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Novel Silica Structures Which Are Prepared by Transcription of Various Superstructures Formed in Organogels Jong Hwa Jung, Yoshyuki Ono, and Seiji Shinkai* Chemotransfiguration Project, Japan Science and Technology Corporation (JST), 2432 Aikawa, Kurume, Fukuoka 839-0861, Japan Received July 9, 1999. In Final Form: October 21, 1999 Three cholesterol-based gelators were synthesized which have a monobenzo-18-crown-6 (2), monoaza18-crown-6 (3), and 1,10-diaza-18-crown-6 (4), respectively. These gelators could gelatinize 8 of 14 organic solvents tested herein, indicating that they possess a versatile gelation ability. Scanning electron microscopy observations of these xerogels showed that in cyclohexane 2, 3, and 4 assemble into a fibrous network structure, a curved lamellar structure, and a cylindrical tubular structure, respectively. Sol-gel polymerization of tetraethoxysilane was carried out in these gel systems. The silica obtained from 2 in the absence of metal salt had a conventional granular structure whereas that in the presence of KClO4 had a hollow fiber structure featuring the rough surface and the thick tube wall. This structure is created by the adsorption of anion-charged silica particles onto the cation-charged organogel fibers. On the other hand, the silica obtained from 3 and 4 had a hollow fiber structure featuring the smooth surface and the thin tube wall both in the absence and the presence of metal salt. In the absence of metal salt, the cationic charge generated by protonation of azacrown ethers plays a crucial role in the creation of such a hollow fiber structure. In the presence of KClO4 or CsClO4, sol-gel polymerization resulted in the tubular silica with a multilayer structure like a roll of paper. The findings suggest that sol-gel polymerization proceeds along the surface of the curved lamellar surface of 3 or 4 and the silica eventually grows up as a tubular structure. These results indicate that various novel silica structures can be prepared by transcription using various superstructures in organogels as a template.
Introduction Recently, exploitation of new organic gelators which can gelate various organic solvents has become an active research area of endeavor.1-13 These organic gels are of particular interest in that being different from polymer gels, fibrous aggregations of low-molecular-weight compounds formed by noncovalent interactions are responsible for such gelation phenomena. More recently, it was newly found that sol-gel polymerization of tetraethoxysilane (TEOS) gelated by a cholesterol-based gelator bearing a quaternary ammonium group (1b) results in novel silica (1) Ono, Y.; Nakashima, K.; Sano, M.; Kanekiyo, Y.; Inoue, K.; Hojo, J.; Shinkai, S. Chem. Commun. 1998, 1477. (2) (a) Vries, E. J. de.; Kellogg, R. M. J. Chem. Soc., Chem. Commun. 1993, 238. (b) Loos, M. de; Esch, J. van; Stokroos, I.; Kellogg, R. M.; Feringa, B. L. J. Am. Chem. Soc. 1997, 119, 12675. (3) Aoki, M.; Nakashima, K.; Kawabata, H.; Tsutsui, S.; Shinkai, S. J. Chem. Soc., Perkin Trans. 2 1993, 347. (4) (a) Hanabusa, K.; Okui, K.; Karaki, K.; Koyama, T.; Shirai, H. J. Chem. Soc., Chem. Commun. 1992, 1371. (b) Hanabusa, K.; Kawakami, K.; Kimura, M.; Shirai, H. Chem. Lett. 1997, 191 and references therein. (5) Sohna, J.-E. S.; Fages, F. Chem. Commun. 1997, 327. (6) Otsuni, E.; Kamaras, P.; Weiss, R. G. Angew. Chem., Int. Ed. Engl. 1996, 35, 1324 and references therein. (7) Terech, P.; Furman, I.; Weiss, R. G. J. Phys. Chem. 1995, 99, 9558 and references therein. (8) Murata, K.; Aoki, M.; Suzuki, T.; Harada, T.; Kawabata, H.; Komori, T.; Ohseto, F.; Ueda, K.; Shinkai, S. J. Am. Chem. Soc. 1994, 116, 6664 and references therein. (9) James, T. D.; Murata, K.; Harada, T.; Ueda, K.; Shinkai, S. Chem. Lett. 1994, 273. (10) Jeong, S. W.; Murata, K.; Shinkai, S. Supramol. Sci. 1996, 3, 83. (11) Brotin, T.; Utermo¨hlen, R.; Fages, F.; Bouas-Laurent, H.; Desvergne, J.-P. J. Chem. Soc., Chem. Commun. 1991, 416 (12) (a) For recent comprehensive reviews, see: Terech, P.; Weiss, R. G. Chem. Rev. 1997, 97, 3133. (b) Shinkai, S.; Murata, K. J. Mater. Chem. (Feature Article) 1998, 8, 485. (13) Ono, Y.; Kanekiyo, Y.; Inoue, K.; Hojo, J.; Shinkai, S. Chem. Lett. 1999, 23.
Scheme 1
with a hollow fiber structure.1 It was proposed that the unique structure is created by a template effect of the fibrous gelator aggregations which, after calcination, eventually constitute the hollow moiety. In contrast, solgel polymerization of TEOS gelated by a cholesterol-based gelator without a quaternary ammonium group (1a) did not result in any novel silica structure.1 The contrasting influence suggests that as frequently seen in conventional cationic surfactants used as templates for sol-gel polymerization, the cationic group in 1b may play an essential role in the creation of the novel hollow fiber structure. However, it is still ambiguous whether one can attribute the difference solely to this cationic charge, because the gelation properties are somewhat different between 1a and 1b.1,13
10.1021/la990901p CCC: $19.00 © 2000 American Chemical Society Published on Web 12/01/1999
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Table 1. Gelation Abilitya of Cholesterol-Based Gelators solvent
2
3
4
methanol ethanol 1-butanol 1-hexanol 1-octanol acetone acetonitrile dimethylformamide tetrahydrofuran dichloromethane benzylamine cyclohexane n-hexane
I G G G G I R G S S S G G
G G G G G I G G S S S PG(G)b I
G G G G G I G G S S S PG(G)b I
a [gelator] ) 5.0 wt %. Key: G ) stable gel formed at room temperature; S ) solution; I ) insoluble; PG ) partially gelatinized. b [gelator] ) 10.0 wt %.
To obtain a further insight into the mechanism for the construction of novel hollow fiber silica (“macaroni silica”), sol-gel polymerization of TEOS was carried out in the organogels prepared in the presence of a benzo-18-crown6-containing cholesterol gelator (2).13 It was shown that hollow fiber silica is obtained only in the presence of the high concentration of KClO4.13 The findings support the view that the cationic charge plays a role indispensable to the construction of the tubular structure. The results imply that not only the superstructures in organogels but also the silica structures which are constructed by template sol-gel polymerization of TEOS in the gel phase can be diversified by a combination of appended crown ethers and metal cations. We thus newly synthesized gelators 3 and 4 as shown in Scheme 1. It was found that 2, 3, and 4 afford different gelation abilities as well as different superstructures and these superstructures are transcripted into silica structures according to a template effect.14 Results and Discussion Xerogel Superstructures As Observed by Scanning Electron Microscopy (SEM). The gelation ability was tested using 14 organic solvents. As summarized in (14) Preliminary communication; Jung, J. H.; Ono, Y.; Shinkai, S. J. Chem. Soc., Perkin Trans. 2, in press.
Figure 1. SEM images of xerogels prepared from the cyclohexane gels of 2 (A), 3 (B), and 4 (C).
Table 1, these three compounds can gelate 8 of 14 organic solvents, indicating that they act as versatile gelators. In addition, 3 and 4 partially gelate cyclohexane when the gelator concentration was increased to 10.0 wt % from 5.0 wt %. In particular, it is seen from Table 1 that their gelation ability for alcohols is excellent. The superstructures constructed in organogels were observed by SEM. As shown in Figure 1, those constructed in the cyclohexane gels were very different among three gelators. Compound 2 resulted in a translucent organogel
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Table 2. Conditions for Sol-Gel Polymerization run 1 2 3 4 5
gelatora 2 2 2 2 none
[KClO4]/mmol
major solvent
silica structureb
40 20 10 0 40
1-butanol 1-butanol 1-butanol aniline 1-butanol
tubular tubular granular granular granular
a [gelator] ) 40 mmol. b The tubular structure was observed both by TEM and SEM whereas the granular structure was observed only by SEM.
Figure 2. SEM pictures in the absence of metal salt (A) (run 4 in Table 2) and SEM and TEM pictures in the presence of KClO4 ((B) and (C), respectively) for 2.
with cyclohexane. The xerogel featured the fibrous network structure with 25-62 nm diameter, and the fibers were partially twisted in a helical fashion (arrows in Figure 1A). This type of superstructure is frequently seen in the organogels prepared with azobenzene-appended cholesterol gelators.8 In contrast, compound 3 (or their metal complexes) did not give good organogels with cyclohexane at 5.0 wt % as those obtained in the previous systems,1,8
Figure 3. Schematic representation for the creation of hollow fiber silica by sol-gel polymerization of TEOS in the organogel state of 2: (A) mixture of gelators and TEOS; (B) gelation; (C) sol-gel polymerization of TEOS and adsorption onto the cationic gelator fibrils; (D) before calcination; (E) the hollow fiber silica formation after calcination.
only resulting in viscous turbid solutions. Thus, the SEM pictures of the dry samples were obtained only from a few limited solutions. As shown in parts B and C of Figure 1, the SEM image did not show the fibrous structure characteristic of organogel systems but rather featured filmlike aggregates with 30-40 nm thickness, which probably consist of lamellar structure of 3. It is noteworthy that some films are curved (arrows in Figure 1B) to form a pseudocylindrical structure. The similar filmlike aggregates were observed for the dry samples obtained from other solvents in the absence and the presence of metal salts. The most interesting is the xerogel obtained from a 4+cyclohexane system. This system did not result in a good organogel as in the case of a 2+cyclohexane system. As shown in Figure 1C, the xerogel featured a tubular structure with 45-75 nm wall thickness and 170-390 nm inside tube diameter. Careful examination of this picture reveals that the wall consists of a multilayer structure. Presumably, the curved lamellae as seen for 3 (Figure 1B) have developed to roll up to a tubular structure. It is not clear, however, why the growth of the curved lamellae stops in 3 whereas it continues to grow up to the “paperlike roll” structure in 4. Sol-Gel Polymerization of TEOS and SEM/TEM Observations of Silica Structure. The sol-gel polymerization was carried out as follows. Compound 2 (5.8 × 10-6 M) and KClO4 (for the amount see Table 2) were dissolved in dichloromethane (1.0 g). The solution was evaporated to dryness. The details of the sol-gel experiments are described in Experimental Section. Run 1 containing a high concentration of KClO4 results in fibrous silica as shown in the SEM image in Figure 2B. To see the inside of this fibrous silica, a transmission electron microscopy (TEM) picture was taken. As shown in Figure 2C, this silica features a tubular structure, which was similar to that obtained from sol-gel polymerization in the gel phase of 1b.1 The similar SEM and TEM pictures were also obtained from run 2, but the silica structure obtained from run 1 (outer diameter ∼50 nm, inner diameter ∼10 nm) was smaller than that obtained from run 2 (outer diameter 100-200 nm, inner diameter ∼50 nm). In run 3 where sol-gel polymerization was carried out at the low KClO4 concentration, in contrast, the resultant silica only showed the conventional granular structure similar to that prepared from a solution in the absence of the gelator (run 5) or from an organic gel in the presence of 1a.1 The 1-butanol solution was not gelated by 2 in the absence of KClO4. Since 2 could gelate aniline, we performed the same sol-gel polymerization in aniline/ TEOS/ water/ benzylamine ) 45.0/ 15.0/ 5.7/ 5.6 (mg, run 4). Again, the product was the granular silica (Figure 2A). The foregoing results consistently support the view that the construction of the hollow fiber silica is profoundly
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Figure 4. SEM and TEM pictures in the absence of metal salt ((A) and (B), respectively) and those in the presence of CsClO4 ((C) and (D), respectively) for 3. Similar SEM/TEM pictures were also obtained from the samples in the presence of KClO4. However, the pictures obtained in the presence of CsClO4 gave better resolution and a clearer multilayer structure.
related to the specific K+-benzo-18-crown-6 interaction.15 It is now clear, therefore, that the tubular structure did not originate from a difference in the gelation state between 1a and 1b but is more closely related to the specific influence of the cationic charge on the sol-gel polymerization process. When the sol-gel polymerization is carried out in an alkaline solution, the propagation species is considered to be anionic.16 Hence, the anionic oligomeric silica species are adsorbed onto the cationic gelator fibrils and the polymerization further proceeds along these fibrils. This propagation mode can eventually yield the fibrous silica with a tubular structure (Figure 3). The similar cationic-charge effect can be reproduced by the specific (15) The stabilization constants of 2 for K+ and Li+ (used as their picrate salts) in 1-butanol are 1.4 × 104 and 1.7 × 103 M, respectively (25 °C). If the silicate solution is replaced by 1-butanol, the percentage of the complex would be 96% for run 1, 50% for run 2, and 25% for run 3. One may consider, therefore, that 2 in the sol-gel solution mostly binds K+ and the hollow fiber silica results when the percentage is higher than ca. 50%. (16) Huo, Q.; Margolese, D. I.; Ciesla, U.; Feng, P.; Gier, T. E.; Sieger, P.; Leon, R.; Petroff, P. M.; Schu¨th, F.; Stucky, G. D. Nature 1994, 368, 317.
K+-benzo-18-crown-6 interaction, instead of the quaternary ammonium ion. In other words, the organogels prepared from 2 cannot act as a template in the absence of K+ as neutral 1a could not,1 whereas those prepared from 2 in the presence of K+ can act as a template as cationic 1b could.1 Interestingly, sol-gel polymerization in the 1-butanol gels of 3 and 4 resulted in a tubular structure even in the absence of metal salt (Figure 4A,B and Figure 5A,B). Judging from the foregoing information obtained from insight into the origin of the hollow fiber silica formation, we consider that this structure is also due to the cationic charge arising from protonation of the monoaza- and the diaza-18-crown-6. It is known that their pKa values are relatively high,17 and they should partially protonate under the sol-gel polymerization conditions. To neutralize this cationic charge, we added a small amount of Et4NOH (17) (a) Sakamoto, H.; Kimura, K.; Matsuo, M.; Shono, T. J. Org. Chem. 1986, 51, 5974. (b) Shukla, J. P.; Jeon, E. G.; Knudsen, B. E.; Pugia, M. J.; Bradshaw, J. S.; Bartsch, R. A. Thermochim. Acta 1988, 130, 103. (c) Spiess, B.; Arnaud-Neu, F.; Schwing-Weill. M. J. Helv. Chim. Acta 1979, 62, 1531.
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Figure 5. SEM and TEM pictures in the absence of metal salt ((A) and (B), respectively) and those in the presence of KClO4 ((C) and (D), respectively) for 4.
(tetraethylammonium hydroxide, 1.0 equiv to 3 or 4). As expected, the silica obtained from 3 was changed to the conventional granular structure as in Figure 2A. The result again supports the importance of the cationic charge in the creation of hollow fiber silica. In contrast, 4 still yielded the hollow fiber silica even in the presence of Et4NOH. Since the pKa for diaza-18-crown-6 (10.64) is higher than that for monoaza-18-crown-6 (ca.9.0-10.20),17 a trace amount of the cationic charge still remains in the gel fibers of 4, which eventually plays a role to create the hollow fiber silica. In addition, this finding indicates that benzylamine used as a polymerization catalyst does not play any significant role to change the silica structure. It seems to us, however, that the mechanism of the hollow fiber silica formation from 3 and 4 is somewhat different from that of 2 (as shown in Figure 3). It is seen from panels B and C of Figure 2 that the surface of the hollow fiber silica obtained from 2 is very rough and irregular and the tube wall is relatively thick. This structure is reasonably explained by the propagation mechanism proposed in Figure 3. In contrast, the surface
of the hollow fiber silica obtained from 3 and 4 is rather smooth and the tube wall is rather thin, giving rise to a large inner diameter (Figures 4B and 5B). Presumably, sol-gel polymerization of TEOS proceeds along the surface of the lamellar aggregates of the organogels (Figure 1B,C) to grow up as a tubular structure. This view is further supported by sol-gel polymerization in the presence of metal salts. As shown in the SEM and TEM pictures in panels C and D of Figure 4, the tube wall of the silica obtained from 3 features a paperlike roll multilayer structure. The tube wall of the silica obtained from 4 (Figure 5C,D) is thinner than that from 3. However, careful observation of the tube end reveals that these silica fibers also have the multilayer structure. As a summary of the foregoing observations, we now propose the mechanism for the formation of novel multilayered silica as observed in Figure 6: that is, not only the cationic charge but also the curved lamellar structure is indispensable as a template for this sol-gel polymerization process. The organogel morphology is clearly different between 3 and 4: 3 gave the lamellar structure
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Figure 6. Schematic representation for the creation of paperlike roll silica by sol-gel polymerization of TEOS in the organogel state of 3 (upper) and 4 (lower): (A) mixture of gelators and TEOS; (B) gelation; (C) sol-gel polymerization of TEOS and adsorption onto the cationic gelator; (D) before calcination; (E) paperlike roll multilayer structure of the silica formed after calcination.
whereas 4 gave the paperlike roll structure. This implies that the lamellar aggregates grow up more efficiently in diamine 4 than in monoamine 3 (illustration C in Figure 6). On the other hand, the final silica structures are similar to each other, giving rise to the paperlike roll structure. This implies that in 3 the paperlike roll silica grows up during the sol-gel process whereas in 4 the organogel structure is directly transcribed to the silica. Conclusions The present study has demonstrated that the novel tubular structures of the silica were produced by two different mechanisms. The hollow fiber structure of the silica prepared from an organogel 2 as a template is transformed from the granular one to the hollow fiber one. The most important factor which governs this transformation process is the “cationic charge density” along the organic gel fibers. On the other hand, sol-gel polymerization of TEOS in the presence of the lamellae aggregates of an azacrown-appended cholesterol derivatives such as 3 and 4 occurs along the lamellar surface and is useful to create the novel “paperlike roll” silica
structure. We believe that various novel silica structures can be prepared by transcription using various superstructures in organogels as a template. Experimental Section 1H and 13C NMR spectra were measured on a Bruker ARX 300
apparatus. IR spectra were obtained in KBr pellets using a Shimadzu FT-IR 8100 spectrometer, and MS spectra were obtained by a Hitachi M-2500 mass spectrometer. TEM was performed on a Hitachi H-7100 at 100 kV. Samples were prepared by adhering a large number of silica particles of calcined material onto a carbon film on a Cu grid. All reactions were conducted under dry N2 unless otherwise stated. All reagents were the best grade commercially available ones which were distilled, recrystallized, or used with further purification, as appropriate. SEM Measurements. A Hitachi S-14500 scanning electron microscope was used for taking the SEM pictures. The thin gel was prepared in a 1-2 mL bottle and frozen in liquid nitrogen or dry ice-acetone. The frozen specimen was evaporated by a vacuum pump for 24 h. The dry sample was coated by palladiumplatinum. The accelerating voltage of SEM was 5-15 kV, and the emission current was 10 µA. Gelation Test of Organic Fluids. The gelator and the solvent were put in a septum-capped test tube and heated until the solid
Novel Silica Structures was dissolved. The solution was cooled at room temperature. If the stable gel was observed at this stage, it was classified as G. Sol-Gel Polymerization of TEOS. In a typical preparation a 5.8 × 10-6 M quantity of gelator and metal salt (5.8 × 10-6 M) were dissolved in 1.0 g of dichloromethane. The solution was evaporated to dryness. The residual solid was added to 1-butanol (95 mg)/TEOS (15.0 mg)/water (5.7 mg)/benzylamine (5.6 mg) and warmed until a transparent solution was obtained. The reaction mixture was placed at room temperature under the static conditions for 1 day. The product was dried by a vacuum pump at room temperature. Finally, the gelator was removed by calcination at 200 °C for 1 h, 500 °C for 2 h under a nitrogen atmosphere, and 500 °C for 4 h under aerobic conditions. 4-((4-(((Cholesteryloxy)carbonyl)methoxy)phenyl)azo)benzo-18-crown-6 (2). This compound was prepared as described previously.8 4-n-Monobromobutoxyl-4′-((cholesteryloxy)carbonyl)azobenzene (6). 4-((Bromobutyloxypheyl)azo)benzoic acid 5 (0.7 g, 1.86 mmol) and cholesterol (0.718 g, 2.23 mmol) were dissolved in 20 mL of dichloromethane under a nitrogen atmosphere. The solution was maintained at 0 °C by ice bath. The dicyclohexylcarbodiimide (DCC) (0.383 g, 1.86 mmol) and (dimethylamino)pyridine (DMAP) (0.022 g, 0.186 mmol) were then added, the reaction mixture being stirred for 4 h at 0 °C. The reaction mixture was filtered and the filtrate was washed with acidic and basic aqueous solutions (50 mL each). The organic layer was evaporated by dryness. The residue was purified by a silica gel column eluting with THF/n-hexane (1:6 v/v) to give compound 6 in yield 26% as yellow solid (mp ) 141.5 °C). 1H NMR (300 MHz, CDCl3): δ (ppm) 8.17 (2H, d, J ) 9.0 Hz), 7.72 (2H, d, J ) 9.0 Hz), 7.90 (2H, d, J ) 9.0 Hz), 7.10 (2H, d, J ) 9.0 Hz), 5.45 (1H, d, J ) 6.3 Hz), 5.02-4.88 (1H, m), 41 (2H, t, J ) 6.3 Hz), 3.52 (2H, t, J ) 6.2 Hz), 2.49 (2H, d, J ) 6.2 Hz), 2.28-0.94 (35H, m), 0.88 (3H, s). 13C NMR (75 MHz, CDCl ): δ (ppm) 165.1, 161.88, 155.20, 146.98, 3 139.9, 130.2, 125.18, 122.84, 122.28, 114.72, 67.22, 66.67, 56.67, 56.11, 50.01, 42.30, 39.71, 39.50, 38.20, 37.01, 36.64, 36.17, 35.79, 33.32, 31.92, 31.86, 29.3, 28.32, 28.01, 27.88, 27.78, 24.28, 23.82, 22.83, 22.56, 21.04, 19.38, 19.38, 18.71, 11.86. MS (secondary ion mass spectrometry (SIMS)) 745 [M + H]+. IR (KBr): 3005, 1722, 1603, 1579, 1500, 1468, 1284, 1116, 1047 cm-1.
Langmuir, Vol. 16, No. 4, 2000 1649 4-(N-Monoaza-18-crown-6-butoxy)-4′-((cholesteryloxy)carbonyl)azobenzene (3). A mixture of the compound 5 (0.25 g, 0.335 mmol), monoaza-18-crown-6 (0.0790 g, 0.300 mmol), and sodium carbonate (0.317 g, 3.00 mmol) in dry butyronitrile (30 mL) was refluxed for 24 h. The solution was filtered after cooling, the filtrate being concentrated to dryness by a vacuum evaporator. The residue was purified by an aluminum oxide column with ethanol/dichloromethane (1:30 v/v) to give the desired product in yield 43.3% as a yellow solid (mp ) 128-130 °C). 1H NMR (300 MHz, CDCl3): δ (ppm) 8.17 (2H, d, J ) 9.1 Hz), 7.93 (2H, d, J ) 9.1 Hz), 7.88 (2H, d, J ) 9.0 Hz), 7.01 (2H, d, J ) 9.0 Hz), 5.45 (1H, d, J ) 6.5 Hz), 4.90 (1H, m), 4.08 (2H, t, J ) 6.5 Hz), 3.733.61 (26H, m), 2.78 (4H, t, J ) 12.1 Hz), 2.75 (2H, t, J ) 6.5 Hz), 2.49 (2H, d, J ) 6.3 Hz), 2.01-0.69 (39H, m). 13C NMR (75 MHz, CDCl3): δ (ppm) 165.47, 162.13, 155.19, 146,80, 139.54, 134.77, 130.48, 125.13, 122.79, 122.22, 114.72, 74.79, 70.84, 70.73, 70.70, 70.35, 68.14, 56.62, 56.06, 53.94, 49.87, 42.25, 39.66. 39.45, 38.16, 36.97, 36.60, 36.12, 35.75, 31.88, 28.19, 27.96, 27.84, 26.96, 24.24, 23.78, 22.79, 22.53, 21.00, 19.34, 18.67, 11.81. MS (SIMS) 929 [M + 2H]+. IR (KBr): 2943, 2868, 1711, 1599, 1581, 1500, 1468, 1419, 1404, 1275, 1140, 1109 cm-1. Anal. Calcd for C56H85N3O8: C, 72.49; H, 9.22; N, 4.27. Found: C, 71.79; H, 9.18; N, 4.45. 4-(N-1,10-Diaza-18-crown-6-butoxy)-4′-((cholesteryloxy)carbonyl)azobenzene (4). The method described above for the synthesis of 3 was followed, and the title compound was obtained in 25.0% yield as a yellow solid (mp ) 123.5-125.0 °C). 1H NMR (300 MHz, CDCl3): δ (ppm) 8.17 (2H, d, J ) 9.0 Hz), 7.93 (2H, d, J ) 9.0 Hz), 7.88 (2H, d, J ) 9.0 Hz), 7.01 (2H, d, J ) 9.0 Hz), 5.45 (1H, d, J ) 6.3 Hz), 5.02-4.88 (1H, m), 4.90 (1H, m), 4.05 (2H, t, J ) 6.3 Hz), 3.73-3.61 (20H, m), 2.83-2.80 (9H, m), 2.60 (2H, t, J ) 6.2 Hz) 2.01-0.69 (42H, m), 13C NMR (75 MHz, CDCl3): δ (ppm) 165.47, 162.13, 155.19, 146.98, 139.54, 130.48, 125.13, 122.24, 114.72, 86.94, 70.84, 70.73, 70.70, 70.73, 68.14, 56.62, 56.06, 53.94, 49.22, 39.66, 39.45, 38.16, 37.01, 36.97, 36.17, 36.60, 36.12, 35.75, 31.88, 28.19, 27.96, 27.84, 24.24, 23.78, 22.79, 22.53, 21.00, 19.34, 18.67, 11.86. MS (SIMS) 745 [M + H]+. IR (KBr): 3005, 1722, 1603, 1579, 1500, 1468, 1284, 1116, 1047 cm-1. Anal. Calcd for C56H86N4O7: C, 72.46; H, 9.34; N, 6.04. Found: C, 72.05; H, 9.28; N, 6.18.
LA990901P
