JP2523181B2 - Light-responsive artificial exciter membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a biological membrane such as a cell membrane partitioning between a high-concentration and a low-concentration salt solution, which generates a membrane potential and is excited to express information, transmit information, and process information. It is related to an artificial exciter membrane (called an artificial exciter membrane) that mimics the fact that a person is performing an action. In particular, an artificial exciter membrane that can control the membrane potential change by light (this is called a photoresponsive artificial exciter membrane). It is related to.

(Prior Art) A conventional computer is mainly composed of an inorganic material such as a silicon semiconductor element, and its processing function is to perform serial logical operation by the Von Neumann method. there were. Although this method can perform accurate logical operations, it has the drawback that, for example, it is difficult to perform many information processing operations in parallel, which are necessary for pattern recognition, which the brains of higher organisms are good at. It was

On the other hand, in recent years, the research on the cognitive function of the living body has been rapidly advanced, and for example, a plurality of nerve cells (neurons) that compose the above-mentioned brain are appropriately connected with each other as the living body learns and remembers. It is becoming clear that they have been changed and have so-called plasticity. However, there are many unclear points about what principle the functions such as pattern recognition, learning and memory found in the brain are executed, and what constituent components are used. Are being clarified by researchers.

Organisms accept various stimuli that can be accepted from the outside world by sensory organs and transmit them to the brain via synapses that connect between Huron and multiple neurons, and then recognize information in the brain consisting of many neurons. Explaining an example of such a recognition function, first, a stimulus (information) from the outside world is converted into an electrical signal, and a nerve impulse is generated. When this nerve impulse reaches the end of the axon that constitutes a neuron, a chemical substance called a neurotransmitter, which is contained in a vesicle, is released. Acetylcholine, adrenaline, serotonin, glutamic acid and the like are known as such neurotransmitters. The neurotransmitter released to the outside of the cell is received in the next cell via, for example, a receptor present in the biological membrane of the synapse. Then, in this cell, ions such as sodium ion and potassium ion flow into or out of the cell to generate a membrane potential on a biological membrane such as a cell membrane. As a result, a new nerve impulse is induced. Furthermore, from the presynaptic membrane of the synapse that received the nerve impulse, release of neurotransmitters occurs in the same manner as described above, and diffuses to the adjacent postsynaptic membrane,
It is taken up through the receptor and the nerve impulse is induced. Such a series of information transmission through nerve impulses is called excitement, and reaches the brain through multiple synapses. Further, the impulse reaching the brain excites a huge number of nerve cells in the brain, resulting in various information processing.

Therefore, an attempt to realize a functional element that mimics a biological system by using the lipids that compose the biological membrane described above has been performed, for example, in the literature (“Phase transition and self-oscillation phenomenon in synthetic lipid membrane”).
(Toki Kiyoshi et al., Membrane (MEM-BRANE), 12 (1), P.12-21,1
987). According to this document, a self-excited oscillation phenomenon of an artificial exciter membrane in which a synthetic lipid (hereinafter, referred to as a lipid-like substance) is adsorbed on a porous membrane is reported.
Here, the lipid-like substance is an amphipathic substance such as dioleic acid, trioleic acid, Span 80, dioleyl phosphate, or the like, a surfactant, or the like.

 The self-oscillation phenomenon described above will be briefly described below.

An artificial exciter membrane is prepared by adsorbing dioleyl phosphate, which is a lipid-like substance, to a porous membrane having a pore size of about several μm. One side of such an artificial exciter membrane is brought into contact with a high-concentration salt solution, and the other side is brought into contact with a low-concentration salt solution. The artificial exciter membrane placed in such a state causes a predetermined potential difference between these salt solutions in a cycle of several minutes to several tens of minutes, and an electric impulse is generated.

It is considered that the above-mentioned mechanism of self-oscillation is accompanied by a change in the lipid aggregate structure from the oil droplet state to the multi-layered state. This mechanism will now be explained in a little more detail with reference to the above mentioned references.

FIGS. 4 (A) and 4 (B) are diagrams used for the explanation, and an artificial structure in which a lipid or a lipid-like substance is impregnated in the micropores 11a of the support 11 having the microscopic through-holes 11a. FIG. 3 is a diagram showing a state in which a low concentration salt solution 13 and a high concentration salt solution 15 are partitioned by an exciter membrane. In particular, it is shown focusing on the periphery of one minute hole.

Lipids and lipid-like substances (hereinafter sometimes abbreviated as lipids, etc.) have stable oil droplets in a low-concentration salt solution and a multilayer film in a high-concentration salt solution with a certain salt concentration as a boundary. The condition is stable. Therefore, as shown in FIG. 4 (A), at the outlet of the micropores 11a on the side of the low-concentration salt solution, lipids and the like become oil droplets 17 and block the micropores, and the cations 19 are high in the micropores 11a. The oil drops change to the multilayer film 21 because they flow from the salt solution side of the concentration. In such a state, the cations selectively flow into the micropores 11a more than the anions in the salt solution, so that the anions are left on the support 11 and a membrane potential is generated. However, the fourth
As shown in FIG. 7B, when the oil droplet 17 changes to the multilayer film 21 and the oil droplet 17 that has blocked the minute hole 11a becomes smaller and the outlet is opened and the minute hole 11a penetrates, the inside of the minute hole 11a The high-concentration cation flows out to the low-concentration salt solution side due to diffusion, and the cation concentration in the micropores 11a decreases. From this time, the anion left on the support 11 disappears within a certain relaxation time due to diffusion of the anion itself and recombination with the diffused cation. After that, the concentration of cations in the micropores has decreased, and the lipid droplets are in a stable oil droplet state, so that the state returns to the state shown in FIG. 4 (A) again. In this way, the artificial exciter membrane repeats self-excited oscillation. The characteristics of the artificial exciter membrane described with reference to FIGS. 4 (A) and 4 (B) are summarized in Table 1.

By using the artificial exciter membrane as described above, it becomes possible to construct a bio element that imitates a neuron or a synapse. As an example thereof, there are elements proposed by the inventors of the present application in Japanese Patent Application No. 63-96851 and Japanese Patent Application No. 63-192116, which are applied to, for example, biocomputers and various sensors. Is expected.

(Problems to be Solved by the Invention) However, in the conventional artificial exciter membrane described with reference to FIG. 4, for example, the solution is pressurized from the high-concentration salt solution side and an electric current is applied to the solution. However, it was not possible to control the stop of oscillation and the progress of oscillation by optical stimulation. That is, the membrane potential could not be controlled by light stimulation. If the control of the self-excited oscillation can be performed by optical stimulation, there is an advantage that the sensor can be controlled without contact when the biosensor or the like is realized by the artificial exciter membrane, which is very useful.

The present invention has been made in view of the above points, and therefore, an object of the present invention is to reversibly stop and start oscillation caused by a change in membrane potential of an artificial exciter membrane by light without contact. It is to provide a controllable light-responsive artificial exciter membrane.

(Means for Solving the Problems) In order to achieve this object, according to the photoresponsive artificial exciter membrane of the present invention, one surface thereof is brought into contact with a high-concentration salt solution, and the other surface is brought into contact with a low-concentration salt solution. It is an artificial excitable membrane that can generate self-oscillation by bringing it into contact with a solution to change the membrane potential, and adsorbs a mixture of dioleyl phosphate represented by the following formula and azobenzene represented by the following formula on a support having micropores. It is characterized in that the oscillation start and oscillation stop of self-excited oscillation are controlled by visible light and ultraviolet light.

According to the photoresponsive artificial exciter membrane of the present invention, a support having micropores is adsorbed with a mixture of dioleyl phosphate represented by the above formula and azobenzene represented by the above formula, and the mixture is contained in the micropores. Is in the impregnated state. Here, since the structure of azobenzene changes three-dimensionally between visible light irradiation and ultraviolet light irradiation, one of the states in this structural change may interfere with the formation of the multilayer film described with reference to FIG. Become. For this reason, the micropores remain blocked by the oil droplets, and penetration of the micropores is blocked. As a result, the change in the membrane potential of the artificial exciter membrane is blocked, oscillation can be stopped, and oscillation can be controlled.

 This will be described in detail below.

Azobenzene is known to reversibly undergo a cis-trans geometric isomerization reaction as shown in the following formula by selectively irradiating ultraviolet light (UV) and visible light (VIS). (Reference: Polymer 22 (198
1) p.1511).

The trans-type azobenzene molecule has a structure in which two benzene ring planes are located on one plane when viewed from the side, and the cis-type azobenzene molecule has a bulky structure in which two benzene rings are bent in a V shape.

Therefore, when the mixture of azobenzene and dioleyl phosphate is irradiated with ultraviolet rays to make azobenzene into a cis type, since this is a bulky structure, the arrayed molecules are widened, and as a result, the multilayer structure of dioleyl phosphate becomes unstable. Will be transformed. Therefore, the penetration of the micropores is blocked, and the oscillation of the artificial exciter membrane can be stopped, and as a result, the oscillation can be controlled.

(Examples) Examples of the photoresponsive artificial exciter membrane of the present invention will be described below with reference to the drawings. It should be noted that in the following description, specific conditions are illustrated and described to the extent that the present invention can be understood, but it should be understood that the present invention is not limited to these conditions. In addition, although the sources of the chemicals used in the following examples may be omitted in some cases, all of the chemicals that can be easily obtained and are chemically pure enough were used.

Description of the procedure for producing an artificial exciter membrane First, a support having micropores is a porous membrane made of cellulose ester (Millipore filter, manufactured by Millipore) having a large number of through holes with a pore size of 8 μm, and a lipid-like substance having the following structure. Diol phosphate represented by the formula (Diol
eyl Phosphate. Hereinafter, it may be abbreviated as DOPH. )
Of the photoresponsive artificial exciter membrane of the example of the example in which the substance whose structure is three-dimensionally changed by light is azobenzene represented by the above formula (hereinafter sometimes simply referred to as the artificial exciter membrane of the example). The manufacturing procedure will be described.

DOPH used in this example was synthesized and purified as follows.

Oleyl alcohol (manufactured by Kanto Chemical Co., Inc.) and phosphorus oxychloride (POCl ₃ ) (manufactured by Kanto Chemical Co., Ltd.) were used as starting materials, and these were reacted by a well-known synthetic means. Hydrolyze the substance. In this way, DOPH as shown in the above structural formula was obtained and purified by the chromatographic method.

In the case of this example, azobenzene used was that manufactured by Tokyo Kasei Kogyo that was purified by the recrystallization method.

Next, azobenzene is weighed so as to be 5% by weight of DOPH, and then these DOPH and azobenzene are dissolved in benzene as a solvent.

Next, the above-mentioned porous film made of cellulose ester is immersed in this solution. After the immersion, the porous membrane is taken out and benzene is evaporated to obtain the artificial excitable membrane of the example in which the mixture of DOPH and azobenzene is adsorbed. In this Example, the adsorbed amount of the mixture was set to 4 (mg / cm ² ).

Further, in order to make a comparison with the example, the artificial exciter membrane according to the prior art (hereinafter, the artificial exciter membrane of the comparative example is used) in the same procedure as described above except that only the DOPH is adsorbed on the porous membrane. (Referred to as a membrane) was prepared with an adsorption amount of 4 (mg / cm ² ).

Description of Self-Excited Oscillation Device Next, a device for confirming self-excited oscillation of the artificial excitable membranes of Examples and Comparative Examples (hereinafter, referred to as a self-excited oscillation device) will be described. FIG. 2 is an explanatory diagram showing a schematic configuration of the self-oscillation device used in this embodiment. In the figure, some hatching and the like showing the cross section are omitted.

As shown in FIG. 2, the artificial exciter membrane of the example or comparative example (represented by 31 in the figure as a representative) has a 100 mM KCl aqueous solution having one surface accommodated in the first electrolytic cell 33a. 35a in contact with the other surface of the second electrolytic cell 33b in 5mM KCl
It is supported in contact with the aqueous solution 35b.

A facility for circulating constant temperature water (not shown) is provided around the first and second electrolytic cells 33a, 33b, and the temperature in the vessel can be controlled to an arbitrary value. In this example, KCl aqueous solution 35a, 3
The temperature of 5b is set to 20 ℃ ± 1 ℃. Further, a light transmission window 37c for irradiating the artificial exciter film 31 with ultraviolet light and visible light is provided in a part of the second electrolytic cell 33b.

The two KCl aqueous solutions 35a and 35b contain silver-silver chloride (Ag
A standard electrode 37a or 37b composed of -AgCl) is immersed. Then, the high-concentration 100 mM KCl aqueous solution 35
The standard electrode 37a immersed in a is connected to the anode side of the DC power supply 39, and the standard electrode 3 in the 5mM KCl aqueous solution 35b, which is the low concentration side,
7b is connected to the cathode side of the DC power supply 39 described above, and a constant current is applied to the artificial exciter membrane.

Further, this self-excited oscillating device is equipped with a measuring instrument 41 consisting of a high impedance electrometer and an XY recorder for measuring and recording the time change of the potential difference applied to the artificial membrane 31. Then, the standard electrode 43a or 43b connected to the measuring instrument 41 is immersed in each of the above KCl aqueous solutions 35a and 35b.

Further, this self-excited oscillating device comprises a manometer 45 connected to the first electrolytic cell 33a, and only through this manometer 45, the external pressure indicated by the arrow a in the figure,
It has a configuration that can be added to the artificial membrane 31. In this embodiment, the pressure applied by the manometer 45 described above will be described as the applied pressure.

The applied current and applied pressure described above are conditions necessary for causing oscillation of the artificial exciter membranes of the examples and comparative examples, and are set to certain values.

Furthermore, this self-excited oscillation device is a light source for selectively irradiating either the ultraviolet light or the visible light to the artificial exciter film 31 through the dark box 47 that houses the electrolytic cells 33a and 33b and the light transmission window 37c.
With 49. The light source 49 comprises a mercury lamp for physics and chemistry as a light source for ultraviolet light, and a halogen lamp equipped with a colored glass filter for removing light having a wavelength of 450 nm or less and a multilayer filter for removing light having a wavelength of 700 nm or more as a light source for visible light. It has.

Description of Self-Excited Oscillation Measurement Results Next, using the above-described self-excited oscillation device, self-excited oscillations of the artificial exciter membranes of Examples and Comparative Examples were measured as described below.

<Measurement of Oscillation Conditions> First, the self-excited oscillation conditions of the artificial exciter membranes of Examples and Comparative Examples were measured. This measurement was performed using a DC power source 39 and an artificial exciter membrane.
The applied pressure a was gradually increased while applying a constant current of 0.5 (μA) to 39. However, for the artificial excitable membrane of the example, in addition to the above conditions, when 90% or more of the azobenzene contained therein was irradiated with visible light so as to isomerize into the trans form, and 90% or more of the azobenzene The measurement was performed under two conditions of irradiation with ultraviolet light so as to isomerize into cis type. The light irradiation conditions for achieving the above isomerization are determined in advance.

According to these measurement results, it was found that the artificial exciter membrane of the comparative example requires 18 cmH ₂ O as the oscillation start applied pressure and the oscillation frequency at that time is 0.57 sec ⁻¹ . On the other hand, in the artificial exciter membrane of the example, oscillation was observed when visible light was irradiated, and 16 cmH ₂ O was required as the oscillation start applied pressure, and it was found that the oscillation frequency at that time was 0.60 sec ^-1 . But,
It was found that when the film was irradiated with ultraviolet light, the membrane potential increased, but the potential did not return and oscillation did not appear.

In FIG. 3, in order to explain the measurement results of the above-mentioned oscillation conditions, the applied pressure is plotted on the horizontal axis and the oscillation frequency is plotted on the vertical axis.
It is the figure which showed the relationship between the applied pressure and the oscillation frequency. Third
In the figure, the curve indicated by I is the characteristic of the artificial excitable membrane of the example after irradiation with visible light, and II is the characteristic of the artificial excitable membrane of the comparative example. Comparing the curves I and II, it can be said that the artificial exciter membrane of the example irradiated with visible light slightly oscillates more easily than the artificial exciter membrane of the comparative example, but this is considered to be within the error range, and both are substantially. It seems that they can be considered to be the same.

As is clear from the above experimental results, even if azobenzene is contained in DOPH, the azobenzene molecule does not decrease the stability of the DOPH multilayer structure when the azobenzene molecule is in the trans type. Can say But,
When this azobenzene is in cis form, this is DO
Because the PH multilayer structure is unstable, DOPH does not have a multilayer structure and is in an oil drop state. The reason for this is that the cis-type azobenzene molecules between the DOPH molecules arranged in a multilayer film structure have a V-shaped bulky structure, so the distance between the arranged molecules is widened and the DOPH multilayer film structure becomes unstable. It is thought to be to change.

<Confirmation of Photoresponsiveness> Next, whether or not the oscillation of the artificial exciter membranes of Examples and Comparative Examples is controlled by light was examined by an experiment as described below.

First, the artificial exciter membrane of the example was set in the self-excited oscillation device described with reference to FIG. 2, and then the artificial exciter membrane was irradiated with visible light. Next, the applied pressure of the device for self-excited oscillation is 20 cm.
H ₂ O and applied current of 0.5 μA. As a result, the artificial exciter membrane of the embodiment repeats the oil drop state and the multilayer film state,
Membrane potential changes appeared periodically and self-excited oscillation. Next, when the artificial excitable membrane of this example in the oscillated state was irradiated with ultraviolet light, the oscillation stopped and the membrane potential became a constant value in a high state. Next, the artificial exciter membrane of the example in which the oscillation was stopped by the irradiation with ultraviolet light was irradiated with visible light after a while after the irradiation with ultraviolet light was stopped. Then, the artificial exciter membrane oscillated again. The photoresponsiveness of the above-mentioned oscillation of the artificial exciter membrane of the example is shown in FIG. 1 (A), where the vertical axis represents the membrane potential and the horizontal axis represents the time.

Subsequently, also in the artificial exciter membrane of the comparative example, as in the case of the artificial exciter membrane of the example, self-excited oscillation was performed by applying a pressure of 20 cmH ₂ O and a current of 0.5 μA, and the artificial exciter membrane of the example. The ultraviolet light and the visible light were sequentially irradiated in the same manner as in the above case. However, the oscillation state of the artificial exciter membrane of the comparative example was not changed by the light irradiation. The state of the optical response of the above-mentioned oscillation of the artificial exciter membrane of the comparative example is shown in FIG. 1 (B), in which the vertical axis represents the membrane potential and the horizontal axis represents the time.

As described above, it was found that the artificial exciter membrane according to the present invention can control stop / start of self-excited oscillation by selectively irradiating the artificial exciter membrane with ultraviolet light and visible light.

The above is the description of the embodiments of the present invention. However, the present invention is not limited to the above-described embodiments, and various modifications as described below can be added.

For example, the mixing ratio of DOPH and azobenzene described in the examples, and the adsorption amount of the mixture of DOPH and azobenzene on the support are merely examples. It should be understood that these values are variously changed according to the design within the range where the self-excited oscillation and the light controllability can be secured. The adsorption amount can be controlled easily by changing the amounts of DOPH and azobenzene dissolved in benzene.

Further, the support used in the examples is merely an example,
The material, the diameter of the micropores, etc. can be changed according to the design. In principle, it can be said that the support may have only one micropore.
Further, for example, a support made of an inorganic material such as a silicon substrate provided with micropores may be used.

In addition, in the above-described embodiments, in order to facilitate the description of the effect, the case where various characteristics are measured was described by exemplifying a specific experimental apparatus. However, it is clear that the effect of the artificial exciter membrane of the present invention is not achieved only by a specific device.

(Effect of the invention) As is clear from the above description, the photoresponsive artificial exciter membrane of the present invention is said to generate a membrane potential and self-oscillate when a solution having a different salt concentration is partitioned by the photoresponsive artificial exciter membrane. In addition to the physical properties of the conventional artificial exciter film, the artificial exciter film has new physical properties that the self-excited oscillation is stopped when the artificial exciter film is externally irradiated with ultraviolet light, and the self-excited oscillation is restarted when the visible light is irradiated.

Therefore, when a device imitating a nerve cell, a five-sense sensor or the like is constructed by using the photoresponsive artificial exciter membrane of the present invention, there is an advantage that the device can be reversibly controlled without contact.

[Brief description of drawings]

1 (A) and 1 (B) are diagrams for explaining the photoresponsiveness of oscillation of the artificial exciter membranes of Examples and Comparative Examples, and FIG. 2 shows the device used to confirm self-sustained pulsation. FIG. 3 is a diagram for explanation, FIG. 3 is a diagram showing a relationship between an applied pressure and an oscillation frequency, and FIGS. 4 (A) and 4 (B) are diagrams for explaining a mechanism of self-excited oscillation. 11 ... Support, 11a ... Micropores 13 ... Salt solution with low salt concentration, 15 ... Salt solution with high salt concentration 17 ... Lipids in oil drop state, 19 ... Cation 21 ... Multilayer state Lipids, etc. 31 …… Artificial exciter membrane of Comparative Example or Example 33a …… First electrolytic cell, 33b …… Second electrolytic cell 35a …… 100mM KCl aqueous solution 35b …… 5mM KCl aqueous solution 37a, 37b, 43a, 43b …… Standard electrode 37c …… Light transmission window, 39 …… DC power supply 41 …… Measuring instrument, 45 …… Manometer a …… External pressure, 47 …… Dark box 49 …… Light source.

Front Page Continuation (72) Inventor Hiroo Miyamoto 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd. (56) References JP 63-191929 (JP, A) JP 63- 32364 (JP, A)

Claims (1)

(57) [Claims] 1. A method of contacting one surface thereof with a high-concentration salt solution,
An artificial excitable membrane capable of self-oscillation in which the other surface is brought into contact with a low-concentration salt solution to generate a membrane potential change, and a dioleyl phosphate represented by the following formula on a support having micropores and the following formula An optically responsive artificial exciter film, characterized in that it adsorbs a mixture with the indicated azobenzene, and the start and stop of self-excited oscillation are controlled by visible light and ultraviolet light.