Catalysis of a Micellar Assembly
FULL PAPER
zyl alcohol as a matrixon a JEOL JMS-AX505H spectrometer. Infrared
spectra of KBr pellet samples were recorded on a JASCO FT/IR-600
Fourier transform infrared spectrophotometer. XRD analysis was carried
out on a Rigaku model RINT 2400 X-ray diffractometer. DSC-TG pro-
files were recorded on a Shimadzu model TGA 50 thermogravimetric an-
alyzer. Gas chromatography was carried out on a Shimadzu GC-14 A.
Calcination of composite silica was carried out at 5608C for 6 h with an
ADVANTEC model KM-160 electric muffle furnace.
on its surface, was prepared. Although the total organic con-
tent in 1-AS (26 wt%) was not as high as that in 1-MS
(46 wt%), 1-AS displayed a marked drop of the catalytic ac-
tivity and resulted in the formation of the acetal in only 5%
yield in 24 h (Table 1, entry 8). It is clear that a large surface
area of the silica support for 1 in 1-MS can contribute to
high accessibility of the reactants to the catalytic sites. In ad-
dition to this, the above contrasting observations may also
indicate again the importance of the amphiphilic, coaxial
structure of the micellar assembly of 1, maintained by the
hexagonal silicate channels, for the simultaneous admission
of hydrophilic and hydrophobic reactants into the catalyti-
cally active channels.
Synthesis of 2: N-Bromoacetyl-l-alanine hexadecyl ester was synthesized
by using the method reported previously.[7] A 28% aqueous solution of
trimethylamine (0.62 g, 2.94 mmol) was added to an EtOH/CH2Cl2
(50 mL/50 mL) solution of the ester (1.28 g, 2.95 mmol), and the mixture
was stirred at room temperature for 2 d and then evaporated to dryness.
The residue was subjected to chromatography on silica gel with CHCl3/
EtOH (75:25 v/v) as an eluent to allow isolation of 2 (72%, 1.05 g).
1H NMR (270 MHz, [D6]DMSO, 208C): d=9.01 (d, J=6.5 Hz, 1H),
4.32–4.27 (m, 1H), 4.10 (s, 2H), 4.06–4.04 (d, 2H), 3.20 (s, 9H), 1.55 (br,
2H), 1.31 (d, J=7.3 Hz, 3H), 1.22 (m, 26H), 0.84 ppm (t, J=6.8 Hz,
3H); IR (KBr): n˜ =3230m, 3072m, 2917s, 2850s, 1751m, 1736m, 1685m,
1468w, 1209w, 1169w cmÀ1; MALDI-TOF-MS (dithranol): m/z: calcd for
C24H49N2O3: 413.37; found: 413.40 [MÀBrÀ]+; elemental analysis calcd
Conclusion
We have developed novel engineered solid catalyst 1-MS,
which is composed of a coaxial peptidic rod micelle cova-
lently immobilized in the regularly aligned hexagonal chan-
nels of mesoporous silica. As a result of the amphiphilic
core–shell architecture of the immobilized rod micelle, hy-
drophobic and hydrophilic reactants can be incorporated si-
multaneously into the silica channels and activated through
hydrogen-bonding interactions with the peptidic functionali-
ties located at the core–shell interface. Mesoporous silica
has caught particular attention as a catalyst support due to a
high accessibility of substrates to the interior channels,
along with their practical advantages in separation and recy-
cling. Hence, immobilization of metal complexes and en-
zymes by post-treatment of mesoporous silica has so far
been reported.[13] However, in contrast to these previous ex-
amples, our design strategy made use of templated hydro-
thermal synthesis of mesostructured silica with engineered
amphiphiles, which allowed three-dimensional design of cat-
alytic and substrate-binding sites—essential elements for en-
zymes—in the silica channels. Therefore, the present work
provides a novel and general strategy for rational molecular
design of bioinspired solid catalysts.
(%) for C24H49BrN2O3·1= H2O: C 57.36, H 10.03, N 5.57; found: C 57.23,
2
H 10.09, N 5.39.
Synthesis of 3: Hexadecyl bromide (7.20 g, 23.5 mmol) was dissolved in a
mixture of EtOH (50 mL) and CH2Cl2 (50 mL) containing 3-dimethyla-
minopropyl-diethoxymethylsilane (1.29 g, 5.90 mmol), and the resulting
solution was stirred at room temperature for 7 d and then evaporated to
dryness. The residue was subjected to chromatography on silica gel with
acetone/EtOH (50:50 v/v) as an eluent to allow isolation of 3 (50%,
1.57 g). 1H NMR (270 MHz, [D6]DMSO, 208C): d=3.72 (q, 4H), 3.20
(br, 4H), 2.98 (s, 6H), 1.63 (br, 4H), 1.22 (m, 26H), 1.16 (t, 6H), 0.84 (t,
3H), 0.52–0.47 (m, 2H), 0.10 ppm (s, 3H); 13C NMR (67.5 MHz,
[D6]DMSO, 208C): d=68.4, 65.0, 62.9, 49.9, 31.2, 29.0, 28.6, 25.8, 21.8,
18.3, 15.9, 13.9, 11.6, À2.8 ppm; IR (KBr) n˜ =2954s, 2914s, 2858s, 1633w,
1467m, 1259m, 1078m, 950w, 806w cmÀ1; MALDI-TOF-MS (dithranol):
m/z: calcd for C26H58NO2Si: 444.42; found: 444.35 [MÀBrÀ]+; HRMS (3-
nitrobenzylalcohol): m/z: calcd for C26H58NO2Si: 444.4231; found:
444.4225 [MÀBrÀ]+.
Amorphous silica with immobilized peptide amphiphile 1 (1-AS): 1-AS
was prepared by using a method analogous to that reported previously.[15]
Under an Ar atmosphere, a solution of 1 (250 mg) in toluene (10 mL)
was added to silica gel (500 mg; Wakogel C-300HG, 0.040–0.060 mm in
diameter), which had been dried under reduced pressure (1 mmHg) at
2008C for 12 h. The mixture was shaken overnight and then left at reflux
for 3 h. After half of the volume of the solvent was distilled off from the
reaction mixture, toluene (5 mL) was added to the residue, and then
5 mL of a volatile fraction was distilled off again. The resulting mixture
was filtered to isolate an insoluble fraction, which was washed subse-
quently with hot toluene (30 mL) and hot EtOH (50 mL), and then dried
overnight under vacuum. Thermogravimetric analysis indicated that 1-AS
has a total organic content of 26 wt%.
Experimental Section
Materials: All reagents for synthesis were used as received from Peptide
Institute, Tokyo Kasei, Wako Pure Chemical Industries, Nacalai Tesque,
Shin-etsu Chemical Industries, and Kanto Kagaku. Cyclohexanone and
octane were dried over Na2SO4 and then distilled. Anhydrous grade etha-
nol, commercially available from Kanto Kagaku, was used without fur-
ther dehydration treatment. Cyclohexanone diethyl acetal was identified
by comparison of their NMR spectra and GC profiles with those of the
authentic sample, prepared according to a literature method.[14] Amphi-
philes 1–3 and corresponding composites 1-MS–3-MS were prepared by
using methods analogous to those reported previously.[7]
[1] a) E. H. Cordes, R. B. Dunlap, Acc. Chem. Res. 1969, 2, 329–337;
b) T. Kunitake, S. Shinkai, Prog. Polym. Sci. 1982, 8, 435–487.
[2] J. H. Fendler, E. J. Fendler, Catalysis in Micellar and Macromolecu-
lar Systems, Academic Press, London, 1975.
[3] J. H. Fendler, P. Tundo, Acc. Chem. Res. 1984, 17, 3–8.
[4] a) C. T. Kresge, M. E. Leonowicz, W. J. Roth, J. C. Vartuli, J. S.
Beck, Nature 1992, 359, 710–712; b) J. S. Beck, J. C. Vartuli, W. J.
Roth, M. E. Leonowicz, C. T. Kresge, K. D. Schmitt, C. T.-W. Chu,
D. H. Olson, E. W. Sheppard, S. B. McCullen, J. B. Higgins, J. L.
Schlenker, J. Am. Chem. Soc. 1992, 114, 10834–10843.
[5] a) T. Aida, K. Tajima, Angew. Chem. 2001, 113, 3919–3922; Angew.
Chem. Int. Ed. 2001, 40, 3803–3806; b) Y. Lu, Y. Yang, A. Sellinger,
M. Lu, J. Huang, H. Fan, R. Haddad, G. Lopez, A. R. Burns, D. Y.
Sasaki, J. Shelnutt, C. J. Brinker, Nature 2001, 410, 913–917.
Measurements: Electronic absorption spectra were recorded on
a
JASCO U-best V-570 spectrophotometer. 1H and 13C NMR spectra were
recorded on a JEOL GSX-270 spectrometer. MALDI-TOF-MS spectra
were recorded by using dithranol as a matrixon an Applied Biosystems
BioSpectrometry Workstation Voyager-DE STR spectrometer. High-res-
olution mass spectroscopy (HRMS) was carried out by using 3-nitroben-
Chem. Eur. J. 2007, 13, 1731 – 1736
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1735