Peptide Nanofiber Templated Zinc Oxide Nanostructures as Non-precious Metal Catalyzed N-Arylation of Amines, One-Pot Synthesis of ImidazoHeterocycles and Fused Quinazolines

Article abstract of DOI:10.1007/s10562-018-2580-4

In the present study, peptide nanofiber was used to immobilize zinc oxide. This nanoparticle was prepared through self-assembly in an aqueous solution. The structural properties of the prepared catalyst were examined by a series of techniques, such as FT-IR, EDS, SEM, TEM, XRD, ICP-OES (inductively coupled plasma optical emission spectrometry), and ultraviolet–visible (UV–Vis) spectroscopy. TEM images showed the necklace model for peptide nanofiber decorated with zinc oxide. The versatility of the method was investigated by N-arylation using reaction of amines with hydroxybenzotriazole as a novel phenylating reagent, one-pot synthesis of imidazoheterocycles by a three-component reaction of 2-aminopyridine, aldehyde, terminal alkyne and preparation of tetracyclic quinazolinone ring by one-pot reaction of isatoic anhydride, amine, and ninhydrin. High yields, low cost of catalyst, environmental friendliness, efficient recovery and recyclability of catalyst are the most important features of this catalytic system.

Full text of DOI:10.1007/s10562-018-2580-4

Catalysis Letters
https://doi.org/10.1007/s10562-018-2580-4
Peptide Nanofiber Templated Zinc Oxide Nanostructures as Non-
precious Metal Catalyzed N-Arylation of Amines, One-Pot Synthesis
of ImidazoHeterocycles and Fused Quinazolines
Zahra Taherinia1 · Arash Ghorbani‑Choghamarani1 · Maryam Hajjami1
Received: 23 July 2018 / Accepted: 26 September 2018
© Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract
In the present study, peptide nanofiber was used to immobilize zinc oxide. This nanoparticle was prepared through self-
assembly in an aqueous solution. The structural properties of the prepared catalyst were examined by a series of techniques,
such as FT-IR, EDS, SEM, TEM, XRD, ICP-OES (inductively coupled plasma optical emission spectrometry), and ultra-
violet–visible (UV–Vis) spectroscopy. TEM images showed the necklace model for peptide nanofiber decorated with zinc
oxide. The versatility of the method was investigated by N-arylation using reaction of amines with hydroxybenzotriazole as
a novel phenylating reagent, one-pot synthesis of imidazoheterocycles by a three-component reaction of 2-aminopyridine,
aldehyde, terminal alkyne and preparation of tetracyclic quinazolinone ring by one-pot reaction of isatoic anhydride, amine,
and ninhydrin. High yields, low cost of catalyst, environmental friendliness, efficient recovery and recyclability of catalyst
are the most important features of this catalytic system.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-018-2580-4) contains
supplementary material, which is available to authorized users.
* Arash Ghorbani-Choghamarani
arashghch58@yahoo.com; a.ghorbani@ilam.ac.ir
1
Department of Chemistry, Faculty of Science, Ilam
University, P.O. Box 69315516, Ilam, Iran
Vol.:(0123456789)
1 3

Z. Taherinia et al.
Graphical Abstract
O
H
N
NH3
N
N
HO
HO
O
N
HO
HO
O
H
O
N
H
N
OH
H
N
O
N
O
HO
O
NO2
O
HN
O
HO
N
O
C
O
O
N
O
O
H
Zn
N
HN
O
O2N
NH2
O
N
N
O
H
O
O
HO
O
OH
O
O
N
Zn
OH
OH
O
NH3
N
N
O
+
+
HO
HO
O
HN
N
H
N
OH
N
H
O
O
O
O
O
OH
HO
Keywords Peptide nanofiber · Hydroxybenzotriazole · ZnO nanoparticles · Tetracyclic quinazolinone · Imidazo [1,2-a]
pyridine
reduction of the generation of chemical waste, environmen-
tal [5].
1 Introduction
Imidazo [1,2-a] pyridine and tetracyclic quinazolinone
are an emerging class of heterocycles, which is extensively
investigated for useful pharmaceutical activity [6] and bio-
logical activity [7]. A variety of methods have been devel-
oped for preparation of imidazo [1,2-a] pyridines imidazole.
Of these, multicomponent reactions (MCRs) involve the
one-pot combination of three component coupling (3CC)
of 2-aminopyridine, aldehyde, and alkyne is one of the
most attractive methods for the synthesis of imidazo [1,2-a]
pyridines. A number of transition metal salts such as Ag(I)
[8], InBr3 [9], Au(III) [10], and Cu(II) [11, 12] have been
employed to accomplish this three-component coupling for
the synthesis of imidazo [1,2-a] pyridines.
The catalytic formation of carbon–heteroatoms bond has
received significant interest in recent years due to its mul-
tiple applications in the pharmaceutical, natural products,
organic materials and dye industries [1, 2]. The cross-cou-
pling of amines with aryl halides to their corresponding C–N
is the most common method in the presence of stoichiomet-
ric or catalytic amounts of either copper [3] or palladium
[4]. for N-arylation formation. Although these methods are
very effective, they have drawbacks. For example, aryl hal-
ides are generally environmental pollutants, and syntheses
are carried out in the presence of expensive noble metals,
needing of stoichiometric amounts of catalyst and high-
temperature reaction media. Multi-component (MCRs) and
domino reactions are a valuable strategy in the green chem-
istry and involve the combination of more than two compo-
nents in a single synthetic operation [4]. The major advan-
tages of MCRs include atom efficiency, high selectivity, and
Quinazolinones are important class of fused heterocy-
clic alkaloids showing a wide range of biological [13] and
pharmacological activities [14]. Consequently, methods have
been reported for the synthesis of tetracyclic quinazolinone:
1 3

Peptide Nanofiber Templated Zinc Oxide Nanostructures as Non-precious Metal Catalyzed…
(i) the condensation of isatoic anhydride and amine with
ninhydrin in aqueous HCl [15], (ii) utilizing palladium-cata-
lyzed carbonylation of commercially available 2-bromoben-
zyl amine and 2-bromoaniline as the starting materials [16].
Although all of these methods are beneficial, a number of
them have one or more of the following drawbacks: tedious
workup of the reaction mixture, long reaction times, low
yields of products, expensive metal and difficulty in sepa-
ration and recovery of the catalyst. Hence, the choice of a
suitable catalyst and environmentally benign method that
avoids all of these drawbacks is of key importance to get
good results. The great interest in catalysis using nanoma-
terials due to increased accessibility to surface atoms has
prompted the synthesis and investigation of diverse highly
functionalized NPs. Since NPs easily agglomerate and oxi-
dize due to high surface energy in aqueous solution, in many
cases, metal nanoparticles are immobilized on the various
support, such as zeolites [17], boehmite [18], dendrimers
[19], silicates [20], activated carbon [21] and nanofiber [22].
Nature-inspired peptide nanofiber networks have wide
applications for biomedical such as drug delivery [23], vac-
cinations [24], and tissue engineering [25]. Interactions
among peptide-based nanostructures can lead to the forma-
tion of various functional nanostructures such as nanotubes,
spherical vesicles, nanofibrils, nanowires, and necklaces.
The self-assembled peptide is formed by inter- and intramo-
lecular forces such as hydrogen bond formation, hydropho-
bic and electrostatic interactions, van der Waals forces, and
π–π stacking and this process is controlled by the balance
of attractive/repulsive forces within and between molecules.
Recent reports show that a nanostructured peptide has been
used as a template to stabilize metal nanoparticles and to
prevent aggregation of the nanoparticles [26]. For example,
Maity et al. [27] reported peptide nanofiber-supported palla-
dium nanoparticles as an efficient catalyst for the removal of
N-terminus protecting groups, and Wang et al. [28] reported
the synthesis of a new hairpin peptide decorated with
copper(II), which were utilized as templates for the synthesis
of long, ultrathin CuS nanowires. Moreover, Acar et al. [29]
demonstrated peptide nanofiber templated synthesis of TiO2
nanostructures, Khalily et al. [30] reported bioinspired supra-
molecular peptide nanofiber templated Pd0 hybrid nanocata-
lyst and Kim et al. [31] reported the synthesis of a sphere-to-
bridge-shaped peptide nanostructure was constructed from a
tyrosine-rich peptide (HYYACAYY-OH) via mediating Pd2+
ions as an efficient catalyst for the Suzuki coupling reac-
tion. In this context, efforts have been directed toward other
synthetic methods, which include noteworthy features such
as low price and efficient catalytic activity, being reusable
more than once and free-from aryl halide. In our previous
report [22], we developed the synthesis of biphenyls using
the reaction of aryl halides with hydroxybenzotriazole as a
novel phenylating agent. Herein we would like to describe
the N-arylation reaction using hydroxybenzotriazole, one-
pot synthesis of imidazoheterocycles by a three-component
reaction of 2-aminopyridine, aldehyde and terminal alkyne
and tetracyclic quinazolinone ring synthesis from isatoic
anhydride, amine, and ninhydrin in the presence of peptide
nanofiber decorated with ZnO. In this regard, we describe
approaches based on the self-assembly of peptide-histidine
(Fig. 4) has been shown to be an effective template for cata-
lysts due to their high surface area-to-volume ratio, giving
the reactants easy access to a large number of active sites.
2 Experimental Section
2.1 Materials
All reactants were purchased from Merck and Aldrich
Chemical Company and used without further purification.
2.2 Preparation of Histidine Ethyl Ester
Hydrochloride (1)
In our experiment (6.0 mL, 82.1 mmol) thionyl chloride was
added dropwise to a stirred mixture of histidine (54.7 mmol)
in Ethanol (100 mL) at 0 °C. The mixture was stirred for
24 h at room temperature. The precipitate was removed by
filtration. The crude product was purified by recrystallization
using EtOAc/EtOH (80:20) to give a white solid [30]. FT-IR
(KBr) νmax/cm−1: 1392, 1479, 1586, 1622, 1738, 2570, 2793,
2883, 3019, and 3100.
2.3 Synthesis of Compound (2)
In a typical procedure, 0.5 g (5 mmol) succinic anhydride
was dissolved in 3 mL of DMF in an ice-water bath and
stirred for 5 min. Followed by adding (5 mmol) of histidine
ethyl ester hydrochloride, subsequently (5 mmol) N-methyl
morpholine was added to this mixture. The resultant was
stirred for overnight. Finally, 50 mL ethyl acetate was added
to the reaction mixture and the resulting precipitate was
removed by filtration and purified by recrystallization using
EtOAc/EtOH (80:20) to yield compound 2 as a white solid
[30]. FT-IR (KBr) νmax/cm−1: 1073, 1125, 1179, 1225, 1339,
1419, 1494, 1644, 1736, and 3415.
2.4 Synthesis of Compound (3)
The compound 2 (3.5 mmol) in 3 mL of DMF was stirred
in an ice-water bath, then (7 mmol) of histidine ethyl este-
rhydrochloride was added to this mixture. In the next step
ethyl acetate (10 mL) was added followed by mixing with
0.68 g (3.85 mmol) DCC and 0.520 g (3.85 mmol) of HOBt.
Afterward, the reaction mixture was stirred overnight and
1 3

Z. Taherinia et al.
washed repeatedly with ethyl acetate to remove DCU. The
2.8 Preparation of Peptide Nanofiber (7)
crude product was purified by recrystallization using EtOAc/
EtOH (80:20) to give a white solid [30]. FT-IR (KBr) νmax
/
26.65 mg (0.04 mmol) of the synthesized peptide was
dissolved in an aqueous solution containing 0.2 mL dou-
ble distilled water and 0.8 mL phosphate buffer solution
(pH 5) followed by adding 32 mg (0.31 mmol) of suc-
cinic anhydride to the peptide solution and sonicated for a
few minutes. This mixture was stirred overnight at 80 °C.
FT-IR (KBr) νmax/cm−1: 1066, 1178, 1405, 1558, 1646,
1722, 2859, 2930, 3438.
cm−1: 693, 936, 999, 1289, 1399, 1454, 1622, 1655, 1839,
1926, 2045, 2265, 2548, 2925 and 3086.
2.5 Synthesis of Compound (4)
To a round bottom flask, containing (2.7 mmol) of com-
pound 3, EtOH (6 mL), 2 M NaOH (2 mL) was added drop-
wise. The reaction mixture was stirred overnight. After
completion of the reaction, the pH was adjusted to 1 by
dropwise addition of 1 M HCl followed by addition of the
ethyl acetate (50 mL). After filtration and removal of the
solvent, the white solid of the desired compound produce
[32]. FT-IR(KBr) νmax/cm−1: 1071, 1351, 1425, 1575, 1624,
1729, 2886, 3008, 3083, 3265, 3570, and 3745.
2.9 Synthesis of ZnO Nanoparticle Supported
on the Peptide Nanofiber (ZnO NP‑PNF)(8)
Peptide 30.14 mg (0.04 mmol) was dissolved in 0.2 mL of
double distilled water. then 0.8 mL phosphate buffer solu-
tion (pH 5) was added. The solution was sonicated for a
few minutes. This mixture was stirred overnight at 80 °C.
In the next step Zn(NO3)2·6H2O (5.94 mg, 0.02 mmol) was
added to the reaction mixture and stirred for 12 h at 80 °C,
to obtain ZnO NP-PNF quantitatively.
2.6 Synthesis of Compound (5)
A mixture of compound 4 (2.42 mmol) in 3 mL DMF was
cooled in an ice-water bath, then (9.7 mmol) of histidine
ethyl ester hydrochloride was added followed by adding
0.68 g (3.85 mmol) DCC and 0.520 g (3.85 mmol) of HOBt.
Afterwards, the reaction mixture was stirred for overnight,
and then washed repeatedly with ethyl acetate to remove
any residual DCU byproduct. The solvent was removed and
evaporated to provide compound 4. The crude product was
purified by recrystallization using EtOAc/EtOH (80:20)
[30]. FT-IR (KBr) νmax/cm−1: 1075, 1132, 1184, 1339, 1405,
1462, 1491, 1631, 1737, 1842, 1929, 2616, 2704, 2888,
3099 and 3414.
2.10 General Procedure for the Synthesis
of Secondary Amines
The reaction was conducted at 130 °C in DMSO (3 mL)
with the substituted amine (2 mmol), hydroxybenzotria-
zole (1 mmol), KOH (5 mmol) and 0. 75 mg of catalyst.
The progress of the reaction was monitored by TLC. After
reaction completion, the mixture was cooled to room tem-
perature and was extracted with ethyl acetate (2 × 20 mL).
The organic extract was washed twice with water and dried
with anhydrous Na2SO4, then filtered and the solvent was
evaporated to achieve corresponding aryl amine. In order
to obtain high pure arylamine, the crude product purified
by preparative TLC.
2.7 Synthesis of Compound (6)
In a round bottom flask, 2 M NaOH was added drop-wise
to (1.8 mmol) of compound 5 in 10 mL EtOH. The reac-
tion mixture was stirred overnight. After completion of the
reaction, the pH was adjusted to 1 by dropwise addition of
1 M HCl, followed by addition of the ethyl acetate (50 mL)
filtered to provide compound 6 [32]. 1H NMR (400 MHz,
D2O) δ2.84 (s, 2H), 3.25–2.96 (m, 4H, CβH), 4.07–3.90 (m,
2H, CαH), 6.95 (d, J=9.2 Hz, 2H, ArH), 7.67 (s, 1H, ArH),
7.89 (s, 1H, ArH), 13CNMR (100 MHz, D2O) (δ, ppm):
28.3, 29.4, 54.8, 56.4, 116.9, 117.8, 132.1, 136.4, 160.4,
163.6, 174.4, 180.1. FT-IR (KBr) νmax/cm−1: 1084, 1125,
1390, 1624, 1729, 2792, 2883, 3101, 3441. Anal. Calcd for
C28H34N12O8: C, 49.40; H, 6.19; N, 26.21; O, 18.20.
2.11 General Procedure for the Synthesis
of Imidazoheterocycles
A catalytic amount of ZnO nanoparticle decorated on pep-
tide nanofibers (0.75 mg) was added to a mixture of benza-
ldehyde (1 mmol), 2-aminoazine (1 mmol), and phenyla-
cetylene (1 mmol). The reaction mixture was then stirred
at 100 °C. Reaction progress was monitored by TLC. Upon
the reaction completion, the product was extracted with
ethyl acetate (2 × 10 mL). The resultant organic layer was
washed with distilled water, dried over anhydrous sodium
sulfate, and concentrated to give the crude solid crystal-
line product.
1 3

Peptide Nanofiber Templated Zinc Oxide Nanostructures as Non-precious Metal Catalyzed…
1
Compound 6 (Table 3): δ H NMR (400 MHz, CDCl3) δ
8.3 (t, J=7.2, 1H), 8.2 (d, J=7.6, 1H), 8.10–8.0 (m, 1H),
7.99–7.98 (m, 1H), 7.82–7.81 (m, 2H), 7.47 (d, J=8.8, 2H),
2.77 (t, J=7.8 Hz, 2H), 1.34–1.31 (m, 4H), 0.914 (t, J=7.6,
2H). 13C NMR (100 MHz, CDCl3): δ=202.6, 162.4, 152.2,
138.6, 134.9, 128.3, 123.3, 115.0, 40.9, 30.0, 20.2, 13.8.
2.12 General Procedure for the Synthesis
of Quinazoline Tetracyclic Derivatives
A mixture of isatoic anhydride (1 mmol), amine (1 mmol)
and 0.625 mg of catalyst in PEG, was stirred at 100 °C.
After the reaction was completed, ninhydrin (1 mmol) was
added into the resulting mixture. Then the mixture was
heated at 100 °C and the reaction was monitored by TLC
for an appropriate time. After completion, the mixture was
cooled to room temperature and 20 mL of ethyl acetate
was added to the organic phase and washed with water,
dried over anhydrous Na2SO4, and filtered. The residue
was purified by column chromatography (silica gel, hex-
ane/ethyl acetate) to afford the corresponding product.
1
Compound 8 (Table 6): H NMR (400 MHz, DMSO) δ
7.8 (d, J= 8, 2H), 7.62–7.55 (m, 2H), 7.26–7.02 (m, 4H),
2.51–2.41 (m, 1H), 1.75–1.59 (m, 10H), FT-IR (KBr) νmax
/
cm−1:2927, 2858, 1726, 1655, 1475, 1429, 1374, 1302,
1255, 1185, 1075, 1019, 973, 899, 725, 680.
1
Compound 9 (Table 6): H NMR (400 MHz, DMSO) δ
1
8.4 (s, 1H), 8.17 (d, J = 8, 1H), 8.17 (d, J = 8, 1H), 7.92
(d, J = 8, 1H), 7.84 (q, J = 4.9, 2H), 7.69–7.63 (m, 1H),
7.55 (t, J = 7.2, 1H), 7.21 (q, J = 8.5, 1H), 3.36–3.32 (m,
1H), 1.48–1.37 (m, 14H). 13C NMR (100 MHz, CDCl3):
δ=186.8, 159.8, 147.8, 146.6, 139.9, 135.2, 134.6, 127.5,
127.4, 126.7, 123.4, 122.8, 121.9, 115.2, 40.6, 39.3, 26.4,
26.3, 25. FT-IR (KBr) νmax/cm−1:3056, 3020, 2923, 2846,
1711, 1656, 1609, 1403, 1153, 1100, 1022, 942, 821, 743,
676, 537, 463.
Compound 1 (Table 2): δ HNMR (CDCl3, 400 MHz):
δ=7.96 (d, J=7.3, 6H), 7.56–7.47 (m, 4H), 6.7 (br, 1H, NH).
1
Compound 5 (Table 2): δ HNMR (CDCl3, 400 MHz):
δ=7.85 (t, J=6.8 Hz, 2H), 7.75–7.73 (m, 1H), 7.58–7.49
(m, 5H), 6.95–6.88 (m, 1H) 6.4 (s, 1H), 4.2 (s, 3H).
Compound 3 (Table 4): 1H NMR (400 MHz, CDCl3) δ 9.9
(s, 1H), 8.4 (d, J=8.4, 4H), 8.12–8.10 (m, 3H), 7.8–7.72 (m,
3H), 7.35 (d, J=8, 1H), 7.03 (d, J=8.8, 1H), 3.69 (s, 2H).
Compound 4 (Table 4): 1H NMR (400 MHz, DMSO) δ 9.90
(s, 1H), 7.9 (s, 1H), 7.43–7.37 (m, 2H), 7.32–7.03 (m, 3H),
6.71–6.56 (m, 3H), 6.48–6.42 (m, 4H), 3.56 (s, 2H).
3 Results and Discussion
A schematic illustration of the preparation strategy of the
peptide nanofiber templated ZnO nanostructures (ZnNP-
PNF) was shown in Scheme 1. Peptide 6 employed in this
report was synthesized by conventional solution phase meth-
odology. The C-terminus of amino acid was protected as
ethyl ester. Couplings were mediated by dicyclohexylcar-
bodiimide-1-hydroxybenzotriazole (DCC-HOBt). The final
1
Compound 5 (Table 4): H NMR (400 MHz, DMSO) δ
8.50–8.48 (m, 2H), 7.99–7.86 (m, 4H), 7.35–7.21 (m, 3H),
6.48–6.44 (m, 3H), 3.40 (s, 2H).
Compound 1 (Table 6): 1H NMR (400 MHz, DMSO) δ 8.14
(t, J = 7.6, 2H), 8.07 (s, 1H), 7.90–7.87 (m, 3H), 7.55 (d,
J=8.4, 2H), 7.55 (d, J=8.4, 2H), 7.41 (t, J=4.2, 2H), 4.44
(s, 2H), 13C NMR (100 MHz, CDCl3): δ = 180.8, 178.0,
145.0, 137.4, 137.7, 134.6, 133.6, 133.1, 127.1, 126.6,
126.5, 119.2, 117.6, 114.2, 41.1.
1
compounds were purified and fully characterized by H
NMR and 13CNMR spectral studies. In this work, the effect
of phosphate buffer solutions on the structure of peptide
nanofiber was investigated. After the peptides nanofiber was
designed and synthesized Zn(NO3)2·3H2O was immobilized
on the surface of this nanostructural compound (Scheme 1).
The structure of the ZnO nanoparticles product was eluci-
dated on the basis of FT-IR, EDS, SEM, XRD, ICP-OES,
TEM and fluorescence spectroscopy. The FT-IR spectra pro-
vide valuable information regarding the nature of the func-
tional group attached to the metal atom. In order to study the
bending mode of the peptide nanofiber decorated with ZnO,
the IR spectrum of the peptide nanofiber was compared with
the peptide nanofiber decorated with ZnO. Peptide nanofiber
mainly exhibited four characteristic peaks at 1722, 1646,
1177, and 1067 cm−1, corresponding to (C=O), (N–H), and
(C–OH), respectively. However, the corresponding peaks of
peptide nanofiber/ZnO were changed to 1719, 1639, 1179,
and 1057 cm−1. The position and intensity of characteristic
Compound 4 (Table 6): 1H NMR (400 MHz, DMSO) δ 7.93
(d, J=8, 3H), 7.68–7.64 (m, 3H), 7.23–7.19 (m, 4H), 2.55
(q, J = 7.4 3H), 1.5 (t, J = 7.3 3H). 13C NMR (100 MHz,
CDCl3): δ = 188.9, 168.08, 147.0, 144.4, 142.7, 134.3,
131.8, 128.7, 128.6, 126.5, 123.7, 106.7, 28.6, 15.4. FT-IR
(KBr) νmax/cm−1: 3062, 3023, 2926, 2849, 1714, 1652, 1477,
1435, 1408, 1161, 1091, 1019, 726, 680, 527, 462.
Compound 5 (Table 6): 1H NMR (400 MHz, CDCl3) δ 8.17
(d, J = 7.6, 3H), 7.66–7.62 (m, 2H), 7.29 (q, J= 6.8, 3H),
7.17 (d, J=8, 2H), 2.77 (m, 1H), 1.32 (d, J=8, 6H). FT-IR
(KBr) νmax/cm−1:3024, 2924, 1708, 1630, 1503, 1511, 1408,
1312, 1249, 1033, 951, 901, 819, 737, 662, 540.
1 3

Z. Taherinia et al.
peaks were known to reflect the coordination behavior of
peptide nanofiber and ZnO. We also found that there are
two new peaks at 450.51–665 cm−1, which were assigned
to the characteristic peaks of zinc oxide nanoparticles [33]
(Fig. 1). The structure and phase purity of peptide nanofiber
and peptide nanofiber templated zinc oxide nanostructures
were studied by X-ray diffraction analysis (XRD). Figure 2
shows the XRD pattern of nanoparticles. From the analysis
of the XRD pattern of nanoparticles clearly seen that the pre-
pared ZnO nanoparticles showed a single-phase nature with
N
H2N
OH
N
O
H
A=SOCl2,EtOH B=Succinic anhydride, DMF,N-methyle morpholine
C=HOBt, DCC, DMF D=EtOH,NaOH E=HOBt, DCC and DMF
F=EtOH,NaOH G=phosphate buffer solutions (pH 5) and succinic anhydride
H= Zn(NO3)2.3H2O
A
N
H2N
OCH2CH3
N
O
H
1
B
H3CH2CO
H
N
E
O
O
HO
HO
HO
O
Peptide nanofiber
synthesis cycle
O
H
N
O
O
N
N
N
O
H
N
NH
HN
OCH2CH3
HN
OCH2CH3
O
NH
NH
N
N
2
O
O
D
C
NH
O
HN
H
4
O
N
H3CH2CO
N
O
5
H
H3CH2CO
O
O
H
N
O
NH
NH
N
N
O
H
N
N
F
H2N
OCH2CH3
NH
NH
N
N
N
N
N
H
O
3
HN
HN
OH
O
OH
1
OH
OH
O
O
NH
O
O
O
OH
O
OH
HN
O
H
O
O
O
N
O
O
O
O
HO
OH2
OH
HO
OH2
N
O
N
N
N
N
O
OH
H
OH
O
O
H
O
H
OH
OH
OH
O
N
O
OH
O
OHO
HN
NH
O
N
O
OHO
O
NH
N
HO
O
HO
O
N
O
HO
HO
OH
OH
H
N
H
G
O
6
O
O
ZnO
O
N
HN
HN
O
HN
O
O
H
O
O
N
O
N
N
N
O
H
O
H
ZnO
H
H
O
N
O
NH
N
O
N
O
N
OH
O
HN
O
OH
HN
HN
O
O
O
O
O
O
H-bonding interaction
H-bonding interaction
O
O
OH
OH
OH
OH
8
7
HO
HO
OH
OH
Scheme 1 Schematic synthesis of ZnO nanoparticles supported on the peptide nanofiber
1 3

Peptide Nanofiber Templated Zinc Oxide Nanostructures as Non-precious Metal Catalyzed…
adding Zn(NO3)2·6H2O this is probably due to the effects
of ZnO nanoparticle on morphology of peptide nanofiber.
The optical properties of the peptide nanofiber deco-
rated with Zn were investigated by UV–Vis spectroscopy
(Fig. 3). For comparison, UV–Vis spectra of the prepared
ZnOPNF, and zinc metallic and peptide nanofiber at room
temperature using water as the solvent are also presented in
Fig. 2. For peptide nanofiber the observed absorption band
at λ = 280–300 nm is assigned to π–π* upon coordination
with zinc ions, and there are minor changes of these bands.
The visible spectra of the desired peptide nanofiber deco-
rated with zinc show the maximum absorption at 285 nm,
which can be assigned to d to d electron transition or metal
to ligand charge transfer (MLCT). The presence of Zn metal
on the surface of peptide nanofiber was determined, by an
EDS technique (Fig. 4). As shown in Fig. 4, the EDS spec-
trum of ZnO PNF shows the presence of O, C, N and as
well as Zn species in the ZnONP-PNF. The morphology
of peptide nanofiber decorated with ZnO nanocatalyst was
also studied by SEM and TEM techniques (Figs. 5, 6). SEM
images of ZnONP-PNF indicate a very uniform size distri-
bution of zinc nanoparticles without agglomeration (Fig. 5).
This observation from the TEM image indicates that peptide
nanofiber spontaneously changes into metastable necklace-
like structures. In order to determine the exact amount of
Zn in ZnONP-PNF. ICP-OES was used. From this analysis,
the amount of Zn in the catalyst is found to be 2607 ppm
or 0.01 g.
Fig. 1 FT-IR spectra of peptide powder (a), the peptide nanofiber (b),
and peptide nanofibers decorated with ZnO nanoparticles (c)
a hexagonal quartzite structure. The peaks have occurred
for ZnO at an angle of 2Ɵ=33.3° and 34° which leads the
crystalline nature [34, 35]. Also, the other peaks related to
peptide nanofiber structure which has a different pattern with
XRD peak positions related to the peptide nanofiber before
3.1 Catalytic Study
To investigate the catalytic activity of the prepared pep-
tide nanofiber decorated with ZnO as a nanocatalyst in
Fig. 2 The X-ray diffraction pattern of peptide nanofiber and ZnO immobilized on peptide nanofibers
1 3

Z. Taherinia et al.
entry 2). Base NaOH was tested and led to the formation of
lesser amounts of the desired product. Potassium hydroxide
(KOH) in dimethyl sulfoxide (DMSO) forms a superbasic
medium that allows to access cross-coupling products from
reactions of aryl halides with nitrogen-based nucleophiles
by the SNAr mechanism or aryne formation. Among the
known superbases, two-phase systems such as an alkali
metal hydroxide–dipolar nonhydroxylic solvent are believed
to be the most universal, available, stable, and convenient
to handle. And among these the KOH/DMSO suspension is
the champion. In the light of the presented literature data,
we hypothesized that this in situ formed superbase would be
active enough to allow arylations of nucleophiles leading to
cross-coupling products [35, 36].
Fig. 3 UV–Visible absorption spectra for Zn(NO3)2·6H2O, peptide
nanofibe and ZnO NP-PNF
We also investigated the effect of temperature on the
reaction. When the reaction was conducted at a low tem-
perature, the yields observed were very low (Table 1,
entries 10 and 11). The ideal temperature for the reaction
was found to be130 °C. The best result was obtained when
the reaction was pursued at 130 °C, using 0.75 mg of pep-
tide nanofiber decorated with ZnO in the presence of KOH
(5 mmol) and DMSO (2.0 mL). To clarify the especial
catalytic activity of ZnONP-PNF in N-arylation, in a set
of experiments the model reaction was carried out in the
presence of Zn(NO3)2·3H2O and CuNP-PNF respectively
(Table 1). When the reaction was conducted in the presence
of Zn(NO3)2·3H2O and CuNP-PNF the yield observed was
low compared to ZnONP-PNF.
To examine the general applicability of the ZnONP-PNF
catalyst for N-arylation and the scope of the process, various
substituted aliphatic and aromatic amines were investigated,
as shown in Table 2.
Fig. 4 EDS spectrum of peptide nanofibers decorated with Zn nano-
The second portion of this work involves the application
of our protocol to the synthesis of imidazoheterocycles by
a three-component reaction of 2-aminopyridine, aldehyde,
and terminal alkyne. The reaction of 2-aminopyridine,
4-nitrobenzaldehyde with phenylacetylene was chosen as
model substrates to optimize the reaction conditions, and
several parameters such as the amount of catalyst, base, sol-
vent, and temperature were screened (Table 3). Firstly, the
effect of solvents was investigated and it was observed that
the desired product was obtained in the PEG (Table 3, entry
2). The desired product was not obtained in the presence of
bases such as KOH, K2CO3, Na2CO3, Et3N, and NaHSO4,
and even at 130 °C, the yield did not change.
particles
N-arylation, we started this synthesis by conducting the reac-
tion of aniline and hydroxybenzotriazole, at 130 °C using
DMSO in the absence of the catalyst. The progress of the
reaction was monitored by TLC. The control experiment
confirmed that the reaction did not occur in the absence of
the catalyst. When the reaction was conducted in the pres-
ence of ZnOPNF, at 130 °C, the desired product was formed.
Next, the influence of the amount of catalyst on the yield of
the product was evaluated. It was observed that 0.75 mg of
peptide nanofiber decorated with ZnO was found to be opti-
mal, a lower yield was observed and a longer reaction time
was required when the amount of the catalyst was decreased
(entry 11). Increasing the amount catalyst could increase
the yield of the desired product (entry 13 and 14). Then,
we performed the model reaction using different solvents
such as PEG, DMSO, H2O, DMF, THF, and dioxane, DMSO
was found to be the most effective. Among various bases
screened, KOH was found to be an excellent base (Table 1,
Finally, the amount of catalyst was screened, and 0.75 mg
of ZnOPNF was found to be optimal (Table 3, entry 2).
Encouraged by the above interesting results, we studied the
coupling reaction of various aldehydes, 2-aminopyridine and
phenylacetylene, under optimized conditions. The results are
shown in Table 2. All of the reactions proceeded smoothly
to afford the corresponding imidazoheterocycles in good
yields. Aromatic aldehydes carrying electron-withdrawing
1 3

Peptide Nanofiber Templated Zinc Oxide Nanostructures as Non-precious Metal Catalyzed…
Fig. 5 a–cSEM images of solution peptide by adding succinic anhydride at pH 5 and d SEM image of immobilized ZnO nanoparticles on the
surface of the peptide nanofiber
substituents showed reactivity and reacted efficiently to yield
the desired product. Moreover, heterocyclic aldehydes such
as thiophene-2-carbaldehyde (Table 4, entry 5) also dis-
played a high reactivity under this standard condition.
A possible mechanism has been proposed for the forma-
tions of imidazoheterocycles in Scheme 2. Firstly, imine
has been synthesized by condensation of an aldehyde with
2-aminopyridine in the presence of ZnONP-PNF. Then,
the resulting products are treated with phenylacetylene to
generate propargylamine. Tautomerizes of propargylamine
to intermediate 3 is followed by 5-exo-dig cyclization to
afford 4, which finally isomerized to product 5.
Later, the one-pot synthesis of tetracyclic quinazolinone
by a three-component reaction of isatoic anhydride, nin-
hydrin and aromatic and aliphatic amines such as ben-
zylamine, methoxybenzylamine, cyclopropyle, cyclohexyl,
cycloctyle, isopropyl, ethylaniline, and aniline were stud-
ied. We started quinazolinone synthesis by reaction of
benzyl amine, isatoic anhydride, and ninhydrin, as the
model case for condition optimization. The results are
summarized in Table 5. Initially, various solvents were
1 3

Z. Taherinia et al.
Fig. 6 TEM images of immobilized ZnO nanoparticles on the surface of the woven nanofibers (a–f)
1 3

Peptide Nanofiber Templated Zinc Oxide Nanostructures as Non-precious Metal Catalyzed…
Table 1 Optimization of the
reaction conditions for the
C–N coupling reaction in the
presence of ZnO nanoparticle
supported on the peptide
nanofibera
Entrya
Cat. (mg)
Solvent
Base
Temp. (ºC)
Yieldb (%)
Time (h)
1
2
3
4
5
6
7
8
–
0.5
0.5
0.5
0.5
0.5
0.5
0.75
0.25
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
DMSO
DMSO
H2O
DMF
THF
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOH
NaOH
K2CO3
Na2CO3
Et3N
130
130
130
130
130
130
130
130
130
100
80
130
130
130
130
130
130
130
N.R
70
N.R
23
N.R
N.R
N.R
80
50
68
15
63
N.R
N.R
N.R
N.R
33
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
PEG
Dioxane
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
9
10
11
12
13
14
15
16
17c
18d
KF
KOH
KOH
65
aReaction conditions: hydroxybenzotriazole (1 mmol), aniline (2 mmol), base 5 mmol
bIsolated yield
c,dWhen the reaction was conducted in the presence of Zn(NO3)2·3H2O and CuNP-PNF respectively
Table 3 Optimization of
the reaction conditions
for imidazoheterocycles
using 2-aminopyridine,
4-nitrobenzaldehyde and phenyl
acetylenea
Entry
Cat (mg)
Solvent
Temp. (ºC)
Base
Yield (%)b
1
2
3
4
5
6
7
8
0. 75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.75
0.5
DMSO
PEG
DMF
H2O
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
PEG
100
100
100
100
100
100
100
100
100
80
–
–
–
–
N.R
80
N.R
N.R
N.R
N.R
Trace
N.R
N.R
55
Na2CO3
K2CO3
KOH
Et3N
9
NaHSO4
10
11
12
13
–
–
–
–
100
100
100
58
23
N.R
0.25
–
aReaction conditions: 4-nitrobenzaldehyde (1 mmol), 2-aminopyridine (1 mmol), phenyl acetylene
(1 mmol), base (2 mmol)
bIsolated yield
screened. It was observed that this reaction proceeds well
in PEG. In DMF and DMSO, (Table 6, entries 5–7), the
yield of the product was less than 50%. The reaction did
not occur when conducted at room temperature and 50 °C
(Table 5, entries 5 and 6). The ideal temperature for the
reaction was found to be 100 °C. Next, the influence of
the different amount of catalyst on the reaction was tested,
and 0.62 mg of catalyst was found to be optimal. A lower
yield was observed when the amount of the catalyst was
decreased (Table 5, entry 8). Also, the control experiment
confirmed that the reaction did not occur in the absence of
the catalyst. With the optimal reaction conditions in hand,
we then investigated the scope reaction for synthesis of
quinazolinone derivatives and the results are summarized
in Table 6. The protocol is applicable to a wide variety
1 3

Z. Taherinia et al.
Table 2 Synthesis of secondary
amines via reaction of
hydroxybenzotriazole and
amines catalyzed by peptide
nanofibers decorated with ZnO
nanoparticles (ZnNP-PNF) in
DMSO
Time
(h)
Yield
(%)b
Entry
Amine
Product
10
80
1
8
88
2
3
15
53
10
12
63
55
4
5
6
15
12
12
47
68
53
7
8
9
8
8
73
78
10
aReaction conditions: hydroxybenzotriazole (1 mmol), amine (2 mmol), ZnONP-PNF
(0.75 mg), KOH 5 mmol, 130 °C
bIsolated yield
of aromatic and aliphatic amines providing moderate to
excellent yield of desired products.
aziridine compound D, and the subsequent rearrangement
leads to tetraheterocyclic product F.
The possible mechanism for the formation of tetracyclic
quinazolinone was proposed as shown in Scheme 3. Attack
of the N nucleophile at the electrophilic C of the C=O group
of isatoic anhydride related to ring opening and decarboxy-
lation to form compound B. Then followed by nucleophilic
attack of amine to the keto group of ninhydrin to afford C,
nucleophilic attack of amine on the keto group provide fused
One major advantage of the catalyst is its recyclabil-
ity and it makes them useful for commercial applications.
Therefore, the recovery and reusability of our supported cat-
alyst was investigated in N-arylation of aniline with hydroxy-
benzotriazole under optimized conditions for four runs. The
reaction was performed in DMSO at 130 °C, using 1 mmol
aniline, 1 mmol hydroxybenzotriazole and 5 mmol KOH in
1 3

Peptide Nanofiber Templated Zinc Oxide Nanostructures as Non-precious Metal Catalyzed…
Table 4 Synthesis of
imidazoheterocycles
ZnO
Time
(h)
Yield
(%)b
Entrya
1
Amine
Aldehyde
Product
14
10
55
85
2
3
10
88
4
12
95
5
20
63
6
10
75
7
13
90
aReaction conditions: benzaldehyde (1 mmol), 2-aminopyridine (1 mmol), phenyl
acetylene (1 mmol) and ZnONP-PNF (0.75 mg)
bIsolated yield
the presence of ZnO NP-PNF (0.75 mg), upon completion
empirical, and numerical studies suggest that fiber diameter
is reduced by decreasing viscosity [37–39].
of the reaction, the mixture was cooled to room temperature.
20 mL of ethyl acetate was added to the reaction mixture,
which led to the precipitation of ZnONP-PNF. The resulting
precipitate was washed twice with ethyl acetate (2×10 mL),
dried and applied for the next run. It was found that ZnONP-
PNF could be reused at least four times without a significant
loss of its catalytic activity (Fig. 7).
4 Conclusions
In summary, we describe a simple and ‘‘green’’ method
for the synthesis of peptide nanofiber decorated with
ZnO. FT-IR, EDS, SEM, TEM, ICP-OES (inductively
coupled plasma optical emission spectrometry), and ultra-
violet–visible (UV–Vis) spectroscopy results proved that
peptide nanofiber decorated with ZnO was formed. TEM
Also the morphology of peptide nanofiber templated
ZnO nanostructures the recovered for for130 °C reaction
temperature was studied by SEM technique (Fig. 8). It was
easily observed that solvent evaporation leads to larger fiber
diameters. It is worth mentioning that previous analytical,
1 3

Z. Taherinia et al.
ZnO
ZnO
PNHF
Peptide nanofibers decorated with ZnO
N
NO2
N
ZnO
ZnO
O
5
N
+
H
NH2
isomerization
O2N
N
NO2
N
4
N
N
NO2
NO2
N
NH
5-exo-dig cyclization
H
N
1
NO2
N
2
3
ZnO
Scheme 2 Proposed mechanism for the synthesis of imidazo [1,2-a] pyridine through three-component reaction of 2-aminopyridine, aldehyde
and phenyl acetylene catalyzed by ZnOPNF
Table 5 Optimization of the reaction conditions for tetracyclic quina-
images showed the necklace model for peptide nanofiber
decorated with ZnO. Peptide nanofibers provide a favora-
ble environment for the synthesis of metal nanoparticles
without adding any further stabilizer. Peptide nanofiber
decorated with ZnO can catalyze N-arylation of aryl hal-
ides using hydroxybenzotriazole as a phenylating reagent,
synthesis of imidazoheterocycles and tetracyclic quina-
zolinon. High yields, low cost of catalyst, environmental
friendliness, efficient recovery and recyclability of catalyst
are the most important features of this catalytic system.
zolinone using isatoic anhydride, ninhydrin and benzyl aminea
Entry
Cat (mg)
Solvent
Temp. (ºC)
Yield (%)b
1
2
3
4
5
5
6
7
8
9
0.62
0.62
0.62
0.62
0.62
0.62
0.62
0.62
0.25
–
DMSO
PEG
DMF
Dioxane
H2O
PEG
PEG
PEG
PEG
PEG
100
100
100
100
100
25
50
80
100
100
44
78
23
N.R
N.R
N.R
N.R
63
44
N.R
aReaction conditions: isatoic anhydride (1 mmol), ninhydrin
(1 mmol), solvent (2 mL)
bIsolated yield (Time 8 h)
1 3

Peptide Nanofiber Templated Zinc Oxide Nanostructures as Non-precious Metal Catalyzed…
Table 6 Synthesis of tetracyclic
quinazolinone
ZnO
Time
(h)
Entrya
1
Amine
product
Yieldb
8
78
2
8
90
3
4
9
85
10
75
5
10
90
6
7
CH3CH2CH2CH2NH2
7
55
12
80
8
14
15
78
69
9
aReaction conditions: isatoic anhydride (1 mmol), ninhydrin (1 mmol), ZnONP-PNF
(0.625 mg), PEG (2 mL)
bIsolated yield
1 3

Z. Taherinia et al.
Scheme 3 Proposed mechanism
for the synthesis of tetracyclic
quinazolinone through three-
component reaction of benzyl
amine with isatoic anhydride
and ninhydrin catalyzed by pep-
tide nanofiber decorated with
ZnO nanoparticles
O
O
OH
OH
ZnO
ZnO
ZnO
ZnO
O
O
O
O
NHR
NH2
O
O
+
RNH2
N
H
O
A
B
ZnO
O
O
O
NHR
NR
O
N
N
H
O
O
C
D
O
O
NR
O
NR
O
N
N
-
O
O
E
F
1 3

Peptide Nanofiber Templated Zinc Oxide Nanostructures as Non-precious Metal Catalyzed…
Funding This work was supported by Ilam University
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