Decoration of Au and Ag nanoparticles on self-assembling pseudopeptide-based nanofiber by using a short peptide as capping agent for metal nanoparticles

Article abstract of DOI:10.1021/ol0708471

The surface of a nanofiber that is formed from a self-assembling pseudopeptlde has been decorated by gold and silver nanoparticles that are stabilized by a dipeptide. Transmission electron microscopic images make the decoration visible. In this paper, a new strategy of mineralizing a pseudopeptide based nanofiber by gold and silver nanoparticles with use of a two-component nanografting method is described.

Full text of DOI:10.1021/ol0708471

ORGANIC
LETTERS
2
007
Vol. 9, No. 13
489-2492
Decoration of Au and Ag Nanoparticles
on Self-Assembling
2
Pseudopeptide-Based Nanofiber by
Using a Short Peptide as Capping Agent
for Metal Nanoparticles
†
‡
,†,§
Partha Pratim Bose, Michael G. B. Drew, and Arindam Banerjee*
Department of Biological Chemistry, Indian Association for the CultiVation of Science,
JadaVpur, Kolkata 700032, India, Chemistry DiVision, Indian Institute of Chemical
Biology, JadaVpur, Kolkata 700032, India, and School of Chemistry, The UniVersity of
Reading, Whiteknights, Reading, United Kingdom RG6 6AD
bcab@mahendra.iacs.res.in; arindam@iicb.res.in
Received April 11, 2007
ABSTRACT
The surface of a nanofiber that is formed from a self-assembling pseudopeptide has been decorated by gold and silver nanoparticles that are
stabilized by a dipeptide. Transmission electron microscopic images make the decoration visible. In this paper, a new strategy of mineralizing
a pseudopeptide based nanofiber by gold and silver nanoparticles with use of a two-component nanografting method is described.
3
The shape and size of nanocrystals govern their catalytic,
optical, and electronic properties. To apply nanocrystals as
cal nanotube surfaces. Controlling diameter and packing
densities of nanocrystals on the surfaces on which they are
to be patterned is of utmost importance to produce nanode-
vices with tunable electronic properties from a single type
of nanocrystal. Biological systems control the mineralization
and nanocrystal synthesis of various metals in exact shapes
1
building blocks for practical electronic, magnetic, and optical
devices, the nanocrystals must be assembled in an ordered
pattern. There are some recent examples of patterned
2
deposition of various nanocrystals on flat surfaces. Recent
4
studies include the patterning of the nanocrystals on cylindri-
and sizes with high accuracy. There are many examples of
using biological molecules as templates on which the
†
Indian Association for the Cultivation of Science.
The University of Reading.
Indian Institute of Chemical Biology.
‡
(2) (a) Xu, J.; Drelich, J.; Nadgorny, E. M. Langmuir 2004, 20, 1021-
1025. (b) Wei, Z.; Zamborini, F. P. Langmuir 2004, 20, 11301-11304. (c)
Gittins, D. I.; Susha, A. S.; Schoeler, B.; Caruso, F. AdV. Mater. 2002, 14,
508-512. (d) Sun, S.; Mendes, P.; Critchley, K.; Diegoli, S.; Hanwell, M.;
Evans, S. D.; Leggett, G. J.; Preece, J. A.; Richardson, T. H. Nano. Lett.
2006, 6, 345-350. (e) Heriot, S. Y.; Pedrosa, J.-M.; Camacho, L.;
Richardson, T. H. Mater. Sci. Eng. 2006, C 26, 154-162.
(3) (a) Dujardin, E.; Peet, C.; Stubbs, G.; Culver, J. N.; Mann, S. Nano
Lett. 2003, 3, 413-417. (b) Behrens, S.; Rahn, K.; Habicht, W.; Bohm,
K.-J.; Rosner, H.; Dinjus, E.; Unger, E. AdV. Mater. 2002, 14, 1621-1625.
§
(1) (a) Puntes, V. F.; Krishnan, K. M.; Alivisatos, A. P. Science 2001,
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91, 2115-2117. (b) Puntes, V. F.; Zanchet, D.; Erdonmez, C. K.;
Alivisatos, A. P. J. Am. Chem. Soc. 2002, 124, 12874-12880. (c) Orendroff,
C. J.; Sau, T. K.; Murphy, C. J. Small 2006, 2, 636-639. (d) Orendroff, C.
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1
0.1021/ol0708471 CCC: $37.00
© 2007 American Chemical Society
Published on Web 06/02/2007

monodisperse nanocrystals have been grown by biominer-
5
alization. Oligomeric DNA, bacteriophages, and other
biomecular components have been used to prepare various
6
nanostructures. Design and construction of supramolecular
architectures of nanoscopic dimensions give access to entities
of increasing complexity with distinct structural and func-
tional properties. The use of intermolecular forces provides
a rational and efficient method to position molecular
components precisely in a well-defined supramolecular
architecture. Self-assembly relies on a sequence of spontane-
ous recognition, growth, and termination steps to form the
final equilibrium supramolecular entity (or a collection of
such) through metal ion coordination, hydrogen bonds, or
hydrophobic or electrostatic interactions. There are a few
examples of mineralization on synthetic nanostructures by
metal nanoperticles or nanocrystals, based on specific
supramolecular intercations.7 Matsui et al. made a template
by immobilizing a histidine containing peptide on the surface
of a nanotube that is made up of self-assembling bis(N-R-
amido-glycylglycine)-1,7-heptane dicarboxilic acid and vari-
ous metal nanoparticles including gold, silver, and platinum
were stabilized on that nanotubular surface.8 Here, we
report a new strategy of mineralizing pseudopeptide-based
nanofiber by gold and silver nanoparticles using a two-
component nanografting method exploiting the rationale of
basic noncovalent interactions between the side chains of
self-assembled pseudopeptides and the peptide capped gold/
silver nanoparticles.
Figure 1. Schematic representation of the synthesis of peptide
capping agent.
,8
nanoparticles. The capping agent is bidentate in nature with
a free amine (-NH ) and free sulfahydryl group (-SH) at
2
the same terminus of the molecule, and this has made it an
efficient capping agent for metal nanoparticles. The peptide
1 was separately stirred with the aqueous solution of HAuCl4
a,b
3 4
and AgNO and then it was reduced with aqueous NaBH
solution, which produced a purple and light gray solution
stabilized by the peptide 1 capping agent. The plasmon band
appeared at 537 and 462 nm (broad) (Figure 2, parts c and
For obtaining an efficient capping agent for gold and silver
nanoparticles, a cysteine containing C-terminally protected
dipeptide (peptide 1) has been synthesized (Figure 1). This
peptide has been purified and characterized with conventional
methods (Supporting Information). We have used methyl-
ester protection at the C-terminus to lower the propensity of
self-assembly of the dipeptide, so that it can be effectively
used as a capping agent for gold and silver nanoparticles
and to control the homogeniety in size of the metal
(
4) (a) Baeuerlein, E. In Biomineralization; Wiley: New York, 2000.
(
b) Niemeyer, C. M. Angew. Chem., Int. Ed. 2001, 40, 4128-4158. (c)
Dujardin, E.; Mann, S. AdV. Mater. 2002, 14, 775-788. (d) Gazit, E. FEBS.
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I. Angew. Chem., Int. Ed. 2002, 41, 2323-2327. (h) Sauza, G. R.;
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5) S o¨ llner, C.; Burghammer, M.; Nentwich, E. B.; Berger, J.; Schwarz,
H.; Riekel, C.; Nicolson, T. Science 2003, 302, 282-286.
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(
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91, 775-778. (b) Niemeyer, C. M. Curr. Opin. Chem. Biol. 2000, 4, 609-
6
18. (c) Whaley, S. R.; English, D. S.; Hu, E. L.; Barbara, P. F.; Belcher,
A. M. Nature 2000, 405, 665-668. (d) Lee, S. W.; Mao, C.; Flynn, C. E.;
Belcher, A. M. Science 2002, 296, 892-895. (e) Rudolph, A. S.; Calvert,
J. M.; Schoen, P. E.; Schnur, J. M. AdV. Exp. Med. Biol. 1988, 238, 305-
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20. (f) Jiang, K.; Eitan, A.; Schadler, L. S.; Ajayan, P. M.; Siegel, R. W.;
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Lett. 2003, 3, 275-277. (g) Banerjee, S.; Wong, S. S. Nano Lett. 2002, 2,
1
95-200.
(
7) Ray, S.; Das, A. K.; Banerjee, A. Chem. Commun. 2006, 2816-
2
818.
Figure 2. (a) Infrared spectra of (i) peptide 1, (ii) peptide 1 capped
gold nanoparticle, and (iii) peptide 1 capped Ag nanoparticle. (b)
Plasmon band of peptide 1 capped gold nanoparticle solution and
(c) plasmon band of peptide 1 capped silver nanoparticle.
(
8) (a) Lingtao, Y.; Banerjee, I. A.; Matsui, H. J. Mater. Chem. 2004,
1
2
4, 739-743. (b) Djalali, R.; Chen, Y.-f.; Matsui, H. J. Am. Chem. Soc.
002, 124, 13660-13661. (c) Rabatic, B. M.; Claussen, R. C.; Stupp, S. I.
Chem. Mater. 2005, 17, 5877-5879. (d) Sone, E. D.; Stupp. S. I. J. Am.
Chem. Soc. 2004, 126, 12756-12757.
2490
Org. Lett., Vol. 9, No. 13, 2007

d, respectively) and transmission electronic microscopic
images (Figure 3a,b) showed the presence of gold/ silver
crystal of pseudopeptide 1 was obtained from solution of
MeOH-H O (2:1) by slow evaporation and single-crystal
X-ray diffraction study of this pseudopeptide 1 was done.
2
12
The self-assembling nature of the pseudopeptide 1 in
methanol-water can be assessed from its crystal structure
in the same solvent system. The crystal structure of the
pseudopeptide 1 reveals that the molecule has crystal-
lographic 3-fold symmetry within a hexagonal unit cell, space
3
group P6 (Supporting Information, Figure S10). This
facilitates the formation of supramolecular columnar packing
along the axis parallel to unique crystallographic c-axis.
These supramolecular columns are regularly aligned via non-
hydrogen bonding, noncovalent interactions to form hierar-
chical supramolecular arrays along the equivalent crystallo-
graphic a and b axes (Supporting Information, Figure S11)
to produce a straight nanofiber, which was observed in the
TEM image (Figure 4c) of pseudopeptide 1 nanofiber. Figure
Figure 3. Transmission electron microscopic (TEM) images of
peptide 1 capped (a) gold nanoparticles and (b) silver nanoparticles.
Size distribution of peptide 1 stabilized (c) gold nanoparticles and
(d) silver nanoparticles.
nanoparticles and their size distributions (Figure 3c,d) which
were stabilized by the peptide 1 capping agent. FT-IR studies
clearly indicate the participation of the side chain thiol group
2
(-SH) and the terminal amino group (-NH ) of the peptide
1
for capping the gold and silver nanoparticles (Figure 2).
Bonding of both amine and sulfydryl groups with gold/silver
nanoparticles was evident from the FT-IR spectra (Figure
2
1
a). In the solid state (KBr), the FT-IR spectrum of peptide
indicates a broad band centered at 3330.4 cm-1 due to the
N-H streching vibrations of the terminal amino group.
However, the N-H streching frequency of peptide 1 capped
gold and silver nanoparticles appeared at 3368.5 and 3354.7
cm , respectively.
The increase in wavenumber can be justified by the
interaction of lone pair of electrons of the free amine group
Figure 4. Transmission electron microscopic images of (a)
nanofiber of pseudopeptide 1 decorated with peptide 1 stabilized
gold nanoparticles, (b) nanofiber of pseudopeptide 1 decorated with
peptide 1 stabilized silver nanoparticles, and (c) nanofiber of
pseudopeptide.
-
1
(
2
-NH ) with the suitable vacant orbital of Au and Ag in
10
their neutral states. Peaks that appeared due to carbonyl
stretching of amide and ester functionalities do not show
significant shifts as they do not involve capping of the metal
5
shows the mechanism of formation of nanofiber in light
of crystallography and self-assembly.
-
1
nanoparticles. Another broad band centered at 2504 cm
Transmission electronic microscopic (TEM) studies were
carried out with the methanol-water (2:1) solution of
pseudopeptide 1 to obtain the information about the nan-
odimensional insight of the pseudopeptide 1 in solution. From
the TEM images (Figure 4c), it was evident that pseudopep-
tide 1 molecules form nanofibers with a width ranging from
was also observed in case of peptide 1 and this peak
disappeared in the spectrum of gold and silver tagged
nanoconjugates. This vividly demonstrates the role of the
11
-
SH group in stabilizing the gold and silver nanoparticles.
Pseudopeptide 1 was prepared by a conventional solution-
12
phase DCC-HOBt coupling method. A good quality single
(
9) Sheehan, J. C.; Yang, D. D. H. J. Am. Chem. Soc. 1958, 80, 1158-
(11) (a) Ihs, A.; Leidberg, B. J. Colloid Interface Sci. 1991, 144, 282-
292. (b) Wang, S.-f.; Du, D.; Zou, Q.-C. Talanta 2002, 57, 687-692.
(12) Bose, P. P.; Das, A. K.; Drew, M. G. B.; Banerjee, A. Chem.
Commun. 2006, 3196-3198.
1
1
164.
(10) Lambropoulos, N. A.; Reimer, J. R. J. Chem. Phys. 2002, 116,
0277-10285.
Org. Lett., Vol. 9, No. 13, 2007
2491

porting Information, Figure S11). Peptide capped metal (gold/
silver) nanoparticles come in contact with the pseudopeptide
1
based nanofibers involving the non-hydrogen bonding
noncovalent interactions among the anchoring groups present
in both interacting surfaces (one suface from the peptide-
metal nanoconjugate and the other from the nanofiber) to
form the gold/silver nanoparticle decorated pseudopeptide
based nanofiber (Figure 5). In this method peptide stabilized
gold or silver nanoparticles are immobilized on the surface
of the pseudopeptide based nanofiber by suitable non-
hydrogen bonding noncovalent interactions between the
interacting groups of the pseudopeptide nanofiber and the
metal nanoparticle-peptide 1 nanoconjugate. We have used
the peptide 1 molecule as a capping agent and the peptide 1
Figure 5. Schematic representation of immobilization of dipeptide
capped metal nanoparticles on the self-assembling pseudopeptide
1
based nanofibers.
2
is a bidentate ligand in which -SH and -NH groups are
in appropriate juxtraposition to stabilize the nascent Au/Ag
nanoparticles to prevent further aggregation of these nano-
particles and thus the size of GNPs and SNPs is somewhat
controlled. Our method differs from the previously reported
method of mineralization on synthetic nanostructure by metal
nanoparticles, as in our method freshly prepared nanoparticles
are first capped by a bidentate ligand (peptide 1) and then
the nanoconjugate comes in contact with the interacting
groups situated on the surface of the pseudopeptide nanofiber.
This is different from Matsui’s method, in which the metal
ions are first stabilized on the surface of the nanotubes and
subsequent reduction of the metal ions by suitable reducing
agent produces the mineralization of metal nanoparticles on
nanostructures.
1
08 to 140 nm. To assess the efficiency of the method of
grafting of peptide stabilized gold and silver nanoparticles
on the pseudopeptide nanofiber, transmission electron mi-
croscopy was carried out. The solution of the pseudopeptide
1
in methanol-water (2:1) was then mixed with the solution
of peptide capped gold/silver nanoparticles and the mixture
was then incubated at 30 °C for 2 h. After that TEM studies
were carried out with these two solutions separately on a
carbon-coated copper grid (300 mesh) by slow evaporation
and vacuum drying at 30 °C for 2 days. The transmission
electron microscopic images showed that gold and silver
nanopaticles (capped with the dipeptide) were uniformly
deposited on the pseudopeptide nanofiber to form gold and
silver nanoparticle decorated nanofibers (Figure 4a,b).
From the above result, it is clear that the metal nanoparticle
coated nanofiber can be made by using this technique, based
on the noncovalent interactions between the peptide capped
Au/Ag nanoparticles and the interacting groups anchored on
the surface of the nanofiber. From crystallography and higher
order packing it is evident that the hydrophobic isopropyl
side chain and hydrophilic methyl carboxylates (-COOMe)
of the valine residues (attached to each of the centrally
positioned aromatic rings) are present at the periphery of
the supramolecular assemblage (Supporting Information,
Figure S9).
Because of this unique positioning of the hydrophilic and
hydrophobic groups along the surface, the pseudopeptide-
based nanofiber adopts a very high recognizing behavior at
the supramolecular level. Here, we used a cysteine-containing
dipeptide (peptide 1) as a stabilizer for Au/Ag nanoparticles.
This capping agent contained a hydrophobic part consisting
of the side chain of the amino acid leucine and a hydrophilic
group (-COOMe) too. The terminally located free amine
Our result describes a new method of fabricating a metal
nanoparticle coated nanofiber based on the rationale of
supramolecular chemistry, involving the noncovalent interac-
tions between the interacting groups present in the nanofibers
(isopropyl and -COOMe from valine residue) and peptide
capped nanoparticles. This method can be utilized for making
new hybrid nanomaterial from synthetic nanomaterials
obtained from self-assembling building blocks and peptide
stabilized metal nanoparticles. The functional nature of the
metal nanoparticle grafted nanofiber is yet to be explored.
Acknowledgment. We thank EPSRC and the University
of Reading, U.K. for funds for Marresearc Image Plate
Systems. P.P. Bose acknowledges the C.S.I.R, New Delhi,
India for financial assistance. Thanks are due to the partial
support from the Nanoscience and Technology Initiative,
DST, Government of India, New Delhi.
Supporting Information Available: Experimental de-
1
tails, synthesis, H NMR and HRMS of all compounds, TEM
group (-NH ) and the sulfahydryl group (-SH) were
2
studies, EDX profiles of gold/silver nanoparticles, and
packing pictures from crystal data of all compounds. This
material is available free of charge via the Internet at
http://pubs.acs.org.
involved in capping the metal nanoparticles. The dipeptide
molecule (peptide 1) capped with the metal (gold/silver)
nanoparticle forms a nanoconjugate in such a way that the
hydrophobic (isopropyl) and hydrophilic (-COOMe) groups
were positioned on the surface of the nanoconjugate (Sup-
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