Fly ash supported NiO as an efficient catalyst for the synthesis of xanthene and its molecular docking study against plasmodium glutathione reductase

Article abstract of DOI:10.1007/s11164-018-3567-x

A novel fly ash supported NiO (FA–NiO) nanocomposite solid heterogeneous catalyst has been prepared by impregnation of Ni(NO₃)₂ · 6H₂O on thermally activated fly ash (FA) support. FT-IR spectroscopy, X-ray diffraction anal

Full text of DOI:10.1007/s11164-018-3567-x

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Fly ash supported NiO as an efficient catalyst
for the synthesis of xanthene and its molecular docking
study against plasmodium glutathione reductase
Ashok V. Borhade1 Dipak R. Tope1 Sachin S. Kushare1
Savita V. Thakare1
•
•
•
Received: 16 May 2018 / Accepted: 16 August 2018
Ó Springer Nature B.V. 2018
Abstract
A novel fly ash supported NiO (FA–NiO) nanocomposite solid heterogeneous
catalyst has been prepared by impregnation of Ni(NO3)2 Á 6H2O on thermally
activated fly ash (FA) support. FT-IR spectroscopy, X-ray diffraction analysis,
scanning electron microscopy, TEM and BET techniques were employed to char-
acterize the catalyst. The catalytic adeptness of FA–NiO was tested and optimized
in xanthene formation. Catalyst gave very high yield and good purity. Stability of
the catalyst could be promising as it easily recovered and reused giving a similar
yield up to four cycles. FA–NiO is an efficient catalyst providing an environmen-
tally clean process for xanthene formation and for developing a revolutionary way
to use the majority of waste fly ash. Further, we have also performed docking
simulation between 1ONF and a xanthene molecule to evaluate binding orientation
and affinity of the ligand.
Keywords Fly ash Á FA–NiO nanocomposite Á Xanthene derivatives Á Docking Á
Glutathione reductase
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11164-
018-3567-x) contains supplementary material, which is available to authorized users.
&
Ashok V. Borhade
ashokborhade2007@yahoo.co.in
1
Department of Chemistry, Research Centre, HPT Arts and RYK Science College (Affiliated to
S.P.P. University, Pune), Nashik, MS, India
123

A. V. Borhade et al.
Introduction
Mesoporous support materials and micelle-templated silica-based solid acids with
high surface area play an important role in creating fine and speciality chemicals
using a green synthesis processes. One of such support material is fly ash (FA). It is
the chief inorganic solid waste of coal combustion from coal-based thermal power
plants. Fly ash constitutes a mixture of inorganic oxides such as SiO2, Al2O3, Fe2O3,
CaO, MgO, K2O, Na2O and TiO2 [1], with minor elements, such as Hg, As, Ge, Ga,
and traces of heavy metals (Cr, Co, Cu, Pb, Mn, Ni, Zn) and rare earths [2]. Fly ash
with the appropriate treatment can be converted into catalytic support material
similar to that of other commercial silica materials. The literature reports the use of
fly ash as a catalyst for different oxidation [3, 4], chlorination [5] and condensation
reactions [6], and as a solid support in the synthesis of 2-mercaptobenzothiazole
derivatives under microwave irradiation [7]. In addition to this, coal fly ash is also
converted to zeolitic materials for various applications [8–11]. Fly ash activated by
a thermal method has also been investigated to catalyze Beckmann rearrangement,
Knoevenagel condensation and Schiff base formation reactions [12]. In recent years,
heterogeneous catalysts have gained interesting attraction due to low cost, easy
availability, ease of handling and removal from reaction mixture, and environmen-
tally safe nature. For a wide range of chemical transformations, heterogeneous
catalysts, particularly where the catalytically active sites are dispersed onto the
surfaces of the porous solid supports, have been used extensively.
The substitution of traditional homogenous Lewis and Brønsted acid catalysts by
heterogeneous ones, e.g. solid acid catalysts such as sulfated zirconia, zeolites,
acidified silica constitutes a more environmentally friendly alternative to the organic
reactions [13, 14]. Because of their particular physical and chemical properties such
as shape, size and structure compared to bulk materials nanostructured transition
metal oxides have attracted great interest [15]. These nanoparticles possess a high
surface area and reactive morphologies and have been considered effective catalysts
for organic reactions such as acetylation, hydrogenation, oxidation, and cross-
coupling [16–25].
Nickel oxide (NiO) is one of the most common metal oxides used for catalytic
purposes. NiO nanoparticles are more effective catalysts than commercial NiO
powder for catalytic reduction [26–30]. Xanthene is a renowned heterocyclic
compound, and with its derivatives possesses wide application as antibacterial [31]
and anti-inflammatory [32] agents. They are being developed to act as new clinical
agents in cancer therapy [33], antivirals [34] and antagonists for paralyzing action of
zoxazolamine and in photodynamic therapy [35, 36].
Malaria endemic areas affect one third of the world’s population. Malaria is an
infectious, hematologic disease and a major cause of morbidity and mortality
throughout the world. Because of malarial infection there are up to 500 million
clinical cases and three million deaths annually all over the world [37]. The majority
of severe disease is due to plasmodium falciparum. It is one of the causative agent
and one of the most frequent acquired red blood cell (RBC) disorders worldwide
[38]. The increasing serious problem of malaria parasite resistance to currently used
123

Fly ash supported NiO as an efficient catalyst for the…
anti-malarial drugs has led to an urgent need to develop new and effective
antimalarial molecules. While studying malaria drug resistance glutathione
reductase which is a flavoenzyme that regenerates glutathione is an important
target as an essential protein for antioxidant defence against cell damage.
The advances in techniques contributed to many structural details of proteins and
protein–ligand complexes allow the computational strategies to permeate all aspects
of drug discovery such as molecular docking [39]. Molecular docking has become
an increasingly important tool for drug discovery. This approach can be used to
model the interaction between a small molecule and a protein at the atomic level,
which allow us to characterize the behaviour of small molecules in the binding site
of target proteins as well as to elucidate fundamental biochemical processes
[40–43].
Fly ash produced in thermal power plants is known as an environmentally
pollutant. Hence, problem must be undertaken to discard it in environment friendly
method. In the present work attempt is made to prepare fly ash supported NiO as
effective catalyst for synthesis of xanthene derivatives. We also showed potential
antimalarial xanthene derivatives having structural features better than standard
drug.
Experimental
Materials
Fly ash sample was collected from Eklahara thermal power station, Nashik district,
Maharashtra (India). The chemicals used are nickel nitrate (Ni(NO3)2.6H2O, Sigma-
Aldrich 99.99%), sodium hydroxide (NaOH, Merck 99%) cetyltrimethylamonium
bromide (CTAB Merck 99%), 5,5 dimethyl 1,3 cyclohexanedione, aldehydes.
Preparation of nanocrystalline NiO
The nanocrystalline NiO was synthesized by the sol–gel method. NiO nanostruc-
tures were synthesized by the sol–gel method using nickel nitrate Ni(NO3)2.6H2O
(1 M) as precursor and CTAB as surfactant dissolved in 150 mL double distilled
water. NaOH solution (1 M) was slowly added dropwise under vigorous stirring
until a precipitate was obtained. Suspension of Ni(OH) was treated in a Teflon-
2
lined autoclave at 120 °C for period of 24 h. The resultant gel was filtered and
repeatedly washed with double distilled water. Subsequently, the washed precipitate
was dried at 80 °C for 16 h. Finally, the precipitate was calcined at 800 °C for 3 h.
Preparation of fly ash supported NiO (FA–NiO)
Fly ash supported NiO (FA–NiO) catalyst was prepared by loading Ni(NO3)2Á6H2O
on activated fly ash (an impregnation method). A 1.5-g sample of nickel nitrate was
dissolved in 100 mL of double distilled water (DDW). A 0.5-g sample of NaOH was
dissolved in another beaker containing 100 mL double distilled water. This NaOH
123

A. V. Borhade et al.
solution was slowly added into the Ni(NO3)2Á6H2O solution and stirred for 3 h. A
light green precipitate was formed. Then, 6 g of calcined fly ash was added to the
precipitate with constant stirring. The slurry obtained was refluxed at 110 °C for
24 h then filtered and washed with double distilled water. The resulting powder was
further dried at 110 °C and calcined at 750 °C for 4 h in air. The synthesized FA–
NiO catalyst was characterised by FTIR, XRD, FE-SEM, EDAX, TEM SAED and
BET technique.
Surface acidity measurements
Catalyst acidity was measured by means of potentiometric titration [44]. A 0.1-mol
amount of the catalyst was suspended in 25 mL of acetonitrile and stirred for 2 h.
The suspension was then potentiometrically titrated with the 0.05 N n-butyl amine
in acetonitrile. The electrode potential variation of the suspended sample was
measured using an Orion 420 digital potentiometer, a model with a double junction
electrode.
General procedure for preparation of 1,8 dioxo-octahydroxanthene
A mixture of 5,5 dimethyl 1,3 cyclohexanedione (2 mmol), aldehyde (1 mmol) and
catalyst FA–NiO (0.5 mol) was stirred for an appropriate time. The progress and
completion of the reaction was monitored by TLC. After completion of the reaction,
the mixture was cooled to room temperature. The mixture was poured into cold
water. The separated solid was filtered by suction to afford crude product. Pure
product was obtained by further crystallization from ethanol to get the desired
compound in pure form (Scheme 1).
The structure of all products was confirmed by using physical and spectroscopic
1
data such as HNMR, 13CNMR and mass spectroscopy. (See supplementary data).
Spectral data of prepared compound
3,3,6,6 Tetramethyl-9 phenyl 1,8 dioxo-octahydroxanthene 3a 1HNMR CDCl3
400 MHz d(ppm) 1.26(s,6H) 2.31-2.51(m,8H) 5.57(s,1H) 7.13-7.27(m,5H) 13C
NMR (100 MHz, CDCl3); dC (ppm): 27.37, 29.33, 31.82, 32.19, 40.93, 50.75,
115.76, 126.39, 128.04, 128.38, 144.04, 162.01, 195.96 HRMS (m/z):350.458.
3,3,6,6Tetramethyl-9(4-chlorophenyl)1,8dioxo-octahydroxanthene
3b 1HNMR
CDCl3 400 MHz d(ppm)0.98 (s,6H) 1.10(s,6H) 2.14-2.25 (m,8H) 4.71(s,1H)
R
CHO
O
O
O
FA-NiO
MeOH/60 oC
O
2
O
3
1
Scheme 1 Synthetic scheme for 3,3,6,6 Tetramethyl-9 phenyl 1,8dioxo-octahydroxanthene
123

Fly ash supported NiO as an efficient catalyst for the…
7.16-7.26(m,4H) 13C NMR (100 MHz, CDCl3); dC (ppm): 27.41, 29.60, 31.42,
32.21, 32.40, 46.42, 47.04, 115.33, 128.19, 129.77, 131.58, 136.69,189.44 HRMS
(m/z):385.1568.
3,3,6,6Tetramethyl-9(4-bromophenyl)1,8dioxo-octahydroxanthene
3c 1HNMR
CDCl3 400 MHz d(ppm)1.10 (s,6H) 1.23(s,6H) 2.14-2.48(s,8H) 5.44(s,1H) 6.94-
(d,2H) 7.36-7.38(d, 2H) 13C NMR (100 MHz, CDCl3); dC (ppm): 27.29, 29.28,
31.42, 32.21, 40.84, 46.41, 50.67, 115.19, 119.64, 128.60, 131.28, 137.27,
162.43,190.66HRMS (m/z):429.1006.
3,3,6,6Tetramethyl-9(4-flurophenyl)1,8dioxo-octahydroxanthene
3d 1HNMR
CDCl3 400 MHz d(ppm)1.11 (s,6H)1.23(s,6H) 2.41(m,8H) 5.50(s,1H) 6.94-
6.99(t,2H) 7.04-7.08(t 2H)13C NMR (100 MHz CDCl3); dC (ppm): 27.39, 29.62,
31.40, 32.21, 46.43, 47.05, 114.91, 115.55, 128.21, 133.58, 159.81, 162.24,
190.57HRMS (m/z):369.1869.
3,3,6,6Tetramethyl-9(4-methylphenyl)1,8dioxo-octahydroxanthene
3e 1HNMR
CDCl3 400 MHz d(ppm) 1.08(s,6H) 1.21(s,6H) 2.28 (s,3H) 2.31-2.41 (m,8H)
5.49(s,1H) 6.96-6.98(d,2H) 7.05-7.07 (d,2H).13CNMR (100 MHz, CDCl3); dC
(ppm):27.35, 29.25, 29.63, 31.41, 32.36, 40.87, 50.63, 115.68, 126.64, 128.95,
128.22, 134.79, 135.29, 190.56HRMS (m/z):365.2118.
3,3,6,6Tetramethyl-9(4-methoxyphenyl)1,8dioxo-octahydroxanthene 3f 1HNMR
CDCl3 400 MHz d(ppm) 1.04 (s,6H) 1.12(s,6H) 2.13-2.25(m,4H) 2.45 (s,4H)
4.69(s,1H) 6.73- 6.75(d,2H) 7.16-7.20(d, 2H) 13C NMR (100 MHz, CDCl3); dC
(ppm):
27.32,29.26,29.68,30.95,32.18,
40.85,50.75,
129.31,136.48,157.96, 162.16,196.58 HRMS (m/z):381.1918.
115.25,115.78,
1-
3,3,6,6Tetramethyl-9(2,5dimethoxyphenyl)1,8dioxo-octahydroxanthene
3g
HNMR CDCl3 400 MHz d(ppm) 0.92-1.16 (s,12H) 2.29-2.37(s,8H) 5.45(s,1H)
6.69 (d,2H) 6.82(d, 1H) 13CNMR (100 MHz, CDCl3); dC (ppm): 29.42, 31.24,
32.39, 32.82, 32.87, 46.70, 55.48, 110.77, 115.77, 116.33, 128.02, 151.44, 153.06,
189.15 HRMS (m/z): 411.1918.
3,3,6,6Tetramethyl-9(4-hydroxyphenyl)1,8dioxo-octahydroxanthene 3h 1HNMR
CDCl3 400 MHz d(ppm) 0.99 (s,6H) 1.09(s,6H) 2.14-2.25 (m,4H) 2.44(s,4H)
4.11(s,1H) 6.64-6.67(dd,2H) 7.13-7.15(dd 2H) 13C NMR(100 MHz, CDCl3); dC
(ppm):27.35,
29.24,
30.96,
32.24,
129.47,136.29,154.18,192.21 HRMS (m/z): 367.1918.
40.86,50.77,115.06,115.82,
3,3,6,6 Tetramethyl-9(2-hydroxyphenyl) 1,8dioxo-octahydroxanthene 3i 1HNMR
CDCl3 400 MHzd(ppm) 0.98 (d,9H) 1.12(s,3H) 1.96-2.60(m,8H) 4.67(s,1H) 6.99-
7.01(t,3H) 7.12-7.16 (m,1H). 13C NMR (100 MHz, CDCl3); dC (ppm): 27.21,
29.16, 30.95, 41.53,49.91, 115.74, 118.31, 124.58, 127.54,151.01,169.16,200.91
HRMS (m/z): 367.1917.
3,3,6,6 Tetramethyl-9(2-nitrophenyl) 1,8dioxo-octahydroxanthene 3j 1HNMR
CDCl3 400 MHz d(ppm) 1.25 (s,12H) 2.19-2.57(s,8H) 6.03(s,1H) 7.23-7.55
123

A. V. Borhade et al.
(m,4H) 13C NMR (100 MHz, CDCl3); dC (ppm):27.41, 29.42, 32.30, 40.99, 50.61,
114.75,123.44, 129.39, 146.71, 151.23,162.45, 195.43 HRMS (m/z):396.1797.
9 phenyl 1-8 dioxo-octahydroxanthene as plasmodium falciparum
glutathione reductase inhibitor
Recombinant E. coli cells containing the plasmodium falciparum glutathione
reductase (PFGR) gene were kindly gifted from Colagen Research Private Limited
(India). These cells were grown in Luria–Bertani medium with 50 lg/mLl
carbenicillin so as to achieve 0.6 absorbance at 600 nm wavelength. For induction
of PFGR expression, 1 mM IPTG was used. These induced cells were incubated at
25 °C for 12 h followed by centrifugation. The bacterial pellet was suspended in
lysis solution (50 mM Tris–HCl,10% glycerol, 150 mM NaCl,1 mg/ml lysozyme,
0.03% Triton X-100, 10 lM phenylmethylsulfonyl fluoride,10 lg/ml DNase I at pH
7.5) and subjected to sonication [45].
After centrifugation, the resulting supernatant was saturated at 4C to 80%
ammonium sulfate for 12 h. The resulting precipitate was collected by centrifuga-
tion and it was dialysed at 4C against 25 mM potassium phosphate, 1 mM EDTA at
pH 7.0. The dialysed solution was applied to a 2P, 5PADP-Sepharose gel filtration
column equilibrated with 25 mM potassium phosphate, 1 mM EDTA at pH 7.0.
Sepharose column was washed and eluted for obtaining PFGR fraction by same
buffer.
Glutathione reductase inhibitory activity was tested by incubating 1.2 lL PFGR
fraction (170 nM) for 30 min at 25C with 100 lM NADPH and 1 mM GSSG
substrate in assay buffer (47 mM potassium phosphate, 200 mM KCl, 1 mM
EDTA) and 10, 100 and 500 lM 9 phenyl 1-8 dioxooctahydro xanthene as potential
inhibitor and then assaying aliquots for enzyme activity. These incubations were
carried out at pH 6.9 [46].
Molecular docking study
In order to find the molecule and its interactions responsible for biological activities,
ten derivatives of xanthene were taken for docking study including methylene blue
as reference drug. The crystal structure of glutathione reductase plasmodium
falciparum (PDBID1ONF) from homosapiens was obtained from a protein data
bank. By using PROCHECK, tertiary structure validation of 1ONF was done, which
revealed high quality structure with 90% residues in most favoured region. Because
of its well confirmed stereochemistry 1ONF was considered for docking study.
Receptor preparation: 1ONF as receptor was prepared using Autodock 4.2 tools.
The Autodock tools package version 1.4.6 was used to generate the docking input
files. A co-crystallized ligand molecule was removed from the enzyme active site.
Binding site was detected from PDB pocket finder. According to this, alanine 110,
glutamic acid 31, glycine 8, glycine12, glutamic acid 31, alanine 147, aspartic acid
275, aspartic acid 311, glycine 310, glutamine 351, threonine 353, leucine 352 were
considered the participating amino acid residues in potential docking sites.
123

Fly ash supported NiO as an efficient catalyst for the…
˚
For the docking, a grid spacing of 0.375 A and 75 9 69 9 76 points was used.
Before docking, all water molecules were removed from the protein structure
followed by addition of hydrogen atoms to the receptor and merging non-polar
hydrogens. Receptor protein was assigned by Kollman united atom charges and
solvation parameters while ligands were assigned by Gasteiger charge. Rigid roots
assigned to the ligand and bonds were made rotatable.
Ligand preparation: The synthesized compounds were taken for prediction of 3D
structures by using Cambridge software. The energy minimization was done by
using open babel in Pyrx virtual screening tool with UFF force field and conjugate
gradient optimization algorithm. Receptor grid generation was done by Autodock
4.2. In the receptor grid generation, the receptor structure was defined by excluding
co-crystallized ligand. This determined the position and size of the active site as it is
represented by receptor grids.
Docking simulation was done using Autodock Vina suite as the molecular-
docking tool. The default optimization parameters were used with the Lamarckian
genetic algorithm with a population size of 150 dockings. The Autodock Vina tool
generated 10 possible binding conformations, i.e. 10 runs for each docking by using
genetic algorithm (GA-LS) searches. A default protocol constituting a maximum
number of 2.5 9 105 energy evaluations, a maximum number of 2.7 9 104
generations and an initial population of 150 randomly placed individuals were
applied. A mutation rate of 0.02 and a crossover rate of 0.8 were used. The grid box
used to specify the search space was set at 75 9 69 9 76 centred on 1ONF with a
˚
default grid point spacing of 0.375 A. Auto Grid was used to obtain pre-calculated
grid maps. After completion of docking, most suitable conformation was chosen
based on lowest docked energy.
Results and discussion
The catalytic performance of FA–NiO nanocomposite catalyst was measured by
condensation reaction of 5,5 dimethyl 1,3 cyclohexanedione and 4-chlorobenza-
ledheyde (Scheme 1). In order to get maximum conversion and yield of the product,
we examined reaction parameters such as the reaction temperature, reaction time,
amount of catalyst and effect of solvent.
To check the effectiveness of FA–NiO, we tried fly ash and synthesized NiO
independently for condensation reaction of dimedone and aldehyde. NiO and fly ash
gave good yield, but required more time as compared to modified FA–NiO catalyst
(Table 1). To optimize amount of catalyst required for condition we tried various
mole equivalent of the catalyst. It was found that when the reaction was carried out
with 0.5 mol equivalent the yield was found 96%. Further increased in mol % of
catalyst was decreased the % yield due to the adsorption of product over surface
area of catalyst, eventually block the active sites of catalyst (Table 2).
Condensation reaction was carried out in different solvent such as DMF,
methanol, ethanol, acetonitrile. Among the solvent tested methanol was found to be
the best choice in terms of time and yield of the reaction (Table 3). Effect of
123

A. V. Borhade et al.
Table 1 Effect of catalytic
performance on the synthesis of
1, 8-dioxo-octahydroxanthene
Catalyst
Time (min)
180
Yield (%)
1
Without catalyst
Reaction
incomplete
2
3
4
Fly ash
NiO
30
25
10
56
71
96
FA–NiO
Table 2 Effect of mole
percentage of FA–NiO
Entry
Amount of catalyst (mol)
Time (min)
Yield (%)
1
2
3
4
5
0.1
0.3
0.4
0.5
0.8
35
30
15
10
10
65
76
82
96
82
temperature shows that maximum yield was found at 60 °C with 96% yield
(Table 4).
After optimizing the reaction conditions, we investigated the applicability of this
synthetic methodology for 9 phenyl-1,8-dioxo-octahydroxanthene derivatives with a
reaction series of 5,5 dimethyl 1,3 cyclohexanedione (2 mmol), and a wide range of
structurally diverse aromatic aldehydes (1 mmol) were treated in the presence of
FA–NiO at 60 °C. In almost all cases the desired product was obtained in good to
excellent yield (Table 5).
In order to study the possibility of reusability of the catalyst, the used catalyst
was washed with acetone and dried in the oven at 110 °C for 2 h followed by
activation at 650 °C before reuse in the next reaction cycle under similar reaction
Table 3 Effect of solvent on the
synthesis of 1, 8-dioxo-
octahydroxanthene
Entry
Solvent
Time (min)
Yield (%)
1
2
3
4
5
Ethanol
Methanol
DMSO
DMF
25
10
30
30
25
65
96
73
71
50
CH2Cl2
Table 4 Effect of temperature
on the synthesis of 1, 8-dioxo-
octahydroxanthene
Entry
Temperature (°C)
Time(min)
Yield (%)
1
2
3
4
5
40
50
10
10
10
25
25
58
69
96
53
54
60
80
100
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Fly ash supported NiO as an efficient catalyst for the…
Table 5 Synthesis of different 9-phenyl 1,8-dioxo-octahydroxanthene derivatives catalysed by FA–NiO
123

A. V. Borhade et al.
Table 5 continued
Table 6 Result of the reaction
run in the presence of FA–NiO
recycled catalyst
Entry
Reaction run
Time (min)
Yield (%)
1
2
3
4
1
2
3
4
10
10
10
10
93
91
89
85
condition. The regenerated catalyst showed similar catalytic activity until the 4th
reaction cycle, which indicates that the sites are not deactivated in the regenerated
catalyst (Table 6).
In order to show the effectiveness of FA–NiO composite as catalyst, results of
catalytic activity were compared with other catalysts reported in the literature
(Table 7). The condensation of benzaldehyde with dimedone catalysed by FA–NiO
composite in methanol offer the corresponding product 3b very fast in excellent
yield in mild conditions, while other catalysts need harsh conditions and longer
reaction times for synthesis of xanthene 3b.
The FT-IR spectra of coal fly ash, NiO nanoparticles and FA–NiO nanocom-
posite are shown in Fig. 1. The IR spectrum of the NiO sample shows various
stretching frequencies at 1473.62, 1041.56, and 501.49. The features particularly at
501.49 are due to the Ni–O stretching mode, which confirms formation of NiO. IR
spectrum of fly ash shows broad range of bands from 1055 to 1100 cm-1, which is
attributed to modes of Si–O-Si asymmetric band stretching vibrations. Low
123

Fly ash supported NiO as an efficient catalyst for the…
Table 7 Comparison of the efficiency of nanoparticles with reported catalysts for the synthesis of xan-
thene derivatives
Entry
Catalyst
Conditions/Temp (°C)
Time (min)
Yield (%) [Ref]
1
2
3
4
5
6
7
ZnO nanoparticles
Alum
EtOH/reflux
90 min
30 min
30 min
14 min
90 min
30 min
10 min
94 [47]
92 [48]
94 [49]
89 [50]
96 [51]
84 [52]
96
H2O/100 °C
H2O/reflux
DIB
CuO
Solvent free/100 °C
Solvent free/80 °C
Solvent free/80 °C
Methanol/60 °C
P2O5/SiO2,
ZrClO2.8H2O
FA–NiO
frequency at 794 cm-1 is due to Si–O-Si symmetric stretching vibrations. The IR
spectrum of fly ash containing NiO shows the stretching frequency between 1083.99
and 459.06 cm-1 , which indicates the formation of composite.
The XRD pattern of fly ash, NiO and FA–NiO composite are depicted in Fig. 2.
The XRD pattern of pure fly ash in Fig. 2a shows quartz, mullite and calcite phases
at 26.65. After loading NiO onto fly ash the silica of fly ash reacts with NiO to form
a nickel silicate phase. Diffraction pattern of FA–NiO from all the reflections of the
Fig. 1 FT-IR spectra of a fly ash, b NiO nanoparticles and c FA- NiO nanocomposite
123

A. V. Borhade et al.
Fig. 2 XRD of a fly ash, b NiO nanoparticles and c FA–NiO nanocomposite
XRD pattern (Fig. 2b) can be indexed to the standard pattern of the pure cubic phase
of NiO (JCPDS No.47-1049). This reveals that the NiO sample synthesized by the
sol–gel method produced a monophase cubic structure. Diffraction peaks (Fig. 2b)
with 2H value of 37.26, 43.24, 62.93, 76.34 and 79.20 originate from crystal planes
(111), (200), (220), (311) and (222) of NiO. Figure 2c shows NiO pattern and the
presence of fly ash peaks, which indicate the formation of fly ash containing NiO.
FE-SEM image of fly ash (Fig. 3a) shows the presence of hollow cenospheres,
irregularly shaped unburned carbon particles and mineral aggregates. FE-SEM
image of synthesized NiO (Fig. 3b) shows cubic shaped nanoparticles with good
uniformity and crystallinity FE-SEM image of FA–NiO (Fig. 3c) shows NiO
particles are also clearly visible on the external surface of spherical silica particle on
fly ash support. The presence of the elemental composition of synthesized NiO, fly
ash and fly ash containing NiO was analysed by EDAX. The typical EDAX
spectrum is shown in Fig. 3.
TEM image and SAED pattern of fly ash (Fig. 4a) shows a spherical shape. TEM
image and SAED pattern of synthesized NiO (Fig. 4b) shows that the particles are
cubic with an average particle size 20 nm. TEM and SAED pattern of fly ash
composed of NiO is presented. Figure 4c shows cubic particles of NiO on the curve
surface of fly ash.
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Fly ash supported NiO as an efficient catalyst for the…
Fig. 3 FE-SEM and EDAX of a fly ash, b NiO nanoparticles and c FA–NiO nanocompasite
From the results based on BET, the surface area and porosity of FA–NiO are
larger than NiO nanoparticles. The surface area of NiO and FA–NiO were 28,800
and 32,050 cm2/g, respectively, while the porosity was 0.007242 and 0.02061,
respectively. These values elucidate the composition of NiO and fly ash increases
the surface area, as well as porosity (Fig. 5).
Acidic strength of synthesized catalysts is proportional to its catalytic activity.
Potentiometric titration is used to estimate the number of acid sites, which correlate
with acidic strength. Potentiometric titration curves (Fig. 6) for NiO nanoparticles,
fly ash and FA–NiO nanocomposite showed that fly ash has lowest acid strength
(Ei = 66 mV) followed by NiO nanoparticles (Ei = 115 mV) and highest electrode
potential of FA–NiO (Ei = 195 mV). The conclusion is that FA–NiO nanocom-
posites possess high acidic strength as compared to fly ash and NiO.
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A. V. Borhade et al.
Fig. 4 TEM and SEAD of a fly ash, b NiO nanoparticles and c FA–NiO nanocomposite
Fig. 5 BET surface area of a NiO and b FA–NiO nanocomposite
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Fly ash supported NiO as an efficient catalyst for the…
Fig. 6 Potentiometric titration curves of n-butylamine in acetonitrile for a fly ash, b NiO and c FA–NiO
nanocomposite
Table 8 Inhibition of plasmodium falciparum glutathione reductase by
octahydroxanthene
9
phenyl 1-8 dioxo-
Sr.
no.
GSSG Conc.
(lM)
Xanthene Conc.
(lM)
Incubation Temp. Incubation time
(min)
Velocity (mL/
mU)
(°C)
01
02
03
04
1
1
1
1
00
10
25
25
25
25
30
30
30
30
4.32
1.76
0.52
0.375
100
500
Inhibition of plasmodium falciparum glutathione reductase by 9 phenyl 1, 8
dioxo-octahydroxanthene was studied. It is observed that when 10 lM 9 phenyl 1,8
dioxo-octahydro xanthene was present in the assay mixture the activity of PFGR
was 40% lower than in the control assay. This inhibition goes up to 60% as inhibitor
concentration increases from 100 to 500 lM. This clearly indicates inhibitory action
of 9 phenyl 1, 8 dioxo-octahydro xanthene against PFGR (Table 8).
Docking protocol was verified by docking with methylene blue in the vicinity of
the same active site of 1ONF. Selected conformations were analysed using Pymol
and Discovery Studio software. All derivatives showed better binding affinity than
the existing reference drug, methylene blue. The 3e molecule showed the highest
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A. V. Borhade et al.
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Fly ash supported NiO as an efficient catalyst for the…
binding affinity with lowest energy -9.0 kcal/mol and 3 g showed the lowest
binding affinity with energy -7.7 kcal/mol. ADME analysis was performed using
Swiss ADME tool. This predicts that the 3a and 3j molecules will pass through the
central nervous system as they are not substrates of the p-glycoprotein. This further
predicts that 3a molecule will pass through the blood–brain barrier. The 3a
molecule showed a maximum of 70%, oral bioavailability, chemical stability at
Fig. 7 3D and 2D molecular docking of 3a and methylene blue against 1ONF protein. a 1ONF protein
crystal structure with binding site, b docking 3a molecule, c docking methylene blue. d 3a mloecule and
methylene blue docked at the same binding site, e methylene blue interaction with binding site amino
acids, f 3a molecule interaction with site amino acids
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A. V. Borhade et al.
acidic pH less than 2, good passive absorption ([ 70%) againsthe t intestinal barrier
with 100% passive absorption with transcellular route, and it does not show first
pass metabolism in the stomach or intestines and has no active transport; its
permeability on human jejunum scale is 7.37 9 10-4 cm/s with Ld 50 in mouse
intraperitoneal is 310 mg/kg with moderate reliability. Molecular descriptor studies
of the ligand reveal that all selected ligands were passed and acted as hydrophilic or
moderately hydrophobic basic drug molecule by their adherence to the properties
(Table 9).
Docking simulation was performed between 1ONF with the 3a molecule to find
the binding orientation and binding affinities of the ligands. According to ADME/
TOX studies, the 3a molecule was identified as a possibly better inhibitor against
1ONF and follows most of the ADME properties, leading to a hydrophilic acidic
drug candidate as mitochondrial target inhibitor antimalarial drug. Thus, with the
least binding energy, least TPSA, with a reasonable hydrogen and Van der Walls
interaction and with no toxicity risk at all, ensures that this ligand is a better source
for inhibiting selectively the plasmodium glutathione reductase. The docking study
showed the binding orientation is in the 1ONF binding pocket (Fig. 7b). Two
methyl substituents on carbon 3 showed significant activity. The 4th carbon of the
3a molecule showed maximum binding to glutathione reductase valine 350 residue.
Pi alkyl interaction with polar uncharged amino acids isoleucine 380 and leucine
352 and Van der Walls interaction with gln 351, lys 213, phe 214, thr 382, Ile 384
are important for inhibitory activity of molecules.
Conclusion
Herein we report an efficient method for the synthesis of 9-phenyl 1,8dioxo-
octahydroxanthene and its derivatives through FA–NiO nanocomposite assisted
one-pot pseudo-three component condensation reaction. In this study we have
prepared a FA–NiO nanocomposite by sol–gel method using nickel nitrate, double
distilled water, fly ash and sodium hydroxide. Potentiometric titration showed
sequential decrease in catalytic activity from FA–NiO to NiO nanoparticles to fly
ash in the formation of 1,8 dioxo-octahydroxanthene and confirmed the increase in
catalytic activity of fly ash after loading it with NiO nanoparticles. Synthesized 1,8
dioxo-octahydroxanthene was assayed to study its inhibitory action against
plasmodium falciparum glutathione reductase. Experimental evidence as PFGR
inhibitor led to further molecular docking study. Molecular docking studies were
done for the analysis with a training set composed of our newly synthesized
compound whose inhibitory activity is unknown against malarial target proteins. On
the basis of molecular docking, oral bioavailability, chemical stability at acidic pH,
absorption against intestinal barrier and ability to cross the blood–brain barrier, it is
concluded that 3,3,6,6 tetramethyl 9 phenyl 1,8 dioxo-octahydroxanthene (3a) can
act as the best glutathione reductase inhibitor drug molecule among all synthesized
derivatives resulting in antimalarial activity.
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Fly ash supported NiO as an efficient catalyst for the…
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