Nitrogen oxide reducing agent

Abstract

The present invention aims to provide a reducing agent for nitrogen oxides. [Solution] The present invention provides a nitrogen oxide reducing agent containing an inclusion complex in which a cyclodextrin dimer represented by the following chemical formula (1) or the like encloses a water-soluble metal porphyrin. JPEG2026126615000014.jpg79153

Description

[Technical Field]

[0001] This invention relates to a reducing agent for nitrogen oxides. [Background technology]

[0002] Nitrogen oxides (NOx) are harmful gases produced during the combustion of organic matter, and are generated in boilers, gasoline-powered vehicles, and waste incinerators. To prevent the release of these NOx into the atmosphere, they are detoxified into nitrogen and other substances using methods such as (1) selective catalytic reduction, (2) NOx storage reduction, and (3) three-way catalytic reduction. However, these methods not only require high temperatures but also use precious metal catalysts as reducing agents or ammonia, which requires a great deal of energy to manufacture, thus requiring significant costs and energy for detoxification.

[0003] The present inventors have previously studied inclusion complexes formed by cyclodextrin dimers in which water-soluble metal porphyrins are inclusion, and have discovered that these inclusion complexes have a high affinity for oxygen (O2) and carbon monoxide (CO), and that their affinity for CO is more than 100 times greater than that of hemoglobin (see Patent Document 1 and Non-Patent Documents 1-2). Patent Document 2 discloses a carbon monoxide scavenging agent containing an inclusion complex formed by cyclodextrin dimers represented by a predetermined formula in which water-soluble metal porphyrins are inclusion as an active ingredient. Cyclodextrin derivatives are also described in Patent Documents 3-6 and Non-Patent Documents 3-4. Furthermore, Non-Patent Document 7 shows that hemoCD3 is bound to hydrogen sulfide. In Non-Patent Document 8, the present inventors have investigated the interaction between hemoCD (hemoCD3) and NO. However, these documents do not describe or suggest the use of hemoCD as a reducing agent for nitrogen oxides. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2006-2077 [Patent Document 2] Japanese Patent Publication No. 2010-194475 [Patent Document 3] Patent No. 6180241 [Patent Document 4] International Publication No. 2023 / 068193 [Patent Document 5] International Publication No. 2021 / 153197 [Patent Document 6] Japanese Patent Publication No. 2015-044961 [Non-patent literature]

[0005] [Non-Patent Document 1] Angew. Chem. Int. Ed., 44, 435-438 (2005) [Non-Patent Document 2] Inorg. Chem. 45, 4448-4460 (2006) [Non-Patent Document 3] ACS Med. Chem. Lett. 2011, 2, 943-947 [Non-Patent Document 4] Angew. Chem. Int. Ed., 52, 6894-6897 (2013) [Non-Patent Document 5] Chem Commun (Camb). 2021 Jan 7; 57(2): 148-173. [Non-Patent Document 6] J Am Chem Soc. 2002 Aug 21; 124(33): 9937-44. [Non-Patent Document 7] Chem Commun (Camb). 2015 Mar 7; 51(19):4059-61. [Non-Patent Document 8] J Am Chem Soc. 2008 Jun 25; 130(25): 8006-15. [Overview of the project] [Problems that the invention aims to solve]

[0006] Therefore, the present invention aims to provide a reducing agent for nitrogen oxides. [Means for solving the problem]

[0007] The inventors, through diligent research, discovered that nitrogen molecules are generated in the reaction between hemoCD and nitric oxide. More specifically, they discovered that hemoCD, which they independently developed, exhibits catalytic activity in efficiently converting nitric oxide (NO), a type of nitrogen oxide, to nitrogen in a weakly acidic to acidic aqueous solution at pH 3 and at room temperature. It is a well-known fact that NO and heme proteins interact, and it is natural that hemoCD (artificial heme protein) and NO would interact. While conducting research to obtain basic knowledge, they accidentally discovered the reduction to nitrogen molecules (N2). Since the reduction from nitrous oxide (N2O) to N2 is a reaction mediated by enzymes different from those of heme proteins, it was unexpected that hemoCD would catalyze the reduction from NO to N2 in one step. While it is generally known that NO binds to heme-like compounds such as hemoCD, there have been no reports of reduction to N2, and in this respect, the findings of the inventors are surprising.

[0008] In other words, the present invention provides the following: [Aspect 1] A reducing agent for nitrogen oxides, comprising an inclusion complex in which a cyclodextrin dimer represented by the following chemical formula (1) or chemical formula (2) encloses a water-soluble metal porphyrin. [ka] [ka] (In Chemical Formula (1), n may be the same or different and represents any one of the numbers 1, 2, and 3; R may be the same or different and represents a hydrogen atom or a hydrocarbon group having 1, 2, or 3 carbon atoms, where the hydrocarbon group may be substituted with one or more hydroxy groups; L may be the same or different and represents a linear or branched hydrocarbon group represented by k carbon atoms, where k represents any one of the numbers 1, 2, 3, 4, and 5, and where the linear or branched hydrocarbon group may have some or all of its carbon atoms replaced by an oxygen atom, a sulfur atom, or a nitrogen atom; J may be substituted with one or more linear or branched hydrocarbon groups and represents a linear, branched, or cyclic hydrocarbon group in which some or all of the carbon atoms may be replaced by a nitrogen atom, an oxygen atom, or a sulfur atom, where the number of carbon atoms in J is any one of 1, 2, 3, 4, 5, 6, 7, and 8; and L is bonded to one carbon of any one of the hydrocarbon groups in J.) (In Chemical Formula (2), n may be the same or different and represents any one of the numbers 1, 2, and 3; R may be the same or different and represents a hydrogen atom or a hydrocarbon group having 1, 2, or 3 carbon atoms, where the hydrocarbon group may be substituted with one or more hydroxy groups; L may be the same or different and represents a linear or branched hydrocarbon group represented by k carbon atoms, where k represents any one of the numbers 1, 2, 3, 4, and 5, and where the linear or branched hydrocarbon group may have some or all of its carbon atoms replaced by an oxygen atom, a sulfur atom, or a nitrogen atom; J may be substituted with one or more linear or branched hydrocarbon groups and represents a linear, branched, or cyclic hydrocarbon group in which some or all of the carbon atoms may be replaced by a nitrogen atom, an oxygen atom, or a sulfur atom, where the number of carbon atoms in J is any one of 1, 2, 3, 4, 5, 6, 7, and 8; and L is bonded to one carbon of any one of the hydrocarbon groups in J.) [Aspect 2] The nitrogen oxide reducing agent according to Aspect 1, which reduces nitrogen oxide to nitrogen molecules. [Aspect 3] The reducing agent for nitrogen oxides according to Aspect 1, wherein the nitrogen oxide is nitric oxide. [Aspect 4] The reducing agent for nitrogen oxides according to Aspect 1, which reduces nitrogen oxides in a weakly acidic to acidic aqueous solution. [Aspect 5] The reducing agent for nitrogen oxides according to Aspect 4, wherein the pH of the aqueous solution is 1 to 6. [Aspect 6] The reducing agent for nitrogen oxides according to Aspect 4, wherein the pH of the aqueous solution is 2 to 4. [Aspect 7] The reducing agent for nitrogen oxides according to Aspect 1, which reduces nitrogen oxides at 15°C to 35°C. [Aspect 8] The reducing agent for nitrogen oxides according to Aspect 1, which reduces nitrogen oxides at 20°C to 30°C. [Aspect 9] The reducing agent for nitrogen oxides according to Aspect 1, wherein the water-soluble metal porphyrin is represented by the following chemical formula (3). [Chemical formula] (In the formula, each A represents either an anionic substituent, a neutral or cationic functional group, and Z represents any one of Fe, Co, Ni, Cu, Ru, and Mn.) [Aspect 10] In chemical formula (3), A represents any one of a sulfo group (-SO3 - ), a sulfonamide group, an amino group, a nitro group, a carboxy group, a hydrogen atom, a chlorine atom, a hydroxyl group, or a group represented by the following chemical formulas (4) to (9). Here, n in chemical formulas (5) and (7) to (9) may be the same or different and represents an integer of 1 to 200, and R in chemical formulas (4) to (5) may be the same or different and represents a hydrogen atom or a hydrocarbon group. The reducing agent for nitrogen oxides according to Aspect 9. [Chemical formula] [Aspect 11] A reducing agent for nitrogen oxides according to Embodiment 1, wherein -LJL- in chemical formula (1) or chemical formula (2) is represented by the following chemical formula (10) or chemical formula (11). [ka] (In the above chemical formula (10), m may be the same or different, and represents an integer between 1 and 2.) [ka] (In the above chemical formula (11), p may be the same or different, and represents an integer between 1 and 2.) [Effects of the Invention]

[0009] The nitrogen oxide reducing agent of the present invention is useful as a means of reducing nitrogen oxides (NOx), which have adverse effects on the environment and human health. In particular, the nitrogen oxide reducing agent of the present invention can be used as a catalyst for reducing nitrogen oxides in room temperature and weakly acidic environments. Since the reduction of NO in acidic solutions is a reaction that occurs to some extent spontaneously (positive oxidation-reduction potential), N2 will be generated over time even with NO alone, but it is thought that the presence of hemoCD has a catalytic effect that rapidly generates N2. The market for NOx reduction technology is expected to continue to expand with the strengthening of environmental regulations. Furthermore, since hemoCD is manufactured by general organic synthesis, there are no concerns about the supply of raw materials such as precious metal materials. In addition, since the reduction reaction to N2 proceeds at room temperature, almost no energy is consumed for detoxification. Thus, the nitrogen oxide reducing agent of the present invention is useful as an environmentally friendly catalyst that does not require expensive precious metal catalysts or NH3, which requires a great deal of energy to manufacture. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 shows the structural formulas of each compound used in the examples of the present invention. [Figure 2] Figure 2 shows the results of an experiment confirming the formation of a complex through the binding of met-hemoCD-I and NO. [Figure 3] Figure 3 shows the results of an experiment to calculate the binding constant in the binding of met-hemoCD-I to NO. [Figure 4] Figure 4 shows the results of an experiment confirming the formation of a complex by binding met-hemoCD-P and NO. [Figure 5] Figure 5 shows the results of an experiment to calculate the binding constant between met-hemoCD-P and NO. [Figure 6] Figure 6 shows the results of an experiment confirming the formation of a complex by the binding of TMe-β-CD / Fe(III)TPPS and NO. [Figure 7] Figure 7 shows the results of an experiment comparing the amount of nitrogen gas generated from NO in an acidic aqueous solution. [Modes for carrying out the invention]

[0011] The present invention provides a nitrogen oxide reducing agent containing an inclusion complex in which a specific cyclodextrin dimer encapsulates a water-soluble metal porphyrin.

[0012] This inclusion complex can be produced by mixing a cyclodextrin dimer with a water-soluble metal porphyrin in an aqueous solvent.

[0013] Cyclodextrin dimer: The cyclodextrin dimer is represented by the chemical formula (1) or chemical formula (2) described above.

[0014] Regarding n in chemical formula (1) or chemical formula (2), β-cyclodextrin with n = 2 is most preferred for complex formation with porphyrin.

[0015] Examples of R in chemical formula (1) or chemical formula (2) include a methyl group, a propyl group, and a hydroxypropyl group (-CH2-CH(OH)-CH3). The hydrocarbon group in R in chemical formula (1) or chemical formula (2) may be substituted with one or more hydroxyl groups, for example, 2, 3, 4, 5, 6, or 7.

[0016] In either chemical formula (1) or chemical formula (2), L can be an amide bond, a thioether bond, or -(CH2) k Examples of hydrocarbon groups are shown by -, where k represents one of the numbers 1, 2, 3, 4, or 5.

[0017] In chemical formula (1) or chemical formula (2), J represents a linear, branched, or cyclic hydrocarbon group which may be substituted with one or more linear or branched hydrocarbon groups, and in which some or all of the carbon atoms may be replaced with nitrogen atoms, oxygen atoms, or sulfur atoms, where examples of the multiple linear or branched hydrocarbon groups which may be substituted include 2, 3, 4, 5, or 6.

[0018] In chemical formula (1) or chemical formula (2), J may be a pyridine or imidazole substituted with one or more linear or branched hydrocarbon groups, where the number of linear or branched hydrocarbon groups may be, for example, 2, 3, 4, 5, or 6. The number of carbon atoms in the hydrocarbon group may be 1, 2, 3, 4, or 5.

[0019] In either chemical formula (1) or chemical formula (2), J can be any structure that donates electrons to the metallic porphyrin. Such structures include those containing a nitrogen atom. Electron donation is also possible with sulfur or oxygen atoms.

[0020] Of the chemical formulas (1) or (2), -LJL- is preferably represented by the chemical formula (10) or (11) described above.

[0021] In order to obtain the effects of the present invention, it is important that the cyclodextrin dimer (1) forms a sufficiently strong complex with the metal porphyrin, and (2) undergoes axial coordination from J to the metal porphyrin. Here, in view of (1), n, R, and L are dominant, with n being 2 and R being CH3, and for L, k being 2 or 3 is considered to be the optimal value. In view of (2), J is dominant.

[0022] This cyclodextrin dimer can be produced, for example, by tosyling and epoxidizing cyclodextrin, then methylating the hydroxyl groups of the cyclodextrin, and finally bonding the methylated cyclodextrin to a linker molecule, as described in prior art documents. The reason for pre-methylating the hydroxyl groups of the cyclodextrin is to prevent the pores of the cyclodextrin from hardening due to hydrogen bonding caused by the hydroxyl groups, which would make it difficult for water-soluble metallic porphyrins to be encapsulated in the pores of the cyclodextrin dimer. A more specific embodiment of the cyclodextrin dimer can be produced, for example, by tosyling and epoxidizing cyclodextrin, then methylating the hydroxyl groups of the cyclodextrin, and finally bonding the methylated cyclodextrin to a linker molecule, as described in Japanese Patent Application Publication No. 2010-194475. By protecting the hydroxyl groups of cyclodextrin with methyl groups beforehand, it is possible to prevent the pores of the cyclodextrin from hardening due to hydrogen bonding caused by the hydroxyl groups, which would make it difficult for water-soluble metallic porphyrins to be encapsulated in the pores of the cyclodextrin dimer. Another specific embodiment of a cyclodextrin dimer can be produced, for example, as described in Japanese Patent Application Publication No. 2013-231111, by tosyling and epoxidizing cyclodextrin, then methylating the hydroxyl groups of this cyclodextrin, and bonding the methylated cyclodextrin with a linker molecule. By protecting the hydroxyl groups of cyclodextrin with methyl groups beforehand, it is possible to prevent the pores of the cyclodextrin from hardening due to hydrogen bonding caused by the hydroxyl groups, which would make it difficult for water-soluble metallic porphyrins to be encapsulated in the pores of the cyclodextrin dimer.

[0023] Examples of cyclodextrins that can be used as raw materials for cyclodextrin dimers include α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin, among which β-cyclodextrin is preferred because it readily encapsulates water-soluble metal porphyrins.

[0024] In the examples described later, Im3CD and Py3CD have an amide bond in their linker structure, and Py3CD has a thioether bond, but the reverse is also true, or a simple hydrocarbon-(CH2) k Similar effects can be expected with - or ether bonds (-O-). Nitrogen atoms such as pyridine and imidazole are necessary for coordination with the metal atoms in water-soluble metal porphyrins, but their substitution is not a problem.

[0025] One of the roles expected of dimerized cyclodextrins such as Im3CD and Py3CD is to encapsulate water-soluble metal porphyrins and prevent the porphyrins themselves from forming aggregates. If they do aggregate, they will not be able to interact sufficiently with nitrogen oxides.

[0026] Cyclodextrin dimers can be expected to have similar effects as long as they do not impair the properties of the hydrophobic cavity formed by the cyclodextrin. Therefore, examples of R in chemical formula (1) or chemical formula (2) above include a methyl group and a propyl group. This is because it is important for the hydrophobic cavity of the cyclodextrin and the hydrophobicity of the porphyrin to interact and form an inclusion complex, and therefore, some modification that does not impair this interaction is considered not to affect the properties. However, methylation increases the flexibility of the cyclodextrin skeleton, which was rigid due to hydrogen bonding, resulting in a structure more suitable for interacting with water-soluble metal porphyrins. The methylation shown in the examples below is the best, and there is a concern that excessive modification may impair the properties.

[0027] In the aforementioned chemical formulas (1) or (2), n=1 is α-cyclodextrin and n=3 is γ-cyclodextrin, with the internal cavity being narrower and wider, respectively, compared to β-cyclodextrin, which forms the backbone of Py3CD. The driving force for inclusion remains the same as before, with the phenyl group of the porphyrin side chain interacting hydrophobically with the internal cavity of the cyclodextrin. To obtain a high level of inclusion, it is thought that there is room to control the behavior, for example, by increasing the value of k in chemical formula (1) for α (n=1) and decreasing the value of k for γ (n=3).

[0028] Regarding k in the aforementioned chemical formula (1), in the case of hemoCD-I, if we replace the amide bond with a hydrocarbon bond, we can estimate that the number of carbon atoms is approximately 2, so it can be considered that k=3 roughly corresponds to hemoCD-I.

[0029] Water-soluble metal porphyrins: Water-soluble metal porphyrins are not particularly limited as long as they are porphyrin compounds that dissolve in water by coordinating a metal ion at their center and can be encapsulated by a cyclodextrin dimer represented by chemical formula (1).

[0030] Examples of water-soluble metal porphyrins include the compound shown in chemical formula (3) above. More specifically, examples of water-soluble metal porphyrins include 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin iron complex (FeTPPS) and 5,15-bis(3,5-dicarboxylatophenyl)-10,20-diphenylporphyrin iron complex. These compounds can be synthesized by known methods, for example, or commercially available products (e.g., Frontier Scientific, Tokyo Chemical Industries, Ltd., etc.) can be used as is.

[0031] In chemical formula (3), A may represent any of the groups shown in chemical formulas (4) to (9) above, where n in chemical formulas (5) and (7) to (9) may be the same or different, and represent an integer from 1 to 200, for example, n is an integer less than or equal to 200, less than or equal to 190, less than or equal to 180, less than or equal to 170, less than or equal to 160, less than or equal to 150, less than or equal to 140, less than or equal to 130, less than or equal to 120, less than or equal to 110, less than or equal to 100, less than or equal to 90, less than or equal to 80, less than or equal to 70, less than or equal to 60, less than or equal to 50, less than or equal to 40, less than or equal to 30, less than or equal to 20, less than or equal to 10, less than or equal to 9, less than or equal to 8, less than or equal to 7, less than or equal to 6, less than or equal to 5, less than or equal to 4, less than or equal to 3, less than or equal to 2, or less than or equal to 1. Furthermore, n is an integer such as 0 or greater, 1 or greater, 2 or greater, 3 or greater, 4 or greater, 5 or greater, 6 or greater, 7 or greater, 8 or greater, 9 or greater, 10 or greater, 20 or greater, 30 or greater, 40 or greater, 50 or greater, 60 or greater, 70 or greater, 80 or greater, 90 or greater, 100 or greater, 110 or greater, 120 or greater, 130 or greater, 140 or greater, 150 or greater, 160 or greater, 170 or greater, 180 or greater, 190 or greater, or 200 or greater. In chemical formula (3), A may represent any of the groups shown in chemical formulas (4) to (9) above, where R in chemical formulas (4) to (5) may be the same or different, and represents a hydrogen atom or a hydrocarbon group. The number of carbon atoms in the hydrocarbon group of R in chemical formulas (4) to (5) may be, for example, 1 to 10.

[0032] In chemical formula (3), A is a functional group, specifically the SO3 group of FeTPPS. - Anionic substituents like the one shown are preferable in terms of the stability of the inclusion complex because they strengthen the inclusion with cyclodextrin. On the other hand, even with neutral or cationic functional groups, nitrogen oxides bond to the metal atom of the porphyrin center, so the effects of the present invention are achieved. The phenyl group is important for inclusion with cyclodextrin. Examples of A include substituents with a molecular weight of 1 to 10000.

[0033] Thus, there are few restrictions on A in chemical formula (3), so A may be any of the substituents shown in the aforementioned chemical formulas (4) to (9). In addition, there are TPP where A is a hydrogen atom, TPPOH where A is an OH group, and further, A may be -O-CH2-CH2-(-O-CH2-CH2)q It has been confirmed that inclusion complexes can be formed even with long molecular chains such as polyethylene glycol chains represented by -OCH3 (where q is a positive integer). Previous studies have confirmed the formation of inclusion complexes with compounds where q is 44 and 112 (compounds with molecular weights of 2000 and 5000, respectively).

[0034] This is because the phenyl group bonded to the porphyrin skeleton has a significant influence on inclusion with the cyclodextrin. Due to the charge imbalance within the cyclodextrin, the inclusion effect is stronger if A is anionic, but inclusion complexes can also be formed with neutral or cationic groups. The bond constant in the formation of large inclusion complexes (CD + FeTPPS → CD / FeTPPS) due to substituents on A has been studied in previous papers (J. AM. CHEM. SOC. 2002, 124, 9937-9944). As shown in Table 2 of that paper for solvents of the EG-H2O system, inclusion complexes are formed. It should be noted that PC3Py and PC7Py, which lack a phenyl group, and TMPyP, in which the phenyl group is substituted with a cationic pyridine skeleton, do not form inclusion complexes.

[0035] As shown in one publication (Chem Rev. 2004 Feb;104(2):403-18) and another publication (Chem. Rev. 2021, 121, 14682-14905), metals other than Fe, such as Co, Ni, Cu, Ru, and Mn, can bond with NO. Therefore, for Z in chemical formula (3), the same effect can be obtained with Co, Ni, Cu, Ru, and Mn as the central metal, in addition to Fe.

[0036] Reducing agents for nitrogen oxides: The nitrogen oxide reducing agent of the present invention preferably reduces nitrogen oxides to nitrogen molecules. In the nitrogen oxide reducing agent of the present invention, the nitrogen oxide is preferably nitric oxide. The nitrogen oxide reducing agent of the present invention preferably reduces nitrogen oxides in a weakly acidic to acidic aqueous solution. Here, the pH of the aqueous solution is, for example, 1 to 6, and the pH of the aqueous solution is, for example, 2 to 4. The nitrogen oxide reducing agent of the present invention preferably reduces nitrogen oxides at 15°C to 35°C. The nitrogen oxide reducing agent of the present invention preferably reduces nitrogen oxides at 20°C to 30°C. [Examples]

[0037] Examples of the present invention are described below. The structural formulas of each compound described in the examples are shown in Figure 1.

[0038] Example 1: Confirmation of NO-hemoCD-I formation by binding of met-hemoCD-I and NO: Met-hemoCD-I was dissolved in a 0.1 M glycine-hydrochloride buffer solution adjusted to a pH of 3 to a concentration of 5 μM. NO was then added to the met-hemoCD-I solution by bubbling NO gas through the solution for 30 seconds. The ultraviolet-visible absorption spectrum of this solution was measured using a Shimadzu UV-2600i. Met-hemoCD-I was synthesized according to the method described in ACS Med. Chem. Lett. 2011, 2, 943-947.

[0039] The results are shown in Figure 2. Met-hemoCD-I with added NO showed a sharp absorption originating from an iron porphyrin complex with a maximum absorption wavelength of 427 nm. From the value of the maximum absorption wavelength and the shape of the absorption spectrum, it was confirmed that an NO-hemoCD-I complex was formed in which NO was bound to trivalent iron.

[0040] Example 2: Calculation of the binding constant between met-hemoCD-I and NO: The binding constant of NO to met-hemoCD-I was calculated by performing curve fitting using a theoretical formula based on 1:1 complex formation on the changes in the absorption spectrum when NO was titrated against met-hemoCD-I (5 μM) in a 0.1 M glycine-hydrochloride buffer solution adjusted to pH 3. The NO concentration in the solution was controlled by the amount of NOC7 (1-Hydroxy-2-oxo-3-(N-methyl-3-aminopropyl)-3-methyl-1-triazene), a NO sustained-release reagent, added.

[0041] The results are shown in Figure 3. In an aqueous solution at 25°C with a pH of 3, the binding constant (K) of NO to met-hemoCD-I is (1.3 ± 0.2) × 10⁻¹⁰. 6 M -1 This was the request.

[0042] Example 3: Confirmation of NO-hemoCD-P formation by binding of met-hemoCD-P and NO: NO-hemoCD-P formation was confirmed using the same procedure as in Example 1, except that met-hemoCD-P was used instead of met-hemoCD-I. Met-hemoCD-P was synthesized by the method described in Angew. Chem. Int. Ed. 2005, 44, 435-438.

[0043] The results are shown in Figure 4. Met-hemoCD-P with added NO showed a sharp absorption originating from an iron porphyrin complex with a maximum absorption wavelength of 426 nm. From the value of the maximum absorption wavelength and the shape of the absorption spectrum, it was confirmed that an NO-hemoCD-P complex was formed in which NO was bound to trivalent iron.

[0044] Example 4: Calculation of the binding constant between met-hemoCD-P and NO: The NO binding constant to met-hemoCD-P was calculated using the same procedure as in Example 2, except that met-hemoCD-P was used instead of met-hemoCD-I.

[0045] The results are shown in Fig. 5. In an aqueous solution at 25 °C with a pH of 3 for the solution, the binding constant (K) of NO to met - hemoCD - P was determined to be (8.9 ± 1.2) × 10 5 M -1 .

[0046] Comparative Example 1: Confirmation of NO-TMe-β-CD / Fe(III)TPPS formation by binding of TMe-β-CD / FeTPPS with NO: Confirmation of the formation of NO - TMe - β - CD / Fe(III)TPPS was carried out in the same procedure as in Example 1, except that TMe - β - CD / Fe(III)TPPS was used instead of met - hemoCD - I.

[0047] The results are shown in Fig. 6. An absorption spectrum with a maximum absorption wavelength near 430 nm, indicating the binding of NO to trivalent iron, was not observed. Since the observed absorption spectrum showed a maximum absorption wavelength at 402 nm, from the value of the maximum absorption wavelength and the shape of the spectrum, it was suggested that NO - TMe - β - CD / Fe(II)TPPS was generated by a reductive nitrosylation reaction, and it was shown that a stable NO - TMe - β - CD / Fe(III)TPPS complex was not generated.

[0048] Example 5: Determination of nitrogen gas production by reaction of met-hemoCD-I and NO in an acidic solution: Dissolved air was removed from a 0.1 M glycine-hydrochloride buffer solution, whose pH was adjusted to 3, by bubbling it with helium gas for 20 minutes. 5 mL of this solution was taken into a vial, and met-hemoCD-I was then dissolved in the solution to a concentration of 25 μM. NO gas was bubbling through this met-hemoCD-I solution for 30 seconds to dissolve the NO. After sealing the vial with a rubber stopper, the gas phase in the vial was replaced with helium gas. After standing for 10 minutes, 0.5 mL of the gas phase containing the generated gas was collected using a gas-tight syringe, and the gas components were analyzed by gas chromatography. Gas chromatography analysis was performed using a Shimadzu GC-2014 equipped with a headspace sampler, and a Shimadzu TCD detector was used. A Shincarbon ST 50 / 80 column (3.0 mm, 2.0 m) manufactured by Shinwa Chemical was used, and helium gas was used as the carrier gas at a flow rate of 40 mL / min. The temperatures of the sample inlet, column, and detector were set to 120°C, 40°C, and 120°C, respectively. The amount of nitrogen gas generated was quantified using a pre-prepared nitrogen gas calibration curve. The influence of air contamination on nitrogen gas detection during the measurement procedure was eliminated by the following method: The same experimental procedure was performed without adding met-hemoCD-I and NO, and the amount of nitrogen gas obtained was subtracted as a blank to quantify the amount of nitrogen generated by the reaction with NO.

[0049] Example 6: Determination of nitrogen gas production by reaction of met-hemoCD-P and NO in an acidic solution: The amount of nitrogen gas generated was quantified using the same procedure as in Example 5, except that met-hemoCD-P was used instead of met-hemoCD-I.

[0050] Comparative Example 2: Determination of nitrogen gas production by reaction of TMe-β-CD / Fe(III)TPPS with NO in an acidic solution: The amount of nitrogen gas generated was quantified using the same procedure as in Example 5, except that TMe-β-CD / Fe(III)TPPS was used instead of met-hemoCD-I.

[0051] Comparative Example 3: Determination of nitrogen gas production by reaction of Fe(III)TPPS and NO in an acidic solution: The amount of nitrogen gas generated was quantified using the same procedure as in Example 5, except that Fe(III)TPPS was used instead of met-hemoCD-I.

[0052] Comparative Example 4: Determination of nitrogen gas production by reaction of Im3CD / TPPS with NO in an acidic solution: The amount of nitrogen gas generated was quantified using the same procedure as in Example 5, except that Im3CD / TPPS was used instead of met-hemoCD-I.

[0053] Comparative Example 5: Determination of nitrogen gas production by reaction of TPPS and NO in an acidic solution: The amount of nitrogen gas generated was quantified using the same procedure as in Example 5, except that TPPS was used instead of met-hemoCD-I.

[0054] Comparative Example 6: Determination of nitrogen gas generation from NO alone in an acidic solution: The amount of nitrogen gas generated was quantified using the same procedure as in Example 5, except that met-hemoCD-I was not added.

[0055] The results for Examples 5 and 6 and Comparative Examples 2-6 are shown in Figure 7. A significant increase in nitrogen gas generation was observed in the solutions containing met-hemoCD-I and met-hemoCD-P, suggesting that met-hemoCD-I and met-hemoCD-P catalytically reduce NO by promoting the reduction reaction to nitrogen molecules after complex formation with NO.

Claims

1. A reducing agent for nitrogen oxides, comprising an inclusion complex in which a cyclodextrin dimer represented by the following chemical formula (1) or chemical formula (2) encloses a water-soluble metal porphyrin. 【Chemistry 1】 【Chemistry 2】 (In chemical formula (1), n ​​may be the same or different number, representing 1, 2, or 3; R may be the same or different number, representing a hydrogen atom or a hydrocarbon group having 1, 2, or 3 carbon atoms, where the hydrocarbon group may be substituted with one or more hydroxyl groups; L may be the same or different number, representing a linear or branched hydrocarbon group having k carbon atoms, where k is the number 1, 2, 3, 4, or 5, where linear or branched) A branched hydrocarbon group may have some or all of its carbon atoms replaced by oxygen, sulfur, or nitrogen atoms; J represents a linear, branched, or cyclic hydrocarbon group which may be substituted with one or more linear or branched hydrocarbon groups, and which may have some or all of its carbon atoms replaced by nitrogen, oxygen, or sulfur atoms, where the number of carbon atoms in J is one, two, three, four, five, six, seven, or eight; and L is bonded to one carbon of any of the hydrocarbon groups in J. (In chemical formula (2), n may be the same or different number, and represents one of 1, 2, or 3; R may be the same or different number, and represents a hydrogen atom or a hydrocarbon group having 1, 2, or 3 carbon atoms, where the hydrocarbon group may be substituted with one or more hydroxyl groups; L may be the same or different number, and represents a linear or branched hydrocarbon group having k carbon atoms, where k is the number 1, 2, 3, 4, or 5, where linear or branched) A branched hydrocarbon group may have some or all of its carbon atoms replaced by oxygen, sulfur, or nitrogen atoms; J represents a linear, branched, or cyclic hydrocarbon group which may be substituted with one or more linear or branched hydrocarbon groups, and which may have some or all of its carbon atoms replaced by nitrogen, oxygen, or sulfur atoms, where the number of carbon atoms in J is one, two, three, four, five, six, seven, or eight; and L is bonded to one carbon of any of the hydrocarbon groups in J.

2. A reducing agent for nitrogen oxides according to claim 1, which reduces nitrogen oxides to nitrogen molecules.

3. The nitrogen oxide reducing agent according to claim 1, wherein the nitrogen oxide is nitric oxide.

4. A nitrogen oxide reducing agent according to claim 1, which reduces nitrogen oxides in a weakly acidic to acidic aqueous solution.

5. A reducing agent for nitrogen oxides according to claim 4, wherein the pH of the aqueous solution is 1 to 6.

6. A reducing agent for nitrogen oxides according to claim 4, wherein the pH of the aqueous solution is 2 to 4.

7. A nitrogen oxide reducing agent according to claim 1, which reduces nitrogen oxides at 15°C to 35°C.

8. A nitrogen oxide reducing agent according to claim 1, which reduces nitrogen oxides at 20°C to 30°C.

9. The reducing agent for nitrogen oxides according to claim 1, wherein the water-soluble metal porphyrin is represented by the following chemical formula (3). 【Transformation 3】 (In the formula, A represents either an anionic substituent, a neutral or cationic functional group, and Z represents one of Fe, Co, Ni, Cu, Ru, or Mn.)

10. In chemical formula (3), A is a sulfo group (-SO 3 - The reducing agent for nitrogen oxides according to claim 9, wherein n represents one of the following: a sulfonamide group, an amino group, a nitro group, a carboxyl group, a hydrogen atom, a chlorine atom, or a hydroxyl group, or one of the groups shown in the following chemical formulas (4) to (9), where n in chemical formulas (5) and (7) to (9) may be the same or different and represent an integer from 1 to 200, and R in chemical formulas (4) to (5) may be the same or different and represent a hydrogen atom or a hydrocarbon group. 【Chemistry 4】

11. A reducing agent for nitrogen oxides according to claim 1, wherein -LJL- in chemical formula (1) or chemical formula (2) is represented by the following chemical formula (10) or chemical formula (11). 【Transformation 5】 (In the above chemical formula (10), m may be the same or different, and represents an integer between 1 and 2.) 【Transformation 6】 (In the above chemical formula (11), p may be the same or different, and represents an integer between 1 and 2.)

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