Cerium oxide nanoparticles, antibacterial agents, antiviral agents, and method for producing cerium oxide nanoparticles

Abstract

The present invention addresses the problem of providing cerium oxide nanoparticles having high antibacterial activity and antiviral activity. The present invention pertains to cerium oxide nanoparticles that are surface-coated with a polyvalent carboxylic acid and a compound having a heterocyclic amine structure.

Description

[Technical Field]

[0001] The present invention relates to cerium oxide nanoparticles whose surfaces are coated with a vinyl polymer or polyamide, antibacterial agents and antiviral agents containing the nanoparticles, and a method for producing the nanoparticles. [Background technology]

[0002] In recent years, with growing awareness of safety and hygiene management, antibacterial technology that decomposes microorganisms and harmful substances has been attracting attention. For example, titanium dioxide has the ability to oxidize and decompose organic matter through its photocatalytic properties. These oxidative decomposition properties are expected to be used as an antibacterial agent to inactivate microorganisms such as viruses, bacteria, mold, and yeast, as well as to decompose low-molecular-weight substances such as acetaldehyde and ammonia, as well as harmful substances such as allergens.

[0003] On the other hand, cerium oxide nanoparticles (nanoceria) have catalytic activity similar to that of oxidizing enzymes such as oxidase and peroxidase, and are expected to be used as antibacterial agents that utilize their oxidative properties. Because this catalytic activity does not require a special light source such as ultraviolet light, it is expected to be used in applications different from those of titanium oxide. Metal oxides generally have the property of being positively charged, and cerium oxide nanoparticles are also positively charged in the acidic to neutral pH range. However, positively charged cerium oxide nanoparticles have the problem of nonspecific adsorption with serum proteins. When antibacterial processing is applied to medical devices and they are used in vivo, it is necessary to suppress nonspecific adsorption, which leads to a decrease in antibacterial activity. To suppress such nonspecific adsorption, methods of coating the particle surface with a stabilizer are being investigated. For example, Non-Patent Document 1 discloses that nanoceria coated on the surface with polyacrylic acid has antibacterial activity, and Non-Patent Document 2 discloses that cerium oxide produced using ethylenediaminetetraacetic acid (EDTA) as a stabilizer has antibacterial activity. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Qi Wang, J Manuel Perez, and Thomas J Webster [Non-patent document 2] Thammadihalli Nanjundaiah Ravishankar Thippeswamy Ramakrishnappa Ganganagappa Nagaraju Hanumanaika Rajanaika ChemistryOpen 2015, 4, 146-154. Summary of the Invention [Problem to be solved by the invention]

[0005] The present inventors evaluated the antibacterial activity of cerium oxide nanoparticles using polyacrylic acid (described in Non-Patent Document 1) or EDTA (described in Non-Patent Document 2) as stabilizers. However, neither of these stabilizers was found to have a sufficient rate of inhibiting the growth of Escherichia coli. Therefore, further investigation was carried out with the aim of finding cerium oxide nanoparticles with even greater antibacterial activity. [Means for solving the problem]

[0006] As a result of investigations aimed at solving the above problems, the present inventors discovered that coating the surface of cerium oxide nanoparticles with a compound having a heterocyclic amine skeleton in addition to polycarboxylic acids such as polyacrylic acid and EDTA improves antibacterial activity. They also discovered that cerium oxide nanoparticles whose surfaces are coated with a polycarboxylic acid and a compound having a heterocyclic amine skeleton also have improved antiviral performance, leading to the completion of the present invention.

[0007] The present invention comprises the following aspects. (1) Cerium oxide nanoparticles whose surfaces are coated with a compound having a polycarboxylic acid and a heterocyclic amine skeleton. (2) The cerium oxide nanoparticles according to (1), wherein the polycarboxylic acid has a valence of three or more. (3) Cerium oxide nanoparticles according to (1) or (2), wherein the compound having a heterocyclic amine skeleton is a vinyl polymer or polyamide having a heterocyclic amine skeleton in the main chain or side chain. (4) The cerium oxide nanoparticles according to any one of (1) to (3), wherein the heterocyclic amine skeleton is composed of any one of piperazine, pyridine, imidazole, and carbazole. (5) The cerium oxide nanoparticles according to (3) or (4), wherein the vinyl polymer is a polymer having the heterocyclic amine skeleton in a side chain. (6) The cerium oxide nanoparticles according to (3) or (4), wherein the polyamide is a polymer having the heterocyclic amine skeleton in its main chain. (7) The cerium oxide nanoparticles according to (1) or (2), wherein the compound having a heterocyclic amine skeleton is a monocyclic or bicyclic aromatic heterocyclic compound having a five-membered ring and / or a six-membered ring structure.

[0008] (8) The cerium oxide nanoparticles according to (1) or (2), wherein the compound having a heterocyclic amine skeleton is a compound represented by general formula (I): [ka] In formula (I), X is NR 2 , O, S, R 1 and R 2 represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group having 1 to 4 carbon atoms, an aminoalkyl group having 1 to 4 carbon atoms, or a sulfonic acid alkyl group having 1 to 4 carbon atoms. 1 and R 2 may be the same or different. (9) An antibacterial agent containing the cerium oxide nanoparticles according to any one of (1) to (8). (10) An antiviral agent containing the cerium oxide nanoparticles according to any one of (1) to (8). (11) A method for producing cerium oxide nanoparticles whose surfaces are coated with a polycarboxylic acid and a compound having a heterocyclic amine skeleton, the method comprising: Step A: preparing a solution containing a polycarboxylic acid, a vinyl polymer or polyamide having a heterocyclic amine skeleton, and cerium (III) ions; and Step B: adding an oxidizing agent to the solution obtained in Step A. [Effects of the Invention]

[0009] According to the present invention, it is possible to obtain cerium oxide nanoparticles having high antibacterial and antiviral activity. DETAILED DESCRIPTION OF THE INVENTION

[0010] The cerium oxide nanoparticles of the present invention have their surfaces coated with a polycarboxylic acid and a compound having a heterocyclic amine skeleton, which are used as stabilizers for the cerium oxide nanoparticles in the present invention.

[0011] The polycarboxylic acid is a carboxylic acid having multiple carboxyl groups or its salt, or a mixture of the carboxylic acid and its salt. Preferred polycarboxylic acids are tricarboxylic or higher carboxylic acids and / or their salts. Examples of tricarboxylic acids include citric acid, nitrilotriacetic acid (NTA), and hydroxyethylethylenediaminetriacetic acid (HEDTA). Examples of tetracarboxylic acids include ethylenediaminetetraacetic acid (EDTA), ethylenediaminedisuccinic acid (EDDS), and glycoletherdiaminetetraacetic acid (EGTA). Examples of pentacarboxylic acids include hydroxyethylethylenediaminetetraacetic acid (HEDTA) and (DTPA). Examples of hexacarboxylic acids include triethylenetetraminehexaacetic acid (TTHA). Examples of heptacarboxylic acids or higher include polyacrylic acid and / or their salts.

[0012] Examples of the compound having a heterocyclic amine skeleton used in the present invention include aromatic heterocyclic compounds, alicyclic amines, and vinyl polymers or polyamides having a heterocyclic amine skeleton in the main chain or side chain.

[0013] The aromatic heterocyclic compound used in the present invention is preferably a monocyclic or bicyclic aromatic heterocyclic compound having a five-membered ring and / or six-membered ring structure, such as pyridine, pyridazine, pyrimidine, imidazole, pyrazole, benzimidazole, and carbazole. The aromatic heterocyclic compound may have a substituent. The substituent here is preferably an alkyl group, an acetyl group, a hydroxyl group, an amino group, a cyano group, a carboxyl group, an ester group, an aldehyde group, an amide group, an ether group, a ketone group, a halogen group, a sulfonic acid group, or a phosphate group. The number of substituents may be single or multiple.

[0014] The alicyclic amine used in the present invention is exemplified by the alicyclic amine represented by general formula (I). [ka] In formula (I), X is NR 2 , O, S, R 1 and R 2 represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group having 1 to 4 carbon atoms, an aminoalkyl group having 1 to 4 carbon atoms, or a sulfonic acid alkyl group having 1 to 4 carbon atoms. 1 and R 2 may be the same or different.

[0015] In a more preferred embodiment of the alicyclic amine, X is NR 2 , indicates O and R 1 and R 2 R represents a hydrogen atom, an alkyl group having 1 to 2 carbon atoms, a hydroxyalkyl group having 2 to 3 carbon atoms, an aminoalkyl group having 2 to 3 carbon atoms, or a sulfonic acid alkyl group having 2 to 3 carbon atoms. 1 and R 2 may be the same or different.

[0016] Examples of alicyclic amines include piperazine, 1-methylpiperazine, N,N'-dimethylpiperazine, 1-ethylpiperazine, N,N'-diethylpiperazine, 1-(2-hydroxyethyl)piperazine, 1,4-bis(2-hydroxyethyl)piperazine, N-(2-aminoethyl)piperazine, 1,4-bis(2-aminoethyl)piperazine, 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid, piperazine-1,4-bis(2-ethanesulfonic acid), morpholine, 4-methylmorpholine, 4-ethylmorpholine, 4-(2-aminoethyl)morpholine, 4-(2-hydroxyethyl)morpholine, 2-morpholinoethanesulfonic acid, and 3-morpholinopropanesulfonic acid.

[0017] The vinyl polymer or polyamide having a heterocyclic amine skeleton in the main chain or side chain used in the present invention (hereinafter sometimes abbreviated as "polymer having a heterocyclic amine skeleton") has a heterocyclic amine skeleton such as pyrrolidine, pyrrole, pyrazole, piperazine, pyridine, diazine, imidazole, or carbazole in the main chain or side chain, and those having piperazine, pyridine, imidazole, or carbazole in the main chain or side chain are preferred. The vinyl polymer or polyamide having a heterocyclic amine skeleton of the present invention may have a substituent at any position in the main chain or side chain, or may have a substituent at any position in the heterocyclic amine skeleton. Examples of the vinyl polymer or polyamide having a heterocyclic amine skeleton in the main chain and a substituent at the side chain include polymers having a heterocyclic amine skeleton with a substituent at the main chain, polymers having a heterocyclic amine skeleton with a substituent at the side chain, and polymers having a heterocyclic amine skeleton in the side chain via a substituent. The substituent here is preferably an alkyl group, an acetyl group, a hydroxyl group, an amino group, a cyano group, a carboxyl group, an ester group, an aldehyde group, an amide group, an ether group, a ketone group, a halogen group, a sulfonic acid group, or a phosphoric acid group. The number of the substituent may be one or more.

[0018] The vinyl polymer having a heterocyclic amine skeleton used in the present invention is a polymer (polyvinyl) having a polyethylene structure in the main chain formed by condensation of vinyl monomers as monomers. As an example, the structure of a vinyl polymer having a piperazine skeleton in the main chain or side chain is shown in the following general formula (II) or (III). As shown in general formula (II), when the main chain has a piperazine skeleton, the piperazine skeleton is present as part of the polyethylene structure of the main chain. When the main chain has other heterocyclic amine skeletons such as pyridine, imidazole, or carbazole skeletons, the heterocyclic amine skeleton is present as part of the polyethylene structure of the main chain, as in general formula (II). [ka] In formula (II), n represents any integer.

[0019] [ka] In formula (III), n represents an arbitrary integer.

[0020] When the vinyl polymer having a heterocyclic amine skeleton used in the present invention has a piperazine skeleton in a side chain, for example, as shown in general formula (III), the piperazine skeleton may be directly bonded to the polyethylene main chain, or the piperazine skeleton may be bonded via an alkylene group, an amino group, etc. When the vinyl polymer has another heterocyclic amine skeleton such as a pyridine, imidazole, or carbazole skeleton, the heterocyclic amine skeleton such as a pyridine, imidazole, or carbazole skeleton may be directly bonded to the polyethylene main chain, or the piperazine skeleton may be bonded via an alkylene group, an amino group, etc., as in the case of having the piperazine skeleton shown in general formula (II).

[0021] The vinyl polymer having a heterocyclic amine skeleton used in the present invention is preferably a vinyl polymer having a piperazine, pyridine, imidazole, or carbazole skeleton in the side chain, which can be obtained by polymerization of a vinyl monomer having a piperazine, pyridine, imidazole, or carbazole skeleton.

[0022] Specific examples of the vinyl monomer in this case include 1-vinylpiperazine, (4-vinylpiperazin-1-yl)methanamine, 2-(4-vinylpiperazin-1-yl)ethan-1-amine, 2-vinylpiperazine, (3-vinylpiperazin-1-yl)methanamine, 2-(3-vinylpiperazin-1-yl)ethan-1-amine, (2-vinylpiperazin-1-yl)methanamine, 2-(2-vinylpiperazin-1-yl)ethan-1-amine, 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine, 1-vinylimidazole, 2-vinylimidazole, 4-vinylimidazole, 9-vinylcarbazole, etc. The vinyl monomer may have a substituent at any position other than the vinyl group, for example, a methyl group or a cyano group as a substituent.

[0023] The vinyl polymer having a heterocyclic amine skeleton used in the present invention may be a homopolymer or a copolymer made from two or more types of vinyl monomers as raw materials. Specific preferred examples of the vinyl polymer used in the present invention include poly(1-vinylpiperazine), poly((4-vinylpiperazin-1-yl)methanamine), poly(2-(4-vinylpiperazin-1-yl)ethan-1-amine), poly(2-vinylpyridine), poly(3-vinylpyridine), poly(4-vinylpyridine), poly(1-vinylimidazole), poly(2-vinylimidazole), poly(4-vinylimidazole), and poly(9-vinylcarbazole).

[0024] The polyamide having a heterocyclic amine skeleton used in the present invention is a polymer having an amide bond in its main chain, and has a heterocyclic amine skeleton such as a piperazine, pyridine, imidazole, or carbazole skeleton in its main chain or side chain. The following general formula (IV) shows the structure of a polyamide having a piperazine skeleton as the heterocyclic amine skeleton in its main chain. Here, the piperazine skeleton is present as part of the amide structure that is the main chain, and the nitrogen in the heterocyclic ring of the piperazine skeleton and the carbonyl group form an amide bond. When the main chain has other heterocyclic amine skeletons such as a pyridine, imidazole, or carbazole skeleton having an amino group as a substituent, the heterocyclic amine skeleton is present as part of the amide structure, as in general formula (IV). [ka] In formula (IV), n represents an arbitrary integer.

[0025] When the polyamide having a heterocyclic amine skeleton used in the present invention has a piperazine skeleton in its side chain, for example, as shown in the following general formula (V), the piperazine skeleton may be directly bonded to the polyamide main chain, or may be bonded via an alkyl group, an amino group, etc. When other heterocyclic amine skeletons such as pyridine, imidazole, or carbazole skeletons are used, the heterocyclic amine skeletons such as pyridine, imidazole, or carbazole skeletons may be directly bonded to the polyamide main chain, or may be bonded via an alkylene group, an amino group, etc., as in the case of having the piperazine skeleton shown in general formula (V). [ka] In formula (V), n represents an arbitrary integer.

[0026] The polyamide having a heterocyclic amine skeleton used in the present invention is preferably a polymer having a heterocyclic amine skeleton such as a piperazine skeleton in the main chain, as represented by general formula (IV). The polyamide having a piperazine skeleton in the main chain used in the present invention can be obtained by a condensation reaction between an amine having a heterocyclic amine skeleton such as a piperazine skeleton and a dicarboxylic acid.

[0027] Preferred examples of amines having a heterocyclic amine skeleton include piperazine, (aminomethyl)piperazine, (aminoethyl)piperazine, (aminopropyl)piperazine, (aminobutyl)piperazine, 1,4-bis(aminomethyl)piperazine, 1,4-bis(2-aminoethyl)piperazine, 1,4-bis(3-aminopropyl)piperazine, 1,4-bis(4-aminobutyl)piperazine, diaminopyridine, aminoimidazole, and aminocarbazole. Among these, (aminoethyl)piperazine and 1,4-bis(3-aminopropyl)piperazine are more preferred. Furthermore, these amines may have a substituent at any position other than the nitrogen atom capable of forming an amide bond.

[0028] Preferable examples of the dicarboxylic acid include 1H-imidazole-2,4-dicarboxylic acid, 1H-imidazole-2,5-dicarboxylic acid, 1H-imidazole-4,5-dicarboxylic acid, pyridine-2,3-dicarboxylic acid, pyridine-2,4-dicarboxylic acid, pyridine-2,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, pyridine-3,4-dicarboxylic acid, pyridine-3,5-dicarboxylic acid, adipic acid, sebacic acid, dodecadicarboxylic acid, terephthalic acid, isophthalic acid, etc. These dicarboxylic acids may have a substituent at any position other than the carboxyl group capable of forming an amide bond.

[0029] The polyamide having a heterocyclic amine skeleton used in the present invention is preferably a polyamide obtained by combining the above-mentioned amine with a dicarboxylic acid, and particularly preferably a polyamide obtained by combining (aminoethyl)piperazine with adipic acid. The polyamide having a heterocyclic amine skeleton used in the present invention may have a polyalkylene glycol structure in a part of the polyamide main chain, specifically, polyamides having a skeleton of (aminoethyl)piperazine, adipic acid, and bis(aminopropyl)polyethylene glycol.

[0030] The polyamide having a heterocyclic amine skeleton used in the present invention may be a copolymer of a polyamide having a heterocyclic amine skeleton such as piperazine, pyridine, imidazole, or carbazole with another polymer. In this case, specific examples of the other polymer include polycaproamide (nylon 6), polyhexamethylene adipamide (nylon 66), polytetramethylene adipamide (nylon 46), polypentamethylene adipamide (nylon 56), polypentamethylene sebacamide (nylon 510), polyhexamethylene sebacamide (nylon 610), polyhexamethylene dodecamide (nylon 612), and polyhexamethylene adipamide. Examples include polyhexamethylene adipamide / polyhexamethylene terephthalamide copolymer (nylon 66 / 6T), polyhexamethylene adipamide / polyhexamethylene terephthalamide / polyhexamethylene isophthalamide copolymer (nylon 66 / 6T / 6I), polyhexamethylene terephthalamide / polyhexamethylene isophthalamide copolymer (nylon 6T / 6I), and polyxylylene adipamide (nylon XD6).

[0031] The molecular weight of the vinyl polymer or polyamide having a heterocyclic amine skeleton used in the present invention is preferably 3,000 or more and 1,000,000 or less, and more preferably 10,000 or more and 50,000 or less.

[0032] The cerium oxide nanoparticles of the present invention have a structure in which a cerium oxide particle (hereinafter referred to as a "core") composed of a mixture of Ce2O3 and CeO2 is at the center, and the surface of the core is coated with a compound having a polycarboxylic acid and a heterocyclic amine skeleton. The particle diameter of the core is preferably approximately 1 nm or more and 100 nm or less. The particle diameter can be determined by measuring two or more of the major axis diameter, minor axis diameter, and unidirectional diameter using a transmission electron microscope, and calculating the average value as the particle diameter.

[0033] The ratio of Ce2O3 to CeO2 in the core can be calculated as the ratio of cerium (III) to cerium (IV) by drying the cerium oxide nanoparticles of the present invention and performing the calculation using X-ray photoelectron spectroscopy (XPS).

[0034] The particle size of the cerium oxide nanoparticles of the present invention, including the surface compound layer, is preferably 200 nm or less in terms of hydrodynamic diameter. The hydrodynamic diameter is determined by dissolving the cerium oxide nanoparticles of the present invention in a solvent such as water or ethanol, measuring dynamic light scattering to derive an autocorrelation function, analyzing the result by the Marquadt method, and calculating the average particle size from a number-transformed histogram. Dynamic light scattering measurements are performed using an ELS-Z (manufactured by Otsuka Electronics Co., Ltd.).

[0035] The cerium oxide nanoparticles of the present invention can be produced by a method for producing cerium oxide nanoparticles, which includes step A of obtaining a solution containing a polycarboxylic acid, a compound having a heterocyclic amine skeleton, and cerium (III) ions, and step B of adding an oxidizing agent to the solution obtained in step A. Below, the method for producing cerium oxide nanoparticles of the present invention will be explained step by step.

[0036] Step A is a step of mixing a polycarboxylic acid (including a polycarboxylic acid ion or salt), a compound having a heterocyclic amine skeleton, and cerium (III) ions (including a cerium (III) salt) to obtain a mixed solution. The polycarboxylic acid used in step A can be a solution prepared by dissolving the polycarboxylic acid or a salt thereof in any solvent. In this case, the solvent is preferably water or a solvent compatible with water. If the polycarboxylic acid is difficult to dissolve in the solvent, it can be dissolved by heating or ultrasonic treatment, or the pH can be adjusted with an acid or base.

[0037] The compound having a heterocyclic amine skeleton used in step A can be used as a solution by dissolving the compound having a heterocyclic amine skeleton in any solvent. The solvent is preferably water or a solvent compatible with water. If the compound having a heterocyclic amine skeleton is difficult to dissolve in the solvent, it may be dissolved by heating or ultrasonic treatment, or the pH may be adjusted with an acid or base. Specific examples of solvents for polycarboxylic acids and compounds having a heterocyclic amine skeleton include methanol, ethanol, propanol, isopropanol, butanol, tetrahydrofuran, glycerol, ethylene glycol, acetone, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), triethylamine, and pyridine.

[0038] The cerium(III) ions (including cerium(III) salts) used in step A can be dissolved in any solvent and used as a solution. For example, cerium(III) nitrate hexahydrate can be used as the cerium(III) salt. The method for mixing a solution containing a polycarboxylic acid or a salt of a polycarboxylic acid, a solution of a compound having a heterocyclic amine skeleton, and a solution containing cerium(III) ions or a cerium(III) salt is not particularly limited. For example, a preferred method is to add a solution containing cerium(III) ions or a cerium(III) salt to a solution containing ions of a polycarboxylic acid and a polymer having a heterocyclic amine skeleton. Examples of such methods include mixing a solution containing ions of a polycarboxylic acid with a solution of a compound having a heterocyclic amine skeleton and then adding a solution containing cerium(III) ions or a cerium(III) salt; dissolving a compound having a heterocyclic amine skeleton in a solution containing ions of a polycarboxylic acid and then adding a solution containing cerium(III) ions or a cerium(III) salt; or dissolving a salt of a polycarboxylic acid in a solution of a compound having a heterocyclic amine skeleton and then adding a solution containing cerium(III) ions or a cerium(III) salt. In this case, to dissolve the cerium salt, the solvent for the mixed solution must ultimately be water or a water-compatible solvent containing at least 10% water.

[0039] In the mixed solution obtained in step A, the concentration of the polycarboxylic acid is preferably 0.05 to 5 molar equivalents, more preferably 0.1 to 1 molar equivalent, relative to cerium (III) ions when the valence is from 3 to 6. When the valence is from 7 to 8, the mass concentration is preferably 0.01 to 5%, more preferably 0.1 to 1%.

[0040] In the mixed solution, the concentration of the compound having a heterocyclic amine skeleton is preferably 0.01% or more and 5% or less, more preferably 0.1% or more and 2% or less, in terms of mass concentration. When cerium(III) nitrate hexahydrate is used in the mixed solution, the mass ratio of cerium(III) nitrate hexahydrate to the compound having a heterocyclic amine skeleton is preferably 0.1 to 5.0. The mixed solution is preferably mixed for 5 minutes or more until the solution becomes homogeneous.

[0041] Step B is a step of adding an oxidizing agent to the solution obtained in Step A. Examples of oxidizing agents used in step B include nitric acid, potassium nitrate, hypochlorous acid, chlorous acid, chloric acid, perchloric acid, halogens, hydrogen halides, permanganates, chromic acid, dichromate, oxalic acid, hydrogen sulfide, sulfur dioxide, sodium thiosulfate, sulfuric acid, and hydrogen peroxide. Among these, hydrogen peroxide is particularly preferred. The amount added may be 0.1 to 10 molar equivalents, preferably 0.5 to 2 molar equivalents, relative to the cerium (III) ion.

[0042] When an oxidizing agent is added to the solution obtained in step A, cerium (III) ions are oxidized to cerium (IV), initiating a reaction to form particles centered around a cerium oxide particle (core) composed of a mixture of Ce2O3 and CeO2, the surface of which is coated with the compound having a polycarboxylic acid and a heterocyclic amine skeleton. When an oxidizing agent is added to the solution obtained in step A, the reaction to form the cerium oxide nanoparticles of the present invention begins. During this reaction, the solution becomes colored, such as yellow, orange, red, or brown. This coloration is due to the conversion of cerium (III) ions to cerium (IV), and the degree of coloration is determined by the ratio of cerium (III) to cerium (IV) present on the surface of the cerium oxide nanoparticles. The completion of the reaction can be determined when the color change ceases. The reaction usually completes within 30 minutes to 1 hour.

[0043] For example, if 47 μl of a 0.5 M EDTA solution is added to 10 ml of a 0.5% by mass aqueous solution of polyvinylimidazole, 200 μl of a 10% by mass aqueous solution of cerium (III) nitrate hexahydrate is added, and the mixture is mixed. Then, 200 μl of a 1.2% by mass aqueous solution of hydrogen peroxide is added and the mixture is stirred at 25°C, the solution initially turns yellow, then gradually becomes darker in color, and finally turns brown, completing the reaction.

[0044] After the reaction is complete, the pH of the dispersion may be adjusted. The pH adjustment may be performed in step A, or after purifying the dispersion by filtration using an ultrafiltration membrane or dialysis using a semipermeable membrane, as described below. The pH of the dispersion of the present invention may be in the range of pH 2 to 12. The pH may be adjusted by adding a buffer solution, or by adding an acid such as nitric acid, sulfuric acid, or hydrochloric acid, or a base such as sodium hydroxide or potassium hydroxide.

[0045] The zeta potential of the cerium oxide nanoparticles of the present invention is higher than that of nanoparticles stabilized with a polycarboxylic acid, but lower than that of nanoparticles stabilized with a compound having a heterocyclic amine skeleton. The zeta potential can be adjusted by adjusting the concentrations of the polycarboxylic acid and the compound having a heterocyclic amine skeleton; increasing the concentration of the polycarboxylic acid decreases the zeta potential of the particles, while increasing the concentration of the compound having a heterocyclic amine skeleton increases the zeta potential of the particles.

[0046] The cerium oxide nanoparticles of the present invention may be stored in the dispersion after the reaction is complete, or may be removed from the dispersion after the reaction is complete and stored in a dried state. When stored in a dispersion, refrigerated storage is preferred. When drying the cerium oxide nanoparticles of the present invention, first, the solution after the reaction is complete is filtered through an ultrafiltration membrane or dialyzed through a semitransparent membrane to remove unreacted polycarboxylic acids, oxidizing agents, cerium (III) ions, and excess compounds remaining in the dispersion after the reaction is complete, and then the nanoparticles are dried using an evaporator, freeze dryer, or the like.

[0047] Ion components that can be added to the dispersion of cerium oxide nanoparticles of the present invention after the reaction is completed include components that impart buffering properties, such as acetic acid, phthalic acid, succinic acid, carbonic acid, Tris(hydroxymethyl)aminomethane (Tris), 2-Morpholinoethanesulfonic acid, monohydrate (MES), Bis(2-hydroxyethyl)iminotris(hydroxymethyl)methane (Bis-Tris), N-(2-Acetamido)iminodiacetic acid (ADA), Piperazine-1,4-bis(2-ethanesulfonic acid) (PIPES), N-(2-Acetamido)-2-aminoethanesulfonic acid (ACES), 2-Hydroxy-3-morpholinopropanesulfonic acid (MOPSO), N,N-Bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (BES), 3-Morpholinopropanesulfonic acid, acid(MOPS), N-Tris(hydroxymethyl)methyl-2-aminoethanesulfonic acid(TES), 2-[4-(2-Hydroxyethyl)-1-piperazinyl]ethanesulfonic acid(HEPES), 2-Hydroxy-N-tris(hydroxymethyl)methyl-3-aminopropanesulfonic(TAPSO), Piperazine-1,4-bis(2-hydroxy-3-propanesulfonic acid)(POPSO), 2-Hydroxy-3-[4-(2-hydroxyethyl)-1-piperazinyl]propanesulfonic acid(HEPSO), 3-[4-(2-Hydroxyethyl)-1-piperazinyl]propanesulfonic acid(HEPPS), (Tricine), N,Examples of ionic components include N-Bis(2-hydroxyethyl)glycine (Bicine) and N-Tris(hydroxymethyl)methyl-3-aminopropanesulfonic acid (TAPS), and components that do not impart buffering properties include sodium chloride and potassium chloride. These ionic components can be added so that the final concentration is in the range of 0.1 mM to 1 M. These ionic components may be added to the dispersion after the reaction is completed, or may be added after the dispersion is filtered through an ultrafiltration membrane, or may be used as a dialysis solution, or may be added to the dispersion after dialysis. They may also be added to dried cerium oxide nanoparticles to form a dispersion.

[0048] The dispersion of cerium oxide nanoparticles of the present invention may be sterilized before use, for example by passing it through a sterilizing filter.

[0049] In the present invention, antimicrobial refers generally to inhibiting the growth of microorganisms such as viruses, bacteria, and fungi, and includes killing of microbes, removal of microbes, sterilization, microbiostasis, control of microbes, and microbial inhibition.

[0050] The cerium oxide nanoparticles of the present invention can be used as an antibacterial agent. Methods for evaluating antibacterial performance include, for example, mixing a microbial suspension with a test solution, culturing the mixture on an agar medium, and observing the growth state; observing growth inhibition on an agar medium containing the test solution, and measuring the growth inhibition zone. Another method involves adding a test solution to a liquid medium and measuring growth inhibition. In these evaluations, the medium components may contain nutrients such as glucose, milk casein or soybean-derived peptone, or extracts derived from fish meat or yeast to promote microbial growth. If antibacterial activity is observed, the growth state of the microorganisms on the agar medium in the presence of the test solution will deteriorate, resulting in a decrease in the size and number of colonies. Furthermore, in liquid medium, the increase in turbidity associated with microbial growth will disappear. In the present invention, the method of adding a test solution to a liquid medium and observing growth inhibition is preferably used to evaluate antibacterial activity. The method of inhibiting microbial growth by adding a test solution to a liquid culture medium is used as an indicator of antibacterial activity, as it shows the microbial growth inhibitory effect. Specifically, the microbial growth inhibition rate of the cerium oxide nanoparticles of the present invention is calculated as follows: First, a solution of the cerium oxide nanoparticles of the present invention is mixed with a liquid culture medium, and a microorganism such as Escherichia coli is inoculated. As a control, the same process is performed on a liquid culture medium that does not contain cerium oxide nanoparticles. Before starting the culture, the turbidity (OD600 value) of the solution is measured. The microorganisms are cultured at a specified temperature and for a specified time while stirring using a shaker or the like. After the culture, the turbidity (OD600 value) of all solutions is measured. For each solution, the difference between the turbidity after culture and the turbidity before culture is calculated. The turbidity difference of the control (I c The difference in turbidity (I) between the solution containing cerium oxide nanoparticles and the control solution was calculated. c ) is calculated as the growth inhibition rate.

[0051] Examples of microorganisms against which the cerium oxide nanoparticles of the present invention exhibit antibacterial activity include the following: Bacteria include Gram-positive and Gram-negative bacteria. Gram-negative bacteria include, for example, Escherichia bacteria such as Escherichia coli, Salmonella bacteria such as Salmonella, Pseudomonas bacteria such as Pseudomonas aeruginosa, Shigella bacteria such as Shigella, Klebsiella bacteria such as Klebsiella pneumoniae, and Legionella bacteria such as Legionella pneumophila. Gram-positive bacteria include, for example, Staphylococcus bacteria such as Staphylococcus, Bacillus bacteria such as Bacillus subtilis, and Mycobacterium bacteria such as Mycobacterium tuberculosis. Fungi include fungi and yeast. Examples of fungi include filamentous fungi of the genus Aspergillus, such as Aspergillus niger; filamentous fungi of the genus Penicillium, such as Penicillium niger; filamentous fungi of the genus Cladosporium, such as Aspergillus niger; filamentous fungi of the genus Alternaria, such as Sooty mold; filamentous fungi of the genus Trichoderma, such as Aspergillus niger; and filamentous fungi of the genus Chaetomium, such as Chaetomium niger. Examples of yeasts include yeasts of the genus Saccharomyces, such as baker's yeast and brewer's yeast, and yeasts of the genus Candida, such as Candida albicans. Examples of viruses include poliovirus, rotavirus, norovirus, enterovirus, sapovirus, influenza virus, respiratory syncytial virus, adenovirus, and herpes virus. The nanoparticles of the present invention exhibit high antibacterial activity, particularly against bacteria.

[0052] The cerium oxide nanoparticles of the present invention can be dispersed and used, for example, as a disinfectant in swimming pools, bathtubs, hot springs, etc., or as a body soap, handwash, disinfectant, gargle, mouthwash, etc., or as a disinfectant for cleaning clothes, tableware, kitchens, toilets, washrooms, bathrooms, desks, chairs, tables, beds, medical instruments, etc. In this case, the cerium oxide nanoparticle dispersion may contain other components with bactericidal, disinfecting, sterilizing, bacteriostatic, bacteriostatic, or growth-inhibiting effects. Specific examples include solvent components such as ethanol and isopropyl alcohol, oxidizing agents such as hydrogen peroxide, povidone-iodine, and sodium hypochlorite, and surfactant components such as benzalkonium chloride, benzethonium chloride, and alkylpolyaminoethylglycine.

[0053] In addition, the cerium oxide nanoparticles of the present invention can be used as an additive for imparting antibacterial activity by adding them to fibers, tubes, beads, rubber, films, plastics, etc. during molding, or by coating them on their surfaces for antibacterial treatment. Examples of items that can be antibacterial treated with the cerium oxide dispersion of the present invention include kitchen sink drain covers, drain stoppers, window glass fixing gaskets, mirror fixing gaskets, waterproof gaskets for bathrooms, washbasins, and kitchens, refrigerator door lining gaskets, bath mats, non-slip rubber for washbasins and chairs, hoses, shower heads, gaskets used in water purifiers, plastic products for water purifiers, gaskets used in washing machines, plastic products for washing machines, masks, medical caps, medical shoe covers, air conditioner filters, air purifier filters, and vacuum cleaner filters. Examples of suitable applications include filters, ventilation fan filters, vehicle filters, air conditioning filters, air conditioner fins, air conditioner outlet louvers, and other plastic parts and fans, car air conditioner fins, car air conditioner outlet louvers, and other plastic parts and fans, clothing, bedding, netting for screen doors, chicken coop netting, mosquito netting, wallpaper, windows, blinds, interior materials for buildings such as hospitals, interior materials for trains and automobiles, vehicle seats, blinds, chairs, sofas, virus-handling equipment, and building materials such as doors, ceiling panels, floor panels, and windows. Thus, products processed with the dispersion of cerium oxide nanoparticles of the present invention can be used in a variety of fields as sanitary materials.

[0054] Furthermore, the cerium oxide nanoparticles or dispersion thereof of the present invention can be used as an antiviral agent. To evaluate their performance as an antiviral agent, the cerium oxide nanoparticles or dispersion thereof of the present invention are brought into contact with or mixed with a virus, and then the amount of virus is quantified. Examples of methods for quantifying the virus include measuring the amount of virus antigens by ELISA, quantifying viral nucleic acids by PCR, measuring the infectivity titer by the plaque method, and measuring the infectivity titer by the 50% infectivity dose assay. In the present invention, the antiviral performance is preferably measured by measuring the infectivity titer by the plaque method or the 50% infectivity dose assay. The unit of the virus infectivity titer is TCID when tested on cultured cells in the 50% infectivity dose assay. 50 (Tissue culture infectious dose 50), EID 50 (Egg infectious dose 50), LD in animals 50 The infectivity titer is expressed as Lethal dose 50 (Lethal dose 50). Methods for calculating the infectivity titer from the data obtained in the 50% infectivity dose measurement method include the Reed-Muench method, the Behrens-Kaeber method, and the Spearman-Karber method, but in the present invention, it is preferable to use the Reed-Muench method. The standard for judging antiviral activity is generally that the antiviral activity is judged to be effective if the logarithmic reduction in infectivity titer is 2.0 or more compared to the infectivity titer before the application of the cerium oxide nanoparticles of the present invention or a control not containing the nanoparticles of the present invention.

[0055] Examples of viruses that can be inactivated by the cerium oxide nanoparticles or dispersions thereof of the present invention include rhinovirus, poliovirus, foot-and-mouth disease virus, rotavirus, norovirus, enterovirus, hepatovirus, astrovirus, sapovirus, hepatitis E virus, influenza A, B, and C viruses, parainfluenza virus, mumps virus, measles virus, human metapneumovirus, respiratory syncytial virus, Nipah virus, Hendra virus, yellow fever virus, dengue virus, Japanese encephalitis virus, West Nile virus, hepatitis B and C viruses, eastern and western equine encephalitis virus, Onyong-nyong virus, rubella virus, and Lassa virus. , Junin virus, Machupo virus, Guanarito virus, Sabia virus, Crimean-Congo hemorrhagic fever virus, sandfly fever, hantavirus, Sin Nombre virus, rabies virus, Ebola virus, Marburg virus, bat lyssavirus, human T-cell leukemia virus, human immunodeficiency virus, human coronavirus, SARS-CoV, SARS-CoV 2, human porvovirus, polyomavirus, human papillomavirus, adenovirus, herpesvirus, varicella-zoster virus, Epstein-Barr virus, cytomegalovirus, smallpox virus, monkeypox virus, cowpox virus, molluscipox virus, and parapox virus.

[0056] When used as an antiviral agent, the cerium oxide nanoparticles of the present invention or a dispersion thereof can be kneaded as an additive into materials such as fibers, tubes, beads, rubber, films, and plastics, or coated on the surface of these materials. For example, they can be used in a variety of fields, including masks, medical caps, medical shoe covers, air conditioner filters, air purifier filters, vacuum cleaner filters, ventilation fan filters, vehicle filters, air conditioning filters, plastic parts and blower fans such as air conditioner fins and air conditioner outlet louvers, car air conditioner fins and car air conditioner outlet louvers, plastic parts and blower fans, clothing, bedding, nets for screen doors, chicken coop nets, and mosquito nets, wallpaper, windows, blinds, interior materials for buildings such as hospitals, interior materials for trains and automobiles, vehicle seats, blinds, chairs, sofas, virus-handling equipment, and building materials such as doors, ceiling panels, floor panels, and windows. [Example]

[0057] The present invention will be further illustrated by the following examples. Materials and Methods Sodium polyacrylate and M9 Minimal Salts were obtained from Merck Ltd., poly(1-vinylimidazole) from Maruzen Petrochemical Co., Ltd., cerium (III) nitrate hexahydrate and 30% by mass hydrogen peroxide solution from Fujifilm Wako Pure Chemical Industries, Ltd., Luria Broth Base from Thermo Fisher Scientific, and Escherichia coli (DH5α) from Takara Bio Inc. Other reagents were purchased from Fujifilm Wako Pure Chemical Industries, Ltd., Tokyo Chemical Industry Co., Ltd., and Sigma-Aldrich Japan LLC, and were used as is without further purification.

[0058] In the following examples, as polyamides having a heterocyclic amine skeleton in the main chain, a polymer having (aminoethyl)piperazine and adipic acid as structural units (polyamide (1)) and a polymer having (aminoethyl)piperazine, bis(aminopropyl)polyethylene glycol, and adipic acid as structural units (polyamide (2)) were used, and these polymers were prepared with reference to JP-A-11-166121.

[0059] LB liquid medium was prepared by dissolving Luria Broth Base at a concentration of 25 g / L and sterilizing it in an autoclave. M9 liquid medium was prepared by mixing 890 ml of sterilized distilled water, 100 ml of 10x M9 Minimal Salts, 1 ml of 1 M MgSO, 10 ml of 20% glucose, and 100 μl of 1 M CaCl. The hydrodynamic diameter and zeta potential of the cerium oxide nanoparticles were measured using the Otsuka Electronics Co., Ltd. Zeta Potential and Particle Measurement System ELS-Z, the OD600 value was measured using the Beckman Coulter DU530, and the shaker for E. coli culture was the TAITEC BIO-SHAKER BR-40LF.

[0060] Example 1: Synthesis of cerium oxide nanoparticles coated with polyacrylic acid and poly(1-vinylimidazole) 5 ml of a 1% by weight aqueous solution of sodium polyacrylate and 5 ml of a 1% by weight aqueous solution of polyvinylimidazole were mixed, and 200 μl of a 10% by weight aqueous solution of cerium (III) nitrate hexahydrate was added and stirred for 15 minutes. 200 μl of a 1.2% by weight aqueous solution of hydrogen peroxide was then added, and the mixture was allowed to react at room temperature for 1 hour. The reaction solution was purified using a 30 kD ultrafiltration membrane, yielding an orange dispersion containing cerium oxide nanoparticles.

[0061] Example 2: Synthesis of cerium oxide nanoparticles coated with polyacrylic acid and polyamide (1) A reaction was carried out under the same conditions as in Example 1, except that a 1 mass % aqueous solution of polyamide (1) was used instead of 5 ml of a 1 mass % aqueous solution of polyvinylimidazole, to obtain an orange aqueous solution containing cerium oxide nanoparticles.

[0062] Example 3: Synthesis of cerium oxide nanoparticles coated with polyacrylic acid and polyamide (2) A reaction was carried out under the same conditions as in Example 1, except that a 1 mass % aqueous solution of polyamide (2) was used instead of 5 ml of a 1 mass % aqueous solution of polyvinylimidazole, to obtain an orange aqueous solution containing cerium oxide nanoparticles.

[0063] Example 4: Synthesis of cerium oxide nanoparticles coated with EDTA and poly(1-vinylimidazole) To 10 ml of 0.5% polyvinylimidazole aqueous solution, 47 μl of 0.5 M EDTA·2Na aqueous solution was added, followed by 200 μl of 10% cerium(III) nitrate hexahydrate aqueous solution, and the mixture was stirred for 15 minutes. Then, 200 μl of 1.2% hydrogen peroxide aqueous solution was added, and the mixture was allowed to react at room temperature for 1 hour. The reaction solution was purified using a 30 kD ultrafiltration membrane, yielding a brown dispersion containing cerium oxide nanoparticles.

[0064] Example 5: Synthesis of cerium oxide nanoparticles coated with EDTA and polyamide (1) A reaction was carried out under the same conditions as in Example 4, except that a 0.5% by mass aqueous solution of polyamide (1) was used instead of 10 ml of a 0.5% by mass aqueous solution of polyvinylimidazole, to obtain a brown aqueous solution containing cerium oxide nanoparticles.

[0065] Example 6: Synthesis of cerium oxide nanoparticles coated with EDTA and polyamide (2) A reaction was carried out under the same conditions as in Example 4, except that a 0.5% by mass aqueous solution of polyamide (2) was used instead of 10 ml of a 0.5% by mass aqueous solution of polyvinylimidazole, to obtain a brown aqueous solution containing cerium oxide nanoparticles.

[0066] Example 7: Synthesis of cerium oxide nanoparticles coated with polyacrylic acid and piperazine A reaction was carried out under the same conditions as in Example 1, except that a 24.6 mg / 5 ml aqueous piperazine solution was used instead of 5 ml of a 1 mass % aqueous polyvinylimidazole solution, to obtain a yellow aqueous solution containing cerium oxide nanoparticles.

[0067] Example 8: Synthesis of cerium oxide nanoparticles coated with polyacrylic acid and N-(2-aminoethyl)piperazine A reaction was carried out under the same conditions as in Example 1, except that a 20 mg / 5 ml N-(2-aminoethyl)piperazine aqueous solution was used instead of 5 ml of a 1 mass % polyvinylimidazole aqueous solution, to obtain a yellow aqueous solution containing cerium oxide nanoparticles.

[0068] Example 9: Synthesis of cerium oxide nanoparticles coated with polyacrylic acid and 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid A reaction was carried out under the same conditions as in Example 1, except that 5 ml of a 36.8 mg / 5 ml aqueous solution of 2-[4-(2-hydroxyethyl)-1-piperazinyl]ethanesulfonic acid was used instead of 5 ml of a 1 mass % aqueous solution of polyvinylimidazole, to obtain a yellow aqueous solution containing cerium oxide nanoparticles.

[0069] Example 10: Synthesis of polyacrylic acid and morpholine-coated cerium oxide nanoparticles A reaction was carried out under the same conditions as in Example 1, except that a 27 mg / 5 ml aqueous morpholine solution was used instead of 5 ml of a 1 mass % aqueous polyvinylimidazole solution, to obtain a yellow aqueous solution containing cerium oxide nanoparticles.

[0070] Example 11: Synthesis of EDTA and piperazine-coated cerium oxide nanoparticles A reaction was carried out under the same conditions as in Example 4, except that a 24.6 mg / 10 ml aqueous piperazine solution was used instead of 10 ml of a 0.5 mass % aqueous polyvinylimidazole solution, to obtain a brown aqueous solution containing cerium oxide nanoparticles.

[0071] Example 12: Synthesis of cerium oxide nanoparticles coated with polyacrylic acid and pyridine A reaction was carried out under the same conditions as in Example 1, except that a 12 mg / 5 ml aqueous piperazine solution was used instead of 5 ml of a 1 mass % aqueous polyvinylimidazole solution, to obtain a yellow aqueous solution containing cerium oxide nanoparticles.

[0072] Example 13: Synthesis of cerium oxide nanoparticles coated with polyacrylic acid and imidazole A reaction was carried out under the same conditions as in Example 1, except that a 10 mg / 5 ml imidazole aqueous solution was used instead of 5 ml of a 1 mass % polyvinylimidazole aqueous solution, to obtain a yellow aqueous solution containing cerium oxide nanoparticles.

[0073] Example 14: Synthesis of cerium oxide nanoparticles coated with polyacrylic acid and benzimidazole A reaction was carried out under the same conditions as in Example 1, except that 5 ml of an 18 mg / 5 ml aqueous solution of benzimidazole was used instead of 5 ml of a 1 mass % aqueous solution of polyvinylimidazole, to obtain a yellow aqueous solution containing cerium oxide nanoparticles.

[0074] Example 15: Synthesis of cerium oxide nanoparticles coated with EDTA and pyridine A reaction was carried out under the same conditions as in Example 4, except that a 12 mg / 10 ml aqueous pyridine solution was used instead of 10 ml of a 0.5 mass % aqueous polyvinylimidazole solution, to obtain a brown aqueous solution containing cerium oxide nanoparticles.

[0075] (Comparative Example 1) Synthesis of polyacrylic acid-coated cerium oxide With reference to Non-Patent Document 1, cerium oxide nanoparticles were prepared for comparison of antibacterial activity. To 10 ml of a 0.5% by mass aqueous solution of sodium polyacrylate, 200 μl of a 10% by mass aqueous solution of cerium (III) nitrate hexahydrate was added and stirred at room temperature for 5 minutes. 200 μl of a 1.2% by mass aqueous solution of hydrogen peroxide was then added, and the mixture was heated to 40°C and reacted for 1 hour. The reaction solution was purified using a 30 kD ultrafiltration membrane to obtain a yellow dispersion containing cerium oxide nanoparticles.

[0076] (Comparative Example 2) Synthesis of EDTA-coated cerium oxide nanoparticles A brown dispersion containing cerium oxide nanoparticles was obtained by carrying out the reaction under the same conditions as in Comparative Example 1, except that 10 ml of a 2.35 mM EDTA·2Na aqueous solution was used instead of 10 ml of a 0.5 mass % sodium polyacrylate aqueous solution.

[0077] (Comparative Example 3) Synthesis of poly(1-vinylimidazole)-coated cerium oxide nanoparticles A reaction was carried out under the same conditions as in Comparative Example 1, except that 10 ml of a 0.5 mass % aqueous solution of poly(1-vinylimidazole) was used instead of 10 ml of a 0.5 mass % aqueous solution of sodium polyacrylate in Comparative Example 1, to obtain an orange dispersion containing cerium oxide nanoparticles.

[0078] (Example 16) Measurement of the hydrodynamic diameter of cerium oxide nanoparticles The hydrodynamic diameters of the cerium oxide nanoparticles prepared in Examples 1 to 15 and Comparative Examples 1 to 3 were measured by dynamic light scattering (DLS). The solvent used during measurement was M9 medium, and the average particle size of the hydrodynamic diameter was calculated by number conversion. The obtained values ​​are shown in Table 1. The particles obtained in Examples 1 to 15 were confirmed to be nanoparticles with an average particle size of 3.3 to 18.2 nm, and the particles obtained in Comparative Examples 1, 2, and 3 were confirmed to be nanoparticles with average particle sizes of 5.0 nm, 3.0 nm, and 12.4 nm, respectively.

[0079] [Table 1]

[0080] (Example 17) Inhibition of Escherichia coli growth by cerium oxide nanoparticles To evaluate the antibacterial activity of the cerium oxide nanoparticles of the present invention, the growth inhibition of Escherichia coli was evaluated. Solutions of cerium oxide nanoparticles prepared in Examples 1 to 15 and Comparative Examples 1 and 2 were each adjusted to a concentration of 2 mg / ml and passed through a 0.2 μm ultrafiltration membrane. The flow-through solution was used to evaluate the inhibition of Escherichia coli growth. For preculture, E. coli was inoculated into LB liquid medium and cultured at 32°C for 24 hours while stirring at 200 rpm using a shaker. After culture, the medium was centrifuged (4000 rpm, 5 minutes) to remove the supernatant, and the E. coli pellet was washed with 2 ml of saline. This washing was repeated once more, and the pellet was resuspended in 2 ml of M9 liquid medium. 9.5 ml of M9 liquid medium was mixed with 500 μl of each 2 mg / ml cerium oxide nanoparticle solution, and 25 μl of resuspended E. coli suspension was added. As a control, a solution containing saline instead of the cerium oxide nanoparticle solution was also prepared. The mixture was cultured at 32°C for 24 hours while stirring at 200 rpm using a shaker, and the OD600 value was measured. The OD600 value at the start of culture was 0.033 for all solutions. The growth inhibition rate was analyzed by calculating the difference of 0.033, the initial value, between the OD600 values ​​of the control and each example after culture. The difference between the OD600 value of the control and the OD600 value of each example was calculated, and the ratio to the OD600 value of the control was used to calculate the growth inhibition rate. The results are shown in Table 2.

[0081] Comparing Examples 1 to 15 with Comparative Examples 1 and 2 described below, it was revealed that, compared to cerium oxide nanoparticles coated only with polycarboxylic acid, the cerium oxide nanoparticles of the present invention whose surfaces are coated with polycarboxylic acid and a vinyl polymer or polyamide having a heterocyclic amine skeleton all had a growth inhibition rate of 95% or more against Escherichia coli, demonstrating significantly improved antibacterial activity.

[0082] [Table 2]

[0083] (Example 18) Virus inactivation by cerium oxide nanoparticles 0.9 ml of the dispersion of cerium oxide nanoparticles prepared in Examples 1 to 15 and Comparative Examples 1 to 3, adjusted to 5 mg / ml, was mixed with 0.1 ml of a virus solution (influenza virus, ATCC, VR-1679, Influenza A virus (H3N2)) and allowed to react for 1 hour. PBS was then added as a stop solution to stop the action against the virus. This solution was used as a stock solution for the sample for virus titer measurement, and the infectivity titer was measured by plaque assay. The logarithmic reduction in infectivity titer relative to the infectivity titer before the application of cerium oxide nanoparticles is shown in Table 3. These results demonstrate that the cerium oxide nanoparticles of Comparative Examples 1 and 2 have no antiviral activity, whereas the cerium oxide nanoparticles of Comparative Example 3 have antiviral activity. It was also confirmed that the antiviral activity of the cerium oxide nanoparticles of Examples 1 to 15 is relatively higher than that of the cerium oxide nanoparticles of Comparative Example 3.

[0084] [Table 3]

Claims

1. Cerium oxide nanoparticles have a structure in which the surface of a cerium oxide particle, which is a core, is coated with a compound having a polycarboxylic acid and a heterocyclic amine skeleton.

2. 2. The cerium oxide nanoparticles according to claim 1, wherein the polycarboxylic acid has a valence of three or more.

3. 3. The cerium oxide nanoparticles according to claim 1, wherein the compound having a heterocyclic amine skeleton is a vinyl polymer or polyamide having the heterocyclic amine skeleton in the main chain or side chain.

4. 4. The cerium oxide nanoparticles according to claim 3, wherein the heterocyclic amine skeleton is composed of any one of piperazine, pyridine, imidazole, and carbazole.

5. Cerium oxide nanoparticles as described in claim 1 or 2, wherein the heterocyclic amine skeleton is composed of either pyridine, pyridazine, pyrimidine, imidazole, pyrazole, benzimidazole or carbazole, or an alicyclic amine.

6. Cerium oxide nanoparticles described in claim 1 or 2, wherein the heterocyclic amine skeleton is composed of piperazine.

7. 5. The cerium oxide nanoparticles according to claim 3, wherein the vinyl polymer is a polymer having the heterocyclic amine skeleton in a side chain.

8. 5. The cerium oxide nanoparticles according to claim 3, wherein the polyamide is a polymer having the heterocyclic amine skeleton in the main chain.

9. 3. The cerium oxide nanoparticles according to claim 1, wherein the compound having a heterocyclic amine skeleton is a monocyclic or bicyclic aromatic heterocyclic compound having a five-membered ring and / or a six-membered ring structure.

10. 3. The cerium oxide nanoparticles according to claim 1, wherein the compound having a heterocyclic amine skeleton is a compound represented by general formula (I): 【Chemical 1】 (In the general formula (I), X is NR ２ , O, S, and R １ and R ２ represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group having 1 to 4 carbon atoms, an aminoalkyl group having 1 to 4 carbon atoms, or a sulfonic acid alkyl group having 1 to 4 carbon atoms. １ and R ２ may be the same or different.)

11. An antibacterial agent comprising the cerium oxide nanoparticles according to any one of claims 1 to 10.

12. An antiviral agent comprising the cerium oxide nanoparticles according to any one of claims 1 to 10.

13. A method for producing cerium oxide nanoparticles whose surfaces are coated with a polycarboxylic acid and a compound having a heterocyclic amine skeleton, comprising the steps of: A step A of preparing a solution containing a polycarboxylic acid, a compound having a heterocyclic amine skeleton, and cerium (III) ions, and a step B of adding an oxidizing agent to the solution obtained in the step A; A method for producing cerium oxide nanoparticles, comprising:

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