Self-Organization of Amide Dendrons and Their ... - ACS Publications

Percec, V.; Cho, W.-D.; Möller, M.; Prokhorova, S. A.; Ungar, G.; Yeardley, D. J. P. J. Am. Chem. Soc. 2000, 122, 4249. [ACS Full Text ACS Full Text ...
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Langmuir 2006, 22, 3812-3817

Self-Organization of Amide Dendrons and Their Dendronized Macromolecules Chiyoung Park,† Kyoung Sik Choi,† Yumi Song,† Hye-Jin Jeon,‡ Hyun Hoon Song,‡ Ji Young Chang,§ and Chulhee Kim*,† Department of Polymer Science and Engineering, Hyperstructured Organic Materials Research Center, Inha UniVersity, Incheon 402-751, Korea, Department of Polymer Science and Engineering, Hannam UniVersity, Daejeon 300-791, Korea, and School of Materials Science and Engineering, Hyperstructured Organic Materials Research Center, Seoul National UniVersity, Seoul 151-744 Korea ReceiVed October 22, 2005. In Final Form: February 3, 2006 A polymerizable methacryl unit was introduced at the focal moiety of the amide dendrons which have amide branches and alkyl periphery. Their dendronized polymers were also prepared by the radical polymerization of the methacryl units. The self-organization characteristics of dendrons and dendronized polymers were then investigated in both the organic and aqueous phases. The amide dendrons (1M and 2M) in which the focal carboxyl group was blocked with methacryl units did not form gel in organic media such as chloroform or THF, whereas amide dendrons with a free carboxyl group at the focal point form self-organized structures. In the aqueous phase, 1M and 2M formed spherical vesicular assemblies. The dendronized polymers with first and second generation dendrons, 1P and 2P, respectively, exhibited lamellar and columnar organization in toluene. In addition to hydrogen bonding between the dendritic amide branches and van der Waals interactions between the alkyl periphery, steric confinement of dendritic side groups along the polymer backbone played a key role in the packing process of the dendronized polymers. In aqueous phase, 1P and 2P showed spherical vesicular aggregates with persistent stability in the presence of Triton X-100.

Introduction The self-organization of a variety of molecular building blocks toward well-defined architectures with appropriate functions is a key issue in the construction of functional nanomaterials. There are numerous examples of building blocks including small molecules and high polymers.1-3 In particular, the self-assembly of building molecules with an amphiphilic nature in selective solvents has produced a variety of morphologies such as micelles, vesicles, cylindrical micelles, tubular assemblies, and helical ribbons.1-3 Recently, dendrimers or dendrons have attracted much attention in the area of self-assembly due to their unique assembly characteristics.4-9 In particular, the structural uniqueness of dendronized polymers with tightly packed dendron sequences provide an opportunity to construct unprecedented functional nanomaterials.10-14 The self-organization of dendron building * To whom correspondence [email protected]. † Inha University. ‡ Hannam University. § Seoul National University.

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(1) Estroff, L. A.; Hamilton, A. D. Chem. ReV. 2004, 104, 1201. (2) Fuhrhop, J.-H.; Wang, T. Chem. ReV. 2004. 104, 2901. (3) Brunsveld, L.; Folmer, B. J. B.; Meijer, E. W.; Sijbesma, R. P. Chem. ReV. 2001, 101, 4071. (4) Fre´chet, J. M. J. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 4787. (5) Zimmerman, S. C.; Lawless, L. J. Top. Curr. Chem. 2001, 217, 95. (6) Genderen, M. H.; Meijer, E. W. Supramolecular Materials and Technologies; Wiley: New York, 1999; p 47. (7) Newkome, G. R.; Moorefield, C. N. Chem. ReV. 1999, 99, 1689. (8) Zeng, F.; Zimmerman, S. C. Chem. ReV. 1997, 97, 1681. (9) Hecht, S.; Fre´chet, J. M. J. Angew. Chem., Int. Ed. Engl. 2001, 40, 74. (10) Schlu¨ter, A. D.; Rabe, J. P. Angew. Chem., Int. Ed. 2000, 39, 864. (11) Gossl, I.; Shu, L.; Schlu¨ter, A. D.; Rabe, J. P. J. Am. Chem. Soc. 2002, 124, 6860. (12) Lee, C. C.; Yoshida, M.; Frechet, J. M. J.; Dy, E. E.; Szoka, F. C. Bioconjugate Chem. 2005, 16, 535. (13) Shu, L.; Schlu¨ter, A. D.; Ecker, C.; Severin, N.; Rabe, J. P. Angew. Chem., Int. Ed. 2001, 40, 4666.

blocks into ordered supramolecular structures has been demonstrated in various conditions such as in a thermotropic fashion in the solid state,15-22 in aqueous phase23,24,34-36 and organic (14) Bo¨ttcher, C.; Schade, B.; Ecker, C.; Rabe, J. P.; Shu, L.; Schlu¨ter, A. D. Chem. Eur. J. 2005, 11, 2923. (15) Hudson, S. D.; Jung, H.-T.; Percec, V.; Cho, W.-D.; Johansson, G.; Ungar, G.; Balagurusamy, V. S. K. Science 1997, 278, 449. (16) Percec, V.; Ahn, C.-H.; Ungar, G.; Yeardley, D. J. P.; Mo¨ller, M.; Sheiko, S. S. Nature 1997, 391, 161. (17) Percec, V.; Cho, W.-D.; Ungar, G.; Yeardley, D. J. P. Angew. Chem., Int. Ed. Engl. 2000, 39, 1598. (18) Percec, V.; Cho, W.-D.; Mo¨ller, M.; Prokhorova, S. A.; Ungar, G.; Yeardley, D. J. P. J. Am. Chem. Soc. 2000, 122, 4249. (19) Percec, V.; Cho, W.-D.; Ungar, G.; Yeardley, D. J. P. J. Am. Chem. Soc. 2001, 123, 1302. (20) Percec, V.; Glodde, M.; Bera, T. K.; Miura, Y.; Shiyanovskaya, I.; Singer, K. D.; Balagurusamy, V. S. K.; Heiney, P. A.; Schnell, I.; Rapp, A.; Spiess, H.-W.; Hudson, S. D.; Duan, H. Nature 2002, 417, 384. (21) Ungar, G.; Liu, Y.; Zeng, X.; Percec, V.; Cho, W.-D. Science 2003, 299, 1208. (22) Percec, V.; Glodde, M.; Johansson, M.; Balagurusamy, V. S. K.; Heiney, P. A. Angew. Chem., Int. Ed. Engl. 2003, 42, 4338. (23) Newkome, G. R.; Baker, G. R.; Saunders, M. J.; Russo, P. S.; Gupta, V. K.; Yao, Z.; Miller, J. E.; Bouilion, K. J. Chem. Soc., Chem. Commun. 1986, 752. (24) Newkome, G. R.; Moorfield, C. N.; Baker, G. R.; Behera, R. K.; Escamillia, G. H.; Saunders, M. J. Angew. Chem., Int. Ed. Engl. 1992, 31, 917. (25) Kim, C.; Kim, K. T.; Chang, Y.; Song, H. H.; Jeon, H.-J. J. Am. Chem. Soc. 2001, 123, 5586. (26) Kim, C.; Lee, S. J.; Lee, I. H.; Kim, K. T.; Song, H. H.; Jeon, H.-J. Chem. Mater. 2003, 15, 3638. (27) Enomoto, M.; Kishimura, A.; Aida, T. J. Am. Chem. Soc. 2001, 123, 5608. (28) Jang, W.-D.; Jiang, D. L.; Aida, T. J. Am. Chem. Soc. 2000, 122, 3232. (29) Jang, W.-D.; Aida, T. Macromolecules 2003, 36, 8461. (30) Zubarev, E. R.; Parlle, M. U.; Sone, E. D.; Stupp, S. I. J. Am. Chem. Soc. 2001, 123, 4105. (31) Zubarev, E. R.; Stupp, S. I. J. Am. Chem. Soc. 2002, 124, 5762. (32) Hirst, A. R.; Smith, D. K.; Feiters, M. C.; Geurts, H. P. M.; Wright, A. C. J. Am. Chem. Soc. 2003, 125, 9010. (33) Ko, H. S.; Park, C.; Lee, S. M.; Song, H. H.; Kim, C. Chem. Mater. 2004, 16, 3872. (34) Kim, K. T.; Lee, I. H.; Park, C.; Song, Y.; Kim, C. Macromol. Res. 2004, 12, 528. (35) Chang, Y.; Park, C.; Kim, K. T.; Kim, C. Langmuir 2005, 21, 4334. (36) Park, C.; Lee, I. H.; Lee, S.; Song, Y.; Rhue, M.; Kim, C. Proc. Natl. Acad. Sci. U.S.A. 2006, 103, 1199.

10.1021/la0528448 CCC: $33.50 © 2006 American Chemical Society Published on Web 03/18/2006

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Scheme 1. Amide Dendrons (1M, 2M) and Dendronized Polymers (1P, 2P)

media,25-33 and at liquid-solid interfaces.33 The self-assembly behaviors of dendronized polymers have also been investigated under lyotropic conditions and air-water interfaces.10,14 Recently, we reported on the unique self-assembly characteristics of some amide dendrons.25,26,33-36 In organic media, amide dendrons formed thermoreversible supramolecular gels, and then lamella or columnar hexagonal arrays were formed in the dry state depending on the generation of the dendrons.25,26 The key structural elements required for the self-assembly of the amide dendron, for example, dendron 2 in Scheme 1, are amide branches for hydrogen bonding, carboxyl functionality at the focal point, and alkyl tails to stabilize the assembled structures via van der Waals interactions. Transmission electron microscope (TEM) and X-ray diffraction (XRD) studies showed that the dimeric form of dendron 2, induced by hydrogen bonding at the focal carboxyl groups of the two dendron units, is the primary building block in the self-aggregation process. Accordingly, it was suggested that dendron dimers covalently bridged at their focal points should be able to form similar self-assembled supramolecular structures. Indeed, the dendron dimers with aromatic bridge units formed lamella ribbons in organic media or at the solid-liquid interface.33 In addition, the amphiphilic nature due to the hydrophilic amide branch units and the hydrophobic alkyl peripheries provides an opportunity for amide dendrons to selforganize in an aqueous phase. For example, we previously reported that the transition of a self-organized vesicular structure to rods and spherical micelles was triggered by an increase in the molecular weight of the hydrophilic PEG focal moiety.34 Therefore, we reasoned that dendronized polymers with amide dendron side groups might self-organize in organic solvents or water, because the dendron units are confined along the polymer chain so that the amide dendrons would have an opportunity to stack together to form self-assembled structure. In this work, a polymerizable moiety was introduced at the focal point of amide dendrons, and their dendronized polymers were prepared by the radical polymerization. The self-organization characteristics of these methacryl-functionalized dendrons and

their dendronized polymers were then investigated not only in organic phase but also in aqueous phase.

Results and Discussion Synthesis. The preparation of the dendronized polymers is summarized in Scheme 1. The amide dendrons, 1 and 2, were synthesized as described previously.25 The methacryl moiety was introduced at the focal point of the first and second generation dendrons by coupling the focal carboxyl group of 1 and 2 with 2-hydroxyethyl methacrylate. The polymerization of the dendron monomers was carried out in toluene using 2,2′-azobisisobutylronitrile (AIBN) as a radical initiator. The polymer was purified by precipitation from THF into toluene. Structural characterizations were performed by using NMR, IR, elemental analysis, and MALDI-TOF mass spectrometry. The Mn values of 1P and 2P, based on the GPC analysis, were 35 000 (Mw/Mn ) 1.6) and 14 000 (Mw/Mn ) 1.2), respectively. In the case of 2P, the molecular weight was relatively low compared with 1P possibly due to bulkiness of the dendronized monomer. Self-Organization Behavior of Dendrons. Dendrons 1 and 2 form thermoreversible gels in organic media, such as, chloroform and THF. In the dry state, they form lamellar or hexagonal cylinder array depending on the generation of the dendron building block.25 The focal carboxyl units are a key factor required for the self-assembly of these dendritic building blocks in organic media, because they allow the formation of dimeric dendrons by hydrogen bonding. Dendrons 1M and 2M, on the other hand, in which the focal carboxyl moiety was blocked by methacryl units do not form gels in organic media, such as, chloroform or THF. This result is possibly due to the absence of hydrogen bonding between focal carboxyl moieties, which are masked by the methacryl unit. However, in water, 1M and 2M form vesicular assemblies as evidenced by the results of dynamic light scattering (DLS), TEM, environmental scanning electron microscopy (E-SEM), and gel filtration experiment. The hydrodynamic diameters of the vesicles from 1M and 2M were

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was added to a THF solution of a dendron sample (0.5 mg). After removal of THF on a rotary evaporator, the remaining solution (0.5 mL) was passed through a Sephadex G-100 column (2.5×20 cm) and 40∼60 fractions (2 mL each) were collected. All fractions were subjected to DLS and fluorescence measurements to obtain elution profiles and confirm the existence of water entrapped in the self-organized aggregates (Figure 2). For example, in Figure 2A, DLS and fluorescence experiments showed that selfaggregates (average diameter 150-250 nm) containing watersoluble dye were eluted in fractions 11-15. The vesicular structure was further evidenced by investigating the release profile of the entrapped dye molecules before and after addition of Triton X-100. As shown in Figure 3, after release of dye during the initial 50 and 180 min respectively for 1M and 2M, no further leakage of entrapped dye was observed over a period of 3 and 6 h respectively for 1M and 2M, indicating that the vesicles are stable toward leakage. However, after adding Triton X-100 to aqueous solution of dendrons 1M and 2M, respectively, a prompt release of the water-soluble dye molecules from the interior of the vesicle was observed (Figures 3 and 4). Release profiles were calculated using the following formula:

release percentage (%) ) (It - I0)/(I∞ - I0) × 100

Figure 1. TEM images of the self-aggregates of (A) 1M, (B) 1P, (C) 2M, and (D) 2P in water, and E-SEM images of (E) 2M and (F) 2P in water.

279 nm (polydispersity index; PDI ) 0.161) and 220 nm (PDI ) 0.073), respectively. The typical microscopic images from E-SEM, and TEM exhibited spherical morphology (Figure 1). Gel filtration experiment coupled with DLS confirmed the existence of water entrapped in the interior of spherical supramolecular assembly. For the gel filtration experiment,37-39 an aqueous solution of resorufin sodium salt (0.14 mM, 10 mL)

where I0 is initial fluorescence intensity, It is fluorescence intensity at time t, and I∞ is fluorescence intensity after addition of Triton X-100.37,38 Self-Organization Behavior of Dendronized Polymers. The dendronized polymers 1P and 2P form a thermoreversible gel from at 3 wt % in toluene solution. For example, gels of 1P in toluene redissolved at 57-58 °C and of 2P at 58-59 °C, respectively. After cooling to room temperature, immobile gels were obtained after several hours. The structure of dry gels was characterized by using XRD. The dry gel of 1P showed a lamellar structure with an interlamellar spacing of 63.94 Å (Figure 5A). In contrast, the gel of 2P exhibited the hexagonal columnar structure with a column diameter of 81.5 Å by XRD (Figure 5B). Considering the dimension of the fully stretched form of monomeric units of the dendronized polymers, 1M (33 Å) and 2M (43 Å), it appears that lamellar layer thickness or the diameter

Figure 2. Elution profiles in gel filtration of the self-aggregates of (A) 1M, (B) 1P, (C) 2M, and (D) 2P in water. Each fraction was subjected to DLS and fluorescence measurement.

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Figure 3. Release profile of the dye from the vesicle of (A) 1M and (B) 2M.

of the cylinder is associated with two monomeric units. Therefore, two dendritic side units along the main chain of the dendronized polymer would be packed as a basic building block to give a lamellar or cylindrical organization (Scheme 2). The structural driving force of this self-organization is suggested to include hydrogen bonding between amide branches and van der Waals interaction between peripheral alkyl groups. In addition, confinement of dendritic building blocks along the main chain would enhance the organization tendency of the dendritic side groups. It is also interesting to note that 1P and 2P self-organize in water to form vesicular aggregates due to their amphiphilic balances (Figure 1). The self-organized structure of 1P and 2P in aqueous phase was characterized by using TEM, DLS, E-SEM, and gel filtration experiment. Spherical vesicular images of 1P and 2P were obserbed by TEM. DLS studies revealed that 1P and 2P form stable vesicles with average diameter of 237 nm (PDI ) 0.173) and 234 nm (PDI ) 0.143), respectively. The E-SEM image also showed that the vesicular forms produced by 2P have a spherical morphology. The vesicular structure of 2P was also evidenced by gel filtration experiment (Figure 2). The elution profiles in Figure 2 suggest that the vesicles separated by gel filtration contain water-soluble dye in the interior of vesicle. It is interesting to note that the vesicle from the dendronized polymer showed remarkably enhanced stability compared with that from the dendrons. The stability of the vesicles from the dendrons and their dendronized polymers was investigated by comparing the stability of the dye-loaded vesicles after addition of a surfactant, Triton X-100. DLS studies showed that the vesicles of 1P and 2P remained similar in size upon addition of Triton X-100, whereas the vesicles of 1M and 2M were completely (37) Thompson, D. H.; Gerasimov, O. V.; Wheeler, J. J.; Rui, Y.; Anderson, V. C. Biochim. Biophys. Acta 1996, 1279, 25. (38) Zhu, J.; Munn, R. J.; Nantz, M. H. J. Am. Chem. Soc. 2000, 122, 2645. (39) Ravoo, B. J.; Darcy, R. Angew. Chem., Int. Ed. 2000, 39, 4324.

Figure 4. Normalized fluorescence intensity of dye-entrapped vesicles before and after addition of Triton X-100. (A) 1M and 1P. (B) 2M and 2P.

Figure 5. XRD data of the dry gel of (A) 1P and (B) 2P (S (Å-1) ) (nλ/2 sinΘ)).

dissolved by adding Triton X-100.37,38,40 The stability of dendronized polymer vesicles was further confirmed using a dye-loading test (Figure 4). When dyes were encapsulated in the inner space of the vesicle, fluorescence self-quenching of dye molecules was observed due to high local concentration inside (40) Yang, D.; O’Brien, D. F.; Marder, S. R. J. Am. Chem. Soc. 2002, 124, 13388.

3816 Langmuir, Vol. 22, No. 8, 2006 Scheme 2

the vesicle. In addition, self-quenching was recovered due to the outburst of water-soluble dye from the vesicle by destroying the vesicular membrane with the surfactant (Triton X-100).37,38 The dye-loaded vesicles of 1P and 2P did not show an abrupt burst of entrapped dye from the vesicle upon addition of Triton X-100. However, a prompt release of the entrapped dye molecules was observed with the vesicles of 1M and 2M upon addition of Triton X-100.

Conclusions In this study, dendronized polymers were prepared by the radical polymerization of amide dendrons containing methacryl focal units. Amide dendrons, 1M and 2M, where the focal carboxyl group was blocked by methacryl units did not form gel in organic media such as chloroform or THF. The results are apparently due to the absence of hydrogen bonding between focal carboxyl groups. In aqueous phase, 1M and 2M formed stable vesicles. The dendronized polymers with first and second generation dendrons, 1P and 2P, formed thermoreversible gels in toluene, and their dry gels exhibited lamellar and columnar organization, respectively. In addition to hydrogen bonding of the dendritic amide branches and van der Waals interactions of the alkyl periphery, the steric confinement of the dendritic side groups along the polymer backbone plays a key role in the packing process of the dendronized polymers. In aqueous phase, the dendronized polymers, 1P and 2P, produced spherical vesicular aggregates with higher stability than the vesicles of the dendrons. Experimental Section 1. Materials and Equipments. Lauric acid and 1,1′-carbonyldiimidazole (CDI) from Aldrich were used as received. N-(3Aminopropyl)-propandiamine (APPDA) and triethylamine (TEA) from Aldrich were vacuum distilled under calcium hydride. Succinic anhydride (Aldrich) was recrystallized from n-hexane/acetone (2:8, v/v). 2-Hydroxyethyl methacrylate (HEMA) from TCI was used as received. 2,2′-Azobisisobutylronitrile (AIBN, Junsei chemical) was recrystallized from ethanol. All solvents were purified using published procedures.41 1H and 13C NMR spectra were recorded on a Varian UNITY INOVA 400 at 400 and 100 MHz, respectively, and were referenced to TMS. FT-IR spectra were obtained using Perkin-Elmer System 2000 FT-IR spectrophotometer. Molecular weights and weight distributions were estimated using a GPC equipped with a Waters Associates 410 RI detector, a 510 HPLC pump and µ-Styragel columns with pore size of 102, 500, 103, and 104 Å. The eluent used was THF and the molecular weights were determined using calibrated polystyrene standards. MALDI spectra were obtained using a Voyager (41) Armarego, W. L. F.; Perrin, D. D. Purification of Laboratory Chemicals, 4th ed.; Butterworth-Heinemann: Oxford, U.K., 1996.

Park et al. Biospectrometry time-of-flight mass spectrometer (PerSeptive Biosystems) operated at an accelerating voltage of 25 kV in reflector mode with positive ionization. Dithranol (solvent: CHCl3) was used as the matrix. 2. Synthesis. Synthesis of 1 and 2. The first and second generation of amide dendrons 1 and 2 were synthesized as described previously.25 Synthesis of 1M. A chloroform solution (100 mL) of dendron 1 (5.0 g, 8.3 mmol) and 1,1′-carbonyldiimidazole (1.62 mg, 10 mmol) was stirred at 45 °C for 6 h under nitrogen. A chloroform solution (20 mL) of HEMA (5.4 g, 41.5 mmol) was then added and stirred at 50 °C for 12 h. Solvent was removed under reduced pressure and the product was reprecipitated from chroloform/ethyl acetate (1:9 v/v) (yield 5.8 g, 99%). 1H NMR (400 MHz, CDCl ) δ 0.85 (t, J ) 6.8 Hz, 6H, CH 3 3 CH2-), 1.17-1.24 (s, 32H, -CH2-), 1.58-1.85 (br, 8H, -CH2CH2-CO-, NH-CH2-CH2-CH2-NH), 1.90 (s, 3H, CH2(CH3)d CH2), 2.11-2.16 (m, 4H, -CH2-CO-), 2.51-2.67 (m, 4H, -COCH2CH2-CO-), 3.12-3.36 (m, 8H, -CO-CH2-CH2-CH2-CON-, -CO-NH-CH2, -CH2-N-CO-), 4.25 (s, 4H, COO-CH2CH2-OOC), 5.58 (s, 1H, CH2(CH3)dCH2), 6.1 (s, 1H, CH2(CH3)d CH2); 13C NMR (CDCl3) δ 14.01, 18.18, 22.56, 25.68, 27.31, 27.55, 28.78, 29.06, 29.22, 29.52, 31.78, 35.51, 36.56, 36.75, 36.81, 42.16, 45.07, 62.16, 62.24, 126.05, 135.72, 171.58, 172.91, 173.37, 173.58; IR (KBr) 3319, 3085, 2921, 2852, 1722, 1645, 1551, 1161; MS (MALDI-TOF) calculated for C40H73N3O7 708.14, found 709.32 (M+1H), 731.32 (M+Na); Anal. Calcd for C40H73N3O7: C, 67.86; H, 10.39; N, 5.93. Found: C, 67.60; H, 10.61; N, 6.46. Synthesis of 1P. A freshly distilled toluene solution (4 g, 43 mmol) of 1M (2 g, 2.82 mmol) and AIBN (0.028 mmol, 1 mol %) was degassed by three freeze-pump-thaw cycles and stirred at 65 °C for 20 h. Solvent was removed under reduced pressure, and the product was purified by reprecipitation from THF/toluene (yield 1.84 g, 92%). 1H NMR (400 MHz, CDCl ) δ 0.82-0.86 (br, 6H, CH -CH -), 3 3 2 1.17-1.25 (32H, -CH2-), 1.57 (br, 8H, -CH2-CH2-CO-, NHCH2-CH2-CH2-NH), 1.78-1.79 (br, 3H, CH2(CH3)dCH2), 2.14 (s, 4H, -CH2-CO-), 2.604 (br, 4H, -CO-CH2CH2-CO-), 3.103.43 (br, 8H, -CO-CH2-CH2-CH2-CO-N-, -CO-NH-CH2, -CH2-N-CO-), 4.21 (br, COO-CH2-CH2-OOC); 13C NMR (CDCl3) δ 0.95, 14.06, 22.63, 25.92, 27.66, 27.80, 29.03, 29.18, 29.31, 29.42, 29.48, 29.59, 29.62, 29.66, 31.18, 31.86, 36.51, 36.70, 36.91, 38.09, 171.37, 172.90, 172.98, 173.68, 173.93; GPC (THF): Mn) 35,000, Mw/Mn) 1.6; Anal. Calcd for C1969H3591N149O343: C, 67.87; H, 10.39; N, 5.99. Found: C, 67.65; H, 10.63; N, 5.95. Synthesis of 2M. A chloroform solution (150 mL) of dendron 2 (5.0 g, 3.6 mmol) and 1,1′-carbonyldiimidazole (696 mg, 4.3 mmol) was stirred at 50 °C for 12 h under nitrogen. A chloroform solution (20 mL) of HEMA (2.34 g, 18 mmol) was then added and stirred at 60 °C for 12 h. Solvent was removed under reduced pressure and purified product was obtained by reprecipitation from chroloform/ ethyl acetate (1:9 v/v) (yield 5.34 g, 99%). 1H NMR (400 MHz, CDCl ) δ 0.85(t, J ) 6.8 Hz, 12H, CH 3 3 CH2-), 1.17-1.24(s, 64H, -CH2-), 1.58-1.84(br, 20H, -CH2CH2-CO-, -NH-CH2-CH2-CH2-N-), 1.92(s, -CH2(CH3) d CH2-), 2.11-2.17(m, 8H, -CH2-CO-), 2.47-2.66(br, 12H, -COCH2-CH2-CO-), 3.11-3.34(br, 24H, -CO-NH-CH2-, -CH2N-CO-), 4.32(s, 4H, CO-O-CH2-CH2-O-CO-), 5.58(s, 1H, CH2(CH3)dCH2), 6.1(s, 1H, CH2(CH3)dCH2); 13C NMR (CDCl3) δ 14.04, 18.21, 22.61, 25.76, 25.81, 27.61, 28.06, 28.46, 29.27, 29.34, 29.36, 29.48, 29.55, 29.58, 31.04, 31.84, 36.37, 36.56, 36.75, 45.22, 62.26, 62.34, 126.14, 135.80, 167.14, 171.38, 172.24, 172.43, 172.80, 173.18, 173.57, 173.93; IR (KBr) 1465, 1558, 1640, 1723, 2918, 3085, 3309; MS (MALDI-TOF) calculated for C84H155N9O13 1499.21, found 1521.32 (M+Na), 1523.32 (M+2H+Na); Anal. Calcd for C84H155N9O13: C, 67.30; H, 10.42; N, 8.41. Found: C, 67.02; H, 10.56; N, 8.74. Synthesis of 2P. A freshly distilled toluene solution (8 g, 86 mmol) of 2M (3 g, 2.0 mmol) and AIBN (0.02 mmol, 1 mol %) was degassed by three freeze-pump-thaw cycles and stirred at 65 °C for 20 h.

Self-Organization of Amide Dendrons Solvent was removed under reduced pressure and the product was purified by reprecipitation from THF into toluene (yield 2.76 g, 92%). 1H NMR (400 MHz, CDCl ) δ 0.82-0.86 (br, 12H, CH -CH -), 3 3 2 1.17-1.25 (64H, -CH2-), 1.57 (br, 20H, -CH2-CH2-CO-, NHCH2-CH2-CH2-NH), 1.78-1.79 (br, 3H, CH2(CH3)dCH2), 2.14 (s, 8H, -CH2-CO-), 2.604 (br, 8H, -CO-CH2CH2-CO-), 3.103.43 (br, 26H, -CO-CH2-CH2-CH2-CO-N-, -CO-NH-CH2, -CH2-N-CO-), 4.21 (br, COO-CH2-CH2-OOC); 13C NMR (CDCl3) δ 14.0, 22.6, 25.9, 29.3, 29.4, 31.8, 36.5, 36.6, 173.6, 173.9; GPC (THF): Mn)14,000, Mw/Mn) 1.2; IR (KBr) 1263, 1467, 1555, 1639, 1734, 2921, 3086, 3314; Anal. Calcd for C764H1404N83O117: C, 67.33; H, 10.41; N, 8.53. Found: C, 66.63; H, 10.53; N, 8.66. 3. Typical Sample Preparation. A 30 mg of sample was placed in a 100 mL round-bottom flask and dissolved in 3-5 mL of THF. Doubly distilled water (60 mL) was then slowly added with gentle stirring. After vigorous stirring for 15 min, THF was evaporated under reduced pressure. The solution, which has a slight blue hue, was filtered through a syringe filter (0.45 µm, cellulose acetate membrane filter). The amide dendrons, 1M, 1P, 2M, and 2P formed vesicles in water without sonication. 4. Dynamic Light Scattering. Dynamic light scattering measurements were performed using a Brookhaven BI-200SM goniometer and BI-9000AT digital autocorrelator. All the measurements were carried out at room temperature. Sample solutions (100 mg/L) were purified through a Millipore 0.45 µm filter. The scattered light of a vertically polarized He-Ne laser (632.8 nm) was measured at 90° and was collected on an autocorrelator. The hydrodynamic diameters (d) of vesicles were calculated by using the Stokes-Einstein equation d ) kBT/3πηD, where kB is the Boltzmann constant; T is the absolute temperature; η is the solvent viscosity; and D is the diffusion coefficient. The polydispersity factor of micelles, represented as µ2/Γ2, where µ2 is the second cumulant of the decay function and Γ is the average characteristic line width, was calculated using the cumulant method42,43 CONTIN algorithms were used in the Laplace inversion of the autocorrelation function to obtain the size distribution.44 (42) Harada, A.; Kataoka, K. Macromolecules 1995, 28, 5294. (43) Harada, A.; Kataoka, K. Macromolecules 1998, 31, 288.

Langmuir, Vol. 22, No. 8, 2006 3817 5. Fluorescence Measurements. All the fluorescence measurements were performed using a Shimadzu RF-5301PC spectrofluorophotometer. To measure emission spectra (resorufin sodium salt), emission and excitation slit widths were set at 1.5 nm with λex ) 577 nm. 6. Transmission Electron Microscopy. Transmission electron microscopy (TEM) was performed using a Philips CM 200, operated at an acceleration voltage of 80 kV. To prepare dispersed samples in water, a drop of sample solution (100 mg/L) was placed onto a 300-mesh carbon-coated copper grid. About 2 min later surface water was removed from the grid with filter paper, and samples were allowed to air-dry.45,46 The grid was shadowed with Au/Pd of 8∼10 Å thickness at 20° tilting angle. Negative staining was performed by using a droplet of a 2 wt % uranyl acetate solution. The samples were air-dried before being examined. 7. Environmental Scanning Electron Microscopy. Environmental scanning electron microscopy (E-SEM) was carried out on an FEI XL-30 field emission gun E-SEM instrument (accelerating voltage: 10∼15 kV, pressure range: 08∼0.9 Torr). E-SEM samples were prepared by transferring a drop of sample solution onto a 200 mesh carbon-coated copper grid. About 5 min later excess water was removed with filter paper. 8. X-ray Diffraction. X-ray diffraction experiments were performed utilizing a synchrotron radiation source (2.5 GeV, 150 mA) at the Pohang Accelerator Laboratory, Korea. The wavelength was 1.6083 Å and the collimated beam size was 0.3 mm × 0.3 mm. Scattered X-ray intensities were collected using a position sensitive area detector.

Acknowledgment. This work was supported by KOSEF (R012005-000-10343-0). C.K. also thanks HOMRC for support. X-ray diffraction was performed at the 4C1 and 4C2 beamlines at the Pohang Accelerator Laboratory. LA0528448 (44) Wilhelm, M.; Zhao, C.-L.; Wang, Y.; Xu, R.; Winnik, M. A.; Mura, J.-L.; Riess, G.; Croucher, M. D. Macromolecules 1991, 24, 1033. (45) Ma, Y.; Cao, T.; Webber, S. E. Macromolecules 1998, 31, 1773. (46) Zhang, L.; Eisenberg, A. J. Am. Chem. Soc. 1996, 118, 3168.