Selective head-to-tail recognition in hydrazide-based molecular duplex strands induced by spectator secondary electrostatic interactions

Article abstract of DOI:10.1039/b811272j

Due to spectator secondary electrostatic interactions, nonsymmetric mono-Boc-mono-acetyl terminated hydrazide-based oligomers displayed a head-to-tail dimerization mode, which was evidenced by ¹H NMR, and 2D NOESY experiments. Dynamic behavior of the molecular duplex strands was also explored by variable temperature ¹H NMR experiments.

Full text of DOI:10.1039/b811272j

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www.rsc.org/obc | Organic & Biomolecular Chemistry
Selective head-to-tail recognition in hydrazide-based molecular duplex strands
induced by spectator secondary electrostatic interactions†
Yong Yang, Jun-Feng Xiang, Min Xue, Hai-Yu Hu and Chuan-Feng Chen*
Received 2nd July 2008, Accepted 5th August 2008
First published as an Advance Article on the web 19th September 2008
DOI: 10.1039/b811272j
Due to spectator secondary electrostatic interactions, nonsymmetric mono-Boc-mono-acetyl
terminated hydrazide-based oligomers displayed a head-to-tail dimerization mode, which was
evidenced by 1H NMR, and 2D NOESY experiments. Dynamic behavior of the molecular duplex
strands was also explored by variable temperature 1H NMR experiments.
is suggested as a secondary electrostatic effect by Jorgensen et al.
Introduction
based the results of theoretical studies.9 Zimmerman et al. further
provided experimental evidence for this theory.10 Based on the
analysis of the stability constants of sufficiently large experimental
data sets, Schneider et al. even derived an empirical formula
for predicting the association constants for multiple hydrogen
bonded systems: 7.9 kJ mol-1 for each primary hydrogen bond and
2.9 kJ mol-1 for each secondary one.11 In the case of a hydrogen
bonded system as shown in Fig. 1, “over-hanging” or “spectator”
hydrogen bonding sites not participating in primary hydrogen
bonding interaction can also affect the stability of the complex
substantially due to their being adjacent to other hydrogen
bonding sites in space.12 In hydrazide-based quadruply hydrogen
bonded systems we reported recently, as shown in Fig. 2, that the
spectator secondary electrostatic interactions inherent with the
Boc groups substantially affected the stability of the complexes:
weak association was observed for 1·4 (two fold repulsive spectator
secondary electrostatic interactions); (1.4 0.1) ¥ 103 M-1 for 2·4
(no spectator secondary electrostatic interaction) and (5.6 0.6) ¥
102 M-1 for 3·4 (one repulsive spectator secondary electrostatic
interaction), respectively.13 Further investigations revealed that the
Boc groups also affected substantially the dynamic behavior of the
hydrazide-based molecular duplex strands.13,14
The ability of biomolecules to adopt three-dimensional shapes
and to interact specifically through cooperative action of many
non-covalent attractions1 has inspired chemists to design, syn-
thesize, and characterize chemical models to mimic structures
of biomolecules. Among the many biostructures, discovery of
the double helical structure of DNA2 via hydrophobic effects,
hydrogen bonds, and p–p stacking interactions and elucidation
of its function as genetic information carrier have founded the
basis of modern molecular biology.3 Recent studies revealed that
the b-sheet protein secondary structure plays an important role
in many diseases, such as Alzheimer’s disease, the prion dis-
ease, and other neurodegenerative disorders.4 Other double- and
multiple-stranded complexes self-assembled from linear oligomers
with encoded recognition sites are ubiquitous in nature, and
are the foundation of other higher structures and functions of
biomolecules. Inspired by the elegant functions of these structures
in nature and for scientific and aesthetic reasons, there is currently
an intensive focus of chemical research on the construction
of stable molecular duplex strands from unnatural backbones
for structure mimicking and potential applications.5 Hydrogen
bonding, as adopted by natural DNA, with characteristics of
strength and directionality, has been described as the “masterkey
interaction in supramolecular chemistry” 6 and is an ideal non-
covalent interaction for this mission. Hydrogen bonding modules
assembled with high stability, fidelity, and selectivity, are favored
in this field. Heterocycle based building blocks (usually urea
derivatives)7 and linear materials composed of arrays of hydrogen
bonding sites8 have gained great success.
The stability of multiply hydrogen bonded complexes is deter-
mined by many factors, including the number and geometry of
individual hydrogen bonds, the acidity or basicity of hydrogen
bonding donor or acceptor sites, and the solvent polarity. In arrays
with adjacent hydrogen bonding sites, the stability is also affected
by the sequence arrangement of hydrogen bonding sites, which,
Fig. 1 Representation of secondary electrostatic interactions and spec-
tator secondary electrostatic interactions in hydrogen bonded dimer
structures (DADD·DADAAA) with adjacent hydrogen bonding sites.
Double headed arrows: repulsive interactions; single headed arrows:
attractive interactions.
In this paper, mono-Boc-mono-acetyl terminated non-
symmetric hydrazide-based oligomers D series were designed
and synthesized (Fig. 3). Due to spectator secondary repulsive
electrostatic interactions12 inherent with Boc groups, the Boc
termini did not participate in important intermolecular hydrogen
bonding interactions and a head-to-tail recognition directed
dimerization mode for this series was proposed.15 Moreover,
Beijing National Laboratory for Molecular Sciences, Center for Chemical Bi-
ology, Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100190,
China. E-mail: cchen@iccas.ac.cn; Fax: +86-10-62554449; Tel: +86-10-
62588936
† Electronic supplementary information (ESI) available: Stacked partial
1H NMR spectra of D2–D4 and typical mono-Boc and mono-acetyl ter-
minated oligomers at different temperatures. See DOI: 10.1039/b811272j
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Fig. 2 Representation of spectator secondary repulsive electrostatic interactions in hydrazide-based quadruply hydrogen bonded systems.
Fig.
3
Chemical structures of mono-Boc-mono-acetyl terminated
oligomers D1–D4 used in this study, with proton-labeling scheme
indicated.
dynamic behavior for the duplex strands was also investigated
via variable temperature 1H NMR experiments.
Results and discussion
Fig. 4 Chemical shifts for NHs of D1 at different concentrations,
300 MHz, in CDCl3, 298 K.
Synthesis
Due to the non-symmetric nature of the oligomers, an iterative
sequentially homologated method has been devised (Scheme 1).
Starting from the Boc termini, the oligomers were lengthened
stepwise. The methyl termini were finally attached. The key step
is the coupling reaction between carboxylic acid and hydrazide
derivatives. It was found that EDC·HCl could be utilized as an
efficient coupling reagent for this kind of reaction, and in most
cases, high yields were obtained. Hydrolysis of esters was generally
achieved by a solution of NaOH in THF or C2H5OH. The full
synthetic methods and characterization data for new compounds
are provided in the Experimental section.
1H NMR analysis
Firstly, dilution 1H NMR experiments on D1 revealed that only the
signal for Hb displayed a large concentration-dependency (Fig. 4),
which might suggest that only Hb was involved in important
intermolecular hydrogen bonding. With the chain length of this
series extended to longer oligomers D2–D4, we found that the
signals for Hc and Hd were also unaffected (Fig. 5). While for
the structure-similar self-complementary mono-Boc-terminated
series, the position of NHs adjacent to Boc groups shifted substan-
tially with chain length.13 These findings might suggest that the Boc
termini in D series were not involved in important intermolecular
hydrogen bonding. Thus, a selectivity for acetyl termini (we
call tail) over Boc termini (we call head) was obtained and a
head-to-tail recognition directed dimerization mode was proposed
(Scheme 2, left). In head-to-tail dimers, there were no spectator
secondary repulsive electrostatic interactions; while in head-to-
1
Fig. 5 Stacked partial H NMR spectra (600 MHz, CDCl3, 10 mM) of
(a) D1, 298K; (b) D2, 298K; (c) D2, 223K; (d) D3, 298K; (e) D3, 223K;
(f) D4, 298K; (g) D4, 223K.
head dimers (Scheme 2, right), there was one spectator secondary
repulsive electrostatic interaction. This difference rendered the
equilibrium shift substantially to head-to-tail dimers.
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Scheme 1 Synthetic routes to D1–D4.
A dimerization constant of 79 23 M-1 was determined for
D1·D1 in CDCl3 at room temperature by nonlinear regression
analysis of the dilution 1H NMR experiment data.16 Dimerization
constants for longer oligomers were not determined due to signal
overlapping and no obvious chemical shift changes observed by
dilution 1H NMR experiments.
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Scheme 2 Representation of equilibrium between head-to-tail dimmers (left) and head-to-head dimers (right) for self-assembly of the oligomers D1–D4,
with spectator secondary repulsive electrostatic interactions highlighted.
2D NOESY analysis and dynamic behavior
sites. We believe that this selective head-to-tail dimerization and
unique dynamic behavior will find practical applications in the
design of hydrazide-based functional materials, which is under
investigation in our laboratory.
2D NOESY experiments further confirmed the above hypothesis.
Cross contacts between Hf and the h zone (inter-carbonyl aromatic
protons), g zone (methylene protons of malonyl groups) and h
zone were observed. Variable temperature 1H NMR experiments
revealed dynamic behavior for the D series similar to those for the
mono-Boc terminated series (see ESI for more details).13 With
lowering of temperature, in addition to signal sharpening, no
apparent changes were observed (Fig. 6). While for the structure-
similar mono-acetyl terminated series, new peaks corresponding
to the NHs not involved in intermolecular hydrogen bonding
appeared with lowering of temperature.13 These findings indicated
that no shuttle movement perpendicular to the hydrogen bonds
and no dimeric-polymeric equilibrium existed for the D series.
Experimental
General procedure for the coupling reaction of carboxylic acids and
hydrazide derivatives (procedure A)
To an equimolar mixture of a carboxylic acid and a hydrazide
derivative in dry CH2Cl2 (usually 10 mL per mmol) in an ice–
water bath was added 1.1 or 1.2 equiv. of EDC·HCl. The mixture
was stirred at room temperature for 5 h, and then concentrated
under reduced pressure. The pure product as a white solid was
obtained by recrystallization from hot acetonitrile.
Conclusions
General procedure for hydrolysis of esters (procedure B)
In summary, we presented the synthesis and self-assembly of a
new series of mono-Boc-mono-acetyl terminated non-symmetric
hydrazide-based oligomers (D series). Due to spectator secondary
repulsive electrostatic interactions inherent with Boc groups, a
head-to-tail dimerization mode was observed in solution for this
series, which was evidenced by dilution 1H NMR and 2D NOESY
experiments. Variable temperature 1H NMR experiments further
revealed similar dynamic behavior for the D series as for those of
the Boc-terminated series with complementary hydrogen bonding
To a solution or suspension of ester in THF or C2H5OH (usually
10 mL per mmol) was added a solution of NaOH (usually 3 equiv.)
in an equal volume of water (relative to THF or C2H5OH). Then
the mixture was stirred at room temperature and the reaction was
monitored by TLC. The reaction completed in 5 h, and sometimes
heating was necessary for the completion of the reaction. The
organic solvent was evaporated under reduced pressure, and the
residue was acidified with concentrated HCl. Upon acidification a
white solid precipitated from the solution and the crude product
Fig. 6 Partial 2D NOESY spectra for (a) D2, (b) D3, (c) D4, 10 mM in CDCl3, 600 MHz, 298 K, showing contacts between Hf and h zone, h zone and
g zone.
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was collected by filtration. The pure product as a white solid was
obtained by recrystallization from hot acetonitrile.
All experiments were carried out at the 0.1–1.0 mmol scale.
Compounds D1, 5, 7, 8 were synthesized previously.13
H-Ar), 8.96 (s, 1H, Ar-H), 7.15–7.04 (br, 1H, H-Ar), 6.52 (s, 2H,
Ar-H), 4.30–4.15 (m, 12H, OCH2 and COCH2CO), 2.14–1.97 (m,
8H, CH2), 1.50–1.28 (m, 49H, CH2 and OC(CH3)3), 0.90–0.83
(m, 12H, CH3). 13C NMR (75 MHz, DMSO-d6, ppm): d 168.7,
166.5, 163.1, 162.9, 162.8, 162.5, 161.3, 160.6, 160.4, 160.3, 160.1,
134.2, 113.2, 112.9, 112.8, 112.4, 98.0, 79.1, 69.7, 69.4, 31.2, 28.8,
28.63, 28.60, 28.3, 28.1, 28.0, 25.4, 22.0, 20.3, 13.9. IR (KBr, cm-1):
3353.6, 3223.4, 2927.4, 2859.0, 1628.6, 1461.8.
Compound 6: general procedure B. Yield: 95%. Mp: 163–
◦
1
164 C. H NMR (300 MHz, DMSO-d6, ppm): d 12.49 (s, 1H,
COOH), 10.96 (d, J = 3.7 Hz, 1H, H-N), 10.20 (d, J = 3.2 Hz,
1H, H-N), 9.40 (s, 1H, H-N), 9.02 (s, 1H, H-Ar), 8.33 (s, 1H,
H-N), 6.81 (s, 1H, H-Ar), 4.29–4.22 (m, 4H, OCH2), 3.31 (s, 2H,
COCH2CO), 1.88–1.77 (m, 4H, CH2), 1.43–1.26 (m, 29H, CH2
and OC(CH3)3), 0.86 (t, J = 6.9 Hz, 5.1 Hz, 6H, CH3). 13C NMR
(75 MHz, DMSO-d6, ppm): d 168.8, 164.2, 162.3, 160.6, 160.3,
160.0, 155.1, 134.1, 114.0, 112.4, 97.8, 79.1, 69.6, 69.3, 31.23, 31.19,
28.8, 28.63, 28.61, 28.3, 28.0, 25.5, 22.09, 22.06, 13.89, 13.88. IR
(KBr, cm-1): 3369.03, 3316.96, 3218.61, 2926.45, 2858.95, 1740.44,
1713.44, 1616.06, 1466.6. MS (MALDI-TOF): m/z 659.1 [M +
Na]+, 675.0 [M + K]+. MS (ESI): m/z 635.06 [M - H]-. Elemental
analysis calcd (%) for C32H52N4O9: C 60.36, H 8.23, N 8.80; found:
C 60.21, H 8.27, N 9.14.
Compound D3: general procedure A. Yield: 94%. Mp: 218–
◦
1
219 C. H NMR (300 MHz, CDCl3, ppm): d 11.72–11.50 (m,
10H, H-N), 9.46–9.40 (br, 1H, H-N), 9.15 (s, 1H, H-Ar), 9.10 (s,
1H, H-Ar), 8.97 (s, 1H, H-Ar), 7.12–6.96 (br, 1H, H-N), 6.53 (s,
1H, H-Ar), 6.52 (s, 1H, H-Ar), 6.47 (s, 1H, H-Ar), 4.23–4.20 (m,
16H, OCH2 and COCH2CO), 2.35 (s, 3H, COCH3), 2.11–1.94 (m,
12H, CH2), 1.50–1.25 (m, 69H, CH2 and OC(CH3)3), 0.90–0.84
(m, 18H, CH3). 13C NMR (75 MHz, CDCl3, ppm): d 165.0, 160.92,
160.87, 160.7, 160.5, 160.0, 156.8, 156.5, 155.0, 137.0, 136.7, 112.8,
112.2, 111.9, 111.8, 96.3, 81.3, 70.2, 21.8, 31.7, 29.7, 29.4, 29.32,
29.26, 29.23, 29.13, 29.0, 28.8, 28.6, 28.2, 26.1, 26.0, 25.8, 25.7,
22.60, 22.57, 20.4, 14.0. IR (KBr, cm-1): 3348.78, 3228.25, 2927.41,
2857.99, 1628.59, 1457.92. MS (MALDI-TOF): m/z 1652.0 [M +
Na]+. Elemental analysis calcd (%) for C85H136N12O19·H2O: C
61.95, H 8.44, N 10.20; found: C 61.90, H 8.35, N 10.69.
C◦ompound D2: general procedure A. Yield: 87%. Mp: 132–
133 C. 1H NMR (300 MHz, CDCl3, ppm): d 11.78 (d, J = 8.0 Hz,
1H, N-H), 11.49 (d, J = 8.3 Hz, 1H, N-H), 11.22 (d, J = 8.2 Hz,
1H, N-H), 11.14 (d, J = 8.1 Hz, 1H, N-H), 10.97 (d, J = 8.2 Hz,
1H, N-H), 10.88 (d, J = 8.1 Hz, 1H, N-H), 9.43 (s, 1H, N-H), 9.12
(s, 1H, Ar-H), 9.03 (s, 1H, Ar-H), 7.22–7.05 (br, 1H, N-H), 6.51 (s,
2H, Ar-H), 4.25–4.10 (m, 10H, OCH2 and COCH2CO), 2.38 (s,
3H, COCH3), 2.15–1.93 (m, 8H, CH2), 1.55–1.20 (m, 49H, CH2
and OC(CH3)3), 0.90–0.83 (m, 12H, CH2). 13C NMR (75 MHz,
CDCl3, ppm): d 165.2, 162.9, 160.9, 160.8, 160.5, 157.2, 157.0,
155.1, 136.8, 112.9, 112.3, 111.9, 96.3, 81.3, 70.3, 38.9, 31.7, 29.3,
29.2, 29.1, 29.0, 28.8, 28.6, 28.2, 26.1, 26.0, 25.9, 25.8, 22.6, 20.6,
14.1. IR (KBr, cm-1): 3343.96, 3227.29, 2928.38, 2858.95, 1630.52,
1457.92. MS (ESI): m/z 1110.09 [M]-. Elemental analysis calcd
(%) for C58H94N8O13: C 62.68, H 8.52, N 10.08; found: C 62.61, H
8.48, N 10.22.
Compound 11: general procedure A. Yield: 92%. Mp: 117–
◦
1
118 C. H NMR (300 MHz, CDCl3, ppm): d 11.82–11.17 (m,
10H, H-N), 9.44–9.39 (br, 1H, H-N), 9.20–9.08 (m, 3H, H-Ar),
7.14–7.02 (br, 1H, H-N), 6.52–6.50 (m, 3H, H-Ar), 4.30–4.10
(m, 20H, OCH2 and COOCH2 and COCH2CO), 2.10–1.80 (m,
12H, CH2), 1.50–1.10 (m, 72H, COOCH2CH3 and CH2), 0.88–
0.85 (m, 18H, CH3). IR (KBr, cm-1): 3348.78, 3225.78, 2927.41,
2857.99, 1628.59, 1457.92, 1281.47. MS (MALDI-TOF): m/z
1723.4 [M + Na]+, 1739.4 [M + K]+. Elemental analysis calcd
(%) for C88H140N12O21·H2O: C 60.81, H 8.31, N 9.67; found: C
60.66, H 8.19, N 10.12.
Compound D4: general procedure A. Yield: 85%. Mp: >215 ◦C,
decomposition. 1H NMR (600 MHz, CDCl3, 10 mM, 258K, ppm):
d 12.0–11.56 (m, 14H, H-N), 9.46 (s, 1H, H-N), 9.20–9.00 (m,
4H, H-Ar), 6.97 (s, 1H, H-N), 6.49 (s, 4H, H-Ar), 4.30–4.15 (m,
22H, OCH2 and COCH2CO), 2.19–1.99 (m, 16H, CH2), 1.36–
1.00 (m, 89H, CH2 and OC(CH3)3), 0.84–0.78 (m, 24H, CH3). IR
(KBr, cm-1): 3356.5, 2927.41, 2858.95, 1627.63, 1459.85. Elemental
analysis calcd (%) for C112H178N16O25·2H2O: C 61.57, H 8.40, N
10.26; found: C 61.38, H 8.25, N 10.40.
Compound 9: general procedure A. Yield: 83%. Mp: 114–
115 ◦C. 1H NMR (300 MHz, CDCl3, ppm): d 11.66 (d, J =
8.2 Hz, 1H, N-H), 11.45 (d, J = 8.0 Hz, 1H, N-H), 11.35 (d,
J = 7.6 Hz, 1H, N-H), 11.07 (d, J = 8.1 Hz, 1H, N-H), 10.94
(d, J = 8.0 Hz, 1H, N-H), 10.81 (d, J = 7.9 Hz, 1H, N-H),
9.48–9.37 (br, 1H, N-H), 9.09 (s, 1H, Ar-H), 8.97 (s, 1H, Ar-H),
7.37–7.26 (br, 1H, N-H), 6.51 (s, 1H, Ar-H), 6.49 (s, 1H, Ar-H),
4.23–4.10 (m, 12H, OCH2 and COCH2CO and COOCH2CH3),
3.75 (s, 2H, COCH2CO), 2.13–1.92 (m, 8H, CH2), 1.53–1.19 (m,
52H, CH2 and COOCH2CH3 and OC(CH3)3), 0.90–0.83 (m, 12H,
CH3). 13C NMR (75 MHz, CDCl3, ppm): d 167.5, 162.7, 161.00,
160.95, 160.9, 160.8, 160.7, 160.6, 160.5, 158.1, 157.5, 157.3, 155.1,
136.7, 112.9, 112.2, 112.0, 111.7, 96.3, 81.2, 70.3, 70.1, 61.3,
40.6, 38.9, 32.0, 31.7, 29.3, 29.24, 29.20, 29.12, 29.09, 29.0, 28.8,
28.6, 28.2, 26.1, 26.0, 25.84, 25.79, 22.6, 14.0. IR (KBr, cm-1):
3345.89, 3223.43, 2928.38, 2858.95, 1737.55, 1631.48, 1457.92.
MS (ESI): m/z 1181.97 [M - H]-. Elemental analysis calcd (%)
for C61H98N8O15: C 61.91, H 8.35, N 9.47; found: C 61.89, H 8.33,
N 9.72.
Acknowledgements
We thank the National Natural Science Foundation of
China (20625206), the National Basic Research Program
(2007CB808004, 2008CB617501) and CMS-Y 200708 for financial
support.
Notes and references
1 D. E. Metzler, Biochemistry: The Chemical Reactions of Living Cells,
Academic Press, New York, 2003.
2 J. D. Watson and F. C. H. Crick, Nature, 1953, 171, 737–738; W.
Saenger, Principles of Nucleic Acid Structure, Springer, New York,
1984.
Compound 10: general procedure B. Yield: 93%. Mp: 140–
◦
1
141 C. H NMR (300 MHz, CDCl3, ppm): d 11.66–11.18 (m,
7H, COOH and N-H), 9.65–9.47 (br, 1H, N-H), 9.12 (s, 1H,
4202 | Org. Biomol. Chem., 2008, 6, 4198–4203
This journal is
The Royal Society of Chemistry 2008
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3 W. H. Elliott, and D. C. Elliott, Biochemistry and Molecular Biology,
Oxford University Press, New York, 2005.
2006, 128, 12307–12313; A. P. Bisson, F. J. Carver, C. A. Hunter and
J. P. Waltho, J. Am. Chem. Soc., 1994, 116, 10292–10293; J. S. Nowick,
Org. Biomol. Chem., 2006, 4, 3869–3885 and references therein; P. S.
Corbin, S. C. Zimmerman, P. A. Thiessen, N. A. Hawryluk and T. J.
Murray, J. Am. Chem. Soc., 2001, 123, 10475–10488; S. T. Phillips, M.
Rezac, U. Abel, M. Kossenjans and P. A. Bartlett, J. Am. Chem. Soc.,
2002, 124, 58–66; T. Moriuchi, T. Tamura and T. Hirao, J. Am. Chem.
Soc., 2002, 124, 9356–9357.
4 E. V. Roloff and B. Platt, Cell. Mol. Life Sci., 1999, 55, 601–616;
S. M. Yatin, M. Aksenova, M. Aksenov, W. R. Markesbery and D. A.
Butterfield, J. Mol. Neurosci., 1998, 11, 183–198; S. B. Prusiner, M. R.
Scott, S. DeArmond and F. E. Cohen, Cell, 1998, 93, 337–348.
5 M. Albrecht, Angew. Chem., Int. Ed., 2005, 44, 6448–6451; K. Tanaka,
A. Tengeiji, T. Kato, N. Toyama and M. Shionoya, Science, 2003, 299,
1212–1213; J.-M. Lehn, A. Rigault, J. Siegel, J. Harrowfield, B. Chevrier
and D. Moras, Proc. Natl. Acad. Sci. U. S. A., 1987, 84, 2565–2569; J.
Sa´nchez-Quesada, C. Seel, P. Prados and J. de Mendoza, J. Am. Chem.
Soc., 1996, 118, 277–278; Y. Tanaka, H. Katagiri, Y. Furusho and E.
Yashima, Angew. Chem., Int. Ed., 2005, 44, 3867–3870; V. Berl, I. Huc,
R. G. Khoury, M. J. Krische and J.-M. Lehn, Nature, 2000, 407, 720–
723; D. Haldar, H. Jiang, J.-M. Le´ger and I. Huc, Angew. Chem., Int.
Ed., 2006, 45, 5483–5486.
9 W. L. Jorgensen and J. Pranata, J. Am. Chem. Soc., 1990, 112, 2008–
2010; J. Pranata, S. G. Wierschke and W. L. Jorgensen, J. Am. Chem.
Soc., 1991, 113, 2810–2819.
10 T. J. Murray and S. C. Zimmerman, J. Am. Chem. Soc., 1992, 114,
4010–4011; S. C. Zimmerman and P. S. Corbin, Struct. Bonding, 2000,
96, 63–94.
11 J. Sartorius and H.-J. Schneider, Chem.–Eur. J., 1996, 2, 1446–1452.
12 S. C. Zimmerman and T. J. Murray, Tetrahedron Lett., 1994, 35, 4077–
4080; F. H. Beijer, R. P. Sijbesma, J. A. J. M. Vekemans, E. W. Meijer,
H. Kooijman and A. L. Spek, J. Org. Chem., 1996, 61, 6371–6380.
13 Y. Yang, Z.-Y. Yang, Y.-P. Yi, J.-F. Xiang, C.-F. Chen, L.-J. Wan and
Z.-G. Shuai, J. Org. Chem., 2007, 72, 4936–4946.
14 Y. Yang, J.-F. Xiang and C.-F. Chen, Org. Lett., 2007, 9, 4355–4357;
Y. Yang, T. Chen, J.-F. Xiang, H.-J. Yan, C.-F. Chen and L.-J. Wan,
Chem.–Eur. J., 2008, 14, 5742–5746.
15 In 2-aminotriazine based molecular duplex strands reported by Krische
et al., three isomeric duplex bonding modes were proposed for the
nonsymmetric monomers. Selectivity was not achieved. E. A. Archer
and M. J. Krische, J. Am. Chem. Soc., 2002, 124, 5074–5083.
16 C. S. Wilcox, in Frontiers in Supramolecular Organic Chemistry and
Photochemistry, ed. H.-J. Schneider and H. Durr, VCH, New York,
1991. pp. 123–143; K. A. Conners, Binding Constants: The Measure-
ment of Molecular Complex Stability, Wiley-Interscience, New York,
1987.
6 J.-M. Lehn, Supramolecular Chemistry, VGH publishers, Inc., New
York, 1995; J. W. Steed and J. L. Atwood, Supramolecular, Chemistry,
John Wiley & Sons Ltd, New York, 2000.
7 Selected examples: P. S. Corbin and S. C. Zimmerman, J. Am.
Chem. Soc., 1998, 120, 9710–9711; T. Park, S. C. Zimmerman and S.
Nakashima, J. Am. Chem. Soc., 2005, 127, 6520–6521; F. H. Beijer, H.
Kooijman, A. L. Spek, R. P. Sijbesma and E. W. Meijer, Angew. Chem.,
Int. Ed., 1998, 37, 75–78; R. P. Sijbesma, F. H. Beijer, L. Brunsveld,
B. J. B. Folmer, J. H. K. K. Hirschberg, R. F. M. Lange, J. K. L. Lowe
and E. W. Meijer, Science, 1997, 278, 1601–1604; Y. Yang, H.-J. Yan,
C.-F. Chen and L.-J. Wan, Org. Lett., 2007, 9, 4991–4994.
8 Selected examples: B. Gong, Polym. Int., 2007, 56, 436–443; E. A.
Archer, A. E. Sochia and M. J. Krische, Chem.–Eur. J., 2001, 7, 2059–
2065; X. Zhao, X.-Z. Wang, X.-K. Jiang, Y.-Q. Chen, Z.-T. Li and G.-J.
Chen, J. Am. Chem. Soc., 2003, 125, 15128–15139; J. Zhu, J.-B. Lin,
Y.-X. Xu, X.-B. Shao, X.-K. Jiang and Z.-T. Li, J. Am. Chem. Soc.,
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