JP2000294033A - Proton conductive polymer film using dna - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a film showing proton conductivity in a dry state by compositing the film of doping strong acid to a DNA film. SOLUTION: A DNA film is produced by casting DNA in aqueous solution of sodium salt. Because DNA does not dissolve in polarized solvent, a membrane of sodium salt is dipped in such organic solvent to become insoluble in water. This insoluble membrane is dipped again in polarized organic solvent added with strong acid, and the strong acid is doped. For example, DNA sodium salt extracted from salmon's spermatozoon is dissolved in water and solution is extended on a substrate having a smooth surface to produce the DNA film. A film is dipped in the polarized solvent such as methanol or ethanol to become the DNA film. Doping of the strong acid is performed by previously dissolving phosphate or the like in a dip solution. The film is separated from the substrate, cleaned, and dried to provide a proton conductive polymer film having 10-2-10-5 Scm-1 conductivity in a dry state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a proton conductive polymer film using DNA and a method for producing the same.

[0002] Proton conductive polymer films are useful as fuel cell membranes or as gas sensors that conduct gas molecules in the ionic state.

[0003] The proton conductive polymer films known hitherto are divided into two types. One has a structure in which a side chain having a sulfonic acid group or a carboxylic acid group at the terminal is grafted to a polyfluoroethylene skeleton, and transfers a proton as a hydronium ion in a water-containing state. Therefore, maintaining conductivity at 100 ° C. (boiling point of water) or more is a problem. Another type is a complex of a basic polymer such as poly (ethylene imine) and poly (acrylamide) and a strong acid, and can exhibit proton conductivity in a dry state. Also, it has been found that by using phosphoric acid among the strong acids, no decrease in conductivity is observed even in a temperature region of 100 ° C. or higher.

[0004]

It is an object of the present invention to provide a new proton conductive polymer film in which the latter type, that is, a strong acid forms a complex with a basic polymer and exhibits proton conductivity in a dry state.

[0005] This problem is solved by the present invention by providing a proton conducting polymer film which is complexed by doping a DNA film with a strong acid.

[0006]

Detailed Discussion As is well known, DNA has a double helix structure, in which the base portion of one strand is connected to the base portion of the other strand which is complementary to the base portion by a hydrogen bond, such that Many base pairs are stacked perpendicular to the helical axis. It is already known that various molecules or compounds can be intercalated into this part of the DNA, but no attempt has been made to dope a strong acid.

[0007] Okahata et al. Am. Chem. So
c. , 118: 10679 (1996) discloses D-soluble organic solvents obtained by ion exchange between DNA and lipids.
It has been reported that a dye is intercalated between base pairs of DNA by forming an independent film from a solution of NA and immersing the film in an aqueous solution of ethidium bromide dye.

By applying this principle to a DNA molecule with a strong acid, a complex of the strong acid and the DNA molecule can be formed. However, when doping with a strong acid, the use of the DNA-lipid complex of Okahata et al. Is not appropriate. Strong acid is D
This is because the lipid ionically bonded to the phosphate group of NA is eliminated, thereby impairing the integrity of the film.

Therefore, to dope a strong acid, DN
Casting of the aqueous solution of the sodium salt of A gives D
Make NA film. Since DNA is insoluble in polar organic solvents such as methanol and ethanol, immersing a sodium salt membrane in such an organic solvent renders the membrane insoluble in water. Then, the insoluble film thus obtained is immersed again in a polar organic solvent to which a strong acid has been added, thereby doping the strong acid.

Alternatively, the insolubilization of the film and the doping of the strong acid can be carried out in one step. In that case, the sodium salt film may be immersed in a polar solvent containing a strong acid. Examples of strong acids that can be used for this purpose are hydrogen chloride, sulfuric acid,
Including phosphoric acid, methanesulfonic acid and ethanesulfonic acid, examples of polar organic solvents include lower alkanols such as methanol, ethanol, isopropanol and the like. Phosphoric acid solutions in methanol or ethanol are preferred. 100 ℃
This is because there is little decrease in conductivity in the above temperature range and the heat resistance is excellent. The concentration of the strong acid in the solution is generally 5 to 50%, preferably 10 to 30%.

Although DNA of any origin can be used, DNA sodium salt extracted from salmon sperm is readily available. DNA films can be made by dissolving the sodium salt in water to a concentration suitable for casting, and casting this solution onto a substrate having a smooth surface. It is preferable to use a substrate having releasability, such as Teflon. Then, after at least partially removing water from the film, the film is immersed in a polar solvent such as methanol or ethanol to obtain a water-soluble DNA film.

The doping of the strong acid may be carried out by dissolving the strong acid in the above immersion solvent, adding the strong acid to the organic solvent during the immersion, or pulling the film from the organic solvent and then immersing the film in the strong acid solution. Can be done by Thereafter, the film is peeled from the substrate, washed well, and dried to obtain the proton conductive polymer film of the present invention. At this time, by stretching the film in one direction before drying, a film in which DNA molecules are oriented parallel to the stretching direction is obtained.

In general, the mechanical strength of a DNA film is not as high as that of a plastic film. Therefore, when a film having high mechanical strength is desired, a porous plastic film is used for reinforcement, and the DNA film of the present invention can be formed thereon as a skin layer. This technique is applied to a reverse osmosis membrane or the like which is required to withstand high pressure, and is known per se. However, the reinforcement must be able to withstand the processing and use conditions of the film according to the invention.

Thus, according to the present invention, the dried state (100
(° C. or more), a proton conductive film having a conductivity on the order of 10 ⁻² to 10 ⁻⁵ Scm ⁻¹ is obtained. In a water-containing state, the conductivity shows a value two to three orders of magnitude higher.

Hereinafter, the present invention will be further described with reference to examples.

Example 1 A 5% aqueous solution of commercially available salmon sperm DNA sodium salt was cast on a Teflon plate, and most of the water was removed by air drying. The resulting film was immersed in methanol overnight with the support, pulled up once, phosphoric acid was added to methanol to a concentration of 20 vol%, stirred until uniform, and then the upper film was immersed in it all day and night. , Raised. The film was alternately washed with deionized water and methanol, the solvent was removed by air drying, and then gently peeled off from the support to obtain a milky white translucent DNA film having a thickness of about 100 μm.

The conductivity of the film in the water-containing state was in the order of 10 ^-2 Scm ^-1 at 80 ° C.
The conductivity after drying in an oven at 120 ° C. until it no longer showed a loss on heating was of the order of 10 ⁻³ Scm ⁻¹ at 80 ° C. and 160 ° C.

Example 2 A proton conductive DNA film was obtained in the same manner as in Example 1, except that ethanesulfonic acid was used instead of phosphoric acid, and the acid concentration during re-immersion was 20 vol%. The conductivity at 80 ° C. in a water-containing state and the conductivity at 160 ° C. in a dry state were 10 ⁻³ , respectively.
They were on the order of Scm ^-1 and 10 ^-5 .

Example 3 Example 3 was carried out in the same manner as in Example 1 except that sulfuric acid was used instead of phosphoric acid, and the sulfuric acid concentration during reimmersion was 20 vol%. The electrical conductivity at a water-containing state of 80 ° C. and a dry state of 140 ° C. were 10 ⁻³ Scm ⁻¹ and 10 ⁻⁵ Scm ⁻¹ , respectively.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) // H01M 8/02 C12N 15/00 A 5H026 F term (reference) 4B024 AA20 CA01 4C057 BB02 BB04 CC03 DD01 MM04 4F071 AA70 AB13 AB23 AB25 AC05 AC14 AG12 AH02 AH15 BA02 BB02 BC01 4J002 AJ001 DD016 DG046 DH026 EC037 GD00 5G301 CA30 CD01 CD10 CE01 5H026 AA06 BB03 CX04 EE17

Claims (6)

[Claims] 1. A proton conductive polymer film which is complexed by doping a DNA film with a strong acid. 2. The proton conductive polymer film according to claim 1, wherein the complexed strong acid is hydrogen chloride, sulfuric acid, phosphoric acid, methanesulfonic acid or ethanesulfonic acid. 3. A method for producing a proton conductive polymer film, comprising immersing a DNA sodium film in a strong acid in a polar organic solvent and doping the insolubilized film with a strong acid. 4. The method according to claim 3, wherein the strong acid is hydrogen chloride, sulfuric acid, phosphoric acid, methanesulfonic acid or ethanesulfonic acid. 5. The method according to claim 3, wherein the polar organic solvent is methanol or ethanol. 6. The method of claim 3 further comprising the step of stretching the insolubilized and doped film.