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Modulated Supramolecular Assemblies Composed of Tripeptide Derivatives: Formation of Micrometer-Scale Rods, Nanometer-Size Needles, and Regular Patterns with Molecular-Level Flatness from the Same Compound Katsuhiko Ariga,*,† Jun-ichi Kikuchi,† Masanobu Naito,‡ Emiko Koyama,‡,§ and Norihiro Yamada‡ Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), 8916-5 Takayama, Ikoma, Nara 630-0101, Japan and Faculty of Education, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan Received February 22, 2000 In this paper, we demonstrated that supramolecular structures of amphiphilic tripeptides can be effectively modulated by selecting the appropriate casting solvents. The tripeptide derivatives having an ammonium head and hydrophobic tails were dispersed in three kinds of solvents (nonpolar, medium nonpolar, and polar) followed by casting the solutions onto fleshly cleaved mica. The supramolecular structures in the cast films were observed using an atomic force microscope (AFM). The tripeptide derivative possessing the Ala-Ala-Glu sequence formed needles with nanometer-scale width, micrometer-scale rods, and patterns with molecular-level flatness by casting from H2O, CCl4, and CHCl3, respectively. Since the major driving forces of the assembly are significantly influenced by the polarity of the surrounding media, the assembling process can be altered depending on the nature of the solvents. In polar H2O, the hydrophobic interaction is dominant and the resulting assemblies are supported by hydrogen bonding. The strong hydrophobic interaction led to formation of a charged surface of unit structures and they were hardly fused upon solvent evaporation. As a result, thin needlelike structures remained in the cast film. In a nonpolar solvent such as CCl4, the assembly was driven by the insolubility of a polar part of the component and the hydrogen bonding, and solidification at the hydrophobic tails is induced only upon solvent evaporation. This two-step assembling process led to growth of the assembly, resulting in a larger structure. A medium nonpolar solvent, i.e., CHCl3 is not good for both interactions, thus resulting in a nonassembling structure in the solution. Therefore, assembly occurred only when the solvent was evaporated. This process gave a twodimensional pattern with molecular-level flatness. By using the solvents with a wide range of polarities, a variety of assembling processes leads to successful modulation of the supramolecular structures.
Introduction Supramolecular approaches have successfully provided various nanoarchitectures.1-8 Well-designed building block molecules are assembled on the basis of specific interactions such as hydrogen bonding and metal coordination. The building block has information about the completed motif of the supermolecules, i.e., information about the supramolecular structure is programmed in the unit block.1,5 Such programmed structures are commonly found in biological systems. The three-dimensional architecture of proteins is defined by the amino acid sequence which is programmed in the DNA.9 However, proteins †
Nara Institute of Science and Technology. Chiba University. § Present address: National Institute for Advanced Interdisciplinary Research (NAIR), 1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan. ‡
(1) Lehn, J.-M. Supramolecular Chemistry; VCH Press: New York, 1995. (2) Templating, Self-assembly and Self-Organization. In Comprehensive Supramolecular Chemistry; Sauvage, J.-P., Hosseini, M. W., Eds.; Pergamon: Elmsford, NY, 1995; Vol. 9. (3) Fujita, M. Chem. Soc. Rev. 1998, 27, 417. (4) Scwab, P. F. H.; Levin, M. D.; Michl, J. Chem. Rev. 1999, 99, 1863. (5) Storhoff, J. J.; Mirkin, C. A. Chem. Rev. 1999, 99, 1849. (6) Hartgerink, J. D.; Clark, T. D.; Ghadiri, M. R. Chem. Eur. J. 1998, 4, 1367. (7) Stupp, S. I.; LeBonheur, V.; Walker, K.; Li, L. S.; Huggins, K. E.; Keser, M.; Amstutz, A. Science 1997, 276, 384. (8) Orr, G. W.; Barbour, L. J.; Atwood, J. L. Science 1999, 285, 1049. (9) Anfinsen, C. B. Science 1973, 181, 223.
run the risk of forming a metastable conformation. This misfolding process sometimes causes fatal diseases such as amyloidoses.10-14 Diversity in protein folding would also create another possibility of protein engineering. Recently, Shinde et al. demonstrated an artificial misfolding process to alter enzyme functions.15 They used a modified chaperone to produce misfolded subtilisin which has a high activity to specific substrates. This strategy can be applied to artificial supermolecules. The introduction of the concept of modulating the programmed structures would lead to a large increase in the variety of nanostructures. As seen in the example of the protein misfolding, the assembling of peptide molecules is an attractive target to obtain the modulated supramolecular structure. On the other hand, it is widely known that the assembly of amphiphilic molecules is an efficient method to obtain various nanostructures.16-27 Therefore, the control of the assembling behavior of an amphiphilic peptide28,29 would be one of the best choices for our purpose. The assembly of amphiphilic molecules possesses a bilayer structure in water, where all the components align parallel with each (10) Fink, A. L. Folding Des. 1998, 3, R9 and references therein. (11) Inouye, H.; Fraser, P. E.; Kirschner, D. A. Biophys. J. 1993, 64, 502. (12) Symmons, M. F.; Buchanan, S. G. St. C.; Clarke, D. T.; Jones, G.; Gay, N. J. FEBS Lett. 1997, 412, 397. (13) Zhang, S.; Rich, A. Proc. Natl. Acad. Sci. 1997, 94, 23. (14) Aggeli, A.; Bell, M.; Boden, N.; Keen, J. N.; Knowles, P. F.; McLeish, T. C. B.; Pitkeathly, M.; Radford, S. E. Nature 1997, 386, 259. (15) Shinde, U. P.; Liu, J. J.; Inouye, M. Nature 1997, 389, 520.
10.1021/la000249u CCC: $19.00 © 2000 American Chemical Society Published on Web 04/29/2000
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Ariga et al. Chart 1
other. The peptide parts included in the amphiphile structure should align parallel in accord with the arrangements of the amphiphilic components. From this point of view, we have been investigating the assembling behaviors of amphiphilic tripeptides mainly in solution media.30 The advantage of using tripeptides lies in their ambidexterity; these tripeptides can form an aggregate not only in water but also in nonpolar oraganic solvents. The aggregate in organic solvents contained a parallel β-sheet structure in common with the conventional bilayer aggregate in water. Therefore, control of the assembling behavior of an amphiphilic tripeptide can be achieved (16) (a) Fuhrhop, J.-H.; Ko¨ning, J. Membranes and Molecular Assemblies: The Synkinetic Approach; Royal Society of Chemistry: Cambridge, 1994. (b) Fuhrhop, J.-H.; Helfrich, W. Chem. Rev. 1993, 93, 1565-1582 and references therein. (c) Fuhrhop, J.-H.; Svenson, S.; Boettcher, C.; Ro¨ssler, E.; Vieth, H.-M. J. Am. Chem. Soc. 1990, 112, 4307. (17) (a) Kunitake, T. Angew. Chem. 1992, 104, 692 and references therein. (b) Nakashima, N.; Asakuma, S.; Kunitake, T. J. Am. Chem. Soc. 1985, 107, 509. (18) Tachibana, T.; Kambara, H. J. Am. Chem. Soc. 1965, 87, 3015. (19) Yamada, K. Ihara, H.; Ide T.; Tsukumoto, T.; Hirayama, C. Chem. Lett. 1989, 1713. (20) (a) Schnur, J. M. Science 1993, 262, 1669. (b) Spector, M. S.; Selinger, J. V.; Singh, A.; Rodriguez, J. M.; Price, R. R.; Schnur, J. M. Langmuir 1998, 14, 3493. (21) van Nostrum, C. F.; Picken, S. J.; Schouten, A.-J.; Nolte, R. J. M. J. Am. Chem. Soc. 1995, 117, 9957. (22) Frankel, D. A.; O’Brien, D. F. J. Am. Chem. Soc. 1994, 116, 10057. (23) Thomas, B. N.; Corcoran, R. C.; Cotant, C. L.; Lindemann, C. M.; Kirsch, J. E.; Persicjini, P. J. J. Am. Chem. Soc. 1998, 120, 12178. (24) Menger, F. M.; Lee, S. J. J. Am. Chem. Soc. 1994, 116, 5987. (25) (a) Shimizu, T.; Ohnishi, S.; Kogiso, M. Angew. Chem., Int. Ed. 1998, 37, 3260. (b) Shimizu, T.; Kogiso, M. Masuda, M. Nature 1996, 383, 487. (26) Examples of formation of supramolecular structure of amphiphilic molecules in organic solvents: (a) Ishikawa, Y.; Kuwahara, H.; Kunitake, T. J. Am. Chem. Soc. 1994, 116, 5579. (b) Kimizuka, N.; Tokuhiro, M.; Miyauchi, H.; Wakiyama, T.; Kunitake, T. Chem. Lett. 1997, 1049. (27) Examples of formation of supramolecular structure of small galator in organic solvents: (a) Terech, P.; Weiss, R. G. Chem. Rev. 1997, 97, 3133 and references therein. (b) Vanesch, J.; Defeyter, S.; Kellog, R. M.; Deschryver, F.; Feringa, B. L. Chem. Eur. J. 1997, 3, 1238. (c) Hanabusa, K.; Tange, J.; Taguchi, Y.; Koyama, T.; Shirai, H. J. Chem. Soc., Chem. Commun. 1993, 390. (28) Yu, Y.-C.; Berndt, P.; Tirrell, M.; Fields, G. B. J. Am. Chem. Soc. 1996, 118, 12515. (29) Burkoth, T. S.; Benzinger, T. L. S.; Urban, V.; Lynn, D. G.; Meredith, S. C.; Thiyagarajan, P. J. Am. Chem. Soc. 1999, 121, 7429. (30) (a) Yamada, N.; Ariga, K.; Naito, M.; Matsubara, K.; Koyama, E. J. Am. Chem. Soc. 1998, 120, 12192. (b) Yamada, N.; Koyama, E.; Kaneko, M.; Seki, H.; Ohtsu, H.; Furuse, T. Chem. Lett. 1995, 387. (c) Yamada, N.; Koyama, E.; Imai, T.; Matsubara, K.; Ishida, S. Chem. Commun. 1996, 2297. (d) Yamada, N.; Matsubara, K.; Koyama, E.; Fujioka, M. Chem. Lett. 1997, 1033. (e) Yamada, N.; Koyama, E.; Maruyama, K. Kobunshi Ronbunshu 1995, 52, 629.
Figure 1. Schematic illustration of assembling behavior of the tripeptide derivatives in solution. Table 1. Dispersion State of Tripeptide Derivatives in Different Media solvent
dielectric constant
water ethanol 1,1,2,2-tetrachloroethane chloroform benzene carbon tetrachloride cyclohexane n-hexane
78.39 (25 °C) 24.55 (25 °C) 8.20 (25 °C) 4.81 (20 °C) 2.28 (25 °C) 2.24 (25 °C) 2.02 (25 °C) 1.88 (25 °C)
tripeptide derivativesa 1 2 3 4 5 T S S S G G G I
T S S S G G G P
T S S S G G G I
T S S S G G G I
T S S I G P I
a Abbreviations: T, translucent solution; S, transparent solution; G, gel; I, insoluble; P, precipitate.
using various media, which would be one of the most fruitful approaches for our purpose.30 The amphiphiles having various tripeptide units between a polar ammonium head and hydrophobic alkyl tails (see Chart 1) assemble through hydrogen bonding and solvophobic interactions.26a We particularly selected amino acid residues with an aliphatic side chain as the tripeptide component to avoid any complicated interaction. Systematic studies using Fourier-transform infrared (FT-IR)
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Figure 2. (A and B) AFM images of cast film of 1 from CCl4. The film was prepared immediately after 1 was dispersed in CCl4 (1 mM). The solvent was spontaneously evaporated. (C and D) AFM images of cast film of 1 from CCl4. The film was prepared after a 3-day incubation period in CCl4 (1 mM). The solvent was spontaneously evaporated.
spectroscopy and transmission electron micrography (TEM) indicated that the aggregation behavior of the tripeptide derivatives significantly depends on the nature of the surrounding solvents (Figure 1). The tripeptide derivatives efficiently aggregate in polar and nonpolar solvents, but not in medium nonpolar solvents. This diversity in its assembling property would be useful for modulation of the supramolecular structures. To investigate the details of the formed supramolecular structures of the tripeptide derivatives, their morphologies in the cast films have to be observed by using an atomic force microscope (AFM). Our preliminary AFM results suggest that these tripeptide derivatives possibly form various supramolecular structures in dried films.30a,31 In this paper, we systematically analyzed the AFM results of the supramolecular structures formed in the cast films from three different kinds of solvents, i.e., nonpolar (CCl4),
medium nonpolar (CHCl3), and polar (water). Modulation of the supramolecular structures by selecting the casting process is discussed in this paper. We demonstrated the formation of ultrathin needles, micrometer-scale rods, and regular patterns with molecular-level flatness from the same compounds. Experimental Section Materials and Film Preparation. Details of the synthetic procedure for tripeptide derivatives 1-5 (see Chart 1) were reported elsewhere.30a The tripeptide derivatives were dispersed in solvents with the help of sonication (PE2B55A-type sonicator, Japan Servo Co.). The obtained solution was allowed to stand at (31) (a) Ariga, K.; Yamada, N.; Naito, M.; Koyama, E.; Okahata, Y. Chem. Lett. 1998, 493. (b) Ariga, K.; Kikuchi, J.; Narumi, K.; Koyama, E.; Yamada, N. Chem. Lett. 1999, 787.
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Figure 3. (A and B) AFM images of cast film of 1 from diluted CCl4 solution (0.1 mM). The film was prepared after a 3-day incubation period in CCl4. The solvent was spontaneously evaporated. (C and D) AFM images of cast film of 1 from CCl4 using quick drying process. The film was prepared after a 3-day incubation period in CCl4 (1 mM). The solvent was quickly evaporated under reduced pressure. room temperature for 3 days. No precipitation was observed. produced a transparent solution except for n-hexane. The The cast film was obtained by casting of the solution of the state of the solutions after a 1-day incubation at room tripeptides onto freshly cleaved mica followed by air-drying. temperature is summarized in Table 1 along with dielectric Unless otherwise noted, the cast film was obtained under these constants.32 Solubility of the tripeptide derivatives deconditions. pends on the tested solvents, and the solvents can be Atomic Force Microscopy (AFM). The AFM images were classified into major three categories. The nonpolar solvent taken using a Nanoscope IIIa (Digital Instruments, Santa (benzene, CCl4, and cyclohexane) with a small dielectric Barbara, CA) with tapping mode in air. According to the constant (
