JP6699322B2 - Peptide, rare earth element recovery material and rare earth element recovery method - Google Patents

Description

  The present invention relates to a peptide, a rare earth element recovery material, and a rare earth element recovery method.

  Conventionally, solvent extraction has been performed as a method for separating and purifying rare earth elements. In the solvent extraction, a rare earth metal is extracted into a solvent by dissolving the rare earth element in an acid solution with strong acidity (low pH) and using an extractant suitable for adsorbing and separating the rare earth element. Furthermore, it is a separation and purification means for increasing the purity of the rare earth element by repeating the steps similar to the above.

  When separating rare earth elements by solvent extraction, large amounts of solvent and organic extractant are used. Further, since the extractant has low selectivity, complicated steps and repeated purification cycles are required to obtain the desired rare earth element with high purity. Therefore, there is a problem that the environmental load is high.

  Therefore, as a method of separating a rare earth element without using a solvent, a step of separating and recovering a rare earth element using a peptide having selective adsorption has been proposed (see Patent Documents 1 and 2). Patent Document 1 discloses that a rare earth element is selectively adsorbed and a metal other than the rare earth element is separated by forming a peptide structure in which a site for selectively adsorbing rare earth metal is sandwiched by a β sheet structure. There is. Further, Patent Document 2 discloses a peptide (four-helix bundle structure) that selectively adsorbs rare metals.

JP, 2014-511449, A JP, 2013-181021, A

  However, the methods described in Patent Documents 1 and 2 cannot selectively adsorb a specific type of rare earth element (for example, neodymium) to a peptide.

  In view of the above points, an object of the present invention is to provide a peptide capable of efficiently recovering a specific type of rare earth element, a rare earth element recovery material, and a rare earth element recovery method.

In order to achieve the above-mentioned object, the invention according to claim 1 is a peptide used for recovering neodymium, which consists of the amino acid sequence of any of SEQ ID NOs: 1 to 5.

Neodymium can be efficiently recovered by using the peptide of the present invention.

The rare earth element recovery material of the present invention contains the above-mentioned peptide and is used for the recovery of neodymium . Using the rare earth element recovery material of the present invention, neodymium can be efficiently recovered.

The rare earth element recovery method of the present invention is characterized by including a step of bringing the above-described rare earth element recovery material into contact with a liquid containing neodymium . By using the rare earth element recovery method of the present invention, neodymium can be efficiently recovered.

It is a conceptual diagram which shows the whole structure of an evaluation apparatus. It is a figure which shows the adsorption breakthrough curve of neodymium. It is a figure which shows the neodymium adsorption amount of peptides NdDP01-NdDP05. It is a figure which shows the adsorption breakthrough curve of neodymium and iron.

  Embodiments to which the present invention is applied will be described below.

〔peptide〕
The peptide of this embodiment has the amino acid sequence of either (a) or (b) below.

  (A) The amino acid sequence of any of SEQ ID NOs: 1 to 5.

  (B) An amino acid sequence in which one or several amino acids are deleted, substituted or added in any of the amino acid sequences of SEQ ID NOs: 1 to 5.

  The amino acid sequence of SEQ ID NO: 1 is “Glu Gly His Thr Asp Ala Glu Asp Glu Tyr Glu His (EGHTDAEDEYEH)”. The amino acid sequence of SEQ ID NO: 2 is “Glu Leu Asn Thr Asp Ala Asp Asn Leu Tyr Asn Glu (ELNTDADNLYNE)”. The amino acid sequence of SEQ ID NO: 3 is “Glu Leu Asp Thr Glu Gly Thr Asn Asp Tyr Leu Asp (ELDTEGTNDYLD)”. The amino acid sequence of SEQ ID NO: 4 is “Glu Leu Glu Ala Glu Ala Glu Asn Glu Tyr Leu Glu (ELEAEAENEYLE)”. The amino acid sequence of SEQ ID NO: 5 is “Asp Leu Asp Ala Asp Ala Asp Asn Asp Tyr Leu Glu (DLDADADNDYLE)”.

  The peptide of this embodiment has a property of selectively binding to a specific type of rare earth element. Here, “selectively binds” means that the peptide of the present embodiment is more relative to a specific type of rare earth element (eg, neodymium) than a predetermined element other than the specific type of rare earth element (eg, iron). It means that they are easily combined. In other words, it does not mean that the peptide of the present embodiment does not necessarily bind to any element other than the specific type of rare earth element.

  The rare earth element is a generic term for lanthanoids of 15 elements from lanthanum (atomic number 57) to lutetium (atomic number 71), scandium, and yttrium in the periodic table. The peptide of this embodiment has a property of selectively binding to neodymium. Therefore, the peptide of this embodiment can be suitably used for the purpose of recovering neodymium.

  The peptide of the present embodiment may be composed of only the amino acid sequences of (a) and (b) above, and may also have other amino acid sequences. Moreover, the peptide of the present embodiment may have an amino acid sequence in which the amino acid sequences of (a) and (b) above are repeated a plurality of times.

  In the present specification, the peptide means a peptide in which two or more amino acids are bound by a peptide bond, and the number of amino acids to be bound can be set appropriately. Therefore, the peptide of this embodiment may be a polypeptide. However, the number of amino acids (residue number) in the peptide is preferably in the range of 6 to 48. Within this range, the effect of recovering the rare earth element is further enhanced.

  The C-terminal of the peptide of the present embodiment is not particularly limited, and may be, for example, any of a carboxy group, a carboxylate, an amide, and an ester.

  The peptide of this embodiment may form a salt. Examples of the salt include salts with acids such as hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, trifluoroacetic acid, lactic acid, tartaric acid, maleic acid, fumaric acid, oxalic acid, malic acid, citric acid, oleic acid, and palmitic acid. Alternatively, it may be a salt with an alkali metal or alkaline earth metal such as sodium, potassium or calcium, or a salt with a hydroxide or carbonate of luminium, triethylamine, benzylamine, diethanolamine, t-butylamine, dicyclohexylamine. Alternatively, a salt with arginine may be used.

  The amino acid sequences of SEQ ID NOS: 1 to 5 consist of the amino acid sequence “Gly Leu His Thr Ser Ala Thr Asn Leu Tyr Leu His (GLHTSATNLYLH)” of SEQ ID NO: 1 disclosed in Japanese Patent Laid-Open No. 2016-47810 by the present applicant. Peptides can be made as templates. By substituting the amino acids contained in this template peptide, the amino acid sequences of SEQ ID NOs: 1 to 5 of this embodiment can be obtained.

  The peptide of this embodiment can be synthesized by a known method. Examples of the synthesis method include solid-phase peptide synthesis (SPPS) using Fmoc group and Boc group, liquid-phase peptide synthesis (LPPS), cell-free protein synthesis system ( Cell-free protein synthesis system), a synthetic method using a bacterial expression system, and the like.

  The structure of the peptide of this embodiment is designed based on the following guidelines.

According to HSAB (Hard and Soft Acid and Bases), the rare earth element ion is a hard acid and a useful bond with a hard base is considered. For example, a hard base chelating agent containing a large amount of a carboxyl group (—COOH) (eg, EDTA or DTPA) forms a stable complex with a neodymium ion (Nd ³⁺ ). Therefore, it is considered that among the amino acids, aspartic acid (Asp, D) and glutamic acid (Glu, E) having a carboxy group serving as a hard base are more useful for binding to a rare earth element ion than other amino acids.

  The neodymium ion is 9-coordinated, forming 6-coordinates with the ligand and 3-coordinates with water molecules. Therefore, the peptide of the present embodiment preferably contains an amino acid having 6 carboxy groups capable of coordinating with a neodymium ion (Reference: S. Cotton, Coordination Chemistry of the Lanthanides, in Lanthanide. and Actinide Chemistry, John Wiley and Sons, Ltd., West Sussex, p.42-43 (2006)).

The peptide of this embodiment is based on the amino acid sequence of the EF hand loop. The EF hand has a helix-loop-helix structure, and it is known that a calcium ion (Ca ²⁺ ) is coordinated in the central loop region (Reference: F. Friedberg, Calcium binding protein families: The'). EF Hand' family, Biochem. Edu 16(1) (1988).). The loop region is composed of a sequence of about 12 amino acid residues involved in calcium binding, and it is known that the sequence has a certain regularity.

  Since the ionic radius (0.99Å) of calcium ion is close to the ionic radius of rare earth element ion (for example, 0.98Å for neodymium ion), the peptide of this embodiment should be designed based on the amino acid sequence of the EF hand loop. Therefore, it is considered that the bondability with the rare earth element can be improved.

  In consideration of the above matters, the present inventors have found that the amino acid sequence having the following features can improve the binding property to neodymium ion. That is, in the amino acid sequence of 12 amino acid residues, the 1,3,5,7,9,12 amino acids are aspartic acid (Asp,D) and glutamic acid (Glu,E) each having a carboxyl group, Amino acids other than the 1, 3, 5, 7, 9, and 12th amino acids, that is, the 2, 4, 6, 8, 10, and 11th amino acids are alanine (Ala, A), leucine (Leu, L), glutamic acid (Glu, E), any of the amino acids derived from the template peptide. The amino acids derived from the template peptide are leucine (Leu, L) at the second position, threonine (Thr, T) at the fourth position, alanine (Ala, A) at the sixth position, and asparagine (Asn, N) at the eighth position. Tyrosine (Tyr, Y), 11th is leucine (Leu, L).

  By using the amino acid sequence having the above characteristics as the final target pattern and substituting the amino acids contained in the template peptide, the amino acid sequences of SEQ ID NOs: 1 to 5 can be obtained. The amino acid sequences of SEQ ID NOs: 4 and 5 correspond to the amino acid sequence of the final target pattern.

  Here, the procedure for producing the amino acid sequences of SEQ ID NOs: 1 to 5 of the present embodiment using the template peptide will be described.

  The amino acid sequence of SEQ ID NO: 1 can be obtained by increasing the number of acidic amino acids with respect to the template peptide. Acidic amino acids are aspartic acid (Asp,D) and glutamic acid (Glu,E). The amino acid sequence of SEQ ID NO: 2 can be obtained by increasing the number of acidic amino acids and asparagine (Asn, N) with respect to the amino acid of SEQ ID NO: 1. The amino acid sequence of SEQ ID NO: 3 can be obtained by increasing acidic amino acids and decreasing histidine (His, H) with respect to the amino acids of SEQ ID NO: 1. It is assumed that the amino acid sequences of SEQ ID NOs: 4 and 5 are obtained by increasing the number of acidic amino acids and the number of amino acids that are likely to have a secondary structure with respect to the amino acids of SEQ ID NO: 3. Among the above-mentioned amino acids, amino acids that tend to have a secondary structure are glutamic acid (Glu, E), leucine (Leu, L) and alanine (Ala, A). However, these amino acids do not always have a secondary structure.

[Rare earth element recovery material]
The rare earth element recovery material of the present embodiment contains the peptide described above. The rare earth element recovery material is used for recovering rare earth elements (particularly neodymium). The rare earth element recovery material may be composed of the above-mentioned peptide (for example, substantially free of the constituents other than the peptide), or may further contain constituents other than the peptide.

  The rare earth element recovery material of the present embodiment may include, for example, a solid phase carrier carrying a peptide. The material of the solid phase carrier can be appropriately selected, and examples thereof include inorganic substances such as glass, silica and bentonite, synthetic polymer substances such as polystyrene, polyethylene and polypropylene, agarose gel, dextran gel, insoluble polysaccharides such as cellulose and paper. Be done.

  Further, the shape of the solid phase carrier can be appropriately selected and, for example, can be hollow tubular, spherical, particulate, rod-shaped, sheet-shaped, plate-shaped, box-shaped or the like. The method for supporting the peptide on the solid phase carrier can be appropriately selected from known methods, and for example, it can be supported via covalent bond, physical adsorption, or ionic bond.

  The rare earth element recovery material of the present embodiment can include, for example, a phage (Phage) having the above-described peptide bound to the N-terminus or Lys side chain of the coat protein. Phage (bacteriophage) is a general term for viruses that infect and propagate in bacteria. Phage has a structure in which a nucleic acid is wrapped in a coat protein shell.

The phage can be appropriately selected from known phages, and for example, M13 phage and the like can be used. The method for binding the above-mentioned peptide to the N-terminus or Lys side chain of the phage coat protein can be appropriately selected from known methods, and examples thereof include an amino group (-NH ₂ ) and a carboxy group (-COOH). A method utilizing a dehydration condensation reaction or an amine coupling reaction with can be used.

In this method, first, WSC (Water soluble carbodiimide) is used to allow the above peptide to stand at room temperature for 1 hour to activate the carboxy group of the peptide. Then, a -NH ₂ (N-terminal or Lys side chain) in the coat protein of a wild strain M13 phage, causing a coupling reaction with the carboxy group of the peptide. As a result, the above-mentioned peptide binds to the N-terminus or Lys side chain of the phage coat protein. Alternatively, the phage coat protein may be provided with the above-mentioned peptide as a part thereof by recombining the phage gene.

[Recovery method for rare earth elements]
The rare earth element recovery method of the present embodiment includes a step of bringing the rare earth element recovery material described above into contact with a liquid containing a rare earth element. In this step, the rare earth element recovery material (particularly, the peptide contained in the rare earth element recovery material) bonds with the rare earth element.

  The rare earth element recovery material combined with the rare earth element can be taken out of the liquid by a method such as centrifugation or filtration. After that, for example, the rare earth element can be recovered by a method such as incineration of the rare earth element recovery material or dissociation of the rare earth element from the rare earth element recovery material.

  The liquid containing a rare earth element (for example, neodymium) can contain, for example, ions of a rare earth element. The liquid containing the rare earth element may contain only the rare earth element, or may contain other elements in addition to the rare earth element. In addition, solid matter (for example, particles) may be dispersed in the liquid containing the rare earth element.

  The mode of the step of bringing the rare earth element recovery material into contact with the liquid containing the rare earth element can be appropriately selected. For example, the rare earth element recovery material can be added to the liquid containing the rare earth element. Further, a liquid containing a rare earth element may be dropped on the rare earth element recovery material.

  Further, when the rare earth element recovery material is composed of a solid phase carrier and a peptide supported thereon, a liquid containing a rare earth element may be injected into a column packed with the rare earth element recovery material. At this time, the rare earth element contained in the liquid is bonded to the rare earth element recovery material in the column. On the other hand, among the liquid components, the component to which the peptide is difficult to bind passes through the column. As a result, the rare earth element contained in the liquid can be recovered.

  The rare earth element recovery method of the present embodiment preferably includes a step of adding a chelating agent to the liquid containing the rare earth element. In that case, the property that the rare earth element recovery material selectively bonds with the rare earth element becomes more remarkable. Examples of the chelating agent include EDTA (ethylenediaminetetraacetic acid, edetic acid), NTA (sodium nitrilotriacetate), IDA (iminodiacetic acid) and the like. The timing of adding the chelating agent to the liquid may be before, at the same time, or after the step of bringing the rare earth element recovery material and the liquid into contact with each other. The concentration of the chelating agent in the liquid can be equal to or higher than the concentration of the rare earth element in the liquid, for example.

(Example 1)
In Example 1, the peptides having the amino acid sequences of SEQ ID NOs: 1 to 5 were used to measure the adsorption performance of neodymium. The peptides having the amino acid sequences of SEQ ID NOs: 1 to 5 are also referred to as NdDP01 to NdDP05, respectively.

  As shown in FIG. 1, in Example 1, an evaluation device including a container 1, a pump 2, a column 3, and a fraction collector 4 was used.

The container 1 contains a solution containing neodymium ions. Solution, water is a liquid for a medium, neodymium ions, was used _{Nd (NO 3) 3 · 6H} 2 O ( Wako Pure Chemical Industries, Ltd.). The neodymium concentration in the solution was 5 mg/L.

For the solution, PIPES (piperazine-N,N'-bis(2-ethanesulfonic acid), Dojindo Laboratories Co., Ltd.) was adjusted to 10 mM (=mmol/L) as a buffer, and the pH was adjusted to 5.7. It was adjusted. Furthermore, NaNO ₃ (Wako Pure Chemical Industries, Ltd.) was adjusted to 0.3 mM in the solution.

  The pump 2 is a device that delivers the solution in the container 1 to the column 3. The pump 2 can flow the solution into the column 3 at a predetermined flow rate.

  As the column 3, a coupling column for ligand immobilization “HiTrap NHS-activated HP columns (GE Healthcare Japan Co., Ltd.)” was used. In column 3, peptides NdDP01 to NdDP05 were loaded on a solid-phase carrier agarose gel as a rare earth element recovery material. Specifically, the peptide was supported on the agarose modified with N-hydroxysuccinimide by an amine coupling reaction. The amount of peptide immobilized on the solid phase carrier was 0.4 to 1.0 μmol per gram. The volume of the column 3 is 1 mL.

  Using the evaluation apparatus described above, the solution was continuously flown through the column 3 with the pump 2 at a flow rate of 4 to 5 mL/h, and the fraction collector 4 sampled every 30 minutes. The temperature of the solution was 20 to 27°C.

  The evaluation device measured the neodymium concentration in the solution before and after passing through the column 3. Neodymium concentration was measured by inductively coupled plasma optical emission spectroscopy (ICP/AES). An ICP emission spectrometer "ICPS-7510 (Shimadzu Corporation)" was used to measure the neodymium concentration. The measurement interval was 30 minutes. The neodymium concentration Ci before passing through the column 3 is also referred to as the initial concentration Ci, and the neodymium concentration Ct after passing through the column 3 is also referred to as the post-adsorption concentration Ct.

  FIG. 2 shows the adsorption breakthrough curve of neodymium. The vertical axis is the adsorbate fraction, and the horizontal axis is the adsorption time. The adsorbate fraction is the concentration after adsorption Ct/the initial concentration Ci. In FIG. 2, the adsorption breakthrough curve of neodymium when using the column 3 on which the peptide is not immobilized is shown as a comparative example.

  In the state where all the neodymium in the solution is adsorbed by the peptide, the concentration Ct after adsorption becomes zero and Ct/Ci=0. When the neodymium adsorption amount of the peptide decreases, the post-adsorption concentration Ct increases and Ct/Ci>0. When the amount of neodymium adsorbed on the peptide reaches the upper limit and becomes saturated, the adsorbed concentration Ct=initial concentration Ci and Ct/Ci=1.

  As shown in FIG. 2, in the comparative example in which no peptide was used, the neodymium adsorption capacity was not effective, and the saturated state was reached immediately. In contrast, when the column 3 on which the peptides NdDP01 to NdDP05 are immobilized is used, the time when Ct/Ci=0 is long (2 to 4.5 hours) and the neodymium adsorption capacity is high. .

  Based on the difference (Ci-Ct) in the neodymium concentration before and after passing through the column 3, the amount of neodymium adsorbed until the peptides NdDP01 to NdDP05 are saturated can be calculated. The neodymium adsorption amount q (mg/g) by the peptides NdDP01 to NdDP05 can be calculated by the following mathematical expression (1).

ｗｔ_pepはペプチド量（ｍｇ）である。ｖは測定対象の溶液量（ｍＬ）である。実施例１では３０分毎にサンプリングを行っているので、ｖは２．５ｍＬ程度となる。Ｃｉはカラム通過前のネオジム濃度（μｇ／ｍＬ）である。Ｃｔはカラム通過後のネオジム濃度（μｇ／ｍＬ）である。

wt _pep is the amount of peptide (mg). v is the solution volume (mL) to be measured. In Example 1, since sampling is performed every 30 minutes, v is about 2.5 mL. Ci is the neodymium concentration (μg/mL) before passing through the column. Ct is the neodymium concentration (μg/mL) after passing through the column.

  FIG. 3 shows the neodymium adsorption amount q of the peptides NdDP01 to NdDP05 calculated by Equation 2. As shown in FIG. 3, the amounts of neodymium adsorbed by the peptides NdDP01 to NdDP05 are in the order of NdDP02<NdDP01<NdDP3<NdDP04<NdDP05.

(Example 2)
In Example 2, a mixed solution containing neodymium ions and iron ions was used as the solution. The neodymium concentration in the solution was 5 mg/L, and the iron concentration in the solution was 15 mg/L. Furthermore, EDTA is added to the solution. The pH of the solution was adjusted to 5.6.

  In Example 2, using the same evaluation apparatus as in Example 1, the solution was continuously flown through the column 3 with the pump 2 at a flow rate of 4.7 mL/h and sampled with the fraction collector 4 every 30 minutes. In column 3, the peptide NdDP04 consisting of the amino acid sequence of SEQ ID NO: 4 was immobilized.

  FIG. 4 shows adsorption breakthrough curves for neodymium and iron. In FIG. 4, the adsorption breakthrough curves of neodymium and iron when using the column 3 in which the peptide is not immobilized are shown as a comparative example.

  As shown in FIG. 4, in the comparative example in which the peptide was not immobilized, the neodymium adsorption capacity and iron adsorption capacity were not effective, and the saturated state was reached immediately. Further, even when the column 3 with the peptide NdDP04 immobilized thereon was used, the adsorption breakthrough curve of iron was almost the same as that of the comparative example, and the saturated state was reached immediately.

  On the other hand, the neodymium concentration when using the column 3 on which the peptide NdDP04 is immobilized has a long Ct/Ci=0 time (2.5 hours) and a high neodymium adsorption capacity.

  According to Example 2, by using the column 3 on which the peptide NdDP04 was immobilized, neodymium could be selectively adsorbed from the mixed solution of neodymium and iron.

  Moreover, in Example 2, EDTA was added to the mixed solution of neodymium and iron. Iron ions form more stable complexes with EDTA than neodymium ions. Therefore, when iron ions and neodymium ions are present, iron ions preferentially form a complex with EDTA. Neodymium existing in an ionic state is adsorbed by the peptide in column 3, and the iron forming a complex with EDTA passes through column 3 without being adsorbed by the peptide. As a result, the selectivity of neodymium by the peptide can be improved.

(Other embodiments)
The present invention is not limited to the above-described embodiments, but can be variously modified as follows without departing from the spirit of the present invention. Further, the means disclosed in each of the above embodiments may be appropriately combined within a practicable range.

  (1) Instead of the peptides NdDP01 to NdDP05, peptides having an amino acid sequence in which one or several amino acids are deleted, substituted or added in the amino acid sequences of SEQ ID NOs: 1 to 5 may be used.

  (2) The rare earth element recovery material having adsorbed neodymium may be incinerated to recover neodymium alone or as neodymium oxide.

Claims (4)

A peptide used to recover neodymium,
A peptide comprising the amino acid sequence of any of SEQ ID NOs: 1 to 5. A rare earth element recovery material containing the peptide according to claim 1 and used for recovery of neodymium . A rare earth element recovery method comprising a step of bringing the rare earth element recovery material according to claim 2 into contact with a liquid containing neodymium . The rare earth element recovery method according to claim 3 , comprising a step of adding a chelating agent to the liquid.

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