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Spontaneous Formation of Helically Twisted Fibers from 2-Glucosamide Bolaamphiphiles: Energy-Filtering Transmission Electron Microscopic Observation and Even-Odd Effect of Connecting Bridge Ikuo Nakazawa,† Mitsutoshi Masuda,‡ Yuji Okada,‡ Takeshi Hanada,‡ Kiyoshi Yase,‡ Michihiko Asai,‡ and Toshimi Shimizu*,‡ Joint Research Center for Precision Polymerization, Japan Chemical Innovation Institute, NIMC, and National Institute of Materials and Chemical Research, 1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan Received December 14, 1998. In Final Form: April 15, 1999 A series of nonionic sugar-based bolaamphiphiles having n-alkylene chain length of 9, 10, 11, 12, 13, 14, 16, or 18 carbon atoms, N,N′-bis(2-deoxy-D-glucopyranosid-2-yl)alkane-1,n-dicarboxamide, 1(n), have been synthesized in one step from commercially available glucosamine hydrochloride. Their self-assembling morphologies in 50% aqueous methanolic solutions have been studied using energy-filtering transmission electron microscopy (EF-TEM). The bolaamphiphiles 1(n) (n ) 10, 12, and 14) with an even-numbered carbon bridge produced well-defined helically twisted fibers of 8-25 nm width with a high axial ratio. The fiber morphology was found to display a pronounced even-odd dependence upon the number of carbons (n) in the connecting alkylene bridge. A similar trend was also exhibited by the infrared band frequencies and by the wide-angle X-ray diffraction patterns. Anomeric ratios of 1(n) were approximately constant across the series and had no remarkable effect upon the fiber morphology.
Introduction Nano- and mesoscale chiral self-assembling superstructures with high axial ratios have attracted a great deal of attention with their potential for hierarchical organization,1,2 chiral morphology control,3 and industrial application,4 provoking a wide range of theoretical and mechanistic studies.5 Typically studied systems to date include the self-assembly of diverse chiral amphiphiles derived from fatty acids,6 amino acids,2a,7 aldonamides,2b,2c nucleic acids,1 phospholipids,8 and other chiral surfac* To whom correspondence should be addressed. † Joint Research Center for Precision Polymerization, Japan Chemical Innovation Institute, NIMC. ‡ National Institute of Materials and Chemical Research. (1) Yanagawa, H.; Ogawa, Y.; Furuta, H.; Tsuno, K. J. Am. Chem. Soc. 1989, 111, 4567-4570. (2) (a) Nakashima, N.; Asakuma, S.; Kunitake, T. J. Am. Chem. Soc. 1985, 107, 509-510. (b) Fuhrhop, J. H.; Schnieder, P.; Rosenberg, J.; Boekema, E. J. Am. Chem. Soc. 1987, 109, 3387-3390. (c) Fuhrhop, J.-H.; Schnieder, P.; Boekema, E.; Helfrich, W. J. Am. Chem. Soc. 1988, 110, 2861-2867. (3) (a) Fuhrhop, J.-H.; Boettcher, C. J. Am. Chem. Soc. 1990, 112, 1768-1776. (b) Sommerdijk, N. A. J. M.; Buynsters, P. J. J. A.; Pistorius, A. M. A.; Wang, M.; Feiters, M. C.; Nolte, R. J. M.; Zwanenburg, B. J. Chem. Soc., Chem. Commun. 1994, 1941-1942. (c) Kimura, T.; Shinkai, S. Chem. Lett. 1998, 1035-1036. (4) (a) Varadan, V. K.; Varadan, V. V. USP 4948922, 1990. (b) Hafkamp, R. J. H.; Kokke, A. P. A.; Danke, I. M.; Geurts, H. P. M.; Rowan, A. E.; Feiters, M. C.; Nolte, J. M. Chem. Commun. 1997, 545546. (c) Hanabusa, K.; Tanaka, R.; Suzuki, M.; Kimura, M.; Shirai, H. Adv. Mater. 1997, 9, 1095-1097. (d) Motojima, S.; Iwanaga, H.; Varadan, V. K. Surface 1998, 36, 140-148. (e) Kato, T.; Kondo, G.; Hanabusa, K. Chem. Lett. 1998, 193-194. (5) (a) Helfrich, W.; Prost, J. Phys. Rev. A 1988, 38, 3065-3068. (b) Selinger, J. V.; Schnur, J. M. Phys. Rev. Lett. 1993, 71, 4091-4098. (c) Nandi, N.; Bagchi, B. J. Am. Chem. Soc. 1996, 118, 11208-11216. (d) Nandi, N.; Bagchi, B. J. Phys. Chem. A 1997, 101, 1343-1351. (6) Tachibana, T.; Kambara, H. J. Am. Oil. Chem. Soc. 1965, 87, 3015-3016. (7) (a) Hidaka, H.; Murata, M.; Onai, T. J. Chem. Soc., Chem. Commun. 1984, 562-564. (b) Yamada, K.; Ihara, H.; Ide, T.; Fukumoto, T.; Hirayama, C. Chem. Lett. 1984, 1713-1716. (c) Imae, T.; Takahashi, Y.; Muramatsu, H. J. Am. Chem. Soc. 1992, 114, 3414-3419. (8) Schnur, J. M. Science 1993, 262, 1669-1676.
tants,9 with the molecular packing observed depending markedly on the length10 and even-odd carbon numbers11 of the hydrophobic chains of the amphiphile under investigation. While reports on this last even-odd phenomenon are at present rare,12 the effect should be particularly pronounced in bola-form amphiphilic compounds (bolaamphiphiles13) where two hydrophilic moieties are separated by a long alkylene chain. Indeed, we have previously demonstrated a significant even-odd dependence in the supramolecular fiber and microtube formation from 1-glucosamide-based 2(n)14,15 and glycylglycine bolaamphiphiles,16 respectively. Our particular interest in oligosaccharides in terms of systematically tunable chiral hydrophilic moieties arises from the versatile stereochemistry associated with their multiple hydroxyl groups.17 While a great deal of work has been carried out on the phase behavior of stereochemically pure glycolipids in (9) Sommerdijk, N. A. J. M.; Buynsters, P. J. J. A.; Akdemir, H.; Geurts, D. G.; Pistorius, A. M. A.; Feiters, M. C.; Nolte, R. J. M.; Zwanenburg, B. Eur. J. Chem. 1998, 4. (10) Kunitake, T.; Okahata, Y.; Shimomura, M.; Yasunami, S.; Takarabe, K. J. Am. Chem. Soc. 1981, 103, 5401-5413. (11) (a) Yamada, N.; Kawasaki, M. J. Chem. Soc., Chem. Commun. 1990, 568-569. (b) Yamada, N.; Okuyama, K.; Serizawa, T.; Kawasaki, M.; Oshima, S. J. Chem. Soc., Perkin Trans. 2 1996, 2707-2714. (12) Schade, B.; Hubert, V.; Andre, C.; Luger, P.; Fuhrhop, J.-H. J. Peptide Res. 1997, 49, 363-368. (13) (a) Fuhrhop, J.-H.; David, H. H.; Mathieu, J.; Liman, U.; Winter, H. J.; Boekema, E. J. Am. Chem. Soc. 1986, 108, 1785-1791. (b) Escamilla, G. H.; Newkome, G. R. Angew. Chem., Int. Ed. Engl. 1994, 33, 1937-1940. (14) Shimizu, T.; Masuda, M. J. Am. Chem. Soc. 1997, 119, 28122818. (15) Shimizu, T.; Masuda, M.; Kogiso, M.; Asakawa, M. Kobunshi Ronbunsyu 1997, 54, 815-828. (16) Kogiso, M.; Ohnishi, S.; Yase, K.; Masuda, M.; Shimizu, T. Langmuir 1998, 14, 4978-4986. (17) (a) Shimizu, T.; Minamikawa, H.; Murakami, T.; Hato, M. Chem. Lett. 1993, 567-570. (b) Masuda, M.; Shimizu, T. Carbohydr. Res. 1997, 292, 47-59. (c) Shimizu, T.; Masuda, M.; Shibakami, M. Chem. Lett. 1997, 12, 232-234. (d) Masuda, M.; Hanada, T.; Yase, K.; Shimizu, T. Macromolecules 1998, 31, 9403-9405.
10.1021/la981714e CCC: $18.00 © 1999 American Chemical Society Published on Web 05/27/1999
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concentrated aqueous solution,18 little is known about chiral fiber formation from closed chain form glycolipids,19 except for our previous report.14 Here we report the facile preparation of a series of nonionic 2-glucosamide bolaamphiphiles 1(n) (n ) 9, 10, 11, 12, 13, 14, 16, and 18) where long alkylene bridges link the C-2 positions of two glucopyranose rings with connection via an amide linkage. Employment of energyfiltering transmission electron microscopy has allowed the direct observation of intact helically twisted fibers that form spontaneously from these closed-chain glycolipids. The fiber morphology was also found to display a pronounced even-odd variation with the number of carbon atoms in the linker chain. This effect on the molecular packing and orientation is discussed in conjunction with that arising from the geometry at the anomeric center and variations in the length of the alkylene chain.
Nakazawa et al.
Figure 1. Partial 1H NMR spectra of 1(11) in (a) DMSO-d6 and (b), (c) DMSO-d6 plus one drop of D2O at 25 °C. The spectrum (b) was obtained in 1 day after addition of D2O to the sample in DMSO-d6. The spectrum (c) was measured in 2 days after sonication of the DMSO-d6-D2O solution obtained in (b). Table 1. Dependence of the Anomeric Ratio of 1(n) on the Connecting Bridge Length (n) (in DMSO-d6 at 25 °C) anomeric ratio [R/(R + β)] (%) n
from NH protona
from OH protona
9 10 11
75.6 74.8 80.2
77.0 74.8 78.2
12
75.1
74.8
13 14 16 18
75.1 71.8 72.6 70.6
74.8 72.8 72.8 71.4
from C-1 carbonb
72 73
Results
a
Effect of Anomeric Linkage. The highly pure 2-glucosamide bolaamphiphiles 1(n) were efficiently and easily synthesized in one step, starting from commercially available, unprotected glucosamine hydrochloride. The present synthetic route provides convenient method of obtaining nonionic sugar-based bolaamphiphiles.20 1H NMR spectra of 1(11) clearly display two sets of welldefined signals for the amide NH (δ ) 7.50 and 7.63 ppm, in Figure 1a), hydroxyl O-1-H (δ ) 6.40 and 6.45 ppm, in Figure 1a), and the H-1 anomer protons (δ ) 4.89 and 4.40 ppm, in Figure 1c). The presence of these two sets of signals with an average integral ratio of 79:21 implies that the bolaamphiphile 1(11) exists as a mixture of Rand β-anomers in solution, with similar 1H NMR spectra being obtained for the remaining bolaamphiphiles of the series. The ratios of the R- and β-anomers [anomeric ratio ) R/(R + β)] were evaluated from a comparison of the (18) (a) Curatolo, W. Biochim. Biophys. Acta 1987, 906, 111-136. (b) Curatolo, W. Biochim. Biophys. Acta 1987, 906, 137-160. (c) Mannock, D. A.; Lewis, R. N. A. H.; Sen, A.; McElhaney, R. N. Biochemistry 1988, 27, 6852-6859. (d) Hinz, H.-J.; Kuttenreich, H.; Meyer, R.; Renner, M.; Frund, R. Biochemistry 1991, 30, 5125-5138. (e) Tamada, K.; Minamikawa, H.; Hato, M.; Miyano, K. Langmuir 1996, 12, 1666-1674. (f) Hato, M.; Minamikawa, H. Langmuir 1996, 12, 1658-1665. (g) Minamikawa, H.; Hato, M. Langmuir 1997, 13, 2564-2571. (19) (a) Giulieri, F.; Guillod, F.; Greiner, J.; Krafft, M.-P. Chem. Eur. J. 1996, 2, 1335-1339. (b) A.-Velty, R.; Benvegnu, T.; Plusquellec, D.; Mackenzie, G.; Haley, J. A.; Goodby, J. W. Angew. Chem., Int. Ed. Engl. 1998, 37, 2511-2515. (20) (a) G.-Calvet, R.; Brisset, F.; Rico, I.; Lattes, A. Synth. Commun. 1993, 23, 35-44. (b) Goueth, P.; Ramiz, A.; Ronco, G.; Mackenzie, G.; Villa, R. Carbohydr. Res. 1995, 266, 171-189. (c) Lafont, D.; Boullanger, P.; Chevalier, Y. J. Carbohydr. Chem. 1995, 14, 533-550. (d) Bertho, J.-N.; Ferrieres, V.; Plusquellec, D. J. Chem. Soc., Chem. Commun. 1995, 1391-1393.
Calculated from peak areas of the amide NH or OH protons in NMR. b Calculated from peak height of C-1 carbon signals in CP-MAS 13C NMR.
1H
peak areas of the NH and OH protons (Table 1) and were found generally to be in the range of 75 ( 4%, independent of the chain length (n) of the connecting bridge. EF-TEM of Helically Twisted Fibers. In marked contrast to the previously reported 1-glucosamide bolaamphiphiles 2(n),21 the 2-glucosamide homologues 1(n) proved only sparingly soluble in both bulk boiled water and an array of organic solvents such as methanol, chloroform, and pyridine. The translocation of the alkylene bridge junction from the C-1 to the C-2 position drastically alters the hydrogen-bonding networks available to 1(n) and thus its solubility. Indeed, tests were able to indicate that only DMF, DMSO, and a mixed solvent of water and methanol dissolve 1(n), regardless of the alkylene bridge length (n). When allowed to slowly cool and stand at room temperature, saturated 50% aqueous methanolic solutions (0.5 mg/mL) of 1(n) produced fibrous assemblies. In order to explore the fine morphologies of these structures, we carried out energy-filtering transmission electron microscopy (EF-TEM)22 on the unstained specimens. Although the EF-TEM has proved a powerful tool for elemental and chemical mapping of fine particles made of metals and inorganic compounds,23 there seem to be few similar reports about the observation of organic (21) Masuda, M.; Shimizu, T. J. Carbohydr. Chem. 1998, 17, 405416. (22) Reimer, L. Energy-Filtering Transmission Electron Microscopy; Reimer, L., Ed.; Springer-Verlag: Berlin, 1995.
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Table 2. Self-Assembling Morphologies of 1(n) in 50% Aqueous Methanolic Solutions
a
n
morphology
helical pitcha (nm)
width (nm)
fiber length (µm)
10 11 12 13 14 16 18
helical twisted fiber thin ribbon helical twisted fiber amorphous ribbon and sheet helical twisted fiber ill-defined fiber, ribbon, and sheet ill-defined fiber, ribbon, and sheet
50-75 b 60-80 b 35-140 7 >7
∼10 ∼20 ∼20 ∼20 ∼10 ∼5 ∼3
Evaluated from the length dependence of the black and white image contrast. b No helical structures were found.
Figure 2. Diverse fibrous assemblies with different morphologies formed from (a) 1(10), (b) 1(11), (c) 1(12), and (d) 1(13), observed using EF-TEM.
supramolecular self-assemblies.17d,24 However, EF-TEM should provide a useful method for the examination of organic samples since it can create an image by electron spectroscopic imaging (ESI) without the need for prior staining. The obtained self-assembling morphologies and their dimensions are summarized in Table 2. The EF-TEM revealed that 1(10), 1(12), and 1(14) produced selfassembled helically twisted fibers of 8-25 nm in width (Figures 2a,c and 3). These fibers have high axial ratios and extend in length to several tens of micrometers. The helical twists become more pronounced for 1(14), and we were able to observe left-handed, triplicate twisted yarn structures, where three single fibers are helically intertwined. The EF-TEM image shown in Figure 3 gives a typical example of the structural hierarchy1,16,25 found, from single twisted fibers to higher ordered yarns, with (23) (a) Starosud, A.; B.-Jones, D. P.; Langford, C. H. Chem. Commun. 1997, 443-444. (b) Kurata, H.; Isoda, S.; Kobayashi, T. J. Electron Microsc. 1996, 45, 317-321. (24) Kogiso, M.; Hanada, T.; Yase, K.; Shimizu, T. Chem. Commun. 1998, 17, 1791-1792. (25) (a) Gulik-Krzywicki, T.; Fouquey, C.; Lehn, J.-M. Proc. Natl. Acad. Sci. U.S.A. 1993, 90, 163-167. (b) Shimizu, T.; Ohnishi, S.; Kogiso, M. Angew. Chem., Int. Ed. Engl. 1998, 37, 3260-3262.
the helical pitches of these assemblies readily and quantitatively evaluated from the length dependence of the black and white image contrast (Figure 4). The bolaamphiphiles with a longer connecting bridge [1(16) and 1(18)], gave only ill-defined fibers, ribbons, and sheets (Figure 5). Somewhat surprisingly, the odd-numbered bolaamphiphiles 1(11) and 1(13) produced no long fibers with well-defined morphologies, giving only apparently stiff, crystalline rods and ribbons with widths of 10-150 nm and low axial ratios (Figure 2, b and d). The helical features associated with these structures are also ambiguous when compared with those from the evennumbered homologues. Thus, in analogous fashion to that demonstrated previously for the 1-glucosamide bolaamphiphiles 2(n),14 the use of EF-TEM has allowed the evenodd effect of the alkylene bridge upon the self-assembling morphology to be explicitly demonstrated. Infrared Spectroscopy. FT-IR spectroscopy provides a powerful tool for investigating amide-amide hydrogen bonds. Dehydrated powders of 1(n) (n ) 9-14, 16, and 18) displayed amide I and II bands at 1650-1640 and 1550-1555 cm-1, respectively,26 and Figure 6 shows the (26) FT-IR spectra of 1(n) (n ) 9-14, 16, and 18), see Supporting Information.
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Figure 4. Length dependence of black and white image contrast for the single twisted fibers and triplicate twisted yarn. The three image contrasts were examined along the fiber portion denoted by arrows in Figure 3b. Figure 3. Helically twisted fibers formed from 1(14), observed using EF-TEM.
dependence of these frequencies on the alkylene chain length (n) in comparison with those of 2(n)14sboth clearly indicating an even-odd effect for all chain lengths (9 e n e 14). This alternating feature, although relatively weak, contrasts well with that of 2(n) in that the even-odd effect of the alkylene carbon numbers is reversed on moving between 1(n) and 2(n). On the basis of the relation between the bond energies and the band frequencies,11b the even-numbered bolaamphiphiles 1(n) (n ) 10, 12, 14, 16, and 18) should form stronger amide-amide hydrogen bonds than the odd-numbered derivatives 1(n) (n ) 9, 11, and 13). A comparison of the FT-IR spectra shows a shift to relatively lower frequencies for the amide I bands and to relatively higher frequencies for the amide II bands on moving from 1(n) to 2(n), a factor which suggests that the 2-glucosamide bolaamphiphiles 1(n) form relatively stronger or more extended hydrogen-bonding networks than the corresponding 1-glucosamide bolaamphiphiles 2(n).
Except for those of 1(9) and 1(10), the CH2 antisymmetric and symmetric stretching bands appear at identical wavenumbers (2920 and 2850 cm-1, respectively),26 indicating highly populated all-trans conformation in the oligomethylene chain.27 The anomalous CH2 antisymmetric stretching of 1(9) at 2927 cm-1 is indicative of the existence of a gauche conformation. Furthermore, the CH2 scissoring and rocking bands display alternating broad and sharp peaks with respect to the even and odd carbon numbers of the bridge, respectively.26 Thus, subtle differences in the oligomethylene chain packing11b,28 are closely related to the more apparent even-odd effect. Powder X-ray Diffraction. The molecular arrangement and ordering of the assemblies were examined by powder X-ray diffraction analysis. Small-angle regions of the X-ray diagrams for 1(n) revealed a series of sharp (27) Snyder, R. G.; Strauss, H. L. J. Phys. Chem. 1982, 86, 51455150. (28) (a) Garti, N.; Sato, K. Crystallization and Polymorphism of Fats and Fatty Acids; Marcel Dekker: New York, 1988. (b) Parikh, A. N.; Schivley, M. A.; Koo, E.; Seshadri, K.; Aurentz, D.; Mueller, K.; Allara, D. L. J. Am. Chem. Soc. 1997, 119, 3135-3143.
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Figure 5. Fibrous assemblies formed from (a) 1(16) and (b) 1(18), observed using EF-TEM.
Figure 7. Powder X-ray diffraction diagrams (reflection mode) of 1(n).
fibers. The chain-length dependence of the long periods displayed an approximately linear relationship. On the other hand, the wide-angle regions show a distorted hexagonal packing of the oligomethylene group29 characterized by two ill-defined, strong reflection peaks (d ) 0.440 and 0.427 nm) which merged in the case of the oddnumbered 1(n) and a single weak peak (d ) 0.393 nm) which displayed a similar even-odd variation in intensity. This would further reinforce the notion of slight differences in the packing order of the oligomethylene chains between the odd and even numbered 1(n) suggested from the variation in the CH2 scissoring and rocking bands found in the FT-IR spectra.26 Discussion
Figure 6. Dependence of typical infrared band frequencies on the connecting bridge length (n) for 1(n) (s) and 2(n) (- - -).
reflection peaks up to third order with long-range spacings of 2.43-3.11 nm (Figure 7). We can therefore assume that the hierarchically organized twisted fibers are built up from layer structures, with the long periods corresponding to the respective thickness of a unit monolayer within the
In the case of 1(n) and 2(n), the stereochemistry of the amino group is similar (i.e., equatorial) for both bolaamphiphiles. However, changing the location at the junction to the alkylene bridge induces a rearrangement of the hydrogen-bond networks associated with both the glucopyranose rings and the amide groups and concomitantly results in the crystallization or formation of different types of self-assemblies. This is strikingly demonstrated by the (29) (a) Goto, M. J. Jpn. Oil Chem. Soc. (YUKAGAKU) 1970, 19, 583-599. (b) Svenson, S.; Koening, J.; Fuhrhop, J.-H. J. Phys. Chem. 1994, 98, 1022-1028.
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Figure 8. CP-MAS solid state and (b) 1(12).
13C
Nakazawa et al.
NMR spectra of (a) 1(11)
drastic reduction in solubility of 1(n) in a variety of solvents. We previously reported that 2(n) forms intraand interlayer two-dimensional hydrogen-bond networks between sugar hydroxyl groups,30 with the total number of hydrogen bonds formed per molecule reaching 24.17b In spite of this multiplicity of hydrogen bonds, 2(n) is remarkably soluble in hot water. In contrast, the epimeric homologues with an axial hydroxyl group at the C4 position [1-galactosamide bolaamphiphiles 3(n)] convert the hydrogen-bond network between sugar headgroups into three-dimensional one14,17c and, as a result, single needle crystals were obtained from 3(10) and 3(12). We should note here that the difference in the stereochemistry of only one hydroxyl group has a great influence on the morphology and even the crystallinity of the assembled fibers. Interestingly, the dependence of the crystallinity on the even and odd carbon numbers of the connecting bridge has an opposite tendency between the 1-glucosamide17b and 1-galactosamide17c homologues. The axial hydroxyl group at the C1 position of 1(n) (R-anomer) will contribute to the formation of the hydrogen-bond networks to the axial direction of the pyranose ring. The fact that the axial O-1-H(R) protons only slowly exchange with D2O, as shown in Figure 1, b and c, supports this notion. The poor solubility of 1(n) results from the formation of threedimensionally extended networks of hydrogen bonds. The presence of epimeric mixtures with respect to the C-1 carbon (R- and β-anomers) could conceivably complicate the formation of hydrogen-bond network and selfassembling morphologies.18d,31 For example, a 1:1 epimeric mixture of 2(12) and 3(12) produced a homogeneous hydrogel, whereas mixtures of 2(10) and 3(10) or 2(14) and 3(14) gave crystalline assemblies of the separate components.32 In case of 1(n), the CP-MAS 13C NMR rules out the possibility of homo-assembly from either R- or β-anomer since the dehydrated fibers from 1(11) and 1(12) exhibit two sets of split signals for the C-1 and CdO carbons (Figure 8). The peak height ratios of these signals are well consistent with the 1H NMR results obtained in (30) Masuda, M.; Shimizu, T. Chem. Commun. 1996, 1057-1058. (31) (a) Jarrell, J. C.; Wand, A. J.; Giziewicz, J. B.; Smith, I. C. P. Biochim. Biophys. Acta 1987, 897, 69-82. (b) Asgharian, B.; Cadenhead, D. A.; Mannock, D. A.; Lewis, R. N. A. H.; McElhaney, R. N. Biochemistry 1989, 28, 7102-710. (32) Masuda, M.; Shimizu, T., unpublished results.
Figure 9. Schematic illustration of the transformation of a layered ribbon structure into a helically coiled ribbon. The direction of the twist is counterclockwise enforced. The coiled ribbons are not always generated via twisted assemblies. The formation process depends on the ordered state of molecules (membrane stiffness).
free solution (Table 1). We can thus conclude that the self-assembled fibers include anomeric mixtures whose ratio is independent of the bridge length and that the even-odd effect does not stem from the difference in the anomeric ratio. The helical morphologies of the fibers from 1(n) appear to be different both from those of 2(n) (n ) 10 and 12)14 and other representative chiral amphiphiles.1,2a,c,3a So far, only two kinds of helical assemblies (namely coiled and twisted morphologies of long ribbons) have been reported (Figure 9).33 Cooling of aqueous solutions containing spherical vesicles formed from chiral amphiphiles typically leads to the appearance of coiled ribbons in a gel state.1,7b These have highly curved uni- or multilamellar membranes, resulting in some cases in the formation of tubules.8 Alternatively, the twisted ribbons can frequently be seen in organogels formed from chiral gelating compounds. These have a relatively small curvature of the membrane and, unlike typical chiral amphiphiles, they exhibit no remarkable morphological change of helical ribbons into vesicles upon heating.4c,34 By using long-chain glutamate lipids with a oligopeptide headgroup as a hydrophilic moiety, we previously demonstrated the correlation between the headgroup conformation and the self-assembled helical bilayer morphologies.35 The lipids with an oligosarcosine headgroup, which takes an extending conformation, give a twisted fiber, whereas the lipids with an oligoproline, which takes a helical conformation, produce a coiled ribbon. This finding shows that the bilayer curvature is sensitive to the headgroup (33) (a) Fuhrhop, J.-H.; Helfrich, W. Chem. Rev. 1993, 93, 15651582. (b) Fuhrhop, J.-H.; Koening, J. Membranes and Molecular Assemblies: The Synkinetic Approach; The Royal Society of Chemistry: Cambridge, UK, 1994; Vol. 5. (34) (a) Hanabusa, K.; Okui, K.; Karaki, K.; Koyama, T.; Shirai, H. J. Chem. Soc., Chem. Commun. 1992, 1371-1373. (b) Hanabusa, K.; Tange, J.; Taguchi, Y.; Koyama, T.; Shirai, H. J. Chem. Soc., Chem. Commun. 1993, 390-392. (c) Hanabusa, K.; Yamada, M.; Kimura, M.; Shirai, H. Angew. Chem., Int. Ed. Engl. 1996, 35, 1949-1951. (35) Shimizu, T.; Hato, M. Biochim. Biophys. Acta 1993, 1147, 5058.
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Figure 10. Possible molecular packing and orientation of 1(14) within the twisted fibers. In this illustration, the membrane of the twisted fiber is tentatively composed of three unit monolayers arranged in parallel with each other. As an alternative model, a pleated sheet structure of multimonolayers is also possible. For clarity, the amide linkages have been omitted.
conformation and chirality of the amphiphiles. Thus, the even-odd phenomena of 1(n) can perhaps be explained in a similar fashion; i.e., the chiral membranes formed from the even-numbered bolaamphiphiles are more highly ordered than those from the odd-numbered homologues. FT-IR results revealed that except for 1(9) and 1(10) the alkylene bridge takes an all-trans zigzag conformation. Considering the 3.34 nm length calculated for the fully extended molecule of 1(14), the molecules are tilted with the alkylene chain at 33° against the monolayer plane normal within the fibers (Figure 10). In addition, intralayer and interlayer networks of hydrogen bonds14,17b,c,36 should be formed between the sugar headgroups, depending sensitively upon the relative amount of R- and β-anomers. In a manner similar to that described for the 1-glucosamide bolaamphiphiles 2(n), the orientation of the amide hydrogen-bond chain and the packing mode of unit monolayer (polytype37) will also enforce the chiral membrane formation of 1(10), 1(12), and 1(14). In conclusion, the easily prepared 2-glucosamide bolaamphiphiles allowed the formation of a new type of helically twisted fiber and displayed characteristic evenodd effects of the alkylene chain length. The EF-TEM measurement proved effective in presenting high-contrast electron microscopic images from unstained organic supramolecular self-assemblies. The position and stereochemistry of the hydroxyl groups in the glucopyranose rings were found to dramatically influence the selfassembling morphologies of the sugar-based bolaamphiphiles. Experimental Section Materials and General Methods. Glucosamine hydrochloride was purchased from Kanto Chemicals Co. Inc. and was used as received. Other chemicals were commercially available highpurity grades and were used without further purification. The structures of the final products were confirmed by FT-IR, NMR spectroscopy, MALDI-TOFMS, and elemental analysis. Melting points were recorded on a Yanaco micro melting point apparatus, MP-500D, and are uncorrected. Solution 1H NMR spectra were recorded with a JEOL 600 spectrometer by using tetramethylsilane as an internal standard for the organic solutions. For the (36) Mo, F.; Jensen, L. H. Acta Crystallogr. 1975, B31, 2867-2873. (37) Amelinckx, S. Acta Crystallogr. 1956, 9, 217-224.
Langmuir, Vol. 15, No. 14, 1999 4763 FT-IR and TOFMS measurement, JASCO FT/IR-620 (resolution ) 4 cm-1) and Shimadzu Kratos KOMPACT MALDI III (matrix: 2,5-dihydroxybenzoic acid) were used, respectively. Synthesis of 2-Glucosamide Bolaamphiphiles 1(n). Brisset et al. have recently described the first synthesis of 1(8) and 1(10) with a relatively shorter alkylene bridge.38 Independently, we modified the method previously described by Inouye et al.,39 by using long-chain 1,n-alkane dicarboxylic acid dichlorides. Our procedure proves useful only for the longer bolaamphiphiles with more than a C10 alkylene bridge, since these products are only sparingly soluble in water. In a typical synthesis, glucosamine hydrochloride (6.4 g, 29.7 mmol) was dissolved in 1 N NaOH (30 mL) at -15 °C. To this aqueous solution, a solution of tridecanedioic acid dichloride (2.08 g, 7.40 mmol) in methylene chloride (20 mL) and 4 mL of 1 N NaOH solution was slowly added over a period of 30 min with vigorous stirring at -10 to -15 °C. During this treatment, the pH value of the reaction mixture was carefully maintained at 7-8. Stirring was continued at 0 °C for 2 h and subsequently at 15 °C for 3 h. The reaction mixture was then allowed to warm to room temperature and the pH of the solution was adjusted to ∼1 with 1 N HCl. The white precipitate obtained was filtered, thoroughly washed with 1 N HCl and water, and dried in vacuo. The raw product was powdered and washed with a hot 1:1 mixture of methanol and water until reaction byproducts and unreacted starting materials were completely removed. Drying this residue gave the final product 1(11) as a white solid (1.93 g, 3.41 mmol) with satisfactory spectra and C, H, and N analytical data. Mp ) 210-230 °C (dec); MALDI-TOFMS (in 2,5-dihydroxybenzoic acid) m/z 589.3 (MW + Na+); 1H NMR (600 MHz, in DMSO-d6 plus 1 drop of D2O at 25 °C) δ 7.63 (d, J ) 8.43, 0.22H, NH, β), 7.50 (d, J ) 8.06, 0.78H, NH, R), 4.89 (d, J ) 3.30, 0.75H, H-1, R), 4.40 (d, J ) 8.06, 0.25H, H-1, β), 3.1-3.7 (m, 6H, H-2, H-3, H-4, H-5, H-6a, and H-6b), 2.50 (dd, 2H, -CH2CONH), 1.46 (m, 4H, -CH2CH2CONH), 1.24 [s, 14H, -(CH2)7-]. Anal. Calcd for C25H46N2O12: C, 52.99; H, 8.18; N; 4.94. Found: C, 52.79; H, 8.40; N; 4.73. Other 2-glucosamide bolaamphiphiles 1(n) (n ) 9, 10, 12, 13, 14, 16, and 18) also gave satisfactory 1H NMR spectra and elemental analyses. Water of crystallization proved impossible to remove from 1(10), 1(14), 1(16), and 1(18) even after the drying at 70 °C in a vacuum. More aggressive drying at 120 °C in vacuo for 1 day caused decomposition of the samples. 1(9): mp ) 210-220 °C (dec). Anal. Calcd for C23H42N2O12: C, 51.29; H, 7.86; N; 5.20. Found: C, 50.86; H, 8.15; N; 4.79. 1(10): mp ) 208-219 °C (dec). Anal. Calcd for C24H44N2O12‚ 1/ H O: C, 51.33; H, 8.08; N; 4.99. Found: C, 51.33; H, 8.32; N; 2 2 4.82. 1(12): mp ) 215-230 °C (dec). Anal. Calcd for C26H48N2O12: C, 53.78; H, 8.33; N; 4.82. Found: C, 53.56; H, 8.59; N; 4.62. 1(13): mp ) 220-230 °C (dec). Anal. Calcd for C27H50N2O12: C, 54.53; H, 8.47; N; 4.71. Found: C, 54.11; H, 8.73; N; 4.66. 1(14): mp ) 205-220 °C (dec). Anal. Calcd for C28H52N2O12‚ 1/ H O: C, 54.44; H, 8.65; N; 4.53. Found: C, 54.44; H, 8.89; N; 2 2 4.36. 1(16): mp ) 208-220 °C (dec). Anal. Calcd for C30H56N2O12‚ 1/ H O: C, 56.06; H, 8.89; N; 4.36. Found: C, 56.08; H, 9.20; N; 3 2 4.09. 1(18): mp ) 214-224 °C (dec). Anal. Calcd for C32H60N2O12‚ 1/ H O: C, 57.04; H, 9.12; N; 4.16. Found: C, 57.18; H, 9.28; N; 2 2 3.82. Self-Assembling Procedure. All self-assembly experiments were performed in 50% aqueous methanolic solutions. Methanol was spectroscopic grade from Wako chemicals. The aqueous solutions of 1(n) (ca. 8 × 10-4 M) were obtained by sonication of a weighed bolaamphiphile sample at 80 °C (Branson ultrasonicator model 1200, 47 kHz, 60 W). Each solution was allowed to stand at room temperature for 2-3 days. Self-assembled molecular objects in the solutions were then subjected to energyfiltering transmission electron microscopy. Energy-Filtering Transmission Electron Microscopy (EF-TEM). Unstained specimens for the electron microscopy (38) Brisset, F.; G.-Calvet, R.; Azema, J.; Chebli, C.; R.-Lattes, I.; Lattes, A.; Moisand, A. New J. Chem. 1996, 20, 595-605. (39) Inouye, Y.; Onodera, K.; Kitaoka, S.; Hirano, S. J. Am. Chem. Soc. 1956, 78, 4722-4724.
4764 Langmuir, Vol. 15, No. 14, 1999 were prepared by placing a 3 µL drop of the dispersion on an amorphous carbon supporting film mounted on a standard TEM grid. The drop was then blotted off with filter paper. The dried specimens were examined by electron spectroscopic imaging using an electron microscope (Carl Zeiss EM902) operated at 80 keV with Castain-Henry type electron energy filter at room temperature. Zero-loss bright field images were recorded on an imaging plate (Fuji Photo Film Co., Ltd. FDL 5000) with a 20 eV energy windows at 3000-250 000× and digitally enlarged. The zeroloss filtering image improved contrast allows a reduction in the amount of defocusing, giving better spatial resolution. Powder X-ray Diffraction. All powder spectra were taken by the reflection method with a Rigaku RAD-C powder diffractometer (40 kV and 35 mA). The Cu KR beam was taken out via a graphite monochromator (reflection mode). The spectra were measured at room temperature between 1° and 36° in the 2θ/θ scan mode with steps of 0.01° in 2θ and 0.6 s measurement time per step.
Nakazawa et al. CP-MAS Solid State 13C NMR Spectra. Isolated fibers of 1(11) and 1(12) were dehydrated and dried in vacuo. Solid state 13C NMR spectra were recorded using a Bruker DPX400 spectrometer at spinning rates of 4000 rotations per second. Glycine (δ ) 176.1 ppm) was used as external standard.
Acknowledgment. This work was supported by New Energy and Industrial Technology Development Organization (NEDO) for the project on Technology for Novel High-Functional Materials Program, AIST, MITI. Supporting Information Available: FT-IR spectra of the 2-glucosamide bolaamphiphiles 1(n) (n ) 9-14, 16, and 18) mentioned in the text. This material is available free of charge via the Internet at http://pubs.acs.org. LA981714E
