JP2004099418A - Method for producing integrated porous material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a material coated with an oxide layer corresponding to a compound to be separated on a gel framework which forms macro-pores of a separation medium. <P>SOLUTION: A porous gel which consists of a siloxane network with continuous through holes is produced by causing sol-gel transition accompanied by phase separation. A substance to be a precursor of an objective metal oxide is introduced into the pores of the porous gel and a hydrolysis/polycondensation reaction with a silanol group at pore surfaces is caused and then an integrated porous material is produced. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a metal oxide layer on the surface of a porous material having a sharp pore size distribution obtained by using silica or an alkyl-modified polysiloxane or a copolymerized composition thereof by utilizing hydrolysis of a metal alkoxide or the like. The present invention relates to a method for producing an integral porous material coated with, and an integral separation medium obtained thereby. The separation medium of the present invention is suitably used for analyzing chemical substances in cells such as nucleic acids and proteins.
[0002]
[Prior art]
Since titanium oxide (titania) and zirconium oxide (zirconia) strongly adsorb compounds containing a phosphate group, porous materials coated with these oxides are used as a liquid phase separation medium such as liquid chromatography. be able to. Particularly, it is suitable as a separation medium for analyzing a chemical substance (nucleic acid or protein) in a cell containing a phosphate group.
A conventional separation medium made of titania or zirconia is a material in which a particulate material is packed in a column. This column is generally called a frit with a relatively low porosity, in which a particulate inorganic filler is packed into a capillary tube by a physical method and the particles are prevented from moving and changing the packed state. The part is made by sealing the ends of the capillary.
[0003]
On the other hand, by a sol-gel method utilizing phase separation, an integrated porous material including an organic-inorganic hybrid composition containing a metal oxide and a siloxane bond and a hydrocarbon chain forming a silicon dioxide (silica) or gel network. Is known to be manufactured with good reproducibility (for example, see Patent Document 1). An appropriately prepared porous material obtained by a sol-gel method utilizing phase separation requires extremely low pressure (column pressure) required for liquid sending, and can be expected to have extremely high separation efficiency as a separation medium for liquid chromatography.
[0004]
[Patent Document 1]
JP-A-10-182260 [0005]
[Problems to be solved by the invention]
However, a column packed with particles requires a complicated packing method and requires a long time, and it is difficult to reproduce a packed state having excellent separation performance. Further, as the column length increases, uniform packing of fine particles becomes extremely difficult, so that it is difficult to improve the separation performance by increasing the column length. In addition, in a column packed with particles, there is a problem that air bubbles are often generated in the sample solution in the space between the frit and the packed bed, thereby deteriorating the separation performance.
On the other hand, a column using an integrated porous body has not been sufficiently developed conventionally, mainly because it is difficult to control the structure of the carrier column and to improve the performance thereof.
Therefore, the present inventor studied that a gel composed of a siloxane network was formed so as to have continuous through holes in a micrometer region, and the surface thereof was formed of an oxide layer such as titanium oxide (titania) and zirconium oxide (zirconia). It has been found that the material coated with is able to flow at a lower pressure than the packed column, and it is possible to arbitrarily control the size of the gel skeleton, which greatly affects the separation efficiency.
[0006]
Further, it is difficult to prepare a separation medium in a capillary having a small diameter by filling particles, but in the case of a gel having continuous through-holes, it is only necessary to introduce a reaction solution into the capillary and solidify it. The separation medium can be produced even in a very thin capillary having a diameter of 50 μm or less or in a fine groove (a so-called minute space) formed on a substrate.
The present invention provides a material in which the gel skeleton forming the macropores of the separation medium is coated with an oxide layer corresponding to the compound to be separated.
[0007]
[Means for Solving the Problems]
That is, the present invention produces a porous gel composed of a siloxane network having continuous through-holes by causing a sol-gel transition accompanied by phase separation, and aims within the pores of the porous gel. A monolithic porous material characterized by producing a monolithic porous material by introducing a substance serving as a precursor of a metal oxide and causing a hydrolysis / polycondensation reaction with silanol groups on the surface of the pores Is a manufacturing method.
Further, the porous gel is produced by dissolving a water-soluble polymer in an acidic aqueous solution, adding a metal compound having a hydrolyzable functional group thereto, and causing a hydrolysis / polycondensation reaction. The porous gel has a through-hole having a pore diameter of 100 nm or more, preferably 200 to 10000 nm, and a continuous three-dimensional mesh-like pore, and pores having a pore diameter of 50 nm or less formed on the inner wall surface of the through-hole. The volume ratio of the pores in the pores is 10% or more, preferably 20%, and more preferably 40% or more.
The porous body according to the present invention can be formed in a space of a limited shape and size surrounded by a rigid container wall, and the substantial porosity is extremely close to 100% in such a limited space. It is also possible to prepare. Since the macropores having a diameter of 100 nm or more are formed as regions occupied by the solvent phase generated during phase separation, they are formed without burning or thermal decomposition by a normal drying operation. When forming a so-called co-continuous structure that is entangled and continuous, an extremely sharp size distribution can be obtained. By adjusting to a higher porosity and a larger average size, it is possible to reduce the pressure loss of the integrated reactive porous column. The liquid can be passed by driving with a pump.
[0008]
Phase separation is a widespread phenomenon in which a region having a component different from the starting component is generated by precipitation or precipitation in a material manufacturing process. Generally, in a sol-gel reaction system, a phase rich in a network-forming component causing gel formation is formed. Separation occurs between a (gel phase) and a phase rich in a solvent component that does not cause gel formation (solvent phase). In forming each phase region, diffusion of components against the concentration gradient occurs using the difference in chemical potential as a driving force, and mass transfer continues until each phase region reaches the equilibrium composition at the given temperature and pressure. I do.
[0009]
The precursor of the network component causing gel formation used in the sol-gel reaction includes metal alkoxides, complexes, metal salts, organically modified metal alkoxides, organic cross-linked metal alkoxides, and partial hydrolysis products and partial polymerization products thereof. Can be used. Sol-gel transition by changing the pH of water glass or other aqueous silicate solutions can be used as well.
[0010]
The water-soluble polymer is a water-soluble organic polymer that can theoretically be formed into an aqueous solution having an appropriate concentration, and is uniformly dispersed in a reaction system containing an alcohol generated by a metal compound having a hydrolyzable functional group. Any substance that can be dissolved may be used, but specifically, a sodium or potassium salt of polystyrene sulfonic acid, which is a polymer metal salt, polyacrylic acid, which is a polymer acid and dissociates into a polyanion, or a polymer base Polyallylamine and polyethyleneimine which produce polycations in aqueous solution, or polyethylene oxide, polyvinylpyrrolidone, polyacrylamide, or polyoxyethylene-polyoxypropylene-polyoxy, which is a neutral polymer and has an ether bond in the main chain Ethylene block copolymers and the like are preferred. Further, an organic solvent having a relatively high polarity, specifically, a polyhydric alcohol, an acid amide, or a surfactant may be used in place of the organic polymer, in which case, as the polyhydric alcohol, ethylene glycol and glycerin are used. Formamide is most suitable as acid amide, and cationic surfactant such as quaternary ammonium salt and nonionic surfactant such as polyoxyethylene alkyl ether are most suitable as surfactant.
[0011]
As the metal compound having a hydrolyzable functional group, a metal alkoxide or an oligomer thereof can be used. For example, those having a small number of carbon atoms, such as a methoxy group, an ethoxy group, and a propoxy group, are preferable. As the metal, a metal of an oxide finally formed, for example, Si, Ti, Zr, or Al is used. One or more of these metals may be used. On the other hand, any oligomer may be used as long as it can be uniformly dissolved and dispersed in alcohol, and specifically, up to about 10-mers can be used. Alkoxyalkoxysilanes in which some of the alkoxy groups of these silicon alkoxides are substituted with alkyl groups, crosslinked alkoxides in which two or more metals are linked by a crosslinked structure mainly composed of hydrocarbons, and 10 Oligomer up to about a monomer is preferably used. Alkyl-substituted metal alkoxides in which the central metal element is replaced with titanium, zirconium, aluminum or the like instead of silicon can also be used.
[0012]
Further, in the present invention, when producing the porous gel, the thermally decomposable compound may be dissolved in the reaction solution in advance. By dissolving the pyrolyzable compound in the reaction solution in advance, heating the wet gel causes the pyrolyzable compound to thermally decompose and raises the pH of the solvent in contact with the inner wall surface of the skeletal phase. I do. Then, the solvent erodes the inner wall surface and changes the unevenness of the inner wall surface, thereby gradually expanding the pore diameter. In the case of a gel containing silica as the main component, the degree of change is very small in the acidic or neutral region, but as the thermal decomposition becomes active and the basicity of the aqueous solution increases, the parts constituting the pores dissolve. However, by re-precipitation on a flatter portion, a reaction of increasing the average pore diameter becomes remarkable.
Specific examples of the thermally decomposable compound include urea and organic amides such as hexamethylenetetramine, formamide, N-methylformamide, N, N-dimethylformamide, acetamide, N-methylacetamide, N, N-dimethylacetamide. Although the pH value of the solvent after heating is an important condition, there is no particular limitation as long as the compound makes the solvent basic after thermal decomposition.
The coexistence of the thermally decomposable compound depends on the type of the compound. For example, in the case of urea, the amount is 0.05 to 0.8 g, preferably 0.1 to 0.7 g, per 10 g of the reaction solution. The heating temperature is, for example, 40 to 200 ° C. in the case of urea, and the pH value of the solvent after heating is preferably 6.0 to 12.0.
Further, a compound which produces a compound having a property of dissolving silica, such as hydrofluoric acid, by thermal decomposition can be similarly used.
[0013]
The acidic aqueous solution is preferably one having a mineral acid such as hydrochloric acid or nitric acid of 0.001 N or more, or one having an organic acid such as formic acid or acetic acid of 0.1 N or more.
Hydrolysis can be achieved by storing the solution at room temperature to 80 ° C. for 0.5 to 3 hours. The gelled product is left at 40 to 80 ° C for several hours to several tens of hours, dried, and then heated at about 600 to 1000 ° C.
[0014]
In the present invention, a substance serving as a precursor of a target metal oxide is introduced into the pores of the produced porous gel to cause a hydrolysis / polycondensation reaction with silanol groups on the surface of the pores.
The target metal oxides include titanium oxide and zirconium oxide, which have a high affinity for phosphate compounds, as well as aluminum oxide, iron oxide, and nickel oxide. Any metal oxide exhibiting surface chemical characteristics different from those described above may be used, and is not limited thereto.
Examples of the precursor of the metal oxide include a metal alkoxide having a corresponding central metal, a β-diketone complex, an organic acid salt such as oxalate and acetate, and an inorganic acid such as nitrate, sulfate and chloride. Acid salts.
The hydrolysis / polycondensation reaction can be performed by immersing the porous gel in the metal oxide solution, and the concentration of the metal oxide solution is preferably 2 to 20% by weight in terms of oxide. The hydrolysis / polycondensation reaction can be achieved by storing the solution at 20 to 80 ° C for 2 to 20 hours.
[0015]
According to the production method of the present invention, it is possible to produce an integrated separation medium suitably used for analyzing intracellular chemical substances such as nucleic acids and proteins.
Further, the material of the present invention can be manufactured in a member having a gap of 1 mm or less. The member having a gap of 1 mm or less is composed of, for example, a capillary tube, two flat plates, a honeycomb, or the like. In the case of a capillary tube, the gap corresponds to the inner diameter, and in the case of two flat plates, the gap corresponds to the interval between opposed flat plates. I do. These capillaries, flat plates and the like are made of, for example, silica glass, and the gap is preferably 30 to 200 μm. When a flat plate is used, the size of the flat plate itself is preferably 0.3 to 10 mm in thickness, 3 to 500 mm in width, and 3 to 500 mm in length. The number of flat plates is not limited to two, and a plurality of flat plates may be sequentially faced to form a plurality of gaps. Further, the number of gaps in the honeycomb is not limited. A multi-capillary can be manufactured by using these plural flat plates and honeycombs. Further, a plurality of capillaries may be bundled.
[0016]
【Example】
The experimental procedure is as shown in FIG.
(Example 1)
First, 0.7 g of polyethylene glycol and 0.5 g of urea were dissolved in 10 ml of a 0.01 molar acetic acid aqueous solution, and 5 ml of tetramethoxysilane was added thereto with stirring to carry out a hydrolysis / polycondensation reaction. The obtained homogeneous solution was allowed to stand at 40 ° C. in a closed container to gel. Thereafter, the sample is aged at 120 ° C. for 2 hours in a sealed state, subsequently dried at 60 ° C., and finally heat-treated at 600 ° C. for 2 hours to obtain a macroporous silica sample having a narrow pore size distribution in a micrometer region. Obtained.
Next, the columnar macroporous silica was immersed in a 2-propanol solution (25% by volume) of titanium tetraisopropoxide as a metal alkoxide at 40 ° C. for 1 hour. By this operation, the surface of the silica skeleton forming the macropores is coated with the titanium oxide layer. Further, the sample was heat-treated at 500 ° C. for 3 hours to convert the titanium oxide layer into an anatase crystal layer.
The thus obtained columnar sample of titanium oxide-coated macroporous silica was covered with a resin on the side, and connection parts to a liquid chromatography device were attached at both ends to form a separation column for liquid chromatography. When the retention behavior of adenosine, adenosine monophosphate (AMP), adenosine diphosphate (ADP), and adenosine triphosphate (ATP) was examined using this column, different retention times were obtained as shown in FIG. It was found that these mixtures were well separated.
[0017]
(Example 2)
In the same manner as in Example 1, the surface of the silica skeleton was coated with a titanium oxide layer, and heat treatment was performed. Thereafter, a titanium oxide precursor solution was repeatedly passed through, followed by dry heat treatment. By this operation, the thickness of the titanium oxide layer can be increased, as shown in FIG. 3, by electron microscopy (SEM), X-ray diffraction measurement (XRD) and weight measurement (weighing with a precision electronic balance). confirmed. 3A shows untreated silica, FIG. 3B shows one coating, and FIG. 3C shows five coatings. FIG. 3 shows an electron microscope observation (SEM) diagram, an X-ray diffraction measurement (XRD) diagram, and a column weight in order from the top.
The single coating resulted in a weight gain of 126% and the five coatings resulted in a weight gain of 245%. At this time, the thickness of the titanium oxide layer was calculated to be about 22 nanometers for one coating and about 120 nanometers for five coatings, and the thickness of the coating layer increased almost in proportion to the number of coatings. The X-ray diffraction pattern gave clear diffraction lines specific to the anatase phase titanium oxide (IV) as the number of coatings increased, and thus it was confirmed that the present example can cover the anatase type titanium oxide.
[0018]
(Example 3)
A reaction solution having the same composition as that of Example 1 was prepared, and a macroporous silica capillary was obtained in the same manner as in Example 1 except that the container to be gelled was a fused silica capillary having an inner diameter of 100 μm.
In the same manner as in Example 1, a titanium oxide precursor solution was passed through the inside of the macroporous silica, and dried and heat-treated to obtain a titanium oxide-coated macroporous silica capillary.
When separation of the phosphate compound was attempted in the same manner as in Example 1, good separation was confirmed.
[0019]
【The invention's effect】
According to the present invention, a gel formed of a siloxane network having continuous through-holes in a micrometer region, and the surface of which is coated with an oxide layer such as titanium oxide (titania) and zirconium oxide (zirconia) is The liquid can be passed at a pressure lower than that of the packed column, and the size of the gel skeleton, which greatly affects the separation efficiency, can be arbitrarily controlled.
[Brief description of the drawings]
FIG. 1 is a diagram showing the experimental procedure of the present invention. FIG. 3 is a diagram illustrating the retention behavior. FIG. 3 is a diagram in which the thickness of a titanium layer is measured by electron microscopy (SEM) and weight measurement, and the anatase crystal phase is confirmed by X-ray diffraction measurement (XRD).

Claims (7)

By causing a sol-gel transition accompanied by phase separation, a porous gel having continuous through-holes and comprising a siloxane network is produced, and a precursor of a target metal oxide is formed in the pores of the porous gel. A method for producing an integral porous material, comprising introducing a substance to cause a hydrolysis / polycondensation reaction with a silanol group on the surface of a pore to produce an integral porous material. 2. The porous gel is produced by dissolving a water-soluble polymer in an acidic aqueous solution and adding a metal compound having a hydrolyzable functional group thereto to cause a hydrolysis / polycondensation reaction. A method for producing an integrated porous material. 3. The method according to claim 1, wherein the porous gel is produced in a member having a gap of 1 mm or less. The target metal oxide is a metal oxide, such as titanium oxide, zirconium oxide, aluminum oxide, iron oxide, and nickel oxide, which exhibits surface chemical properties different from silanol groups that are often present in a siloxane gel as a base material. 4. The method for producing an integrated porous material according to any one of 1 to 3. The precursor of the metal oxide is a metal alkoxide having the corresponding central metal, a β-diketone complex, and an organic acid salt such as oxalate and acetate, and an inorganic acid such as nitrate, sulfate and chloride. The method for producing an integrated porous material according to claim 4, which is a salt. An integrated separation medium manufactured according to claim 1. An analytical method, wherein an intracellular chemical substance is analyzed using the integrated separation medium according to claim 6.

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