7512 J. Phys. Chem. B, Vol. 103, No. 35, 1999
Hasegawa et al.
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1
-1
peak at 1754 cm . The small peak is clearly recognized in the
decreases greatly in the spectrum at 5 mN m . The change is
common for both interaction times. Instead, the band at 1648
-
1
two spectra at low surface pressures (5 and 10 mN m ). On
closer inspection, the intensity of the νs(CH2) band relatively
increases in comparison to the νa(CH2) band. This suggests that
the film molecules are getting tilted in the direction of the side
view. In other words, the film molecules show biaxial change
with the surface pressure, although the fine chemical mechanism
is not clear in this study.
-
1
or 1705 cm increases in intensity relatively.
Although the band at 1648 or 1705 cm indicates that the
2C TAZ monolayers partially react with BA molecules, the
residual band at 1597 cm indicates that the reaction is
imperfect for the films at a high surface pressure. Probably,
many BA molecules that stack on the 2C TAZ monolayers may
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1
1
8
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1
18
The results indicate that the accumulated layer has an
imperfect hydrogen bonding network, since the band at 1707
cover other nonreacted parts of the monolayer to avoid the
perfect reaction.
-
1
cm is weak. The broad band that is comprised of the bands
The same dipping experiment was performed for loosely
-1
-1
at 1740 and 1755 cm does not change in intensity significantly
with an increase of the surface pressure. This must be because
the surface area of C18BA is about 25% smaller than that of
compressed (5 mN m ) 2C18TAZ monolayers. The spectra of
the monolayers are also available in Supporting Information.
-
1
The intensity of the band at 1597 cm largely decreases, and
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1
-1
2
C18TAZ at 20 mN m (refs 25 and 26). At the small surface
the bands at 1705 and 1648 cm increase. These results indicate
area, the molecular packing of C18BA monolayer is highly
condensed. The 2C18TAZ monolayer is, therefore, difficult to
incorporate into the condensed C18BA monolayer deeply. This
feature does not depend on the surface pressure of the 2C18-
TAZ monolayer, since the molecular interaction of film-to-film
is principally governed by the molecular packing of the C18BA
monolayer. Strictly speaking, a very loose 2C18TAZ monolayer
could interact with the C18BA monolayer, since the film property
is a little lost at a very low surface pressure. The split shoulder
that the loosely compressed 2C18TAZ monolayers bind more
BA molecules than the highly compressed monolayers. It is
found, however, the film-to-monomer interaction is not so
positive compared to the film-to-film interaction.
Conclusion
The film-to-film interaction between the C18BA and 2C18-
TAZ monolayers was revealed to be a unique interaction to
produce specific hydrogen bonding networks. When both the
two monolayers are highly compressed, molecular interaction
between the films becomes weaker due to the imperfect
complementary hydrogen bonding formation. In this case,
however, the film molecule packing is stabilized by the
hydrophobic molecular aggregation force, which results in tilting
of film molecules. This process yields many free (non-hydrogen
bonded) carbonyl groups. The unique hydrogen bonding network
is not recognized between the film-to-monomer interaction.
These results indicate that the potential of hydrogen bonding
networks of monolayers is very strong, which is not found in
monomer interactions. In other words, two-dimensional molec-
ular assemblies were revealed to have the unique ability of
molecular recognition.
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1
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peak at 1755 cm , perceived only for 5 and 10 mN m , is
consistent with the above speculation.
The C-H stretching vibration region shows no drastic change.
One notable point is that the relative intensity of the νs(CH2)
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1
band to the νas(CH2) one increases above 15 mN m . This
change indicates the biaxial change of the tilt angle of the
4
7
molecular axis. The result indicates that the molecular plane
tilts when the surface pressure is high. The positions of the νas-
-1
(
CH2) and νs(CH2) bands are 2919 and 2851 cm , respectively,
and they do not change with the surface pressure.
In the C-D stretching vibration region, the bands that arise
from the underlayer do not change at all. The relative intensity
of the νas(CD2) band to νs(CD2) is also stable against the change
-
of surface pressure. The change of νs(COO ) and δ(CH2) bands
are not significant. The nonsystematic variance of the band
intensity of some bands should be caused by an experimental
error.
Molecular Interaction between 2C18TAZ LB Film and BA
from Aqueous Solution. The above results strongly indicate
that the film-to-film interaction responds uniquely to the surface
density of the film molecules. To examine the characteristic of
the film-to-film interaction, another series of experiment on
molecular interaction were performed.
Acknowledgment. This work was supported by Grant-in-
aid for Scientific Research 09771955 from the Ministry of
Education, Science and Culture, Japan to whom the authors’
thanks are due.
Supporting Information Available: One figure is available
as Supporting Information showing IRRA spectra of 2C18TAZ
monolayer LB film after dipping in a 1 mM BA aqueous
solution. This material is available free of charge via the Internet
at http://pubs.acs.org.
The 2C18TAZ monolayers were prepared at 5 and 20 mN
m- on a gold substrate covered with a CdSt-d35 monolayer,
and the LB films were dipped in a 1 mM BA (without alkyl
chains) aqueous solution for 5 and 60 min. After the dipping,
they were immediately rinsed by pure water and dried suf-
ficiently in a desiccator. The dried LB films were subjected to
IRRA measurements. The RA spectra of the dipped LB films
are available in Supporting Information.
1
References and Notes
(
1) Jeong, K.-S.; Tjivikua, T.; Rebek, J., Jr. J. Am. Chem. Soc. 1990,
112, 3215.
(2) Jacquemain, D.; Leveiller, F.; Weinbach, S. P.; Lahav, M.;
Leiserowitz, L.; Kjaer, K.; Als-Nielsen, J. J. Am. Chem. Soc. 1991, 113,
684.
3) Nowick, J. S.; Chen, J. S.; Noronha, G. J. Am. Chem. Soc. 1993,
115, 7636.
(4) Nowick, J. S.; Chen, J. S.; Noronha, G. J. Am. Chem. Soc. 1994,
16, 3285.
5) Kielkopf, C. L.; White, S.; Szewczyk, J. W.; Turner, J. M.; Baird,
7
(
The RA spectra of 2C18TAZ monolayer LB films at 20 and
-1
5
mN m are taken for the same LB film after an equilibration
1
time of 5 and 60 min in the BA solution. All the spectra show
a large difference from those of the film-to-film deposited LB
films (Figures 3 and 6). Of particular note is that the spectra
(
E. E.; Dervan, P. B.; Rees, D. C. Science 1998, 282, 111.
(6) Franklin, S. J.; Barton, J. K. Biochemistry 1998, 37, 16093.
(7) Owen, D. J.; Evans, P. R. Science 1998, 282, 1327.
-
1
clearly show a broad band centered at 1597 cm where many
bands are overlapped with each other. This feature is not found
in a spectrum when 2C18TAZ reacts well with the BA moiety
through hydrogen bonding (Figure 3). The intensity of this band
(
8) Woods, R. J.; Pathiaseril, A.; Wormald, M. R.; Edge, C. J.; Dwek,
R. A. Eur. J. Biochem. 1998, 258, 372.
9) Bousse, L.; McReynolds, R. J.; Kirk, G.; Dawes, T.; Lam, P.;
Bemiss, W. R.; Parce, J. W. Sens. Actuators, B: Chem. 1994, B20, 145.
(