A tyrosine-rich peptide induced flower-like palladium nanostructure and its catalytic activity

Article abstract of DOI:10.1039/c5ra11817d

A specifically designed peptide, Tyr-Tyr-Ala-His-Ala-Tyr-Tyr (YYAHAYY), induced the formation of a flower-like palladium (Pd) nanostructure by controlling the size and shape of nanoparticles (NPs). The flower-shaped Pd NPs showed excellent catalytic activ

Full text of DOI:10.1039/c5ra11817d

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Tyrosine-rich peptide induced flower-like palladium
nanostructure and its catalytic activity
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
a
b
Young-O Kim,‡ Hyung-Seok Jang,‡ Yo-han Kim, Jae Myoung You, Yong-Sun Park, Kyoungsuk
b
c
b
c
d
a
Jin, Onyu Kang, Ki Tae Nam, Jung Won Kim,* Sang-Myung Lee* and Yoon-Sik Lee*
DOI: 10.1039/x0xx00000x
www.rsc.org/
A
specifically designed peptide, Tyr-Tyr-Ala-His-Ala-Tyr-Tyr control the size and stability of Pd NPs, His was inserted at the
(
YYAHAYY), induced the formation of flower-like palladium (Pd) center of the peptide sequence. His can coordinate with several
1
9
nanostructure by controlling the size and shape of nanoparticles transition metal ions and nucleate the formation of metal NPs.
(
NPs). The flower-shaped Pd NPs showed excellent catalytic We inserted His between the two Tyrs to control the size of Pd NPs
activities in copper-free Sonogashira cross-coupling reaction in by the peptide folding. As it turned out, Pd NPs (4-5 nm size) with
water.
flower shapes can be synthesized by Tyr-H7mer in water.
Nature determines protein structures by arranging amino acid
sequences through genetic controls. The protein tertiary structures
can control the exquisite sizes and morphologies of inorganic hybrid
1
structures with high reproducibility under physiological conditions.
For example, homogeneous iron oxide nanoparticles (NPs) (about
2
8
~9 nm) are formed inside hollow polypeptide ferritin shells. We
speculated that not only the self-assembly of peptides but also the
interaction between the peptides and metal ions is a key factor in
fabricating organic-inorganic hybrid nanostructures. By mimicking
3
-5
6-8
9-11
12-14
this biological process, various metal (Au, Ag, Pd, Pt
and
1
5, 16
Cu
) NPs have been developed by using peptide templates with
controllable geometrical, physical and chemical parameters.
However, understanding the design rule for peptide sequences still
remains a challenge.
We designed a heptapeptide, Tyr-Tyr-Ala-His-Ala-Tyr-Tyr (YYAHAYY)
(
Tyr-H7mer), to synthesize Pd NPs under ambient conditions. In our
17
previous study, we reported that Tyr-containing peptides could be
assembled into several nanostructures and at least two consecutive
Tyrs were necessary for the peptide assembly. The Tyr also has a
1
8
potential as a bio-catalyst due to its redox active property. To
Fig. 1 (a) Schematic illustration of the formation of Pd nanoflowers covered
by peptides. (b-f) HR-TEM/EDS mapping images of Pd NFs. The
homogeneous distributions of palladium (c), nitrogen (d), oxygen (e) and
merged one (f). (g) TEM images of Pd nanoflowers obtained by using the
Tyr-H7mer as a template without reducing agent.
Among numerous metals, Pd has attracted much interest as an
excellent catalyst for C-C cross coupling reactions, which are key
reactions to produce fine chemicals such as dyes, pharmaceutical
2
0
and agricultural intermediates, and so on. The Pd catalysts can be
2
+
0
used in the form of Pd coordinated with ligands or metallic Pd .
Regarding Pd NP catalysts in particular, it is essential to precisely
control the surface morphology of Pd nanostructures to improve
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21
the catalytic activity. Here, we apply a biomimetic synthesis of Pd The assembly mechanism for Tyr-H7mer during the formation of Pd
NPs using a newly designed peptide template. The resulting Pd NPs NFs was identified by circular dichroism (CD) and Fourier transform-
were used as eco-friendly heterogeneous catalysts for copper-free infrared (FT-IR) spectroscopy (Figure 3a). The richness of Tyr
Sonogashira C-C cross coupling reactions. The catalytic reaction was residues in our peptide sequence affected the entire pattern of the
1
7
performed in an aqueous medium and under mild conditions (65-75 CD spectra. The positive peaks at 202 and 227 nm are originated
o
C) with high conversion.
from the contributions of the phenolic side chains of the Tyr
2
+
Figure 1a illustrates the scheme for the formation of Pd residues. After adding Pd , the peak at 227 nm increased positively
2
+
nanoflowers with Tyr-H7mer. Pd ions are coordinated with His and was slightly red-shifted. The peak shifts of the Tyr residues
2
+
24, 25
residues of Tyr-H7mer in water, resulting in peptide folding. We indicate that Pd ions are involved in peptide ordering. The
found that the hydrophobic nature of the Tyr-H7mer/Pd complex negative peak at 190 nm was reduced and shifted to 195 nm. It
2
+
2
+
accelerated the peptide assembly and the Pd ions were gradually seems that the alpha helical conformation of Tyr-H7mer is affected
2
+
reduced to Pd NPs. During the reduction process by ascorbic acid as by Pd mediated peptide assembly. In addition, the amide I band
-1
a reducing agent, the color of the Tyr-H7mer/Pd solution turned region (Figure 3b, 1600-1700 cm ) was analysed to identify any
from pale yellow to dark brown. The UV/Vis spectra also showed conformational changes of the Tyr-H7mer during the assembly
2
6, 27
the absorption changes during the formation of Pd NPs by Tyr- process.
As shown in Figure 3b, the alpha helical peak at 1670
-1
-1
H7mer in water (Figure S1 in Supporting Information). As shown in cm was shifted to 1633 cm , which corresponds to the beta sheet
2
+
2+
-1
Fig. S1, the absorbance peak of Pd at 207 nm gradually decreased structure. After the reduction of Pd , the 1633 cm peak was
-
1
and broadened during the formation of the Pd NPs.
shifted slightly to 1628 cm .
Transmission electron microscopy (TEM) analysis revealed that
uniform sized Pd NPs (4-5 nm) were assembled into flower-like
shapes with our heptapeptides (Figure 1b). The EDS elemental
mapping showed the distributions of Pd, N and O on the surface of
Pd nanoflowers (NFs) (Figure. 1c-f). Interestingly, the final
morphologies of Pd NPs seemed to be dependent on the central
amino acid in our peptide sequence. When His was substituted with
Ala to produce YYAAAYY (Tyr-A7mer), irregular shaped Pd nano-
aggregates were formed (Figure S2). His could play an important
2
+
role in peptide assembly with Pd ions because the imidazole group
of His can bind strongly with metal ions. Thus, the His residues of
the peptides provided the nucleation sites for Pd NFs formation
10
before nucleation and growth of Pd NPs. The sizes of Pd NFs were
between 39 and 100 nm, with an average of 66 nm ± 5 nm (Figure
S3). The Pd NPs could also be formed without adding any reducing
agents. However, it took a very long time to form Pd NFs (4 weeks
at room temperature) (Figure 1c). This seems to be related to the
Fig. 3 a-b, Spectroscopic data for confirming peptide structural changes.
2+
Peptide, Pd /peptide complex, and reduced Pd NF produced by using
2
2
weak reducing activity of Tyr residues.
peptide are indicated by line, dotted line, and dash line, respectively. (a) CD
spectra of peptide changed by each steps (b) The FTIR spectra of peptide
changed by each step. AmideⅠ band peaks are marked with star (*).
Histidine-related peaks are marked with circle (•) (c) Proposed mechanism
2
+
based on FTIR data focusing on interaction between Pd and histidine
residue in peptide
We could also confirm the interaction between the His residue and
2
+
Fig. 2 (a) HR-TEM image of Pd nanoflowers. (b) HR-TEM image recorded
from the particle (ca. 4 nm) marked by a red square in (a). (c) PXRD pattern
of the Pd nanoflower. Pd peaks are indicated with a star (*).
the Pd ion by analysing FT-IR spectra of various protonated forms
2
8
+
2
of the His side chain (imidazole group). The His peak (HisH ) at
-1
-1
1635 cm of free Tyr-7Hmer in water was shifted to 1578 cm after
the formation of Pd NFs, indicating the removal of one proton from
+
2+
2
The Pd NF was further characterized by high resolution transmission HisH . Afterward, the reduction of Pd caused the peak to further
-1
electron microscopy (HR-TEM) and powder X-ray diffraction (XRD) shift to 1562 cm . It may be possible that the His residue interacts
to identify the structure (Figure 2). The lattice structure of a single with the closest His residue in the vicinity to produce dimers
Pd particle in the Pd NF indicates the (111) plane of Pd (d-spacing at connected by hydrogen bonds. Considering all these, we believe
2
+
0
.23 nm) (Figure 2b and Figure S4). The Powder XRD pattern shows that the Tyr-H7mer can act as a template for organizing the Pd
the crystallinity of Pd NFs. As shown in Figure 2c, peaks at 40.1°, ions to form Pd NFs.
6.8°, 68°, 82.2°, and 86.4° correspond to the results indexed to the For atom efficiency and sustainability, a mild reaction condition for
111), (200), (220), (311), and (222) lattice planes of face-centered the Sonogashira cross-coupling reaction without using Cu(I) co-
4
(
2
3
cubic (fcc) Pd.
catalysts and phosphine ligands has been pursued. Fortunately, the
Pd NFs have ideal properties as a catalyst for the Sonogashira cross-
2
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coupling reaction under ambient aerobic conditions; accelerating
Acknowledgement
0
oxidative addition of Pd with aryl halide by peptide ligand having
This work was supported by Samsung Research Funding Center of
Samsung Electronics under Project Number SRFC-MA1401-01.
29
steric and proper electronic property, and enhancing the
3
0
formation of arylalkynylpalladium species
.
a
Table 1. Aqueous copper-free Sonogashira cross-coupling reaction using Pd NFs.
Notes and references
b
Yield
Entry
1
Aryl halide
Alkyne
Product
1
2
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Reactions were performed using 0.5 mmol substrate, 2.5 eq. triethylamine, and
b
0
.5 mol% Pd NFs in water (10 mL). Determined by GC-MS through the corrected
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reaction catalyzed by Pd NFs was successfully performed in an
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generated the corresponding products in 96 % and 81 % yields,
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4
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nanostructure with a flower-like morphology using the Tyr-H7mer
peptide template. The peptide folding and the interaction of Pd ions
with His residues in the Tyr-H7mer are crucial for the nucleation
and growth of Pd NPs to the Pd NFs. The Pd NFs are very reactive in
copper-free Sonogashira cross-coupling reactions in an eco-friendly
water solvent system. We demonstrate that controlling the
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