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Bilayer-Immobilized Films Containing Mesogenic Azobenzene AmphiphilesЧElectrically Controllable Permeability.

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solved in chloroform and cast on a polyester minigrid (270
mesh, 38 mm2). The thickness of the cast film was estimated to be 100 pm from scanning electron microscopic
observations. The polyionic film was transparent, mechanically stable, and water-insoluble.
The bilayer characteristics of the polyionic film were
confirmed by X-ray diffraction analysis of l a : a strong diffraction pattern with 3.5-nm spacing was observed, which
is consistent with the bimolecular length of tilted l a . The
structural data are similar to those obtained for aqueous
dispersions and cast films prepared from 1 These results
clearly indicate that the films formed from azobenzene amphiphiles have extended lamellar structure like that observed for dialkylamphiphile-immobilized film."' The
films obtained from the azobenzene amphiphiles were
shown by DSC'(differentia1 scanning calorimetry) measurements to have the following phase-transition temperatures for transformation from the solid to the liquid-crystalline state: la, 25 " C ; l b , 56 " C ; l c , 64 "C.
The permeation of the water-soluble, nonionic fluorescent probe 2l6]
M) through the l @ / P S S o film cast on
Bilayer-Immobilized Films Containing
Mesogenic Azobenzene AmphiphilesElectrically Controllable Permeability**
By Yoshio Okahata,* Shinsuke Fujita, and Noami Iizuka
Immobilization of synthetic or natural lipid bilayers facilitates their use as novel functional materials, such as
permeability-controllable membranes."] Previously, we
prepared a bilayer-corked capsule membranel2I and a bilayer-immobilized film from dialkylammonium amphiphiles and p o I y a n i o n ~ ,and
[ ~ ~ were able to control their permeability by application of an electric field across the
membrane (Fig. 1, method B). The electrical field generates transient pores in the bilayer of the capsule membrane
or film, resulting in a large increase in the permeability of
the membrane. We report here the preparation of bilayerimmobilized films from the liquid-crystalline-type amphiphiles la-c containing an azobenzene chromophore. The
permeability of the film can be controlled by application
of an electric field parallel to the membrane (Fig. 1, method
A), which causes the orientation of the chromophores in
the bilayer film to change.
OH
2
0 C. power supply
method A
I
lQ/PSSO
a: n.12, m.4,
b:n=12,m=10;
CH3
The preparation of the azobenzene-containing amphiand the films
philes la-c has been described
were prepared according to the previously reported method.I3l An aqueous dispersion (2 mL) of azobenzene amphiphiles la-c (3 x
mol) and an aqueous solution (2 mL)
of sodium polystyrenesulfonate (NaPSS) (M,=2 x lo6,
3 x lo-' mol) were mixed at 70 "C. The precipitate was
washed, dissolved in chloroform, and reprecipitated with
ethanol. The dried, yellow powder (recovery: 80%) was dis-
[*I
[**I
Dr. Y. Okahata, S . Fujita, N. Iizuka
Department of Polymer Chemistry, Tokyo Institute of Technology,
Ookayama, Meguro-ku, Tokyo 152 (Japan)
Permeability-Controllable Membranes, Part 6 . We thank Prof. M. Shimomura. Tokyo University of Agriculture and Technology, for helpful
discussions.-Part 5 : Y. Okahata, K. Ariga, 0. Shimizu, Langrnuir. in
press.
Angew. Chem. Inr. Ed. Engl. 25 (1986) No. 8
Fig. I. Schematic drawing of the experimental setup (see text).
C: n=8, m.10
a polyester mesh was followed fluorophotometrically at
A = 340 nm (excitation at A = 280 nm) (Fig. 1). Permeation
rates were obtained both in the absence and presence of an
electric field, which was applied either parallel (method A)
or perpendicular (method B) to the film plane. The results
are summarized in Table 1. The nonionic compound 2 was
chosen to avoid the effect of electrostatic interaction with
the electrodes and the polyionic, bilayer films.
The permeation of 2 through the 1°/PSSo film wilh
very slow in the absence of an electric field, irrespective of
both the chain length of the spacer and the alkyl end group
of 1 @.When a potential of 4 V (250 PA) was applied between two electrodes with the field gradient parallel to the
membrane (method A), however, the permeability was immediately increased by a factor of 5.0-10; it reverted to the
cm2 s - ' ) when the
original low value (P=(1.8-2.2)x
potential was turned off, even after 5-10 min, irrespective
0 VCH Verlagsgeseilschaft mbH, 0-6940 Weinhelm. 1986
0570-0833/86/0808-0751 .S 02.50/0
75 1
Table I. Permeation rates (P)of the water-soluble dye 2 across bilayerimmobilized films upon application of a n electric field ( 4 V between two Pt
electrodes) at SO "C.
P [ I O - 9 em's-'1
Film
Method B
Method A
Po [a1
lao/PSSQ
2.0
1b O/PSSQ
1.8
l c a/PSSe
I .6
2 c , x i 3 2 c , / P s s e 12
P
10
11
16
12
P
PO
5.0
6. I
10
10
Po la1
P
P
-
2.0
1.8
I .6
12
3.5
2.2
2. I
120
I .4
I .3
10
groups by contact with the polyanions, but still have the
fluid bilayer properties. These artificial membranes, whose
permeability is controllable by application of an electric
field, may provide a new tool to study transport mechanisms in biological membranes.
Received: February 17, 1986;
revised: Apirl 15, 1986 [Z 1671 IE]
German version: Angew. Chem 98 (1986) 723
Po
1.8
CAS Registry numbers:
la"/PSSe, 103368-69-0; Ibe/PSSe, 103368-71-4; Ic/PSSo, 103368-73-6; 2 ,
103368-74-7; 2C,,N2C, '/PSSe, 99742-69.5.
[a] P,=permeation rate in the absence of an electric field.
of the chain length of the spacer and the alkyl end groups.
The permeability change occurred within 30 s after application of the electric field, and there was no induction period due to swelling of the membrane. This permeability
change could be observed at various temperatures (between 10 and 60 "C), irrespective of the phase-transition
temperature of the bilayers, and could be reproduced repeatedly without damaging the films. The increase in permeability was observed only above 1.5 V (50 FA) and increased linearly with increasing potential in the range 1.58.0 V (50-500 PA).
When a potential of 4 V was applied across the membrane (method B), the permeability of the 1 @/PSSQfilms
was only slightly increased by a factor of 1.3-1.8. For
films prepared from dimethyldioctadecylammonium
(2C,8N@2C,)amphiphile and PSSO, the permeability is
largely enhanced (10 times) when the electric field is applied across the membrane (method B).I3=I In the latter
case, the film acts as a capacitor because of its poor conductivity; the electric transmembrane potential can produce transient pores in the fluid bilayers by electrically induced "breakdown," which results in permeability enhancement. In contrast, the 1 @/PSS" films contain highly
conductive chromophores in the bilayers, so that a high
transmembrane potential cannot form and no "breakdown" occurs.
When a potential is applied parallel to the l@/PSS"
films, the orientation of the azobenzene chromophore in
the bilayers presumably changes, and the permeability of
the resulting disordered bilayers increases. The orientation
of mesogenic azobenzene chromophores in bilayers of 1
is well known to be sensitive to temperature changes;
moreover, the UV/VIS spectra of the chromophores
change upon phase transition of the bilayers.lsl The absorption spectra of the l@/PSSQfilms, however, d o not
change, irrespective of whether the electric field is parallel
or perpendicular to the film plane. The permeability of
2Cl8N@2Cl/PSSefilms does not change when the electric
field is applied parallel to the. membrane because the
poorly conductive, "dialkyl" bilayers are not oriented by
the electric field. Thus, the permeability of the bilayer-immobilized film containing the conductive, liquid-crystalline chromophores changes when the electric field is applied parallel to the membrane; on the contrary, the permeability of the film from the poorly conductive, dialkyl
bilayers changes when the electric field is applied perpendicular to the membrane.
The fluid bilayer structure is very important for the electrically controlled change in permeability, because the
change is not observed when rigid, polymeric liquid crystals such as poly(benzy1 glutamate) are employed. The bilayers of 1' are immobilized at the hydrophilic head
@
752
0 VCH Verlagsgesellschafr mbH. 0-6940 Weinheim. 1986
[ I ] Y. Okahata, Acc. Chem. Res. 19 (1986) 57; 1 Kunitake, A. Tsuge, N. Nakashima, Chem. Lett. 1984. 1783; T. Kajiyama, A. Kumano, M. Takayanagi, T. Kunitake, Y. Okahata, Ber. Bunsenges. Phys. Chem. 88 (1984)
1216.
[2] Y. Okahata, S. Hachiya, T. Seki, J . Chem. SOC. Chem. Commun. 1985.
1377; Y. Okahata, S. Hachiya, K. Ariga, T. Seki, J . Am. Chem. SOC. 108
(1986) 2863.
[3] a ) Y. Okahata, K. Taguchi, T. Seki, J . Chem. SOC.Chem. Commun. 1985.
1122: b) Y. Okahata, G. En-na, K. Taguchi, T. Seki, J. Am. Chem. Sor.
I07 (1985) 5300.
[4] T. Kunitake, Y. Okahata, M. Shimomura, S. Yasunami, K. Takarabe, J.
Am. Chem. Sor. 103 (1981) 5401: M. Shimomura, R. Ando, T. Kunitake,
Ber. Bunsenges. Phys. Chem. 87 (1983) 1134.
[5] T. Kunitake, S. Shimomura, T. Kajiyama, A. Harada, K. Okuyama, M.
Takayanagi, 7 X n Solid Films 121 (1984) 89.
[61 Y. Okahata, N. lizuka, G. Nakamura,T. Seki, J. Chem. SOC.Perkin Trans.
2 1985. 1591.
E,Te3Hal, Mixed Valency Tellurohalides of Gallium
and Indium with One-Dimensional Structural
Units**
By Sabine Paashaus and Riidiger Kniep*
The ternary systems E-Te-Hal ( E = G a , I n ; Hal=Cl, Br,
I) contain the phases ETeHal, having incongruent melting
behavior, on the E,Te3-EHal, sections.['I Along the sections from these ternary phases to the binary chalcogenides ETeIZ1we have been able to identify thermodynamically stable, mixed valency compounds of the formula
E3Te3Hal. The following compounds have so far been obtained in pure form: Ga3Te3C1 (m.p. =718"C, congruent),
Ga3Te3Br (m.p. = 733"C, congruent), and Ga,Te31
(m.p. = 692"C, congruent) by crystallization from the melt
according to the Bridgman method and In3Te3Br
(m.p. = 381 " C, incongruent) and In3Te31(m.p. =394"C, incongruent) by annealing of stoichiometric mixtures at
240°C. The intense red crystals have high reflecting power
and an acicular habit and are very easily cleaved aIong the
fibers.
The first crystal structure analysis was carried out on
GaTe,I.I3l Figure I shows the macromolecular elements of
the structure, in which GaTe3,,I tetrahedra and Ga,TehI3
structural units (staggered conformation) are linked. The
shortest Ga-Ga distances in the central six-membered
rings (2.454(2) A) are comparable to the Forresponding
bond lengths in Ga2I3 (Ga:Ga:'I,; 2.388(5) A'41) and GaTe
(2.434 Arz'), so that the oxidation state + 2 has to be assumed for these G a atoms; on the other hand, for the iodine-bonded G a atoms (Ga-I: 2.536(1) A) the oxidation
[*I
Prof. Dr. R. Kniep, Dipl.-Chem. S. Paashaus
lnstitut fur Anorganische Chemie und Strukturchemie der Universitat
Universitatsstrasse 1, D-4000 Dusseldorf (FRG)
[**I This work was supported by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie.
0570-0833/86/0808-0752 $ 02.50/0
Angew. Chem. In!. Ed. Engl. 25 (1986) No. 8
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containing, immobilized, films, amphiphilesчelectrically, controllable, mesogenic, permeability, azobenzene, bilayers
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