Structural, thermal, morphological and biological studies of proton-transfer complexes formed from 4-aminoantipyrine with quinol and picric acid

Article abstract of DOI:10.1016/j.saa.2012.11.042

4-Aminoantipyrine (4AAP) is widely used in the pharmaceutical industry, biochemical experiments and environmental monitoring. However, residual amounts of 4AAP in the environment may pose a threat to human health. To provide basic data that can be used to extract or eliminate 4AAP from the environment, the proton-transfer complexes of 4AAP with quinol (QL) and picric acid (PA) were synthesized and spectroscopically investigated. The interactions afforded two new proton-transfer salts named 1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H- pyrazol-4-aminium-4-hydroxyphenolate and 1,5-dimethyl-3-oxo-2-phenyl-2,3- dihydro-1H-pyrazol-4-aminium-2,4,6-trinitrophenolate for QL and PA, respectively, via a 1:1 stoichiometry. Elemental analysis (CHN), electronic absorption, spectrophotometric titration, IR, Raman, ¹H NMR and X-ray diffraction were used to characterize the new products. The thermal stability of the synthesized CT complexes was investigated using thermogravimetric (TG) analyses, and the morphology and particle size of these complexes were obtained from scanning electron microscopy (SEM). It was found that PA and 4AAP immediately formed a yellow precipitate with a remarkable sponge-like morphology and good thermal stability up to 180 °C. Finally, the biological activities of the newly synthesized CT complexes were tested for their antibacterial and antifungal activities. The results indicated that the [(4AAP)(QL)] complex exhibited strong antimicrobial activities against various bacterial and fungal strains compared with standard drugs.

Full text of DOI:10.1016/j.saa.2012.11.042

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 1–13
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Structural, thermal, morphological and biological studies of proton-transfer
complexes formed from 4-aminoantipyrine with quinol and picric acid
⇑
Abdel Majid A. Adam
Department of Chemistry, Faculty of Science, Taif University, Al-Haweiah, P.O. Box 888, Zip Code 21974, Taif, Saudi Arabia
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
Sponge-like morphology of [(4AAP)(PA)] complex.
"
Two new CT complexes of 4-
aminoantipyrine with QL and PA are
obtained.
"
"
Various spectroscopic and thermal
analysis are used.
The complex obtained with PA has a
remarkable morphology and good
thermal stability.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 13 October 2012
Received in revised form 12 November 2012
Accepted 15 November 2012
Available online 29 November 2012
4-Aminoantipyrine (4AAP) is widely used in the pharmaceutical industry, biochemical experiments and
environmental monitoring. However, residual amounts of 4AAP in the environment may pose a threat to
human health. To provide basic data that can be used to extract or eliminate 4AAP from the environment,
the proton-transfer complexes of 4AAP with quinol (QL) and picric acid (PA) were synthesized and
spectroscopically investigated. The interactions afforded two new proton-transfer salts named 1,5-
dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-aminium-4-hydroxyphenolate and 1,5-dimethyl-
3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-aminium-2,4,6-trinitrophenolate for QL and PA, respectively,
via a 1:1 stoichiometry. Elemental analysis (CHN), electronic absorption, spectrophotometric titration, IR,
Raman, 1H NMR and X-ray diffraction were used to characterize the new products. The thermal stability
of the synthesized CT complexes was investigated using thermogravimetric (TG) analyses, and the mor-
phology and particle size of these complexes were obtained from scanning electron microscopy (SEM). It
was found that PA and 4AAP immediately formed a yellow precipitate with a remarkable sponge-like
morphology and good thermal stability up to 180 °C. Finally, the biological activities of the newly synthe-
sized CT complexes were tested for their antibacterial and antifungal activities. The results indicated that
the [(4AAP)(QL)] complex exhibited strong antimicrobial activities against various bacterial and fungal
strains compared with standard drugs.
Keywords:
4-Aminoantipyrine
Proton-transfer
XRD
SEM
Thermal analysis
Ó 2012 Elsevier B.V. All rights reserved.
⇑
Tel.: +966 2727 2020/502099808; fax: +966 2727 4299.
E-mail address: majidadam@yahoo.com
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.11.042

2
Abdel Majid A. Adam / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 1–13
reddish-brown precipitate was filtered off, washed several times
NH2
O
with methanol and then dried under vacuum over anhydrous cal-
cium chloride. In the case of the 4AAP/PA complex, upon addition
of PA to 4AAP dissolved in methanol, a yellow precipitate formed
immediately.
N
N
Spectrophotometric titration measurements
Formula I. Molecular structure of 4-aminoantipyrine.
Spectrophotometric titration measurements were performed
for the reactions of 4AAP with QL or PA against methanol as a blank
at wavelengths of 286 and 281 nm, respectively. A 0.25, 0.50, 0.75,
1.00, 1.50, 2.0, 2.50, 3.00, 3.50 or 4.00 ml aliquot of a standard solu-
tion (5.0 ꢁ 10ꢂ4 M) of the appropriate acceptor in MeOH was
added to 1.00 ml of 5.0 ꢁ 10ꢂ4 M 4AAP, which was also dissolved
in MeOH. The total volume of the mixture was 5 ml. The concentra-
tion of 4AAP (Cd) in the reaction mixture was maintained at
5.0 ꢁ 10ꢂ4 M, whereas the concentration of the acceptors (Ca)
changed over a wide range of concentrations (0.25 ꢁ 10ꢂ4 M to
4.00 ꢁ 10ꢂ4 M) to produce solutions with an acceptor molar ratio
that varied from 4:1 to 1:4. The stoichiometry of the molecular
CT complexes was obtained from the determination of the conven-
tional spectrophotometric molar ratio according to known meth-
ods [25] using a plot of the absorbance of each CT complex as a
function of the Cd:Ca ratio. Modified Benesi–Hildebrand plots were
constructed [26,27] to allow the calculation of the formation con-
Introduction
4-Aminoantipyrine (4AAP, Formula I) is a metabolite of amino-
phenazone and is an aromatic substance with analgesic, antipy-
retic, antiphlogistic and anti-inflammatory properties [1–6].
Although today 4AAP is scarcely ever administered as an analgesic
drug because of its side effects, it is still used as a precursor of 4AAP
derivatives, which have better biological activities [7,8]. In addi-
tion, the compound is used as a reagent for biochemical reactions
that produce peroxides or phenols [9,10] and can also be used to
detect phenols in the environment [11]. Because 4AAP is widely
used in pharmacological [12], clinical [13], biological, biochemical
[14] and analytical applications [15], as well as in environmental
monitoring, 4AAP has become an environmental pollutant [16].
The toxic effect of 4AAP on animals has been reported experimen-
tally [17]. 4AAP can reduce blood flow [18] and form stable com-
plexes with heme [19]; moreover, it has an obvious denaturing
effect on bovine hemoglobin [20]. In recent years, 4AAP transition
metal complexes and their derivatives have been extensively
examined due to their wide biological, analytical and therapeutic
applications. Furthermore, they have been investigated due to their
diverse biological properties as antifungal, antibacterial, analgesic,
sedative, antipyretic, anti-inflammatory and DNA-binding agents
[21–24].
stant, KCT, and the absorptivity, eCT, values for each CT complex in
this study.
Instrumental analyses
Elemental analyses
The elemental analyses of the carbon, hydrogen and nitrogen
contents were performed by the microanalysis facility at Cairo Uni-
versity, Egypt, using a Perkin–Elmer CHN 2400 (USA).
This paper aims to investigate the 4AAP charge-transfer com-
plexes, which are readily prepared from the reaction of 4AAP with
quinol (benzene-1,4-diol, QL) and picric acid (2,4,6-trinitrophenol,
PA). The synthesized CT complexes were structurally characterized
using elemental analysis; infrared (IR), Raman, 1H NMR and elec-
tronic absorption spectroscopy; powder X-ray diffraction; and
scanning electron microscopy (SEM). The thermal behavior of the
obtained complexes and the kinetic and thermodynamic parame-
Electronic spectra
The electronic absorption spectra of methanolic solutions of the
donor, acceptors and resulting CT complexes were recorded over a
wavelength range of 200–800 nm using a Perkin–Elmer Lambda 25
UV/Vis double-beam spectrophotometer at Taif University, Saudi
Arabia. The instrument was equipped with a quartz cell with a
1.0 cm path length.
ters (Eꢀ, A,
D D D
Sꢀ, Hꢀ and Gꢀ) were also investigated. Finally, the
Infrared and Raman spectra
antimicrobial activity of the 4AAP complexes was determined
against various bacterial and fungal strains.
The mid-infrared (IR) spectra (KBr discs) within the range of
4000–400 cmꢂ1 for the solid CT complexes were recorded on a Shi-
madzu FT-IR spectrophotometer with 30 scans at 2 cmꢂ1 resolu-
tion. The Raman laser spectra of the samples were measured on
a Bruker FT-Raman spectrophotometer equipped with a 50 mW
laser at Taif University, Saudi Arabia.
Experimental
Reagents
1H NMR spectra
4-Aminoantipyrine (4AAP) (C11H13N3O) was obtained from
Sigma–Aldrich Chemical Company, USA, with a stated purity of
greater than 99% and was used without further purification. Quinol
(benzene-1,4-diol, QL) and picric acid (2,4,6-trinitrophenol, PA)
were purchased from Merck Chemical Co. and were also used as
received.
1H NMR spectra were collected by the Analytical Center at King
Abdul Aziz University, Saudi Arabia, on a Bruker DRX-250 spec-
trometer operating at 250.13 MHz with a dual 5 mm probe head.
The measurements were performed at ambient temperature using
DMSO-d6 (dimethylsulfoxide, d6) as a solvent and TMS (tetrameth-
ylsilane) as an internal reference. The 1H NMR data are expressed
in parts per million (ppm) and are internally referenced to the
residual proton impurity in the DMSO solvent.
Synthetic procedure
The solid CT complexes of 4AAP with QL or PA were synthesized
by mixing 1 mmol 4AAP with 1 mmol of each acceptor in methanol
(10 ml). The mixtures were stirred at room temperature for 10 min,
which resulted in the precipitation of the products. In the 4AAP/QL
system, upon addition of QL to a solution of 4AAP, the color of the
solution changed from light yellow to red to reddish-brown. A dark
Thermal analysis
Thermogravimetric analysis (TGA) was performed under an air
atmosphere between room temperature and 800 °C at a heating
rate of 10 °C/min using a Shimadzu TGA-50H thermal analyzer at
the Central Lab at Ain Shams University, Egypt.

Abdel Majid A. Adam / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 1–13
3
X-ray diffraction patterns
(2) [(4AAP)(PA)]; C17H16N6O8; Mol. wt. = 432.34; Calc.: %C,
The X-ray diffraction patterns for the obtained CT complexes
were collected on a PANalytical X’Pert PRO X-ray powder diffrac-
tometer at the Central Lab at Ain Shams University, Egypt. The
instrument was equipped with a Ge(III) monochromator, and a
Cu Ka1 X-ray source with a wavelength of 0.154056 nm was used.
47.19; %H, 3.70; %N, 19.43, Found: %C, 46.88; %H, 3.51; %N,
19.70
The resulting values are in good agreement with the calculated
values, and the suggested values are in agreement with the molar
ratios determined from the spectrophotometric titration curves.
SEM and EDX detection
Scanning electron microscopy (SEM) images and energy-disper-
sive X-ray spectroscopy (EDX) patterns were collected on a Jeol
JSM-6390 instrument at Taif University, Saudi Arabia. The instru-
ment was operated at an accelerating voltage of 20 kV.
Determination of stoichiometry of the resulting CT complexes
The electronic absorption spectra of the donor 4AAP, acceptors
QL and PA and the complexes are shown in Fig. 1. These spectra re-
vealed new absorption bands that are attributed to the CT interac-
tions. These bands are observed at 286 and (281 and 353) nm for
the 4AAP/QL and 4AAP/PA complexes, respectively. These peak
absorbance values were measured and plotted as a function of
the Cd:Ca ratio according to a known method. Spectrophotometric
titration plots based on these measurements (Fig. 2) confirmed
the complex formation at a ratio (4AAP:acceptor) of 1:1 in both
cases. Based on the obtained data, the formed charge-transfer or
proton-transfer complexes were formulated as [(4AAP)(QL)] and
[(4AAP)(PA)].
Biological assessment
Antibacterial activity
The antimicrobial activities of the newly synthesized 4AAP CT
complexes and the pure solvent were tested in vitro against two
Gram-positive bacteria, Staphylococcus aureus (MSSA 22) and Bacil-
lus subtilis (ATCC 6051), and two Gram-negative bacteria, Esche-
richia coli (K 12) and Pseudomonas aeruginosa (MTCC 2488), using
a modified Bauer–Kirby disc diffusion method [28]. The microanal-
ysis facility at Cairo University, Egypt performed the investigations.
For these investigations, 100
fresh medium until they reached a count of approximately 108 -
cells/ml for bacteria or 105 cells/ml for fungi [29]. Then, 100
ll test bacteria were grown in 10 ml
Determination of the formation constant and the molar extinction
coefficient
l
l
microbial suspension was spread onto agar plates. The nutrient
agar medium for the antibacterial tests consisted of 0.5% peptone,
0.1% beef extract, 0.2% yeast extract, 0.5% NaCl and 1.5% agar-agar
[30]. Isolated colonies of each strain were selected from the pri-
mary agar plates and tested for susceptibility. After the plates were
incubated for 48 h at 37 °C, the inhibition (sterile) zone diameters
(including the disc) were measured using slipping calipers from
the National Committee for Clinical Laboratory Standards (NCCLS,
1993) [31] and are expressed in mm. The screening was performed
The spectrophotometric titrations of the intermolecular charge-
transfer complexes formed from the reaction of 4AAP with QL or
PA indicated the formation of 1:1 CT complexes; therefore, the
formation constant (KCT) and the molar absorptivity (e) of these
CT band (286 nm)
1.2
1.0
0.8
0.6
using 100
lg/ml CT complex. An antibiotic disc of tetracycline
(30 g/disc, Hi-Media) was used as a positive control.
l
Antifungal activity
The newly synthesized complexes were also screened for their
antifungal properties against Aspergillus flavus (laboratory isolate)
and Candida albicans (IQA-109) in DMSO using a modified Bauer–
Kirby disc diffusion method [28]. The complex was dissolved in
DMSO. The medium for the antifungal tests consisted of 3% su-
crose, 0.3% NaNO3, 0.1% K2HPO4, 0.05% KCl, 0.001% FeSO4 and 2%
agar-agar [30]. The disc diffusion method for the filamentous fungi
was tested using the M38-A standard method [32], whereas the
disc diffusion method for yeast was tested using the M44-P stan-
dard method [33]. Plates inoculated with filamentous fungi or
yeast were incubated for 48 h at 25 °C or 30 °C, respectively. The
antifungal activity of the CT complexes was compared with that
0.4
QL
4AAP
0.2
CT- complex
0.0
250
300
350
400
Wavelength (nm)
CT bands (281 and 353 nm)
2.0
of amphotericin B (30 lg/disc, Hi-Media) as a standard antifungal
agent. Antifungal activity was determined by measuring the diam-
eters of the sterile zone (mm) in triplicate.
1.5
1.0
0.5
0.0
Results and discussion
PA
Elemental analysis
4AAP
CT- complex
Elemental analyses (C, H, and N) of the 4AAP CT complexes were
performed, and the obtained results are as follows:
300
400
500
Wavelength (nm)
(1) [(4AAP)(QL)]: C17H19N3O3; Mol. wt. = 313.35; Calc.: %C,
65.10; %H, 6.06; %N, 13.40, Found: %C, 65.37; %H, 5.95; %N,
13.58
Fig. 1. Electronic absorption spectra of 4AAP-QL and 4AAP-PA CT complexes at the
detectable peaks of 286 and (281 and 353) nm, respectively.

4
Abdel Majid A. Adam / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 1–13
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
4AAP- QL
4AAP- QL
2.5
2.0
1.5
1.0
286 nm
0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
100 150 200 250 300 350 400 450 500 550
ml added of QL
(Cdo+Cao)X10-6
5
4AAP- PA
4AAP- PA
1.95
1.90
1.85
1.80
4
3
2
1
0
2.0
1.5
1.0
0.5
0.0
281 nm
353 nm
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
ml added of PA
100 150 200 250 300 350 400 450 500 550
Fig. 2. Spectrophotometric titration curves for 4AAP-QL and 4AAP-PA systems at
detectable peaks.
(Cdo+Cao)X10-6
Fig. 3. The modified Benesi–Hildebrand plots of 4AAP-QL and 4AAP-PA systems at
detectable peaks of 286 and 281 nm, respectively.
complexes were calculated by applying the 1:1 modified Benesi–
Hildebrand equation in the following equation [26]:
Determination of oscillator strength (f)
From the CT absorption spectra, the oscillator strength (f) can be
estimated using the approximate formula [34]:
Z
ðCaCdÞ=A ¼ 1=K
e
þ ðCa þ CdÞ=
e
ð1Þ
where Ca and Cd are the initial concentrations of the acceptor and
the donor, respectively, and A is the absorbance of the strongly de-
tected CT band. When the (CaCd)/A values for the 1:1 charge-transfer
complex are plotted against the corresponding (Ca + Cd) values, a
f ¼ 4:319 ꢁ 10ꢂ9
eCTdm
ð2Þ
R
straight line is obtained with a slope of 1/
/K . The modified Benesi–Hildebrand plots are shown in Fig. 3,
and the values of Cd, Ca, (Cd + Ca) and (CdCa)/A are listed in Table 1.
The values of both KCT and associated with the complexes are gi-
ven in Table 2. These complexes exhibit high values for both the for-
mation constants (KCT) and the extinction coefficients ( ). The high
e and an intercept of 1
where
eCTdm is the area under the curve of the extinction coeffi-
e
cient of the absorption band in question plotted as a function of fre-
quency. To a first approximation:
e
f ¼ 4:319 ꢁ 10ꢂ9eCTm1=2
ð3Þ
e
where
m
eCT is the maximum extinction coefficient of the CT band, and
values of KCT reflect the high stabilities of the formed CT complexes
as a result of the expected strong donation from 4AAP, which con-
tains one amine group and nitrogen atoms. The data also reveal that
the [(4AAP)(QL)] complex shows a higher KCT value compared with
the [(4AAP)(PA)] complex.
1/2 is the half-bandwidth in cmꢂ1 (i.e., the bandwidth at half of the
maximum extinction coefficient value).
Determination of transition dipole moment (l)
The transition dipole moments (l) of the complexes have been
calculated from the following equation [35]:
Determination of the spectroscopic and physical data
1=2
l
¼ 0:0958½eCTm1=2
=
mmax
ꢃ
ð4Þ
The spectroscopic and physical data, such as the standard free
energy (
D
Go), the oscillator strength (f), the transition dipole mo-
The transition dipole moment can be used to determine if a par-
ment ( ), the resonance energy (RN), and the ionization potential
(IP), were estimated for samples dissolved in methanol at 25 °C.
l
ticular transition is allowed; the transition from a bonding p orbi-
tal to an antibonding pꢀ orbital is allowed because the integral that
The calculations can be summarized as follows.
defines the transition dipole moment is nonzero.

Abdel Majid A. Adam / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 1–13
5
Table 1
The values of Cd, Ca, Cd + Ca and CdCa/A, for the 4AAP CT complexes.
Ratio
(A:D)
Cd
Ca
Cd + Ca
CdCa
4AAP-QL complex
4AAP-PA complex
(ꢁ10ꢂ4
)
(ꢁ10ꢂ4
)
(ꢁ10ꢂ6
)
(ꢁ10ꢂ8
)
Abs.
CdCa /A
Abs.
CdCa /A
Abs.
353 nm
CdCa /A
(ꢁ10ꢂ8
286 nm
(ꢁ10ꢂ8
)
281 nm
(ꢁ10ꢂ8
)
)
0.25
0.50
0.75
1.00
1.50
2.00
2.50
3.00
3.50
4.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
1.00
0.25
0.50
0.75
1.00
1.50
2.00
2.50
3.00
3.50
4.00
125
150
175
200
250
300
350
400
450
500
0.25
0.50
0.75
1.00
1.50
2.00
2.50
3.00
3.50
4.00
0.4844
0.7507
0.9664
1.1648
1.3101
1.3859
1.4909
1.5404
1.6201
1.6327
0.5161
0.6660
0.7761
0.8585
1.1450
1.4431
1.6768
1.9475
2.1604
2.4499
1.7858
1.8211
1.8490
1.8816
1.8989
1.9152
1.9321
1.9462
1.9564
1.9575
0.1400
0.2746
0.4056
0.5315
0.7899
1.0443
1.2939
1.5415
1.7890
2.0434
0.4259
0.9149
1.3214
1.6356
2.0712
2.5453
2.9929
3.4511
4.0631
4.1010
0.1400
0.2746
0.4056
0.5315
0.7899
1.0443
1.2939
1.5415
1.7890
2.0434
Table 2
Spectrophotometric results of the 4AAP CT complexes.
Complex
kmax (nm)
ECT (eV)
K (Lmolꢂ1
)
emax (Lmolꢂ1cmꢂ1
)
f
l
Ip
D
RN
D )
Go (25 °C) (kJmolꢂ1
[(4AAP)(QL)]
[(4AAP)(PA)]
286
281
4.349
4.426
4.02 ꢁ 104
1.95 ꢁ 104
21.01
17.07
35.73
31.93
11.11
11.21
32.70
32.70
1.23
1.25
ꢂ37,680
ꢂ34,357
1.06 ꢁ 104
1.98 ꢁ 104
Determination of ionization potential (IP) of the donor
The calculated spectroscopic and physical values (f,
Go) for the 4AAP complexes using these equations are presented
in Table 2. [(4AAP)(QL)] exhibits higher values for both the oscilla-
tor strength (f) and the transition dipole moment ( ). These high f
l, IP, RN and
The ionization potentials (IP) of the 4AAP donor in the com-
plexes were calculated using the empirical equation derived by
Aloisi and Pignataro represented in the following equation [36]:
D
l
values indicate a strong interaction between the donor–acceptor
pairs with relatively high probabilities of CT transitions [40]. One
important aspect of characterizing CT complexes is the calculation
of the ionization potential (IP) of the donor. The calculated IP value
for the highest filled molecular orbital that participates in the CT
interaction of the 4AAP is approximately 11.15. The ionization po-
tential of the electron donor has been reported to be correlated
with the charge-transfer transition energy of the complex [41].
Further evidence for the nature of the CT interactions is the calcu-
IPðeVÞ ¼ 5:76 þ 1:53 ꢁ 10ꢂ4mCT
ð5Þ
where mCT is the wavenumber in cmꢂ1 that corresponds to the CT
band formed from the interaction between the donor and the
acceptor. The electron-donating power of a donor molecule is mea-
sured by its ionization potential, which is the energy required to re-
move an electron from the highest occupied molecular orbital.
Determination of resonance energy (RN)
Briegleb and Czekalla [37] theoretically derived the following
relationship to obtain the resonance energy (RN):
lation of the standard free energy change (D
Go). The obtained val-
ues of
D
Go for the 4AAP/QL and 4AAP/PA complexes are ꢂ38 and
ꢂ34 kJ molꢂ1, respectively; these values indicate that the interac-
eCT ¼ 7:7 ꢁ 10ꢂ4=½h
m
CT=½RNꢃ ꢂ 3:5ꢃ
ð6Þ
tion between 4AAP and the acceptors is exothermic and spontane-
ous. In general,
D
Go values are more negative as the formation
where eCT is the molar absorptivity coefficient of the CT complex at
constants of the CT complexes increase.
the maximum of the CT absorption, mCT is the frequency of the CT
peak, and RN is the resonance energy of the complex in the ground
state, which contributes to the stability constant of the complex (a
ground-state property).
IR and Raman spectra
The assignments for the characteristic IR and Raman spectral
bands for the complexes are shown in Table 3, whereas the full
assignment of the IR bands in the spectrum is listed in Tables 4
and 5. The full IR and Raman spectra of the CT complexes are
shown in Figs. 4 and 5, respectively. The formation of the CT com-
plexes during the reaction of 4AAP with QL or PA is strongly sup-
ported by the observation of main infrared bands of the donor
(4AAP) and acceptors (QL and PA) in the product spectra. However,
the bands of the donor and acceptors in the spectra of the
complexes reveal small changes in frequency and in their band
intensities compared with those of the free donor and acceptors.
This result could be attributed to the expected changes in symme-
try and electronic structure upon the formation of the CT com-
plexes. The characteristic bands of 4AAP observed at 3432 and
3326 cmꢂ1, which are assigned to -NH2 asymmetric and symmetric
stretching vibrations, respectively [42], shifted to lower values and
reduced in intensity after complexation. This observation clearly
indicates that the ANH2 group in the donor participates in the
complexation process. The IR spectra of the 4AAP/QL and 4AAP/
Determination of energy of the charge-transfer complex (ECT
)
The energy values (ECT) of the n?pꢀ and pꢀ interactions be-
p–
tween the donor (4AAP) and the acceptors were calculated using
the equation derived by Briegleb [38]:
ECT ¼ ðhmCTÞ ¼ ð1243:667=kCT
Þ
ð7Þ
where kCT is the wavelength of the CT band.
Determination of standard free energy changes (
D
Go)
D
Go) for each com-
The standard free energy of complexation (
plex was calculated from the formation constants using the equa-
tion derived by Martin et al. [39]:
D
Gꢄ ¼ ꢂ2:303RT log KCT
ð8Þ
where
D
Go is the free energy of the CT complexes (kJ molꢂ1), R is the
gas constant (8.314 J molꢂ1 Kꢂ1), T is the absolute temperature in K,
and KCT is the formation constant of the complex (L molꢂ1) at room
temperature.

6
Abdel Majid A. Adam / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 1–13
Table 3
Assignments of the characteristic IR and Raman spectral bands (cmꢂ1) for [(4AAP)(QL)] and [(4AAP)(PA)] complexes.
dðNHþ3 Þdef
dðNHþ3 Þsym
q
D
ðNHþ3 Þ
Complex
m(NH)
IR
Raman
IR
Raman
IR
Raman
IR
Raman
[(4AAP)(QL)]
[(4AAP)(PA)]
3213
3345
3064
3082
1588
1564
1595
1580
1314
1318
1327
1313
832
837
854
826
Table 5
Table 4
a
Characteristic infrared frequencies (cmꢂ1
and their complex.
)
and tentative assignments for 4AAP, PA
a
Characteristic infrared frequencies (cmꢂ1
and their complex.
)
and tentative assignments for 4AAP, QL
b
b
4AAP
PA
Complex [(4AAP)(PA)]
Assignments
4AAP
QL
Complex [(4AAP)(QL)]
Assignments
m
m
m
m
m
m
(NAH); 4AAP
as(CAH); 4AAP
(OAH); PA
m
m
m
m
m
(NAH); 4AAP
as(CAH); 4AAP
(OAH); QL
3432 ms
3326 ms
3207 s
3416 br
3103 ms
3427 m, br
3345 m
3432 ms
3326 ms
3207 s
3737 w
3390 w
3316 mw
3213 br
3262 br
3031 m
(CAH); aromatic
(CAH); aromatic
(NHþ3
)
(NHþ3
)
–
2980 sh
2872 w
–
–
2926 m, br
s(CAH)+mas(CAH)
2857 m
2836 m
2716 m
Hydrogen bonding
Over tone/ combination
m
–
2840 w
2731 m, br
ms(CAH)+mas(CAH)
–
2362 mw
1633 vs
Hydrogen bonding
1651 vs
(C@O); 4AAP
(NAH) scissoring; 4AAP
–
2593 w
2471 vw
2361 m
1608 vs
1632 vs
1608 vs
mas(NO2); PA
2590 w
2467 vw
–
Over tone/ combination
dðNHþ3 Þdef , complex
1590 ms
1564 s
1492 s
1529 vs
m
m
(C@C) (in-ring), aromatic
(C@O)+m(C@N)
1651 vs
m(C@O); 4AAP
(NAH) scissoring; 4AAP
dðNHþ3 Þdef , complex
d(CAH) deformation
Ring breathing bands
1628 w
1590 ms
1609 w
1518 vs
1588 vs
1507 vs
m(C@C) (in-ring), aromatic
1498 ms
1456 s
m
m
(CAH); alkanes; 4AAP
(C@C) (in-ring), aromatic
m(C@O)+m(C@N)
1432 s
1435 m
d(CAH) deformation
Ring breathing bands
d(CAH) deformation
dðNHþ3 Þsym, complex
1498 ms
1456 s
m(CAH); alkanes; 4AAP
1353 ms
1343 ms
1312 w
1364 m
1318 vs
m(CAC)+m(CAO)+mas(CAN)
1477 vs
1466 sh, s
m(C@C) (in-ring), aromatic
CAH rock, alkanes; 4AAP
d(CAH) deformation
dðNHþ3 Þsym, complex
m(CAC)+m(CAO)+mas(CAN)
m
sNO2
1311 m
1274 ms
1230 m
1118 m
1074 m
1025 m
1271 m
1162 m
1126 w
1078 m
913 m
1353 ms
1366 ms
1363 m
1314 s
1263 w
1150 ms
1086 s
m
m
s(CAN); 4AAP
(CAO); 4AAP
CAH rock, alkanes; 4AAP
1311 m
1274 ms
1230 m
1118 m
1074 m
d(CAH) in plane bending
drock; NH
1244 vs
1222 vs
1210 vs
1164 ms
1097 m
1242 s
ms(CAN); 4AAP
917 vs
1215 sh, s
1139 vw
1096 w
m(CAO); 4AAP, QL
d(CAH) in plane bending
drock; NH
ðNHþ3 Þ), complex
829 w
781 s
732 s
837 mw
766 mw
714 s
(
q
759 vs
CAH out of plane bending
drock, CH2 rock
NAH wag
skeletal vibrations
NAH twisting
NACH3 wagging
d(ONO); PA
1025 m
q
(NHþ3 ), complex
CAH out of plane bending
drock, CH2 rock
NAH wagging
Skeletal vibrations
NAH twisting
572 m
501 m
703 s
652 sh
522 ms
703 ms
666 mw
575 m
759 vs
827 s
759 vs
832 ms
764 vs
CNC deformation
572 m
501 m
616 m
525 ms
698 ms
579 m
521 mw
NACH3 wagging
CNC deformation
a
s, strong; w, weak; m, medium; sh, shoulder; v, very; vs very strong; br, broad.
b
m, stretching; ms , symmetrical stretching; mas , asymmetrical stretching; d,
bending.
a
s, strong; w, weak; m, medium; sh, shoulder; v, very; vs very strong; br, broad.
b
m, stretching; ms , symmetrical stretching; mas , asymmetrical stretching; d,
bending.
bands confirmed that the complexation occurs through the proton-
ation of the 4AAP amine by the phenolic groups of the acceptors
[44–48].
PA complexes are characterized by a broad medium band that ap-
pears between 2400–2800 cmꢂ1 (2731 cmꢂ1 for the QL complex;
2926 cmꢂ1 for the PA complex), which does not appear in the spec-
tra of the free 4AAP donor or those of the QL and PA acceptors.
These broadened peaks are due to hydrogen bonding in the com-
plex formed through the transfer of a proton from QL or PA to
the amine of 4AAP [43]. This assumption is strongly supported
by the appearance of the characteristic absorption bands that re-
1H NMR spectra
The 400 MHz 1H NMR spectra of the complexes were measured
in DMSO-d6 at room temperature and are given in Fig. 6. The chem-
ical shifts (d) of the different types of protons of the CT complexes
are given below. The results obtained from the elemental analyses,
infrared spectra, and photometric titrations are in agreement with
the 1H NMR spectra, which allows for an interpretation of the mode
of interaction between the donor and the acceptor. The reaction of
4AAP with QL yielded a new charge-transfer complex, 1,5-di-
methyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-aminium-4-
+
sult from the stretching and bending deformation of the NH3
group. IR and Raman spectra confirm the presence of these bands;
the m(NH), m q
def(NHþ), dsym(NHþ) and (NHþ3 ) absorptions are ob-
3 3
served for [(4AAP)(QL)] and [(4AAP)(PA)] at approximately 3200,
1600, 1300 and 800 cmꢂ1, respectively. The presence of these

Abdel Majid A. Adam / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 1–13
7
hydroxyphenolate, which produced signals (Fig. 6) at
D
= 2.09 (s,
and PA, the proton of the AOH group of PA is transferred to the
amine of 4AAP to form an ion-paired compound named 1,5-di-
methyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-aminium-
2,4,6-trinitrophenolate. The two signals of equal intensity at
2.27 ppm (3H) and 3.02 ppm (3H), corresponding to the protons
of CACH3 and NACH3 groups, respectively [49,50]. The new peak
observed at 3.89 ppm in the complex, which is not detected in
the spectrum of the free donor, is attributed to the formation of
3H, CH3, antipyrine C3), 2.73 (s, 3H, N-CH3), 3.83 (s, 3H, ꢂNHþ),
3
6.56 (s, 4H, ArAH, quinol ring protons), 7.21 (t, 1H, ArAH, phenyl
C4), 7.34 (m, 2H, ArAH, phenyl C3 and C5), 7.50 (t, 2H, ArAH, phe-
nyl C2 and C6), 8.59 (s, 1H, ArAOH, 4-hydroxyphenolate). The 1H
NMR spectrum of this complex displays two signals of equal inten-
sity at 2.09 ppm (3H) and 2.73 ppm (3H), corresponding to the pro-
tons of CACH3 and NACH3 groups, respectively [49,50]. The
spectrum indicated that the phenolic proton (AOH) signal, which
is observed at approximately 9 ppm in the spectrum of the QL
acceptor, decreased in intensity with an upfield shift (8.59 ppm).
This result indicates the involvement of the phenolic group in
the chelation of the donor via deprotonation and an overall de-
crease in the negative charge on the quinol ring due to the forma-
tion of the complex. In addition, the disappearance of the ANH2
protons from 4AAP and the appearance of a weak broad band at
3.83 ppm, which is attributed to the ammonium protons, indicate
the involvement of the amine group in the complexation process.
Based on these data, the structure suggested for the 4AAP/QL com-
plex is shown in Formula II.
a
hydrogen bond [51] between PA and 4AAP. The peak at
d = 11.94 ppm, which is assigned to the AOH proton of picric acid
[52], was absent in the spectrum of this complex. Together, these
data indicate that the amine and phenolic groups are involved in
the formation of the CT complex between 4AAP and PA. The inten-
sities and chemical shifts of the aromatic signals were significantly
affected by the complexation process and the accompanying
changes in the structural configuration. According to these obser-
vations, the suggested structure for the 4AAP/PA complex is illus-
trated in Formula III.
Thermal analysis
The 1H NMR spectrum for the CT complex formed with 4AAP
and PA is shown in Fig. 6 and is summarized as follows:
D = 2.27
To examine the thermal stability of the new complexes, the
thermogravimetric analysis of the complexes were carried out over
the temperature range of 25–800 °C under an air atmosphere. The
TG curves were redrawn as mass loss versus temperature. Typical
TG curves of the complexes are presented in Fig. 7, and the
(s, 3H, CH3, antipyrine C3), 3.02 (s, 3H, NACH3), 3.89 (s, 3H,
ꢂNHþ3 ), 7.34 (t, 1H, ArAH, phenyl C4), 7.36 (m, 2H, ArAH, phenyl
C3 and C5), 7.50 (t, 2H, ArAH, phenyl C2 and C6), 8.59 (s, 2H, ArAH,
picrate C3 and C5). In the charge-transfer reaction between 4AAP
0.04
[(4AAP)(QL)] complex
0.03
0.02
0.01
0.00
[(4AAP)(QL)] complex
3500
3000
2500
2000
1500
1000
500
3500
3000
2500
2000
1500
1000
500
0
Wavenumbers (cm-1)
Wavenumbers (cm-1)
0.12
0.09
0.06
0.03
0.00
[(4AAP)(PA)] complex
[(4AAP)(PA)] complex
3500
3000
2500
2000
1500
1000
500
3500
3000
2500
2000
1500
1000
500
0
Wavenumbers (cm-1)
Wavenumbers (cm-1)
Fig. 4. Infrared spectra of 4AAP CT complexes.
Fig. 5. Raman spectra of 4AAP CT complexes.

8
Abdel Majid A. Adam / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 1–13
O2N
H3N
O
NO2
N
O2N
O
N
Formula III. Suggested structure for the [(4AAP)(PA)] complex.
10
8
6
4
2
0
[(4AAP)(QL)] complex
0
200
400
600
800
Temp [oC]
12
10
8
6
4
Fig. 6. 1H NMR spectrum of (A) 4AAP-QL and (B) 4AAP-PA complexes.
2
[(4AAP)(PA)] complex
0
H3N
OH
O
0
200
400
600
800
Temp [oC]
N
O
N
Fig. 7. TG curves of 4AAP CT complexes.
loss of 3 C2H2, CO2, NH3 and NO2 molecules in good agreement
with the calculated value of 48.83%. The second stage of decompo-
sition proceeds within the temperature range of 320–800 °C and
corresponds to the liberation of 3 C2H2, NO2 and 2 H2 molecules.
The weight loss associated with this stage (35.75%) is in excellent
agreement with the calculated value (35.74%). The total mass loss
is 84.3% with only carbon remaining as a final residue. [(4AAP)(-
PA)] begins to decompose at ꢅ180 °C in two clear decomposition
steps within the 25–800 °C temperature range. The first decompo-
sition step within the temperature range of 25–220 °C
(obs. = 52.10%, calc. = 53.43%) is attributed to the liberation of 2
C2H2, 2 CO2, NH3 and 3 NO2 molecules. The second decomposition
Formula II. Suggested structure of the [(4AAP)(QL)] complex.
thermoanalytical results are listed in Table 6. Comparison of the
thermograms revealed that [(4AAP)(PA)] is more stable than
[(4AAP)(QL)].
The thermal analysis curve of [(4AAP)(QL)] indicates that its
decomposition begins at ꢅ80 °C and finishes at ꢅ640 °C. The
decomposition reactions of the complex occur in two main stages
within the given temperature range. The first stage of decomposi-
tion within the temperature range of 25–320 °C proceeds with a
weight loss value of 48.55%. This stage might be associated with

Abdel Majid A. Adam / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 1–13
9
Table 6
Thermal decomposition data for the 4AAP CT complexes.
Complex
Stage
TG range (°C)
Mass loss (%)
Found
Evolved moiety
Calculated
[(4AAP)(QL)] (C17H19N3O3)
I
II
25–320
320–800
–
48.55
35.75
15.70
48.83
35.74
15.32
3C2H2+CO2+NH3+NO2
3C2H2+NO2+2H2
Residual carbons
Residue
[4AAP)(PA)] (C17H16N6O8)
I
II
25–220
220–800
–
52.10
35.99
11.91
53.43
35.39
11.10
2C2H2+2CO2+NH3+3NO2
3C2H2+CO2+NH3+NO2
Residual carbons
Residue
Table 7
Kinetic parameters determined using the Coats–Redfern (CR) and Horowitz–Metzger (HM).
Complexes
Stage
Method
Parametersa
r
Eꢀ
A
D
Sꢀ
D
Hꢀ
D
Gꢀ
[(4AAP)(QL)]
[(4AAP)(PA)]
1st
1st
CR
HM
7.46 ꢁ 104
7.04 ꢁ 104
ꢂ1.57 ꢁ 102
7.02 ꢁ 104
1.54 ꢁ 105
0.99289
0.98919
7.97 ꢁ 104
5.82 ꢁ 105
ꢂ1.39 ꢁ 102
7.53 ꢁ 104
1.49 ꢁ 105
CR
HM
6.19 ꢁ 105
6.14 ꢁ 105
1.25 ꢁ 106
4.53 ꢁ 106
1.02 ꢁ 103
1.01 ꢁ 102
6.15 ꢁ 105
6.10 ꢁ 105
1.27 ꢁ 105
1.26 ꢁ 105
0.95530
0.95055
a
Units of parameters: E in kJ molꢂ1, A in sꢂ1
,
D
S in J molꢂ1Kꢂ1
,
D
H and
D
G in kJ molꢂ1
.
-11.5
-12.0
-12.5
-13.0
-13.5
-14.0
-14.5
0.2
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
4AAP/QL, (CR), Stage 1
4AAP/QL, (HM), Stage 1
0.0017
0.0018
0.0019
0.0020
-40
-20
0
20
40
60
1000/T(K-1)
θ (Κ)
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
-1.2
-1.4
-11.5
-12.0
-12.5
-13.0
-13.5
-14.0
-14.5
4AAP/PA, (CR), Stage 1
4AAP/PA, (HM), Stage 1
0.00207
0.00208
0.00209
0.00210
0.00211
-6
-5
-4
-3
-2
-1
0
1
2
3
1000/T(K-1)
θ (Κ)
Fig. 8. The diagrams of kinetic parameters of 4AAP complexes using Coats–Redfern (CR) and Horowitz–Metzger (HM) equations.
step within the 220–800 °C temperature range (obs. = 35.99%,
calc. = 35.39%) is reasonably explained by the loss of 3 C2H2, CO2,
NH3 and NO2 molecules. The overall loss of mass by this complex
is 88.1%.
Kinetic and thermodynamic studies
Kinetic studies on thermal processes are expected to provide
information regarding the Arrhenius parameters, such as the

10
Abdel Majid A. Adam / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 1–13
where
a is the fraction of the sample decomposed at time t, T is the
1200
1000
800
600
400
200
0
[(4AAP)(QL)] complex
derivative peak temperature, A is the frequency factor, R is the gas
constant, Eꢀ is the activation energy, and
u is the linear heating rate.
A plot of the left-hand side (LHS) against 1/T was constructed. Eꢀ is
the activation energy in kJ molꢂ1 and was calculated from the slope.
The A (sꢂ1) value was calculated from the intercept. The entropy of
activation,
D
Sꢀ, in (J Kꢂ1 molꢂ1) was calculated using the equation:
D
Sꢀ ¼ R lnðAh=kTsÞ
ð11Þ
where k is the Boltzmann constant, h is Planck’s constant, and Ts is
the DTG peak temperature.
Horowitz–Metzger equation
The Horowitz–Metzger equation (Eq. (12)) is given in the fol-
lowing form:
10
20
30
40
50
60
log½logðwa=wcÞꢃ ¼ Eꢀh=2:303RT2 ꢂ log 2:303
where h = T–Ts, w = w –w, w is the mass loss at the completion of
ð12Þ
s
2θ
c
a
a
the reaction, and w is the mass loss at time t.
[(4AAP)(PA)] complex
The plot of log [log (w /w )] versus h was constructed and was
350
300
250
200
150
100
50
a
c
observed to be linear, and Eꢀ was calculated from its slope. The pre-
exponential factor, A, was calculated from the following equation:
Eꢀh=RT2s ¼ A=½
u
expðꢂEꢀ=RTsÞꢃ
ð13Þ
From the TG curves, the activation energy, Eꢀ, the entropy of activa-
tion,
Sꢀ, the enthalpy of activation, Hꢀ, and the Gibbs free energy,
Gꢀ, were calculated from:
D
D
D
D
Hꢀ ¼ Eꢀ ꢂ RT and
D
Gꢀ ¼
D
Hꢀ ꢂ T
D
Sꢀ
The evaluated kinetic parameters for the first stages based on the
Coats–Redfern and Horowitz–Metzger equations are listed in Table
7, and the linear curves from the Coats–Redfern and Horowitz–
Metzger plots are shown in Fig. 8. The results indicate that the ki-
netic data obtained from the two methods are comparable and in
agreement with each other. The activation energy of the complexes
is expected to increase with increasing thermal stability of com-
plexes. Hence, the Eꢀ value for [(4AAP)(PA)] is much higher than
for [(4AAP)(QL)], which indicates the higher thermal stability of
[(4AAP)(PA)]. The calculated Eꢀ values using the Coats–Redfern
and Horowitz–Metzger methods for the main decomposition stage
of the complexes are found to be 6.17 ꢁ 105 kJ molꢂ1 for [(4AAP)(-
PA)] and 7.72 ꢁ 104 kJ molꢂ1 for [(4AAP)(QL)]. Satisfactory values
for the correlation coefficients from the Arrhenius plots of the ther-
mal decomposition steps were observed to be r ꢅ1 in all cases,
which indicates a good fit with the linear function and reasonable
agreement between the experimental data and the kinetic parame-
0
10
20
30
40
50
60
2θ
Fig. 9. X-ray diffraction pattern for [(4AAP)(QL)] and [(4AAP)(PA)] complexes.
Table 8
XRD spectral data of 4AAP CT complexes.
Complex
2h (°)
d
Full width at half
maximum
(FWHM)
Relative
intensity
(%)
Particle
size
value
(Å)
(nm)
[(4AAP)(QL)] 26.278 3.386
[(4AAP)(PA)] 18.480 4.800
0.35
0.15
100
100
4.25
9.78
ters. The negative values of
D
Sꢀ observed for [(4AAP)(QL)] indicate
that the reaction rate is slower than normal [55].
activation energy (Eꢀ), the frequency factor (A), the enthalpy of
activation (Hꢀ), the entropy of activation (Sꢀ), and the free energy
of activation (Gꢀ). Two methods were used to evaluate the kinetic
thermodynamic parameters: the Coats–Redfern method [53] and
the Horowitz–Metzger [54] method.
X-ray powder diffraction investigation
To investigate the crystal structures of the complexes, X-ray
powder diffraction patterns in the range of 5 < 2h < 60° for the ob-
tained complexes were examined, and the recorded patterns are
shown in Fig. 9. The main characteristic scattering peak of
[(4AAP)(QL)] occurs at 26.278°, whereas this peak occurs at
18.480° for [(4AAP)(PA)]. Based on these investigations, the sharp
and well-defined Bragg peaks at specific 2h angles confirm the
semi-crystalline nature of the investigated CT complexes. The par-
ticle size of these two complexes were estimated from their XRD
patterns based on the highest intensity value compared with the
other peaks using the well-known Debye–Scherrer formula given
in the Eq. (14) [56]:
Coats–Redfern equation
The Coats–Redfern Eq. (9), which is an atypical integral method,
can be represented as:
Z
Z
ꢀ
n
da=ð1 ꢂ
a
Þ ¼ ðA=
u
Þ
eꢂE =RT dT
ð9Þ
0!1
T1!T2
For convenience, the lower limit T1 is usually taken as zero. After
integration, this equation can be represented as:
Þ=T2ꢃ ¼ ꢂEꢀ=RT þ ln½AR=
u
Eꢀꢃ
ð10Þ
D ¼ Kk=b cos h
ð14Þ
Ln½ꢂ lnð1 ꢂ
a

Abdel Majid A. Adam / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 1–13
11
Fig. 10. SEM images and EDX spectra of (A) [(4AAP)(QL)] and (B) [(4AAP)(PA)] complexes.
Table 9
The inhibition diameter zone values (mm) for 4AAP and its CT complexes.
Sample
Inhibition zone diameter (mm/mg sample)
Bacteria
Fungi
Bacillus subtilis,
Escherichia coli,
Pseudomonas
Staphylococcus aureus, Aspergillus
Candida
albicans
(G+)a
(Gꢂ)
aeuroginosa, (Gꢂ)
(G+)
flavus
Control: DMSO
Standard Tetracycline (antibacterial
0.0
34.0
0.0
32.0
0.0
34.0
0.0
30.0
0.0
–
0.0
–
agent)
Amphotericin B (antifungal
agent)
–
–
–
–
18.0
19.0
4AAP
[(4AAP)(QL)]
[(4AAP)(PA)]
6
20.0
11.0
7
20.0
13.0
5
17.0
12.0
6
22.0
12.0
0.0
12.0
0.0
0.0
17.0
0.0
a
G: Gram reaction.
where D is the apparent particle size of the grains, K is a constant
(0.94 for Cu grid), k is the X-ray wavelength used (1.5406 Å), h is half
the scattering angle (the Bragg diffraction angle), and b is the full-
width at half-maximum (FWHM) of the X-ray diffraction line (addi-
tional peak broadening) in radians. Table 8 presents the XRD spectral
data for the complexes. The particle sizes of the complexes were
estimated according to the highest intensity value compared with
the other peaks and were found to be ꢅ4 and ꢅ10 nm for the
[(4AAP)(QL)] and [(4AAP)(PA)] complexes, respectively. These val-
ues confirmed that the particle sizes are within the nanoscale range.
cle size, chemical composition and porous structures of the sur-
faces. Fig. 10 shows the SEM surface images of the complexes
along with their EDX spectra. The analysis of the SEM images of
the complexes showed the following:
ꢆ The morphological phases of these complexes have a homoge-
neous matrix, as indicated by the uniformity and similarity of
the particles of the synthesized CT complexes.
ꢆ The sizes of the particles are quite different with different
acceptors.
ꢆ The complexes are semi-crystalline, and some single-phase for-
mations exhibit well-defined shapes.
SEM and EDX studies
ꢆ The [(4AAP)(QL)] particles exhibit different flake shapes con-
taining sharp edges with a particle size of ꢅ100
lm.
The morphological features of the complexes were investigated
using scanning electron microscopy (SEM). SEM provides general
information about the microstructure, surface morphology, parti-
ꢆ The [(4AAP)(PA)] particles are sponge-shaped with a porous
nature and a particle size of ꢅ50 m.
l

12
Abdel Majid A. Adam / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 1–13
plex exhibited moderate inhibitory results against all of the
Gram-positive and Gram-negative bacterial species, as reported
in Table 9.
Antifungal activity studies
The 4AAP and its synthesized CT complexes were also screened
for their antifungal properties against two fungal species, A. flavus
and C. albicans. Amphotericin B was used as a positive control, and
the screening data are reported in Table 9 and statistically pre-
sented in Fig. 12. The data revealed that the [(4AAP)(QL)] complex
had a significant antifungal response against C. albicans. The
[(4AAP)(PA)] complex exhibited no inhibitory activity against
either fungal species, as shown in Table 9. It is obvious that the
antimicrobial activities of the 4AAP CT complexes are more than
that of free 4AAP. The [(4AAP)(QL)] complex shows good antifungal
activities, while the free 4AAP has no such activity which makes
this complex of interest. The most reasons for lethal action of
tested 4AAP CT complexes may be due to their interactions with
critical intracellular sites causing the death of cells. The variety
of antimicrobial activities of tested 4AAP CT complexes may due
to a different degree of tested complexes penetration through cell
membrane structure of target organism [57].
B. subtilis
E. coli
P. aeuroginosa
S. aureus
Fig. 11. Statistical representation for antibacterial activity of 4AAP and its
complexes.
Conclusion
Structural studies of the newly synthesized charge-transfer
complexes of 4-aminoantipyrine (4AAP) with quinol (QL) and pic-
ric acid (PA) were carried out. Two new proton-transfer salts,
named 1,5-dimethyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-
aminium-4-hydroxyphenolate and 1,5-dimethyl-3-oxo-2-phenyl-
2,3-dihydro-1H-pyrazol-4-aminium-2,4,6-trinitrophenolate for QL
and PA, respectively, are formed via a 1:1 donor/acceptor stoichi-
ometry. The IR, Raman and 1H NMR spectra show that the com-
plexes formed between 4AAP and QL or PA are stabilized by
hydrogen bonding, which is formed between the phenolic group
of the acceptors and the primary amine of 4AAP. The obtained
complexes are nanoscale, semi-crystalline particles, and the com-
pound formed with PA is thermally stable up to 180 °C with a
remarkable sponge-like morphology. The antibacterial and anti-
fungal activities of the newly synthesized CT complexes were stud-
ied using the disc diffusion method, and [(4AAP)(QL)] exhibited
good microbial activities against various bacterial and fungal
strains compared with standard drugs.
Aspergillus flavus
Candida albicans
Fig. 12. Statistical representation for antifungal activity of 4AAP and its complexes.
In addition, the chemical compositions of the complexes were
determined using energy-dispersive X-ray diffraction (EDX). The
chemical analysis results from the EDX analysis for the formed
complexes showed a homogeneous distribution of each acceptor.
In the EDX profile, the peaks refer to all elements that constitute
the molecules of these complexes; these elements were clearly
identified, and the results confirmed the proposed structures.
References
Pharmacology
[1] Y.M. Chen, Y.P. Chen, Fluid Phase Equilibr. 282 (2009) 82.
[2] Y. Teng, F. Ji, C. Li, Z. Yu, R. Liu, J. Lumin. 131 (2011) 2661.
[3] Y. Teng, R. Liu, C. Li, H. Zhang, J. Hazard. Mater. 192 (2011) 1766.
[4] A. Lang, C. Hatscher, C. Wiegert, P. Kuhl, Amino Acids 36 (2009) 333.
[5] V. Mishra, R. Kumar, Carbohydr. Polym. 86 (2011) 296.
[6] A. Lang, C. Hatscher, P. Kuhl, Tetra. Lett. 48 (2007) 3371.
[7] S. Cunha, S.M. Oliveira, M.T. Rodriques, R.M. Bastos, J. Ferrari, C.M.A. de
Oliveira, L. Kato, H.B. Napolitano, I. Vencato, C. Lariucci, J. Mol. Struct. 752
(2005) 32.
The 4AAP and its CT complexes were screened in vitro for their
antibacterial and antifungal activity. The CT complexes to be tested
were dissolved in DMSO to obtain 100 lg/ml stock solutions. The
diameter zones were measured to determine their effects on the
growth of the tested microorganisms.
[8] S. Prasad, R.K. Agarwal, Transit. Metal Chem. 32 (2007) 143.
[9] J.F. Van Staden, N.W. Beyene, R.I. Stefan, H.Y. Aboul-Enein, Talanta 68 (2005)
401.
Antibacterial activity studies
[10] J. Kasthuri, J. Santhanalakshmi, N. Rajendiran, Transit. Metal Chem. 33 (2008)
899.
[11] C.Z. Katsaounos, E.K. Paleologos, D.L. Giokas, M.I. Karayannis, Int. J. Environ.
Anal. Chem. 83 (2003) 507–514.
[12] A.M. Farghaly, A. Hozza, Pharmazie 35 (1980) 596.
[13] D. Chiaramonte, J.M. Steiner, J.D. Broussard, K. Baer, S. Gumminger, E.M.
Moller, D.A. Williams, R. Shumway, Can. J. Vet. Res. 67 (2003) 183.
[14] P.M. Selvakumar, E. Suresh, P.S. Subramanian, Polyhedron 26 (2007) 749.
[15] N.L. Olenovich, L.I. Koval Chuk, Zh. Anal. Khim 28 (1975) 2162.
[16] Y. Teng, R. Liu, C. Li, Q. Xia, P. Zhang, J. Hazard. Mater. 190 (2011) 574.
[17] A.M. Vinagre, E.F. Collares, Braz. J. Med. Biol. Res. 40 (2007) 903.
[18] S.G. Sunderji, A. El Badry, E.R. Poore, J.P. Figueroa, P.W. Nathanielsz, Am. J.
Obstet. Gynecol. 149 (1984) 408.
The antibacterial activity of the 4AAP and its complexes were
tested in vitro against two Gram-positive bacterial strains, S. aureus
(S. aureus) and B. subtilis, and two Gram-negative bacterial strains,
E. coli (E. coli) and P. aeruginosa (P. aeruginosa). The activity was
determined by measuring the inhibition zone diameter values
(mm) of the complexes against the microorganisms. Tetracycline
was used as a positive control. The screening data are given in Ta-
ble 9 and are statistically presented in Fig. 11. The data reveal that
the [(4AAP)(QL)] complex showed good inhibitory activity against
the growth of the tested bacterial strains. The [(4AAP)(PA)] com-

Abdel Majid A. Adam / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 104 (2013) 1–13
13
[19] S.C. Pierre, R. Schmidt, C. Brenneis, M. Michaelis, G. Geisslinger, K. Scholich,
Brit. J. Pharmacol. 151 (2007) 494.
[37] G. Briegleb, J. Czekalla, Z. Physikchem. Frankfurt 24 (1960) 237.
[38] G. Briegleb, Z. Angew. Chem. 72 (1960) 401 (Z. Angew. Chem. 76 (1964) 326).
[39] A.N. Martin, J. Swarbrick, A. Cammarata, Physical Pharmacy, third ed., Lee and
Febiger, Philadelphia, PA, 1969. p. 344.
[40] M.S. Refat, A. Elfalaky, E. Elesh, J. Mol. Struct. 990 (2011) 217.
[41] M. Pandeeswaran, K.P. Elango, Spectrochim. Acta A 65 (2006) 1148.
[42] J. Swaminathan, M. Ramalingam, V. Sethuraman, N. Sundaraganesan, S.
Sebastian, Spectrochim. Acta A 73 (2009) 593.
[43] M.S. Refat, L.A. El-Zayat, O.Z. Yesilel, Spectrochim. Acta A 75 (2010) 745.
[44] M.S. Refat, H.A. Saad, A.A. Adam, J. Mol. Struct. 995 (2011) 116.
[45] L.J. Bellamy, The Infrared Spectra of Complex Molecules, Chapman & Hall,
London, 1975.
[46] R. Bharathikannan, A. Chandramohan, M.A. Kandhaswamy, J. Chandrasekaran,
R. Renganathan, V. Kandavelu, Cryst. Res. Technol. 43 (6) (2008) 683.
[47] A.S. Gaballa, S.M. Teleb, E. Nour, J. Mol. Struct. 1024 (2012) 32.
[48] A.A. Adam, J. Mol. Struct (2012).
[49] R.M. Issa, A.M. Kheder, H.F. Rizk, Spectrochim. Acta A 62 (2005) 621.
[50] S. Fazil, R. Ravindran, A.S. Devi, B.K. Bijili, J. Mol. Struct. 1021 (2012) 147.
[51] N. Singh, A. Ahmad, J. Mol. Struct. 977 (2010) 197.
[52] R.D. Kross, V.A. Fassel, J. Am. Chem. Soc. 79 (1957) 38.
[53] A.W. Coats, J.P. Redfern, Nature (London) 201 (1964) 68.
[54] H.H. Horowitz, G. Metzger, Anal. Chem. 35 (1963) 1464.
[55] A.A. Frost, R.G. Pearson, Kinetics and Mechanism, Wiely, New York, NY, USA,
1961.
[20] Y. Teng, R. Liu, S. Yan, X. Pan, P. Zhang, M. Wang, J. Fluoresc. 20 (2010) 381.
[21] S. Chandra, D. Jain, A.K. Sharma, P. Sharma, Molecules 14 (2009) 174.
[22] N. Raman, S. Sobha, A. Thamaraichelvan, Spectrochim. Acta A78 (2011) 888.
[23] N. Raman, S. Sobha, Inorg. Chem. Commun. 17 (2012) 120.
[24] M.R. Saber, F.A. Mauther, J. Mol. Struct. 1020 (2012) 177.
[25] D.A. Skoog, Principle of Instrumental Analysis, third ed., Saunders, New York,
USA, 1985 (Chapter 7).
[26] H.A. Benesi, J.H. Hildebrand, J. Am. Chem. Soc. 71 (1949) 2703.
[27] R. Abu-Eittah, F. Al-Sugeir, Can. J. Chem. 54 (1976) 3705.
[28] A.W. Bauer, W.M. Kirby, C. Sherris, M. Turck, Am. J. Clin. Pathol. 45 (1966) 493.
[29] M.A. Pfaller, L. Burmeister, M.A. Bartlett, M.G. Rinaldi, J. Clin. Microbiol. 26
(1988) 1437.
[30] D.J. Beecher, A.C. Wong, Appl. Environ. Microbiol. 60 (1994) 1646.
[31] National Committee for Clinical Laboratory Standards. Methods for
Antimicrobial Susceptibility Testing of Anaerobic Bacteria: Approved
Standard M11-A3. NCCLS, Wayne, PA, USA, 1993.
[32] National Committee for Clinical Laboratory Standards. Reference Method for
Broth Dilution Antifungal Susceptibility Testing of Conidium-Forming
Filamentous Fungi: Proposed Standard M38-A. NCCLS, Wayne, PA, USA, 2002.
[33] National Committee for Clinical Laboratory Standards. Method for Antifungal
Disk Diffusion Susceptibility Testing of Yeast: Proposed Guideline M44-P.
NCCLS, Wayne, PA, USA, 2003.
[34] H. Tsubomura, R.P. Lang, J. Am. Chem. Soc. 83 (1961) 2085.
[35] R. Rathone, S.V. Lindeman, J.K. Kochi, J. Am. Chem. Soc. 119 (1997).
[36] G. Aloisi, S. Pignataro, J. Chem. Soc. Faraday Trans. 69 (1972) 534.
[56] S.J.S. Qazi, A.R. Rennie, J.K. Cockcroft, M. Vickers, J. Colloid Interface Sci. 338
(2009) 105.
[57] A.A. El-Habeeb, F.A. Al-Saif, M.S. Refat, J. Mol. Struct. 1034 (2013) 1.