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S.R. Nam et al. / Tetrahedron 64 (2008) 10531–10537
tube-like structures, helical structures formed by disk shape ag-
gregates, etc.). The gels show well-defined thermoreversible sol–
gel transitions and the Tgel values increased with the increasing
strength of aromatic stacking. It is clear that the number of hy-
drogen bonds and aromatic stackings have a pronounced effect on
the gelation properties and the microstructure of the gels. This two-
component gelation approach could be useful for controlling the
microscopic and macroscopic properties, and have potentially in-
teresting applications.
a mixture of water (120 mL) and concd HCl (3 mL). Addition of 50%
aqueous NaOH gave a yellow precipitate, which was purified by
reprecipitation (4.6 g, 71.3% yield). The analytical data were in ac-
cordance with those reported in Ref. 11.
4.1.5. Tris(4-aminophenyl)amine
A mixture of tris(4-nitrophenyl)-amine (3.00 g, 7.89 mmol) and
tin granules (27.0 g, 0.227 mol) in 12 N HCl (150 mL) was refluxed
for 3 h. After cooling to room temperature, the insoluble residue
was removed by filtration. The filtrate was diluted with distilled
water. The aqueous solution was adjusted to pH 12 by the addition
of NaOH and filtered. Volatiles were removed in vacuo to give
a purple solid (1.12 g, 50.3% yield). The analytical data were in ac-
cordance with those reported in Ref. 12.
4. Experimental section
4.1. Synthesis
4.1.1. General
All chemicals and solvents were purchased from Aldrich or
Tokyo Kasei Chemicals, and were used as-received. Deuterated
solvents were acquired from Cambridge Isotopic Laboratories and
were used for NMR spectrometric measurements. All NMR spectra
were recorded on a Bruker Advance DPX-300. All 1H NMR and 13C
NMR were recorded in DMSO-d6 at 298 K (spectral width: ꢁ1 to
4.1.6. General method for the preparation of the gels
The aromatic cores (1–6) were mixed in a ratio of 3:1 or 2:1 with
1. The mixtures were dissolved in CHCl3 and MeOH (v/v¼1:1). Clear
solution was concentrated and dried in vacuo. These solids were
used for the gelation test. These tests were performed by solubi-
lizing a weighed amount of a mixture in a measured volume of the
selected organic solvent (AxN1¼20 mM in cyclohexane or decalin,
N¼1–6, x¼2 or 3). The mixtures were heated until clear and cooled
at room temperature. The minimum gel concentration of each gel is
about 1.03% w/v (9 mM of complex) in cyclohexane. Samples for the
cyclohexane gel and decalin gel images were dried in the air before
examining SEM images. The solid in the vial was carefully picked up
and applied to the polymer or stainless steel stubs by carbon tape.
For the image of separated microtubules, filtered microtubules
were dried in a vacuum and applied to polymer or stainless steel
stubs by carbon tape. The Tgel values were measured using an
inverted test tube method: a vial (diameter¼1 cm) containing the
gel was inverted and the temperature gradually increased to the
point where the gel begins to flow.
14 ppm). The reference peaks were set to
d 2.49 and d 39.51 ppm
from tetramethylsilane for the 1H and 13C NMR spectra, re-
spectively. The XWINNMR program was used for the pulse
program.
4.1.2. 3,5-Diaminobenzoic acid methyl ester
HCl gas was bubbled into a solution of 3,5-diaminobenzoic acid
(98%, Aldrich) (5.0 g, 32.9 mmol) in 150 mL of dry CH3OH and
stirred at 0 ꢀC for 2 h. The resulting white precipitate was filtered
and refluxed in 150 mL of dry CH3OH for 4 h. All the volatile com-
ponents were evaporated and the residue was basified with
NaHCO3 and filtered. The crude product was purified by re-
crystallization (CH2Cl2–hexane) to provide white solid (4.64 g, 85%
yield).
1H NMR (300 MHz, DMSO-d6): 3.73 (3H, s), 4.99 (4H, s), 6.01
(1H, t, J¼1.97 Hz), 6.41 (2H, d, J¼1.95 Hz).
4.2. Scanning electron microscopy
SEMs (scanning electron micrographs) were recorded using
a JEOL JSM 5410LV. Dried gel samples were applied to polymer or
stainless steel stubs by carbon tape. Prior to examination, the gels
were coated with a thin gold layer by gold deposition (5 mA, 7 min).
4.1.3. 3,5-Bis(dodecanoylamino)benzoic acid
To a solution of 3,5-diaminobenzoic acid methyl ester (4 g,
24.1 mmol) in 150 mL of dry CH2Cl2 were added slowly dodeca-
noylchloride (>98%, TCI) (11.1 g, 50.6 mmol) and Et3N (4.87 g,
48.1 mmol) by syringe. The resulting solution was stirred at 0 ꢀC for
3 h. All the volatile components were evaporated and the residue
was partitioned between CH2Cl2 and water. The organic phase was
washed with water (ꢂ3) and then dried over Na2SO4. The white
solid was treated with KOH (5.4 g, 96.3 mmol) and stirred in 150 mL
of CH3OH at room temperature for 10 h. Removal of CH3OH fol-
lowed by neutralization with 1 N HCl and filtration provided the
crude product, which was purified by recrystallization (CH3OH–
CH2Cl2) to furnish white solid (9.82 g, 79% yield).
Acknowledgements
This work was supported by the MOCIE (Grant No. 10022945)
and the Seoul R&BD. H.Y.L. and S.R.N. are grateful to the Ministry of
Education for a BK 21 fellowship.
References and notes
1H NMR (300 MHz, DMSO-d6): 0.85 (6H, t, J¼6.61 Hz), 1.23 (32H,
m), 1.57 (4H, m), 2.29 (4H, t, J¼7.21 Hz), 7.87 (2H, d, J¼1.29 Hz), 8.17
(1H, s), 10.02 (2H, s), 12.99 (1H, br s). 13C NMR (75 MHz, DMSO-d6):
171.95, 167.62, 140.14, 131.95, 115.04, 113.98, 36.82, 31.76, 29.48,
29.46, 29.39, 29.23, 29.19, 29.06, 25.56, 22.56, 14.41. HRMS (FAB):
calculated (C31H53N2O4)¼517.7728. Found¼517.7755.
1. For comprehensive reviews for organogels, see: (a) van Esch, J.; Schoonbeek, F.;
de Loos, M.; Kooijman, H.; Veen, E. M.; Kellogg, R. M.; Feringa, B. L. In Supra-
molecular Science: Where It Is and Where It Is Going; Ungaro, R., Dalcanale, E.,
Eds.; Kluwer: Dordrecht, 1999; pp 233–259; (b) Melendez, R. E.; Carr, A. J.;
Linton, B. R.; Hamilton, A. D. Struct. Bonding 2000, 96, 31–61; (c) Shinkai, S.;
Murata, K. J. Mater. Chem. 1998, 8, 485–495; (d) Haering, G.; Luisi, P. L. J. Phys.
Chem. 1986, 90, 5892–5895.
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Feringa, B. L. Angew. Chem., Int. Ed. 2000, 39, 2263–2266; For LMW hydrogels
and hydrogelators, see: Estroff, L. A.; Hamilton, A. D. Chem. Rev. 2004, 104,
1201–1218.
3. (a) Gronwald, O.; Shinkai, S. Chem.dEur. J. 2001, 7, 4328–4334; (b) Monir-
uzzaman, M.; Sundararajan, P. R. Langmuir 2005, 21, 3802–3807; (c) Shimizu, T.
Macromol. Rapid Commun. 2002, 23, 311–331; (d) Tamaru, S.; Nakamura, M.;
Takeuchi, M.; Shinkai, S. Org. Lett. 2001, 3, 3631–3634; (e) John, G.; Zhu, G.; Li, J.;
Dordick, J. S. Angew. Chem., Int. Ed. 2006, 45, 4772–4775; (f) Zhu, G.; Dordick, J. S.
Chem. Mater. 2006, 18, 5988–5995; (g) Yagai, S.; Iwashima, T.; Kishikawa, K.;
Nakahara, S.; Karatsu, T.; Kitamura, A. Chem.dEur. J. 2006, 12, 3984–3994.
4.1.4. 1,3,5-Tris(4,5-dihydro-1H-imidazol-2-yl)benzene
A
mixture of benzene-1,3,5-tricarboxylic acid (4.80 g,
22.84 mmol), ethylenediamine (5.03 mL, 75.38 mmol), ethyl-
enediamine dihydrochloride (10.02 g, 75.38 mmol), p-toluene-
sulfonic acid (348 mg, 1.83 mmol), and ethylene glycol (30 mL) was
heated to reflux for 3 h. About half of ethylene glycol was then
slowly removed by distillation. The residual solution was concen-
trated to dryness at reduced pressure and was dissolved in