Crystal of reduced glutathione
The present invention provides a crystal of reduced glutathione that is stable, and is easy to process, and a method for producing the crystal. According to the present invention, a crystal of a metal salt of reduced glutathione is produced by suspending an amorphous solid of a metal salt of reduced glutathione in a hydrophobic organic solvent, and adding water to the resulting suspension to precipitate a crystal of a metal salt of reduced glutathione.
1. A crystal of a metal salt of reduced glutathione, which is a monohydrate crystal of a salt of reduced glutathione and sodium, and has peaks at a diffraction angle (2θ) of 19.90°±0.20°, 25.58°±0.20°, and 26.88°±0.20° in powder X-ray diffraction.
2. The crystal according to claim 1 , which has peaks also at a diffraction angle (2θ) of 20.16°±0.20°, 24.68°±0.20°, 26.30°±0.20°, 27.68°±0.20°, and 33.20±0.20° in powder X-ray diffraction.
3. The crystal according to claim 2 , which has peaks also at a diffraction angle (2θ) of 17.90°±0.20°, 20.86°±0.20°, 22.10°±0.20°, and 25.30°±0.20° in powder X-ray diffraction.
4. The crystal according to claim 3 , which has peaks also at a diffraction angle (2θ) of 6.42±0.20°, 18.90±0.20°, and 29.30±0.20° in powder X-ray diffraction.
5. A crystal of a metal salt of reduced glutathione, which is a monohydrate crystal of a salt of reduced glutathione and sodium, and has the following brief unit cell parameters: a=27.881 Å, b=10.818 Å, c=4.881 Å, α=90°, β=90°, γ=90°, V=1472.2 Å 3 , and Z=4 with a space group P2 1 2 1 2 1 (#19), as measured by single-crystal X-ray structure analysis at −173° C.
6. A method for producing a crystal of a metal salt of reduced glutathione, the method comprising dissolving a free form of reduced glutathione in a metal hydroxide aqueous solution, and adjusting the pH of the solution to 5.0 to 8.0 to obtain an aqueous solution of a metal salt of reduced glutathione; concentrating the resulting aqueous solution, and gradually adding a C1 to C6 alcohol to the concentrated aqueous solution in small portions in an amount 0.1 to 3 times the amount of the concentrated aqueous solution; and adding a crystal of a metal salt of reduced glutathione as a seed crystal to precipitate a crystal of a metal salt of reduced glutathione.
7. The method for producing a crystal of a metal salt of reduced glutathione according to claim 6 , wherein the C1 to C6 alcohol is methanol or ethanol.
8. The method for producing a crystal of a metal salt of reduced glutathione according to claim 6 , wherein the crystal of a metal salt of reduced glutathione is a monohydrate crystal of a salt of reduced glutathione and a metal selected from the group consisting of sodium, potassium, calcium, and magnesium.
9. The method for producing a crystal of a metal salt of reduced glutathione according to claim 6 , wherein the crystal of a metal salt of reduced glutathione is a monohydrate crystal of a reduced glutathione-sodium salt.