JP2005194155A - Surface modifying method for monolithic silica - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To modify the surface of a silica by the adsorption action between functional groups by infiltrating a reagent, with which the surface of the silica is desired to be modified, into the silica. <P>SOLUTION: In this method, a dimethyl ethylene diamine and an octadecyl isocyanate are mutually reacted in a toluene solvent at 60 °C to synthesize a dimethylethylene diamine having a hydrophobic group, and 0.05 g of the synthesized reagent is dssolved in 50 mL of a methanol-water (75/25, v/v) at room temperature. The dissolved solid phase reagent is passed through the monolithic silica at room temperature at a flow velocity of 0.05 mL/min. for 15 hours or longer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to surface modification of a porous continuous (monolith type) silica prepared by a sol-gel method using phase separation. The functional group to be modified is, for example, an ion exchange group, a chiral separation group or the like, and the modification method is not limited to a conventional chemical bond but limited to adsorption interaction.

In high-performance liquid chromatography, in a system that normally uses particle-packed silica, the silica load pressure increases as the flow rate increases, and the separation performance decreases. Therefore, in order to maximize the performance of packed silica, the performance required for a hardware system including a detector, a data processor and the like is adjusted, which is measured at an optimum flow rate.
High performance liquid chromatography is one of the analytical tools supported in a wide range of fields. Currently, it is difficult to separate various solutes at once in chromatography, and it is also difficult to separate solutes in a short time, and many studies have been made to overcome these problems. In high performance liquid chromatography, solute separation medium is silica, which is usually filled with particles made of inorganic or organic substances. In such a particle-packed silica, there is an optimum flow rate at which the performance of the silica can be maximized. However, when high-speed separation is attempted and the sample flow rate is increased, the silica load pressure increases and the separation performance decreases.
Here, in order to cope with high-speed separation, so-called monolithic silica that does not rely on packing has been proposed (Patent Document 1). This silica is a double-structured silica having a macro through-hole and pores formed on the inner wall surface of the through-hole using a sol-gel method porous glass manufacturing method.

JP-A-6-265534

In the conventional monolithic silica, ion exchange groups and chiral separation groups are modified on the silica surface by chemical bonds. However, in order to react with the functional group on the silica surface, high temperature or high pressure conditions were required.
In the present invention, the functional group to be modified is, for example, an ion exchange group, a chiral separation group or the like, and the modification method is not limited to a conventional chemical bond but limited to adsorption interaction.
The adsorption interaction is an interaction that does not cause a chemical change, and includes, for example, a hydrophobic interaction, a hydrogen bond, a dispersion force, a dipole interaction, and an electrostatic attractive force. These interactions are exhibited between the functional group chemically bonded to the silica surface or the silica surface and the functional group possessed by the reagent to be modified. For example, the hydrophobic interaction is an interaction between the hydrophobic group chemically bonded to the silica surface and the hydrophobic group of the modifying reagent, specifically, an octadecyl group chemically bonded to the silica surface and an ion It is modified by interaction with the octadecyl group of a modifying reagent obtained by reacting octadecylisocytanate with dimethylethylenediamine as an exchange group. As an example of the interaction by hydrogen bonding, the interaction between the silanol group and the nitro group of R-(-)-N- (3,5-dinitolbenzoyl) -α-phenylglycine, which is a chiral separation reagent, is used. Modified by action.
According to the present invention, if the reagent to be modified penetrates into the monolithic silica, the modification is performed by the adsorption interaction between the functional groups. Furthermore, according to the present invention, the stationary phase reagent can be washed and easily regenerated.

That is, the present invention is a method for surface modification of monolithic silica comprising the following steps.
Step for preparing monolithic silica Step for dissolving a stationary phase reagent having a functional group in a solvent Step for fixing the dissolved stationary phase reagent to monolithic silica by adsorption interaction

Here, the functional group is an ion exchange group or a chiral separation group.
Examples of the ion exchange group include —SO 3 H, —COOH, —PO (OH) 2, —N (CH 3) 3 Cl, —NH 2, —NHR, —NR 2 and the like.
Examples of the hydrophobic group to be bonded include hydrocarbon groups such as alkyl groups and phenyl groups. Specific examples include an octadecyl silylating agent and a trimethyl silylating agent. Examples of the octadecyl silylating agent include octadecyldimethyl-N, N-diethylaminosilane, and examples of the trimethylsilylating agent include 1,1, 1,3,3,3-hexamethyldisilazane and the like can be used.
Examples of the reagent having a chiral separating group include 2-amino-1- (3 chlorophenyl) ethanol, 2-chloromandelic acid, d-tryptophan, 5 chloro-2-pentanol, 2-oxylanilacetate, 2- Examples include oxyanilanisole, 1,3-butanediol, 1,2-propanediol, 4chloro-3hydroxybutanoate, 2chloro-4hydroxybutanoate, and 2-hydroxy-4-phenylbutyric acid. Although it can, it is not limited to these.
The solvent for dissolving the stationary phase reagent is not particularly limited as long as the reagent can be dissolved. For example, water, methanol, acetonitrile, tetrahydrofuran, pyridine and the like can be used.
The concentration of the solvent is not particularly limited, and for example, 1 μmol to 1 mol is preferable.
The dissolution temperature may be either room temperature or warming. Preferably, it is 20-80 degreeC.

  The reagent may be immobilized by either a liquid flow method or a batch method. In the liquid flow method, the reagent is allowed to flow at a flow rate of 0.01 to 1 mL / min, preferably 0.05 to 0.1 mL / min. In the case of a batch method, immerse in the solution for 12 hours or longer. The temperature is 20 to 80 ° C., preferably in the vicinity of room temperature, in both the liquid passing method and the batch method.

  Monolithic silica is preferably prepared by a sol-gel method utilizing phase separation, and this silica exhibits high speed and high separation performance. In addition, since monolithic silica enables liquid feeding at a high flow rate, it has an advantage that separation of compounds can be achieved in a short time. By using this monolith type silica for multidimensional chromatography, it becomes possible to separate various solutes in a short time.

The monolith type silica in the present invention is an inorganic porous continuous body in which macropores having a diameter of 100 nm to 10000 nm and a skeleton have a co-continuous structure, and the skeleton has mesopores having a diameter of 2 nm to 50 nm.
The inorganic porous continuum is obtained by causing a reaction solution containing silica as a main component to undergo a sol-gel transition accompanied by phase separation. Examples of the precursor of the network component that causes gel formation used in the sol-gel reaction include 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 and other silicate aqueous solutions can be used as well.
More specifically, the means for achieving the above-mentioned object is to generate a water-soluble polymer and a compound that thermally decomposes in an acidic aqueous solution, add a metal compound having a hydrolyzable functional group, and perform a hydrolysis reaction. After the product has solidified, the wet gel is preferably heated to thermally decompose the low molecular weight compound previously dissolved at the time of gel preparation, and then dried and heated.

   Here, the water-soluble polymer is theoretically a water-soluble organic polymer that can be formed into an aqueous solution having an appropriate concentration, and in a reaction system including an alcohol generated by a metal compound having a hydrolyzable functional group. The polymer metal salt is a sodium salt or potassium salt of polystyrene sulfonic acid, which is a polymer metal salt, polyacrylic acid which is a polymer acid and dissociates to form a polyanion, Polyallylamine and polyethyleneimine, which are molecular bases that generate polycations in aqueous solution, or neutral polymers, such as polyethylene oxide having an ether bond in the main chain and polyvinylpyrrolidone having a carbonyl group in the side chain are suitable. . In addition, formamide, polyhydric alcohol, or surfactant may be used in place of the organic polymer. In this case, glycerin is optimal as the polyhydric alcohol, and polyoxyethylene alkyl ethers are optimal as the surfactant.

   As the metal compound having a hydrolyzable functional group, a metal alkoxide or an oligomer thereof can be used, and those having a small number of carbon atoms such as a methoxy group, an ethoxy group, and a propoxy group are preferable. Further, as the metal, an oxide metal finally formed, for example, Si, Ti, Zr, or Al is used. The metal may be one type or two or more types. On the other hand, any oligomer can be used as long as it can be uniformly dissolved and dispersed in alcohol.

   Moreover, as acidic aqueous solution, the thing of 0.001 mol concentration or more of mineral acids, such as hydrochloric acid and nitric acid, or 0.01 mol concentration or more of organic acids, such as an acetic acid and formic acid, is preferable normally.

  The phase separation and gelation can be achieved by storing the solution in the groove of the plate-like member at room temperature of 40 to 80 ° C. for 0.5 to 5 hours. Phase separation / gelation is a process in which an initially transparent solution becomes cloudy, causing phase separation between a silica phase and an aqueous phase and finally gelling. By this phase separation / gelation, the water-soluble polymers are in a dispersed state and their precipitation does not substantially occur.

Specific examples of the thermally decomposable compound that coexists in advance include urea or hexamethylenetetramine, formamide, N-methylformamide, N, N-dimethylformamide, acetamide, N-methylacetamide, N, N-dimethylacetamide and the like. However, since the pH value of the solvent after heating is an important condition, there is no particular limitation as long as it is a compound that makes the solvent basic after thermal decomposition.
Although the thermally decomposable compound to coexist depends on the kind of the compound, for example, in the case of urea, it is 0.05 to 0.8 g, preferably 0.1 to 0.7 g, with respect to 10 g of the reaction solution. The heating temperature is preferably 40 to 200 ° C. in the case of urea, for example, and the pH value of the solvent after heating is preferably 6.0 to 12.0.
Moreover, what produces the compound with the property to melt | dissolve a silica like hydrofluoric acid by thermal decomposition can be utilized similarly.

In the above method, when a water-soluble polymer is dissolved in an acidic aqueous solution and a hydrolysis reaction is performed by adding a metal compound having a hydrolyzable functional group thereto, a solvent-rich phase and a skeleton phase are separated in the groove. A gel is formed. After the product (gel) has solidified, after a suitable aging time, the wet gel is heated to thermally decompose the amide compound dissolved in the reaction solution in advance, and the inner wall surface of the skeletal phase The pH of the solvent in contact with increases. The solvent erodes the inner wall surface, and gradually changes the pore size by changing the uneven state of the inner wall surface.
In the case of gels containing silica as the main component, the degree of change is very small in the acidic or neutral region, but as thermal decomposition becomes more vigorous and the basicity of the aqueous solution increases, the part constituting the pore dissolves. Then, by reprecipitation in a flatter portion, a reaction in which the average pore diameter becomes large occurs remarkably.

  In gels that have only three-dimensionally confined pores without huge pores, the elution substance cannot be diffused to the external solution even if it can be dissolved as an equilibrium condition. Remains in a considerable proportion. On the other hand, in a gel having a solvent-rich phase that becomes giant pores, there are many pores that are restricted only two-dimensionally, and exchange of substances with an external aqueous solution occurs frequently enough. In parallel with the development, small pores disappear and the entire pore size distribution does not spread significantly.

  In the heating process, it is effective to place the gel in a hermetically sealed condition so that the vapor pressure of the pyrolysis product is saturated and the pH of the solvent quickly takes a steady value.

  The heat treatment time required for the dissolution / reprecipitation reaction to reach a steady state and to obtain the corresponding pore structure varies depending on the size of the huge pores and the volume of the sample. It is necessary to determine the shortest processing time at which the pore structure does not change.

  The gel after the heat treatment becomes a dry gel in close contact with the tube wall in the groove by vaporizing the solvent. Since coexisting substances in the starting solution may remain in the dried gel, the target inorganic porous material can be obtained by heat treatment at an appropriate temperature and thermally decomposing organic matter. it can. In addition, drying is performed by leaving at 30-80 degreeC for several hours-several dozen hours, and heat processing is heated at about 200-800 degreeC.

The size of the monolith type silica is preferably 2 mm to 5 mm in inner diameter and 2 cm to 15 cm in length.
Furthermore, by using a hybrid gel for the production of a monolithic column, it is possible to cope with alkaline reagents.
The hybrid column includes an organometallic compound having a hydrolyzable functional group, a non-hydrolyzable organic functional group and a hydrolyzable functional group bonded via at least one metal / carbon bond. After the compound is hydrolyzed and polymerized to gel the reaction solution system, it can be prepared by removing unnecessary substances in the gel and heating.
Here, the capacity of the organometallic compound containing a non-hydrolyzable organic functional group and a hydrolyzable functional group bonded via at least one metal / carbon bond is an organic compound having a hydrolyzable functional group. It is preferably 1/10 or more of the capacity of the metal compound.
In addition, as an organometallic compound containing a non-hydrolyzable organic functional group and a hydrolyzable functional group bonded through at least one metal / carbon bond, for example, methyltrimethoxysilane, ethyltrimethoxysilane, vinyl Trimethoxysilane, γ-glyoxydoxypropyltrimethoxysilane, γ-glyxidoxypropyltriethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, N-β (aminoethyl) γ-aminopropyltri Methoxysilane, N-β (aminoethyl) γ-aminopropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, 3-acryloxypropyltrimethoxy Silane can be used.

For example, when immobilizing a reagent by hydrophobic interaction, a hydrophobic group is chemically bonded to the monolithic silica surface, and the hydrophobic group is also bonded to the reagent to be immobilized. It can be bound to hydrophobic groups on the silica surface by hydrophobic interactions. Examples of the hydrophobic group to be bonded include hydrocarbon groups such as alkyl groups and phenyl groups. Specific examples include an octadecyl silylating agent and a trimethyl silylating agent. Examples of the octadecyl silylating agent include octadecyldimethyl-N, N-diethylaminosilane, and examples of the trimethylsilylating agent include 1,1, 1,3,3,3-hexamethyldisilazane and the like can be used.

According to the present invention, various surface modifications are possible without impairing the characteristics of monolithic silica such as low pressure and high resolution. In the case of immobilization by the liquid passing method, the operation is simple.
Further, any stationary phase reagent having a hydrophobic group can be applied to reagents having various resolutions.

Experimental example 1 (Example 1 of hydrophobic interaction)
Next, a method for modifying the ion exchange group on the surface in which the hydrophobic group is modified by chemical bonding to the monolith type silica will be described.
(1) Preparation of monolithic silica In 10 ml of 0.01 molar acetic acid aqueous solution, 0.7 g of polyethylene glycol and 0.5 g of urea are dissolved, and 5 ml of tetramethoxysilane is added to this with stirring, followed by hydrolysis and polycondensation reaction. Went. The obtained uniform solution was allowed to gel in a closed container at 40 ° C. After that, it was aged at 120 ° C. for 2 hours in a sealed state, then dried at 60 ° C. and finally heat treated at 600 ° C. for 2 hours to obtain monolithic silica showing a narrow pore size distribution in the micrometer region. .
The hydrophobic group was bonded to the monolithic silica surface by reacting octadecyldiethylamine and the silanol group on the silica surface in a toluene solvent at 60 ° C. to chemically bond the octadecyl group to the silanol group.
(2) Preparation of stationary phase reagent Dimethylethylenediamine and octadecyl isocyanate were reacted in a toluene solvent at 60 ° C. to synthesize dimethylethylenediamine having a hydrophobic group. 0.05 g of the synthesized reagent was dissolved in 50 mL methanol-water (75/25, v / v) at room temperature.
(3) The dissolved stationary phase reagent was passed through monolithic silica at room temperature for 15 hours or more at a flow rate of 0.05 mL / min. FIG. 1 shows a chromatogram obtained by analyzing AMP and ATP after passing through. The analysis conditions are as follows.
Mobile phase: 100 mM KH2PO4
Column length: 100mm x 4.6mmID
Detector: UV-Visible Absorbance Meter (UV260nm)
FIG. 1 (a) shows the analysis result by the column of the present invention, and FIG. 1 (b) shows the analysis result by the ODS column.

Experimental example 2 (Example 2 of hydrophobic interaction)
A method for modifying a chiral separation group on a surface in which a hydrophobic group is modified by chemical bonding to monolithic silica will be described.
The same monolith type silica as in Experimental Example 1 was used.
(1) Preparation of stationary phase reagent
0.05 g of N, S-dioctyl- (D) -penicylamine was dissolved in 50 mL of methanol-water (50/50, v / v) at room temperature.
(2) The dissolved stationary phase reagent was passed through monolithic silica at room temperature for 15 hours or more at a flow rate of 0.05 mL / min. FIG. 2 shows a chromatogram obtained by analyzing D, L-phenylalanine and D, L-leucine after passing through. The analysis conditions are as follows.
Mobile phase: 2 mM copper sulfate-water-methanol (70:30)
Column length: 370mm x 0.2mmID
Detector: UV-Vis Absorbance Meter (UV254nm)
Fig. 2 (a) is the analysis result of D, L-phenylalanine, Fig. 2 (b) is the analysis result of D, L-leucine, and Fig. 2 (c) is the analysis of D, L-leucine when the linear velocity is increased. It is a result.

Experimental example 3 (example of hydrogen bonding)
The modification method of the chiral separation reagent to the silanol of monolithic silica is shown.
(1) Preparation of stationary phase reagent
1 g of R-(-)-N- (3,5-dinitolbenzoyl) -α-phenylglycine was dissolved in 20 mL of tetrahydrofuran at room temperature.
(2) The dissolved stationary phase reagent was passed through a monolithic column at room temperature for 15 hours or more at a flow rate of 0.05 mL / min. After passing through the solution, 2,2,2-trifluoro-1- (9-anthryl) ethanol was separated.
Mobile phase: Hexane-isopropyl alcohol (98: 2)
Column length: 100mm x 4.6mmID
Detector: UV-Vis Absorbance Meter (UV254nm)

  The column produced by the method of the present invention can be used for a liquid chromatograph column and the like.

The figure which shows the analysis result by the column (Example 1 of hydrophobic interaction) of this invention The figure which shows the analysis result by the column (Example 2 of hydrophobic interaction) of this invention

Claims (4)

(A) Step of preparing monolithic silica (b) Step of dissolving a stationary phase reagent having a functional group in a solvent (c) Step of fixing the dissolved stationary phase reagent to the monolithic silica by adsorption interaction A method for surface modification of monolithic silica. In step (a), after dissolving the water-soluble polymer and the thermally decomposable compound in an acidic aqueous solution, adding a metal compound having a hydrolyzable functional group to the hydrolyzed reaction, and then solidifying the product, The method for surface modification of monolithic silica according to claim 1, wherein the low-molecular compound dissolved in advance during gel preparation is thermally decomposed by heating the wet gel, followed by drying and heating. The method for modifying the surface of a monolithic silica according to claim 1, wherein the functional group is an ion exchange group or a chiral separation group. The method for modifying the surface of monolithic silica according to claim 1, wherein the reagent is immobilized by a liquid method or a batch method.

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