Insights into self-assembling nanoporous peptide and in situ reducing agent

Article abstract of DOI:10.1039/c0ce00143k

A tripeptide containing an Aib (α-amino isobutyric acid) residue self-assembles to form porous nanomaterials in solid state. In spite of having a hollow nanotubular structure, the self-assembly nature of the peptide is different, which leads to the formation of pores with different internal diameters. The single-crystal X-ray diffraction study reveals that the peptide forms continuous hydrogen-bonded poly-disperse nanopores (3, 5 and 8 membered) starting from the β-turn conformation as an associating sub-unit. The field emission scanning electron micrograph (FESEM) shows that the average pore sizes are in the range of 20 to 200 nm, although a few large pores are also visible. Moreover, the peptide 1 acts as an in situ reducing agent to synthesize hexagonal gold nanoparticles (GNP).

Full text of DOI:10.1039/c0ce00143k

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Insights into self-assembling nanoporous peptide and in situ reducing agent†
*
Poulami Jana, Sibaprasad Maity and Debasish Haldar
Received 28th April 2010, Accepted 14th September 2010
DOI: 10.1039/c0ce00143k
A tripeptide containing an Aib (a-amino isobutyric acid) residue self-assembles to form porous
nanomaterials in solid state. In spite of having a hollow nanotubular structure, the self-assembly nature
of the peptide is different, which leads to the formation of pores with different internal diameters. The
single-crystal X-ray diffraction study reveals that the peptide forms continuous hydrogen-bonded poly-
disperse nanopores (3, 5 and 8 membered) starting from the b-turn conformation as an associating sub-
unit. The field emission scanning electron micrograph (FESEM) shows that the average pore sizes are in
the range of 20 to 200 nm, although a few large pores are also visible. Moreover, the peptide 1 acts as an
in situ reducing agent to synthesize hexagonal gold nanoparticles (GNP).
templates.10 Yaghi and co-workers have reported the develop-
Introduction
ment of highly porous, organic, three-dimensional crystalline
covalent networks.11 We are developing nanostructured mate-
rials by molecular recognition and self-association of peptides
and oligoamides.12
Nanoporous materials having unique bulk, surface and struc-
tural properties are an emerging area of current research due to
their potential importance in various fields, like catalysis,
sensors, ion exchange, separation, purifications and bio-molec-
ular isolation.1 Depending on the size, microporous (pore size
There has been tremendous interest in recent times in assem-
bling nanoparticles in close-packed aggregates because of their
unusual optoelectronic and chemical properties,13which have
potential applications in nanoelectronics,14 bio-analytical
processes15 and catalysis.16 Among these, gold nanoparticles
(GNPs) are of much contemporary interest and have been
extensively investigated.17 Generally GNPs are prepared by the
reduction of HAuCl4 with NaBH4 or citrate in presence of
a stabilizer,16,18 but the by- product of these reducing agents and
the stabilizer may create complications when used in some bio-
analytical applications. Therefore, the in situ reduction technique
is important in order to avoid this problem.19
below
2 nm), mesoporous (2–50 nm) and macroporous
(exceeding 50 nm) solids can be constructed efficiently from
a single molecule or ionic template or the molecular recognition
and association of organic templates.2 The nanoporous materials
have a wide propensity to interact with atoms, ions and mole-
cules, which adsorb on their nanometre sized pore space and in
the large interior surfaces.3 Over the last few decades, enormous
efforts have been devoted to the synthesis and characterization of
nanoporous materials with a uniform pore size and pore struc-
ture due to their attractive textual and structural features, such as
highly ordered structures, tuneability and ultra-high surface
areas.4 However, a hybrid material containing both inter-
connected macroporous and mesoporous structures have
enhanced properties compared with single-sized pore materials
due to the increased mass transport through the material and the
maintenance of a specific surface area on the level of fine pore
systems.5 Many studies have been made of inorganic micropo-
rous materials, such as zeolites, which have well-defined network
structures of silicon and aluminium atoms linked via oxygen
atoms.6 But, it has proved difficult to form organic polymer
networks with perfectly controlled pore dimensions.7 Most of the
reports consist of metal–organic frameworks, in which rigid
organic components are linked by noncovalent interactions, such
as metal–ligand or hydrogen bonds.8 Surfactants and amphi-
philic copolymers can be used as templates to synthesize ordered
mesoporous materials9 and periodic three-dimensional arrays of
macropores have been fabricated using latex spheres as
Herein we have analyzed by means of field emission scanning
electron microscopy and single-crystal X-ray crystallography,
the formation of a novel supramolecular nanoporous material
from a terminally blocked tripeptide Boc-Tyr(1)-Aib(2)-Val(3)-
OMe 1, which self-associates, exploiting the hydrogen-bonding
functionalities of the peptide bonds. Moreover, the peptide 1 acts
as an in situ reducing agent in the synthesis of hexagonal gold
nanoparticles.
Results and discussion
Synthesis and FTIR analysis
The tripeptide Boc-Tyr(1)-Aib(2)-Val(3)-OMe
1 has been
synthesized by conventional solution phase methodology20 (ESI,
Fig. S1†) and purified, characterized and studied. The terminally
protected tripeptide 1 contains a helicogenic a-amino isobutyric
acid residue21 at a central position. Solid-state FTIR spectros-
copy was performed to study the secondary structure of the
peptide 1. The region 1800–1500 cmꢀ1 is important for the
stretching band of amide I, the bending peak of amide II and the
hydrogen bonded urethane groups.22 Another informative
frequency range is 3500–3200 cmꢀ1, corresponding to the N–H
stretching vibrations of the peptide.22 The FTIR study shows
that the peptides molecules are strongly intermolecularly
Department of Chemical Sciences, Indian Institute of Science Education
and Research – Kolkata, Mohanpur, West Bengal 741252, India. E-mail:
deba_h76@yahoo.com; deba_h76@iiserkol.ac.in; Fax: +91-34-73
279131; Tel: +91-34-73 279130
† Electronic
supplementary
information
(ESI)
available:
Crystallographic file, 1H-NMR, 13C NMR, HRMS spectra. CCDC
reference number 753226. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c0ce00143k
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Table 1 Selected backbone torsion angles (ꢁ) for peptide 1
hydrogen bonded in the solid state (ESI, Fig. S2†). An intense
band at 3272 cmꢀ1 and 3291 cmꢀ1 were observed for the reported
peptide, indicating the presence of strongly hydrogen-bonded
C9-N1-C12-O5
C12-N1-C9-C15
N1-C9-C15-N3
C24-N3-C15-C9
179.44
53.07
u0 N2-C11-C24-N3
f1 C9-N2-C11-C24
ꢀ16.10
ꢀ171.25 u2
f3
ꢀ145.92 c3
c2
NH groups. No band has been observed at around 3400 cmꢀ1
,
ꢀ128.03 c1 C11-N2-C20-C18 131.15
ꢀ171.25 u1 O1-C18-C20-N2
f2
indicating that all NH groups are involved in intermolecular
hydrogen bonding.23 The characteristic IR absorption bands at
about 1567, 1616, 1645, 1675, 1699 and 1727 cmꢀ1 suggest that
the peptides have no distinguished structure, such as the typical
parallel or antiparallel b-sheet or helical structures.24
C15-N3-C24-C11 ꢀ67.70
Morphology and characterization
To obtain insight about the morphology of the reported peptide,
field-emission scanning electron microscopic (FE-SEM)
measurements were carried out.26 For FE-SEM experiments,
dilute solutions (0.5 mM) of tripeptide 1 in methanol–water
(1 : 1 v/v) were placed on a microscopic glass slide and then dried
under vacuum for two days. Fig. 5 depicts the FE-SEM image of
the peptide. From Fig. 5, the micrograph shows the porous
nanostructure morphology in the self-assembled state and the
pores are polydisperse in nature with different diameters.
Average pores size are 20–200 nm. These values are much higher
than the values obtained from single-crystal X-ray
Crystallographic analysis
The colourless orthorhombic crystals of peptide 1, suitable for
single-crystal X-ray diffraction analysis, were obtained from
a methanol–water solution by slow evaporation. The molecular
conformation of peptide 1 in the crystal is represented in Fig. 1.
From Fig. 1 it is evident that there is an intramolecular hydrogen
bond between the BOC C]O and the Val NH, resulting in a ten
membered hydrogen-bonded b-turn conformation in the solid
state.25 The backbone torsion angles of peptide 1 (Table 1) reveal
that the turn is of Type II or b-turn. The Aib(2) residue occupies
the i + 2 position of the b-turn. The individual b-turn sub-units of
this peptide are themselves regularly inter-linked via multiple
intermolecular hydrogen bonds N1-H111/O1, N3-H333/O7
and O2–H2/O6 and thereby form a three membered supra-
molecular nanopore along the crystallographic b axis direction
(Fig. 2). The average internal diameter for the three membered
ꢀ
pore is 7.7 A. The b-turn-containing peptide 1 sub-unit has the
potential to further self-assemble into a five membered supra-
molecular pore-like structure in the solid state. In this case, the
molecules are bound by five intermolecular hydrogen bonds N1–
H111/O1, N3–H333/O7 and three O2–H2/O6 bonds, along
the crystallographic c axis direction (Fig. 3). Moreover, the
packing diagram shows that there is also the possibility to form
an 8 membered supramolecular porous structure (Fig. 4) through
intermolecular hydrogen bonds along the crystallographic c axis.
There are eight intermolecular hydrogen bonds (four N1–
H111.O1, three N3–H333.O7 and one O2–H2.O6) that are
responsible for connecting individual molecules in order to create
and stabilize the moderate-size pore-like self-assemblage. The
hydrogen bonding parameters of peptide 1 are listed in Table 2.
Fig. 2 The three membered nanopore (a) in ball and stick model, (b)
space-filling representation showing higher-ordered supramolecular
assembly along the crystallographic b direction, (c) packing of the tri-
peptide 1 in a higher order assembly. Hydrogen bonds are shown as
dotted lines.
Fig. 3 The ball and stick presentation of five membered nanopore along
crystallographic c axis direction. Hydrogen bonds are shown as dotted
lines. Nitrogen atoms are blue, oxygen atoms are red and carbon atoms
are gray.
Fig. 1 The ORTEP diagram of tripeptide 1 showing the atomic
numbering scheme. Ellipsoids are drawn at the 30% probability level.
Intramolecular hydrogen bond is shown as a dotted line.
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based peptides.29 Incorporating the redox active tyrosine residue
into the nanopore forming tripeptides template, we want to
fabricate the in situ synthesis of gold nanoparticles. The
following method was used for the synthesis of the gold nano-
particles with peptide 1. An aqueous yellow coloured solution
(0.5 mL) of HAuCl4 (20 mg in 2 mL) was added to the methanol–
water (1 : 0.5 v/v) solution of the peptide 1 (1 mg mLꢀ1) and was
stirred to produce a homogeneous solution. The yellow colora-
tion of the mixture was not changed for several days. NaOH
solution (2 M) was added dropwise into the yellow solution to
adjust the pH at 9. Immediately the yellow colour changed to
a colourless solution [Au(III) to Au(I)] and finally it turned into
a violet solution within a few minutes indicating the formation of
gold nanoparticles [Au(0)] via the oxidation of the tyrosine
residues of peptide 1. The presence of a surface Plasmon band at
around 548 nm suggests the existence of gold nanoparticles (ESI,
Fig. S5†).29 Field-emission scanning electron microscopy was
used to characterize the gold nanoparticles. A drop of the violet
coloured gold nanoparticle solution (methanol–water 1 : 1) was
placed on a microscopic glass slide and it was allowed to dry
under reduced pressure at room temperature for two days. Fig. 6
shows the image of the gold nanoparticles with a hexagonal
shape, with various particle sizes ranging from 50 nm to 80 nm in
diameter.
Fig. 4 The nanopore obtained by self-assembly of eight b-turn subunits
along the c axis direction.
Table 2 Hydrogen bonding parameters of peptide 1a
ꢀ
ꢀ
D–H/A
H/A/A
D/A/A
D–H/A/ꢁ
O2–H2/O6b
N1–H111/O1e
N2–H222/O4
N2–H222/N3
N3–H333/O7f
1.98
2.29
2.46
2.41
2.00
2.71
3.04
3.20
2.77
2.89
169.00
169.00
162.00
110.00
171.00
Experimental
General methods and materials
All L-amino acids (L-tyrosine, L-valine and a-amino isobutyric
acid) were purchased from Sigma chemicals. HOBt (1-hydrox-
ybenzotriazole) and DCC (dicyclohexylcarbodiimide) were
purchased from SRL.
a
Symmetry equivalent: b ¼ [4655.00] ¼ 1 ꢀ x, 1/2 + y, 1/2 ꢀ z, e ¼
[2554.00] ¼ 1/2 ꢀ x, ꢀy, ꢀ1/2 + z, f ¼ [3456.00] ¼ ꢀ1/2 + x, 1/2 ꢀ y, 1
ꢀ z.
Synthesis
crystallography. This indicates that the self-assembled states are
actually the supramolecular clusters of several molecules.
Further BET analysis27 of the crystallized peptide 1 (degassed at
150 ꢁC) exhibits more information about the pore size dimen-
sions of the nanoporous material (ESI, Fig. S3 and S4†).28
The peptides were synthesized by conventional solution-phase
methodology, by using a racemization free fragment condensa-
tion strategy (see the ESI† for detailed synthetic procedure). The
Boc group was used for N-terminal protection and the C-
terminus was protected as a methyl ester. Couplings were
mediated by dicyclohexylcarbodiimide–1-hydroxybenzotriazole
(DCC–HOBt). Deprotection of the methyl ester was performed
using the saponification method. All of the intermediates were
Synthesis and characterization of GNP
Previous reports have demonstrated that gold nanoparticles have
been synthesized using tyrosine, alkylated tyrosine and tyrosine-
Fig. 5 FE-SEM image of tripeptide 1 showing nanoporous morphology
Fig. 6 FE-SEM image of hexagonal gold nanoparticles obtained by the
in situ reducing properties of tripeptide 1.
in the solid state.
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characterized by 500 MHz 1H NMR and mass spectrometry. The
chromatography (TLC). The reaction mixture was stirred. After
10 h, methanol was removed under vacuum; the residue was
dissolved in 50 mL of water and washed with diethyl ether (2 ꢂ
50 mL). Then the pH of the aqueous layer was adjusted to 2 using
1M HCl and it was extracted with ethyl acetate (3 ꢂ 50 mL). The
extracts were pooled, dried over anhydrous sodium sulfate, and
evaporated under vacuum to obtained compound as a waxy
solid. Yield 3.8 g (10.38 mmol, 89.6%). 1H NMR (500MHz,
DMSO-d6, d in ppm): 12.75 (br, 1 H, –COOH), 9.14 (s, 1 H, Tyr
–OH), 8.02 (s, 1 H, Aib(2) NH), 7.01–7.03 (d, 2 H, J ¼ 10 Hz, Tyr
phenyl ring protons), 6.66 (d, 1 H, J ¼ 5 Hz, Tyr NH), 6.61–6.63
(d, 2 H, J ¼ 10 Hz, Tyr phenyl ring protons), 4.01 (m, 1 H, Tyr Ca
H), 2.78–2.81 (m, 2H, Tyr Cb H), 1.34 (s, 3 H, Aib Cb H), 1.32 (s,
3 H, Aib Cb H), 1.30 (s, 9 H, BOC CH3). HRMS m/z 405.66 [M +
K]+, Mcalcd 366.41. 13C NMR (125 MHz, DMSO-d6, d in ppm):
175.43, 170.95, 155.64, 130.14, 128.02, 114.69, 177.91, 155.61,
28.10, 24.70. Anal. calcd for C18H26N2O6 (366): C 59.00, H 7.15,
N 7.65. Found: C 58.98, H 7.18, N 7.63.
1
final compound was fully characterized by 500 MHz H NMR
spectroscopy, 13C NMR spectroscopy (125 MHz), mass spec-
trometry and IR spectroscopy. The peptide 1 was characterized
by single-crystal X-ray crystallography.
(a) Boc-Tyr-OH. A solution of L-tyrosine (3.62 g, 20 mmol) in
a mixture of dioxane (40 mL), water (20 mL) and 1M NaOH
(20 mL) was stirred and cooled in an ice–water bath. Di-tert-
butylpyrocarbonate (4.8 g, 22 mmol) was added and stirring was
continued at room temperature for 6 h. Then the solution was
concentrated under vacuum to about 20–30 mL, cooled in an ice–
water bath, covered with a layer of ethyl acetate (about 50 mL)
and acidified with a dilute solution of KHSO4 to pH 2–3 (congo
red). The aqueous phase was extracted with ethyl acetate and this
operation was done repeatedly. The ethyl acetate extracts were
pooled, washed with water and dried over anhydrous Na2SO4
and evaporated under vacuum. The pure material was obtained
as a waxy solid. Yield 4.87 g (17 mmol, 85%). 1H NMR
(500MHz, CDCl3, d in ppm): 12.75 (br, 1 H, –COOH), 9.21 (s,
1 H, Tyr –OH), 7.02–7.00 (d, 2 H, J ¼ 10 Hz, Tyr phenyl ring
protons), 6.65–6.63 (d, 2 H, J ¼ 10 Hz, Tyr phenyl ring protons),
4.04 (m, 1 H, Tyr Ca H), 3.91 (d, 1 H, J ¼ 8 Hz, Tyr NH), 2.88 (m,
2 H, Tyr Cb H), 1.42 (s, 9 H, BOC CH3). 13C NMR (125 MHz,
CDCl3, d in ppm): 173.74, 155.78, 129.96, 127.98, 114.87, 55.50,
35.61, 28.13. Anal. calcd for C14H19NO5 (281): C 59.78, H 6.81,
N 4.98. Found: C 59.81, H 6.79, N 4.99.
(d) Boc-Tyr(1)-Aib(2)-Val(3)-OMe. 3.7 g (10.1 mmol) Boc-
Tyr-Aib–OH was dissolved in 10 mL of DMF in an ice–water
bath. H-Val-OMe 3.34 g (20 mmol) was isolated from the cor-
responding methyl ester hydrochloride by neutralization and
subsequent extraction with ethyl acetate and the ethyl acetate
extract was concentrated to 7 mL. Then it was added to the
reaction mixture, followed immediately by 2.08 g (10.11 mmol)
of dicyclohexylcarbodiimide (DCC) and 1.37 g (10.11 mmol) of
HOBt. The reaction mixture was allowed to come to room
temperature and then stirred for 72 h. The residue was taken in
30 mL ethyl acetate and dicyclohexylurea (DCU) was filtered off.
The organic layer was washed with 2 M HCL (3 ꢂ 50 mL), brine
(2 ꢂ 50 mL), then 1 M sodium carbonate (3 ꢂ 30 mL) and brine
(2 ꢂ 30 mL) and dried over anhydrous sodium sulfate and
evaporated under vacuum to yield the tripeptide 1 as a white
solid. Purification was done by silica gel column (100–200 mesh
size) with an ethyl acetate and hexane mixture 1 : 2 as the eluent.
Yield 4.4g (9.17 mmol, 90%). Mp. 140–143 ꢁC. 1H NMR
(500MHz, DMSO-d6, d in ppm): 9.15 (s, 1 H, Tyr –OH), 7.93 (s,
1 H, Aib(2) NH), 7.28 (d, 1 H, J ¼ 10 Hz, Val NH), 7.02–7.03 (d,
2 H, J ¼ 5 Hz, Tyr phenyl ring protons), 6.89 (d, 1 H, J ¼ 10 Hz,
Tyr NH), 6.63–6.64 (d, 2 H, J ¼ 5 Hz, Tyr phenyl ring protons),
4.14 (m, 1 H, Tyr Ca H), 4.05 (m, 1 H, Val Ca H), 3.62 (s, 3 H,
-OCH3), 2.92–3.03 (m, 2 H, Tyr Cb H), 2.16–2.19 (m, 1 H, Val Cb
H), 1.31 (s, 9 H, BOC CH3), 1.25 (s, 6 H, Aib Cb H), 0.83 (d, 6 H,
J ¼ 10 Hz, Val Cg H). [a]D27.8 ꢀ35.7 (c 2.10, CHCl3). HRMS m/z
502.26 [M + Na]+, Mcalcd 479.57. FTIR (KBr): 1518, 1532, 1567,
(b) Boc-Tyr(1)-Aib(2)-OMe. 4.5 g (16 mmol) of Boc-Tyr-OH
was dissolved in 25 mL DCM in an ice-water bath. H-Aib-OMe
was isolated from 4.91 g (32 mmol) of the corresponding methyl
ester hydrochloride by neutralization and subsequent extraction
with ethyl acetate and the ethyl acetate extract was concentrated
to 10 mL. It was then added to the reaction mixture, followed
immediately by 3.3 g (16 mmol) dicyclohexylcarbodiimide
(DCC) and 2.2 g (16 mmol) of HOBt. The reaction mixture was
allowed to come to room temperature and stirred for 48 h. DCM
was evaporated and the residue was dissolved in ethyl acetate
(60 mL) and dicyclohexylurea (DCU) was filtered off. The
organic layer was washed with 2M HCl (3 ꢂ 50 mL), brine (2 ꢂ
50 mL), 1M sodium carbonate (3 ꢂ 50 mL) and brine (2 ꢂ
50 mL) and dried over anhydrous sodium sulfate. It was evap-
orated in a vacuum to yield Boc-Tyr-Aib-OMe as a white solid.
Yield 4.56 g (12 mmol, 75%). Mp.122–128 ꢁC. 1H NMR
(500MHz, CDCl3, d in ppm): 9.21 (s, 1 H, Tyr –OH), 7.03–7.02
(d, 2 H, J ¼ 5 Hz, Tyr phenyl ring protons), 6.75–6.74 (d, 2 H,
J ¼ 5 Hz, Tyr phenyl ring protons), 6.48 (s, 1 H, Aib(2) NH), 5.22
(d, 1 H, J ¼ 5 Hz, Tyr NH), 4.22 (m, 1 H, Tyr Ca H), 3.70 (s, 3 H,
–OCH3), 2.95–2.90 (m, 2 H, Tyr Cb H), 1.44 (s, 6 H, Aib Cb H),
1.41 (s, 9 H, BOC CH3). HRMS m/z 403.10 [M + Na]+, Mcalcd
380.44. FTIR (KBr): 1519, 1595, 1682, 2852, 2932, 2982, 3063,
3329. 13C NMR (125 MHz, CDCl3, d in ppm): 174.17, 170.74,
155.66, 130.58, 127.97, 115.56, 56.45, 53.45, 37.58, 29.70, 24.74.
Anal. calcd for C19H28N2O6 (380): C 59.98, H 7.42, N 7.36.
Found: C 60.01, H 7.38, N 7.38.
1616, 1645, 1675, 1699, 1727, 2969, 3086, 3273, 3346 cmꢀ1 13C
.
NMR (125 MHz, CDCl3, d in ppm): 174.13, 172.38, 171.19,
155.40, 130.46, 127.83, 115.73, 57.54, 52.15, 37.37, 31.14, 28.27,
25.74, 24.56, 29.03, 17.80. Anal. calcd for C24H37N3O7 (479): C
60.11, H 7.78, N, 8.76. Found: C 60.07, H 7.73, N 8.80.
NMR experiments
€
All NMR studies were carried out on a Bruker AVANCE 500
(c) Boc-Tyr(1)-Aib(2)-OH. To 4.4 g (12 mmol) of Boc-Tyr-
Aib-OMe, 25 mL MeOH and 2M 15 mL NaOH were added and
the progress of saponification was monitored by thin layer
MHz spectrometer at 298 K. The compounds concentrations
were in the range 1–10 mmol in CDCl3 and (CD3)2SO.
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FTIR spectroscopy
Conclusions
All reported solid-state FTIR spectra were obtained with a Per-
kin Elmer Spectrum RX1 spectrophotometer with the KBr disk
technique.
In conclusion, we have demonstrated the self-assembly of a tri-
peptide containing a-amino isobutyric acid to form porous
nanomaterials in the solid state. The solid state FTIR study
shows that the tripeptide 1 has a highly hydrogen bonded
network but a lack of distinguished classical structure. These
differences in the self-assembly nature of the peptides leads to the
formation of pores with different internal diameters. The field-
emission scanning electron microscopy reveals a porous nano-
structure with average pore sizes in the range of 20 to 200 nm in
the solid state. The single-crystal X-ray diffraction study shows
that the peptide forms continuous hydrogen-bonded poly-
disperse nano pores (3, 5 and 8 membered) starting from the b-
turn conformation as an associating sub-unit. Moreover, the
peptide 1 acts as an in situ reducing agent and synthesizes
hexagonal gold nanoparticles (GNP). The results presented here
have formed a novel understanding of structure formation and
will provide useful guidelines for the design of nanomaterials
with predefined functionality.
Mass spectrometry
Mass spectra were recorded on a Q-Tof Micro YA263 high-
resolution (Waters Corporation) mass spectrometer by positive-
mode electrospray ionization.
Polarimeter
Rudolph Research analytical instrument. Model Autopol IV
Polarimeter was used.
Scanning electron microscopy
The morphologies of the reported materials were investigated by
field emission scanning electron microscopy (FE-SEM). For the
SEM study, the peptide solution (methanol–water 1 : 1 v/v) was
drop cast on a clean and dry microscopic glass slide, dried and
coated with platinum. Then the micrographs were taken in
a SEM apparatus (JEOL Microscope JSM-6700F).
Acknowledgements
We acknowledge the DST, New Delhi, India, for financial
assistance Project No. (SR/FT/CS-041/2009). P. Jana and
S. Maity wish to acknowledge the C.S.I.R, New Delhi, India for
research fellowships. We are thankful to Dr Raju Mandal,
Department of Inorganic Chemistry, I. A. C. S., Jadavpur,
Kolkata 700032, India for his assistance in single-crystal X-ray
crystallography data refinement. We gratefully acknowledge the
I. A. C. S., Jadavpur, Kolkata 700032, India, for using the Mass
Spectrometry, X-ray crystallography and FE-SEM facilities.
X-Ray crystallography
Single-crystal X-ray analysis of tripeptide 1 was recorded on
a Bruker high resolution X-ray diffractometer instrument.
Crystallographic data
Crystal data for peptide 1: C24H37N3O7, Mr ¼ 479.57, ortho-
rhombic, crystal size 0.14 ꢂ 0.26 ꢂ 0.32 mm, spacegroup
Notes and references
1 (a) A. Stein, Adv. Mater., 2003, 15, 763–775; (b) M. E. Davis, Nature,
2002, 417, 813–821; (c) D. Zhao, J. Feng, Q. Huo, N. Melosh,
G. H. Fredrickson, B. F. Chmelka and G. D. Stucky, Science, 1998,
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G. D. Stucky, J. Am. Chem. Soc., 1998, 120, 6024–6036; (e) J. Fan,
C. Yu, J. Lei, Q. Zhang, T. Li, B. Tu, W. Zhou and D. Zhao,
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ꢀ
P212121, a ¼ 10.840(10), b ¼ 14.535(13), c ¼ 18.079(16) A, U ¼
3
2849 A , Z ¼ 4, dm ¼ 1.118 M g mꢀ3 Intensity data were collected
ꢀ
with Mo-Ka radiation at room temperature using Bruker
APEX-2 CCD diffractometer. The crystal was positioned at 70
mm from the image plate. 100 frames were measured at 2ꢁ
intervals with a counting time of 5 min to give 5000 independent
reflections. Data were processed using the Bruker SAINT
package and the structure solution and refinement procedures
were performed using SHELX97.30 The non-hydrogen atoms
were refined with anisotropic thermal parameters. The hydrogen
atoms were included in geometric positions and given thermal
parameters equivalent to 1.2 times those of the atom to which
they were attached. The final R values were R1 0.0504 and wR2
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