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Molecular recognition by amphiphilic cyclodextrins in Langmuir-Blodgett films
Thin Solid Films, 210/211 (1992) 803 805
803
Molecular recognition by amphiphilic cyclodextrins in Langmuir- Blodgett films Mutsuyoshi
Matsumoto,
Motoo
Tanaka,
Reiko Azumi,
Hiroaki
Tachibana,
Takayoshi Nakamura and Yasujiro Kawabata National Chemical Laboratory for Industry, Tsukuba 305 (Japan) Tomohiko Miyasaka and Waichiro Tagaki Faculty of Engineering, Osaka City University, Osaka 558 (Japan) Hiroo Nakahara and Kiyoshige Fukuda Faculty of Science, Saitama University, Urawa 338 (Japan)
Abstract Azobenzene derivativeswere recognized by amphiphilic cyclodextrins (CDs) in LB films. The amount of ortho isomer of methyl red incorporated in the LB film was very small for any of the CDs used, whereas considerable amounts of the para and meta isomers were kept in the films, most of which were included in the cavity. The size of the cavity of the CDs was reflected in the out-of-plane anisotropy and the peak shift in the polarized absorption spectra of the LB films of the CDs containing the azobenzene derivatives.
1. Introduction L a n g m u i r - B l o d g e t t films have been extensively studied from the viewpoint of constructing future electronic devices, taking advantage of ordered structures realized in the films [1]. We have examined the structures of LB films of amphiphilic cyclodextrins (CDs), and found that various azobenzene molecules are incorporated in the films [2-4]. A m o n g others, azobenzene molecules in the C D films show a reversible cis-trans photoisomerization, indicating the feasibility of the LB films of this type as optical memory devices [5-7]. These LB films are prepared by spreading chloroform solutions of equimolar mixtures of alkylamino derivatives of CDs and azobenzene derivatives on a water surface. In this system, the amounts of azobenzene molecules incorporated in the films depend on the structures of both C D and azobenzene derivatives, and hence they can measure the interaction between the two. This provides us with a means of molecular recognition. In this study, the possibilities are examined to use amphiphilic cyclodextrins for molecular recognition of o-, m-, and p-isomers of an azobenzene derivative, methyl red.
2. Experimental details The amphiphilic cyclodextrins used in this study were synthesized as reported previously [8] and the azoben-
0040-6090/92/$5.00
zene derivatives were commercially available. Monolayers were spread from a 1:1 mixed chloroform solution of CD and the azobenzene derivative (trans isomer) on the water surface at 290 K. The monolayers were compressed and transferred at 30 m N m -~ onto solid substrates precoated with five monolayers of cadmium icosanoate. Polarized absorption spectra of the LB films at 45 ° incidence were measured with a Jasco HSSP-1 spectrophotometer. The amounts of azobenzene derivatives incorporated in the LB films were determined spectroscopically by dissolving the LB films into methanol using ultrasonication.
3. Results and discussion 3. I. A m o u n t o f azobenzene incorporated in the L B film In a previous paper [3], we demonstated that there are structural requirements for the azobenzene derivative to be incorporated in the LB film of CD; the CD mtist have an amino moiety ( - N H - ) and the dye must have an acidic group such as - C O O H or - S O 3 H . On the basis of these results, alkylamino derivatives of ~-, fl-, 7-CD and o-, m-, p-isomers of methyl red (Fig. 1) were used in this study. The molar ratios of azobenzene derivatives incorporated in CDs in the LB films are listed in Table 1. It is clearly seen that the bulkiest dye, o-MR, is not easily incorporated in LB films of any of the CDs used. On the other hand, considerable amounts of m - M R and
© 1992 - - Elsevier Sequoia. All rights reserved
M. Matsumoto et al. / Molecular recognition by amphiphilic CDs in LB films
804
p-MR.
~ O H _ _CH2NHCI6H33 _~
COOH
0 I
.
OH
)n
n=6 : ~-CD n=7 : B-CD n=8 : .y-CD
Fig.
1.
ortho isomer: o-MR meta isomer: m-MR para isomer: p-MR
Molecules used in this study.
TABLE 1. The molar ratios of azobenzene derivatives to CDs in the LB films c~-CD
#-CD
7-
0.03 0.28 0.40
0.08 0.41 0.51
0.08 0.44 0.38
CD o-MR m-MR p-MR
p-MR were kept in the LB films for the three CDs. These results indicate that the CDs of this type have the ability of molecular recognition in LB films.
3.2. Orientation of azobenzene derivatives in LB films Figure 2 shows the polarized absorption spectra of LB films of e-CD with p-MR. The transition moment of p-MR in a monomeric state is parallel to the long axis of the molecule. There are two types of p-MR present in the LB films: one is responsible for the peak at about 390 nm with its transition moment perpendicular to the film surface (major component) and the other is related to the peak at about 415 nm (minor component). The direction of the transition moment of the latter peak is not identifiable. It seems to be improbable that the two peaks originate from a single aggregate (Davydov effects). We consider that the major component is assigned to the p-MR included in the cavity of c~-CD in the LB film and the minor component is ascribed to the p-MR outside the cavity due to the following reasons.
, s-polarization; ...... , p-polarization.
(1) The important driving force of the inclusion in chloroform solutions is a salt formation between the amino group of the host and the acidic group of the guest, which should also be significant in the case of LB films. The inclusion of p-MR in ~-, #-, and 7-CD in chloroform solutions was confirmed by N M R and induced circular dichroism spectra [9]. The cis isomer of p-MR was also included. (2) The host-guest complex formation is essential for azobenzene to be incorporated in the LB films. The p-MR was not incorporated in the LB films of Nmethyloctadecylamine or in the mixed LB films of N-methyloctadecylamine and methyloctadecanoate, although the salt formation was possible [3]. (3) The direction of the transition moment perpendicular to the film surface is better explained by the model in which this component is located in the cavity rather than outside the cavity. (4) The difference between the cases of p-MR and o-MR could be unexplained if most of the azobenzene molecules were situated outside the cavity. (5) The almost identical n - A isotherms of :~-CD with and without p-MR (data not shown) supports the model that the major part of p-MR is located inside the cavity. The presence of the minor component of p-MR suggests that the ~-CD creates outside the cavity a site which is different from the ones existing in the LB films of N-methyloctadecylamine or in the mixed LB films of N-methyloctadecylamine and methyloctadecanoate. The polarized absorption spectra of the LB films of 7-CD containing p-MR are shown in Fig. 3. A clear difference is seen between the cases of e- and 7-CD; the out-of-plane anisotropy is less pronounced for 7-CD. An intermediate behavior was observed for #-CD.
These results are understood in terms of the size of the cavity. Only one azobenzene molecule is accommodated in the cavity of ~-CD, whereas 1:2 complex formation was observed in the case of 7-CD [10]. The
*J
az
x
t t
(z)
400
500
WAVELENGTH (nm)
Fig. 2. Polarized absorption spectra of LB films of :~-CD containing
400
500
WAVELENGTH (nm)
Fig. 3. Polarized absorption spectra of LB films of 7-CD containing p-MR. , s-polarization; ...... , p-polarization.
M. Matsumoto et al. / Molecular recognition by amphiphilic CDs in LB films
large cavity o f 7 - C D s h o u l d allow p - M R to be inclined to the n o r m a l o f the film surface when only one molecule is included in the cavity. This effect decreases the intensity o f the p e a k in the p - p o l a r i z e d s p e c t r u m a n d increases t h a t in the s-polarized s p e c t r u m c o m p a r e d with the case o f ~ - C D . The red shift o f the p e a k in the p - p o l a r i z e d s p e c t r u m f r o m the ~ - C D to the ~ - C D films seems to reflect a difference in the electronic state o f the included p - M R .
4. Conclusion This p a p e r d e m o n s t r a t e s t h a t a z o b e n z e n e derivatives can be recognized b y C D s in the LB films. T h e a m o u n t s o f a z o b e n z e n e derivatives i n c o r p o r a t e d in the LB films d e p e n d on the size o f the azobenzenes. O n the o t h e r h a n d , the size o f the cavity o f the C D s is reflected in the o u t - o f - p l a n e a n i s o t r o p y a n d the p e a k shift in the p o l a r ized a b s o r p t i o n spectra o f the host-guest LB films. H o w e v e r , it is very difficult to m a k e a q u a n t i t a t i v e analysis o f the a z o b e n z e n e derivatives included in the cavity o f the C D s due to a difference in the direction o f the t r a n s i t i o n m o m e n t s a n d also to the o v e r l a p p i n g o f the two species in the a b s o r p t i o n spectra. F u r t h e r w o r k is n o w in p r o g r e s s on the ability o f m o l e c u l a r recognition o f a m p h i p h i l i c C D s in the f o r m o f a m o n o l a y e r at the a i r - w a t e r interface.
805
References 1 K. Fukuda and M. Sugi (eds.), Proc. 4th Int. Conf. LB Films, Tsukuba, 1989; Thin Solid Films, 178 180 (1989); F. T. Hong (ed.), Molecular Electronics: Biosensors and Biocomputers, Plenum Press, New York, 1989. 2 Y. Kawabata, M. Matsumoto, M. Tanaka, H. Takahashi, Y. Irinatsu, S. Tamura, W. Tagaki, H. Nakahara and K. Fukuda, Chem. Lett., (1986) 1933. M. Tanaka, Y. Ishizuka, M. Matsumoto, T. Nakamura, A. Yabe, 3 H. Nakanishi, Y. Kawabata, H. Takahashi, S. Tamura, W. Tagaki, H. Nakahara and K. Fukuda, Chem. Lett., (1987) 1307. Y. Kawabata, M. Matsumoto, T. Nakamura, M. Tanaka, E. Manda, H. Takahashi, S. Tamura, W. Tagaki, H. Nakahara and K. Fukuda, Thin Solid Films, 159 (1988) 353. 5 A. Yabe, Y. Kawabata, H. Niino, M. Tanaka, A. Ouchi, H. Takahashi, S. Tamura, W. Tagaki, H. Nakahara and K. Fukuda, Chem. Lett., (1988) 1. 6 H. Niino, A. Yabe, A. Ouchi, M. Tanaka, Y. Kawabata, S. Tamura, T. Miyasaka, W. Tagaki, H. Nakahara and K. Fukuda, Chem. Lett., (1988) 1227; H. Niino, A. Ouchi, Y. Kawabata, A. Yabe, H. Nakahara, K. Fukuda, T. Miyasaka and W. Tagaki,' Nippon Kagaku Kaishi, (1990) 1189. 7 A. Yabe, Y. Kawabata, H. Niino, M. Matsumoto, A. Ouchi, H. Takahashi, S. Tamura, W. Tagaki, H. Nakahara and K. Fukuda, Thin Solid Films, 160 (1988) 33. 8 H. Takahashi, Y. lrinatsu, S. Kozuka and W. Tagaki, Mere. Fac. Eng. Osaka City Univ., 26 (1985) 93. 9 Y. Kawabata, Y. Ishizuka, H. Nakanishi, H. Takahashi, S. Tamura and W. Tagaki, Abstract of the 5th Symposium on Cyclodextrin, 1986, Kyoto; W. Tagaki, Aburakagaku, 37 (1988) 10. 10 H. Hirai, N. Toshirna and S. Uenoyama, Bull. Chem. Soc. Jpn., 58 1985) 1156.
803
Molecular recognition by amphiphilic cyclodextrins in Langmuir- Blodgett films Mutsuyoshi
Matsumoto,
Motoo
Tanaka,
Reiko Azumi,
Hiroaki
Tachibana,
Takayoshi Nakamura and Yasujiro Kawabata National Chemical Laboratory for Industry, Tsukuba 305 (Japan) Tomohiko Miyasaka and Waichiro Tagaki Faculty of Engineering, Osaka City University, Osaka 558 (Japan) Hiroo Nakahara and Kiyoshige Fukuda Faculty of Science, Saitama University, Urawa 338 (Japan)
Abstract Azobenzene derivativeswere recognized by amphiphilic cyclodextrins (CDs) in LB films. The amount of ortho isomer of methyl red incorporated in the LB film was very small for any of the CDs used, whereas considerable amounts of the para and meta isomers were kept in the films, most of which were included in the cavity. The size of the cavity of the CDs was reflected in the out-of-plane anisotropy and the peak shift in the polarized absorption spectra of the LB films of the CDs containing the azobenzene derivatives.
1. Introduction L a n g m u i r - B l o d g e t t films have been extensively studied from the viewpoint of constructing future electronic devices, taking advantage of ordered structures realized in the films [1]. We have examined the structures of LB films of amphiphilic cyclodextrins (CDs), and found that various azobenzene molecules are incorporated in the films [2-4]. A m o n g others, azobenzene molecules in the C D films show a reversible cis-trans photoisomerization, indicating the feasibility of the LB films of this type as optical memory devices [5-7]. These LB films are prepared by spreading chloroform solutions of equimolar mixtures of alkylamino derivatives of CDs and azobenzene derivatives on a water surface. In this system, the amounts of azobenzene molecules incorporated in the films depend on the structures of both C D and azobenzene derivatives, and hence they can measure the interaction between the two. This provides us with a means of molecular recognition. In this study, the possibilities are examined to use amphiphilic cyclodextrins for molecular recognition of o-, m-, and p-isomers of an azobenzene derivative, methyl red.
2. Experimental details The amphiphilic cyclodextrins used in this study were synthesized as reported previously [8] and the azoben-
0040-6090/92/$5.00
zene derivatives were commercially available. Monolayers were spread from a 1:1 mixed chloroform solution of CD and the azobenzene derivative (trans isomer) on the water surface at 290 K. The monolayers were compressed and transferred at 30 m N m -~ onto solid substrates precoated with five monolayers of cadmium icosanoate. Polarized absorption spectra of the LB films at 45 ° incidence were measured with a Jasco HSSP-1 spectrophotometer. The amounts of azobenzene derivatives incorporated in the LB films were determined spectroscopically by dissolving the LB films into methanol using ultrasonication.
3. Results and discussion 3. I. A m o u n t o f azobenzene incorporated in the L B film In a previous paper [3], we demonstated that there are structural requirements for the azobenzene derivative to be incorporated in the LB film of CD; the CD mtist have an amino moiety ( - N H - ) and the dye must have an acidic group such as - C O O H or - S O 3 H . On the basis of these results, alkylamino derivatives of ~-, fl-, 7-CD and o-, m-, p-isomers of methyl red (Fig. 1) were used in this study. The molar ratios of azobenzene derivatives incorporated in CDs in the LB films are listed in Table 1. It is clearly seen that the bulkiest dye, o-MR, is not easily incorporated in LB films of any of the CDs used. On the other hand, considerable amounts of m - M R and
© 1992 - - Elsevier Sequoia. All rights reserved
M. Matsumoto et al. / Molecular recognition by amphiphilic CDs in LB films
804
p-MR.
~ O H _ _CH2NHCI6H33 _~
COOH
0 I
.
OH
)n
n=6 : ~-CD n=7 : B-CD n=8 : .y-CD
Fig.
1.
ortho isomer: o-MR meta isomer: m-MR para isomer: p-MR
Molecules used in this study.
TABLE 1. The molar ratios of azobenzene derivatives to CDs in the LB films c~-CD
#-CD
7-
0.03 0.28 0.40
0.08 0.41 0.51
0.08 0.44 0.38
CD o-MR m-MR p-MR
p-MR were kept in the LB films for the three CDs. These results indicate that the CDs of this type have the ability of molecular recognition in LB films.
3.2. Orientation of azobenzene derivatives in LB films Figure 2 shows the polarized absorption spectra of LB films of e-CD with p-MR. The transition moment of p-MR in a monomeric state is parallel to the long axis of the molecule. There are two types of p-MR present in the LB films: one is responsible for the peak at about 390 nm with its transition moment perpendicular to the film surface (major component) and the other is related to the peak at about 415 nm (minor component). The direction of the transition moment of the latter peak is not identifiable. It seems to be improbable that the two peaks originate from a single aggregate (Davydov effects). We consider that the major component is assigned to the p-MR included in the cavity of c~-CD in the LB film and the minor component is ascribed to the p-MR outside the cavity due to the following reasons.
, s-polarization; ...... , p-polarization.
(1) The important driving force of the inclusion in chloroform solutions is a salt formation between the amino group of the host and the acidic group of the guest, which should also be significant in the case of LB films. The inclusion of p-MR in ~-, #-, and 7-CD in chloroform solutions was confirmed by N M R and induced circular dichroism spectra [9]. The cis isomer of p-MR was also included. (2) The host-guest complex formation is essential for azobenzene to be incorporated in the LB films. The p-MR was not incorporated in the LB films of Nmethyloctadecylamine or in the mixed LB films of N-methyloctadecylamine and methyloctadecanoate, although the salt formation was possible [3]. (3) The direction of the transition moment perpendicular to the film surface is better explained by the model in which this component is located in the cavity rather than outside the cavity. (4) The difference between the cases of p-MR and o-MR could be unexplained if most of the azobenzene molecules were situated outside the cavity. (5) The almost identical n - A isotherms of :~-CD with and without p-MR (data not shown) supports the model that the major part of p-MR is located inside the cavity. The presence of the minor component of p-MR suggests that the ~-CD creates outside the cavity a site which is different from the ones existing in the LB films of N-methyloctadecylamine or in the mixed LB films of N-methyloctadecylamine and methyloctadecanoate. The polarized absorption spectra of the LB films of 7-CD containing p-MR are shown in Fig. 3. A clear difference is seen between the cases of e- and 7-CD; the out-of-plane anisotropy is less pronounced for 7-CD. An intermediate behavior was observed for #-CD.
These results are understood in terms of the size of the cavity. Only one azobenzene molecule is accommodated in the cavity of ~-CD, whereas 1:2 complex formation was observed in the case of 7-CD [10]. The
*J
az
x
t t
(z)
400
500
WAVELENGTH (nm)
Fig. 2. Polarized absorption spectra of LB films of :~-CD containing
400
500
WAVELENGTH (nm)
Fig. 3. Polarized absorption spectra of LB films of 7-CD containing p-MR. , s-polarization; ...... , p-polarization.
M. Matsumoto et al. / Molecular recognition by amphiphilic CDs in LB films
large cavity o f 7 - C D s h o u l d allow p - M R to be inclined to the n o r m a l o f the film surface when only one molecule is included in the cavity. This effect decreases the intensity o f the p e a k in the p - p o l a r i z e d s p e c t r u m a n d increases t h a t in the s-polarized s p e c t r u m c o m p a r e d with the case o f ~ - C D . The red shift o f the p e a k in the p - p o l a r i z e d s p e c t r u m f r o m the ~ - C D to the ~ - C D films seems to reflect a difference in the electronic state o f the included p - M R .
4. Conclusion This p a p e r d e m o n s t r a t e s t h a t a z o b e n z e n e derivatives can be recognized b y C D s in the LB films. T h e a m o u n t s o f a z o b e n z e n e derivatives i n c o r p o r a t e d in the LB films d e p e n d on the size o f the azobenzenes. O n the o t h e r h a n d , the size o f the cavity o f the C D s is reflected in the o u t - o f - p l a n e a n i s o t r o p y a n d the p e a k shift in the p o l a r ized a b s o r p t i o n spectra o f the host-guest LB films. H o w e v e r , it is very difficult to m a k e a q u a n t i t a t i v e analysis o f the a z o b e n z e n e derivatives included in the cavity o f the C D s due to a difference in the direction o f the t r a n s i t i o n m o m e n t s a n d also to the o v e r l a p p i n g o f the two species in the a b s o r p t i o n spectra. F u r t h e r w o r k is n o w in p r o g r e s s on the ability o f m o l e c u l a r recognition o f a m p h i p h i l i c C D s in the f o r m o f a m o n o l a y e r at the a i r - w a t e r interface.
805
References 1 K. Fukuda and M. Sugi (eds.), Proc. 4th Int. Conf. LB Films, Tsukuba, 1989; Thin Solid Films, 178 180 (1989); F. T. Hong (ed.), Molecular Electronics: Biosensors and Biocomputers, Plenum Press, New York, 1989. 2 Y. Kawabata, M. Matsumoto, M. Tanaka, H. Takahashi, Y. Irinatsu, S. Tamura, W. Tagaki, H. Nakahara and K. Fukuda, Chem. Lett., (1986) 1933. M. Tanaka, Y. Ishizuka, M. Matsumoto, T. Nakamura, A. Yabe, 3 H. Nakanishi, Y. Kawabata, H. Takahashi, S. Tamura, W. Tagaki, H. Nakahara and K. Fukuda, Chem. Lett., (1987) 1307. Y. Kawabata, M. Matsumoto, T. Nakamura, M. Tanaka, E. Manda, H. Takahashi, S. Tamura, W. Tagaki, H. Nakahara and K. Fukuda, Thin Solid Films, 159 (1988) 353. 5 A. Yabe, Y. Kawabata, H. Niino, M. Tanaka, A. Ouchi, H. Takahashi, S. Tamura, W. Tagaki, H. Nakahara and K. Fukuda, Chem. Lett., (1988) 1. 6 H. Niino, A. Yabe, A. Ouchi, M. Tanaka, Y. Kawabata, S. Tamura, T. Miyasaka, W. Tagaki, H. Nakahara and K. Fukuda, Chem. Lett., (1988) 1227; H. Niino, A. Ouchi, Y. Kawabata, A. Yabe, H. Nakahara, K. Fukuda, T. Miyasaka and W. Tagaki,' Nippon Kagaku Kaishi, (1990) 1189. 7 A. Yabe, Y. Kawabata, H. Niino, M. Matsumoto, A. Ouchi, H. Takahashi, S. Tamura, W. Tagaki, H. Nakahara and K. Fukuda, Thin Solid Films, 160 (1988) 33. 8 H. Takahashi, Y. lrinatsu, S. Kozuka and W. Tagaki, Mere. Fac. Eng. Osaka City Univ., 26 (1985) 93. 9 Y. Kawabata, Y. Ishizuka, H. Nakanishi, H. Takahashi, S. Tamura and W. Tagaki, Abstract of the 5th Symposium on Cyclodextrin, 1986, Kyoto; W. Tagaki, Aburakagaku, 37 (1988) 10. 10 H. Hirai, N. Toshirna and S. Uenoyama, Bull. Chem. Soc. Jpn., 58 1985) 1156.