Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2001-01-09
2001-09-04
Higel, Floyd D. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C548S494000, C548S496000
Reexamination Certificate
active
06284897
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for crystallizing tryptophan to obtain spherical crystals having a large particle size which are excellent in handling at separation and drying.
2. Background Art Relating to the Invention
In general, since crystals of tryptophan are in the form of fine powder and each of the crystals has a thin plate-like shape, there are problems that the crystals are difficult to flow or precipitate in slurry conditions, and furthermore, it is difficult to handle them at solid-liquid separation or drying after the separation. Therefore, as crystals of tryptophan, it is desirable to obtain spherical crystals having a large particle size. For that purpose, in methods for crystallizing tryptophan from a solution of water or a mixed solvent of water and an organic solvent, conditions, such as a temperature, a pH, a composition of solvents and the like, are controlled (e.g., JP-A-59-39857) or a third substance is added (e.g., JP-B-5-76463 and WO 90/09372) to control the particle size and the crystal form.
Among these methods, the method in which the operating conditions are improved achieves only slight enlargement of the particle size while maintaining the shape, and cannot improve the thin plate-like shape of tryptophan crystals. Also, the method in which a third substance is added can be expected to afford larger effects on both of the particle size and the shape than the method in which the operating conditions are improved. However, in the industrial operation, an additional apparatus and step for adding the third substance are newly required, so that there are problems that not only the method is economically disadvantageous but also complicated steps are required.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method for crystallizing tryptophan in which at least one of the above defects is improved based on the chemical properties possessed by tryptophan per se.
According to the present invention, the above problems are solved, and tryptophan is crystallized by storing a tryptophan solution under alkaline conditions at room temperature or higher within a definite period of time, followed by crystallization, so that at least one of (1) tryptophan crystals having a large particle size and (2) tryptophan crystals having a spherical shape is obtained.
Specifically, the present invention relates to a method for crystallizing tryptophan, comprising storing a tryptophan solution at a pH of 8 to 13 and at a temperature of room temperature to 100° C. for 0.5 hour to 1 week, followed by crystallization.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, the room temperature is not particularly limited so long as it is a temperature at which chemical experimentation is generally carried out, and it is preferably 4° C. or higher.
Preferred conditions for the storage are shown in Table 1. When the crystallization is carried out at the pH, temperature and storage period ranges according to Table 1, effective change can be observed at the resulting crystals, and tryptophan is hardly chemically decomposed. Furthermore, when the temperature is low, a long storage period is necessary, while when the temperature is high, the effect can be obtained for a relatively short period. Among the conditions, the pH, temperature, and storage period are preferably 9.5 to 10.5, 40 to 60° C., and 1 to 2 days, respectively, in view of easy operation.
TABLE 1
pH
Temperature
Period
8-13
30-80 ° C.
1 hour to 1 week
8-13
60-100 ° C.
0.5 hour to 2 hours
As a result that the crystallization is carried out after the storage under such conditions, (1) tryptophan crystals having a particle size as large as several hundred &mgr;m to several mm are obtained and/or (2) tryptophan crystals having a spherical shape are obtained. The resulting crystals can be separated by a usual solid-liquid separating method, such as centrifugation, filtration in vacuo, or the like.
Tryptophan used in the present invention can be L-isomer or D-isomer. Examples of the tryptophan solution include a solution in which powdered tryptophan is dissolved, and a microorganism fermented liquid and an enzymatic reaction solution containing tryptophan, which can be optionally treated with, e.g., an ion-exchange resin. Examples of a solvent for dissolving tryptophan include water and a mixed solvent of water and a water-soluble organic solvent (e.g., methanol, ethanol, acetone, or the like). The pH of the solution can be adjusted by adding an alkali. The alkali used for adjusting the pH is not particularly limited, and examples thereof include sodium hydroxide, ammonia, and the like. In addition, the tryptophan concentration of the solution is also not particularly limited.
In the present invention, tryptophan is crystallized after the tryptophan solution is stored under the conditions as described above. Any method for crystallization usually used for crystallizing tryptophan can be used. Specific examples of the method for the crystallization include a method in which tryptophan is crystallized at the same time when the solution is neutralized by adding an acid; a method in which after neutralization, the solution is concentrated or cooled, or a water-soluble organic solvent (e.g., methanol, ethanol, acetone, or the like) is added thereto; and the like.
According to the present invention, as a result that a tryptophan solution is only stored, at least one of the particle size and the shape of crystals of tryptophan after crystallization can be improved. The resulting crystals of tryptophan which have been stored are more easily handled in solid-liquid separation than those which have not been stored, and have at least one characteristic of (1) a large particle size and (2) a spherical shape.
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Osinovskii, et al, 1989, Biotekhnologiya, 5(3), 338-342.
Endo Shuichi
Fuke Ichiro
Funatsu Seiji
Ajinomoto Co. Inc.
D'Souza Andrea M.
Higel Floyd D.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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