigated by PXRD. The PXRD patterns of pure 3ABP, 2ABP and the
corresponding inclusion complexes are shown in Fig. S7. In con-
trast to the 3ABP complexes, we observed that diffraction pattern
completely diffused, which reveals its amorphous nature. How-
ever, in 3ABP complexes, the characteristic high-intensity diffrac-
tion peaks were detected for each complex which explains the
crystallinity form. The above result indicates that the interaction
between 2ABP, 3ABP and CDs, that led to formation of a new solid
phase and taken as an evidence for the formation of inclusion com-
plexes. The PXRD patterns of 2ABP/CD and 3ABP/CD were charac-
terized by higher diffraction peaks, moreover there is no
possibilities to identified the characteristic peak of pure 3ABP,
2ABP and CDs. This result proves that 3ABP and 2ABP are no longer
present as a crystalline materials and 3ABP, 2ABP was dispersed in
a molecular state with the CD cavity. The crystalline nature diffrac-
tion patterns of all samples were good agreement with SEM
crystalline morphology.
Differential scanning calorimetry
The DSC profiles of pure components (3ABP, 2ABP, a-CD and b-
CD) and binary systems in the melting region of the ABPs and com-
plex dehydrations are shown in Fig. S6. The thermal curve of the
raw materials (3ABP, 2ABP and CDs) was compared with inclusion
complexes confirm the interaction between the guests and host
also show a real inclusion and crystalline nature of the complex.
The DSC curves appeared at 78.8 °C, 108.5 °C, and 135.4 °C for pure
a-CD and 128.0 °C for pure b-CD. In fact, the formation of an inclu-
sion complex was suggested by the absence of the melting endo-
therm of 3ABP at 82.3 °C and 2ABP at 106.3 °C. The inclusion
complex endothermic peaks, for the 3ABP/a-CD: 75.4 °C,
128.2 °C; 3ABP/b-CD: 125.8 °C and 2ABP/ -CD: 74.7 °C, 124.2 °C;
a
2ABP/b-CD: 67.9 °C, 129.2 °C. Further, 3ABP/b-CD curve displayed
an exothermic peak at 174.2 °C associated to the 3ABP/b-CD tran-
sition into the crystal phase. The above endothermic peak indicates
that in the inclusion complexes 3ABP and 2ABP has maintained its
original crystallinity.
Proton nuclear magnetic resonance spectroscopy
1H NMR study is a better technique for analysis of encapsulation
of a guest molecule into the hydrophobic CD cavities (Figs. S8 and
S9). The interior of the CD cavity hydrogen atoms (H3 and H5) are

60
N. Rajendiran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 52–60
usually shifted in the presence of guest molecule. The changes of
the proton chemical shifts were conformed the formation of inclu-
sion complexes. Further the detailed variation of CDs with ABPs
chemical shifts are shown below:
fellowship. The authors acknowledge UGC Networking Resource
Centre School of Chemistry and Centre for Nanotechnology,
University of Hyderabad for providing equipment facilities for char-
acterization. We gratefully acknowledge Prof. M.V. Rajasekharan,
Dean School of Chemistry, University of Hyderabad for his kind
help. We thank Dr. P. Ramamurthy, Director, National Centre
for Ultrafast Processes, University of Madras for allowing the
fluorescence lifetime measurements for this work.
3ABP/a-CD complex/b-CD complex: Ha-7.716/7.691/7.697; Hb-
7.656/7.673/7.604; Hc-7.568/7.567/7.509; Hd-7.7181/7.181/7.181;
He-6.944/6.944/6.954; Hf-6.843/6.839/6.843; Hg-6.822/6.820/
6.826; Hj- 5.408/5.401/5.412.
2ABP/a-CD complex/b-CD complex: Ha-7.536/7.562/7.578; Hb-
7.528/7.541/7.551; Hc-7.510/7.529/7.535; Hd-7.508/7.515/7.523;
He-7.288/7.289/7.286; Hf-7.251/7.274/7.250; Hg-6.868/6.867/
6.863; Hj-6.505/6.505/6.500.
In 3ABP, protons of the two aromatic rings (A and B) were
appeared individually. In the presence of CD, the Ha and Hb protons
in ‘A’ ring and Hc protons in ‘B’ ring were found resonating at a
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2014.02.024.
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This work is supported by the CSIR (No. 01(2549)/12/EMR-II)
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