Spectroscopic studies of inclusion complex of β-cyclodextrin and benzidine diammonium dipicrate

Article abstract of DOI:10.1016/j.saa.2009.09.018

Formation of inclusion complex between benzidine diammonium dipicrate and β-cyclodextrin with stoichiometry 1:2 (guest-host) has been established by UV, ¹H NMR, ¹³C NMR, IR spectra and powder X-ray diffractometry. ¹H NMR studies are used to confirm the inclusion and to provide information on the geometry of dipicrate inside the cavity of β-cyclodextrin.

Full text of DOI:10.1016/j.saa.2009.09.018

Spectrochimica Acta Part A 75 (2010) 32–36
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Spectroscopic studies of inclusion complex of ␤-cyclodextrin and benzidine
diammonium dipicrate
H. Hamdi, R. Abderrahim∗, F. Meganem
Laboratory of Organic Synthesis, Department of Chemistry, Faculty of Science of Bizerte, 7021 Jarzouna, Bizerte, Tunisie
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 11 March 2009
Received in revised form 13 August 2009
Accepted 12 September 2009
Formation of inclusion complex between benzidine diammonium dipicrate and ␤-cyclodextrin with sto-
ichiometry 1:2 (guest–host) has been established by UV, 1H NMR, 13C NMR, IR spectra and powder X-ray
diffractometry. 1H NMR studies are used to confirm the inclusion and to provide information on the
geometry of dipicrate inside the cavity of ␤-cyclodextrin.
© 2009 Elsevier B.V. All rights reserved.
Keywords:
␤-Cyclodextrin
Benzidine diammonium
Dipicrate
Inclusion complex
1. Introduction
The supramolecular chemistry is that discipline of chemistry
which involves all intermolecular interactions where covalent
bonds are not established between the interacting species. The
majority of these interactions are of the host–guest type. Among
the majority of host, the cyclodextrin seemS to be the most impor-
tant host to form inclusion complexes especially with wide variety
of guest molecules with suitable polarity and dimension [1,2].
The cyclodextrins are cyclic oligosaccharides (A) obtained from
simple enzymatic degradation. The most important structural
feature of these compounds is the hydrophobic internal cavity
and hydrophilic external surfaces (B) [3]. The inclusion com-
plex between the cyclodextrin host and the guest is determined
by several weak forces, including Van der Waals, hydrophobic
dipole–dipole and hydrogen bonding interactions [4].
Cyclodextrins are widely used in pharmaceutical industry [5]
with the aim of enhancing drug solubility in aqueous solutions,
reducing toxicity and to control the rate of release.
Benzidine is often used to produce dyes. The major class of
dyes are derived from benzidine and are used primarily to colour
textiles, leather, and paper. However it is also one of the serious
organic contaminations and it is usually difficult to treat indus-
trial waste and living sewage. To solve the problem environmental
cyclodextrin [6] can increase solubility of some contaminations,
reduce their toxicity and catalyze their decomposition. On account
of all the previous reasons, we report here the synthesis of benzi-
dine diammonium dipicrate and the synthesis and spectroscopic
studies of the new inclusion complex formed from dipicrate and
␤-cyclodextrin which makes the solubility of benzidine in water
increase.
∗
Corresponding author. Tel.: +216 98948066.
E-mail address: Abderrahim raoudha@yahoo.fr (R. Abderrahim).
1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.09.018

H. Hamdi et al. / Spectrochimica Acta Part A 75 (2010) 32–36
33
2. Experimental
2.1. Apparatus
IR spectra were recorded on Perkin Elmer Paragon 1000
PC spectrometer using sample dispersed in spectroscopi-
cally pure potassium bromide pellets. Spectra resolution was
4 cm−1
a
.
1H NMR and 13C NMR spectra were recorded with DMSO-d6
solvent containing TMS (tetramethylsilane) on a Bruker 300 spec-
trometer (1H: 300 MHz, 13C: 75.47 MHz). The chemical shifts (ı)
are reported in ppm relative to TMS (internal reference). For the
1H NMR, the multiplicities of signals are indicated by the follow-
ing abbreviations: s: singlet, d: doublet, t: triplet, q: quartet, m:
multiple.
The powder X-ray diffraction patterns were obtained by PHILIPS
PW 1729 diffractometer. The UV–visible spectrum was recorded in
the range 200–400 nm with an UV JENWAY 6405 spectra photome-
ter equipped with a stoppered quartz cell with 1.0 cm optical path
length.
Fig. 1. Powder X-ray diffractometry of (a) physical mixture in molar ratio 1:2
(guest:host), (b) inclusion compound, (c) ␤-cyclodextrin and (d) dipicrate.
DSC–TGA analysis was performed using TA DSC-TGA SDT-2960
instrument in flowing N2 with an average heating rate of 5 ◦C/min
between room temperature and 450 ◦C.
icrate, ␤-cyclodextrin monomer, inclusion compound and physical
mixture in molar ratio 1:2 (guest:host). The powder X-ray pattern
of the inclusion compound shown in Fig. 1 was different from that
of dipicrate and ␤-cyclodextrin monomer. The difference between
the spectra of dipicrate, the ␤-cyclodextrin and the spectra of inclu-
sion compound is due to the interactions of ␤-cyclodextrin with
dipicrate and produces a new structure.
2.2. Reagents
␤-Cyclodextrin, picric acid, benzidine-3,3ꢀ-diamine were
obtained from Aldrich Chemical Co. Other chemical reagents of
analytical reagent grade were used as commercial.
3.2. Thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC)
2.3. Synthesis of benzidine diammonium dipicrate
10−4 mol (0.0229 g) of picric acid was dissolved in diethyl
ether and 5 × 10−5 mol (0.0092 g) of benzidine-diamine dissolved
in diethyl ether was slowly dropped into ␤-CD–diethyl ether solu-
tion with sufficient stirring. The stirring operation was kept for
at least 24 h at room temperature. At the end of the reaction, a
great deal of yellow crystal precipitate, the dipicrate was obtained
by filtration. The product was washed with dichloro methane for
three times. The product obtained was confirmed by powder X-ray
diffractometry, 1H NMR, 13C NMR, IR and UV spectra.
The thermogravimetric analysis and differential scanning
calorimetry of ␤-cyclodextrin, physical mixture in molar
ratio 1:2 (guest:host) and inclusion compound are shown in
Fig. 2.
Thermogravimetric analysis has mainly been applied to demon-
strate the different behaviour of an inclusion compound relative to
its physical mixture of component compound [8].
Thermogravimetric analysis of inclusion compound shows a
weight loss at 250 ◦C. The weight loss should correspond to the
beginning of the degradation of the complex.
DSC analysis further supports the formation of a dipicrate: ␤-
CD inclusion compound. A comparison of the TGA and DSC (Fig. 2)
traces of the complex, the physical mixture and ␤-CD showed sig-
nificant differences. The difference between them confirms the
formation of the complex. The melting point was determined by
TGA trace and are listed in Table 1.
2.4. Synthesis of inclusion complex
0.5 × 10−3 mol (0.5675 g) of ␤-cyclodextrin and 0.25 × 10−3 mol
(0.16 g) of benzidine diammonium dipicrate were dissolved by
30 mL distilled water and 20 mL EtOH respectively. Then ben-
zidine diammonium dipicrate–EtOH solution was dropped into
␤-cyclodextrin aqueous solution with continuous stirring. The stir-
ring operation was left for 72 h at room temperature after which it
gave birth to a yellow solid product, inclusion complex of benzi-
dine diammonium dipicrate and ␤-cyclodextrin (␤-CD) that was
obtained by filtration. The yellow precipitate was washed with
ether for three times in turn, respectively to clean the residual guest
and host monomers. Then it was dried in vacuum oven at 40 ◦C for
48 h (yield = 80%). Elemental analysis: % C: 42.43; % H: 5.23; % N:
3.67.
Table 1
Melting point of dipicrate, ␤-cyclodextrin and inclusion compound.
Peak
Melting point
(◦C)
Benzidine diammonium dipicrate
␤-Cyclodextrin
Inclusion complex (␤-cyclodextrin/dipicrate)
Exothermic
Endothermic
Endothermic
253.6
300
239
The structure of inclusion complex was confirmed by powder
X-ray diffractometry UV absorption, IR, 1H NMR, 13C NMR spectra.
Table 2
Absorption spectral data of dipicrate and inclusion complex.
3. Results and discussion
ꢀmax (nm)
A
ε (L mol cm−1)
3.1. X-ray powder diffraction
Benzidine
Diammonium dipicrate
Complex
280
355
288
363
0.812
0.978
0.377
0.433
27,066
32,600
12,566
14,433
The formation of the inclusion complex was confirmed by X-ray
diffractometry [7]. Fig. 1 refers to the powder X-ray pattern of dip-
(␤-Cyclodextrin/dipicrate)

34
H. Hamdi et al. / Spectrochimica Acta Part A 75 (2010) 32–36
Fig. 3. Absorption spectra of (a) dipicrate, (b) inclusion complex and (c) ␤-CD.
sion complex, then we can suggest that the solution still contains
dipicrate and ␤-CD with 1:2 molar ratio (guest:host).
3.4. Infrared spectral studies
In comparison with dipcrate, the +NH3 stretching vibrations
were in the region (3040, 3240 and 3400 cm−1) and symmetri-
cal/asymmetrical +NH3 vibrations (2450, 2600 cm−1) are largely
affected in the inclusion compound 3318 and 2922 cm−1, respec-
tively. The symmetrical/asymmetrical NO2 (1300, 1500 cm−1) are
also affected by the complexation (1330, 1490 cm−1).
The C C bending vibration of aromatic (1450, 1500, and
1600 cm−1) is also blue shifted to 1433, 1490, 1555 cm−1, respec-
tively.
In comparison with ␤-CD, the C–O vibration of primary and sec-
ondary alcohol were in the region (1100, 1050 cm−1) respectively
these are largely affected in the complex (1080, 1029 cm−1).
The intensity diminishing in the inclusion compound FTIR
spectrum can prove the inclusion because the inclusion complex
between the cyclodextrin host and the guest causes the change
of the microenvironment of the guest, host and the formation of
hydrogen bonding between the heteroatom of the guest and the
primary hydroxyl group at the edge of the ␤-CD cavity. These rea-
sons induce a decrease of the value of the absorption of stretching
and bending vibration modes of different groups such as C–O (alco-
hol), +NH3, C C, NO2 group.
Fig. 2. Thermogravimetric analysis and differential scanning calorimetry thermo-
grams of (a) ␤-cyclodextrin, (b) physical mixture in molar ratio 1:2 and (c) inclusion
compound.
3.3. Absorption spectra
All the frequencies of different group were affected by the com-
plexation. This finding indicates that dipicrate is included in the
␤-CD cavity.
Absorption spectral data of dipicrate and inclusion complex in
the mixture of water and ethanol (60/40, v/v) (C = 3 × 10−5 M) are
listed in Table 2.
Fig. 3 shows the absorption spectra of dipicrate and inclusion
complex. We establish that the absorption peaks of dipicrate at 280
and 355 nm were slightly shifted to longer wavelengths. This find-
ing indicates the formation of dipicrate–␤-CD inclusion complex.
The concentration of dipicrate and ␤-CD in the filtrate was deter-
mined by UV spectroscopy. The UV spectrum of the filtrate in the
mixture of water/ethanol (60/40, v/v) and in the C = 3 × 10−5 M was
shown to be nearly identical with the UV spectrum of the inclu-
3.5. 1H NMR spectrum
The 1H NMR has proved to be a useful tool in the study of
cyclodextrin inclusion complex [9–11]. Direct evidence for the for-
mation of dipicrate and the inclusion complex can be obtained by
1H NMR and 13C NMR spectra. The information gained from NMR
spectroscopy relies on the observation of selective line broadening
and/or chemical shift of displacement of 1H NMR spectral signals
Table 3
Chemical shifts ı and ꢁı of protons of ␤-cyclodextrin in free host, dipicrate in free guest and inclusion complex.
H2
3.299
H4
3.281
H3
3.608
H5 and H6ab
3.420
H1
4.811
Hi
He
Hp
ı (␤-Cyclodextrin)
Dipicrate
7.380
7.740
8.610
ı(Dipicrate–␤-cyclodextrin)
ꢁı
3.291
−0.008
3.279
−0.003
3.543
−0.065
3.340
−0.080
4.803
−0.008
7.240
−0.140
7.670
−0.070
8.572
−0.038

H. Hamdi et al. / Spectrochimica Acta Part A 75 (2010) 32–36
35
Fig. 4. 1H NMR spectra in DMSO-d6 of the inclusion complex (dipicrate–␤-CD).
Fig. 6. 13C NMR spectra in DMSO-d6 of the inclusion complex (Dept 135).
Fig. 5. 13C NMR spectra in DMSO-d6 of the inclusion complex.
of the guest and host protons [9–11]. It is well known that H5 and
Fig. 7. 13C NMR spectra of correlation 1H–13C.
H3 protons are located in the interior of the ␤-cyclodextrin’s cavity,
and it is, therefore, likely that the inclusion of dipicrate with ␤-CD
will affect the chemical shifts of theses two protons [12,13].
The significant distinction between the 1H NMR spectra of dip-
icrate, ␤-CD and the inclusion complex of dipicrate with ␤-CD in
DMSO-d6 (Fig. 4) confirm that the inclusion complex was formed.
The value of chemical shifts for different protons in ␤-CD, dipicrate
and dipicrate–␤-CD inclusion complex was listed in Table 3.
The complexation causes an upfield shift of ␤-CD protons; a
great upfield was recorded for H5 and H3. (Table 4) However, the
variation of the shift is not the same for all protons. H3 signal shows
an upfield shift of about 0.065 ppm. Since H3 is located in the inte-
rior of the cavity, we suggest that H5 signal shows approximately
similar amount of upfield shift because both are located inside the
cavity and will suffer similar amount of shielding. The upfield shift
observed for H5 and H3 confirms the inclusion inside the cavity.
However, an exact value of the shift was hard to be determined
due to the complication in the spectrum upfield on inclusion. Fur-
ther confirmation was obtained by observing the changes in the
chemical shifts of dipicrate.
The 1H NMR spectrum of dipicrate in DMSO-d6 has revealed that
dipicrate has four types of protons: the Hi doublet at ı 7.38, the He
appears as a doublet at ı 7.74; the Hp signal appears as singlet at ı
8.61 and the Ha (+NH3) at 3.5.
The phenyl ring of dipicrate made the signals of protons (H3 and
H5) upfield shift. Whereas the chemical shifts of H1, H2, H4 and H6ab
,
which are on the outer surface of ␤-CD, were only slightly affected
by the guest molecule, the chemical shifts of Hi, He, Hp of dipicrate
was affected by the complexation.
The 1H NMR spectrum of an inclusion complex between dipi-
crate and ␤-CD has revealed a broad signal attributed to the protons
of OH of the water molecules within the ␤-CD cavity
Table 4
Chemical shifts ı of carbons in ␤-CD in free host, dipicrate in free host and inclusion complex.
C1
C2
C3
C4
C5
C6
ı (␤-CD) in free host
ı (␤-CD) in the complex
101.91
102,30
71.93
72.78
72.34
72.40
81.52
81,92
72.94
73.42
59.87
60
C(Hi)
122.50
C(Hp)
C(He)
C(NO2)
160.88
C(Hii)
124.33
C(+NH3)
141.90
ı (Dipicrate) in free guest
ı (Dipicrate) in the complex
125.43
125.50
127.90
128.00
122.70
161.10
124.60
142,20

36
H. Hamdi et al. / Spectrochimica Acta Part A 75 (2010) 32–36
Fig. 10. Approach of an incoming cyclodextrin molecules to benzidine diammonium
dipicrate molecule.
4. Stoichiometry of the inclusion complex
The stoichiometry of the complex of dipicrate with ␤-CD at 25 ◦C
was determined by 1H NMR, 1H–1H NMR NOE (Figs. 8 and 9) or by
using UV–vis spectroscopy.
The ratio of dipicrate to ␤-CD in inclusion complex can be deter-
mined by the peak area of proton of dipicrate and ␤-CD in inclusion
complex respectively. The integrated intensities of H4 in ␤-CD res-
onance and the dipicrate Hi resonance are approximately 14 and
4 respectively. These values confirm that the ratio of dipicrate to
␤-CD in inclusion complex is 1:2.
Fig. 8. 1H–1H NOE spectra of the inclusion complex dipicrate–␤-CD.
The NOE experiments were particularly useful for the determi-
nation of structural arrangements of molecular complexes.
Figs. 8 and 9 showed 1H–1H NMR NOE (NOESY) and 1H–1H NMR
COSY spectra in DMSO-d6. It can be seen from these spectrums, that
the presence of the correlation between the Hi of dipicrate with
the H3 and H5 of ␤-CD, with strong intensity suggested that the
dipicrate completely entered into two hydrophobic cavities of two
␤-CDs (Fig. 10).
The chemical shifts of Hi, Hp, He located in the hydrophobic cav-
ity of ␤-CD were also significantly affected by the protons H3 and H5
of the host molecule because of the intermolecular interaction (for-
mation of hydrogen bonding) between dipicrate and ␤-CD. From
these results, we can suggest that the ratio of dipicrate ion to ␤-CD
in inclusion complex is 1:2 (guest:host).
Acknowledgement
Authors thank the Secretary of State for Scientific Research and
Technology (UR-05/12) for the financial support of this work, code.
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C(NO2), C(Hii), C(+NH3)) (Fig. 5).
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