Chemistry Letters Vol.33, No.9 (2004)
1119
for 30-layers on CaF2 plate. The polarized transmission meas-
urements for the inclined CaF2 plate can evaluate the tilt angle
of alkyl chains from the dichroic ratio of the band.9 The CH2
symmetric and antisymmetric stretching vibration bands due to
the hydrocarbon chains appeared at 2850 and 2917 cmꢁ1, re-
spectively. These wavenumbers indicate that the alkyl-chains
are mostly in a trans-zigzag conformation involving a certain
number of gauche states.10 Assuming a uniaxial distribution of
transition dipole moments, the tilt angle of the alkyl chains from
the normal line of the CaF2 plate can be estimated to be ca. 10ꢂ.
Out-of plane XRD patterns obtained for 30-layers of the mono-
layer of 1 showed that the long spacing of the film is 3.2 nm. This
value is similar to that estimated from Chem 3D modeling (not
containing counter anion). The in-plane XRD (Bruker AXS,
MXP-BX) gave single diffraction (d ¼ 0:41 nm), suggesting a
hexagonal packing with 0.41 nm spacing among the hydrocar-
bon chains.11 The polarized IR and XRD profiles indicate the
presence of a highly ordered layer structure (Figure 2).
0.1
0.06
0.02
0
20
40
60
80 100
[anion] / [picrate]
Figure 3. Absorbance at 365 nm of the film of 1 deposited from
different concentrations of anions in the presence of 1 ꢁM of
picrate at 24 mN mꢁ1 and 20 ꢂC: ( ) NaH2PO4, ( ) NaOAc,
( ) NaCl.
to design new types of film-based sensor systems for detecting
anions in water. Further investigation is underway involving
the exploration of a more powerful indicator than picrate.
d1 = d2 = d3 = 0.41nm
ca. 10o
This research is financially supported by Shorai Foundation
of Science and Technology and Izumi Science and Technology
Foundation.
d
1
1
3.2 nm
d
2
References and Notes
d
1
For current reports, see: a) H. R. Seong, D.-S. Kim, S.-G. Kim,
H.-J. Choi, and K. H. Ahn, Tetrahedron Lett., 45, 723 (2004). b)
Y. Kubo, M. Kato, Y. Misawa, and S. Tokita, Tetrahedron Lett.,
45, 3769 (2004). c) R. Kato, Y.-Y. Cui, S. Nishizawa, T.
Yokobori, and N. Teramae, Tetrahedron Lett., 45, 4273 (2004).
K. Ariga and T. Kunitake, Acc. Chem. Res., 31, 371 (1998).
M. Liu, A. Kira, and H. Nakahara, Langmuir, 13, 779 (1997); Y.
Zheng, J. Orbulescu, X. Ji, F. M. Andreopoulos, S. M. Pham,
and R. M. Leblanc, J. Am. Chem. Soc., 125, 2680 (2003).
D. D. Perrin, Pure Appl. Chem., 20, 133 (1969); S. Nishizawa
and N. Teramae, Anal. Sci., 13, Suppl., 485 (1997).
3
Figure 2. Schematic representation of the film of 1 ( : alkyl
chain, : S-benzyl-N,N0-dimethylisothiouronium segment).
Since significant interaction of the monolayer of 1 and pic-
rate was observed in the ꢀ-A isotherm experiment (Figure 1B),
we tried to read out selective H2PO4ꢁ-binding using LB films
fabricated from the monolayer under competitive conditions
for anions with picrate indicator. The 30-layer LB films were
prepared in the presence of picrate (1 ꢁM) deposited on the
quart plate; the color was light yellow. The UV–vis spectra were
then recorded, showing an absorption band at 365 nm. This
implies that the prepared LB film contained the picrate. When
similar films were prepared with picrate and H2PO4ꢁ in the sub-
phase, the absorption intensity at 36ꢁ5 nm significantly decreased
with increasing amounts of H2PO4 as a result of competitive
binding between picrate and the anion at the air-water interface.
Subsequently there is almost no absorption of the films in the
presence of 20 equiv. of H2PO4ꢁ. In contrast, AcOꢁ and Clꢁ
scarcely induced any change in the absorption spectra. The in-
2
3
4
5
For an example at the electrode surface, see: K. P. Xiao, P.
Buhlmann, and Y. Umezawa, Anal. Chem., 71, 1183 (1999);
¨
For examples at the liquid-liquid interface, see: K. Shigemori,
S. Nishizawa, T. Yokobori, T. Shioya, and N. Teramae, New
J. Chem., 26, 1102 (2002); ref. 1c.
´
´
´
6
7
R. Martınez-Man˜ez and F. Sancenon, Chem. Rev., 103, 4419
(2003); C. Suksai and T. Tuntulani, Chem. Soc. Rev., 32, 192
(2003).
1H NMR (400 MHz, CDCl3, TMS) ꢂ 9.14 (br s, 1H), 8.63 (br s,
1H), 6.52 (s, 2H), 6.39 (t, J ¼ 2:1 Hz, 1H), 4.56 (s, 2H), 3.91 (t,
J ¼ 6:5 Hz, 4H), 3.25 (s, 3H), 3.10 (s, 3H), 1.79–1.72 (m, 4H),
1.47–1.39 (m, 4H), 1.35–1.26 (m, 56H), 0.88 (t, J ¼ 6:8 Hz,
6H). FAB-MS, m=z ¼ 732½M ꢁ Brꢃþ. Anal. Calcd for
ꢁ
tensity change at 365 nm with 50 ꢁM of H2PO4 is larger than
those with other anions under similar conditions by a factor of 8
for AcOꢁ and 25 for Clꢁ, respectively (Figure 3). Clear selectiv-
ity was therefore observed, being consistent with the results of
the ꢀ-A isotherm experiments (Figure 1). Although in this ap-
proach we used 30-layer LB films because of the low color value
of picrate, the obtained result is promising for the design of new
types of sensor films, since recognition and sensing of anion spe-
cies in water has still been a challenge12 due to the fact that the
water molecules surrounding the anion (e.g. phosphates) inter-
fere with the desired host/guest interactions.
.
C46H87BrN2O2S 0.5 H2O: C, 67.28; H, 10.80; N, 3.41. Found:
C, 67.57; H, 10.83; N, 3.32%.
8
9
As a control experiment, S-methyl-N,N0-ꢁdimethylisothiouroni-
um iodide does not interact with H2PO4 in an aqueous solu-
tion, being checked by 1H NMR study in D2O–CD3CN (9:1v/
v) at 23 ꢂC.
H. Akutsu, Y. Kyogoku, H. Nakahara, and K. Fukuda, Chem.
Phys. Lipids, 15, 222 (1975).
10 T. Seki, T. Fukuchi, T. Kobayashi, and K. Ichimura, Bull.
Chem. Soc. Jpn., 76, 2217 (2003).
In conclusion, we have shown that an organized film com-
posed of an isothiouronium-derived amphiphile exhibits signifi-
cant H2PO4ꢁ-selectivity on the surface of aqueous subphases
containing anion species, and we can read out the anion through
a competitive assay with picrate. This provides a promising way
11 A. Fujimori, Y. Sugita, H. Nakahara, E. Ito, M. Hara, N.
Matsuie, K. Kanai, Y. Ouchi, and K. Seki, Chem. Phys. Lett.,
387, 345 (2004).
12 For a current example, see: A. Ojida, Y. Mito-oka, K. Sada, and
I. Hamachi, J. Am. Chem. Soc., 126, 2454 (2004).
Published on the web (Advance View) July 31, 2004; DOI 10.1246/cl.2004.1118