Porous organic material from discotic tricarboxyamide: Side chain-core interactions

Article abstract of DOI:10.1021/ol402865t

The benzene-1,3,5-tricarboxyamide containing three l-methionine (1) self-assemble through 3-fold amide-amide hydrogen bonds and π-π stacking to fabricate one-dimensional nanorod like structure. However, the tyrosine analogue (2) carrying multiple H-bonding side chains lost the C₃ symmetry and 3-fold amide-amide hydrogen bonds and developed a porous structure. The porous material exhibits ten times more N₂ sorption (155 cc/g) than the columnar one, indicating that side chain-core interactions have a drastic effect on structure and function.

Full text of DOI:10.1021/ol402865t

Letter
pubs.acs.org/OrgLett
Porous Organic Material from Discotic Tricarboxyamide: Side Chain−
Core interactions
Poulami Jana, Arpita Paikar, Santu Bera, Suman Kumar Maity, and Debasish Haldar*
Department of Chemical Sciences, Indian Institute of Science Education and Research Kolkata, Mohanpur, West Bengal 741252,
India
S
* Supporting Information
ABSTRACT: The benzene-1,3,5-tricarboxyamide containing three L-methionine (1)
self-assemble through 3-fold amide−amide hydrogen bonds and π−π stacking to
fabricate one-dimensional nanorod like structure. However, the tyrosine analogue (2)
carrying multiple H-bonding side chains lost the C3 symmetry and 3-fold amide−amide
hydrogen bonds and developed a porous structure. The porous material exhibits ten
times more N2 sorption (155 cc/g) than the columnar one, indicating that side chain−
core interactions have a drastic effect on structure and function.
he organization of building blocks in a particular fashion is
tricarboxyamide. However, the tricarboxyamide possesses the
Tthe key step toward the fabrication of new materials and remarkable ability to form columnar superstructures consisting
devices.1 The organized materials are developed by association
of cofacially stacked π face in its interior, while its exterior is
surrounded by a hydrocarbon wrapper. The reported tyrosine-
containing chiral tricarboxyamide 2 adopts nanoporous
structures.
of the cooperative building blocks through H-bonding, metal−
ion complexation, electrostatic interactions, and hydrophobic
interactions. The numbers of such organized materials by
assembly of synthetic building blocks are growing.2
For tricarboxyamides 1 and 2 the design principle explored
was how to use the chiral amino acid side chains to force the
amides functional groups out of the plane of the central
aromatic ring and adopt a conformation that facilitates
formation of three intermolecular hydrogen bonds. For
tricarboxyamide 2, we used the Tyr residue to introduce
additional hydrogen bonds and steric hindrence. Target
compounds 1 and 2 were synthesized by functionalizing
benzene-1,3,5-tricarboxylic acid with the appropriate chiral
amino acid methyl ester following a high purity, as confirmed
Over the past decades, large numbers of discotic building
blocks with a wide range of amplified properties have been
heavily studied.3 A broad range of discotic benzene-1,3,5-
tricarboxyamides have been synthesized and studied in detail.2e
Various functional groups such as alkyl,4 aryl,5 pyridyl,6
bipyridyl,7 porphyrinyl,8 triphenylyl,9 oligo(p-phenyleneviny-
lene),10 amino acid,11 dipeptide,12 oligopeptide,13 oligo-
(ethyleneoxy),14 and benzocrown ethers15 have been incorpo-
rated in the tricarboxyamide. The tricarboxyamides may be
chiral nonracemic, racemic, or achiral. When three identical
functional groups are connected to the amides, the tricarbox-
yamides are C3 symmetric. These tricarboxyamide derivatives
have wide applications such as organogels,16 hydrogels,17 liquid
crystals,18 nanostructured materials,19 MRI contrast reagents,20
nucleating agents for polymers,21 metal complexation
reagents,11d and microcapsules for drug delivery.22 Until now,
studies on tricarboxyamides have focused on the aggregations
by core−core interactions and 3-fold amide−amide hydrogen
bonding. However, the report on the effect of side chain−core
interactions on the self-assembly of discotic tricarboxyamides is
rare.2e
1
by H NMR, 13C NMR, FTIR, and mass spectrometry (MS)
analysis.
The self-assembly of the reported discotic compounds 1 and
2 containing chiral side chains has been studied using a wide
variety of different spectroscopic techniques in dilute methanol.
From solution-state studies, the UV−vis spectroscopy of
tricarboxyamides 1 and 2 in methanol shows a bathochromic
shift of the absorption maximum with increasing concentration
(Figure 1). Circular dichroism (CD) spectroscopy of discotic
compound 1 in dilute methanol solutions indeed shows a
strong Cotton effect centered around 218 nm, confirming the
helical nature of the aggregates (Figure 1, Supporting
Information).23 Further analysis reveals that the tricarboxya-
Here, we describe an example of very unusual nonhelical
assembly from discotic tricarboxyamides at the atomic level.
Specifically, we show that the side-chain−core interactions have
a significant effect on self-assembly of chiral benzene-1,3,5-
Received: October 4, 2013
Published: December 18, 2013
© 2013 American Chemical Society
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Letter
Figure 1. (a) UV−vis absorption spectra of the tricarboxyamide 2 at
different concentrations in methanol. (b) CD spectra of 2 at different
concentrations in methanol.
Figure 4. N2 sorption isotherm of (a) tricarboxyamide 1 and (b)
tricarboxyamide 2 at 77 K (P0 = 1 atm). Black circle: sorption. White
circle: desorption.
mide 2 in dilute methanol solutions shows strong Cotton
effects around 210 and 237 nm. However, with increasing
concentration the peak at 210 nm disappeared and intensity of
237 nm peak increased. The results indicate that the self-
assembly pattern of tricarboxyamide 2 is significantly different
from that of 1.
Further, the solid state FT-IR spectroscopy has been used to
investigate the self-assembly and arrangement of the
intermolecular H-bonding of tricarboxyamides. FT-IR spectra
of methionine substituted symmetric discotic compound 1 gave
rise to typical NH, amide I and amide II vibrations at 3231,
1641, and 1555 cm−1 confirming the presence of 3-fold
intermolecular H-bonding (Figure 2, Supporting Information).
These results indicate that the presence of methionine side
chains next to the amide core does not affect the H-bonding
pattern in discotic tricarboxyamide 1. For more polar tyrosine
substituted discotic tricarboxyamide 2, the H-bonding pattern
changes in the solid state as evidenced by FT-IR spectroscopy.
The N−H stretch appears at 3378 cm−1 and CO stretch at
1656 cm−1 suggesting the loss of 3-fold intermolecular H-
bonding (Figure 3, Supporting Information).24 This result
indicates a lack of columnar order in compound 2 at room
temperature. Meijer and co-workers have reported the presence
of 3-fold intermolecular H-bonding in phenylalanine sub-
stituted symmetric discotic compound by the solid state FT-IR
spectroscopy and concluded that the presence of bulky benzyl
groups next to the amide core does not necessarily affect the H-
bonding pattern.11e Hence, lack of columnar order in
tricarboxyamide 2 may be attributed to competitive inter-
molecular H-bonding between tyrosine phenolic oxygen and
amide hydrogen of the tricarboxyamide core.
Figure 2. (a, b) Top and side view of tricarboxyamide 1 with
intermolecular hydrogen bonds in the solid state. (c) Columnar
assembly through multiple intermolecular N−H···O hydrogen bonds
and π−π stacking interactions of 1. (d, e) Solid state molecular
structures of tricarboxyamide 2. (f) Cagelike packing of 2 in the solid
state by multiple intermolecular N−H···O and O−H···O hydrogen-
bonding interactions. Hydrogen bonds are shown as dotted lines. In
(a), (b), (d), and (e), amino acid side chains, α-hydrogens, and acid
groups have been removed to clarify the view.
Figure 3. AFM image of tricarboxyamide 1 showing helical nano
fibers. (b) AFM image showing polydisperse nanoporous morphology
of tricarboxyamide 2.
Finally, X-ray crystallography sheds some light on molecular
structures and self-assembly pattern of the chiral tricarbox-
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Organic Letters
Letter
yamides 1 and 2. Colorless hexagonal crystals of compound 1
and colorless monoclinic crystals of compound 2 suitable for X-
ray diffraction studies were obtained from their respective
methanol−water solutions by slow evaporation.25 Shown in
Figure 2a is the crystal structure of compound 1. From the
crystal structure, the amide groups are out of the central ring
plane and Met side chains are in same face of compound 1.
However, aromatic amides prefer coplanarity26 of the carbonyl
functional group with the aryl system to optimize conjugation,
in compound 1 the amides are tilted toward the same direction.
This is because of the competition between the demand of
conjugation (amide and aryl) and that of intermolecular NH···
OC H-bonding. Hence the crystal structure of discotic
compound 1 showed 3-fold intermolecular H-bonding.27 The
center-to-center distance between the benzene rings in
columnar assembly is about 3.35 Å. The amide twist angle
(38.5°, 41.8,° and 42.4°) out of the central benzene ring plane
modulates the distance between adjacent molecules. From
Figure 2b, each molecule of 1 has a permanent dipole moment.
The direction of the dipole moment is perpendicular to the
central benzene ring plane. Hence in the columnar stacking the
dipoles could sum to generate a macroscopic dipole moment.
The torsion angles (ω, ϕ, ψ) around the methionine residues
appears to play a critical role in dictating the overall structural
features and columnar stacking of 1. The helical columnar
assemblies are further stabilizing by three cooperative hydrogen
bonding interactions of amide groups (Figure 2c) (Table, 1,
Supporting Information). For 1, in higher order assembly, a
honeycomb-like structure has been observed (Figure 4,
Supporting Information). From the solid-state structure of
discotic compound 2, the amide groups are almost in the same
plane of the central benzene ring though the molecule contains
sterically hindered tyrosines (Figure 2d,e).The three amides
make torsion angles of 17.6°, 18.7°, and 162.2° with the aryl
mean plane. The solid state structure of 2 exhibits that the two
tyrosine side chains are in the same face and the third one is in
the opposite face of the central benzene ring (Figure 5,
Supporting Information). The crystal structure of discotic
triacrboxyamide 2 showed no 3-fold intermolecular NH···O
C hydrogen bonding and the loss of C3 symmetry.
compound 1 is 5.44 nm and N2 uptake was 14.99 cc/g. The N2
sorption studies with evacuated sample of compound 2 exhibit
a type-I isotherm (Figure 4b). The pore size distribution curve
of compound 2 showed three peaks at 5.77, 25.99, and 61.34
nm indicating a polydisperse nanoporous structure. The N2
uptake of compound 2 was found to be 155 cc/g. Hence the
unusual packing of compound 2 helps to adsorb N2 ten times
more than that of compound 1. The PXRD spectra of 2 used
for gas sorption experiment (Figure 6a, Supporting Informa-
tion) and the powder pattern from X-ray crystallography
(Figure 6b, Supporting Information) of 2 confirmed the
existence of same structure in both.
In summary, the atomic level analysis reveals that benzene-
1,3,5-tricarboxyamide-containing methionine faciliates forma-
tion of the cofacially stacked columnar structure but the
tyrosine analogue self-assembles to form nanoporous material.
The tricarboxyamide 2 exhibits 10 times higher N2 sorption
than 1. These findings indicate that the side chain−core
interactions have drastic effects on structure and function.
Further studies on these compounds should reveal additional
novelties.
ASSOCIATED CONTENT
* Supporting Information
■
S
Experimental procedures, spectral characterization, and crys-
tallographic data for 1 and 2 (CIF). This material is available
free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
■
*E-mail: deba_h76@yahoo.com.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We acknowledge the CSIR, New Delhi, India (Project No 01/
2507/11-EMR-II). P.J. and S.K.M. thank CSIR, India, for
fellowships. A.P. and S.B. thank UGC, India, for fellowship.
The steric hindrance and competitive intermolecular H-
bonding between side chains and tricarboxyamide core appear
to play a critical role in dictating the overall structural features
of 2. Moreover, each molecule of compound 2 interacts with six
surrounding molecules through multiple N−H···O and O−H···
O intermolecular hydrogen bonds between tyrosine phenolic
oxygen and amide hydrogen of the tricarboxyamide core and
developed a porous structure in higher order assembly (Figure
2f).
The analysis of the morphology of compound 1 by atomic
force microscopy (AFM) reveals the formation of fibers have
diameter c.a. 100 nm and several micrometer in length (Figure
3a). The compound 1 shows spontaneous nucleation,
interfacial control, and one-dimensional growth which results
in the molecules stacking into fibers. However, the AFM images
of tricarboxyamide 2 show polydisperse nanoporous morphol-
ogy (Figure 3b). The loss of C3 symmetry and 3-fold
intermolecular amide−amide hydrogen bonding have pro-
moted the phenolic oxygen and core hydrogen bonds and
cluster formation.
REFERENCES
■
(1) (a) Lehn, J. M. Supramolecular Chemistry; VCH: Weinheim, 1995.
(b) Mastalerz, M.; Oppel, I. M. Angew. Chem., Int. Ed. 2012, 51, 5252.
(c) Mastalerz, M. Chem.Eur. J. 2012, 18, 10082.
(2) (a) Hecht, V.; Huc, I. Foldamer; Wiley-VCH: Weinheim, 2007.
(b) Nagai, A.; Chen, X.; Feng, X.; Ding, X.; Guo, Z.; Jiang, D. Angew.
Chem., Int. Ed. 2013, 52, 3770. (c) Hoeben, F. J. M.; Jonkheijm, P.;
Meijer, E. W.; Schenning, A. Chem. Rev. 2005, 105, 1491. (d) Zayed, J.
M.; Nouvel, N.; Rauwald, U.; Scherman, O. A. Chem. Soc. Rev. 2010,
39, 2806. (e) Cantekin, S.; Greef, T. F. A.; Palmans, A. R. A. Chem. Soc.
Rev. 2012, 41, 6125.
(3) Bushey, M. L.; Nguyen, T. Q.; Zhang, W.; Horoszewski, D.;
Nuckolls, C. Angew. Chem., Int. Ed. 2004, 43, 5446.
(4) (a) Matsunaga, Y.; Miyajima, N.; Nakayasu, Y.; Sakai, S.;
Yonenaga, M. Bull. Chem. Soc. Jpn. 1988, 61, 207. (b) Stals, P. J. M.;
Everts, J.; de Bruijn, R.; Filot, I. A. W.; Smulders, M. M. J.; Martín-
Rapu n, R.; Pidko, E. A.; de Greef, T. F. A.; Palmans, A. R. A.; Meijer,
́
E. W. Chem.Eur. J. 2010, 16, 810.
(5) (a) van Gorp, J. J.; Vekemans, J. A. J. M.; Meijer, E. W. J. Am.
Chem. Soc. 2002, 124, 14759. (b) Bernet, A.; Albuquerque, R. Q.;
Behr, M.; Hoffmann, S. T.; Schmidt, H.-W. Soft Matter. 2012, 8, 66.
(6) Palmans, A. R. A.; Vekemans, J. A. J. M.; Meijer, E. W.;
Kooijmans, H.; Spek, A. L. Chem. Commun. 1997, 2247.
(7) Brunsveld, L.; Zhang, H.; Glasbeek, M.; Vekemans, J. A. J. M.;
Meijer, E. W. J. Am. Chem. Soc. 2000, 122, 6175.
In order to examine the porous structure, gas absorption
studies have been performed. Tricarboxyamide 1 exhibits a
type-III N2 sorption isotherm (Figure 4a). The pore size in
40
dx.doi.org/10.1021/ol402865t | Org. Lett. 2014, 16, 38−41

Organic Letters
Letter
(8) van Hameren, R.; Scho n, P.; van Buul, A. M.; Hoogboom, J.;
̈
Lazarenko, S. V.; Gerritsen, J. W.; Engelkamp, H.; Christianen, P. M.;
Heus, H. A.; Maan, J. C.; Rasing, T.; Speller, S.; Rowan, A. E.;
Elemans, J. A. A. W.; Nolte, R. J. M. Science 2006, 314, 1433.
(9) Paraschiv, I.; Giesbers, M.; van Lagen, B.; Grozema, F. C.;
Abellon, R. D.; Siebbeles, L. D. A.; Marcelis, A. T. M.; Zuilhof, H.;
Sudho lter, E. J. R. Chem. Mater. 2006, 18, 968.
̈
(10) van Herrikhuyzen, J.; Jonkheijm, P.; Schenning, A. P. H. J.;
Meijer, E. W. Org. Biomol. Chem. 2006, 4, 1539.
(11) (a) de Loos, M.; van Esch, J. H.; Kellogg, R. M.; Feringa, B. L.
Tetrahedron 2007, 63, 7285. (b) Bose, P. P.; Drew, M. G. B.; Das, A.
K.; Banerjee, A. Chem. Commun. 2006, 3196. (c) Besenius, P.; Portale,
G.; Bomans, P. H. H.; Janssen, H. M.; Palmans, A. R. A.; Meijer, E. W.
Proc. Natl. Acad. Sci. U.S.A. 2010, 107, 17888. (d) Gelinsky, M.;
Vogler, R.; Vahrenkamp, H. Inorg. Chem. 2002, 41, 2560. (e) Veld, M.
A. J.; Haveman, D.; Palmans, A. R. A.; Meijer, E. W. Soft Matter 2011,
7, 524.
(12) Hout, K. P. v. d.; Martín-Rapun, R.; Vekemans, J. A. J. M.;
́
Meijer, E. W. Chem.Eur. J. 2007, 13, 8111.
(13) Matsuura, K.; Murasato, K.; Kimisuka, N. J. Am. Chem. Soc.
2005, 127, 10148.
́
́
(14) Stals, P. J. M.; Haveman, J. F.; Martín-Rapun, R.; Fitie, C. F. C.;
Palmans, A. R. A.; Meijer, E. W. J. Mater. Chem. 2009, 19, 124.
(15) Lee, S.; Lee, J.-S.; Lee, C. H.; Jung, Y.-S.; Kim, J.-M. Langmuir
2011, 27, 1560.
(16) Shikata, T.; Ogata, D.; Hanabusa, K. J. Phys. Chem. B 2004, 108,
508.
(17) Shi, N.; Dong, H.; Yin, G.; Xu, Z.; Li, S. Adv. Funct. Mater. 2007,
17, 1837.
(18) Matsunaga, Y.; Miyajima, N.; Nakayasu, Y.; Sakai, S.; Yonenaga,
M. Bull. Chem. Soc. Jpn. 1988, 61, 207.
́
(19) Fitie, C. F. C.; Tomatsu, I.; Byelov, D.; de Jeu, W. H.; Sijbesma,
R. P. Chem. Mater. 2008, 20, 2394.
(20) Besenius, P.; Heynens, J. L. M.; Straathof, R.; Nieuwenhuizen,
M. M. L.; Bomans, P. H. H.; Terreno, E.; Aime, S.; Strijkers, G. J.;
Nicolay, K.; Meijer, E. W. Contrast Media Mol. Imaging 2012, 7, 356.
(21) Blomenhofer, M.; Ganzleben, S.; Hanft, D.; Schmidt, H.-W.;
Kristiansen, M.; Smith, P.; Stoll, K.; Maeder, D.; Hoffmann, K.
Macromolecules 2005, 38, 3688.
(22) Broaders, K. E.; Pastine, S. J.; Grandhe, S.; Frec
́
het, J. M. J.
Chem. Commun. 2011, 47, 665.
(23) Brunsveld, L.; Schenning, A. P. H. J.; Broeren, M. A. C.; Janssen,
H. M.; Vekemans, J. A. J. M.; Meijer, E. W. Chem. Lett. 2000, 292.
(24) Stals, P. J. M.; Smulders, M. M. J.; Martín-Rapu n, R.; Palmans,
́
A. R. A.; Meijer, E. W. Chem.Eur. J. 2009, 15, 2071.
(25) Crystallographic data: Compound 1: C27H39N3O9S3, Mw
=
645.82, hexagonal, space group P65, a = 16.4549(12) Å, b =
16.4549(12) Å, c = 21.286(3) Å, V = 4991.3 (9)Å3, Z = 6, dm = 1.289
Mg m−3, K = 100, R1 0.0780 and wR2 0.2483 for 5031data with I >
2σ(I). Compound 2: C39H39N3O12, Mw = 741.73, monoclinic, space
group P21, a = 9.122(2) Å, b = 16.331(4) Å, c = 12.941(3) Å, V =
1833.3 (8)Å3, Z = 2, dm = 1.344 Mg m−3, K = 100, R1 0.0477 and
wR2 0.1094 for 6341 data with I > 2σ(I). Intensity data were collected
with MoKα radiation for compounds 1 and 2 using Bruker APEX-2
CCD diffractometer. Data were processed using the Bruker SAINT
package and the structure solution and refinement procedures were
performed using SHELX97. The non-hydrogen atoms were refined
with anisotropic thermal parameters. The data have been deposited at
the CCDC with reference number CCDC 884523 and 884524,
respectively.
(26) Konig, B.; Moller, O.; Bubenitschek, P.; Jones, P. G. J. Org.
Chem. 1995, 60, 4291.
(27) Rajput, L.; Biradha, K. J. Mol. Struct. 2008, 876, 339.
41
dx.doi.org/10.1021/ol402865t | Org. Lett. 2014, 16, 38−41