Nanostaircase formation in the solid state from self-assembling synthetic terephthalamides with a common molecular scaffold

Article abstract of DOI:10.1016/j.tet.2006.07.092

The design and construction of nanostructured materials using proper self-assembling molecular building blocks is a real challenge to scientists. Here, we present the formation of a new nano-architecture, i.e., nanostaircase in the solid state by using mo

Full text of DOI:10.1016/j.tet.2006.07.092

Tetrahedron 62 (2006) 9603–9609
Nanostaircase formation in the solid state from self-assembling
synthetic terephthalamides with a common molecular scaffold
Sudipta Ray,a Raghurama P. Hegde,b Apurba Kumar Das,a
a,
N. Shamalab, and Arindam Banerjee
*
*
aDepartment of Biological Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
bDepartment of Physics, Indian Institute of Science, Bangalore 560012, India
Received 21 March 2006; revised 10 July 2006; accepted 27 July 2006
Available online 21 August 2006
Abstract—The design and construction of nanostructured materials using proper self-assembling molecular building blocks is a real chal-
lenge to scientists. Here, we present the formation of a new nano-architecture, i.e., nanostaircase in the solid state by using molecular building
blocks, which are amenable to self-assembly in a directed manner to form the specific nanostructure. The molecular building blocks are
terephthalamides 1–4, which are bis-terephthalamides of methyl esters of various a-amino acids including L-leucine 1, D-leucine 2, L-isoleucine
3, and a-aminoisobutyric acid (Aib) 4. All terephthalamides presented here, irrespective of their different side chain residues or stereochem-
istry, self-assemble to form supramolecular nanostaircase structures in crystals. Each terephthalamide contains two good hydrogen-bond
donors and two hydrogen-bond acceptors. Two N–H/O hydrogen bonds and C–H/p interactions are responsible for the formation and
stabilization of the nanostaircase structures in crystals. The molecular building blocks are packed orthogonally to each other in crystals
and this arrangement can help the formation of nanostaircase structure upon self-assembly.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
as structure directed synthesis of silver nanowires,5 electro-
chemical applications.6 There are also numerous examples
of self-assembling peptide based nanofibers.7
Fabrication of various nanomaterials can be achieved by
mainly two approaches: one approach is photolithography
and the other is the ‘bottom-up’ approach. Using photo-
lithography only two-dimensional nano-scaled materials can
be prepared. However, using ‘bottom-up’ approach, where
molecular self-assembly plays a key role, three-dimensional
nanostructured materials can be constructed.1 Another ad-
vantage of using a bottom-up approach is that well-defined
nanostructured materials can be prepared by using suitable
molecular building blocks and the property of the nanomate-
rials can be tuned by designing appropriate, self-assembling,
molecular building blocks. The design and construction
of various nanostructured materials using molecular self-
assembly is a very active area of current research.2 Nano-
tubes obtained from various, suitable, self-assembling,
organic compounds based molecular building blocks have
been well studied.3 Similarly peptide based nanorods have
been constructed using oligopeptide scaffolds.4 Peptide
nanotubes have been used in many applications such
There are several examples of metal ion directed supra-
molecular staircase formation.8 Several structures of tereph-
thalamides have also been reported using either single crystal
X-ray diffraction studies or neutron fiber diffraction studies.
However, in all previously mentioned bis-terephthalamide
structures only intermolecularly hydrogen-bonded supra-
molecular b-sheets,9 ribbon10 or helix11 are reported, but not
a supramolecular nanostaircase. We decided it would be in-
teresting to use a conformationally rigid molecular scaffold,
which can pack at about right angles to each other using
intermolecular hydrogen bonding and other noncovalent
interactions like C–H/p, p/p interactions to form a spe-
cific, well-defined, supramolecular nano-architecture.
In the course of our continuing interest in constructing var-
ious supramolecular nano-architectures including nanorod4
and nanotube,12 we have synthesized and characterized four
compounds 1–4, which are bis-terephthalamides of methyl
esters of a-amino acids L-leucine, D-leucine, L-isoleucine,
and a-aminoisobutyric acid (Aib), respectively. A schematic
representation of all four terephthalamides is shown in
Figure 1. In this paper, we present the formation of nano-
staircase structures in crystals from a series of self-assem-
bling terephthalamides with a common molecular scaffold.
Keywords: C–H/p interactions; Nanostaircase; Terephthalamide; Self-
assembly; Hydrogen bonds.
* Corresponding authors. Tel.: +91 33 2473 4971; fax: +91 33 2473 2805;
e-mail addresses: shamala@physics.iisc.ernet.in; bcab@mahendra.iacs.
res.in
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.07.092

9604
S. Ray et al. / Tetrahedron 62 (2006) 9603–9609
2. Results and discussion
R1
H
R2
O
N
H3COOC
R2
COOCH3
Colorless single crystals of terephthalamides 1–4weregrown
from methanol–water solution by slow evaporation. The
crystal structure data for four terephthalamides are given
in Table 1. Terephthalamides 1–3 crystallize in the mono-
clinic space group P21 with one molecule in the asymmetric
unit. The monoclinic crystals of terephthalamide 4 crystal-
lize in the centrosymmetric space group P21/c with 1/2
molecule in the asymmetric unit. Selected backbone torsion
angles of all terephthalamides are listed in Table 2. In tereph-
thalamides 1 and 2 the isobutyl groups have large atomic dis-
placement parameters (ADPs). In residues with long side
chains, the side chains are more flexible, hence large ADPs
are observed for these groups. From the crystal structure of
terephthalamide 1, it is evident that there is no intramolecular
N
O
H
R1
1: R1 = -CH2CH(CH3)2, R2 = H
2: R1 = H, R2 = -CH2CH(CH3)2
3: R1 = -CH(CH3)(CH2CH3), R2 = H
4: R1 = R2 = -CH3
Figure 1. Schematic representation of terephthalamides 1, 2, 3, and 4.
These supramolecular nanostaircase structures are formed
and stabilized by various noncovalent interactions includ-
ing intermolecular hydrogen bonding and C–H/p inter-
actions.
Table 1. Crystallographic data for terephthalamides 1, 2, 3, and 4
1
2
3
4
Formula
C22H32N2O6
420.5
Methanol–water
Monoclinic
293
C22H32N2O6
420.5
Methanol–water
Monoclinic
293
C22H32N2O6
420.5
Methanol–water
Monoclinic
293
C18H24N2O6
364.39
Methanol–water
Monoclinic
293
Formula weight
Crystallizing solvent
Crystal system
Temperature [K]
Space group
P21
P21
P21
P21/c
˚
a [A]
10.022 (6)
10.094 (6)
12.626 (7)
108.719 (9)
1209.7 (12)
2
9.9970 (12)
10.1066 (13)
12.6432 (16)
108.679 (2)
1210.1 (3)
2
10.148 (7)
10.645 (7)
11.592 (8)
109.795 (10)
1178.2 (14)
2
11.288 (5)
9.657 (4)
9.601 (4)
110.008 (7)
983.3 (7)
2
˚
b [A]
˚
c [A]
b [ꢀ]
3
V [A ]
˚
Z
rcalcd [g cmꢁ3
]
1.154
1.154
1.185
1.231
˚
l [A]
0.71073
0.084
46.6
452
7458
1831
1610
271
0.0884
0.71073
0.084
46.6
452
7471
1834
1630
271
0.0925
0.71073
0.086
53
452
8599
2344
2065
303
0.0480
0.71073
0.093
53.2
388
7173
1925
1654
166
0.0665
0.1984
0.50, ꢁ0.25
m [mmꢁ1
2qmax
F(000)
]
Total reflns
Unique reflns
Reflns used
Parameters
R1 [I>2s(I)]
wR2
0.2586
0.31, ꢁ0.20
0.2742
0.35, ꢁ0.25
0.1376
0.19, ꢁ0.14
Max. and min.
electron density [e/A ]
3
˚
Table 2. Selected backbone torsional angles (ꢀ) of terephthalamides 1, 2, 3, and 4
Terephthalamide 1
C2M–O2M–C20–C2A
O2M–C20–C2A–N2
C20–C2A–N2–C8
C2A–N2–C8–C5
174.6 (14)
167.8 (8)
C1M–O1M–C10–C1A
ꢁ170.3 (16)
O1M–C10–C1A–N1
C10–C1A–N1–C1
C1A–N1–C1–C2
ꢁ45.5 (13)
ꢁ82.0 (9)
179.5 (7)
ꢁ110.6 (8)
ꢁ179.8 (6)
Terephthalamide 2
C2M–O2M–C20–C2A
O2M–C20–C2A–N2
C20–C2A–N2–C8
C2A–N2–C8–C5
167.8 (16)
45.9 (12)
83.4 (8)
C1M–O1M–C10–C1A
O1M–C10–C1A–N1
C10–C1A–N1–C1
C1A–N1–C1–C2
ꢁ176.1 (14)
ꢁ167.9 (8)
110.3 (8)
179.0 (6)
179.4 (6)
Terephthalamide 3
C2M–O2M–C20–C2A
O2M–C20–C2A–N2
C20–C2A–N2–C8
C2A–N2–C8–C5
177.2 (4)
168.4 (3)
C1M–O1M–C10–C1A
O1M–C10–C1A–N1
C10–C1A–N1–C1
C1A–N1–C1–C2
ꢁ179.2 (4)
169.6 (3)
ꢁ133.6 (3)
ꢁ103.7 (3)
178.0 (2)
175.6 (3)
Terephthalamide 4 (the atom names with a terminating ‘a’ belong to the second half of the molecule related by a inversion center)
C1M–O1M–C10–C1A
O1M–C10–C1A–N1
C10–C1A–N1–C4
C1A–N1–C4–C2
ꢁ174.8 (3)
C1Ma–O1Ma–C10a–C1Aa
O1Ma–C10a–C1Aa–N1a
C10a–C1Aa–N1a–C4a
C1Aa–N1a–C4a–C2a
174.8 (3)
49.6 (3)
47.6 (3)
ꢁ49.6 (3)
ꢁ47.6 (3)
ꢁ175.36 (16)
175.36 (16)

S. Ray et al. / Tetrahedron 62 (2006) 9603–9609
9605
Figure 2. ORTEP diagram of terephthalamide 1 with atomic numbering scheme. Ellipsoids at 30% probability.
hydrogen bond and the molecule possesses an overall ex-
tended backbone conformation (Fig. 2). Terephthalamide 1
self-assembles to form a supramolecular nanostaircase struc-
ture in crystals with various noncovalent interactions being
present including intermolecular hydrogen bonding and
CH/p interactions (Fig. 3). There are two intermolecular
˚
˚
hydrogen bonds (N1–H1/O02, 2.058 (5) A, 2.882 (7) A,
160.03 (35)ꢀ, symmetry equivalent ꢁx+1, y+0.5, ꢁz+2
ꢀ
˚
˚
and N2–H2/O01, 2.141 (5) A, 2.945 (7) A, 155.35 (36) ,
symmetry equivalent ꢁx, yꢁ0.5, ꢁz+2) that connect the
individual molecules of terephthalamide 1 to form supra-
molecular nanostaircase structure in which the length of
˚
the steps is 7.5 A (0.75 nm) and the height of the steps of the
˚
staircases is also 7.5 A (0.75 nm). In crystals, individual
molecules are stacked orthogonally to each other using
N–H/O hydrogen bonding and C–H/p interactions and
this particular arrangement helps to form the supramolecular
nanostaircase structure. There is a C–H/p interaction13
between C2D2–H2D6 with the centroid of the phenyl ring
˚
of terephthalamide moiety (C2D2–H2D6/p, 3.26 A,
ꢀ
of the terephthalamide 1.
˚
4.047 A, 140.97 ) (Fig. 6a) in supramolecular nanostaircase
Terephthalamide 2 contains two D-leucine residues and
adopts a molecular structure, which is a mirror image of tere-
phthalamide 1 (Fig. 4). The only difference between them is
the reversal of sign of the comparable backbone torsion
angles (O2M–C20–C2A–N2 and O1M–C10–C1A–N1; C20–
C2A–N2–C8 and C10–C1A–N1–C1) of terephthalamide 2
with respect to terephthalamide 1 (Table 2). Terephthalamide
2 also self-assembles to form a supramolecular nano-
staircase (Fig. 5) in crystals through various noncovalent
interactions including intermolecular hydrogen bꢀonding
˚
˚
(N1–H1/O02, 2.144 (5) A, 2.946 (8) A, 154.90 (39) , sym-
metry equivalent ꢁx+2, y+0.5, ꢁz+2 and N2–H2/O01,
Figure 3. Crystal packing diagram of the terephthalamide 1 illustrating the
supramolecular nanostaircase structure.
Figure 4. ORTEP representation of terephthalamide 2 with atomic numbering scheme. Ellipsoids at 30% probability.

9606
S. Ray et al. / Tetrahedron 62 (2006) 9603–9609
Figure 5. Nanostaircase arrangement of terephthalamide 2 in crystals and
its schematic representation.
ꢀ
˚
˚
2.050 (5) A, 2.877 (7) A, 160.84 (35) , symmetry equivalent
ꢁx+1, yꢁ0.5, ꢁz+2). There is a C–H/p interaction
between C1D2–H1D5 with centroid of the phenyl ring
˚
of terephthalamide moiety (C1D2–H1D5/p, 3.18 A,
˚
3.982 A, 142.66 ) (Fig. 6b) in supramolecular nanostaircase
ꢀ
of the terephthalamide 2.
Both L-leucine residues of terephthalamide 1 have been
substituted by L-isoleucine residues in terephthalamide 3
(Fig. 7). However, the inherent characteristic feature of
terephthalamide 3 is similar to that of terephthalamide 1.
The only difference between them is the difference among
numerical values of the comparable backbone torsion
angles (O2M–C20–C2A–N2 and O1M–C10–C1A–N1; C20–
C2A–N2–C8 and C10–C1A–N1–C1) of terephthalamide 3
(Table 2). Terephthalamide 3 also self-associates to form a
supramolecular nanostaircase architecture utilizing two
intermolecular hydrogen bonds (N1–H1/O02, 2.211
Figure 6. Packing modes of nanostaircase structures by C–H/p inter-
actions in (a) terephthalamide 1 and (b) terephthalamide 2 in crystals.
ꢀ
˚
˚
moiety (C1B2–H1B5/p, 3.427 A, 4.355 A, 162.54 )
(Fig. 11) of the terephthalamide 4.
ꢀ
˚
˚
(36) A, 2.999 (4) A, 166.88 (341) , symmetry equivalent
˚
All four terephthalamides with different amino acid side
chains or stereochemistry self-assemble in a similar manner
in which the molecular building blocks are packed against
each other orthogonally to form a nanostaircase structure
utilizing N–H/O hydrogen bonding and C–H/p inter-
actions. It is interesting to note that the previously reported
crystal structure of N,N0-bis(methoxycarbonylmethyl)-
terephthalamide10 (molecule A), reveals that the molecule A
self-assembles through two intermolecular hydrogen bonds
along the crystallographic b axis to form a supramolecular
ribbon or sheet-like structure (Fig. 12). In this molecular
packing, the aromatic rings of these adjacent molecules are
ꢁx+1, y+0.5, ꢁz+1 and N2–H2/O01, 2.337 (42) A, 3.089
ꢀ
˚
(5) A, 163.16 (387) , symmetry equivalent ꢁx, yꢁ0.5,
ꢁz+1) (Fig. 8). There is a C–H/p interaction between
C2D1–H2D2 with centroid of the phenyl ring of tereph-
˚
˚
thalamide moiety (C2D1–H2D2/p, 3.378 A, 4.009 A,
125.2ꢀ) in the supramolecular nanostaircase of terephthal-
amide 3.
The achiral terephthalamide 4 also adopts an extended back-
bone molecular conformation (Fig. 9). The comparable
backbone torsion angles of the symmetric terephthalamide
4 (O1M–C10–C1A–N2 and O1Ma–C10a–C1Aa–N1a; C10–
C1A–N1–C4 and C10a–C1Aa–N1a–C4a) have the same
numerical values but are opposite in sign (Table 2). Utilizing
two intermolecular hydrogen bondꢀs (N1–H3/O01, 2.022
˚
close to perpendicular direction with a distance of 5.13 A be-
tween the centers of the two aromatic rings. In the formation
of the above mentioned ribbon or sheet-like structure, the
self-assembling molecules are stacked atop one another
and they are interconnected by only N–H/O hydrogen
bonding. However, in our case molecular building blocks
are stacked almost orthogonally to each other in all four tere-
phthalamides and they are associated with intermolecular
–C]O/H–N– hydrogen bonding as well as C–H/p inter-
actions. This helps to form supramolecular nanostaircase
˚
˚
(25) A, 2.856 (3) A, 174.10 (221) , symmetry equivalent
˚
x, ꢁy+0.5, zꢁ0.5 and N1a–H3a/O01, 2.022 (25) A,
ꢀ
˚
2.856 (3) A, 174.10 (221) , symmetry equivalent ꢁx+1,
y+0.5, ꢁz+0.5, the ‘a’ after atom name indicates that the
second half of the molecule is related by an inversion cen-
ter), terephthalamide 4 forms a supramolecular nanostair-
case architecture (Fig. 10). The nanostaircase structure is
also stabilized by C–H/p interaction between C1B2–
H1B5 with centroid of the phenyl ring of terephthalamide
˚
structures. The step-length of the nanostaircase is w7.5 A
˚
and the height of the steps is w7.5 A. Here, the reported
terephthalamides 1–4 fail to stack atop one another to

S. Ray et al. / Tetrahedron 62 (2006) 9603–9609
9607
Figure 7. Molecular conformation of terephthalamide 3 with atomic numbering scheme. Thermal ellipsoids are shown at 30% probability level.
Figure 8. Supramolecular staircase structure obtained from the higher order
self-assembly of the terephthalamide 3 in crystals. The C–H/p inter-
actions are shown as dotted line.
Figure 10. Packing diagram of the terephthalamide 4 showing the supra-
molecular staircase architecture in crystals stabilized by multiple inter-
molecular hydrogen bonds.
Figure 9. The molecular structure of terephthalamide 4 with atomic numbering scheme. Ellipsoids at 30% probability.
form supramolecular sheet- or ribbon-like structure, which
might be due to the steric hindrances associated with
the bulky amino acid side chains. Orthogonal packing
between the self-associating molecular building blocks
(terephthalamides 1–4) may be favored by the presence of
C–H/p interactions between the amino acid side chain
H-atoms and the centrally located aromatic moiety, which
was absent in the molecular packing of the molecule A.

9608
S. Ray et al. / Tetrahedron 62 (2006) 9603–9609
4. Experimental
4.1. General
Reagent or analytical grade material was obtained from
commercial suppliers and used without further purification.
Terephthalamides 1, 2, 3, and 4 were synthesized by the
conventional solution phase methodology.15 A solution of
terephthalic acid (0.83 g, 5 mmol) in 10 mL of DMF was
cooled in an ice-water bath. The H–Xxx–OMe (Xxx¼Leu,
D-Leu, Ile, and Aib) was isolated from the corresponding
methyl ester hydrochloride (20 mmol) by neutralization,
subsequent extraction with ethyl acetate and the ethyl ace-
tate extract was concentrated to 10 mL. This was then added
to the reaction mixture, followed immediately by DCC
(2.06 g, 10 mmol) and HOBt (1.35 g, 10 mmol). The reac-
tion mixture was stirred for three days. The residue was
taken in ethyl acetate (60 mL) and the DCU was filtered
off. The organic layer was washed with 2 M HCl
(3ꢂ50 mL), brine (2ꢂ50 mL), 1 M sodium carbonate
(3ꢂ50 mL), and brine (2ꢂ50 mL), then dried over
anhydrous sodium sulfate and evaporated in vacuo to yield
terephthalamides 1–4 as white solid. Purification was done
by silica gel column (100–200 mesh) using ethyl acetate
as eluent. The final compounds were fully characterized by
IR spectroscopy, 300 MHz 1H NMR spectroscopy, and
mass spectrometry. Optical rotations were measured on a
Perkin–Elmer 341LC polarimeter. IR spectra were recorded
Figure 11. A view of interconnected C–H/p interactions in terephthal-
amide 4.
on a Shimadzu (Japan) model FTIR spectrophotometer with
€
1
KBr pellets. H NMR spectra were recorded with a Bruker
DPX 300 MHz spectrometer. Mass spectra were recorded
on a Hewlett Packard Series 1100MSD spectrometer.
4.1.1. Terephthalamide 1. Yield¼1.68 g (4 mmol, 80%);
Rf¼0.72 (EtOAc); [a]2D0 +42.3 (c¼0.7 in chloroform); mp
1
144–146 ꢀC; H NMR (300 MHz, CDCl3, 25 ꢀC, TMS):
d 7.85 (s, 4H; Aromatic ring Hs), 6.65 (d, J¼8.1 Hz,
2H; Leu NH), 4.9–4.83 (m, 2H; Leu CaH), 3.78 (s, 6H;
–OCH3), 1.79–1.65 (m, 6H; Leu CbH & CgH), 1.01–
d
ꢀ
0.97 ppm (m, 12H; Leu C H); IR (KBr): n¼3325, 1747,
Figure 12. Crystal packing of terephthalamide A showing the formation of
intermolecularly hydrogen-bonded ribbon-like structure. Intermolecular
hydrogen bonds are shown as dotted lines.
1635, 1550 cmꢁ1; MS (ESI): m/z (%): 421.3 (48) [M+H]+,
841.5 (100) [2M+H]+; elemental analysis calcd (%) for
C22H32N2O6 (420): C 62.85, H 7.6, N 6.66; found: C 63.1,
H 7.8, N 7.03.
3. Conclusion
This paper clearly demonstrates the formation and stabiliza-
tion of supramolecular nanostaircase structures in crystals
using suitable self-assembling synthetic terephthalamides
with a common molecular scaffold. Here, the self-assembly
of molecular building blocks is guided in such a way that
individual molecules can pack at about right angles to
each other using various noncovalent interactions including
C]O/H–N hydrogen bonding and CH/p interactions to
form nanostaircase structures. We have identified here
a common structural unit (i.e., bis-terephthalamide based
methyl esters of various a-amino acids containing different
side chains or stereochemistry), which self-assembles in
similar fashion to form a well-defined nanostructure,
namely, a nanostaircase. This result may open up a new field
of constructing new supramolecular nano-structures (using
appropriate molecular building blocks), which has some use-
ful implications in supramolecular chemistry and as well as
in crystal engineering.14
4.1.2. Terephthalamide 2. Yield¼1.50 g (3.5 mmol, 71%);
Rf¼0.75 (EtOAc); [a]2D0 ꢁ42.9 (c¼0.7 in chloroform);
1
mp 138–140 ꢀC; H NMR (300 MHz, CDCl3, 25 ꢀC,
TMS): d 7.85 (s, 4H, Aromatic ring Hs), 6.69 (d, J¼8.4 Hz,
2H; D-Leu NH), 4.87–4.83 (m, 2H; D-Leu CaH), 3.79
(s, 6H; –OCH3), 1.78–1.65 (m, 6H; D-Leu CbH & CgH),
d
ꢀ
1.01–0.93 ppm (m, 12H; D-Leu C H); IR (KBr): n¼3325,
1746, 1636, 1548, 1500 cmꢁ1; MS (ESI): m/z (%): 421.3
(33) [M+H]+; 863.3 (100) [2M+Na]+; elemental analysis
calcd (%) for C22H32N2O6 (420): C 62.85, H 7.6, N 6.66;
found: C 62.51, H 7.92, N 7.15.
4.1.3. Terephthalamide 3. Yield¼1.6 g (3.8 mmol, 76%);
Rf¼0.6 (EtOAc); [a]2D0 +46.4 (c¼0.7 in chloroform); mp
1
82–84 ꢀC; H NMR (300 MHz, CDCl3, 25 ꢀC, TMS):
d 7.87 (s, 4H, Aromatic ring H), 6.70 (d, J¼8.4 Hz, 2H;
Ile NH), 4.84–4.8 (m, 2H; Ile CaH), 3.79 (s, 6H; –OCH3),
2.17–2.0 (m, 2H; Ile CbH), 1.16–1.5 (m, 10H; Ile CgH),

S. Ray et al. / Tetrahedron 62 (2006) 9603–9609
9609
d
ꢀ
2. (a) Gao, X.; Matsui, H. Adv. Mater. 2005, 17, 2037–2050; (b)
Bong, D. T.; Clark, T. D.; Granja, J. R.; Ghadiri, M. R.
Angew. Chem., Int. Ed. 2001, 40, 988–1011.
3. (a) Reches, M.; Gazit, E. Nano Lett. 2004, 4, 581–585; (b)
Ghadiri, M. R.; Granja, J. R.; Buehler, L. K. Nature 1994,
369, 301–304.
0.99–0.97 ppm (m, 6H; Ile C H); IR (KBr): n¼3411, 3345,
1744, 1636, 1548, 1503 cmꢁ1; MS (ESI): m/z (%): 421.3
(55) [M+H]+; 841.5 (100) [2M+H]+; elemental analysis
calcd (%) for C22H32N2O6 (420): C 62.85, H 7.6, N 6.66;
found: C 63.21, H 7.52, N 6.95.
4. Haldar, D.; Banerjee, A.; Drew, M. G. B.; Das, A. K.; Banerjee,
A. Chem. Commun. 2003, 1406–1407.
5. Reches, M.; Gazit, E. Science 2003, 300, 625–627.
6. Yemini, M.; Reches, M.; Rishpon, J.; Gazit, E. Nano Lett. 2005,
5, 183–186.
7. (a) Yokoi, H.; Kinoshita, T.; Zhang, S. Proc. Natl. Acad. Sci.
U.S.A. 2005, 102, 8414–8419; (b) Guler, M. O.; Soukasene,
S.; Hulvat, J. F.; Stupp, S. I. Nano Lett. 2005, 5, 249–252; (c)
Sone, E. D.; Stupp, S. I. J. Am. Chem. Soc. 2004, 126,
12756–12757.
4.1.4. Terephthalamide 4. Yield¼1.3 g (3.5 mmol, 72%);
Rf¼0.7 (EtOAc); [a]2D0 0.01 (c¼0.7 in chloroform); mp
1
220–222 ꢀC; H NMR (300 MHz, CDCl3, 25 ꢀC): d 7.84
(s, 4H; Aromatic ring H), 6.84 (s, 2H; Aib NH), 3.80 (s,
6H; –OCH3), 1.7 ppm (s, 12H; Aib CbH); IR (KBr):
n¼3322, 3226, 1741, 1631, 1560 cmꢁ1; MS (ESI): m/z
ꢀ
(%): 388.0 (100) [M+Na+H]+; 366.0 (52) [M+2H]+; elemen-
tal analysis calcd (%) for C18H24N2O6 (364): C 59.34, H
6.59, N 7.69; found: C 60.01, H 6.98, N 7.75.
8. (a) Ghosh, S. K.; Bharadwaj, P. K. Eur. J. Inorg. Chem. 2005,
4886–4889; (b) Gabbai, F. P.; Schier, A.; Riede, J. Angew.
Chem., Int. Ed. 1998, 37, 622–624; (c) Fortin, D.; Drouin,
M.; Harvey, P. D. J. Am. Chem. Soc. 1998, 120, 5351–5352;
(d) Nagata, N.; Kugimiya, S.; Fujiwara, E.; Kobuke, Y. New
J. Chem. 2003, 27, 743–747; (e) Ren, C.-X.; Zhu, H.-L.;
Yang, G.; Chen, X.-M. J. Chem. Soc., Dalton Trans. 2001,
85–90; (f) Alexakis, A.; Tomassini, A.; Chouillet, C.; Roland,
S.; Mangeney, P.; Bernardinelli, G. Angew. Chem., Int. Ed.
2000, 39, 4093–4095.
9. (a) Cobbledick, R. E.; Small, R. W. H. Acta Crystallogr., Sect. B
1972, 28, 2893–2896; (b) Gardner, K. H.; English, A. D.;
Forsyth, V. T. Macromolecules 2004, 37, 9654–9656.
10. Armelin, E.; Escudero, E.; Campos, L.; Puiggali, J. Acta
Crystallogr., Sect. C 2001, 57, 172–173.
4.2. X-ray crystallography
All crystal data were measured on a Bruker AXS Smart
˚
Apex CCD diffractometer with Mo Ka (l¼0.71073 A) radi-
ation at 20 ꢀC. The structure was obtained by direct methods
using SHELXS-97.16 Refinement was carried out with a full
matrix least squares method against F2 using SHELXL97.17
CCDC-229937 (1), CCDC-600050 (2), CCDC-229938 (3),
and CCDC-229939 (4) contain the supplementary crystallo-
graphic data for the paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or
from the Cambridge Crystallographic Data Centre, 12 Union
Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033; or
e-mail: deposit@ccdc.cam.ac.uk).
11. Yin, H.; Lee, G.; Sedey, K. A.; Rodriguez, J. M.; Wang, H.-G.;
Sebti, S. M.; Hamilton, A. D. J. Am. Chem. Soc. 2005, 127,
5463–5468.
Acknowledgements
This research is supported by a grant from Department of
Science and Technology (DST), India (Project No. SR/S5/
OC-29/2003). We thank the Department of Science and
Technology, India, for data collection on the CCD facility
funded by the IRHPA-DST program at the Indian Institute
of Science. S.R. and A.K.D. wish to acknowledge the
CSIR, New Delhi, India for financial assistance.
12. Ray, S.; Haldar, D.; Drew, M. G. B.; Banerjee, A. Org. Lett.
2004, 6, 4463–4465.
13. Brandl, M.; Weiss, M. S.; Jabs, A.; S€uhnel, J.; Hilgenfeld, R.
J. Mol. Biol. 2001, 307, 357–377.
14. (a) Arora, K. K.; Pedireddi, V. R. J. Org. Chem. 2003, 68,
9177–9185; (b) Varughese, S.; Pedireddi, V. R. Chem.—Eur.
J. 2006, 12, 1597–1609; (c) Desiraju, G. R. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 2311–2327; (d) Aitipamula, S.;
Thallapally, P. K.; Thaimattam, R.; Jaskolski, M.; Desiraju,
G. R. Org. Lett. 2002, 4, 921–924.
References and notes
15. Bodanszky, M.; Bodanszky, A. The Practice of Peptide
Synthesis; Springer: New York, NY, 1984; pp 1–282.
16. Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467–473.
17. Sheldrick, G. M. SHELXL97 Program for Crystal Structure
1. (a) Seeman, N. C.; Belcher, A. M. Proc. Natl. Acad. Sci. U.S.A.
2002, 99, 6451–6455; (b) Zhang, S. Nat. Biotechnol. 2003, 21,
1171–1178; (c) Whitesides, G. M.; Mathias, J. P.; Seto, C. T.
Science 1991, 254, 1312–1319.
€
Refinement;UniversityofGottingen:Gottingen,Germany, 1997.
€