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4120057 
Journal Article 
Studies on the stability of vitamin D2 powder preparations. VI. Influence of some vitamins and acids on the isomerization of vitamin D2 
Takahashi, T; Yamamoto, R 
1969 
1 
Yakugaku Zasshi
ISSN: 0031-6903
EISSN: 1347-5231 
IPA/70/04983 
Pharm 
Yakugaku Zasshi 
938-942 
IPA COPYRIGHT: ASHP Examination was made on the relationship between acid strength (pKa) of solid surfaces and isomerization of vitamin D2 (D2; ergocalciferol). A mixture of D2 and other powdered vitamins was stored at 37DG in vacuum (1 mmHg). It was found that D2 was readily isomerized by vitamins such as ascorbic acid, folic acid, thiamine HCl, or pyridoxine HCl, as well as by talc or CaHPO4, because each vitamin has a pKa of 2.0 to 4.0 in the dry state. Nicotinamide and calcium pantothenate, both having a pKa of 4.8 to 6.8, did not isomerize D2. D2 was also isomerized by citric acid or phosphoric acid in dry preparations. It is undesirable, therefore, to use any of the above acids as a synergist for an antioxidant to prevent the oxidation of D2. The main isomerization products of D2 were isocalciferol, 5,6-cis-isocalciferol, and isotachysterol.