Molecular recognition of 1,5 diamino anthraquinone by p-tert-butyl-calix(8) arene

Article abstract of DOI:10.1007/s10895-010-0651-z

The molecular recognition properties of p-tert-butyl-calix(8)arene with 1,5-diamino anthraquinone (1,5 DAAQ) were studied by using UV-Visible and Fluorescence spectroscopic techniques. The binding constant was determined by using the Benesi-Hilde brand expression. It was found that the host-guest complex was formed between 1,5 DAAQ and p-tert-butyl- calix(8)arene in the 1:2 Stoichiometry ratio. Springer Science+Business Media, LLC 2010.

Full text of DOI:10.1007/s10895-010-0651-z

J Fluoresc (2010) 20:1017–1022
DOI 10.1007/s10895-010-0651-z
ORIGINAL PAPER
Molecular Recognition of 1,5 Diamino Anthraquinone
by p-tert-butyl-Calix(8)arene
G. Suganthi & C. Meenakshi & V. Ramakrishnan
Received: 8 December 2009 /Accepted: 24 March 2010 /Published online: 18 May 2010
#
Springer Science+Business Media, LLC 2010
Abstract The molecular recognition properties of p-tert-
butyl-calix(8)arene with 1,5 -diamino anthraquinone (1,5
DAAQ) were studied by using UV–Visible and Fluores-
cence spectroscopic techniques. The binding constant was
determined by using the Benesi-Hilde brand expression. It
was found that the host–guest complex was formed
between 1,5 DAAQ and p-tert-butyl- calix(8)arene in the
industry for colouring textile materials and in medicine as
an antioxidant. The biological effects of these drugs are due
to the interaction of the chromophore group with DNA [2].
Diamino anthraquinones find applications in the field of
biochemistry and electrochemistry. They are used in the
synthesis of electroactive dendrimers and preparation of
solid state redox super capacitors [3]. In general the optical
properties of the anthraquinone derivatives depend on the
position of the substituents, the ability to form hydrogen
bonds and the occurrence of intermolecular interactions [4].
Calixarenes are a class of versatile molecular hosts with
growing applications in the field of supramolecular chem-
istry [5]. The calixarenes which are macrocyclic com-
pounds containing cavities of molecular sized dimensions,
are interesting because of their potential as enzymic mimics
1
:2 Stoichiometry ratio.
.
Keywords 1, 5 -Diaminoanthraquinone p-tert-butyl-calix
.
.
.
(
8)arene Molecular recognition Host–Guest interaction
Absorption and fluorescence spectroscopy
Introduction
[
6]. Calixarenes have hydrophobic cavities that can hold
Anthraquinone is an aromatic organic compound and it is
the most important quinone derivative of anthracene. The
anthraquinone is chemically stable under normal condi-
tions. Anthraquinones naturally occur in some plants like
aloe, cascara, senna, buckthorn etc. Natural anthraquinone
derivatives tend to have laxative effects [1]. Anthraquinone
derivatives are important class of a system that absorb in
the visible region. They are used principally in photograph-
ic dye chemicals, in paper industries as a catalyst, in textile
smaller molecules or ions. The molecular recognition refers
to the specific interaction between two or more molecules
through non covalent bonding such as hydrogen bonding,
hydrophobic forces and Vander waals forces. Because of its
special cavity structure, high melting point and thermal
stability, it was found to be useful in gas chromatography as
stationary phase [7]. Calixarene is an ideal candidate for the
construction of new types of dendrimers and plays very
important role in the recognition for cations, anions and
neutral molecules [8, 9]. Calixarenes are basket-like
macrocyclic receptor molecules consisting of cyclic arrays
of phenol moieties linked by methylene groups. Calixarenes
possess functionalization sites on both upper and lower
rims [10].
:
G. Suganthi (*) V. Ramakrishnan
Department of Laser Studies, School of Physics,
Madurai Kamaraj University,
Madurai 625 021, India
e-mail: sugiphys@yahoo.co.in
Calixarenes have internal cavities of different size
formed by a belt of phenyl rings; these cavities are capable
to accommodate a guest molecule of a definite size, which
allows their use in molecular recognition. Expenses for the
preparation of calixarenes from P-substituted phenols and
C. Meenakshi
Department of Chemistry,
Sri Meenakshi Government College for Women, (Autonomous),
Madurai 625 002, India

1
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J Fluoresc (2010) 20:1017–1022
formaldehyde are relatively low, which is important factor
for practical applications [11]. They have been widely
investigated and used because of their complex forming
properties and their derivatives are used as sensing
components in ionic sensors [12]. The recognition of neutral
organic molecules by synthetic receptors is a topic of current
interest in supramolecular and also in analytical chemistry.
The selectivity character of calixarene for complexation with
different species can be modified by changing the cavity size
by the different functionalization at the lower and upper rims
of the molecule. The interactions of calixarene with neutral
species involve competition between complexation and
solvation process. Non electrostatic forces resulting from
the interaction of the electronic systems of neutral host and
those of neutral guest are of primary importance in “host–
guest interaction”. Calixarenes form complexes with elec-
tron deficient neutral aromatics predominantly through π–π
type interaction [13]. Many articles are published in recent
years on theoretical and experimental works on Calixarene
purification. Chloroform was used as a solvent for this
study. Chloroform from Merck chemical laboratory with
99% purity was used without further purification.
Calix (8) arene was prepared from p-tert butyl phenol
and formaldehyde [17]. Thirty grams of p-tert-butyl phenol
and 9.5 g of formaldehyde were dissolved in 150 ml of
xylene. The mixture was refluxed at 120 °C for about four
hours in an inert atmosphere to get a pale brown coloured
precipitate. It was washed with suitable solvents and recrys-
tallized to get a pure white powder of p-tert-butyl -calix (8)
arene (Scheme 1).
The guest (1,5 DAAQ) and host (p-tert-butyl-calix(8)
arene) solutions were prepared by using chloroform as a
solvent. To determine the stoichiometry ratio by Job’s
continuous variation method, the two stock solutions of
host and guest were mixed to a nine different ratio 1:9,
2:8, 3:7, 4:0, 5:5, 0:4, 7:3, 8:2, 9:1, keeping the total
concentrations equal to 0.02 mM (i.e.[H]+[G]=0.02 mM).
To determine the binding constant, 1,5DAAQ(0.01 mM)
was added to the dilute solution of p-tert-butyl calix(8)
arene at different concentrations [0.01 mM, 0.015 mM,
0.02 mM, 0.025 mM, 0.03 mM, 0.035 mM, 0.04 mM,
0.045 mM, 0.05 mM]. The solutions were kept in
Ultrasonicator for 5 min in order to make the mixture
homogeneous. The optical absorption spectra were
recorded using Shimadzu UV-2450 spectrophotometer.
Fluorescence measurements were made by Cary Varian
Spectro fluorimeter. All the experiments were performed
at room temperature.
[
12–14]
There are number of analytical techniques available for the
investigations of host–guest complexation studies. Among the
analytical methods we have used UV–visible absorption and
Fluorescence spectroscopic techniques to study the molecular
recognition of 1, 5 DAAQ with p-tert-butyl Calix (8) arene.
Our group has recently been reported guest–host interaction
of p-tert-butyl Calix(8)arene with 2 methyl-1,4 napthoqui-
none [15] and p-tert-butyl Calix(8)arene with 2,3 bis
Chloromethyl-1,4 Anthraquinone [16]. In the present study
we have choosen p-tert-butyl-Calix(8)arene as a host and 1,5
Diamino anthraquinone as a guest to investigate the
molecular recognition of 1,5 DAAQ with p-tert-butyl Calix
Results and discussion
(
8)arene. In the present study we have determined stoichi-
ometry ratio and the binding constant between 1,5 - DAAQ -
UV–visible spectral study
p-tert-butyl Calix(8)arene.
The molecular structure of 1,5-DAAQ was shown in
Fig. 1. 1,5- DAAQ shows the absorption band in the
visible region 400–500 nm. The absorption spectrum of
Experimental
*
anthraquinone derivatives give five Characteristic Л–Л
1
,5-DAAQ was kindly given by chemical physics group,
bands, four bands in the region of the wavelength between
220 nm and 350 nm and an n-Л band at the longer
*
TIFR, Mumbai. This dye was used without further
Scheme 1

J Fluoresc (2010) 20:1017–1022
1019
Fig. 1 Molecular structure of 1,5 diamino anthraquinone
wavelength near 400 nm. When an electron donating
group such as hydroxyl or amino group is substituted a
*
new Л–Л absorption band appears in the visible region
Fig. 3 Absorption spectra of calix(8)arene+1,5 DAAQ in different
molar ratios
[
18]. 1,5 DAAQ is a bifunctional molecule. It has both
electron donor and acceptor groups [19]. The absorption
spectrum of 1,5 DAAQ in chloroform shows a absorption
maximum at 475 nm. The molecular structure of p-tert-
butyl-calix (8) arene is shown in Fig. 2. p-tert-butyl-calix
tion. For the molar ratio from 1:9 to 9:1 there is no change
in the λmax (291 nm), but there is a change in the optical
density. The optical density of 291 nm band decreased
with increasing the concentration of 1,5 DAAQ. The
absorption spectra of 1,5 DAAQ with p-tert-butyl-calix(8)
arene does not show isobestic point, which indicates the
multiple site binding and dye aggregation may occur
within the used range of concentration [20]. The absence
of new absorption bands has ruled out the formation of
the charge transfer complex between the 1,5-DAAQ and
p-tert-butyl-calix(8)arene.
(
8)arene consists of 8 phenol units connected via methy-
lene bridges in the ortho position with respect to hydroxyl
group. Figure 3 shows the absorption spectrum of p-tert-
butyl-calix (8) arene and 1,5-DAAQ in different molar
ratios keeping the total concentration 0.02 mM. In the
UV–visible spectrum of 1,5 DAAQ with p-tert-butyl-calix
(
8)arene, there are three absorption bands at 241 nm,
2
2
91 nm and 475 nm. Among the three, we have taken
91 nm band for this investigation of host–guest interac-
We have used Job’s continuous variation method to
determine the stoichiometric ratio of the Guest–Host
complex formed. Figure 4 shows the job’s plot for 1,5-
DAAQ -p-tert-butyl-calix(8)arene complex in absorption
spectroscopy. Generally continuous variation plot shows a
maximum δA at a particular mole fraction of host which
provides the stoichiometry of the complex formed. That is
the absorbance value of the complex is higher than that of
the free guest [21]. In our case we did not observe
Fig. 4 Job’s plot-Variation of δA at 291 nm with the mole fraction of
Fig. 2 Molecular structure of p-tert-butyl-Calix(8)arene
calix(8)arene[Total concentration of Guest+Host=0.02 mM]

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J Fluoresc (2010) 20:1017–1022
Fig. 7 Variation of F/F
0
with the mole fraction of Calix(8)arene [Total
concentration of Guest+Host=0.02 mM]
Fig. 5 Plot of [G]/A vs 1/[H] at 291 nm
maximum δA value than free guest .But we observed a
lower absorbance value in the p-tert-butyl-calix(8)arene-
Bensi–Hildebrand method [22] to determine the association
constant K. The following equation has been employed to
determine the association constant between calixarene–
quinone complexes [2]
1
,5- DAAQ complex than the free guest. This may be due
to the intermolecular hydrogen bond formation between
guest and host molecules [16].
The calixarene–quinone interaction was further investi-
gated by determining the association constant (K). The
association constant can be measured by various spectro-
scopic methods. Among those methods here we used
CalixðnÞarene þ Quinone $ CalixareneꢀQuinone complex
In the present case
pꢀtertꢀbutylꢀCalixð8Þarene þ 1;5 DAAQ $ Calixð8Þareneꢀ1;5 DAAQ complex
H þ G $ HG
½
HGꢁ
To determine the association constant the absorptivities
were measured at various ratios of p-tert-butyl-calix(8)arene
to 1,5 DAAQ and the data were analysed by the Bensi–
Hildebrand expression
K ¼
ð1Þ
½
Hꢁ½Gꢁ
Where [H] is the concentration of p-tert-butyl-calix(8)
arene, [G] is the concentration of 1,5 DAAQ and [HG] is
the concentration of calixarene–quinone complex.
½
Gꢁ
1
1
¼
þ
ð2Þ
n
A
Ka½Hꢁ
a
Fig. 6 Fluorescence spectra of calix(8)arene+1,5 DAAQ in different
molar ratios
Scheme 2

J Fluoresc (2010) 20:1017–1022
1021
Where A is absorptivity at 291 nm, α is the constant and
K is the association constant for p-tert-butyl-calix(8)arene-
cavity of the p-tert-butyl-calix(8)arene is small compared to
that of guest molecule, inclusion of two guest molecules
inside the p-tert-butyl-calix(8)arene is not possible. p-tert-
butyl-calix(8)arene exists in pinched cone conformation [9,
25, 26]. The observed stoichiometry ratio 1:2 is due to the
intermolecular hydrogen bonding between carbonyl oxygen
of the guest molecule and the hydroxyl group of host
molecule [Scheme 2].
1
,5 DAAQ complex.
By plotting [G]/A vs 1/ [H] (Fig. 5) with different n
n
values, the n that results a straight line was taken as the
number of host molecules. From the intercept and the slope
of the straight line the association constant has been
determined. The association constant (K) is found to be
3
−1
1
×10 M .
Fluorescence studies
Conclusions
Figure 6 shows the emission spectrum of p-tert-butyl-calix
Optical absorption and fluorescence spectroscopic studies
on 1,5 DAAQ were carried out to study the host–guest
interaction of 1,5 DAAQ with p-tert-butyl-calix(8)arene.
The stoichiometric ratio for 1,5 DAAQ with p-tert-butyl-
calix(8)arene is 1:2 and the binding constant is found to be
1×10 M . Our results suggest that intermolecular
hydrogen bonding is mainly responsible for the strong
binding between 1,5 DAAQ and p-tert-butyl-calix(8)arene.
(
8)arene and 1,5-DAAQ in different molar ratios keeping
the total concentration 0.02 mM. 1,5-DAAQ has a fluores-
cence maximum at 546 nm. When the p-tert-butyl-calix(8)
arene is added to 1,5 DAAQ in different molar ratio, there
are changes in the fluorescence signatures. During the
increased addition of p-tert-butyl-calix (8) arene the
fluorescence maximum is red shifted up to the molar ratio
3
−1
7
:3 with respect to neat. Further addition of p-tert-butyl-
calix(8)arene shows blue shift. Fluorescence quenching is
also observed during the increased addition of p-tert-butyl-
calix (8)arene. The observed fluorescence quenching may
be due to the binding of 1,5 DAAQ with of p-tert-butyl-
calix(8)arene. Generally an isoemissive point indicates two
species are in equilibrium (i.e. formation of 1:1 complex)
Acknowledgement One of the authors (VRK) is thankful to CSIR,
Government of India for the financial assistance provided in the form
of a research project. The authors are thankful to Prof. S. Shamuga
Sundaram Department of Micro-bio technology, Madurai Kamaraj
University for permitting to make use of the Spectrofluorimeter. UGC,
Government of India is gratefully acknowledged for providing the
Rajeev Gandhi national fellowship to one of the authors (GS). The
authors are grateful to UGC for the financial support extended under
DRS Phase III for establishing UV–Visible spectrometer facility.
[
23]. In the present case we did not observe the iso-
emissive point. The absence of iso-emissive point in our
case may be due to the interaction between more than one
molecule of 1,5 DAAQ with one molecule of p-tert-butyl-
calix(8)arene.
Generally larger red shifts are observed in polar solvents
than in aploar solvents, which indicate that the excited
states of the anthraquinone are more stabilized by polar
solvents [16]. In the present case chloroform is a polar
aprotic solvent. As already mentioned it shows a red shift in
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