Impact of inclusion complex formation on absorption and emission characteristics of some 4-arylidenamino-5-phenyl-4H-1,2,4-triazole-3-thiols

Article abstract of DOI:10.14233/ajchem.2016.19556

The inclusion complexes of a series of 4-arylidenamino-5-phenyl-4H-1,2,4-triazole-3-thiols have been synthesized with β-cyclodextrin. The compounds and their inclusion complexes have been characterized by studying their physical and spectral properties. The thermodynamic stability constant and free energy of activation have been determined to know the stability of inclusion complexes and type of host-guest relation. Finally, the absorption, excitation and emission spectra of the compounds and their inclusion complexes have been taken to examine whether the inclusion complex formation has any impact on absoption and emission characteristics of 4-arylidenamino-5-phenyl-4H-1,2,4-triazole-3-thiols. It is found that inclusion complex formation brings about a drastic change in absorption, excitation and emission spectra of newly synthesized compounds.

Full text of DOI:10.14233/ajchem.2016.19556

Asian Journal of Chemistry; Vol. 28, No. 5 (2016), 981-986
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2016.19556
Impact of Inclusion Complex Formation on Absorption and Emission
Characteristics of Some 4-Arylidenamino-5-phenyl-4H-1,2,4-triazole-3-thiols
*
SUNAKAR PANDA , SASHIKANTA NAYAK, P.K. DAS and D.L. SINGH
P.G. Department of Chemistry, Berhampur University, Bhanjabihar-760 007, India
*
Corresponding author: E-mail: sunakar_panda@yahoo.com
Received: 10 August 2015;
Accepted: 6 October 2015;
Published online: 30 January 2016;
AJC-17729
The inclusion complexes of a series of 4-arylidenamino-5-phenyl-4H-1,2,4-triazole-3-thiols have been synthesized with β-cyclodextrin.
The compounds and their inclusion complexes have been characterized by studying their physical and spectral properties. The thermodynamic
stability constant and free energy of activation have been determined to know the stability of inclusion complexes and type of host-guest
relation. Finally, the absorption, excitation and emission spectra of the compounds and their inclusion complexes have been taken to
examine whether the inclusion complex formation has any impact on absoption and emission characteristics of 4-arylidenamino-5-
phenyl-4H-1,2,4-triazole-3-thiols. It is found that inclusion complex formation brings about a drastic change in absorption, excitation and
emission spectra of newly synthesized compounds.
Keywords: Triazole-3-thiol, Inclusion complex, Absorption spectra, Excitation spectra, Emission spectra.
INTRODUCTION
EXPERIMENTAL
The drugs containing 1,2,4-triazole nucleus are reported
All the chemicals used in the present work were procured
from local market. Double distilled water was used as solvent.
The elemental analysis was performed in a CHN analyzer.
Melting points were recorded by open capillary method.
Electronic spectra were recorded in Shimadzu UV-1800
spectrophotometer and IR spectra were recorded in KBr pellets
to exhibit a wide spectrum of pharmacological activities like
antimicrobial [1-5], anticancer [6,7], antiviral [8], antiinfla-
mmatory [9], analgesic [10], anticonvulsant [11] etc. It is
known that the formation of inclusion complex of variety of
drug molecules with β-cyclodextrin improves their solubility,
stability as well as bioavailability [12-16]. But transference of
drug molecules which are usually non-polar in nature, into
hydrophobic core of β-cyclodextrin causes a drastic change
in its microenvironment. Since the spectral chacteristics of
molecules depend upon the molecular structure and its micro-
environment [17-23] such a transference will definitely have
some impact on absorption and emission characteristics of the
molecules.
In view of these facts, an attempt has been made to
synthesize some 4-arylidenamino-5-phenyl-4H-1,2,4-triazole-
-thiol (Schiff bases) in their purest forms and prepare their
inclusion complexes with β-cyclodextrin. The absorption,
excitation and emission spectra of the compounds and their
inclusion complexes are taken to examine whether the
inclusion complex formation has any impact on absoption and
emission characteristics of 4-arylidenamino-5-phenyl-4H-
1
in Shimadzu 8400 FT-IR spectrophotometer. H NMR spectra
were obtained with Brukers spectrophotometer model ultra-
shield at 300 MHz in DMSO-d solution with TMS as internal
6
standard. The purity of the newly synthesized compounds were
checked by TLC. Fluorescence spectra and intensity measu-
rements were made on a Shimadzu RF-1501 spectrofluorimeter
equipped with a150 W xenon lamp.
The synthesis of the titled compoundsA, B, C and D were
carried out as per Panda et al. [24] as shown in Scheme-I.
Phase solubility measurements: The aqueous phase solubi-
lity of the compounds at various concentrations of β-cyclodextrin
(0-10 mM) was studied by Higuchi-Conner method [25].
Synthesis of inclusion complexes: Co-precipitation
method was used for the preparation of inclusion complexes
of the compounds with β-cyclodextrin [15,26].
3
Study of thermodynamic properties: The stability
constants of the complexes (K) were calculated from plot of
1
,2,4-triazole-3-thiols.

982 Panda et al.
Asian J. Chem.
O
C H OH (Absolute)
2
5
NH NH
C H COOC H
2 5
2
2
C
NHN H2
6
5
comp-1
COMP: Ar-CHO
CS /KO H
2
C H OH (Absolute)
2
5
Cl
O
C
O
S
C
A
ortho-Chlorobenzaldeyde
NHNH
S
K
comp-2
Cl
B
O
para-Chlorobenzaldeyde
NH NH
2
2
N
N
O
N+
O
O-
C
SH
meta-Nitrobenzaldeyde
N
NH2
comp-3
O
D
Cinnamaldehyde
Ar-CHO/
HOAc
N
N
SH
N
N
HC Ar
Compound 4 (A-d)
A = 4-[2-Chlorobenzilidenamino]-5-phenyl-4H-1,2,4-triazole-3-thiol; B = 4-[4-Chlorobenzilidenamino]-5-phenyl-4H-1,2,4-triazole-3-thiol;
C = 4-[3-Nitrobenzilidenamino]-5-phenyl-4H-1,2,4-triazole-3-thiol; D = 4-[(E)-3-phenylallylideneamino]-5-phenyl-4H-1,2,4-triazole-3-thiol
Scheme-I
inverse of change in absorbance versus inverse concentration
of β-cyclodextrin using Benesi-Hilderband relation [27].
RESULTS AND DISCUSSION
Four different 4-arylidenamino-5-phenyl-4H-1,2,4-
triazole-3-thiols (A, B, C and D) have been synthesized as
shown in Scheme-I in their purest forms. The inclusion comp-
lexes ofA, B,C and D have been prepared with β-cyclodextrin
after determining the optimum concentration of host and guest
through aqueous phase solubility study (Fig. 1). The structures
of the compounds (A, B, C and D) and their inclusion comp-
lexes have been confirmed from the study of their physical
1
/∆A = 1/∆ε + 1/K [Guest]
where ∆A is change in absorbance, ∆ε is change in absorption
coefficient, K stability constant, [Guest] is the concentration
o
·[β-CD]
o
of compound and [β-CD] is the concentration of β-cyclodextrin.
The values of Kfor all the complexes are calculated using the
relation.
K = Intercept/Slope
1
properties, elemental composition, IR and H NMR data
The value of ∆G at 298 K was calculated using the equation:
(
Tables 1 and 2). The elemental composition of the compounds
matches with theoretical data (Table-2). The IR and H NMR
1
∆G = -RT ln K

Vol. 28, No. 5 (2016)
Impact of Inclusion Complex Formation on Some 4-Arylidenamino-5-phenyl-4H-1,2,4-triazole-3-thiols 983
TABLE-1
SOME PHYSICAL PROPERTIES OF SYNTHESIZED COMPOUNDS AND THEIR COMPLEXES
S. No.
1
Compound/Complex
Compound-A
Inclusion complex A
Compound-B
Inclusion complex B
Compound-C
Inclusion complex C
Compound-D
Inclusion complex D
m.f.
m.w.
314.79
Colour
Yellow
White
Light yellow
White
Yellowish white
Dull white
Brown
m.p. (°C)
148-150
280
165-170
273-275
185-190
282-284
95
Yield (%)
C H N SCl
77
77
63
76
70
75
70
72
1
5
11
4
2
3
4
C H N SCl
314.79
325.35
306. 38
1
5
11
4
C H N O S
1
5
11
5
2
C H N S
1
7
14
4
White
282-285
TABLE-2
SPECTRAL DATA AND ELEMENTAL COMPOSITION OF THE COMPOUNDS AND THEIR INCLUSION COMPLEXES
Elemental analysis (%):
Calcd. (Found)
S.
No.
Compound/
Complex
-
1
IR (KBr, νmax, cm )
NMR (DMSO-d )
6
C
H
N
9
41.26 (N-C-S str), 3072.60, 3132.70 (Ar-H str),
7
1
.49-7.88 (m, 9H, Ar-H), 14.30 (s,
H, SH), 10.43 (s, 1H, N=CH)
A
1502.56 (C=C str), 696.30 (C-S str), 1350.17
C-N str), 769.60 (C-Cl str), 1610.56 (C=N str)
(
5
7.23
3.52
(3.42)
11.26
(11.22)
1
2
3
4
937.40 (N-C-S str), 2931.80, (Ar-H str), 1408.04
(C=C str), 1656.85 (C=N str), 756.10 (C-S str),
complex A 1332.81, (C-N str), 792.74 (C-Cl str), 3363.86 (OH
7.94-7.96 (m, 9H, Ar-H), 3.34 (s,
1H, β-CD), 3.37 (s, 1H, β-CD), 3.54
(s, 1H, β-CD), 3.60 (s, 1H, β-CD),
3.62 (s, 1H, β-CD)
(
(
57.07)
Inclusion
str, β-CD), 2931.80 (C-H str, β-CD)
941.26 (N-C-S str), 3034.03, 3099.61 (Ar-H str),
7
1
.52-7.92 (m, 9H, Ar-H), 14.243 (s,
H, SH), 9.7 65 (s, 1H, N=CH).
B
1502.55 (C=C str), 696.30 (C-S str), 1350.17 (C-N
str), 769.60 (C-Cl str). 1610.56 (C=N str)
57.23
3.52
(3.45)
11.26
(11.13)
937.40 (N-C-S str), 2931.80 (Ar-H str), 1409.96
(C=C str), 705.95 (C-S str), 1348.24 (C-N str),
complex B 792.74 (C-Cl str), 1658.78 (C=N str), 3367.71 (OH
7.95-7.98 (m, 9H, Ar-H), 3.58 (s,
1H, β-CD), 3.61 (s, 1H, β-CD), 3.63
(s, 1H, β-CD), 3.65 (s, 1H, β-CD),
3.66 (s, 1H, β-CD),
57.09)
Inclusion
str, β-CD), 2931.80 (C-H str, β-CD)
943.19 (N-C-S str), 3032.10, 3088.03 (Ar-H str),
7
1
.52-8.33 (m, 9H, Ar-H), 14.34 (s,
H, SH), 10.023 (s, 1H, N=CH).
C
1508.33 (C=C str), 675.09 (C-S str), 1350.17 (C-N
str), 1537.27, 1350.17 (NO ), 1608.63 (C=N str)
2
55.37
3.41
(3.32)
21.53
(21.42)
937.40 (N-C-S str), 2933.73 (Ar-H str), 1660.71
(C=C str), 705.95 (C-S str), 1361.74 (C-N str),
7.94-8.23 (m, 9H, Ar-H), 3.37 (s,
1H, β-CD), 3.54 (s, 1H, β-CD), 3.61
), 1660.71 (C=N str), 3367.71 (OH str, (s, 1H, β-CD), 3.62 (s, 1H, β-CD),
55.47)
Inclusion
complex C 1409.96 (NO
2
β-CD), 2933.73 (C-H str, β-CD)
3.65 (s, 1H, β-CD),
9
41.26 (N-C-S str), 3143.97 (Ar-H str), 696.30 (C-S
str), 1573.91 (C=C str), 1350.17 (C-N str). 1610
C=N str), 1649.14 (C=C unsaturated)
D
6.93-7.87 (m, 8H, Ar-H),
(
66.64
4.61
(4.66)
18.29
(18.24)
937.40 (N-C-S str), 2933.73 (Ar-H str), 1409.96
(C=C str), 705.95 (C-S str), 1361.74 (C-N str),
complex D 1658.78 (C=N str), 3356.14 (OH str, β-CD),
7.94-8.28 (m, 9H, Ar-H), 3.27 (s,
1H, β-CD), 3.29 (s, 1H, β-CD), 3.37
(s, 1H, β-CD), 3.61 (s, 1H, β-CD),
3.65 (s, 1H, β-CD),
(
66.69)
Inclusion
2914.44 (C-H str, β-CD)
data of the compounds confirm the expected structures. The
synthesis of inclusion complexes of the compounds have been
confirmed from the changes in melting point,colour and IR
β-cyclodextrin interaction leading to inclusion complex
formation is further supported by NMR data (Table-2). It is
seen that the NMR signals due to different protons undergo
smaller shifts (small shift towards down field in case of all the
compounds) after their inclusion complex formations which
may be due to changes in the microenvironment of the
compound after encapsulation.
1
and H NMR spectral characteristics (Tables 1 and 2). The
higher melting point of the inclusion complexes than their
corresponding compounds may be attributed to the fact that
extra amount of thermal energy is required for the latter to
bring it out of β-cyclodextrin cavity [15]. The IR-stretching
frequencies due to different bonds undergo downward shift
towards lower energy and the peaks become broader, weaker
and smoother which may be attributed to the restriction on the
compounds for undergoing vibration due to the development
of weak interaction like H-bonding, vander-Waal forces and
hydrophobic interactions, etc. within the cavity. This obser-
vation clearly demonstrates transference of the compound from
a more protic environment (aqueous media) to a less protic
environment (cavity of β-cyclodextrin). The compound and
The aqueous phase-solubility diagrams of the compounds
with β-cyclodextrin are shown in Fig. 1. It is seen that aqueous
solubility of the compounds increase linearly as a function of
th
the concentration of β-cyclodextrin up to 5 point followed
by a decline. This clearly indicates that the concentration at
th
5 point is the optimum concentration for inclusion complex
formation. The plot of inverse absorbance against inverse
concentration of β-cyclodextrin gives straight lines with definite
slope and intercept for different compounds (Fig. 2).The
equilibrium constants (K) have been calculated from the slope

984 Panda et al.
Asian J. Chem.
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
absorption maxima shifts towards lower wavelength (Table-
Comp-A
Comp-B
Comp-C
Comp-D
4
) and the intensity of the peaks becomes higher (Figs. 3-6)
after their inclusion complex formation. However, although
the excitation and emission peaks shift towards lower wave-
length, the intensity of the peaks becomes lower after their
inclusion complex formation (Figs. 7-10). The shifting of
absorption and excitation peak positions may be due to the
fact that more amount of energy is required for the compounds
for their excitation after encapsulation because the molecules
get stabilized within the cavity of β-cyclodextrin through some
weak intermolecular forces.
TABLE-4
ABSORPTION, EXCITATION AND EMISSION PEAK POSITION
OF THE COMPOUNDS AND THEIR INCLUSION COMPLEXES
Exitation
peak
position
Emission
peak
position
0
.001
0.002
0.003
0.004
0.005
0.006
Absorption
maximum
λmax (nm)
S.
No.
Compound/
Complex
Concentration of
β-cyclodextrin
Fig. 1. Phase solubility study of the synthesized compounds in aqueous
λ (nm)
λ (nm)
solution of β-cyclodextrin
1
2
3
4
Compound-A
Inclusion complex A
Compound-B
Inclusion complex B
Compound-C
Inclusion complex C
Compound-D
290
278
288
270
280
266
274
261
318
303
325
307
308
285
310
290
453
442
450
439
453
435
442
427
1
1
0.5
0.0
Comp-A
Intercept 2.34094
Slope
Comp-A
Comp-B
Comp-C
Comp-D
9
9
8
8
7
7
6
6
5
5
4
4
3
3
2
2
.5
.0
.5
.0
.5
.0
.5
.0
.5
.0
.5
.0
.5
.0
.5
.0
0.00279
Comp-B
Intercept 1.98148
Slope
Comp-C
Intercept 3.64824
Slope
0.00247
Inclusion complex D
0.00408
0
.300
Comp-D
Intercept 4.70637
Slope 0.00542
β
-Cyclodextrin
0.200
I.C. A
2
00
400
600
800
1000
1/Concentration of
β
-cyclodextrin
Fig. 2. Plot of inverse absorbance against inverse concentration of β-
0.100
cyclodextrin
Comp-A
and intercept [27] and are found to be in the range of 457.07
to 893.58 (Table-3). Since all the values are remaining within
ideal range [28], complexes formed are quite stable. Further,
it is found that the values of all the slopes are less than one
indicating the inclusion complexes to have 1:1 stoichiometry
0
.000
2
30.00 250.00
300.00
Wavelength (nm)
350.00
400.00
Fig. 3. UV spectrum of β-cyclodextrin, compoundA and its inclusion complex
[
14-16]. Negative values of free energy changes for all the
inclusion complexes (Table-3) further suggest that the process
of inclusion complex formation is spontaneous and thermo-
dynamically allowed.
0.200
0.150
0.100
0.050
β-Cyclodextrin
TABLE-3
THERMODYNAMIC STABILITY CONSTANT AND FREE
ENERGY CHANGE OF INCLUSION COMPLEXES
S.
No.
Inclusion complex of
compound
Equilibrium
constant (K) in M
∆G
I.C. B
-
1
(kJ/mol)
1
2
3
4
Inclusion complex A
Inclusion complex B
Inclusion complex C
Inclusion complex D
839.04
802.21
894.17
868.33
-16.679
-16.568
-16.837
-16.764
Comp-B
It is interesting to note that the absorption and emission
characterestics of all the compounds (A, B, C and D) undergo
drastic changes after their inclusion complex formation. The
0.000
30.00 250.00
2
300.00
Wavelength (nm)
350.00
400.00
Fig. 4. UV spectrum of β-cyclodextrin, compound B and its inclusion complex

Vol. 28, No. 5 (2016)
Impact of Inclusion Complex Formation on Some 4-Arylidenamino-5-phenyl-4H-1,2,4-triazole-3-thiols 985
0.200
0.150
0.100
0.050
0.000
500
EXCITATION
400
300
200
100
0
Comp-B
I.C.B
β
-Cyclodextrin
2
00
250
300
350
400
450
500
550
600
Wavelength (nm)
500
400
300
200
I.C. C
EMISSION
Comp-B
I.C.B
Comp-C
100
0
230.00 250.00
300.00
Wavelength (nm)
350.00
400.00
2
00
250
300
350
400
450
500
550
600
Fig. 5. UV spectrum of β-cyclodextrin, compound C and its inclusion
Wavelength (nm)
complex
Fig. 8. Excitation and emission spectra of compound B and its inclusion
complex
5
4
3
00
00
00
EXCITATION
0
0
0
0
0
.200
.150
.100
.050
.000
Comp-C
I.C.C
β
-Cyclodextrin
200
100
0
200
250
300
350
400
450
500
550
600
Wavelength (nm)
500
400
EMISSION
Comp-C
Comp-C
I.C.D.
300
200
100
0
Comp-D
2
30.00 250.00
300.00
Wavelength (nm)
350.00
400.00
200
250
300
350
400
450
500
550
600
Fig. 6. UV spectrum of β-cyclodextrin, compound D and its inclusion
Wavelength (nm)
complex
Fig. 9. Excitation and emission spectra of compound C and its inclusion
complex
5
00
00
00
00
00
EXCITATION
4
Comp-A
I.C.A
250
EXCITATION
200
3
Comp-D
1
50
00
2
I.C.D
1
1
5
0
0
0
2
00
250
300
350
400
450
500
550
600
2
00
250
300
350
400
450
500
550
600
Wavelength (nm)
Wavelength (nm)
5
00
00
00
00
00
250
200
150
100
4
EMISSION
Comp-A
I.C.A
EMISSION
Comp-D
I.C.D
3
2
1
50
0
0
200
250
300
350
400
450
500
550
600
200
250
300
350
400
450
500
550
600
Wavelength (nm)
Wavelength (nm)
Fig. 10. Excitation and emission spectra of compound D and its inclusion
complex
Fig. 7. Excitation and emission spectra of compound A and its inclusion
complex

986 Panda et al.
Asian J. Chem.
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The above results established the fact that inclusion compl-
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