Synthesis of peptide nanofibers decorated with palladium nanoparticles and its application as an efficient catalyst for the synthesis of sulfides: Via reaction of aryl halides with thiourea or 2-mercaptobenzothiazole

Article abstract of DOI:10.1039/c6ra02264b

In this work supported Pd nanoparticles on a peptide nanofiber (PdNP-PNF) have been prepared via fabrication of self-assembled woven nanofiber from peptide, subsequently immobilization of palladium nanoparticles on this nanostructural compound. To obtain self-assembled woven nanofiber, we designed and synthesized a peptide using arginine as building block. The C-terminus of amino acid was protected as ethylester. Coupling was mediated by dicyclohexylecarbodiimide-1-hydroxybenzotriazole (DCC-HOBT). TEM, SEM, XRD, ICP and FT-IR techniques were employed to characterize prepared nanofiber materials. In this work, the effect of phosphate buffer solutions pH 8 and pH 11 (isoelectric point of arginine amino acid) on the structure of peptide nanofiber was investigated. Supported Pd nanoparticles on the peptide nanofiber (PdNP-PNF) were applied for the C-S coupling reaction using two different sulfur transfer reagents (thiourea and 2-mercaptobenzothiazole).

Full text of DOI:10.1039/c6ra02264b

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ARTICLE
Synthesis of peptide nanofibers decorated with
palladium nanoparticles and its application as an
http://pubs.rsc.org/en/content/articlela
nding/2016/cy/c5cy01276g#!divAbstrac efficient catalyst for the synthesis of sulfides via
thttp://pubs.rsc.org/en/content/articlel
anding/2016/cy/c5cy01276g#!divAbstra reaction of aryl halides with thiourea or 2-
cthttp://pubs.rsc.org/en/content/article
landing/2016/cy/c5cy01276g#!divAbstr mercaptobenzothiazole
actCite this: DOI: 10.1039/x0xx00000x
∗
Arash GhorbaniꢀChoghamarani and Zahra Taherinia
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
In this work supported Pd nanoparticles on the peptide nanofiber (PdNPꢀPNF) has been
prepared via fabrication of selfꢀassembled woven nanofiberfrom peptide, subsequently
www.rsc.org/
immobilization of palladium nanoparticles on this nanostructural compound. To obtain
selfꢀassembled woven nanofiber, we designed and synthesized a peptide using arginine as
building block. The Cꢀterminus of amino acid was protected as ethylester. Coupling was
mediated by dicyclohexylecarbodiimideꢀ1ꢀhydroxybenzotriazole (DCCꢀHOBT). TEM, SEM,
XRD, ICP and FTꢀIR techniques were employed to characterize prepared nanofiber materials.
In this work, the effect of phosphate buffer solutions (pH 8 and pH 11 (isoelectric point of
arginine amino acid) on the structure of peptide nanofiber was investigated. Supported Pd
nanoparticles on the peptide nanofiber (PdNPꢀPNF) were applied for the C–S coupling
reaction using two different sulfur transfer reagents (thiourea and 2ꢀmercaptobenzothiazole).
∗Address correspondence to A. GhorbaniꢀChoghamarani, Department of Chemistry,Ilam University, P.O. Box
6
9315516, Ilam, Iran; Tel/Fax: +98 841 2227022; Eꢀmail address: arashghch58@yahoo.comor
a.ghorbani@mail.ilam.ac.ir
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1
Introduction
Production of nanofibers ranging from micron to Therefore, nanofibers, are irrespective of their method
nanometer scales have been studied due to their special ofsynthesis. Among different nanoparticles, selfꢀ
properties such as up grading human artificial tissue assembling peptides are the best choice due to unique
1
2
3
4
including bone , cartilage , ligament , skeleton muscle , properties such as high surface areaꢀtoꢀvolume and they
5
6
7
skin , vascular tissue engineering , neural , and as carriers are desirable in order to allow delivery of a high density of
for the controlled delivery , protines and controlled DNA cells and tissue engineering. Among the applications of
delivery. Nanofiber can be produced in many different peptide nanofiber, their catalytic applications in organic
8
9
1
0
11
12
ways,
for
example
selfꢀassembly ,
drawing , reactions have attracted extensive attention; for example
1
3
14
20
electrospining , template synthesis . Among these IndrajitMaity reported the fabrication of peptide capped
methods, electrospinning is a wellꢀknown technique to Pd nano particles, which enhanced the catalytic activity of
2
1
make a layer of nanofibers. In this layer, though, each C–C coupling reactions in aerobic conditions. Khalily
nanofiber cannot be separated without their destruction and reported a supramolecular peptide nanofiber templated Pd
electrospinning needs larger electric fields, sensitivity to nano catalyst for efficient Suzuki coupling reactions under
2
2
variability in solution conductivity and low production aqueous conditions. Shao reported coupling reactions of
speed. Template synthesis is an efficacious route to aromatic halides in the presence of palladium catalyst
produce nanofibers or nanotubes using a nanoporous immobilized on poly (vinylalcohol) nanofiber. We
membrane as a template. Yet,
a
disadvantage of this demonstrate for the first time, the use of peptide nanofibers
method is that it cannot make continuous nanofibers one decorated with Pd nanoparticles with sizes ranging from
by one. However, the template method is possible by 7.1 to 10.28 nm for the C–S coupling reactions using two
controllingparameters such as melt time and temperature. different sulfur transfer reagents. Sulfides have shown
Selfꢀassembling is a procedure by which molecules widely applications as potent drugs for HIV , cancer ,
organize and arrange themselves into patterns or structures Alzheimer and Parkinsons diseases. They are useful
through nonꢀcovalent forces such as hydrogen bonding, compounds in chemistry due to their role as important
23
24
2
5
26
2
7
hydrophobic forces, and this technique shows good intermediates in organic synthesis. Therefore, there is
potential for designing novel scaffolds for tissue still a great interest to find a new reagent or system to
engineering applications. Several factors including, the synthesis sulfides. Herein, we present for the first time the
concentration of peptide molecules, pH, solvent polarity, crossꢀcoupling reactions of aryl/alkyl halides using 2ꢀ
sonication, ionic strength and interaction with anions such mercaptobenzothiazole or thioureaas efficient sulfur
as phosphate have been used to tune the peptide selfꢀ transfer reagent to afford symmetrical sulfides, which has
15
assembly process. DaꢀWei. indicated that the selfꢀ been catalyzed by immobilized palladium nanoparticles on
assembling process is enhanced at a low concentration of peptide nanofiber.
phosphate and the length of the fibrils is longer than that in
16
pure water. Goldberger. designed a series of PAs that can 2 Results and discussion
selfꢀassemble into nanofibers when the solution pH is In this work, to achieve an efficient and simple nanofiber
decreased from the normal physiological condition 7.4 to support we performed the selfꢀassembly of a peptide with
1
7
6
.6, Smith. saw that the overall length of the nanofibers arginine as building block. After converting of this peptide
increased as the initial concentrationof insulin peptide into nanofiber, palladium nanoparticles were immobilized
1
8
increased. Prabhu has shown that ultrasonicationꢀinduced on the surface of this nanostructural compound (Scheme 1).
fibrilꢀformation by
1
9
a
bolaform peptide. Shen
demonstrated solventeffects for dissolved βꢀamyloid in
different solvents of various concentrations, and found that
the growth rate of the nanofibers was reduced. In the case
of 100% dimethyl sulfoxide, no βꢀsheet content is visible,
but in 10% dimethyl sulfoxide, nanofibers are seen to
contain the rigid, hydrogenꢀbonded βꢀsheet structure.
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Scheme 1 Schematic synthesis of Pd nanoparticles supported on the peptide nanofiber.
We studied a simple, economic and environmentally woven morphology of the nanofiber was observed in the
friendly approach to the selfꢀassembly of a peptide using SEM image (Fig. 4). The pH effect can be explained since
+
ꢀ2
ꢀ
phosphate buffer solutionin an aqueous media. Since one a high pH environment dissociates H of HPO /H PO , it
4 2 4
way to control the density and growth rate of nanofibers is is known that one divalentanion have a charge of ꢀ2 and
through the use of the solvent that destabilize the peptide can effectively interact with two positively charged groups
structure, so we decided to use water as selfꢀassembling of the peptide molecule like a bridge. Since distance
media because when we used peptide powder, no obvious between two nearest arginine resides of the same peptide
ꢀ2
selfꢀassembly of nanofiber was observed in the SEM molecule is much larger than the size of HPO , one
4
image (Fig. 1). Since the peptides formed various divalent anion can hardly interact with two arginine
hydrogels depending on amino acids charges, therefore we residues simultaneously, which leads to form a short
investigate the effect of phosphate buffer solution at pH 8 nanofibers aggregated before the peptide molecules selfꢀ
and pH 11 (isoelectric point of arginine amino acid) on the assembled to grow longer nanofibers.
structure of peptide nanofiber. The pH value was changed
2ꢀ
ꢀ
by adjusting the ratio of [HPO ]/ H PO ] while keeping
4
2
4
the total concentration of phosphate constant. The effect of
pH 11 solution was evaluated in two ways: i) when peptide
solution was investigated at the pH 11 without adding
succinic anhydride, colloidal solution was formed and no
obvious selfꢀassembly was observed in the scanning
electron microscopy image (Fig. 2), ii) when succinic
anhydride added to the peptide solution, the final pH of the
solution was found to be 10 due to hydrolysis of succinic
anhydride to succinic acid, microscopic images showed the
formation of microꢀcrystals (Fig. 3). Surprisingly, at pH 8
by adding succinic anhydride to the peptide solution,
which the final pH of the solution was found to be 7, the
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succinic anhydride.
Fig. 1 SEM images of powder peptide
Fig. 3 SEM images of peptide solution
at pH 11 in the presence of succinic
anhydride
Fig. 4 SEM image of peptide solution at pH 8
In the presence of succinic anhydride
Fig. 2 SEM images of solution
peptide at pH 11 without adding
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When the pH is raised to 11, it results in a negative The selfꢀassembly study of the peptide was investigated
deprotonated carboxylate of arginine and one positive using various spectroscopic and microscopic techniques.
protonated nitrogen atom (the arginine residue to be FTꢀIR spectroscopy was used to study the structure of the
ꢀ
1
natural), thus, there is no electrostatic interaction between nanofiber solution; a peak that appear at 1644cm is
ꢀ2
HPO4 ion and arginine residues of the peptide molecule. correspondence to bending vibration of NH groups, while
ꢀ1
But, when pH changes to 7, it results in a negative this peak for the peptide powder appear at 1629 cm , the
deprotonated carboxylate and two positive protonated observed shift is probably due to signifies selfꢀassembling
nitrogen atoms (overall charge of +1) (Scheme 2). Since and hydrogen bonding between phosphate and peptide. As
one monovalavet anion takes one negative charge and can a general rule, hydrogen bonding decreases the frequency
interact with one positively charged groups of the peptide of stretching vibrations, since it decreases the restoring
molecule therefore the monovalent ions can distribute the force, but increases the frequency of bending vibrations
2
8
charges between the polar head groups to reduce since it produces an additional restoring force
.
(Fig. 5).
electrostatic repulsion, which makes the more ordered
nanoꢀfibrils (Scheme 3). However increase of pH value
The SEM images show that the peptide molecules selfꢀ
assembled into woven nanofiber structures (Fig.4).
2
9
2ꢀ
results in the increase of [HPO ], which makes conditions
4
unfavorable for the formation of nanofiber network. But at
ꢀ2
pH 7 the concentration of the HPO4 is lower than the
ꢀ
concentration of the monovalent anion H PO ; therefore
2
4
the monovalent anions play a major role in the shielding of
charges on the peptide molecules.
PH=7
PH=11
H
O
O
H
H N
O
2
H N
3
O
N H
N H
NH2
NH2
NH2
NH2
+
1ꢀ1=0
+
1+1ꢀ1=+1
Scheme 2 Arginine.amino acid charge at the pH 7 and 11
Fig. 5 FTꢀIR spectra of peptide powder (blue line); the peptide
nanofiber (red line)
2
.2 Characterization of supported Pd nanoparticles on the
peptide nanofiber
The effect in the secondary structure of the peptide via the
interaction between the metal nanoparticles and peptide
was considered by FTꢀIR, SEM and TEM analysis. In the
IR spectrum of supported Pd nanoparticles on the peptide
nanofiber, the bending vibration of NH groups appeared at
ꢀ1
1
648 cm (Fig. 6). The SEM and TEM images show that
the Pd nanoparticles were regularly immobilized on the
surface of woven peptide nanofibers (Fig. 7). The amount
of Pd incorporated into the nanofiber found to be 250 ppm
that determined by inductively coupled plasma optical
emission spectrometry (ICPꢀOES). Xꢀray diffraction
patterns of peptide nanofibers decorated with palladium is
Scheme 3 Schematic illustration of the proposed mechanism for the
templateꢀfree formation of woven nanofiber in an aqueous solution
shown in (Fig. 8). The strong diffraction peaks about at
30ꢀ31
2
Ɵ values of 41
º, 47
º
, and 69
º
is related to Pd (0)
2
.1Characterizationof peptide nanofiber
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nanoparticles; also the other peaks related to peptide
nanofiber structure.
Fig. 6 FTꢀIR spectra of the peptide solution without Pd nanoparticles
(
(
black line), peptide nanofibers decorated with Pd nanoparticles
blue line).
Fig. 7 (a) SEM image of immobilized Pd nanoparticles on the
surface of the woven nanofibers; (b), (c), (d) (e) and (f) TEM surface
of the woven nanofibers at pH 8.
Fig. 8 The Xꢀray diffraction pattern of Pd immobilized on peptide
nanofibers
2
.3 Catalytic studies
After preparation and characterization of Pd nanoparticle
supported on the peptide nanofiber catalytic activity of this
compound was investigated for CꢀS coupling reaction. A
variety of symmetrical aryl/alkyl sulfides can beobtained
in moderate to excellent yields (up to 90%). In this work
thiourea and 2ꢀmercaptobenzothiazole(as
a
new
heterocyclic sulfur donor) has been utilized for the direct
synthesis of organic sulfides from aryl/alkyl halides in the
presence of a peptide nanofibers decorated with Pd
nanoparticles (PdNPꢀPNF) that effectively led to the
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production of sulfides in high yield. In order to optimize
the reaction conditions, the reaction of iodobenzene with
2
ꢀmercaptobeczothiazole in the presence of PdNPꢀPNF has
Entry Solvent
Temp. Base
(ºC)
Time Yield
b
been selected as model reaction and different parameters
including the type of base, solvent and temperature has
been studied (Table 1). It was found that the base and
solvent significantly influenced the outcome of CꢀS
coupling reaction. Also, the reaction rate was increased by
rising reaction temperature. With optimal conditions in
hand, a variety of symmetrical diaryl/alkyl sulfides were
(h)
(%)
1
2
DMSO 130
KOH
2
90
DMF
130
KOH
KOH
KOH
KOH
KOH
NaOH
2
2
2
2
2
2
2
2
N.R
N.R
N.R
N.R
N.R
43
3
4
5
6
7
8
9
PEG
130
CH CN 130
3
synthesized
mercaptobenzothiazole at 130 °C with high purity (Table
). Also, resulting optimized generally, the CꢀS coupling
using
1.3
equivalents
of
2ꢀ
H O
2
130
130
2
reactions of aryl halides with electron with drawing groups
preceded more rapidly and high yields of products have
been obtained. However, the CꢀS coupling reaction
including aryl chlorides showed less reactivity than that of
aryl iodides and bromides.Suggested mechanism for these
transformations has been illustrated in Schemes 4 and 5.
Iinitially aryl halide reacts with Pd by oxidative addition to
form intermediate (a), then the intermediate (a) reacts with
EtOH
DMSO 130
DMSO 130
DMSO 130
2
K CO3
N.R
N.R
Na CO3
2
1
1
0
1
DMSO 130
DMSO 130
Et N
3
2
2
N.R
N.R
2
ꢀmercaptobeczothiazole to produce intermediate (b),
which is transformed into thiol anion in the presence of
KOH. Then thiol anion reacts with intermediate (a) via
reductive elimination reaction to afford sulfide and
releases palladium nanoparticle. It should be noted that
GraciaꢀEspono et al reported when thiolated substrates are
used, such as SꢀrGOx, the Pd nanoparticles exhibit smaller
sizes, improved spatial distribution, and poor or null
agglomeration because of the stronger interaction with the
thiolated graphene surface. The thiol bridges play an Finally, the recoverability and reusability of the Pd
active role in the adsorption mechanism of the Pd cluster, nanoparticle supported on the peptide nanofiber in the
which would increase the reactivity. During the theoretical synthesis of sulfides via reaction of iodobenzene with
studies GraciaꢀEspono et al observed the following thiourea over four successive runs, was investigated.
NaOEt
1
2
DMSO 100
KOH
KOH
2
2
63
13
DMSO
80
trace
mmol,
a
Reaction
conditions:
iodobenzene
1
2ꢀ
b
mercaptobenzothiazole 1.3 mmol, PdNPꢀPNF (200µL), base .1 gr,
Isolated yield.
32
chemical reactions:
Reaction was performed in DMSO at 130 °C, using 1
mmol iodobenzene, 1 .3 mmol thiourea and 1 gr KOH in
the presence of PdNPꢀPNF (200µl), upon completion of
the reaction, the mixture was cooled to room temperature.
(
(
(
1) C H SH + rGOxꢀVc → rGOx−H−S−C H
7
7
7
7
2)C H SH + rGOx−OH → rGOx−S−C H + H O
7
7
7
7
2
3) C H SH + rGOx−NH → rGOx−S−C H + NH
7
7
2
7
7
3
The chemical reaction shown in eq 1 was observed during
the first adsorption event, while the chemical reactions in
2
0 mL of ethyl acetate was added to the reaction mixture,
which led to the precipitation of PdNPꢀPNF. The resulting
precipitate was washed twice with ethyl acetate (2 x 10
mL), dried and applied for the next run. It was found that
Pd NPꢀPNF could be reused at least four times without a
significant loss of its catalytic activity.
3
0
eqs 2 and 3 were not observed until Pd13 adsorption .
Thus, according to results we can conclude that thiol anion
is more willing to react with palladium. Because otherwise
if that reacts with functional groups on the surface of
peptide, no disulfide could be synthesized in eq 4.
Table 1 Optimization of the reaction conditions for the CꢀS coupling
a
using 2ꢀmercaptobenzothothiazol as sulfur transfer agent.
Fig. 8 Reusability of the Pd immobilized on peptide nanofiber
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for the synthesis of symmetrical sulfides via reaction of thiourea
with iodobenzene
the reaction mixture, and 0.5 g (5 mmol) Nꢀmethyl
morpholine was added to this mixture. The reaction mixture
was stirred for overnight. After completion, ethyl
In order to evaluate the catalytic activity of peptide
nanofibers decorated with palladium nanoparticles, we
compared the results for the synthesis of diphenyl sulfide
in the presence of described catalyst with previously
reported methods in the literature (Table 4). This catalyst
leads to good reaction time and higher yield than the other
acetate (50 mL) was added to the reaction mixture.
Solvent was removed under reduced pressure to yield
ꢀ1
compound 1 as a white solid. FTꢀIR (KBr) νmax/cm :
3
608, 3566, 1718, 1648.
catalysts.
More importantly, compared with other
Synthesis of compound 2
.917 g (3.5 mmol) of compound 1 in 3 mL of DMF was
catalysts, PdNPꢀPNF is easily prepared and can be reused
at least four times without any significant loss of its
catalytic activity.
0
cooled in an iceꢀwater bath then arginine ethyl ester in
ethyl acetate (10 mL) was added to this mixture, which
was isolated from 1.72 g (7 mmol) of arginine ethyl ester
hydrochloride via neutralization. Then 0.68 g (3.85 mmol)
DCC and 0.520 g (3.85 mmol) of HOBt was added to this
mixture. The reaction mixture was stirred for overnight.
Then ethyl acetate (50 mL) was added and the DCU was
filtered off. The filtrate was washed with sodium
carbonate solution to yield compound 2 as a white solid.
s.
4
Conclusions
In summary, we demonstrate an effective route to fabricate
peptide nanofiber in an aqueous solution using phosphate
buffer solutions with pH 8. This peptide nanofiber was
used as nano support to immobilized palladium
nanoparticles. PdNPꢀPNF with special properties such as
large specific surface area and with sizes ranging from 7.1
to 10.28 nm was use as catalyst for the synthesis of
alkyl/aryl sulfides. We describe for the first time the
ꢀ1
FTꢀIR (KBr) νmax/cm : 3336, 3173, 2931, 2855, 1735,
1
660, 1526, 1460, 1380, 1303, 1223, 1174, 1104, 1025.
5
.3 Synthesis of compound 3
To the 1.31 g (2.7 mmol) of compound 2,in 6 mL EtOH in
a round bottom flask, 2M NaOH (2mL) was added drop
wise. The reaction mixture was stirred for overnight. Then
reactivity
of
2ꢀmercaptobenzothiazoleas
a
new
heterocyclic sulfur transfer agent for direct synthesis of
symmetric sulfides with aryl/alkyl halides in the presence
of this peptide nanofiber decorated with Pd nanoparticles
5
mL of distilled water was added to the reaction mixture
and EtOH was removed under vacuum. The residue was
washed with diethyl ether (2 x 30 mL). Then it was cooled
down under iceꢀwater bath for 10 minute and then pH was
adjusted to 1 by drop wise addition of 1 M HCl. Then ethyl
acetate (50 mL) was added and filtered off. The filtrate
was washed with sodium carbonate solution to yield
5
Experimental
5
.1 Preparation of arginine ethyl ester hydrochloride
Thionyl chloride (6.0 mL, 82.1 mmol) was added via
dropping funnel to a stirred suspension of arginine (9.03 g,
5
4.7 mmol) in Ethanol (100 mL) at0 °C. The mixture
ꢀ
1
compound 3 as a white solid. FTꢀIR (KBr) νmax/cm
wasstirred for 24 h at room temperature, and then solvent was
removed. The crude product was recrystallized from EtOAc
:
3
1
440, 3288, 3176, 2978, 1706, 1641, 1571, 1453, 1413,
339, 1053, 1021.
/
EtOH (95:5) to give a white solid of the title compound
33
ꢀ1
melting pointꢀ 46ꢀ48°C , FTꢀIR (KBr) ν /cm : 3428,
max
5
.4 Preparation of peptide nanofiber (PNF)
3
190, 2876, 2940, 2874, 1735, 1658, 1735.
In our experiment 30.14 mg (0.04 mmol) of peptide was
dissolved in 0.2 mL of doubly distilled water and 0.8 mL
phosphate buffer solution (pH 8). Then 32 mg (0.31 mmol) of
succinic anhydride were added to the peptide solution. The
mixture sonicated for a few minutes, and then heated at 80°C
overnight to form nanofiber solution.
5
0
.2 Synthesis of compound 1
.5 g (5 mmol) Succinic anhydride in 3 mL of DMF were
cooled in an iceꢀwater bath and in another round bottom flask,
.235 g (5 mmol) of arginine ethyl ester hydrochloride was
1
neutralized in ethyl acetate (10 mL), which was then added to
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Table 2 Synthesis of symmetrical sulfides via reaction of 2ꢀmercaptobenzothiazole and aryl/alkyl halides catalyzed by peptide nanofibers
a
decorated with Pd nanoparticles (PdNPꢀPNF) in DMSO.
b
Yield
Entry
1
ArꢀX
Product
S
Time (h)
(
%)
I
5
92
87
43
63
Br
S
S
S
S
2
3
4
6
Cl
12
8.5
I
Me
Me
Me
Me
Me
Me
Br
5
6
10
1
57
83
Br
S
S
N
N
N
I
7
25 min
55
O N
O N
NO2
2
2
Br
I
S
S
8
9
50 min
41
61
O N
O N
NO2
2
2
7
HO
HO
OH
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Br
S
1
1
0
1
9
2
53
92
HO
HO
OH
OMe
OMe
S
OMe
I
I
1
1
2
3
10
70
83
S
a
Br
S
Reaction
1
b
conditions: aryl halides (1 mmol), 2ꢀmercaptobenzothiazole (1.3 mmol), PdNPꢀPNF (200µL), base (1 gr) and DMSO (2 mL). Isolated yield.
Table 3 Synthesis of symmetrical sulfides via reaction of thiourea and aryl/alkyl halides catalyzed by peptide nanofibers decorated with Pd
a
nanoparticles (PdNPꢀPNF) in DMSO.
b
Time
Yield
(%)
Entry
1
ArꢀX
Product
S
(
h)
I
2
95
88
47
Br
S
S
2
3
3
Cl
10
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DOI: 10.1039/C6RA022 B
S
S
I
4
5
7
9
65
55
Me
Me
Me
Me
Me
Br
Me
Br
S
3
0
6
7
87
55
min
N
N
N
I
S
1
0
O N
O
2
N
NO2
min
2
S
Br
4
0
8
9
50
O N
2
NO2
O N
min
2
I
S
S
6
67
53
HO
HO
HO
HO
OH
OH
Br
1
0
1
9
OMe
OMe
OMe
S
I
1
2
92
I
1
1
2
3
10
70
83
S
Br
S
1
a
b
Reaction conditions: aryl halides (1 mmol), 2ꢀmercaptobenzothiazole (1.3 mmol), PdNPꢀPNF (200µL), base (1 gr) and DMSO (2 mL).
Isolated yield.
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Scheme 4. Proposed mechanism for the synthesis of sulfides through crossꢀ coupling reactions of aryl halides with 2ꢀmercaptobenzothiazole
catalyzed by peptide nanofibers decorated with Pd nanoparticles.
Scheme 5 Proposed mechanism for the synthesis of aryl sulfides through crossꢀcoupling reactions of aryl halides with thiourea catalyzed by
peptide nanofibers decorated with Pd nanoparticle.
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Table 4. Comparison of PdNPꢀPNF for the synthesis of diphenyl sulfide
with previously reported procedures
Entry
Catalyst
Yield
Time
(h)
Ref.
a
(
%)
1
2
MCMꢀ41ꢀ2NꢀCuI
CuO nanoparticles
Trace
48
37
38
70
15
20
21
15
3
3
4
5
6
Nano copper oxide
CuI
63
N.R
85
39
40
41
Pd
2
(dba)
3
/Xantphos
PdNPꢀPNF
88
This
work
a
Isolated yield
1
Yellow liquid; H NMR (CDCl , 400 MHz) δ
3
1
3
5
.5 Synthesis of Pd nanoparticle supported on
(ppm)= 6.88ꢀ7.30 (m, 8H), 3.87 (s, 6H); C NMR
(CDCl , 100 MHz), δ (ppm)= 157.7, 132.5, 128.4,
122.3, 121.3, 110.8, 55.8.
the peptide nanofiber (PdNP-PNF)
3
Peptide 30.14 mg (0.04 mmol) was dissolved in 0.2
mL in doubly distilled water and 0.8 mL phosphate
buffer solution (pH 8) was added. Then solution
was sonicated for a few minutes. This mixture was
stirred overnight at 80 °C. In the next step
3
6
Bis-(1-naphthyl) sulfide White solid, m.p. 156ꢀ
1
158 °C; H NMR (CDCl
7.47ꢀ8.49 (m, 2H), 7.37ꢀ7.94 (m, 12H); C NMR
(CDCl , 100 MHz) δ (ppm)=134.2, 132.7, 132.6,
3
, 400 MHz) δ (ppm)=
13
Pd(OAc)
reaction mixture and stirred for 12 hour at 80 °C,
then NaBH (6 mg, 0.15 mmol) was added and the
2
(2.5 mg, 0.01 mmol) was added to
3
130.0, 128.7, 128.0, 126.5, 126.3, 126.0, 125.1.
4
mixture kept under stirring for 2h to obtain PdNPꢀ
PNF quantitatively.
Acknowledgements
Authors thank the research facilities of Ilam
University, Ilam, Iran, for financial support of this
research project.
5
.6 General procedure for the sulfides synthesis
A round bottom flask was charged with of 1.3
mmol of thiourea or 2ꢀmercaptobenzothiazole,
1
mmol aryl/alkyl halide, 1 g KOH, 200µL of the
solution containing Pd nanoparticle decorated on
nanofibers and DMSO (2mL). Then reaction
mixture was stirred at 130°C. The progress of
reaction was monitored by TLC. After reaction
completion, the mixture was extracted with
dichloromethane (2×20 mL). The organic extract
was washed twice with water and dried with
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Synthesis of peptide nanofibers decorated with palladium
nanoparticles and its application as an efficient catalyst for the
synthesis of sulfides via reaction of aryl halides with thiourea or 2-
mercaptobenzothiazole
Arash Ghorbani-Choghamarani* and Zahra Taherinia