An environmentally friendly method to remove and utilize the highly toxic strychnine in other products based on proton-transfer complexation

Article abstract of DOI:10.1016/j.molstruc.2015.08.065

The study of toxic and carcinogenic substances represents one of the most demanding areas in human safety, due to their repercussions for public health. There is great motivation to remove and utilize these substances in other products instead of leaving

Full text of DOI:10.1016/j.molstruc.2015.08.065

Journal of Molecular Structure 1102 (2015) 170e185
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Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
An environmentally friendly method to remove and utilize the highly
toxic strychnine in other products based on proton-transfer
complexation
,
,
,
, e
Abdel Majid A. Adam a *, Moamen S. Refat a b, Hosam A. Saad a c, Mohamed S. Hegab d
a Department of Chemistry, Faculty of Science, Taif University, Al-Haweiah, P.O. Box 888, 21974 Taif, Saudi Arabia
b Department of Chemistry, Faculty of Science, Port Said University, Port Said, Egypt
c Department of Chemistry, Faculty of Science, Zagazig University, Zagazig, Egypt
d Deanship of the Preparatory Year, Taif University, Al-Haweiah, P.O. Box 888, 21974 Taif, Saudi Arabia
e Department of Chemistry, Faculty of Science, Ain Shams University, P.O. Box 11566, Cairo, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
The study of toxic and carcinogenic substances represents one of the most demanding areas in human
safety, due to their repercussions for public health. There is great motivation to remove and utilize these
substances in other products instead of leaving them contaminate the environment. One potentially toxic
compound for humans is strychnine (Sy). In the present study, we attempted to establish a quick, simple,
direct and efficient method to remove and utilize discarded Sy in other products based on proton-
transfer complexation. First, Sy was reacted with the acido organic acceptors PA, DNBA and CLA. Then,
the resultant salts were direct carbonized into carbon materials. Also, this study provides an insight into
the structure and morphology of the obtained products by a range of physicochemical techniques, such
as UVevisible, IR, 1H NMR and 13C NMR spectroscopies; XRD; SEM; TEM; and elemental and thermal
analyses. Interestingly, the complexation of Sy with the PA or DNBA acceptor leads to a porous carbon
material, while its complexation with CLA acceptor forms non-porous carbon product.
Received 17 May 2015
Received in revised form
26 August 2015
Accepted 29 August 2015
Available online 3 September 2015
Keywords:
Strychnine
Proton-transfer
Nanoporous carbon
SEM
TEM
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
animals and the margin between therapeutic and toxic doses is
very narrow as it was reported to be fatal to man at doses of
Strychnine (Sy), chemically strychnidin-10-on, the structure of
which is shown in Fig.1, is a monoterpene indole alkaloid found as a
white odorless and bitter crystalline powder. The primary natural
source of Sy is the seeds of Strychnos nux-vomica L. (Loganiaceae), a
tree grown extensively in China and southern Asian countries [1,2].
It is found together with brucine and other indole alkaloids in
various plants of the strychnine family [2]. It has been effectively
used in traditional Chinese medicine to treat central nervous sys-
tem diseases and to alleviate allergic symptoms, joint pain and
traumatic pain [3]. Sy when ingested could stimulate the central
nervous system and make the sensory organs more sensitive [4]. So
at low doses (such as at 10 mg daily dose) it is often used to treat
nervous diseases and vomiting as well as arthritic and traumatic
pains [5]. However, Sy is highly toxic to humans and most domestic
30e90 mg [6]. It has been demonstrated that a high of the Sy can
induce convulsions of the central nervous system and death
through respiratory or spinal paralysis or cardiac arrest [7].
Nowadays, Sy is no longer used as a therapeutic drug and its
availability to the public is controlled by legislations in various ju-
risdictions, but it is still in limited use as a rodenticide, pesticide,
fungicide and an adulterant in street drugs [8,9]. Porous and
nanostructured carbon materials have attracted much attention
because of their versatile applications in catalysis, sensors, elec-
tronic devices, electrodes, gas and liquid separation, and memory
storage [10e12]. Activated porous carbons have received significant
attention as potential hydrogen storage media due to their low
density, high surface area, large pore volume, god chemical stabil-
ity, and high storage capacity [13]. For several years, we have
investigated the synthesis, characterization and application of
various charge-transfer (CT) and proton-transfer (PT) interactions
[14e28]. As part of our continuing interest in this field, in this work,
we originally report a method to remove and utilize discarded Sy in
* Corresponding author.
E-mail address: majidadam@yahoo.com (A.M.A. Adam).
http://dx.doi.org/10.1016/j.molstruc.2015.08.065
0022-2860/© 2015 Elsevier B.V. All rights reserved.

A.M.A. Adam et al. / Journal of Molecular Structure 1102 (2015) 170e185
171
200e800 nm using a PerkineElmer Lambda 25 UV/Vis double-
beam spectrophotometer with quartz cells. The path length of the
cells was 1.0 cm.
N
H
O
Cl
OH
Cl
H
2.2.3. IR spectra
H
O
N
HO
The infrared (IR) spectra of the solid products (as KBr discs) were
acquired at room temperature using a Shimadzu FT-IR spectro-
O
photometer (Japan) over the range of 4000e400 cmꢂ1
.
O
H
CLA
Sy
2.2.4. 1H and 13C spectra
1H and 13C NMR spectra were collected on a Bruker DRX-250
spectrometer operating at 600 MHz. The measurements were
performed at ambient temperature using DMSO-d6 (dimethylsulf-
oxide, d6) as the solvent and TMS (tetramethylsilane) as the internal
reference.
OH
COOH
NO2
O2N
2.2.5. Thermal analysis
O2N
NO2
Thermogravimetric (TG) analysis was performed using a Shi-
madzu TGAe50H thermal analyzer (Japan) with standard platinum
TG pans. The measurements were conducted at a constant heating
rate of 10 ꢀC/min over the temperature range of 25e600 ꢀC in a
nitrogen atmosphere using alumina powder as the reference
material.
NO2
PA
DNBA
Fig. 1. The structure of strychnine (Sy) and organic acceptors.
2.2.6. XRD analysis
The X-ray diffraction (XRD) profiles were obtained using a
PANalytical X'Pert PRO X-ray powder diffractometer. The instru-
ment was equipped with a Ge(III) secondary monochromator, and
Cu Ka1 was employed as the radiation source, with a wavelength of
other products as porous carbon material. First, Sy was directly
reacted with acido organic acceptors (PA, DNBA and CLA) to form
proton-transfer salts. Then, the resultant salts were direct carbon-
ized at 400 ꢀC into carbon materials. The obtained products were
characterized by elemental, thermal and spectroscopic data
(UVeVis, IR, 1H and 13C NMR). Their morphology and nanometry
were observed and differentiated using X-ray diffraction (XRD),
scanning electron microscopy (SEM) and transmission electron
microscopy (TEM) techniques.
0.154056 nm. The samples were scanned with 2
q
between 5ꢀ and
90ꢀ.
2.2.7. SEM analysis
The microstructure and morphology were analyzed by a scan-
ning electron microscope (SEM, Quanta FEG 250 instrument). The
instrument was operated at an accelerating voltage of 20 kV.
2. Experiment and calculations
2.2.8. TEM analysis
2.1. Chemicals and solutions
The particle size was analyzed by transmission electron micro-
scope (TEM, JEOL JEM-1200 EX II, Japan). The instrument was
operated at an accelerating voltage of 60e70 kV.
All of the chemicals used were of analytical grade and were used
as purchased. Strychnine (Sy; C21H22N2O2, 334.42) was supplied by
SigmaeAldrich Chemical Co. (USA). The organic acceptors picric
acid (PA; C6H3N3O7; 229.10), 3,5-dinitrobenzoic acid (DNBA;
C7H4O6N2; 212.12), and chloranilic acid (CLA; C6H2Cl2O4; 208.98)
were purchased from Merck (Darmstadt, Germany) and were used
without modification. HPLC-grade methanol and chloroform were
also purchased from Merck. Standard stock solutions at a concen-
tration of 5.0 ꢁ 10ꢂ3 M were freshly prepared prior to each series of
measurements by dissolving precisely weighed quantities in a
100 mL volumetric flask. The stock solutions were protected from
light. Solutions for spectroscopic measurements were prepared by
mixing appropriate volumes of the Sy and acceptor stock solutions
with the solvent immediately before recording the spectra.
2.3. Preparation of materials
2.3.1. Preparation of the salts
A simple synthetic protocol has been used for the preparation of
PT complexes of Sy donor. A typical procedure for the preparation is
briefly described as follows. First, 2 mmol of Sy in chloroform
(20 ml) was added to 20 ml of a solution containing 2 mmol of the
acceptor (either PA, DNBA or CLA) in the methanol solvent. The
resulting mixture was stirred at room temperature for approxi-
mately half an hour, where the resulting precipitation were isolated
as yellow canary, white and reddish-brown powder for SyePA,
SyeDNBA and SyeCLA salts, respectively. The formed products
were isolated, filtered and further purified using methanol-
chloroform solvent and a recrystallization process to obtain the
pure products. The products were then collected and dried in vacuo
for 48 h. The products were characterized by spectroscopy (UVeVis,
IR, 1H and 13C NMR) as well as elemental and thermal analyses. The
excellent agreement between the experimental and calculated
values of C, H and N indicates that the obtained products are free of
impurities. The stoichiometry of the Sy interaction with the ac-
ceptors was found to have a 1:1 ratio.
2.2. Characterization methods
2.2.1. CHN analysis
To ascertain the constituents, purity and compositions of the
synthesized salts, the carbon, hydrogen and nitrogen contents were
analyzed with a PerkineElmer 2400 series CHN microanalyzer
(USA).
2.2.2. UVeVis spectra
The UVeVis spectra were recorded over a wavelength range of
2.3.1.1. Sy free. white powder; IR (KBr, cmꢂ1): ymax 3050e2950

172
A.M.A. Adam et al. / Journal of Molecular Structure 1102 (2015) 170e185
n
(CeH), 1697 nas (C]O), 1672 ns(C]O), 1670e1479
n
(C]C), 1385
2.3.1.4. SyeDNBA complex. white powder; IR (KBr, cmꢂ1): ymax
…
…
nas(CeN). 1H NMR (DMSO-d6, 600 MHz):
d
¼ 1.20 (m, 1H, C(13)H
3430
1677 nas (C]O), 1619 ns(C]O), 1543, 1470
1H NMR (DMSO-d6, 600 MHz):
¼ 1.43 (m, 1H, C(13) H proton), 1.46
y
(þNeH Oꢂ), 2962, 2927
n
(CeH), 2883, 2851
y(NeH O),
proton), 1.40 (m, 1H, C(15)Ha proton), 1.82 (m, 2H, C(17) Ha, Hb
protons), 1.90 (m, 1H, C(15) Hb proton), 2.30 (dd, 1H, C(11) Hb pro-
ton), 2.65 (d, 1H, C(20) Ha proton), 2.85 (m, 1H, C(18) Hb proton),
3.17e3.95 (m, 6H, C(11)Ha, C(14) H, C(18) Ha, C(20) Hb, C(8) H and C(16)
H protons), 4.13e4.32 (m, 4H, C(23) Ha, Hb, C(12) H), 5.84 (dd, 1H,
C(22) H protons), 7.09 (dd, 1H, C(2) H proton), 7.15 (d, 1H, C(1)
proton), 7.20 (dd, 1H, C(3) H proton), 8.10 (d, 1H, C(4) H proton). 13
NMR (DMSO-d6, 150 MHz):
n(C]C), 1349 nas(CeN).
d
(m, 1H, C(15) Ha proton), 1.59 (m, 2H, C(17) Ha, Hb protons), 2.15 (m,
1H, C(15) Hb proton), 2.66 (dd, 1H, C(11) Hb proton), 2.94 (d, 1H, C(20)
Ha proton), 3.32 (m, 1H, C(18) Hb proton), 4.06e4.18 (m, 6H, C(11) Ha,
C(14) H, C(18) Ha, C(20) Hb, C(8) H and C(16) H protons), 4.45e4.48 (m,
4H, C(23) Ha, Hb, C(12) H, C(22) H protons), 6.34 (s, 1H, Nþ(19)H), 7.14
(dd, 1H, C(2) H proton), 7.28 (d, 1H, C(1) H proton), 7.45 (dd, 1H, C(3) H
proton), 7.93 (d, 1H, C(4) H proton), 8.92 (s, 2H, dinitrobenzoic acid
H
C
d
¼ 26.71, 31.45, 42.33, 42.74, 48.07,
50.19, 52.53, 59.96, 60.04, 64.46, 77.44 (sp3 carbons, CH, CH2),
116.0, 122.1, 124.0, 127.0, 128.3, 132.6, 140.4, 142.0, 169.1 (sp2 car-
bons AreC, C]C and C]O). Anal. Calcd for C21H22N2O2 (334.42),
C, 75.35; H, 6.58; N, 8.37; Found, C, 75.15; H, 6.66; N, 8.20. The
structure of the Sy with its corresponding atom numbering
scheme is shown in Fig. 2.
C
(2,6) H protons), 8.95 (s, 1H, dinitrobenzoic acid C(4) H proton). 13
C
NMR (DMSO-d6, 150 MHz):
d
¼ 24.52, 29.87, 40.55, 41.18, 47.50,
51.40, 51.82, 52.22, 58.67, 60.35, 63.62, 77.50 (sp3 carbons, CH, CH2),
115.2, 120.8, 122.9, 124.2, 128.7, 129.1, 129.3, 132.0, 134.0, 137.6,
141.8, 148.1, 164.8, 168.8 (sp2 carbons AreC, C]C and 2C]O). Anal.
Calcd for C28H26N4O8 (546.54), C, 61.48; H, 4.76; N, 10.25; Found, C,
61.53; H, 4.81; N, 10.07.
2.3.1.2. Free acceptors. (a) PA; 1H NMR (DMSO-d6, 600 MHz):
2.3.1.5. SyeCLA complex. reddish-brown powder; IR (KBr, cmꢂ1):
d
¼ 8.59 (s, 2H, picric acid C3, C5 protons), 9.94 (s, 1H, picric acid OH
protons). 13C NMR (DMSO-d6, 150 MHz):
¼ 126.5, 140.8, 142.6,
156.3 (sp2 carbons AreC). (b) DNBA; 1H NMR (DMSO-d6, 600 MHz):
¼ 9.11 (s, 2H, dinitrobenzoic acid C(2,6) H protons), 9.18 (s, 1H,
dinitrobenzoic acid C(4) H proton), 12.10 (s, 1H, dinitrobenzoic acid
COOH proton). 13C NMR (DMSO-d6, 150 MHz):
¼ 123.3, 130.0,
134.3, 148.7, 163.9 (sp2 carbons AreC and C]O). (c) CLA; 1H NMR
ymax 3438
O), 1572
y
n
(þNeH … Oꢂ), 2962
n
(CeH), 1681 nas (C]O), 1617 ns(C]
d
(C]C), 1317 nas(CeN). 1H NMR (DMSO-d6, 600 MHz):
d
d
¼ 1.40 (m, 1H, C(13) H proton),1.49 (m,1H, C(15) Ha proton),1.57 (m,
2H, C(17) Ha, Hb protons), 2.13 (m, 1H, C(15) Hb proton), 2.67 (dd, 1H,
C(11) Hb proton), 2.95 (d, 1H, C(20) Ha proton), 3.32 (m, 1H, C(18) Hb
d
proton), 4.07e4.20 (m, 6H, C(11) Ha, C(14) H, C(18) Ha, C(20) Hb, C(8)
H
(DMSO-d6, 600 MHz):
d
¼ 10.68 (s, 1H, chloranilic acid OH proton).
and C(16) H protons), 4.44e4.50 (m, 4H, C(23) Ha, Hb, C(12) H, C(22) H
13C NMR (DMSO-d6, 150 MHz):
AreC, C]C and 2C]O).
d
¼ 124.5, 163.9, 168.2 (sp2 carbons
protons), 6.36 (s, 1H, Nþ(19) H), 7.14 (dd, 1H, C(2) H proton), 7.28 (d,
1H, C(1) H proton), 7.45 (dd, 1H, C(3) H proton), 7.93 (d, 1H, C(4)
H
proton), 8.72 (s,1H, chloranilic acid OH proton). 13C NMR (DMSO-d6,
150 MHz):
d
¼ 24.37, 29.67, 39.51, 42.54, 47.90, 50.14, 51.88, 53.52,
2.3.1.3. SyePA complex. Yellow canary powder; IR (KBr, cmꢂ1): ymax
58.66, 61.89, 64.12, 76.84 (sp3 carbons, CH, CH2), 115.5, 121.1, 122.5,
124.5, 127.2, 129.3, 129.7, 133.8, 135.1, 136.9, 142.9, 146.4, 163.4,
164.1, 167.4 (sp2 carbons AreC, C]C and 3C]O). Anal. Calcd for
C27H24Cl2N2O6 (543.40), C, 59.62; H, 4.42; N, 5.15; Found, C, 59.66;
H, 4.23; N, 5.11.
…
…
3439
1657 nas (C]O), 1622 ns(C]O), 1565, 1480
1H NMR (DMSO-d6, 600 MHz):
y
(þNeH Oꢂ), 2989, 2945
n
(CeH), 2855, 2756
(C]C), 1325 nas(CeN).
¼ 1.44 (m, 1H, C(13) H proton), 1.61
y(NeH O),
n
d
(m, 1H, C(15) Ha proton), 1.95 (m, 2H, C(17) Ha, Hb protons), 2.16 (m,
1H, C(15) Hb proton), 2.68 (dd, 1H, C(11) Hb proton), 2.95 (d, 1H, C(20)
Ha proton), 3.52 (m, 1H, C(18) Hb proton), 4.07e4.17 (m, 6H, C(11) Ha,
C(14) H, C(18) Ha, C(20) Hb, C(8) H and C(16) H protons), 4.43e4.50 (m,
2.3.2. Preparation of carbon materials
In a typical process, the salts were dried at 110 ꢀC overnight,
then carbonized into carbon material in a furnace at 400 ꢀC under
N2 flow for 1.0 h. The as-prepared non-activated carbon product
was ground into powder with a particle size of 2e3 mm and
characterized by XRD, SEM and TEM techniques.
4H, C(23) Ha, Hb, C(12) H, C(22) H protons), 6.45 (s, 1H, Nþ
H), 7.14
(19)
(dd, 1H, C(2)H proton), 7.29 (d, 1H, C(1) H proton), 7.43 (dd, 1H, C(3) H
proton), 7.93 (d, 1H, C(4) H proton), 8.58 (s, 2H, picric acid protons).
13C NMR (DMSO-d6, 150 MHz):
d
¼ 24.79, 30.11, 40.50, 41.20, 47.50,
51.41, 51.82, 52.22, 59.00, 62.11, 63.62, 77.50 (sp3 carbons, CH, CH2),
115.7, 118.3, 122.1, 125.6, 125.8, 129.0, 129.30, 130.0, 135.3, 140.4,
142.3, 161.2, 169.3 (sp2 carbons AreC, C]C and C]O). Anal. Calcd
for C27H25N5O9 (563.52), C, 57.50; H, 4.44; N, 12.42; Found, C, 57.46;
H, 4.48; N, 12.40.
2.4. Calculation details
2.4.1. Calculations of the spectroscopic parameters
2.4.1.1. Calculation of the formation constant and molar extinction
coefficient. The formation constant (K) and the molar extinction
coefficient (ε) were determined spectrophotometrically using the
1:1 BenesieHildebrand equation (Eq. (1)) [29]. Ca and Cd are the
initial concentrations of the acceptor and donor, respectively, and A
is the absorbance of the CT band. By plotting the (Ca Cd)/A values for
the 1:1 CT complex as a function of the corresponding (Ca þ Cd)
values, a straight line is obtained with a slope of 1/ε and an inter-
cept at 1/Kε.
Hb
19
Hb
Ha
Hb
Ha
N
20
Hb
18
17
Ha
16
1
4
2
3
15
Ha
6
7
8
H
21
9
Ha
Hb
Hb
Ha
ðCaCdÞ=A ¼ 1=Kε þ ðCa þ CdÞ=ε
(1)
14
5
N
13
22
23
H 12
H
10
2.4.1.2. Calculation of the energy value. The energy values (ECT) of
the n / p* and p* interactions between the donor and the
acceptor were calculated using the equation derived by Briegleb
(Eq. (2)) [30], where lCT and nCT are the wavelength and wave-
number of the complexation band of the formed complex,
11
O
p
/
O
Ha
H
Hb
24
Fig. 2. The structure of Sy with atom numbering.

A.M.A. Adam et al. / Journal of Molecular Structure 1102 (2015) 170e185
173
½
respectively.
m ðDebyeÞ ¼ 0:0958 ½εCT n =nmaxꢃ
(5)
½
ECT ¼ ðhnCT Þ ¼ 1243:667=lCT ðnmÞ
(2)
2.4.1.5. Calculation of the standard free energy change. The values of
the standard free energy change (
Gꢀ) were calculated from the
formation constants using Eq. (6) [33].
Gꢀ is the standard free
energy change of the complexes (J molꢂ1), R is the universal gas
2.4.1.3. Calculation of the oscillator strength. The oscillator strength
(f) is a dimensionless quantity used to express the transition
probability of a band. From the absorption spectra, f can be ob-
D
D
tained using the approximate formula given in Eq. (3) [31]. !εCT dn is
constant (8.314 J molꢂ1
K
ꢂ1), T is the absolute temperature in
the area under the curve of the extinction coefficient of the ab-
sorption band in question plotted as a function of the frequency. To
a first approximation, f can be calculated using Eq. (4). εCT is the
Kelvin, and K is the formation constant of the complex (L molꢂ1) at
room temperature.
maximum extinction coefficient of the CT band, and
n
½
is the full-
width at half-maximum (FWHM) in cmꢂ1
.
DGꢀ ¼ ꢂ2:303RT log KCT
(6)
Z
f ¼ 4:319 ꢁ 10ꢂ9 εCT dn
(3)
2.4.2. Calculation of the particle sizes
The particle size of the complexes was estimated from their XRD
patterns based on the highest intensity line using the well-known
DebyeeScherrer formula, given in the following equation [34]:
f ¼ 4:319 ꢁ 10ꢂ9εCT
n
(4)
½
2.4.1.4. Calculation of the transition dipole moment. The transition
dipole moments ( ) are calculated using Eq. (5) [32], where nmax is
the full width of the CT band at maximum in cmꢂ1. The transition
dipole moment ( ) can be employed to determine whether a
particular transition is allowed. The transition from a bonding
orbital to an antibonding
* orbital is allowed because the integral
that defines the transition dipole moment is nonzero.
m
D ¼ 0:94l=bcosq
(7)
m
where D is the apparent particle size of the grains in nanometers,
p
0.94 is the Scherrer constant (for a Cu grid), is the wavelength of
the incident X-ray (Cu K ; 0.15406 nm), is the position of the
selected diffraction peak (i.e., the Bragg diffraction angle), and is
l
p
a
q
b
Fig. 3. Electronic absorption spectra of the Sy complexes with PA, DNBA and CLA acceptors.

174
A.M.A. Adam et al. / Journal of Molecular Structure 1102 (2015) 170e185
the FWHM of the characteristic X-ray diffraction peak (with addi-
tional peak broadening) in radians.
measurable absorption. This new strong broadening band at longer
wavelengths are presumably caused by the SyeCLA interaction and
is indicative of the formation of a PT complex.
The stoichiometry of the Syeacceptor interactions in solution
was obtained from the spectrophotometric titrations by deter-
mining the conventional molar ratio according to previously pub-
lished protocols [35]. The electronic spectra of the Syeacceptor
systems were recorded at varying acceptor concentrations and a
constant Sy concentration. The composition of the complexes was
determined graphically by plotting the absorbance on the ordinate
against the volume of the acceptor (in mL) on the abscissa.
Representative spectrophotometric titration plots based on the
characterized absorption bands are shown in Fig. 4. The results
show that the greatest interaction between Sy and each acceptor
occurred at a donor: acceptor ratio of 1:1, indicating that 1:1
complexes were formed. These stoichiometric values are consistent
with the data obtained by the elemental analysis of the solid-state
complexes.
3. Results and discussion
3.1. Spectral properties
3.1.1. UVevisible measurements
Sy (5.0 ꢁ 10ꢂ4 M) was mixed with each acceptor solution
(5.0 ꢁ 10ꢂ4 M), and the reaction was allowed to proceed at room
temperature. The UVevisible spectrum of each reaction mixture
was then recorded against a reagent blank solution. Fig. 3 displays
the UVevisible absorption spectra of the Sy and acceptors, along
with the spectra of the prepared complexes. This figure indicates a
remarkable change in the UVeVis spectrum of the Sy upon the
addition of acceptor to the solution. The absorption spectrum of Sy
has two lmax at 207 nm and 252 nm, while PA acceptor displays two
measurable absorption band lmax at 207 nm and 353 nm. When Sy
and PA are mixed together, these characteristic bands increases
strongly in intensity and becomes more broad. These changes
provided strong evidence of interaction between Sy and PA and the
formation of PT complex. Interestingly, on mixing the solutions of
the Sy and DNBA, a very strong broad band was observed at 258 nm
that correspond to the PT interaction. The spectrum of the SyeCLA
complex was characterized by a new absorption band appeared at a
longer wavelength (330 nm) in regions where Sy has no
3.1.2. The spectroscopic data
The 1:1 BenesieHildebrand equation was used to determine the
spectroscopic parameters of the synthesized complexes. Fig. 5
shows a representative 1:1 BenesieHildebrand plot of the Sy
complexes. The values of both K and ε have been determined from
these data and, along with the other spectroscopic parameters (e.g.,
f, m, ECT and D
Gꢀ), are provided in Table 1. Fig. 5 reveals that the
Fig. 4. Spectrophotometric titration curves for the Sy complexes with PA, DNBA and CLA acceptors.

A.M.A. Adam et al. / Journal of Molecular Structure 1102 (2015) 170e185
175
Fig. 5. The 1:1 BenesieHildebrand plots of the Sy complexes with PA, DNBA and CLA acceptors.
correlation coefficient (r) of the straight lines is > 0.99. The complex
containing the DNBA acceptor shows a higher K value than the
other complexes. This high value of K reflects the relatively high
electron acceptance ability of DNBA and suggests that the
SyeDNBA complex is strongly bound and highly stable. The sta-
bility of the complexes decreases in the following order:
the different acceptors are ordered as follows: PA > DNBA > CLA.
We note that this ordering is consistent with the stability of the Sy
complexes. Linear correlations were observed between several
pairs of spectroscopic parameters (Fig. 6). For example, a very
strong linear correlation (r ¼ 0.9999) exists between the oscillator
strength (f) and the dipole moment (m) in solution. This finding
SyePA > SyeDNBA > SyeCLA. All the
D
Gꢀ values are negative,
indicates that the oscillator strength values of the complexes in
solution increased as their dipole moment values increased. A
strong linear relationship (r ¼ 0.9865) was obtained between f and
indicating that the complexation between Sy and the acceptors is
exothermic and spontaneous. The
D
Gꢀ values of the complexes for
Table 1
Spectral properties of the Sy complexes.
Property
Complex
SyePA
SyeDNBA
SyeCLA
lmax (nm)
353
258
330
Formation constant; K (Lmolꢂ1
)
31 ꢁ 105
54 ꢁ 104
3.52
15.5 ꢁ 105
385 ꢁ 104
4.82
10.5 ꢁ 105
24 ꢁ 104
3.77
Extinction coefficient; εmax (Lmolꢂ1 cmꢂ1
Energy value; ECT (eV)
)
Oscillator strength; f
2.32
33.22
2.58
Dipole moment;
Standard free energy change;
m
1.32
4.26
1.34
D
Gꢀ (kJ molꢂ1
)
ꢂ3.71 ꢁ 104
ꢂ3.53 ꢁ 104
ꢂ3.44 ꢁ 104

176
A.M.A. Adam et al. / Journal of Molecular Structure 1102 (2015) 170e185
extinction coefficient (εmax). In addition, a strong linear correlation
(r ¼ 0.9394) is observed between the f and the energy value (ECT).
Finally, a strong linear relationship (r ¼ 0.9752) is also observed
between the standard free energy change (D
Gꢀ) and the formation
O
O
N
N
D
Gꢀ become more negative as the for-
N
constant (K). The values of
N
H
H
mation constant for the molecular complex increases.
H
H
H
H
3.1.3. IR measurements
H
H
O
O
The molecular structure of Sy consists of seven condensed rings
with six asymmetric centers. On account of reducing the strain in
the oligocyclic ring system, the rings are non-planar [36]. In addi-
tion there is a planar phenyl ring. The ring system contains two
ternary nitrogen atoms in (CeN) groups; the nitrogen of the tet-
rahydropyridoindol nucleus which is bonded to a carbonyl group
and the nitrogen of the octahydroethanoindole nucleus, and all of
them are sp3 hybridized nitrogens. They differ from each other in
basicity, mainly due to resonance, which decreases the basicity and
the steric hindrance. The least basic one is the nitrogen of the tet-
rahydropyridoindol nucleus, due to the resonance effect of the
amide nitrogen with the adjacent carbonyl group leading to partial
positive charge on nitrogen atom for somewhat as shown in Fig. 7.
The most basic one is the nitrogen of the octahydroethanoindole
nucleus, due to the absent of adjacent resonance and the electron
repelling effect of the three attached alkyl groups along with the
less steric hindrance around its lone pair of electron. The last is the
Fig. 7. Resonating structures of the amide carbonyl group.
nitrogen atom most expected to be able to accept the acidic proton
of acceptors. The IR spectrum of the free Syꢂw1 as characterized by
principal absorption peaks at 3050-2950 cm for CeH symmetric
and asymmetric stretching, 1697 and 1672 cmꢂ1 for
n
(C]O) of the
amide group, 1670-1479 cmꢂ1 for
n
(C]C), and 1465 cmꢂ1 for
nas(CeN) [37]. The IR spectra of the SyePA and SyeDNBA com-
plexes are characterized by a group of medium bands at 2855 and
2756 cmꢂ1 for PA complex, and at 2883 and 2851 cmꢂ1 for DNBA
complex (Fig. 8). These new broadened bands are attributed to
n
(þNeH) and confirm the migration of the PA or DNBA proton to-
wards the nitrogen of the Sy octahydroethanoindole nucleus to
form an intermolecular H-bonded ion pair (þNeH … Oꢂ). Generally,
Fig. 6. Linear correlations of some spectroscopic parameters.

A.M.A. Adam et al. / Journal of Molecular Structure 1102 (2015) 170e185
177
Fig. 8. IR spectra of the Sy complexes.
…
the intermolecular hydrogen bonding that exists in a PT complex is
expected to be found at approximately 3400 cmꢂ1 [38]. The bands
observed at approximately 3439 cmꢂ1 for the PA complex, at
3430 cmꢂ1 for the DNBA complex, and at 3438 cmꢂ1 for the CLA
complex are a result of the stretching vibration of (þNeH Oꢂ).
Additionally, the characteristic band observed at 1385 cmꢂ1 that
results from the
n(CeN) vibration of the free Sy shifts to
~1325 cmꢂ1 in SyePA, ~1349 cmꢂ1 in SyeDNBA, and ~1317 cmꢂ1 in
NO2
O
O2N
O
O
N
N
O
NO2
NH O
NH
H
NO2
H
H
H
H
H
O2N
H
O
H
O
Cl
O
O
N
OH
O
NH
H
H
Cl
H
O
H
O
Fig. 9. Proposed structural formula of the SyePA and SyeDNBA and SyeCLA proton-transfer complex.

178
A.M.A. Adam et al. / Journal of Molecular Structure 1102 (2015) 170e185
Table 2
~12.09 ppm [46] in the spectra of free PA and DNBA acceptors,
respectively, is no longer observed. Instead, a new signal is
observed at approximately ~6.45 ppm for PA complex and ~6.34 for
DNBA complex. This singlet signal is assigned to the proton of the
þNeH species formed by the proton-transfer from the OH group of
PA or DNBA to the nitrogen atom of the Sy [47]. This upfield shift in
Thermal decomposition data for the synthesized Sy complexes.
Compound
SyePA
Stages
TG range (ꢀC)
TG% mass loss
Lost species
Found
Calculated
I
II
190e350
350e600
e
40.84
50.32
8.40
40.67
50.81
8.52
PA
C17H22N2O2
4C
frequency has been attributed to an increase in
p electron density
Residue
on the PA or DNBA portion of the complex. The electronic envi-
ronments of the Sy protons were affected by the presence of the
(NþeH) interaction. The singlet peak observed at 6.36 ppm in the
SyeCLA complex has been assigned to the þNeH proton, while the
singlet centered at 8.72 ppm is attributed to the non-hydrogen-
bonded proton of the CLA moiety. Likewise, this peak is shifted
slightly relative to the observed peak (at approximately
SyeDNBA
SyeCLA
I
II
130e320
320e600
e
38.62
41.50
19.48
99.72
38.81
41.43
19.76
100.0
DNBA
C12H22N2O2
9C
SyþCLA
Residue
I
200e600
SyeCLA. The observed shift in the n(CeN) band upon complexation
suggests that this group participated directly in the complexation.
All these observations indicate the presence of hydrogen bonding
in these complexes [39e44].
d~9.15 ppm) in the spectrum of free CLA [48]. Some changes are
observed in the values of the chemical shifts of the Sy protons
because of the presence of PT interactions between Sy and the
acceptor molecules. The 13C NMR spectrum of free Sy showed 20
resolved carbon signals (11 signals for sp3 carbons and 9 signals for
sp2 carbons). In the 13C NMR spectra of the products, the appearance
of 25 (12 signals for sp3 carbons and 13 signals for sp2 carbons), 26
(12 signals for sp3 carbons and 14 signals for sp2 carbons) and 27 (12
signals for sp3 carbons and 15 signals for sp2 carbons) distinct
3.1.4. 1H and 13C NMR measurements
The 600 MHz 1H and 13C NMR spectra of the synthesized salts
were measured in DMSO-d6 at room temperature. It has been found
that the signal due to the phenolic proton (eOH) of the PA and
DNBA acceptors, which is observed at
d ~11.94 ppm [45] and
Fig. 10. TG thermograms plots of the Sy complexes with PA, DNBA and CLA acceptors.

A.M.A. Adam et al. / Journal of Molecular Structure 1102 (2015) 170e185
179
Fig. 11. XRD spectra of the Sy complexes with PA, DNBA and CLA acceptors.
resonant carbon signals in the spectra of the PA, DNBA and CLA
complexes, respectively, is consistent with the proposed molecular
structure of these complexes. For all complexes, common changes
in the values of the 13C chemical shifts in Sy can be observed as a
result of its complexation with the organic acceptors. The struc-
tures of the synthesized complexes have been confirmed by IR, 1H
and 13C NMR spectral data. The data obtained by these techniques
are consistent with each other and support the predicted struc-
tures. Fig. 9 illustrates the proposed structures of the Sy complexes.
complex is decomposes in two degradation steps. The first
decomposition step in the temperature range of 190e350 ꢀC has a
weight loss of approximately 40.84% and is attributed to the loss of
the PA moiety. The final decomposition step occurred within the
350e600 ꢀC temperature range corresponding to loss of
C17H22N2O2 moiety representing a weight loss of (obs. ¼ 50.32,
cal. ¼ 50.81%) then leaving residual carbon as final products. The
complex containing the DNBA acceptor was thermally decomposed
in nearly two decomposition steps within the 130e600 ꢀC tem-
perature range. The first stage of decomposition corresponds to the
loss of acceptor molecule with a weight loss of 38.62%, which is in
good agreement with the calculated value (38.81%). The second
stage of decomposition corresponds to the removal of C12H22N2O2
moiety with a weight loss of 41.50% very close to the expected
theoretical value of 41.43%. The final decomposition of the complex
is the residual carbon atoms. The thermal degradation of the
SyeCLA complex occurs in one degradation stage. The complex
begins decomposed at ~200 ꢀC and was complete at ~600 ꢀC, and
3.2. Thermal properties
3.2.1. Thermogram measurements
The thermal decomposition and stability of the synthesized salts
were investigated by thermogravimetric (TG) analysis. The possible
thermal degradation patterns for these salts are collected in Table 2,
and their representative TG thermograms are depicted in Fig. 10.
The TG thermogram of the SyePA complex indicated that this
Table 3
XRD spectral data for the synthesized complexes.
Complex
2
q
; (ꢀ)
q
; (ꢀ)
d-spacing value; (Å)
Height
b; FWHM
Particle size (nm)
SyePA
SyeDNBA
SyeCLA
7.96
7.27
7.06
3.98
3.64
3.53
11.0981
12.1498
12.5107
7561.533
7368.619
6178.710
0.10
0.29
0.05
83
25.6
166.2

180
A.M.A. Adam et al. / Journal of Molecular Structure 1102 (2015) 170e185
Fig. 12. (A). SEM and TEM images of the SyePA complex. (B). SEM and TEM images of the SyeDNBA complex. (C). SEM and TEM images of the SyeCLA complex.
v) The PA and DNBA complexes were thermally decomposed in
the observed weight loss associated with this step is (obs. ¼ 99.72,
cal. ¼ 100.0%), which can be attributed to the removal of the donor
and acceptor moieties.
approximately two decomposition steps.
vi) Generally, the first decomposition step is corresponded to
the removal of the acceptor moiety.
vii) The decomposition in the second step is probable due to the
donor removal.
viii) The decomposition of the CLA complex is almost complete
without any carbon residue.
3.2.2. Comparison of the thermograms
The analyses of the TG thermograms of these salts provided the
following observations:
ix) The decomposition of PA and DNBA complexes led to resid-
ual carbon atoms as a final product.
x) The degradation data strongly support the formation of the
synthesized salts and their proposed structures.
i) The observed weight loss is in excellent agreement with the
theoretical predictions.
ii) The SyeCLA complex exhibited good thermal stability up to
200 ꢀC.
iii) The complexes are stable up to ~190, 130 and 200 ꢀC for
SyePA, SyeDNBA and SyeCLA, respectively. Thus, these salts
are stable in the solid state at room temperature and can be
stored for several months without degradation.
iv) The CLA complex exhibit a one-stage degradation process.
3.3. Structural properties
The surface morphology, nanometry, structural features and
characteristics of the synthesized salts were observed by XRD, SEM

A.M.A. Adam et al. / Journal of Molecular Structure 1102 (2015) 170e185
181
DebyeeScherrer formula. The calculated particle diameters of the
SyePA, SyeDNBA and SyeCLA complexes were ~83, 26 and 166 nm,
respectively, which are in good agreement with the results ob-
tained by TEM. These values suggest that the particle sizes of the
complexes are within the nanoscale range. Fig. 12(A, B and C)
presents multiple SEM micrographs of the outer surfaces of the
synthesized complexes at different levels of magnification (i.e.,
x500, x1000, x2000, x4000, x8000). The SEM micrographs of the
particles revealed that all of the complexes have a well-defined
shape, uniform matrix, distinct size and morphology with homo-
geneously dispersed nanoparticles, indicating the formation of
homogeneous material. Visible morphological change is observed
between the Sy complexes. From the high-quality and well-focused
TEM micrographs (Fig.12), it is inferred that all of the complexes are
spherical nanoparticles that are homogeneously dispersed with no
particle agglomeration. According to these micrographs, most of
the nanoparticles of the SyePA, SyeDNBA and SyeCLA complexes
exhibit diameters in the range of 54e90 nm, 10e30 nm and
~150 nm and main diameters of 72, 20 and 150 nm, respectively.
We note that these diameters are in good agreement with the re-
sults calculated from the XRD data.
Fig. 13. IR spectra of the resultant carbon material samples.
and TEM analyses. Fig. 11 shows the indexed XRD patterns of the
salts, and Table 3 presents the XRD spectral data for these salts. The
3.4. Characteristics of carbon materials
strongest diffraction peak was observed at diffraction angles 2
q
of
The as-prepared non-activated carbon products obtained from
the direct carbonization of the SyePA (Sample 17), SyeDNBA
(Sample 23) and SyeCLA (Sample 57) were ground into powder and
characterized by IR, XRD, SEM and TEM techniques. Fig. 13 shows
the IR spectra of the resultant carbon samples. The three samples
exhibited similar IR spectra. In the these samples, the bands
centered at 1000ꢂ1300 cmꢂ1 are related to the CeOH stretching
7.96ꢀ, 7.27ꢀ, and 7.06ꢀ for the SyePA, SyeDNBA and SyeCLA com-
plexes, respectively. The appearance of a strong and narrow sharp
diffraction peak indicated that the as-synthesized complex was
well crystallized and has a well-defined structure. The particle size
of these complexes was estimated from their XRD patterns based
on the highest-intensity value using the well-known
Fig. 14. XRD spectra of the resultant carbon material samples.

182
A.M.A. Adam et al. / Journal of Molecular Structure 1102 (2015) 170e185
Fig. 15. (A). SEM and TEM images of carbon product obtained by the carbonization of SyePA complex; Sample 17. (B). SEM and TEM images of carbon product obtained by the
carbonization of SyeDNBA complex; Sample 23. (C). SEM and TEM images of carbon product obtained by the carbonization of SyeCLA complex; Sample 57.

A.M.A. Adam et al. / Journal of Molecular Structure 1102 (2015) 170e185
183
Fig. 15. (continued).

184
A.M.A. Adam et al. / Journal of Molecular Structure 1102 (2015) 170e185
Fig. 15. (continued).

A.M.A. Adam et al. / Journal of Molecular Structure 1102 (2015) 170e185
92e98.
185
vibration and eOH bending vibration [49]. The band 1730 cmꢂ1
could be ascribed to C]O stretching vibration, and the other
adsorption bands at 1400ꢂ1500 cmꢂ1 and 2900ꢂ3020 cmꢂ1
correspond to the CeH bending vibration and stretching vibration,
respectively [50]. The absorptions at around 3600 cmꢂ1 could be
attributed to OeH stretching vibration and the strong band around
1215 cmꢂ1 could be assigned to the CeN stretching vibration. Thus,
the IR analysis confirms the existence of oxygen-, nitrogen- and
hydrogen-containing functional groups in the carbon samples. To
confirm the framework structure of materials, XRD patterns of
resultant carbons were characterized and shown in Fig. 14. The
three samples exhibited similar XRD patterns. The profiles of these
[3] A. Rathi, N. Srivastava, S. Khatoon, A.K.S. Rawat, Chromatographia 67 (2008)
607e613.
[4] E.P. Marques, F. Gli, P. Proenca, P. Monsanto, M.F. Oliveira, A. Castanheira,
D.N. Vieira, Forensic Sci. Int. 110 (2000) 145e152.
[5] X.H. Zang, C.R. Li, Q.H. Wu, C. Wang, D.D. Han, Z. Wang, Chin. Chem. Lett. 18
(2007) 316e318.
[6] A.J. Duke, Handbook of Medicinal Plants, vol. 20, Coordinating Research
Council Press, Boca Raton, Florida, 1985, pp. 34e35.
ꢀ
ꢀ
[7] G. Philippe, L. Angenot, M. Tits, M. Frederich, Toxicon 44 (2004) 405.
[8] L. Yu, Q. Xu, Y. Yu-Wei, P. Yang, B. Hui-Min, Chin. J. Nat. Med. 12 (10) (2014)
760e767.
[9] S. Kodikara, J. Forensic Leg. Med. 19 (2012) 40e41.
[10] Y.P. Zhai, Y.Q. Dou, D.Y. Zhao, P.F. Fulvio, R.T. Mayes, S. Dai, Adv. Mater 23
(2011) 4828e4850.
[11] I.I. Zhang, X.S. Zhao, Chem. Soc. Rev. 38 (2009) 2520e2531.
[12] M. Inagakia, H. Konno, O. Tanaike, J. Power Sources 195 (2010) 7880e7903.
[13] J. Zhu, J. Cheng, A. Dailly, M. Cai, M. Beckner, P. Shen, Int. J. Hydrogen Energy
39 (2014) 14843e14850.
[14] M.S. Refat, H.A. Saad, A.M.A. Adam, Spectrochim. Acta A 141 (2015) 202e210.
[15] M.S. Refat, L.A. Ismail, A.M.A. Adam, Spectrochim. Acta A 134 (2015) 288e301.
[16] M.S. Refat, A.M.A. Adam, H.A. Saad, J. Mol. Strut. 1085 (2015) 178e190.
[17] A.M.A. Adam, M.S. Refat, J. Mol. Liq. 209 (2015) 33e41.
[18] A.M.A. Adam, Russ. J. Gen. Chem. 84 (6) (2014) 1225e1236.
[19] A.M.A. Adam, M.S. Refat, Russ. J. Gen. Chem. 84 (9) (2014) 1847e1856.
[20] A.M.A. Adam, Spectrochim. Acta A 127 (2014) 107e114.
[21] M.S. Refat, O.B. Ibrahim, H.A. Saad, A.M.A. Adam, J. Mol. Struct. 1064 (2014)
58e69.
[22] M.S. Refat, A.M.A. Adam, J. Mol. Liq. 196 (2014) 142e152.
[23] M.S. Refat, A.A. Gobouri, A.M.A. Adam, H.A. Saad, Phys. Chem. Liqs. 52 (5)
(2014) 680e696.
[24] A.M.A. Adam, Spectrochim. Acta A 104 (2013) 1e13.
[25] A.M.A. Adam, M.S. Refat, H.A. Saad, J. Mol. Strut. 1051 (2013) 144e163.
[26] A.M.A. Adam, M.S. Refat, H.A. Saad, J. Mol. Strut. 1037 (2013) 376e392.
[27] A.M.A. Adam, M.S. Refat, T. Sharshar, Z.K. Heiba, Spectrochim. Acta A 95 (2012)
458e477.
samples displayed one broad peak located at a 2q of approximately
25ꢀ. It matches well with the profiles previously reported [51e53]
for non-graphitic carbon. The absence of a sharp diffraction
pattern indicated that the resulting porous carbon mainly pos-
sesses an amorphous structure [54,55]. Furthermore, no impurity
diffraction was observed, confirming the absence of any other x-ray
traceable compounds in the carbon product. To reveal the
morphology of all carbon materials and investigate the influence of
acceptor molecule on the morphology, SEM and TEM images of all
carbon products are shown in Fig. 15(A, B and C). The multiple SEM
micrographs at different degrees of enlargement (i.e., x5000,
x10000, x20000) indicate the carbons have uniform morphology.
We surprisingly found that the complexation of Sy with the PA or
DNBA acceptor leads to a well-developed porosity carbon material,
while its complexation with CLA acceptor forms non-porous carbon
product. The highly magnified (x80000ꢂ150000) TEM micro-
graphs show that the length of the carbon particles is approxi-
mately 100 nm. The XRD, SEM and TEM analyses confirm that the
direct carbonization of the PA and DNBA complexes leads to
nanoporous carbon material.
[28] A.M.A. Adam, J. Mol. Struct. 1030 (2012) 26e39.
[29] H.A. Benesi, J.H. Hildebrand, J. Am. Chem. Soc. 71 (1949) 2703e2707.
[30] G. Briegleb, Z. Angew. Chem. 76 (1964) 326e341.
[31] H. Tsubomura, R.P. Lang, J. Am. Chem. Soc. 83 (1961) 2085e2092.
[32] R. Rathone, S.V. Lindeman, J.K. Kochi, J. Am. Chem. Soc. 119 (1997)
9393e9404.
[33] G.G. Aloisi, S. Pignataro, J. Chem. Soc. Faraday Trans. 69 (1973) 534e539.
[34] M.A. Estermann, W.I.F. David, in: W.I.F. David, K. Shankland, I.B. Mccusker,
Ch Baerlocher (Eds.), Structure Determination from Powder Diffraction Data
(SDPD), Oxford Science Publications, New York (, 2002.
4. Conclusions
[35] D.A. Skoog, Principle of Instrumental Analysis, third ed., Saunders, New York,
USA, 1985 [Chapter 7].
[36] N. Islam, S. Niaz, T. Manzoor, A.H. Pandith, Spectrochim. Acta A 131 (2014)
461e470.
[37] V.A. Narayanan, N.A. Stump, G.D. Del Cul, T. Vo-Dinh, J. Raman Spectrosc. 30
(1999) 435e439.
[38] M. Manikandan, T. Mahalingam, Y. Hayakawa, G. Ravi, Spectrochim. Acta A
101 (2013) 178e183.
A method was proposed to remove and utilize strychnine (Sy)
based on complexation with acido organic acceptors (PA, DNBA and
CLA) followed by direct carbonization of the resultant salts into
carbon materials. The structure, spectroscopic properties and
morphology of the products were fully characterized by using
physicochemical and spectroscopic techniques, such as UVevisible,
IR, 1H NMR and 13C NMR spectroscopies; XRD; SEM; TEM; and
elemental analysis. The results indicate that all salts are formed
based on a 1:1 stoichiometric ratio. The IR, 1H and 13C NMR spectra
of the products clearly indicate the formation of the complexes. Our
findings indicated that the paired molecules in the SyePA and
SyeDNBA and SyeCLA are linked by intermolecular hydrogen-
bonding interactions. The proposed method is simple, environ-
mentally friendliness, direct without complicates procedures and
can be generally used in preparation of porous and non-porous
carbons.
[39] N. Singh, A. Ahmad, J. Mol. Strut. 1074 (2014) 408e415.
[40] E. Selvakumar, G. Anandha babu, P. Ramasamy, A. Chandramohan, Spec-
trochim. Acta A 122 (2014) 436e440.
[41] M.Y. El-Sayed, M.S. Refat, Spectrochim. Acta A 137 (2015) 1270e1279.
[42] N. Singh, I.M. Khan, A. Ahmad, S. Javed, J. Mol. Liq. 191 (2014) 142e150.
[43] N. Singh, I.M. Kahn, A. Ahmed, S. Javed, Mol. Struct. 1065e1066 (2014) 74e85.
[44] X. Ding, Y. Li, S. Wang, X. Li, W. Huang, J. Mol. Struct. 1062 (2014) 61e67.
[45] R. Bharathikannan, A. Chandramohan, M.A. Kandhaswamy, J. Chandrasekaran,
R. Renganathan, V. Kandavelu, Cryst. Res. Technol. 43 (2008) 683e688.
[46] N. Singh, I.M. Khan, A. Ahamd, S. Javed, J. Mol. Strut. 1066 (2014) 74e85.
[47] A.A. Rzokee, A. Ahmad, J. Mol. Struct. 1076 (2014) 453e460.
[48] A.S. AL-Attas, M.M. Habeeb, D.S. AL-Raimi, J. Mol. Struct. 928 (2009) 158.
[49] R. Demir-Cakan, N. Baccile, M. Antonietti, M.M. Titirici, Chem. Mater 21 (2009)
484e490.
[50] S. Ikeda, K. Tachi, Y.H. Ng, Y. Ikoma, T. Sakata, H. Mori, T. Harada,
M. Matsumura, Chem. Mater 19 (2007) 4335e4340.
Conflict of interests
[51] X. Yan, X. Li, Z. Yan, S. Komarnei, Appl. Surf. Sci. 308 (2014) 306e310.
[52] J. Zhu, J. Cheng, A. Dailly, M. Cai, M. Beckner, P. Shen, Int. J. Hydrogen Energy
39 (2014) 14843e14850.
[53] Y. Xiao, H. Chen, M. Zheng, H. Dong, B. Lei, Y. Liu, Mater. Lett. 116 (2014)
185e187.
The authors declare no financial/commercial conflict of interests
regarding the study.
References
[54] M. Okamura, A. Takagaki, M. Toda, J.N. Kondo, T. Tatsumi, K. Domen, M. Hara,
S. Hayashi, Chem. Mater 18 (2006) 3039e3045.
[55] B.H. Zhang, J.W. Ren, X.H. Liu, Y. Guo, Y.L. Guo, G.Z. Lu, Y.Q. Wang, Catal.
Commun. 11 (2010) 629e632.
[1] R. Bhati, A. Singh, V.A. Saharan, V. Ram, A. Bhandari, J. Ayurveda Integr. Med. 3
(2) (2012) 80e84.
[2] F. Liu, X. Wang, X. Han, X. Tan, W. Kang, Int. J. Biol. Macromol. 77 (2015)