Methods to isolate cyclodextrins

Abstract

This disclosure relates to methods of isolating CDs. The method includes contacting a CD production mixture containing CD, CD, CD, and CD production byproducts with a metal salt; and forming CD-MOF complexes containing at least a metal cation and a plurality of CD components.

Claims

1. A method for isolating cyclodextrins, comprising: forming an aqueous solution of a cyclodextrin (CD) production mixture with CD, CD, and CD therein; adding a square planar metal complex to the aqueous solution of the CD production mixture to selectively form an CD-metal organic framework (MOF) complex and precipitate the CD-MOF complex out of the solution as a solid CD-MOF complex with the CD, and CD remaining in the aqueous solution; separating the solid CD-MOF complex from the aqueous solution with the CD, and the CD remaining in the aqueous solution; adding a solvent and a metal salt to the aqueous solution with the CD, and CD remaining therein to selectively form a CD-MOF complex and precipitate the CD-MOF complex out of a mixture of the aqueous solution and solvent as a solid CD-MOF complex with the CD remaining in the aqueous solution, wherein: the solvent is a C.sub.1-10 alcohol, C.sub.1-10 alkane, methylene chloride, acetone, acetic acid, acetonitrile, benzene, toluene, dimethylformamide, or a mixture thereof; separating the solid CD-MOF complex from the mixture of the aqueous solution and solvent with the CD remaining therein; and concentrating or lowering the temperature of the mixture of the aqueous solution and solvent with the CD remaining therein to precipitate the CD out of the aqueous solution as solid CD.

2. The method of claim 1, wherein, forming the aqueous solution of the CD production mixture further comprises: treating an aqueous solution of a polysaccharide with a CD glycosyltransferase (CGTase); and then treating the aqueous solution of the polysaccharide with an amylase.

3. The method of claim 1, wherein the metal salt has a metal cation selected from the group consisting of Group IA metal cations, Group IIA metal cations, and transition metal cations.

4. The method of claim 3, wherein the metal cation is K.sup.+, Rb.sup.+, Na.sup.+, Cs.sup.+, Li.sup.+, Mg.sup.2+, Cd.sup.2+, Sn.sup.2+, Ag.sup.+, Yb.sup.+, Ba.sup.2+, Sr.sup.2+, Ca.sup.2+, Pb.sup.2+, or La.sup.3+.

5. The method of claim 1, wherein the metal salt has an anion selected from the group consisting of Cl.sup., Br.sup., C.sub.7H.sub.5O.sub.2.sup., F.sup., S.sup.2, CrO.sub.4.sup.2, and CN.sup..

6. The method of claim 1, wherein the metal salt is potassium chloride or potassium benzoate.

7. The method of claim 1, wherein the solvent is a C.sub.1-10 alkane, methylene chloride, acetic acid, benzene, toluene, or a mixture thereof.

8. The method of claim 7, wherein the solvent is vapor diffused into the aqueous solution with the CD, and the CD remaining therein.

9. The method of claim 1, wherein, forming the aqueous solution of the CD production mixture further comprises: treating an aqueous solution of a polysaccharide with an amylase; and then treating the aqueous solution of the polysaccharide with a CD glycosyltransferase (CGTase).

10. The method of claim 9, wherein the amylase is an -amylase, -amylase, or -amylase.

11. The method of claim 1, further comprising dissolving the solid CD-MOF complex in a second solvent with heating to form an CD solution and the passing the CD solution through an ion exchange resin to isolate the CD from the CD solution.

12. The method of claim 11, wherein the second solvent comprises C.sub.1-10 alcohol, C.sub.1-10 alkane, methylene chloride, acetone, acetic acid, acetonitrile, benzene, toluene, dimethylformamide, or a mixture thereof.

13. The method of claim 1, further comprising dissolving the solid CD-MOF complex in water to produce a CD aqueous solution.

14. The method of claim 13, further comprising passing the CD aqueous solution through an ion exchange resin to isolate the CD from the CD aqueous solution.

15. The method of claim 1, further comprising isolating the solid CD from the aqueous solution by filtration or centrifugation.

16. A method for isolating cyclodextrins, comprising: treating a polysaccharide composition with a cyclodextrin glycosyltransferase (CGTase) to form a cyclodextrin (CD) production mixture; and treating the polysaccharide composition with an amylase prior to treating the polysaccharide composition with the CGTase or treating the CD production mixture with an amylase after treating the polysaccharide composition with the CGTase, forming CD-metal organic framework (MOF) complexes, the forming comprising contacting a CD production mixture with a metal compound, wherein the CD production mixture comprises CD, CD, CD, and CD production byproducts, and each CD-MOF complex comprises at least a metal cation and a plurality of CD components.

17. The method of claim 16, comprising treating the polysaccharide composition with the amylase prior to treating the polysaccharide composition with the CGTase.

18. The method of claim 17, wherein the amylase is an -amylase, -amylase, or -amylase.

19. The method of claim 16, comprising treating the CD production mixture with the amylase after treating the polysaccharide composition with the CGTase.

20. The method of claim 19, wherein the amylase is an -amylase, -amylase, or -amylase.

21. A method for isolating cyclodextrins, comprising: forming an aqueous solution of a cyclodextrin (CD) production mixture with CD, CD, and CD therein; concentrating or lowering the temperature of the CD production mixture to precipitate the CD out of the aqueous solution as a solid CD with the CD, and CD remaining in the aqueous solution; separating the solid CD from the aqueous solution with the CD, and CD remaining therein; adding a square planar metal complex to the aqueous solution with the CD, and CD remaining therein to selectively form an CD-metal organic framework (MOF) complex and precipitate the CD-MOF complex out of the aqueous solution as a solid CD-MOF complex with the CD remaining in the aqueous solution; separating the solid CD-MOF complex from the aqueous solution with the CD remaining therein; adding a solvent and a metal salt to the aqueous solution with the CD remaining therein to form a CD-MOF complex and precipitate the CD-MOF complex out of the solution as a solid CD-MOF complex, wherein the solvent is a C.sub.1-10 alcohol, C.sub.1-10 alkane, methylene chloride, acetone, acetic acid, acetonitrile, benzene, toluene, dimethylformamide, or a mixture thereof, and, the metal salt includes a metal cation consisting of Group IA metal cations; and separating the solid CD-MOF complex from the aqueous solution.

22. The method of claim 21, wherein the square planar metal complex comprises a noble metal.

23. The method of claim 22, wherein the noble metal is gold, platinum, or palladium.

24. The method of claim 21, wherein the square planar metal complex is potassium tetrabromoaurate or potassium tetrachloroaurate.

25. The method of claim 21, wherein, forming the aqueous solution of the CD production mixture further comprises: treating an aqueous solution of a polysaccharide composition with an amylase; and then treating the polysaccharide composition with a CD glycosyltransferase (CGTase).

26. The method of claim 21, wherein, forming the aqueous solution of the CD production mixture further comprises: treating the polysaccharide composition with a CD glycosyltransferase (CGTase); and then treating an aqueous solution of a polysaccharide composition with an amylase.

27. The method of claim 26, wherein the amylase is an -amylase, -amylase, or amylase.

28. The method of claim 21, wherein separating the solid CD-MOF complex from the aqueous solution with the CD remaining therein comprises filtration or centrifugation.

29. The method of claim 21, further comprising dissolving the solid CD-MOF complex in water with heating to produce an CD aqueous solution.

30. The method of claim 29, further comprising passing the CD aqueous solution through an ion exchange resin to isolate the CD.

31. The method of claim 21, wherein the solvent is a C.sub.1-10 alkane, methylene chloride, acetic acid, benzene, toluene, or a mixture thereof.

32. The method of claim 21, further comprising dissolving the solid CD-MOF complex in water to produce a CD aqueous solution.

33. The method of claim 32, further comprising passing the CD aqueous solution through an ion exchange resin to isolate the CD.

34. The method of claim 21, wherein separating the solid CD from the aqueous solution further comprises collecting CD crystals from the aqueous solution with the CD, and CD remaining therein by filtration or centrifugation.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 illustrates the structure of -1,4-linked D-glucopyranosyl residue.

(2) FIG. 2 illustrates the structure of a CD ring.

(3) FIG. 3 illustrates the eight monosaccharide residues in CD form a truncated cone with the C6 hydroxy (OH) groups constituting the primary (1) face and the C2 and C3 OH groups constituting the secondary (2) face.

DETAILED DESCRIPTION

(4) This disclosure relates generally to methods to isolate CDs, e.g., CDs, CDs, and/or CDs, by forming CD-MOF complexes. In general, the CD isolation methods include contacting a CD production mixture with a metal salt and forming CD-MOF complexes.

(5) Isolation of CDs can start by producing a CD production mixture from at least one polysaccharide, e.g., starch, glycogen, cellulose, amylose, or any combination thereof. The polysaccharide can be obtained from a natural source, e.g., potato, rice, wheat, and maize. Alternatively or in addition, the polysaccharide can be chemically synthesized. Regardless of the source, the polysaccharide can be provided in a composition (e.g., an aqueous solution) at a concentration ranging from at least about 10% by weight (e.g., at least about 15%, at least about 20% by weight, at least about 25% by weight, or at least about 30% by weight) to at most about 50% by weight (e.g., at most about 40% by weight, at most about 35% by weight, at most about 30% by weight, or at most about 25% by weight). For example, the composition can include from at least about 10% by weight to at most about 30% by weight of the polysaccharide. The polysaccharide can be disposed in a solvent, e.g., water, at a suitable temperature (e.g., from at least about 20 C. to at most about 90 C.) to produce a composition (e.g., a solution, suspension, or dispersion).

(6) To produce a CD production mixture containing CD, CD, and CD, a composition containing a polysaccharide can be treated with at least one CD glycosyltransferase (CGTase). CGTase (EC 2.4.1.19) is a bacterial enzyme capable of catalyzing the synthesis of CDs by cyclizing part of a (1.fwdarw.4)-alpha-D-glucan chain by formation of a (1.fwdarw.4)-alpha-D-glucosidic bond. CGTase is an enzyme common in many bacterial species, in particular the Bacillus genus (e.g., B. macerans, B. coagulans, B. alkalophilic, B. circulans, B. macerans, and B. stearothermophilus), as well as in some archaea. CGTase can be isolated from bacterial fermentation cultures of Bacillus. See, e.g., Jozsef Szejtli, Cyclodextrin Technology, Springer, 1988; Karl-Heinz Fromming and Jozsef Szejtli, Cyclodextrin in Pharmacy, Kluwer Academic Publishers, 1994; James N. BeMiller and Roy L. Whistler, Starch: Chemistry and Technology, Academic Press, 2009; and Zheng-Yu Jin, Cyclodextrin Chemistry: Preparation and Application, World Scientific Publishing, 2013, the contents of which are hereby incorporated by reference in their entirety. Alternatively, CGTase can be purchased from commercial sources, e.g., SBH Sciences, Natick, Mass. The CGTase can be an CGTase, a CGTase, or a CGTase, which preferentially form CD, CD, and CD, respectively upon contacting a polysaccharide. In some embodiments, the composition containing the polysaccharide can be treated with a mixture of CGTases to form a CD production mixture.

(7) In some embodiments, a CGTase is added to the composition containing a polysaccharide (e.g., a polysaccharide aqueous solution) to produce a CD production mixture. The CD production mixture can include different CDs, e.g., CDs, CDs, and CDs, and CD production byproducts. The CD production byproducts can include, e.g., unconverted polysaccharides, oligosaccharides, disaccharides (e.g., maltose), monosaccharides (e.g., glucose). The relative ratios and yields of the different CDs will depend on the starting polysaccharide substrate and reaction conditions, such as the selected CGTase enzyme, polysaccharide concentration, reaction time, temperature, pH, additives, and precipitants. To improve yield and reduce purification cost, production ratios can be biased to a particular type of CD by using selective , , and CGTase enzymes that predominantly produce , , and CDs, respectively, depending on the CD of interest.

(8) In some embodiments, the CD isolation methods described herein can optionally include a step of treating the composition containing a polysaccharide with an amylase prior to contacting the composition with a CGTase. The amylase can be an -amylase, -amylase, and/or -amylase. The -amylases (EC 3.2.1.1) break down long-chain polysaccharides. For example, -amylase can digest amylose to yield maltotriose and maltose. Because -amylase can act anywhere on the polysaccharide substrate, -amylase tends to be faster-acting than -amylase. In animals, -amylase is a major digestive enzyme, and its optimum pH is 6.7-7.0. -amylase (EC 3.2.1.2) works from the non-reducing end of the polysaccharide substrate and catalyzes the hydrolysis of the second -1,4 glycosidic bond, cleaving off two glucose units (maltose) at a time. The optimum pH for -amylase is 4.0-5.0. In contrast, -amylase (EC 3.2.1.3) can cleave (1-6) glycosidic linkages, as well as the last (1-4)glycosidic linkages at the nonreducing end of polysaccharide substrates, to yield glucose. The -amylase has optimal activity at around pH 3.0. These three amylases can be readily obtained from commercial sources, e.g., Sigma-Aldrich Co. As known in the art, amylase activity can be stopped by acidification to a pH lower than optimal activity for the amylase, e.g., about pH 1.0 to pH 2.0 and/or by raising the temperature to at least about 55 C. (e.g., at least about 60 C., at least about 70 C., at least about 80 C., or at least about 90 C.) and/or at most about 100 C. (e.g., at most about 60 C., at most about 70 C., at most about 80 C., or at most about 90 C.) to denature the amylase. Optimal digestion of the polysaccharide can be readily determined by a skilled practitioner. In some embodiments, the composition containing a polysaccharide can be treated with a mixture of amylases prior to contacting the composition with a CGTase. Without wishing to be bound by theory, it is believed that an advantage of this additional amylase-treating step is that the amylase can break down the polysaccharide to make it easier for the CGTase to convert the polysaccharide to form CDs, thereby increasing the yield of the CDs.

(9) In an exemplary method, after contacting the composition containing a polysaccharide with a CGTase, a CD production mixture containing CD, CD, CD, and CD production byproducts thus formed can be contacted with a metal salt in order to form CD-MOF complexes. For example, the metal salt can have a Group IA metal cation, Group IIA metal cation, or transition metal cation. In some instances, the metal cation is K.sup.+, Rb.sup.+, Na.sup.+, Cs.sup.+, Li.sup.+, Mg.sup.2+, Cd.sup.2+, Sn.sup.2+, Yb.sup.+, Ba.sup.2+, Sr.sup.2+, Ca.sup.2+, Pb.sup.2+, or La.sup.3+. In some embodiments, the metal salt has an OH.sup., Cl.sup., Br.sup., C.sub.7H.sub.5O.sub.2.sup., CO.sub.3.sup.2, F.sup., S.sup.2, CrO.sub.4.sup.2, or CN.sup. anion. As an example, the metal salt can be potassium hydroxide, rubidium hydroxide, potassium chloride, potassium benzoate, cesium hydroxide, or sodium carbonate.

(10) In some embodiments, CD-MOF complexes can be formed by the following method. At ambient temperatures and pressures, the CD production mixture containing a metal salt obtained above can be contacted with a first solvent. The first solvent can contain C.sub.1-10 alcohol (e.g., ethanol), C.sub.1-10 alkane, methylene chloride, acetone, acetic acid, acetonitrile, benzene, toluene, dimethylformamide, or a mixture thereof. In the some embodiments, the first solvent can include a mixture of water and at least one of the solvents described above. In some embodiments, the first solvent can be vapor diffused into the CD production mixture to form CD-MOF complexes (e.g., CD-MOF and CD-MOF complexes) in crystalline form with a relative large crystal size.

(11) Other methods of forming CD-MOF complexes include those described in U.S. Pat. No. 9,085,460, WO 2014/172667, and Liu et al. (Pure Appl Chem 86:1323-1334, 2014), the contents of which are hereby incorporated by reference in their entireties.

(12) The CD-MOF complexes generally include at least one metal cation (e.g., a plurality of metal cations) and a plurality of CD components (such as those of Formula (I) below). The at least one metal cation is generally coordinated with the plurality of CD molecules or CD derivatives. In general, the CD-MOF complexes are porous.

(13) In general, the main building block for CD-MOF complexes is CD, a cyclic oligosaccharide that includes monosaccharide residues linked in a circular ring. Suitable CDs that can be used in the CD-MOF complexes include, for example, , , and CDs. FIG. 1 illustrates the structure of -1,4-linked D-glucopyranosyl residue. FIG. 2 illustrates the structure of a CD ring. FIG. 3 illustrates the eight monosaccharide residues in CD form a truncated cone with the C6 hydroxy (OH) groups constituting the primary (1) face and the C2 and C3 OH groups constituting the secondary (2) face. CDs can be mass-produced through enzymatic degradation of a renewable source (e.g., starch). In some embodiments, a CD-MOF complex can be made from one or more CD derivatives (such as those shown in Formula (I) below). Without wishing to be bound by theory, it is believed that the CD rings in a CD-MOF complex adopt the faces of a cube, with their primary (1) faces pointing towards the interior of the cube and their secondary (2) faces pointing outward. Further, without wishing to be bound by theory, it is believed that the CD rings in a CD-MOF complex are linked together by coordination of the metal cations to the primary C6 OH groups and the glycosidic ring oxygen atoms. The individual cubes pack to form the body-centered cubic crystal through coordination of more alkali metal cations to the C2 and C3 OH groups of the secondary faces of the CD rings.

(14) In some embodiments, the CD-MOF complexes described herein include a CD component and a metal-containing component. The metal-containing component can have the formula MN. M can be a Group IA metal cation, Group IIA metal cation, or a transition metal cation, and N can be an organic or inorganic, monovalent or multivalent anion. Suitable inorganic anions include, for example, hydroxide, chloride, bromide, sulfinate, carbonate, fluoride, sulfide, chromate, and cyanide. Suitable organic anions include, for example, benzoate, azobenzene-4,4-dicarboxylate, acetate, and oxalate. The CD component of the CD-MOF complexes can be a compound of the Formula (I):

(15) ##STR00001##
in which n=0-10; R is selected from the group consisting of OH; NRR; C.sub.1-C.sub.18 alkyl optionally substituted with one, two, three, four or five R.sub.1 groups; C.sub.2-C.sub.18 alkenyl optionally substituted with one, two, three, four or five R.sub.1 groups; C.sub.2-C.sub.18 alkynyl optionally substituted with one, two, three, four or five R.sub.1 groups; C.sub.1-C.sub.18 alkoxy optionally substituted with one, two, three, four or five R.sub.1 groups; S(O).sub.2R; S(O)OR; S(O)R; C(O)OR; CN; C(O)R; SR, NN.sup.+N.sup.; NO.sub.2, OSO.sub.2R; C(O)OR; O(S)SR; P(O)(OR).sub.2; OP(O)(OR).sub.2; P(O)(OR)R; NRR; NRP(OR)(OR); OC(O)NRR; aryl optionally substituted with one, two, three, four or five R.sub.2 groups; heteroaryl optionally substituted with one, two, three, four or five groups independently selected from R.sub.2 groups; and cycloalkyl optionally substituted with one, two, three, four or five groups independently selected from R.sub.2 groups; each R.sub.1 group is independently selected from the group consisting of hydroxyl, halo, C.sub.1-C.sub.6 alkoxy, NRR; S(O).sub.2R; S(O)OR; S(O)R; C(O)OR; CN; C(O)R; SR, NN.sup.+N.sup.; NO.sub.2, OSO.sub.2R; C(O)OR; O(S)SR; P(O)(OR).sub.2; OP(O)(OR).sub.2; P(O)(OR)R; NRR; NRP(OR)(OR); OC(O)NRR; aryl optionally substituted with one, two, three, four or five R groups; heteroaryl optionally substituted with one, two, three, four or five groups independently selected from R groups; and cycloalkyl optionally substituted with one, two, three, four or five groups independently selected from R groups; each R.sub.2 group is independently selected from the group consisting of C.sub.1-C.sub.6 alkyl, C.sub.2-C.sub.6 alkyenyl, C.sub.2-C.sub.6 alkynyl, hydroxyl, halo, C.sub.1-C.sub.6 alkoxy, NRR; S(O).sub.2R; S(O)OR; S(O)R; C(O)OR; CN; C(O)R; SR, NN.sup.+N.sup.; NO.sub.2, OSO.sub.2R; C(O)OR; O(S)SR; P(O)(OR).sub.2; OP(O)(OR).sub.2; P(O)(OR)R; NRR; NRP(OR)(OR); OC(O)NRR; aryl optionally substituted with one, two, three, four or five R groups; heteroaryl optionally substituted with one, two, three, four or five groups independently selected from R groups; and cycloalkyl optionally substituted with one, two, three, four or five groups independently selected from R groups; and wherein each R, R, and R are independently selected from the group consisting of H, C.sub.1-C.sub.6 alkyl, and aryl. Examples of compounds of Formula (I) include , , and CDs.

(16) As used herein, the term alkyl refers to a straight or branched chain alkyl radical. Examples include, but are not limited, to methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, 2-pentyl, isopentyl, neopentyl, hexyl, 2-hexyl, 3-hexyl, and 3-methylpentyl. Each alkyl group may be optionally substituted with one, two, or three substituents such as a halo, cycloalkyl, aryl, alkenyl, or alkoxy group.

(17) As used herein, the term lower alkenyl refers to a straight or branched hydrocarbon radical having one or two double bonds and includes, for example, ethenyl, propenyl, 1-but-3-enyl, 1-pent-3-enyl, and 1-hex-5-enyl. The alkenyl group can also be optionally mono-, di-, or trisubstituted with, for example, halo, aryl, cycloalkyl, or alkoxy.

(18) As used herein, the term alkynyl refers to a straight or branched hydrocarbon radical having one or two triple bonds and includes, for example, propynyl and 1-but-3-ynyl. The alkynyl group can also be optionally mono-, di-, or trisubstituted with, for example, halo, aryl, cycloalkyl, or alkoxy.

(19) As used herein, the term alkoxy refers to an O-alkyl group in which the alkyl is as defined above.

(20) As used herein, the term halo or halogen refers to a halogen radical of fluorine, chlorine, bromine, or iodine.

(21) As used herein, the term aryl refers to an aromatic carbocylic radical having a single ring (e.g., phenyl), multiple rings (e.g., biphenyl), or multiple fused rings in which at least one is aromatic (e.g., 1,2,3,4-tetrahydronaphthyl).

(22) As used herein, the term heteroaryl refers to one aromatic ring or multiple fused aromatic ring systems of 5-, 6-, or 7-membered rings containing at least one and up to four heteroatoms (e.g., nitrogen, oxygen, or sulfur). Examples include, but are not limited to, furanyl, thienyl, pyridinyl, pyrimidinyl, benzimidazolyl, and benzoxazolyl.

(23) As used herein, the term cycloalkyl refers to a carbocylic radical having a single ring (e.g., cyclohexyl), multiple rings (e.g., bicyclohexyl) or multiple fused rings (e.g., decahydronaphthalenyl). In addition, the cycloalkyl group may have one or more double bonds.

(24) In some embodiments, the CD isolation methods described herein can optionally include a step of treating the CD production mixture with an amylase (1) after the CD production mixture is formed but prior to contacting the CD production mixture and the metal salt with a first solvent or (2) after contacting the CD production mixture and the metal salt with a first solvent. Without wishing to be bound by theory, it is believed that this amylase-treating step can break down unconverted polysaccharides (e.g., unconverted oligosaccharides or disaccharides) in the CD production mixture to form CD production byproducts that have a higher solubility in the CD production mixture, thereby allowing the CD-MOF complexes to be separated from the CD production mixture more easily.

(25) In some embodiments, after contacting the CD production mixture with the first solvent, a mixture of solid CD-MOF complexes (which can include predominantly CD-MOF and CD-MOF complexes) can be collected from the CD production mixture by filtration and/or centrifugation. The CD-MOF complexes thus formed can be nano-crystalline or crystalline. The collected CD-MOF complex can then be separated from the mixture by selective dissolution in a second solvent to produce an CD solution. Examples of suitable second solvents include C.sub.1-10 alcohol (e.g., ethanol), C.sub.1-10 alkane, methylene chloride, acetone, acetic acid, acetonitrile, benzene, toluene, dimethylformamide, and a mixture thereof. In some embodiments, the second solvent can include a mixture of water and one or more of the solvents described above to produce an CD aqueous solution. In some embodiments, the dissolution of the CD-MOF complex can be performed at an elevated temperature. For example, the CD-MOF complex can be selectively dissolved in the second solvent at a temperature from at least about 25 C. (e.g., at least about 30 C., at least about 50 C., at least about 60 C., at least about 80 C., at least about 90 C., at least about 100 C., at least about 130 C., at least about 150 C., or at least about 180 C.) to at most about 200 C. (e.g., at most about 180 C., at most about 150 C., at most about 130 C., at most about 100 C., at most about 90 C., at most about 80 C., at most about 60 C., at most about 50 C., or at most about 30 C.). In some embodiments, the CD solution thus formed can be separated from the solid CD-MOF complex by filtration and/or centrifugation. In some embodiments, CD can be isolated from the CD solution by passing the CD solution through an ion exchange resin. CD can also be separated from the metal salt by crystallization since CD is typically not as soluble as the metal salt. Alternatively, CD can be separated from the metal salt through use of molecular sieves since CD is generally much larger than the metal salt. The solid CD-MOF complex can be dissolved in a suitable solvent (e.g., water) to produce a CD solution (e.g., a CD aqueous solution). The CD can then be isolated from the CD solution by passing the CD solution through an ion exchange resin. In some embodiments, CD can also be separated from the metal salt by crystallization since CD typically is not as soluble as the metal salt. Alternatively, CD can be separated from the metal salt through use of molecular sieves since CD is generally much larger than the metal salt.

(26) In some embodiments, prior to contacting the CD production mixture with the first solvent to form CD-MOF complexes, insoluble impurities in the mixture (if present) can be removed from the CD production mixture by filtration and/or centrifugation to improve the purity of the CD-MOF complexes thus formed.

(27) In some embodiments, CD can be removed from the CD production mixture before contacting the CD production mixture with the first solvent to form solid CD-MOF and CD-MOF complexes. In such embodiments, to remove CD, the CD production mixture can be concentrated by vacuum distillation and/or can have its temperature lowered to a suitable temperature (e.g., from about 25 C. to about 4 C.) to crystallize CD. Crystalline CDs can then be separated from the CD production mixture by filtration and/or centrifugation, and washed and recrystallized in appropriate solvents for higher purity, as described in Jozsef Szejtli, Cyclodextrin Technology, Springer, 1988; Karl-Heinz Fromming and Jozsef Szejtli, Cyclodextrin in Pharmacy, Kluwer Academic Publishers, 1994; James N. BeMiller and Roy L. Whistler, Starch: Chemistry and Technology, Academic Press, 2009; and Zheng-Yu Jin, Cyclodextrin Chemistry: Preparation and Application, World Scientific Publishing, 2013, the contents of which are hereby incorporated by reference in their entirety. In some embodiments, CD can be removed from the CD production mixture (e.g., by crystallization) after CD-MOF and CD-MOF complexes are formed and removed from the CD production mixture.

(28) Alternatively, in some embodiments of the CD isolation methods described herein, rather than using a metal salt to form a mixture of CD-MOF complexes (which can include both CD-MOF and CD-MOF complexes) from the CD production mixture, the CD-MOF complex can be selectively formed from the CD production mixture using a square planar metal complex without substantially forming a CD-MOF complex. For example, a composition containing a polysaccharide (e.g., a polysaccharide aqueous solution) can first be treated with a CGTase to form a CD production mixture, as described above. The CD production mixture can be contacted with a square planar metal complex to selectively form an CD-MOF complex that has at least a metal cation and a plurality of CD components without substantially forming a CD-MOF complex. The CD-MOF complex can then be separated from the CD production mixture.

(29) In some embodiments, upon contacting the CD production mixture with a square planar metal complex, an CD-MOF complex forms and quickly precipitates out of the CD production mixture. As a non-limiting example, the metal in the square planar metal complex is a noble metal, e.g., gold, platinum, or palladium. For example, the square planar metal complex can be potassium tetrabromoaurate or potassium tetrachloroaurate.

(30) Once the CD-MOF complex is formed, it can be separated from the CD production mixture by filtration and/or centrifugation. CD can then be isolated from the CD-MOF complex thus formed by using the same methods described above (e.g., dissolving the CD-MOF complex in a suitable solvent to form an CD solution and then passing the CD solution through an ion exchange resin to isolate CD, crystallization, or use of a molecular sieve). The square planar metal complex can be recovered from the ion exchange resin and recycled.

(31) After separating the CD-MOF complex from the CD production mixture, CD can be isolated from the CD production mixture by using the same method described above. For example, the CD production mixture can be treated with a metal salt (such as those described herein) and a suitable solvent (such as those described herein) to form a CD-MOF complex. The metal salt and the solvent can be added simultaneously or sequentially. The CD-MOF complex thus formed can then be separated from the CD production mixture (e.g., by filtration or centrifugation). The isolated CD-MOF complex can subsequently be dissolved in a suitable solvent (e.g., water) to form a CD solution (e.g., a CD aqueous solution). The CD solution can then be passed through an ion exchange resin to separate the CD from the metal salt. Alternatively, as described herein, CD can be separated from the metal salt by crystallization or use of molecular sieves.

(32) In embodiments where a square planar metal complex is used to isolate CD, the CD isolation methods described herein can optionally include (1) a step of treating a composition containing a polysaccharide with amylase prior to contacting the composition with a CGTase, (2) a step of treating the CD production mixture with an amylase after the CD production mixture is formed but prior to contacting the CD production mixture and the square planar metal complex with a solvent to form a CD-MOF complex, (3) a step of treating the CD production mixture with an amylase after the CD-MOF complex is formed but before the formation of a CD-MOF complex, or (4) a step of treating the CD production mixture with an amylase after the CD-MOF complex is formed.

(33) In embodiments where a square planar metal complex is used to isolate CD, the CD isolation methods described herein can optionally remove CD from the CD production mixture (1) before forming an CD-MOF complex, (2) after forming an CD-MOF complex, but before forming a CD-MOF complex, or (3) after forming a CD-MOF complex. For example, to remove CD before forming an CD-MOF complex, the CD production mixture can be concentrated by vacuum distillation and/or can have its temperature lowered to a suitable temperature (e.g., from about 25 C. to about 4 C.) to crystallize the CD. Crystalline CD can then be separated from the CD production solution by filtration and/or centrifugation. Optionally, the CD can be washed and recrystallized in suitable solvents for higher purity.

Other Embodiments

(34) It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.