METHOD FOR PRODUCING REDUCED COENZYME Q10 FORM II CRYSTALS
20230339836 · 2023-10-26
Assignee
Inventors
Cpc classification
International classification
Abstract
An efficient production method for obtaining a reduced coenzyme Q10 Form II-type crystal having a stable crystal form is disclosed. The production method includes adding a seed crystal of a Form II-type crystal to a solution including ethanol and reduced coenzyme Q10; and precipitating a Form II-type crystal, wherein a dissolved concentration C.sub.i of reduced coenzyme Q10 before adding the seed crystal is equal to or more than a saturated concentration of a Form II-type crystal and less than a saturated concentration of a Form I-type crystal at a temperature T.sub.i when adding the seed crystal. The crystal precipitation step may include controlling a temperature T.sub.p of the solution so that a dissolved concentration C.sub.p of reduced coenzyme Q10 is equal to or more than the saturated concentration of the Form II-type crystal and less than the saturated concentration of the Form I-type crystal.
Claims
1. A method for producing a reduced coenzyme Q10 Form II-type crystal, comprising: adding a reduced coenzyme Q10 Form II-type crystal as a seed crystal to a solution comprising ethanol and reduced coenzyme Q10; and precipitating a reduced coenzyme Q10 Form II-type crystal from the solution after adding the seed crystal, wherein a dissolved concentration C.sub.i of reduced coenzyme Q10 in the solution before adding the seed crystal is equal to or more than a saturated concentration of a Form II-type crystal and less than a saturated concentration of a Form I-type crystal at a temperature T.sub.i of the solution when adding the seed crystal, and precipitating the reduced coenzyme Q10 Form II-type crystal comprises controlling a temperature T.sub.p of the solution so that a dissolved concentration C.sub.p of reduced coenzyme Q10 in the solution is equal to or more than the saturated concentration of the Form II-type crystal and less than the saturated concentration of the Form I-type crystal.
2. The production method according to claim 1, wherein the ethanol further contains water, and an ethanol concentration based on a total volume of the water and the ethanol is Z % (v/v), the Z is from 90 to 100, and when units of the C.sub.i and the C.sub.p are each designated to be % by weight and units of the T.sub.i and the T.sub.p are each designated to be K, if the C.sub.i and the C.sub.p are 1.5% by weight or more, all of the following conditions are satisfied:
A.sub.II.Math.T.sub.i+B.sub.II≤log C.sub.i<A.sub.I.Math.T.sub.i+B.sub.I, (Expression 1)
A.sub.II.Math.T.sub.p+B.sub.II≤log C.sub.p<A.sub.I.Math.T.sub.p+B.sub.I, (Expression 2)
A.sub.I=0.0089.Math.Z−0.6754, (Expression 3)
B.sub.I=−2.3607.Math.Z+172.70, (Expression 4)
A.sub.II=0.0086.Math.Z−0.6844, and (Expression 5)
B.sub.II=−2.3178.Math.Z+178.26. (Expression 6)
3. The production method according to claim 1, wherein the T.sub.i is from 20° C. to 43° C.
4. The production method according to claim 1, wherein the T.sub.i is from 20° C. to lower than 32° C.
5. The production method according to claim 1, wherein the T.sub.p is from 5° C. to 43° C.
6. The production method according to claim 1, wherein precipitation of the reduced coenzyme Q10 Form II-type crystal comprises maintaining the T.sub.p at a constant temperature.
7. The production method according to claim 1, wherein precipitation of the reduced coenzyme Q10 Form II-type crystal comprises decreasing over time the T.sub.p.
8. The production method according to claim 1, wherein precipitation of the reduced coenzyme Q10 Form II-type crystal comprises: maintaining the T.sub.p at a constant temperature within a range of 20° C. to 43° C. and then lowering the temperature of the solution to a temperature that is equal to or lower than 25° C. and lower than the constant temperature at a rate of −15° C./hour or less.
9. The production method according to claim 2, wherein the T.sub.i is from 20° C. to 43° C.
10. The production method according to claim 2, wherein the T.sub.i is from 20° C. to lower than 32° C.
11. The production method according to claim 2, wherein the T.sub.p is from 5° C. to 43° C.
12. The production method according to claim 2, wherein precipitation of the reduced coenzyme Q10 Form II-type crystal comprises maintaining the T.sub.p at a constant temperature.
13. The production method according to claim 2, wherein precipitation of the reduced coenzyme Q10 Form II-type crystal comprises decreasing over time the T.sub.p.
14. The production method according to claim 2, wherein precipitation of the reduced coenzyme Q10 Form II-type crystal comprises: maintaining the T.sub.p at a constant temperature within a range of 20° C. to 43° C. and then lowering the temperature of the solution to a temperature that is equal to or lower than 25° C. and lower than the constant temperature at a rate of −15° C./hour or less.
15. The production method according to claim 1, wherein the ethanol content per total volume of solvent is 95% (v/v) or more.
16. The production method according to claim 1, wherein the dissolved concentration C.sub.i of the reduced coenzyme Q10 before the addition of seed crystals is 2% by weight or more and 50% by weight or less.
17. The production method according to claim 1, wherein the added amount of reduced coenzyme Q10 Form II-type crystals used as seed crystals is 0.1% by weight or more and 20% by weight or less.
18. The production method according to claim 1, wherein precipitating the reduced coenzyme Q10 Form II-type crystal comprises a cooling rate at which the temperature drop range per hour is 15° C. or lower and 1° C. or higher.
19. The production method according to claim 1, after precipitating the reduced coenzyme Q10 Form II-type crystal, further comprising drying the reduced coenzyme Q10 Form II-type crystal at a temperature of 46° C. or higher and 52° C. or lower.
20. The production method according to claim 19, wherein the drying is carried out for 4 hours or more.
Description
BRIEF DESCRIPTION OF DRAWINGS
[0031]
[0032]
[0033]
[0034]
[0035]
[0036]
[0037]
[0038]
DESCRIPTION OF EMBODIMENTS
[0039] Hereinafter, the present invention will be described in detail.
<Reduced Coenzyme Q10>
[0040] The “reduced coenzyme Q10” herein may partially include oxidized coenzyme Q10, if it includes reduced coenzyme Q10 as a main component. The “main component” herein means that it is included in a proportion of, for example, 50% by weight or more, usually 60% by weight or more, preferably 70% by weight or more, more preferably 80% by weight or more, further preferably 90% by weight or more, particularly preferably 95% by weight or more, and further particularly preferably 98% by weight or more. Herein, the above-described percentage is the percentage of the reduced coenzyme Q10 to the total weight of coenzyme Q10.
[0041] Besides, as mentioned above, the reduced coenzyme Q10 includes two types of crystal polymorphisms, namely, the conventionally known Form I-type and a recently newly discovered Form II-type. Specifically, the crystal form of reduced coenzyme Q10 having a melting point around 48° C. and showing characteristic peaks at diffraction angles (2θ±0.2°) of 3.1°, 18.7°, 19.0°, 20.2° and 23.0° in powder X-ray (Cu-Kα) diffraction is Form I-type, whereas the crystal form of reduced coenzyme Q10 having a melting point around 52° C. and showing characteristic peaks at diffraction angles (2θ±0.2°) of 11.5°, 18.2°, 19.3°, 22.3°, 23.0° and 33.3° in powder X-ray (Cu-Kα) diffraction is Form II-type. In the present description, the crystal of reduced coenzyme Q10 that satisfies at least one of the following conditions is referred to as a “reduced coenzyme Q10 Form II-type crystal”: when the temperature is increased at a rate of 5° C./min by differential scanning calorimetry (DSC), the reduced coenzyme Q10 crystal has an endothermic peak at 54±2° C.; the same measurement is carried out at a temperature rising rate of 1° C./min, the reduced coenzyme Q10 crystal has an endothermic peak at 52±2° C.; and in powder X-ray (Cu-Kα) diffraction, the reduced coenzyme Q10 crystal shows characteristic peaks at diffraction angles (2θ±0.2°) of 11.5°, 18.2°, 19.3°, 22.3°, 23.0° and 33.3°. Of course, it may also be adequate if the reduced coenzyme Q10 crystal satisfies all of these conditions.
[0042] Moreover, the “crystalline solid” is used in the present description to mean a solid containing therein an amorphous component having no crystal structure, as well as a portion having a crystal structure.
<Ethanol>
[0043] The present inventors found that the saturated concentration of the Form II-type crystal is smaller than the saturated concentration of the Form I-type crystal in ethanol and further found that the temperature of mixture containing ethanol and reduced coenzyme Q10 is controlled so that the dissolved concentration of reduced coenzyme Q10 is equal to or more than the saturated concentration of the Form II-type crystal and less than the saturated concentration of the Form I-type crystal in ethanol, thereby making it possible to efficiently precipitate the Form II-type crystal.
[0044] In the present invention, ethanol may be any solvent containing ethanol as the main component and may be hydrous ethanol containing water. Surprisingly, the difference between the saturated concentration of the Form II-type crystal and the saturated concentration of the Form I-type crystal in ethanol is larger as the water content in ethanol is lower, which makes it easy to selectively precipitate the Form II type crystal under the same temperature conditions. Therefore, it is preferable that the ethanol concentration is, for example, preferably 80% (v/v) or more, 90% (v/v) or more, or 95% (v/v) or more, and 100% (v/v) or less, 99.8% (v/v) or less, or 99.5% (v/v) or less based on the total volume of water and ethanol.
<Method for Producing Reduced Coenzyme Q10 Form II-Type Crystal>
[0045] The method for producing a reduced coenzyme Q10 Form II-type crystal according to one or more embodiments of the present invention is characterized by comprising: [0046] adding a reduced coenzyme Q10 Form II-type crystal as a seed crystal to a mixed solution containing ethanol and reduced coenzyme Q10; and [0047] precipitating a reduced coenzyme Q10 Form II-type crystal in the mixed solution after adding the seed crystal, [0048] wherein a dissolved concentration C.sub.i of reduced coenzyme Q10 in the mixed solution before adding the seed crystal is equal to or more than a saturated concentration of a Form II-type crystal and less than a saturated concentration of a Form I-type crystal at a temperature T.sub.i of the mixed solution when adding the seed crystal, and [0049] the step of precipitating the crystal comprises controlling a temperature T.sub.p of the mixed solution so that a dissolved concentration C.sub.p of reduced coenzyme Q10 in the mixed solution is equal to or more than the saturated concentration of the Form II-type crystal and less than the saturated concentration of the Form I-type crystal.
[0050] In the following description, the step of the addition of seed crystals may be referred to as a “seed crystal addition step” and the step of precipitating a reduced coenzyme Q10 Form II-type crystal may be referred to as a “crystal precipitation step.”
[0051] The mixed solution containing ethanol and reduced coenzyme Q10 is not particularly limited as long as it contains ethanol and reduced coenzyme Q10. It may be a uniform solution in which reduced coenzyme Q10 is dissolved in ethanol or a slurry in which part of reduced coenzyme Q10 is dissolved in ethanol but the other part is not dissolved and is suspended. However, it is preferably a uniform solution in which reduced coenzyme Q10 is dissolved in ethanol.
[0052] The reduced coenzyme Q10 used in the mixed solution containing ethanol and reduced coenzyme Q10 may be either a crystalline or amorphous state, and the crystal polymorphism thereof is not limited. Accordingly, the conventionally known reduced coenzyme Q10 Form I-type can also be used. In addition, since the purity of the reduced coenzyme Q10 can be increased in precipitation of a crystal, reduced coenzyme Q10 having impurities, or unpurified or roughly purified reduced coenzyme Q10 may also be used. Furthermore, an extract of the reduced coenzyme Q10 obtained by a conventionally known method, or a reaction solution containing reduced coenzyme Q10 obtained from oxidized coenzyme Q10 by a known reduction method may also be used as the mixed solution, directly, or after purification and/or solvent substitution, as necessary.
[0053] The mixed solution containing ethanol and reduced coenzyme Q10 may further comprise a different organic solvent other than the ethanol (including hydrous ethanol). However, the ethanol content per total volume of solvent components is preferably 95% (v/v) or more, 97% (v/v) or more, or 99% (v/v) or more, and the upper limit thereof is preferably 100% (v/v) or less. It is most preferably 100% (v/v). Examples of the other organic solvents include at least one organic solvent selected from the group consisting of an alcohol other than the ethanol, a hydrocarbon, a fatty acid ester, and a nitrogen compound.
[0054] The dissolved concentration C.sub.i of the reduced coenzyme Q10 before the addition of seed crystals in the mixed solution containing ethanol and reduced coenzyme Q10 may be equal to or more than the saturated concentration of the Form II-type crystal and less than the saturated concentration of the Form I-type crystal at temperature T.sub.i. The dissolved concentration C.sub.i of the reduced coenzyme Q10 before the addition of seed crystals can be, for example, 2% by weight or more, preferably 3% by weight or more, more preferably 5% by weight or more, even more preferably 7% by weight or more, further preferably 9% by weight or more, still further preferably 10% by weight or more, and can be, for example, 50% by weight or less, preferably 45% by weight or less, more preferably 30% by weight or less.
[0055] In the mixed solution containing ethanol and reduced coenzyme Q10, the dissolved concentration C.sub.i of the reduced coenzyme Q10 is equal to or more than the saturated concentration of the Form II-type crystal and less than the saturated concentration of the Form I-type crystal at a temperature T.sub.i of the mixed solution when the addition of seed crystals. Therefore, it is a saturated or supersaturated solution of the Form II-type crystal and an unsaturated solution of the Form I-type crystal. Such a solution is obtained by heating a raw material mixture containing ethanol and reduced coenzyme Q10 to a temperature of 42° C. or higher, more preferably 70° C. or lower, particularly preferably 55° C. or lower so that the reduced coenzyme Q10 is dissolved, and then cooling the heated solution to a temperature T.sub.i to prepare a saturated or supersaturated solution of the Form II-type crystal.
[0056] The added amount of reduced coenzyme Q10 Form II-type crystals used as seed crystals (the added amount of seed crystals) is not particularly limited, but it is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, further preferably 0.8% by weight or more, particularly preferably 1% by weight or more based on the amount of reduced coenzyme Q10 in the mixed solution before the addition of seed crystals. The upper limit thereof is not particularly limited, but it is preferably 20% by weight or less, more preferably 4% by weight or less, particularly preferably 2% by weight or less based on the amount of reduced coenzyme Q10 in the mixed solution before the addition of seed crystals. Besides, the reduced coenzyme Q10 crystals used as seed crystals may also comprise reduced coenzyme Q10 Form I-type crystals or amorphous solids, as long as the reduced coenzyme Q10 crystals comprise reduced coenzyme Q10 Form II-type crystals. However, the reduced coenzyme Q10 crystals comprising reduced coenzyme Q10 Form II-type crystals having a high purity are preferable. It is preferable to use, as seed crystals, reduced coenzyme Q10 crystals comprising, for example, 50% by weight or more, preferably 75% by weight or more, even more preferably 80% by weight or more, further preferably 90% by weight or more of reduced coenzyme Q10 Form II-type crystals.
[0057] The temperature T.sub.i of the mixed solution when the addition of seed crystals is preferably within a range of 20° C. to 43° C. When the temperature T.sub.i is 20° C. or higher, the difference between the saturated concentration of the Form II-type crystal and the saturated concentration of the Form I-type crystal is large and the saturated concentration of the Form I-type crystal is high, which is thus appropriate for selective precipitation of the Form II-type crystal. When the temperature T.sub.i is 43° C. or lower, the crystal formation rate is high. When the temperature T.sub.i is more preferably 25° C. or higher, even more preferably 30° C. or higher, further preferably 32° C. or higher, still further preferably 35° C. or higher, the difference between the saturated concentration of the Form II-type crystal and the saturated concentration of the Form I-type crystal is greater than the above, and the saturated concentration of the Form I-type crystal is high, which thus makes it easier to selectively precipitate the Form II-type crystal. The upper limit of the temperature T.sub.i is more preferably 40° C. or lower. When the T.sub.i is from 20° C. to lower than 32° C., it is also one preferred embodiment of the present invention.
[0058] The crystal precipitation step comprises controlling a temperature T.sub.p of the mixed solution after seed crystal addition so that a dissolved concentration C.sub.p of reduced coenzyme Q10 in the mixed solution is equal to or more than the saturated concentration of the Form II-type crystal and less than the saturated concentration of the Form I-type crystal.
[0059] The temperature T.sub.p can be appropriately controlled depending on the dissolved concentration C.sub.p of the reduced coenzyme Q10 at that time. For example, the temperature T.sub.p can be from 5° C. to 43° C. In the crystal precipitation step, the temperature T.sub.p may be a constant temperature. However, as the dissolved concentration C.sub.p of the reduced coenzyme Q10 declines with the precipitation of crystals, it is preferable to carry out cooling crystallization to decrease the temperature T.sub.p of the mixed solution over time for the purpose of promoting crystallization. The expression “decrease the temperature T.sub.p over time” includes decreasing the temperature T.sub.p stepwise or continuously over time.
[0060] In the crystal precipitation step, the formation of supersaturation is preferably regulated by controlling the amount of crystals precipitated per unit time. The preferred amount of crystals precipitated per unit time is, for example, the rate of precipitating approximately 50% of the total amount of crystals precipitated per unit time, or lower (i.e., at maximum, 50% amount/hour), and is preferably the rate of precipitating approximately 25% of the total amount of crystals precipitated per unit time, or lower (i.e., at maximum, 25% amount/hour).
[0061] One preferred example of the crystal precipitation step includes maintaining the temperature T.sub.p at a constant temperature, for example, a temperature range mentioned above as a preferred range of the temperature T.sub.i when the addition of seed crystals, for example, at a constant temperature within a range of 20° C. to 43° C. In particular, it is more preferable that the step includes maintaining the temperature T.sub.p for 1 hour or longer after the addition of seed crystals within the temperature range mentioned above as a preferred range of the temperature T.sub.i when the addition of seed crystals, for example, at a constant temperature within a range of 20° C. to 43° C. The time period of maintaining the mixed solution within the above temperature range is, but is not particularly limited to, preferably 1 hour or longer, more preferably 2 hours or longer, even more preferably 4 hours or longer, particularly preferably 10 hours or longer. The upper limit of the time period of maintaining the mixed solution within the above temperature range is not particularly limited, but sufficient effects can be obtained for approximately 24 hours. Here, the expression “maintaining at a constant temperature” means preferably maintaining at a specific temperature (preset temperature) ±3° C., more preferably maintaining at a specific temperature (preset temperature) ±1° C., further preferably maintaining at a specific temperature (preset temperature) ±0.5° C.
[0062] When carrying out cooling crystallization, it is preferable to maintain the temperature T.sub.p of the mixed solution within the above temperature after the addition of seed crystals, and then decrease the temperature stepwise or continuously. The rate of decreasing the temperature T.sub.p (cooling rate) may be either constant or varied.
[0063] The cooling rate when carrying out cooling crystallization is, but is not particularly limited to, for example, a cooling rate at which the temperature drop range per hour is preferably 15° C. or lower (=a temperature change rate of −15° C./hour or less), more preferably 10° C. or lower, even more preferably 5° C. or lower, more preferably 1° C. or higher, even more preferably 2° C. or higher. One example of carrying out cooling crystallization can be an aspect in which the temperature T.sub.p of the mixed solution is maintained within the above temperature after the addition of seed crystals, and then the temperature of the mixed solution is decreased to a temperature that is equal to or lower than 25° C. and lower than the above constant temperature at a rate of −15° C./hour or less. When the temperature of the mixed solution is decreased over time, the cooling rate may be either constant or varied. In particular, according to an embodiment in which the above-described cooling rate continuously or stepwise increases, namely, the temperature decrease width per hour increases, as the temperature of the mixed solution decreases, the reduced coenzyme Q10 whose amount remaining in the liquid phase decreases as the temperature of the mixed solution decreases can be efficiently crystallized. For example, until the temperature of the mixed solution reaches 25° C., the mixed solution can be cooled at a rate in which the temperature decrease width per hour is preferably 5° C. or lower, and more preferably 3° C. or lower. Then, at the stage in which the mixed solution is further cooled to lower than 25° C., the mixed solution can be cooled at a rate in which the temperature decrease width per hour is preferably 6° C. or higher, and more preferably 8° C. or higher. The end-point temperature when carrying out cooling crystallization is preferably 25° C. or lower, more preferably 20° C. or lower, even more preferably 10° C. or lower, further preferably 7° C. or lower, and still further preferably 5° C. or lower. The lower limit of the above-described end-point temperature is the solidification temperature of the system of the mixed solution and is preferably 0° C. or higher, and more preferably 3° C. or higher.
[0064] Precipitation of crystals is preferably carried out, while forced-flowing the mixed solution after the addition of seed crystals. In order to suppress the formation of supersaturation and smoothly conduct nucleation and/or crystal growth, or from the viewpoint of the achievement of high quality, flowing may be given to the mixed solution at a power required for stirring per unit volume of generally approximately 0.01 kW/m.sup.3 or more, preferably 0.03 kW/m.sup.3 or more, more preferably 0.1 kW/m.sup.3 or more, and further preferably 0.3 kW/m.sup.3 or more. The forced-flowing is generally given by the rotation of a stirring blade. However, if the above-described flowing is obtained, the use of the stirring blade is not always necessary, and for example, a method involving circulation of the mixed solution or the like may be utilized.
[0065] the crystallization step may comprise controlling a temperature T.sub.p of the mixed solution so that a dissolved concentration C.sub.p of reduced coenzyme Q10 is equal to or more than the saturated concentration of the Form II-type crystal and less than the saturated concentration of the Form I-type crystal. For example, during a time period in which preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 85% by weight or more, further preferably 90% by weight or more of the total amount of the reduced coenzyme Q10 contained in the mixed solution is precipitated as crystals after the addition of seed crystals, or during a time period in which the dissolved concentration C.sub.p of reduced coenzyme Q10 reaches 1.5% by weight or less after the addition of seed crystals, if the temperature T.sub.p of the mixed solution is controlled to satisfy the above-described conditions, as most of the reduced coenzyme Q10 is precipitated in the form of Form II-type crystals, the temperature conditions may deviate from the above conditions thereafter.
[0066] Surprisingly, the present inventors found that when based on the total volume of water and ethanol in the mixed solution, the ethanol concentration is Z % (v/v), the Z is from 90 to 100, the unit of the dissolved concentration C of reduced coenzyme Q10 in the mixed solution is designated to be % by weight, and the unit of temperature T of the mixed solution is designated to be K, the solubility of the Form I-type crystal at a temperature T (K) (saturated concentration) C.sub.I (% by weight) and the solubility of the Form II-type crystal at a temperature T (K) (saturated concentration) C.sub.II (% by weight) can be expressed by the following Expressions 7 and 8, respectively, where A.sub.I, B.sub.I, A.sub.II, and B.sub.II are independently constants.
log C.sub.I=A.sub.I.Math.T+B.sub.I (Expression 7)
log C.sub.II=A.sub.II.Math.T+B.sub.II (Expression 8)
[0067] The present inventors further found that each of the constants A.sub.I, B.sub.I, A.sub.II, and B.sub.II can be expressed by the following Expressions 3, 4, 5, and 6, respectively, with the ethanol concentration Z as a variable.
A.sub.I=0.0089.Math.Z−0.6754 (Expression 3)
B.sub.I=−2.3607.Math.Z+172.70 (Expression 4)
A.sub.II=0.0086.Math.Z−0.6844 (Expression 5)
B.sub.II=−2.3178.Math.Z+178.26 (Expression 6)
[0068] Therefore, in the seed crystal addition step, when the dissolved concentration C.sub.i of the reduced coenzyme Q10 and the temperature T.sub.i of the mixed solution satisfy the following Expression 1, the dissolved concentration C.sub.i of the reduced coenzyme Q10 is equal to or more than the saturated concentration of the Form II-type crystal and less than the saturated concentration of the Form I-type crystal. Here, the unit of C.sub.i is designated to be % by weight, and the unit of T.sub.i is designated to be K. It was found that Expression 1 is established when C.sub.i is equal to or more than 1.5% by weight.
A.sub.II.Math.T.sub.i+B.sub.II≤log C.sub.i<A.sub.I.Math.T.sub.i+B.sub.I (Expression 1)
[0069] Similarly, in the crystal precipitation step, when the dissolved concentration C.sub.p of the reduced coenzyme Q10 and the temperature T.sub.p of the mixed solution satisfy the following Expression 2, the dissolved concentration C.sub.p of the reduced coenzyme Q10 is equal to or more than the saturated concentration of the Form II-type crystal and less than the saturated concentration of the Form I-type crystal. Here, the unit of C.sub.p is designated to be % by weight and the unit of T.sub.p is designated to be K. It was found that Expression 2 is established when C.sub.p is equal to or more than 1.5% by weight. In preferred embodiments of the present invention, all of Expressions 1 to 6 are satisfied.
A.sub.II.Math.T.sub.p+B.sub.II≤log C.sub.p<A.sub.I.Math.T.sub.p+B.sub.I (Expression 2)
[0070] The reduced coenzyme Q10 Form II-type crystal or crystalline solid obtained by the above method is recovered through a step of solid-liquid separation and drying by a conventionally known method described in, for example, Patent Literature 2 or 3. For example, pressure filtration or centrifugal filtration can be used for solid-liquid separation. In addition, the crystal or crystalline solid after drying can also be recovered by pulverization or classification (sieving), if necessary.
[0071] In the present invention, as one of more preferred aspects, after completion of the aforementioned solid-liquid separation, the reduced coenzyme Q10 Form II-type crystal or the crystalline solid is dried with warming, so that the content rate of the reduced coenzyme Q10 Form II-type crystal can be improved. For this purpose, the drying temperature is preferably 46° C. or higher, more preferably 47° C. or higher, and further preferably 49° C. or higher. The upper limit of the drying temperature is generally 52° C. or lower, and preferably 51° C. or lower. When the drying temperature is lower than 46° C., drying progresses, but the content rate of the reduced coenzyme Q10 Form II-type crystal is hardly improved. On the other hand, when the drying temperature exceeds 52° C., there may be a case where the reduced coenzyme Q10 crystal is melted during the drying. In addition, the warming time in the case of carrying out drying under the aforementioned conditions is not particularly limited, but it is preferably 4 hours or more, more preferably 10 hours or more, and further preferably 20 hours or more.
[0072] Besides, when the desired content rate of the reduced coenzyme Q10 Form II-type crystal has already been achieved in the crystal precipitation step, the aforementioned drying conditions shall not apply, and the drying may be carried out at a temperature of, for example, 25° C. or higher, preferably 30° C. or higher, and more preferably 35° C. or higher.
[0073] Besides, individual steps in the method of the present invention, specifically, the above-described seed crystal addition step, crystal precipitation step, recovery step such as solid-liquid separation or drying, and other subsequent treatment steps are preferably carried out under a deoxidizing atmosphere. The deoxidizing atmosphere can be achieved by the replacement of the atmosphere with an inert gas, reduction of the pressure, boiling, or a combination thereof. The replacement of the atmosphere with an inert gas, namely, an inert gas atmosphere is preferably used. Examples of the inert gas include nitrogen gas, helium gas, argon gas, hydrogen gas, and carbon dioxide, and preferred is nitrogen gas.
[0074] Whether or not the reduced coenzyme Q10 Form II-type crystal is contained in the obtained reduced coenzyme Q10 crystal or crystalline solid, and the content rate thereof can be determined by measuring with, for example, a differential scanning calorimeter (DSC).
[0075] As mentioned above, when the reduced coenzyme Q10 Form II-type crystal is measured with DSC at a temperature rising rate of 1° C./min, it exhibits an endothermic peak around 52±2° C. On the other hand, the reduced coenzyme Q10 Form I-type crystal exhibits an endothermic peak around 48±1° C. under the same conditions as those described above. Even in a state in which the reduced coenzyme Q10 Form II-type crystal is mixed with the conventional reduced coenzyme Q10 Form I-type crystal or a crystalline solid thereof, the presence or absence of the reduced coenzyme Q10 Form II-type crystal or the content rate thereof can be determined based on the presence or absence of the above-described peak around 52±2° C., the height of the endothermic peak, or the ratio of the endothermic amount. According to the method of the present invention, a reduced coenzyme Q10 Form II-type crystal or a crystalline solid having a high purity can be efficiently obtained.
Examples
[0076] Hereinafter, the present invention will be more specifically described based on Examples. However, the technical scope of the present invention is not intended to be limited to these Examples.
<Percentage of Reduced Coenzyme Q10 Form II-Type Crystal>
[0077] Regarding the percentage of Form II-type crystals in recovered reduced coenzyme Q10 crystals, the recovered crystals were analyzed by DSC measurement under the following conditions. From the height (Difference Y) of the endothermic peak of reduced coenzyme Q10 Form I-type crystals (hereinafter referred to as “Difference I-Y”) and the height (Difference Y) of the endothermic peak of reduced coenzyme Q10 Form II-type crystals (hereinafter referred to as “Difference II-Y”) obtained above, the percentage of the reduced coenzyme Q10 Form II-type crystals (Form II rate) was calculated based on the following formula.
(DSC Measurement Conditions)
[0078] Apparatus: DSC 6220, manufactured by SII Nano Technology Inc. [0079] Sample container: Aluminum pan & cover (SSC000C008) [0080] Rate of temperature rise: 1° C./min [0081] Amount of sample: 5±2 mg
<Measurement of Dissolved Concentration of Reduced Coenzyme Q10 in Liquid Phase>
[0082] The dissolved concentration of reduced coenzyme Q10 in a liquid phase was measured by analyze a liquid phase sample by high performance liquid chromatography under the following conditions.
(HPLC Conditions)
[0083] Column: SYMMETRY C18 (manufactured by Waters); 250 mm (length), 4.6 mm (inner diameter) [0084] Mobile phase: C.sub.2H.sub.5OH:CH.sub.3OH=4:3 (v:v) [0085] Detection wavelength: 210 nm [0086] Flow rate: 1 ml/min [0087] Retention time of reduced coenzyme Q10: 9.1 min.
<Experiment 1>
[0088] The solubility (saturated concentration) (% by weight) of each of a reduced coenzyme Q10 Form I-type crystal (Form I-type crystal) and a reduced coenzyme Q10 Form II-type crystal (Form II-type crystal) in hydrous ethanol with an ethanol concentration per total volume of 99.5% (v/v), 95% (v/v), and 90% (v/v) at temperatures of 298.15K (25° C.), 303.15K (30° C.), 308.15K (35° C.), and 313.15K (40° C.) was obtained.
[0089] The solubility was measured by the following procedures.
[0090] To approximately 30 g of each hydrous ethanol, approximately 10 g of a Form I-type crystal or a Form II-type crystal was added, the mixture was stirred under a nitrogen atmosphere and maintained for approximately 1 hour at temperatures of 25° C., 30° C., 35° C., and 40° C. Sampling was performed at each temperature and each sample was filtered quickly to obtain a liquid phase sample. Each sample was analyzed under the above HPLC conditions and the solubility was calculated.
[0091] The measurement results are shown in Tables 1 to 3. In addition,
TABLE-US-00001 TABLE 1 Solubility in 99.5% (v/v) ethanol Solubility Temperature (% by weight) (K) Form I Form II 298.15 2.01 1.22 303.15 4.53 2.32 308.15 12.6 5.51 313.15 46.3 17.9
TABLE-US-00002 TABLE 2 Solubility in 95% (v/v) ethanol Solubility Temperature (% by weight) (K) Form I Form II 298.15 0.65 0.37 303.15 1.01 0.52 308.15 2.33 0.86 313.15 8.98 2.81
TABLE-US-00003 TABLE 3 Solubility in 90% (v/v) ethanol Solubility Temperature (% by weight) (K) Form I Form II 298.15 0.13 0.10 303.15 0.18 0.13 308.15 0.29 0.23 313.15 0.88 0.41
[0092] As shown in Tables 1 to 3 and
[0093]
log C.sub.I=A.sub.I.Math.T+B.sub.I (Expression 7)
log C.sub.II=A.sub.II.Math.T+B.sub.II (Expression 8)
[0094] The values of A.sub.I, B.sub.I, A.sub.II, and B.sub.II at the respective ethanol concentrations are shown below.
TABLE-US-00004 TABLE 4 Ethanol concentration % (v/v) A.sub.I B.sub.I A.sub.II B.sub.II 99.5 0.2087 −61.639 0.1785 −53.137 95 0.1743 −52.609 0.1317 −40.448 90 0.1243 −39.267 0.0961 −31.040
[0095]
[0096] It was confirmed that A.sub.I and A.sub.II are directly proportional to the changes in the concentration of hydrous ethanol, and B.sub.I and B.sub.II are inversely proportional to changes in the concentration of hydrous ethanol. These results confirmed that the values of the constants A.sub.I, B.sub.I, A.sub.II, and B.sub.II, and the ethanol concentration Z (% (v/v)) have a relationship represented by Expressions 3, 4, 5, and 6, respectively.
<Experiment 2>
[0097] The inside of a separable flask (made of borosilicate glass) with a volume of 500 mL was replaced with nitrogen, and 40.0 g of reduced coenzyme Q10 and 360 g of 99.5% ethanol were then charged thereto (reduced coenzyme Q10 concentration: 10 wt %). Thereafter, the obtained mixture was warmed to 42° C. while stirring with a stirring blade (power required for stirring: 0.1 kw/m.sup.3) to obtain a homogeneous solution. This solution was cooled to 35° C., and thereafter, 0.4 g (1 wt %) of reduced coenzyme Q10 crystals comprising reduced coenzyme Q10 Form II-type crystals were added as seed crystals to the reaction solution.
[0098] The mixed solution obtained after the addition of seed crystals was kept at 35° C. for 15 hours to precipitate crystals. Thereafter, the mixed solution was cooled to 25° C. at a constant cooling rate of −2° C./hour over 5 hours, and was then cooled to 10° C. at a constant cooling rate of −10° C./hour over 1.5 hours, to further precipitate crystals. After the temperature had reached 10° C., the mixed solution was filtrated for solid-liquid separation. The obtained crystal was dried under reduced pressure at 35° C. for 10 hours to obtain a reduced coenzyme Q10 Form II-type crystal (Form II rate: 100%; recovery rate: 97%).
[0099] In the present experiment, the liquid phase of the mixed solution was sampled immediately before the addition of seed crystals (at 0 hour), and then at 3 hours, 6 hours, 9 hours, 12 hours, 15 hours (so far, at 35° C.), 17.5 hours (30° C.), 20 hours (25° C.), 20.5 hours (20° C.), and 21.5 hours (10° C.) after addition of the seed crystals. The dissolved concentration C (wt %) of reduced coenzyme Q10 in the liquid phase sample was measured according to high performance liquid chromatography. The measurement results are shown in Table 5. Table 5 also shows the natural logarithm Log C of the measured dissolved concentration C.
[0100] Further, the ethanol concentration of 99.5% (v/v) was assigned to Z of Expressions 3, 4, 5, and 6 to obtain the values of the constants A.sub.I, B.sub.I, A.sub.II, and B.sub.II. Using these constants, the Log C.sub.I of the saturated concentration C.sub.I (% by weight) of the Form I-type crystal and the Log C.sub.II of the saturated concentration C.sub.II (% by weight) of the Form II-type crystal were obtained at each temperature (converting the unit to Kelvin) shown in Table 5 according to Expressions 7 and 8 above.
TABLE-US-00005 TABLE 5 Dissolved Crystal- concentration C lization of reduced time Temperature coenzyme Q10 (h) (° C.) (% by weight) LogC LogC.sub.I LogC.sub.II 0 35 10.0 2.303 2.568 0.425 3 35 9.9 2.293 2.568 0.425 6 35 9.6 2.262 2.568 0.425 9 35 9.2 2.219 2.568 0.425 12 35 8.5 2.140 2.568 0.425 15 35 7.2 1.974 2.568 0.425 17.5 30 3.1 1.131 1.517 −0.432 20 25 1.5 0.405 0.467 −1.288 20.5 20 0.8 −0.223 −0.584 −2.145 21.5 10 0.3 −1.204 −2.686 −3.858
[0101] At the time of the addition of seed crystals at 35° C. and a time point up to 20 hours of crystallization after maintaining the temperature at 35° C. and then cooling to 25° C., the dissolved concentration C of reduced coenzyme Q10 in the liquid phase was equal to or more than the saturated concentration CH of the Form II-type crystal and less than the saturated concentration C.sub.I of the Form I-type crystal. At time points of 20.5 hours (20° C.) and 21.5 hours (10° C.) of crystallization, the dissolved concentration C exceeded the saturated concentration Ci of the Form I-type crystal while at a time point of 20 hours of crystallization, the dissolved concentration C of reduced coenzyme Q10 in the liquid phase decreased to as low as 1.5% by weight. Since crystal precipitation of most of the reduced coenzyme Q10 dissolved at the time of the addition of seed crystals took place under conditions that allowed the dissolved concentration C in the liquid phase to be equal to or more than the saturated concentration C.sub.II of the Form II-type crystal and less than the saturated concentration C.sub.I of the Form I-type crystal, Form II-type crystals were obtained at a rate of 100%.
[0102] All publications, patents and patent applications cited in the present description are incorporated herein by reference in their entirety.